Method for producing precursor particles of lithium transition metal composite oxide, method for producing lithium transition metal composite oxide, and method for producing lithium ion secondary battery

Abstract

To provide a method for producing precursor particles capable of realizing a high-capacity lithium ion secondary battery.SOLUTION: The method disclosed for producing precursor particles containing a lithium element and a transition metal element and converted into a lithium transition metal complex oxide by calcination comprises an initial liquid preparation step (S1) of preparing an initial liquid containing at least water, and a crystallization step (S2) of preparing a reaction liquid by adding a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound to the initial liquid, and depositing the precursor particles in the reaction liquid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing precursor particles of a lithium transition metal composite oxide, a method for producing a lithium transition metal composite oxide, and a method for producing a lithium ion secondary battery. [Background technology]

[0002] Conventionally, lithium ion secondary batteries using a lithium transition metal composite oxide as a positive electrode active material have been known. Prior art documents relating to methods for producing lithium transition metal composite oxides include Patent Documents 1 to 5. For example, Patent Document 1 discloses a method for producing a lithium transition metal composite oxide for lithium ion secondary batteries, which includes a crystallization step of obtaining a carbonate composite (precursor) containing transition metal but not lithium using a crystallization reaction, and a firing step of mixing this carbonate composite with a lithium source and firing the mixture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-136096 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-026559 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-002120 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-171744 [Patent Document 5] Japanese Patent Application Publication No. 2017-228535 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a method for producing precursor particles that are converted into a lithium transition metal composite oxide by calcination, and that can realize a high-capacity lithium ion secondary battery. [Means for solving the problem]

[0005] The present invention provides a method for producing precursor particles containing lithium and a transition metal element and converted to a lithium-transition metal composite oxide by calcination. The method includes an initial solution preparation step of preparing an initial solution containing at least water, and a crystallization step of adding a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound to the initial solution to prepare a reaction solution, and precipitating precursor particles containing the lithium and the transition metal in the reaction solution.

[0006] By using the fired product of the precursor particles produced by such a method as a positive electrode active material, a high-capacity lithium ion secondary battery can be suitably realized. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a flowchart illustrating a method for producing precursor particles according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view that schematically shows the configuration of a lithium ion secondary battery that uses a fired product of precursor particles according to one embodiment. [Figure 3] FIG. 3 is a schematic exploded view showing the configuration of the wound electrode body of the lithium ion secondary battery of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that matters necessary for carrying out the present invention other than those specifically mentioned in this specification (e.g., the general configuration and manufacturing process of a lithium-ion secondary battery that do not characterize the present invention) can be understood as design matters for those skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are designated by the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0009] In this specification, the term "lithium ion secondary battery" refers to all secondary batteries that use lithium ions as charge carriers and achieve charging and discharging by the transfer of charge associated with the lithium ions between positive and negative electrodes, and is a term that also includes lithium ion capacitors and the like.

[0010] [Precursor particles] First, the precursor particles obtained by the manufacturing method disclosed herein will be described. The precursor particles according to this embodiment are particles that can be converted into a lithium transition metal composite oxide by calcination. The precursor particles can be used as a positive electrode active material for a lithium ion secondary battery by being converted into a lithium transition metal composite oxide by calcination. Therefore, the precursor particles can also be called lithium-containing precursor particles used as a positive electrode active material for a lithium ion secondary battery. The precursor particles are preferably particles that can be converted into a lithium transition metal composite oxide with a layered rock salt crystal structure by calcination. The crystal structure of the particles can be confirmed by a conventionally known method (for example, X-ray diffraction (XRD)).

[0011] The precursor particles are particulate compounds that can be converted into a lithium transition metal composite oxide. The precursor particles may be compounds such as carbonates, hydroxides, sulfates, nitrates, and oxalates. Of these, the precursor particles are preferably carbonates.

[0012] The precursor particles contain lithium (Li) and transition metal (TM) elements within each particle. Therefore, the precursor particles disclosed herein are different from a mixture of first particles containing Li but not TM elements and second particles containing TM elements but not Li. The TM element is not particularly limited and may be, for example, at least one element selected from the group consisting of Zr, Mo, Co, Fe, Ni, Mn, Cu, Cr, V, Nb, Pt, Pd, Ru, Rh, Au, Ag, Ti, Nb, and W. The TM element preferably contains at least one element selected from the group consisting of Ni, Co, and Mn, and more preferably contains Ni, Co, and Mn. This improves battery characteristics (e.g., high-rate characteristics and cycle characteristics).

[0013] The precursor particles typically contain all of the metal elements contained in the lithium transition metal composite oxide (for example, Li, Ni, Co, and Mn in the case of a lithium nickel cobalt manganese composite oxide). The precursor particles may further contain metal elements other than transition metals, such as Na, Mg, Ca, Al, Zn, and Sn. The precursor particles may further contain metalloid elements, such as B, Si, and P, and non-metal elements, such as S, F, Cl, Br, and I.

[0014] The precursor particles preferably further contain oxygen. For example, when the precursor particles are carbonates, they contain oxygen and carbon. The types of elements contained in the precursor particles can be confirmed by a conventionally known method (for example, inductively coupled plasma (ICP) emission spectroscopy).

[0015] In the precursor particles, the atomic ratio of lithium element to transition metal element (when multiple types are contained, the total of the elements) (Li element / TM element) is preferably 0.75 to 1.25, more preferably 0.8 to 1.2, and even more preferably 1.05 to 1.1. This makes it possible to particularly reduce the initial resistance of the lithium ion secondary battery. The atomic ratio of lithium element to transition metal element can also be confirmed by a conventionally known method (for example, the above-mentioned ICP atomic emission spectroscopy).

[0016] The precursor particles are typically in the form of powder. The precursor particles are typically approximately spherical. However, they may have an irregular shape, etc. In this specification, the term "approximately spherical" refers to a shape that can be regarded as roughly a sphere as a whole, and an average aspect ratio (major axis / minor axis ratio) based on a cross-sectional observation image using an electron microscope is approximately 1 to 2, preferably 1 to 1.5, and more preferably 1 to 1.2.

