Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery

Abstract

To provide a positive electrode active material for lithium secondary battery that enables the provision of a lithium secondary battery with high initial discharge capacity and low gas generation even during charging.SOLUTION: A positive electrode active material for a lithium secondary battery includes a lithium metal composite oxide in which primary particles are aggregated into secondary particles and a boron-containing compound, and satisfies the following formula (A): 0.5<Y / X<1.0 ... Formula (A) (In Formula (A), X is the percentage (%) of boron element present on the surface of the lithium secondary battery positive electrode active material, measured by X-ray photoelectron spectroscopy, Y is the percentage (%) of boron element present on the surface of the lithium secondary battery positive electrode active material after powder compaction at 50 MPa, measured by X-ray photoelectron spectroscopy.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery. [Background technology]

[0002] A positive electrode active material for lithium secondary batteries is used for the positive electrode that constitutes the lithium secondary battery. Patent Document 1 discloses a lithium-nickel-manganese composite oxide as a positive electrode active material for lithium secondary batteries, which is composed of secondary particles formed by aggregation of multiple primary particles. Patent Document 1 discloses that high battery capacity and output characteristics are achieved simultaneously with low electrical conductivity by segregating boron on the surfaces of the primary particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP-A-2020-102432 Summary of the Invention [Problem to be solved by the invention]

[0004] As the application fields of lithium secondary batteries expand, there is a demand for further improvement in initial discharge capacity. Furthermore, batteries in a charged state are prone to gas generation. Gas can be generated by decomposition of the electrolyte or by a reaction between the electrolyte and residual lithium present on the surface of the positive electrode active material. The generated gas can cause battery swelling and lead to battery deterioration. For this reason, batteries that are less likely to generate gas when charged are desired.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a positive electrode active material for a lithium secondary battery that can provide a lithium secondary battery that has a high initial discharge capacity and is less likely to generate gas even in a charged state. Furthermore, an object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery containing the positive electrode active material for a lithium secondary battery described above. **Means for Solving the Problems**

[0006] The present invention includes the following [1] to [9]. [1] A positive electrode active material for a lithium secondary battery, comprising a lithium metal composite oxide which is secondary particles in which primary particles are aggregated, and a boron-containing compound, and satisfying the following formula (A). 0.5 < Y / X < 1.0 ··· Formula (A) (In formula (A), X is the abundance ratio (%) of boron element on the surface of the positive electrode active material for a lithium secondary battery measured by X-ray photoelectron spectroscopy, and Y is the abundance ratio (%) of boron element on the surface of the positive electrode active material for a lithium secondary battery after being compacted at 50 MPa measured by X-ray photoelectron spectroscopy.) [2] The positive electrode active material for a lithium secondary battery according to [1], wherein the proportion of boron element contained in the positive electrode active material for a lithium secondary battery is 0.2 mol% or more and 3 mol% or less. [3] The positive electrode active material for a lithium secondary battery according to [1] or [2], wherein X is 30% or more and 99% or less. [4] The positive electrode active material for a lithium secondary battery according to any one of [1] to [3], represented by the following composition formula (I). Li 1+α Ni (1-x-y-z) M1 x M2 y B z O2 Composition formula (I) (In composition formula (I), M1 is one or more elements selected from the group consisting of Mn, Al, and Co, M2 is one or more elements selected from the group consisting of Ti, Mg, Ca, Zn, Sn, Zr, Si, Nb, W, Mo, Ta, Ba, S, and P, and -0.1 ≦ α ≦ 0.2, 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, and 0.002 ≦ z ≦ 0.03 are satisfied.) [5] The positive electrode active material for a lithium secondary battery according to any one of [1] to [4], satisfying the following formula (B). 1.1 < T / S ≤ 2.0 ··· Formula (B) (In Formula (B), S is the BET specific surface area (m 2 / g) of the positive electrode active material for the lithium secondary battery, and T is the BET specific surface area (m 2 / g) of the positive electrode active material for the lithium secondary battery after pressure compaction at 50 MPa.) [6] The S is 0.1 m 2 / g or more and 2.0 m 2 / g or less, the positive electrode active material for a lithium secondary battery according to [5]. [7] D obtained from the volume-based cumulative particle size distribution curve measured by the laser diffraction scattering method 50 is 5 μm or more and 20 μm or less, the positive electrode active material for a lithium secondary battery according to any one of [1] to [6]. [8] A positive electrode for a lithium secondary battery containing the positive electrode active material for a lithium secondary battery according to any one of [1] to [7]. [9] A lithium secondary battery having the positive electrode for a lithium secondary battery according to [8].

Advantages of the Invention

[0007] According to the present invention, it is possible to obtain a positive electrode active material for a lithium secondary battery that can provide a lithium secondary battery with a high initial discharge capacity and less gas generation even in a charged state. Furthermore, according to the present invention, it is possible to provide a positive electrode for a lithium secondary battery and a lithium secondary battery containing the positive electrode active material for a lithium secondary battery.

Brief Description of the Drawings

[0008] [Figure 1] It is a schematic diagram showing an example of a lithium secondary battery. [Figure 2] It is a schematic diagram showing an example of an all-solid-state lithium secondary battery. [Figure 3] It is a schematic diagram of a pressure compaction device.

Embodiments for Carrying Out the Invention

[0009] In this specification, metal composite compound will be referred to as "MCC", lithium metal composite oxide will be referred to as "LiMO", and cathode active material for lithium secondary batteries will be referred to as "CAM".

[0010] "Ni" refers to nickel atoms, not nickel metal. Similarly, "Co" and "Li" refer to cobalt atoms, lithium atoms, etc.

[0011] When a numerical range is stated as, for example, "1-10 μm" or "1 to 10 μm," it means a range from 1 μm to 10 μm, including the lower limit of 1 μm and the upper limit of 10 μm. The upper and lower limits of the numerical ranges in this specification can be arbitrarily combined. The numerical ranges of the respective physical properties, compositions, and production conditions can be arbitrarily combined.

[0012] The lithium secondary battery refers to a lithium ion secondary battery.

[0013] The initial discharge capacity of the lithium secondary battery is measured by the following method.

[0014] [Measurement of initial discharge capacity] (Production of positive electrodes for lithium secondary batteries) The CAM, conductive material, and binder are mixed in a mass ratio of 92:5:3 to prepare a paste-like positive electrode mixture. N-methyl-2-pyrrolidone is used as the organic solvent when preparing the positive electrode mixture. Acetylene black is used as the conductive material. Polyvinylidene fluoride is used as the binder.

[0015] The resulting positive electrode mixture was applied to a 20 μm thick Al foil as a current collector, dried at 60°C for 1 hour, and then vacuum dried at 150°C for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of ​​this positive electrode for a lithium secondary battery was 34.96 cm. 2 Let's say.

