Lithium nickel manganese composite oxide particles, positive electrode plate, lithium-ion secondary battery

Abstract

The present invention provides lithium nickel manganese composite oxide particles that have a hollow structure that allows for high battery capacity and output characteristics, while reducing the amount of residual solvent and suppressing defects during battery manufacturing. [Solution] Lithium nickel manganese composite oxide particles used as a positive electrode active material for lithium-ion secondary batteries, The lithium nickel manganese composite oxide particles contain secondary particles formed by the aggregation of primary particles containing lithium nickel manganese composite oxide having a hexagonal crystal structure with a layered structure. The secondary particle has a hollow structure comprising an outer shell and a hollow portion formed inside the outer shell. The lithium nickel manganese composite oxide particles contain 20% or more of the total number of secondary particles, each having through-holes that penetrate the outer shell portion from the outside of the outer shell portion to the hollow portion.

Description

[Technical Field]

[0001] This invention relates to lithium nickel manganese composite oxide particles, a positive electrode plate, and a lithium-ion secondary battery. [Background technology]

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of small, lightweight, non-aqueous electrolyte rechargeable batteries with high energy density. Furthermore, there is a strong demand for the development of high-output rechargeable batteries for motor power supplies, particularly for power supplies in transportation equipment.

[0003] Lithium-ion batteries are a type of secondary battery that meets these requirements. Lithium-ion batteries consist of a negative electrode, a positive electrode, an electrolyte, etc., and the active materials of the negative and positive electrodes are materials that can detach and insert lithium.

[0004] For lithium-ion secondary batteries to achieve good performance (high cycle characteristics, low resistance, high output), the positive electrode material must be composed of particles with uniform and appropriate particle size.

[0005] Using a cathode material with large particle size and low specific surface area results in insufficient reaction area with the electrolyte, leading to increased reaction resistance and preventing the acquisition of a high-power battery. Furthermore, using a cathode material with a wide particle size distribution results in uneven voltage application to the particles within the electrode, causing selective degradation of the fine particles after repeated charging and discharging cycles, leading to a decrease in capacity.

[0006] To increase the power output of lithium-ion secondary batteries, it is effective to shorten the distance lithium ions travel between the positive and negative electrodes. Therefore, it is desirable to manufacture the positive electrode plate thinly, and from this perspective, using a positive electrode material with a small particle size is useful.

[0007] A positive electrode active material has been proposed that can ensure a sufficient reaction surface area with such electrolytes and consists of small, uniformly sized particles.

[0008] For example, Patent Document 1 discloses a positive electrode active material composed of a lithium nickel manganese composite oxide composed of a hexagonal lithium-containing composite oxide having a layered structure, having an average particle size of 2 to 8 μm, and an index indicating the spread of the particle size distribution, [(d90 - d10) / average particle size], being 0.60 or less, and having a hollow structure composed of an outer shell portion in which aggregated primary particles are sintered and a hollow portion existing inside thereof, which is a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0009] When this positive electrode active material is used in a non-aqueous secondary battery, it has a high capacity, good cycle characteristics, and enables high output, and a non-aqueous secondary battery composed of a positive electrode containing the positive electrode active material is said to have excellent battery characteristics.

[0010] Patent Document 2 discloses that the oil absorption amount with respect to NMP (N-methylpyrrolidone) measured by a method conforming to JIS K5101-13-1 is 30 mL or more and 50 mL or less per 100 g of powder, and Li a Fe w Ni x Mn y Co z O2 (1.0 < a / (w + x + y + z) < 1.3, 0.8 < w + x + y + z < 1.1), and discloses a positive electrode active material for a lithium ion battery containing at least three or more of the components of Fe, Ni, Mn, and Co.

[0011] This positive electrode active material is said to have excellent coating properties and high battery characteristics.

[0012] On the other hand, it is possible to improve battery performance by increasing the reaction area with the electrolyte. However, when the reaction area with the electrolyte is increased, the residual amount of the solvent used in the manufacturing process of the positive electrode layer in the positive electrode layer increases. And it has been pointed out that when the solvent residual amount increases, problems such as a large voltage drop and self-discharge during storage occur.

[0013] For example, Patent Document 3 discloses a non-aqueous electrolyte battery comprising a positive electrode containing a transition metal composite oxide containing lithium as a positive electrode active material, a negative electrode containing a carbon, metal or alloyable material capable of doping and undoping lithium as a negative electrode active material, and a non-aqueous electrolyte, wherein the average amount of N-methyl-2-pyrrolidone (NMP) remaining in the positive electrode and the negative electrode is 70 μl / m 2 There is disclosed a non-aqueous electrolyte battery having the following characteristics.

[0014] According to this battery, it is said that decomposition of NMP is reduced, and an excellent non-aqueous electrolyte battery with less potential drop and self-discharge during long-term storage can be realized.

[0015] Further, Patent Document 4 discloses a method for manufacturing an electrode for a secondary battery, which includes a first drying step of drying a wet electrode in which a coating agent containing an active material, a binder, and N-methyl-2-pyrrolidone is applied to a current collector, and during or after the first drying step, a coating material solution composed of a low-boiling solvent having a lower boiling point than N-methyl-2-pyrrolidone and dissolving N-methyl-2-pyrrolidone and a coating material dissolved or dispersed in the low-boiling solvent is brought into contact with the wet electrode to extract N-methyl-2-pyrrolidone contained in the wet electrode into the coating material solution to form a NMP-reduced wet electrode, and a second drying step of drying the NMP-reduced wet electrode to form a coating layer made of the coating material on the surface of the active material, which are performed in this order.

[0016] According to this manufacturing method, it is said that an electrode for a secondary battery that can reduce the amount of residual NMP without degrading the coating workability on the current collector and can withstand high-voltage driving can be provided.

[0017] In order to evaluate the influence of the residual solvent during the formation of such a positive electrode layer, a method for accurately evaluating the residual solvent is required, and proposals have also been made regarding such an evaluation method.

[0018] For example, Patent Document 5 discloses a method for evaluating the solvent drying properties of a positive electrode active material by applying a positive electrode mixture paste, obtained by mixing a positive electrode active material, a conductive additive, a binder, and a solvent, onto a current collector, drying it, and then measuring the amount of solvent residue on the electrode piece obtained by cutting it. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] International Publication No. 2012 / 131881 [Patent Document 2] International Publication No. 2010 / 064504 [Patent Document 3] Japanese Patent Publication No. 2002-252038 [Patent Document 4] Japanese Patent Publication No. 2013-254698 [Patent Document 5] Japanese Patent Publication No. 2018-73643 [Overview of the Initiative] [Problems that the invention aims to solve]

[0020] In recent years, there has been a growing movement to use lithium-ion secondary batteries in large-scale secondary batteries, with particular expectations for their use as power sources for hybrid and electric vehicles. When used as a power source for automobiles, lithium-ion secondary batteries that offer both high capacity and high output are desired.

[0021] The improvement in battery performance achieved by increasing the reaction area with the electrolyte, as described in Patent Documents 1 and 2, and the adverse effects of solvents remaining in the positive electrode layer, as described in Patent Documents 3 and 4, are contradictory, and it is necessary to achieve both.

[0022] Therefore, in view of the problems of the above-mentioned conventional technology, one aspect of the present invention aims to provide lithium nickel manganese composite oxide particles that have a hollow structure that can obtain high battery capacity and output characteristics, while reducing the amount of residual solvent and suppressing the occurrence of defects during battery manufacturing. [Means for solving the problem]

[0023] To solve the above problems, according to one aspect of the present invention, lithium nickel manganese composite oxide particles used as a positive electrode active material for lithium-ion secondary batteries, The lithium nickel manganese composite oxide particles contain secondary particles formed by the aggregation of primary particles containing lithium nickel manganese composite oxide having a hexagonal crystal structure with a layered structure. The secondary particle has a hollow structure comprising an outer shell and a hollow portion formed inside the outer shell. The lithium nickel manganese composite oxide particles provide lithium nickel manganese composite oxide particles in which 20% or more of the total number of secondary particles are through-hole-containing secondary particles having through-holes with an average diameter of 20 nm or more that penetrate the outer shell from the outside of the outer shell to the hollow part. [Effects of the Invention]

[0024] According to one aspect of the present invention, lithium nickel manganese composite oxide particles can be provided that have a hollow structure that provides high battery capacity and output characteristics, while reducing the amount of residual solvent and suppressing the occurrence of defects during battery manufacturing. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is an explanatory diagram of the through-hole-containing secondary particles contained in the lithium nickel manganese composite oxide particles according to this embodiment. [Modes for carrying out the invention]

[0026] The following describes embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below, and various modifications and substitutions can be made to the embodiments described below without departing from the scope of the present invention. In the following description, the notation "A to B" means "A or more and B or less".

