JP2018077965A - Active material for nonaqueous electrolyte secondary battery, method for manufacturing the same, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an active material for a nonaqueous electrolyte secondary battery, which has a high discharge capacity and enables the suppression of the decrease in average discharge potential accompanying charge and discharge cycles; and a method for manufacturing the active material.SOLUTION: An active material for a nonaqueous electrolyte secondary battery comprises a lithium transition metal composite oxide. The lithium transition metal composite oxide has an α-NaFeOstructure, and includes, as a transition metal element, Mn and Ni, or Mn, Ni and Co (hereinafter "Mn and Ni, or Mn, Ni and Co" is referred to as Me). In the active material for a nonaqueous electrolyte secondary battery, the mole ratio Mn/Me of Mn to Me satisfies 0.5<Mn/Me, and the mole ratio Li/Me of Li to Me satisfies 1<Li/Me. The active material includes V(trivalent) or Ge at 3 mol% or less to Me. When V(trivalent) is included, the mole ratio Co/Me of Co to Me satisfies Co/Me≤0.1.SELECTED DRAWING: None

Description

  The present invention relates to an active material for a non-aqueous electrolyte secondary battery, a manufacturing method thereof, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries have been increasingly used in recent years, and development of higher-capacity cathode materials has been demanded.
Conventionally, lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure have been studied as positive electrode active materials for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries using LiCoO ₂ have been widely put into practical use. It was. However, the discharge capacity of LiCoO ₂ was about 120 to 130 mAh / g.

As the transition metal (Me) constituting the lithium transition metal composite oxide, abundant Mn is used as an earth resource, and the molar ratio Li / Me of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. In addition, a so-called “LiMeO ₂ type” active material having a Mn molar ratio Mn / Me in the transition metal of 0.5 or less has been put into practical use. For example, a positive electrode active material containing LiNi _1/2 Mn _1/2 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ has a discharge capacity of 150 to 180 mAh / g.
The molar ratio of Mn in the transition metal (Me) to the transition metal constituting the lithium transition metal composite oxide exceeds 0.5, and the molar ratio of Li to the transition metal (Me) Li Since the so-called “lithium-excess type” active material with / Me exceeding 1 has a higher discharge capacity than the “LiMeO ₂ type” active material, studies have been conducted for its practical use.

Patent Document 1 states that “a positive electrode active material for a lithium secondary battery including a lithium-excess layered oxide (OLO) represented by the following chemical formula 1. [Chemical formula 1] Li _a Ni _b Co _c Mn _d MeO ₂ (the above chemical formula 1, 1.1 <a <1.5, 0 <b <1, 0 ≦ c <1, 0 <d <1, 0 <e <1, and 0.8 ≦ b + c + d + e <1, and M is V, Ga, Zr, Mg, Al, Ti, Cr, Fe, W, Mo, Si, or a combination thereof.) ”(Claim 1).

Then, for the embodiment of the active material, "Example _{1 Ni (OH) 2 22.21g,} Co (OH) 2 22.27g, Mn 3 O 4 54.82g and _NH 4 _VO 3 0.70 g raw mixture of Was placed in distilled water and evenly dispersed using a ball mill (0.3 mm ZrO ₂ balls) over about 2 hours, and NH ₄ VO ₃ was 0.5 mol% based on the total amount of the mixed raw materials. The dispersion obtained by the dispersion was about 100 nm, and then the dispersion was spray-dried at about 245 ° C. at 15 mm / min using a spray drying method to be doped with vanadium. to obtain a precursor. then, the vanadium was mixed with the solid phase condensable method the doped precursor 61.78g and _Li 2 _CO 3 38.22 g. the mixed mixture And heat-treated over the 750 ° C. for 10 hours under air atmosphere to prepare a positive active material _{Li 1.170 Ni 0.164 Co 0.167 Mn 0.498} V 0.005 O 2. "(The paragraph [0096]) Have been described.
Further, regarding the lithium secondary battery (paragraphs [0108] and [0109]) using the active material of Example 1 as the positive electrode, the initial efficiency is 84.6% in Table 1 (paragraph [0121]). Table 2 (paragraph [0125]) shows that the capacity maintenance rate is 97.7% (10 times / 1 time), 95.4% (30 times / 1 time), and 94.5% (40 times / 1). Times).

Patent Document 2, _{"xLi 2 MnO 3 - (1-} x) LiNi a Mn b Co c M d O 2 (0.3 ≦ x ≦ 0.7,0.33 ≦ a ≦ 0.5,0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.33, 0.01 ≦ d ≦ 0.06), and M has a positive electrode active material that is one or more elements selected from V and Mo. "Characteristic positive electrode material for lithium ion secondary battery" (Claim 1).

And about the Example of this positive electrode active material, "(Preparation of positive electrode active material) After dissolving lithium acetate, nickel acetate, manganese acetate, cobalt acetate, vanadium oxide, molybdic acid, etc. in purified water, a spray-drying apparatus is used. The resulting precursor was baked in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide, and the resulting lithium transition metal oxide was pelletized. Thereafter, it was baked in the air for 12 hours at 800 to 1000 ° C. The baked pellets were pulverized in an agate mortar and classified with a 45 μm sieve to obtain a positive electrode active material ”(paragraph [0024]). .
In Table 1 (paragraph [0027]), as Example 8, positive electrode active material 8 (x: 0.3, a: 0.33, b: 0.33, c: 0.29, M: V , D: 0.04), that is, 0.3Li ₂ MnO ₃ —0.7LiNi _0.33 Mn _0.33 Co _0.29 V _0.04 O ₂ (when rewritten, Li _1.3 Ni _0.231 Mn _{0 .531} Co _0.203 V _0.028 O _2.3 ). For the prototype battery having the positive electrode using the active material of Example 8, in Table 3 (paragraph [0037]), the discharge capacity ratio with respect to Comparative Example 1 containing no V is 0.92, and the calorific value ratio is It is described that it is 0.64.

Patent Document 3 discloses that “Li _{1 + x} (Mn _a Ni _b M _c ) _1-x O ₂ type lithium-rich layered oxide particles and Li _y covering at least a part of the lithium-rich layered oxide particles. VO _z type metal oxide, where 0.1 ≦ x ≦ 0.25, a + b + c = 1, a, b and c are not 0, and M is Mg, Zn, Al, Na, A two-phase positive electrode material for a lithium battery, which is a metal selected from the group consisting of Ca and K, and 0 <y ≦ 3 and 2.5 <z <4. ”(Claim 1),“ Metal oxidation ” Material according to claim 1, characterized in that the object corresponds to the formula LiVO ₃ (claim 2).

