KR20160063982A - Method for manufacturing cathode electrode materials - Google Patents

Abstract

Provided is a method for manufacturing a positive electrode active material by which a mixture with a compound containing lithium carbonate and Ni is plasticized so that the positive electrode active material consisting of lithium composite oxide of high Ni concentration can be industrially manufactured. The method of the present invention includes: a mixing step (S1) of mixing a compound containing lithium carbonate and Ni; and a plasticization step (S2) of obtaining a lithium composite compound of high Ni concentration by performing plasticization in an oxidizing atmosphere on the mixture obtained in the mixing step (S1). The plasticization step (S2) includes: a first heat treatment step (S21) of obtaining a first precursor by performing a heat treatment on the mixture for 0.5 to five hours at a heat treatment temperature of 200 to 400°C a second heat treatment step (S22) of obtaining a second precursor by performing a heat treatment on the first precursor for two to 50 hours at a heat treatment temperature of 450 to 700°C and a third heat treatment step (S23) of obtaining a lithium composite compound by performing a heat treatment on the second precursor at a heat treatment temperature of 700 to 850°C. The oxygen concentration of the oxidizing atmosphere in the second heat treatment step (S22) and the third heat treatment step (S23) is at least 80%.

Description

METHOD FOR MANUFACTURING CATHODE ELECTRODE MATERIALS [0001]

The present invention relates to a method for producing a positive electrode active material used for a positive electrode of a lithium ion secondary battery.

A non-aqueous secondary battery that mediates electrical conduction between electrodes is a lithium ion secondary battery. The lithium ion secondary battery is a secondary battery in which lithium ions take charge of electric conduction between electrodes in a charge and discharge reaction and has a higher energy density than other secondary batteries such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, And the effect is small. Therefore, the lithium ion secondary battery can be used as a power source for small-sized power sources such as portable electronic devices and household electrical appliances, power sources for power storage devices, uninterruptible power supply devices, power leveling devices, ships, railways, hybrid cars, To the medium-sized and large-sized power source such as the driving power source of the power source.

Particularly, when a lithium ion secondary battery is used as a medium-sized / large-sized power source, high energy density of the battery is required. In order to achieve high energy density of a battery, high energy density of the positive electrode and the negative electrode is required, and high capacity of the active material used for the positive electrode and the negative electrode is required. As a cathode active material having a high charge / discharge capacity, a powder of a lithium composite compound represented by the general formula LiM'O ₂ having an? -NaFeO ₂ type layer structure (M 'represents an element such as Ni, Co, Mn) It is known. The positive electrode active material tends to have a higher capacity as the proportion of Ni increases, so that it is expected as a positive electrode active material for realizing high energy of a battery.

As such a cathode active material, _a powder of a lithium-containing compound represented by Li _a Ni _b M1 _c M2 _d (O) ₂ (SO ₄ ) _X and a production method thereof are disclosed (refer to Patent Document 1 below). The invention disclosed in Patent Document 1 aims at providing a lithium mixed metal oxide in which secondary particles are not destroyed in a battery production (anode) and does not become a powder state. As a means for solving the problem, the difference between the initial powder and the D10 value measured according to ASTM B 822 as the powder after being compressed to 200 MPa is set to 1.0 탆 or less.

The process for producing a powder of a lithium-containing compound described in Patent Document 1 includes a step of preparing a coprecipitated nickel-containing precursor having a predetermined porosity and a step of mixing the nickel-containing precursor and a lithium-containing compound to obtain a precursor mixture . Examples of the lithium-containing compound include lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium oxide, lithium nitrate, and mixtures thereof. Further, disintegration of the powder of the resulting precursor mixture, the CO _2-free step of, using the (CO ₂ content of 0.5ppm or less), the oxygen-containing carrier gas is heated in multiple stages by 200~1000 ℃ preparing a powder product and, ultrasound and And a step of performing a sieve of the pulverized powder.

According to Patent Document 1, it is said that a product which does not aggregate strongly secondary sintered particles is obtained by the reaction control associated with the temperature holding step of the above-mentioned manufacturing process. Accordingly, it is said that in the electrode production, the crushing step in which angular particles having an angle, which causes destruction of particles in a material bed (material bed) under high pressure, can be omitted.

Japanese Patent Specification No. 2010-505732

On the other hand, as in Patent Document 1, the precursor mixture is not heated, but a mixture of lithium carbonate and a compound containing Ni is sintered to form, for example, LiM'O ₂ (M ' ) Has an atomic ratio (Ni / M ') of Ni in M' of 0.7 or more in order to produce a lithium composite compound having a layered structure of high concentration of Ni. In order to industrially mass-produce the lithium composite oxide of high concentration of Ni, it is necessary to carry out the synthesis reaction in a large amount and uniformly. However, it has been found that when a mixture of a compound containing lithium carbonate and Ni is heated, a large amount of carbonic acid gas is generated from lithium carbonate, and thus a large amount and uniform synthesis reaction is inhibited. When carbon dioxide gas is generated, the oxygen partial pressure is lowered and the reaction of oxidizing the Ni valence from two to three sides is inhibited. Particularly, it has been found that there is a problem such that when the oxidation of Ni is insufficient in the lithium composite compound of high concentration of Ni, the capacity is largely lowered.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a positive electrode active material capable of industrially mass-producing a positive electrode active material composed of a lithium composite oxide of high Ni concentration by firing a mixture of lithium carbonate and a compound containing Ni And to provide the above objects.

In order to achieve the above object, a method for producing a positive electrode active material according to the present invention is a method for producing a positive electrode active material for use in a positive electrode of a lithium ion secondary battery, which comprises lithium carbonate and a metal element other than Li in the formula (1) And a firing step of firing the mixture obtained in the firing step in an oxidizing atmosphere to obtain a lithium composite compound represented by the following formula (1), wherein the firing step is a step of firing the mixture at 200 ° C or higher Treating the first precursor at a heat treatment temperature of 450 ° C or more and 700 ° C or less for 2 hours or more and 50 hours or less at a heat treatment temperature of 400 ° C or less; A second heat treatment step of heat treating the second precursor at a temperature of 700 ° C or higher and 850 ° C or lower at 2 ° C By the heat treatment over a period of less than 50 hours has a third heat treatment step of obtaining the lithium composite compound, the second heat treatment step and the oxygen concentration in the oxidizing atmosphere of the third heat treatment step is characterized in that not less than 80%.

Li _{1 + a} Ni _b Mn _c Co _d M _e O _{2 + α} ... (One)

In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, B? 0.9,? C? 0.35, 0.05? D? 0.30, 0? E? 0.35, b + c + d + e = 1, and -0.1? .

Industrial Applicability According to the present invention, it is possible to industrially mass-produce a positive electrode active material composed of a Ni composite lithium oxide having a layered structure and a high concentration.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1A is a flow chart showing an embodiment of a method for producing a positive electrode active material of the present invention. FIG.
Fig. 1B is a flow chart showing a modification of the method for producing the positive electrode active material shown in Fig. 1A. Fig.
2 is a schematic partial cross-sectional view showing one embodiment of a lithium ion secondary battery having a positive electrode including a positive electrode active material.