[0027] The inventors of this invention conducted extensive research to solve the problems of the present invention. During their research, they found that when using a positive electrode active material composed of particles with a hollow structure to improve the battery capacity and output characteristics of lithium-ion secondary batteries, solvent residue tends to remain during the manufacturing of the positive electrode layer, increasing the occurrence of defects during battery manufacturing. However, they found that the amount of solvent residue can be reduced by using a particle structure with through holes, and that the occurrence of defects during battery manufacturing can also be suppressed, thus completing the present invention.

[0028] 1. Lithium nickel manganese composite oxide particles The lithium nickel manganese composite oxide particles of this embodiment (hereinafter sometimes simply referred to as "composite oxide particles") can be used as a positive electrode active material for lithium-ion secondary batteries (hereinafter sometimes simply referred to as "positive electrode active material"). The composite oxide particles of this embodiment may contain secondary particles formed by the aggregation of primary particles containing lithium nickel manganese composite oxide having a layered hexagonal crystal structure. The composite oxide particles of this embodiment can also consist only of the above secondary particles, but this does not eliminate the possibility of impurities being introduced during the manufacturing process. (1) Structure and number ratio of secondary particles and through-hole-containing secondary particles As schematically shown in the cross-sectional view in Figure 1, the secondary particles contained in the composite oxide particles of this embodiment can have a hollow structure having an outer shell portion 11 and a hollow portion 12 formed inside the outer shell portion 11. When the composite oxide particles of this embodiment are used as the positive electrode active material of a lithium-ion secondary battery (hereinafter sometimes simply referred to as "battery"), the hollow portion 12 inside the particle, specifically the inner circumferential surface of the outer shell portion 11, can be used as the reaction interface. Therefore, the reaction area between the composite oxide particles of this embodiment and the electrolyte can be increased.

[0029] The composite oxide particles of the present embodiment can include through-hole-containing secondary particles 10 having through-holes 13 with an average diameter of 20 nm or more that penetrate the outer shell portion 11 from the outside of the outer shell portion 11 to the hollow portion 12. The number of through-holes 13 contained in the through-hole-containing secondary particles 10 is not particularly limited, and for example, it can have one or more.

[0030] And the composite oxide particles of the present embodiment contain through-hole-containing secondary particles at 20% or more of the total number of secondary particles.

[0031] The average diameter, which is the average value of the diameters D13 of the through-holes 13 of the through-hole-containing secondary particles 10, is more preferably 25 nm or more.

[0032] In the through-hole-containing secondary particles 10, the electrolyte sufficiently penetrates from the outside of the outer shell portion 11 into the hollow portion 12, and the insertion and extraction of lithium also occur at the reaction interface on the surface of the primary particles on the hollow portion 12 side inside the particles. Further, the through-holes 13 facilitate the movement of Li ions and electrons, and can reduce the resistance of the positive electrode when the battery is charged and discharged.

[0033] The through-hole-containing secondary particles 10 preferably have an average volume of the through-holes 13 of 1×10 5 nm 3 or more, more preferably 3×10 5 nm 3 or more, and even more preferably 5×10 5 nm 3 or more. By setting the average volume of the through-holes 13 within the above range, the penetration of the electrolyte from the outside of the outer shell portion 11 into the hollow portion 12 can be made easier.

[0034] The upper limit values of the average diameter and average volume of the through-holes 13 in the through-hole-containing secondary particles 10 are not particularly limited as long as the through-hole-containing secondary particles 10 can have sufficient strength. For example, the average diameter may be 200 nm or less. Also, the average volume may be 5×10 7 nm 3 or less. (Regarding the average diameter and volume of the through-holes) The diameter D13 of the through-hole 13 in the through-hole-containing secondary particle 10 is determined by using the area of ​​the opening on the secondary particle surface in the through-hole 13 as the diameter of a circle with the same area. In other words, the diameter D13 of the through-hole 13 corresponds to the circular equivalent diameter (circular conversion diameter) of the opening of the through-hole 13 on the secondary particle surface of the through-hole-containing secondary particle 10.

[0035] As a method for evaluating the average diameter of through-holes, for example, the evaluation method disclosed in Japanese Patent Publication No. 2022-127593 can be used, and the average diameter of the through-holes 13 can be determined by the following procedure. The composite oxide particles to be evaluated are embedded in resin, and the cross-section of the secondary particles contained in the composite oxide particles is repeatedly obtained by FIB cross-section processing and observed with a scanning electron microscope (SEM) to construct a three-dimensional image of the secondary particles. The presence or absence of through-holes is confirmed from the three-dimensional image constructed by binarizing the particle portion and the void portion, and the diameter D13 of the through-hole 13 is determined from the area of ​​the opening of the through-hole 13 confirmed in the outer shell of the secondary particle. Then, for example, 10 or more secondary particles are evaluated using three-dimensional images, and the average value (arithmetic mean) of the diameter D13 of the through-holes 13 contained in the evaluated through-hole-containing secondary particles can be taken as the average diameter of the through-holes 13.

[0036] The volume of each part of the through-hole-containing secondary particle 10 can be determined by summing the areas of each cross-section that make up the three-dimensional image, and the volume can be determined separately for the entire particle, the outer shell portion, and the void portion. Therefore, the volume of the portion corresponding to the through-hole 13 contained in the through-hole-containing secondary particle 10 can be taken as the volume of the through-hole 13 of the through-hole-containing secondary particle 10. Then, for example, if 10 or more secondary particles are evaluated, the average value (arithmetic mean) of the volume of the through-hole 13 contained in the evaluated through-hole-containing secondary particles can be taken as the average volume of the through-hole 13. (Percentage of secondary particles containing through-holes) As mentioned above, it is preferable that the proportion of through-hole-containing secondary particles in the total number of secondary particles (hereinafter sometimes simply referred to as the "proportion of through-hole-containing secondary particles") is 20% or more. When the proportion of through-hole-containing secondary particles is 20% or more, even in secondary particles where through-holes cannot be confirmed, it is considered that there are a sufficient number of through-holes between the primary particles contained in the outer shell, formed by grain boundaries or voids that allow the electrolyte to penetrate into the hollow portion. In secondary particles with through-holes formed by grain boundaries or voids that allow the electrolyte to penetrate into the outer shell, the surface of the primary particles inside the particle acts as a reaction interface, similar to through-hole-containing secondary particles, and lithium insertion and removal, as well as the movement of Li ions and electrons, occur.

[0037] Therefore, by using composite oxide particles having a secondary particle content of 20% or more, preferably 30% or more, of the above-mentioned through-holes as the positive electrode active material, the resistance of the positive electrode active material as a whole during charging and discharging of the battery can be reduced, and the output characteristics of the battery can be improved.

[0038] The proportion of secondary particles containing through-pores does not need to be determined from all secondary particles contained in the composite oxide particles. Instead, a certain number of secondary particles, for example 10 or more, can be randomly selected from the composite oxide particles, and the presence and shape of through-pores can be measured to determine the proportion of secondary particles containing through-pores.

[0039] When forming the positive electrode layer of a battery, it is common practice to mix the positive electrode material containing the positive electrode active material with a solvent to form a paste, coat it, and then dry it to remove the solvent. In this process, if composite oxide particles consisting of hollow particles are used as the positive electrode active material, the solvent will penetrate into the interior of the hollow particles. If solvent remains inside the hollow particles after the formation of the positive electrode layer, the remaining solvent will inhibit contact between the electrolyte and the primary particle surface inside the hollow particles. As a result, the primary particle surface will not function adequately as a reaction interface, leading to a decrease in the battery's output characteristics and causing defects.

[0040] In the case of secondary particles containing through-holes as described above, the solvent used to form the positive electrode layer of the battery can be discharged to the outside through the through-holes, making it easier to remove and reducing the amount of residual solvent. Furthermore, when the proportion of secondary particles containing through-holes is 20% or more, even in secondary particles where through-holes cannot be confirmed, it is considered that there are a sufficient number of through-holes between the primary particles contained in the outer shell, formed by grain boundaries or voids through which the solvent can penetrate. Therefore, even in secondary particles where through-holes cannot be confirmed, the solvent can be discharged to the outside through the through-holes formed by grain boundaries and voids, making it easier to remove.

[0041] Here, the aforementioned grain boundaries or voids in the composite oxide particles form minute through-pores that are too small to be detected, and the absence of detectable through-pores in secondary particles within the composite oxide particles does not mean that there are no through-pores at all.

[0042] Therefore, by including secondary particles with through-holes as described above in 20% or more of the total number of particles, solvent removal from the composite oxide particles becomes easier, and the amount of residual solvent in the formed positive electrode layer can be reduced. As a result, the occurrence of defects due to a decrease in output characteristics during battery manufacturing can be suppressed. (Average thickness of the outer shell) The average thickness T11 of the outer shell 11 is preferably 400 nm or more, and more preferably 500 nm or more. By setting the average thickness of the outer shell 11 to 400 nm or more, the strength of the composite oxide particles can be increased, which suppresses particle breakage and generation of fine particles, leading to deterioration of performance, during powder handling and when used as the positive electrode layer of a battery.

