JP5625273B2 - Method for producing positive electrode material for lithium ion battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode material for a lithium ion battery. More specifically, the present invention relates to an improvement for increasing the capacity of a battery.

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there is a great expectation for the reduction of carbon dioxide emissions by the introduction of electric vehicles and hybrid electric vehicles, and motor drive batteries that hold the key to commercialization of these are actively being developed.

  As a battery for driving a motor, a lithium ion battery having a relatively high theoretical energy is attracting attention, and is currently being developed rapidly. In general, a lithium ion battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of the negative electrode current collector using a binder. It is connected via an electrolyte layer and is configured to be stored in a battery case.

  In order for electric vehicles equipped with such a lithium ion battery to be widely spread, it is necessary to make the lithium ion battery high performance and cheaper. In particular, for an electric vehicle, it is necessary to make one charging mileage closer to a gasoline engine vehicle, and a battery with higher energy is desired. In order to make the battery have a high energy density, it is necessary to increase the electric capacity per unit mass of the positive electrode and the negative electrode.

A lithium manganese composite oxide having a layered structure has been proposed as a positive electrode material that can meet this demand. Among them, the solid solution of the electrochemically inactive layered Li ₂ MnO ₃ and the electrochemically active layered LiMO ₂ (where M is a transition metal such as Co or Ni) is 200 mAh / g. It is expected as a candidate for a high-capacity positive electrode material capable of exhibiting a large electric capacity exceeding 1 (for example, see Patent Document 1).

Special table 2004-528691 gazette

  In the technique described in Patent Document 1, the capacity of the positive electrode material is increased by performing a rapid cooling process after firing. However, since such a rapid cooling process has low production efficiency, it is applied to mass production. There is a problem that productivity and efficiency are remarkably lowered in terms of resources and costs.

  Therefore, an object of the present invention is to provide a positive electrode material obtained by a simple and highly productive method and having stable battery characteristics (particularly, high capacity).

  The present inventors have intensively studied to solve the above problems. As a result, in the positive electrode solid solution material, it was found that the above-mentioned problems can be solved by performing heat treatment in an inert atmosphere after firing, and the present invention has been completed.

  That is, the present invention includes a step of obtaining a mixture by mixing a Li compound, a Mn compound, a Ni compound, and, if necessary, a raw material containing a Co compound, and a step of firing the mixture at 900 to 1000 ° C. to obtain a fired product. And a step of heat-treating the fired product at 600 to 800 ° C. in an inert gas atmosphere.

In the present invention, a high-capacity positive electrode active material can be obtained by a simple method by performing a heat treatment in an inert atmosphere after firing. In particular, according to the method of the present invention, a high-capacity positive electrode active material can be obtained even when a large amount of electrochemically inactive layered Li ₂ MnO ₃ is contained. Thereby, since content of expensive transition metals, such as Ni and Co, can be reduced, the positive electrode material which is advantageous in terms of cost and resources and has a high capacity can be obtained.

1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery, which is a representative embodiment of the present invention. Li is a _{[Li 1/3 Mn 2/3 O 2]} -LiNi 1/2 Mn 1/2 O 2 -LiNi 1/3 Mn 1/3 Co 1/3 basic composition diagram of _{O 2} system. Li [Li _1/3 Mn _2/3 O ₂ ]. (1-x) [yLiNi _1/2 Mn _1/2 O _2. (1-y) LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ] Is a schematic diagram showing a unit cell of FIG. 1 is a perspective view schematically showing an appearance of a stacked battery which is an embodiment of the present invention. FIG. 5A is an external view of an assembled battery according to an embodiment of the present invention, FIG. 5A is a plan view of the assembled battery, FIG. 5B is a front view of the assembled battery, and FIG. 5C is a side view of the assembled battery. It is a conceptual diagram of the vehicle carrying the assembled battery which concerns on one Embodiment of this invention. It is a graph which shows each measurement result of the X-ray-diffraction measurement of the positive electrode active material obtained in Example 1-1 (y = 1.00). It is a graph which shows each measurement result of the X-ray-diffraction measurement of the positive electrode active material obtained in Example 1-2 (y = 0.75). It is a graph which shows each measurement result of the X-ray-diffraction measurement of the positive electrode active material obtained in Example 1-3 (y = 0.50). It is a graph which shows each measurement result of the X-ray-diffraction measurement of the positive electrode active material obtained in Example 1-4 (y = 0.25). It is a graph which shows each measurement result of the X-ray-diffraction measurement of the positive electrode active material obtained in Example 1-5 (y = 0.00). It is a graph which shows each measurement result of the Raman spectroscopic measurement of the positive electrode active material obtained in Example 1-1 (y = 1.00). It is a graph which shows each measurement result of the Raman spectroscopic measurement of the positive electrode active material obtained in Example 1-2 (y = 0.75). It is a graph which shows each measurement result of the Raman spectroscopic measurement of the positive electrode active material obtained in Example 1-3 (y = 0.50). It is a graph which shows each measurement result of the Raman spectroscopic measurement of the positive electrode active material obtained in Example 1-4 (y = 0.25). It is a graph which shows each measurement result of the Raman spectroscopic measurement of the positive electrode active material obtained in Example 1-5 (y = 0.00). It is a graph which shows the measurement result of the discharge capacity and charge capacity in the cell for evaluation obtained in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5. It is a graph which shows the measurement result of the discharge capacity and charge capacity in the cell for evaluation of Comparative Example 1-1 to Comparative Example 3-5.

