JP3355126B2 - Positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, miniaturization and high performance of electronic equipment have been advanced, and attention has been paid to secondary batteries as power sources for driving them. In particular, lithium ion secondary batteries have high voltage and high energy density. Is highly expected as a battery having As a positive electrode active material of such a battery, lithium ions are intercalated and deintercalated.
Layered compounds, such as LiCoO
A composite oxide mainly composed of lithium and a transition metal such as LiNiO ₂ or LiNiO ₂ (hereinafter referred to as lithium composite oxide) is used.

Among such lithium composite oxides, LiCoO ₂ is a positive electrode active material for lithium secondary batteries which has already been put into practical use. However, since cobalt is rare and expensive as a resource, Lower cost and higher energy
LiNiO ₂ as a lithium composite oxide capable of density,
Materials such as LiNi _1-y Co _y O ₂ , a lithium composite oxide containing nickel as a main transition metal element, have been vigorously developed.

[0004] In a lithium ion secondary battery using such a nickel-based lithium composite oxide as a positive electrode active material, the electrolyte solution on the surface of the positive electrode active material during high-temperature storage in a charged state or during use in a high-temperature environment. Decomposition reaction easily occurs. Therefore, there is a problem that the internal pressure of the battery is abnormally increased by the decomposition product gas, or the surface of the active material is coated with the decomposition product, so that the battery capacity is significantly reduced. In addition, nickel-based lithium composite oxides release oxygen at a relatively low temperature and rapidly oxidize the surrounding electrolyte when the lithium ions are heated while being deintercalated from the crystal lattice during charging. There was also the problem of thermal stability.

Techniques for solving these problems include replacing part of nickel in the crystal lattice with another element, coating the surface of the positive electrode active material with a metal, an inorganic compound, an organic substance, or the like. Many attempts have been made such as adding various compounds to the positive electrode mixture.

[0006]

However, in these conventional techniques, although the function of suppressing the reaction between the positive electrode active material and the electrolyte and the thermal stability of the positive electrode active material are improved, the nickel-based lithium It has been difficult to obtain a positive electrode active material that does not impair the large discharge capacity expected of the composite oxide. Therefore, an object of the present invention is to improve the function of suppressing the reaction with the electrolytic solution and the thermal stability,
Accordingly, it is an object of the present invention to provide a high-capacity positive electrode active material with improved safety, a method for producing the same, and a lithium ion secondary battery using the same.

[0007]

Means for Solving the Problems The present inventors have studied in detail the firing conditions of a lithium composite oxide mainly composed of nickel and have obtained the following findings. Fine core particles generated in the early stage of firing grow by liquid phase sintering at the grain interface,
In this process, the composition ratio of lithium and nickel in the vicinity of the grain interface tends to locally produce a non-stoichiometric composition. If lithium is insufficient, particles grow abnormally, and a compound with a nickel-excess non-stoichiometric composition is introduced into the crystal. When mixed, the charge / discharge characteristics deteriorate. Further, when the sintering is performed at a temperature exceeding 800 ° C. for a long time, nickel is diffused into lithium sites, and the reduction in discharge capacity becomes more remarkable.

When calcination is carried out at a low temperature in order to avoid the incorporation of a non-stoichiometric compound accompanying the growth of particles and the diffusion of nickel into lithium sites, the resulting particles have low crystallinity and a low surface area. Therefore, the obtained active material is inferior in thermal stability and cannot suppress the reactivity with the electrolytic solution. As a means for solving these problems, the present inventors first set a firing step in the manufacturing method.
The sintering was performed in two stages of secondary sintering and secondary sintering, and the sinter obtained by the primary sintering was pulverized and dispersed in water to an average particle size of 1 μm or less to form a slurry. As a result, the composition ratio of lithium and transition metal near the particle surface could be made uniform for each particle.
After granulating the slurry into a spherical shape by spray drying, it was found that by performing secondary firing at a temperature higher than the primary firing, generation of the non-stoichiometric composition compound was suppressed, and the crystallinity was increased.

The composite oxide thus obtained is spherical secondary particles formed by joining primary particles with an inorganic compound containing an inorganic oxide mainly composed of Li, and is formed under an inert gas atmosphere. The differential heat loss when the temperature was raised to 750 ° C. was 0.
It has been found that when the content is 5% by weight or less, a positive electrode active material having a high capacity and improved reactivity with an electrolytic solution and thermal stability can be obtained.