And for this embodiment of the two-phase cathode material, “lithium corresponding to 2 grams of the pre-synthesized layered oxide Li _1.2 (Mn _0.7625 Ni _0.225 Mg _0.0125 ) _0.8 O ₂ The rich layered oxide was suspended in 10 ml of 0.25 M NH ₄ VO ₃ aqueous solution obtained by dissolving 0.283 g NH ₄ VO ₃ in 10 ml H ₂ O at 80 ° C. for 4 hours. Once the suspension has been carried out, the solution is kept stirred for 24 hours at 80 ° C. and then the resulting powder is heat-treated at a temperature of 300 ° C. for 4 hours under air in order to carry out the drying by evaporation. To obtain a finely divided compound ”(paragraph [0029]).
Further, with respect to the fine powdery compound, “It was shown that a Li _y VO _z phase was present on the surface of the lithium-rich layered oxide particle” (paragraph [0033]), which was used as a positive electrode material. In lithium batteries, “the addition of LiVO ₃ phase shows a very significant reduction in irreversible capacity in the first cycle (change from 23% to 4%)” (paragraph [0037]), “very Shows high specific capacity and very good cycleability "(paragraph [0038]).

  In Patent Document 4, “a compound having a layered structure and represented by the following formula (1), a columnar Li and V composite oxide having an average aspect ratio of 16 or more and 62 or less, LiyNiaCobMncMdOx (1) [In the above formula (1), the element M consists of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba, and V. At least one element selected from the group, 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.0 <y ≦ 1.3, 0 <a ≦ 0.3, 0 <b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.9 ≦ x ≦ 2.1] ”(Claim 1).

Then, for Example 1 of the active material, _{"Li 1.2 Ni 0.17 Co 0.08 Mn 0.55} O 2 " (paragraph [0055]) in which "compound _V 2 _{O 5} of 90:10 After mixing for about 10 minutes using a mortar at a weight ratio of 1, an active material in which a compound compound of Li and V and a compound were mixed was obtained by firing in the atmosphere at 400 ° C. for 3 hours. The active material was analyzed by powder X-ray diffractometry. The coating of Example 1 was Li ₃ VO ₄ ”(paragraph [0056]). For a lithium ion secondary battery (paragraphs [0058] to [0060]) having a positive electrode manufactured using this active material, “a composite oxide of Li and V having an average aspect ratio of 16 to 62” When the compound was mixed, the initial charge / discharge efficiency was improved "(paragraph [0072]).

Japanese Patent Laying-Open No. 2015-15244 JP 2013-175401 A JP 2014-506387 A JP 2013-206558 A

  In a lithium-excess active material having a high discharge capacity, there are problems such as improvement of initial efficiency, suppression of capacity reduction accompanying charge / discharge cycles, and reduction of average discharge potential particularly when used in a high potential region.

Patent Document 1 discloses initial efficiency and capacity maintenance of a lithium secondary battery having a positive electrode using a lithium-rich active material obtained by heat-treating a precursor doped with V and lithium carbonate in an air atmosphere. It is described that the rate is improved.
Patent Document 2 discloses a positive electrode material having a positive electrode active material of a lithium transition metal oxide obtained by firing in air the precursor containing Li, Mn, Ni, Co, and V obtained by spray drying. A high discharge capacity and a low calorific value ratio (high safety) are described.
Patent Document 3 discloses a lithium secondary battery using a fine powdery compound obtained by suspending a lithium-rich layered oxide in an NH ₄ VO ₃ aqueous solution and then heat-treating in air as a positive electrode material. It is described that the irreversible capacity in one cycle is reduced, and a high specific capacity and good cycle characteristics are exhibited.
In Patent Document 4, a compound which is Li _1.2 Ni _0.17 Co _0.08 Mn _0.55 O ₂ and V ₂ O ₅ are mixed and fired in the air, and the above compound and aspect ratio are obtained. It is described that when an active material in which a columnar Li and V composite oxide having an average value of 16 to 62 is mixed is used for the positive electrode, the initial charge and discharge efficiency is improved.

However, Patent Documents 1 to 4 do not describe anything about suppression of a discharge potential drop accompanying a charge / discharge cycle in a lithium-excess type active material.
Moreover, since the positive electrode active material of patent documents 1-4 is heat-processed in air | atmosphere after mixing V raw material with another active material raw material, it contains pentavalent V.

  The present invention relates to an active material for a non-aqueous electrolyte secondary battery that has a high discharge capacity and suppresses a decrease in average discharge potential associated with a charge / discharge cycle, a method for producing the active material, and a non-aqueous solution containing the active material. It is an object of the present invention to provide a positive electrode for an electrolyte secondary battery and a nonaqueous electrolyte secondary battery including the positive electrode.

A first aspect of the present invention is an active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ structure, and a transition metal Mn and Ni as elements, or Mn, Ni and Co (hereinafter, “Mn and Ni, or Mn, Ni and Co” is referred to as Me), and the molar ratio of Mn to Me is Mn / Me: 0.5 <Mn / Me, the molar ratio of Co to Me, Co / Me is Co / Me ≦ 0.1, the molar ratio of Li to Me, Li / Me is 1 <Li / Me, and contains trivalent V, It is an active material for non-aqueous electrolyte secondary batteries.

A second aspect of the present invention is a non-aqueous electrolyte secondary battery active material containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ structure, Mn and Ni as elements, or Mn, Ni and Co, molar ratio of Mn to Me, Mn / Me is 0.5 <Mn / Me, and molar ratio of Li to Me, Li / Me is 1 <Li / Me And an active material for a non-aqueous electrolyte secondary battery containing Ge.