  One exemplary embodiment of the present invention includes a step of mixing a Li compound, a Mn compound, a Ni compound, and, if necessary, a raw material containing a Co compound to obtain a mixture, and firing the mixture at 900 to 1000 ° C. A process for obtaining a fired product, and a process for heat-treating the fired product at 600 to 800 ° C. in an inert gas atmosphere.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited only to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

  First, a basic configuration of a lithium ion battery to which a positive electrode material obtained by the manufacturing method of the present embodiment can be applied will be described with reference to the drawings.

[Battery overall structure]
In the present invention, the lithium ion battery is not particularly limited as long as it uses a positive electrode material for a lithium ion battery obtained by the production method of the present embodiment.

  For example, when the lithium ion battery is distinguished by its form / structure, it can be applied to any conventionally known form / structure, such as a stacked (flat) battery or a wound (cylindrical) battery. is there. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. is there.

  In the following description, as a representative embodiment, a case of a non-bipolar (internal parallel connection type) lithium ion secondary battery using a positive electrode material for a lithium ion battery will be described as an example. However, the technical scope of the present invention is not limited to the following forms.

  FIG. 1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) according to an embodiment of the present invention. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the negative electrode in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11, the electrolyte layer 17, and the positive electrode active material layer 15 are disposed on both surfaces of the positive electrode current collector 12. It has a configuration in which a positive electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are stacked in this order so that one negative electrode active material layer 13 and the positive electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent negative electrode, electrolyte layer, and positive electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 of the present embodiment has a configuration in which a plurality of the single battery layers 19 are stacked and electrically connected in parallel. In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer negative electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the outermost positive electrode current collector is arranged on one or both surfaces A positive electrode active material layer may be disposed.

  The negative electrode current collector 11 and the positive electrode current collector 12 are attached to a negative electrode current collector plate 25 and a positive electrode current collector plate 27 that are electrically connected to the respective electrodes (negative electrode and positive electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 are ultrasonically welded to the negative electrode current collector 11 and the positive electrode current collector 12 of each electrode via a negative electrode lead and a positive electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  Hereinafter, members constituting the battery of this embodiment will be described in detail.

(Positive electrode material for lithium ion battery)
In the present invention, the main active material (positive electrode material) of the positive electrode (positive electrode active material layer) is obtained by performing a heat treatment in an inert atmosphere after firing. That is, according to one aspect of the present invention, (1) a step of mixing a Li compound, a Mn compound, a Ni compound, and, if necessary, a raw material containing a Co compound to obtain a mixture (a raw material mixing step); 2) a step of firing the mixture at 900 to 1000 ° C. to obtain a fired product (main firing step); and (3) a step of heat-treating the fired product at 600 to 800 ° C. in an inert gas atmosphere (heat treatment step). A manufacturing method is provided. By using such a method, a positive electrode having performance (particularly, high capacity) equivalent to or higher than that of the positive electrode material obtained by the conventional method, without performing a rapid cooling process that is expensive and poor in efficiency and productivity. A material is obtained. This makes it possible to dramatically improve productivity and efficiency during mass production. Hereinafter, it demonstrates in detail in order of a process.

(1) Raw material mixing step First, as a starting material, a metal element compound constituting the positive electrode material, that is, a Li compound, a Mn compound, a Ni compound, and a raw material containing a Co compound as required, is weighed in a predetermined amount, Prepare a mixture of these. Although the kind in particular of these compounds is not restrict | limited, For example, a sulfate, nitrate, carbonate, acetate, oxalate, an oxide, a hydroxide, a halide etc. are mentioned.

