CN101694877A - Positive electrode active material for lithium ion secondary battery and method for producing same - Google Patents

Abstract

The invention discloses a positive active material of lithium ion secondary battery and its manufacturing method, the positive active material used in the lithium ion secondary battery has the general formula [ LiCo ]_1-xM_xO₂(M＝Ti、Zr、V、Nb)]A hexagonal lithium cobaltate obtained by mixing a cobalt compound as a cobalt source and a lithium compound as a lithium source at a molar ratio of 1: 1, wherein titanium, zirconium, vanadium, and niobium are added to the cobalt compound by coprecipitation, wherein the amount of titanium added is 0.01 to 1 mol% based on the amount of cobalt, and the amount of zirconium, vanadium, and niobium added is 0.01 to 3 mol% based on the amount of cobalt; and sintering the mixture for 18 to 20 hours at the temperature of 880 to 920 ℃ in the air through a coprecipitation process, a mixing process and a sintering process. The invention has the advantages of not reducing the battery capacity and the charging and discharging efficiency, and improving the thermal stability, the rate capability and the charging and discharging cycle performance.

Description

Lithium-ion secondary battery cathode active material and manufacturing method thereof

technical field

The invention relates to a positive electrode active material of a lithium ion secondary battery and a manufacturing method thereof.

Background technique

In recent years, with the development of portable and wireless equipment, the demand for non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries with small size, light weight and high energy density has been increasing. As we all know, the positive electrode active materials for this non-aqueous electrolyte secondary battery include LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ and other lithium and transition metals. composite oxides or phosphates.

Among them, lithium-ion secondary batteries using lithium cobalt oxide (LiCoO ₂ ) as the positive electrode active material and carbon such as lithium alloy, graphite, and carbon fiber as the negative electrode can obtain a high voltage of 4V, so they are widely used as batteries with high energy density.

However, lithium ion secondary batteries using lithium cobaltate have a problem in that cycle characteristics and safety characteristics are deteriorated due to elution of cobalt sources and the like.

Since lithium cobalt oxide has a potential of 4 V or more relative to lithium, when it is used as a positive electrode active material of a non-aqueous electrolyte secondary battery, cobalt will be eluted from the positive electrode every time the charge and discharge cycle is repeated. Therefore, the positive electrode deteriorates, causing a problem in that capacity characteristics and load characteristics after charge and discharge cycles are degraded. For this reason, Japanese Patent Application Laid-Open No. 2004-047437 discloses the following scheme, that is, adding heterogeneous elements M such as V, Cr, Fe, Mn, Ni, Al, Ti, Zr when synthesizing lithium cobaltate to obtain a common Lithium cobaltate represented by the formula LiCo _1-X M _X O ₂ . Compared with ordinary lithium cobalt oxide, since cobalt can be inhibited from dissolving into the electrolyte, the load performance and charge-discharge cycle performance can be improved.

However, in lithium cobalt oxide to which foreign elements are added, since the foreign elements do not contribute to the battery reaction (charge-discharge reaction), there arises a problem that the capacity of the battery decreases and the charge-discharge efficiency also decreases as the amount of these foreign elements added increases. . In addition, since the addition of a different element lowers the crystallinity, there are also problems in that the thermal stability is lowered and the loading performance is also lowered. Also, there is much room for improvement in the charge and discharge efficiency performance.

Contents of the invention

Therefore, the object of the present invention is to provide a lithium-ion secondary battery cathode active material and a manufacturing method thereof without reducing battery capacity and charge-discharge efficiency, and can improve thermal stability, rate performance and charge-discharge cycle performance.

The object of the present invention is achieved through the following technical solutions: a lithium ion secondary battery cathode active material, the cathode active material is represented by the general formula [LiCo _1-x M _x O ₂ (M=Ti, Zr)] Hexagonal lithium cobaltate compound obtained by mixing a cobalt compound as a cobalt source and a lithium compound as a lithium source at a molar ratio of 1:1, in the cobalt compound, by cobalt Titanium and zirconium are added, wherein the amount of titanium added is 0.01mol%-1mol% relative to the amount of cobalt, and the amount of zirconium added is 0.01mol%-3mol% relative to the amount of cobalt. The production method thereof includes a co-precipitation process, a mixing process, and a sintering process. In the co-precipitation process, titanium and zirconium are added by co-precipitation to an initial cobalt compound used for thermal decomposition to generate a cobalt compound that becomes a cobalt source, wherein titanium The amount of addition is 0.01mol% to 1mol% relative to the amount of cobalt, and the amount of zirconium is 0.01mol% to 3mol% relative to the amount of cobalt. The compounds are obtained by mixing them at a molar ratio of 1:1, and then sintering the obtained mixture in air at a temperature of 880-920° C. for 18-20 hours.

