A concentration gradient manganese-rich cathode material precursor, preparation method thereof and cathode material

Abstract

The present invention provides a concentration gradient manganese-rich cathode material precursor, a preparation method thereof and a cathode material having a chemical formula shown in Formula I: M x Mn y (OH)2 Formula I; in Formula I, M is one or more of Ni, Co, Ti, Zr and Al, x+y=1, 0≤x≤0.5, 0.5≤y≤1; the concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration gradient decreasing from the inside to the outside. The positive electrode material precursor in the present invention has a core with uniform composition and an outer shell with a Mn element concentration gradient decreasing. This not only solves the problem of a loose core during the precursor formation process, but also forms a precursor with a concentration gradient with a more uniform nickel and manganese distribution. The sintered positive electrode material has a concentration gradient composition, has better cycle performance and the performance of suppressing voltage decay.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a concentration gradient manganese-rich positive electrode material precursor, a preparation method thereof, and a positive electrode material. Background Art

[0002] The primary obstacle limiting the range of electric vehicles is the inability to further increase the energy density of lithium-ion batteries, which is primarily limited by the cathode materials. Current technology has almost reached its technological limit in increasing battery energy density by reducing the mass ratio of inactive materials in the cell. Employing cathode and anode materials with higher energy densities is the most direct approach to improving battery energy density. Commercial cathode materials, such as lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and ternary materials, generally suffer from low specific capacity and energy density, making them inadequate for the development of high-energy-density lithium-ion batteries. Due to their advantages of high specific capacity (≥250 mAh / g), low material cost, and excellent thermal stability, lithium-rich manganese-based cathode materials, such as xLi2MnO3·1-xLiTMO2 (TM represents one or more transition metals such as Ni, Co, Mn, and Fe), have attracted widespread attention in recent years and have become a strong contender for the development of high-energy-density lithium-ion batteries. However, lithium-rich manganese-based cathode materials also suffer from low initial efficiency, poor rate performance, and severe voltage decay, hindering their commercialization.

[0003] Strategies such as doping, coating, surface treatment, element ratio design, and concentration gradient design can effectively stabilize the structure and surface of lithium-rich materials, thereby improving cycling performance and suppressing voltage decay. Concentration gradient cathode material modification, which involves creating a continuously varying concentration gradient within the material without introducing other elements or changing the overall metal composition, addresses some inherent material issues through a designed distribution from the interior to the surface. This approach effectively balances structural and surface stability, and has therefore attracted widespread attention.

[0004] However, in practice, patent CN113299902B discloses the preparation of a concentration-gradient magnesium-doped lithium-rich manganese-based oxide cathode material and its application in lithium batteries. Using a co-precipitation method, a gradient distribution of Mg stabilizes the material surface, reducing the presence of transition metals on the surface and, in turn, reducing side reactions with the electrolyte. However, the particle size distribution of the precursor synthesized by this method is uncontrollable, resulting in a high concentration of fine powder. Summary of the Invention

[0005] The purpose of the present invention is to provide a concentration gradient manganese-rich positive electrode material precursor, a preparation method thereof and a positive electrode material. The concentration gradient manganese-rich positive electrode material precursor in the present invention has a controllable particle size distribution, good particle uniformity, and can improve the cycle performance of lithium-ion batteries and inhibit voltage decay.

[0006] The present invention provides a concentration gradient manganese-rich cathode material precursor having a chemical formula shown in Formula I:

[0007] M x Mn y (OH)2 Formula I;

[0008] In formula I, M is one or more of Ni, Co, Ti, Zr and Al, x+y=1, 0≤x≤0.5, 0.5≤y≤1;

[0009] The concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration that decreases from the inside to the outside.

[0010] Preferably, the M is Ni and Co,

[0011] The chemical formula of the concentration gradient manganese-rich positive electrode material precursor is Ni x1 Co x2 Mn y (OH)2, wherein x1+x2+y=1, 0<x1≤0.5, 0<x2≤0.5, 0.5≤y≤1.