Specifically, as the Li _{compound, Li 2 CO 3, Li (} OH), LiNO 3, CH 3 COOLi, can be used Li ₂ O or the like, the _Li 2 CO ₃ preferably with respect less hygroscopic Use. These Li compounds may be used individually by 1 type, and may use 2 or more types together. These Li compounds may be used in the form of hydrates.

As the Mn compound, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , MnSO ₄ , MnCO ₃ , Mn (NO ₃ ) ₂ , (CH ₃ COO) ₂ Mn, etc. can be used. Preferably, MnO ₂ is used from the economical aspect. These Mn compounds may be used individually by 1 type, and may use 2 or more types together. These Mn compounds may be used in the form of hydrates.

As the Ni compound, NiSO ₄ , Ni (OH) ₂ , NiO, NiCO ₃ · 2Ni (OH) ₂ , Ni (NO ₃ ) ₂ or the like can be used, and NiSO ₄ is preferably used from the viewpoint of economy. These Ni compounds may be used individually by 1 type, and may use 2 or more types together. These Ni compounds may be used in the form of hydrates.

Examples of the Co compound include CoSO ₄ , Co (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , (CH ₃ COO) ₂ Co, CoCl ₂ , Co (NO ₃ ) ₂ , C ₂ O ₄ Co, and the like. CoSO ₄ is preferably used from the viewpoint of economy. These Co compounds may be used individually by 1 type, and may use 2 or more types together. These Co compounds may be used in the form of hydrates.

  When other elements are included in addition to Li, Mn, Ni and, if necessary, Co, a compound of the element (for example, sulfate, nitrate, carbonate, acetate, oxalate, oxidation) Products, hydroxides, halides, etc.) may be added to the compounds of the above elements and mixed together.

  Any of these raw materials may be used in powder form. From the viewpoint of improving the uniformity of mixing and the reactivity during firing, the particle diameter of the raw material is preferably 0.01 to 200 μm in average particle diameter.

  The raw materials may be mixed by a method used for normal powder mixing, and either dry mixing or wet mixing can be selected. As a device used for mixing, known means such as a ball mill, a V blender, a mortar, a mixer, and a kneading device can be selected. The mixing time and the mixing temperature are not particularly limited, but are usually room temperature (23 ° C.) or more and 1 minute or more. If the mixing is insufficient, the performance (capacity characteristics, cycleability) of the positive electrode material finally obtained may be deteriorated. Therefore, it is preferable to mix the raw materials sufficiently until the raw materials are in a uniform state at the particle level. . What is necessary is just to determine the compounding quantity of a raw material according to the composition of positive electrode material which it is going to manufacture. The atmosphere at the time of mixing the raw materials is not particularly limited, and may be performed in an inert atmosphere or in the air, but it is preferable to perform in the air in consideration of manufacturing costs.

(Preliminary firing process)
Subsequently, the obtained mixture is preferably calcined before the main firing. However, the preliminary firing step is not an essential step, and the mixture of the raw materials for the positive electrode material obtained above may be subjected to main firing as it is. By performing preliminary firing, segregation of the positive electrode material can be prevented and a uniform mixed state can be obtained. The pre-baking temperature is preferably between 400 ° C and 900 ° C. If it is 400 degreeC or more, reaction will advance, and if it is 900 degreeC or less, it can prevent that baking advances and it becomes difficult to grind | pulverize. The pre-baking time is not particularly limited, but is usually about 24 hours. The atmosphere for pre-baking is not particularly limited as long as it contains oxygen, but it is preferable to perform in the air in consideration of the manufacturing cost.

  Thereafter, the calcined raw material is pulverized again using a ball mill, a V blender, a mortar, a mixer, a kneader, or the like to obtain a mixture of raw material powders. The degree of pulverization is not particularly limited, but pulverization may be performed so that the average particle diameter is 0.01 to 200 μm.

(2) Main firing step The mixture of raw materials obtained above or the mixture of raw material powders after preliminary firing is fired at 900 to 1000 ° C for a predetermined time to obtain a fired product. If the firing temperature is less than 900 ° C., the reaction does not proceed sufficiently, the amount of impurities increases, and the capacity may decrease. On the other hand, when the temperature exceeds 1000 ° C., grain growth is promoted too much, sintering between the particles proceeds excessively, and the capacity may be reduced. From the viewpoint of further increasing the capacity, the firing temperature is preferably 920 to 980 ° C. If necessary, the firing may be performed by multi-stage firing. The firing time may be a time sufficient to complete the firing, and is usually about 24 hours. The firing atmosphere is not particularly limited as long as it contains oxygen. However, considering the manufacturing cost, the firing is preferably performed in the air.

