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 high cycle maintenance rate.SOLUTION: A metal composite compound comprising at least Ni, Co and Al, wherein in a differential pore volume distribution determined by the Barrett-Joyner-Halenda method from a nitrogen gas adsorption isotherm, A / C is 5.00 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 C denotes an integrated area of a region having a pore diameter of more than 50 nm and 100 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 the applications of lithium secondary batteries expand, there is a demand for improved battery performance. To improve the battery performance of lithium secondary batteries, attempts have been made to control the physical properties of metal composite compounds, which are 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 discloses that, when producing a transition metal hydroxide precursor used in producing a lithium transition metal composite oxide, a complexing agent and a reducing agent are dissolved in advance in a reaction vessel before the dropwise addition of an aqueous solution of a transition metal compound, thereby increasing the density of the hydroxide precursor particles. Patent Document 1 also discloses that a positive electrode active material produced using such hydroxide precursor particles has a high discharge capacity per volume (energy density). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7004959 Summary of the Invention [Problem to be solved by the invention]

[0006] As the range of applications for lithium secondary batteries expands, further improvements in cycle retention are required. An object of the present invention is to provide a metal composite compound that can be used to produce a lithium secondary battery with a high cycle retention rate, and a method for producing a positive electrode active material for a lithium secondary battery using the same. [Means for solving the problem]

[0007] The present invention encompasses the following [1] to [7]. [1] A metal composite compound containing at least Ni, Co, and Al, wherein, in a differential pore volume distribution obtained from a nitrogen gas adsorption isotherm by the Barrett-Joyner-Halenda method, the A / C ratio is 5.00 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 C is the integrated area of ​​a region having a pore diameter of more than 50 nm and 100 nm or less. [2] The metal complex compound according to [1], wherein the A / C is 13.0 or less. [3] The metal complex compound according to [1] or [2], wherein, in the differential pore volume distribution, when the integrated area of ​​the region exceeding 100 nm and not more than 200 nm is defined as D, the absolute value of the difference between C and D is less than 0.20. [4] In the differential pore volume distribution, the differential pore volume value X of the first maximum point, which is the largest maximum point, 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 in the differential pore volume distribution, X / Y is 8 or more, where X is the differential pore volume value at the first maximum point, which is the largest maximum point, and Y is the differential pore volume value at the second maximum point, which is the next largest maximum point. [6] A metal complex compound according to any one of [1] to [5], which is represented by the following composition formula (I): Ni (1-x-y-w) Co w Al x M1 y O z (OH) 2-α (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 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 [7][1] to [6] and a lithium compound.

Advantages of the Invention

[0008] According to the present invention, a metal composite compound capable of manufacturing a lithium secondary battery with a high cycle retention rate 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.

Embodiments for Carrying Out the Invention

[0009] 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".

[0010] "Ni" does not refer to nickel metal but to nickel atoms. Similarly, "Co", "Li", etc. refer to cobalt atoms, lithium atoms, etc., respectively.

[0011] When a numerical range is described, for example, as "1 - 10 μm" or "1 ~ 10 μm", it means a range from 1 μm to 10 μm, that is, a numerical range including the lower limit value of 1 μm and the upper limit value of 10 μm.

[0012] [Measurement of Cycle Retention Rate] A lithium secondary battery is fabricated by the following method, and the cycle retention rate is measured.

[0013] 1. Fabrication of Lithium Secondary Battery (Fabrication of CAM) 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 contained in MCC (e.g., Ni, Co, Al, and the element M1 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.

[0014] (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.

[0015] 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.

[0016] (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.

[0017] 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 separator via a gasket, and the battery is crimped with a crimping machine to prepare a lithium secondary battery (half cell of coin-type R2032).