The present inventors have further found that the improvement effect can be enhanced by specifying the inorganic oxide and its raw material form, and reached the present invention.

That is, the present invention firstly provides a compound represented by the general formula: Li
Ni _1-xy Co _x E _y O ₂ (where E is Al or a combination of Al and one or more elements selected from the group consisting of Mn and Ti; 0.10 ≦ x ≦ 0.20; 02 ≦ y
≦ 0.10) is a positive electrode active material for a lithium ion battery including secondary particles formed by joining primary particles of an inorganic compound containing an inorganic oxide mainly composed of Li. A positive electrode active material for a lithium ion secondary battery, wherein a differential thermal weight loss when heated to 750 ° C. in an active gas atmosphere is 0.5% by weight or less; , Y, Zr, B, Al, Co, an oxide of one or more elements selected from the group of P and Li, and the total content of elements other than oxygen of the inorganic compound in the primary particles 3. The positive electrode active material for a lithium ion secondary battery according to the above item 1, wherein the atomic number ratio is 0.002 to 0.03 with respect to the total content of Li, Ni, Co, and the element E; A method for producing a positive electrode active material according to the first aspect, wherein Li, a first baking step of baking a mixture of each compound of i, Co, and element E at 500 to 800 ° C., and dissolving the fired product obtained in the first baking step in water so that the average particle size is 1 μm or less. A dispersion granulation step of spray-drying the slurry in which the granules are dispersed to obtain a spherical granulated powder; and a temperature of the spherical granulated powder obtained in the dispersion granulation step higher than the primary firing temperature by 30 ° C. or more and 900 ° C. or less. And 4. a method for producing a positive electrode active material for a lithium ion secondary battery, the method comprising: A primary baking step of baking a mixture of each compound of Ni, Co and the element E at 500 to 800 ° C., and dissolving the calcined product obtained in the primary baking step in water so that the average particle size becomes 1 μm or less. Lithium dispersed in particles and added to nitric acid and eluted in the liquid phase A slurry obtained by spray-drying a slurry obtained by converting part or all of the powder into lithium nitrate to obtain a spherical granulated powder, and subjecting the spherical granulated powder obtained in the dispersion granulating step to a primary firing temperature of 30 ° C. Higher and 9
A second firing step of firing at a temperature of 00 ° C. or lower; a method for producing a positive electrode active material for a lithium ion secondary battery; A first firing step of firing a mixture of each compound of Li, Ni, Co, and the element E at 500 to 800 ° C;
The fired product obtained in the first firing step is pulverized and dispersed in water so that the average particle diameter is 1 μm or less, and then Mg, Y, Z
A slurry obtained by spray-drying a slurry to which a compound of at least one element selected from the group consisting of r, B, Al, Co, and P was added to obtain a spherical granulated powder, and a dispersion granulating step. The spherical granulated powder is at least 30 ° C. higher than the primary firing temperature and 900 ° C.
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a secondary firing step of firing at the following temperature; sixth, a compound of an element to be added in the dispersion granulation step is nitrate. 7. The method for producing a positive electrode active material for a lithium ion secondary battery according to the above item 5;
A lithium ion secondary battery characterized by using the positive electrode active material according to any one of the first and second aspects as a positive electrode active material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the positive electrode active material of the present invention, the primary particles have the general formula: LiNi _1-xy Co _x E _y O ₂ (provided that:
E is Al or a combination of Al and one or more elements selected from the group consisting of Mn and Ti, 0.10 ≦ x ≦ 0.20,
0.02 ≦ y ≦ 0.10), wherein the primary particles are spherical secondary particles formed by bonding with an inorganic compound containing an inorganic oxide mainly composed of Li. And a differential heat loss when heated to 750 ° C. in an inert gas atmosphere is 0.5% by weight or less, and high capacity, thermal stability, and suppression of reactivity with an electrolytic solution are achieved. Can be compatible.

