JP3968420B2 - Cubic rock salt type lithium ferrite complex oxide and method for producing the same - Google Patents

Description

【００４７】
実施例２および比較例２
上記実施例１および比較例１で得られた各試料を正極材料とし、金属リチウムを負極材料として、LiPF₆をエチレンカーボネートとジメチルカーボネートとの混合溶媒に溶解させた１Ｍ溶液を電解液として、リチウム電池としての充放電特性(電位範囲2.5-4.3V、電流密度7.5mA/g)を検討した(図４)。
【００４８】
実施例1による正極材料と比較例1による正極材料において、初期充電容量はともに130mAh/g以上であるが、初期および10サイクル後の充放電曲線(図４において、右上がりの曲線が充電曲線に対応し、右下がりの曲線が放電曲線に対応する)が著しく異なっている。特に、4V付近の電位平坦部の初期および10サイクル後の容量において、実施例1による試料の方が、比較例1による試料に比して、大きな値を示している。
【図面の簡単な説明】
【図１】本発明によるLi_1+x(Ti_1-y-zFe_yNi_z)_1-xO₂の結晶構造を示す模式的な斜面図である。
【図２】実施例１で得られたLi_1+x(Fe_0.5Ni_0.25Ti_0.25)_1-xO₂のX線回折パターン(a)と比較例１で得られたLi_1+x(Fe_0.5Ti_0.50)_1-xO₂のX線回折パターン(b)とを示す図面である。
【図３】実施例1で得られたLi_1+x(Fe_0.5Ni_0.25Ti_0.25)_1-xO₂の透過型電子顕微鏡写真を電子的に画像処理した図面である。
【図４】実施例１で得られたLi_1+x(Fe_0.5Ni_0.25Ti_0.25)_1-xO₂ (a)および比較例1で得られたLi_1+x(Fe_0.5Ti_0.50)_1-xO₂ (b)をそれぞれ正極材料とし、Li金属を負極材料とする2種のコイン型リチウム電池の初期および10サイクル後の充放電特性を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium ferrite composite oxide useful as a positive electrode material for a next-generation low-cost lithium ion secondary battery and a method for producing the same.
[0002]
[Prior art]
In Japan, most of the secondary batteries installed in portable devices such as mobile phones and notebook computers are lithium ion secondary batteries. In addition, lithium ion secondary batteries are expected to be put into practical use as large batteries for electric vehicles and power load leveling systems in the future, and their importance is increasing.
[0003]
Currently, in lithium ion secondary batteries, a lithium cobalt oxide (LiCoO ₂ ) material is mainly used as a positive electrode material, a carbon material such as graphite is used as a negative electrode material, and an organic electrolyte is used as an electrolyte.
[0004]
In particular, LiCoO ₂ as the positive electrode material has a battery operating voltage (difference between the redox potential of the transition metal in the positive electrode and the redox potential of the negative electrode element), charge / discharge capacity (the amount of Li that can be desorbed and inserted from the positive electrode). ) And other important materials related to battery performance, and demand is expected to increase further in the future. However, since this compound contains cobalt which is a rare metal, it is one of the high cost factors of the lithium ion secondary battery. Furthermore, considering that about 20% of the world's cobalt production is already used in the battery industry, it is unclear whether the cathode material consisting of LiCoO ₂ alone can meet future demand growth. Yes, the danger of cobalt resource depletion cannot be ignored.
[0005]
Currently, as a cheaper and more cathode material less resource limitations, lithium nickel oxide (LiNiO _2), lithium manganese oxide and (LiMn ₂ O ₄₎ or the like are known, some are replaced in LiCoO ₂ practical It has become. However, these materials have problems such as safety problems during battery charging (LiNiO ₂ ) and significant characteristic degradation due to manganese dissolution at 50 ° C. or higher (LiMn ₂ O ₄ ). Replacement of LiCoO ₂ with these materials has not progressed as expected.