[0043] The average thickness of the outer shell 11 is not limited to an upper limit as long as a sufficiently large hollow structure is formed, but it is preferably 45% or less, and more preferably 38% or less, in terms of the ratio to the particle size of the composite oxide particles. By setting the average thickness of the outer shell 11 to 45% or less in terms of the ratio to the particle size of the composite oxide particles, the solvent can be easily evaporated from the positive electrode layer, and the amount of residual solvent can be particularly reduced.

[0044] The average thickness of the outer shell 11 can be determined by cross-sectional observation of secondary particles. For example, composite oxide particles are embedded in resin, and after enabling cross-sectional observation of the secondary particles contained in the composite oxide particles by FIB cross-sectional processing, the particles are observed using a scanning electron microscope (SEM). The obtained cross-sectional observation image is binarized, and the thickness of the outer shell is measured at each part of the recognized particle region, and the average thickness is calculated. (2) Particle size characteristics of lithium nickel manganese composite oxide particles (Average particle size) The composite oxide particles can preferably have an average particle size of 2 μm to 10 μm, more preferably 3 μm to 8 μm.

[0045] By setting the average particle size within the above range, the packing density of the particles when forming the positive electrode layer can be increased, thereby increasing the battery capacity per unit volume of the positive electrode. Furthermore, by setting the average particle size within the above range, the specific surface area of ​​the positive electrode active material can be set within an appropriate range, thereby ensuring a sufficient interface with the battery electrolyte. As a result, when applied to a battery, the resistance of the positive electrode can be reduced, improving the battery's output characteristics. (An indicator showing the extent of particle size distribution) The composite oxide particles preferably have a particle size distribution index of [(d90-d10) / average particle size] of 0.60 or less, and more preferably 0.55 or less.

[0046] By setting the index indicating the extent of particle size distribution to the above range, the presence of very small particles relative to the average particle size and very large coarse particles relative to the average particle size can be reduced. This suppresses adverse effects on battery characteristics caused by localized reactions of fine particles and deterioration of cycle characteristics due to selective degradation of fine particles. Furthermore, by reducing the presence of coarse particles, a sufficient reaction area between the electrolyte and the positive electrode active material can be secured, reducing reaction resistance and increasing battery output.

[0047] The method for determining the average particle size, d90, and d10 is not particularly limited, but for example, it can be determined from the integrated volume measured by a laser diffraction scattering particle size analyzer. Furthermore, d90 refers to the particle size at which, when the number of particles at each particle size is accumulated from the smallest particle size, the accumulated volume accounts for 90% of the total volume of all particles. Similarly, d10 refers to the particle size at which, when the number of particles is accumulated, the accumulated volume accounts for 10% of the total volume of all particles. (3) Composition of lithium nickel manganese composite oxide particles The composition of the composite oxide particles in this embodiment is not particularly limited, but for example, it can contain lithium, nickel, manganese, cobalt, and element M. The composite oxide particles in this embodiment can contain lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co), and element M (M) in a molar ratio of Li:Ni:Mn:Co:M = 1 + u:x:y:z:t. The composite oxide particles in this embodiment can be particles containing a composite oxide having a hexagonal crystal structure with a layered structure. The above composite oxide particles can also be particles made of the above composite oxide, but even in this case, the presence of impurities is not excluded.

[0048] Preferably, the above values ​​of u, x, y, z, and t satisfy -0.05≦u≦0.50, x+y+z+t=1, 0.3≦x≦0.7, 0.1≦y≦0.55, 0≦z≦0.4, and 0≦t≦0.1. Furthermore, element M can be one or more elements selected from magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), and tungsten (W).

[0049] By setting the molar ratio within the above range, the outer shell 11 can be made to have sufficient thickness while also having through holes 13 with particularly appropriate average diameters, thereby increasing the reaction area with the electrolyte and improving battery characteristics, while reducing the amount of solvent remaining during positive electrode fabrication.

[0050] In the above-mentioned composite oxide particles, by setting u, which indicates the excess amount (deficiency amount) of lithium, within the above range, the reaction resistance of the positive electrode in the battery can be reduced, improving the battery output while suppressing a decrease in the battery's initial discharge capacity and an increase in the positive electrode's reaction resistance. To further reduce the reaction resistance, it is preferable to set u to 0.10 or higher, and more preferably to 0.35 or lower.

[0051] Furthermore, by setting x, y, and z, which represent the composition of Ni, Mn, and Co, within the above ranges, it is possible to achieve both good output characteristics and high battery capacity when composite oxide particles are used as the positive electrode active material of a battery and the positive electrode is constructed from them.

[0052] The composite oxide particles of this embodiment may also contain element M, which is an additive element. By including element M in the composite oxide particles, the durability and output characteristics of a battery using the composite oxide particles as a positive electrode active material can be particularly improved. By setting t, which indicates the amount of element M added, within the above range, the reduction of metal elements contributing to the Redox reaction can be reduced, thereby suppressing a decrease in battery capacity while achieving the desired effect.

[0053] Furthermore, when expressing the composition of composite oxide particles using a general formula, Li 1+u Ni x Mn y Co z M t O 2+α It can be expressed as follows. It is preferable that u, x, y, z, and t satisfy the previously described ranges, and that α satisfies -0.2 ≤ α ≤ 0.2.

[0054] 2. Method for producing lithium nickel manganese composite oxide particles The method for producing lithium nickel manganese composite oxide particles according to this embodiment (hereinafter sometimes simply referred to as "method for producing composite oxide particles") will be described below. First, the method for producing nickel manganese composite hydroxide particles that can be used as a precursor in the method for producing composite oxide particles according to this embodiment will be described, and then the method for producing composite oxide particles according to this embodiment will be described.

[0055] 2-1. Method for producing nickel-manganese composite hydroxide particles The precursor, nickel-manganese composite hydroxide particles (hereinafter sometimes simply referred to as "composite hydroxide particles"), can be produced, for example, by a crystallization reaction.

[0056] The method for producing composite hydroxide particles is not particularly limited, but for example, it may include (a) a nucleation step in which nucleation is performed, and (b) a particle growth step in which the nuclei produced (formed) in the nucleation step are grown. The resulting composite hydroxide particles serve as precursors for lithium nickel manganese composite oxide particles used as positive electrode active materials in lithium-ion secondary batteries.

[0057] A method for obtaining composite hydroxide particles by crystallization separated into a nucleation process and a particle growth process is disclosed, for example, in International Publication No. 2012 / 131881, and can narrow the particle size distribution of the resulting composite hydroxide particles. Furthermore, by selecting the conditions of the nucleation process and the particle growth process, the particle structure of the composite hydroxide particles can be made to consist of a central part containing fine primary particles and an outer shell containing plate-like primary particles larger than the fine primary particles.

[0058] In the nucleation process, for example, an aqueous solution of a metal compound is added to a pre-reaction aqueous solution that has been adjusted to a predetermined pH value to form a nucleation aqueous solution, which is the reaction aqueous solution, and crystallization can then be performed.

[0059] In the particle growth process, an aqueous solution of a metal compound is added to the particle growth aqueous solution containing the nuclei formed in the nucleation process to form a reaction aqueous solution for particle growth, and crystallization can be performed.

[0060] When adding an aqueous solution of a metal compound to the reaction solution, a pH-adjusting aqueous solution or a complexing agent may be added as needed to adjust the pH value of the reaction solution. The pH-adjusting aqueous solution is not particularly limited; for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be used. To lower the pH value of the reaction solution, the supply of the alkali metal hydroxide aqueous solution can be temporarily stopped, or an inorganic acid of the same type as the acid that constitutes the metal compound in the reaction solution, such as sulfuric acid, can be used as the pH-adjusting aqueous solution. As a complexing agent, one or more types selected from aqueous solutions of ammonia water, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc., can be used.

[0061] In the nucleation step, an aqueous solution of a metal compound can be added to the pre-reaction aqueous solution to form a nucleation aqueous solution, which is the reaction aqueous solution. The nucleation aqueous solution contains at least a metal compound containing nickel and a metal compound containing manganese. During the nucleation step, the pH value of the nucleation aqueous solution can be controlled to preferably be 11.5 to 14.0, more preferably 11.7 to 13.0, based on a liquid temperature of 25°C (hereinafter, the pH value based on a liquid temperature of 25°C may be simply referred to as "pH value"). The nucleation step can be carried out in an oxidizing atmosphere with an oxygen concentration of 1% by volume or more.

[0062] The particle growth process can grow the nuclei formed in the nucleation process described above. The particle growth process comprises a first particle growth process and a second particle growth process, and the process can be switched from the first particle growth process to the second particle growth process midway through the process.