The purpose of adding Co is to suppress cycle deterioration due to a change in crystal structure during charging and discharging.
Is less than 10 mol%, the effect of improvement is low. If it exceeds 20 mol%, the raw material cost is high, which is not preferable. M
n, Al and Ti are added for the purpose of improving thermal stability. When the substitution amount is small, the improvement effect is low, and when the substitution amount is too large, the charge / discharge capacity is reduced. In the present invention, the positive electrode active material comprises the above 1
It is important that the secondary particles are spherical secondary particles formed by bonding with an inorganic compound containing an inorganic oxide mainly composed of Li.

Known techniques characterized by similar shapes include, for example, Japanese Patent Application Laid-Open Nos. 9-231973 and 9-129.
230, JP-A-8-339806, JP-A-7-3775
6 and others. However, according to the techniques disclosed in these known documents, it is impossible to uniformly control the composition ratio of lithium and the transition metal element on the surface of each particle, and completely prevent sintering between primary particles. Therefore, the discharge capacity of the obtained positive electrode active material cannot be increased.

In the positive electrode active material of the present invention, such a problem is unlikely to occur because a sintering is suppressed by the presence of a uniform binding layer of an inorganic compound containing an inorganic oxide between the primary particles. As a more preferred embodiment of the method for producing a positive electrode active material of the present invention, as an inorganic compound containing an inorganic oxide used for bonding primary particles, Li ₂ is used because a bonding layer can be easily formed.
O is preferred. Further, at least one element selected from the group consisting of Mg, Y, Zr, B, Al, Co, and P is contained in the inorganic compound layer containing the inorganic oxide as an element having an effect of suppressing the reactivity with the electrolytic solution. Is more preferred.

If the amount of the inorganic compound containing an inorganic oxide is too small, a uniform bonding layer cannot be formed, and particle growth and discharge capacity decrease due to sintering. In order to reduce the discharge capacity due to segregation, the total content of elements excluding oxygen in the inorganic compound is L in the primary particles.
It is preferable that the ratio of the number of atoms to the total content of i, Ni, Co, and the element E is in the range of 0.002 to 0.03. Further, it is important that the active material has a differential heat loss of 0.5% by weight or less when heated to 750 ° C. in an inert atmosphere.

It is unclear why the differential thermal weight loss correlates with the characteristics of the positive electrode active material, but the weight loss up to 600 ° C. is caused by the amount of moisture and unreacted substances in the active material, and is reduced at 600 ° C. or higher. Is presumed to be oxygen desorption from the crystal lattice due to low crystallinity, and by suppressing such factors,
It is considered that high charge / discharge capacity and excellent thermal stability were exhibited, and the reactivity with the electrolytic solution could be suppressed. Such control of the differential heat loss value under an inert atmosphere can be achieved by optimizing the manufacturing conditions within the range of the manufacturing method described below.

The method for producing a positive electrode active material according to the present invention is characterized in that a mixture of at least a lithium compound, a transition metal compound mainly composed of nickel and optionally an Al compound, that is, a mixture of each compound of Li, Ni, Co and the element E is prepared. 500
A primary firing step of firing at ~ 800 ° C for 5-20 hours;
A dispersion granulation step of spray-drying a slurry obtained by pulverizing and dispersing the fired product obtained in the primary firing step in water until the average particle diameter becomes 1 μm or less to obtain a spherical granulated powder; And a secondary firing step of firing the spherical granulated powder obtained in the above at a temperature higher than the primary firing temperature by 30 ° C. or more and 900 ° C. or lower for 1 to 5 hours. Similar known production methods include, for example, JP-A-9-251854, JP-A-9-50810, JP-A-8-185611, and JP-A-8-18561.
55624 and JP-A-7-335220.

The first feature of the present invention, however, is that the fired product is pulverized and dispersed in water until the average particle diameter becomes 1 μm or less in the dispersion granulation step after the primary firing. Since the mixing ratio of lithium, transition metal, and, in some cases, Al on the surface of the particles can be adjusted more uniformly, generation of a non-stoichiometric composition excessive in nickel is suppressed, crystallinity is high, and electrolysis on the particle surface is performed. The method of the present invention has an effect of suppressing the decomposition reaction of the liquid, and in these respects, the method of the present invention is far superior to known production methods.