Hereinafter, embodiments of a method for producing a positive electrode active material of the present invention will be described in detail.

The method for producing the positive electrode active material of the present embodiment is a method for producing a positive electrode active material used for a positive electrode of a non-aqueous secondary battery such as a lithium ion secondary battery. First, the cathode active material produced by the method for producing a cathode active material of the present embodiment will be described in detail.

(Cathode active material)

The cathode active material produced by the production method of the present embodiment is a powder of a lithium composite compound having a high concentration of Ni represented by the following formula (1) and having a layer structure of? -NaFeO ₂ type.

Li _{1 + a} Ni _b Mn _c Co _d M _e O _{2 + α} ... (One)

In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, B? 0.9,? C? 0.35, 0.05? D? 0.30, 0? E? 0.35, b + c + d + e = 1, and -0.1? .

The positive electrode active material composed of the powder of the lithium composite compound having a layered structure of the? -NaFeO ₂ type represented by the above formula (1) can be reversibly inserted and desorbed reversibly with charging and discharging, And is a layered positive electrode active material having a low resistance. The particles of the lithium composite compound constituting the positive electrode active material may be primary particles in which individual particles are separated, secondary particles in which a plurality of primary particles are combined by sintering or the like, and a free lithium compound Or may be primary particles or secondary particles.

The average particle diameter of the primary particles of the positive electrode active material is preferably 0.1 mu m or more and 2 mu m or less, for example. By setting the average particle diameter of the primary particles of the positive electrode active material to 2 m or less, the positive electrode active material filling property of the positive electrode is improved and a high energy density positive electrode can be produced when the positive electrode active material is produced . The average particle diameter of the secondary particles of the positive electrode active material is preferably 3 m or more and 50 m or less, for example.

The particles of the cathode active material can be secondary-granulated by granulating the primary particles produced by the production method of a cathode active material described below by dry granulation or wet granulation. As the assembly means, for example, a granulator such as a spray dryer or an electric fluidized bed apparatus can be used.

In the above formula (1), a represents the positive / negative proportion of the positive electrode active material represented by the formula LiM'O ₂ , that is, the excess or deficiency of Li from Li: M ': O = 1: 1: 2. Here, M 'represents a metal element other than Li in the formula (1). The higher the content of Li, the higher the valence of the transition metal before charging, and the ratio of the change in the valence of the transition metal in Li removal is reduced, so that the charge / discharge cycle characteristics of the positive electrode active material can be improved. On the other hand, the higher the content of Li, the lower the charge-discharge capacity of the positive electrode active material. Therefore, by setting the range of a, which represents the excess or deficiency amount of Li in the formula (1), to -0.1 or more and 0.2 or less, the charge / discharge cycle characteristics of the positive electrode active material can be improved and the charge-

More preferably, the range of a in the formula (1) representing the excess and deficiency of Li can be set to be -0.05 or more and 0.1 or less. When a in the above formula (1) is -0.05 or more, a sufficient amount of Li is provided to contribute to charge and discharge, and the capacity of the positive electrode active material can be increased. When a in the above formula (1) is 0.1 or less, charge compensation due to the change in the valence of the transition metal can be sufficiently ensured, and high capacity and high discharge cycle characteristics can be achieved.

When b, which indicates the content of Ni in the above formula (1), is 0.7 or more, sufficient amount of Ni is sufficient to contribute to charging and discharging of the positive electrode active material, and high capacity can be achieved. On the other hand, if b in the above formula (1) exceeds 0.9, a part of Ni is substituted for the Li site, so that a sufficient amount of Li can not be secured to contribute to charging and discharging, and the charge / discharge capacity of the positive electrode active material . Therefore, by setting the value b representing the content of Ni in the formula (1) within the range of 0.7 or more and 0.9 or less, and more preferably 0.75 or more and 0.85 or less, the capacity of the positive electrode active material can be increased, can do.

The addition of Mn also serves to stably maintain the layered structure even if Li is eliminated by charging. However, when c, which represents the content of Mn in the formula (1), exceeds 0.35, the capacity of the positive electrode active material decreases. Therefore, by setting c in the above formula (1) to be in the range of 0 or more and 0.35 or less, it is possible to stably maintain the layered structure of the positive electrode active material and to suppress the capacity decrease of the positive electrode active material even if Li is inserted / can do.

Further, if d, which represents the content of Co in the formula (1), is 0.05 or more, the layered structure of the positive electrode active material can be stably maintained. By keeping the layered structure stably, for example, cation mixing in which Ni is mixed in the Li site can be suppressed, and excellent charge / discharge cycle characteristics can be obtained. On the other hand, if d in the above formula (1) exceeds 0.3, the supply amount is limited and the proportion of Co having a relatively high cost becomes relatively large, which is disadvantageous for industrial production of the positive electrode active material. Therefore, by setting the value d representing the content of Co in the formula (1) within the range of 0.05 to 0.3, more preferably 0.1 to 0.2, the charge / discharge cycle characteristics of the positive electrode active material can be improved, It is also advantageous in industrial mass production of the cathode active material.

In addition, since M in the formula (1) is composed of at least one metal element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, the electrochemical activity in the positive electrode active material is ensured . Further, by substituting the metal sites of the positive electrode active material in these metal elements, it is possible to improve the stability of the crystal structure of the positive electrode active material and the electrochemical characteristics (cycle characteristics, etc.) of the layered positive electrode active material. If e, which represents the content of M in the formula (1), exceeds 0.35, the capacity of the positive electrode active material decreases. Therefore, by setting the range of e in the above formula (1) to be not less than 0 and not more than 0.35, it is possible to suppress the capacity decrease of the positive electrode active material.

In the above formula (1),? Is a range permitting the layered compound attributed to the space group R-3m, and represents the oxygen deficiency amount. From the viewpoint of maintaining the layer structure of the? -NaFeO ₂ type of the positive electrode active material, for example, it is preferable that the range is -0.1 or more and 0.1 or less.

The crystal structure of the particles of the cathode active material can be confirmed by, for example, X-ray diffraction (XRD) or the like. The average composition of the particles of the cathode active material can be confirmed by an inductively coupled plasma (ICP), an atomic absorption spectrometry (AAS), or the like.

The BET specific surface area of the particles of the positive electrode active material is preferably, for example, about 0.2 m 2 / g or more and 2.0 m 2 / g or less. By setting the BET specific surface area of the particles of the positive electrode active material to about 2.0 m < 2 > / g or less, the filling performance of the positive electrode active material in the positive electrode is improved and a positive electrode having a high energy density can be produced. The BET specific surface area can be measured using an automatic specific surface area measuring apparatus.