[0012] The present invention provides a method for preparing a concentration gradient manganese-rich cathode material precursor as described above, comprising the following steps:

[0013] A) adding alkali solution and complexing agent solution into the seed crystal reaction kettle to form a bottom solution;

[0014] B) under an inert gas atmosphere, continuously introducing solution A, alkali solution and complexing agent into the seed crystal reactor to react; when the material in the seed crystal reactor submerges the reactor overflow port, starting the concentrated total reflux;

[0015] The solution A is a mixed metal salt solution with low M and high manganese content;

[0016] C) After the particle size reaches 1 to 3.5 μm, the concentrated material, alkali solution and complexing agent are introduced into a coprecipitation reactor, and solution B is introduced into a storage tank containing solution A, mixed with solution A and continuously introduced into the coprecipitation reactor, and the concentration total reflux is started to carry out a coprecipitation reaction to obtain a precursor slurry;

[0017] The solution B is a mixed metal salt solution with high M and low Mn;

[0018] D) aging the precursor slurry, performing solid-liquid separation, and then drying to obtain a concentration gradient manganese-rich positive electrode material precursor.

[0019] Preferably, the alkali solution includes one or more of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide and lithium hydroxide, and the concentration of the alkali solution is 0.001 to 11 mol / L;

[0020] The complexing agent solution comprises one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, citric acid, oxalic acid, ammonia water and ethylenediaminetetraacetic acid, and the concentration of the complexing agent solution is 0.01-10 mol / L.

[0021] Preferably, the molar ratio of the M element to the Mn element in the solution A is (0.2-0.45): (0.6-0.8).

[0022] Preferably, the molar ratio of the M element to the Mn element in the solution B is (0.7-0.9): (0.1-0.3).

[0023] Preferably, the molar concentrations of solution A and solution B are the same, and the volume ratio of solution A to solution B is (1-5):1;

[0024] In step C), the feeding rate of solution B is 1 / 20 to 1 / 5 of the feeding rate of solution A.

[0025] Preferably, in step B), the pH in the seed crystal reactor is controlled to be 7 to 12.3, the concentration of the complexing agent is 0.01 to 1 mol / L, and the temperature is 35 to 70° C.;

[0026] In the step C), the pH in the coprecipitation reactor is controlled to be 7-12.3, the concentration of the complexing agent is controlled to be 0.01-1 mol / L, and the temperature is controlled to be 35-70°C.

[0027] The present invention provides a positive electrode material, which is obtained by mixing a positive electrode material precursor with a lithium source and then sintering;

[0028] The positive electrode material precursor is the concentration gradient manganese-rich positive electrode material precursor described above or the concentration gradient manganese-rich positive electrode material precursor prepared by the preparation method described above.

[0029] Preferably, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxalate and lithium acetate;

[0030] The sintering is performed by pre-firing at 300-700° C. for 1-10 hours, then heating to 600-1000° C. and keeping the temperature for 6-24 hours.

[0031] The present invention provides a concentration gradient manganese-rich cathode material precursor having a chemical formula shown in Formula I: M x Mn y(OH)2 formula I; in formula I, M is one or more of Ni, Co, Ti, Zr and Al, x+y=1, 0≤x≤0.5, 0.5≤y≤1; the concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration gradient decreasing from the inside to the outside. The positive electrode material precursor in the present invention has a core with uniform composition and an outer shell with a Mn element concentration gradient decreasing. This not only solves the problem of a loose core during the precursor formation process, but also forms a precursor with a concentration gradient with a more uniform nickel and manganese distribution. The sintered positive electrode material has a concentration gradient composition, and has better cycle performance and consistent voltage decay performance.

[0032] In addition, the present invention also provides a method for preparing a concentration gradient manganese-rich positive electrode material precursor, which adopts a seed crystal method to solve the problem of loose core during the nucleation process of the material, and at the same time accurately and continuously controls the thermodynamic equilibrium of the coprecipitation reaction process during operation. The specific strategy is to control the reaction pH value and the concentration of the complexing agent to change with the change of the metal salt component of the feed solution. As the Co content and the Ni content increase, the complexing agent and the pH value change accordingly, providing a more suitable nucleation and growth environment for the feed with continuously changing metal composition, making the growth more orderly, and making the material have better crystallinity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0034] Figure 1 Schematic diagram of the preparation device of the concentration gradient manganese-rich cathode material precursor of the present invention;

[0035] Figure 1 In the figure, 1A is a seed reactor; 1B is a coprecipitation reactor; 2 is a draft tube; 3A is a concentrator; 3B is a concentrator; 4 is a feed tank (solution A); 5 is a feed tank (solution B);

