JP2021034357A - Method for manufacturing positive electrode active material - Google Patents

Abstract

To provide a method for stably manufacturing a positive electrode active material capable of showing superior battery characteristics without causing a handling problem.SOLUTION: A method is arranged for manufacturing a positive electrode active material consisting of a lithium transition metal composite oxide manufactured by performing a thermal treatment on a mixture of a transition metal composite hydroxide of which the compositional formula is represented by e.g. NixMnyCozMt(OH)2+α (M is one or more additive elements selected from a group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W), and a lithium compound. In the method, the thermal treatment is performed preferably in a low-oxidization gas atmosphere of 20-30 vol.% in oxygen density in a low-temperature region of a threshold temperature or below within a range of 700°C up to 900°C, and it is performed in a high-oxidization gas atmosphere of 40 vol.% or higher in oxygen density in a high-temperature region above the predetermined threshold temperature.SELECTED DRAWING: Figure 1

Description

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 using the positive electrode active material.

In recent years, with the spread of small information terminals such as smartphones and tablet PCs, the demand for small and lightweight secondary batteries having high energy density is increasing. Further, as a power source for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles, the development of high-output secondary batteries is strongly desired. As a secondary battery for the above application, a non-aqueous electrolyte secondary battery mainly composed of a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator is known. In addition, an all-solid-state secondary battery using a solid electrolyte is expected as a next-generation energy storage device.

Among the above secondary batteries, a lithium ion secondary battery that uses an active material composed of a layered or spinel-type lithium transition metal composite oxide as a positive electrode material and desorbs and inserts lithium by charging and discharging has already been put into practical use. ing. Lithium-ion secondary batteries can obtain 4V class voltage and have excellent characteristics such as energy density, but research and development are still being actively carried out to further improve the characteristics. As the lithium transition metal composite oxide used as the positive electrode active material of this lithium ion secondary battery, composite oxides having various compositions have been proposed.

For example, lithium cobalt composite oxide (LiCoO _{2 ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO 2} ) using nickel, which is cheaper than cobalt, and lithium manganese composite oxide (LiMn ₂ O) using manganese. ₄ ), lithium nickel-manganese manganese composite oxide (LiNi _0.5 Mn _0.5 O _{2 ), and ternary lithium nickel cobalt manganese composite oxide (LiNi 1/3} Co) in which a part of cobalt is replaced with nickel and manganese. _1/3 Mn _1/3 O ₂ ) and the like can be mentioned.

Further, various forms of the positive electrode active material have been proposed. For example, Patent Document 1 has a form of secondary particles made of a hexagonal lithium-containing composite oxide having a layered structure and having voids. The positive electrode active material is disclosed, and it is described that a secondary battery having a large discharge capacity and a high output can be obtained by setting the average particle size to 3 to 12 μm and suppressing the particle size distribution to be narrow.

Japanese Unexamined Patent Publication No. 2013-229339

As disclosed in Patent Document 1, a lithium ion secondary battery having excellent cycle characteristics and output characteristics by using a positive electrode active material having a relatively small particle size and a narrow particle size distribution, that is, having a uniform particle size. Can be obtained. However, small information terminals and electric vehicles have become more and more sophisticated and high-performance in recent years, and the lithium-ion secondary batteries mounted on them are required to have even higher stability during charging. There is a tendency. In order to meet such a demand, it is considered effective to increase the crystallinity of the positive electrode active material by raising the heat treatment temperature or lengthening the heat treatment time in the manufacturing process of the positive electrode active material.

However, under the above heat treatment conditions, agglomeration and sintering of the particles of the positive electrode active material are promoted, so that agglomerates and sintered bodies are easily formed, and the particles have the form of powder or granular material obtained after the heat treatment. In addition to problems in handling such as a decrease in the fluidity of the positive electrode active material, the battery characteristics of the lithium ion secondary battery using the positive electrode active material may vary. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a positive electrode active material having excellent battery characteristics in a stable manner and without causing problems in handling.

In order to achieve the above object, the method for producing a positive electrode active material according to the present invention comprises a lithium transition metal composite oxide produced by heat-treating a mixture of a transition metal composite hydroxide as a precursor and a lithium compound. A method for producing a positive electrode active material, the heat treatment is performed in a low oxidizing gas atmosphere having an oxygen concentration of 20% by volume or more and 30% by volume or less in a low temperature region below a predetermined threshold temperature, and exceeds the predetermined threshold temperature. In the high temperature region, it is characterized in that it is carried out in a highly oxidizing gas atmosphere having an oxygen concentration of 40% by volume or more.

According to the present invention, a positive electrode active material that is easy to handle and has excellent battery characteristics can be stably produced on an industrial scale.

It is a graph which shows the temperature profile in the furnace of the firing process adopted in the manufacturing method of the positive electrode active material of the Example of this invention. It is a graph which shows the temperature profile in the furnace of the firing process adopted in the manufacturing method of the positive electrode active material of the comparative example of this invention.

The present inventor has made extensive studies on a method for producing a positive electrode active material for a lithium ion secondary battery, which is easy to handle and has excellent output characteristics when used as a positive electrode material for a lithium ion secondary battery. As a positive electrode material for lithium-ion secondary batteries, while suppressing the sintering of particles, the atmosphere when heat-treating the mixture of the transition metal composite hydroxide of the precursor and the lithium raw material is performed under specific conditions. They have found that a positive electrode active material showing excellent output characteristics can be obtained when used, and have completed the present invention. Hereinafter, embodiments of the method for producing the positive electrode active material of the present invention will be described. First, a method for producing transition metal composite hydroxide particles as a precursor as an intermediate raw material in the method for producing the positive electrode active material will be described.