[0063] In the first particle growth step, the aqueous particle growth solution containing the nuclei formed in the nucleation step can be controlled in an oxidizing atmosphere with an oxygen concentration exceeding 1% by volume, so that its pH value at a liquid temperature of 25°C is lower than the pH value of the aqueous nucleation solution in the nucleation step and is between 9.0 and 12.0.

[0064] In the second particle growth process, the oxygen concentration is 1% by volume or less, and the pH value of the aqueous solution for particle growth, based on a liquid temperature of 25°C, can be controlled to be within the same range as in the first particle growth process, in a non-oxidizing atmosphere containing an inert gas.

[0065] In the particle growth process, the process can be switched from the first particle growth process to the second particle growth process when 15% to 30% of the total crystallization time has elapsed, from the start of the nucleation process until the end of the particle growth process. The first particle growth process can be carried out from the start of the particle growth process until the above switchover time, after which the second particle growth process can be carried out.

[0066] By setting the timing of the switch to the second particle growth process within the above range, the ratio of the diameter of the central part to the thickness of the outer shell formed outside the central part can be made particularly appropriate in the composite hydroxide particles. Lithium nickel manganese composite oxide particles obtained from a precursor having such a structure have a hollow structure with an outer shell and a hollow part inside it. By having a hollow structure, when used as a positive electrode active material in a lithium-ion secondary battery, the reaction area with the electrolyte is increased, resulting in high battery capacity and output characteristics.

[0067] Switching to the second particle growth process can be done by changing the atmosphere of the crystallization reaction vessel to a non-oxidizing atmosphere and controlling the pH value of the particle growth aqueous solution.

[0068] As described above, in the first particle growth step, which is crystallization in an oxidizing atmosphere, the pH value at a liquid temperature of 25°C can be controlled to be lower than the pH value of the nucleation aqueous solution in the nucleation step, and to be between 9.0 and 12.0. Furthermore, in the crystallization after switching to a non-oxidizing atmosphere, i.e., the second particle growth step, the pH value can be controlled to be within the same range as in the first particle growth step.

[0069] In the first particle growth process, by using an oxidizing atmosphere and a pH value of 9.0 to 12.0, fine primary particles crystallize around the nuclei formed in the nucleation process, creating a central region. This central region is entirely formed by the aggregation of fine primary particles. Therefore, when mixed with a lithium compound and fired, the sintering of the primary particles proceeds easily, and the central region tends to shrink, forming a space.

[0070] On the other hand, in the second particle growth process, by using a non-oxidizing atmosphere and keeping the pH value within the same range as in the first particle growth process, the precipitation rate slows down and the primary particles grow more efficiently. This makes it easier to grow secondary particles to the desired particle size, and plate-like primary particles crystallize on the outer surface of the central part formed by crystallization in an oxidizing atmosphere, forming an outer shell.

[0071] Furthermore, in the first particle growth step and the second particle growth step, the pH value of the aqueous solution for particle growth should be controlled within the range described above, and the pH value of the aqueous solution for particle growth should be the same or different in the first particle growth step and the second particle growth step.

[0072] The nucleation process, the first particle growth process, and the second particle growth process can be carried out continuously using the same reaction vessel while controlling the atmosphere and the pH value of the reaction aqueous solution. However, the method is not limited to this configuration, and the second particle growth process can also be carried out in a different reaction vessel than the nucleation process and the first particle growth process.

[0073] The concentration of the aqueous solution of the metal compound supplied in the nucleation process and the particle growth process is not particularly limited, but can be, for example, 1.8 mol / L to 2.4 mol / L. By setting the concentration of the aqueous solution of the metal compound within the above range, the concentration of metal ions contained in the aqueous solution for nucleation and the aqueous solution for particle growth can be increased, thereby improving the uniformity of the particle size of the resulting composite hydroxide particles and also improving the tap density.

[0074] In the method for producing composite hydroxide particles in this embodiment, the crystallized particles obtained in the particle growth step can also be washed after solid-liquid separation to reduce impurities. Washing allows for control of the amount of impurities in the composite hydroxide particles. Washing can be carried out using conventional techniques; the washing solution and composite hydroxide particles are mixed to form a slurry, stirred, then solid-liquid separated and dried.

[0075] (Particle composition) The composite hydroxide particles described above can be particles containing nickel-manganese composite hydroxide, which contains Ni (nickel), Mn (manganese), Co (cobalt), and element M in a molar ratio of Ni:Mn:Co:M=x:y:z:t.

[0076] The above-mentioned composite hydroxide particles may also be particles made of the above-mentioned nickel-manganese composite hydroxide, but even in this case, the presence of impurities is not excluded. Preferably, x, y, z, and t satisfy x+y+z+t=1, 0.3≦x≦0.7, 0.1≦y≦0.55, 0≦z≦0.4, and 0≦t≦0.1. Furthermore, element M is an additive element and can be one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W.

[0077] When lithium nickel manganese composite oxide particles, manufactured using composite hydroxide particles having the above composition as a raw material, are used as the positive electrode active material in a battery, the measured resistance value of the positive electrode can be lowered, and the battery performance can be improved.

[0078] When composite hydroxide particles are used as a raw material to produce composite oxide particles, the composition ratio (Ni:Mn:Co:M) of these composite hydroxide particles is maintained in the resulting composite oxide particles. Therefore, it is preferable to adjust the composition ratio of the composite hydroxide particles in this embodiment to be the same as the composition ratio required for the composite oxide particles to be obtained.

[0079] When expressing the composition of the composite hydroxide particles in this embodiment using a general formula, Nix Mn y Co z M t (OH) 2+β It can be expressed as follows. It is preferable that x, y, z, and t satisfy the ranges described above, and it is preferable that β satisfies -0.2 ≤ β ≤ 0.2.

[0080] (Reaction atmosphere) The particle structure of the nickel-manganese composite hydroxide particles described above can be selected by controlling the atmosphere in the reaction vessel during the nucleation and particle growth processes. The atmosphere in the reaction vessel during the crystallization reaction can control the growth of the primary particles that form the nickel-manganese composite hydroxide particles. In an oxidizing atmosphere, low-density particles with many voids and containing fine primary particles are formed, while in a non-oxidizing atmosphere, dense and compact particles with large primary particles are formed. It should be noted that even in a non-oxidizing atmosphere, trace amounts of oxygen may be present, and the non-oxidizing atmosphere also includes a weakly oxidizing atmosphere.

[0081] In other words, for example, by using an oxidizing atmosphere for the nucleation process and the first particle growth process, a central part containing fine primary particles can be formed. Then, by switching from an oxidizing atmosphere to a non-oxidizing atmosphere in the subsequent second particle growth process, the above particle structure can be formed having an outer shell containing plate-like primary particles larger than the fine primary particles on the outside of the central part.

[0082] In the above-described atmosphere-controlled crystallization reaction, the primary particles in the central part typically take on one or more shapes selected from fine plate-like and needle-like forms, while the primary particles in the outer shell are plate-like. However, the primary particles of the nickel-manganese composite hydroxide may take on shapes such as rectangular parallelepipeds, ellipsoids, or ridged faces, depending on their composition, and their shape is not particularly limited.

[0083] The oxidizing atmosphere for forming the central core is defined as an atmosphere in the reaction vessel space where the oxygen concentration exceeds 1% by volume. The oxidizing atmosphere preferably has an oxygen concentration of 2% by volume, more preferably 10% by volume or more, and is particularly preferably an easily controllable atmospheric atmosphere (oxygen concentration: 21% by volume). The upper limit of the oxygen concentration is not particularly limited, but from the viewpoint of suppressing excessive miniaturization of primary particles, it is preferably 30% by volume or less.

[0084] The nucleation process and the first particle growth process can be carried out in an oxidizing atmosphere, but the oxygen concentration in the oxidizing atmosphere may differ between the nucleation process and the first particle growth process. However, from the viewpoint of productivity, it is preferable that the oxygen concentration in the oxidizing atmosphere be the same for both the nucleation process and the first particle growth process.

[0085] On the other hand, the non-oxidizing atmosphere for forming the outer shell is defined as an atmosphere in which the oxygen concentration in the reaction vessel space is 1% by volume or less. The non-oxidizing atmosphere is preferably controlled so that the oxygen concentration is 0.5% by volume or less, more preferably 0.2% by volume or less. The non-oxidizing atmosphere may also contain an inert gas and oxygen within the above range. For this reason, the non-oxidizing atmosphere can be a mixed atmosphere containing, for example, oxygen and an inert gas. Examples of inert gases include nitrogen gas and noble gases.

[0086] By maintaining an oxygen concentration of 1% by volume or less in the reaction vessel space and promoting particle growth, unwanted oxidation of the particles can be suppressed, and the growth of primary particles can be promoted. As a result, secondary particles can be obtained that are larger than the fine primary particles contained in the center, have uniform particle size, and possess a dense, compact outer shell. Means for maintaining such an atmosphere in the reaction vessel space include circulating an inert gas such as nitrogen into the space within the reaction vessel, and further, bubbling the inert gas into the reaction aqueous solution, i.e., the aqueous solution used for particle growth.