[0017] The precursor particles are typically in the form of secondary particles formed by agglomeration of multiple primary particles through physical or chemical bonding forces. However, the precursor particles may contain primary particles or may be composed of primary particles. In this specification, the term "primary particle" refers to the smallest particle unit constituting the precursor particle, specifically, the smallest unit determined from the geometric shape of its appearance.

[0018] The precursor particles are preferably amorphous. This can particularly minimize the increase in resistance during repeated charge and discharge of the lithium ion secondary battery, improving cycle characteristics. This is thought to be because the amorphous nature of the precursor particles facilitates rearrangement of the transition metal elements during firing, making it easier to obtain a lithium transition metal composite oxide with a homogeneous composition (with little variation). However, the precursor particles may also be amorphous. Note that when the precursor particles are carbonates, the precursor particles are usually amorphous. On the other hand, when the precursor particles are hydroxides, the precursor particles are usually crystalline.

[0019] Whether the precursor particles are amorphous (particle crystallinity) can be confirmed by X-ray diffraction (XRD). Specifically, the precursor particles are measured by XRD, and confirmation can be made by observing the peak of the (003) plane of the R3m phase derived from the metal hydroxide in the X-ray diffraction spectrum. If the precursor particles are amorphous, the peak will appear as a broad halo pattern in the X-ray diffraction spectrum. On the other hand, if the precursor particles are crystalline, a sharp peak will be observed in the (003) plane of the R3m phase.

[0020] The average particle size of the precursor particles is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 7 μm or more, and preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. According to the findings of the present inventors, the average particle size of the precursor particles affects the properties of the lithium transition metal composite oxide obtained by firing, and can also have a significant effect on the battery characteristics. As will be described in the test examples below, by setting the average particle size of the precursor particles within the above range, it becomes easier to form a suitable conductive path within the positive electrode (more specifically, between the lithium transition metal composite oxide particles), and the battery characteristics (for example, high-rate characteristics and cycle characteristics) can be improved. In this specification, the term "average particle size" refers to the median diameter (D 50 This refers to the particle size (particle size) and refers to the particle size corresponding to a cumulative frequency of 50% by volume from the smallest particle side in the volume-based particle size distribution based on a laser diffraction / scattering method. The average particle size of the precursor particles can be suitably adjusted, for example, by the reaction time of the crystallization step S2 in the production method described below.

[0021] The tap density of the precursor particles was 1.5 g / cm 3 More than 1.8g / cm is preferable. 3 More preferably, 2.0 g / cm 3 More preferably, 2.8 g / cm 3 Preferably less than 2.5 g / cm 3The following is more preferable. According to the findings of the present inventors, the tap density of the precursor particles affects the properties of the lithium transition metal composite oxide obtained by calcination, and can therefore significantly affect the battery characteristics. As described in the test examples below, by setting the tap density of the precursor particles within the above range, the positive electrode is suitably densified and the packing ratio is increased, which facilitates the formation of suitable conductive paths within the positive electrode and improves battery characteristics (e.g., high-rate characteristics and cycle characteristics). In this specification, "tap density" refers to a value measured using a tapping-type density measuring device in accordance with JIS K1469:2003. The tap density of the precursor particles can be suitably adjusted, for example, by the composition of the initial solution in the initial solution preparation step S1 in the production method described below, or the concentration of ammonium ions in the reaction solution in the crystallization step S2.

[0022] [Method for producing precursor particles] Next, a preferred example of a method for producing precursor particles as described above will be described. FIG. 1 is a flowchart illustrating a method for producing precursor particles according to one embodiment. The method for producing precursor particles according to this embodiment utilizes a coprecipitation method and includes, in this order, an initial solution preparation step S1 for preparing an initial solution and a crystallization step S2 for preparing a reaction solution and precipitating precursor particles in the reaction solution. The production method disclosed herein may further include other steps at any stage.

[0023] The initial liquid preparation step S1 is a step of preparing an initial liquid containing at least water, for example, in a reaction tank. From the viewpoint of preventing the incorporation of impurities, ion-exchanged water, distilled water, ultrafiltrated water, reverse osmosis water, etc. can be suitably used as the water. The initial liquid can function as a buffer liquid that alleviates the crystallization reaction in the crystallization step S2 described below. By carrying out the crystallization reaction via the initial liquid, it becomes easier to control the morphology of the resulting precursor particles, and precursor particles with the above-mentioned properties can be suitably produced. The initial liquid may be composed of only water, or may be in the form of a solution in which a solute is dispersed in water. However, it is preferable that the initial liquid does not contain compounds that cause a crystallization reaction, such as the strongly basic compounds described below.

[0024] In this embodiment, the initial liquid further contains an ammonium ion donor. The initial liquid is typically an aqueous solution in which the ammonium ion donor is dissolved in water as a solvent. By including an ammonium ion donor (specifically, ammonium ions) in the initial liquid, it is possible to promote the generation or growth of nuclei and enhance the adhesiveness or cohesion between primary particles in the crystallization step S2 described below. This allows the precursor particles to be dense, and precursor particles with the above-mentioned properties (especially those satisfying the above-mentioned tap density range) can be suitably produced. This in turn allows the battery characteristics (e.g., high-rate characteristics) to be improved.

[0025] The aqueous solution of the ammonium ion donor may be purchased commercially (ammonia solution), or may be prepared by mixing a solvent containing at least water with the ammonium ion donor in any desired ratio. A conventional stirring and mixing device, such as a magnetic stirrer, planetary mixer, or disperser, can be used appropriately for mixing. Examples of ammonium ion donors that can be used include ammonium sulfate, ammonium nitrate, ammonium hydroxide (NH4OH), ammonium halides, and aqueous ammonia. These compounds may be used alone or in combination. Among these, acidic substances, such as ammonium sulfate, are preferred from the viewpoint of adjusting the pH of the initial solution to the neutral to acidic side. Although not particularly limited, the concentration of ammonium ions in the initial solution is preferably 0.01 to 0.5 mol / L, more preferably 0.05 to 0.3 mol / L, and even more preferably 0.1 to 0.2 mol / L.