[0006]
In addition, lithium ferrite (LiFeO ₂ ) containing iron, which is more abundant in resources, less toxic, and cheaper than manganese and nickel, is being investigated as a potential electrode material. However, lithium ferrite obtained by high-temperature firing using a normal iron source and Li source hardly charges or discharges (that is, has no activity as a positive electrode material of a lithium ion secondary battery).
[0007]
On the other hand, as a starting material alpha-NaFeO ₂ or FeOOH, LiFeO ₂ obtained using the H / Li ion exchange or Na / Li ion exchange method, although a charge flat potential in the vicinity of 4V, discharge potential Is less than 3V. (R. Kanno, T. Shirane, Y. Kawamoto, Y. Takeda, M. Takano, M. Ohashi and Y. Yamaguchi, J. Electrochem. Soc., 143, [8], 2435, (1996); Sakurai, H. Arai, S. Okada and J. Yamaki, J. Power Sources, 68, 711, (1997); L. Guenne, P. Deniard, A. Lecerf, P. Biensan, C. Siret, L. Fournes and R. Brec, Ionics, 4, 220, (1998); JP-A-10-120421, JP-A-8-295518, etc.). Discharge potential of LiFeO ₂ obtained by such ion exchange method, as compared to the discharge potential of LiCoO _2, about 2V or more low, alternative LiCoO ₂ by LiFeO ₂ is rather difficult. As described above, a production technique for lithium ferrite reaching a practical level has not yet been established.
[0008]
The present inventors have prepared a lithium-containing iron-titanium oxide having a cubic rock salt structure ((Li _{1 + x} (Ti _1-y Fe _y ) _1-x O ₂ (where 0 ≦ x <0.33, 0.05 <Y <0.95)) has been found to function as a positive electrode material for a 3V-class lithium secondary battery having a discharge capacity of 100 mAh / g or more (Japanese Patent Application No. 2001- filed on August 1, 2001) 233197; hereinafter, this application is referred to as a "prior application").
[0009]
However, as a positive electrode material that can replace LiCoO ₂ in a lithium secondary battery, it is particularly desirable to have a discharge flat potential in the vicinity of 4V. If a lithium ferrite composite oxide that has an operating voltage of 4 V or higher, is inexpensive, and is not subject to resource constraints, the usefulness of a lithium ion battery that uses this as a positive electrode material becomes more useful. It will be even higher.
[0010]
[Problems to be solved by the invention]
Therefore, the present invention is a novel that can be stably charged and discharged in an operating voltage region (about 4 V) equivalent to that of an existing lithium cobalt oxide-based positive electrode material by using an inexpensive raw material with less resource restrictions. The main purpose is to provide new materials.
[0011]
[Means for Solving the Problems]
The present inventor has intensively studied in view of the problems of the prior art including the invention of the prior application.
[0012]
As a result, the iron-titanium-nickel in which a specific amount of Ni is further dissolved in the lithium-containing iron-titanium oxide Li _{1 + x} (Ti _1-y Fe _y ) _1-x O _{2 according to the} prior application. When the contained solid solution is used as a positive electrode material of a lithium ion secondary battery, it has been found that the cycle deterioration in the 4V region is remarkably improved, and the present invention has been completed.
[0013]
That is, the present invention provides a lithium ferrite composite oxide, a method for producing the lithium ferrite composite oxide, a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery comprising the lithium ferrite composite oxide.
1. Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) in the represented, and Li / (Ti + Fe + Ni ) of values (molar ratio) is 1.2, the lithium ferrite based composite oxide having a cubic rock salt structure.
2. A mixed aqueous solution containing water-soluble titanium salt, water-soluble iron salt and water-soluble nickel salt is coprecipitated with alkali, and the resulting precipitation product is hydrothermally treated in the temperature range of 101 to 400 ° C together with an oxidizing agent and water-soluble lithium salt. Then, after removing excess salts, the hydrothermal treatment reaction product is heat-treated at 300 to 800 ° C. The method for producing a lithium ferrite-based composite oxide according to Item 1 above,
3. Item 3. The method for producing a lithium ferrite composite oxide according to Item 2, wherein the hydrothermal treatment reaction product is heat-treated in air, in an oxidizing atmosphere, or in a reducing atmosphere.