[0016] (Production of negative electrodes for lithium secondary batteries) A paste-like negative electrode mixture is prepared by mixing and kneading artificial graphite, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio of 96.5:2:1.5 (artificial graphite:SBR:CMC). Pure water is used as a solvent when preparing the negative electrode mixture.

[0017] The resulting negative electrode mixture was applied to a 10 μm thick Cu foil as a current collector, dried at 60°C for 1 hour, and then vacuum dried at 120°C for 8 hours to obtain a negative electrode for a lithium secondary battery. The electrode area of ​​this negative electrode for a lithium secondary battery was 37.44 cm. 2 Let's say.

[0018] (Fabrication of lithium secondary batteries) A 12 μm separator (porous polyethylene film) is placed on the negative electrode prepared in (Preparation of a negative electrode for a lithium secondary battery), and the positive electrode for a lithium secondary battery prepared in (Preparation of a positive electrode for a lithium secondary battery) is placed on top of that, and then wrapped in aluminum laminate film. 1000 μl of electrolyte is poured into this, and the aluminum laminate is sealed using a vacuum packaging machine to prepare a lithium secondary battery (pouch type). The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 16:10:74 (volume ratio) solution to which 1 mol% vinylene carbonate has been added, and LiPF6 is further dissolved at a ratio of 1.3 mol / L.

[0019] The lithium secondary battery was charged to 10% SOC at 0.05 CA at a test temperature of 25°C, left at a test temperature of 60°C for 10 hours, and then charged at a constant current and constant voltage of 0.1 CA to 4.2 V at a test temperature of 25°C until the current reached 0.05 CA. The battery was then discharged at 0.2 CA to 2.5 V. The discharge capacity at this time was defined as the initial discharge capacity (mAh / g).

[0020] [Gas generation rate measurement] After measuring the initial discharge capacity, the lithium secondary battery is charged to 4.2 V at 0.2 CA and discharged to 2.5 V at 0.2 CA for two cycles, and then the amount of gas generated is measured using the following method.

[0021] (Measurement method) The volume of the lithium secondary battery is measured using the Archimedes method to determine the volume before storage. The Archimedes method uses an automatic hydrometer to measure the actual volume of the entire lithium secondary battery from the difference between the weight of the lithium secondary battery in air and the weight of the lithium secondary battery in water. Next, the lithium secondary battery is charged to 4.2 V at 0.5 CA and stored in a constant temperature bath at 60°C for 7 days. It is then discharged to 2.5 V at a current value of 0.2 CA. The volume of the lithium secondary battery after discharge (volume after storage) is measured using the Archimedes method. The amount of gas generated (unit: cc / g) is calculated from the difference between the volume after storage and the volume before storage. The amount of gas generated is divided by the initial discharge capacity (Ah / g) converted from the initial discharge capacity (mAh / g) measured above to calculate the amount of gas generated per capacity (cc / Ah).

[0022] In addition, in a test in which a charged lithium secondary battery is stored in a thermostatic chamber at 60°C for 7 days, side reactions are much more likely to occur and gas is more likely to be generated than in a test at room temperature. If the amount of gas generated in the above test is small, it can be evaluated that gas generation is unlikely even in a charged state.

[0023] <Positive electrode active material for lithium secondary batteries> The CAM comprises LiMO and a compound containing boron (hereinafter referred to as "B"). LiMO is a secondary particle formed by aggregation of primary particles. In this specification, the "primary particle" means a particle that does not have grain boundaries on its appearance when observed at a magnification of 5000 times using a scanning electron microscope or the like. The "secondary particle" is an aggregate of primary particles. There are spaces (gaps and pores) inside the secondary particle.

[0024] In this specification, the "surface of CAM" means the range from the outermost surface of CAM to the depth where photoelectrons can escape toward the center in the measurement by X-ray photoelectron spectroscopy described later. For example, it means the range of depth within about 10 nm from the outermost surface of the particles in CAM toward the center. The "outermost surface of CAM" means the outer shell part on the outermost surface side of CAM.

[0025] The compound containing B is a compound having lithium ion conductivity. Examples thereof include lithium boron compounds and lithium boron composite oxides containing at least Li and B.

[0026] CAM satisfies the following formula (A). 0.5 < Y / X < 1.0 ··· Formula (A) (In Formula (A), X is the percentage of the presence of B on the surface of CAM measured by X-ray photoelectron spectroscopy, and Y is the percentage of the presence of B on the surface of CAM after pressing treatment at 50 MPa measured by X-ray photoelectron spectroscopy.)

[0027] [Measurement method of X and Y] For each of CAM before and after pressing treatment, measure the percentage of the presence of B on the surface (%).

[0028] (Measurement by X-ray photoelectron spectroscopy) In this specification, the "X-ray photoelectron spectroscopy" is described as "XPS". According to XPS, by measuring the energy of photoelectrons generated when irradiating X-rays on the surface of CAM, the constituent elements of the surface of CAM can be analyzed.

[0029] Specifically, the binding energy of photoelectrons emitted from the surface of CAM when irradiated with AlKα rays (1486.6 eV) as the excitation X-ray is analyzed. XPS can be used to analyze the abundance ratio of B and other elements on the surface of CAM.

[0030] As the X-ray photoelectron spectrometer, for example, PHI5000 VersaProbe III manufactured by ULVAC-PHI, Inc. can be used. AlKα rays are used as the X-ray source, and a neutralization gun (accelerating voltage 0.3 V, current 100 μA) is used to neutralize the charge during measurement. The measurement conditions are as follows: spot size = 100 μm, pass energy = 112 eV, step = 0.1 eV, dwell time = 50 ms.

[0031] The obtained XPS spectrum was analyzed using analysis software (MultiPak (Version 9.9.0.8)) to calculate the number of elements from the peak area of ​​each element. A few mg of CAM powder was used for the measurement. In addition, charge correction was performed with the C1s peak at 284.6 eV.

[0032] Next, from the calculated number of each element, the abundance ratio (%) of the number of B elements to the total number of elements other than Li and oxygen atoms (e.g., Ni, elements M1, M2, and B described below) detected by XPS measurement is calculated.

[0033] In the XPS analysis, elements that may be present on the surface of CAM are detected as photoelectrons corresponding to the binding energy of each element. The peaks corresponding to each element can be identified using existing databases.

[0034] (Compression processing) The powder compaction process in this embodiment will be described with reference to Fig. 3. A powder compaction processing apparatus 40 shown in Fig. 3 has jigs 41, 42 and 43.

[0035] The jig 41 has a cylindrical shape. The internal space 41a of the jig 41 is cylindrical. The internal diameter LD of the internal space 41a is 15 mm.