1. transition metal composite positive electrode active which is a precursor of a substance transition metal composite hydroxide particles according to the embodiment of the manufacturing method the invention of the hydroxide particles, for example, formula A is, Ni _x Mn _y Co _z M _t (OH) _{2 + α} (in the formula, x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, − 0.20 ≦ α ≦ 0.20, and M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. ).

The transition metal composite hydroxide particles are produced by supplying an aqueous solution containing a transition metal and an aqueous solution containing an ammonium ion feeder prepared in the raw material preparation step to a reaction vessel and performing a crystallization reaction in the reaction vessel. Is preferable. This crystallization reaction is preferably carried out in two steps in the order of the nucleation step and the particle growth step. Specifically, first, in the nucleation step, the pH value of the reaction aqueous solution in the reaction vessel is adjusted to about 12.0 to 14.0 based on the liquid temperature of 25 ° C. to generate nuclei, and then particle growth. In the step, the pH value of the reaction aqueous solution containing the nucleation produced in the nucleation step is preferably 0.5 or more lower than the pH value of the nucleation step based on the liquid temperature of 25 ° C., for example, 10.5-12. Adjust to about 0 to grow the nucleus.

In the initial stages of the nucleation formation step and the particle growth step, the atmosphere in the reaction vessel is made into an oxidizing atmosphere having an oxygen concentration of more than 5% by volume, and in the stages after the initial stage of the particle growth step, the inside of the reaction vessel is made. It is preferable that the atmosphere of the above is a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less. This makes it possible to efficiently generate transition metal composite hydroxide particles having a narrow particle size distribution.

The temperature of the reaction aqueous solution is preferably controlled within the range of 20 to 60 ° C. through the production step and the particle growth step. If the liquid temperature is less than 20 ° C., nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and the average particle size and particle size distribution of the finally obtained transition metal composite hydroxide particles can be controlled. It will be difficult. On the contrary, when the liquid temperature exceeds 60 ° C., the volatilization of ammonia is promoted, so that the supply amount of the aqueous solution containing the ammonium ion feeder increases to compensate for this, and the production cost increases. Hereinafter, each of the above steps constituting the method for producing the transition metal composite hydroxide particles will be specifically described.

1.1 Raw material preparation step First, a raw material aqueous solution containing a transition metal compound that is a raw material of the reaction aqueous solution in which the crystallization reaction is carried out, and an aqueous solution containing an ammonium ion feeder that plays a role of a complexing agent in the reaction aqueous solution. And an alkaline aqueous solution that plays a role in adjusting the pH value of the reaction aqueous solution is prepared by the methods shown below.
(A) Raw Material Aqueous Solution In the preparation of the raw material aqueous solution, the transition metal element contained in the raw material aqueous solution is blended so that the molar-based blending ratio matches the composition of the target transition metal composite hydroxide particles. For example, in the case of producing the transition metal composite hydroxide particles represented by the general formula A described above, the molar ratio of the metal elements in the raw material aqueous solution is Ni: Mn: Co: M = x: y: z: t. (However, x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1).

Each of the above transition metals is added to water in the form of a compound to prepare a raw material aqueous solution. The specific type of compound is not limited, but a water-soluble compound such as nitrate, sulfate, or chloride is preferable from the viewpoint of ease of handling, and among these, a viewpoint of cost and prevention of halogen contamination. Sulfate is particularly preferred. Further, the additive elements M (M is from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) added to the transition metal composite hydroxide particles as needed. As for one or more additive elements selected from the above group), a water-soluble compound is preferable as described above.

The transition metal compound and the compound of the additive element M added as needed preferably have a total molar concentration of 1.0 to 2.6 mol / L in the aqueous solution of the raw material, 1.5 to 2. It is more preferably .2 mol / L. If the molar concentration is less than 1.0 mol / L, the amount of precipitation per unit volume of the reaction aqueous solution is small, so that the productivity is lowered. On the contrary, if this molar concentration exceeds 2.6 mol / L, some of them exceed the saturated concentration at room temperature, so that crystals of the metal compound may reprecipitate and clog the pipe or the like. In addition, in order to prevent the formation of compounds other than the target compound, an aqueous solution may be prepared for each metal compound and introduced into the reaction vessel.

(B) Aqueous Solution Containing Ammonium Feeder The type of aqueous solution containing an ammonium ion feeder is not particularly limited, and for example, an aqueous solution such as aqueous ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride can be used. .. Of these, ammonia water is preferable. When ammonia water is used, its concentration is preferably 20 to 30% by mass, more preferably 22 to 28% by mass. By adjusting the concentration of ammonia water within the range of 20 to 30% by mass, the loss of ammonia due to volatilization and the like can be suppressed, so that the production cost can be suppressed.