4). Item 4. The method for producing a lithium ferrite composite oxide according to Item 3, wherein a lithium salt is added to and mixed with the hydrothermal reaction product before heat treatment, the heat treatment is performed, and then the heat treatment product is washed with a solvent to remove excess lithium salt. .
5). Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) in the represented, and Li / (Ti + Fe + Ni ) of values (molar ratio) is 1.2, a positive electrode material for a lithium ion secondary battery comprising lithium ferrite composite oxide having a cubic rock salt structure.
6). Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) in expressed, and the value of Li / (Ti + Fe + Ni ) ( molar ratio) is 1.2, a lithium ion secondary to a positive electrode material components comprising lithium ferrite composite oxide having a cubic rock-salt type structure Next battery.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The nickel-containing lithium ferrite oxide according to the present invention has a cubic rock salt structure similar to α-LiFeO ₂ . In this structure, Li ions, Fe ions, and Ni ions are randomly distributed at the positions between the octahedral lattices of the oxide ions that are close packed in cubic. In the nickel-containing lithium ferrite-based oxide Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ of the present invention, it is confirmed that Ti and Ni ions occupy the same lattice positions as Fe ions. Features. That is, Fe ions are diluted by coexistence with both ions. LiFeO ₂ in which both ions do not coexist has almost no charge / discharge capacity.
[0015]
Therefore, the amount of Fe ions to be dissolved is preferably about 5 to 95 mol% (0.05 ≦ Fe / Fe + Ti + Ni ≦ 0.95) of the amount of transition metal (Fe + Ti + Ni) ions, 20 to 80 More preferably, it is about mol%. When the amount of solid solution of Fe is too large, Fe that does not participate in charge / discharge increases, which is not preferable in terms of battery characteristics. On the other hand, when the amount of Fe dissolved is too small, the charge / discharge capacity becomes small, which is also not preferable.
[0016]
The amount of Ni ions to be dissolved is preferably 50 mol% (0 <z ≦ 0.5), more preferably 1 to 50 mol%. When the amount of Ni dissolved is too small, the discharge capacity deteriorates in the 4V region, which is not preferable in terms of battery characteristics. On the other hand, when the amount of Ni, which is expensive compared to Ti and Fe, is too large, the low cost characteristic of the material of the present invention is lost.
[0017]
The nickel-containing lithium ferrite-based oxide according to the present invention has an impurity phase such as lithium hydroxide and lithium carbonate derived from the production raw material within a range that does not substantially affect the charge / discharge characteristics (up to about 10 mol%). It may contain a small amount.
[0018]
The composite oxide of the present invention can be produced by a hydrothermal reaction method, a solid phase reaction method, or the like, which is a common composite oxide synthesis method. However, in general, in a solid-phase reaction method using a dry mixing process, it is difficult to homogeneously mix metal ions (particularly, mixing Fe ions, Ti ions, and Ni ions). Therefore, the composite metal oxide of the present invention is more preferably produced by a hydrothermal reaction method using a mixed solution in which a metal salt that is a source of each ion is dissolved in water, a water / alcohol mixture, or the like. .
[0019]
In the present invention, the hydrothermal reaction is usually carried out by adding an alkaline aqueous solution to an aqueous solution containing water-soluble iron salt, water-soluble titanium salt and water-soluble nickel salt or a water-alcohol mixed solution to obtain a coprecipitate, followed by oxidation. This is performed by heating the coprecipitate and the lithium source compound in the presence of the agent.