As a second feature, in the dispersion granulation step, after adding a specific compound to the slurry, spray drying is performed to form an inorganic compound layer containing an inorganic oxide containing a specific element between primary particles. The secondary firing may be performed after the film is formed uniformly. As this effect, sintering of the primary particles during the secondary firing can be further suppressed, and the decomposition reaction of the electrolytic solution can be suppressed. Further, by setting the secondary firing temperature higher than the primary firing temperature, the crystallinity of the positive electrode active material is increased, and the thermal stability is improved.

In a mixture containing a lithium compound and a transition metal salt mainly composed of nickel and possibly an Al compound, the element ratio of lithium and a transition metal containing Al in some cases is preferably lithium-excess. .

The primary sintering step is performed at 500 to 800 ° C. and 5-2.
It is preferable to bake within the range of 0 hours. At a firing temperature lower than 500 ° C., the synthesis reaction does not substantially proceed.
If the temperature exceeds 00 ° C., the particle growth proceeds, and the effect of the present invention is reduced. The purpose of this step is to carry out a synthesis reaction between a lithium salt in the raw material and a transition metal salt mainly composed of nickel (including an Al compound in some cases) while suppressing the growth of primary particles. Low temperature within the range that does not interfere
It is preferable to perform firing for a long time.

The calcined product obtained in the primary calcining step is a slurry which is pulverized and dispersed in water until the average particle diameter becomes 1 μm or less. It is important that the pulverization and dispersion operation at this time is performed to the vicinity of the primary particle diameter.
If the diameter exceeds 1 μm, the mixing ratio of lithium and transition metal (including an Al compound in some cases) near the surface of the primary particles is not sufficiently uniform, and the discharge capacity of the positive electrode active material obtained after secondary firing is reduced. Resulting in. As a suitable pulverizer / disperser, for example, a wet bead mill or the like can be used.

The slurry thus obtained exhibits an alkaline pH of 10 or more because the lithium salt is dissolved in accordance with the excess amount of lithium in the raw material stage. By adding a specific compound to this slurry, it is possible to improve the characteristics of the active material obtained after the secondary firing.
As the form of the compound to be added to the slurry, nitric acid or nitrate is preferable. By the addition of the nitrate group, part or all of the lithium salt in the liquid is converted to lithium nitrate, and in the next firing step, decomposition of lithium nitrate occurs near the primary particles, and the oxidizing power causes the particles to be decomposed. It is considered that the crystallinity of the surface increases. As additional elements, Mg,
More preferably, a compound of at least one element selected from the group consisting of Y, Zr, B, Al, Co, and P is added. By adding these elements, the reactivity with the electrolytic solution is further suppressed. The total addition amount of these elements is desirably in the range of 0.002 to 0.03 in terms of the atomic ratio with respect to the total amount of Li, Ni, Co, and the element E in the primary particles.

The slurry is granulated prior to the next step, secondary firing. As a preferable granulation method, a spray drying method which does not lose the additive in the liquid and causes less segregation of the additive during drying is suitable. You may shape | mold and granulate with a machine etc.

In the second firing step, 30 times more than in the first firing step.
It is preferable to perform calcination at a temperature of at least 900C and not more than 900C for 1 to 5 hours. If the firing time is short, the crystallinity is not improved, so that the thermal stability and the reactivity with the electrolytic solution are not improved. If the firing time is too long, nickel is diffused into lithium sites, and the discharge capacity is reduced. If the firing temperature is not higher than the primary firing temperature by 30 ° C. or more, the improvement in crystallinity will not be remarkable. If the firing temperature is higher than 900 ° C., diffusion of nickel into lithium sites and abnormal grain growth will occur. In addition, 800
When firing at a temperature higher than ℃, it is necessary to perform firing in an oxygen stream. As a sintering furnace method, a pusher furnace, a fluidized sintering furnace, a kiln furnace or the like is used. After the fired product after the completion of the second firing is pulverized and classified in dry air, it is adjusted to a predetermined particle size to obtain a positive electrode active material. The obtained positive electrode active material was measured for differential heat loss when heated to 750 ° C. at a rate of 10 ° C./min in an Ar gas flow using a differential thermal analyzer (TG-TDA).

The production of the battery was performed as follows. First, a positive electrode active material, graphite as a conductive material, and polytetrafluoroethylene (PTFE) as a binder are kneaded and molded in a weight ratio of 87: 8: 5, and then the obtained molded product is molded. The rolled product was used as a positive electrode mixture. Metal lithium was used for the negative electrode, and a polypropylene film cut out was used for the separator. In the electrolyte, ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 1: 1.
The solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L as an electrolyte in the mixed solution was used.