[0087] (Ammonia concentration) The ammonia concentration in the reaction aqueous solution is preferably 1 g / L or more and less than 3 g / L, and more preferably 1 g / L or more and 2.5 g / L. It is preferable to keep the fluctuation of the ammonia concentration in the reaction aqueous solution small during each step of the crystallization process, and it is even more preferable to maintain it at a constant value within the above range.

[0088] Ammonia acts as a complexing agent, and by keeping the ammonia concentration within the above range, the solubility of metal ions can be stabilized, allowing for the formation of particles with uniform shape and particle size. Furthermore, because the ammonia concentration is low, the fine primary particles in the center tend to become even finer, and the sintering of the primary particles during firing proceeds more easily, creating a more sufficient space in the center. On the other hand, the plate-like primary particles that form the outer shell tend to become smaller, increasing shrinkage during firing and making it easier for through-holes to form.

[0089] Therefore, by switching to the second particle growth process and controlling the ammonia concentration, the composite oxide particles produced using the obtained composite hydroxide particles can have through-holes with a particularly appropriate average diameter while maintaining a sufficiently thick outer shell. As a result, the reaction area between the composite oxide particles and the electrolyte can be increased, improving battery characteristics while reducing the amount of solvent remaining during the formation of the positive electrode layer.

[0090] In particular, when using a high-boiling point solvent such as N-methyl-2-pyrrolidone (hereinafter sometimes simply referred to as "NMP") as the solvent during cathode layer formation, the amount of residual solvent in the composite oxide particles can be effectively reduced.

[0091] The ammonium ion supplier is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc., can be used.

[0092] (Control of particle size of composite hydroxide particles) Since the particle size of the above-mentioned composite hydroxide particles can be controlled by the duration of the particle growth process, composite hydroxide particles having the desired particle size can be obtained by continuing the particle growth process until the particle grows to the desired size.

[0093] Furthermore, the particle size of the composite hydroxide particles can be controlled not only by the particle growth process but also by the pH value of the nucleation process and the amount of raw material introduced for nucleation.

[0094] In other words, by increasing the pH value during nucleation, or by lengthening the nucleation time, the amount of raw material input can be increased, thereby increasing the number of nuclei produced. This makes it possible to reduce the particle size of the composite hydroxide particles even when the particle growth process is performed under the same conditions.

[0095] On the other hand, by controlling the number of nuclei to be reduced, the particle size of the resulting composite hydroxide particles can be increased. To achieve an appropriate number of nuclei, the nucleation process time can be set to 1% to 2.5% of the total crystallization time.

[0096] The following describes the conditions for the metal compound, reaction solution temperature, etc. However, the only difference between the nucleation process and the particle growth process is the range to which the pH value and the atmosphere inside the reaction vessel can be controlled. The conditions for the metal compound, reaction solution temperature, etc., can be substantially the same in both processes.

[0097] (metal compound) As the metal compound, a compound containing the target metal element can be used. The composite hydroxide particles of this embodiment can contain nickel and manganese, and optionally cobalt and element M. Therefore, for example, as the metal compound, a compound containing nickel or a compound containing manganese can be used, and optionally, a compound containing cobalt or a compound containing element M can also be used.

[0098] Since the compounds used are preferably added as aqueous solutions, it is preferable to use water-soluble compounds, such as nitrates, sulfates, and hydrochlorides. For example, nickel sulfate, manganese sulfate, and cobalt sulfate can be preferably used. From the viewpoint of controlling the sulfate content of the complex hydroxide, it is preferable to use at least one type of sulfate metal compound in the crystallization step.

[0099] (Additional element) As previously described, the composite hydroxide of this embodiment may also contain element M, which is an additive element. Element M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W.

[0100] As the compound containing element M, it is preferable to use a water-soluble compound. For example, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, zirconium nitrate, niobium oxalate, ammonium molybdate, sodium tungstate, ammonium tungstate, and the like can be used.

[0101] To uniformly disperse the element M within the composite hydroxide particles, the compound containing the element M can be added to the reaction aqueous solution, which is the nucleation aqueous solution or particle growth aqueous solution, along with other metal elements, during the nucleation process or particle growth process. As described above, by adding the compound containing element M to the reaction aqueous solution during the nucleation process, the composite hydroxide particles can be co-precipitated with the added element uniformly dispersed within them.

[0102] However, the method of adding element M is not limited to the method described above. For example, the surface of the composite hydroxide particles can be coated with element M, which is the added element. In this case, element M will be mainly located on the surface side of the composite hydroxide particles.

[0103] Furthermore, the aforementioned metal compounds and compounds containing element M can be added to a reaction aqueous solution, such as a nucleation aqueous solution, as a single aqueous solution containing all the compounds, or some or all of the compounds can be added to the reaction aqueous solution as separate aqueous solutions.

[0104] (Reaction mixture temperature) During the nucleation and particle growth processes, the temperature of the reaction aqueous solutions (reaction solution) in the reaction vessel, namely the nucleation aqueous solution and the particle growth aqueous solution, is not particularly limited, but is preferably set to 20°C or higher, and more preferably to 50°C to 70°C. Setting the reaction solution temperature to 20°C or higher sufficiently increases solubility, making it particularly easy to control nucleation. On the other hand, setting the temperature to 70°C or lower suppresses the volatilization of ammonia, making it easy to control the ammonia concentration in the reaction solution. Furthermore, suppressing the volatilization of ammonia reduces the amount of ammonia supplied, thereby reducing costs.

[0105] (manufacturing equipment) In the method for producing composite hydroxide particles of this embodiment, it is preferable to use an apparatus that does not recover the product until the reaction is complete, such as a batch-type apparatus. For example, a commonly used batch reaction vessel equipped with a stirrer can be suitably used. By adopting a batch-type apparatus, the problem of growing particles being recovered together with the overflow liquid, as in a continuous crystallization apparatus that recovers the product by overflow, does not occur, so it is possible to obtain particles with a narrower particle size distribution and uniform particle size.

[0106] Furthermore, since it is necessary to control the reaction atmosphere, it is preferable to use an atmosphere-controllable apparatus, such as a sealed apparatus. By using an atmosphere-controllable apparatus, the resulting composite hydroxide particles can be easily given the desired structure during the nucleation and particle growth processes. In addition, since the nucleation and particle growth reactions can proceed almost uniformly, particles with excellent particle size distribution (particle size distribution), that is, particles with a narrow range of particle size distribution, can be obtained.

[0107] 2-2. Method for producing lithium nickel manganese composite oxide particles The method for producing lithium nickel manganese composite oxide particles according to this embodiment is a method for producing lithium nickel manganese composite oxide particles that will be used as a positive electrode active material in the positive electrode of a lithium-ion secondary battery. The method for producing lithium nickel manganese composite oxide particles according to this embodiment is not particularly limited and can be any method for producing composite oxide particles as described above. For example, it can be carried out using the composite hydroxide particles described above as a precursor, and other manufacturing conditions can be those of a conventional manufacturing method.

[0108] The composition of the composite oxide particles produced by the method for producing composite oxide particles of this embodiment is not particularly limited, but for example, Li, Ni, Mn, Co, and element M can be contained in a molar ratio of Li:Ni:Mn:Co:M = 1 + u:x:y:z:t. Furthermore, the composite oxide particles produced by the method for producing composite oxide particles of this embodiment can be particles containing a composite oxide having a hexagonal crystal structure with a layered structure. It should be noted that the above composite oxide particles can also be particles consisting of the above composite oxide, but even in this case, the presence of impurities is not excluded.

[0109] Preferably, the above values ​​of u, x, y, z, and t satisfy -0.05 ≤ u ≤ 0.50, x + y + z + t = 1, 0.3 ≤ x ≤ 0.7, 0.1 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, and 0 ≤ t ≤ 0.1. Furthermore, element M can be one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W.

[0110] Furthermore, when expressing the composition of composite oxide particles using a general formula, Li 1+u Ni x Mn y Co z M t O 2+α It can be expressed as follows. It is preferable that u, x, y, z, and t satisfy the previously described ranges, and that α satisfies -0.2 ≤ α ≤ 0.2.

[0111] The method for producing lithium nickel manganese composite oxide particles according to this embodiment may include a mixing step and a calcination step.

[0112] In the mixing process, nickel-manganese composite compound particles can be mixed with lithium compounds to form a lithium mixture. In the firing process, the lithium mixture formed in the mixing process can be fired in an oxidizing atmosphere at a firing temperature of 800°C to 980°C.

[0113] Furthermore, as nickel-manganese composite compound particles, composite hydroxide particles obtained by the method for producing composite hydroxide particles described above, or heat-treated composite hydroxide particles can be used. The heat-treated composite hydroxide particles can be obtained by heat-treating the composite hydroxide particles described above in a heat treatment step.

[0114] The following explains each step.

