Lithium metal composite oxide, positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery

Abstract

Provided are a lithium metal composite oxide capable of improving the first discharge capacity and cycle characteristics of a lithium secondary battery, a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery. A lithium metal composite oxide having a layered structure and satisfying (1), (2), and (3).

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-205622 filed on December 22, 2022, and incorporates its content herein. Background Art

[0003] As a positive electrode active material for a lithium secondary battery, a lithium metal composite oxide is used. For the purpose of improving the performance of a lithium secondary battery, research has been conducted, for example, on controlling the crystal structure of the lithium metal composite oxide.

[0004] It is known that a phenomenon of cation mixing occurs during the manufacturing stage of the lithium metal composite oxide or during the charge and discharge of the lithium secondary battery.

[0005] Cation mixing is a phenomenon in which nickel ions migrate to the sites where lithium ions should be present and lithium ions are replaced by nickel ions in the crystal structure of the lithium metal composite oxide. If cation mixing occurs, the capacity of the lithium secondary battery is lost, and thus the battery performance is likely to deteriorate.

[0006] Therefore, research has been conducted to reduce the proportion of cation mixing in the lithium metal composite oxide.

[0007] For example, Patent Document 1 discloses a hexagonal lithium nickel composite oxide having a layered structure, in which the occupancy of Li positions in the Li main layer is 95% or more.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: JP-A-2010-64944 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In the process of expanding the application field of lithium secondary batteries, further improvement in the initial discharge capacity and cycle characteristics is required.

[0013] The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium metal composite oxide, a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery that can improve the initial discharge capacity and cycle characteristics of the lithium secondary battery.

[0014] Means for Solving the Problems

[0015] The present invention includes the following [1] to [9].

[0016] [1] A lithium metal composite oxide having a layered structure and satisfying the following (1), (2), and (3).

[0017] (1) It is represented by the following compositional formula (I).

[0018] Li[Li m (Ni (1-x-y) Co x M y ) 1-m O2 Compositional formula (I)

[0019] (In the compositional formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Ca, Al, Zn, Sn, Zr, B, Si, Nb, W, Ta, Ba, S, and P, and the compositional formula (I) satisfies -0.1 ≤ m ≤ 0.2, 0 ≤ x ≤ 0.5, 0 < y ≤ 0.7, and x + y < 1.)

[0020] (2) The occupancy of the Me position in the Li site of the layered rock salt-type crystal structure determined by the Rietveld analysis method is 2.0% or more and 7.0% or less.

[0021] (3) 0.45 ≤ (I B +I C ) / I A ≤ 0.70

[0022] (In the powder X-ray diffraction measurement using CuKα radiation, I A is the integrated intensity of the diffraction peak existing in the range of 2θ = 35.5 ± ⁰, I B is the integrated intensity of the diffraction peak on the low-angle side among the two diffraction peaks existing in the range of 2θ = 38.0 ± ⁰, and I C is the integrated intensity of the diffraction peak on the high-angle side among the above two diffraction peaks.)

[0023] [2] The lithium metal composite oxide according to [1], wherein the above compositional formula (I) satisfies 0 ≤ x ≤ 0.1.

[0024] [3] The lithium metal composite oxide according to [1] or [2], wherein D 50 obtained from the volume-based cumulative particle size distribution curve measured by the laser diffraction scattering method is 3 μm or more and 20 μm or less. [[ID=so]]

[0025] [4] The lithium metal composite oxide according to any one of [1] to [3], which satisfies the following (4).

[0026] (4) 0.8 ≤ I D / IE ≤1.8

[0027] (In the powder X-ray diffraction measurement using CuKα rays, I D is the integrated intensity of the diffraction peak existing in the range of 2θ = 18.5 ± 1°, and I E is the integrated intensity of the diffraction peak existing in the range of 2θ = 44.5 ± 1°.)

[0028] [5] The lithium metal composite oxide according to any one of [1] to [4], wherein the average crystallite size calculated by performing Rietveld analysis on the powder X-ray diffraction pattern in the range of 2θ = 10° - 90° obtained by the above powder X-ray diffraction measurement is 80 nm or more and 200 nm or less.

[0029] [6] The lithium metal composite oxide according to any one of [1] to [5], having a BET specific surface area of 0.2 m 2 / g or more and 2.0 m 2 / g or less.

[0030] [7] A positive electrode active material for a lithium secondary battery, containing the lithium metal composite oxide according to any one of [1] to [6].

[0031] [8] A positive electrode for a lithium secondary battery, including the positive electrode active material for a lithium secondary battery described in [7].

[0032] [9] A lithium secondary battery, including the positive electrode for a lithium secondary battery described in [8].

[0033] Advantages of the Invention

[0034] According to the present invention, it is possible to provide a lithium metal composite oxide, a positive electrode active material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery that can improve the first discharge capacity and cycle characteristics of the lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram for explaining the volume change of the lithium metal composite oxide.

[0036] Figure 2 is a schematic diagram for explaining the volume change of the lithium metal composite oxide.

[0037] Figure 3 is a schematic diagram showing a schematic configuration of an example of a lithium secondary battery.

[0038] Figure 4 is a schematic diagram showing a schematic configuration of an example of an all-solid-state lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0039] The definitions of the terms in this specification are as follows.

[0040] The metal composite compound will also be referred to as "MCC" hereinafter.

[0041] The lithium metal composite oxide will also be referred to as "LiMO" hereinafter.

[0042] The cathode active material for lithium secondary batteries will also be referred to as "CAM" hereinafter.

[0043] "Ni" does not represent elemental nickel metal, and the same applies to the descriptions of other elements such as Co and Li.

[0044] When a numerical range is described as, for example, "5 - 15 μm", it means the range from 5 μm to 15 μm, that is, a numerical range including 5 μm as the lower limit value and 15 μm as the upper limit value.

[0045] A lithium secondary battery refers to a lithium-ion secondary battery.

[0046] For the numerical ranges in this specification, the upper limit value and the lower limit value can be arbitrarily combined. The numerical ranges of each physical property, composition, and manufacturing condition can be arbitrarily combined.

[0047] In this specification, the cycle characteristics are evaluated by the discharge capacity retention rate.

[0048] The measurement methods of the initial discharge capacity and the discharge capacity retention rate in this specification are as follows.

[0049] [Measurement Methods of Initial Discharge Capacity and Discharge Capacity Retention Rate]

[0050] Manufacture a cathode for a lithium secondary battery and a lithium secondary battery by the methods described below, and measure the initial discharge capacity and the discharge capacity retention rate.

[0051] [Manufacture of Cathode for Lithium Secondary Battery]

[0052] Use LiMO as the CAM, and prepare a paste-like positive electrode mixture by adding and kneading the CAM, a conductive material (acetylene black), and a binder (PVdF) in a ratio of CAM:conductive material:binder = 92:5:3 (mass ratio). When preparing the positive electrode mixture, use N-methyl-2-pyrrolidone as an organic solvent.

[0053] The obtained positive electrode mixture was coated on an Al foil with a thickness of 40 μm serving as a current collector and 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 set to 1.65 cm 2 .

[0054] <Fabrication of Lithium Secondary Battery>

[0055] The following operations were carried out inside a glove box under an argon atmosphere.

[0056] The above-mentioned positive electrode for a lithium secondary battery was placed on the lower cover of a component for a coin-type battery R2032 (manufactured by Takizawa Co., Ltd.) with the aluminum foil side facing down, and a separator (thickness 25 μm) made of a porous polyethylene film was placed thereon. 300 μl of an electrolyte was injected therein. As the electrolyte, a liquid obtained by dissolving LiPF6 in a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35 to a concentration of 1 mol / l was used.