It is also preferable that the particle breaking strength of the positive electrode active material is 50 MPa to 100 MPa. Thereby, the particles of the cathode active material are not destroyed in the course of electrode production, and when the slurry containing the cathode active material is coated on the surface of the cathode current collector to form the anode mixture layer, defective coating such as peeling is suppressed . The particle breaking strength of the positive electrode active material can be measured using, for example, a micro compression tester.

(Method for producing positive electrode active material)

Next, a method of producing the positive electrode active material of this embodiment for manufacturing the above-mentioned positive electrode active material will be described. 1A is a flow chart showing each step included in the method for producing a positive electrode active material of the present embodiment. Fig. 1B is a flow chart showing each step in a modified example of the method for producing the positive electrode active material of the present embodiment shown in Fig. 1A.

The method for producing the positive electrode active material of the present embodiment comprises a mixing step (S1) of mixing lithium carbonate and a compound each containing a metal element other than Li in the formula (1), and a step of mixing the mixture obtained in the mixing step (S1) And a firing step (S2) of firing in an atmosphere to obtain the lithium composite compound represented by the formula (1).

In the mixing step (S1), as a starting material for the positive electrode active material, in addition to lithium carbonate, a compound containing a metal element other than Li in the formula (1) such as a Ni-containing compound, a Mn- , An M-containing compound, and the like. The M-containing compound is a compound containing at least one metal element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb.

In the mixing step (S1), the starting materials weighed in the ratio of the predetermined element composition corresponding to the formula (1) are mixed to prepare a raw material powder. In the method for producing a positive electrode active material of the present embodiment, lithium carbonate is used as a starting material containing Li. Lithium carbonate is superior in industrial availability and practicality as compared with other Li-containing compounds such as lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride and lithium sulfate.

The Ni-containing compound, the Mn-containing compound and the Co-containing compound as starting materials for the positive electrode active material can be, for example, oxides, hydroxides, carbonates, sulfates or acetic acid salts. In particular, oxides, hydroxides, Is preferably used. As the M-containing compound, for example, an acetate, a nitrate, a carbonate, a sulfate, an oxide, or a hydroxide can be used, and in particular, a carbonate, an oxide, or a hydroxide is preferably used.

In the mixing step (S1), it is preferable that the above starting materials are pulverized by, for example, a pulverizer and mixed. Thus, a uniformly mixed powdery solid mixture can be prepared. As the pulverizer for pulverizing the compound of the starting material, a general precision pulverizer such as a ball mill, a jet mill, and a sand mill can be used. It is preferable that the starting material is pulverized by a wet process. From an industrial viewpoint, the solvent used for wet pulverization is preferably water. The particle size of the pulverized powder of the pulverized starting material in the mixing step (S1) is an index indicating the degree of mixing of the starting material.

The particle size (cumulative distribution) of the practical starting materials that can be industrially practically used, that is, the particle size (cumulative distribution) when measured on a volumetric basis, is D50 of 1 μm or more and D100 of 10 μm or more. In this case, it is preferable that the particle size of the pulverized powder of the starting material when measured on a volumetric basis is 0.3 μm or less for D50 and 1.0 μm or less for D100. By setting the D50 to 0.3 탆 or less in this way, the starting material can be sufficiently pulverized and mixed uniformly. Further, by setting D100 to 1.0 탆 or less, it is possible to promote uniformity of the composition and crystallization in the subsequent firing step (S2). The volume-based particle size distribution can be measured by a laser diffraction particle size distribution meter. By carrying out the pulverization of the starting material in a wet manner, the above-mentioned preferable particle size distribution can be easily reached.

In the mixing step (S1), the solid-liquid mixture obtained by wet pulverization of the starting material can be dried, for example, by a drier. The drier may be, for example, a spray dryer, a fluidized bed (drier) drier, an ebay purifier, or the like. Particularly, it is preferable to obtain a mixed powder by drying the solid-liquid mixture by means of a spray dryer, and drying the mixture to a D50 of not less than 10 mu m and not more than 30 mu m. By setting the D50 of the mixed powder to 10 mu m or more, the D50 of the cathode active material can be 10 mu m or more, and the anode layer can be prevented from peeling from the current collector foil when the cathode active material is made into an electrode. In addition, by setting the D50 of the mixed powder to 30 mu m or less, the filling of the cathode active material in the thickness direction of the electrode can be made uniform, and the conduction path can be prevented from being reduced. In order to satisfy the preferable range of the D50 of such a mixture, a rotary disk type spray dryer is suitable.

The bulk specific gravity of the mixed powder obtained by the mixing step (S1) is preferably 0.6 g / cc or more and 0.8 g / cc or less. By setting the volume specific gravity of the mixed powder to 0.6 g / cc or more, a mixed powder having a small amount of fine powder can be obtained, and the anode layer can be prevented from peeling off from the current collecting foil upon electrode formation. By setting the volume specific gravity of the mixed powder to 0.8 g / cc or less, the particle gap is ensured, and when the mixed powder is filled in the vessel in the sintering step (S2) and heated, Loses.

In the firing step (S2), the mixture obtained in the mixing step (S1) is fired in an oxidizing atmosphere to produce a cathode active material which is a powder of the lithium composite compound represented by the formula (1). The firing step (S2) of the present embodiment has a first heat treatment step (S21), a second heat treatment step (S22), and a third heat treatment step (S23).

In the first heat treatment step (S21), the mixture obtained in the mixing step (S1) is subjected to heat treatment at a heat treatment temperature of 200 ° C or more and 400 ° C or less for 0.5 hour or more and 5 hours or less to obtain a first precursor. The first heat treatment step (S21) is carried out with the aim of removing, from the mixture obtained in the mixing step (S1), a vaporizing component which interferes with the synthesis reaction of the cathode active material. That is, the first heat treatment step (S21) is a heat treatment step for removing vaporized components in the mixture.

In the first heat treatment step (S21), a gas is generated by vaporizing, burning, volatilizing, etc., vaporized components contained in the mixture to be heat-treated, for example, moisture, impurities, and volatile components accompanying pyrolysis. In the case where the mixture contains a carbonate such as lithium carbonate, carbon dioxide gas is generated along with pyrolysis of the carbonate.

If the heat treatment temperature is less than 200 占 폚 in the first heat treatment step (S21), the combustion reaction of the impurities and the pyrolysis reaction of the starting material may be insufficient. If the heat treatment temperature exceeds 400 占 폚 in the first heat treatment step (S21), a layered structure of the lithium composite compound may be formed in an atmosphere containing a gas generated from the mixture by heat treatment. Accordingly, in the first heat treatment step (S21), the mixture is subjected to heat treatment at a heat treatment temperature of 200 ° C or more and 400 ° C or less to obtain a first precursor in which vaporized components are sufficiently removed and a layered structure is not yet formed have.

In the first heat treatment step (S21), if the heat treatment temperature is in the range of 250 deg. C or more and 400 deg. C or less, and more preferably 250 deg. C or more and 380 deg. C or less, the vaporization component removal effect and the formation of the layered structure are suppressed The effect can be further improved. In addition, the heat treatment time can be changed depending on, for example, the heat treatment temperature, the degree of removal of vaporized components, the degree of inhibition of formation of the layered structure, and the like.

