Precursor of positive electrode active material and manufacturing method

Abstract

To provide a technique capable of achieving a lithium ion secondary battery having excellent output characteristics.SOLUTION: A precursor disclosed herein is a precursor of a positive electrode active material that is used in a lithium ion secondary battery. The precursor contains a transition metal composite hydroxide particle 200 having Ni. The transition metal composite hydroxide particle 200 includes: an outer shell part 210 formed by aggregating primary particles 212 with an average aspect ratio (length of long axis / length of short axis) based on SEM observation of 2 or more; and a hollow part 220 surrounded by the outer shell part 210. 50% or more of the primary particles 212 are oriented radially from the center of the transition metal composite hydroxide particle 200 toward the surface, and 90% or more of the primary particles included in the entire transition metal composite hydroxide particle 200 are present in the outer shell part 210.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a precursor of a positive electrode active material and a method for producing the same. [Background technology]

[0002] Patent Document 1 discloses a method for producing a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery. One of the features of this precursor is that it has a laminated structure in which a central portion formed by aggregation of plate-like primary particles is laminated outside the central portion, and a low-density portion formed by aggregation of fine primary particles and a high-density portion formed by aggregation of the plate-like primary particles are laminated outside the central portion. Patent Document 2 also discloses a precursor for producing a porous positive electrode active material. For example, the positive electrode active material can be produced by mixing the precursor with a Li compound and firing the mixture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-154143 [Patent Document 2] Japanese Patent Application Publication No. 2019-021610 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a positive electrode active material is produced by firing a precursor of the positive electrode active material, the reaction with Li may be insufficient, resulting in insufficient output characteristics.

[0005] Therefore, a main object of the present disclosure is to provide a technology that can realize a lithium ion secondary battery with excellent output characteristics. [Means for solving the problem]

[0006] One aspect of the technology disclosed herein is a precursor for a positive electrode active material used in a lithium-ion secondary battery. This precursor contains Ni-containing transition metal composite hydroxide particles, and the transition metal composite hydroxide particles have an outer shell portion formed by aggregation of primary particles having an average aspect ratio (long axis length / short axis length) of 2 or more based on SEM observation, and a hollow portion surrounded by the outer shell portion. 50% or more of the primary particles are oriented radially from the center toward the surface of the transition metal composite hydroxide particle, and 90% or more of the primary particles contained in the entire transition metal composite hydroxide particle are present in the outer shell portion.

[0007] The transition metal composite hydroxide particles (also referred to as precursor particles) contained in the precursor have 90% or more of the primary particles present in the outer shell, and have hollow portions with few or no primary particles. This increases the reactive surface area of ​​the precursor particles, improving the reaction with Li during firing and suppressing unreacted Li. Furthermore, because 50% or more of the primary particles in the outer shell are radially oriented, Li can easily diffuse, improving output characteristics. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of the cross-sectional structure of a precursor particle of a positive electrode active material according to one embodiment. [Figure 2] FIG. 2 is a flow diagram showing an outline of a method for producing a positive electrode active material used in a lithium ion secondary battery in one embodiment. [Figure 3] FIG. 3 is a schematic diagram showing the general configuration of a crystallizer. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line IV-IV shown in FIG. [Figure 5] FIG. 5 is a cross-sectional view schematically showing the configuration of a lithium ion secondary battery using the fired product of precursor particles according to one embodiment. [Figure 6] FIG. 6 is a schematic exploded view showing the configuration of the wound electrode body 20. As shown in FIG. [Figure 7] FIG. 7 is a cross-sectional SEM image of the precursor particle of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology (e.g., the general configuration and manufacturing process of a lithium-ion secondary battery that do not characterize the technology) can be understood as design matters for a person skilled in the art based on conventional technology in the relevant field. The technology can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. The drawings are schematic, and dimensional relationships (length, width, thickness, etc.) do not necessarily reflect actual dimensional relationships. In the drawings described below, components and parts that perform the same function are designated by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0010] In this specification, when a numerical range is described as "A to B (where A and B are any numerical values)," it means "A or more and B or less," and also encompasses the meanings of "greater than A and less than B," "greater than A and B or less," and "greater than A and less than B."

[0011] 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.

[0012] The present disclosure provides a precursor material for a positive electrode active material used in a lithium-ion secondary battery. The precursor material is, for example, in powder form. The precursor material includes a plurality of precursor particles. FIG. 1 is a schematic diagram of the cross-sectional structure of a precursor particle 200 for a positive electrode active material according to one embodiment. The precursor particle 200 has a hollow structure including an outer shell portion 210 and a hollow portion 220.

[0013] The precursor material contains precursor particles 200 as the main component. The precursor particles 200, for example, account for 80 wt% or more, 90 wt% or more, 95 wt% or more, or 100 wt% of the precursor material.

[0014] The precursor particles 200 are particles containing a transition metal composite hydroxide (also referred to as "transition metal composite hydroxide particles 200"). The precursor particles 200 contain a transition metal and preferably contain at least nickel (Ni). The precursor particles 200 are converted into a lithium transition metal composite oxide by being fired in a state where a lithium element (Li element) is supplied. Such a lithium transition metal composite oxide can be used as a positive electrode active material.