[0020]
Source materials for metals other than Li used in the hydrothermal reaction method (Ti, Fe and Ni) include water-soluble salts (chlorides, nitrates, sulfates, oxalates, acetates, etc.), hydroxides, etc. Can be mentioned. These salts may be either anhydrides or hydrates. These salts and hydroxides may be used alone or in combination of two or more for any metal. As the metal source, for any metal, an aqueous solution in which a metal oxide is dissolved with an acid such as hydrochloric acid may be used.
[0021]
As the lithium source to be hydrothermally reacted with the coprecipitate obtained as described above, lithium hydroxide (anhydride and / or hydrate), lithium chloride, lithium nitrate, lithium carbonate and the like are preferable.
[0022]
The Li / (Fe + Ti + Ni) molar ratio in the mixed aqueous solution used in the hydrothermal reaction is appropriately selected according to the Li / (Fe + Ti + Ni) molar ratio in the target composite metal oxide. be able to. This molar ratio is preferably about 1 to 3, and more preferably about 1.5 to 2.5.
[0023]
As an alkali source for forming a coprecipitate from the mixed aqueous solution, lithium hydroxide, sodium hydroxide, potassium hydroxide, aqueous ammonia and the like are preferable.
[0024]
The method for producing a metal composite oxide according to the present invention is classified into two modes depending on whether the removal of the excess lithium compound is performed before or after calcination of the hydrothermal reaction product.
[0025]
More specifically, when producing a metal composite oxide according to an embodiment of the present invention, a total molar ratio of iron salt, titanium salt and nickel salt is about 0.01 to 5M (anhydride conversion), more preferably Dissolve in distilled water or distilled water-alcohol mixed solvent so that the concentration is about 0.1 to 2M. Next, while stirring the obtained mixed solution, an alkaline aqueous solution such as potassium hydroxide corresponding to about 0.1 to 20M, more preferably about 0.5 to 10M is dropped until the mixed solution becomes completely alkaline (pH 11 or more). By doing so, a coprecipitate is generated. After completion of the dropwise addition, the coprecipitate is heated while blowing air into the reaction solution at a temperature of about 0 to 150 ° C., more preferably about 20 to 100 ° C., for about 2 to 7 days, more preferably about 3 to 5 days. Oxidation / aging process is performed. Next, the obtained precipitate is washed with distilled water to remove excess alkali components and residual salts, and the filtered precipitate is dried at a temperature of 80 ° C. or higher (usually about 100 ° C.) to purify the precipitate. Fe-Ni-Ti coprecipitate is obtained.
[0026]
The purified coprecipitate is then mixed with distilled water in a beaker (eg, a polytetrafluoroethylene beaker) to which lithium hydroxide (anhydride and / or hydrate), lithium chloride, lithium nitrate, lithium carbonate Lithium salt such as about 0.1 to 10M, more preferably about 1 to 8M, and further oxidizing agent such as potassium chlorate and hydrogen peroxide is about 0.1 to 10M, more preferably about 0.5 to 5M. After that, the beaker is left in a hydrothermal reactor (for example, a commercially available autoclave), and the mixture is subjected to a hydrothermal reaction. Hydrothermal reaction conditions are not particularly limited, but are usually about 100 to 400 ° C. for about 0.1 to 150 hours, more preferably about 150 to 300 ° C. for about 1 to 100 hours. .
[0027]
After completion of the hydrothermal reaction, the reaction product is washed with water, water-alcohol, acetone, etc. to remove residual salts, filtered, and heated at a temperature of 80 ° C. or higher (more preferably about 100 ° C.). By drying, a desired cubic rock salt type lithium ferrite composite oxide is obtained.
[0028]
In the present invention, if necessary, in order to further improve the crystallinity as a cubic rock salt type lithium ferrite composite oxide, the composite oxide obtained above is pulverized, and is in a powder form or an aqueous solution form. Li salt (lithium hydroxide, lithium chloride, lithium nitrate, lithium carbonate, etc.), in the atmosphere, in an oxidizing atmosphere, in an inert atmosphere or in a reducing atmosphere, about 200-800 ° C. (more preferably 300- It may be fired at about 600 ° C. for about 1 to 100 hours (more preferably about 20 to 60 hours). The lithium salt is more preferably used in the form of an aqueous solution in order to ensure the uniformity of the reaction. Further, after the calcination, if necessary, the baked product is washed with water or a solvent to remove excess lithium salt, filtered, and then filtered at a temperature of 80 ° C. or higher (more preferably about 100 ° C.). ) May be heat-dried.
