JP3695366B2 - Positive electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Description

【００５７】
【発明の効果】
リチウムイオン二次電池の正極活物質として一般式がＬｉ_ｖＣｏ_{１−ｗ−ｘ}Ｔｉ_ｗＭ_ｘＯ_ｙＸ_ｚ（Ｍは少なくとも一種以上のアルカリ土類金属元素、Ｘは少なくとも一種以上のハロゲン元素を示す。ｖは０．９５≦ｖ≦１．０５、ｗは０＜ｗ≦０．０５、ｘは０＜ｘ≦０．１０、ｙは１≦ｙ≦２．５、ｚは０＜ｚ≦０．１０である。）で表される正極活物質を用いることにより、電池内のガス発生を低減し、電池特性（サイクル特性、高負荷特性）及び熱安定性を向上させることができる。
【図面の簡単な説明】
【図１】正極活物質中のＦ量（ｚ値）と電池の膨張率の関係を示す特性図
【図２】正極活物質中のＭｇ量（ｘ値）と電池の膨張率の関係を示す特性図
【図３】正極活物質の比表面積と電池の膨張率の関係を示す特性図
【図４】正極活物質中のＴｉ量（ｗ値）と容量維持率の関係を示す特性図
【図５】正極活物質中のＴｉ量（ｗ値）と高負荷容量容量の関係を示す特性図
【図６】正極活物質中のＬｉ量（ｖ値）と高負荷容量の関係を示す特性図
【図７】正極活物質中のＬｉ量（ｖ値）と放電容量の関係を示す特性図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material used for a lithium ion secondary battery, and in particular, a positive electrode active material that generates less gas and has excellent battery characteristics (cycle characteristics, high load characteristics) and thermal stability, and a method for producing the same. About.
[0002]
[Prior art]
In recent years, lithium-ion secondary batteries having high energy density have been adopted as batteries incorporated in electronic devices such as portable personal computers and video cameras. The lithium ion secondary battery includes a positive electrode plate in which a positive electrode active material such as lithium cobalt composite oxide is held on a positive electrode current collector that is a support, and a negative electrode active material such as lithium metal that is a support. It consists of a negative electrode plate held by a current collector, a nonaqueous electrolyte solution made of an organic solvent in which a lithium salt such as LiPF ₆ is dissolved, and a separator that is interposed between the positive electrode plate and the negative electrode plate to prevent short-circuiting of both electrodes. . Among these, a laminated battery stored in a battery case of a metal-laminated resin film or a battery stored in a thin metal case is wound with a positive electrode plate, a negative electrode plate, and a separator formed into a thin sheet shape. Compared with a battery housed in a metal case of a mold, there is a problem that it easily expands due to gas generation in the battery, heat generation or external heating, and the battery pack case storing the battery also expands and deforms.
[0003]
Conventionally, when LiCoO ₂ is used as the positive electrode active material of a lithium ion secondary battery, when the charging voltage is increased for the purpose of improving the discharge capacity, crystal transition of the positive electrode active material or decomposition of the positive electrode active material occurs. Oxygen from the cobalt acid is released, and this oxygen oxidizes and decomposes the nonaqueous electrolytic solution. As a result, gas is generated in the battery, and the above problem occurs in the laminated battery and the like.
[0004]
Similarly, when the charging voltage is increased for the purpose of improving the discharge capacity, the battery characteristics (cycle characteristics, high load characteristics) and thermal stability are also reduced along with the crystal transition or decomposition of the positive electrode active material. In addition, the positive electrode active material LiCoO ₂ has low conductivity, and therefore the conductivity is improved by coating the conductive carbon. However, when the contact with the carbon is poor, it causes the cycle deterioration. It was.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances. A positive electrode active material capable of reducing gas generation in a lithium ion secondary battery and improving battery characteristics (cycle characteristics, high load characteristics) and thermal stability, and a method for producing the same The purpose is to provide.
[0006]
[Means for Solving the Problems]
The present inventors have result of intensive studies to solve the above problems, the general formula as a cathode active material for a lithium ion secondary battery _{Li v Co 1-w-x} Ti w M x O y X z (M is at least One or more alkaline earth metal elements, X represents at least one halogen element, v is 0.95 ≦ v ≦ 1.05, w is 0 <w ≦ 0.05, x is 0 <x ≦ 0. 10 and y are 1 ≦ y ≦ 2.5 and z is 0 <z ≦ 0.10.) By using a positive electrode active material represented by the following formula, the present invention can be solved. It came to complete.