(C) Alkaline aqueous solution The type of alkaline aqueous solution is not particularly limited, and a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. This alkali metal hydroxide is preferably added in the form of an aqueous solution in order to facilitate pH control. In this case, the concentration of the aqueous solution of the alkali metal hydroxide is preferably 20 to 50% by mass, more preferably 26 to 30% by mass. By adjusting the concentration of the aqueous solution of the alkali metal hydroxide within the range of 20 to 50% by mass as described above, the alkali metal water is suppressed while suppressing the amount of water as a solvent introduced into the crystallization reaction system. It is possible to prevent the pH value from becoming locally high at the position where the oxide is added. As a result, it becomes possible to efficiently obtain composite hydroxide particles having a narrow particle size distribution.

1.2 Nuclear formation step In the nuclear formation step, first, an alkaline aqueous solution prepared in the raw material preparation step and an aqueous solution containing an ammonium ion feeder are introduced into the reaction vessel, and the pH value measured with a pH meter based on a liquid temperature of 25 ° C. 12.0 to 14.0, and an aqueous solution before reaction having an ammonium ion concentration of 3 to 25 g / L measured with an ion meter is prepared.

Next, the raw material aqueous solution prepared in the above raw material preparation step is supplied while stirring the pre-reaction aqueous solution. As a result, a nucleus serving as a core of the transition metal composite hydroxide particles is generated in the reaction vessel. In this nucleation step, it is preferable to control the pH value of the reaction aqueous solution in which nucleation is performed within the range of 12.0 to 14.0 based on the liquid temperature of 25 ° C. This makes it possible to prioritize the generation of new nuclei while suppressing the growth of nuclei, and thus to make the nuclei produced in the nucleation step homogeneous and have a narrow particle size distribution.

If the pH value of this reaction aqueous solution is less than 12.0, the growth of nuclei tends to proceed with nucleation, so that the particle size of the transition metal composite hydroxide particles finally obtained in the crystallization step becomes non-uniform. , The particle size distribution may widen. On the contrary, when this pH value exceeds 14.0, the formed nuclei become too fine, and the reaction aqueous solution may gel. In this nucleation step, it is preferable that the fluctuation range of the pH value is further controlled within ± 0.2. This makes it possible to further narrow the particle size distribution of the transition metal composite hydroxide particles.

In the nucleation step, the pH value and the ammonium ion concentration of the reaction aqueous solution change with the nucleation, so the alkaline aqueous solution and the ammonium feeder are used so that the above pH range and the ammonium ion concentration range are maintained. It is preferable to appropriately supply the containing aqueous solution. The method of supplying the alkaline aqueous solution is not particularly limited, but a pump such as a metering pump that can control the flow rate while sufficiently stirring the reaction aqueous solution is used so that the pH value of the reaction aqueous solution in the reaction vessel does not rise locally. It is preferable to supply. Similarly, it is preferable to supply the aqueous solution containing the ammonium ion feeder by a pump capable of controlling the flow rate.

This nucleation step ends when a predetermined amount of nuclei is formed in the reaction aqueous solution. The time when this predetermined amount of nuclei is generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the reaction vessel. Specifically, it is preferably 0.1 to 2 atomic%, more preferably 0., with respect to all the metal elements in the metal compounds contained in all the raw material aqueous solutions supplied through the nucleation step and the particle growth step. It is preferable to end the nucleation step when 2 to 1.5 atomic% is supplied. This makes it possible to generate transition metal composite hydroxide particles having a narrow particle size distribution.

1.3 Particle growth step In the particle growth step, which is the next step after the above nucleation step, the pH value of the reaction aqueous solution in the reaction vessel is adjusted to 10.5 to 12.0 based on the liquid temperature of 25 ° C., and ammonium ions. Adjust the concentration to 3-25 g / L. As a result, it is possible to grow the nuclei generated in the nucleation step contained in the reaction aqueous solution while suppressing the formation of new nuclei. As a result, the finally produced transition metal composite hydroxide particles can be made more homogeneous and have a narrower particle size distribution.

If this pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, so that the rate of the crystallization reaction slows down and the amount of metal ions remaining in the reaction aqueous solution increases for production. There is a risk of reduced sex. On the contrary, if this pH value exceeds 12.0, the amount of nucleation in the particle growth step increases, and the particle size of the obtained composite hydroxide particles may become non-uniform. In this particle growth step, it is preferable that the fluctuation range of the pH value is further controlled within ± 0.2. This makes it possible to generate transition metal composite hydroxide particles having a narrower particle size distribution. In this particle growth step as well, the pH value and ammonium ion concentration of the reaction aqueous solution change with particle growth, so an alkaline aqueous solution and an ammonia aqueous solution are appropriately supplied so that the above pH value and ammonium ion concentration ranges are maintained. Is preferable.

In any of the above nucleation step and particle growth step, if the ammonium ion concentration is less than 3 g / L, it becomes difficult to keep the solubility of metal ions constant, or the reaction aqueous solution tends to gel. However, it becomes difficult to obtain transition metal composite hydroxide particles having a uniform shape and particle size. On the other hand, if the ammonium ion concentration exceeds 25 g / L, the solubility of the metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, which may cause problems such as composition deviation. It is preferable that the fluctuation range of the ammonium ion concentration is suppressed to a constant fluctuation range of about ± 5 g / L.

At the end of the particle growth step, the slurry in the reaction vessel preferably has a solid content concentration of transition metal composite hydroxide particles in the range of 30 to 200 g / L, preferably 80 to 150 g / L. It is more preferable that it is within the range of. If the solid content concentration is less than 30 g / L, the aggregation of the primary particles may be insufficient. On the contrary, if it exceeds 200 g / L, the diffusion of the transition metal composite hydroxide particles becomes insufficient in the reaction vessel, and there is a possibility that the particle growth is biased.