A lithium ion secondary battery positive electrode active material, the positive electrode active material is a hexagonal lithium cobaltate compound represented by the general formula [LiCo _1-x M _x O ₂ (M=Ti, V, Nb)], The lithium cobaltate is obtained by mixing a cobalt compound as a cobalt source and a lithium compound as a lithium source at a molar ratio of 1:1, and in the cobalt compound, titanium, vanadium, and niobium are added by co-precipitation, The amount of titanium added relative to the amount of cobalt is 0.01mol% ~ 1mol%, the amount of vanadium added relative to the amount of cobalt is 0.01mol% ~ 1.5mol%, the amount of niobium added relative to the amount of cobalt is 0.01mol% ~ 1.5 mol%. The production method thereof includes a co-precipitation process, a mixing process, and a sintering process. In the co-precipitation process, titanium, vanadium, and niobium are added by co-precipitation to an initial cobalt compound used for thermal decomposition to generate a cobalt compound that becomes a cobalt source, wherein The amount of titanium added relative to the amount of cobalt is 0.01mol% to 1mol%, the amount of vanadium added relative to the amount of cobalt is 0.01mol% to 1.5mol%, the amount of niobium added relative to the amount of cobalt is 0.01mol% to 1.5 mol%, the mixing process is obtained by mixing a cobalt compound as a cobalt source and a lithium compound as a lithium source at a molar ratio of 1:1, and then sintering the obtained mixture in air at a temperature of 880 to 920°C for 18 ~20 hours.

A positive electrode active material for a lithium ion secondary battery, the positive electrode active material is hexagonal lithium cobaltate represented by the general formula [LiCo _1-x M _x O ₂ (M=Ti, Zr, V, Nb)] Compound, the lithium cobaltate is obtained by mixing a cobalt compound as a cobalt source and a lithium compound as a lithium source in a molar ratio of 1:1, and in the cobalt compound, titanium, zirconium, vanadium are added by co-precipitation and niobium, wherein the added amount of titanium is 0.01 mol% to 1 mol% relative to the amount of cobalt, and the added amount of zirconium, vanadium and niobium is 0.01 mol% to 1.5 mol% relative to the amount of cobalt. The production method thereof includes a co-precipitation process, a mixing process, and a sintering process. The co-precipitation process adds titanium, zirconium, vanadium, and niobium by co-precipitation to an initial cobalt compound used for thermal decomposition to generate a cobalt compound that becomes a cobalt source , where the amount of titanium added relative to the amount of cobalt is 0.01mol% to 1mol%, the amount of vanadium added relative to the amount of cobalt is 0.01mol% to 1.5mol%, the amount of added zirconium, vanadium and niobium relative to the amount of cobalt 0.01mol%～1.5mol%, the mixing process is obtained by mixing the cobalt compound as the cobalt source and the lithium compound as the lithium source at a molar ratio of 1:1, and then the obtained mixture is mixed in the air at 880 Sinter at ~920°C for 18-20 hours.

Each of the cobalt compounds described above is cobalt carbonate or cobalt hydroxide or cobalt oxyhydroxide. In addition, the lithium cobaltate compound does not undergo a phase change near a charge capacity of 125mAh/g.

The positive electrode active material has hexagonal lithium cobalt oxide represented by the general formula [LiCo _1-x M _x O ₂ (M=Ti, Zr, V, Nb)]. The compound is synthesized with a lithium compound as a lithium source. In the cobalt compound, titanium, zirconium, vanadium, and niobium are added by co-precipitation, wherein the added amount of titanium is more than 0.01mol% and less than 1.0mol%, and zirconium, vanadium And the addition amount of niobium is 0.01 mol% or more and 1.5 mol% or less with respect to the amount of cobalt.

Here, if titanium, zirconium, vanadium, or niobium is added by co-precipitation when synthesizing cobalt compounds such as cobalt carbonate, cobalt hydroxide, and cobalt oxyhydroxide, it is the same as adding titanium, zirconium, and vanadium when sintering oxides containing lithium and cobalt. Compared with the case of niobium or niobium, a small amount of titanium, zirconium, vanadium, or niobium can be uniformly added to the side surface of lithium cobalt oxide. In this case, adding 0.01 mol% to 1.0 mol% of titanium relative to cobalt by co-precipitation when synthesizing the cobalt compound resulted in a significant improvement in performance without accompanying reduction in capacity.

In addition, under normal circumstances, lithium cobalt oxide with 1.50 mol% titanium, zirconium, vanadium or niobium added when mixing sintered cobalt source and lithium source will produce a phase change near the charging capacity of 125mAh/g, and will not improve safety performance , charge-discharge cycle performance, etc. However, in addition to adding titanium, co-precipitated lithium cobalt oxide added with zirconium, vanadium or niobium at the same time does not produce phase change near the charge capacity of 125mAh/g, and improves thermal stability (safety performance), charge-discharge cycle performance etc.