[0036] The jig 42 has a cylindrical plug portion 421 and a flange portion 422 connected to the plug portion 421. The plug portion 421 and the flange portion 422 are connected at the center of the flange portion 422 in a plan view. The diameter of the plug portion 421 is equal to the inner diameter LD of the jig 41, and is sized to fit snugly into the internal space 41a of the jig 41.

[0037] Jig 43 has the same shape as jig 42, and has a cylindrical plug portion 431 and a flange portion 432 connected to plug portion 431. The diameter of plug portion 431 is equal to the inner diameter LD of jig 41, and is sized to fit snugly into internal space 41a of jig 41.

[0038] The powder compaction processing device 40 is used by inserting the plug portion 421 of the jig 42 into the opening at one end of the jig 41 and inserting the plug portion 431 of the jig 43 into the opening at the other end of the jig 41 .

[0039] To perform the powder compaction process for CAM using the powder compaction processing device 40, first, jig 42 is fitted into jig 41, and 3 g of powder Z, i.e., CAM powder, is filled into internal space 41a with flange portion 422 in contact with jig 41. Next, jig 43 is fitted into jig 41, and tip 43A of plug portion 431 is brought into contact with CAM.

[0040] Next, a press machine is used to apply a load F to the jig 43. At this time, the load F is applied to the CAM of the internal space 41a via the jig 43 under the conditions of 50 MPa and for 1 minute.

[0041] After the load is stopped and released, the CAM is taken out of the powder compaction processing device 40, and Y is measured by the method described above (measurement by X-ray photoelectron spectroscopy). Note that the load of 50 MPa is set at a value when the electrode density is 3.50 g / cm when the electrode is produced. 3 This corresponds to the pressure required when the above is taken into consideration.

[0042] X corresponds to the abundance ratio (%) of B present on the surface of secondary particles in LiMO contained in the CAM before powder compaction. Compaction breaks down the agglomerates of primary particles that make up the secondary particles. By measuring the CAM after compaction using XPS, it is possible to measure the proportion of elements on the surface of the primary particles. Therefore, Y corresponds to the proportion (%) of B present on the surface of the primary particles that make up the secondary particles of LiMO.

[0043] The compound containing B has lithium ion conductivity, but its lithium ion conductivity is lower than that of the exposed portion of LiMO. Therefore, if the surfaces of the primary and secondary particles of LiMO are excessively coated with the compound containing B, the initial discharge capacity is likely to decrease.

[0044] The CAM satisfying formula (A) comprises a compound containing B on a portion of the surface of the primary particles and secondary particles of LiMO. When a CAM having a compound containing B on the surface of the secondary particles, in other words, in which the surfaces of the secondary particles are protected by a compound containing B, is used, the decomposition reaction of the electrolyte is effectively suppressed, and gas generation due to the decomposition reaction of the electrolyte is reduced when the lithium secondary battery is in a charged state. Furthermore, the compound containing B coats and inactivates residual lithium present on the surface of the CAM, thereby reducing the generation of gas due to the residual lithium. Furthermore, the surface of the primary particles of LiMO has a large specific surface area, which significantly affects the decomposition reaction of the electrolyte and lithium ion conductivity. A CAM satisfying formula (A) has a compound containing B on a portion of the surface of the primary particles and secondary particles, and a portion of this surface is exposed. Such a CAM is less susceptible to the decomposition reaction of the electrolyte and less likely to reduce lithium ion conductivity, thereby enabling a high initial discharge capacity.

[0045] Y / X is preferably 0.55 or more, more preferably 0.60 or more, and even more preferably 0.65 or more. Y / X is preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less. Examples of Y / X include 0.55-0.99, 0.60-0.98, and 0.65-0.97.

[0046] In CAM with a Y / X ratio of 0.5 or less, the B-containing compound is unevenly distributed on the surface of the secondary particles of LiMO. On the other hand, when the Y / X ratio exceeds 0.5, preferably equal to or greater than the lower limit, the surfaces of the secondary particles and a portion of the surfaces of the primary particles are protected by the B-containing compound. Therefore, the decomposition reaction of the electrolyte can be effectively suppressed, and gas generation is reduced.

[0047] CAM with a Y / X ratio of 1.0 or more has a compound containing B on the entire surface of the secondary particles and the entire surface of the primary particles of LiMO. On the other hand, when Y / X is less than 1.0, preferably not more than the upper limit, the surface of the primary particles is partially exposed. Therefore, the lithium ion conductivity is less likely to decrease, and the initial discharge capacity can be increased.

[0048] X is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. X is preferably 99% or less, more preferably 95% or less, and even more preferably 90% or less. X may be, for example, 30-99%, 40-95%, or 50-90%. When X is equal to or greater than the above lower limit, the decomposition reaction of the electrolyte on the surface of the secondary particles can be effectively suppressed, and gas is less likely to be generated. When X is equal to or less than the upper limit, the surfaces of the secondary particles are partially exposed, so that the lithium ion conductivity is less likely to decrease and the initial discharge capacity can be increased.

[0049] The proportion of B contained in CAM is preferably 0.2 mol % or more, more preferably 0.5 mol % or more, and even more preferably 0.75 mol % or more. The proportion of B is preferably 3 mol % or less, more preferably 2.5 mol % or less, and even more preferably 2 mol % or less. The proportion of B is, for example, 0.2 to 3 mol %, 0.5 to 2.5 mol %, or 0.75 to 2 mol %. When the proportion of B is within the above range, a lithium secondary battery that is less likely to generate gas and has a high initial discharge capacity can be obtained. The proportion of B contained in CAM is the proportion of B relative to the total amount of elements other than Li and oxygen atoms (for example, Ni, elements M1, M2, and B described below), and can be measured by the method described in [Composition Analysis] below.

[0050] [Composition analysis] The composition of CAM is analyzed by dissolving CAM powder in hydrochloric acid and then measuring the composition using an ICP emission spectrometer. As the ICP emission spectrometer, for example, Optima 7300 manufactured by PerkinElmer Co., Ltd. can be used.

[0051] From the viewpoint of increasing the initial discharge capacity, the CAM preferably has a layered structure, and more preferably has a hexagonal crystal structure or a monoclinic crystal structure.

[0052] The hexagonal crystal structure is P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P 31m, P3c1, P31c, R3m, R3c, P-31m, P-31c, P-3m1, P-3c1, R-3m, R-3c, P6, P61, P65, P62, P64, P63 , P-6, P6 / m, P63 / m, P622, P6122, P6522, P6222, P6422, P6322, P6mm, P6cc, P63cm, P63mc, P-6m2, P-6c2, P-62m, P-62c, P6 / mmm, P6 / mcc, P63 / mcm, and P63 / mmc.

[0053] Furthermore, the monoclinic crystal structure belongs to any one space group selected from the group consisting of P2, P21, C2, Pm, Pc, Cm, Cc, P2 / m, P21 / m, C2 / m, P2 / c, P21 / c, and C2 / c.