A third aspect of the present invention is a method for producing an active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, which contains Mn and Ni or Mn, Ni and Co as transition metal elements, A transition metal carbonate precursor in which a molar ratio of Mn to Me, Mn / Me is 0.5 <Mn / Me, and a molar ratio of Co to Me, Co / Me is Co / Me ≦ 0.1 is prepared. A carbonate precursor and a lithium compound are mixed and baked to produce a lithium transition metal composite oxide. A lithium compound and V ₂ O ₃ are added to the lithium transition metal composite oxide, and the mixture is then added in a non-oxidizing atmosphere. Production of an active material for a non-aqueous electrolyte secondary battery comprising calcining and producing a lithium transition metal composite oxide having a Li molar ratio to Me of Li / Me of 1 <Mn / Me and containing trivalent V Is the method.

The fourth aspect of the present invention is a method for producing an active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, comprising Mn and Ni or Mn, Ni and Co as transition metal elements, A transition metal carbonate precursor having a Mn to Me molar ratio Mn / Me of 0.5 <Mn / Me is prepared, the transition metal carbonate precursor and the lithium compound are mixed, GeO ₂ is added, and firing is performed. And the Li molar ratio Li / Me with respect to Me is 1 <Li / Me, It is a manufacturing method of the active material for nonaqueous electrolyte secondary batteries provided with manufacturing the lithium transition metal complex oxide containing Ge.

  The fifth and sixth aspects of the present invention are a positive electrode for a nonaqueous electrolyte secondary battery containing the active material, and a nonaqueous electrolyte secondary battery comprising the positive electrode.

  According to the present invention, an active material for a nonaqueous electrolyte secondary battery that has a high discharge capacity and suppresses a decrease in average discharge potential associated with a charge / discharge cycle, a method for producing the active material, and a non-active material provided with the active material. A positive electrode for a water electrolyte secondary battery and a nonaqueous electrolyte secondary battery having the positive electrode can be provided.

The perspective view which shows one Embodiment of the nonaqueous electrolyte secondary battery which concerns on 1 side of this invention Schematic showing a power storage device comprising a plurality of non-aqueous electrolyte secondary batteries according to one aspect of the present invention

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or examples are merely examples in all respects, and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

<Positive electrode active material (lithium transition metal composite oxide)>
The positive electrode active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention (hereinafter referred to as “this embodiment”) is a positive electrode active material containing a lithium transition metal composite oxide.
In the lithium transition metal composite oxide, Mn and Ni, or Mn, Ni and Co (hereinafter referred to as “Mn and Ni, or Mn, Ni and Co”) are referred to as Me as transition metal elements because a high discharge capacity can be obtained. .), And further contains trivalent V (hereinafter also referred to as “V (trivalent)”) or Ge. Typically, it is represented by the composition formula Li _{1 + x} MeV _y O _{2 + z} or Li _{1 + x} MeGe _y O _{2 + z} . In order to obtain a nonaqueous electrolyte secondary battery having a high discharge capacity, the molar ratio of Mn to the transition metal element Me, Mn / Me, is larger than 0.5, and the molar ratio of Li to Me, Li / Me ((1 + x in the above composition formula) )) Is a lithium-rich active material of 1 <Li / Me.

The Li / Me molar ratio Li / Me is preferably 1.15 to 1.5, and more preferably 1.2 to 1.45. Within this range, the discharge capacity is particularly improved.
The molar ratio of Mn to Me, Mn / Me, is preferably 0.60 to 0.75, more preferably 0.60 to 0.70, and particularly preferably 0.65 to 0.70. Within this range, the energy density is improved.
Co contained in the lithium transition metal composite oxide has the effects of improving the initial efficiency and enhancing the high rate discharge performance, but is preferably less in order to suppress the decrease in the average discharge potential. Moreover, since it is a scarce resource, it is expensive. Therefore, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.20 or less, more preferably 0.10 or less, and may be 0. When V is added, Co / Me is 0.10 or less.
The molar ratio of Ni to Me, Ni / Me, is preferably 0.10 to 0.40, and more preferably 0.15 to 0.35. Within this range, the energy density is improved.

  In the lithium transition metal composite oxide (lithium-excess type positive electrode active material) according to the present embodiment, the addition of V (trivalent) or Ge suppresses a decrease in the average discharge potential after the charge / discharge cycle. The reason is not necessarily clear, but it is presumed that the crystal structure of the lithium-excess type positive electrode active material was stabilized by the solid solution of V (trivalent) or Ge.

  In the lithium transition metal composite oxide according to this embodiment, the content of V (trivalent) and Ge with respect to Me is preferably 3 mol% or less (y in the composition formula is y ≦ 0.03). By setting it to 3 mol% or less, it is possible to suppress a decrease in initial discharge capacity.

The value of z calculated stoichiometrically from the composition formula is z = x + y. However, as long as it has an α-NaFeO ₂ type crystal structure, the value of z does not necessarily have to be the stoichiometric ratio.
The lithium transition metal composite oxide is a transition represented by alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and 3d transition metals such as Fe, as long as the effects of the present invention are not impaired. It does not exclude the inclusion of a small amount of other metals such as metals.

The lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charging and discharging) is attributed to the space group P3 ₁ 12 or R3-m. Among these, those belonging to the space group P3 ₁ 12 are superlattice peaks (Li [Li _1/3 Mn _2/3 ] O ₂ near 2θ = 21 ° on the X-ray diffraction diagram using the CuKα tube. The peak observed in the monoclinic type) is confirmed. However, when charging is performed once and Li in the crystal is desorbed, the symmetry of the crystal changes, whereby the superlattice peak disappears and the lithium transition metal composite oxide belongs to the space group R3-m. Will come to be. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” is originally written by adding a bar “-” on “3” of “R3m”.

<Method for producing active material>
≪Including trivalent V≫
In the present embodiment, a non-aqueous electrolyte secondary battery active material including a lithium transition metal composite oxide containing trivalent V is prepared as a transition metal carbonate precursor containing Mn and Ni or Mn, Ni and Co. Then, the precursor and the lithium compound are mixed and baked to produce a lithium-excess type lithium transition metal oxide, and the lithium compound and V ₂ O ₃ are added to the lithium transition metal composite oxide, and then non-oxidized. Manufactured by firing in an atmosphere.
The transition metal carbonate precursor is basically prepared a raw material aqueous solution containing each element according to the composition of the transition metal element Me (Mn and Ni or Mn, Ni and Co) constituting the active material, This aqueous solution can be dropped into the solution to produce a coprecipitate in which each element is present in one particle.