(3) Heat treatment process under inert gas atmosphere The fired product obtained above is heat treated at 600 to 800 ° C. under an inert gas atmosphere. By performing heat treatment under an inert gas atmosphere, structural changes such as rearrangement of atoms in the transition metal layer, stacking faults in the transition metal layer, generation of oxygen defects, etc. are promoted, so that high capacity can be expressed. It is thought that it becomes. At a temperature of 600 ° C. or higher, oxygen gas (O ₂ ) is actively stored and released, and microscopic structural changes of the fired product are likely to occur. However, a temperature of less than 600 ° C. is not preferable because microscopic structural changes of the fired product hardly occur. On the other hand, when it exceeds 800 ° C., crystallization may proceed excessively, which is not preferable. Although the time of heat processing is not specifically limited, Preferably it is 1 hour or more, More preferably, it is 4 to 24 hours. With such a time, the microscopic structural change of the fired product is sufficiently achieved, and a high-capacity positive electrode material can be obtained. As a kind of inert gas, there are noble gases such as nitrogen, hydrogen, and argon, preferably noble gases such as nitrogen and argon, and more preferably nitrogen.

Preferably, the main active material of the positive electrode (positive electrode active material layer) is Li [Li _1/3 Mn _2/3 ] O ₂ -LiNi _1/2 Mn _1/2 O ₂ -LiNi _1/3 Mn _{1 / It is a 3} Co _1/3 O ₂ based solid solution material. That is, in the manufacturing method according to an embodiment of the present invention, the lithium ion positive electrode material has the general formula:

And has a monoclinic (C2 / m) structure.

Conventionally, a so-called solid solution positive electrode material represented by xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMO ₂ (M is a transition metal such as Co or Ni) has been used. Although expected as a high-capacity material, battery characteristics differed greatly depending on the synthesis conditions such as the synthesis method and the amount of charged lithium, and it was difficult to obtain a positive electrode material having stable battery characteristics.

In contrast, in the present embodiment, a high-capacity positive electrode active material can be obtained even when a large amount of electrochemically inactive layered Li [Li _1/3 Mn _2/3 O ₂ ] is contained. . Thereby, since the content of expensive transition metals such as Ni and Co can be reduced, a positive electrode material having a high capacity and advantageous in terms of cost and resources can be obtained.

FIG. 2 shows a basic composition diagram of the Li [Li _1/3 Mn _2/3 ] O ₂ -LiNi _1/2 Mn _1/2 O ₂ -LiNi _1/3 Mn _1/3 Co _1/3 O ₂ system. As shown in FIG. 2, the solid solution materials are Li [Li _1/3 Mn _2/3 ] O ₂ , LiNi _1/2 Mn _1/2 O ₂ , and LiNi _1/3 Mn _1/3 Co _1/3. Consists of O ₂ . And the positive electrode material of this embodiment has the composition which belongs to the shaded part of FIG. Since Li [Li _1/3 Mn _2/3 ] O ₂ can also be expressed as Li ₂ MnO ₃ , in this specification, the solid solution material is referred to as “Li ₂ MnO ₃ —LiNi _1/2 Mn _1/2 O”. _It may be referred to as “ _2- LiNi _1/3 Mn _1/3 Co _1/3 O ₂ -based solid solution material”. The general formula (1) can also be expressed as the following formula (2).

  X in the general formulas (1) and (2) may be any number that satisfies 0.6 ≦ x <1. Particularly preferably, x = 0.6.

  Y in the general formulas (1) and (2) may be any number satisfying 0 ≦ y ≦ 1. However, 0 ≦ y ≦ 0.5 is preferable for a hybrid electric vehicle, and 0.5 ≦ y ≦ 1 is preferable for an electric vehicle.

The positive electrode material of this embodiment has a monoclinic crystal (C2 / m) structure. FIG. 3 shows Li [Li _1/3 Mn _2/3 O ₂ ]. (1-x) [yLiNi _1/2 Mn _1/2 O _2. (1-y) LiNi _1/3 Mn _1/3 Co _{1 / 3} is a schematic diagram showing a unit cell of [ ₃ O ₂ ]. FIG. Such a structure can be confirmed by X-ray diffraction measurement or Raman spectroscopic measurement.