[0018] 2.Method for measuring cycle maintenance rate In this specification, the term "high cycle retention rate" means that the value of the cycle retention rate measured by the method described below exceeds 85%. The assembled coin-type lithium secondary battery 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. The test temperature was 25°C, and the current setting for both charging and discharging was 0.2 CA. Metallic lithium was used as the negative electrode, and the maximum charging voltage was 4.3 V and the minimum discharging voltage was 2.5 V. Next, the test temperature was 25° C., and constant current / constant voltage charging and constant current discharging were repeated under the following conditions: The number of charge / discharge cycles was 50. Charging: Current setting value 1CA, maximum voltage 4.3V, constant voltage constant current charging Discharge: Battery setting value 1CA, minimum voltage 2.5V, constant current discharge The cycle retention rate is calculated using the following formula from the discharge capacity at the 1st cycle and the discharge capacity at the 50th cycle. The higher the cycle retention rate, the more desirable the battery performance, as it suppresses the decrease in battery capacity after repeated charging and discharging. Cycle retention rate (%) = 50th cycle discharge capacity (mAh / g) / 1st cycle discharge capacity (mAh / g) × 100

[0019] <Metal composite compounds> This embodiment is an MCC containing at least Ni, Co, and Al. An example of an MCC is a hexagonal compound having a layered structure. The MCC may be a metal composite oxide, a metal composite hydroxide, or a mixture thereof. The metal composite hydroxide may also include a partially oxidized compound. One aspect of MCC is secondary particles that are aggregates of primary particles.

[0020] The MCC may further contain an element M1, which 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.

[0021] [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.

[0022] First, 0.3 g of MCC powder was 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) was measured using the above-mentioned measuring apparatus, and a nitrogen adsorption isotherm was created.

[0023] 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.

[0024] The obtained nitrogen adsorption isotherm is analyzed by the BJH method to determine the differential pore volume distribution in the pore diameter range of 200 nm or less. The differential pore volume distribution is plotted on the horizontal axis as pore diameter (nm) and on the vertical axis as differential pore volume (cm 3 / g).

[0025] In the differential pore volume distribution obtained by the above method, the integrated area of ​​the region where the pore diameter is 1-50 nm is defined as A, the integrated area of ​​the region where the pore diameter is more than 50 nm and less than or equal to 100 nm is defined as C, and the integrated area of ​​the region where the pore diameter is more than 100 nm and less than or equal to 200 nm is defined as D.

[0026] 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 with a pore diameter exceeding 50 nm are defined as large pores, and pores that satisfy this range are referred to as a "second group of pores."

[0027] The A / C of MCC satisfies 5.00 or more, preferably 5.50 or more, and more preferably 6.00 or more. Furthermore, A / C is preferably 13.00 or less, more preferably 12.00 or less, and even more preferably 11.00 or less. The above upper and lower limits of A / C can be combined arbitrarily. A / C is preferably 5.00-13.00, more preferably 5.50-12.00, and even more preferably 6.00-11.00.

[0028] An MCC with an A / C ratio within the above range means that the first pore group is more numerous than the second pore group. Such an MCC makes it difficult for lithium compounds to penetrate into the interior of the particles, and when the MCC and lithium compound are mixed and fired, the reaction between the MCC and the lithium compound is likely to occur on the surface of the MCC. As a result, a CAM is obtained in which lithium is unevenly distributed near the surface rather than the center of the particles. When lithium is unevenly distributed on the surface of the CAM, lithium ions are more likely to migrate on the surface of the CAM, resulting in a lithium secondary battery with low charge transfer resistance. A lithium secondary battery with low charge transfer resistance is more likely to maintain its lithium ion migration rate, making it less likely to lose capacity or cycle retention even with repeated charging and discharging.

[0029] The differential pore volume distribution of an MCC having an A / C ratio within the above range has a sharp peak on the side of fine pores with pore diameters of 50 nm or less.

[0030] The absolute value of the difference between C and D defined above in the MCC is preferably less than 0.20, more preferably 0.18 or less. 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 less than 0.20 indicates a broad peak in the pore diameter range exceeding 50 nm in the differential pore volume distribution. Under conditions where A / C satisfies the above range, this indicates that the second pore group is almost absent, or the volume of the second pore group that exists is small. Because lithium compounds have difficulty penetrating the interior of such MCC particles, the charge transfer resistance is low, as mentioned above, making it easy to produce lithium secondary batteries with high cycle retention.