In the first heat treatment step (S21), for the purpose of exhausting the gas generated from the mixture, it is preferable to carry out the heat treatment under the exhaust gas of an atmospheric gas or a pump. It is preferable that the flow rate per minute of the atmospheric gas or the amount of exhaust per 1 minute by the pump is larger than the volume of the gas generated from the mixture. The volume of the gas generated from the mixture can be calculated based on, for example, the mass of the starting material contained in the mixture and the ratio of the vaporized component.

Further, the first heat treatment step (S21) may be performed under a reduced pressure of atmospheric pressure or lower. In addition, the oxidizing atmosphere in the first heat treatment step (S21) may be increased because the oxidation treatment is not the primary target in the first heat treatment step (S21). By using the atmosphere as the oxidizing atmosphere in the first heat treatment step (S21), the structure of the heat treatment apparatus can be simplified, the atmosphere can be supplied easily, and the productivity of the cathode active material can be improved. In addition, the atmosphere of the heat treatment in the first heat treatment step (S21) is not limited to the oxidizing atmosphere but may be a non-oxidizing atmosphere such as an inert gas.

In the firing step (S2), the second heat treatment step (S22) is performed after the end of the first heat treatment step (S21). However, as shown in FIG. 1A, during the step of the first heat treatment step (S21) The first gas replacement step (S24). Further, as shown in Fig. 1B, the first gas replacement step (S24) may be performed after the end of the first heat treatment step (S21). In the first gas replacement step (S24), the oxidative atmosphere used in the first heat treatment step (S21) is evacuated and a second oxidative atmosphere is introduced to perform the second heat treatment. By performing the gas replacement step (S24) in this manner, it is possible to prevent the gas generated from the mixture of the starting materials by the heat treatment in the first heat treatment step (S21) from affecting the second heat treatment step (S22).

Further, in the first gas replacement step (S24), the first precursor may be once taken out of the heat treatment apparatus and then put in the heat treatment apparatus again. In this case, when the first precursor is taken out from the heat treatment apparatus, the oxidizing atmosphere used in the first heat treatment step (S21) is evacuated and a new oxidizing atmosphere is introduced into the same or another heat treatment apparatus together with the first precursor, S22) may be performed.

The first heat treatment step (S21), the first gas replacement step (S24) and the second heat treatment step (S22) are continuously performed in the case of performing the heat treatment in the first heat treatment step (S21) or after the heat treatment . In this case, in the first gas replacement step (S24), the oxidizing atmosphere may be continuously replaced in the same heat treatment apparatus without taking out the first precursor from the heat treatment apparatus.

In the second heat treatment step (S22), the first precursor obtained in the first heat treatment step (S21) is heat-treated at a heat treatment temperature of 450 DEG C or more and less than 700 DEG C for 2 hours or more and 50 hours or less to obtain a second precursor. The second heat treatment step (S22) is performed with the Ni in the first precursor 2 that the primary purpose of synthesizing the compound of the layered structure represented by the composition formula ₂ with LiM'O Sikkim 3 Horizontal oxide from horizontal. That is, the second heat treatment step (S22) is a heat treatment step of performing oxidation reaction of Ni and formation of a layered structure in the first precursor.

In order to develop a high-capacity positive electrode active material having a range of b, which indicates the content of Ni in the above formula (1), is 0.7 or more and 0.9 or less, it is necessary to oxidize Ni singly from two to three in the sintering step (S2) . The divalent Ni easily occupies the Li position in the layered structure LiM'O ₂ , which causes the capacity of the positive electrode active material to be lowered. Therefore, in the firing step (S2), the mixture is fired in an oxidizing atmosphere to change the valence of Ni from two to three.

In order to synthesize a layered compound represented by the formula LiM'O ₂ , it is necessary that the first precursor reacts with oxygen in the atmosphere. The reaction for synthesizing LiNiO ₂ from lithium oxide and nickel oxide contained in the first precursor is represented by the following formula (2).

Li₂O + 2NiO + (1/2) O₂→ 2LiNiO₂ ... (2)

In order to promote the Ni oxidation reaction and the reaction of the formula (2), the atmosphere of the heat treatment in the second heat treatment step (S22) is an oxidizing atmosphere containing oxygen, the oxygen concentration is preferably 80% or more, More preferably 90% or more, more preferably an oxygen concentration of 95% or more, and even more preferably an oxygen concentration of 100%. In order to allow the Ni oxidation reaction and the reaction of the formula (2) to progress sequentially, oxygen is preferably continuously supplied during the heat treatment in the second heat treatment step (S22), and heat treatment is carried out under an air stream of the oxidizing atmosphere gas desirable.

In the second heat treatment step (S22), a gas such as carbon dioxide gas is generated from the first precursor at the time of the heat treatment by heat-treating the first precursor from which the vaporized components in the mixture of starting materials have been removed in the first heat treatment step (S21) The oxygen concentration in the oxidizing atmosphere can be suppressed from being lowered. Therefore, the second precursor in which the oxidation reaction of Ni of the first precursor in the second heat treatment step (S22) proceeds smoothly and the formation reaction of the lithium composite compound proceeds uniformly can be obtained. In addition, residues derived from the starting material can be sufficiently reduced.

When the heat treatment temperature in the second heat treatment step (S22) is less than 450 占 폚, the progress of the formation reaction of the layered structure is remarkably retarded when the first precursor is heat-treated to form the second precursor having a layered structure. On the other hand, when the heat treatment temperature in the second heat treatment step (S22) is 700 DEG C or more, when the first precursor is heat-treated to form the second precursor having a layered structure, grain growth progresses during formation, Is insufficient.

Therefore, when the heat treatment temperature in the second heat treatment step (S22) is set to 450 deg. C or more and less than 700 deg. C, when the first precursor is heat treated to form the second precursor having a layered structure, It is possible to suppress the growth of oxygen and insufficient reaction with oxygen. In addition, by setting the heat treatment temperature in the second heat treatment step (S22) to 450 deg. C or higher and 660 deg. C or lower, it is possible to further improve the grain growth suppressing effect.

In order to sufficiently react the first precursor with oxygen in the temperature range of the heat treatment in the second heat treatment step (S22), the heat treatment time can be set to 2 hours or more and 100 hours or less. From the viewpoint of improving the productivity, the heat treatment time in the second heat treatment step (S22) is preferably from 2 hours to 50 hours, more preferably from 2 hours to 15 hours.

In the firing step (S2), the third heat treatment step (S23) is performed after the end of the second heat treatment step (S22). However, as shown in FIG. 1A, during the step of the second heat treatment step (S22) And a second gas replacement step (S25). Further, as shown in Fig. 1B, the second gas replacement step (S25) may be performed after the end of the second heat treatment step (S22). In the second gas replacement step (S25), the oxidative atmosphere used in the second heat treatment step (S22) is discharged, and a new oxidative atmosphere is introduced to perform the third heat treatment. Thus, the gas generated from the first precursor by the heat treatment in the second heat treatment step (S22) can be prevented from affecting the third heat treatment step (S23).