[0057] Next, metallic lithium was used as the negative electrode and placed on the upper side of the above-mentioned separator, and the upper cover was covered via a gasket and caulked with a caulking machine to fabricate a coin-type lithium secondary battery (coin-type half-cell R2032).

[0058] By allowing the assembled lithium secondary battery to stand at room temperature for 12 hours, the electrolyte was sufficiently infiltrated into the separator and the positive electrode mixture layer.

[0059] At a test temperature of 25 °C, the current set value was set to 0.2 CA for both charging and discharging, and constant current constant voltage charging and constant current discharging were performed respectively. The maximum charging voltage was set to 4.3 V, and the minimum discharging voltage was set to 2.5 V. The discharging capacity was measured, and the obtained value was taken as the "initial discharging capacity" (mAh / g).

[0060] In this specification, "high initial discharging capacity" means that the initial discharging capacity measured by the above method is 180 mAh / g or more.

[0061] Next, at a test temperature of 25 °C, constant current constant voltage charging and constant current discharging were repeated under the following conditions. The number of charge-discharge cycles was 50 times.

[0062] Charging: Current set value 0.5 CA, maximum voltage 4.3 V, constant current constant voltage charging

[0063] Discharging: Battery set value 1 CA, minimum voltage 2.5 V, constant current discharging

[0064] The discharge capacity retention rate is calculated from the discharge capacity of the 1st cycle and the discharge capacity of the 50th cycle by the following formula. The higher the discharge capacity retention rate, the less likely the capacity of the battery is to decrease after repeated charging and discharging, and the higher the cycle characteristics.

[0065] Discharge capacity retention rate (%) = Discharge capacity of the 50th cycle (mAh / g) / Discharge capacity of the 1st cycle (mAh / g) × 100

[0066] In this specification, "good cycle characteristics" means that the discharge capacity retention rate measured by the above method is 80% or more.

[0067] <limo>

[0068] "Crystal Structure"

[0069] LiMO has a layered structure.

[0070] The so-called layered structure is a crystal structure formed by alternating layers of a lithium layer and a transition metal layer other than lithium sandwiching an oxygen layer. The transition metal layer is composed of transition metal ions, and the oxygen layer is composed of oxygen ions. The crystal structure of the layered rock salt type is typically the crystal structure of α-NaFeO2 type.

[0071] [Method for Confirming Crystal Structure]

[0072] The crystal structure of LiMO can be confirmed by observing using a powder X-ray diffraction measuring device.

[0073] For powder X-ray diffraction measurement, an X-ray diffractometer can be used, such as UltimaIV manufactured by Rigaku Corporation.

[0074] The crystal structure of LiMO is more preferably a hexagonal crystal structure or a monoclinic crystal structure.

[0075] The hexagonal crystal structure belongs to any one of the space groups selected from the group consisting of P3, P31, P32, R3, P-3, R-3, P312, P321, P3112, P3121, P3212, P3221, R32, P3m1, P31m, 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.

[0076] In addition, the monoclinic crystal structure belongs to any one of the space groups 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.

[0077] Among them, in order to obtain a lithium secondary battery with a high initial discharge capacity, the crystal structure is particularly preferably a hexagonal crystal structure belonging to the space group R-3m, or a monoclinic crystal structure belonging to C2 / m.

[0078] LiMO satisfies the following (1), (2), and (3).

[0079] It is represented by the following compositional formula (I).

[0080] Li[Li m (Ni (1-x-y) Co x M y ) 1-m O2 Compositional formula (I)

[0081] (In the compositional formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Ca, Al, Zn, Sn, Zr, B, Si, Nb, W, Ta, Ba, S, and P, and the compositional formula (I) satisfies -0.1 ≤ m ≤ 0.2, 0 ≤ x ≤ 0.5, 0 < y ≤ 0.7, and x + y < 1.)

[0082] (2) The occupancy of the Me position in the Li site of the layered rock salt-type crystal structure determined by the Rietveld analysis method is 2.0% or more and 7.0% or less.

[0083] (3) 0.45 ≤ (I B +I C ) / I A ≤ 0.70

[0084] (In the powder X-ray diffraction measurement using CuKα radiation, I A is the integrated intensity of the diffraction peak existing in the range of 2θ = 35.5 ± 1°, I B is the integrated intensity of the diffraction peak on the low-angle side among the two diffraction peaks existing in the range of 2θ = 38.0 ± 1°, and I C is the integrated intensity of the diffraction peak on the high-angle side among the above two diffraction peaks.)

[0085] 《Composition》

[0086] LiMO is represented by the above compositional formula (I).

[0087] (m)

[0088] From the viewpoint of improving the cycle characteristics, m is preferably -0.08 or more, more preferably -0.06 or more, and particularly preferably -0.04 or more. In addition, from the viewpoint of obtaining a lithium secondary battery with a high initial discharge capacity, m is preferably 0.1 or less, more preferably 0.08 or less, and particularly preferably 0.05 or less.

[0089] m satisfies, for example, -0.08 ≤ m ≤ 0.1, -0.06 ≤ m ≤ 0.08, or -0.04 ≤ m ≤ 0.05.

[0090] (x)

[0091] Cations are particularly likely to be generated when mixed in LiMO with a low Co content ratio. Therefore, from the perspective of obtaining LiMO that satisfies the above (2), x is preferably 0.5 or less, more preferably 0.2 or less, particularly preferably 0.1 or less, and further preferably 0.05 or less. The lower limit value of x is, for example, 0.

[0092] x satisfies, for example, 0 ≤ x ≤ 0.2, 0 ≤ x ≤ 0.1, or 0 ≤ x ≤ 0.05. From the perspective of improving the initial discharge capacity and cycle characteristics, the composition formula (I) preferably satisfies 0 ≤ x ≤ 0.1.

[0093] (y)

[0094] From the perspective of improving the cycle characteristics, y is preferably 0.0002 or more, more preferably 0.0005 or more. In addition, y is preferably 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.10 or less.

[0095] y satisfies, for example, 0.0002 ≤ y ≤ 0.5, 0.0005 ≤ y ≤ 0.3, or 0.0002 ≤ y ≤ 0.10.

[0096] The composition formula (I) preferably satisfies 0.0002 ≤ y ≤ 0.10.

[0097] x + y is greater than 0. In addition, from the perspective of obtaining a lithium secondary battery with a high initial discharge capacity, x + y is preferably 0.5 or less, more preferably 0.25 or less, particularly preferably 0.2 or less, and further preferably 0.1 or less.

[0098] x + y satisfies, for example, 0 < x + y ≤ 0.5, 0 < x + y ≤ 0.25, 0 < x + y ≤ 0.2, or 0 < x + y ≤ 0.1.

[0099] From the perspective of improving the cycle characteristics and the initial discharge capacity, M is preferably at least one element selected from the group consisting of Mn, Ti, Mg, Ca, Al, Zr, B, Si, Nb, and W.

[0100] LiMO preferably contains Li, Ni, and at least one element M1 selected from the group consisting of Mn and Al, and is more preferably represented by the following composition formula (I’).

[0101] Li[Li m (Ni (1-x-y) Co x M1 z M2 w ) 1-m O2 Composition formula (I’)

[0102] (In the compositional formula (I'), M1 is one or more elements selected from the group consisting of Mn and Al, M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Ca, Zn, Sn, Zr, B, Si, Nb, W, Ta, Ba, S, and P. The ranges of m and x are the same as those of m and x in the above compositional formula (I), and the range of z + w is the same as that of y in the above compositional formula (I).)