[0031] MCC is the differential pore volume distribution where the differential pore volume value X of the first maximum point, which is the largest maximum point, is 0.08 cm 3 / g or more, and 3 / g or more is more preferable. The upper limit of X is, for example, 0.20 cm 3 / g or less is preferable, and 0.18cm 3 / g or less is more preferable. The upper and lower limits of X can be arbitrarily combined. X is 0.08-0.20cm 3 / g is preferred, 0.09-0.18cm 3 / g is more preferred.

[0032] Here, the local maximum point is the point at which the differential coefficient changes from positive to negative in the distribution curve of the differential pore volume distribution. In this embodiment, the distribution curve of the differential pore volume distribution is a curve in which 30 or more differential pore volumes are plotted within the pore diameter range of 1 to 200 nm.

[0033] Under the condition that A / C satisfies the above range, an MCC in which X satisfies the above range has a high peak derived from the first pore group. Such an MCC has a large amount of the first pore group. Since lithium compounds are less likely to penetrate into the interior of such an MCC particle, the charge transfer resistance is low as described above, and as a result, a lithium secondary battery with a high cycle retention rate is more likely to be obtained.

[0034] In the differential pore volume distribution, the ratio X / Y of the value Y of the differential pore volume at the second maximum point, which is the maximum point next to the first maximum point, is preferably 8.0 or more, more preferably 8.5 or more. X / Y is preferably, for example, 35.0 or less, more preferably 30.0 or less. X / Y is preferably 8.0 - 35.0, more preferably 8.5 - 30.0.

[0035] Under the condition that A / C satisfies the above range, the MCC for which X / Y satisfies the above range has substantially one peak derived from the first pore group and shows a normal distribution within the range of the first pore group. In this case, it means that the first pore group has no variation in pore diameter. Such an MCC makes it difficult for the lithium compound to penetrate into the interior of the particles, so that, as described above, a lithium secondary battery having a low charge transfer resistance and as a result a high cycle retention rate can be easily obtained.

[0036] The MCC is preferably represented by the compositional formula (I). Ni (1-x-y-w) Co w Al x M1 y O z (OH) 2-α (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 Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

[0037] Describe the preferred ranges of w, x, y, and x + y + w in the compositional formula (I).

[0038] ·w w is preferably more than 0, more preferably 0.005 or more, still more preferably 0.01 or more. Also, w is preferably 0.35 or less, more preferably 0.30 or less, still more preferably 0.25 or less. The above upper and lower limit values of w can be arbitrarily combined. As an example of a combination, w is preferably more than 0 and not more than 0.35, more preferably 0.005 to 0.30, and even more preferably 0.01 to 0.25.

[0039] x x is preferably greater than 0, more preferably 0.005 or greater, and even more preferably 0.01 or greater. Also, x is preferably 0.30 or less, more preferably 0.25 or less, and even more preferably 0.10 or less. The upper and lower limits of x can be combined arbitrarily. As an example of a combination, x is preferably more than 0 and not more than 0.30, more preferably 0.005 to 0.25, and even more preferably 0.01 to 0.10.

[0040] ·y y is preferably equal to or greater than 0. Furthermore, y is preferably equal to or less than 0.20, more preferably equal to or less than 0.10, and even more preferably equal to or less than 0.05. The upper and lower limits of y can be combined in any desired manner. As an example of a combination, y is preferably 0 to 0.20, more preferably 0 to 0.10, and even more preferably 0 to 0.05.

[0041] x+y+w x+y+w preferably exceeds 0. Furthermore, x+y+w is preferably 0.70 or less, more preferably 0.40 or less, and even more preferably 0.30 or less. The upper and lower limits of x+y+w can be combined in any desired manner. As an example of the combination, x+y+w is preferably greater than 0 and not greater than 0.70, more preferably greater than 0 and not greater than 0.40, and even more preferably greater than 0 and not greater than 0.30.

[0042] [Composition analysis] The composition of MCC is measured by dissolving MCC in hydrochloric acid and then using an ICP emission spectrometer, such as Optima 7300 (manufactured by PerkinElmer Co., Ltd.).

[0043] <MCC manufacturing method> MCC can be produced by batch co-precipitation or continuous co-precipitation. The production method will be described in detail below using a metal composite oxide containing Ni, Co, and Al as an example.