[0015] In some embodiments, the precursor particles 200 have the following general formula (i): Ni (1-x-y-z) Co x Mn y A z (OH) 2+a (i) and have a composition represented by. However, in the general formula (i), it is assumed that 0 ≦ x < 0.5, 0 ≦ y < 0.5, 0 ≦ z ≦ 0.1, 0 ≦ a ≦ 0.5, and x + y + z < 1 are satisfied. Also, in the general formula (i), A is at least one element selected from the group consisting of Mg, Ca, V, Cr, Al, Ti, Zr, Nb, Mo, and W is at least one element selected from the group.

[0016] In some embodiments, the proportion of Ni is higher than the total proportion of Co and Mn. That is, in the general formula (i), x + y + z < 0.5 may be satisfied.

[0017] In some embodiments, the precursor particles 200 contain Ni, Co, and Mn. That is, in the general formula (i), 0 < x < 0.5 and 0 < y < 0.5 may be satisfied. Also, in some embodiments, 0 < x < 0.3 and 0 < y < 0.3 may be satisfied.

[0018] In some embodiments, precursor particles 200 are generally spherical, or in some embodiments, precursor particles 200 may be irregularly shaped, etc. As used herein, "substantially spherical" refers to a shape that can be considered roughly spherical overall, with an average aspect ratio based on cross-sectional electron microscope images of approximately 1 to 2, preferably 1 to 1.5, and more preferably 1 to 1.2. Furthermore, as used herein, "aspect ratio" refers to the value obtained by dividing the long side of the rectangle with the smallest area among rectangles circumscribing the particle outline by the short side. Furthermore, "average aspect ratio" refers to the arithmetic mean of the aspect ratios of at least 100 randomly selected particles.

[0019] The average particle size of the precursor particles 200 is, for example, 3.0 μm or more, preferably 4.0 μm or more, and more preferably 4.5 μm or more, and the average particle size of the precursor particles 200 is, for example, 9.0 μm or less, preferably 7.0 μm or less, and more preferably 5.5 μm or less. In this specification, the term "average particle size" refers to the median diameter (D 50 This refers to the particle size (particle size) that corresponds to a cumulative frequency of 50% by volume from the smallest particle size side in the volume-based particle size distribution based on the laser diffraction / scattering method.

[0020] The outer shell 210 includes a plurality of primary particles 212. In this embodiment, the outer shell 210 is formed by agglomerating the plurality of primary particles 212 through physical or chemical bonding forces. In this specification, the term "primary particle" refers to the smallest unit of particles that make up the precursor particle 200, and more specifically, refers to the smallest unit determined from the geometric shape of its appearance.

[0021] The outer shell 210 may have a single layer structure, or may have a multi-layer structure in which multiple layers are stacked.

[0022] The average thickness of the outer shell 210 may be, for example, 1 / 5 or less, and preferably 1 / 6 or less, of the average particle size of the precursor particles 200. The average thickness of the outer shell 210 may be, for example, 1 / 10 or more, or 1 / 8 or more, of the average particle size of the precursor particles 200. By making the average thickness of the outer shell 210 thinner than the average particle size of the precursor particles 200, the diffusion resistance of Li ions is reduced, and output characteristics are improved. In this specification, the thickness of the outer shell 210 refers to the thickness measured in a cross-sectional observation image of the precursor particle 200 taken with an electron microscope, and the average thickness of the outer shell 210 refers to the arithmetic mean of the thicknesses of the outer shell 210 measured for at least 100 precursor particles 100.

[0023] The shape of the primary particles 212 may be, for example, needle-like, plate-like, elliptical, or the like. The average aspect ratio (length of major axis / length of minor axis) of the precursor particles 200 based on a cross-sectional observation image taken with an electron microscope is, for example, 2 or more, preferably 3 or more, and more preferably 5 or more. The longer the average aspect ratio of the primary particles 212, the more likely the diffusion resistance of Li ions will be reduced. The average aspect ratio of the primary particles 212 may be, for example, 50 or less, 20 or less, or 10 or less.

[0024] The average length of the major axes of the primary particles 212 is, for example, 0.05 μm or more, 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more, and the average length of the major axes of the primary particles 212 is, for example, 1.2 μm or less, 1 μm or less, or 0.8 μm or less.

[0025] The average length of the minor axes of the primary particles 212 is, for example, 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more, and the average length of the minor axes of the primary particles 212 is, for example, 0.6 μm or less, 0.4 μm or less, or 0.2 μm or less.

[0026] The average lengths of the major and minor axes of the primary particles 212 are measured based on an electron microscope cross-sectional observation image of the precursor particles 200. In this specification, the average lengths of the major and minor axes of the primary particles 212 refer to the arithmetic mean of the major and minor axes of at least 100 primary particles 212.