[0007]
That is, the positive electrode active material for a lithium ion secondary battery of the present invention, the general formula _{Li v Co 1-w-x} Ti w M x O y X z (M is at least one or more alkaline earth metal elements, X is At least one halogen element, v is 0.95 ≦ v ≦ 1.05, w is 0 <w ≦ 0.05, x is 0 <x ≦ 0.10, and y is 1 ≦ y ≦ 2.5. , Z is 0 <z ≦ 0.10), and the alkaline earth metal element M is preferably Be, Mg, Ca, Sr, or Ba, and particularly Mg, Ca Ba is preferred. Further, as the halogen element X, F, Cl, Br, and I are preferable, and F and Cl are particularly preferable. The Li amount (v value) in the composition affects the discharge capacity and high load capacity of the lithium ion secondary battery, and is preferably in the range of 0.95 ≦ v ≦ 1.05. In addition, Ti amount (w value), M amount (x value) and X amount (z value) in the composition contribute to gas generation, battery characteristics (cycle characteristics, high load characteristics) and thermal stability of lithium ion secondary batteries. The range of 0 <w ≦ 0.05, 0 <x ≦ 0.10, and 0 <z ≦ 0.10 is preferable, and 0.0001 ≦ w ≦ 0.05, 0 <x ≦ 0. A range of 01, 0.001 ≦ z ≦ 0.07 is more preferable. The amount of O (y value) in the composition varies depending on the method of introducing a halogen element into the positive electrode active material, and is in the range of 1 ≦ y ≦ 2.5.
[0008]
The positive electrode active material for a lithium ion secondary battery of the present invention has a specific surface area in the range of 0.2 to 2.0 m ² / g. The specific surface area of the positive electrode active material greatly affects the gas generation of the lithium ion secondary battery. In particular, in the case of the positive electrode active material of the present invention represented by the above general formula, the specific surface area is 0.2 to 2.0 m ² / Gas generation can be greatly reduced in the range of g. More preferably, it is the range of 0.4-0.8 m < ² > / g.
[0009]
The method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention includes firing a raw material mixture obtained by mixing a lithium compound, a cobalt compound, a titanium compound, a compound containing an alkaline earth metal element, and a compound containing a halogen element. It is characterized by crushing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As shown below, the synthesis of the positive electrode active material for lithium ion secondary battery of the present invention is a raw material in which a lithium compound, a cobalt compound, a titanium compound, a compound containing an alkaline earth metal element, and a compound containing a halogen element are mixed. This is done by calcining the mixture after firing.
[0011]
As a compound containing a lithium compound, a cobalt compound, a titanium compound, and an alkaline earth metal element, oxides, hydroxides, carbonates, nitrates, sulfates, acetates, halides, and the like are used. As the compound, alkali metal halides, ammonium salts and the like are used. For example, Li ₂ O, LiOH, Li ₂ CO ₃ , LiHCO ₃ , LiNO ₃ , Li ₂ SO ₄ , Li (CH ₃ COO), LiCl, or the like is used as the lithium compound, and Co ₃ O is used as the cobalt compound. ₄ , Co ₂ O ₃ , CoCO ₃ , Co (NO ₃ ) ₂ , CoCl _{2 and the} like are preferably used. As the titanium compound, TiO ₂ , Ti (NO ₃ ) ₄ , Ti (SO ₄ ) ₂ or the like is used, and as the compound containing an alkaline earth metal element, MgCO ₃ , Mg (NO ₃ ) ₂ , MgCl ₂ , CaCO ₃ , Ca (NO ₃ ) ₂ , CaCl ₂ , BaCO ₃ , Ba (NO ₃ ) ₂ , BaSO _4, etc. are used, and compounds containing halogen elements include LiF, LiCl, LiBr, LiI, NH ₄ F, NH ₄ Cl, NH ₄ Br, NH ₄ I and the like are preferably used. In mixing these raw materials, the powdery raw materials may be mixed as they are, or may be mixed as a slurry using water or an organic solvent. The slurry mixture is dried to obtain a raw material mixture.
