Concentration gradient precursor, positive electrode material, and preparation method for concentration gradient precursor

Abstract

Disclosed are a concentration gradient precursor, a positive electrode material, and a preparation method for the concentration gradient precursor. The concentration of nickel, cobalt and manganese in the concentration gradient precursor is in a gradient transition between a core and a shell. The preparation method for the concentration gradient precursor comprises the following step: in a protective atmosphere, mixing a nickel source solution, a cobalt source solution, a manganese source solution, a precipitating agent, and a complexing agent for coprecipitation reaction to obtain the concentration gradient precursor, wherein during the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution and the manganese source solution remains unchanged, and the nickel source solution, the cobalt source solution and the manganese source solution gradually change on the basis of the gradient transition. The concentration gradient precursor structure provided by the present application can effectively avoid core-shell separation, and effectively improve the cycle safety performance of high-nickel materials, the preparation method is simple, the metal content at each point of spherical particles can be accurately controlled, the product consistency is high, and industrialization is easy to achieve.

Description

A concentration gradient precursor, positive electrode material and preparation method thereof Technical Field

[0001] The embodiments of the present application relate to the field of battery technology, such as a battery material, and more particularly to a concentration gradient precursor, a positive electrode material, and a preparation method thereof. Background Art

[0002] The surface crystal structure of the ternary high-nickel positive electrode material will change with the cycle, and NiO phase will be produced in the high-lithiation state. At the same time, the material structure is prone to oxygen release, resulting in unstable material structure. What is more serious is that the released oxygen reacts with the electrolyte, causing a series of problems such as flatulence, thermal runaway and even explosion.

[0003] CN114613987A discloses a nickel-cobalt-manganese-oxide gradient positive electrode material and a preparation method thereof, comprising the following steps: obtaining a nickel-cobalt-manganese-oxide gradient positive electrode material precursor; wherein the nickel content in the nickel-cobalt-manganese-oxide gradient positive electrode material precursor decreases gradually from the core to the shell, and the cobalt and manganese contents increase gradually from the core to the shell; and uniformly mixing the nickel-cobalt-manganese-oxide gradient positive electrode material precursor and a lithium source and then gradient calcining to obtain the nickel-cobalt-manganese-oxide gradient positive electrode material.

[0004] Coating a high-nickel material with a high-stability high-manganese material can effectively solve this problem. However, due to the large difference in the concentration of core-shell elements, core-shell separation is likely to occur during the cycle, resulting in a sharp decline in performance. Therefore, it is necessary to provide a concentration gradient precursor with excellent cycle life, a positive electrode material and a preparation method thereof.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The embodiments of the present application provide a concentration gradient precursor, a positive electrode material, and a preparation method thereof. The concentration gradient precursor structure can effectively avoid core-shell separation and effectively improve the cycle safety performance of high-nickel materials. The preparation method is simple and can accurately control the metal content at each point of the spherical particles. The product has high consistency and is easy to industrialize.

[0008] In the first aspect, the present invention provides a concentration gradient precursor, wherein the core composition of the concentration gradient precursor is Ni x Co y Mn z (OH)2, where 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2;

[0009] The shell composition of the concentration gradient precursor is Ni a Cob Mn c (OH)2, where 0≤a≤0.2, 0≤b≤0.5, 0.3≤c≤1;

[0010] The concentrations of the three elements nickel, cobalt and manganese in the concentration gradient precursor are in a gradient transition between the core and the shell.

[0011] The core composition of the concentration gradient precursor provided in this application is Ni x Co y Mn z (OH)2, where 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2.

[0012] Specifically, the value range of x is 0.8≤x≤1, for example, it can be 0.8, 0.85, 0.9, 0.95 or 1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0013] The value range of y is 0≤y≤0.2, for example, it can be 0, 0.01, 0.05, 0.1, 0.15 or 0.2, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable.

[0014] The value range of z is 0≤z≤0.2, for example, it can be 0, 0.01, 0.05, 0.1, 0.15 or 0.2, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0015] The shell composition of the concentration gradient precursor provided in this application is Ni a Co b Mn c (OH)2, where 0≤a≤0.2, 0≤b≤0.5, 0.3≤c≤1.