[0027] At least 50% of the primary particles 212 contained in the outer shell 210 are oriented radially from the center of the precursor particle 200 toward the surface of the precursor particle 200. In a preferred embodiment, the oriented primary particles 212 account for at least 60%, more preferably at least 65%, and even more preferably at least 70%. Radially oriented primary particles 212 in a larger number can reduce the diffusion resistance of Li ions and improve output characteristics. The percentage of the primary particles 212 mentioned above indicates a percentage based on the number, and indicates the percentage of radially oriented primary particles 212 out of the total number (at least 100) of measured primary particles 212. In this specification, "primary particles are radially oriented" means that the angle formed by the long axis direction of the primary particle 212 with respect to a reference line connecting the center of the primary particle 212 and the center of the precursor particle 200 is 30° or less. Note that this measurement can be performed by processing a cross section of the precursor particle 200 with an ion beam and observing the cross section with an electron microscope. Note that as another method, the orientation can also be confirmed by electron backscatter diffraction (EBSD).

[0028] The hollow portion 220 is a space surrounded by the outer shell portion 210. The hollow portion 220 does not have to be completely surrounded by the outer shell portion 210, and includes embodiments in which a portion of the outer shell portion 210 is missing. The number of primary particles in the hollow portion 220 is fewer than that in the outer shell portion 210, or there are no primary particles in the hollow portion 220. That is, the proportion of primary particles 212 contained in the outer shell portion 210 among the primary particles contained in the entire precursor particle 200 can be, for example, 90% or more, 95% or more, 98% or more, or 100%. This makes it possible to obtain an active material that reacts well with Li during firing. In this specification, the proportion of such primary particles is measured by area ratio in a cross-sectional SEM.

[0029] 2 is a flow diagram showing an outline of a method for producing a positive electrode active material for use in a lithium-ion secondary battery according to one embodiment. This production method includes a raw material preparation step S10, a crystallization step S20, a mixing step S30, and a firing step S40. The raw material preparation step S10 and the crystallization step are included in the production process for the precursor particles 200 described above. Note that the production method disclosed herein may further include other steps at any stage.

[0030] The raw material preparation step S10 is, for example, a step of preparing raw materials for the precursor material. Examples of precursor materials include a metal compound containing the metal element contained in the precursor particle 200 and an ammonium ion donor. The metal compound containing the metal element contained in the precursor particle 200 may be, for example, a water-soluble salt. Examples of such water-soluble salts that can be used appropriately include sulfates, nitrates, and oxalates. These water-soluble salts may be used alone or in combination of two or more. The metal element contained in the precursor particle 200 is, for example, a metal element represented by the above general formula (1) and includes at least Ni.

[0031] In the raw material preparation step S10, for example, the metal compound is dissolved in water to prepare a raw metal aqueous solution containing the metal element contained in the precursor particles 200. As the water, ion-exchanged water, distilled water, ultrafiltered water, reverse osmosis water, etc. can be suitably used from the viewpoint of preventing the incorporation of impurities.

[0032] In the raw material preparation step S10, an ammonium ion donor is prepared. The ammonium ion donor is, for example, an aqueous solution containing ammonia ions. Such an aqueous solution may be purchased commercially (ammonia water), or may be prepared by dissolving a compound that supplies ammonium ions in a solvent containing water. Examples of such compounds that can be used include ammonium sulfate, ammonium nitrate, ammonium hydroxide, aqueous ammonium halide, and ammonia. These compounds may be used alone or in combination of two or more. In the crystallization step S20 described below, ammonium ions can promote the formation or growth of nuclei and increase the adhesiveness or adhesion between primary particles. Although not limited thereto, the aqueous solution containing ammonium ions contains, for example, 0.1 wt to 5 wt %, preferably 0.5 wt to 2 wt %, of ammonium ions.

[0033] In the crystallization step S20, precursor particles are prepared using a crystallizer. The crystallizer is preferably a device capable of generating a Taylor vortex flow in the reaction field. The device for generating a Taylor vortex flow may be a commercially available product. FIG. 3 is a schematic diagram showing the general configuration of the crystallizer. FIG. 4 is a schematic diagram of a cross section taken along line IV-IV shown in FIG. 3. L and R in FIG. 3 indicate left and right, respectively, but this does not limit the installation mode of the crystallizer.

[0034] The crystallizer 300 shown in Figure 3 includes an outer cylinder 310, an inner cylinder 320, and a motor 322. The crystallizer 300 has a reaction chamber 330 between the outer cylinder 310 and the inner cylinder 320. The reaction chamber 330 is a region where a crystallization reaction occurs and where Taylor vortices are generated. The Taylor vortices refer to the flow of a fluid that generates Taylor vortices. The Taylor vortices refer to a form of vortex that flows in a circular pattern.

[0035] In this embodiment, the outer cylinder 310 is cylindrical. The central axis of the outer cylinder 310 extends in the left-right direction in Fig. 3. Here, the outer cylinder 310 is fixed so as not to rotate around the central axis.

[0036] In this embodiment, the outer cylinder 310 is provided with a first supply port 312, a second supply port 314, a third supply port 316, and an outlet 318. All of these are in communication with the reaction chamber 330.