[0012]
The raw material mixture thus obtained is fired in the temperature range of 500 to 1000 ° C. for 1 to 24 hours in air or in a weakly oxidizing atmosphere. Preferably, baking is performed at a temperature range of 800 to 1000 ° C. for 6 to 12 hours. When the firing temperature is less than 500 ° C., unreacted raw materials remain in the positive electrode active material, and the original characteristics of the positive electrode active material cannot be utilized. On the other hand, when the temperature exceeds 1000 ° C., the particle size of the positive electrode active material becomes too large and the battery characteristics deteriorate. When the firing time is less than 1 hour, the diffusion reaction between the raw material particles does not proceed. When 24 hours have elapsed, the diffusion reaction is almost completed, and thus no further firing is necessary.
[0013]
The fired product obtained by the above firing is pulverized using a roughing machine, and the positive electrode of the present invention has a specific surface area of 0.2 to 2.0 m ² / g and an average particle size of 1.0 to 12.0 μm. Get the active material.
[0014]
In the lithium ion secondary battery using the positive electrode active material of the present invention, the oxidative decomposition reaction of the electrolytic solution is suppressed, and the amount of gas generated in the battery is reduced. Characteristics, high load characteristics) and thermal stability are also improved.
[0015]
Next, a lithium ion secondary battery is produced using the positive electrode active material of the present invention, and the results of measuring gas generation, battery characteristics (cycle characteristics, high load characteristics) and thermal stability will be described.
[0016]
(Production of lithium ion secondary battery)
A paste is prepared by kneading 90 parts by weight of a positive electrode active material powder, 5 parts by weight of acetylene black as a conductive agent, and 5 parts by weight of polyvinylidene fluoride, applying this to a positive electrode current collector, and drying to form a positive electrode plate And Further, natural graphite is used for the negative electrode, a porous propylene film is used for the separator, and a solution in which LiPF ₆ is dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) is used as the electrolyte. To produce a lithium ion secondary battery. Here, a thin sheet of a positive electrode plate, a negative electrode plate and a separator is wound to produce a laminated battery housed in a battery case of a metal laminated resin film.
[0017]
(Evaluation of gas generation)
The general formula is LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ F _z , LiCo _0.999 Ti _0.001 O ₂ F _z , LiCo _0.999 Mg _0.001 O ₂ F _z and LiCoO ₂ F _z A laminate battery is manufactured using various positive electrode active materials represented by the following formula, and is charged at a constant current up to 4.2 V at a charging load of 0.5 C, and then stored at 80 ° C. for 2 days. ) Is obtained from the following equation (where 1C is a current load that completes charging or discharging in one hour).
Expansion coefficient of battery = {(battery thickness after storage at 80 ° C.−battery thickness before measurement) / battery thickness before measurement} × 100
[0018]
FIG. 1 shows the relationship between the amount of F (z value) in the positive electrode active material and the expansion coefficient of the battery. As is clear from this figure, the expansion rate of the battery using the positive electrode active material LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ F _z (1a) of the present invention is such that the z value is 0 <z ≦ 0. It is low in the range of .10, particularly very low in the range of 0.001 ≦ z ≦ 0.07, indicating that the amount of gas generated in the battery is reduced. Further, a positive electrode active material LiCo _0.999 Ti _0.001 O ₂ F _z (1b) not containing Mg element, a positive electrode active material LiCo _0.999 Mg _0.001 O ₂ F _z (1c) not containing Ti element, and It can be seen that the expansion coefficient is very low as compared with the battery using the positive electrode active material LiCoO ₂ F _z (1d) containing neither Mg element nor Ti element. Thus, by including all three types of elements, Ti element, Mg element and F element, in the positive electrode active material, the expansion coefficient of the battery is greatly reduced. Similar characteristics are also exhibited when an alkaline earth metal element other than Mg and a halogen element other than F are included.
[0019]
In the same manner as above, the general formulas are LiCo _0.999-x Ti _0.001 Mg _x O ₂ F _0.002 , LiCo _0.999-x Ti _0.001 Mg _x O ₂ , LiCo _1-x Mg _x O. _A laminate battery is produced using various positive electrode active materials represented by ₂ F _0.002 and LiCo _1-x Mg _x O ₂ , and the expansion coefficient of the battery is obtained. FIG. 2 shows the relationship between the amount of Mg (x value) in the positive electrode active material and the expansion coefficient of the battery. As is clear from this figure, the expansion coefficient of the battery using the positive electrode active material LiCo _0.999-x Ti _0.001 Mg _x O ₂ F _0.002 (2a) of the present invention is such that the x value is 0 <x It is found that the amount of gas generated in the battery is reduced because the amount is less in the range of ≦ 0.10, particularly in the range of 0 <x ≦ 0.01. The positive electrode active material _{LiCo 0.999-x Ti} 0.001 _Mg containing no F element x _O 2 (2b), not containing Ti element cathode active material _{LiCo 1-x Mg x O 2} F 0.002 (2c ) and compared to a battery using both containing no cathode active material _{LiCo 1-x Mg x O 2} (2d) the F element and the Ti element, the expansion ratio is seen to be very low. Thus, by including all three types of elements, Ti element, Mg element and F element, in the positive electrode active material, the expansion coefficient of the battery is greatly reduced. Similar characteristics are also exhibited when an alkaline earth metal element other than Mg and a halogen element other than F are included.