In addition, in the second gas replacement step (S25), the second precursor may be once taken out of the heat treatment apparatus and then placed in the heat treatment apparatus again. In this case, when the second precursor is taken out from the heat treatment apparatus, the oxidizing atmosphere used in the second heat treatment step (S22) is evacuated and a new oxidizing atmosphere is introduced into the same or another heat treatment apparatus together with the second precursor, S23) may be performed. Since the vaporization component of the mixture of the starting materials is removed in the first heat treatment step, the second precursor is not removed from the heat treatment apparatus without performing the second gas replacement step (S25), the second heat treatment step (S22) And the third heat treatment step (S23) may be performed continuously.

In the third heat treatment step (S23), the second precursor obtained in the second heat treatment step (S22) is heat-treated at a heat treatment temperature of 700 DEG C or higher and 850 DEG C or lower to obtain a cathode active material composed of a lithium composite compound. In the third heat treatment step (S23), the Ni oxidation reaction for oxidizing Ni in the second precursor three to two times from the horizontal direction is sufficiently advanced, and the positive electrode active material composed of the lithium composite compound obtained by the heat treatment exhibits electrode performance , And the main purpose is to grow crystal grains. That is, the third heat treatment step (S23) is a heat treatment step of performing Ni oxidation reaction and crystal grain growth in the second precursor.

In order to sufficiently accelerate the oxidation reaction of Ni, the atmosphere of the heat treatment in the third heat treatment step (S23) is an oxidizing atmosphere containing oxygen, and the oxygen concentration is preferably 80% or more, more preferably 90% , An oxygen concentration of 95% or more is more preferable, and an oxygen concentration of 100% is more preferable.

If the heat treatment temperature in the third heat treatment step (S23) is less than 700 deg. C, the crystallization of the second precursor becomes insufficient. When the temperature exceeds 850 deg. C, the layered structure of the second precursor decomposes to produce bivalent Ni, The capacity of the battery is deteriorated. Therefore, by setting the heat treatment temperature in the third heat treatment step (S23) to 700 DEG C or higher and 850 DEG C or lower, it is possible to promote grain growth of the second precursor, suppress decomposition of the layered structure, and improve the capacity of the obtained cathode active material have. Further, by setting the heat treatment temperature in the third heat treatment step (S23) to 700 ° C or higher and 840 ° C or lower, it is possible to further improve the grain growth promoting effect and the layer structure decomposition inhibiting effect.

Further, in the third heat treatment step (S23), when the oxygen partial pressure is low, heat is required to promote the Ni oxidation reaction. Therefore, when the oxygen supply to the second precursor is insufficient, it is necessary to raise the heat treatment temperature. When the heat treatment temperature is raised, decomposition of the layered structure becomes inevitable, and good electrode characteristics can not be obtained in the obtained positive electrode active material. Therefore, in order to sufficiently supply oxygen to the second precursor, the time of the heat treatment in the third heat treatment step (S23) may be from 2 hours to 100 hours. From the viewpoint of improving the productivity of the cathode active material, the heat treatment time in the third heat treatment step (S23) is preferably from 2 hours to 50 hours, more preferably from 2 hours to 15 hours.

As described above, in the method for producing a positive electrode active material of the present embodiment, in the first heat treatment step (S21) of the firing step (S2) for firing the mixture obtained in the mixing step (S1) A sufficient amount of gas can be generated to obtain a first precursor in which generation of carbon dioxide gas by heating is suppressed. In the second heat treatment step (S22) of the firing step (S2), the generation of carbon dioxide gas from the first precursor is suppressed, so that the decrease of the oxygen partial pressure in the oxidative atmosphere is suppressed and the Ni oxidation reaction of the first precursor is promoted So that the second precursor is obtained in a large amount and uniformly. In addition, even in the third heat treatment step (S23) of the firing step (S23), the generation of carbon dioxide gas from the second precursor is suppressed, whereby the lowering of the oxygen partial pressure of the oxidative atmosphere is suppressed, and the Ni oxidation reaction of the second precursor And the growth of the crystal grains progresses. Therefore, it is possible to obtain a positive active material having a high capacity and a high capacity retention ratio, in which divalent Ni remaining in the Ni composite lithium-containing compound having a layered structure is reduced.

The method of manufacturing the positive electrode active material of the present embodiment becomes remarkable when the weight of the produced positive electrode active material becomes, for example, a large amount of several hundred g or more. If the weight of the active material to be produced is a few grams, the influence of the gas generated from the starting material in the firing step (S2) is small, but if the mass production of the cathode active material is carried out on an industrial scale, The volume of the gas generated from the raw material is increased and the partial pressure of oxygen in the oxidizing atmosphere in the heat treatment process tends to decrease.

If the first heat treatment step (S21) is omitted in the firing step (S2), the oxygen partial pressure decreases in the second heat treatment step (S22) and the third heat treatment step (S23). As a result, it is necessary to perform heat treatment at a higher temperature in order to sufficiently promote the formation reaction of the layered structure involving the oxidation of Ni, resulting in exceeding a favorable temperature range. If the second heat treatment step (S22) is omitted, the oxidation reaction of Ni proceeds insufficiently, which is undesirable. If the third heat treatment step (S23) is omitted, proper electrode characteristics can not be obtained.

(Positive electrode and lithium ion secondary battery)

Hereinafter, the structure of a positive electrode for a nonaqueous secondary battery using the positive electrode active material produced by the above-described method for producing a positive electrode active material and a nonaqueous secondary battery having the same will be described. 2 is a schematic partial cross-sectional view of a positive electrode 111 of the present embodiment and a non-aqueous secondary battery 100 having the same.

The non-aqueous secondary battery 100 of the present embodiment is, for example, a cylindrical lithium ion secondary battery. The nonaqueous secondary battery 100 includes a battery can 101 having a cylindrical shape and containing a non-aqueous electrolyte, A winding electrode group 110 accommodated in the battery case 101 and a battery cover 102 on the disk that seals the upper opening of the battery can 101. [ The battery can 101 and the battery cover 102 are made of a metallic material such as stainless steel or aluminum and are bonded to each other through a sealing material 106 made of a resin material having an insulating property, The battery can 101 is sealed by the battery lid 102 and electrically insulated from each other by being fixed to the can 101 by caulking or the like. The shape of the non-aqueous secondary battery 100 is not limited to a cylindrical shape, and any other shape such as a square shape, a button shape, a laminate sheet shape, or the like can be adopted.