[0037] In this embodiment, the first supply port 312 is a portion that supplies a raw metal aqueous solution to the reaction chamber 330. The second supply port 314 is a portion that supplies a pH adjuster to the reaction chamber 330. The third supply port 316 is a portion that supplies an ammonium ion supplier to the reaction chamber 330. Although three supply ports are provided in this embodiment, the number is not particularly limited and may be one, two, or four or more. The type of supply may be different for each supply port, or two or more types of supply may be supplied from a single supply port.

[0038] The outlet 318 is provided to discharge the fluid inside the reaction chamber 330. The fluid discharged from the outlet 318 contains the precursor particles 200 obtained by the crystallization reaction. This allows the precursor particles 200 to be recovered from the reaction chamber 330.

[0039] In this embodiment, the inner cylinder 320 is cylindrical. However, the inner cylinder 320 may be cylindrical. The diameter of the inner cylinder 320 is designed to be smaller than the diameter of the outer cylinder 310. The space between the inner diameter of the outer cylinder 310 and the outer diameter of the inner cylinder 320 is the reaction chamber 330. The diameter of the inner cylinder 320 is designed to be large enough to generate a Taylor vortex flow in the reaction chamber 330. The central axis of the inner cylinder 320 extends in the left-right direction in FIG. 3. In this embodiment, the central axis of the inner cylinder 320 is arranged to overlap with the central axis of the outer cylinder 310.

[0040] The inner cylinder 320 is connected to a motor 322 and is designed so that the inner cylinder 320 can rotate clockwise or counterclockwise around its central axis by the motor 322. By rotating the inner cylinder 320, Taylor vortices can be generated in the fluid (e.g., liquid phase) in the reaction chamber 330.

[0041] The rotation speed of the inner cylinder 320 about its central axis is not particularly limited as long as it can generate a Taylor vortex flow, but is, for example, 300 rpm or more, 500 rpm or more, 1000 rpm or more, 1500 rpm or more, or 2000 rpm or more. The rotation speed of the inner cylinder 320 about its central axis is, for example, 3000 rpm or less, 2800 rpm or less, or 2600 rpm or less.

[0042] To prepare precursor particles 200 using the crystallizer 300, for example, a reaction solution containing a metal compound containing a metal element contained in the precursor particles and an ammonium ion donor is prepared in the reaction chamber 330. Such a reaction solution is prepared, for example, by supplying a raw metal aqueous solution and an ammonium ion donor to the reaction chamber 330. Alternatively, a mixture of the raw metal aqueous solution and the ammonium ion donor may be supplied to the reaction chamber 330.

[0043] The crystallization step S20 is preferably performed by adjusting the oxygen concentration in the reaction field. The oxygen concentration in the reaction chamber 330 may be, for example, 20 vol% or more, and preferably 22 vol% or more. The oxygen concentration in the reaction chamber 330 is, for example, 40 vol% or less, preferably 35 vol% or less, more preferably 30 vol% or less, and even more preferably 25 vol% or less. The greater the supply of oxygen in the reaction chamber 330, the higher the proportion of hollow portions in the precursor particles tends to be. That is, the greater the supply of oxygen in the reaction chamber 330, the smaller the thickness of the outer shell relative to the average particle size of the precursor particles can be.

[0044] The pH of the reaction solution at 25°C is, for example, 9 or higher, preferably 10.5 or higher, more preferably 10.8 or higher, even more preferably 11 or higher, and particularly preferably 11.4 or higher. Furthermore, although not particularly limited, the pH of the reaction solution at 25°C is, for example, 13.5 or lower, preferably 13 or lower, more preferably 12.5 or lower, and even more preferably 12 or lower. In some preferred embodiments, the pH of the reaction solution is maintained constant from the start to the end of the crystallization reaction. Under such conditions, the pH does not change during the crystallization reaction, thereby improving the production efficiency of the precursor particles 200. Note that the constant pH does not have to be exactly the same pH value; for example, a pH change of ±0.3, preferably ±0.2, from the pH at the start of the crystallization reaction is acceptable.

[0045] To adjust the pH of the reaction solution, for example, a pH adjuster can be used. Examples of pH adjusters that can be used include carbonates, hydroxides, sulfates, etc. of alkali metals or alkaline earth metals. These pH adjusters may be used alone or in combination of two or more. Among these, the use of hydroxides of alkali metals or alkaline earth metals is preferred, with sodium hydroxide being particularly preferred.

[0046] The reaction solution contained in the reaction chamber 330 is stirred by rotating the inner tube 320 around the central axis. Rotating the inner tube 320 generates Taylor vortices in the reaction solution. The Taylor vortices are generated in at least a portion of the reaction solution in the reaction chamber 330. They may also be generated throughout the reaction solution. For example, a pair of a first Taylor vortex 332 and an adjacent second Taylor vortex 334 are generated. The first Taylor vortex 332 is generated along the circumference of the inner tube 320 and has a clockwise vortex in the circumferential direction. The second Taylor vortex 334 is generated along the circumference of the inner tube 320 and has a vortex that rotates counterclockwise relative to the first Taylor vortex in the circumferential direction. The Taylor vortices themselves are generated in a ring shape along the circumference of the inner tube 320, but the fluid forming the Taylor vortices moves to the adjacent Taylor vortex (moving from left to right in FIG. 3 ). Therefore, the reaction liquid stirred by the Taylor vortex moves from the supply ports 312 , 314 , and 316 toward the discharge port 318 while crystallization progresses, and the precursor particles 200 can be collected from the discharge port 318 .