[0020]
This is because the lattice constant is reduced by dissolving an alkaline earth metal element in the positive electrode active material, the volume change associated with charge / discharge is reduced, and the stress applied to the particles is alleviated. It is considered that the amount of gas generated in the battery is reduced as a result of suppressing the decomposition of the electrolyte and the oxidative decomposition reaction of the electrolyte. Furthermore, it is thought that the amount of gas is reduced because the alkaline earth metal element and the halogen element that are not in solid solution react with each other and the positive electrode active material is coated to reduce the influence on the negative electrode. It is done. Further, regarding the Mg amount (x value) in the positive electrode active material, if the x value exceeds 0.10, not only the expansion coefficient of the battery increases but also the discharge capacity decreases, so 0 <x ≦ 0. A range of 10 is preferred.
[0021]
Next, a laminate battery is manufactured using various positive electrode active materials LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ F _0.002 having different specific surface areas, and the expansion coefficient (%) of the battery is similarly obtained. . FIG. 3 shows the relationship between the specific surface area of the positive electrode active material and the expansion coefficient of the battery. As is clear from this figure, the expansion coefficient of the battery is small at a specific surface area of 2.0 m ² / g or less, particularly very low at 0.8 m ² / g or less, and the amount of gas generated in the battery is small. It can be seen that it is reduced. When the specific surface area is larger than 2.0 m ² / g, it is considered that the reactivity of the oxidative decomposition reaction of the electrolytic solution occurring on or near the surface of the positive electrode active material increases, and as a result, the amount of gas generated in the battery increases. On the other hand, when the specific surface area is smaller than 0.4 m ² / g, the particle size of the positive electrode active material becomes too large and the battery characteristics are deteriorated.
[0022]
(Evaluation of cycle characteristics)
Laminated batteries were prepared using various positive electrode active materials represented by the general formula LiCo _0.999-w Ti _w Mg _0.001 O ₂ F _0.002 , and charged at a normal temperature (25 ° C.) of 0. After charging at a constant current up to 4.2 V at 5 C, 500 cycles of charge and discharge discharging to 2.75 V at 1.0 C are performed, and the capacity retention rate (%) at the 500th cycle is obtained from the following equation.
Capacity retention rate = (discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100
[0023]
FIG. 4 shows the relationship between the amount of Ti (w value) in the positive electrode active material and the capacity retention rate. As is apparent from this figure, the capacity retention ratio is high when the w value is in the range of 0 <w ≦ 0.05, particularly very high in the range of 0.0001 ≦ w ≦ 0.05. It turns out that it is excellent.
[0024]
(Evaluation of high load characteristics)
Laminate batteries were prepared using various positive electrode active materials represented by the general formula LiCo _0.999-w Ti _w Mg _0.001 O ₂ F _0.002 , and the voltage was set to 4.2 V at a charging load of 2.0 C. After current charging, the discharge capacity when discharged to 2.75 V at 2.0 C is obtained as the high load capacity (mAh / g).
[0025]
FIG. 5 shows the relationship between the amount of Ti (w value) in the positive electrode active material and high load capacity. As is apparent from this figure, the high load capacity is high when the w value is in the range of 0 <w ≦ 0.05, particularly very high in the range of 0.0001 ≦ w ≦ 0.05. It is understood that is superior.
[0026]
By including Ti element in the positive electrode active material in this manner, it is considered that the battery characteristics (cycle characteristics, high load characteristics) are improved as a result of suppressing crystal transition or decomposition of the positive electrode active material.
[0027]
Similarly, a laminated battery is manufactured using a positive electrode active material represented by a general formula of Li _v Co _0.998 Ti _0.001 Mg _0.001 O ₂ F _0.002 , and has a high load capacity (mAh / g). Ask for. FIG. 6 shows the relationship between the Li amount (v value) in the positive electrode active material and the high load capacity. From this figure, it can be seen that the high load capacity decreases when the v value becomes larger than 1.05.