[0044] 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 cobalt salt solution, an aluminum salt solution, an alkaline aqueous solution, and optionally a complexing agent are mixed in a reaction tank to produce a metal composite hydroxide containing Ni, Co, and Al.

[0045] 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.

[0046] As the cobalt salt that is the solute of the cobalt salt solution, for example, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate can be used.

[0047] As the aluminum salt that is the solute of the aluminum salt solution, for example, aluminum sulfate or sodium aluminate can be used.

[0048] The above metal salts are used in proportions corresponding to the composition ratio of the above composition formula (I), and water is used as the solvent.

[0049] When nickel salt solution, cobalt salt solution, aluminum salt solution, alkaline aqueous solution, and optionally a complexing agent are continuously supplied to the reaction vessel, Ni, Co, and Al react to form Ni. a Co b Al (1-a-b)Nuclei of (OH)₂ (0 < a + b < 1) crystals are generated. Further, by continuously supplying the raw materials, the nuclei grow. At this time, the nickel salt solution, cobalt salt solution, and aluminum salt solution may be mixed before sharing in the reaction tank to form a mixed solution and then supplied to the reaction tank. Also, the nickel salt solution, cobalt salt solution, aluminum salt solution, and mixed solution may be added to the reaction tank from a plurality of inlets respectively. Here, the reaction slurry is a mixture of solid and liquid present in the reaction tank, specifically referring to a mixture containing the nickel salt solution, metal salt solution, mixed solution, complexing agent, and alkaline aqueous solution, as well as the solid content including the precipitate generated by the reaction.

[0050] The complexing agent is a compound capable of forming a complex with Ni in an aqueous solution. For example, ammonium ion donors, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine can be mentioned.

[0051] Examples of ammonium ion donors include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

[0052] The complexing agent may not be included. When the complexing agent is included, the amount of the complexing agent contained in the reaction slurry is, for example, such that the molar ratio to the total number of moles of the metal salts contained in the reaction slurry is greater than 0 and 2.0 or less.

[0053] In the coprecipitation method, in order to adjust the pH value of the above reaction slurry, an alkaline aqueous solution is added to the mixed solution before the pH of the mixed solution changes from alkaline to neutral. Sodium hydroxide aqueous solution and potassium hydroxide aqueous solution can be used as the alkaline aqueous solution.

[0054] Note that the pH value in this specification is defined as the value measured when the temperature of the reaction slurry is 40°C. When the temperature of the reaction slurry sampled from the reaction tank is not 40°C, the reaction slurry is heated or cooled to 40°C to measure the pH.

[0055] During the reaction, the temperature of the reaction slurry in the reaction vessel is controlled to a predetermined temperature. Here, the above-mentioned nickel salt solution, cobalt salt solution, aluminum salt solution, and mixed solution are referred to as raw material solutions. During the reaction, if the temperature of the raw material solution is excessively low or high due to seasonal conditions, it is preferable to adjust it to about room temperature (10-40°C).

[0056] Furthermore, the temperature of the reaction slurry in the reaction vessel is controlled within the range of 30-75°C, preferably 40-60°C.

[0057] By adjusting the temperature of the reaction slurry to the above range and conducting the reaction under conditions adjusted to a higher temperature than the raw material liquid, nuclei are more likely to be generated due to the temperature difference between the raw material liquid and the reaction slurry. More specifically, it is preferable to set the temperature of the reaction liquid at a temperature 15-30°C higher than the temperature of the raw material liquid. Under the above temperature difference conditions, the nucleation rate tends to be faster than the nucleus growth rate, and an MCC consisting of a large number of aggregated fine primary particles is likely to be obtained. In this case, an MCC with many fine pores and an A / C ratio that satisfies the range of this embodiment, i.e., an MCC with many first pore groups, is obtained.

[0058] During the reaction, the pH value of the reaction slurry is controlled within the range of 9 to 13, preferably 11 to 13.

[0059] 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.

[0060] In order to control the atmosphere inside the reaction vessel to a desired level, a predetermined gas may be passed through the reaction vessel or the reaction slurry may be directly bubbled.