In producing a transition metal coprecipitation precursor, Mn of Ni, Co and Mn is easily oxidized, and it is not easy to produce a coprecipitation precursor in which Ni, Co and Mn are uniformly distributed in a divalent state. Therefore, uniform mixing at the atomic level of Ni, Co, and Mn tends to be insufficient. Therefore, it is preferable to remove dissolved oxygen in order to suppress oxidation of Mn present in the coprecipitation precursor. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used.

  Carbonate precursors and hydroxide precursors are known as transition metal coprecipitation precursors. When a carbonate precursor is used, spherical active material particles having a larger specific surface area than when using a hydroxide precursor can be obtained. Since the positive electrode active material having a large specific surface area has a short diffusion distance from the active material / electrolyte interface to the inside of the particle, a positive electrode active material having a high discharge capacity and high initial efficiency can be obtained. Therefore, in this embodiment, the manufacturing method using a carbonate precursor is selected.

  The pH in the step of preparing a precursor by co-precipitation of a compound containing Ni, Co, and Mn in the solution is not limited, but in the case of preparing a carbonate precursor, 7.5 to 11 can be used. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cc or more, and the high rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The raw material of the coprecipitation precursor is nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate or the like as the Ni compound, and cobalt sulfate, cobalt nitrate, cobalt acetate, or the like as the Mn compound as the Co compound. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate and the like.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. The preferred dropping rate is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL / min or less, and most preferably 5 mL / min or less.

Further, when a complexing agent such as NH ₃ is present in the reaction tank and a certain convection condition is applied, by continuing the stirring after the dropwise addition of the raw material aqueous solution, the rotation of the particles and in the stirring tank are performed. Revolution is promoted, and in this process, particles collide with each other, and the particles grow into concentric spheres step by step. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferable stirring duration after the dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 hours or more in order to grow the particles as uniform spherical particles The reaction time is preferably 1 hour or longer. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, it is preferably 30 hours or less, more preferably 25 hours or less, and most preferably 20 hours or less.

  Since the coprecipitation precursor obtained as described above basically contains each element according to the composition of Me constituting the active material, the molar ratio of Mn to Me, Mn / Me, is 0.5 <Mn. The molar ratio of Co to Me, Co / Me, is Co / Me ≦ 0.1.

The coprecipitation precursor and the lithium compound are mixed and fired to produce lithium transition metal composite oxide particles. Next, a lithium compound and V ₂ O ₃ are added to the lithium transition metal composite oxide, and additional firing is performed in a non-oxidizing atmosphere to produce a lithium transition metal composite oxide containing trivalent V. Hereinafter, the firing for producing the lithium transition metal composite oxide from the coprecipitation precursor and the lithium compound is referred to as “first firing step”, and the additional firing of the lithium transition metal composite oxide is referred to as “second firing step”. The lithium compound used in the first and second firing steps can be lithium hydroxide, lithium carbonate, or the like.

The amount of V ₂ O ₃ added in the second firing step is preferably 3 mol% or less with respect to Me, and the amount of lithium compound added is about mol% of V with respect to Me. It is preferable. Therefore, the mixing ratio of the lithium compound and the coprecipitation precursor in the first firing step is determined by considering the amount of the lithium compound added in the second firing step, and the molar ratio of Li to Me of the target active material. Set to Li / Me. However, with respect to the amount of the lithium compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of Li during firing.

The first and second firing temperatures affect the reversible capacity of the active material.
If the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present embodiment, the firing temperature is preferably 800 ° C. or higher. By setting the temperature to 800 ° C. or higher, active material particles having a high degree of sintering can be obtained, and charge / discharge cycle performance can be improved.
On the other hand, if the firing temperature is too high, the structure changes from a layered α-NaFeO ₂ structure to a rock salt cubic structure, which is disadvantageous for lithium ion movement in the active material during the charge / discharge reaction, and the discharge performance decreases. . In the present embodiment, the firing temperature is preferably 950 ° C. or lower. By setting the temperature to 950 ° C. or lower, the charge / discharge cycle performance can be improved.
Therefore, when producing the positive electrode active material containing the lithium transition metal composite oxide according to the present embodiment, the firing temperature is preferably 800 to 950 ° C. in order to improve the charge / discharge cycle performance. The atmosphere during the first firing is preferably an oxidizing gas atmosphere, more preferably normal air. The firing time is preferably 1 to 30 hours.

In order to produce a lithium transition metal composite oxide containing trivalent V, the second baking step is performed in a non-oxidizing atmosphere. This is because, when the trivalent compound V ₂ O ₃ is heated to high temperature in the air, the pentavalent compound V ₂ O ₅ is obtained. The non-oxidizing atmosphere is preferably a nitrogen atmosphere or an inert gas atmosphere.

≪When Ge is included≫
The active material for a water electrolyte secondary battery in the present embodiment in the case of containing Ge produces a transition metal carbonate precursor containing Mn and Ni or Mn, Ni and Co, and the precursor, lithium compound and GeO _2. It is produced by mixing and baking.
The precursor can be produced in the same manner as when trivalent V is contained.
The reason why Ge is not mixed at the time of preparing the coprecipitation precursor is that Ge is difficult to coprecipitate with Ni, Mn and the like.

The mixing ratio of the precursor, the lithium compound, and GeO ₂ is set according to the composition ratio of the target active material. The molar ratio of Li to Me, Li / Me, is set to exceed 1. The Ge content relative to Me is preferably set to be 3 mol% or less. However, with respect to the amount of the lithium compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of Li during firing.
Firing after mixing is preferably performed under the same conditions as in the first firing step in the case of containing trivalent V.

<Negative electrode material>
The lithium-rich active material according to the present embodiment is a material used for a positive electrode for a nonaqueous electrolyte secondary battery. Hereinafter, a material for a negative electrode for a secondary battery combined with this positive electrode material will be described.
The negative electrode material is not limited, and any negative electrode material that can release or occlude lithium ions can be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure typified by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based materials, lithium metal, lithium Alloys (lithium-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), oxidation In addition to silicon, alloys that can occlude / release lithium, carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.), and the like can be given.