[0047] The precursor particles 200 recovered from the reaction chamber 330 can be separated by a solid-liquid separation method such as filtration, washed with water or the like, and dried to recover the precursor particles 200.

[0048] Although not particularly limited, the reaction time of the crystallization reaction is, for example, 0.1 to 5 hours, preferably 0.3 to 2 hours, and more preferably 0.5 to 1 hour. Here, the reaction time of the crystallization reaction can be measured, for example, as the time from when the raw metal aqueous solution is supplied to the reaction chamber 330 through the first supply port 312 with the ammonium ion donor accommodated in the reaction chamber 330 to when the precursor particles 200 are first recovered from the discharge port 318.

[0049] In some preferred embodiments, an ammonium ion donor is supplied to the reaction chamber 330 before the aqueous raw metal solution is supplied to the reaction chamber 330. At this time, the ammonium ion donor is preferably adjusted to achieve the oxygen concentration and pH of the reaction solution in the reaction chamber 330 described above. This allows the crystallization reaction to start when the aqueous raw metal solution is supplied to the reaction chamber 330 from the first supply port 312, making it possible to control the time from the start of the crystallization reaction to the collection of the precursor particles 200 from the outlet 318, thereby making it possible to make the particle size distribution of the precursor particles more uniform.

[0050] In some preferred embodiments, it is preferable to rotate the inner cylinder 320 in the reaction chamber 330 to generate a Taylor vortex in the ammonium ion supplier before supplying the raw metal aqueous solution to the reaction chamber 330. This makes it possible to maintain constant stirring conditions in the reaction chamber 330 from the start of the crystallization reaction until the precursor particles are recovered, thereby making it possible to make the quality of the precursor particles more uniform.

[0051] In some preferred embodiments, the rotation speed of the inner cylinder 320 is kept constant from the start to the end of the crystallization reaction, which suppresses variations in the quality of the precursor particles 200, eliminates the need for complicated operations, and improves production efficiency.

[0052] In some preferred embodiments, the raw metal aqueous solution is continuously supplied to the reaction solution in the reaction chamber 330. This allows the precursor particles 200 obtained by the crystallization reaction to be continuously collected from the outlet 318, thereby improving the production efficiency of the precursor particles. Also, preferably, an ammonium ion donor is continuously supplied to the reaction solution in the reaction chamber 330. This allows the concentration balance between the metal compounds and ammonium ions in the reaction solution in the reaction chamber 330 to be maintained.

[0053] In the mixing step S30, the obtained precursor particles 200 are mixed with a lithium compound. The mixing method is not particularly limited, and for example, a known mixing device (e.g., a shaker mixer, a V blender, a ribbon mixer, a Julia mixer, a Lödige mixer, etc.) can be used to mix the precursor particles 200 and obtain a mixture. As the lithium compound, a compound that can be converted to an oxide by firing can be used, and for example, lithium carbonate, lithium nitrate, lithium hydroxide, etc. can be used appropriately.

[0054] In the calcination step S40, the mixture obtained above is calcined to obtain a positive electrode active material that is a lithium transition metal composite oxide. Calcination can be carried out in a conventionally known calcination furnace. Although not particularly limited, the calcination temperature is preferably about 600 to 1000°C. The calcination temperature refers to the temperature inside the calcination furnace. The calcination 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 calcination 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.

[0055] The lithium ion secondary battery using the lithium transition metal composite oxide obtained by firing has excellent output characteristics and cycle characteristics. Specific configuration examples of the lithium ion secondary battery will be described below with reference to the drawings.

[0056] FIG. 5 is a cross-sectional view schematically illustrating the configuration of a lithium-ion secondary battery 100 using a fired product of precursor particles 200 according to one embodiment. The lithium-ion secondary battery 100 of FIG. 5 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.

[0057] FIG. 6 is a schematic exploded view showing the configuration of the wound electrode body 20. As shown in FIGS. 5 and 6, 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 separators 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 current collector exposed portion 52a (i.e., a portion where the positive electrode current collector 52 is exposed because the positive electrode active material layer 54 is not formed) and the negative electrode current collector exposed portion 62a (i.e., a portion where the negative electrode current collector 62 is exposed because the negative electrode active material layer 64 is not formed) 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. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to the positive electrode current collector exposed portion 52a and the negative electrode current collector exposed portion 62a, respectively.

[0058] 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).

[0059] 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).

[0060] 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).

[0061] 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.

[0062] 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.

[0063] Such a lithium ion secondary battery 100 can be manufactured by a manufacturing method including a positive electrode manufacturing step of manufacturing a positive electrode sheet 50 using the positive electrode active material (lithium transition metal composite oxide) manufactured by the above manufacturing method.

[0064] 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.

[0065] 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.