The winding electrode group 110 is manufactured by winding a long strip-shaped anode 111 and a cathode 112 which are opposed to each other via a long strip-shaped separator 113 around a winding central axis . The winding electrode group 110 is formed in such a manner that the positive electrode collector 111a is electrically connected to the battery lid 102 via the positive electrode lead piece 103 and the negative electrode collector 112a contacts the negative electrode lead piece 104 And is electrically connected to the bottom of the battery can 101. An insulating plate 105 is disposed between the winding electrode group 110 and the battery lid 102 and between the winding electrode group 110 and the bottom of the battery can 101 to prevent a short circuit. The positive electrode lead piece 103 and the negative electrode lead piece 104 are members for drawing electric current and made of the same material as the positive electrode collector 111a and the negative electrode collector 112a, And the anode current collector 112a by spot welding or ultrasonic welding.

The anode 111 of the present embodiment has a cathode current collector 111a and a cathode mixture layer 111b formed on the surface of the cathode current collector 111a. As the positive electrode collector 111a, for example, metal foil such as aluminum or aluminum alloy, expanded metal, punching metal, or the like can be used. The metal foil may have a thickness of, for example, about 15 μm or more and about 25 μm or less. The positive electrode material mixture layer 111b includes the positive electrode active material produced by the above-described method for producing a positive electrode active material. The positive electrode material mixture layer 111b may contain a conductive material, a binder, and the like.

The cathode 112 has an anode current collector 112a and a cathode mixture layer 112b formed on the surface of the anode current collector 112a. As the anode current collector 112a, metal foil such as copper or copper alloy, nickel or nickel alloy, expanded metal, punching metal, or the like can be used. The metal foil can have a thickness of, for example, about 7 탆 or more and 10 탆 or less. The negative electrode material mixture layer 112b includes a negative electrode active material used in a general lithium ion secondary battery. The negative electrode material mixture layer 112b may contain a conductive material, a binder, and the like.

As the negative electrode active material, for example, at least one of a carbon material, a metal material, and a metal oxide material can be used. As the carbon material, graphite such as natural graphite and artificial graphite, carbonized materials such as coke and pitch, amorphous carbon, carbon fiber and the like can be used. As the metal material, a metal oxide including tin, silicon, lithium, titanium and the like can be used as the material of lithium, silicon, tin, aluminum, indium, gallium, magnesium, alloys thereof and metal oxide.

As the separator 113, for example, a polyolefin resin such as polyethylene, polypropylene or polyethylene-polypropylene copolymer, a microporous film such as a polyamide resin or an aramid resin, or a nonwoven fabric may be used.

The anode 111 and the cathode 112 can be manufactured, for example, through a compound adjusting step, a compound coating step, and a molding step. In the compounding adjusting step, for example, the positive electrode active material or the negative electrode active material is mixed with a solution containing a conductive material and a binder, for example, using stirring means such as a planetary mixer, a disper mixer, Followed by stirring and homogenization to prepare a slurry.

As the conductive material, a conductive material used in general lithium ion secondary batteries can be used. Specifically, for example, carbon particles such as graphite powder, acetylene black, furnace black, thermal black and channel black, carbon fibers, and the like can be used as the conductive material. The conductive material may be used in an amount of, for example, 3 mass% or more and 10 mass% or less with respect to the mass of the whole mixture.

As the binder, a binder used in general lithium ion secondary batteries can be used. Concretely, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethylcellulose, polyacrylonitrile, modified polyacrylonitrile, Can be used. The binder may be used in an amount of, for example, 2% by mass or more and 10% by mass or less with respect to the mass of the whole mixture. The mixing ratio of the negative electrode active material and the binder is preferably 95: 5 by weight, for example.

As the solvent of the solution, depending on the kind of the binder, it is possible to use a solvent such as N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, Glycol, glycerin, dimethyl sulfoxide, tetrahydrofuran and the like.

In the compounding coating process, first, the compounding slurry containing the mixed slurry containing the cathode active material adjusted in the compounding adjusting step and the negative active material is applied by a coating means such as, for example, a bar coater, a doctor blade, Are respectively applied to the surfaces of the positive electrode collector 111a and the negative electrode collector 112a. Next, the positive electrode current collector 111a and the negative electrode current collector 112a coated with the compounded slurry are heat-treated to remove the solvent of the solution contained in the mixed slurry by volatilization or evaporation, and the positive electrode current collector 111a and the negative electrode On the surface of the collector 112a, a positive mix material layer 111b and a negative mix material layer 112b are formed, respectively.

The positive electrode material mixture layer 111b formed on the surface of the positive electrode collector 111a and the negative electrode material mixture layer 112b formed on the surface of the negative electrode collector 112a are formed by a roll press or the like Respectively, using a pressurizing means. Thus, the thickness of the positive electrode material mixture layer 111b is set to, for example, about 100 μm or more and 300 μm or less, and the thickness of the negative electrode material mixture layer 112b is, for example, about 20 μm or more and 150 μm or less . Thereafter, the positive electrode collector 111a and the positive electrode material mixture layer 111b and the negative electrode collector 112a and the negative electrode material mixture layer 112b are cut into long strips to form the positive electrode 111 and the negative electrode 112 ) Can be produced.

The positive electrode 111 and the negative electrode 112 manufactured as described above are wound around the winding central axis in a state of being opposed to each other via the separator 113 to become the winding electrode group 110. The winding electrode group 110 is formed in such a manner that the anode current collector 112a is connected to the bottom of the battery can 101 via the anode lead piece 104 and the anode current collector 111a is connected to the anode lead piece 103 And is short-circuited with the battery can 101 and the battery cover 102 by the insulating plate 105 or the like and is accommodated in the battery can 101. [ Thereafter, the nonaqueous electrolyte solution is injected into the battery can 101, the battery lid 102 is fixed to the battery can 101 via the sealing material 106, and the battery can 101 is sealed, (100) can be produced.

Examples of the electrolytic solution injected into the battery can 101 include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC) Lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), or the like is dissolved as an electrolyte in a solvent such as methylene carbonate (EMC) or methylpropyl carbonate (MPC) . The concentration of the electrolyte is preferably 0.7 M or more and 1.5 M or less. A compound having a carboxylic acid anhydride group, a compound having a sulfur element such as propane sultone, or a compound having boron may be mixed in these electrolytic solutions. The object of the addition of these compounds is to prevent reduction of the electrolytic solution on the surface of the negative electrode and to prevent reduction of metal elements such as manganese and the like eluted from the positive electrode on the negative electrode and to improve the ionic conductivity of the electrolytic solution, You can choose the enemy.

The non-aqueous secondary battery 100 having the above-described configuration has the battery lid 102 as a cathode external terminal and the bottom of the battery can 101 as a cathode external terminal, and supplies power supplied from the outside to the winding electrode group 110 The electric power accumulated in the winding electrode group 110 can be supplied to an external device or the like. As described above, the non-aqueous secondary battery 100 of the present embodiment can be used for a small-sized power source such as a portable electronic device or a household electric device, a power source for a stationary power source such as an uninterruptible power source or a power leveling device, , Electric vehicles, and the like.

Hereinafter, a comparative example different from the embodiment based on the method for producing the positive electrode active material of the present invention and the method for producing the positive electrode active material of the present invention will be described.