[0028]
FIG. 7 shows the relationship between the Li amount (v value) in the positive electrode active material and the discharge capacity when discharged at a normal current density (0.25 C). From this figure, it can be seen that the discharge capacity decreases when the v value becomes smaller than 0.95.
[0029]
Accordingly, considering both the high load capacity and the normal discharge capacity, the v value needs to be set in the range of 0.95 ≦ v ≦ 1.05.
[0030]
Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to specific examples.
[0031]
【Example】
[Example 1]
Lithium carbonate (Li ₂ CO ₃ ), cobalt trioxide (Co ₃ O ₄ ), titanium dioxide (TiO ₂ ), magnesium carbonate (MgCO ₃ ), and ammonium fluoride (NH ₄ F), v = 1.0, Weigh so that w = 0.001, x = 0.001, z = 0.002 and dry mix. The obtained raw material mixture was calcined in the air at 900 ° C. for 10 hours, and then pulverized using a raking machine to obtain a positive electrode active material powder having a specific surface area of 0.63 m ² / g and an average particle size of 3.5 μm. LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ F _0.002 is obtained.
[0032]
The specific surface area is a value measured by a constant pressure BET one-point method using nitrogen gas adsorption, and the average particle diameter is a value obtained by measuring the specific surface area by an air permeation method and obtaining the average value of the particle diameters of primary particles. It is a value measured using a Fisher sub-sieve sizer (FSSS).
[0033]
[Example 2]
The positive electrode active material powder LiCo _0.994 Ti _0.005 Mg _{0. 0} having a specific surface area of 0.65 m ² / g and an average particle size of 3.4 μm was the same as in Example 1 except that w = 0.005 _{. 001} O ₂ F _0.002 is obtained.
[0034]
[Example 3]
The positive electrode active material powder LiCo _0.997 Ti _0.001 Mg _{0. 0} having a specific surface area of 0.63 m ² / g and an average particle size of 3.3 μm was the same as in Example 1 except that x = 0.002 _{. 002} O ₂ F _0.002 is obtained.
[0035]
[Example 4]
A positive electrode active material powder LiCo _0.994 Ti _0.001 Mg _{0. 0} having a specific surface area of 0.63 m ² / g and an average particle size of 3.3 μm, except that x = 0.005 _{. 005} O ₂ F _0.002 is obtained.
[0036]
[Example 5]
The positive electrode active material powder LiCo _0.989 Ti _0.001 Mg _{0. 0} having a specific surface area of 0.63 m ² / g and an average particle size of 3.3 μm was the same as in Example 1 except that x = 0.01 _{. 010} O ₂ F _0.002 is obtained.
[0037]
[Example 6]
A positive electrode active material powder LiCo _0.998 Ti _0.001 Mg ₀ .0 having a specific surface area of 0.62 m ² / g and an average particle size of 3.5 μm, except that z = 0.006 _{. 001} O ₂ F _0.006 is obtained.
[0038]
[Example 7]
The positive electrode active material powder LiCo _0.998 Ti _0.001 Mg ₀ .0 having a specific surface area of 0.62 m ² / g and an average particle size of 3.5 μm was obtained in the same manner as in Example 1 except that z = 0.01 _{. 001} O ₂ F _0.01 is obtained.
[0039]
[Example 8]
Positive electrode active material powder having a specific surface area of 0.59 m ² / g and an average particle size of 3.7 μm, as in Example 1, except that calcium carbonate (CaCO ₃ ) is used instead of magnesium carbonate (MgCO ₃ ). LiCo _0.998 Ti _0.001 Ca _0.001 O ₂ F _0.002 is obtained.
[0040]
[Example 9]
Positive electrode active material powder having a specific surface area of 0.62 m ² / g and an average particle size of 3.5 μm, as in Example 1, except that barium carbonate (BaCO ₃ ) is used instead of magnesium carbonate (MgCO ₃ ). LiCo _0.998 Ti _0.001 Ba _0.001 O ₂ F _0.002 is obtained.
[0041]
[Example 10]
A positive electrode having a specific surface area of 0.61 m ² / g and an average particle diameter of 3.6 μm, as in Example 1, except that ammonium chloride (NH ₄ Cl) is used instead of ammonium fluoride (NH ₄ F). An active material powder LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ Cl _0.002 is obtained.