[0066] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Section 1: A precursor of a positive electrode active material used in a lithium ion secondary battery, The transition metal composite hydroxide particles contain Ni, The transition metal composite hydroxide particles have an outer shell portion formed by aggregation of primary particles having an average aspect ratio (length of major axis / length of minor axis) of 2 or more based on SEM observation, and a hollow portion surrounded by the outer shell portion, 50% or more of the primary particles are oriented radially from the center toward the surface of the transition metal composite hydroxide particles, A precursor in which 90% or more of the primary particles contained in the entire transition metal composite hydroxide particle are present in the outer shell portion. Item 2: The precursor according to Item 1, wherein the average thickness of the outer shell portion is one-sixth or less of the average particle size of the transition metal composite hydroxide particles. Item 3: The transition metal composite hydroxide particles are represented by the general formula: Ni (1-x-y-z) Co x Mn y A z (OH) 2+a (where 0≦x<0.5, 0≦y<0.5, 0≦z≦0.1, 0≦a≦0.5, x+y+z<1A is at least one element selected from the group consisting of Mg, Ca, V, Cr, Al, Ti, Zr, Nb, Mo, and W) Item 3. The precursor according to item 1 or 2, which is a compound represented by the formula: Item 4: The precursor according to any one of Items 1 to 3, wherein the primary particles have an average length of the major axis of 0.05 μm or more and 1.2 μm or less. Section 5: A method for producing a precursor of a positive electrode active material for use in a lithium ion secondary battery, comprising: providing a metal compound containing Ni and an ammonium ion donor; preparing an apparatus including an outer cylinder, an inner cylinder disposed inside the outer cylinder, and a reaction chamber disposed between the outer cylinder and the inner cylinder, and rotating the inner cylinder around the axial direction of the inner cylinder to generate Taylor vortices in a reaction solution that contains the metal compound and the ammonium ion donor and is contained in the reaction chamber, thereby crystallizing a transition metal composite hydroxide; Including, the pH of the reaction solution at 25°C is 9 or higher, The oxygen concentration in the reaction chamber is 20 vol% or more and 50 vol% or less, The rotation speed of the inner cylinder is 300 rpm or more and 3000 rpm or less. Manufacturing method. Item 6: The method according to item 5, wherein the pH of the reaction solution at 25°C is 10.5 or higher and 13 or lower. Section 7: A method for producing a positive electrode active material for use in a lithium ion secondary battery, comprising: Item 5 or 6. Mixing the precursor obtained by the production method according to item 5 or 6 with a lithium compound; and baking the mixed mixture; The manufacturing method includes the steps of: Item 8: A method for producing a lithium ion secondary battery, comprising producing a positive electrode containing the positive electrode active material obtained by the production method according to Item 7.

[0067] Test examples relating to the present technology will be described below, but the present technology is not limited to those shown in the following test examples.

[0068] Example 1 [Precursor crystallization] A crystallizer capable of generating Taylor vortexes in the reaction chamber was used. The general configuration of the crystallizer was similar to that of the crystallizer 300 described above. The oxygen concentration in a 0.1 L reaction chamber was adjusted to 25 vol%, 1 wt% ammonia water was added, and the inner cylinder of the device was rotated at 2000 rpm to generate Taylor vortices in the ammonia water in the reaction chamber. Next, 30 wt% sodium hydroxide aqueous solution was supplied to the reaction chamber, and the mixed solution in the reaction chamber was adjusted to pH 12 at a liquid temperature of 25°C. Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water to prepare a 1 mol / L aqueous solution of raw metals, with a molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate of 60:20:20. The raw metal aqueous solution, 30 wt% sodium hydroxide aqueous solution, and 1 wt% ammonia aqueous solution were fed into the mixed solution in the reaction chamber, where Taylor vortices were generated, in a volumetric ratio of 1:1:1, and crystallization was carried out for 30 minutes at a pH of 12. The crystallized product was then washed with water, filtered, and dried to obtain a powdery composite hydroxide (precursor). The composite hydroxide obtained above was analyzed by ICP emission spectroscopy.0.6 Co 0.2 Mn 0.2 (OH)2 was confirmed.

[0069] [Active material firing] A lithium compound was mixed with the composite hydroxide so that the molar ratio (Li:M) of lithium (Li) to metal elements other than lithium (M) was 1.1:1. This mixture was calcined in a calcination furnace at 700°C under an oxidizing atmosphere for 5 hours. This produced a positive electrode active material.

[0070] [Preparation of positive electrode plate] The obtained positive electrode active material, conductive material, and binder were mixed with N-methyl-2-pyrrolidone (NMP) in a ratio of 100:1:1 (by weight) to prepare a positive electrode mixture paste. Acetylene black was used as the conductive material, and PVDF was used as the binder. The prepared positive electrode mixture paste was applied to 15 μm aluminum foil and dried, then pressed to the specified thickness and processed to the specified size to produce a positive electrode plate.

[0071] [Preparation of negative electrode plate] The graphite, SBR, and CMC were mixed with water in a ratio of 100:1:1 (by weight) to prepare a negative electrode mixture paste. The prepared negative electrode mixture paste was applied to copper foil, dried, pressed to a specified thickness, and cut to a specified size to produce a negative electrode plate.