[0061] After the reaction, the neutralized reaction precipitate is washed with water and then isolated. For example, the slurry containing the reaction precipitate (i.e., coprecipitate slurry) is dehydrated by centrifugation, suction filtration, or the like. The isolated reaction precipitate is washed, dehydrated, dried and sieved as necessary to obtain a metal composite hydroxide.

[0062] The reaction precipitate is preferably washed with water, weak acid water, or an alkaline washing solution. In this embodiment, washing with an alkaline washing solution is preferred, and washing with an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is more preferred. It is preferable to wash with water, weak acid water, or alkaline washing solution in an amount 10 times by mass or more of the mass of the reaction precipitate, and the temperature of the weak acid water or alkaline washing solution is preferably 30° C. or higher. Furthermore, it is preferable to wash at least once. After washing with a solution other than water, it is preferable to further wash with water to prevent compounds derived from the raw material solution from remaining in the reaction precipitate.

[0063] 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 normal pressure or reduced pressure.

[0064] When producing a metal composite oxide as MCC, a metal composite hydroxide may be heated to form the metal composite oxide. If necessary, multiple heating steps may be performed. The heating temperature in this specification 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.

[0065] The heating temperature is preferably 400 to 700°C, and more preferably 450 to 680°C. When the heating temperature is 400 to 700°C, the metal composite hydroxide is sufficiently oxidized, and a metal composite oxide having a BET specific surface area in an appropriate range is obtained. When the heating temperature is equal to or higher than the lower limit of the above range, the metal composite hydroxide is sufficiently oxidized. When the heating temperature is equal to or lower than the upper limit of the above range, excessive oxidation of the metal composite hydroxide is suppressed, and a decrease in the BET specific surface area of ​​the metal composite oxide is suppressed.

[0066] The time for maintaining the heating temperature can be 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 can be air, oxygen, nitrogen, argon, or a mixed gas thereof.

[0067] The interior of the heating device may be an atmosphere containing a moderate amount of oxygen. The oxygen-containing atmosphere may be a mixed gas atmosphere of an inert gas and an oxidizing gas, or may be an inert gas atmosphere in the presence of an oxidizing agent. By providing an atmosphere containing a moderate amount of oxygen inside the heating device, the transition metal contained in the metal composite hydroxide is oxidized appropriately, making it easier to control the morphology of the metal composite oxide.

[0068] The oxygen or oxidizing agent in the oxygen-containing atmosphere should have enough oxygen atoms to oxidize the transition metal. When the oxygen-containing atmosphere is a mixed gas atmosphere of an inert gas and an oxidizing gas, the atmosphere in the heating device can be controlled by a method such as passing an oxidizing gas through the heating device. As the oxidizing agent, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, ozone, or the like can be used.

[0069] After drying, the MCC may be classified as appropriate.

[0070] <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.

[0071] 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.

[0072] [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.

[0073] 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.

[0074] [Firing process] The resulting mixture is fired. By firing the mixture, CAM crystals grow. The firing process is carried out, for example, at a firing temperature of 500-1000°C in an oxygen-containing atmosphere.

[0075] 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 at which firing is carried out at the highest holding temperature among the stages.

[0076] The firing temperature is preferably 550 to 900°C, more preferably 600 to 800°C.

[0077] The time for which the firing temperature is maintained is, for example, 0.1 to 30 hours, preferably 0.5 to 20 hours.

[0078] It is also preferable to carry out the firing in an oxygen-containing atmosphere, specifically, by introducing oxygen gas into the firing furnace to create an oxygen-containing atmosphere.

[0079] [Cleaning process] In this embodiment, the fired product may be washed with a cleaning solution such as pure water or an alkaline cleaning solution. After washing, the fired product may be dried appropriately.

[0080] The fired product is then washed as appropriate, and then crushed and sieved as appropriate to obtain CAM.

[0081] According to the MCC having the above-mentioned configuration, a CAM having a high cycle retention rate of a lithium secondary battery can be produced.

[0082] Furthermore, according to the above-described method for producing CAM, by using the above-described MCC as a raw material, it is possible to suitably produce CAM having a high cycle retention rate for lithium secondary batteries.

[0083] <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.

[0084] 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.

[0085] <All-solid-state lithium secondary battery> The CAM can be used as a CAM for an all-solid-state lithium secondary battery.

