Metal composite compound and method for producing positive electrode active material for lithium secondary battery

Abstract

To provide a metal composite compound that enables production of a lithium secondary battery with low charge transfer resistance.SOLUTION: A metal composite compound comprising at least Ni and Mn, wherein in a differential pore volume distribution determined by the Barrett-Joyner-Halenda method from a nitrogen gas adsorption isotherm, A / B is 1.5 or more where A denotes an integrated area of a region having a pore diameter of 1 nm or more and 50 nm or less and B denotes an integrated area of a region having a pore diameter of more than 50 nm and 200 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a metal composite compound and a positive electrode active material for a lithium secondary battery. [Background technology]

[0002] The positive electrode active material contained in the positive electrode of a lithium secondary battery can be obtained, for example, by mixing a lithium compound and a metal composite compound containing a metal element other than Li, and baking the mixture.

[0003] As a technique for improving the battery performance of lithium secondary batteries, attempts have been made to control the physical properties of metal composite compounds that serve as raw materials for the positive electrode active material.

[0004] For example, Patent Document 1 discloses a method for producing a high-density hydroxide precursor as a metal composite compound and using the precursor to produce a lithium transition metal composite oxide. Patent Document 1 also discloses that the positive electrode active material produced using such a hydroxide precursor has a large discharge capacity (energy density) per volume. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP-B-7004959 Summary of the Invention [Problem to be solved by the invention]

[0006] As the application fields of lithium secondary batteries expand, there is a demand for reducing charge transfer resistance.

[0007] An object of the present invention is to provide a metal composite compound that can be used to produce a lithium secondary battery with low charge transfer resistance, and a method for producing a positive electrode active material for a lithium secondary battery using the same. [Means for solving the problem]

[0008] The present invention encompasses the following [1] to [7]. [1] A metal composite compound containing at least Ni and Mn, wherein, in a differential pore volume distribution obtained from a nitrogen gas adsorption isotherm by the Barrett-Joyner-Halenda method, the ratio A / B is 1.5 or more, where A is the integrated area of ​​a region having a pore diameter of 1 nm or more and 50 nm or less, and B is the integrated area of ​​a region having a pore diameter of more than 50 nm and 200 nm or less. [2] The metal complex compound according to [1], wherein the A / B is 10 or less. [3] In the differential pore volume distribution, when the integrated area of ​​the region of 50 nm or more and 100 nm or less is defined as C and the integrated area of ​​the region of more than 100 nm and 200 nm or less is defined as D, the absolute value of the difference between C and D is 0.40 or less. [4] The metal complex compound according to [1] or [2]. [4] Among the maximum points present in the differential pore volume distribution, the differential pore volume value X of the first maximum point having the largest differential pore volume is 0.08 cm 3 The metal complex compound according to any one of [1] to [3], wherein the metal complex compound has a molecular weight of 1 / g or more. [5] The metal composite compound according to any one of [1] to [4], wherein, among the local maximum points present in the differential pore volume distribution, a ratio X of the differential pore volume of a first local maximum point having the largest differential pore volume to a differential pore volume of a second local maximum point having the second largest differential pore volume after the first local maximum point, X / Y, is 7 or more. [6] The metal complex compound according to any one of [1] to [5], which is represented by the following formula (I): Ni (1-x-y-w) Mn w M1 x M2 y O z (OH) 2-α (I) (In formula (I), 0 < w ≤ 0.4, 0 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.2, 0 < x + y + w < 1, 0 ≤ z ≤ 3, -0.5 ≤ α ≤ 2, and α - z < 2, M1 is one or more elements selected from the group consisting of Co and Al, and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.) A method for producing a cathode active material for a lithium secondary battery, comprising a step of firing a mixture of the metal composite compound according to any one of [1] to [6] and a lithium compound.

Advantages of the Invention

[0009] According to the present invention, a metal composite compound capable of manufacturing a lithium secondary battery with low charge transfer resistance can be obtained. Furthermore, a method for producing a cathode active material for a lithium secondary battery using such a metal composite compound can be provided.

Brief Description of the Drawings

[0010] [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.

Modes for Carrying Out the Invention

[0011] In the present specification, the metal composite compound (Metal Composite Compound) is hereinafter referred to as "MCC", and the cathode active material for a lithium secondary battery (Cathode Active Material for lithium secondary batteries) is hereinafter referred to as "CAM".

[0012] "Ni" does not refer to nickel metal but to nickel atoms. Similarly, "Co", "Li", etc. refer to cobalt atoms, lithium atoms, etc., respectively. The lithium secondary battery refers to a lithium-ion secondary battery.

[0013] 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.

[0014] [Charge transfer resistance measurement] A lithium secondary battery is produced by the following method, and the charge transfer resistance is measured.

[0015] 1. Fabrication of Lithium Secondary Batteries (CAM creation) MCC and lithium hydroxide monohydrate powder are weighed and mixed in a ratio such that the molar ratio of Li contained in the lithium hydroxide monohydrate powder to the total amount of elements other than oxygen atoms contained in MCC (e.g., Ni, Mn, and the element M1 or element M2 described below) is 1.05, to obtain a mixture. The resulting mixture is calcined in an oxygen atmosphere at 650°C for 5 hours, and then calcined again in an oxygen atmosphere at 750°C for 5 hours to obtain CAM.