This is considered to be due to the fact that when zirconium, vanadium, or niobium are co-precipitated and added in addition to titanium, the effect of inhibiting the dissolution of cobalt by adding titanium and the effect of inhibiting phase transformation by adding zirconium, vanadium, or niobium are both produced. , The effect of promoting crystal growth, through these synergistic effects can significantly improve the characteristics.

Moreover, in order to obtain the positive electrode active material as described above, it is only necessary to have a coprecipitation step, a mixing step, and a sintering step. To add titanium, zirconium, vanadium or niobium, wherein, relative to the amount of cobalt, the amount of titanium added is 0.01mol% to 1.0mol%, and the amount of zirconium, vanadium and niobium added is 0.01mol% to 0.01mol% relative to the amount of cobalt 1.5mol%; the above mixing step is to form a mixture by mixing the first component formed by co-precipitating the cobalt compound obtained by co-precipitating titanium, zirconium, vanadium and niobium with the second component composed of the lithium compound as the lithium source; In the sintering process described above, the mixture is sintered.

In addition, in the present invention, in order to provide a lithium-ion secondary battery with good thermal stability, high safety, improved charge-discharge cycle characteristics, and suppressed deterioration during charge and storage, it is characterized in that a specific battery is used. positive active material. Therefore, conventionally known materials can be used for the negative electrode material, the separator material, the nonaqueous electrolyte material, and the binder material.

In the present invention, hexagonal lithium cobaltate represented by the general formula [LiCo _1-x M _x O ₂ (M=Ti, Zr, V, Nb)] is used as the positive electrode active material. A cobalt compound as a cobalt source and a lithium compound as a lithium source are synthesized. In the cobalt compound, titanium, zirconium, vanadium, and niobium are added by co-precipitation, wherein the amount of titanium added is 0.01mol% to 1.0mol%. The added amount of zirconium, vanadium and niobium is 0.01 mol% to 1.5 mol% relative to the amount of cobalt. Accordingly, by adding a small amount of titanium, it is possible to obtain a lithium-ion secondary battery having improved thermal stability, rate performance, and charge-discharge cycle performance without reducing battery capacity and charge-discharge efficiency.

The invention has the advantages of not reducing battery capacity and charge-discharge efficiency, and can improve thermal stability, rate performance and charge-discharge cycle performance.

Description of drawings

Fig. 1 is a schematic diagram showing the inflection point of the charge-discharge curve of the positive electrode produced by phase transition;

Fig. 2 is a schematic diagram showing that the charging and discharging curve of the positive electrode does not produce an inflection point;

Detailed ways

1. Fabrication of positive electrode

(1) Production of lithium cobalt oxide with Ti and Zr added

First, after adding prescribed amounts of titanyl sulfate [TiOSO ₄ ] and zirconium sulfate [Zr(SO ₄ ) ₂ ] to cobalt sulfate (CoSO ₄ ) solution, by adding sodium hydroxide and ammonia water, cobalt hydroxide [ Co(OH) ₂ ] Co-precipitates titanium (Ti) and zirconium (Zr). Then, by subjecting these to thermal decomposition reaction, tricobalt tetroxide (Co ₃ O ₄ ) to which titanium and zirconium were added is obtained as a starting material of a cobalt source.

Next, after preparing lithium carbonate (Li ₂ CO ₃ ) as an initial raw material as a lithium source, it was weighed with a scale so that the molar ratio of lithium to cobalt was 1:1. Then, these were mixed with a mortar, and the obtained mixture was sintered in air at 900° C. for 20 hours to synthesize a sintered product of lithium cobaltate powder having titanium and zirconium added to the surface. Thereafter, the synthesized sintered product was pulverized into an average particle diameter of 12 μm, and used as a positive electrode active material.

Here, the positive electrode active material synthesized in such a way that the addition amount of titanium is 0.50 mol % and the addition amount of zirconium is 0.01 mol % relative to the amount of cobalt is used as the positive electrode active material a1, and the addition amount of zirconium is 0.50 mol %. The positive electrode active material synthesized by the above method is used as the positive electrode active material a2, and the positive electrode active material synthesized in the mode that the addition amount of zirconium is 1.00 mol% is used as the positive electrode active material a3, and the positive electrode active material synthesized in the mode that the addition amount of zirconium is 1.20 mol% The active material was the positive electrode active material a4, and the positive electrode active material synthesized so that the added amount of zirconium was 1.50 mol% was used as the positive electrode active material a5.