1.4 Coating step The additive element M added as needed may be prepared as a raw material aqueous solution together with the essential transition metal as described above, but in this coating step, the transition metal obtained by the particle growth step is described. It may be added by coating the surface of the composite hydroxide particle with a compound containing the additive element M. Specifically, after adding water to the transition metal composite hydroxide particles generated in the particle growth step to form a slurry, a compound containing the additive element M while controlling the pH value of the slurry within a predetermined range. Add the coating aqueous solution in which is dissolved. As a result, a compound containing the additive element M is precipitated on the particle surface of the transition metal composite hydroxide, so that coated transition metal composite hydroxide particles can be obtained.

Instead of the above aqueous solution for coating, an alkoxide solution of the additive element M may be added to the slurry of transition metal composite hydroxide particles for coating, or an aqueous solution in which a compound containing the additive element M is dissolved. Alternatively, the slurry may be coated by spraying the transition metal composite hydroxide particles as they are and drying them. As yet another coating method, the slurry prepared by mixing the transition metal composite hydroxide particles and the compound containing the additive element M may be spray-dried to coat the transition metal composite hydroxide particles. It may be coated by mixing the compound containing the additive element M by the solid phase method.

In this way, when the surface of the transition metal composite hydroxide particles is coated with the additive element M, the overall composition of the coated transition metal composite hydroxide particles is matched with the target composition. It is necessary to appropriately adjust the composition of each of the raw material aqueous solution and the coating aqueous solution and their blending ratios. Further, this coating step may be performed after the drying step in the method for producing a positive electrode active material described later.

2. Method for Producing Positive Electrode Active Material Next, a method for producing the positive electrode active material according to the embodiment of the present invention using the above transition metal composite hydroxide particles as an intermediate raw material will be described. The method for producing the positive electrode active material according to the embodiment of the present invention includes a drying step S1 in which the transition metal composite hydroxide particles are heated and dried, and a lithium compound is added to the heat-dried transition metal composite hydroxide particles. The mixing step S2 in which the above is added and mixed, the firing step S3 in which the lithium mixture obtained in the mixing step S2 is preferably fired at 850 to 850 ° C., and the agglomerates and sintered bodies produced in the firing step S3 are combined. It has a crushing step S4 for crushing as needed. Hereinafter, each step will be described in detail.

2.1 Drying step In the drying step S1, the transition metal composite hydroxide particles are preferably heated to 105 to 150 ° C. and dried. As a result, excess water contained in the transition metal composite hydroxide particles can be removed to some extent, so that the water remaining in the positive electrode active material particles after the firing treatment in the firing step S3 in the subsequent step can be effectively reduced. As a result, variations in the composition of the positive electrode active material can be suppressed.

If the heating temperature is less than 105 ° C., the removal of excess water contained in the transition metal composite hydroxide particles becomes insufficient, and the composition of the finally obtained positive electrode active material may vary greatly. On the contrary, even if the heating temperature exceeds 150 ° C., not only the further effect cannot be expected, but also the production cost increases, which is not preferable. The atmosphere during the heat treatment is preferably a non-reducing atmosphere, more preferably in an air stream that can be easily performed. The drying treatment time is preferably at least 1 hour, more preferably 5 to 15 hours, from the viewpoint of sufficiently removing excess water in the transition metal composite hydroxide particles.

2.2 Mixing step In the mixing step S2, a lithium compound is added to the transition metal composite hydroxide particles heat-dried in the drying step S1 and sufficiently mixed to obtain a lithium mixture. In the mixing of the transition metal composite hydroxide particles and the lithium compound, lithium atoms relative to the total number of atoms (Me) of nickel, cobalt, manganese, and additive element M, which are metal atoms other than lithium in the lithium mixture. The compounding is performed so that the ratio (Li / Me) of the number (Li) matches the desired Li / Me of the positive electrode active material finally produced. The reason is that Li / Me does not change before and after the firing step S3 in the subsequent step. Specifically, in this mixing step S2, Li / Me is preferably 0.95 to 1.5, more preferably 1.0 to 1.5, and even more preferably 1.0 to 1. 35 is most preferably blended in an amount of 1.0 to 1.2.

From the viewpoint of easy availability, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used as the lithium compound added to the transition metal composite hydroxide in the mixing step S2. Among these, lithium hydroxide or lithium carbonate is more preferable, and lithium carbonate is most preferable, from the viewpoint of ease of handling and stability of quality.

For mixing the above transition metal composite hydroxide particles with the lithium compound, a general mixer such as a shaker mixer, a ladyge mixer, a julia mixer, or a V blender can be used, but at that time, fine powder is not generated. It is preferable to mix well with. If this mixing is insufficient, a portion that locally deviates greatly from the desired Li / Me value may occur, and good battery characteristics may not be obtained.