[0016] (Production of positive electrodes for lithium secondary batteries) The resulting CAM, a conductive material (acetylene black), and a binder (PVdF) were mixed in a mass ratio of CAM:conductive material:binder = 92:5:3 and kneaded to prepare a paste-like positive electrode mixture. N-methyl-2-pyrrolidone was used as the organic solvent when preparing the positive electrode mixture.

[0017] The resulting positive electrode mixture is applied to a 40 μm thick Al foil as a current collector and dried in a vacuum 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 is 1.65 cm2. 2 Let's say.

[0018] (Fabrication of lithium secondary batteries) The following operations are carried out in a glove box under an argon atmosphere. The lithium secondary battery positive electrode prepared in (Preparation of a lithium secondary battery positive electrode) is placed on the bottom cover of a coin-type battery R2032 part (for example, manufactured by Hosen Co., Ltd.) with the aluminum foil side facing down, and a separator (porous polyethylene film) is placed on top of that. 300 μL of electrolyte is poured into this. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, with LiPF6 dissolved at a concentration of 1.0 mol / L.

[0019] Next, metallic lithium is used as the negative electrode, and the negative electrode is placed on the separator, and the top lid is placed on the negative electrode via a gasket, and the battery is crimped with a crimping machine to prepare a lithium secondary battery (coin-type (R2032) half cell).

[0020] 2.Method for measuring charge transfer resistance The lithium secondary battery produced by the above method is left standing at room temperature for 12 hours to allow the separator and the positive electrode mixture layer to be sufficiently impregnated with the electrolyte.

[0021] After leaving the lithium secondary battery stationary, it was charged at a constant current and constant voltage with a current setting of 0.1 CA for both charging and discharging at a test temperature of 25°C, and then discharged at a constant current and constant voltage. The maximum charging voltage was 4.3 V, and the minimum discharging voltage was 2.5 V. Next, after discharging, the lithium secondary battery was charged again at a constant current and constant voltage with a current setting of 0.1 CA up to the maximum charging voltage, and the voltage after charging was determined to be SOC 100%.

[0022] Next, the lithium secondary battery after standing is used to perform electrochemical impedance (EIS) measurement of the battery as follows, and the charge transfer resistance of the CAM is calculated from the obtained results. The EIS measurement is performed at a test temperature of 25°C and an SOC of 100%. Under the conditions of an applied voltage of 0 V and an amplitude voltage of 10 mV, the response frequency is 0.01 Hz to 10 6 Hz, and in the Cole-Cole plot created from the measurement data, the response frequency ranges from several hundred Hz to several tens -1The charge transfer resistance (Ω) of the CAM is calculated from the size of the arc that appears in Hz. The charge transfer resistance of the CAM is calculated using the Instant Fit function of Solartron's analysis software ZView2.

[0023] <Metal composite compounds> MCC contains at least Ni and Mn. An example of MCC is a hexagonal compound having a layered structure. MCC may be a metal composite oxide, a metal composite hydroxide, or a mixture thereof. The metal composite hydroxide may also include a compound in which the metal composite hydroxide is partially oxidized. One aspect of MCC is secondary particles that are aggregates of primary particles.

[0024] MCC may further contain elements M1 and M2. Element M1 is one or more elements selected from the group consisting of Co and Al, and element M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.

[0025] [How to obtain differential pore volume distribution] The "differential pore volume distribution" can be determined by analyzing the nitrogen adsorption isotherm obtained by measuring the MCC powder at liquid nitrogen temperature using the Barrett-Joyner-Halenda (BJH) method. The nitrogen adsorption isotherm can be measured using an automatic specific surface area / pore size distribution analyzer (Tristar II 3020, manufactured by Shimadzu Corporation), for example.

[0026] First, 1 g of MCC powder is degassed with nitrogen at 105°C for 30 minutes using a degassing apparatus (VacPrep061, Shimadzu Corporation). After the treatment, the amount of nitrogen adsorbed by the MCC powder at liquid nitrogen temperature (77 K) is measured using the above-mentioned measuring apparatus, and a nitrogen adsorption isotherm is created.

[0027] The nitrogen adsorption isotherm is plotted as follows: the horizontal axis is the ratio of the adsorption equilibrium pressure to the saturated vapor pressure (relative pressure (ρ / ρ0)), and the vertical axis is the adsorption amount of gaseous nitrogen (cm) at standard temperature and pressure (STP).3 The values ​​are plotted as (STP) / g.

[0028] The obtained nitrogen adsorption isotherm is analyzed by the BJH method to determine the differential pore volume distribution in the region of pore diameters of 200 nm or less. The differential pore volume distribution is plotted with the pore diameter (nm) on the horizontal axis and the differential pore volume (cm) on the vertical axis. 3 / g).