[0103] [Composition analysis]

[0104] The composition analysis of LiMO can be carried out by dissolving the obtained LiMO powder in hydrochloric acid and then measuring it using an ICP emission spectroscopic analysis device.

[0105] As the ICP emission spectroscopic analysis device, for example, SPS3000 manufactured by SII NanoTechnology Co., Ltd. can be used.

[0106] 《Me site occupancy》

[0107] LiMO satisfies the above (2). The above Me site occupancy is preferably 2.1% or more, more preferably 2.2% or more. The Me site occupancy represents the occupancy ratio of metal elements other than Li (for example, Ni, Co, and the elements listed in M of the compositional formula (I)) in the lithium layer (Li site) of the layered structure.

[0108] If the Me site occupancy is at least the above lower limit value, the volume change amount during repeated charging and discharging can be reduced. As a result, the cycle characteristics can be improved.

[0109] In addition, the Me site occupancy is preferably 6.8% or less, more preferably 6.5% or less.

[0110] If the Me site occupancy is at most the above upper limit value, the increase in resistance can be suppressed, and the decrease in the first discharge capacity can be suppressed. In addition, the deterioration of the structure during the charge-discharge reaction due to the excessive increase in resistance can be suppressed, and the cycle characteristics can be improved.

[0111] The Me site occupancy is, for example, 2.1 - 6.8% or 2.2 - 6.5%.

[0112] [Method for measuring Me site occupancy]

[0113] The Me site occupancy is calculated by performing Rietveld analysis on the powder X-ray diffraction pattern obtained by powder X-ray diffraction measurement. The Rietveld analysis method is a method of comparing the measured powder X-ray diffraction pattern with a simulated pattern from a crystal structure model and optimizing the crystal structure parameters in the crystal structure model so that the difference between the two becomes the smallest.

[0114] The powder X-ray diffraction measurement is performed using an X-ray diffraction device. As an X-ray diffraction device, for example, D8 Advance manufactured by Bruker can be used. Specifically, the powder of LiMO is filled into a dedicated substrate, and a CuKα ray source is used to measure the powder X-ray diffraction pattern under the conditions of a diffraction angle of 2θ = 10°-90° and a sampling width of 0.02°. The obtained powder X-ray diffraction pattern is subjected to Rietveld analysis. The Rietveld analysis software used is TOPAS ver.4.2 manufactured by Bruker. At this time, a layered rock salt type crystal structure (Li 1-n Me n )(Me 1-n Li n )O2, and optimize the Me position occupancy n in the Li site.

[0115] I A ,I B and I C 》

[0116] LiMO satisfies the above (3).

[0117] [I A ,I B and I C How to obtain [

[0118] In powder X-ray diffraction measurements using CuKα radiation, LiMO exhibits a diffraction peak A within the range of 2θ = 35.5 ± 1° and two diffraction peaks within the range of 2θ = 38.0 ± 1°. The two peaks refer to the peak with the highest intensity and the peak with the second highest intensity. Of the two peaks, the peak at the lower angle is designated as Peak B, and the peak at the higher angle is designated as Peak C.

[0119] The area of the mountain-shaped portion formed between the line connecting the lowest points on the left and right sides of the diffraction peak A and the curve of peak A, between the line connecting the lowest points on the left and right sides of the diffraction peak B and the curve of peak B, and between the line connecting the lowest points on the left and right sides of the diffraction peak C and the curve of peak C, i.e., the integrated intensity, is set as I A ,I B ,I C .

[0120] From the powder X-ray diffraction pattern obtained in the above-mentioned [Method for determining the site occupancy of Me], I was calculated using comprehensive powder X-ray analysis software. A ,I B , and I C The powder X-ray diffraction analysis software used was DIFFRAC.EVA manufactured by Bruker.

[0121] (I B + I C ) / I A is preferably 0.46 or more, more preferably 0.48 or more, and particularly preferably 0.50 or more. (I B + I C ) / I A is preferably 0.69 or less, more preferably 0.67 or less, and particularly preferably 0.65 or less.

[0122] LiMO preferably satisfies any one of the following (3)-1 to (3)-3.

[0123] (3)-1 0.46 ≤ (I B + I C ) / I A ≤ 0.69

[0124] (3)-2 0.48 ≤ (I B + I C ) / I A ≤ 0.67

[0125] (3)-3 0.50 ≤ (I B + I C ) / I A ≤ 0.65

[0126] Peak A is the peak corresponding to the (101) plane, peak B is the peak corresponding to the (006) plane, and peak C is the peak corresponding to the (012) plane.

[0127] If the above (1), (2), and (3) are satisfied, the first discharge capacity of the lithium secondary battery is high, and the cycle characteristics are improved. The reason is speculated as follows.

[0128] The volume change of LiMO generated during repeated charging and discharging is one of the reasons for the deterioration of the cycle characteristics of the lithium secondary battery. If LiMO with a large volume change is used for CAM, cracks are generated in the CAM during cycling, side reactions occur on the newly generated surface through the cracks, gases are generated, and a resistance layer is formed. In addition, parts with low contact with the conductive additive are generated. Due to the above reasons, the electron conductivity and the lithium ion conductivity are reduced, and the resistance increases. Therefore, the cycle characteristics deteriorate.

[0129] Regarding this volume change, it is explained using the schematic diagram of LiMO shown in Figure 1 . Figure 1 In, LiMO41 is the state when lithium ions are inserted (corresponding to before charging or during discharging of the battery), and LiMO42 is the state after lithium ion deintercalation (corresponding to after charging of the battery).

[0130] Figure 1 It shows the state where LiMO41 becomes LiMO42 as lithium ions are deintercalated during charging. When lithium ions are deintercalated, the negatively charged oxygen ions repel each other. As a result, the layers of the transition metals expand the interlayer space between each other, and the volume increases. That is, the interlayer space expands from L1 to L2, and the volume increases.

[0131] LiMO41 does not produce cation mixing or has a low ratio of cation mixing. Therefore, when the lithium site becomes an empty position during charging, the repulsion between oxygen ions is not canceled, and the interlayer space between the layers of the transition metals is easily expanded.

[0132] During discharging, lithium ions are intercalated, and it changes from LiMO42 to LiMO41. In this case, the interlayer space contracts from L2 to L1, and the volume decreases. The greater the difference between L1 and L2, the greater the volume change amount during repeated charging and discharging, which is one of the reasons for deteriorating the cycle characteristics.

[0133] Figure 2 It is a schematic diagram showing the volume change of LiMO of the present embodiment in which cation mixing has occurred. Figure 2 Among them, LiMO51 is the state when lithium ions are intercalated (equivalent to before charging or during discharging of the battery), and LiMO52 is the state after lithium ions are deintercalated (equivalent to after charging of the battery). LiMO51 becomes LiMO52 as lithium ions are deintercalated during charging. If lithium ions are intercalated during discharging, LiMO52 changes to LiMO51.

[0134] Since a part of the lithium site in LiMO51 is replaced by nickel ions, even if lithium ions are detached during charging, the nickel ions remain at the lithium site. The remaining nickel ions neutralize the repulsion between oxygen ions, so the interlayer space between the layers of the transition metals is not easily expanded. That is, although the interlayer space expands from L3 to L4, because the difference is small, the volume is not easily increased. As a result, the cycle characteristics are not easily deteriorated.