[0072] [Fabrication of non-aqueous electrolyte secondary battery] The fabricated positive and negative electrode plates were stacked together with a separator interposed between them to produce a stacked electrode assembly. Leads were attached to each of the positive and negative electrode plates. The fabricated stacked electrode assembly was housed in an exterior case made of an aluminum laminate sheet, after which a nonaqueous electrolyte was poured in and the opening of the exterior case was sealed to produce a test cell. The nonaqueous electrolyte used contained a solvent consisting of EC:FEC:EMC:DMC = 15:5:40:40 (by volume) and 1M LiPF6 as the Li salt.

[0073] <SEM observation of precursor> After cross-sectionally processing the above-mentioned composite hydroxide particles (precursor particles) with an ion beam, the cross-section of the particles was observed by SEM. The structure of the precursor particles was evaluated by SEM observation. Fig. 7 shows the cross-sectional SEM image of the precursor particles obtained in Example 1.

[0074] Also, the orientation of the primary particles contained in the outer shell part was confirmed by SEM observation of the cross-section of the composite hydroxide particles. Specifically, with respect to the reference line connecting the center of the primary particle and the center of the composite hydroxide particle, those in which the angle formed by the long axis direction of the primary particle is 30° or less were evaluated as being radially oriented. More than 100 primary particles contained in the outer shell part were randomly observed, and the ratio of the radially oriented primary particles was determined. The results are shown in Table 1.

[0075] Also, the thickness of the outer shell part was measured by SEM observation of the cross-section of the composite hydroxide particles. The thicknesses of the outer shell parts of more than 100 particles were randomly measured, and their arithmetic mean was determined. The value obtained by dividing the arithmetic mean of the thickness of the outer shell part by the average particle size of the composite hydroxide particles shown below is shown in Table 1 as the "thickness of the outer shell part relative to the average particle size".

[0076] <Analysis of the average particle size of the precursor> The average particle size of the composite hydroxide particles was defined as the particle size (D50) corresponding to 50% cumulative in the volume-based particle size distribution measured by a laser diffraction scattering type particle size analyzer.

[0077] <IV Resistance Measurement> In an environment at 25°C, the test cell was charged so that the state of charge (SOC) was 50% and left standing for 1 hour. Then, it was discharged at a current of 5C for 10 seconds. When the OCV voltage immediately before discharge was V0 and the voltage at the 10-second discharge time was V1, Formula: IV resistance = (V0 - V1) / 5C current value was used to determine the IV resistance value. Table 1 shows the results as a ratio based on Comparative Example 1 described later.

[0078] <Measurement of cycle capacity retention rate> In a 25°C environment, CCCV charging at 0.4C, 4.2V, and 0.1C cut was performed, followed by CC discharging at 0.4C, 2.5V cut, which was defined as one cycle, and 250 cycles were repeated. Formula: 250th cycle capacity / 1st cycle capacity x 100 (%) The capacity retention rate was calculated using the above formula, and the results are shown in Table 1.

[0079] Example 2 The oxygen concentration in the reaction chamber was changed from the precursor crystallization conditions in Example 1 to 30 vol%. In addition, the rotation speed of the inner cylinder of the crystallizer was changed to 700 rpm. In addition, a 30 wt% aqueous sodium hydroxide solution was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 10.8 at a liquid temperature of 25°C. Except for these, a powdery composite hydroxide was obtained in the same manner as in Example 1. The subsequent procedures up to the preparation of the test cell, and the evaluation of the precursor and the test cell were the same as in Example 1 (the same applies to the following examples).

[0080] Example 3 The oxygen concentration in the reaction chamber was changed to 22 vol% from the precursor crystallization conditions in Example 1. The rotation speed of the inner cylinder of the crystallizer was also changed to 2600 rpm. A 30 wt% aqueous solution of sodium hydroxide was supplied to the reaction chamber so that the mixed solution in the reaction chamber had a pH of 11.4 at a liquid temperature of 25°C. A 1 mol / L aqueous solution of raw metals was prepared so that the molar ratio of nickel sulfate:cobalt sulfate:manganese sulfate:zirconium sulfate was 59.9:19.9:19.9:0.3. A powdered composite hydroxide was obtained in the same manner as in Example 1, except for these points. The obtained composite hydroxide was analyzed by an ICP emission spectrometer to determine whether it contained Ni 0.599 Co 0.199 Mn 0.199 Zr 0.003 (OH)2 was confirmed.

[0081] Example 4 The oxygen concentration in the reaction chamber was changed to 22 vol% from the conditions for precursor crystallization in Example 1. In addition, a 30 wt% aqueous sodium hydroxide solution was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 13.5 at a liquid temperature of 25°C. Except for these, a powdery composite hydroxide was obtained in the same manner as in Example 1.

[0082] Example 5 Based on the conditions for precursor crystallization in Example 1, a 30 wt % aqueous solution of sodium hydroxide was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 9 at a liquid temperature of 25° C. A powdery composite hydroxide was obtained in the same manner as in Example 1 except for this.