In addition, the positive electrode active material synthesized by adding 0.50 mol % of titanium and 3 mol % of zirconium was referred to as the positive electrode active material a6, and the positive electrode active material synthesized without adding zirconium was referred to as the positive electrode active material x1. In addition, the addition amount of titanium and zirconium is the value obtained by ICP (Inductively Coupled Plasma; plasma emission spectrometry) analysis.

(2) Production of lithium cobalt oxide with addition of Ti, V and Nb

First, after adding prescribed amounts of titanyl sulfate [TiOSO ₄ ], vanadyl sulfate [VOSO ₄ ], and sodium niobate [Na ₃ NbO ₄ ] to a cobalt sulfate (CoSO ₄ ) solution, by adding sodium hydroxide and ammonia water, On the other hand, when cobalt hydroxide [Co(OH) ₂ ] is synthesized, titanium (Ti) is co-precipitated with vanadium (V) and niobium (Nb). Then, tricobalt tetroxide (Co ₃ O ₄ ) to which titanium, vanadium, and niobium were added was obtained as a starting material of a cobalt source by subjecting these to a thermal decomposition reaction.

Next, after preparing lithium carbonate (Li ₂ CO ₃ ) as an initial raw material as a lithium source, it was weighed with a scale so that the molar ratio of lithium to cobalt was 1:1. Then, these were mixed with a mortar, and the obtained mixture was sintered in air at 900° C. for 20 hours to synthesize a sintered product of lithium cobaltate powder having titanium, vanadium, and niobium added to the surface. Thereafter, the synthesized sintered product was pulverized into an average particle diameter of 12 μm, and used as a positive electrode active material.

Here, the positive electrode active material synthesized in such a way that the addition amount of titanium is 0.50 mol % and the addition amount of vanadium and niobium is 0.01 mol % relative to the amount of cobalt is used as the positive electrode active material b1, and the addition amount of vanadium and niobium is The positive active material synthesized in the manner of 0.50 mol% is used as the positive active material b2, the positive active material synthesized in the manner of adding 1.00 mol% of vanadium and niobium is used as the positive active material b3, and the vanadium and niobium The positive electrode active material synthesized so that the addition amount was 1.20 mol% each was called the positive electrode active material b4, and the positive electrode active material synthesized so that the addition amount of vanadium and niobium were each 1.50 mol% was called the positive electrode active material b5.

In addition, the positive electrode active material synthesized so that the addition amount of titanium was 0.50 mol%, and the addition amount of vanadium and niobium were each 3 mol% was made into positive electrode active material b6. In addition, the added amounts of titanium, vanadium, and niobium are values obtained by ICP (Inductively Coupled Plasma; plasma emission spectroscopy) analysis.

(3) Production of lithium cobalt oxide with Ti, Zr, V and Nb added

First, add specified amount of titanyl sulfate [TiOSO ₄ ], zirconium sulfate [Zr(SO ₄ ) ₂ ], vanadyl sulfate [VOSO ₄ ] and sodium niobate [Na ₃ NbO _{4 ]} to cobalt sulfate (CoSO ₄ ) solution ] After that, titanium (Ti), zirconium (Zr), vanadium (V) and niobium (Nb) were co-precipitated when cobalt hydroxide [Co(OH) ₂ ] was synthesized by adding sodium hydroxide and ammonia water. Then, tricobalt tetroxide (Co ₃ O ₄ ) to which titanium, zirconium, vanadium, and niobium were added was obtained as a starting material of a cobalt source by subjecting these to a thermal decomposition reaction.

Next, after preparing lithium carbonate (Li ₂ CO ₃ ) as an initial raw material as a lithium source, it was weighed with a scale so that the molar ratio of lithium to cobalt was 1:1. Then, these were mixed with a mortar, and the obtained mixture was sintered in air at 900° C. for 20 hours to synthesize a sintered product of lithium cobaltate powder having titanium, zirconium, vanadium, and niobium added to the surface. Thereafter, the synthesized sintered product was pulverized into an average particle diameter of 12 μm, and used as a positive electrode active material.

Here, the positive electrode active material synthesized in such a manner that the addition amount of titanium is 0.50 mol%, the addition amount of zirconium is 1.00 mol%, and the addition amount of vanadium and niobium is 0.01 mol% is the positive electrode active material c1 . In addition, in the case where the addition amount of titanium and zirconium is the same as that of c1 above, the positive electrode active material synthesized with the addition amount of vanadium and niobium being 0.50 mol% each is used as the positive electrode active material c2, and the addition amount of vanadium and niobium is The positive active material synthesized with the addition amount of 1.00mol% each as positive active material c3, the positive active material synthesized with the addition of vanadium and niobium each as 1.20mol% as the positive active material c4, the vanadium and niobium The positive electrode active material synthesized so that the addition amount of niobium was 1.50 mol% each was used as positive electrode active material c5. In addition, when the addition amounts of titanium and zirconium were the same as c1 above, the cathode active material synthesized so that the addition amounts of vanadium and niobium were each 3 mol % was referred to as cathode active material c6.