[0135] Generally, if the cation mixing is large, a rock salt-type structure is easily formed. Since the rock salt-type structure is electrochemically inactive, it becomes a resistance during the deintercalation and intercalation of lithium ions. If the resistance is high, the initial discharge capacity is easily reduced, and in addition, the cycle characteristics are easily deteriorated due to the structural deterioration during the charge-discharge reaction. On the other hand, if the amount of the rock salt-type structure is too small, rapid structural deterioration and volume change are likely to occur during the charge-discharge reaction, and the cycle characteristics are easily deteriorated. Since the rock salt-type structure exists in an appropriate amount in LiMO of the present embodiment, the initial discharge capacity is high, and the cycle characteristics can be improved.

[0136] Since LiMO of the present embodiment satisfies the above (2), the volume change amount during repeated charging and discharging is small, and since it satisfies the above (3), the rock salt-type structure exists in an appropriate amount. Therefore, it is speculated that the initial discharge capacity is high and the cycle characteristics are not easily deteriorated.

[0137] D of LiMO 50 is preferably 3 μm or more, more preferably 8 μm or more, and particularly preferably 10 μm or more. D 50 is preferably 20 μm or less, more preferably 18 μm or less, and particularly preferably 17 μm or less. D 50 For example, it is 3 - 20 μm, 8 - 18 μm, or 10 - 17 μm.

[0138] D 50 is the 50% cumulative volume particle size (μm) obtained from the cumulative particle size distribution curve based on volume measured by the laser diffraction scattering method.

[0139] D 50 LiMO satisfying the above range is easily filled when manufacturing the positive electrode, has good contact with the conductive additive, and a positive electrode with a high initial discharge capacity can be manufactured.

[0140] [Measurement method of D 50

[0141] D of LiMO 50 can be measured by the following laser diffraction scattering method.

[0142] Specifically, first, 2 g of powdered LiMO is put into 50 ml of an aqueous solution of 0.2 mass% sodium hexametaphosphate to obtain a dispersion by dispersing LiMO.

[0143] Next, for the obtained dispersion, the particle size distribution is measured using a laser diffraction particle size distribution analyzer to obtain a cumulative particle size distribution curve based on volume. In the obtained cumulative particle size distribution curve, the particle size value when 50% is accumulated from the side of fine particles is D 50 (μm).

[0144] As the laser diffraction particle size distribution analyzer, for example, MS2000 manufactured by Malvern can be used.

[0145] LiMO preferably further satisfies the following (4).

[0146] (4) 0.8 ≤ I D / I E ≤ 1.8

[0147] (In powder X-ray diffraction measurement using CuKα rays, I D is the integrated intensity of the diffraction peak existing in the range of 2θ = 18.5 ± 1°, and I E is the integrated intensity of the diffraction peak existing in the range of 2θ = 44.5 ± 1°.)

[0148] [I D and I E Obtaining method]

[0149] In the powder X-ray diffraction measurement using CuKα rays, LiMO has a diffraction peak D in the range of 2θ = 18.5 ± 1°, and a diffraction peak E in the range of 2θ = 44.5 ± 1°. The areas of the mountain-shaped parts between the line connecting the lowest points on the left and right sides of the diffraction peak D and the curve of peak D, and between the line connecting the lowest points on the left and right sides of the diffraction peak E and the curve of peak E, that is, the integrated intensities, are respectively set as I D 、I E 。

[0150] Peak D is the peak corresponding to the (003) plane, and peak E is the peak corresponding to the (104) plane.

[0151] From the powder X-ray diffraction pattern obtained by the above [Measurement method of Me site occupancy], using the integrated powder X-ray analysis software, I D and I E are calculated. The powder X-ray diffraction analysis software uses DIFFRAC.EVA manufactured by Bruker Corporation.

[0152] I D / I E is preferably 0.9 or more, more preferably 1.0 or more. It is considered that when I D / I E is above the lower limit value, the crystal structure in the layer direction of LiMO is developed relative to the plane direction in the layered structure, and the initial discharge capacity is likely to increase.

[0153] I D / I E is preferably 1.7 or less, more preferably 1.5 or less. When I D / I E is below the upper limit value, the crystal structure in the layer direction in the layered structure of LiMO is not overly developed, the volume change in the layer direction during charge and discharge cycles can be suppressed, and the cycle characteristics are likely to improve.

[0154] I D / I E For example, the following (4)-1 or (4)-2 can be cited.

[0155] (4)-1 0.9 ≤ I D / I E ≤ 1.7

[0156] (4)-2 1.0 ≤ I D / I E ≤ 1.5

[0157] The average crystallite size of LiMO is preferably 80 - 200 nm.

[0158] [Method for measuring average crystallite size]

[0159] The average crystallite size is calculated by performing Rietveld analysis on the powder X-ray diffraction pattern in the range of 2θ = 10° - 90° obtained in the above [Method for measuring Me site occupancy].

[0160] The average crystallite size is preferably 85 nm or more, more preferably 90 nm or more. LiMO with an average crystallite size of the above lower limit or more exhibits high crystallinity. Such LiMO has few lattice defects and small resistance at grain boundaries, so the insertion and extraction of lithium ions proceed smoothly, and the initial discharge capacity is easily increased.

[0161] The average crystallite size is preferably 170 nm or less, more preferably 150 nm or less. The LiMO crystallites with an average crystallite size of the above upper limit or less do not grow excessively, and the diffusion resistance of lithium ions in the crystal structure easily becomes small, and the initial discharge capacity is easily increased.

[0162] The average crystallite size is, for example, 85 - 170 nm, or 90 - 150 nm.

[0163] The BET specific surface area of LiMO is preferably 0.2 m 2 / g or more, more preferably 0.3 m 2 / g or more. The BET specific surface area is preferably 2.0 m 2 / g or less, more preferably 1.9 m 2 / g or less. The BET specific surface area is, for example, 0.2 - 2.0 m 2 / g, or 0.3 - 1.9 m 2 / g.

[0164] If LiMO with a BET specific surface area of the above lower limit or more is used, the contact area between LiMO and the electrolyte increases, and the initial discharge capacity easily becomes high.

[0165] If LiMO with a BET specific surface area of the above upper limit or less is used, the contact area between LiMO and the electrolyte increases, and the generation of gas due to the decomposition of the electrolyte is easily suppressed, and the cycle characteristics are easily improved.

[0166] [Method for measuring BET specific surface area]

[0167] The BET specific surface area of LiMO or the metal composite hydroxide described below can be measured using a BET specific surface area measuring device. As the BET specific surface area measuring device, for example, Macsorb (registered trademark) manufactured by Mountech Co., Ltd. can be used. As the pretreatment before measurement, it is preferable to dry LiMO or the metal composite hydroxide in a nitrogen atmosphere at 105°C for 30 minutes.

[0168] <Manufacturing method of LiMO>

[0169] The manufacturing method of LiMO preferably includes a step of obtaining MCC and a step of obtaining LiMO. Hereinafter, the step of obtaining MCC and the step of obtaining LiMO will be described in sequence.

[0170] [Step of obtaining MCC]

[0171] First, prepare MCC containing Ni and one or more elements selected from the group consisting of Co and element M. Element M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Ca, Al, Zn, Sn, Zr, B, Si, Nb, W, Ta, Ba, S, and P.

[0172] MCC can be manufactured by the batch coprecipitation method or the continuous coprecipitation method. Hereinafter, taking a metal composite oxide containing Ni and element M as an example, its manufacturing method will be described in detail.