<Positive electrode / Negative electrode>
The positive electrode active material powder and the negative electrode material powder preferably have an average particle size (D50) of 100 μm or less. In particular, the positive electrode active material powder is preferably 50 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery, and preferably 3 μm or more in order to maintain charge / discharge cycle performance. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained liquid mixture is applied on a current collector described in detail below, or pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. . About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  As the current collector, a current collector foil such as an Al foil or a Cu foil can be used. The positive electrode current collector foil is preferably an Al foil, and the negative electrode current collector foil is preferably a Cu foil. The thickness of the current collector foil is preferably 10 to 30 μm. Further, the thickness of the mixture layer is preferably 40 to 150 μm (excluding the current collector foil thickness) after pressing.

<Nonaqueous electrolyte>
The nonaqueous electrolyte used for the nonaqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C _{4 H 9) 4 NI, (} C 2 H 5) 4 N-mal _{ate, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phthalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

<Separator>
As a separator used for the non-aqueous electrolyte secondary battery according to the present embodiment, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  Other battery components include a terminal, an insulating plate, a battery case, and the like, but these components may be used as they are.

<Nonaqueous electrolyte secondary battery>
FIG. 1 shows a lithium secondary battery which is an embodiment of a non-aqueous electrolyte secondary battery according to one aspect of the present invention. FIG. 1 is a perspective view of the inside of a rectangular lithium secondary battery seen through. The lithium secondary battery 1 is assembled by injecting a nonaqueous electrolyte (electrolytic solution) into the battery container 3 in which the electrode group 2 is housed. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.
The shape of the lithium secondary battery according to this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like.

  The present invention can also be realized as a power storage device in which a plurality of the above lithium secondary batteries are assembled as another aspect. An example of the power storage device is illustrated in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of lithium secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

It can be confirmed that the positive electrode active material used for the positive electrode included in the nonaqueous electrolyte battery contains trivalent V by performing X-ray photoelectron spectroscopy (XPS) analysis according to the following procedure.
If the sample to be used for measurement is an active material powder before electrode preparation, it is used for measurement as it is. When a sample is collected from an electrode taken out by disassembling the battery, the battery is put into a discharged state by the following procedure before disassembling the battery. With a current of 0.1 CmA, constant current discharge is performed until the positive electrode potential reaches a battery voltage of 3.0 V (vs. Li ^/ Li ⁺ ), and a discharge end state is obtained. If the battery uses a metal lithium electrode as the negative electrode, the battery may be disassembled after the battery is brought into the end-of-discharge state or the end-of-charge state, and the electrode may be taken out. In order to accurately control the positive electrode potential, after disassembling the battery in the discharged state and taking out the electrode, after assembling the cell with the metal lithium electrode as the counter electrode, adjusting to the end of discharge state according to the above procedure . When the electrode potential is less than 3.0 V (vs. Li ^/ Li ⁺ ), the battery is once charged and then discharged under the above conditions. The charging conditions here are constant current charging with a charging current of 0.1 CmA and a charge end voltage of 4.3 to 4.5 V (vs. Li / Li ⁺ ). The charge termination condition is when the current value is attenuated to 1/6. The work from disassembly of the battery or cell to measurement is performed in an argon atmosphere with a dew point of −60 ° C. or lower. The taken-out positive electrode plate wash | cleans the electrolyte solution adhering to the electrode fully using dimethyl carbonate, cuts an electrode into predetermined size (for example, 2x2 cm) after drying at room temperature all day and night, and uses for XPS measurement.
The apparatus and measurement conditions used for XPS measurement are as follows.
Equipment: “AXIS NOVA” from KRATOS ANALYTICAL
X-ray source: Monochromatic AlKα
Acceleration voltage: 15 kV
Analysis area: 700 μm × 300 μm
Measurement range: O1s = 543-522eV, V2p3 / 2 = 512-520eV, V3p = 38-50eV
Measurement interval: 0.1 eV
Measurement time: O1s = 52.5 seconds / time, V2p3 / 2 = 70.0 seconds / time, V3p = 70.0 seconds / time Integration frequency: O1s = 8 times, V2p3 / 2 = 15 times, V3p = 15 times

Example 1
<Precursor production process>
36.3 g of nickel sulfate hexahydrate and 63.1 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 200 mL of ion-exchanged water. The molar ratio of Ni: Mn was 34.5: 65.5. A 2.0 M aqueous sulfate solution was prepared. On the other hand, 750 mL of ion exchange water was poured into a ₂ L reaction vessel, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred while stirring the reaction vessel with a baffle plate at a rotational speed of 1000 rpm using a disc turbine blade equipped with a stirring motor. The solution was added dropwise at a rate of 3 mL / min. Here, during the period from the start to the end of dropping, an aqueous solution containing 1.0 M sodium carbonate and ammonia is appropriately dropped, so that the pH in the reaction tank is always 8.0 (± 0.05), the ammonia concentration. Was controlled to maintain 0.5 g / L. After completion of the dropwise addition, stirring in the reaction vessel was further continued for 3 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.
Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and an electric furnace is used. And dried at 80 ° C. under normal pressure in an air atmosphere. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

<First firing step>
Lithium carbonate 1.22g is added to the coprecipitated carbonate precursor 3.00g and mixed well using a smoked automatic mortar, and the molar ratio of Li: (Ni, Mn) is 1.33: 1 A powder was prepared. The mixed powder formed into pellets is placed in an alumina crucible, placed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere at normal pressure to 890 ° C. over 10 hours. Firing was performed at 890 ° C. for 5 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina crucible placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. In this way, a lithium transition metal composite oxide Li _1.33 Ni _0.345 Mn _0.655 O _{2 + z according} to Comparative Example 1 was produced. Here, the value of z calculated stoichiometrically from the composition formula is 0.33, but the value of z is not necessarily in accordance with the stoichiometric ratio as long as it has an α-NaFeO ₂ type crystal structure. It is not necessary. The same applies to the following examples and comparative examples.

<Second firing step>
Add lithium carbonate 0.0108g and vanadium oxide (V ₂ O ₃ ) 0.0219g to the lithium transition metal composite oxide 3.0g synthesized in the first firing step, and mix well using a smoked automatic mortar, A mixed powder having a molar ratio of Li: (Ni, Mn): V of 1.34: 1: 0.01 was prepared. The mixed powder formed into pellets is placed in an alumina crucible and placed in a box-type electric furnace (model number: AMF20), and the temperature is increased from room temperature to 890 ° C. at a rate of 1.5 ° C./min in a nitrogen atmosphere. The temperature was raised at a temperature rate, and firing was performed at 890 ° C. for 5 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina crucible placed in the furnace. As a result, the temperature drop rate is slightly moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, to prepare a lithium transition metal composite oxide _{Li 1.34 Ni 0.345 Mn 0.655 V 0.01} O 2 + z according to the first embodiment. Here, the value of z calculated stoichiometrically from the composition formula is 0.35, but the value of z is not necessarily in the stoichiometric ratio as long as it has an α-NaFeO ₂ type crystal structure. It is not necessary. The same applies to the following examples and comparative examples.