[0016] Specifically, the value range of a is 0≤a≤0.2, for example, it can be 0, 0.05, 0.1, 0.15 or 0.2, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] The value range of b is 0≤b≤0.5, for example, it can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0018] The value range of c is 0.3≤c≤1, for example, it can be 0.3, 0.4, 0.5, 0.6, 0.8 or 1, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0019] In the concentration gradient precursor provided by the present application, there is a gradient transition between the core and the shell, and the length L of the transition region satisfies 0 < L ≤ R, where R is the radius of the concentration gradient precursor. This structure can effectively prevent core-shell separation and improve the cycling performance of the resulting material. When preparing the cathode material using the concentration gradient precursor provided by the present application, it is mixed with a process amount of lithium source and calcined to obtain the cathode material integrated with the concentration gradient precursor structure.

[0020] Preferably, the particle size D50 of the concentration gradient precursor is 2 - 20 μm, for example, it can be 2 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm or 20 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the gradient transition includes at least 1 gradient, for example, it can be 1, 2, 3, 4 or 5, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing the concentration gradient precursor described in the first aspect. The preparation method includes the following steps:

[0023] Under a protective atmosphere, a co-precipitation reaction is carried out by mixing a nickel source solution, a cobalt source solution, a manganese source solution, a precipitating agent and a complexing agent to obtain the concentration gradient precursor;

[0024] During the co-precipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution and the manganese source solution remains unchanged, and the nickel source solution, the cobalt source solution and the manganese source solution change gradually according to the gradient transition.

[0025] The preparation method provided by the present application has a simple process. By separately introducing the nickel source solution, the cobalt source solution and the manganese source solution, the preparation of the concentration gradient precursor is achieved. The obtained concentration gradient precursor has high consistency and is easy for industrial production.

[0026] The gas used for the protective atmosphere in the present application includes nitrogen and / or inert gas; the inert gas includes any one or at least two combinations of helium, neon or argon. Typical but non-limiting combinations include the combination of helium and neon, the combination of neon and argon, the combination of helium and argon, or the combination of helium, neon and argon.

[0027] Preferably, during the co-precipitation reaction, the pH value of the reaction system is 9 - 13, for example, it can be 9, 10, 11, 12 or 13, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the temperature of the coprecipitation reaction is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, during the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5-15 g / L, for example, 5 g / L, 6 g / L, 8 g / L, 10 g / L, 12 g / L or 15 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the coprecipitation reaction is carried out under stirring conditions, and the stirring speed is 100-500 rpm, for example, it can be 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the nickel source in the nickel source solution includes any one or a combination of at least two of nickel sulfate, nickel nitrate or nickel chloride. Typical but non-limiting combinations include a combination of nickel sulfate and nickel nitrate, a combination of nickel nitrate and nickel chloride, a combination of nickel sulfate and nickel chloride, or a combination of nickel sulfate, nickel nitrate and nickel chloride.

[0032] Preferably, the concentration of the nickel source solution is 1-3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the cobalt source in the cobalt source solution includes any one or a combination of at least two of cobalt sulfate, cobalt nitrate or cobalt chloride. Typical but non-limiting combinations include a combination of cobalt sulfate and cobalt nitrate, a combination of cobalt nitrate and cobalt chloride, a combination of cobalt sulfate and cobalt chloride, or a combination of cobalt sulfate, cobalt nitrate and cobalt chloride.

[0034] Preferably, the concentration of the cobalt source solution is 1-3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the manganese source in the manganese source solution includes any one or a combination of at least two of manganese sulfate, manganese nitrate or manganese chloride. Typical but non-limiting combinations include a combination of manganese sulfate and manganese nitrate, a combination of manganese nitrate and manganese chloride, a combination of manganese sulfate and manganese chloride, or a combination of manganese sulfate, manganese nitrate and manganese chloride.