[0026] The solvent is typically water, but may also be a mixed solvent mainly composed of water. The solvent other than water constituting the mixed solvent may be an organic solvent that is uniformly miscible with water, such as a lower alcohol or a lower ketone. In this case, the initial liquid may be an aqueous solution.

[0027] In a preferred embodiment, the initial solution further contains a water-soluble salt of lithium and a water-soluble salt of a transition metal. The water-soluble salt of lithium serves as a lithium source (Li source) for the precursor particles, and the water-soluble salt of the transition metal serves as a transition metal source (TM source) for the precursor particles. These raw materials are typically the same as those used in the crystallization step S2. That is, a portion of the Li source and the TM source are added to the initial solution in advance. In the initial solution, the transition metal element (TM element) can form a complex with the ammonium ion donated by the ammonium ion donor. By including the Li source and the TM source in the initial solution in advance, the Li precipitation rate can be increased in the crystallization step S2 described below. This improves the Li recovery rate (the ratio of the amount of precipitated Li to the amount of input Li) and enhances productivity. Furthermore, since the amount of input Li can be reduced, excess anion components derived from Li can be reduced, thereby improving battery characteristics (e.g., high-rate characteristics and cycle characteristics).

[0028] The pH of the initial solution is preferably adjusted to less than 8, more preferably less than 7.5, for example, 5 to 7. The temperature environment of this step is preferably 10°C or higher, more preferably 25°C or higher. On the other hand, from the viewpoint of suppressing the volatilization of ammonia, the temperature is preferably 50°C or lower, more preferably 35°C or lower.

[0029] The crystallization step S2 is a step in which, for example, in a reaction tank, a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound are added to and mixed with the initial solution prepared in the initial solution preparation step S1 to prepare a reaction solution, and precursor particles containing lithium and the transition metal are precipitated in the reaction solution. The order in which the water-soluble salt of lithium, the water-soluble salt of the transition metal, the ammonium ion donor, and the strongly basic compound are added is not particularly limited. For example, the water-soluble salt of lithium and the water-soluble salt of the transition metal may first be mixed to prepare a mixed solution, and then this mixed solution, the ammonium ion donor, and the strongly basic compound may be added to the initial solution approximately simultaneously. Furthermore, a conventional stirring and mixing device such as that described above may be used appropriately for mixing.

[0030] By adding and mixing these raw materials, a crystallization reaction occurs in the reaction solution, and precursor particle nuclei containing Li and TM elements are precipitated. Furthermore, by continuing the crystallization reaction for a predetermined time, the precipitated nuclei grow, and precursor particles having a desired particle size (typically a secondary particle size) can be obtained.

[0031] As described above, the water-soluble salt of lithium is the Li source for the precursor particles. Examples of the water-soluble salt of lithium that can be used include water-soluble ionic compounds such as lithium halides (e.g., lithium chloride), lithium sulfate, and lithium nitrate. These compounds may be used alone or in combination of two or more. Among these, lithium halides are preferred from the viewpoint of reactivity, and lithium chloride is more preferred because it can be derived from natural resources. The water-soluble salt of lithium may be in the form of a hydrate.

[0032] Although not particularly limited, the water-soluble salt of lithium is preferably added so that the lithium concentration in the reaction solution is in the range of approximately 0.1 to 2 mol / L, more preferably 0.4 to 1.0 mol / L, 1.0 to 1.4 mol / L, or 1.1 to 1.4 mol / L, for example. This allows precursor particles with the above-mentioned properties to be suitably produced.

[0033] As described above, the water-soluble salt of a transition metal is a TM source for the precursor particles. Examples of water-soluble salts of transition metals that can be used include sulfates, nitrates, and oxalates of transition metals. These compounds may be used alone or in combination of two or more. Of these, acidic substances, such as sulfates, are preferred. The water-soluble salt of a transition metal may be in the form of a hydrate. In the reaction solution, the transition metal element (TM element) can form a complex with ammonium ions donated by the ammonium ion donor in the initial solution.

[0034] Although not particularly limited, the water-soluble salt of a transition metal is preferably added so that the concentration of the transition metal in the reaction solution (when multiple types are included, the total concentration) is in the range of approximately 0.1 to 0.5 mol / L, more preferably 0.1 to 0.3 mol / L, 0.1 to 0.29 mol / L, or 0.3 to 0.4 mol / L, for example. This allows the precursor particles having the above-mentioned properties to be suitably produced.

[0035] Although not particularly limited, the molar ratio of lithium to transition metal (when multiple types are contained, the total of the transition metals) (Li / TM) in the reaction solution is preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 1 or more. This ensures a sufficient amount of lithium, allowing precursor particles satisfying the above-mentioned properties, such as the above-mentioned atomic ratio (Li element / TM element), to be suitably produced. The molar ratio (Li / TM) is preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, particularly preferably 2 or less, and even more preferably 1.7 or less, 1.5 or less, 1.3 or less, 1.2 or less, or 1.1 or less. This prevents lithium salts from being mixed into the precipitated precursor particles, thereby improving battery characteristics (e.g., high-rate characteristics and cycle characteristics). Furthermore, the amount of Li used can be reduced, improving the Li recovery rate (the ratio of the amount of precipitated Li to the amount of Li input), and increasing productivity. The molar ratio of transition metal to lithium corresponds to the ratio of the molar concentration of transition metal to the molar concentration of lithium.

[0036] As the ammonium ion donor, any of the compounds exemplified in the initial solution preparation step S1 can be used as appropriate, but it is preferable to use the same compound as that used in the initial solution preparation step S1. For example, if ammonium sulfate is used in the initial solution preparation step S1, it is preferable to use ammonium sulfate in this step as well.