(Example 2)
In the second baking step, 0.0324 g of lithium carbonate and 0.0656 g of vanadium oxide (V ₂ O ₃ ) are added to 3.0 g of the lithium transition metal composite oxide synthesized in the first baking step, and Li: (Ni , Mn): V molar ratio of 1.36: 1: 0.03 A lithium transition metal composite oxide Li _{1 according} to Example 2 was prepared in the same manner as Example 1, except that a mixed powder was prepared _. the _{36 Ni 0.345 Mn 0.655 V 0.03 O} 2 + z were prepared. The value of z calculated stoichiometrically from the composition formula is 0.39.

(Comparative Example 1)
Li _1.33 Ni _0.345 Mn _0.655 O _{2 + z} synthesized in the first firing step of Example 1 was used as the lithium transition metal composite oxide according to Comparative Example 1.

(Comparative Example 2)
In the second firing step, the lithium transition metal composite oxide Li _1.33 Ni _{0.345 according to} Comparative Example 2 is the same as Example 1 except that lithium carbonate and vanadium oxide (V ₂ O ₃ ) are not added. Mn _0.655 O _{2 + z} was produced.

(Example 3)
Lithium carbonate 1.24 g and germanium oxide (GeO ₂ ) 0.0260 g are added to 3.00 g of the coprecipitated carbonate precursor synthesized in Example 1, and the molar ratio of Li: (Ni, Mn): Ge is 1. Except for preparing the mixed powder of 35: 1: 0.01, the same firing as in the first firing step of Example 1 was performed, and the lithium transition metal composite oxide Li _1.35 Ni _{0 according to} Example 3 was performed. _.345 Mn _0.655 Ge _0.01 O _{2 + z} was produced. Here, the value of z calculated stoichiometrically from the composition formula is 0.36.

Example 4
1.28 g of lithium carbonate and 0.0780 g of germanium oxide (GeO ₂ ) are added to 3.00 g of the coprecipitated carbonate precursor synthesized in Example 1, and the molar ratio of Li: (Ni, Mn): Ge is 1. 39: 1: 0.03 Except that the mixed powder was prepared, the same firing as in the first firing step of Example 1 was performed, and the lithium transition metal composite oxide Li _1.39 Ni _{0 according to} Example 4 was performed. _.345 Mn _0.655 Ge _0.03 O _{2 + z} was produced. Here, the value of z calculated stoichiometrically from the composition formula is 0.42.

(Comparative Example 3)
In the second firing step, 0.0216 g of lithium carbonate and 0.0374 g of molybdenum oxide are added to 3.0 g of the lithium transition metal composite oxide synthesized in the first firing step, and Li: (Ni, Mn): Mo A lithium transition metal composite oxide Li _1.35 Ni _0.345 Mn according to Comparative Example 3 was prepared in the same manner as in Example 1 except that a mixed powder having a molar ratio of 1.35: 1: 0.01 was prepared. _0.655 Mo _0.01 O _{2 + z} was produced. The value of z calculated stoichiometrically from the composition formula is 0.36.

(Comparative Example 4)
In the second baking step, 0.0647 g of lithium carbonate and 0.1121 g of molybdenum oxide are added to 3.0 g of the lithium transition metal composite oxide synthesized in the first baking step, and Li: (Ni, Mn): Mo A lithium transition metal composite oxide Li _1.39 Ni _0.345 Mn according to Comparative Example 4 was prepared in the same manner as in Example 1 except that a mixed powder having a molar ratio of 1.39: 1: 0.03 was prepared. _0.655 Mo _0.03 O _{2 + z} was produced. The value of z calculated stoichiometrically from the composition formula is 0.42.

(Comparative Example 5)
In the first firing step, the lithium transition metal composite oxide Li _1.35 Ni _{0.345 according to} Comparative Example 5 was used in the same manner as in Example 3 except that 0.0375 g of tin oxide was added instead of germanium oxide. Mn _0.655 Sn _0.01 O _{2 + z} was produced.

(Comparative Example 6)
In the first firing step, the lithium transition metal composite oxide Li _1.39 Ni _{0.345 according to} Comparative Example 6 was used in the same manner as in Example 4 except that 0.1124 g of tin oxide was added instead of germanium oxide. Mn _0.655 Sn _0.03 O _{2 + z} was produced.

(Comparative Example 7)
In the first firing step, the lithium transition metal composite oxide Li _1.35 Ni _{0.345 according to} Comparative Example 7 was used in the same manner as in Example 3 except that 0.0199 g of titanium oxide was added instead of germanium oxide. Mn _0.655 Ti _0.01 O _{2 + z} was produced.

(Comparative Example 8)
In the first firing step, lithium transition metal composite oxide Li _1.39 Ni _{0.345 according to} Comparative Example 8 was used in the same manner as in Example 4 except that 0.0596 g of titanium oxide was added instead of germanium oxide. Mn _0.655 Ti _0.03 O _{2 + z} was produced.

(Comparative Example 9)
In the first firing step, the lithium transition metal composite oxide Li _1.35 Ni _{0.345 according to} Comparative Example 9 was used in the same manner as in Example 3 except that 0.0331 g of ruthenium oxide was added instead of germanium oxide. Mn _0.655 Ru _0.01 O _{2 + z} was produced.

(Comparative Example 10)
In the first firing step, the lithium transition metal composite oxide Li _1.39 Ni _{0.345 according to} Comparative Example 10 was used in the same manner as in Example 4 except that 0.0992 g of ruthenium oxide was added instead of germanium oxide. Mn _0.655 Ru _0.03 O _{2 + z} was produced.

(Comparative Examples 11 and 12)
In the second firing step, lithium transition metal composite oxides according to Comparative Example 11 and Comparative Example 12 were produced in the same manner as in Example 1 and Example 2 except that the firing atmosphere was changed from nitrogen to air.