[0029] In the differential pore volume distribution obtained by the above method, the integrated area of ​​the pore diameter region of 1-50 nm is defined as A, the integrated area of ​​the region of more than 50 nm and not more than 200 nm is defined as B, the integrated area of ​​the region of 50-100 nm is defined as C, and the integrated area of ​​the region of more than 100 nm and not more than 200 nm is defined as D.

[0030] Hereinafter, in the differential pore volume distribution obtained by the above method, pores having a pore diameter of 1 to 50 nm are defined as fine pores, and pores that satisfy this range are referred to as a "first pore group." Furthermore, pores having a pore diameter of more than 50 nm and not more than 200 nm are defined as large pores, and pores that satisfy this range are referred to as a "second group of pores."

[0031] The A / B ratio of the MCC is 1.5 or more, preferably 1.8 or more, and more preferably 1.9 or more. Furthermore, A / B is preferably 10 or less, more preferably 10.0 or less, even more preferably 8.0 or less, and particularly preferably 6.0 or less. The above lower and upper limits of A / B can be combined arbitrarily. A / B is preferably 1.5 to 10, more preferably 1.5 to 10.0, even more preferably 1.8 to 8.0, and particularly preferably 1.9 to 6.0.

[0032] MCC with an A / B ratio within the above range has more pores in the first group than in the second group. When such MCC is mixed with a lithium compound, the lithium compound does not easily penetrate into the interior of the particles, and when the mixture of MCC and the lithium compound is fired, the reaction between the MCC and the lithium compound is likely to occur on the surface of the MCC. As a result, CAM is obtained in which Li is unevenly distributed near the surface rather than the center of the particles. When Li is unevenly distributed on the surface of the CAM, lithium ions can easily move on the surface of the CAM, resulting in a lithium secondary battery with low charge transfer resistance.

[0033] A is preferably 0.8 or more, more preferably 1.0 or more. A is preferably 10.0 or less, more preferably 8.0 or less. The above lower and upper limits of A can be combined arbitrarily. A is preferably 0.8 to 10.0, more preferably 1.0 to 8.0. When A is in the above range, the charge transfer resistance can be further reduced.

[0034] B is preferably 0.2 or more, more preferably 0.3 or more. B is preferably 8.0 or less, more preferably 7.0 or less. The above lower and upper limits of B can be combined arbitrarily. B is preferably 0.2 to 8.0, more preferably 0.3 to 7.0. When B is in the above range, the charge transfer resistance can be further reduced.

[0035] The differential pore volume distribution of an MCC in which A / B satisfies the above range has a sharp peak on the side of fine pores with pore diameters of 50 nm or less.

[0036] The absolute value of the difference between C and D defined above in the MCC is preferably 0.40 or less, more preferably 0.35 or less. The absolute value of the difference between C and D may be 0. Both C and D define the amount of pores present in the second pore group. An absolute value of the difference between C and D of 0.40 or less means that the differential pore volume distribution has a broad peak in the pore diameter range of 50 nm or more. Under conditions where A / B satisfies the above range, an MCC in which the absolute value of the difference between C and D is within the above range has almost no second pore group, or the volume of the second pore group that exists is small. Such an MCC makes it more difficult for lithium compounds to penetrate into the interior of the particles, which, as explained above, makes it easier to obtain a lithium secondary battery with lower charge transfer resistance.

[0037] C is preferably 0.05 or more, more preferably 0.1 or more. C is preferably 8.0 or less, more preferably 7.0 or less. The above lower and upper limits of C can be arbitrarily combined. C is preferably 0.05 to 8.0, more preferably 0.1 to 7.0. When C is in the above range, the charge transfer resistance can be further reduced.

[0038] D is preferably 0.05 or more, more preferably 0.1 or more. D is preferably 8.0 or less, more preferably 7.0 or less. The above lower and upper limits of D can be combined arbitrarily. D is preferably 0.05 to 8.0, more preferably 0.1 to 7.0. When D is in the above range, the charge transfer resistance can be further reduced.

[0039] Among the maximum points present in the differential pore volume distribution of MCC, the differential pore volume value X of the first maximum point, which has the largest differential pore volume, is 0.08 cm 3 / g or more is preferable, and 0.10 cm 3 / g or more is more preferable. X is 1.0 cm 3 / g or less is preferable, and 0.50 cm 3 / g or less is more preferable. The above lower and upper limits of X can be arbitrarily combined. X is 0.08-1.0 cm 3 / g is preferred, 0.10-0.50cm 3 / g is more preferred.

[0040] The maximum point here is the point where the differential coefficient changes from positive to negative in the distribution curve of the differential pore volume distribution. The distribution curve of the differential pore volume distribution used has 30 or more plots of differential pore volume in the region of pore diameters of 200 nm or less.

[0041] Under the condition that A / B satisfies the above range, an MCC having X satisfying the above range has a high peak derived from the first group of pores, and has a large amount of the first group of pores. Since such an MCC makes it difficult for a lithium compound to penetrate into the interior of the particles, as described above, it is easy to obtain a lithium secondary battery with lower charge transfer resistance.