[0054] From the viewpoint of obtaining a lithium secondary battery with a high initial discharge capacity, it is more preferable that CAM has a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal structure belonging to the space group C2 / m.

[0055] [How to confirm the crystal structure] The crystal structure of CAM can be confirmed by observation using a powder X-ray diffraction measurement device (for example, Ultima IV manufactured by Rigaku Corporation).

[0056] (composition formula) CAM preferably contains Li, Ni, and an element M1. The element M1 is one or more elements selected from the group consisting of Mn, Al, and Co. CAM is preferably represented by the following composition formula (I): Li 1+α Ni (1-x-y-z) M1 x M2 y B z O2 composition formula (I) (In composition formula (I), M1 is one or more elements selected from the group consisting of Mn, Al, and Co, and M2 is one or more elements selected from the group consisting of Ti, Mg, Ca, Zn, Sn, Zr, Si, Nb, W, Mo, Ta, Ba, S, and P, and the following conditions are satisfied: -0.1≦α≦0.2, 0≦x≦0.3, 0≦y≦0.1, and 0.002≦z≦0.03.)

[0057] In the composition formula (I), M1 may be two or more or three elements selected from the group consisting of Mn, Al, and Co. In the composition formula (I), M2 is more preferably one or more elements selected from the group consisting of Ti, Mg, Ca, Zr, Si, Nb, W, Ba, S, and P.

[0058] In the composition formula (I), α is preferably −0.09 or more, more preferably −0.08, and is preferably 0.15 or less, more preferably 0.12 or less. Examples of α include −0.09 to 0.15 or −0.08 to 0.12.

[0059] In the compositional formula (I), x is preferably 0.01 or more, more preferably 0.02 or more. Also, x is preferably 0.25 or less, and even more preferably 0.20 or less. Examples of x include 0.01 - 0.25, or 0.02 - 0.20.

[0060] When CAM contains M2, in the compositional formula (I), y is preferably 0.0001 or more, more preferably 0.0002 or more. Also, y is preferably 0.0095 or less, and more preferably 0.0090 or less. Examples of y include 0.0001 - 0.0095, or 0.0002 - 0.0090.

[0061] In the compositional formula (I), z is preferably 0.003 or more, more preferably 0.004 or more. Also, z is preferably 0.029 or less, and more preferably 0.028 or less. Examples of z include 0.003 - 0.029, or 0.004 - 0.028.

[0062] x + y + z is less than 1, preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.2 or less. x + y + z exceeds 0, and is preferably 0.02 or more. Examples of x + y + z include exceeding 0 and less than 1, exceeding 0 and 0.5 or less, exceeding 0 and 0.3 or less, 0.02 - 0.3, or 0.02 - 0.2.

[0063] The composition of CAM can be measured by the method described in the above [Composition Analysis].

[0064] CAM preferably satisfies the following formula (B). 1.1 < T / S ≤ 2.0 ··· Formula (B) (In formula (B), S is the BET specific surface area (m 2 / g) of CAM, and T is the BET specific surface area (m 2 / g) of CAM after pressure compaction treatment at 50 MPa.)

[0065] For each of the CAMs before and after pressure compaction treatment, the BET specific surface area (m 2 / g) is measured. The compaction process breaks down the agglomerates of primary particles that make up the secondary particles, exposing the surfaces of the primary particles. The more easily the secondary particles crack, and the greater the degree of exposure of the primary particle surfaces, the larger T becomes.

[0066] The powder compaction treatment for measuring T is carried out in the same manner as in the method described above (Powder compaction treatment).

[0067] [BET specific surface area measurement] The BET specific surface area of ​​each CAM before and after compaction can be measured using a BET specific surface area measuring device. For example, a Macsorb (registered trademark) manufactured by Mountech Co., Ltd. can be used as the BET specific surface area measuring device. When measuring powdered CAM, it is preferable to dry it in a nitrogen atmosphere at 105°C for 30 minutes as a pretreatment.

[0068] T / S is preferably greater than 1.1, more preferably 1.12 or greater, even more preferably 1.13 or greater, and even more preferably 1.14 or greater, and is preferably 2.0 or less, more preferably 1.8 or less, even more preferably 1.75 or less, and even more preferably 1.7 or less. Examples of T / S include greater than 1.1 and not greater than 2.0, 1.12-1.8, 1.13-1.75, or 1.14-1.7.

[0069] When T / S is equal to or greater than the lower limit, the secondary particles in the CAM are less likely to crack, and the surfaces of the primary particles that do not contain B are less likely to be exposed. Such a CAM can effectively suppress the decomposition reaction of the electrolyte solution and reduce the amount of gas generated. When T / S is equal to or less than the upper limit, the surface of the primary particles is partially exposed, so that the lithium ion conductivity is less likely to decrease, the initial discharge capacity can be increased, and the amount of gas generation can be reduced.

[0070] S is 0.1m 2 / g or more is preferable, and 0.2m 2 / g or more is more preferable, and 0.3m 2 / g or more is more preferable. 2 / g or less is preferable, and 1.5m 2 / g or less is more preferable, and 1.0m 2 / g or less is more preferable. For example, S is 0.1-2.0m 2 / g, 0.2-1.5m 2 / g, or 0.3-1.0m 2 / g is an example. When S is equal to or greater than the lower limit, the contact area between the surface of the secondary particles and the electrolyte increases, and the initial discharge capacity can be increased. When S is equal to or less than the upper limit, the contact area between the surface of the secondary particles and the electrolyte is less likely to increase, and gas resulting from decomposition of the electrolyte is less likely to be generated.

[0071] CAM's D 50 is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 8 μm or more. 50 is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. D 50 Examples of the diameter include 5-20 μm, 6-18 μm, or 8-15 μm. D 50 In the CAM having a ρ in the above range, when a positive electrode active material layer is prepared from the CAM, the particles in the CAM are easily packed together in an ideal manner, and as a result, lithium ions can efficiently move within the positive electrode active material layer during operation of the lithium secondary battery, thereby increasing the initial discharge capacity.

[0072] [D 50 Measurement of CAM's D 50 (μm) can be measured by the following dry method.

[0073] Specifically, first, dry particle size distribution is measured using 2 g of CAM with a laser diffraction particle size distribution analyzer, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the particle size value at 50% accumulation from the fine particle side is D 50 is. As the laser diffraction particle size distribution meter, for example, MS2000 manufactured by Malvern can be used.

[0074] <Manufacturing method of CAM> The manufacturing method of CAM is a method of sequentially performing the manufacturing process of MCC and the manufacturing process of CAM.