[0037] Although not particularly limited, the ammonium ion donor may be an ammonium ion (NH4 +The ammonium ion concentration is preferably 0.1 to 1.5 mol / L, more preferably 0.2 to 1.2 mol / L, and even more preferably 0.3 to 1.1 mol / L. This allows the transition metal elements in the reaction solution to be suitably complexed, and as will be described in the test examples below, precursor particles having the above-described properties (particularly those satisfying the above-described tap density range) can be suitably produced. This in turn improves battery characteristics (e.g., high-rate characteristics and cycle characteristics). The ammonium ion concentration is preferably 0.45 mol / L or higher, more preferably 0.6 mol / L or higher, even more preferably 0.75 mol / L or higher, and particularly preferably 0.9 mol / L or higher.

[0038] The strongly basic compound is a component for precipitating elemental lithium and transition metal elements as nuclei, i.e., a compound that has the ability to form precipitates. Examples of the strongly basic compound include carbonates, hydroxides, and sulfates of alkali metals or alkaline earth metals. These strongly basic compounds may be used alone or in combination. Among these, carbonates of alkali metals or alkaline earth metals are preferred. Examples of carbonates include sodium carbonate, potassium carbonate, and calcium carbonate, with sodium carbonate being preferred. According to the inventors' studies, elemental lithium is relatively more difficult to crystallize than TM elements. However, by using carbonates, elemental lithium can be favorably crystallized as Li2CO3. Furthermore, by precipitating elemental lithium and TM elements in solution as carbonates, amorphous precursor particles can be obtained.

[0039] The strongly basic compound may be added all at once, but is preferably added dropwise slowly to prevent a sudden change in the pH of the reaction solution. The strongly basic compound is preferably added so that the pH of the solution becomes alkaline, and is preferably added so that the pH is 7.5 or higher, for example, in the range of 7.5 to 10, or even 8 to 9. In this case, the concentration of the basic compound in the solution can be, for example, 1 to 10 mol / L, preferably about 3 to 7 mol / L. It is preferable to maintain the pH of the reaction solution approximately constant (within a range of about ±0.5) during the crystallization reaction.

[0040] The reaction solution may be composed of water, a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound, or may further contain other compounds. Examples of components that may be contained in the reaction solution include semimetallic elements (e.g., B, Si, P, etc.) and nonmetallic elements (e.g., S, F, Cl, Br, I, etc.) that may be contained in the precursor particles.

[0041] The reaction temperature in this step is preferably 10°C or higher, more preferably 25°C or higher, from the viewpoints of the solubility of the raw materials used and promoting nucleation, etc. On the other hand, from the viewpoints of suppressing the volatilization of ammonia, etc., the reaction temperature is preferably 50°C or lower, more preferably 35°C or lower.

[0042] The reaction time in this step is not particularly limited, as it can vary depending on, for example, the concentration of ammonium ions in the reaction solution and the reaction temperature, but is preferably approximately 1 to 50 hours, and more preferably 5 to 40 hours. This allows precursor particles with the above-described properties (particularly those satisfying the above-described range of average particle diameter), as described in the test examples below, to be suitably produced. This in turn allows for improved battery characteristics (e.g., high-rate characteristics and cycle characteristics). The reaction time may be, for example, 10 hours or more, or 15 hours or more. From the viewpoints of work efficiency and productivity, the reaction time is preferably, for example, 30 hours or less, and more preferably 20 hours or less.

[0043] In this step, it is preferable to irradiate the reaction solution with ultrasonic waves in order to promote the crystallization reaction (particularly nucleation). As described in the test examples below, this improves the Li recovery rate (the ratio of the amount of precipitated Li to the amount of added Li) and increases productivity. Furthermore, it also suppresses particle aggregation, making it easier to obtain precursor particles with the above-mentioned properties (particularly those satisfying the above-mentioned average particle size range). Ultrasonic irradiation can be performed by ultrasonically vibrating the reaction vessel itself, or by inserting an ultrasonic vibration probe into the reaction vessel (reaction solution). The ultrasonic vibration conditions can be appropriately set depending on, for example, the composition of the reaction solution and the size of the reaction vessel. However, it is preferable to set the frequency to approximately 5 to 100 kHz, 10 to 50 kHz, or 10 to 30 kHz, and the output to approximately 10 to 500 W, 50 to 100 W, or 100 to 200 W.

[0044] When an alkali metal or alkaline earth metal carbonate is used as the strongly basic compound, this step is preferably carried out in a CO2 atmosphere. It is more preferable to carry out all steps from the initial solution preparation step S1 to the crystallization step S2 (this step) in a CO2 atmosphere. This promotes the crystallization reaction (particularly nucleation), resulting in the active production of lithium carbonate (Li2CO3), as described in the test examples below. Therefore, Li, which is difficult to crystallize, can be favorably crystallized as a carbonate. However, the initial solution preparation step S1 to the crystallization step S2 (this step) may also be carried out in an inert gas atmosphere, such as nitrogen (N2) or argon (Ar).

[0045] The crystallization reaction can produce the precursor particles as a precipitate. The precipitate can be recovered by a known method. For example, the precipitate can be recovered by a solid-liquid separation method such as filtration, washed with water, and dried to obtain the precursor particles.

[0046] [Method for producing lithium transition metal composite oxide] The precursor particles according to this embodiment are converted into a lithium transition metal composite oxide by calcination. That is, the technology disclosed herein provides a method for producing a lithium transition metal composite oxide, which includes a calcination step of calcining the precursor particles. This lithium transition metal composite oxide can be suitably used as a positive electrode active material for lithium-ion secondary batteries.

[0047] In addition, in a conventional method for producing a positive electrode active material, as described in Patent Document 1, for example, a lithium source is mixed with a carbonate composite (precursor) that does not contain lithium but contains a transition metal, and the mixture is fired. In contrast, the precursor particles of this embodiment contain Li in addition to the TM element, so when using the precursor particles of this embodiment, it is not necessary to add a Li salt. Therefore, a positive electrode active material can be produced easily, and the productivity of the positive electrode active material can be improved.