[0042] Among the maximum points present in the differential pore volume distribution, the ratio X / Y, which is the ratio of X to the differential pore volume value Y of the second maximum point having the next largest differential pore volume after the first maximum point, is preferably 7 or more, and more preferably 9 or more. X / Y is preferably 50 or less, and more preferably 40 or less. The above lower and upper limits of X / Y can be arbitrarily combined. X / Y is preferably 7 to 50, and more preferably 9 to 40.

[0043] Under the condition that A / B satisfies the above range, an MCC with X / Y satisfying the above range has substantially one peak derived from the first pore group and exhibits a normal distribution within the range of the first pore group. This means that there is no variation in the pore diameter of the first pore group. Such an MCC makes it difficult for lithium compounds to penetrate into the interior of the particles, which, as explained above, makes it easier to obtain a lithium secondary battery with lower charge transfer resistance.

[0044] The MCC is preferably represented by the following formula (I): Ni (1-x-y-w) Mn w M1 x M2 y O z (OH) 2-α (I) (In formula (I), 0 < w ≤ 0.4, 0 ≤ x ≤ 0.4, 0 ≤ y ≤ 0.2, 0 < x + y + w < 1, 0 ≤ z ≤ 3, -0.5 ≤ α ≤ 2, and α - z < 2, M1 is one or more elements selected from the group consisting of Co and Al, and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

[0045] (w) w is preferably 0.005 or more, more preferably 0.01 or more. w is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.2 or less. The above lower and upper limits of w can be arbitrarily combined. From the viewpoint of reducing the charge transfer resistance of the battery, w is preferably more than 0 and 0.3 or less, more preferably 0.005 - 0.25, and even more preferably 0.01 - 0.2.

[0046] (x) x is preferably 0.005 or more, more preferably 0.01 or more. x is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. The above lower and upper limits of x can be arbitrarily combined. From the viewpoint of reducing the charge transfer resistance of the battery, x is preferably 0 - 0.3, more preferably 0.005 - 0.2, and even more preferably 0.01 - 0.1.

[0047] (y)[[ID=2))5]] y is preferably 0.15 or less, more preferably 0.10 or less, and even more preferably 0.05 or less. The above lower and upper limits of y can be arbitrarily combined. From the viewpoint of reducing the charge transfer resistance of the battery, y is preferably 0 - 0.15, more preferably 0 - 0.10, and even more preferably 0 - 0.05.

[0048] (x + y + w) x + y + w exceeds 0. x + y + w is preferably 0.7 or less, more preferably 0.4 or less, and even more preferably 0.3 or less. The above lower and upper limits of x+y+w can be combined arbitrarily. From the viewpoint of reducing the charge transfer resistance of the battery, x+y+w is preferably greater than 0 and equal to or less than 0.7, more preferably greater than 0 and equal to or less than 0.4, and even more preferably greater than 0 and equal to or less than 0.3.

[0049] From the viewpoint of obtaining a lithium secondary battery with low charge transfer resistance, the element M2 is preferably one or more elements selected from the group consisting of Ti, Mg, W, Nb, and Zr.

[0050] [Composition analysis] The composition of MCC is measured by dissolving MCC in hydrochloric acid and then using an ICP emission spectrometer, such as Optima 8300 (manufactured by PerkinElmer Co., Ltd.).

[0051] <MCC manufacturing method> MCC can be produced by a batch co-precipitation method or a continuous co-precipitation method. The production method will be described in detail below using a metal composite hydroxide containing Ni, Mn, and element M1 as an example.

[0052] First, by a co-precipitation method, particularly the continuous co-precipitation method described in JP-A-2002-201028, for example, a nickel salt solution, a manganese salt solution, a metal salt solution of element M1, an alkaline aqueous solution, and, if necessary, a complexing agent are mixed in a reaction tank to produce a metal composite hydroxide containing Ni, Mn, and element M1.

[0053] As the nickel salt that is the solute of the nickel salt solution, for example, one or more of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.

[0054] 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.

[0055] As the metal salt of element M1, which is the solute of the metal salt solution of element M1, for example, cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt acetate, aluminum sulfate, sodium aluminate, etc. can be used.

[0056] The above metal salts are used in proportions corresponding to the composition ratio of the above formula (I), and water is used as the solvent.

[0057] When a nickel salt solution, a manganese salt solution, a metal salt solution of element M1, an alkaline aqueous solution, and optionally a complexing agent are continuously supplied to a reaction vessel, Ni, Mn, and element M1 react to form Ni (1-x-w) Mn w M1 x (OH) 2-α Crystal nuclei are generated. Furthermore, by continuously supplying these raw materials, the nuclei grow. In this case, the nickel salt solution, manganese salt solution, and metal salt solution of element M1 may be mixed to prepare a mixed solution before being supplied to the reaction vessel, and the mixed solution may be supplied to the reaction vessel. Furthermore, the nickel salt solution, manganese salt solution, metal salt solution of element M1, and mixed solution may each be supplied to the reaction vessel from multiple supply ports.