In addition, the added amounts of titanium, zirconium, vanadium, and niobium are values obtained by ICP (Inductively Coupled Plasma; plasma emission spectroscopy) analysis.

Then, using each of the positive electrode active materials a1-a6, x1, b1-b6, c1-c6 made as above, with these positive electrode active materials as 85 parts by mass, carbon powder as a conductive agent as 10 parts by mass, as a viscous The polyvinylidene fluoride (PVdF) powder of the binder was mixed so as to be 5 parts by mass to prepare a positive electrode mixture. Then, after mixing the positive electrode mixture obtained with N-methylpyrrolidone (NMP) to form a positive electrode slurry, the positive electrode slurry is coated by a doctor blade method on both sides of a positive electrode current collector (aluminum foil) with a thickness of 20 μm, and the positive electrode slurry is coated on the positive electrode Active material layers are formed on both surfaces of the current collector. After drying, it was rolled to a predetermined thickness using a compression roll, and then cut into a predetermined size to prepare positive electrodes.

Then, the lithium metal is made to face each positive electrode prepared as above, and it is immersed in an organic electrolyte solution, which is a mixture composed of equal volumes of ethylene carbonate (EC) and diethyl carbonate (DEC). LiPF ₆ was dissolved in a solvent to prepare LiPF ₆ at 1 mol/l, and a charge curve was obtained by plotting the potential change when charging with a constant current of 300 mA. Then, in the positive electrode using the positive electrode active material x1, as shown in FIG. 1 , an inflection point H due to phase transition was found in the charge curve around 125 mAh/g. On the other hand, in the positive electrodes using positive electrode active materials a1 to a6, b1 to b6, and c1 to c6, as shown in FIG. 2 , no inflection point due to phase transition was found in the charging curve around 125 mAh/g.

2. Preparation of negative electrode

In addition, 95 parts by mass of natural graphite powder and 5 parts by mass of polyvinylidene fluoride (PVdF) powder as a binder were mixed, and then mixed with N-methylpyrrolidone (NMP) to prepare a negative electrode slurry. Thereafter, the obtained negative electrode slurry was coated on both surfaces of a negative electrode current collector (copper foil) having a thickness of 18 μm by a doctor blade method to form active material layers on both surfaces of the negative electrode current collector. After drying, it is rolled to a predetermined thickness with a compression roll, and then cut into a predetermined size to produce a negative electrode.

3. Fabrication of lithium-ion secondary battery

Next, using the above-mentioned positive electrode and negative electrode, and sandwiching a separator made of a polyethylene porous film between them, they were stacked, and wound up in a spiral shape with a winding machine to produce a spiral electrode group. . After that, inject the prepared organic electrolyte solution into the packaging shell, wherein the organic electrolyte solution is dissolved LiPF ₆ in a mixed solvent composed of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in equal volumes, LiPF ₆ was prepared at 1 mol/l to fabricate lithium ion secondary batteries each having a diameter of 18 mm, a height of 65 mm, and a design capacity of 1600 mAh. [A1～A6, B1～B6, C1～C6 and X1]

Here, the lithium ion secondary battery that has used positive electrode active material a1 is used as battery A1, the lithium ion secondary battery that has used positive electrode active material a2 is used as battery A2, and the lithium ion secondary battery that has used positive electrode active material a3 is used as battery A1. Battery A3, the lithium ion secondary battery that has used positive electrode active material a4 is used as battery A4, the lithium ion secondary battery that has used positive electrode active material a5 is used as battery A5, and the lithium ion secondary battery that has used positive electrode active material a6 As battery A6. In addition, the lithium ion secondary battery using the positive electrode active material b1 is designated as battery B1, the lithium ion secondary battery using the positive electrode active material b2 is designated as battery B2, and the lithium ion secondary battery using the positive electrode active material b3 is designated as battery B1. Battery B3, the lithium ion secondary battery that has used the positive electrode active material b4 is used as battery B4, the lithium ion secondary battery that has used the positive electrode active material b5 is used as battery B5, and the lithium ion secondary battery that has used the positive electrode active material b6 As battery B6.

In addition, the lithium ion secondary battery using the positive electrode active material c1 is designated as battery C1, the lithium ion secondary battery using the positive electrode active material c2 is designated as battery C2, and the lithium ion secondary battery using the positive electrode active material c3 is designated as battery C1. Battery C3, the lithium ion secondary battery that has used the positive electrode active material c4 is used as battery C4, the lithium ion secondary battery that has used the positive electrode active material c5 is used as battery C5, and the lithium ion secondary battery that has used the positive electrode active material c6 As battery C6. In addition, a lithium ion secondary battery using the positive electrode active material x1 was used as battery X1.