[0048] The firing can be carried out in a conventionally known firing furnace. The firing temperature is not particularly limited, but may be, for example, about 600 to 1000°C. The firing time is generally 1 hour or more, for example, 1 to 48 hours, and preferably 5 to 24 hours. From the viewpoint of enhancing the crystallinity of the resulting oxide, the firing atmosphere is preferably an oxygen-containing atmosphere, for example, an oxygen atmosphere or an air atmosphere. The oxygen concentration of the oxygen-containing atmosphere is preferably 10% by volume or more, more preferably 18 to 100% by volume.

[0049] [Lithium-ion secondary battery] A lithium-ion secondary battery using the lithium transition metal composite oxide obtained by firing has improved initial capacity. Preferably, the initial resistance and the rate of increase in resistance after cycling are small, and the battery has excellent high-rate characteristics and cycle characteristics. Specific configuration examples of lithium-ion secondary batteries will be described below with reference to the drawings.

[0050] FIG. 2 is a cross-sectional view schematically illustrating the configuration of a lithium-ion secondary battery 100 using a fired product of precursor particles according to one embodiment. The lithium-ion secondary battery 100 of FIG. 2 is a sealed battery in which a flat wound electrode assembly 20 and a nonaqueous electrolyte (not shown) are housed in a flat, rectangular battery case (i.e., outer container) 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, as well as a thin-walled safety valve 36 that is designed to release internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. The positive and negative electrode terminals 42 and 44 are electrically connected to positive and negative electrode current collector plates 42a and 44a, respectively. The battery case 30 is made of a lightweight metal material with good thermal conductivity, such as aluminum.

[0051] FIG. 3 is a schematic exploded view showing the configuration of the wound electrode body 20. As shown in FIGS. 2 and 3, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped with two long separator sheets 70 interposed therebetween and wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long negative electrode current collector 62. The positive electrode active material layer-free portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer-free portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the wound electrode body 20. The positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a are joined to the positive electrode current collector 42a and the negative electrode current collector 44a, respectively.

[0052] The positive electrode current collector 52 constituting the positive electrode sheet 50 may be, for example, aluminum foil. The positive electrode active material layer 54 contains, as a positive electrode active material, at least a lithium transition metal composite oxide, which is a fired product of the precursor particles according to the present embodiment. The positive electrode active material layer 54 may further contain a conductive material, a binder, and the like. Suitable conductive materials include carbon black such as acetylene black (AB) and other carbon materials (such as graphite). Suitable binders include, for example, polyvinylidene fluoride (PVDF).

[0053] The negative electrode current collector 62 constituting the negative electrode sheet 60 may be, for example, copper foil. The negative electrode active material layer 64 includes a negative electrode active material. Examples of the negative electrode active material that can be used include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material layer 64 may further include a binder, a thickener, and the like. Examples of the binder that can be used include styrene butadiene rubber (SBR). Examples of the thickener that can be used include carboxymethyl cellulose (CMC).

[0054] The separator 70 can be made of various porous sheets similar to those conventionally used in lithium-ion secondary batteries, including porous resin sheets made of resins such as polyethylene (PE) and polypropylene (PP). Such porous resin sheets may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). The separator 70 may also have a heat-resistant layer (HRL).

[0055] The nonaqueous electrolyte can be the same as that used in conventional lithium-ion secondary batteries, and typically, a supporting salt can be used in an organic solvent (nonaqueous solvent). The nonaqueous solvent can be an aprotic solvent such as carbonates, esters, or ethers. Among these, carbonates are preferred because they are particularly effective in reducing low-temperature resistance due to the positive electrode material. Examples of carbonates include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). These nonaqueous solvents can be used alone or in appropriate combinations of two or more. Suitable supporting salts include lithium salts such as LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), etc. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0056] The nonaqueous electrolyte may contain components other than the nonaqueous solvent and supporting salt described above, such as various additives such as a gas generating agent, a film-forming agent, a dispersant, and a thickener, as long as the effects of the present invention are not significantly impaired.

[0057] Such a lithium ion secondary battery 100 can be produced by a production method including a positive electrode production step of producing a positive electrode sheet 50 using the lithium transition metal composite oxide produced by the above production method.

[0058] The foregoing describes a prismatic lithium ion secondary battery having a flat wound electrode assembly as a preferred example. However, the lithium transition metal composite oxide obtained by firing the precursor particles according to this embodiment can also be used in other types of lithium ion secondary batteries using known methods. For example, a lithium ion secondary battery having a stacked electrode assembly (i.e., an electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked) can be constructed using the lithium transition metal composite oxide obtained by firing the precursor particles according to this embodiment. Furthermore, a cylindrical lithium ion secondary battery, a coin-type lithium ion secondary battery, a laminated lithium ion secondary battery, etc. can also be constructed using the lithium transition metal composite oxide obtained by firing the precursor particles according to this embodiment. Furthermore, an all-solid-state secondary battery using a solid electrolyte can also be constructed.

[0059] The lithium ion secondary battery 100 can be used for a variety of purposes. Suitable applications include a driving power source mounted on vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The lithium ion secondary battery 100 can also be used as a storage battery for small power storage devices and the like. The lithium ion secondary battery 100 can also be used in the form of an assembled battery in which a plurality of batteries are connected in series and / or parallel.

[0060] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0061] <Test Example I> <Preparation of Precursor Particles (Comparative Examples 1 and 2, Examples 2 to 12)> Comparative Example 1 In Comparative Example 1, precursor particles were obtained by mixing the raw materials all at once without preparing an initial solution. Specifically, in an N2 atmosphere, 2.4 mol / L of lithium chloride (LiCl) as a Li source, 1.4 mol / L of a transition metal sulfate hydrate as a TM source, 0.7 mol / L of ammonium hydroxide (NH4OH) as an ammonium ion donor, and 5.1 mol / L of sodium carbonate (Na2CO3) as a strongly basic compound were added to a reaction vessel to prepare a reaction solution, and a crystallization reaction was carried out for 5 hours. Solid-liquid separation was then performed to extract the precipitate. This precipitate was immersed in ion-exchanged water and washed, and solid-liquid separation was again performed to recover the precipitate. The recovered precipitate was dried to obtain the precursor particles of Comparative Example 1.