[0029]
Furthermore, by repeating a series of operations of pulverizing, baking, washing, and drying this heat-dried product, the excellent properties of lithium ferrite-based composite oxides (operation as a positive electrode material for lithium ion secondary batteries) Stable charge / discharge characteristics in the voltage region, high capacity, etc.) can be further improved.
[0030]
The lithium ion secondary battery using the lithium ferrite composite oxide according to the present invention can be manufactured by a known method. That is, the novel composite oxide according to the present invention is used as the positive electrode material, the known metal lithium, carbon-based material (activated carbon, graphite), etc. are used as the negative electrode material, and the known ethylene carbonate and dimethyl are used as the electrolyte. Assembling a lithium ion secondary battery according to a conventional method using a solution in which a lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a solvent such as carbonate, and using other known battery components Can do.
[0031]
【The invention's effect】
According to the present invention, a novel lithium ferrite composite oxide that can be stably charged and discharged in an operating voltage range (about 4 V) equivalent to that of an existing lithium cobalt oxide-based positive electrode material using an inexpensive raw material Material can be obtained.
[0032]
The lithium ferrite composite oxide according to the present invention is extremely useful as a low-cost positive electrode material for lithium ion secondary batteries with little cycle deterioration.
[0033]
【Example】
Examples and comparative examples are shown below to further clarify the features of the present invention. The present invention is not limited to these examples.
[0034]
The crystal phase of each oxide sample obtained in the following examples and comparative examples is determined by X-ray diffraction analysis, the composition is determined by inductively coupled plasma spectroscopy (ICP) and atomic absorption analysis, and the particle size is determined by transmission electron. Each was evaluated with a microscope (TEM). Moreover, a coin-type lithium battery using each oxide as a positive electrode material and metallic lithium as a negative electrode material was produced, and its charge / discharge characteristics were measured.
Example 1
Iron sulfate (II) sulfate heptahydrate 34.75 g, nickel chloride (II) hexahydrate 14.86 g and 30% titanium sulfate (IV) aqueous solution 50 g (total amount 0.25 mol, Fe: Ti: Ni molar ratio = 2: 2: 1) was added to 400 ml of distilled water and completely dissolved. While this aqueous solution was stirred, a potassium hydroxide aqueous solution (a solution obtained by dissolving 100 g of sodium hydroxide in 400 ml of distilled water) was gradually added dropwise to form a precipitate. After confirming that the reaction solution was completely alkaline (pH 11 or higher) and stirring, the reaction solution containing the coprecipitate was blown at room temperature for 3 days to oxidize the reaction solution. The precipitate was aged by holding for one day.
[0035]
The resulting precipitate was washed with distilled water and filtered, then placed in a polytetrafluoroethylene beaker with 40 g of lithium hydroxide monohydrate, 40 g of potassium chlorate, and 200 ml of distilled water. It was placed in a thermal reactor (autoclave) and hydrothermally treated at 220 ° C. for 8 hours.
[0036]
After the hydrothermal treatment is completed, the reaction furnace is cooled to near room temperature, the beaker containing the hydrothermal treatment reaction solution is taken out of the autoclave, and the generated precipitate is washed with distilled water to remove excess lithium hydroxide and the like. Salts were removed, filtered and dried to give a powdered product.