FIG. 1 is a schematic cross-sectional view of the test battery manufactured as described above. In the figure, 1 is a stainless steel case, 2 is a gasket, 3 is a sealing plate, 4 is a negative electrode, 5 is a positive electrode, 6 is a separator, 7 is a negative electrode current collector, and 8 is a positive electrode current collector.
The charge / discharge test was performed at a current density of 0.5 mA / cm ² ,
The battery was charged to 4.3 V and then discharged to 2.7 V, and the amount of electricity per unit weight of the positive electrode active material was defined as the discharge capacity. The thermal stability of the positive electrode active material was evaluated as follows. 2
The first charge was performed at a final voltage of +4.3 V, the positive electrode mixture was taken out of the charged battery, and the positive electrode mixture was sealed in a stainless steel sealed cell in an Ar atmosphere.
The temperature was increased at a rate of in and calorimetric measurement was performed to determine the rapid peak temperature at this time, and the thermal stability of the positive electrode active material was evaluated using this value (this evaluation method is hereinafter abbreviated as DSC method). . In a positive electrode active material having high thermal stability, the peak temperature of rapid heating shifts to a higher temperature side.

The evaluation of the reactivity between the positive electrode active material and the electrolyte was performed as follows. The second charge is the end voltage +
The operation was performed at 4.3 V, the positive electrode mixture was taken out of the charged battery, sealed in a sealed aluminum container having a pressure resistance of 3 kgf / cm ² , and heated to 300 ° C. at a rate of 10 ° C./min by a differential thermal analyzer. Then, the temperature at which the airtightness of the container was broken due to an increase in internal pressure due to the generated gas was measured, and the reactivity between the positive electrode active material and the electrolyte was evaluated based on this temperature value (this evaluation method is hereinafter abbreviated as TG method). ). In a positive electrode active material in which the reactivity with the electrolytic solution is suppressed, the temperature at which the airtightness of the container is broken shifts to a higher temperature side. Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

[0030]

EXAMPLE 1 Lithium hydroxide, nickel hydroxide, cobalt hydroxide and aluminum hydroxide were mixed in a molar ratio of 105: 8.
After weighing each so as to be 0: 15: 5, they were pulverized and mixed by a ball mill, and the obtained mixed powder was 1 ton / cm ^2.
, And the resulting molded body was used as a raw material for firing. This raw material was fired (primary firing) at 700 ° C. for 10 hours in an air stream. The obtained calcined product and pure water are combined at 40:
After mixing at a weight ratio of 60, the mixture was pulverized and dispersed in a wet bead mill for 2 hours to obtain a slurry having an average particle diameter of 0.4 μm, and dried and granulated in a spherical shape by a spray dryer. This granulated powder is fired at 850 ° C. for 2 hours in an oxygen stream (secondary firing)
The resulting mixture was pulverized with a mortar mill and then sized with a screen classifier.

The positive electrode active material thus obtained is spherical secondary particles formed by joining primary particles having a particle size of 0.5 to 2 μm with lithium carbonate and lithium oxide. An electron micrograph showing the structure was as shown in FIG. 2, and the differential heat loss was 0.3% by weight. FIG. 3 shows the results of differential thermal analysis when this active material was heated to 750 ° C. in an Ar gas flow.

The discharge capacity of this active material is 195 mAh
/ G, the thermal stability by the DSC method was 248 ° C, and the reactivity with the electrolytic solution by the TG method was 178 ° C. FIG. 4 shows the results of measuring the thermal stability of the active material by the DSC method. FIG. 5 is a graph showing the results of measuring the reactivity of the active material with the electrolytic solution by the TG method.

[0033]

Comparative Example 1 The firing raw material used in Example 1 was heated at 850 ° C.
For 10 hours in an oxygen stream, pulverized with a mortar type pulverizer, and then sized with a screen type classifier. The obtained positive electrode active material was a particle having a particle diameter of 1 to 15 μm and having a wide particle size distribution after sintering, and had a differential weight loss of 0.8% by weight. The discharge capacity of this active material was 178 mAh /
g, thermal stability by the DSC method was 230 ° C., and reactivity with the electrolytic solution by the TG method was 157 ° C.