[0173] First, by the coprecipitation method, particularly the continuous coprecipitation method described in JP-A-2002-201028, react a nickel salt solution, a metal salt solution containing element M, and an optional complexing agent as needed to manufacture Ni (1-y) M y (OH)2 (where y is the same as y in the above compositional formula (I)) represents a metal composite hydroxide.

[0174] 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.

[0175] As the metal salt which is the solute of the metal salt solution containing element M, sulfates, chlorides, acetates, hydroxide salts, etc. of element M can be cited.

[0176] For example, as the manganese salt which is the solute of the manganese salt solution, one or more of manganese sulfate, manganese nitrate, and manganese chloride can be used.

[0177] As the aluminum salt which is the solute of the aluminum salt solution, for example, aluminum sulfate, sodium aluminate, etc. can be used.

[0178] The above metal salts are in the same ratio as the above Ni (1-y) M y (OH)2 is used in a proportion corresponding to its composition ratio. In addition, water is used as the solvent.

[0179] The complexing agent is a compound that can form a complex with Ni and the ions of element M in an aqueous solution. Examples thereof include ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine.

[0180] Examples of the ammonium ion donor include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

[0181] The complexing agent may be absent. When the complexing agent is included, the amount of the complexing agent contained in the mixed solution of the nickel salt solution, the metal salt solution containing element M, and the complexing agent is, for example, greater than 0 and 2.0 or less in terms of the molar ratio to the total number of moles of the nickel salt and the metal salt.

[0182] In the coprecipitation method, in order to adjust the pH value of the above-mentioned mixed solution, an alkaline aqueous solution is added to the mixed solution before the pH of the mixed solution changes from alkaline to neutral. As the alkaline aqueous solution, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution can be used.

[0183] It should be noted that the pH value in this specification is defined as the value measured when the temperature of the mixed solution is 40 °C. When the temperature of the mixed solution sampled from the reaction tank is not 40 °C, the mixed solution is heated or cooled to 40 °C and then the pH is measured.

[0184] During the reaction, the temperature of the reaction tank is controlled within a range of, for example, 20 - 80 °C, preferably 30 - 70 °C.

[0185] In addition, during the reaction, the pH value in the reaction tank is controlled within a range of, for example, 9 or more and less than 12, preferably 10 or more and less than 12.

[0186] The substances in the reaction tank are appropriately stirred and mixed.

[0187] The reaction tank used in the continuous coprecipitation method can be a type of reaction tank that overflows for separating the formed reaction precipitate.

[0188] In order to control the reaction tank to a target atmosphere, a specified gas can be introduced into the reaction tank, or the liquid in the reaction tank can be directly bubbled.

[0189] After the above reaction, a metal composite hydroxide can be obtained by washing the obtained reaction precipitate with water and then drying it. In addition, when inclusions derived from the mixed solution remain when the reaction precipitate is washed only with water, the reaction precipitate can also be washed with weak acid water or an alkaline solution containing sodium hydroxide or potassium hydroxide as needed.

[0190] After drying the reaction precipitate, classification can also be appropriately carried out.

[0191] The BET specific surface area of the metal composite hydroxide is preferably 10 - 40 m 2 / g, more preferably 14 - 30 m 2 / g.

[0192] The BET specific surface area of the metal composite hydroxide can be adjusted by the pH value in the reaction tank during production.

[0193] The obtained metal composite hydroxide is oxidized (oxidation step) to obtain MCC as a metal composite oxide.

[0194] The oxidation temperature preferably has the maximum holding temperature set at 500 - 800 °C, more preferably set at 550 - 750 °C.

[0195] The oxidation time is preferably 1 - 10 hours, more preferably 2 - 6 hours. It should be noted that the oxidation time refers to the total time from the start of heating until reaching the maximum holding temperature and starting to cool down.

[0196] The gas flow rate per unit time in the oxidation step is preferably adjusted within an appropriate range. The gas flow rate in the oxidation step is preferably 0.5 - 10.0 L / min, more preferably 1.0 - 5.0 L / min.

[0197] Relative to the BET specific surface area of the metal composite hydroxide (unit: m 2 / g), the total flow rate of the gas supplied in the oxidation step (unit: m 3 ) preferably satisfies the following (A).

[0198] (A) 0.08 m·g ≤ total flow rate of gas supplied in oxidation step / BET specific surface area of metal composite hydroxide / ≤ 0.12 m·g

[0199] The total flow rate of the gas supplied in the oxidation step in this specification refers to the total flow rate of the gas flowing from the start of heating until reaching the maximum holding temperature and starting to cool down in the oxidation step. The total flow rate of the above gas can be calculated from the gas flow rate per unit time and the oxidation time.

[0200] By controlling the oxidation temperature, oxidation time, and gas flow rate within the above ranges, and oxidizing the metal composite hydroxide under the conditions that satisfy the above (A), carbonate ions, etc. in the MCC can be removed, and the MCC can be formed within the range of not excessively forming a rock salt type structure. Moreover, in the subsequent step, when the MCC is mixed with a lithium compound and fired, since the cation mixing is controlled within an appropriate range and the layered structure is fully developed, LiMO that satisfies the above (2) and (3) can be manufactured.

[0201] In the oxidation process, the heating rate until the maximum holding temperature is reached is preferably 80 °C / hour or more, more preferably 100 °C / hour or more, and particularly preferably 120 °C / hour or more.

[0202] The maximum holding temperature in this specification refers to the maximum temperature of the holding temperature of the atmosphere in the oxidation device or the firing furnace (hereinafter, also collectively referred to as the "heating device") in the oxidation process or the firing process described later (hereinafter, also collectively referred to as the "heating process"). In the case of performing oxidation or firing in multiple stages, the maximum holding temperature refers to the maximum temperature of the stage in which oxidation or firing is performed at the highest holding temperature in the heating process.

[0203] The heating rate in this specification is calculated from the time from the start of heating to the time when the maximum holding temperature is reached in the heating device and the temperature difference in the heating device from the temperature at the start of heating to the maximum holding temperature.

[0204] As the gas during oxidation, oxygen or air (atmosphere) can be used.

[0205] In addition to the control of the above conditions, various gases, such as inert gases such as nitrogen, argon, and carbon dioxide, oxidizing gases such as air and oxygen, or a mixed gas thereof, can be supplied into the reaction tank to control the oxidation state of the obtained reaction product.

[0206] In addition, oxidants such as peroxides such as hydrogen peroxide, peroxide salts such as permanganates, perchlorates, hypochlorites, nitric acid, halogens, and ozone can also be used.

[0207] The obtained MCC can also be appropriately classified.

[0208] [Process for obtaining LiMO]

[0209] The process for obtaining LiMO includes a mixing process of mixing MCC with a lithium compound and a firing process of firing the obtained mixture.

[0210] · Mixing process

[0211] Mix MCC with a lithium compound.

[0212] As the lithium compound, at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium hydroxide hydrate, lithium oxide, lithium chloride, and lithium fluoride can be used. Among them, at least one of lithium hydroxide, lithium hydroxide hydrate, and lithium carbonate is preferred.

[0213] A lithium compound and MCC are mixed in consideration of the composition ratio of the final target product to obtain a mixture of the lithium compound and MCC. The amount of Li is preferably 0.90 - 1.10, more preferably 0.91 - 1.10, and particularly preferably 0.92 - 1.10 relative to the total amount 1 (molar ratio) of elements other than oxygen atoms contained in MCC (such as Ni, Co, element M).