2.3 Firing step In the firing step S3, the lithium mixture obtained in the mixing step S2 is charged into a firing furnace and fired under predetermined conditions. As a result, the transition metal composite hydroxide is decomposed and oxidized, and lithium diffuses into the particles of the transition metal composite hydroxide to form a lithium transition metal composite oxide, which is further oxidized and diffused to cause defects. Is reduced, and lithium transition metal composite oxide particles in which the crystallinity of each particle is enhanced are produced. The firing furnace used in the firing step S3 is not particularly limited and may be a batch type or a continuous type, but an electric furnace that does not generate gas is preferable so that the atmosphere inside the furnace can be easily adjusted, which will be described later. Hereinafter, the processing conditions for this firing process will be specifically described.

(A) Maximum temperature and holding time at that temperature In the firing step S3, the lithium mixture is charged into a firing furnace, the temperature inside the furnace (also referred to as atmospheric temperature) is gradually raised, and the temperature inside the furnace becomes preferable. When the maximum temperature (also referred to as firing temperature) of 850 ° C. or higher and 1050 ° C. or lower, more preferably 900 ° C. or higher and 1000 ° C. or lower is reached, the firing treatment is performed by holding the maximum temperature for a predetermined time. If this maximum temperature is less than 850 ° C., lithium may not be sufficiently diffused in the transition metal composite hydroxide particles, and excess lithium or unreacted transition metal composite hydroxide particles may remain, or finally, the transition metal composite hydroxide particles may remain. The crystallinity of the obtained lithium transition metal composite oxide particles may be insufficient. On the contrary, when the maximum temperature exceeds 1050 ° C., sintering of the lithium transition metal composite oxide particles is promoted, and the content ratio of the irregular coarse particles may increase.

The holding time of the maximum temperature is preferably 2 hours or more, more preferably 4 hours or more and 24 hours or less. If this holding time is less than 2 hours, lithium may not be sufficiently diffused in the transition metal composite hydroxide particles as in the above case, and excess lithium and unreacted transition metal composite hydroxide particles remain. Or, the crystallinity of the obtained lithium transition metal composite oxide particles may be insufficient. On the contrary, even if this holding time exceeds 24 hours, no further effect can be expected, which is not preferable from the viewpoint of productivity.

(B) Temperature rise rate and temperature decrease rate The temperature rise rate up to the above maximum temperature is preferably 2 to 10 ° C./min, more preferably 5 to 10 ° C./min. As a result, it is possible to suppress the generation of thermal stress in the transition metal composite hydroxide particles, so that it is possible to prevent quality problems such as cracks from occurring in the transition metal composite hydroxide particles. When the temperature is raised, it is preferably maintained at a temperature near the melting point of the lithium compound for preferably about 1 to 5 hours, more preferably about 2 to 5 hours. Thereby, the transition metal composite hydroxide particles and the lithium compound can be reacted more uniformly. After the elapse of the predetermined holding time at the maximum temperature, cooling is preferably performed at a temperature lowering rate of 2 to 10 ° C./min, more preferably 3 to 7 ° C./min until the maximum temperature reaches 200 ° C. Is preferable. As a result, it is possible to prevent equipment such as a saggar from being damaged by quenching while ensuring productivity.

(C) Firing atmosphere In the firing process, the low temperature range from the start of the temperature rise in the furnace to the arrival at the predetermined threshold temperature and the predetermined holding at the maximum temperature after the threshold temperature is exceeded. The atmosphere inside the firing furnace is switched between the high temperature range and the high temperature range until the passage of time. Specifically, as described above, in the firing process in which the lithium mixture is charged into the firing furnace and heat-treated according to a predetermined temperature profile, the temperature inside the furnace starts to rise and then the predetermined temperature is equal to or lower than the maximum temperature. In the low temperature range until the threshold temperature is reached, heat treatment is performed in a low oxidizing gas atmosphere having an oxygen concentration of 20% by volume or more and 30% by volume or less, and a predetermined holding time at the maximum temperature elapses after the threshold temperature is exceeded. In the high temperature region until the heat treatment is performed, the heat treatment is performed in a highly oxidizing gas atmosphere having an oxygen concentration of 40% by volume or more. The above threshold temperature is preferably in the range of 700 ° C. or higher and 900 ° C. or lower.

By switching the firing atmosphere before and after the threshold temperature as described above, the crystallinity of the transition metal composite oxide particles can be enhanced without increasing the maximum temperature or extending the holding time at the maximum temperature. Therefore, a positive electrode active material having high crystallinity can be produced without increasing the content ratio of the aggregate or the sintered body. In particular, when tungsten (W) is contained in the transition metal composite hydroxide which is a precursor, the treatment has conventionally been performed at a high heat treatment temperature in order to improve the crystallinity, but according to the method of the embodiment of the present invention. It is effective because the heat treatment temperature can be lowered as compared with the conventional case.

That is, conventionally, in order to increase the crystallinity of the positive electrode active material, the heat treatment temperature is raised or the heat treatment time is extended during the firing treatment of the precursor. However, since the transition metal composite hydroxide particles and their oxide particles are easily sintered with each other, the obtained positive electrode active material has problems in handling such as a decrease in fluidity, or when it is used as a positive electrode material. There was a problem that the quality varied greatly. In this case, it is conceivable to reduce the oxygen defect portion and reduce the diffusion rate of the transition metal by performing the firing treatment in an oxygen atmosphere, thereby suppressing the sintering of the particles, but under these treatment conditions, the crystals are crystalline. Could not be high enough.