4. Determination of battery characteristics

(1) Thermal analysis of the charging positive electrode (measurement of DSC heating start temperature) Next, use these batteries A1~A6, B1~B6, C1~C6 and X1 respectively, and charge them at a constant current at a charging current of 100mA in a temperature environment of 25°C. until the battery voltage reaches 4.2V. Then, these batteries were disassembled in a dry box, and the positive electrodes were taken out, washed with dimethyl carbonate, and vacuum-dried to obtain test pieces. 1 mg of ethylene carbonate was added to 4 mg of these test pieces, and then sealed in an aluminum cell in an argon atmosphere. Then, these batteries were put into a differential scanning calorimeter (DSC), and the temperature was raised at a heating rate of 5° C./min, and the temperature at which each test piece itself started to generate heat (DSC heating start temperature) was measured, and the following Table 1 was obtained. The results shown.

(2) Initial capacity

In addition, using these batteries A1~A6, B1~B6, C1~C6 and X1 respectively, in a temperature environment of 25°C, charge at a constant current of 1600mA until the voltage reaches 4.2V, and then charge at a constant voltage of 4.2V Carry out constant voltage charging until the termination current reaches 30mA. Thereafter, the battery was discharged at a discharge current of 1600 mA until the battery voltage reached 2.75 V, and the discharge capacity of the first cycle was obtained from the discharge time, and the results shown in Table 1 below were obtained.

(3) Magnification performance

Similarly, use these batteries A1~A6, B1~B6, C1~C6, and X1 respectively, charge at a constant current of 1600mA at a temperature of 25°C until the voltage reaches 4.2V, and then charge at a constant voltage of 4.2V Carry out constant voltage charging until the termination current reaches 30mA. Thereafter, the battery was discharged until the battery voltage reached 2.75 V at a discharge current of 1600 mA, which was used as the charge and discharge of the first cycle. Next, charge with a constant current of 1600mA until the voltage reaches 4.2V, and then perform constant voltage charge with a constant voltage of 4.2V until the termination current reaches 30mA. Thereafter, the battery was discharged until the battery voltage reached 2.75 V at a discharge current of 4800 mA, which was used as the charge and discharge of the second cycle. Next, the ratio (%) of the discharge capacity at the second cycle to the discharge capacity at the first cycle was obtained as the rate performance (%), and the results shown in Table 1 below were obtained.

(4) 25°C charge-discharge cycle capacity retention rate

In addition, using these batteries A1~A6, B1~B6, C1~C6 and X1 respectively, in a temperature environment of 25°C, charge at a constant current of 1600mA until the voltage reaches 4.2V, and then charge at a constant voltage of 4.2V Carry out constant voltage charging until the termination current reaches 30mA. Thereafter, the battery was discharged until the battery voltage reached 2.75 V at a discharge current of 1600 mA, which was used as the charge and discharge of the first cycle. Then, such a charge-discharge cycle was repeated 300 times, and the ratio (%) of the discharge capacity of the 300th cycle to the discharge capacity of the first cycle was obtained as the 25°C charge-discharge cycle capacity retention rate (%), and The results are shown in Table 1 below.

(5) 60°C charge-discharge cycle capacity retention rate

In addition, these batteries A1~A6, B1~B6, C1~C6 and X1 were used respectively, and charged at a constant current of 1600mA at a temperature of 60°C until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V Carry out constant voltage charging until the termination current reaches 30mA. Thereafter, the battery was discharged until the battery voltage reached 2.75 V at a discharge current of 1600 mA, which was used as the charge and discharge of the first cycle. Then, such a charge-discharge cycle was repeated 300 times, and the ratio (%) of the discharge capacity of the 300th cycle to the discharge capacity of the first cycle was obtained as the 60° C. charge-discharge cycle capacity retention rate (%). The results are shown in Table 1 below.

(6) Presence or absence of phase transition

In addition, when these batteries A1 to A6, B1 to B6, C1 to C6, and X1 were charged and discharged, an inflection point due to phase transition was found in the charge and discharge curves with a charge capacity of around 125 mAh/g. It was judged that there was a phase transition, and when no inflection point was found, it was judged that there was no phase transition. The results are shown in Table 1 below.