[0036] Figure 2 This is an SEM image of the concentration gradient precursor prepared in Example 1 of the present invention;

[0037] Figure 3 1 is a charge and discharge curve diagram of Example 1 of the present invention and Comparative Example 1;

[0038] Figure 4 1 is a cycle curve diagram of Example 1 of the present invention and Comparative Example 1;

[0039] Figure 5This is a scatter plot of element distribution of the concentration gradient precursor prepared in Example 1 of the present invention;

[0040] Figure 6 1 is a voltage attenuation diagram of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0041] The present invention provides a concentration gradient manganese-rich cathode material precursor having a chemical formula shown in Formula I:

[0042] M x Mn y (OH)2 Formula I;

[0043] In formula I, M is one or more of Ni, Co, Ti, Zr and Al, x+y=1, 0≤x≤0.5, 0.5≤y≤1;

[0044] The concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration that decreases from the inside to the outside.

[0045] In the present invention, M is preferably Ni and Co, that is, the chemical formula of the concentration gradient manganese-rich positive electrode material precursor is Ni x1 Co x2 Mn y (OH)2, wherein 0<x1≤0.5, preferably, 0.1≤x1≤0.4, such as x1 is 0.1, 0.2, 0.3, 0.4 or 0.5, preferably, the range value with any of the above values ​​as the upper or lower limit; 0<x2≤0.5, preferably, 0.1≤x2≤0.4, such as x2 is 0.1, 0.2, 0.3, 0.4 or 0.5, preferably, the range value with any of the above values ​​as the upper or lower limit.

[0046] Preferably, 0.5≤y≤1, more preferably, 0.6≤y≤0.9, such as y can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, preferably a range value with any of the above values ​​as the upper or lower limit.

[0047] In the present invention, the core is composed of M and Mn elements with uniform composition distribution, preferably, Ni and Mn elements with uniform composition distribution, while the shell is composed of M and Mn elements with concentration gradient variation. Preferably, the shell contains Ni, Co and Mn elements with concentration gradient variation. Specifically, from the inside to the outside, the concentrations of Ni and Co elements in the shell increase in a gradient, while the concentration of Mn element decreases in a gradient. The positive electrode material prepared by the present invention is a manganese-rich material with a manganese content of ≥50%. The present invention sets manganese as an element with a decreasing concentration gradient, which is beneficial to the synthesis of the precursor material and can avoid surface manganese dissolution. In the present invention, the "inside" in the "from inside to outside" refers to the side in contact with the core, and the "outside" refers to the outer surface side of the shell.

[0048] In the present invention, the diameter of the inner core is preferably 1 to 3 μm, the thickness of the shell is 1 to 7 μm, the particle size of the concentration gradient manganese-rich positive electrode material precursor is preferably 3 to 12 μm, and the particle size distribution span of the concentration gradient manganese-rich positive electrode material precursor is (D90-D10) / D50 in the range of 0.4 to 1.2.

[0049] The present invention also provides a method for preparing a concentration gradient manganese-rich cathode material precursor, comprising the following steps:

[0050] A) adding alkali solution and complexing agent solution into the seed crystal reaction kettle to form a bottom solution;

[0051] B) under an inert gas atmosphere, continuously introducing solution A, alkali solution and complexing agent into the seed crystal reactor to react; when the material in the seed crystal reactor submerges the reactor overflow port, starting the concentrated total reflux;

[0052] The solution A is a mixed metal salt solution with low M and high manganese content;

[0053] C) After the particle size reaches 1 to 3.5 μm, the concentrated material, alkali solution and complexing agent are introduced into a coprecipitation reactor, and solution B is introduced into a storage tank containing solution A, mixed with solution A and continuously introduced into the coprecipitation reactor, and the concentration total reflux is started to carry out a coprecipitation reaction to obtain a precursor slurry;

[0054] The solution B is a mixed metal salt solution with high M and low Mn;

[0055] D) aging the precursor slurry, performing solid-liquid separation, and then drying to obtain a concentration gradient manganese-rich positive electrode material precursor.