[0034]

COMPARATIVE EXAMPLE 2 The raw material for firing used in Example 1 was fired at 700 ° C. for 10 hours in an air stream, then fired at 850 ° C. for 2 hours in an oxygen stream, and pulverized with a mortar pulverizer. ,
The particles were sized using a screen classifier. The obtained positive electrode active material is a particle having a particle diameter of 0.5 to 10 μm and having a wide particle size distribution with advanced sintering, and a differential weight loss of 0.9% by weight.
Met. The discharge capacity of this active material was 180 mAh.
/ G, the thermal stability by the DSC method was 233 ° C, and the reactivity with the electrolytic solution by the TG method was 165 ° C.

[0035]

Comparative Example 3 The firing raw material used in Example 1 was fired in an air stream at 700 ° C. for 10 hours, and then pulverized with an impact-type pulverizer. The obtained particles were agglomerated secondary particles in which primary particles having a particle size of 0.1 to 0.5 micron were aggregated, and the average particle size of the secondary particles was 15 microns. This powder was subsequently calcined at 850 ° C. for 2 hours in an oxygen stream, pulverized with a mortar type pulverizer, and then sized with a screen type classifier. The obtained positive electrode active material has a particle diameter of 0.1 to 5 microns,
The particles had a wide particle size distribution after sintering, and the differential heat loss was 0.6% by weight. The discharge capacity of this active material was 184 mAh / g, and the thermal stability by the DSC method was 232.
The reactivity with the electrolytic solution by the TG method was 163 ° C.

[0036]

Comparative Example 4 Example 1 was repeated except that the slurry was pulverized and dispersed in a wet bead mill for 10 minutes to obtain a slurry having an average particle size of 4 microns.
A positive electrode active material was prepared in the same manner as described above. The obtained positive electrode active material was spherical secondary particles in which primary particles having a particle size of 0.5 to 5 μm were joined with lithium carbonate and lithium oxide, and had a differential heat loss of 0.7% by weight. Was. The discharge capacity of this active material was 179 mAh / g, the thermal stability by the DSC method was 246 ° C., and the reactivity with the electrolytic solution by the TG method was 17
It was 0 ° C.

[0037]

Example 2 A positive electrode active material was prepared in the same manner as in Example 1 except that the slurry was pulverized and dispersed in a wet bead mill for 1 hour to obtain a slurry having an average particle size of 1 micron. The obtained positive electrode active material was spherical secondary particles in which primary particles having a particle size of 0.5 to 2 μm were joined with lithium carbonate and lithium oxide, and had a differential heat loss of 0.4% by weight. Was. The discharge capacity of this active material was 190 mAh / g, the thermal stability by the DSC method was 243 ° C., and the reactivity with the electrolytic solution by the TG method was 17
7 ° C.

From the results of Examples 1-2 and Comparative Examples 1-4,
It can be seen that the positive electrode active material obtained by the production method of the present invention has a high discharge capacity, and has improved thermal stability and reactivity with the electrolytic solution. In particular, by reducing the average particle diameter of the particles in the slurry obtained in the crushing and dispersing step to around the primary particle diameter after the first firing, that is, 1 μm or less, to prevent a decrease in the discharge capacity of the active material. I understand.
Except that the primary sintering temperature was changed, the results of producing the positive electrode active material in the same manner as in Example 1 were shown in Examples 3 to 5 and Comparative Example 5.
Are shown in Table 1 as .about.6. From this table, the primary firing temperature is 5
It can be seen that when the temperature is in the range of 00 ° C. to 800 ° C., the obtained positive electrode active material shows a high discharge capacity.

[0039]

[Table 1]

The results of producing positive electrode active materials in the same manner as in Example 1 except that the primary firing time was changed are shown in Table 2 as Examples 6 to 7 and Comparative Examples 7 and 8. From this table, it can be seen that when the primary firing time is in the range of 5 to 20 hours, the obtained positive electrode active material shows a high discharge capacity.