[0062] Comparative Example 2 In Comparative Example 2, precursor particles were obtained without preparing an initial solution and without using an ammonium ion donor. Specifically, in an N2 atmosphere, a 6.0 mol / L aqueous solution of lithium chloride (LiCl) and a 1.5 mol / L aqueous solution of a transition metal sulfate were first added to a reaction vessel in a liquid volume ratio of 1:2.3 and mixed. Sodium carbonate (Na2CO3) was added dropwise to the reaction solution to adjust the pH to 8, and a crystallization reaction was carried out for 10 hours. The precipitate was then recovered in the same manner as in Comparative Example 1, yielding precursor particles for Comparative Example 2.

[0063] [Example 1] In Example 1, first, a 0.1 mol / L aqueous solution of ammonium sulfate ((NH4)2SO4) was prepared as an initial solution in a reaction vessel in an N2 atmosphere. To this initial solution, a 6.0 mol / L aqueous solution of lithium chloride (LiCl) and a 1.5 mol / L aqueous solution of a transition metal sulfate were added in a liquid ratio of 1:1.2. Further, a 5.8 mol / L aqueous solution of ammonium sulfate ((NH4)2SO4) was added in an amount equivalent to the amount of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + A reaction solution was prepared by adding sodium carbonate (Na2CO3) dropwise to adjust the pH to 8, and the reaction solution was subjected to a crystallization reaction for 50 hours. Thereafter, the precipitate was collected in the same manner as in Comparative Example 1, and precursor particles of Example 1 were obtained.

[0064] [Examples 2 to 12] In Example 2, the ammonium sulfate aqueous solution was added in an amount 4.0 times the amount of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + Precursor particles were obtained in the same manner as in Example 1, except that the concentration of ammonium ions (NH4) was 1.2 mol / L and the reaction time was 20 hours. In Example 3, precursor particles were obtained in the same manner as in Example 1, except that the reaction time was 10 hours. In Example 4, precursor particles were obtained in the same manner as in Example 1, except that the reaction time was 5 hours. In Example 5, the ammonium sulfate aqueous solution was added in an amount 1.5 times the amount of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + Precursor particles were obtained in the same manner as in Example 1, except that the concentration of ) was 0.45 mol / L and the reaction time was 5 hours.

[0065] In Example 6, the ammonium sulfate aqueous solution was added in an amount 1.5 times the amount of the aqueous solution of the transition metal sulfate (i.e., ammonium ion (NH + Precursor particles were obtained in the same manner as in Example 1, except that the aqueous ammonium sulfate solution was added in an amount twice the volume of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + Precursor particles were obtained in the same manner as in Example 1, except that the aqueous ammonium sulfate solution was added in an amount 2.5 times the amount of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + Precursor particles were obtained in the same manner as in Example 1, except that the aqueous ammonium sulfate solution was added in an amount three times the amount of the aqueous solution of the transition metal sulfate (i.e., the amount of ammonium ions (NH4 + Precursor particles were obtained in the same manner as in Example 1, except that the concentration of ) was 0.9 mol / L and the reaction time was 30 hours.

[0066] In Example 10, an aqueous ammonium sulfate solution was added at 3.5 times the liquid volume of the aqueous transition metal sulfate solution (i.e., so that the concentration of ammonium ions (NH4 + ) was 1.05 mol / L), and precursor particles were obtained in the same manner as in Example 1 except that the reaction time was 40 hours. In Example 11, an aqueous ammonium sulfate solution was added at 3.5 times the liquid volume of the aqueous transition metal sulfate solution (i.e., so that the concentration of ammonium ions (NH4 + ) was 1.05 mol / L), and precursor particles were obtained in the same manner as in Example 1 except that the reaction time was 20 hours. In Example 12, precursor particles were obtained in the same manner as in Example 3 except that the initial liquid was only water (no ammonium ion donor was added to the initial liquid). The summary of the synthesis conditions is shown in Table 1.

[0067] <Measurement of properties of precursor particles> · Average particle diameter: Using a commercially available laser diffraction / scattering type particle size distribution measuring device, the volume-based particle size distribution of the precursor particles was measured, and the particle diameter corresponding to a cumulative frequency of 50% by volume from the side of fine particles with a small particle diameter was determined as the average particle diameter (D 50 ). The results are shown in Table 1. · Tap density: Using a commercially available tapping type density measuring device, the tap density of the precursor particles was measured in accordance with JIS K1469:2003. The results are shown in Table 1.

[0068] The Li recovery rate was calculated by dividing the amount of Li precipitated (the amount recovered as precursor particles) by the amount of Li input. The results are shown in Table 1.

[0069] <Fabrication of lithium ion secondary battery for evaluation> The precursor particles of each example were calcined in an oxygen-containing atmosphere at 850°C for 10 hours to obtain a lithium transition metal composite oxide. The resulting lithium transition metal composite oxide (positive electrode active material), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone (NMP) in a mass ratio of positive electrode active material:AB:PVDF = 85:10:5 to prepare a paste for forming a positive electrode active material layer. This paste was applied to a 15 μm thick aluminum foil and dried to produce a positive electrode sheet.

[0070] A paste for forming a negative electrode active material layer was prepared by mixing natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio of C:SBR:CMC = 98:1:1 in ion-exchanged water. This paste was applied to a copper foil with a thickness of 10 μm and dried to prepare a negative electrode sheet.

[0071] In addition, a porous polyolefin sheet having a thickness of 20 μm and a three-layer structure of PP / PE / PP was prepared as a separator sheet.

[0072] The positive electrode sheet, negative electrode sheet, and separator sheet were stacked together, and electrode terminals were attached and housed in a laminate case. A non-aqueous electrolyte was then poured into the laminate case, which was then airtightly sealed. The non-aqueous electrolyte was a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, with LiPF6 dissolved as a supporting electrolyte at a concentration of 1.0 mol / L. In this manner, lithium ion secondary batteries for evaluation were obtained for each example.