[0037]
Next, in order to improve the crystallinity of the resulting product, the product powder and lithium hydroxide aqueous solution in which 0.25 mol (10.49 g) of lithium hydroxide monohydrate was dissolved in 150 ml of distilled water were mixed, It was dried at 100 ° C. and pulverized, and the obtained powder was calcined at 500 ° C. for 20 hours in the air. Subsequently, in order to remove excess lithium salt, the fired product was washed with distilled water, filtered and dried to obtain a black powdery product.
[0038]
The X-ray diffraction pattern of this final product is shown in FIG. All peaks are shown in the existing powder X-ray diffraction data (JCPDS card 17-0938 and “JCMikkelsen, J. AM. Ceram. Soc., 63, 332, (1980)”). -LiFeO ₂ and Li _1.33 Ti _0.67 O ₂ unit cells (space group: Fm3m, a = 4.158 and 4.140 Å) could be indexed.
[0039]
The lattice constant (a = 4.1437 ± 0.0002Å) calculated from each peak of the final product obtained in this example has an intermediate value between α-LiFeO ₂ and Li _1.33 Ti _0.67 O _2. According to chemical analysis (Table 1 below), Fe and Ni are contained almost as much as 51 ± 1 mol% and 26 ± 1 mol%, respectively, and the Li / (Fe + Ti + Ni) value Since it was approximately 1.2, it was confirmed that Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ was obtained in this example.
[0040]
FIG. 3 is a drawing of electronic image processing of an electron micrograph of Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ obtained in this example. From FIG. 3, it is clear that Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ according to this example is composed of fine particles having a particle size of about 100 nm and having almost the same shape. .
Comparative Example 1
34.75 g of iron (II) sulfate heptahydrate and 50 g of 30% titanium sulfate (IV) aqueous solution (total amount 0.25 mol, Fe: Ti molar ratio = 1: 1) were added to 400 ml of distilled water and completely dissolved. While this aqueous solution was stirred, a potassium hydroxide aqueous solution (a solution obtained by dissolving 100 g of sodium hydroxide in 400 ml of distilled water) was gradually added dropwise to form a precipitate. After confirming that the reaction solution was completely alkaline (pH 11 or higher) and stirring, the reaction solution containing the coprecipitate was blown at room temperature for 3 days to oxidize the reaction solution. The precipitate was aged by holding for one day.
[0041]
The resulting precipitate was washed with distilled water and filtered, then placed in a polytetrafluoroethylene beaker with 40 g of lithium hydroxide monohydrate, 40 g of potassium chlorate, and 200 ml of distilled water. It was placed in a thermal reactor (autoclave) and hydrothermally treated at 220 ° C. for 8 hours.
[0042]
After the hydrothermal treatment is completed, the reaction furnace is cooled to near room temperature, the beaker containing the hydrothermal treatment reaction solution is taken out of the autoclave, and the generated precipitate is washed with distilled water to remove excess lithium hydroxide and the like. Salts were removed, filtered and dried to give a powdered product.
[0043]
Next, in order to improve the crystallinity of the resulting product, the product powder and lithium hydroxide aqueous solution in which 0.25 mol (10.49 g) of lithium hydroxide monohydrate was dissolved in 150 ml of distilled water were mixed, It was dried at 100 ° C. and pulverized, and the obtained powder was calcined at 500 ° C. for 20 hours in the air. Subsequently, in order to remove excess lithium salt, the fired product was washed with distilled water, filtered and dried to obtain a powdery product.
[0044]
The X-ray diffraction pattern of this final product is shown in FIG. All peaks are shown in existing powder X-ray diffraction data (JCPDS card 17-0938 and “JCMikkelsen, J. Am. Ceram. Soc., 63, 332, (1980)”). -LiFeO ₂ and Li _1.33 Ti _0.67 O ₂ unit cells (space group: Fm3m, a = 4.158 and 4.140 Å) could be indexed.