[0058] The complexing agent is a compound capable of forming a complex with ions of Ni, Mn, and element M1 in an aqueous solution, such as ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

[0059] Examples of the ammonium ion donor include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

[0060] The complexing agent may not be included. When the complexing agent is included, the amount of the complexing agent contained in the mixed solution containing the nickel salt solution, the manganese salt solution, the metal salt solution of the element M1, and the complexing agent is, for example, such that the molar ratio of the amount of the complexing agent to the total number of moles of the nickel salt, the manganese salt, and the metal salt of the element M1 contained in the mixed solution is greater than 0 and less than or equal to 2.0.

[0061] In the coprecipitation method, in order to adjust the pH value of the mixed solution, an alkaline aqueous solution is added to the mixed solution before the pH of the mixed solution changes from alkaline to neutral. Examples of the alkaline aqueous solution include an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide.

[0062] The pH value in this specification is defined as the value measured when the temperature of the mixed solution is 40° C. If the temperature of the mixed solution sampled from the reaction tank is not 40° C., the pH is measured after heating or cooling the mixed solution to 40° C.

[0063] During the reaction, the temperature of the liquid raw material supplied to the reaction vessel is controlled within a predetermined range. Here, the liquid raw material refers to a nickel salt solution, a manganese salt solution, a metal salt solution of element M1, or a mixed solution thereof supplied to a reaction vessel. During the reaction, the temperature of the liquid raw materials is adjusted to 10-40° C. When multiple types of liquid raw materials are used, the temperatures of the liquid raw materials may be different or the same as long as they are within the above temperature range. Furthermore, the set temperature of the reaction vessel is adjusted to within the range of 30-70°C, preferably 40-55°C. The set temperature of the reaction vessel and the temperature of the liquid raw material are adjusted so that the temperature difference between the set temperature of the reaction vessel and the temperature of the liquid raw material is less than 30°C.

[0064] Nuclei are easily generated by adjusting the set temperature of the reaction vessel within the above range and adjusting the temperature difference between the set temperature of the reaction vessel and the temperature of the liquid raw material so that it is less than 30°C. Under the above temperature difference conditions, the nucleation rate tends to be faster than the nuclei growth rate, and an MCC consisting of a large number of aggregated fine primary particles is likely to be obtained. As a result, an MCC with many fine pores and many first pore groups, i.e., an MCC with A / B in the above range, is obtained. Furthermore, by performing the process under these conditions, an MCC with the absolute value of the difference between C and D, X, and X / Y in the above range can be obtained.

[0065] It is preferable to carry out the reaction under conditions where the ratio of the total flow rate (L / h) of the liquid raw materials supplied to the reaction vessel to the volume (L) of the reaction vessel is 0.10 or less. Supplying the liquid raw materials within this range moderates the generation of heat of neutralization caused by a rapid neutralization reaction, preventing the temperature of the liquid in the reaction vessel from rising above the set value. Therefore, the temperature difference between the set temperature of the reaction vessel and the liquid raw materials can be maintained at less than 30°C. When multiple liquid raw materials are supplied to the reaction vessel from multiple supply ports, the total flow rate (L / h) of the liquid raw materials supplied to the reaction vessel refers to the sum of the flow rates (L / h) of all the liquid raw materials supplied to the reaction vessel. For example, when a mixed solution V consisting of a nickel salt, a manganese salt, and a metal salt of a certain element M1 and a metal salt solution W of another element M1 are supplied to the reaction vessel from two supply ports, respectively, the total flow rate of the liquid raw materials supplied to the reaction vessel is the sum of the flow rates of the mixed solution V and the metal salt solution W.

[0066] During the reaction, the pH value of the mixture in the reaction vessel is controlled within the range of 9 to 13, preferably 10 to 13.

[0067] The materials in the reaction vessel are mixed by suitable stirring. As a reaction vessel used in the continuous coprecipitation method, an overflow type reaction vessel can be used in order to separate the formed reaction precipitate.

[0068] In order to control the atmosphere inside the reaction vessel to the desired level, a predetermined gas may be passed through the reaction vessel or the liquid present in the reaction vessel may be directly bubbled. After the reaction, the resulting reaction precipitate is washed with water and then isolated, for example, by dehydrating a slurry containing the reaction precipitate by centrifugation or suction filtration. The isolated reaction precipitate is washed, dehydrated, dried and sieved as necessary to obtain a metal composite hydroxide. After drying, classification may be carried out as appropriate.

[0069] The reaction precipitate is preferably washed with a washing liquid such as water, weak acid water, or alkaline washing liquid, etc. As the washing liquid, an alkaline washing liquid is preferred, and an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is more preferred. It is preferable to wash with a washing solution having a mass of 10 times or more the mass of the reaction precipitate. The temperature of the washing solution used is preferably 30° C. or higher. Furthermore, it is preferable to wash at least once. After washing with a washing liquid other than water, it is preferable to further wash with water to prevent compounds derived from the washing liquid from remaining in the reaction precipitate.