[0075] (Manufacturing process of MCC) MCC is a compound containing Ni and an arbitrary element M1, and may contain the above M2. Examples of MCC include metal composite hydroxides, metal composite oxides, and mixtures thereof containing each element in the molar ratio represented by the following formula (I'). Ni:M1:M2=(1-x-y):x:y (I’) In the above formula (I’), M1, M2, x, and y are the same as M1, M2, x, and y in the above compositional formula (I). MCC can be manufactured by the coprecipitation method. As the coprecipitation method, a batch coprecipitation method or a continuous coprecipitation method can be used. Hereinafter, taking the metal composite hydroxide containing Ni and element M1 as an example, the manufacturing method of MCC will be described in detail.

[0076] First, by the coprecipitation method, particularly the continuous coprecipitation method described in JP-A2002-201028, a nickel salt solution, a metal salt solution of element M1, and a complexing agent are reacted to produce a metal composite hydroxide represented by Ni (1-x) M1 x (OH)2 (x is the same as in the above compositional formula (I)). The metal salt solution of element M1 is, for example, a cobalt salt solution, a manganese salt solution, or an aluminum salt solution.

[0077] As the nickel salt which is the solute of the above nickel salt solution, for example, one or more of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.

[0078] As the cobalt salt which is the solute of the above cobalt salt solution, for example, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used.

[0079] As the manganese salt that is the solute of the manganese salt solution, for example, one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate can be used.

[0080] As the aluminum salt that is the solute of the aluminum salt solution, for example, one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride can be used.

[0081] The above metal salts are used in proportions corresponding to the composition ratio of the above formula (I'). That is, the amount of each metal salt is specified so that the molar ratio of Ni in the solute of the nickel salt solution to the element M1 in the solute of the salt solution of the element M1 corresponds to (1-x):x in the above formula (I').

[0082] The solvent for the nickel salt solution and the metal salt solution of element M1 is water.

[0083] The complexing agent is one that can form a complex with nickel ions and ions of the element M1 in an aqueous solution, and examples thereof include ammonium ion donors such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine, with ammonium ion donors being preferred.

[0084] The amount of complexing agent contained in the mixed solution containing the nickel salt solution, the metal salt solution of element M1, and the complexing agent is, for example, a molar ratio of the amount of complexing agent to the total number of moles of the nickel salt and the metal salt of element M1 that is greater than 0 and less than or equal to 2.0.

[0085] When an ammonium ion donor is used as the complexing agent, the ammonia concentration relative to the total volume of the mixed solution in the reaction tank is preferably 0.5 to 10 g / L, more preferably 1 to 7 g / L, and even more preferably 1.5 to 5 g / L.

[0086] To adjust the pH of the mixture, an alkaline solution is added to the mixture before the pH of the mixture changes from alkaline to neutral. Examples of the alkaline solution include an aqueous solution of an alkali metal hydroxide. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide.

[0087] The pH value in the reaction tank is, for example, 9 to 13, and preferably 10.5 to 13. The pH value in this specification is defined as the value measured when the temperature of the mixed liquid is 40° C. If the temperature of the mixed liquid sampled from the reaction tank is not 40° C., the mixed liquid is cooled or heated to 40° C., and then the pH of the mixed liquid is measured.

[0088] During the reaction, the temperature in the reaction vessel is controlled within the range of, for example, 20 to 80°C, preferably 30 to 70°C.

[0089] The materials in the reaction vessel are mixed by suitable stirring. The reaction vessel used in the continuous coprecipitation method may be a type that allows the formed reaction precipitate to overflow for separation.

[0090] In addition to controlling the above conditions, various gases, for example, inert gases such as nitrogen, argon, and carbon dioxide, oxidizing gases such as air and oxygen, or a mixture thereof, may be supplied into the reaction vessel.

[0091] After the above reaction, the resulting reaction precipitate is washed with water, dehydrated, and dried to obtain a metal composite hydroxide. After drying, the precipitate may be classified as appropriate.

[0092] The tap density of metal composite hydroxides is 1.0-2.0g / cm 3 Preferably, it is 1.1-1.9 g / cm 3 By appropriately adjusting the pH of the reaction vessel, the ammonia concentration in the reaction vessel, and the temperature in the reaction vessel within the above-mentioned ranges, the tap density of the metal composite hydroxide and the D of the resulting CAM can be controlled. 50can be controlled within the above range.

[0093] [Method for measuring tap density] The tap density of the metal composite hydroxide is a tap bulk density measured by the method described in JIS R 1628-1997.

[0094] By using a metal composite hydroxide whose tap density is adjusted to fall within the above range, the compound containing B can easily penetrate into the gaps between the primary particles that make up the secondary particles, and a CAM in which Y / X satisfies formula (A) can be obtained.

[0095] When producing a metal composite oxide as MCC, the metal composite oxide can be prepared by oxidizing a metal composite hydroxide. The oxidation temperature is preferably 400-700°C, more preferably 450-680°C. The oxidation time, measured from the start of temperature increase to the end of temperature maintenance after reaching the temperature, is preferably 1-30 hours. The rate of temperature increase until the oxidation temperature is reached is preferably 180°C / hour or more, more preferably 200°C / hour or more, and even more preferably 250°C / hour or more.

[0096] The temperature rise rate in this specification is calculated from the time from when the temperature rise starts until the oxidation temperature (or the firing temperature described below) is reached in the device used, and the temperature difference from the temperature at which the temperature rise starts in the device to the oxidation temperature (or the firing temperature described below).

[0097] MCC can be produced by the above steps.

[0098] [CAM obtaining process] The process for obtaining CAM includes a mixing step of mixing MCC with a lithium compound, a firing step of firing the resulting mixture, and a B addition step of mixing the resulting LiMO with a B raw material and heat-treating the mixture.

[0099] ·Mixing process MCC and a lithium compound are mixed. The lithium compound may be at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, lithium chloride, and lithium fluoride. Of these, lithium hydroxide, lithium hydroxide hydrate, and lithium carbonate, or a mixture thereof, is preferred.

[0100] A mixture is obtained by mixing a lithium compound and MCC in consideration of the composition ratio of the final target product. The amount (molar ratio) of Li contained in the lithium compound relative to the total amount of elements other than oxygen atoms contained in MCC is preferably 0.9 to 1.2, more preferably 0.91 to 1.18, and even more preferably 0.92 to 1.15.

[0101] In the mixing step, raw materials for the elements M1 and M2 may be further added, for example, zirconium oxide or aluminum hydroxide.

[0102] Firing process The mixture obtained in the mixing step is fired, which causes crystals to grow and yields LiMO.

[0103] The firing may be a single firing or may include multiple firing steps. In this embodiment, it is preferable to provide a pre-baking step and a main baking step in which baking is performed at a higher temperature than in the pre-baking step.