The positive electrode material of the present embodiment may have a solid solution other than transition metal elements other than Mn, Ni, and Co. For example, the Mn site of Li [Li _1/3 Mn _2/3 O ₂ ] may be substituted with one or more transition metals selected from the group consisting of Ti and Zr. In the form of adding appropriate amounts of Ti and Zr to Mn, Ti and Zr are inferior in capacity characteristics compared to Mn, but contribute to the stabilization of the crystal structure, so a part of the high capacity of Mn (effect of increasing discharge capacity) Can be effectively utilized in applications where stabilization is required even at the expense of sacrificing the range. In addition, Mn, Ni, and Co sites of LiNi _1/2 Mn _1/2 O ₂ and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ are made of Cr, Al, Zr, Ti, Fe, Mg, and Zn. It may be substituted with at least one transition metal element selected from the group consisting of When these transition metals are added, a positive electrode material having a high capacity and good cycle durability can be produced.

  The solid solution represented by the general formula (1) can be identified by using X-ray diffraction (XRD), Raman spectroscopy, and inductively coupled plasma (ICP) elemental analysis.

  The above is the description regarding the characteristic configuration requirements of the lithium ion battery of the present embodiment, and the other configuration requirements are not particularly limited. Therefore, in the following, other constituent features than the characteristic constituent features of the lithium ion battery of the present invention will be described with a focus on the stacked battery shown in FIG. However, the present invention is not limited to these.

[Current collector]
As the current collector (the negative electrode current collector 11, the positive electrode current collector 12; the current collector 14), any member conventionally used as a current collector material for a battery can be appropriately employed. As an example, examples of the positive electrode current collector and the negative electrode current collector include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. Among these, from the viewpoints of electron conductivity and battery operating potential, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector. A typical thickness of the current collector is 10 to 20 μm. However, a current collector having a thickness outside this range may be used. The current collector plate can also be formed of the same material as the current collector.

[Active material layer]
The active material layers (the negative electrode active material layer 13 and the positive electrode active material layer 15) are configured to include an active material (negative electrode active material, positive electrode active material, reference electrode active material). In addition, these active material layers include a binder, a conductive agent for increasing electric conductivity, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and an electrolyte supporting salt for increasing ionic conductivity as necessary. (Lithium salt) and the like.

(A) Active material The material (material) of the positive electrode active material and the negative electrode active material is not particularly limited as long as it has the characteristic constituent features of the lithium ion battery of the present invention. What is necessary is just to select suitably according to the kind of.

Specifically, as the positive electrode active material, a positive electrode material for a lithium ion battery obtained by the above-described manufacturing method is used as a main active material of the positive electrode. As the positive electrode active material, a positive electrode material for a lithium ion battery obtained by the above-described production method may be used alone, or, if necessary, another conventionally known positive electrode active material may be used in combination. Conventionally known positive electrode active materials include lithium-manganese composite oxides (such as LiMn ₂ O ₄ ), lithium-nickel composite oxides (such as LiNiO ₂ ), lithium-cobalt composite oxides (such as LiCoO ₂ ), and lithium-iron. Complex oxides (such as LiFeO ₂ ), lithium-nickel-manganese complex oxides (such as LiNi _0.5 Mn _0.5 O ₂ ), lithium-nickel-cobalt complex oxides (LiNi _0.8 Co _0.2 O ₂₎ Etc.), lithium-transition metal phosphate compounds (such as LiFePO ₄ ), and lithium-transition metal sulfate compounds (Li _x Fe ₂ (SO ₄ ) ₃ ).

The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and any conventionally known negative electrode active material can be used. For example, high crystalline carbon graphite (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, Carbon materials such as thermal black), fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril; Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like, and simple elements of these elements alloyed with lithium oxide containing (silicon monoxide (SiO), SiO _x 0 <x <2), tin _{(SnO 2} dioxide), SnO x (0 <x <2), etc. SnSiO ₃₎ and carbides (such as silicon carbide (SiC)) or the like; a metal material of a lithium metal or the like; lithium - titanium Lithium-transition metal composite oxides such as composite oxides (lithium titanate: Li ₄ Ti ₅ O ₁₂ ); and other conventionally known negative electrode active materials can be used. The negative electrode active material may be used alone or in the form of a mixture of two or more.

  The average particle diameter of each active material contained in each active material layer (13, 15) is not particularly limited, but is usually about 0.1 to 100 μm from the viewpoint of high capacity, reactivity, and cycle durability. The thickness is preferably 1 to 20 μm.

The compounding ratio of the components contained in each active material layer (13, 15) is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries or lithium ion batteries. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a lithium ion secondary battery or a lithium ion battery can be referred suitably. For example, the thickness of the active material layer is about 2 to 100 μm. (B) Binder A binder is added to maintain the electrode structure by binding the active materials or the active material and the current collector. Is done.

  As such a binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA), Thermosetting resins such as polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), epoxy resins, polyurethane resins, and urea resins And rubber-based materials such as styrene butadiene rubber (SBR).