[0086] An example of an all-solid-state lithium secondary battery includes a laminate having a positive electrode, a negative electrode, and a solid electrolyte layer, and an exterior housing that houses the laminate. The all-solid-state lithium secondary battery 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. [Example]

[0087] Next, the present invention will be described in more detail with reference to examples.

[0088] <Composition analysis> The composition of the MCC was analyzed by the method described above in [Composition Analysis].

[0089] <Obtaining differential pore volume distribution> The differential pore volume distribution of MCC was obtained using the method described above in [Method for obtaining differential pore volume distribution], and the above-defined A, C, D, and maximum points were determined. From the obtained values, A / C, the absolute value of the difference between C and D, the differential pore volume X at the first maximum point, and X / Y (X is the differential pore volume at the first maximum point, which is the largest maximum point, and Y is the differential pore volume at the second maximum point, which is the next largest maximum point) were determined.

[0090] <Measurement of cycle maintenance rate> The cycle retention rate was measured by the method described in [Measurement of cycle retention rate] above.

[0091] Example 1 Raw material liquid 1, which was an aqueous solution in which nickel sulfate, cobalt sulfate, and aluminum sulfate were dissolved in a molar ratio of nickel:cobalt:aluminum of 91:4:5, was maintained at 25°C, and raw material liquid 1, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization process.

[0092] In the crystallization step, the raw material liquid was continuously added dropwise, the temperature of the mixed liquid in the reaction tank was maintained at 45° C., and the mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with a stirring blade while maintaining the pH of the mixed liquid in the reaction tank at 12.22 at a liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0093] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC1, a powdery transition metal-containing hydroxide.

[0094] <Example 2> Raw material liquid 2, which was an aqueous solution in which nickel sulfate, cobalt sulfate, and aluminum sulfate were dissolved in a molar ratio of nickel:cobalt:aluminum of 87:9:4, was maintained at 25°C, and raw material liquid 2, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization step.

[0095] In the crystallization process, the raw material liquid was continuously added dropwise, the temperature of the mixed liquid in the reaction tank was maintained at 40° C., and the mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with a stirring blade while maintaining the pH of the mixed liquid in the reaction tank at 12.13 based on the liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0096] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC2, a powdery transition metal-containing hydroxide.

[0097] Example 3 A raw material liquid 3, which was an aqueous solution in which nickel sulfate, cobalt sulfate, and aluminum sulfate were dissolved in a molar ratio of nickel:cobalt:aluminum of 91:3:6, was maintained at 25°C, and the raw material liquid 3, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization step.

[0098] In the crystallization process, the raw material liquid was continuously added dropwise, and the temperature of the mixed liquid in the reaction tank was maintained at 54° C. The mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with a stirring blade while maintaining the pH of the mixed liquid in the reaction tank at 12.22 at a liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0099] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC3, a powdery transition metal-containing hydroxide.

[0100] <Comparative Example 1> A raw material liquid 11, which was an aqueous solution in which nickel sulfate, cobalt sulfate, and aluminum sulfate were dissolved in a molar ratio of nickel:cobalt:aluminum of 88:9:3, was maintained at 25°C, and the raw material liquid 11, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization step.

[0101] In the crystallization process, the raw material liquid was continuously added dropwise, the temperature of the mixed liquid in the reaction tank was maintained at 70° C., and the mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with a stirring blade while maintaining the pH of the mixed liquid in the reaction tank at 12.20 at a liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0102] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC11, a powdery transition metal-containing hydroxide.

[0103] <Comparative Example 2> A raw material liquid 12, which was an aqueous solution in which nickel sulfate, manganese sulfate, and aluminum sulfate were dissolved in a molar ratio of nickel:manganese:aluminum of 92:3:5, was maintained at 25°C, and the raw material liquid 12, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization step.

[0104] In the crystallization step, the raw material liquid was continuously added dropwise, the temperature of the mixed liquid in the reaction tank was maintained at 45° C., and the mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with a stirring blade while maintaining the pH of the mixed liquid in the reaction tank at 12.20 at a liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0105] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC12, a powdery transition metal-containing hydroxide.