[0036] Preferably, the concentration of the manganese source solution is 1-3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] In this application, the influence of the concentration of the precipitant and the complexing agent on the final product is negligible, and this application does not make any specific restrictions on this. It is sufficient to control the amount of precipitant added and the amount of complexing agent added so that the concentration of the precipitant and the complexing agent in the reaction system meet the requirements.

[0038] Preferably, the precipitating agent comprises sodium hydroxide and / or potassium hydroxide.

[0039] Preferably, the complexing agent comprises any one or a combination of at least two of ammonia water, ethylenediaminetetraacetic acid, sodium citrate, oxalic acid, acetic acid or ammonium bicarbonate. Typical but non-limiting combinations include a combination of ammonia water and ammonium bicarbonate, a combination of ethylenediaminetetraacetic acid and sodium citrate, a combination of sodium citrate, oxalic acid and acetic acid, a combination of ethylenediaminetetraacetic acid, sodium citrate, oxalic acid and acetic acid, or a combination of ammonia water, sodium citrate and ammonium bicarbonate.

[0040] As a preferred technical solution of the preparation method described in the second aspect of this application, the preparation method comprises:

[0041] Under a protective atmosphere and a stirring condition of 100-500 rpm, a nickel source solution, a cobalt source solution, a manganese source solution, a precipitant and a complexing agent are mixed in parallel and a coprecipitation reaction is performed to obtain the concentration gradient precursor;

[0042] During the coprecipitation reaction, the pH value of the reaction system is 9-13 and the temperature is 40-80°C;

[0043] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5-15 g / L;

[0044] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution and the manganese source solution remains unchanged, and the nickel source solution, the cobalt source solution and the manganese source solution gradually change according to the gradient transition;

[0045] The concentrations of the nickel source solution, the cobalt source solution and the manganese source solution are independently 1-3 mol / L.

[0046] As a further preferred technical solution, when the gradient transition includes two gradients, the end point of the first gradient is that the particle size D50 reaches 1 / 2 of the target concentration gradient precursor particle size D50; when the gradient transition includes three gradients, the end point of the first gradient is that the particle size D50 reaches 1 / 3 of the target concentration gradient precursor particle size D50, and the end point of the first gradient is that the particle size D50 reaches 2 / 3 of the target concentration gradient precursor particle size D50; and so on.

[0047] In a third aspect, an embodiment of the present application provides a positive electrode material, which is prepared from the concentration gradient precursor described in the first aspect.

[0048] In a fourth aspect, an embodiment of the present application provides a method for preparing the positive electrode material according to the third aspect, the preparation method comprising the following steps:

[0049] The lithium source and the concentration gradient precursor are mixed and calcined in an oxygen atmosphere to obtain the positive electrode material.

[0050] Preferably, the lithium source comprises lithium carbonate and / or lithium hydroxide.

[0051] Preferably, the calcination temperature is 600-900°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the calcination time is 10-20 h, for example, 10 h, 12 h, 15 h, 16 h, 18 h or 20 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0053] Compared with the related art, the embodiments of the present application have the following beneficial effects:

[0054] The concentration gradient precursor structure provided in the embodiment of the present application can effectively avoid core-shell separation, effectively improve the cycle safety performance of high-nickel materials, and the preparation method is simple, and the metal content at each point of the spherical particles can be accurately controlled. The product has high consistency and is easy to industrialize.

[0055] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0056] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0057] Example 1-1

[0058] This embodiment provides a method for preparing a positive electrode material, the preparation method comprising the following steps:

[0059] (1) Under nitrogen atmosphere protection and stirring at a speed of 300 rpm, 2 mol / L nickel sulfate solution, 2 mol / L cobalt sulfate solution, 2 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated. The slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0060] During the coprecipitation reaction, the pH value of the reaction system was 12.2 and the temperature was 65°C;

[0061] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 10 g / L;

[0062] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feed is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 98:1:1. When the particle size D50 grows to 8 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 5:2:3, and the reaction is continued until the particle size D50 reaches 11 μm.