[0070] The drying temperature is preferably 80 to 250° C., more preferably 90 to 230° C. The drying time is preferably 0.5 to 30 hours, more preferably 1 to 25 hours. The drying pressure may be either normal pressure or reduced pressure.

[0071] When producing a metal composite oxide as MCC, the metal composite oxide can be obtained by heating a metal composite hydroxide. If necessary, multiple heating steps may be performed. In this specification, the heating temperature refers to the set temperature of the heating device. In the case of multiple heating steps, the heating temperature refers to the temperature at the highest holding temperature in each heating step.

[0072] The heating temperature is, for example, 300 to 700°C, preferably 400 to 700°C, and more preferably 450 to 680°C. The time for maintaining the heating temperature is, for example, 0.1 to 20 hours, preferably 0.5 to 10 hours. The rate of temperature increase to the heating temperature is, for example, 50 to 400°C / hour. The heating atmosphere may be air, oxygen, nitrogen, argon, or a mixed gas thereof.

[0073] <Method of manufacturing a positive electrode active material for lithium secondary batteries> CAM can be produced using the above-mentioned MCC as a raw material.

[0074] The method for producing CAM includes a calcination step of calcining a mixture of MCC and a lithium compound. The method for producing CAM may include a mixing step of mixing MCC and a lithium compound before the calcination step, and a washing step of washing the calcined product obtained after the calcination step.

[0075] [Mixing process] MCC and a lithium compound are mixed. As the lithium compound, one or more compounds selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate can be used.

[0076] The 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 (molar ratio) of Li contained in the lithium compound relative to the total amount of elements other than oxygen atoms contained in MCC, 1, is preferably 0.96 to 1.20, more preferably 0.98 to 1.18, and even more preferably 1.00 to 1.16.

[0077] [Firing process] The resulting mixture is fired. By firing the mixture, CAM crystals grow. The firing process may include multiple firing stages with different firing temperatures.

[0078] The firing temperature in this specification refers to the temperature of the atmosphere in the firing furnace, and means the maximum temperature that can be maintained (maximum maintenance temperature). When the firing process has a plurality of firing stages, the firing temperature means the temperature of the stage in which firing is carried out at the highest holding temperature among the firing stages.

[0079] The firing temperature is preferably 400 to 1000°C, more preferably 500 to 980°C, and even more preferably 600 to 960°C.

[0080] The time for maintaining the firing temperature is, for example, 0.1 to 30 hours, preferably 0.5 to 20 hours.

[0081] In the firing step, firing is preferably carried out in an oxygen-containing atmosphere. Specifically, oxygen gas is preferably introduced into the firing furnace to create an oxygen-containing atmosphere.

[0082] [Cleaning process] In this embodiment, the fired product may be washed with a cleaning solution such as pure water or an alkaline cleaning solution, and the fired product after washing may be dried as appropriate.

[0083] The fired product, which has been washed and dried as appropriate, may be crushed and sieved as appropriate. Through the above steps, a CAM is obtained.

[0084] According to the MCC having the above-mentioned configuration, the charge transfer resistance of the lithium secondary battery can be reduced.

[0085] Furthermore, according to the above-described method for producing CAM, by using the above-described MCC as a raw material, it is possible to obtain CAM that can reduce the charge transfer resistance of lithium secondary batteries.

[0086] <Lithium secondary battery> A positive electrode for a lithium secondary battery suitable for use with the above-mentioned CAM will be described below. Hereinafter, the positive electrode for a lithium secondary battery may be referred to as the positive electrode. Furthermore, a lithium secondary battery suitable for use as a positive electrode will be described.

[0087] An example of a suitable lithium secondary battery for use with CAM 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] <All-solid-state lithium secondary battery> The CAM can be used as a CAM for an all-solid-state lithium secondary battery.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 .

[0103] 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.

[0104] 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).

[0105] 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.

[0106] 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.

[0107] The present invention further includes the following

[11] to

[17] .

[11] MCC containing at least Ni and Mn, with an A / B ratio of 1.9 or greater.

[12] The MCC described in

[11] , in which A / B is 6.0 or less.

[13] The MCC according to

[11] or

[12] , wherein the absolute value of the difference between C and D is 0.35 or less.

[14] X is 0.10-0.50cm 3 / g.

[15] The MCC according to any one of

[11] to

[14] , wherein X / Y is 9-40.

[16] The MCC according to any one of

[11] to

[15] , which is represented by the above formula (I).

[17] A method for producing CAM, comprising a step of firing a mixture of the MCC according to any one of

[11] to

[16] and a lithium compound.

[0108] 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]

[0109] Next, the present invention will be described in more detail with reference to examples.

[0110] <Composition analysis> The composition of the MCC was analyzed by the method described above in [Composition Analysis].

[0111] <Obtaining differential pore volume distribution> As described above in [Method for obtaining differential pore volume distribution], the differential pore volume distribution of MCC was obtained, and the values ​​of A, B, C, and D defined above and the positions of the maximum points were determined. From the obtained values, A / B, the absolute value of the difference between C and D (|CD|), X, and X / Y were calculated.