[0041]

[Table 2]

The results of producing positive electrode active materials in the same manner as in Example 1 except that the primary sintering temperature and the secondary sintering temperature were changed are shown in Table 3 as Examples 8 to 11 and Comparative Examples 9 to 13. From this table, the temperature difference between the primary firing and the secondary firing is 30.
It is found that the effect of improving the thermal stability and the reactivity with the electrolytic solution is low if the temperature is not higher than ° C, and that the discharge capacity is significantly reduced if the secondary firing temperature is higher than 900 ° C.

[0043]

[Table 3]

A positive electrode active material was produced in the same manner as in Example 1 except that the secondary firing time was changed.
Table 4 shows No. 3 and Comparative Examples 14 to 15. From this table, it can be seen that when the secondary firing time is in the range of 1 to 5 hours, a high discharge capacity and the effect of improving the reactivity with the electrolytic solution and the thermal stability are compatible.

[0045]

[Table 4]

[0046]

Example 14 A baked product obtained after the first calcination and pure water were mixed at a weight ratio of 60:40, and the mixture was pulverized and dispersed by a wet bead mill to obtain a slurry having a pH of 13.7. While stirring this slurry, a dilute nitric acid solution was added to
After adjusting H to 12, pure water was added to make the slurry concentration 4
A positive electrode active material was prepared in the same manner as in Example 1, except that the drying and granulation were performed at 0% by weight. The positive electrode active material thus obtained is spherical secondary particles formed by joining primary particles having a particle size of 0.2 to 1 μm with lithium oxide, and has a differential heat loss of 0.2. % By weight.

[0047]

Example 15 A positive electrode active material was produced in the same manner as in Example 14 except that the pH of the slurry was adjusted to 10.

[0048]

Embodiment 16 The fired product obtained after the first firing and pure water were mixed in 6 parts.
After mixing at a weight ratio of 0:40, the slurry pulverized and dispersed by a wet bead mill was added with magnesium nitrate in which Mg is 1 atomic% in atomic ratio to the total amount of Ni and Co,
A positive electrode active material was prepared in the same manner as in Example 1, except that the slurry was dissolved in pure water in an amount necessary to make the final slurry concentration 40% by weight and added to the slurry. The positive electrode active material thus obtained is spherical secondary particles formed by joining primary particles having a particle size of 0.2 to 1 μm with lithium oxide and magnesium oxide, and has a differential heat loss. 0.2% by weight.

[0049]

Examples 17 to 20 A positive electrode active material was produced in the same manner as in Example 16 except that yttrium nitrate, zirconium nitrate, aluminum nitrate and cobalt nitrate were used instead of magnesium nitrate.

[0050]

Examples 21 to 22 Instead of dissolving magnesium nitrate in pure water, magnesium hydroxide and aluminum hydroxide were dispersed in pure water and then added to the slurry. Was prepared.

[0051]

Examples 23 and 24 A positive electrode active material was produced in the same manner as in Example 16 except that boric acid and phosphoric acid were used instead of magnesium nitrate. Table 5 shows the evaluation results of the positive electrode active materials obtained in Examples 14 to 24. It can be seen that the addition of these compounds improves the thermal stability and the reactivity with the electrolyte.

[0052]

[Table 5]

The amount of boric acid added was 0.1 mol%, 0.2
A positive electrode active material was produced in the same manner as in Example 23 except that the mol%, 3 mol%, and 5 mol% were used. Table 6 shows the evaluation results of the obtained positive electrode active materials. If the amount of the additive is too small, no improvement effect is obtained, and if the amount is too large, the discharge capacity is significantly reduced. Therefore, it is understood that the amount of the additive is desirably in the range of 0.2 to 3.0 mol%.

[0054]

[Table 6]

A positive electrode active material was prepared in the same manner as in Example 1, except that the composition ratio of the firing raw materials was changed as shown in Table 7. Incidentally, manganese oxyhydroxide is used as the Mn compound,
Titanium tetrahydroxide was used as the Ti compound. If the added amount of Co is less than 10 mol%, the thermal stability and the reactivity with the electrolytic solution are not improved. Also, it can be seen that when the content is more than 20 mol%, the discharge capacity is reduced. It can be seen that when Al is partially replaced with Mn, the reactivity with the electrolytic solution is suppressed, and when Ti is replaced with Ti, the discharge capacity is improved.