(Example 1)

First, lithium carbonate, nickel hydroxide, cobalt carbonate and manganese carbonate were prepared as starting materials for the positive electrode active material. Next, each starting material was weighed so as to have an atomic ratio of Li: Ni: Co: Mn of 1.04: 0.80: 0.10: 0.10, pulverized by a pulverizer and wet mixed to prepare a slurry, ) Was dried with a spray dryer (mixing step). Thereafter, the dried mixture was fired to obtain a small component (firing step).

Specifically, a bead mill was used as a pulverizer, wet mixing was performed using water as a solvent, and the operation was continued until the particle size became stable. The particle size of the obtained slurry was measured by a laser diffraction particle size distribution meter, and D50 = 0.13 占 퐉 and D100 = 0.26 占 퐉. The slurry was dried by using a rotary disk type spray drier to obtain a dry mixed powder having a D50 of 17 mu m and a bulk specific gravity of 0.74 g / cc.

Next, 1 kg of the mixture (mixed powder) obtained in the mixing step was charged into an alumina container having a length of 300 mm, a length of 300 mm and a height of 100 mm, and was subjected to continuous heat treatment at a heat treatment temperature of 350 ° C The heat treatment was performed over time (first heat treatment step). In the first heat treatment step, water vapor accompanying pyrolysis of nickel hydroxide and carbon dioxide accompanied by thermal decomposition of cobalt carbonate and manganese carbonate are generated. Next, the obtained powder (first precursor) was subjected to a heat treatment for 10 hours at a heat treatment temperature of 600 占 폚 in an oxygen stream by a continuous carrier furnace in which the atmosphere was replaced with an atmosphere having an oxygen concentration of 90% or more (second heat treatment step) . In the second heat treatment step, cobalt carbonate and manganese carbonate which have not reacted in the first heat treatment step are thermally decomposed to generate carbon dioxide. Further, since it reacts with each oxide of nickel, cobalt and manganese after pyrolysis to form a precursor of the lithium composite oxide, lithium carbonate decomposes and releases carbon dioxide. The resultant powder (second precursor) was heat-treated for 10 hours at a heat treatment temperature of 800 占 폚 in an oxygen stream by a continuous transport path in which the atmosphere was replaced with an atmosphere having an oxygen concentration of at least 90% ) (Third heat treatment step). In the third heat treatment step, the reaction of the formula (2) proceeds by the oxidation of nickel, so that lithium carbonate as a reaction residue is decomposed into lithium oxide and carbon dioxide, and carbon dioxide is generated. In order to synthesize the lithium composite oxide, sufficient oxygen is needed to rapidly exhaust the carbon dioxide generated in the second and third heat treatment steps and accelerate the oxidation reaction.

The resulting cow component was classified into openings of 53 mu m or less to obtain a positive electrode active material. The elemental consumption of the cathode active material was analyzed by ICP. As a result, Li: Ni: Mn: Co was 1.02: 0.80: 0.10: 0.10. As a result of X-ray diffraction measurement, a diffraction pattern corresponding to the layer structure of? -NaFeO ₂ type was obtained, and the lattice constants were a = 0.287 nm and c = 1.42 nm. The specific surface area was 0.37 m < 2 > / g.

(Example 2)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the first heat treatment step at 350 占 폚 in Example 1 was lowered to 250 占 폚.

(Example 3)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the second heat treatment step, which was 600 ° C in Example 1, was increased to 650 ° C.

(Example 4)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the second heat treatment step, which was 600 占 폚 in Example 1, was lowered to 550 占 폚.

(Example 5)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the second heat treatment step, which was 600 ° C in Example 1, was lowered to 500 ° C.

(Comparative Example 1)

In the firing step, the cathode active material was synthesized in the same manner as in Example 1 except that the first heat treatment step was omitted, and X-ray diffraction measurement and specific surface area were measured. The obtained lattice constants were a = 0.287 nm and c = 1.41 nm. The specific surface area was 0.40 m < 2 > / g.

(Comparative Example 2)

The cathode active material was synthesized in the same manner as in Example 1 except that the first heat treatment step and the second heat treatment step were omitted in the firing step, and X-ray diffraction measurement and specific surface area were measured. The obtained lattice constants were a = 0.287 nm and c = 1.42 nm. The specific surface area was 0.38 m < 2 > / g.

(Comparative Example 3)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the first heat treatment step at 350 占 폚 in Example 1 was lowered to 150 占 폚.

(Comparative Example 4)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the second heat treatment step, which was 600 ° C in Example 1, was increased to 700 ° C.

(Comparative Example 5)

A cathode active material was prepared in the same manner as in Example 1 except that the temperature of the second heat treatment step, which was 600 ° C in Example 1, was lowered to 400 ° C.

(Comparative Example 6)

A cathode active material was prepared in the same manner as in Example 1 except that the second heat treatment and the third heat treatment performed in the oxidizing atmosphere of oxygen concentration of 90%

(Preparation of Lithium Ion Secondary Battery)

Using the cathode active materials prepared in Examples 1 to 5 and Comparative Examples 1 to 6, lithium ions of the lithium ions of Examples 1 to 5 and Comparative Examples 1 to 6 A secondary battery was produced.

First, a positive electrode active material, a binder, and a conductive material were mixed to prepare a positive electrode material mixture slurry. Then, the prepared positive electrode material mixture slurry was applied to an aluminum foil having a thickness of 20 mu m as a positive electrode current collector, dried at 120 DEG C, compression-molded by a press so as to have an electrode density of 2.0 g / The anode was punched out by a counter-current. Further, a negative electrode was fabricated by using metal lithium as the negative active material.

Next, using the prepared positive electrode, negative electrode and non-aqueous electrolyte, a lithium ion secondary battery was produced. As the non-aqueous electrolyte, a solution prepared by dissolving LiPF ₆ so as to have a final concentration (final concentration) of 1.0 mol / L was used in a solvent in which ethylene carbonate and dimethyl carbonate were mixed so that the volume ratio was 3: 7.

Next, charging and discharging tests were conducted on each of the lithium ion secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 6, and the initial discharging capacity was measured. The charging was carried out at a constant current of 0.2 CA and a constant current of up to 4.4 V at a constant current and a constant voltage. The discharging was performed at a constant current of 0.2 CA for the discharge end voltage of 2.5 V. Thereafter, charging and discharging were repeated for 50 cycles at a charging and discharging current of 1.0 CA, a charging end voltage of 4.4 V and a discharge end voltage of 2.5 V. The percentage of the value obtained by dividing the discharge capacity measured at the 50th cycle by the discharge capacity measured at the first cycle was calculated and defined as the capacity retention rate. The results are shown in Table 1.

[Table 1]

From the above results, in the lithium ion secondary battery of Example 1 using the positive electrode active material produced through the sintering process with the first heat treatment, the second heat treatment and the third heat treatment as the positive electrode, the 0.2C discharge capacity was 198 Ah / kg, The initial discharge was 180 Ah / kg, and the capacity retention rate was 81%. The second heat treatment step was performed at a temperature of 250 ° C or higher and 400 ° C or lower, the second heat treatment step was performed at a temperature of 450 ° C or higher and lower than 700 ° C, and the third heat treatment step was performed at 700 ° C or higher and 840 ° C or lower. Good results were obtained in the lithium ion secondary battery of Example 5 as well.