[0112] <Charge transfer resistance measurement> The charge transfer resistance was measured by the method described in [Measurement of Charge Transfer Resistance] above.

[0113] Example 1 Water was placed in a reaction vessel equipped with a rotary stirring device with stirring blades and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied, and the liquid temperature was maintained at 45°C (the set temperature of the reaction vessel). A mixed solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of manganese sulfate, and an aqueous solution of aluminum sulfate so that the molar ratio of Ni:Mn:Al was 93.0:3.5:3.5, and was maintained at 25°C (temperature of the liquid raw materials).

[0114] Next, the mixed solution was continuously fed into the reaction vessel under stirring so that the total flow rate (L / h) of the mixed solution relative to the volume (L) of the reaction vessel was 0.10 or less, and at the same time, an aqueous solution of ammonium sulfate was continuously fed as a complexing agent. At this time, while maintaining the liquid temperature at 45°C (the set temperature of the reaction vessel), 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 12.0 (measurement temperature: 40°C), and reaction precipitate 1 was obtained.

[0115] Reaction precipitate 1 was washed using a 20-fold mass of aqueous sodium hydroxide solution (sodium hydroxide concentration: 5 mass%) relative to the mass of reaction precipitate 1. After washing, the precipitate was dehydrated using a filter press, washed with water, dehydrated, isolated, and dried at 125°C for 24 hours to obtain metal composite hydroxide 1. When the composition of metal composite hydroxide 1 is represented by the above formula (I), w was 0.035, x was 0.035, y was 0, and M1 was Al.

[0116] <Example 2> Water was placed in a reaction vessel equipped with a rotary stirring device with stirring blades and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied, and the liquid temperature was maintained at 40°C (the set temperature of the reaction vessel). A mixed solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate so that the molar ratio of Ni:Co:Mn was 83.5:5.1:11.4, and the mixed solution was maintained at 25°C (temperature of the liquid raw materials).

[0117] Next, the mixed solution was continuously fed into the reaction vessel under stirring so that the total flow rate (L / h) of the mixed solution relative to the volume (L) of the reaction vessel was 0.10 or less, and at the same time, an aqueous solution of ammonium sulfate was continuously fed as a complexing agent. At this time, while maintaining the liquid temperature at 40°C (the set temperature of the reaction vessel), 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 10.6 (measurement temperature: 40°C), and reaction precipitate 2 was obtained.

[0118] Reaction precipitate 2 was washed using a 20-fold mass of aqueous sodium hydroxide solution (sodium hydroxide concentration: 5 mass%) relative to the mass of reaction precipitate 2. After washing, the precipitate was dehydrated using a filter press, washed with water, dehydrated, isolated, and dried at 105°C for 20 hours to obtain metal composite hydroxide 2. When the composition of metal composite hydroxide 2 is represented by the above formula (I), w was 0.114, x was 0.051, y was 0, and M1 was Co.

[0119] <Comparative Example 1> Water was placed in a reaction vessel equipped with a rotary stirring device with stirring blades and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied, and the liquid temperature was maintained at 70°C (the set temperature of the reaction vessel). A mixed solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate so that the molar ratio of Ni:Co:Mn was 83.0:12.1:4.9, and the mixed solution was maintained at 25°C (temperature of the liquid raw materials).

[0120] Next, the mixed solution was continuously fed into the reaction vessel under stirring so that the total flow rate (L / h) of the mixed solution relative to the volume (L) of the reaction vessel was 0.10 or less, and at the same time, an aqueous solution of ammonium sulfate was continuously fed as a complexing agent. At this time, while maintaining the liquid temperature at 70°C (the set temperature of the reaction vessel), 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 11.2 (measurement temperature: 40°C), and reaction precipitate 3 was obtained.

[0121] Metal composite hydroxide 3 was obtained in the same manner as in Example 2, except that reaction precipitate 3 was used instead of reaction precipitate 2. When the composition of metal composite hydroxide 3 is represented by the above formula (I), w was 0.049, x was 0.121, y was 0, and M1 was Co.

[0122] <Comparative Example 2> Water was placed in a reaction vessel equipped with a rotary stirring device with stirring blades and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied, and the liquid temperature was maintained at 70°C (the set temperature of the reaction vessel). A mixed solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of manganese sulfate, and an aqueous solution of aluminum sulfate so that the molar ratio of Ni:Mn:Al was 93.0:1.0:6.0, and the mixed solution was maintained at 25°C (temperature of the liquid raw materials).

[0123] Next, the mixed solution was continuously fed into the reaction vessel under stirring so that the total flow rate (L / h) of the mixed solution relative to the volume (L) of the reaction vessel was 0.10 or less, and at the same time, an aqueous solution of ammonium sulfate was continuously fed as a complexing agent. At this time, while maintaining the liquid temperature at 70°C (the set temperature of the reaction vessel), 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 10.8 (measurement temperature: 40°C), and reaction precipitate 4 was obtained.