On the other hand, as described above, in the production method of the embodiment of the present invention, in the low temperature region below the threshold temperature, the lithium mixture is heat-treated in a low oxidizing gas atmosphere having an oxygen concentration of 20% by volume or more and 30% by volume or less. By applying the above, an appropriate oxygen defect portion is introduced into the crystal structure of the transition metal composite hydroxide particles and the lithium transition metal composite oxide particles before the crystallinity is enhanced, so that it is possible to promote crystal growth. become. On the other hand, in the high temperature region after the above threshold temperature at which the diffusion rate of the transition metal becomes remarkably high is exceeded, the lithium mixture is heat-treated in a highly oxidizing gas atmosphere having an oxygen concentration of 40% by volume or more. Since the oxygen defects on the surface of the oxide particles and / or the oxide particles are reduced, the diffusion of the transition metal is suppressed, and as a result, the lithium transition metal composite oxide particles are suppressed from sintering with each other. Can be done. The upper limit of the oxygen concentration in the high temperature region is not particularly limited, but 100% by volume is preferable.

2.4 Crushing step As described above, in the firing step S3, heat treatment is performed under conditions that are difficult to sinter, but due to sintering necking between secondary particles, the lithium transition metal composite oxide particles after the firing process are coagulated. May include aggregates and lightly sintered sintered bodies. Therefore, it is preferable to apply mechanical energy to the agglomerates and sintered bodies of the lithium transition metal composite oxide particles to crush them by going through the crushing step S6 as necessary. Thereby, the average particle size and the particle size distribution of the finally obtained positive electrode active material can be adjusted within a suitable range.

The device for performing this crushing is not particularly limited as long as it can loosen the agglomerates and sintered bodies without destroying the secondary particles themselves, and for example, a pin mill or a hammer mill is preferable. Can be used. When crushing using these devices, pre-sampled lithium transition metal composite oxide particles are used to investigate the crushing state when conditions such as the rotation speed of the crushing device are changed. As a result, it is preferable to obtain conditions such as the number of rotations at which an appropriate crushing force that does not destroy the secondary particles acts, and to perform the crushing treatment under those conditions.

3. 3. Positive Active Material for Lithium Ion Secondary Battery The positive positive active material produced by the above method for producing a lithium transition metal composite oxide according to the embodiment of the present invention includes, for example, lithium, nickel and manganese as essential elements, and optional elements. a lithium-nickel-manganese composite oxide containing cobalt and additive element M, the formula B _{is, Li 1 + u Ni x Mn} y Co z M t O 2 + β (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1 , 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, -0.2 ≤ β ≤ 0.2, M , Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W). This composite oxide has a hexagonal layered crystal structure.

(A) Volume average particle size ratio In the positive electrode active material produced by the production method of the above embodiment of the present invention, the median diameter D50 of the positive electrode active material is used as a precursor of the positive electrode active material, which is a transition metal composite hydroxylation. The ratio of D50 obtained by dividing by the median diameter D50 of the particles "hereinafter, also referred to as D50 (positive electrode material) / D50 (precursor)" can be less than 1.05. That is, since the particle size does not increase significantly before and after the firing process in the firing step S3, variations in quality can be suppressed.

When "D50 (positive electrode material) / D50 (precursor)", which is the ratio of the median diameter D50 of the particles before and after the firing treatment, is 1.05 or more, the ratio of aggregates and sintered bodies contained in the positive electrode active material. Therefore, the battery characteristics of the lithium ion secondary battery using this positive electrode active material as the positive electrode material may deteriorate. The median diameter D50 of the positive electrode active material and the transition metal composite hydroxide particles can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size analyzer.

(B) Crystallet diameter In the positive electrode active material produced by the above-mentioned production method of the embodiment of the present invention, the (003) plane diffraction peak is measured by the X-ray diffraction method (XRD), and the peak width is substituted into the Scheller equation. The crystallite diameter (hereinafter, (003) plane crystallite diameter) obtained by the above can be preferably 1000 Å (100 nm) or more, and more preferably 1200 Å (120 nm) or more. In a secondary battery using a positive electrode active material having a high crystalline (003) planar crystallite diameter of 1000 Å or more as a positive electrode material, the positive electrode resistance is lowered, so that the output characteristics are improved and the thermal stability is also improved. On the other hand, when the (003) plane crystallite diameter is less than 1000 Å, the crystallinity may be insufficient or the thermal stability of the secondary battery may be lowered. The (003) plane crystallite diameter can be adjusted by appropriately changing the firing temperature and holding time in the firing step S3.

4. Lithium-ion secondary battery 4.1 Non-aqueous electrolyte secondary battery The positive electrode active material produced by the production method of the above-described embodiment of the present invention is generally composed mainly of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. It can be suitably used as a material for the positive electrode of a non-aqueous electrolyte secondary battery, which is a typical lithium ion secondary battery. The shape of this non-aqueous electrolyte secondary battery is not particularly limited, and can be various shapes such as a cylindrical shape and a laminated shape. Regardless of the shape, the electrode body consisting of the positive electrode and the negative electrode arranged via the separator is impregnated with the non-aqueous electrolyte solution, and between the current collector of the positive electrode and the positive electrode terminal leading to the outside, and A non-aqueous electrolyte secondary battery is manufactured by connecting the current collector of the negative electrode and the negative electrode terminal leading to the outside by using a current collecting lead or the like, and housing the battery in a battery case to seal the battery. Can be done. Hereinafter, each component will be described.