(C) Conductive agent A conductive agent means the conductive additive mix | blended in order to improve electroconductivity. The conductive agent that can be used in the present embodiment is not particularly limited, and a conventionally known one can be used. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the conductive agent is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement in reliability by improving output characteristics of the battery and improving liquid retention of the electrolyte.

(D) Electrolyte As the electrolyte, a liquid electrolyte, a gel polymer electrolyte, and an intrinsic polymer electrolyte described in the section of [Electrolyte layer] described later can be used without particular limitation. Specific forms of the liquid electrolyte, the gel polymer electrolyte, and the intrinsic polymer electrolyte will be described later in the section of (electrolyte layer), and the details are omitted here. These electrolytes may be used alone or in combination of two or more. Moreover, an electrolyte different from the electrolyte used for the electrolyte layer described later may be used, or the same electrolyte may be used.

[Electrolyte layer]
The electrolyte layer is a layer containing a non-aqueous electrolyte. A nonaqueous electrolyte (specifically, a lithium salt) contained in the electrolyte layer has a function as a carrier of lithium ions that moves between the positive and negative electrodes during charge and discharge. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte may be used.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). As the supporting salt (lithium _{salt), Li (CF 3 SO 2} ) 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 Compounds that can be added to the electrode mixture layer, such as SO _3, can be employed as well.

  On the other hand, the polymer electrolyte is classified into a gel polymer electrolyte containing an electrolytic solution (gel electrolyte) and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), polyacrylonitrile (PAN), Examples thereof include polymethyl methacrylate (PMMA) and copolymers thereof. Here, the ion conductive polymer may be the same as or different from the ion conductive polymer used as the electrolyte in the active material layer, but is preferably the same. The type of the electrolytic solution (electrolyte salt and plasticizer) is not particularly limited, and an electrolyte salt such as the lithium salt exemplified above and a plasticizer such as carbonates may be used.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

  The non-aqueous electrolyte contained in these electrolyte layers may be one kind alone, or two or more kinds.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel polymer electrolyte, a separator is used for the electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  It can be said that the thinner the electrolyte layer, the better to reduce the internal resistance. The thickness of the electrolyte layer is usually 1 to 100 μm, preferably 5 to 50 μm.

[Exterior body]
In a lithium ion secondary battery, it is desirable to accommodate the entire power generating element in an exterior body in order to prevent external impact and environmental degradation during use. As the exterior body, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

[Battery appearance]
FIG. 4 is a perspective view schematically showing the appearance of the stacked battery according to an embodiment of the present invention. As shown in FIG. 4, the stacked battery 10 has a rectangular flat shape, and a negative electrode current collector plate 25 and a positive electrode current collector plate 27 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 21 is encased in an outer package 29 of the battery 10 and the periphery thereof is heat-sealed. The power generation element 21 is sealed with the negative electrode current collector plate 25 and the positive electrode current collector plate 27 drawn out. Here, the power generation element 21 corresponds to the power generation element 21 of the stacked battery 10 shown in FIG. 1, and is composed of a negative electrode (negative electrode active material layer) 13, an electrolyte layer 17, and a positive electrode (positive electrode active material layer) 15. A plurality of battery layers (single cells) 19 are stacked.

  The lithium ion secondary battery of the present invention is not limited to a flat shape (stacked type) as shown in FIG. For example, the wound type lithium ion battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. . In the cylindrical shape, a laminate sheet or a conventional cylindrical can (metal can) may be used as the exterior material, and there is no particular limitation.

  Further, the removal of the current collector plates 25 and 27 shown in FIG. 4 is not particularly limited, and the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be drawn out from the same side or the negative electrode current collector plate 25. The positive electrode current collector plate 27 may be divided into a plurality of pieces and taken out from each side. Further, in a wound bipolar secondary battery, a terminal may be formed using, for example, a cylindrical can (metal can) instead of the current collector plate.

  According to this embodiment, a high-capacity lithium ion secondary battery can be provided. The lithium ion secondary battery of the present embodiment is a power source for driving a vehicle that requires a high volume energy density and a high volume output density as a large capacity power source such as an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, and a hybrid fuel cell vehicle. It can be suitably used for an auxiliary power source.

[Battery]
A plurality of the batteries of this embodiment may be connected in parallel and / or in series to form an assembled battery. FIG. 5 is an external view of an assembled battery according to an embodiment of the present invention. 5A is a plan view of the assembled battery, FIG. 5B is a front view of the assembled battery, and FIG. 5C is a side view of the assembled battery.