[0115] (Heat treatment process) As described above, in order to supply a heat-treated composite hydroxide particle in the mixing process, the method for producing composite oxide particles in this embodiment may also include a heat treatment step in which the composite hydroxide particles are heat-treated before the mixing process.

[0116] The heat treatment process involves heating nickel-manganese composite hydroxide particles to a temperature of 105°C to 750°C to remove moisture contained in the composite hydroxide particles. By performing this heat treatment process, the amount of moisture remaining in the particles until the firing process can be reduced to a certain level. This further reduces variations in the ratio of metal atoms and lithium atoms in the resulting composite oxide particles. For this reason, it is preferable to perform the heat treatment process in the manufacturing method of the composite oxide particles of this embodiment.

[0117] Furthermore, it is sufficient to remove moisture to the extent that there is no variation in the ratio of metal atoms and lithium atoms in the composite oxide particles; therefore, it is not necessary to convert all of the composite hydroxide in the composite hydroxide particles into nickel-manganese composite oxide. However, in order to further reduce the above variation, it is more preferable to heat the mixture to 500°C or higher and convert all of the composite hydroxide into nickel-manganese composite oxide.

[0118] By pre-determining the metal components contained in the composite hydroxide particles based on heat treatment conditions through analysis, and by determining the ratio with the lithium compound, the above-mentioned variations can be particularly suppressed.

[0119] (Mixing process) The mixing step involves mixing nickel-manganese composite compound particles, which are composite hydroxide particles or heat-treated composite hydroxide particles (hereinafter sometimes simply referred to as "heat-treated particles"), with a lithium-containing substance, such as a lithium compound, to obtain a lithium mixture.

[0120] In the mixing process, it is preferable to prepare a lithium mixture by mixing nickel-manganese composite compound particles, which are composite hydroxide particles or heat-treated particles, with a lithium compound so that the Li / Me ratio is 0.95 to 1.50. Li / Me refers to the ratio of the number of lithium atoms (Li) to the sum of the number of atoms of metals other than lithium contained in the lithium mixture, i.e., the sum of the number of atoms of nickel, manganese, cobalt, and element M (Me). The above Li / Me ratio is more preferably 1.00 to 1.50, and even more preferably 1.02 to 1.35.

[0121] Since the Li / Me ratio hardly changes before and after the firing process, the Li / Me ratio of the lithium mixture prepared in the mixing process becomes the Li / Me ratio in the composite oxide particles. Note that the Li / Me ratio in the composite oxide particles refers to the ratio of the number of lithium atoms (Li) to the sum of the number of atoms of metals other than lithium contained in the composite oxide particles, i.e., the sum of the number of atoms of nickel, manganese, cobalt, and element M (Me). Therefore, it is preferable to mix the lithium mixture so that the Li / Me ratio in the lithium mixture is the same as the Li / Me ratio in the composite oxide particles to be obtained.

[0122] The lithium compound used to form the lithium mixture is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium nitrate, and lithium carbonate, or a mixture of one or more selected from the above compounds, is preferred because it is readily available. In particular, considering ease of handling and stability of quality, the lithium compound is more preferably lithium hydroxide or lithium carbonate.

[0123] (Firing process) The calcination process involves calcining the lithium mixture obtained in the mixing process described above to form lithium nickel manganese composite oxide particles. When the lithium mixture is calcined in the calcination process, lithium diffuses and reacts with nickel manganese composite compound particles, such as composite hydroxide particles or heat-treated particles, to form lithium nickel manganese composite oxide particles.

[0124] The lithium mixture is fired at a temperature of 800°C to 980°C (firing temperature), more preferably at a temperature of 820°C to 960°C. Furthermore, the holding time at the above firing temperature is preferably at least 2 hours, and more preferably 4 to 24 hours. Holding for this duration ensures sufficient formation of composite oxide particles, further improving crystallinity.

[0125] Furthermore, in the firing process, the lithium mixture can be pre-fired at a temperature of 350°C to 800°C, preferably 450°C to 780°C (pre-fire temperature) before firing. The above pre-fire temperature is preferably lower than the firing temperature. The time for pre-fire at the above temperature (pre-fire temperature) is not limited, but it is preferable to hold it for about 1 to 10 hours, preferably 3 to 6 hours. Pre-fire allows for sufficient diffusion of the lithium, and more uniform composite oxide particles can be obtained.

[0126] The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an oxygen concentration of 18% to 100% by volume, and particularly preferably a mixed atmosphere of oxygen at the above oxygen concentration and an inert gas. For example, firing in air or an oxygen stream can increase crystallinity and particularly improve battery characteristics.

[0127] A crushing step may be performed after the firing process to crush the fired material, thereby eliminating the aggregation of secondary particles and further reducing the inclusion of coarse particles.

[0128] 3. Positive electrode plate, lithium-ion secondary battery The positive electrode plate of this embodiment may contain lithium nickel composite oxide particles according to one aspect of the present disclosure as the positive electrode active material.

[0129] The lithium-ion secondary battery of this embodiment (hereinafter sometimes simply referred to as "secondary battery") may include the positive electrode plate of this embodiment. Accordingly, the positive electrode of the secondary battery of this embodiment may include lithium nickel manganese composite oxide particles according to one aspect of the present disclosure. Hereinafter, an example of the configuration of the secondary battery of this embodiment will be described for each component.

[0130] The secondary battery of this embodiment has a structure substantially the same as a general lithium-ion secondary battery, except that the positive electrode material, more specifically the positive electrode active material, is a composite oxide particle as described above.

[0131] Specifically, the secondary battery of this embodiment has a structure comprising a case, a positive electrode plate (which is the positive electrode), a negative electrode plate (which is the negative electrode), a non-aqueous electrolyte, and a separator as needed, all housed within the case. More specifically, for example, when using a non-aqueous electrolyte, the positive electrode plate and the negative electrode plate are stacked with a separator in between to form an electrode body, the resulting electrode body is impregnated with the non-aqueous electrolyte, the positive electrode current collector of the positive electrode plate and the positive electrode terminal that is open to the outside are connected using current collector leads or the like, and the case is sealed to form the secondary battery of this embodiment.

[0132] It goes without saying that the structure of the secondary battery in this embodiment is not limited to the above example, and various shapes such as cylindrical or stacked can be adopted for its external form.

[0133] 3-1. Positive plate First, the positive electrode plate, which is a characteristic feature of the secondary battery of this embodiment, will be described. The positive electrode plate is a sheet-like material, and is formed, for example, by applying and drying a positive electrode composite paste containing the aforementioned composite oxide particles as the positive electrode active material to the surface of a current collector made of aluminum foil.

[0134] Therefore, as described above, the positive electrode plate of this embodiment can contain composite oxide particles according to one aspect of the present disclosure.

[0135] Furthermore, the positive electrode plate is processed appropriately according to the battery being used. For example, it may be cut to an appropriate size according to the intended secondary battery, or compressed using a roll press or similar method to increase electrode density.

[0136] The positive electrode composite paste is formed by adding a solvent to the positive electrode composite and kneading it. The positive electrode composite is formed by mixing the aforementioned powdered composite oxide particles with a conductive material and a binder.

[0137] Conductive materials are added to electrodes to provide them with appropriate conductivity. While the conductive material is not particularly limited, examples include graphite (natural graphite, artificial graphite, and expanded graphite, etc.) and carbon black-based materials such as acetylene black and Ketjenblack®.

[0138] The binder plays the role of holding the positive electrode active material particles together. The binder used in the positive electrode composite is not particularly limited, but examples of binders that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resins, and polyacrylic acid.

[0139] Furthermore, activated carbon may be added to the positive electrode composite material, and by adding activated carbon, the electrical double layer capacity of the positive electrode can be increased.

[0140] The solvent dissolves the binder, dispersing the positive electrode active material, conductive material, activated carbon, etc., within the binder. While the solvent is not particularly limited, organic solvents such as N-methyl-2-pyrrolidone can be used.

[0141] Furthermore, the mixing ratio of each substance in the positive electrode composite paste is not particularly limited. For example, if the solid content of the positive electrode composite material excluding the solvent is 100 parts by mass, the content of the positive electrode active material can be 60 to 99 parts by mass, the content of the conductive material can be 0.5 to 20 parts by mass, and the content of the binder can be 0.5 to 20 parts by mass, similar to the positive electrode of a general lithium-ion secondary battery.

[0142] 3-2. Other Configurations (Negative electrode plate) The negative electrode plate is a sheet-like component formed by applying a negative electrode composite paste to the surface of a metal foil current collector, such as copper, and drying it. Although the components and formulation of the negative electrode composite paste and the material of the current collector differ, this negative electrode plate can be formed in substantially the same manner as the positive electrode plate, and various treatments are performed as necessary, just as with the positive electrode plate.

[0143] The negative electrode composite paste is made by mixing the negative electrode active material and binder, and then adding a suitable solvent to form a paste.