[0056] The preparation device used in the preparation method of the present invention is as follows Figure 1As shown, it includes a seed reactor 1A, a concentrator 3A and a concentrator 3B, and a co-precipitation reactor 1B connected in sequence; the seed reactor 1A is connected to the inlet of the concentrator 3A, and the outlet of the concentrator 3A is connected to the top of the seed reactor 1A; the seed reactor 1A is provided with an agitator, a feed pipe, a nitrogen conduit, a liquid level gauge, a draft tube, etc.; the overflow port of the seed reactor 1A is connected to the top of the co-precipitation reactor 1B, the co-precipitation reactor 1B is connected to the inlet of the concentrator 3B, and the outlet of the concentrator 3B is connected to the top of the co-precipitation reactor 1B; a feed trough 4 is also provided to connect the top of the seed reactor and the top of the co-precipitation reactor.

[0057] The invention firstly introduces alkali liquor and complexing agent solution into a seed crystal reactor to form a bottom liquid for starting the reaction, and the bottom liquid covers a stirring paddle at the bottom of the seed crystal reactor.

[0058] In the present invention, the alkali solution preferably includes one or more of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide and lithium hydroxide, more preferably sodium hydroxide, and the concentration of the alkali solution is preferably 0.001-11 mol / L, more preferably 0.5-10 mol / L, such as 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, preferably with any of the above values ​​as the upper limit or The lower limit of the range value; the complexing agent solution preferably includes one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, citric acid, oxalic acid, ammonia water and ethylenediaminetetraacetic acid, and the concentration of the complexing agent solution is preferably 0.01 to 10 mol / L, more preferably 0.1 to 9 mol / L, such as 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, preferably with any of the above values ​​as the upper or lower limit of the range value.

[0059] In the present invention, it is preferred to control the concentration of the bottom liquid so that the pH value of the bottom liquid and the concentration of the complexing agent reach the parameter indicators that need to be controlled in the seed crystal reactor. The pH value of the bottom liquid in the seed crystal reactor is 7 to 12.3, more preferably 8 to 12, such as 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.3, preferably a range value with any of the above values ​​as the upper or lower limit; the concentration of the complexing agent is preferably 0.01 to 1 mol / L, more preferably 0.05 to 0.9 mol / L, such as 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, preferably a range value with any of the above values ​​as the upper or lower limit.

[0060] After obtaining the base liquid, the present invention continuously introduces an inert gas, such as nitrogen, into the base liquid for 10 to 30 minutes to remove dissolved oxygen from the base liquid. The seed crystal reactor is kept sealed and slightly positively pressurized. The entire reaction is carried out under the protection of the inert gas. Then, while maintaining a certain temperature and stirring speed, Solution A, an alkali solution, and a complexing agent solution are continuously introduced in parallel to carry out the reaction.

[0061] In the present invention, in the seed crystal reactor, the reaction temperature is preferably 35-70°C, more preferably 40-65°C, such as 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, preferably a range value with any of the above values ​​as the upper or lower limit; the stirring speed during the reaction process is preferably 300-1000r / min, more preferably 400-800r / min.

[0062] In the present invention, the solution A is a low-M high-manganese mixed metal salt solution, that is, the concentration of the metal salt of M in the solution A is relatively low, while the concentration of the manganese salt is relatively high. In the solution A, the M element is preferably Ni, and the molar ratio of the M element to the Mn element in the solution A is preferably (0.2-0.45): (0.6-0.8), more preferably (0.25-0.35): (0.75-0.65). Specifically, in an embodiment of the present invention, the molar ratio of Ni to Mn in the solution A can be 0.25:0.75, or 0.35:0.65.

[0063] The present invention does not impose any particular restriction on the flow rates of the solution A, alkali solution and complexing agent solution continuously introduced into the seed crystal reactor, as long as the pH value and complexing agent concentration required by the above reaction are maintained.

[0064] With the continuous feeding reaction, the material in the seed reactor gradually increases. When the material exceeds the overflow port of the seed reactor, the concentrator is started for full reflux. After the particle size reaches 1-3 μm, the concentrated material is introduced into the co-precipitation reactor. At the same time, the feeding system of the co-precipitation reactor is started, and solution B is introduced into the storage tank of solution A. After mixing with solution A, it is introduced into the co-precipitation reactor. At the same time, the alkali solution and the complexing agent solution are continuously introduced into the co-precipitation reactor in parallel, and the concentration full reflux is started to carry out the co-precipitation reaction.