[0104] The calcination temperature in the pre-calcination step is, for example, in the range of 200 to 800°C, preferably 400 to 800°C, and more preferably 450 to 700°C.

[0105] The firing temperature in the main firing step is preferably 600° C. or higher, more preferably 650° C. or higher, and even more preferably over 700° C. The firing temperature in the main firing step is preferably 850° C. or lower, and more preferably 800° C. or lower.

[0106] The firing temperature in the firing step is, for example, 600 to 850°C, 650 to 800°C, or more than 700°C and 800°C or lower.

[0107] In this specification, the firing temperature refers to the temperature of the atmosphere in the firing furnace, and means the highest temperature that can be maintained. If the pre-firing step or the main firing step has multiple firing stages, the firing temperature refers to the temperature of the stage in which firing is performed at the highest temperature that can be maintained.

[0108] By adjusting the firing temperature in the main firing step to the above range, CAM in which Y / X satisfies formula (A) can be obtained. In addition, by adjusting each condition in the firing step to the above range, X, S, T / S, and D of CAM can be obtained. 50 can be adjusted to the above range.

[0109] In the pre-firing step or the main firing step, the holding time at the firing temperature is, for example, 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the firing temperature is, for example, 50 to 400°C / hour, and the rate of temperature decrease from the firing temperature to room temperature is, for example, 10 to 400°C / hour.

[0110] In the firing step, dry air, an oxygen atmosphere, an inert atmosphere, or a mixture of these may be used depending on the desired composition. In this embodiment, an oxygen atmosphere is preferred.

[0111] The firing furnace used in the firing step is not particularly limited, and may be, for example, a continuous firing furnace or a fluidized bed firing furnace. Examples of continuous firing furnaces include tunnel furnaces and roller hearth kilns. Examples of fluidized bed firing furnaces include rotary kilns.

[0112] After firing, the fired product may be washed with a cleaning solution such as pure water or an alkaline cleaning solution. The temperature of the cleaning solution is preferably 15°C or less, more preferably 10°C or less, and even more preferably 8°C or less. By controlling the temperature of the cleaning solution within the above range so that the cleaning solution does not freeze, it is possible to prevent excessive elution of lithium ions from the crystal structure of the fired product into the cleaning solution during cleaning.

[0113] The fired product after washing is dried appropriately. Drying can be carried out, for example, by reduced pressure drying, vacuum drying, air blowing, heating, or a combination thereof. The drying temperature is preferably 80-250°C, and more preferably 100-200°C. LiMO is thus obtained.

[0114] ·B addition process The B raw material is added to LiMO and mixed. Examples of the B raw material include boric acid. The particle size of the B raw material is preferably 5 to 20 μm.

[0115] [Measurement of particle size of raw material B] The particle size of raw material B can be measured by the following method. First, powdered B raw material is placed in an ethanol solution and dispersed in an ultrasonic cleaner for 10 minutes to obtain a dispersion. Next, the particle size distribution of the obtained dispersion is measured using a laser diffraction particle size distribution analyzer, and a volume-based cumulative particle size distribution curve is obtained. In the obtained cumulative particle size distribution curve, the particle size value at 50% accumulation from the fine particle side is the particle size (μm) of B raw material. As the laser diffraction particle size distribution analyzer, for example, MT-3300EXII manufactured by Nikkiso Co., Ltd. can be used.

[0116] LiMO and the B raw material can be mixed using, for example, a mortar or a mixer. The B raw material is mixed with LiMO at a ratio of preferably more than 0.02 mol% to -3.0 mol% or less, more preferably 0.03-2.9 mol%, and even more preferably 0.04-2.8 mol%, based on the total amount of elements other than Li and oxygen atoms contained in LiMO (e.g., Ni, elements M1, and M2).

[0117] After adding and mixing the B raw material to LiMO, heat treatment is performed. The temperature during the heat treatment is preferably 200 to 400° C. The heat treatment time is preferably 1 to 20 hours. Examples of equipment used during the heat treatment include a vacuum drying equipment, a reduced pressure drying equipment, a blower, a heating equipment, and combinations thereof. By carrying out the B addition step under the above conditions, it is possible to obtain a CAM in which Y / X satisfies the above formula (A) and X, S, and T / S preferably fall within the above ranges.

[0118] Through the above steps, a CAM is obtained.

[0119] <Lithium secondary battery> A positive electrode for a lithium secondary battery suitable for use with the CAM of this embodiment will be described. Hereinafter, the positive electrode for a lithium secondary battery may be referred to as a positive electrode. Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

[0120] An example of a suitable lithium secondary battery for use with the CAM of this embodiment has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0121] 1 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0122] First, as shown in the partially enlarged view of FIG. 1 , a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are stacked in this order: separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0123] The positive electrode 2 includes, for example, a positive electrode active material layer 2a containing CAM and a positive electrode current collector 2b having the positive electrode active material layer 2a formed on one surface thereof. Such a positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on one surface of the positive electrode current collector 2b to form the positive electrode active material layer 2a.

[0124] Examples of the negative electrode 3 include an electrode in which a negative electrode mixture containing a negative electrode active material (not shown) is supported on a negative electrode current collector, and an electrode made of a negative electrode active material alone, and can be manufactured in the same manner as the positive electrode 2.

[0125] Next, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing member 8, whereby a lithium secondary battery 10 can be manufactured.

[0126] The shape of the electrode group 4 can be, for example, a columnar shape such that the cross section of the electrode group 4 cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0127] The shape of a lithium secondary battery having such an electrode group 4 can be any shape specified by IEC60086, a standard for batteries established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples of shapes include a cylindrical shape and a rectangular shape.

[0128] Furthermore, the lithium secondary battery is not limited to the above-mentioned wound type configuration, and may be a laminated type configuration in which a laminated structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of laminated lithium secondary batteries include so-called coin type batteries, button type batteries, and paper type (or sheet type) batteries.

[0129] The positive electrode, separator, negative electrode, and electrolyte constituting the lithium secondary battery can be, for example, the configuration, materials, and manufacturing method described in

[0113] to

[0140] of WO2022 / 113904A1.

[0130] <All-solid-state lithium secondary battery> The CAM of this embodiment can be used as a CAM for an all-solid-state lithium secondary battery.

[0131] Fig. 2 is a schematic diagram showing an example of an all-solid-state lithium secondary battery. The all-solid-state lithium secondary battery 1000 shown in Fig. 2 includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an exterior body 200 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which a CAM and a negative electrode active material are disposed on both sides of a current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400.

[0132] The positive electrode 110 has a positive electrode active material layer 111 and a positive electrode current collector 112. The positive electrode active material layer 111 contains the above-mentioned CAM and solid electrolyte. The positive electrode active material layer 111 may also contain a conductive material and a binder.

[0133] The negative electrode 120 has a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains a negative electrode active material. The negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material.