[0214] If the lithium compound and MCC are mixed in the above - mentioned ratio range, there is a sufficient amount of lithium ions relative to MCC, and the number of sites with insufficient lithium ions in the layered structure of the obtained LiMO becomes smaller. Therefore, it becomes easier to obtain LiMO that satisfies the above (1) and (3). In addition, by mixing the lithium compound and MCC in the above - mentioned ratio range, the D 50 , I D / I E , and the average crystallite size can be adjusted to the above - mentioned range.

[0215] ·Firing process

[0216] The obtained mixture is fired. By firing the mixture, the crystal growth of LiMO occurs. For firing, dry air, an oxygen atmosphere, an inert atmosphere, etc. are used according to the desired composition. In this embodiment, firing is preferably carried out in an oxygen atmosphere.

[0217] The firing process can be a single firing or can have multiple firing stages. In the case of having multiple firing stages, the process of firing at the highest temperature is recorded as the formal firing. It is also possible to perform a preliminary firing at a temperature lower than the formal firing before the formal firing. In addition, it is also possible to perform a post - firing at a temperature lower than the formal firing after the formal firing.

[0218] In this embodiment, it is preferable to first perform a preliminary firing and then perform a formal firing. In addition, both the preliminary firing and the formal firing are preferably carried out in an oxygen atmosphere.

[0219] The firing temperature of the preliminary firing is preferably 600 - 900 °C, more preferably 610 - 850 °C, and particularly preferably 620 °C or higher and lower than 700 °C. If the firing temperature is above the lower limit value of the above range, LiMO with a firm crystal structure can be obtained. In addition, if the firing temperature is below the upper limit value of the above range, the volatilization of lithium ions on the particle surface of LiMO can be reduced.

[0220] The firing temperature for the formal firing is preferably 600 - 900 °C, more preferably 650 - 850 °C, and particularly preferably 700 °C - 820 °C. If the firing temperature is at or above the lower limit value of the above range, LiMO with a firm crystal structure can be obtained. In addition, if the firing temperature is at or below the upper limit value of the above range, excessive cation mixing does not occur, and it becomes easier to obtain LiMO that satisfies the above (1) and (3).

[0221] The holding time for each of the preliminary firing and the formal firing is preferably 1 - 50 hours, more preferably 2 - 20 hours. If the holding time during firing is at or below the upper limit value of the above range, the volatilization of lithium ions can be suppressed, and the reduction of battery performance can be inhibited. If the holding time during firing is at or above the lower limit value of the above range, the growth of crystals can be promoted, and the reduction of battery performance can be inhibited.

[0222] The firing temperature in this specification refers to the temperature of the atmosphere in the firing furnace and the highest holding temperature.

[0223] In the firing process, the heating rate until reaching the highest holding temperature is preferably 80 °C / hour or more, more preferably 100 °C / hour or more, and particularly preferably 150 °C / hour or more.

[0224] Firing is carried out using a firing furnace such as a static firing furnace or a fluidized firing furnace. Examples of the static firing furnace include a tunnel furnace or a roller hearth furnace. Examples of the fluidized firing furnace include a rotary furnace.

[0225] By adjusting the above firing conditions, the BET specific surface area, D 50 , I D / I E , and the value of the average crystallite size of LiMO can be adjusted.

[0226] · Washing process

[0227] In this embodiment, it is preferable to wash the fired product with a washing liquid such as pure water or an alkaline washing liquid.

[0228] Examples of the alkaline washing liquid include an aqueous solution of one or more anhydrous substances selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, and ammonium carbonate, and an aqueous solution of a hydrate of the above anhydrous substances. In addition, ammonia can also be used as the alkaline washing liquid.

[0229] In the washing process, as the method of bringing the washing liquid into contact with the fired product, methods such as putting the fired product into each washing liquid and stirring, applying each washing liquid as spray water to the fired product, putting the fired product into the washing liquid and stirring, then separating the fired product from each washing liquid, and then applying each washing liquid as spray water to the separated fired product can be cited.

[0230] The temperature of the washing liquid for washing is preferably 15°C or lower, more preferably 10°C or lower, and still more preferably 8°C or lower. By controlling the temperature of the washing liquid within the above range, excessive dissolution of lithium ions from the crystal structure of the fired product into the washing liquid during washing can be suppressed.

[0231] The fired product after washing can also be appropriately dried. The drying temperature can be, for example, 150 - 300°C.

[0232] Through the above processes, LiMO is obtained.

[0233] <Positive electrode active material for lithium secondary battery>

[0234] The CAM of the present embodiment contains LiMO manufactured by the above method. The content ratio of LiMO relative to the total mass (100% by mass) of the CAM is preferably 70 - 99% by mass, more preferably 80 - 98% by mass.

[0235] The content ratio of LiMO relative to the total mass of the CAM is determined by performing SEM observation by irradiating the CAM with electron rays having an acceleration voltage of 20 kV using SEM (for example, JSM - 5510 manufactured by JEOL Ltd.). The magnification of the SEM photograph is adjusted so that there are 200 - 400 CAM particles of interest in the SEM photograph. As an example, the magnification can also be 1000 - 30000 times.

[0236] <Lithium secondary battery>

[0237] The positive electrode for a lithium secondary battery that is preferable when using the above CAM will be described. Hereinafter, the positive electrode for a lithium secondary battery may sometimes be referred to as the positive electrode.

[0238] Furthermore, a lithium secondary battery that is preferable for use as the positive electrode will be described.

[0239] An example of a preferable lithium secondary battery when using the CAM of the present embodiment has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.

[0240] Figure 3 It is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0241] First, as Figure 3 shown in the partial enlarged view of, an electrode group 4 is formed by laminating and winding 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 in the order of separator 1, positive electrode 2, separator 1, negative electrode 3.

[0242] As an example, the positive electrode 2 has 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 side. Such a positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and forming the positive electrode active material layer 2a by loading the positive electrode mixture onto one side of the positive electrode current collector 2b.

[0243] As an example, the negative electrode 3 may include an electrode in which a negative electrode mixture containing a negative electrode active material (not shown) is loaded on a negative electrode current collector, and an electrode composed of only the negative electrode active material, and can be manufactured by the same method as the positive electrode 2.

[0244] Next, after accommodating the electrode assembly 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, the electrolyte 6 is impregnated into the electrode assembly 4, and an electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Further, by sealing the upper part of the battery can 5 with the top insulator 7 and the sealing body 8, the lithium secondary battery 10 can be manufactured.

[0245] As the shape of the electrode assembly 4, for example, a columnar shape can be cited in which the cross-sectional shape when the electrode assembly 4 is cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle obtained by rounding the corners.

[0246] In addition, as the shape of the lithium secondary battery having such an electrode assembly 4, the shapes specified in IEC60086 or JIS C 8500, which are standards for batteries specified by the International Electrotechnical Commission (IEC), can be adopted. For example, a cylindrical shape or a square shape can be cited.

[0247] Furthermore, the lithium secondary battery is not limited to the above-described wound type configuration, and may also be a stacked type configuration obtained by repeatedly stacking a stacked structure of a positive electrode, a separator, a negative electrode, and a separator. As the stacked type lithium secondary battery, so-called coin type batteries, button type batteries, or paper type (or sheet type) batteries can be cited.

[0248] For the positive electrode, separator, negative electrode, and electrolyte constituting the lithium secondary battery, for example, the configurations, materials, and manufacturing methods described in

[0113] to

[0140] of WO2022 / 113904A1 can be used.