  In the form shown in FIG. 5, a small assembled battery 35 that can be attached and detached by connecting a plurality of the stacked batteries 10 of the above embodiment in series and / or in parallel is formed. A plurality of small assembled batteries 35 that can be attached and detached are connected in series and / or in parallel to form an assembled battery 37. As a result, the assembled battery 37 is an assembled battery 37 having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density. The small assembled batteries 35 that can be attached and detached are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries 35 are stacked in a plurality of stages using a connection jig 39. It is mounted how many non-bipolar or bipolar lithium ion secondary batteries are connected to produce the assembled battery 35, and how many assembled batteries 35 are stacked to produce the assembled battery 37. What is necessary is just to determine according to the battery capacity and output of the vehicle (electric vehicle) to be. According to this embodiment, a high-capacity assembled battery can be provided.

[vehicle]
The stacked battery 10 or the assembled battery 37 can be used as a power source for driving the vehicle. The stacked battery 10 or the assembled battery 37 is, for example, a hybrid electric vehicle, a fuel cell vehicle, and an electric vehicle (all are automobiles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) as well as two-wheeled vehicles. (Including motorcycles and tricycles). Thereby, the motor vehicle excellent in the charge / discharge cycle can be provided. However, the application is not limited to automobiles. For example, if it is another vehicle, it can be applied to various power sources for moving bodies such as trains, and it can be used for mounting uninterruptible power supplies and the like. It can also be used as a power source.

  FIG. 6 is a conceptual diagram of a vehicle equipped with the assembled battery 37 of the present invention. As shown in FIG. 6, in order to mount the assembled battery 37 in a vehicle such as the automobile 40, the assembled battery 37 is mounted under the seat in the center of the vehicle body of the automobile 40. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 37 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or may be mounted in an engine room in front of the vehicle. The automobile 40 using the assembled battery 37 as described above has excellent durability and can provide a sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

1. Synthesis of Solid Solution Cathode Material [Examples 1-1 to 1-5]
(A) Raw material mixing step First, lithium carbonate (Li ₂ CO ₃ ), manganese dioxide (MnO ₂ ), cobalt oxide (Co ₃ O ₄ ), and nickel oxide (NiO) in predetermined amounts (the above general formula (1) and In (2), weighed so that x = 0.6 and the value of y is the value shown in Table 1 below, and mixed them in the atmosphere using an agate mortar and pestle for 1-2 hours. .

(B) Temporary calcination step The obtained mixture was calcined at 600 ° C for 12 hours in the air, and then calcined at 850 ° C for 24 hours. The obtained calcined product was pulverized and mixed using a ball mill.

(C) Main firing step Thereafter, the obtained mixture was fired in the air at 950 ° C for 24 hours.

(D) Heat treatment step under inert gas atmosphere The obtained fired product was heat treated at 600 ° C. for 4 hours under a nitrogen gas atmosphere. Thereby, it has a composition formula of Li [Li _1/5 Mn _{8/15 + y / 15} Ni _{2/15 + y / 15} Co _{2 / 15-2y / 15} ] O ₂ , and y = 0, 0.25, 0.5 , 0.75, and 1 were obtained as solid solution positive electrode materials, respectively. Note that Li [Li _1/5 Mn _{8/15 + y / 15} Ni _{2/15 + y / 15} Co _{2 / 15-2y / 15} ] O ₂ is x = 0.6 in the above general formulas (1) and (2). This corresponds to the composition formula.

[Comparative Examples 1-1 to 1-5]
(D) A solid solution positive electrode material was obtained in the same manner as in Example 1-1 except that the heat treatment step under an inert gas atmosphere was not performed.

[Comparative Examples 2-1 to 2-5]
(C) A solid solution positive electrode material was prepared in the same manner as in Example 1-1 except that it was calcined at 800 ° C. for 24 hours in the main firing step and (d) the heat treatment step in an inert gas atmosphere was not performed. Obtained.

[Comparative Examples 3-1 to 3-5]
(C) A solid solution positive electrode material was prepared in the same manner as in Example 1-1 except that it was calcined at 1000 ° C. for 24 hours in this firing step and (d) the heat treatment step was not performed under an inert gas atmosphere. Obtained.

2. Analysis of Synthetic Sample X-ray diffraction measurement and Raman spectroscopic measurement were performed on the positive electrode materials obtained in Examples 1-1 to 1-5. The measurement results are shown in FIGS. 7A to 7E and FIGS. 8A to 8E, respectively. For reference, X-ray diffraction data of Li ₂ MnO ₃ whose crystal structure belongs to the space group C2 / m is shown in the lower part of FIGS. 7A to 7E, and in the lower part of FIGS. 8A to 8E. The Raman spectroscopic data of Li ₂ MnO ₃ whose crystal structure belongs to the space group C2 / m are shown. From these results, it was confirmed that the crystal structure of the synthesized sample had a monoclinic structure (space group: C2 / m) similar to Li ₂ MnO ₃ .