[0134] The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120.

[0135] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the exterior body 200 , and a sealing body (not shown) that seals the opening 200 a of the exterior body 200 .

[0136] A container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used as exterior body 200. Alternatively, a container formed into a bag shape from a laminate film with corrosion resistance applied to at least one surface can also be used as exterior body 200.

[0137] The all-solid-state lithium secondary battery 1000 may have any shape, such as a coin shape, a button shape, a paper shape (or a sheet shape), a cylindrical shape, a square shape, or a laminate shape (pouch shape).

[0138] The all-solid-state lithium secondary battery 1000 is illustrated as having one laminate 100 as an example, but the present embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may have a configuration in which the laminate 100 is used as a unit cell, and a plurality of unit cells (laminated bodies 100) are sealed inside an exterior body 200.

[0139] For the all-solid-state lithium secondary battery, for example, the configuration, materials, and manufacturing method described in

[0151] to

[0181] of WO2022 / 113904A1 can be used.

[0140] The positive electrode having the above-described configuration contains the above-described CAM, and therefore can provide a lithium secondary battery that has a high initial discharge capacity and is less likely to generate gas even in a charged state.

[0141] Furthermore, since the lithium secondary battery having the above-described configuration has the above-described positive electrode, it has a high initial discharge capacity and is less likely to generate gas even in a charged state.

[0142] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention. [Example]

[0143] Next, the present invention will be described in more detail with reference to examples.

[0144] <Measurement of initial discharge capacity> The initial discharge capacity of the lithium secondary battery is measured by the method described in [Measurement of initial discharge capacity] above.

[0145] <Measurement of Gas Generation Amount> The gas generation amount of the lithium secondary battery is measured by the method described in the above [Measurement of Gas Generation Amount].

[0146] <Measurement of X and Y> X and Y of CAM are measured by the method described in the above [Measurement Method of X and Y]. From the obtained values, Y / X is calculated.

[0147] <Composition Analysis> The composition of CAM and the proportion of B in CAM are carried out by the method described in the above [Composition Analysis].

[0148] <Measurement of BET Specific Surface Area> The BET specific surface area for obtaining T and S is measured by the method described in the above [Measurement of BET Specific Surface Area]. The pressure compaction treatment for measuring T is carried out in the same manner as the method described in the above (Pressure Compaction Treatment). From the obtained T and S, T / S is calculated.

[0149] <D 50 Measurement><F D of CAM 50 [[ID=3**]]is measured by the method described in the above [Measurement of D 50 . <F

[0150] <Measurement of Tap Density> The tap density of the metal composite hydroxide is measured by the method described in the above [Measurement Method of Tap Density]. [[ID=**]]

[0151] <Measurement of Particle Size of Boric Acid>[[ID=**]] The particle size of boric acid is measured by the method described in the above [Measurement of Particle Size of B Raw Material].

[0152] <Example 1> After putting water into a reaction tank equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added, and the temperature of the reaction tank was maintained at 70°C. An aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous manganese sulfate solution were mixed at a ratio such that the molar ratio of Ni, Co, and Mn was 83:12:5 to prepare a mixed raw material solution. Next, an aqueous solution of ammonium sulfate was continuously added as a complexing agent to this mixed raw material liquid in a reaction vessel under stirring. The ammonia concentration in the mixed liquid in the reaction vessel was 2.6 g / L. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the mixed liquid in the reaction vessel became 10.9 (measured at a liquid temperature of 40°C), and a reaction precipitate was obtained. The reaction precipitate was washed, dehydrated in a centrifuge, and dried at 105°C for 20 hours to obtain MCC-1, a metal composite hydroxide. The tap density of MCC-1 was 1.7 g / cm 3 It was.

[0153] MCC-1 and lithium hydroxide monohydrate powder were weighed out in a molar ratio of Li / (Ni + Co + Mn) = 1.14. Aluminum hydroxide was weighed out so that the amount of Al relative to the total amount of Ni, Co, and Mn contained in MCC-1 was 1.0 mol%. Zirconium oxide was weighed out so that the amount of Zr relative to the total amount of Ni, Co, and Mn contained in MCC-1 was 0.2 mol%. MCC-1, lithium hydroxide monohydrate, aluminum hydroxide, and zirconium oxide were mixed to obtain Mixture 1. The obtained Mixture 1 was pre-calcined in an oxygen atmosphere at 650°C for 5 hours, and then further calcined in an oxygen atmosphere at 780°C for 5 hours to obtain Calcined Product 1. Calcined Product 1 was washed with pure water and then vacuum-dried at 120°C for 10 hours to obtain LiMO-1. Boric acid 1 (particle diameter: 17 μm) was weighed out so that the amount of B contained in boric acid 1 was 1.0 mol% relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-1. LiMO-1 and boric acid 1 were mixed and heat-treated at 300°C for 5 hours in an oxygen atmosphere to obtain CAM-1. CAM-1 has the above composition formula (I), where α = 0.08, x = 0.17, y = 0.0019, z = 0.0095, M1 = Mn, Al, Co, and M2 = Zr.

[0154] <Example 2> LiMO-1 was obtained in the same manner as in Example 1. Boric acid 1 was weighed out so that the amount of B contained in boric acid 1 was 1.0 mol % relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-1. LiMO-1 and boric acid 1 were mixed and heat-treated at 350°C for 5 hours in an oxygen atmosphere to obtain CAM-2. CAM-2 had the above composition formula (I), where α = 0.08, x = 0.17, y = 0.0019, z = 0.0095, M1 = Mn, Al, Co, and M2 = Zr.

[0155] <Comparative Example 1> Water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous sodium hydroxide solution was added thereto, and the temperature of the reaction vessel was maintained at 75°C. A mixed raw material liquid was prepared by mixing an aqueous nickel sulfate solution, an aqueous cobalt sulfate solution, and an aqueous manganese sulfate solution in a molar ratio of Ni, Co, and Mn of 83:12:5. Next, an aqueous solution of ammonium sulfate was continuously added as a complexing agent to this mixed raw material solution in a reaction vessel under stirring. The ammonia concentration in the mixed solution in the reaction vessel was 3.1 g / L. An aqueous solution of sodium hydroxide was added dropwise at appropriate times so that the pH of the mixed solution in the reaction vessel became 11.1 (measured at a liquid temperature of 40°C), and a reaction precipitate was obtained. The reaction precipitate was washed, dehydrated in a centrifuge, and dried at 105°C for 20 hours to obtain MCC-3, a metal composite hydroxide. The tap density of MCC-3 was 2.1 g / cm 3 It was.