[0063] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them under an oxygen atmosphere to obtain the positive electrode material; the calcination temperature is 750° C., and the calcination time is 15 hours.

[0064] Example 1-2

[0065] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0066] (1) Under nitrogen atmosphere protection and stirring at a speed of 100 rpm, 3 mol / L nickel sulfate solution, 3 mol / L cobalt sulfate solution, 3 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated. The slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0067] During the coprecipitation reaction, the pH value of the reaction system is 12 and the temperature is 80°C;

[0068] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 15 g / L;

[0069] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feed is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 98:1:1. When the particle size D50 grows to 8 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 5:2:3, and the reaction is continued until the particle size D50 reaches 11 μm.

[0070] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them under an oxygen atmosphere to obtain the positive electrode material; the calcination temperature is 600° C., and the calcination time is 20 hours.

[0071] Examples 1-3

[0072] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0073] (1) Under nitrogen atmosphere protection and stirring at a speed of 500 rpm, 1 mol / L nickel sulfate solution, 1 mol / L cobalt sulfate solution, 1 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated. The slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0074] During the coprecipitation reaction, the pH value of the reaction system was 12.5 and the temperature was 40°C;

[0075] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5 g / L;

[0076] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feed is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 98:1:1. When the particle size D50 grows to 8 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 5:2:3, and the reaction is continued until the particle size D50 reaches 11 μm.

[0077] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them under an oxygen atmosphere to obtain the positive electrode material; the calcination temperature is 900° C., and the calcination time is 10 hours.

[0078] Examples 1-4

[0079] This embodiment provides a method for preparing a positive electrode material, except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 94:5:1; when the particle size D50 grows to 8 μm, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 4:2:4, and the reaction is carried out until the particle size D50 is 11 μm. The rest is the same as Example 1-1.

[0080] Examples 1-5

[0081] This embodiment provides a method for preparing a positive electrode material, except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 90:5:5; when the particle size D50 grows to 8 μm, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 4:3:3, and the reaction is carried out until the particle size D50 is 11 μm. The rest is the same as Example 1-1.

[0082] Examples 1-6

[0083] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 1-1, except that a 2 mol / L nickel sulfate solution, a 2 mol / L cobalt sulfate solution, and a 2 mol / L manganese sulfate solution are first mixed to obtain a nickel-cobalt-manganese mixed solution, and then the nickel-cobalt-manganese mixed solution, a NaOH solution, and an ammonia solution are mixed in parallel.

[0084] Examples 1-7

[0085] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 1-1 except that the pH value of the reaction system is 11.5.

[0086] Examples 1-8

[0087] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 1-1 except that the pH value of the reaction system is 13.

[0088] Example 2-1

[0089] This embodiment provides a method for preparing a positive electrode material, the preparation method comprising the following steps:

[0090] (1) Under nitrogen atmosphere protection and stirring at a speed of 300 rpm, 2 mol / L nickel sulfate solution, 2 mol / L cobalt sulfate solution, 2 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0091] During the coprecipitation reaction, the pH value of the reaction system was 11.8 and the temperature was 60°C;

[0092] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 10 g / L;

[0093] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When feeding begins, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 94:5:1; when feeding ends, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:2:4; during the reaction process, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0094] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them under an oxygen atmosphere to obtain the positive electrode material; the calcination temperature is 750° C., and the calcination time is 15 hours.

[0095] Example 2-2

[0096] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0097] (1) Under nitrogen atmosphere protection and stirring at a speed of 100 rpm, 3 mol / L nickel sulfate solution, 3 mol / L cobalt sulfate solution, 3 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0098] During the coprecipitation reaction, the pH value of the reaction system was 11.5 and the temperature was 80°C;

[0099] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 15 g / L;

[0100] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When feeding begins, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 94:5:1; when feeding ends, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:2:4; during the reaction process, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0101] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them in an air atmosphere to obtain the positive electrode material; the calcination temperature is 600° C., and the calcination time is 20 h.