[0045]
The lattice constant (a = 4.1445 ± 0.0015Å) calculated from each peak of the final product obtained in this comparative example has an intermediate value between α-LiFeO ₂ and Li _1.33 Ti _0.67 O _2. In this comparative example, the chemical analysis (Table 1 below) shows that Fe is contained as much as 54 ± 2 mol% as charged, and the Li / (Fe + Ti) value is approximately 1.4. It was confirmed that Li _{1 + x} (Fe _0.5 Ti _0.50 ) _1-x O ₂ was obtained.
[0046]
[Table 1]

[0047]
Example 2 and Comparative Example 2
Each sample obtained in Example 1 and Comparative Example 1 was used as a positive electrode material, metallic lithium as a negative electrode material, and a 1M solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate as an electrolytic solution. The charge / discharge characteristics (potential range 2.5-4.3V, current density 7.5mA / g) as a battery were examined (FIG. 4).
[0048]
In the positive electrode material according to Example 1 and the positive electrode material according to Comparative Example 1, both initial charge capacities are 130 mAh / g or more, but the initial and 10th cycle charge / discharge curves (in FIG. 4, the upward curve is the charge curve). Correspondingly, the lower right curve corresponds to the discharge curve). In particular, the sample according to Example 1 shows a larger value than the sample according to Comparative Example 1 in the initial stage of the potential flat portion near 4 V and the capacity after 10 cycles.
[Brief description of the drawings]
FIG. 1 is a schematic slope view showing a crystal structure of Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ according to the present invention.
FIG. 2 shows the X-ray diffraction pattern (a) of Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ obtained in Example 1 and Li _{1 + x} (Fe ₁ is a drawing showing an X-ray diffraction pattern (b) of _0.5 Ti _0.50 ) _1-x O ₂ .
3 is a drawing obtained by electronic image processing of a transmission electron micrograph of Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ obtained in Example 1. FIG.
4 shows Li _{1 + x} (Fe _0.5 Ni _0.25 Ti _0.25 ) _1-x O ₂ (a) obtained in Example 1 and Li _{1 + x} (Fe _0.5 Ti _0.50 ) ₁ obtained in Comparative Example 1. FIG. ₂ is a graph showing charge and discharge characteristics of two types of coin-type lithium batteries each having _—x O ₂ (b) as a positive electrode material and Li metal as a negative electrode material, and after 10 cycles.

Claims (6)

Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) And a lithium ferrite based composite oxide having a cubic rock salt structure having a Li / (Ti + Fe + Ni) value (molar ratio) of 1.2. A mixed aqueous solution containing water-soluble titanium salt, water-soluble iron salt and water-soluble nickel salt is coprecipitated with alkali, and the resulting precipitated product is hydrothermally treated in the temperature range of 101 to 400 ° C together with an oxidizing agent and water-soluble lithium salt. 2. The method for producing a lithium ferrite-based composite oxide according to claim 1, wherein after the excess salts are removed, the hydrothermal treatment reaction product is heat-treated at 300 to 800 ° C. The method for producing a lithium ferrite composite oxide according to claim 2, wherein the heat treatment of the hydrothermal treatment reaction product is performed in air, in an oxidizing atmosphere, or in a reducing atmosphere. 4. The method for producing a lithium ferrite composite oxide according to claim 3, wherein a lithium salt is added to and mixed with the hydrothermal reaction product before the heat treatment, the heat treatment is performed, and then the heat treatment product is washed with a solvent to remove excess lithium salt. . Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) in the represented, and Li / (Ti + Fe + Ni ) of values (molar ratio) is 1.2, a positive electrode material for a lithium ion secondary battery comprising lithium ferrite composite oxide having a cubic rock salt structure. Composition formula Li _{1 + x} (Ti _1-yz Fe _y Ni _z ) _1-x O ₂ (However, 0 ≦ x ≦ 0.33, 0 <y ≦ 0.95, 0 <z ≦ 0.5, 0 <y + z <1) in expressed, and the value of Li / (Ti + Fe + Ni ) ( molar ratio) is 1.2, a lithium ion secondary to a positive electrode material components comprising lithium ferrite composite oxide having a cubic rock-salt type structure Next battery.

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