[0073] <Initial capacity measurement> Each evaluation lithium-ion secondary battery was charged at a constant current of 1 C up to 4.1 V, and then discharged at a constant current of 0.2 C down to 3.0 V, and the discharge capacity at this time was calculated as the initial capacity. Then, assuming the initial capacity of the evaluation lithium-ion secondary battery of Comparative Example 1 to be 100, the ratio of the initial capacity of the other evaluation lithium-ion secondary batteries was calculated. The results are shown in Table 1.

[0074] <Initial resistance measurement> The state of charge (SOC) of each evaluation lithium-ion secondary battery was adjusted to 50% and then placed in an environment at 25°C. Discharge was performed for 10 seconds at a current value of 100 mA, and the amount of voltage drop ΔV was determined. The amount of voltage drop ΔV was divided by the discharge current value (100 mA) to calculate the battery resistance, which was taken as the initial resistance. Then, when the initial resistance of the evaluation lithium-ion secondary battery of Comparative Example 1 was set to 200, the ratio of the initial resistance of the other evaluation lithium-ion secondary batteries was determined. The results are shown in Table 1.

[0075] <Evaluation of resistance increase rate after cycling> Each lithium-ion secondary battery for evaluation was placed in a 60°C environment and subjected to a constant current charge of 1C up to 4.1V, followed by a constant current discharge of 1C down to 3.0V. This cycle was repeated 200 times. The battery resistance after 200 cycles was then measured using the same method as for measuring the initial resistance, and the post-cycle resistance increase rate (%) was calculated using the following formula: (battery resistance after 200 cycles / initial resistance) × 100. The results are shown in Table 1.

[0076] [Table 1]

[0077] The results in Table 1 show that Comparative Example 1, in which an initial solution was not prepared and the raw materials were mixed all at once, and Comparative Example 2, in which an initial solution was not prepared and an ammonium ion donor was not used in the crystallization step, had a relatively low initial capacity. In contrast to these Comparative Examples, Examples 1 to 12, in which an initial solution containing at least water was prepared and an ammonium ion donor was added in addition to a strongly basic compound in the crystallization step, had a relatively high initial capacity and high energy density. These results demonstrate the technical significance of the invention disclosed herein.

[0078] Furthermore, in the crystallization process, ammonium ions (NH4 + In Examples 3 to 12, in which the concentration of ammonium ion (NH4) was 0.3 to 1.1 mol / L and the reaction time was 5 to 40 hours, the initial resistance was relatively low and the high-rate characteristics were excellent. + By setting the concentration of ammonium ions (NH4) to 0.45 mol / L or more, both the initial resistance and the rate of increase in resistance after cycling could be reduced to less than half of those in Comparative Example 1. + By increasing the concentration of ammonium ion donor to 0.6 mol / L or more, or even 0.75 mol / L or more, the initial resistance and the rate of increase in resistance after cycling could be further reduced. Furthermore, a comparison between Example 3 and Example 12 shows that the initial resistance could be reduced by adding an ammonium ion donor to the initial solution.

[0079] <Test Example II> <Preparation of precursor particles (Examples 13 to 17)> In Examples 13 to 16, a water-soluble lithium salt and a water-soluble transition metal salt were added to the initial solution. Specifically, in Example 13, a 0.1 mol / L ammonium sulfate ((NH)SO) aqueous solution, a 6.0 mol / L lithium chloride (LiCl) aqueous solution, and a 1.5 mol / L transition metal sulfate aqueous solution were added to a reaction vessel in an N atmosphere in a liquid volume ratio of 6:1:2.4 to prepare an initial solution. A 6.0 mol / L lithium chloride (LiCl) aqueous solution and a 1.5 mol / L transition metal sulfate aqueous solution were added to this initial solution in a liquid volume ratio of 1:2.4. Further, a 5.8 mol / L ammonium sulfate ((NH)SO) aqueous solution was added in an amount 2.5 times the amount of the transition metal sulfate aqueous solution, and sodium carbonate (NaCO) was added dropwise to adjust the pH to 8 to prepare a reaction solution, which was then subjected to a crystallization reaction for 20 hours. Thereafter, the precipitate was collected in the same manner as in Comparative Example 1, and precursor particles of Example 13 were obtained.

[0080] In Example 14, precursor particles were obtained in the same manner as in Example 13, except that the mixing ratio of the lithium chloride aqueous solution to the transition metal sulfate aqueous solution in the initial solution and the reaction solution was 1:3.2 and the reaction was carried out under a CO atmosphere. In Example 15, precursor particles were obtained in the same manner as in Example 14, except that the mixing ratio of the lithium chloride aqueous solution to the transition metal sulfate aqueous solution in the initial solution and the reaction solution was 1:3.5 and an ultrasonic vibration probe was introduced into the reaction solution and vibrations were continuously applied at a frequency of 20 kHz and an output of 150 W during the crystallization reaction. In Example 16, precursor particles were obtained in the same manner as in Example 13, except that the mixing ratio of the lithium chloride aqueous solution to the transition metal sulfate aqueous solution in the initial solution and the reaction solution was 1:3.2 and an ultrasonic vibration probe was introduced into the reaction solution and vibrations were continuously applied at a frequency of 20 kHz and an output of 150 W during the crystallization reaction.

[0081] In Example 17, precursor particles were obtained in the same manner as in Example 6 of Test Example I, except that the mixture ratio of the lithium chloride aqueous solution to the transition metal sulfate aqueous solution in the reaction solution was 1:1.8, the reaction was carried out in a CO atmosphere, and an ultrasonic vibration probe was introduced into the reaction solution during the crystallization reaction, and vibrations were continuously applied at a frequency of 20 kHz and an output of 150 W. An overview of the synthesis conditions is shown in Table 2. Table 2 also shows Example 6 of Test Example I for comparison.