[0102] Example 2-3

[0103] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0104] (1) Under nitrogen atmosphere protection and stirring at a speed of 500 rpm, 1 mol / L nickel sulfate solution, 1 mol / L cobalt sulfate solution, 1 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0105] During the coprecipitation reaction, the pH value of the reaction system is 12 and the temperature is 40°C;

[0106] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5 g / L;

[0107] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When feeding begins, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 94:5:1; when feeding ends, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:2:4; during the reaction process, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0108] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them in an air atmosphere to obtain the positive electrode material; the calcination temperature is 900° C., and the calcination time is 10 hours.

[0109] Examples 2-4

[0110] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 2-1 except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 98:1:1; at the end of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 5:2:3.

[0111] Examples 2-5

[0112] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 2-1 except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 90:5:5; at the end of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 4:3:3.

[0113] Examples 2-6

[0114] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 2-1, except that a 2 mol / L nickel sulfate solution, a 2 mol / L cobalt sulfate solution, and a 2 mol / L manganese sulfate solution are first mixed to obtain a nickel-cobalt-manganese mixed solution, and then the nickel-cobalt-manganese mixed solution, a NaOH solution, and ammonia water are mixed in parallel.

[0115] Examples 2-7

[0116] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 2-1 except that the pH value of the reaction system is 11.

[0117] Examples 2-8

[0118] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 2-1 except that the pH value of the reaction system is 12.5.

[0119] Example 3-1

[0120] This embodiment provides a method for preparing a positive electrode material, the preparation method comprising the following steps:

[0121] (1) Under nitrogen atmosphere protection and stirring at a speed of 300 rpm, 2 mol / L nickel sulfate solution, 2 mol / L cobalt sulfate solution, 2 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0122] During the coprecipitation reaction, the pH value of the reaction system was 11.2 and the temperature was 60°C;

[0123] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 10 g / L;

[0124] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feeding is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 90:5:5; when the reaction reaches a particle size D50 of 5.5 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 8:1:1; when the feeding is finished, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:3:3; during the reaction, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0125] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them under an oxygen atmosphere to obtain the positive electrode material; the calcination temperature is 750° C., and the calcination time is 15 hours.

[0126] Example 3-2

[0127] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0128] (1) Under nitrogen atmosphere protection and stirring at a speed of 100 rpm, 3 mol / L nickel sulfate solution, 3 mol / L cobalt sulfate solution, 3 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0129] During the coprecipitation reaction, the pH value of the reaction system is 11 and the temperature is 80°C;

[0130] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 15 g / L;

[0131] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feeding is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 90:5:5; when the reaction reaches a particle size D50 of 5.5 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 8:1:1; when the feeding is finished, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:3:3; during the reaction, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0132] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them in an air atmosphere to obtain the positive electrode material; the calcination temperature is 600° C., and the calcination time is 20 h.

[0133] Example 3-3

[0134] This embodiment provides a method for preparing a concentration gradient precursor, the preparation method comprising the following steps:

[0135] (1) Under nitrogen atmosphere protection and stirring at a speed of 500 rpm, 1 mol / L nickel sulfate solution, 1 mol / L cobalt sulfate solution, 1 mol / L manganese sulfate solution, 32 wt% NaOH solution and 16 wt% ammonia water were mixed in parallel and coprecipitated to a particle size D50 of 11 μm; the slurry after the reaction was conventionally washed, dried, sieved and iron removed to obtain a concentration gradient precursor;

[0136] During the coprecipitation reaction, the pH value of the reaction system was 11.5 and the temperature was 40°C;

[0137] During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5 g / L;

[0138] During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution, and the manganese source solution remains unchanged. When the feeding is started, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 90:5:5; when the reaction reaches a particle size D50 of 5.5 μm, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 8:1:1; when the feeding is finished, the flow rate ratio of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution is 4:3:3; during the reaction, the flow rates of the nickel sulfate solution, the cobalt sulfate solution, and the manganese sulfate solution change smoothly;

[0139] (2) mixing lithium hydroxide and a concentration gradient precursor, and calcining them in an air atmosphere to obtain the positive electrode material; the calcination temperature is 900° C., and the calcination time is 10 hours.