[0144] The negative electrode active material can be, for example, a lithium-containing material such as metallic lithium or lithium alloy, or a storage material capable of intercalating and deintercalating lithium ions.

[0145] The absorbed material is not particularly limited, but for example, natural graphite, artificial graphite, calcined organic compounds such as phenolic resin, and powdered carbon materials such as coke can be used. When such an absorbed material is used as the negative electrode active material, a fluororesin such as PVDF can be used as a binder, similar to the positive electrode plate, and an organic solvent such as N-methyl-2-pyrrolidone or water can be used as the solvent for dispersing the negative electrode active material in the binder.

[0146] (Separator) A separator is placed between the positive and negative electrode plates when using a non-aqueous electrolyte, and has the function of separating the positive and negative electrodes and holding the electrolyte. The separator can be a thin membrane made of, for example, polyethylene or polypropylene, and can have many fine pores, but is not particularly limited as long as it has the above function.

[0147] (Non-aqueous electrolyte) As a non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0148] As a non-aqueous electrolyte, for example, a lithium salt dissolved in an organic solvent can be used as a supporting salt. Alternatively, a lithium salt dissolved in an ionic liquid may be used as a non-aqueous electrolyte. An ionic liquid is a salt composed of cations and anions other than lithium ions, and is liquid at room temperature.

[0149] As the organic solvent, one of the following may be used alone or in combination with another: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butanesultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0150] As supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts can be used. Furthermore, the non-aqueous electrolyte may contain radical scavengers, surfactants, and flame retardants.

[0151] Furthermore, solid electrolytes may be used as non-aqueous electrolytes. Solid electrolytes have the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0152] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0153] The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be suitably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4) and Li3PO4N. X LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 One or more types selected from O4, etc., can be used.

[0154] The sulfide-based solid electrolyte is not particularly limited, and for example, one or more that contain sulfur (S) and have lithium-ion conductivity and electronic insulation properties can be suitably used. For example, one or more sulfide-based solid electrolytes selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc. can be used.

[0155] Furthermore, other inorganic solid electrolytes may be used besides those mentioned above; for example, Li3N, LiI, Li3N-LiI-LiOH, etc., may be used.

[0156] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity; for example, polyethylene oxide, polypropylene oxide, or copolymers thereof can be used. The organic solid electrolyte may also contain a supporting salt (lithium salt).

[0157] (Shape and composition of secondary batteries) As described above, the secondary battery of this embodiment can be made into various shapes, such as cylindrical or stacked. Regardless of the shape adopted, when the secondary battery of this embodiment uses a non-aqueous electrolyte, the positive electrode plate and the negative electrode plate are stacked with a separator in between to form the electrode body. The resulting electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the positive electrode terminal that is open to the outside, and the negative electrode current collector and the negative electrode terminal that is open to the outside are connected using current collecting leads, etc., and the structure can be sealed in a battery case.

[0158] Furthermore, the secondary battery according to this embodiment is not limited to a form using a non-aqueous electrolyte solution as the non-aqueous electrolyte; for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery, can also be used. In the case of an all-solid-state battery, the components other than the positive electrode active material can be appropriately changed as needed.

[0159] As described above, the secondary battery according to this embodiment uses the composite oxide particles according to this embodiment as the positive electrode material, and therefore has excellent battery capacity and output characteristics. For this reason, the secondary battery according to this embodiment can be suitably used as a rechargeable battery for portable information terminals such as mobile phones, smartphones, tablets or notebook computers, portable music players, digital cameras, medical devices, HEVs, or clean energy vehicles such as EVs or PHEVs. [Examples]

[0160] The present invention will be described more specifically below with reference to the following examples. However, the present invention is not limited to the following examples. [Example 1] (1) Production of composite hydroxide particles (1-1) Nucleation process First, a capacity of 7m 3Water was added to the reaction vessel up to half its volume and stirred while the vessel temperature was set to 40°C. The reaction vessel was under an atmospheric environment (oxygen concentration: 21% by volume). The reaction vessel was kept under an atmospheric environment between the nucleation process and the first particle growth process. Appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia aqueous solution were added to the water in the reaction vessel to prepare a pre-reaction aqueous solution so that the pH value of the reaction solution in the vessel was 12.5, based on a liquid temperature of 25°C.

[0161] Next, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were dissolved in water to prepare a mixed aqueous solution with a concentration of 2.3 mol / L.

[0162] The above mixed aqueous solution and sodium tungstate aqueous solution were simultaneously added at a constant rate to the pre-reaction aqueous solution in the reaction vessel so that the molar ratio of each metal element was Ni:Mn:Co:Zr:W = 33:33:33:0.5:0.5 to prepare the reaction aqueous solution (nucleation aqueous solution). Simultaneously with the above mixed aqueous solution and sodium tungstate aqueous solution, 25% by mass ammonia aqueous solution and 25% by mass sodium hydroxide aqueous solution were also added to this reaction aqueous solution at a constant rate. Under these conditions, crystallization was performed for 2 minutes and 30 seconds while controlling the pH value (at 25°C) of the reaction aqueous solution to 12.0-12.9 (nucleation pH value) and the ammonia concentration to 1-2.5 g / L, thereby inducing nucleation. (1-2) Particle growth process After the nucleation process was completed, the supply of 25% by mass sodium hydroxide aqueous solution was temporarily suspended until the pH value of the reaction aqueous solution reached 11.0 based on a liquid temperature of 25°C. (1-2-1) First particle growth step After the pH of the reaction solution reached 11.0, the supply of 25% by mass sodium hydroxide solution to the reaction solution (particle growth solution) was resumed. After resumption, the ammonia concentration of the reaction solution was maintained within the same range as in the nucleation process, while the pH (based on 25°C) was controlled to be within the range of 9.5 to 11.6. Then, crystallization was continued at a constant rate to grow particles until the time the mixed solution was supplied in the nucleation process and the first particle growth process, i.e., the crystallization time, reached 50 minutes. At the end of the first particle growth process, the pH of the reaction solution was 10.7 based on a liquid temperature of 25°C. (1-2-2) Second particle growth step After the first particle growth step was completed, the supply of liquid to the reaction aqueous solution was stopped, and nitrogen gas was circulated at 5 L / min until the oxygen concentration in the reaction vessel space became a non-oxidizing atmosphere of 0.2% by volume or less. During the second particle growth step, the oxygen concentration in the reaction vessel space was maintained at 0.2% by volume or less. In addition, a 25% by mass sodium hydroxide aqueous solution was added to the reaction aqueous solution to adjust the pH value to 11.0 (based on 25°C). Subsequently, the supply of liquid was restarted, and crystallization was performed for 2.7 hours as the second particle growth step. During the second particle growth step, crystallization was continued at a constant rate, and the pH value of the particle growth aqueous solution (based on 25°C) was controlled within the range of 9.5 to 11.6, and the ammonia concentration was also maintained within the same range as in the nucleation step.

[0163] The product was then washed with water, filtered, and dried to obtain composite hydroxide particles. The time from the start of the nucleation process to the point when the atmosphere was switched from the air atmosphere to the non-oxidizing atmosphere, i.e., when the process was switched from the first particle growth process to the second particle growth process, was 24% of the total crystallization time.

[0164] [Analysis of complex hydroxide particles] The obtained composite hydroxide particles were dissolved in an inorganic acid, and then chemically analyzed by ICP emission spectroscopy. The results showed that they were a composite hydroxide with a molar ratio of Ni:Mn:Co:Zr:W = 33:33:33:0.5:0.5.

[0165] Furthermore, for these composite hydroxide particles, the average particle size and the particle size distribution [(d90-d10) / average particle size] value were calculated from the integrated volume measured using a laser diffraction scattering particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.). As a result, the average particle size was 5.3 μm, and the [(d90-d10) / average particle size] value was 0.51.

[0166] Next, the obtained composite hydroxide particles were observed using a scanning electron microscope (Hitachi High-Technologies Corporation, S-4700) (magnification: 1000x), and it was confirmed that the particle size of these composite hydroxide particles was almost uniform. (2) Manufacturing of composite oxide particles The above composite hydroxide particles were mixed with lithium carbonate weighed to a ratio of Li / Me = 1.05 to prepare a lithium mixture. Note that Li / Me refers to the ratio of the number of lithium atoms (Li) to the sum of the number of atoms of other metals in the lithium mixture, i.e., the sum of the number of atoms of nickel, manganese, cobalt, and element M (Me).

[0167] The obtained lithium mixture was calcined in air (oxygen: 21% by volume) at 500°C for 4 hours, then fired at 900°C for 4 hours, cooled, and then crushed to obtain lithium nickel manganese composite oxide particles, which are the positive electrode active material. (3) Analysis of composite oxide particles The particle size distribution of the obtained composite oxide particles was measured using the same method as for the composite hydroxide particles. The average particle size was 4.5 μm, and the [(d90-d10) / average particle size] value was 0.51.