(A) Positive electrode First, a conductive material and a binder are mixed with the powdered positive electrode active material produced by the production method of the above-described embodiment of the present invention, and the electric double layer capacity is further increased if necessary. Activated carbon for this purpose and a solvent for adjusting the viscosity are added, and these are kneaded to prepare a positive electrode mixture paste. The blending ratio of the materials constituting the positive electrode mixture paste affects the performance of the non-aqueous electrolyte secondary battery, so the blending ratio should be appropriate. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass and the conductive material is similar to the positive electrode of a general non-aqueous electrolyte secondary battery. The content of the binder is preferably 1 to 20 parts by mass, and the content of the binder is preferably 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and the solvent is evaporated by drying. In order to increase the electrode density, pressurization may be performed by a roll press or the like, if necessary. Thereby, after producing the sheet-shaped positive electrode, the positive electrode can be produced by cutting the positive electrode into an appropriate size according to the target battery shape. The method for producing the positive electrode is not limited to this, and other methods may be used for producing the positive electrode.

As the conductive material used as the raw material of the positive electrode mixture paste, for example, graphite such as natural graphite, artificial graphite, expanded graphite, or carbon black material such as acetylene black or Ketjen black can be used. The binder plays a role of binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, or poly. Acrylic acid or the like can be used. Further, the above-mentioned positive electrode active material, the conductive material and the activated carbon to be added as needed may be dispersed, and a solvent having a role of dissolving the binder may be added to the positive electrode mixture. As this solvent, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

(B) Negative electrode For the negative electrode, prepare a negative electrode active material that can occlude and desorb lithium ions, such as metallic lithium or lithium alloy, and add a binder and an appropriate solvent to the negative electrode and knead it to form a paste. To prepare a negative electrode mixture of. This negative electrode mixture paste is applied to the surface of a metal leaf current collector such as copper, dried, and compressed as necessary to increase the electrode density. Thereby, the negative electrode can be manufactured.

As described above, a substance containing lithium such as metallic lithium or a lithium alloy may be used for the negative electrode, or an organic compound calcined body such as natural graphite, artificial graphite or phenol resin capable of occluding / desorbing lithium ions. Alternatively, a powder of a carbon substance such as coke may be used. As with the positive electrode, a fluororesin such as PVDF can be used as the binder for the negative electrode, and N-methyl-2-pyrrolidone or the like can be used as the solvent for dispersing these active substances and the binder. Organic solvent can be used.

(C) Separator The separator plays a role of separating the positive electrode and the negative electrode by interposing between the positive electrode and the negative electrode and holding an electrolyte. Therefore, the material of this separator is preferably, but not limited to, a thin film made of, for example, polyethylene or polypropylene having innumerable fine pores.

(D) Non-aqueous electrolyte solution As the non-aqueous electrolyte solution, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent is preferably used, but a solution in which a lithium salt is dissolved in an ionic liquid may also be used. The ionic liquid is a salt composed of cations and anions other than lithium ions and showing a liquid state even at room temperature. In addition, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, or the like in order to improve the battery characteristics.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. On the other hand, the organic solvent includes cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, tetrahydrofuran and 2-methyl. One selected from the group consisting of ether compounds such as tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or these groups may be used alone. 2 or more types may be mixed and used.

4.2 All-solid-state secondary battery The positive electrode active material produced by the manufacturing method of the embodiment of the present invention described above is also suitable as a positive electrode material for an all-solid-state secondary battery, which is expected as a next-generation lithium-ion secondary battery. Can be used for. As the solid electrolyte used in this all-solid secondary battery, it is preferable to use one having a property of being able to withstand a high voltage. Examples of such a solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte. As the former inorganic solid electrolyte, an oxide-based solid electrolyte or a sulfide-based solid electrolyte is preferably used.

The oxide-based solid electrolyte is not limited, but preferably contains oxygen (O) and has lithium ion conductivity and electronic insulation. Specifically, lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _{4- Li 3} PO ₄ , Li ₄ SiO _{4 -Li 3} VO ₄ , Li ₂ O-B ₂ O _3- P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O _3- ZnO, Li _{1 + x} Al _x Ti _2-x (PO) ₄ ) ₃ (0 ≦ x ≦ 1), Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3x La _{2 / 3-x} TiO ₃ (0 ≦ x ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O _4th grade can be mentioned.

Further, as the sulfide-based solid electrolyte, those containing sulfur (S) and having lithium ion conductivity and electron insulating property are preferably used, although not limited to the above. Specifically, Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li _{2 SP 2} S ₅ , LiI-Li _{2 SB 2} S _{3, Li 3 PO 4 -Li 2} S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O 5, LiI-Li ₃ PO _4- P ₂ S _{5 and the} like can be mentioned.

Further, may be used an inorganic solid electrolyte other than the above, for _example, can be cited Li ₃ N, LiI, and Li 3 N-LiI-LiOH and the like. On the other hand, the latter organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. The organic solid electrolyte may contain a supporting salt (lithium salt).