[0065] In the present invention, the solution B is a mixed metal salt solution with high M and low manganese, that is, the concentration of the metal salt of M in the solution B is relatively high, while the concentration of the manganese salt is relatively low. In the solution B, the M element is preferably Ni and Co. In the solution B, the molar ratio of Ni, Co and Mn elements is preferably (0.4-0.7): (0.2-0.3): (0.1-0.3), more preferably (0.45-0.65): (0.2-0.3): (0.15-0.25). Specifically, in an embodiment of the present invention, the molar ratio of Ni, Co and Mn elements is 0.65:0.2:0.15. Or 0.45:0.3:0.25.

[0066] According to the present invention, solution B is first introduced into a storage tank of solution A, and is continuously introduced into a coprecipitation reactor while being mixed with solution A. As solution B is continuously introduced, the proportion of solution B in the mixed metal salt solution transported to the coprecipitation reactor gradually increases, that is, the content of the Mn element gradually decreases, while the contents of the Ni and Co elements gradually increase. This operation mode can ensure that the concentration gradient of the metal elements introduced into the coprecipitation reactor changes more uniformly and the continuity of the concentration gradient is better.

[0067] In the present invention, the molar concentration of total metal ions in solution A and solution B is preferably the same. Under the premise that the concentrations of solution A and solution B are the same, the volume ratio of solution A to solution B is preferably (1-5):1, more preferably (2-4):1, such as 1:1, 2:1, 3:1, 4:1, 5:1, and preferably a range value with any of the above values ​​as the upper or lower limit; the feeding rate of solution B is preferably 1 / 20-1 / 5 of the feeding rate of solution A, more preferably 1 / 15-1 / 10, such as 1 / 20, 1 / 19, 1 / 18, 1 / 17, 1 / 16, 1 / 15, 1 / 14, 1 / 13, 1 / 12, 1 / 11, 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0068] In the present invention, the temperature of the coprecipitation reaction is preferably a pH of 7 to 12.3, more preferably 8 to 12, such as 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.3, preferably a range value with any of the above values ​​as the upper or lower limit; the concentration of the complexing agent is preferably 0.01 to 1 mol / L, more preferably 0.05 to 0.9 mol / L, such as 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, preferably a range value with any of the above values ​​as the upper or lower limit. The temperature of the coprecipitation reaction is preferably 35 to 70°C, more preferably 50 to 65°C, such as 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, preferably a range value with any of the above values ​​as the upper or lower limit; the stirring speed during the coprecipitation reaction is preferably 300 to 1000 r / min, more preferably 400 to 800 r / min. Specifically, in an embodiment of the present invention, since the feed in the coprecipitation reactor adds cobalt element, in order to maintain the stability of the system in the reactor, the control conditions of the coprecipitation reaction will be slightly adjusted within the range of the above conditions relative to the control conditions in the seed reactor.

[0069] After the particle size reaches 1 to 3 μm, the feeding is stopped and a precursor slurry is obtained in a coprecipitation reactor. The precursor slurry is then aged for 5 to 8 hours and solid-liquid separation is performed. The precipitate obtained by the solid-liquid separation is washed and dried in sequence to obtain a concentration gradient manganese-rich positive electrode material precursor.

[0070] In the present invention, the drying temperature is preferably 50 to 100° C., more preferably 60 to 80° C., and the drying time is preferably 18 to 36 hours, more preferably 24 to 32 hours.

[0071] The present invention also provides a lithium-rich manganese-based positive electrode material, which is obtained by mixing the above-mentioned concentration gradient manganese-rich positive electrode material precursor with a lithium source and then sintering the mixture.

[0072] In the present invention, the lithium source is preferably one or more of lithium hydroxide, lithium carbonate, lithium oxalate and lithium acetate; the molar ratio Li:Me of the lithium source and the concentration gradient manganese-rich positive electrode material precursor described above is (1-2):1, more preferably (1.2-1.8):1, such as 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, preferably a range value with any of the above values ​​as the upper or lower limit; wherein Me is the total molar number of M element and Mn element in the concentration gradient manganese-rich positive electrode material precursor.

[0073] In the present invention, the sintering is specifically:

[0074] In air or oxygen atmosphere, pre-sinter at 300-700℃ for 1-10 hours, then heat to 600-1000℃ and keep warm for 6-24 hours.

[0075] In the present invention, the pre-calcination temperature is preferably 400-600°C, such as 300°C, 400°C, 500°C, 600°C, 700°C, preferably a range value with any of the above values ​​as the upper or lower limit; the pre-calcination time is preferably 1-10 hours, more preferably 3-8 hours, and most preferably 5-6 hours.