[0042]
[Example 11]
A specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm were used in the same manner as in Example 1 except that ammonium bromide (NH ₄ Br) was used instead of ammonium fluoride (NH ₄ F). A positive electrode active material powder LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ Br _0.002 is obtained.
[0043]
[Example 12]
A specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm were used in the same manner as in Example 1 except that ammonium iodide (NH ₄ I) was used instead of ammonium fluoride (NH ₄ F). Positive electrode active material powder LiCo _0.998 Ti _0.001 Mg _0.001 O ₂ I _0.002 is obtained.
[0044]
[Example 13]
Cathode active material powder having a specific surface area of 0.62 m ² / g and an average particle diameter of 3.5 μm, as in Example 1, except that strontium carbonate (SrCO ₃ ) is used instead of magnesium carbonate (MgCO ₃ ). LiCo _0.998 Ti _0.001 Sr _0.001 O ₂ F _0.002 is obtained.
[0045]
[Comparative Example 1]
The specific surface area was 0.61 m ² / g and the average particle size was 3 as in Example 1, except that titanium dioxide (TiO ₂ ), magnesium carbonate (MgCO ₃ ), and ammonium fluoride (NH ₄ F) were not used. A positive electrode active material powder LiCoO ₂ of 6 μm is obtained.
[0046]
[Comparative Example 2]
Positive electrode active material powder having a specific surface area of 0.61 m ² / g and an average particle diameter of 3.6 μm, as in Example 1, except that magnesium carbonate (MgCO ₃ ) and ammonium fluoride (NH ₄ F) are not used. LiCo _0.999 Ti _0.001 O ₂ is obtained.
[0047]
[Comparative Example 3]
Cathode active material powder having a specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm in the same manner as in Example 1 except that titanium dioxide (TiO ₂ ) and ammonium fluoride (NH ₄ F) are not used. LiCo _0.999 Mg _0.001 O ₂ is obtained.
[0048]
[Comparative Example 4]
Cathode active material powder LiCoO ₂ having a specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm in the same manner as in Example 1 except that titanium dioxide (TiO ₂ ) and magnesium carbonate (MgCO ₃ ) are not used. F _0.002 is obtained.
[0049]
[Comparative Example 5]
A positive electrode active material powder LiCo _0.998 Ti _{0. 0} having a specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm in the same manner as in Example 1 except that ammonium fluoride (NH ₄ F) is not used _{. 001} Mg _0.001 O ₂ is obtained.
[0050]
[Comparative Example 6]
A positive electrode active material powder LiCo _0.999 Ti _0.001 O having a specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm, as in Example 1, except that magnesium carbonate (MgCO ₃ ) is not used. ₂ F _0.002 is obtained.
[0051]
[Comparative Example 7]
A positive electrode active material powder LiCo _0.999 Mg _0.001 O having a specific surface area of 0.61 m ² / g and an average particle size of 3.6 μm, as in Example 1, except that titanium dioxide (TiO ₂ ) is not used. ₂ F _0.002 is obtained.
[0052]
(Evaluation)
Laminated batteries were prepared using the positive electrode active material powders obtained in Examples 1 to 13 and Comparative Examples 1 to 7, and the results of gas generation, battery characteristics (cycle characteristics, high load characteristics) and thermal stability were measured. Table 1 summarizes. The expansion coefficient of the battery, the capacity retention ratio at normal temperature (25 ° C.), and the high load capacity are measured in the same manner as described above. The capacity maintenance rate at high temperature (60 ° C.) is measured in a high temperature bath at 60 ° C., and is measured in the same manner as the capacity maintenance rate at room temperature (25 ° C.) except that the capacity maintenance rate (%) at the 300th cycle is obtained. . About thermal stability, differential scanning calorimetry is performed as follows, and it evaluates with heat generation start temperature.
[0053]
(Evaluation of thermal stability)
(1) A demountable cell positive electrode capable of preparing a paste by kneading 90 parts by weight of a positive electrode active material powder, 5 parts by weight of carbon as a conductive agent, and 5 parts by weight of polyvinylidene fluoride, and capable of evaluating this as a single electrode A secondary battery is manufactured by applying to a current collector and using ethylene carbonate as an electrolytic solution.
{Circle around (2)} After charging / discharging with a constant current and charging, charging is performed under a constant current until the battery voltage reaches 4.3V.