[0156] MCC-3 and lithium hydroxide monohydrate powder were weighed out in a molar ratio of Li / (Ni + Co + Mn) = 1.14. Aluminum hydroxide was weighed out so that the amount of Al relative to the total amount of Ni, Co, and Mn contained in MCC-3 was 1.0 mol%. Zirconium oxide was weighed out so that the amount of Zr relative to the total amount of Ni, Co, and Mn contained in MCC-3 was 0.2 mol%. MCC-3, lithium hydroxide monohydrate, aluminum hydroxide, and zirconium oxide were mixed to obtain Mixture 1. The obtained Mixture 1 was pre-calcined in an oxygen atmosphere at 650°C for 5 hours and then further calcined in an oxygen atmosphere at 780°C for 5 hours to obtain Calcined Product 3. Calcined Product 3 was washed with pure water and then vacuum-dried at 120°C for 10 hours to obtain LiMO-3. Boric acid 1 was weighed out so that the amount of B contained in boric acid 1 was 1.0 mol % relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-3. LiMO-3 and boric acid 1 were mixed and heat-treated at 350°C for 2 hours in an oxygen atmosphere to obtain CAM-3. CAM-3 has the above composition formula (I), where α = 0.08, x = 0.17, y = 0.0019, z = 0.01, M1 = Mn, Al, Co, and M2 = Zr.

[0157] <Comparative Example 2> LiMO-1 was obtained in the same manner as in Example 1. Boron oxide was weighed so that the amount of B contained in the boron oxide was 1.0 mol% relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-1. LiMO-1 and boron oxide (particle diameter: 45 μm) were mixed and heat-treated in an oxygen atmosphere at 300°C for 5 hours to obtain CAM-4. CAM-4 has the above composition formula (I), where α = 0.08, x = 0.17, y = 0.0018, z = 0.01, M1 = Mn, Al, Co, and M2 = Zr.

[0158] <Comparative Example 3> LiMO-1 was obtained in the same manner as in Example 1. Boric acid 1 was weighed out so that the amount of B contained in boric acid 1 was 1.0 mol % relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-1. LiMO-1 and boric acid 1 were mixed to obtain CAM-5. CAM-5 had the above composition formula (I), where α = 0.08, x = 0.17, y = 0.0018, z = 0.01, M1 = Mn, Al, Co, and M2 = Zr.

[0159] <Comparative Example 4> Mixture 1 was obtained using the same method as in Example 1. The obtained mixture 1 was pre-calcined in an oxygen atmosphere at 650°C for 5 hours and then further calcined in an oxygen atmosphere at 950°C for 5 hours to obtain calcined product 6. Calcined product 6 was washed with pure water and then vacuum-dried at 120°C for 10 hours to obtain LiMO-6. Boric acid 1 was weighed out so that the amount of B contained in boric acid 1 was 1.0 mol% relative to the total amount of Ni, Co, Mn, Al, and Zr contained in LiMO-6. LiMO-6 and boric acid 1 were mixed and heat-treated in an oxygen atmosphere at 300°C for 5 hours to obtain CAM-6. CAM-6 was represented by the above composition formula (I), where α = 0.07, x = 0.17, y = 0.0018, z = 0.01, M1 = Mn, Al, Co, and M2 = Zr. [Table 1]

[0160] As shown in Table 1 above, Examples 1 and 2 in which Y / X satisfied formula (A) had a high initial discharge capacity and a small amount of gas generation.

[0161] In Comparative Examples 1 to 3, where Y / X was 0.5 or less, the amount of coating with the compound containing B on the surfaces of the primary particles was insufficient, which is thought to have caused a decomposition reaction of the electrolyte and increased the amount of gas generated.

[0162] In Comparative Example 4, where Y / X is 1.0 or more, the surfaces of the primary particles were excessively coated with the compound containing B, and part of the surfaces was not sufficiently exposed, which is thought to have resulted in a decrease in lithium ion conductivity and therefore a decrease in the initial discharge capacity. [Explanation of symbols]

[0163] 1...separator, 2...positive electrode, 2a...positive electrode active material layer, 2b...positive electrode current collector, 3...negative electrode, 4...electrode group, 5...battery can, 6...electrolyte, 7...top insulator, 8...sealing body, 10...lithium secondary battery, 21...positive electrode lead, 31...negative electrode lead, 40...powder compaction processing device, 41, 42, 43...jig, 100...laminated body, 110...positive electrode, 111...positive electrode active material layer, 112...positive electrode current collector, 113...external terminal, 120...negative electrode, 121...negative electrode active material layer, 122...negative electrode current collector, 123...external terminal, 130...solid electrolyte layer, 200...exterior body, 200a...opening, 1000...all-solid-state lithium secondary battery

Claims

1. A positive electrode active material for a lithium secondary battery, comprising a lithium metal composite oxide that is a secondary particle formed by aggregation of primary particles, and a compound containing boron, and satisfying the following formula (A): 0.5<Y / X<1.0...Formula (A) (In formula (A), X is the abundance ratio (%) of boron element on the surface of the positive electrode active material for a lithium secondary battery, as measured by X-ray photoelectron spectroscopy, and Y is the abundance ratio (%) of boron element on the surface of the positive electrode active material for a lithium secondary battery after being compacted at 50 MPa, as measured by X-ray photoelectron spectroscopy.)

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the proportion of elemental boron contained in the positive electrode active material for a lithium secondary battery is 0.2 mol % or more and 3 mol % or less.

3. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein X is 30% or more and 99% or less.

4. 3. The positive electrode active material for a lithium secondary battery according to claim 1, which is represented by the following composition formula (I): Li １＋α Ni （１－ｘ－ｙ－ｚ） M1 ｘ M2 ｙ B ｚ O ２ Composition formula (I) (In composition formula (I), M1 is one or more elements selected from the group consisting of Mn, Al, and Co, and M2 is one or more elements selected from the group consisting of Ti, Mg, Ca, Zn, Sn, Zr, Si, Nb, W, Mo, Ta, Ba, S, and P, and the following conditions are satisfied: -0.1≦α≦0.2, 0≦x≦0.3, 0≦y≦0.1, and 0.002≦z≦0.03.)

5. The positive electrode active material for a lithium secondary battery according to claim 1 or 2, which satisfies the following formula (B): 1.1<T / S≦2.0...Formula (B) (In formula (B), S is the BET specific surface area (m ２ / g), and T is the BET specific surface area (m ２ / g).

6. The above S is 0.1 m ２ / g or more 2.0m ２ The positive electrode active material for a lithium secondary battery according to claim 5, wherein the SiO2 content is 1 / g or less.

7. D obtained from the volume-based cumulative particle size distribution curve measured by a laser diffraction scattering method ５０ The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the average particle diameter is 5 μm or more and 20 μm or less.

8. A positive electrode for a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery according to claim 1 or 2.

9. A lithium secondary battery comprising the positive electrode for lithium secondary batteries according to claim 8.

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