[0106] <Comparative Example 3> A raw material liquid 13, which was an aqueous solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in a molar ratio of nickel:cobalt:manganese of 83:12:5, was maintained at 25°C, and the raw material liquid 13, an aqueous ammonium sulfate solution (ammonium ion donor), and an aqueous sodium hydroxide solution (pH adjuster) were added dropwise to a continuous reaction tank to carry out a crystallization step.

[0107] In the crystallization process, the raw material liquid was continuously added dropwise, the temperature of the mixed liquid in the reaction tank was maintained at 70° C., and the mixed liquid in the reaction tank was continuously stirred with a stirrer equipped with stirring blades while maintaining the pH of the mixed liquid in the reaction tank at 11.20 at a liquid temperature of 40° C. The reaction tank was filled with a nitrogen atmosphere.

[0108] The transition metal-containing hydroxide particles crystallized by the neutralization reaction were allowed to overflow from the overflow pipe of the reaction vessel and collected as a suspension of transition metal-containing hydroxide particles. The suspension of transition metal-containing hydroxide particles collected by overflow as described above was filtered and then washed with an alkaline aqueous solution (8 mass% sodium hydroxide aqueous solution) to perform solid-liquid separation. The separated solid phase was then washed with water, and further subjected to dehydration and drying processes to obtain MCC13, a powdery transition metal-containing hydroxide.

[0109] Table 1 below shows A, C, A / C, D, the absolute value of the difference between C and D, X, and X / Y for MCC1 to 3 produced in Examples 1 to 3 and MCC11 to 13 produced in Comparative Examples 1 to 3. Also shown are the results of cycle retention rates of lithium secondary batteries using positive electrode active materials made from MCC1 to 3 produced in Examples 1 to 3 and MCC11 to 13 produced in Comparative Examples 1 to 3 as raw materials.

[0110] [Table 1]

[0111] As shown in Table 1, Examples 1 to 3, in which A / C was 5.00 or more, the absolute value of the difference between C and D was small, X was large, and X / Y was high, had higher cycle retention rates than Comparative Examples 1 to 3. The MCC in the examples had a large number of first pore groups, which is thought to have made it difficult for lithium compounds to penetrate into the interior of the particles. It is thought that when the MCC in the examples was mixed with the lithium compound and fired, a reaction between the MCC and the lithium compound occurred on the surface of the MCC. As a result, it is thought that a CAM was obtained in which lithium was biased toward the surface rather than the center of the particles. Because lithium ions easily migrate on the surface of such CAM, it is thought that a lithium secondary battery with a high cycle retention rate was obtained.

[0112] In Comparative Examples 1 and 3, A / C was small, the absolute value of the difference between C and D was large, and X / Y was small. It is believed that such MCCs allow lithium compounds to easily penetrate into the interior of the particles, and CAM, in which lithium is concentrated near the surface, was not obtained. This is thought to have resulted in a lithium secondary battery with a higher charge transfer resistance and a lower cycle retention rate than the Examples.

[0113] Comparing Example 1 and Comparative Example 2, it was confirmed that Example 1, which is an MCC containing Ni, Co, and Al, had a higher cycle retention rate than Comparative Example 2.

Claims

1. A metal composite compound containing at least Ni, Co, and Al, 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 100 nm or less is defined as C, A metal complex compound having an A / C ratio of 5.00 or more.

2. The metal complex compound according to claim 1 , wherein the A / C is 13.0 or less.

3. In the differential pore volume distribution, when the integrated area of ​​the region exceeding 100 nm and not exceeding 200 nm is D, The metal complex compound according to claim 1 or 2, wherein the absolute value of the difference between C and D is less than 0.

20.

4. In the differential pore volume distribution, the differential pore volume value X of the first maximum point, which is the largest maximum point, 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 in the differential pore volume distribution, a differential pore volume value X of a first maximum point that is the largest maximum point and a differential pore volume value Y of a second maximum point that is the next largest maximum point are such that X / Y is 8 or more.

6. 3. The metal complex compound according to claim 1, which is represented by the following composition formula (I): Ni （１－ｘ－ｙ－ｗ） Co ｗ Al ｘ M1 ｙ O ｚ (OH) ２－α (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, and M1 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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