On the other hand, in the lithium ion secondary batteries of Comparative Example 1 and Comparative Example 2 in which the first heat treatment in the firing process and the cathode active material in which the first heat treatment and the second heat treatment were omitted as the positive electrode, And the numerical value was lower than the result of the battery. Comparative Example 3 in which the temperature of the first heat treatment step was lowered to 150 캜, Comparative Example 4 in which the temperature of the second heat treatment was raised to 700 캜, and Comparative Example 5 in which the temperature of the second heat treatment step was lowered to 400 캜 The numerical value of the lithium ion secondary battery was lower than that of each example. Further, in the lithium ion secondary battery of Comparative Example 6 in which the entire range from the first heat treatment to the third heat treatment was performed in an atmospheric environment, the discharge capacity significantly decreased. Thus, it was confirmed that the positive electrode active material having a high capacity and a high capacity retention ratio can be obtained by the production method of the positive electrode active material of Examples 1 to 5.

(Example 6)

Next, a cathode active material was produced in the same manner as in Example 1 except that the time for wet mixing in the mixing step was shortened to 50% of Example 1, and a lithium ion secondary battery of Example 6 was produced. In the mixing step, the particle size of the pulverized powder of the starting material contained in the slurry after wet mixing before drying and assembling was measured by a laser diffraction particle size distribution meter, and D50 = 0.18 mu m and D100 = 0.45 mu m.

(Example 7)

Next, a cathode active material was produced in the same manner as in Example 1 except that the time for wet mixing was shortened to 38%, and a lithium ion secondary battery of Example 7 was produced. The particle size of the pulverized powder of the starting material contained in the slurry after the wet mixing measured in the same manner as in Example 6 was D50 = 0.27 mu m and D100 = 1.3 mu m.

(Example 8)

Next, a cathode active material was produced in the same manner as in Example 1 except that the time for wet mixing was shortened to 25%, and a lithium ion secondary battery of Example 8 was produced. The particle size of the pulverized powder of the starting material contained in the slurry after wet mixing measured in the same manner as in Example 6 was D50 = 0.36 mu m and D100 = 5.1 mu m.

Next, for each of the lithium ion secondary batteries of Example 6, Example 7, and Example 8, a charge-discharge test was performed under the same conditions as those of the lithium ion secondary battery of Example 1, the initial discharge capacity was measured, And the capacity retention rate was calculated. Table 2 shows a comparison between the results of the lithium ion secondary batteries of Examples 1 and 6 and the results of the lithium ion secondary batteries of Examples 7 and 8.

[Table 2]

The lithium ion secondary batteries of Examples 1 and 6 exhibited a relatively high discharge capacity and capacity retention rate. On the other hand, in the lithium ion secondary batteries of Examples 7 and 8, the discharge capacity was high similarly to the lithium ion secondary batteries of Examples 1 and 6, but the capacity retention rate after 50 cycles was lowered. Degradation was observed. That is, when the mixing time in the mixing step is short and the D50 and D100 of the mixed ingredients are increased, the capacity after the cycle is lowered.

From the above, it was found that it is necessary to sufficiently mix the starting materials in order to obtain a cathode active material having a high capacity and excellent capacity retention ratio as in Examples 1 and 6. [ It is preferable that the particle size of the pulverized powder of the starting material before drying and granulation in the mixing step is not more than 0.27 mu m and D100 is less than 1.3 mu m, And more preferably 1.0 mu m or less.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific structure is not limited to this embodiment, and even if there is a design change or the like within the range not deviating from the gist of the present invention, They are included in the present invention.

100 ... Lithium ion secondary battery, 111 ... Anode, S1 ... Mixing process, S2 ... Sintering process, S21 ... The first heat treatment step, S22 ... Second heat treatment step, S23 ... The third heat treatment step, S24 ... The first gas replacement step, S25 ... The second gas replacement step

Claims (8)

A method for producing a positive electrode active material for use in a positive electrode of a lithium ion secondary battery,
A mixing step of mixing lithium carbonate and a compound each containing a metal element other than Li in the formula (1)
And a calcination step of calcining the mixture obtained in the mixing step in an oxidizing atmosphere to obtain a lithium composite compound represented by the following formula (1)
In the firing step,
A first heat treatment step of obtaining the first precursor by heat-treating the mixture at a heat treatment temperature of 200 ° C or more and 400 ° C or less for 0.5 hours to 5 hours or less;
A second heat treatment step of heat treating the first precursor at a heat treatment temperature of 450 ° C. or more and less than 700 ° C. for 2 to 50 hours to obtain a second precursor;
Treating the second precursor at a heat treatment temperature of 700 ° C or more and 850 ° C or less for 2 to 50 hours to obtain the lithium composite compound;
, And the oxygen concentration in the oxidizing atmosphere in the second heat treatment step and the third heat treatment step is 80% or more.
Li _{1 + a} Ni _b Mn _c Co _d M _e O _{2 + α} ... (One)
In the above formula (1), M is at least one element selected from the group consisting of Mg, Al, Ti, Zr, Mo and Nb, and a, b, c, d, B? 0.9,? C? 0.35, 0.05? D? 0.30, 0? E? 0.35, b + c + d + e = 1, and -0.1? . The method according to claim 1,
The heat treatment temperature in the first heat treatment step is 250 ° C or more and 400 ° C or less,
The heat treatment temperature in the second heat treatment step is 450 ° C or higher and 660 ° C or lower,
Wherein the heat treatment temperature in the third heat treatment step is 700 DEG C or more and 840 DEG C or less. The method according to claim 1,
Wherein the first heat treatment step is a step of obtaining the first precursor from which the vaporization component contained in the mixture is removed,
The second heat treatment step is a step of advancing a Ni oxidation reaction for oxidizing bivalent Ni contained in the first precursor to trivalent Ni to obtain the second precursor,
Wherein the third heat treatment step is a step of advancing the Ni oxidation reaction and the growth of the crystal grains of the second precursor to obtain the lithium composite compound. The method according to claim 1,
And a first gas replacement step of replacing the oxidative atmosphere during or after the step of the first heat treatment step. 5. The method of claim 4,
Wherein the first gas replacement step is performed after the first heat treatment step and the heat treatment is performed by introducing a new oxidizing atmosphere in the second heat treatment step. The method according to claim 1,
And a second gas replacement step of replacing the oxidative atmosphere during or after the step of the second heat treatment step. The method according to claim 6,
Wherein the second gas replacement step is performed after the second heat treatment step and the heat treatment is performed by introducing a new oxidizing atmosphere in the third heat treatment step. The method according to claim 1,
Wherein the oxidizing atmosphere in the first heat treatment step is air.

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