[0076] In the present invention, there is no special restriction on the heating rate. The insulation temperature is preferably 600-1000°C, more preferably 700-900°C, such as 600°C, 700°C, 800°C, 900°C, 1000°C, preferably a range value with any of the above values ​​as the upper or lower limit; the insulation time is preferably 6-24 hours, more preferably 8-18 hours, and most preferably 10-12 hours.

[0077] The present invention provides a concentration gradient manganese-rich cathode material precursor having a chemical formula shown in Formula I: M x Mn y (OH)2 formula I; in formula I, M is one or more of Ni, Co, Ti, Zr and Al, x+y=1, 0≤x≤0.5, 0.5≤y≤1; the concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration gradient decreasing from the inside to the outside. The positive electrode material precursor in the present invention has a core with uniform composition and an outer shell with a Mn element concentration gradient decreasing. This not only solves the problem of a loose core during the precursor formation process, but also forms a precursor with a concentration gradient with a more uniform nickel and manganese distribution. The sintered positive electrode material has a concentration gradient composition, and has better cycle performance and consistent voltage decay performance.

[0078] In addition, the present invention also provides a method for preparing a concentration gradient manganese-rich positive electrode material precursor, which adopts a seed crystal method to solve the problem of loose core during the nucleation process of the material, and at the same time accurately and continuously controls the thermodynamic equilibrium of the coprecipitation reaction process during operation. The specific strategy is to control the reaction pH value and the concentration of the complexing agent to change with the change of the metal salt component of the feed solution. As the Co content and the Ni content increase, the complexing agent and the pH value change accordingly, providing a more suitable nucleation and growth environment for the feed with continuously changing metal composition, making the growth more orderly, and making the material have better crystallinity.

[0079] In order to further illustrate the present invention, a concentration gradient manganese-rich positive electrode material precursor, a preparation method thereof and a positive electrode material provided by the present invention are described in detail below in combination with examples, but it should not be understood as limiting the scope of protection of the present invention.

[0080] Example 1

[0081] The concentration gradient cathode material prepared in this example is Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2, its preparation method comprises the following steps:

[0082] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L solution A and 2 mol / L solution B, respectively. The molar ratio of Ni:Mn in solution A was 0.35:0.65, and the molar ratio of Ni:Co:Mn in solution B was 0.65:0.2:0.15. At the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0083] (2) Prepare an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide) and an ammonia concentration of 0.4 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. Solution A is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through metering pumps respectively for reaction, controlling the pH value to 11.5 and the ammonia concentration to 0.4 mol / L.

[0084] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feed system of the reactor is started, and solution B is pumped into solution A at a flow rate of 1 / 10 of the feed rate. The pH value is controlled to gradually increase from 11.5 to 11.8, and the ammonia concentration is increased from 0.4 mol / L to 0.5 mol / L. The reaction time is 30 h, and the concentrator is fully refluxed. The required particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0085] (4) The precursor slurry in the reactor was aged for 6 hours, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 hours to obtain a concentration gradient precursor Ni 0.38 Co 0.02 Mn 0.60 (OH)2.

[0086] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2.

[0087] The present invention first obtains a cross section of the material by ion beam cutting (CP), and then performs an element distribution test on the concentration gradient precursor prepared in Example 1 by point scanning in EDS in SEM. The results are as follows: Figure 5 As shown by Figure 5 It can be seen that the target precursor is a precursor with a D50 of about 6.5μm. From the core center to 3μm, the Ni / Mn content ratio is evenly distributed. After 3μm, the cobalt content gradually increases to 0.05, the manganese content gradually decreases from the original 0.65 to 0.5, and the nickel content gradually increases from the original 0.35 to 0.45.

[0088] Example 2

[0089] The concentration gradient cathode material prepared in this example is Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2, its preparation method comprises the following steps:

[0090] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L solution A and 2 mol / L solution B, respectively. The molar ratio of Ni:Mn in solution A was 0.35:0.65, and the molar ratio of Ni:Co:Mn in solution B was 0.65:0.2:0.15. At the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0091] (2) Prepare an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide) and an ammonia concentration of 0.4 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. Solution A is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through metering pumps respectively for reaction, controlling the pH value to 11.5 and the ammonia concentration to 0.4 mol / L.