[0056]

[Table 7]

[0057]

As described above, according to the present invention,
It is possible to provide a high-capacity positive electrode active material having improved reactivity with an electrolyte and thermal stability, and thus improved safety, a method for producing the same, and a lithium ion secondary battery using the same. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a coin battery prepared as a test battery in Examples of the present invention and Comparative Examples.

FIG. 2 is an electron micrograph showing the structure of the active material particles obtained in Example 1.

FIG. 3 shows that the active material obtained in Example 1 was used for 75 times in an Ar gas stream.
It is a figure which shows the differential-thermal-analysis result when it heats up to 0 degreeC.

FIG. 4 shows the thermal stability of the active material obtained in Example 1 as DS.
It is a figure showing the result measured by the C method.

FIG. 5 is a view showing the result of measuring the reactivity of an active material obtained in Example 1 with an electrolytic solution by a TG method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel case 2 Gasket 3 Sealing plate 4 Negative electrode 5 Positive electrode 6 Separator 7 Negative electrode collector 8 Positive electrode collector

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinori Yamanaka 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Kozo Ogi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining (72) Inventor Masayuki Nishina 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-9-129230 (JP, A) JP-A-9-237631 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02 H01M 4/58 H01M 10/40 C01G 53/00

Claims (7)

(57) [Claims] 1. A general formula: LiNi _1-xy Co _x E _y
O ₂ (where E is Al or a group of Al and Mn, Ti
A combination with at least one element selected from the group consisting of 0.10 ≦
(x ≦ 0.20, 0.02 ≦ y ≦ 0.10) Lithium containing secondary particles formed by joining primary particles of an inorganic compound containing an inorganic oxide mainly composed of Li A positive electrode active material for an ion battery, having a differential heat loss of 0.5% by weight when heated to 750 ° C. in an inert gas atmosphere.
A positive electrode active material for a lithium ion secondary battery, comprising: 2. The method according to claim 1, wherein the inorganic oxide is Mg, Y, Zr, B,
At least one element selected from the group consisting of Al, Co, and P and Li
And the total content of elements excluding oxygen of the inorganic compound is 0.002 to 0 in atomic ratio to the total content of Li, Ni, Co, and element E in the primary particles. .0
3. The positive electrode active material for a lithium ion secondary battery according to claim 1. 3. A method for producing a positive electrode active material according to claim 1, wherein a first firing step of firing a mixture of each compound of Li, Ni, Co and element E at 500 to 800 ° C.
A dispersion granulation step of spray-drying a slurry obtained by pulverizing and dispersing the calcined product obtained in the next calcining step in water so that the average particle diameter is 1 μm or less to obtain a spherical granulated powder; A secondary firing step of firing the spherical granulated powder obtained in the above at a temperature higher than the primary firing temperature by at least 30 ° C. and at a temperature of 900 ° C. or lower, producing a positive electrode active material for a lithium ion secondary battery. Method. 4. The method for producing a positive electrode active material according to claim 1, wherein a first firing step of firing a mixture of each compound of Li, Ni, Co and element E at 500 to 800 ° C.
The fired product obtained in the next firing step is disintegrated and dispersed in water so that the average particle size is 1 μm or less, and a part or all of the lithium salt eluted into the liquid phase by adding nitric acid is converted to lithium nitrate. A dispersion granulation step of spray-drying the converted slurry to obtain a spherical granulated powder; and a step of subjecting the spherical granulated powder obtained in the dispersion granulation step to a temperature of 30 ° C. or higher and 900 ° C. or lower than the primary firing temperature. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising a secondary firing step of firing. 5. A method for producing a positive electrode active material according to claim 2, wherein a first firing step of firing a mixture of each compound of Li, Ni, Co and element E at 500 to 800 ° C.
The fired product obtained in the next firing step is pulverized and dispersed in water so that the average particle diameter is 1 μm or less, and then Mg, Y, Z
A slurry obtained by spray-drying a slurry to which a compound of at least one element selected from the group consisting of r, B, Al, Co, and P was added to obtain a spherical granulated powder, and a dispersion granulating step. The spherical granulated powder is at least 30 ° C. higher than the primary firing temperature and 900 ° C.
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a secondary firing step of firing at the following temperature. 6. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the compound of the element added in the dispersion granulation step is a nitrate. 7. A lithium ion secondary battery using the positive electrode active material according to claim 1 as a positive electrode active material.