[0140] Examples 3-4

[0141] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 3-1 except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 98:1:1; at the end of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 5:2:3.

[0142] Examples 3-5

[0143] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 3-1 except that at the beginning of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 94:5:1; at the end of feeding, the flow ratio of nickel sulfate solution, cobalt sulfate solution and manganese sulfate solution is 4:2:4.

[0144] Examples 3-6

[0145] This embodiment provides a method for preparing a positive electrode material, which is the same as Example 3-1, except that a 2 mol / L nickel sulfate solution, a 2 mol / L cobalt sulfate solution, and a 2 mol / L manganese sulfate solution are first mixed to obtain a nickel-cobalt-manganese mixed solution, and then the nickel-cobalt-manganese mixed solution, a NaOH solution, and an ammonia solution are mixed in parallel.

[0146] Examples 3-7

[0147] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 3-1 except that the pH value of the reaction system is 10.5.

[0148] Examples 3-8

[0149] This embodiment provides a method for preparing a positive electrode material, which is the same as that of Example 3-1 except that the pH value of the reaction system is 12.

[0150] Performance Characterization

[0151] The positive electrode materials obtained in each embodiment are prepared into lithium ion batteries by the following preparation method:

[0152] The positive electrode material, binder polyvinylidene fluoride, and conductive agent Super P were added to N-methylpyrrolidone at a mass ratio of 97:1.5:1.5 and stirred to form a first positive electrode slurry; the first positive electrode slurry was then evenly coated on the positive electrode current collector aluminum foil, dried and roll-pressed to obtain a positive electrode sheet;

[0153] Graphite, conductive agent acetylene black, thickener CMC and binder SBR are mixed in a mass ratio of 96:1:1.5:1.5, and deionized water is added as a solvent and stirred thoroughly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained after drying, cold pressing and slitting;

[0154] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then fully dried lithium salt LiPF6 was dissolved in the mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0155] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, then wrapped with aluminum-plastic film. After drying, the electrolyte is injected. After packaging, standing and formation processes, a lithium-ion battery is obtained. The separator is a PE porous film with a thickness of 11μm, an air permeability of 280s / 100mL, and a porosity of 40%.

[0156] The specific capacity, cycle capacity retention rate and rate performance of the obtained lithium-ion battery were tested, and the results are shown in Table 1.

[0157] The specific capacity test method is as follows: using the Blue Electric Battery Test System, at 25°C, the lithium-ion battery is charged and discharged three times in the voltage range of 2V to 4.3V at a charge and discharge rate of 0.04A / g (calculated based on the mass of the positive electrode material) to measure the battery specific capacity;

[0158] The test method for the cycle capacity retention rate is as follows: at 25°C, cycle at a charge and discharge rate of 0.19A / g (calculated based on the mass of the positive electrode material). After 500 cycles, the discharge capacity of the battery at this time is divided by the discharge capacity of the first cycle, which is the battery's 500-cycle capacity retention rate.

[0159] The test method for rate performance is: at 25°C, charge and discharge three times in the voltage range of 2V to 4.3V with a charge and discharge rate of 0.04A / g (calculated based on the mass of the positive electrode material) to obtain the discharge capacity C0 of the last cycle; then, charge the battery to 4.3V with a charge rate of 0.04A / g (calculated based on the mass of the positive electrode material), and discharge the battery to 2V with a discharge rate of 0.12A / g (calculated based on the mass of the positive electrode material) to obtain the discharge capacity C2 of the last cycle; the ratio of C2 / C0 is the rate performance.

[0160] Table 1

[0161] In summary, the concentration gradient precursor structure provided in this application can effectively avoid core-shell separation, effectively improve the cycle safety performance of high-nickel materials, and the preparation method is simple, can accurately control the metal content at each point of the spherical particles, the product has high consistency, and is easy to industrialize.