[0168] Furthermore, surface and cross-sectional observations of the composite hydroxide particles, performed using a scanning electron microscope (SEM) during the analysis, revealed that the obtained composite oxide particles contained secondary particles formed by the aggregation of multiple primary particles, and that their particle size was nearly uniform. On the other hand, cross-sectional SEM observation confirmed that these composite oxide particles had a hollow structure consisting of an outer shell formed by sintering primary particles and a hollow portion inside the outer shell.

[0169] Furthermore, compositional analysis of the composite oxide particles using ICP emission spectroscopy revealed that it was a composite oxide with a molar ratio of Li:Ni:Mn:Co:Zr:W = 1.05:0.33:0.33:0.33:0.005:0.005.

[0170] X-ray diffraction patterns of the obtained composite oxide particles were measured, confirming that they possessed a hexagonal crystal structure with a layered structure. Similar crystal structures were also confirmed for the composite oxide particles obtained in Examples 2 and 3 below.

[0171] Furthermore, the obtained composite oxide particles were embedded in resin, and the average diameter, average volume, and average thickness of the outer shell of the through-holes were measured. A Dual Beam FIB:Scios(DBF) manufactured by FEI Corporation was used for the measurements. + Cross-sectional processing using an ion beam and observation with a scanning electron microscope (SEM) were repeated to construct a 3D image for measurement. The average thickness of the outer shell was also measured from SEM observation of the cross-sectionally processed secondary particles. The measurement conditions are shown in Table 1.

[0172] [Table 1] Ten secondary particles were randomly sampled from a 3D image constructed using DBF and evaluated for the presence or absence of through-pores. Through-pores were confirmed in three secondary particles, resulting in a percentage of through-pore-containing secondary particles of 30%. The average diameter of the through-pores in the through-pore-containing secondary particles was 40 nm, and the average volume of the through-pores was 1.8 × 10⁻⁶. 6 nm 3 The average thickness of the outer shell, measured from SEM observation of the cross-sectionally processed secondary particles, was 590 nm. [Example 2] In the process of producing composite hydroxide particles, the total crystallization time for the nucleation step and the first particle growth step was set to 40 minutes, after which the process switched to the second particle growth step. The time for the nucleation step and the total crystallization time were the same as in Example 1. Except for the above points, composite hydroxide particles and composite oxide particles were obtained and evaluated in the same manner as in Example 1. The time from the start of the nucleation step at the timing of switching from the first particle growth step to the second particle growth step was 19% of the total crystallization time.

[0173] The composition of the obtained composite hydroxide particles and composite oxide particles was the same as in Example 1. The composite hydroxide particles were composed of secondary particles formed by the aggregation of multiple primary particles, similar to Example 1. Furthermore, it was confirmed that the composite oxide particles contained secondary particles formed by the aggregation of multiple primary particles and had a hollow structure consisting of an outer shell formed by sintering primary particles and a hollow portion inside the outer shell.

[0174] Furthermore, when the composite oxide particles were evaluated using DBF in the same manner as in Example 1, the proportion of secondary particles containing through-pores was 30%.

[0175] [Example 3] In the process of producing composite hydroxide particles, the total crystallization time for the nucleation step and the first particle growth step was set to 35 minutes, after which the process switched to the second particle growth step. The time for the nucleation step and the total crystallization time were the same as in Example 1. Furthermore, the aqueous solution (slurry) for particle growth after the completion of the first particle growth step was transferred to a reaction vessel controlled to a non-oxidizing atmosphere with an oxygen concentration of 0.2% by volume or less, and the second particle growth step was carried out in this reaction vessel. Except for the above points, composite hydroxide particles and composite oxide particles were obtained and evaluated in the same manner as in Example 1. The time from the start of the nucleation step to the timing of switching from the first particle growth step to the second particle growth step was 17% of the total crystallization time.

[0176] The composition of the obtained composite hydroxide particles and composite oxide particles was the same as in Example 1. The composite hydroxide particles were composed of secondary particles formed by the aggregation of multiple primary particles, similar to Example 1. Furthermore, it was confirmed that the composite oxide particles contained secondary particles formed by the aggregation of multiple primary particles and had a hollow structure consisting of an outer shell formed by sintering primary particles and a hollow portion inside the outer shell.

[0177] Furthermore, when the composite oxide particles were evaluated using DBF in the same manner as in Example 1, the proportion of secondary particles containing through-pores was 40%.

[0178] [Comparative Example 1] In the process of producing composite hydroxide particles, the total crystallization time for the nucleation step and the first particle growth step was set to 25 minutes, after which the process switched to the second particle growth step. The time for the nucleation step and the total crystallization time were the same as in Example 1. In addition, the ammonia concentration during crystallization was maintained at 10 g / L to 20 g / L. Except for the above points, the process was the same as in Example 1 to obtain and evaluate composite hydroxide particles and composite oxide particles. The time from the start of the nucleation step to the timing of switching from the first particle growth step to the second particle growth step was 12% of the total crystallization time.

[0179] The composition of the obtained composite hydroxide particles and composite oxide particles was the same as in Example 1. The composite hydroxide particles were composed of secondary particles formed by the aggregation of multiple primary particles, similar to Example 1. Furthermore, it was confirmed that the composite oxide particles contained secondary particles formed by the aggregation of multiple primary particles and had a hollow structure consisting of an outer shell formed by sintering primary particles and a hollow portion inside the outer shell.

[0180] Furthermore, when the composite hydroxide particles were evaluated using DBF in the same manner as in Example 1, no through-pore-containing secondary particles were observed.

[0181] [Evaluation of residual solvent content in lithium-ion secondary batteries] A lithium-ion secondary battery was assembled using the obtained composite oxide particles as the positive electrode active material, and the amount of solvent remaining in the positive electrode was evaluated. The solvent is the one contained in the positive electrode slurry when the positive electrode is manufactured, and NMP was used. In the evaluation of through-holes, secondary particles containing through-holes were confirmed to be 30% of the secondary particles by number, and in Example 1, where the average diameter was 40 nm, the voltage drop failure (open circuit voltage (OCV) failure) was reduced and it was judged to be without problems. In other words, it was confirmed that the amount of residual solvent in Example 1 was reduced, and the occurrence of defects during battery manufacturing was suppressed.

[0182] Furthermore, in Example 2, where through-hole-containing secondary particles were confirmed to account for 30% of the secondary particles by number, and in Example 3, where they were confirmed to account for 40% of the secondary particles, the amount of solvent remaining on the positive electrode was reduced, and it was determined that there were no problems. In Examples 2 and 3, the average diameter of the through-holes was 20 nm or more.

[0183] On the other hand, in Comparative Example 1, where no through-holes were observed, it was confirmed that the amount of solvent remaining in the positive electrode exceeded the upper limit at which OCV failure is said to increase.

[0184] From the above, it has been confirmed that by using the lithium nickel manganese composite oxide particles of the present invention as the positive electrode active material of a lithium-ion secondary battery, it is possible to obtain a hollow structure that provides high battery capacity and output characteristics while reducing the amount of residual solvent and suppressing the occurrence of defects during battery manufacturing. [Explanation of symbols]

[0185] 10 Secondary particles containing through-holes 11 Outer shell T11 Thickness of the outer shell 12 Hollow part 13 Through hole D13 Diameter of through hole

Claims

1. Lithium nickel manganese composite oxide particles used as positive electrode active material for lithium-ion secondary batteries, The lithium nickel manganese composite oxide particles contain secondary particles formed by the aggregation of primary particles containing lithium nickel manganese composite oxide having a hexagonal crystal structure with a layered structure. The secondary particle has a hollow structure comprising an outer shell and a hollow portion formed inside the outer shell. The lithium nickel manganese composite oxide particles contain 20% or more of the total number of secondary particles, which are through-hole-containing secondary particles having through-holes with an average diameter of 20 nm or more that penetrate the outer shell from the outside of the outer shell to the hollow part.

2. The lithium nickel manganese composite oxide particles according to claim 1, wherein the average thickness of the outer shell is 400 nm or more.

3. The average particle size is between 2 μm and 10 μm. Lithium nickel manganese composite oxide particles according to claim 1 or claim 2, wherein the index [(d90 - d10) / average particle size], which indicates the extent of the particle size distribution, is 0.60 or less.

4. Lithium nickel manganese composite oxide particles according to claim 1 or claim 2, containing lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co), and element M (M) in a molar ratio of Li:Ni:Mn:Co:M = 1 + u:x:y:z:t (-0.05 ≤ u ≤ 0.50, x + y + z + t = 1, 0.3 ≤ x ≤ 0.7, 0.1 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, where element M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W.

5. A positive electrode plate containing lithium nickel manganese composite oxide particles as described in claim 1 or claim 2 as the positive electrode active material.

6. A lithium-ion secondary battery containing the positive electrode plate described in claim 5.

Images