[0249] <All-solid-state lithium secondary battery>

[0250] The CAM of the present embodiment can be used as the CAM of an all-solid-state lithium secondary battery.

[0251] Figure 4 It is a schematic diagram showing an example of an all-solid-state lithium secondary battery. Figure 4 The all-solid-state lithium secondary battery 1000 shown in [figure] has a laminate 100 including a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer package 200 housing the laminate 100. In addition, the all-solid-state lithium secondary battery 1000 may have a bipolar structure in which a CAM and a negative electrode active material are disposed on both sides of a current collector. As a specific example of the bipolar structure, for example, the structure described in JP-A-2004-95400 can be cited.

[0252] 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-described CAM and a solid electrolyte. In addition, the positive electrode active material layer 111 may contain a conductive material and a binder.

[0253] 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. In addition, the negative electrode active material layer 121 may contain a solid electrolyte and a conductive material.

[0254] The laminate 100 may also 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.

[0255] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the outer package 200 and a sealing body (not shown) that seals the opening 200a of the outer package 200.

[0256] As the outer package 200, a container formed by shaping a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel can be used. In addition, as the outer package 200, a container obtained by processing a laminated film having at least one surface subjected to corrosion-resistant processing into a bag shape can also be used.

[0257] Examples of the shape of the all-solid-state lithium secondary battery 1000 include a coin shape, a button shape, a paper shape (or sheet shape), a cylindrical shape, a square shape, or a laminated shape (bag shape).

[0258] For the all-solid-state lithium secondary battery 1000, a form having one laminate 100 is illustrated as an example, but the present embodiment is not limited thereto. The all-solid-state lithium secondary battery 1000 may also have a configuration in which the laminate 100 is used as a unit cell and a plurality of unit cells (laminates 100) are sealed inside the outer package 200.

[0259] 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.

[0260] In the lithium secondary battery having the above-described configuration, since the above-described LiMO is used, a CAM capable of improving the initial discharge capacity and cycle characteristics can be provided. Further, since the above-described LiMO is used as the CAM, a positive electrode capable of improving the initial discharge capacity and cycle characteristics can be provided.

[0261] Further, since the above-described LiMO is used as the CAM, a lithium secondary battery having improved initial discharge capacity and cycle characteristics can be provided.

[0262] Examples

[0263] Next, the present invention will be described in more detail by way of examples.

[0264] <Measurement of various parameters>

[0265] The crystal structure and various parameters of LiMO produced by the method described below were measured by the methods described in the above [Method for confirming crystal structure], [Method for measuring Me site occupancy], [Composition analysis], [Method for measuring D 50 , [Method for obtaining I A , I B and I C , [Method for obtaining I D and I E , [Method for measuring BET specific surface area], and [Method for measuring average crystallite size]. The BET specific surface area of the metal composite hydroxide produced by the method described below was measured according to the above [Method for measuring BET specific surface area].

[0266] <Method for measuring initial discharge capacity and discharge capacity retention rate>

[0267] The initial discharge capacity and discharge capacity retention rate of the lithium secondary battery were measured by the method described in the above [Method for measuring initial discharge capacity and discharge capacity retention rate].

[0268] <Example 1>

[0269] After adding water to a reaction tank equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added, and the liquid temperature was maintained at 70 ° C (temperature of the reaction tank).

[0270] An aqueous nickel sulfate solution, an aqueous manganese sulfate solution, and an aqueous aluminum sulfate solution were mixed at a molar ratio of Ni: Mn: Al of 93: 3.5: 3.5 to prepare a mixed raw material liquid 1.

[0271] While stirring, a mixed raw material solution 1 and an aqueous ammonium sulfate solution as a complexing agent were continuously added to a reaction tank under a nitrogen flow. An aqueous sodium hydroxide solution was appropriately added dropwise so that the pH of the mixed solution in the reaction tank became 10.7 (measurement temperature: 40 °C), and a reaction precipitate 1 was obtained.

[0272] Using an aqueous sodium hydroxide solution with a mass 20 times that of the reaction precipitate 1, the reaction precipitate 1 was washed. After washing, dehydration was performed using a centrifuge, followed by washing, dehydration, and separation with water, and then drying at 105 °C for 20 hours, thereby obtaining a metal composite hydroxide 1 containing Ni, Mn, and Al. The BET specific surface area of the metal composite hydroxide 1 was 19.1 m 2 / g.

[0273] The metal composite hydroxide 1 was oxidized under the conditions shown in Table 1 to obtain MCC1 as a metal composite oxide. It should be noted that "total gas flow rate / BET specific surface area" in Table 1 is the total flow rate of the gas supplied in the oxidation process relative to the BET specific surface area of the metal composite hydroxide. Air was used as the gas during oxidation.

[0274] Lithium hydroxide monohydrate was weighed in such a proportion that the amount of Li was 1.05 relative to the total amount of Ni, Mn, and Al contained in MCC1 (molar ratio). MCC1 and lithium hydroxide monohydrate were mixed to obtain a mixture 1.

[0275] Next, the obtained mixture 1 was preliminarily fired at 650 °C for 5 hours in an oxygen atmosphere. After that, it was formally fired at 750 °C for 5 hours in an oxygen atmosphere to obtain a powdery fired product 1.

[0276] A slurry prepared by mixing the fired product 1 and pure water with the liquid temperature adjusted to 5 °C in such a proportion that the fired product 1 accounted for 0.5% by mass of the total amount was stirred for 20 minutes. After that, by drying at 210 °C for 10 hours in a nitrogen atmosphere, LiMO1 with a layered structure was obtained.

[0277] <Example 2>

[0278] An aqueous nickel sulfate solution, an aqueous manganese sulfate solution, and an aqueous aluminum sulfate solution were mixed in a molar ratio of Ni:Mn:Al of 93.0:1.0:6.0 to prepare a mixed raw material solution 2.

[0279] Except for using the mixed raw material solution 2, a metal composite hydroxide 2 containing Ni, Mn, and Al was obtained by the same method as in Example 1. The BET specific surface area of the metal composite hydroxide 2 was 19.4 m 2 / g.

[0280] The metal composite hydroxide 2 was oxidized under the conditions shown in Table 1 to obtain MCC2 as a metal composite oxide. Air was used as the gas during oxidation.

[0281] Except for using MCC2, the same operations as in Example 1 were carried out to obtain LiMO2 having a layered structure.

[0282] <Example 3>

[0283] An aqueous solution of nickel sulfate, an aqueous solution of manganese sulfate, an aqueous solution of aluminum sulfate, and an aqueous solution of cobalt sulfate were mixed in a ratio such that the molar ratio of Ni:Mn:Al:Co was 91.2:3.4:3.4:2.0 to prepare a mixed raw material solution 3.

[0284] Except for using the mixed raw material solution 3, a metal composite hydroxide 3 containing Ni, Mn, Al, and Co was obtained by the same method as in Example 1. The BET specific surface area of the metal composite hydroxide 3 was 16.7 m 2 / g.

[0285] The metal composite hydroxide 3 was oxidized under the conditions shown in Table 1 to obtain MCC3 as a metal composite oxide. Air was used as the gas during oxidation.

[0286] Except for using MCC3, the same operations as in Example 1 were carried out to obtain LiMO3 having a layered structure.

[0287] <Comparative Example 1>

[0288] The metal composite hydroxide 1 obtained in Example 1 was oxidized under the conditions shown in Table 1 to obtain MCC4 as a metal composite oxide. Air was used as the gas during oxidation.

[0289] The same operations as in Example 1 were carried out using MCC4 to obtain powdery LiMO4. LiMO4 has a layered structure.