battery type Ti added (mol%) Zr addition amount (mol%) V addition amount (mol%) Amount of Nb added (mol%) DSC heating start temperature (℃) Initial capacity (mAh) Rate performance (%) 25℃ charge-discharge cycle capacity maintenance rate (%) 60℃ charge-discharge cycle capacity maintenance rate (%) With or without phase change X1 0.50 none none none 179 1630 95 93 78 have A1 0.50 0.01 none none 184 1633 95 96 81 none A2 0.50 0.50 none none 186 1634 96 96 82 none A3 0.50 1.00 none none 189 1629 96 97 82 none A4 0.50 1.20 none none 189 1627 96 97 83 none A5 0.50 1.50 none none 191 1630 95 97 82 none A6 0.50 3.00 none none 190 1600 92 97 81 none B1 0.50 none 0.01 0.01 188 1630 98 94 82 none B2 0.50 none 0.50 0.50 192 1628 98 94 85 none B3 0.50 none 1.00 1.00 193 1629 98 93 85 none B4 0.50 none 1.20 1.20 193 1628 98 94 84 none B5 0.50 none 1.50 1.50 194 1626 98 94 83 none B6 0.50 none 3.00 3.00 195 1597 98 94 82 none C1 0.50 1.00 0.01 0.01 196 1634 95 98 84 none C2 0.50 1.00 0.50 0.50 196 1630 95 98 85 none C3 0.50 1.00 1.00 1.00 198 1632 96 97 85 none C4 0.50 1.00 1.20 1.20 199 1627 96 98 85 none C5 0.50 1.00 1.50 1.50 198 1625 96 98 85 none C6 0.50 1.00 3.00 3.00 199 1606 96 97 85 none

From the results in Table 1 above, it is clear that when the amount of zirconium (Zr) added relative to the amount of cobalt is 0.01 mol% or more, the DSC heat generation start temperature rises, and the capacity after 300 cycles at 25°C and 60°C The maintenance rate is significantly improved. This is presumably because when the amount of zirconium added is 0.01 mol% or more relative to the amount of cobalt, the phase transition at a charge capacity around 125 mAh/g is suppressed and the crystal structure becomes stable. Furthermore, X-ray diffraction evaluation at a charge capacity of around 125 mAh/g confirmed that the positive electrode active material x1 used in battery X1 undergoes a phase transition from a hexagonal crystal system to a monoclinic crystal system to a hexagonal crystal system.

However, in the positive electrode active materials a1 to a6 used in the batteries A1 to A6, as shown in FIG. 2 , it was found that there was no phase transition and they were still in the hexagonal crystal system. In addition, when the added amount of zirconium was 3.00 mol% relative to the amount of cobalt, the initial capacity decreased and the rate characteristics also decreased. From these considerations, it can be considered that it is desirable to limit the amount of zirconium added to the amount of cobalt to 0.01 mol% or more and 1.5 mol% or less.

Similarly, it was found that when the added amounts of vanadium and niobium are 0.01 mol% or more, the exothermic start temperature of DSC rises. In addition, it was also found that the capacity retention rate after 300 cycles at 60° C. was significantly improved. This is presumably because when the added amount of vanadium and niobium is 0.01 mol% or more relative to the amount of cobalt, the phase transition at a charge capacity near 125 mAh/g is suppressed and the crystal structure becomes stable. Furthermore, it was confirmed by X-ray diffraction evaluation at a charge capacity of around 125 mAh/g that there was no phase transition, and that it was still a hexagonal crystal system. In addition, when the added amounts of vanadium and niobium were 3.00 mol% relative to the amount of cobalt, the initial capacity decreased and the rate characteristics also decreased. From these considerations, it can be considered that it is desirable to limit the added amount of vanadium and niobium to 0.01 mol% to 1.5 mol% relative to the amount of cobalt.

In contrast, it was found that in batteries C1 to C6 using positive electrode active materials c1 to c6 in which Zr (1 mol%) and vanadium and niobium (0.01 to 3 mol%) were added to Ti (0.5 mol%), DSC The temperature at which heat generation starts becomes high, and the thermal stability of the positive electrode improves. However, as the amount of vanadium and niobium increases, the initial capacity decreases.

In addition, from the results in Table 1 above, it is clear that in battery A3 using positive electrode active material a3 with only Ti (0.5 mol%) and Zr (1 mol%) added and no vanadium or niobium added, the DSC heat generation start temperature becomes lower. , the thermal stability of the positive electrode decreases. It can be considered that it is preferable to limit the addition amount of vanadium and niobium to 0.01 mol% to 1.5 mol% relative to the amount of cobalt.

In addition, in the above-mentioned embodiment, titanium, zirconium, vanadium, and niobium are co-precipitated when synthesizing cobalt hydroxide, and then these are subjected to a thermal decomposition reaction to obtain starting materials as a cobalt source by adding titanium, zirconium, vanadium, and The example of tricobalt tetroxide of vanadium and niobium has been described, but it is also possible to obtain cobalt as cobalt by thermally decomposing them after co-precipitating titanium, zirconium, vanadium and niobium when synthesizing cobalt oxyhydroxide, cobalt carbonate, or cobalt oxalate. The starting material of the source is cobalt tetroxide with addition of titanium, zirconium, vanadium and niobium.