[0083] (Comparative Example 1) The oxygen concentration in the reaction chamber was changed to 10 vol% from the precursor crystallization conditions in Example 1. The rotation speed of the inner cylinder of the crystallizer was also changed to 1000 rpm. A 30 wt% aqueous sodium hydroxide solution was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 11.8 at a liquid temperature of 25°C. A powdery composite hydroxide was obtained in the same manner as in Example 1, except for these points.

[0084] (Comparative Example 2) The rotation speed of the inner cylinder of the crystallizer was changed to 3500 rpm from the conditions for precursor crystallization in Example 1. Except for this, a powdery composite hydroxide was obtained in the same manner as in Example 1. In addition, a 30 wt % aqueous sodium hydroxide solution was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 12.6 at a liquid temperature of 25°C. Except for this, a powdery composite hydroxide was obtained in the same manner as in Example 1.

[0085] (Comparative Example 3) The oxygen concentration in the reaction chamber was changed to 22 vol% from the precursor crystallization conditions in Example 1. The rotation speed of the inner cylinder of the crystallizer was also changed to 200 rpm. A 30 wt% aqueous sodium hydroxide solution was supplied to the reaction chamber so that the mixed liquid in the reaction chamber had a pH of 10.8 at a liquid temperature of 25°C. A powdery composite hydroxide was obtained in the same manner as in Example 1, except for these points.

[0086] [Table 1]

[0087] As shown in Table 1 and FIG. 7, precursor particles having a hollow structure can be produced by carrying out a crystallization reaction accompanied by stirring by Taylor vortex flow in an oxidizing atmosphere (e.g., an oxygen concentration of 20 vol% or more). It is also found that the primary particles constituting the outer shell of the precursor particles produced by this method tend to be radially oriented. It is also found that a lithium ion secondary battery including a positive electrode active material produced using precursor particles having such a structure exhibits reduced resistance and improved output characteristics.

[0088] Although specific examples of the present technology 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 36 Safety valve 42 Positive terminal 42a Positive current collector plate 44 Negative terminal 44a Negative current collector plate 50 positive electrode sheet 52 Positive electrode current collector 52a Exposed part of positive electrode current collector 54 Cathode active material layer 60 negative electrode sheet 62 Negative electrode current collector 62a Exposed part of negative electrode current collector 64 Negative electrode active material layer 70 Separator 100 Lithium-ion secondary battery 200 Precursor particles (transition metal composite hydroxide particles) 210 Outer shell 212 Primary particles 220 Hollow part 300 Crystallizer 310 Outer cylinder 320 Inner cylinder 330 Reaction Chamber

Claims

1. A precursor of a positive electrode active material used in a lithium ion secondary battery, The composite hydroxide particles contain Ni. the transition metal composite hydroxide particles have an outer shell portion formed by aggregation of primary particles having an average aspect ratio (length of major axis / length of minor axis) of 2 or more based on SEM observation, and a hollow portion surrounded by the outer shell portion; 50% or more of the primary particles are oriented radially from the center toward the surface of the transition metal composite hydroxide particle, 90% or more of the primary particles contained in the entire transition metal composite hydroxide particles are present in the outer shell portion. Precursor.

2. The precursor according to claim 1 , wherein the average thickness of the outer shell portion is one-sixth or less of the average particle diameter of the transition metal composite hydroxide particles.

3. The transition metal composite hydroxide particles have the general formula: Ni （１－ｘ－ｙ－ｚ） Co ｘ Mn ｙ A ｚ (OH) ２＋ａ (wherein 0≦x<0.5, 0≦y<0.5, 0≦z≦0.1, 0≦a≦0.5, and x+y+z<1; A is at least one element selected from the group consisting of Mg, Ca, V, Cr, Al, Ti, Zr, Nb, Mo, and W). The precursor according to claim 1, which is a compound represented by the formula:

4. 4. The precursor according to claim 1, wherein the average length of the major axes of the primary particles is 0.05 μm or more and 1.2 μm or less.

5. A method for producing a precursor of a positive electrode active material used in a lithium ion secondary battery, comprising: Preparing a metal compound containing Ni and an ammonium ion donor; an apparatus including an outer cylinder, an inner cylinder disposed inside the outer cylinder, and a reaction chamber disposed between the outer cylinder and the inner cylinder is prepared, and the inner cylinder is rotated around the axial direction of the inner cylinder to generate Taylor vortices in a reaction solution containing the metal compound and the ammonium ion donor contained in the reaction chamber, thereby crystallizing a transition metal composite hydroxide; Including, the pH of the reaction solution at 25°C is 9 or higher, the oxygen concentration in the reaction chamber is 20 vol% or more and 50 vol% or less, The rotation speed of the inner cylinder is 300 rpm or more and 3000 rpm or less. Manufacturing method.

6. The method according to claim 5, wherein the pH of the reaction solution at 25°C is 10.5 or more and 13 or less.

7. A method for producing a positive electrode active material for use in a lithium ion secondary battery, comprising: Mixing the precursor obtained by the method according to claim 5 or 6 with a lithium compound; and baking the mixed mixture; The manufacturing method includes the steps of:

8. A method for producing a lithium ion secondary battery, comprising fabricating a positive electrode containing the positive electrode active material obtained by the method of claim 7.

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