[0290] <Comparative Example 2>

[0291] Except that an aqueous sodium hydroxide solution was added dropwise in a timely manner under the condition that the pH of the mixed solution in the reaction tank was 12.2 (measurement temperature: 40 °C), a metal composite hydroxide 5 was obtained by the same method as in Example 1. The BET specific surface area of the metal composite hydroxide 5 was 47.3 m 2 / g.

[0292] The metal composite hydroxide 5 was oxidized under the conditions shown in Table 1 to obtain MCC5 as a metal composite oxide. Air was used as the gas during oxidation.

[0293] Using MCC5, the same operations as in Example 1 were carried out to obtain powdery LiMO5. LiMO5 has a layered structure.

[0294] <Comparative Example 3>

[0295] Except for not oxidizing the metal composite hydroxide 2, the same operations as in Example 2 were carried out to obtain powdery LiMO6. LiMO6 has a layered structure.

[0296] <Comparative Example 4>

[0297] The metal composite hydroxide 1 obtained in Example 1 was oxidized under the conditions shown in Table 1 to obtain MCC7 as a metal composite oxide. The gas used during oxidation was air.

[0298] Using MCC7, the same operations as in Example 1 were carried out to obtain powdery LiMO7. LiMO7 has a layered structure.

[0299] <Comparative Example 5>

[0300] An aqueous solution of nickel sulfate, an aqueous solution of manganese sulfate, and an aqueous solution of aluminum sulfate were mixed in a molar ratio of Ni:Mn:Al of 93.0:6.0:1.0 to prepare a mixed raw material solution 8.

[0301] Under a nitrogen flow, the mixed raw material solution 8 and an aqueous solution of ammonium sulfate as a complexing agent were continuously added to the reaction tank with stirring. An aqueous solution of sodium hydroxide was added dropwise in a timely manner so that the pH of the mixed solution in the reaction tank became 10.9 (measurement temperature: 40 °C) to obtain a reaction precipitate 8. Except for using the reaction precipitate 8, a metal composite hydroxide 8 was obtained by the same method as in Example 1. The BET specific surface area of the metal composite hydroxide 8 was 13.1 m 2 / g.

[0302] The metal composite hydroxide 4 was oxidized under the conditions shown in Table 1 to obtain MCC8 as a metal composite oxide. The gas used during oxidation was air.

[0303] Using MCC8, the same operations as in Example 1 were carried out to obtain powdery LiMO8. LiMO8 has a layered structure.

[0304] Various parameters of LiMO1 - LiMO8 obtained in Examples 1 - 3 and Comparative Examples 1 - 5 are shown in Table 2. Using the obtained LiMO1 - LiMO8 as the CAM, lithium secondary batteries were fabricated, and the initial discharge capacity and discharge capacity retention rate were measured. The results are shown in Table 2.

[0305] Table 1

[0306]

[0307]

[0308] Examples 1 to 3 satisfy the above (1) to (3), the initial discharge capacity is 180 mAh / g or more, and the discharge capacity retention rate is 80% or more. The initial discharge capacity is high and the cycle characteristics are good. It is considered that this is because: by generating a cation mixture in a specific ratio, the volume change during repeated charging and discharging is suppressed, and the increase in resistance due to the rock salt-type structure is also suppressed.

[0309] In Comparative Example 1, the occupancy rate of the Me position exceeds 7.0%, the initial discharge capacity is low, and the cycle characteristics are also poor. It is considered that this is because: the cation mixing proceeds excessively and the resistance becomes high.

[0310] In Comparative Example 2, (I B +I C ) / I A exceeds 0.70 and the cycle characteristics are poor. It is considered that this is because: the proportion of the rock salt-type structure is large and the resistance becomes high.

[0311] In Comparative Example 3, the occupancy rate of the Me position is less than 2.0% and the cycle characteristics are poor. It is considered that this is because: the suppression effect of the volume change caused by cation mixing is small.

[0312] Although Comparative Example 4 satisfies the above (1) and (2), (I B +I C ) / I A exceeds 0.70 and the initial discharge capacity is low. It is considered that this is because: the proportion of the rock salt-type structure is large and the resistance becomes high.

[0313] Although Comparative Example 5 satisfies the above (1) and (2), (I B +I C ) / I A is less than 0.45, the initial discharge capacity is low, and the cycle characteristics are poor. It is considered that this is because: the proportion of the rock salt-type structure is low and the structural deterioration is likely to occur.

[0314] Explanation of symbols

[0315] 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 solution, 7...Top insulator, 8...Sealing body, 10...Lithium secondary battery, 21...Positive electrode lead, 31...Negative electrode lead, 41, 42, 51, 52...LiMO, 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...Outer packaging body, 200a...Opening, 1000...All-solid-state lithium secondary battery.< / limo>

Claims

1. A lithium metal composite oxide having a layered structure and satisfying the following (1), (2), and (3). (1) It is represented by the following compositional formula (I). Li[Li m (Ni (1-x-y) Co x M y ) 1-m O2 Composition formula (I) In the compositional formula (I), M is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Ca, Al, Zn, Sn, Zr, B, Si, Nb, W, Ta, Ba, S, and P. The compositional formula (I) satisfies -0.1 ≤ m ≤ 0.2, 0 ≤ x ≤ 0.5, 0 < y ≤ 0.7, and x + y < 1. (2) The occupancy of the Me position in the Li site of the layered rock salt-type crystal structure determined by the Rietveld analysis method is 2.0% or more and 7.0% or less. (3) 0.45 ≤ (I B + I C ) / I A ≤ 0.70 In the powder X-ray diffraction measurement using CuKα rays, I A is the integrated intensity of the diffraction peak existing within the range of 2θ = 35.5 ± 1°, I B is the integrated intensity of the diffraction peak on the low-angle side among the two diffraction peaks existing within the range of 2θ = 38.0 ± 1°, I C is the integrated intensity of the diffraction peak on the high-angle side among the said two diffraction peaks.

2. The lithium metal composite oxide according to claim 1, wherein, The compositional formula (I) satisfies 0 ≤ x ≤ 0.

1.

3. The lithium metal composite oxide according to claim 1 or 2, wherein D obtained from the cumulative particle size distribution curve of the volume standard measured by the laser diffraction scattering method 50 is 3 μm or more and 20 μm or less.

4. The lithium metal composite oxide according to claim 1 or 2, wherein Satisfy the following (4), (4) 0.8 ≤ I D / I E ≤ 1.8 In the powder X-ray diffraction measurement using CuKα rays, I D is the integrated intensity of the diffraction peak existing within the range of 2θ = 18.5 ± 1°, and I E is the integrated intensity of the diffraction peak existing within the range of 2θ = 44.5 ± 1°.

5. The lithium metal composite oxide according to claim 1 or 2, wherein The average crystallite size calculated by performing a Rietveld analysis on the powder X-ray diffraction pattern in the range of 2θ = 10° - 90° obtained by the powder X-ray diffraction measurement is 80 nm or more and 200 nm or less.

6. The lithium metal composite oxide according to claim 1 or 2, wherein The BET specific surface area is 0.2 m 2 / g or more and 2.0 m 2 / g or less.

7. A positive electrode active material for a lithium secondary battery, which contains the lithium metal composite oxide according to claim 1 or 2.

8. A positive electrode for a lithium secondary battery, which comprises the positive electrode active material for a lithium secondary battery according to claim 7.

9. A lithium secondary battery, which comprises the positive electrode for a lithium secondary battery according to claim 8.

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