(Comparative Examples 13 and 14)
In the second firing step, vanadium oxide (V ₂ O ₃ ) was changed to ammonium metavanadate (pentavalent V), and the firing atmosphere was changed from nitrogen to air in the same manner as in Example 1 and Example 2. Thus, lithium transition metal composite oxides according to Comparative Example 13 and Comparative Example 14 were produced.

(Comparative Examples 15-18)
The precursors in Comparative Examples 1 and 2 and Examples 1 and 2 were changed to precursors having a Ni: Co: Mn molar ratio of 20.3: 12.0: 67.6. Comparative Examples 1 and 2 and Examples 1 and 2, respectively, except that the first baking step was performed by mixing lithium carbonate such that the molar ratio of Me (Ni, Co, Mn) was 1.44: 1. Similarly, lithium transition metal composite oxides according to Comparative Examples 15 to 18 were produced.

[Confirmation of crystal structure]
Powder X-ray diffraction measurement was performed on the lithium transition metal composite oxides according to Examples 1 to 4 and Comparative Examples 1 to 18 using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). As a result, it was confirmed that the lithium transition metal composite oxides prepared in all Examples and Comparative Examples had an α-NaFeO ₂ structure.

<Preparation of positive electrode for nonaqueous electrolyte secondary battery>
Using the lithium transition metal composite oxides according to Examples 1 to 4 and Comparative Examples 1 to 18 as positive electrode active materials for non-aqueous electrolyte secondary batteries, a positive electrode for non-aqueous electrolyte secondary batteries was prepared according to the following procedure. did. Using N-methylpyrrolidone as a dispersion medium, a coating paste in which a positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5 was prepared. The coating paste was applied to one side of an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate. In addition, the mass and coating thickness of the active material applied per fixed area were standardized so that the test conditions were the same among the nonaqueous electrolyte secondary batteries according to all Examples and Comparative Examples.

<Preparation of nonaqueous electrolyte secondary battery>
As the negative electrode of the nonaqueous electrolyte secondary battery, a metal lithium electrode in which metal lithium having a capacity sufficiently larger than the theoretical capacity of the positive electrode was attached to a nickel current collector was used.

As a non-aqueous electrolyte, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a volume ratio of 6: 7: 7 so that the concentration would be 1 mol / L. Solution was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package.

  The metal resin composite film was molded into a bag shape, and the positive electrode and the negative electrode were accommodated therein so that the open ends of the positive electrode terminal and the negative electrode terminal were exposed to the outside, and the inner surfaces of the metal resin composite film faced each other. The fusion allowance is hermetically sealed except for the portion serving as the injection hole, and after injecting the non-aqueous electrolyte, the injection hole is sealed, and the non-according to Examples 1-4 and Comparative Examples 1-14 A water electrolyte secondary battery was produced.

[Initial charge / discharge process]
About each battery, the initial charge / discharge of 2 cycles was performed at 25 degreeC. Charging was performed at a constant current and constant voltage with a current of 0.1 CmA and a voltage of 4.7 V, and the charge termination condition was when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. Here, a pause process of 10 minutes was provided after charging and discharging, respectively, and the initial discharge capacity was confirmed. The percentages of the initial discharge capacities of Examples 1-4 and Comparative batteries 2-14 with respect to the initial discharge capacity of the comparative battery 1 and the percentage of the initial discharge capacities of comparative batteries 16-18 with respect to the initial discharge capacity of the comparative battery 15 Was defined as “initial discharge capacity ratio (%)”.

[Charge / discharge cycle test]
After confirming the initial discharge capacity, a 25-cycle charge / discharge cycle test was conducted. Charging was performed at a constant current and constant voltage with a current of 0.1 CmA and a voltage of 4.7 V, and the charge termination condition was when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. Here, a pause process of 10 minutes was provided after charging and discharging, respectively.
The percentage of the discharge capacity at the 25th cycle with respect to the discharge capacity at the 1st cycle in the charge / discharge cycle test was calculated as the “capacity maintenance ratio”.

[Measurement of average discharge potential]
In the charge / discharge cycle test, the percentage of the 25th average discharge potential with respect to the average discharge potential of the first cycle was defined as “potential maintenance ratio (%)”. In addition, since the nonaqueous electrolyte secondary battery used in the above example uses metallic lithium for the negative electrode, it is considered that the voltage between the terminals is equal to the positive electrode potential, and the nonaqueous electrolyte secondary battery during the constant current discharge is The average voltage was adopted as the “average discharge potential”.
The results are shown in Table 1.

Comparative Example 1 in Table 1 is an example in which a non-aqueous electrolyte secondary battery was manufactured using a conventional lithium-excess active material that does not contain a different element as a positive electrode (hereinafter referred to as “standard product”). The potential maintenance rate after the charge / discharge cycle test is 96.8%.
On the other hand, in Examples 1 to 4 containing V (trivalent) or Ge as a different element, the potential maintenance rate is 97.0% or more. The initial discharge capacity has a capacity ratio of 95% or more with respect to a standard product, and the capacity maintenance rate is also 100% or more. Therefore, it can be seen that an active material having a high discharge capacity and a suppressed decrease in the average discharge potential accompanying the charge / discharge cycle can be obtained.
Although the comparative example 2 has a 2nd baking process, it differs from Examples 1 and 2 by the point which does not contain a different element. Not only is the effect of suppressing the decrease in the potential maintenance ratio, but the initial discharge capacity relative to the standard product is low (capacity ratio 87%), so a high capacity cannot be obtained. From the comparison between Comparative Example 2 and Examples 1 and 2, it can be seen that the effect of suppressing the decrease in the potential maintenance rate is not due to the second firing step but to the addition of V (trivalent).

  Comparative Examples 3 and 4 are the same as Examples 1 and 2, respectively, except that Mo, which is a transition metal, is added instead of V (trivalent). In Comparative Example 3 in which the amount of Mo added to Me is 1 mol%, the reduction in the potential maintenance rate does not reach that of the standard product, and the capacity maintenance rate is low. In Comparative Example 4 in which the amount of Mo added is 3 mol%, the decrease in the potential maintenance rate is suppressed, but since the initial discharge capacity with respect to the standard product is greatly reduced (capacity ratio 84%), a high discharge capacity is obtained. I can't understand.