[0124] Metal composite hydroxide 4 was obtained in the same manner as in Example 1, except that reaction precipitate 4 was used instead of reaction precipitate 1. When the composition of metal composite hydroxide 4 is represented by the above formula (I), w was 0.010, x was 0.060, y was 0, and M1 was Al.

[0125] <Comparative Example 3> Water was placed in a reaction vessel equipped with a rotary stirring device with stirring blades and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied, and the liquid temperature was maintained at 70°C (the set temperature of the reaction vessel). A mixed solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate so that the molar ratio of Ni:Co:Mn was 82.5:5.1:12.4, and the mixed solution was maintained at 25°C (temperature of the liquid raw materials).

[0126] Next, the mixed solution was continuously fed into the reaction vessel under stirring so that the total flow rate (L / h) of the mixed solution relative to the volume (L) of the reaction vessel was 0.10 or less, and at the same time, an aqueous solution of ammonium sulfate was continuously fed as a complexing agent. At this time, while maintaining the liquid temperature at 70°C (the set temperature of the reaction vessel), 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 (measurement temperature: 40°C), and reaction precipitate 5 was obtained.

[0127] Metal composite hydroxide 5 was obtained in the same manner as in Example 2, except that reaction precipitate 5 was used instead of reaction precipitate 2. When the composition of metal composite hydroxide 5 is represented by the above formula (I), w was 0.124, x was 0.051, y was 0, and M1 was Co.

[0128] [Table 1]

[0129] Table 1 shows A, B, A / B, C, D, |CD|, X, and X / Y of the metal composite hydroxides of Examples 1 and 2 and Comparative Examples 1 to 3, as well as the charge transfer resistance values ​​of the lithium secondary batteries produced using the metal composite hydroxides as MCC. As shown in Table 1, the metal composite hydroxides of Examples 1 and 2, in which A / B was 1.5 or more, had lower charge transfer resistance than the metal composite hydroxides of Comparative Examples 1 to 3. The metal composite hydroxides of Examples 1 and 2 had many first pore groups, and when mixed with a lithium compound, the lithium compound had difficulty penetrating into the interior of the particles. Therefore, when MCC and the lithium compound were mixed and fired, it is thought that a reaction between MCC and the lithium compound occurred on the surface of the MCC. Furthermore, it is thought that a CAM was obtained in which Li was biased toward the surface rather than the center of the particle, resulting in a low charge transfer resistance of the battery.

[0130] The metal composite hydroxides of Comparative Examples 1 to 3 had an A / B ratio of less than 1.5 and higher charge transfer resistance than those of Examples 1 and 2. This is thought to be because the metal composite hydroxides of Comparative Examples 1 to 3 had an overall broad differential pore volume distribution and variations in pore size, which meant that when mixed with a lithium compound, the lithium compound easily penetrated into the interior of the particles, and it was not possible to obtain a CAM in which Li was unevenly distributed near the surface. [Explanation of symbols]

[0131] 1: separator, 2: positive electrode, 2a: positive electrode active material layer, 2b: positive electrode current collector layer, 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, 100: laminate, 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 metal composite compound containing at least Ni and Mn, In the differential pore volume distribution obtained from the nitrogen gas adsorption isotherm by the Barrett-Joyner-Halenda method, when the integrated area of ​​the region where the pore diameter is 1 nm or more and 50 nm or less is defined as A and the integrated area of ​​the region where the pore diameter is more than 50 nm and 200 nm or less is defined as B, the metal composite compound has A metal complex compound having an A / B ratio of 1.5 or more.

2. The metal complex compound according to claim 1 , wherein the ratio A / B is 10 or less.

3. In the differential pore volume distribution, when the integrated area of ​​the region of 50 nm or more and 100 nm or less is defined as C and the integrated area of ​​the region of more than 100 nm and 200 nm or less is defined as D, 3. The metal complex compound according to claim 1, wherein the absolute value of the difference between C and D is 0.40 or less.

4. Among the maximum points present in the differential pore volume distribution, the differential pore volume value X of the first maximum point having the largest differential pore volume is 0.08 cm ３ The metal complex compound according to claim 1 or 2, wherein the metal complex compound has a molecular weight of 1 / g or more.

5. 3. The metal composite compound according to claim 1, wherein, among the local maximum points present in the differential pore volume distribution, a ratio X / Y of a differential pore volume value X of a first local maximum point having the largest differential pore volume to a differential pore volume value Y of a second local maximum point having the second largest differential pore volume after the first local maximum point is 7 or more.

6. The metal complex compound according to claim 1 or 2, which is represented by the following formula (I): Ni （１－ｘ－ｙ－ｗ） Mn ｗ M1 ｘ M2 ｙ O ｚ (OH) ２－α (I) (In formula (I), 0<w≦0.4, 0≦x≦0.4, 0≦y≦0.2, 0<x+y+w<1, 0≦z≦3, −0.5≦α≦2, and α−z<2; M1 is one or more elements selected from the group consisting of Co and Al; and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

7. A method for producing a positive electrode active material for a lithium secondary battery, comprising a step of firing a mixture of the metal composite compound according to claim 1 or 2 and a lithium compound.

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