[0162] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A concentration gradient precursor, wherein: The core composition of the concentration gradient precursor is Ni x Co y Mn z (OH)2, where 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.2; The shell composition of the concentration gradient precursor is Ni a Co b Mn c (OH)2, where 0≤a≤0.5, 0≤b≤0.5, 0.3≤c≤1; The concentrations of the three elements nickel, cobalt and manganese in the concentration gradient precursor are in a gradient transition between the core and the shell.

2. The concentration gradient precursor according to claim 1, wherein The particle size D50 of the concentration gradient precursor is 2-20 μm.

3. The concentration gradient precursor according to claim 1 or 2, wherein The gradient transition includes at least one gradient.

4. A method for preparing a concentration gradient precursor according to any one of claims 1 to 3, comprising the following steps: Under a protective atmosphere, a nickel source solution, a cobalt source solution, a manganese source solution, a precipitant and a complexing agent are mixed to perform a coprecipitation reaction to obtain the concentration gradient precursor; During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution and the manganese source solution remains unchanged, and the nickel source solution, the cobalt source solution and the manganese source solution gradually change according to the gradient transition.

5. The preparation method according to claim 4, wherein During the coprecipitation reaction, the pH value of the reaction system is 9-13.

6. The preparation method according to claim 4 or 5, wherein: The temperature of the coprecipitation reaction is 40-80°C.

7. The preparation method according to any one of claims 4 to 6, wherein: During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5-15 g / L.

8. The preparation method according to any one of claims 4 to 7, wherein: The coprecipitation reaction is carried out under stirring conditions, and the stirring speed is 100-500 rpm.

9. The preparation method according to any one of claims 4 to 8, wherein: The nickel source in the nickel source solution includes any one of nickel sulfate, nickel nitrate or nickel chloride, or a combination of at least two thereof; Preferably, the concentration of the nickel source solution is 1-3 mol / L; Preferably, the cobalt source in the cobalt source solution includes any one of cobalt sulfate, cobalt nitrate or cobalt chloride, or a combination of at least two thereof; Preferably, the concentration of the cobalt source solution is 1-3 mol / L; Preferably, the manganese source in the manganese source solution includes any one of manganese sulfate, manganese nitrate or manganese chloride, or a combination of at least two thereof; Preferably, the concentration of the manganese source solution is 1-3 mol / L.

10. The preparation method according to any one of claims 4 to 9, wherein: The precipitant comprises sodium hydroxide and / or potassium hydroxide; Preferably, the complexing agent includes any one of ammonia water, ethylenediaminetetraacetic acid, sodium citrate, oxalic acid, acetic acid or ammonium bicarbonate, or a combination of at least two thereof.

11. The preparation method according to any one of claims 4 to 10, wherein: The preparation method comprises: Under a protective atmosphere and a stirring condition at a rotation speed of 100-500 rpm, a nickel source solution, a cobalt source solution, a manganese source solution, a precipitant and a complexing agent are mixed in parallel and a coprecipitation reaction is performed to obtain the concentration gradient precursor; During the coprecipitation reaction, the pH value of the reaction system is 9-13 and the temperature is 40-80°C; During the coprecipitation reaction, the concentration of the complexing agent in the reaction system is 5-15 g / L; During the coprecipitation reaction, the total flow rate of the nickel source solution, the cobalt source solution and the manganese source solution remains unchanged, and the nickel source solution, the cobalt source solution and the manganese source solution gradually change according to the gradient transition; The concentrations of the nickel source solution, the cobalt source solution and the manganese source solution are independently 1-3 mol / L.

12. A positive electrode material, wherein: The positive electrode material is prepared from the concentration gradient precursor according to any one of claims 1 to 3.

13. A method for preparing the positive electrode material as claimed in claim 12, comprising the following steps: The lithium source and the concentration gradient precursor are mixed and calcined in an oxygen atmosphere to obtain the positive electrode material.

14. The preparation method according to claim 13, wherein: The lithium source includes lithium carbonate and / or lithium hydroxide.

15. The preparation method according to claim 13 or 14, wherein: The calcination temperature is 600-900°C; Preferably, the calcination time is 10-20 hours.

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