[0082] The properties (average particle size, tap density) of the obtained precursor particles were measured, and the Li recovery rate was calculated, in the same manner as in Test Example I. Furthermore, a lithium ion secondary battery for evaluation was fabricated, and the battery characteristics were evaluated, in the same manner as in Test Example I. The results are shown in Table 2.

[0083] [Table 2]

[0084] As shown in Table 2, Example 13, in which an aqueous solution of lithium chloride and an aqueous solution of a transition metal sulfate were added to the initial solution, had a relatively lower initial resistance and a lower resistance increase rate after cycling compared to Example 8, in which no addition was made. This indicates that the inclusion of a water-soluble lithium salt and a water-soluble transition metal salt in the initial solution can further improve the high-rate characteristics and cycle characteristics of lithium-ion secondary batteries. Furthermore, the Li recovery rate was increased to approximately twice that of Example 8.

[0085] Furthermore, in Example 14, in which the crystallization reaction was carried out in a CO2 atmosphere, the initial resistance and the rate of increase in resistance after cycling were relatively lower than in Example 13, in which the crystallization reaction was carried out in a N2 atmosphere. This indicates that the high-rate characteristics and cycle characteristics of lithium-ion secondary batteries can be further improved by using carbonate as a strongly basic compound and carrying out the crystallization process in a CO2 atmosphere. Furthermore, the Li recovery rate was also increased.

[0086] Furthermore, in Example 15, in which ultrasonic waves were irradiated to the reaction solution under a CO2 atmosphere during the crystallization reaction, the initial resistance and the rate of increase in resistance after cycling were relatively reduced compared to Example 14, in which ultrasonic waves were not irradiated to the reaction solution under a CO2 atmosphere. A comparison of Example 16 (with ultrasonic waves) and Example 13 (without ultrasonic waves) revealed a similar tendency when the crystallization reaction was carried out under a N2 atmosphere. This demonstrates that, regardless of the reaction atmosphere or the composition of the initial solution, irradiating the reaction solution during the crystallization reaction with ultrasonic waves can further improve the high-rate characteristics and cycle characteristics of lithium-ion secondary batteries. Furthermore, the Li recovery rate could also be increased.

[0087] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A method for producing precursor particles that contain lithium and a transition metal element and are converted into a lithium transition metal composite oxide by calcination, the method comprising: an initial solution preparation step of preparing an initial solution containing at least water; and a crystallization step of adding a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound to the initial solution to prepare a reaction solution, and precipitating precursor particles containing the lithium and the transition metal in the reaction solution. Item 2: The production method according to Item 1, wherein in the crystallization step, the ammonium ion concentration in the reaction solution is set to 0.3 mol / L or more and 1.1 mol / L or less, and the reaction time is set to 5 hours or more and 40 hours or less. Item 3: The production method according to Item 1 or 2, wherein the initial solution further contains an ammonium ion donor. Item 4: The production method according to any one of Items 1 to 3, wherein the initial solution further contains the water-soluble salt of lithium and the water-soluble salt of the transition metal. Item 5: The method according to any one of Items 1 to 4, wherein the strongly basic compound is a carbonate of an alkali metal or an alkaline earth metal. Item 6: The production method according to Item 5, wherein at least the crystallization step is carried out under a CO2 atmosphere. Item 7: The production method according to any one of Items 1 to 6, wherein the reaction solution is irradiated with ultrasonic waves in the crystallization step. Item 8: A method for producing a lithium transition metal composite oxide, comprising a calcination step of calcining the precursor particles obtained by the production method according to any one of items 1 to 6. Item 9: A method for producing a lithium ion secondary battery, comprising a positive electrode production step of producing a positive electrode using the lithium transition metal composite oxide obtained by the production method according to Item 8.

[0088] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0089] 20 Wound electrode body 30 Battery case 42 Positive terminal 44 Negative terminal 50 Positive electrode sheet (positive electrode) 54 Cathode active material layer 60 Negative electrode sheet (negative electrode) 64 Negative electrode active material layer 100 Lithium-ion secondary battery

Claims

1. A method for producing precursor particles that contain lithium element and transition metal element and are converted into a lithium transition metal composite oxide by firing, comprising: the precursor particles contain at least one transition metal element selected from Ni, Co, and Mn, and the atomic ratio of the lithium element to the transition metal element (when a plurality of transition metal elements are contained, the total of the transition metal elements) (Li element / TM element) is 0.75 or more and 1.25 or less; an initial solution preparation step of preparing an initial solution containing at least water and having a pH of neutral to acidic; a crystallization step of preparing a reaction solution by adding a water-soluble salt of lithium, a water-soluble salt of a transition metal, an ammonium ion donor, and a strongly basic compound to the initial solution, and precipitating precursor particles containing the lithium and the transition metal in the reaction solution; Including, In the crystallization step, The concentration of ammonium ions in the reaction solution is set to 0.3 mol / L or more and 1.5 mol / L or less, The reaction time is 1 hour or more and 50 hours or less, At least one of sodium carbonate, potassium carbonate, and calcium carbonate is used as the strongly basic compound. Method for producing precursor particles.

2. In the crystallization step, The concentration of the ammonium ions in the reaction solution is set to 0.3 mol / L or more and 1.1 mol / L or less, and The reaction time is 5 hours or more and 40 hours or less. The method of claim 1.

3. The initial liquid further contains an ammonium ion donor. The method according to claim 1 or 2.

4. the initial solution further contains a water-soluble salt of lithium and a water-soluble salt of the transition metal; The method of claim 3.

5. At least the crystallization step is carried out by CO ２ Performed under atmospheric conditions, The method according to claim 1 or 2.

6. In the crystallization step, the reaction solution is irradiated with ultrasonic waves. The method according to claim 1 or 2.

7. A method for producing a lithium transition metal composite oxide, comprising a calcination step of calcining the precursor particles obtained by the method according to claim 1 or 2.

8. A method for producing a lithium ion secondary battery, comprising the step of producing a positive electrode using the lithium transition metal composite oxide obtained by the method according to claim 7.

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