The positive electrode active material and the method for producing the same, and the method for producing a lithium ion secondary battery using the positive electrode active material have been described above, but the present invention is limited to the above embodiment. However, it includes various modified examples and alternative examples. That is, the scope of rights of the present invention extends to the scope of claims and the equivalent scope thereof. Next, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

First, in order to prepare a precursor of the positive electrode active material by a general wet method, an aqueous solution of a raw material containing a transition metal compound, an aqueous solution containing an ammonium ion feeder acting as a complexing agent, and an alkaline aqueous solution are prepared. By supplying these to a reaction vessel and crystallizing them, a nickel-manganese-cobalt composite hydroxide as a precursor was produced. When preparing the raw material aqueous solution, the blending ratio of the compound of the metal element was adjusted to nickel: cobalt: manganese: tungsten = 0.375: 0.319: 0.299: 0.007 on a molar basis.

This composite hydroxide is placed in an alumina saggar, charged into a roller hersquithium simulator furnace (manufactured by Noritake Company, Ltd.), dried in an air atmosphere of 105 ° C for 3 hours, and then separately prepared water. Lithium oxide was added, and this was charged into a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) and mixed to obtain a lithium mixture. The lithium hydroxide was blended so that the Li / Me ratio of the lithium mixture was 1.1.

The lithium mixture obtained above was placed in an alumina saggar and charged into a roller herskill simulator furnace (manufactured by Noritake Company, Inc.), and firing treatment was performed according to the temperature profile shown in FIG. During this firing process, the atmosphere inside the furnace is set to a low oxidizing gas atmosphere with an oxygen concentration of 21% by volume (that is, the atmosphere) in the low temperature range from room temperature to 850 ° C. The atmosphere was a highly oxidizing gas atmosphere having an oxygen concentration of 75% by volume. In this way, a lithium nickel-manganese-cobalt composite oxide of Sample 1 having a composition formula of LiNi _0.375 Co _0.319 Mn _0.299 W _0.007 O _{2 was prepared.}

Lithium nickel-manganese-cobalt composite oxides of Samples 2 to 8 were prepared in the same manner as in Sample 1 except that the treatment conditions during the firing treatment were variously changed. In particular, sample 6 was fired based on the temperature profile shown in FIG. 2 and the atmosphere inside the furnace. The D50 (positive electrode material) of the positive electrode active material of the lithium nickel manganese cobalt composite oxide of these samples 1 to 8 was obtained from the volume distribution measured by the laser light diffraction scattering type particle size distribution meter, and this was obtained from the volume distribution, which is the precursor of the transition metal. The composite hydroxide particles were divided by D50 (precursor) measured by the same method, and the change in particle size due to the firing treatment was examined. Further, the crystallite diameter [Å] of the positive electrode active material was determined by substituting the (003) plane diffraction peak width measured by the XRD method into the Scheller equation. The results are shown in Table 1 below together with the processing conditions for the firing process.

From the results in Table 1 above, the lithium nickel-manganese-cobalt composite oxides of Samples 1 to 4 produced by the production method satisfying the requirements of the present invention are all of the above-mentioned "D50 (positive electrode material) / D50 (precursor)". The value was less than 1.05 and the crystallite diameter exceeded 1300 Å. On the other hand, the lithium nickel-manganese-cobalt composite oxide of Samples 5 to 8 produced by the production method not satisfying the requirements of the present invention has a value of "D50 (positive electrode material) / D50 (precursor)" of 1.05. The above, or the crystallite diameter became less than 1200 Å.

The present invention includes a positive electrode active substance manufacturing method, and a method for manufacturing a lithium ion secondary battery using the positive electrode active material produced in the production method for the lithium ion secondary battery.

Claims (6)

A method for producing a positive electrode active material composed of a lithium transition metal composite oxide produced by heat-treating a mixture of a transition metal composite hydroxide as a precursor and a lithium compound, wherein the heat treatment is below a predetermined threshold temperature. In the low temperature range of the above, perform in a low oxidizing gas atmosphere having an oxygen concentration of 20% by volume or more and 30% by volume or less, and in a high temperature range exceeding the predetermined threshold temperature, perform in a highly oxidizing gas atmosphere having an oxygen concentration of 40% by volume or more. A characteristic method for producing a positive electrode active material. The method for producing a positive electrode active material according to claim 1, wherein the threshold temperature is in the range of 700 ° C. or higher and 900 ° C. or lower. The transition metal complex hydroxide is a composition formula _{Ni x Mn y Co z M t} (OH) 2 + α (x + y + z + t = 1,0.3 ≦ x ≦ 0.95,0.05 ≦ y ≦ 0.55,0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0.20 ≦ α ≦ 0.20, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta The method for producing a positive electrode active material according to claim 1 or 2, wherein the method is represented by one or more additive elements selected from the group consisting of, and W. The lithium transition metal composite oxide, a composition formula _{Li 1 + u Ni x Mn y} Co z M t O 2 + β (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0.20 ≦ β ≦ 0.20, M is Mg, Ca, Al, Ti, V, The method for producing a positive electrode active material according to claim 3, wherein the method is represented by one or more additive elements selected from the group consisting of Cr, Zr, Nb, Mo, Hf, Ta, and W). The method for producing a positive electrode active material according to any one of claims 1 to 4, wherein the lithium compound is lithium carbonate, lithium hydroxide, or a mixture thereof. A lithium ion secondary battery composed of at least a positive electrode, a negative electrode, and an electrolyte, and a positive electrode active material produced by the production method according to any one of claims 1 to 5 is used as the positive electrode material of the positive electrode. A method for manufacturing a lithium ion secondary battery.

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