(3) After charging, the positive electrode is taken out from the secondary battery, washed and dried, and the positive electrode active material is scraped off.
(4) 5 mg of the positive electrode active material and 2 mg of ethylene carbonate scraped from the positive electrode are placed in an Al cell, and differential scanning calorimetry is performed to determine the heat generation start temperature.
[0054]
Differential scanning calorimetry is a method for analyzing the thermal characteristics of a sample material by measuring the temperature difference between the reference material and the sample while heating them simultaneously at a constant rate. Then, the differential scanning calorific value does not change in the low temperature part, but the differential scanning calorific value greatly increases above a certain temperature. The temperature at this time is defined as the heat generation start temperature, and it can be said that the higher the temperature, the better the thermal stability.
[0055]
From Table 1, compared with Comparative Examples 1-7, Examples 1-13 contain the Ti element, alkaline-earth element, and a halogen element in a positive electrode active material, the expansion coefficient of a battery reduces, a capacity maintenance rate, It can be seen that the high load capacity is high and the battery characteristics (cycle characteristics, high load characteristics) are excellent. Regarding the cycle characteristics, it can be seen that the effect is particularly remarkable in the cycle characteristics at a high temperature (60 ° C.) than the cycle characteristics at a normal temperature (25 ° C.). Moreover, it can be seen that the heat generation start temperature is higher than that of the comparative example and is excellent in thermal stability. For example, Comparative Example 1 that does not include any of the three elements of Ti element, Mg element, and F element, Comparative Examples 2 to 4 that include only one kind of element, and Comparative Examples 5 to 7 that include two kinds of elements, In the case of Example 1 including all three types of elements, the expansion coefficient of the battery is low, and the capacity maintenance ratio and the high load capacity are high. Moreover, the heat generation start temperature is also high. Thus, by including all three kinds of elements of Ti element, Mg element and F element in the positive electrode active material, the crystal transition or decomposition of the positive electrode active material is further suppressed as a synergistic effect. Occurrence is remarkably reduced, and battery characteristics (cycle characteristics, high load characteristics) and thermal stability are greatly improved.
[0056]
[Table 1]

[0057]
【The invention's effect】
General formula _Li as a cathode active material for a lithium ion secondary battery _{v Co 1-w-x Ti} w M x O y X z (M is at least one or more alkaline earth metal elements, X is at least one kind of halogen element V is 0.95 ≦ v ≦ 1.05, w is 0 <w ≦ 0.05, x is 0 <x ≦ 0.10, y is 1 ≦ y ≦ 2.5, and z is 0 <z. By using the positive electrode active material represented by ≦ 0.10, gas generation in the battery can be reduced, and battery characteristics (cycle characteristics, high load characteristics) and thermal stability can be improved.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between the amount of F (z value) in the positive electrode active material and the expansion coefficient of the battery. FIG. 2 shows the relationship between the amount of Mg (x value) in the positive electrode active material and the expansion coefficient of the battery. Fig. 3 is a characteristic diagram showing the relationship between the specific surface area of the positive electrode active material and the expansion coefficient of the battery. Fig. 4 is a characteristic diagram showing the relationship between the amount of Ti (w value) in the positive electrode active material and the capacity retention rate. 5] Characteristic diagram showing the relationship between the amount of Ti (w value) in the positive electrode active material and high load capacity capacity. [Fig. 6] Characteristic diagram showing the relationship between the amount of Li (v value) in the positive electrode active material and high load capacity. FIG. 7 is a characteristic diagram showing the relationship between the Li amount (v value) in the positive electrode active material and the discharge capacity.

Claims (3)

General formula _{Li v Co 1-w-x} Ti w M x O y X z (M is at least one or more alkaline earth metal elements, X is indicates at least one or more halogen element .v is 0.95 ≦ v ≦ 1.05, w is 0 <w ≦ 0.05, x is 0 <x ≦ 0.10, y is 1 ≦ y ≦ 2.5, and z is 0 <z ≦ 0.10. A positive electrode active material for a lithium ion secondary battery. ^{2. The} positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the specific surface area is in the range of 0.2 to 2.0 m ² / g. 3. The lithium according to claim 1, wherein a raw material mixture obtained by mixing a lithium compound, a cobalt compound, a titanium compound, a compound containing an alkaline earth metal element, and a compound containing a halogen element is fired and then pulverized. A method for producing a positive electrode active material for an ion secondary battery.

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