3. Evaluation of Positive Electrode Material (1) Preparation of Electrode and Evaluation Cell An evaluation cell was prepared by the following procedure using the positive electrode active materials shown in Tables 1 to 3 above. First, a positive electrode active material: conductive binder (TAB-2) = 66: 34 (mass ratio) was formed into a pellet having a diameter of 16 mm using a kneading method, and a stainless mesh having the same diameter (current collector). The sample was pressure-bonded to 2 tons and dried by heating at 120 ° C. for 4 hours under vacuum to obtain a sample positive electrode. The amount of active material per unit area was fixed at 10 mg.

Metallic lithium was used as the negative electrode. The sample positive electrode and negative electrode obtained above were opposed to each other through two 25 μm-thick polypropylene porous membranes as separators and placed on the bottom of the coin cell. Subsequently, after mounting a gasket for maintaining insulation between the positive electrode and the negative electrode, an electrolyte was injected using a syringe, and a spring and a spacer were laminated. Then, the upper part of the coin cell was overlapped and caulked to obtain an evaluation cell. In addition, as electrolyte solution, electrolyte solution of ethylene carbonate (EC): diethyl carbonate (DEC) = 1: 2 (volume ratio) of 1M LiPF ₆ was used.

(2) Charge / Discharge Test After charging each evaluation cell produced by the above method at a constant current of 0.4 mA until 4.8 V (= maximum potential), 2.0 V (= minimum potential) It was made to discharge until. The charge capacity and discharge capacity at this time were measured. The results are shown in FIG. 9 and FIG.

  FIG. 9 is a graph showing the measurement results of the discharge capacity and the charge capacity in the evaluation cells obtained in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5. From FIG. 9, it is confirmed that the cell of the example in which the heat treatment was performed in the nitrogen gas atmosphere generally has a higher charge capacity and discharge capacity than the cell in which the heat treatment was not performed in the nitrogen gas atmosphere. In particular, the evaluation cells of Examples 1-1 to 1-3, in which the Co content ratio is small and 0.5 ≦ y ≦ 1.0, are compared to the cells that are not heat-treated in a nitrogen gas atmosphere. It was confirmed that the discharge capacity was significantly improved.

  FIG. 10 is a graph showing the measurement results of the discharge capacity and the charge capacity in the evaluation cells of Comparative Examples 1-1 to 3-5. From FIG. 10, the evaluation cell of Comparative Example 1 having a firing temperature of 950 ° C. generally has a charge capacity and a discharge capacity as compared with the evaluation cell of Comparative Example 2 or 3 having a firing temperature of 900 ° C. or 1000 ° C. It is confirmed that it is expensive.

  From the above, it was confirmed that a high-capacity positive electrode active material can be obtained by performing a heat treatment in a nitrogen gas atmosphere. In particular, the effect of increasing the capacity by this heat treatment is remarkably exhibited when the content of expensive Co element is reduced, and it has been found that a high-capacity positive electrode material that is advantageous in terms of cost and resources can be obtained.

10 stacked battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer (negative electrode),
15 positive electrode active material layer (positive electrode),
17 electrolyte layer,
19 Single battery layer (single cell),
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 exterior body (laminate sheet),
35 A small assembled battery that can be attached and detached,
37 battery pack,
39 Connecting jig,
40 cars,
101 lithium atom (Li),
102 oxygen atoms (O),
103 Transition metal atom.

Claims (4)

A step of mixing a raw material containing a Li compound, a Mn compound, a Ni compound, and, if necessary, a Co compound to obtain a mixture;
Firing the mixture at 900 to 1000 ° C. in an oxygen-containing atmosphere to obtain a fired product;
Heat-treating the fired product at 600 to 800 ° C. in an inert gas atmosphere;
Having the general formula:
(In the formula, 0.6 ≦ x <1 and 0 ≦ y ≦ 1)
And a method for producing a positive electrode material for a lithium ion battery having a monoclinic crystal (C2 / m) structure . 0.5 is ≦ y ≦ 1.0, A process according to claim 1. x = 0.6, the manufacturing method according to claim 1 or 2. The lithium ion battery which uses the positive electrode material for lithium ion batteries manufactured by the manufacturing method of any one of Claims 1-3 as a positive electrode active material.