  Comparative Examples 5 and 6 are the same examples as Examples 3 and 4, respectively, except that the same tetravalent Sn was added instead of Ge. Although effective in suppressing the decrease in potential maintenance rate, the initial discharge capacity with respect to the standard product is low (capacity ratio 88%, 88%), so a high discharge capacity cannot be obtained.

  Comparative Examples 7 to 10 are the same as Examples 3 and 4, respectively, except that Ti or Ru, which is a transition metal, is added instead of Ge. In any example, the potential maintenance rate is lower than the standard product.

In Comparative Examples 11 and 12, trivalent V (V ₂ O ₃ ) is used as a raw material for the V component of the active material, but since the second firing step is performed in the air, Included is pentavalent V. In Comparative Examples 13 and 14, pentavalent V (NH ₄ VO ₃ ) is used as a raw material for the V component of the active material, and the second firing step is in the air. V is included. In any of Comparative Examples 11 to 14, the potential maintenance ratio is lower than or equal to that of the standard product. Therefore, even when pentavalent V is added, the effect of suppressing the decrease in potential maintenance ratio is not observed. Further, in Comparative Examples 12 and 14 in which the addition amount of pentavalent V to Me is 3 mol%, an extreme decrease (61%, 72%) in the capacity ratio is observed.

In Comparative Examples 15 to 18, a precursor having a Ni: Co: Mn molar ratio of 20.3: 12.0: 67.6 was used, and the molar ratio of Li: Me (Ni, Co, Mn) was used as the precursor. A positive electrode active material was prepared in the same process as Comparative Examples 1 and 2 and Examples 1 and 2, respectively, except that the first baking step was performed by mixing lithium carbonate so that the ratio was 1.44: 1. Yes.
In Comparative Example 15 in which a different element was not added and the second baking step was not provided, a high initial discharge capacity was obtained because of the high ratio of Co, but the potential maintenance rate was comparable to that of the standard product. Only.
Compared to Comparative Example 15, Comparative Example 16 in which a second baking step in a non-oxidizing atmosphere without adding a different element was added, and trivalent V (V ₂ O ₃ ) was added, and in a non-oxidizing atmosphere In Comparative Example 17 and Comparative Example 18 to which the second firing step in (2) is added, not only does not have an effect of suppressing the addition of the potential maintenance rate, but also the initial discharge capacity ratio is greatly reduced.
Therefore, it can be seen that when the molar ratio Co / Me of Me exceeds 0.1, the effect of adding trivalent V does not occur.

  From the above results, it can be seen that when the lithium-excess active material contains V (trivalent) or Ge, a decrease in the average discharge potential accompanying the charge / discharge cycle is suppressed. Further, it can be seen that this effect is exhibited when the molar ratio Co / Me of Co to Me is 0.1 or less when V (trivalent) is included.

  In an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and the like, it is necessary to always grasp the charge depth (SOC) of the battery in order to estimate the remaining capacity of the battery. The SOC of a battery is often estimated based on the battery voltage or electrode potential. Here, if the average discharge potential of the battery changes as the battery is used, the estimation accuracy of the SOC is affected. Disclosed is a nonaqueous electrolyte secondary battery that has a high discharge capacity and that suppresses a decrease in average discharge potential associated with a charge / discharge cycle by using a positive electrode active material containing a lithium transition metal composite oxide according to the present invention. Therefore, this non-aqueous electrolyte secondary battery is particularly useful as a non-aqueous electrolyte secondary battery for electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

1 Nonaqueous electrolyte secondary battery (lithium secondary battery)
2 Electrode group 3 Battery container 4 Positive electrode terminal 4 ′ Positive electrode lead 5 Negative electrode terminal 5 ′ Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (6)

An active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
The lithium transition metal composite oxide is
having an α-NaFeO ₂ structure,
Mn and Ni, or Mn, Ni and Co (hereinafter, “Mn and Ni, or Mn, Ni and Co” are referred to as Me) as transition metal elements,
The molar ratio of Mn to Me, Mn / Me is 0.5 <Mn / Me,
The molar ratio of Co to Me, Co / Me, is Co / Me ≦ 0.1,
The molar ratio of Li to Me Li / Me is 1 <Li / Me,
Including trivalent V,
Active material for non-aqueous electrolyte secondary batteries. An active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
The lithium transition metal composite oxide is
having an α-NaFeO ₂ structure,
Mn and Ni, or Mn, Ni and Co (hereinafter, “Mn and Ni, or Mn, Ni and Co” are referred to as Me) as transition metal elements,
The molar ratio of Mn to Me, Mn / Me is 0.5 <Mn / Me,
The molar ratio of Li to Me Li / Me is 1 <Li / Me,
Containing Ge,
Active material for non-aqueous electrolyte secondary batteries. A method for producing an active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide,
Mn and Ni or Mn, Ni and Co (hereinafter, “Mn and Ni, or Mn, Ni and Co” are referred to as Me) as transition metal elements, and the molar ratio of Mn to Me, Mn / Me is 0.5. <Mn / Me, a transition metal carbonate precursor in which the molar ratio Co / Me to Me is Co / Me ≦ 0.1,
The transition metal carbonate precursor and the lithium compound are mixed and fired to produce a lithium transition metal composite oxide,
Lithium compound and V ₂ O ₃ are added to the lithium transition metal composite oxide and baked in a non-oxidizing atmosphere. The Li molar ratio Li / Me to Me is 1 <Li / Me, A method for producing an active material for a nonaqueous electrolyte secondary battery, comprising producing a lithium transition metal composite oxide containing V. A method for producing an active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide,
Mn and Ni or Mn, Ni and Co (hereinafter, “Mn and Ni, or Mn, Ni and Co” are referred to as Me) as transition metal elements, and the molar ratio of Mn to Me, Mn / Me is 0.5. <Mn / Me transition metal carbonate precursor is prepared,
The transition metal carbonate precursor and lithium compound are mixed, GeO ₂ is added, calcined, and the Li molar ratio Li / Me to Me is 1 <Li / Me, and the lithium transition metal composite oxide containing Ge The manufacturing method of the active material for nonaqueous electrolyte secondary batteries provided with manufacturing.   The positive electrode for nonaqueous electrolyte secondary batteries containing the active material of Claim 1 or 2. A nonaqueous electrolyte secondary battery comprising the positive electrode, the negative electrode, and the nonaqueous electrolyte according to claim 5.