Claims (8)

1. active material for anode of Li-ion secondary battery, it is characterized in that: described positive active material is with general formula [LiCo _1-xM _xO ₂(M=Ti, Zr)] the cobalt acid lithium compound of hexagonal crystal system of expression, described cobalt acid lithium is by being to mix at 1: 1 to obtain to carrying out as the cobalt compound in cobalt source and lithium compound as the lithium source with mol ratio, in described cobalt compound, by coprecipitated titanium and the zirconium of having added, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, and the addition of zirconium is 0.01mol%～3mol% with respect to the amount of cobalt.

2. active material for anode of Li-ion secondary battery, it is characterized in that: described positive active material is with general formula [LiCo _1-xM _xO ₂(M=Ti, V, Nb)] the cobalt acid lithium compound of hexagonal crystal system of expression, described cobalt acid lithium is by being to mix at 1: 1 to obtain to carrying out as the cobalt compound in cobalt source and lithium compound as the lithium source with mol ratio, in described cobalt compound, by coprecipitated titanium and vanadium, the Niobium of having added, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, the addition of vanadium is 0.01mol%～1.5mol% with respect to the amount of cobalt, and the addition of Niobium is 0.01mol%～1.5mol% with respect to the amount of cobalt.

3. active material for anode of Li-ion secondary battery, it is characterized in that: described positive active material is with general formula [LiCo _1-xM _xO ₂(M=Ti, Zr, V, Nb)] the cobalt acid lithium compound of hexagonal crystal system of expression, described cobalt acid lithium is by being to mix at 1: 1 to obtain to carry out mol ratio as the cobalt compound in cobalt source and lithium compound as the lithium source, in described cobalt compound, by coprecipitated titanium, zirconium, vanadium and the Niobium of having added, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, and the addition of zirconium, vanadium and Niobium is 0.01mol%～1.5mol% with respect to the amount of cobalt.

4. according to any described active material for anode of Li-ion secondary battery in the claim 1 to 3, it is characterized in that: described cobalt compound is cobalt carbonate or cobalt hydroxide or hydroxy cobalt oxide.

5. according to any described active material for anode of Li-ion secondary battery in the claim 1 to 3, it is characterized in that: described cobalt acid lithium compound, near not phase transformation charging capacity 125mAh/g.

6. according to the manufacture method of the described active material for anode of Li-ion secondary battery of claim 1, it is characterized in that: comprise the co-precipitation operation, mixed processes and sintering circuit, described co-precipitation operation, add titanium and zirconium at the initial stage cobalt compound that is used for thermal decomposition and becomes the cobalt compound in cobalt source by co-precipitation, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, the addition of zirconium is 0.01mol%～3mol% with respect to the amount of cobalt, described mixed processes is by being to mix at 1: 1 to obtain to carrying out as the cobalt compound in cobalt source and lithium compound as the lithium source with mol ratio, again with the mixture that obtains in air with 880～920 ℃ of temperature sintering 18～20 hours.

7. according to the manufacture method of the described active material for anode of Li-ion secondary battery of claim 2, it is characterized in that: comprise the co-precipitation operation, mixed processes and sintering circuit, described co-precipitation operation, add titanium and vanadium at the initial stage cobalt compound that is used for thermal decomposition and becomes the cobalt compound in cobalt source by co-precipitation, Niobium, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, the addition of vanadium is 0.01mol%～1.5mol% with respect to the amount of cobalt, the addition of Niobium is 0.01mol%～1.5mol% with respect to the amount of cobalt, described mixed processes is by being to mix at 1: 1 to obtain to carrying out as the cobalt compound in cobalt source and lithium compound as the lithium source with mol ratio, again with the mixture that obtains in air with 880～920 ℃ of temperature sintering 18～20 hours.

8. according to the manufacture method of the described active material for anode of Li-ion secondary battery of claim 3, it is characterized in that: comprise the co-precipitation operation, mixed processes and sintering circuit, described co-precipitation operation, add titanium at the initial stage cobalt compound that is used for thermal decomposition and becomes the cobalt compound in cobalt source by co-precipitation, zirconium, vanadium and Niobium, wherein the addition of titanium is 0.01mol%～1mol% with respect to the amount of cobalt, the addition of vanadium is 0.01mol%～1.5mol% with respect to the amount of cobalt, zirconium, the addition of vanadium and Niobium is 0.01mol%～1.5mol% with respect to the amount of cobalt, described mixed processes is by being to mix at 1: 1 to obtain to carrying out as the cobalt compound in cobalt source and lithium compound as the lithium source with mol ratio, again with the mixture that obtains in air with 880～920 ℃ of temperature sintering 18～20 hours.

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