[0092] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feed system of the reactor is started, and solution B is pumped into solution A at a flow rate of 1 / 10 of the feed rate. The pH value is controlled at 11.5, the ammonia concentration is 0.4 mol / L, the reaction time is 30 h, and the concentrator is fully refluxed. The required particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0093] (4) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain a concentration gradient precursor.

[0094] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2.

[0095] Example 3

[0096] The concentration gradient cathode material prepared in this example is Li 1.2 Ni 0.30 Co 0.02 Mn 0.48O2, its preparation method comprises the following steps:

[0097] (1) Nickel acetate, cobalt acetate, and manganese acetate were dissolved in deionized water to prepare 2 mol / L solution A and 2 mol / L solution B, respectively. The molar ratio of Ni:Mn in solution A was 0.35:0.65, and the molar ratio of Ni:Co:Mn in solution B was 0.65:0.2:0.15. At the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0098] (2) Prepare an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide) and an ammonia concentration of 0.4 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. Solution A is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through metering pumps respectively for reaction, controlling the pH value to 11.5 and the ammonia concentration to 0.4 mol / L.

[0099] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feed system of the reactor is started, and solution B is pumped into solution A at a flow rate of 1 / 10 of the feed rate. The pH value is controlled to gradually increase from 11.5 to 11.8, and the ammonia concentration is increased from 0.4 mol / L to 0.5 mol / L. The reaction time is 30 h, and the concentrator is fully refluxed. The required particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0100] (4) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain a concentration gradient precursor.

[0101] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2.

[0102] Example 4

[0103] The concentration gradient cathode material prepared in this example is Li1.2 Ni 0.22 Co 0.02 Mn 0.56 O2, its preparation method comprises the following steps:

[0104] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L solution A and 2 mol / L solution B, respectively. The molar ratio of Ni:Mn in solution A was 0.25:0.75, and the molar ratio of Ni:Co:Mn in solution B was 0.45:0.3:0.25. At the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0105] (2) Prepare an alkaline bottom liquid with a pH of 11.3 (sodium hydroxide) and an ammonia concentration of 0.45 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. Solution A is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through metering pumps respectively for reaction, controlling the pH value to 11.3 and the ammonia concentration to 0.45 mol / L.

[0106] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feeding system of the reactor is started, and solution B is pumped into solution A at a flow rate of 1 / 10 of the feeding speed. The pH value is controlled to gradually rise from 11.3 to 11.45, and the ammonia concentration is increased from 0.4 mol / L to 0.45 mol / L. The reaction time is 30 h, and the concentrator is fully refluxed. The required particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0107] (4) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain a concentration gradient precursor.

[0108] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 900°C for 12 h. After the reaction, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 1.2 Ni 0.22 Co 0.02 Mn 0.56 O2.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 1 is that no concentration gradient change is achieved.

[0111] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L salt solutions of Ni:Co:Mn (molar ratio) = 0.38:0.02:0.60; at the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0112] (2) Prepare an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide preparation) and an ammonia concentration of 0.4 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. The salt solution is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through a metering pump respectively for reaction, controlling the pH value to 11.5 and the ammonia concentration to 0.4 mol / L.

[0113] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feeding system of the reactor is started, and the concentrator is fully refluxed. The required particle size is achieved through co-precipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0114] (4) The precursor slurry in the reactor was aged for 6 hours, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 hours to obtain the precursor Ni 0.38 Co 0.02 Mn 0.60 (OH)2.

[0115] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain the positive electrode material Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2.

[0116] Comparative Example 2

[0117] The difference between this comparative example and Example 1 is that no concentration gradient change is achieved and the seed crystal method is not adopted.

[0118] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L salt solutions of Ni:Co:Mn (molar ratio) = 0.38:0.02:0.60; at the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0119] (2) In the reactor, an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide preparation) and an ammonia concentration of 0.4 mol / L is prepared to cover the bottom stirring paddle. Nitrogen is continuously introduced for 20 minutes to remove the dissolved oxygen in the bottom liquid, and the reactor is kept sealed and slightly positively pressurized. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. The salt solution is evenly pumped into the reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the reactor at a rate of 5 L / min and 0.7 L / min through a metering pump respectively for reaction, controlling the pH value to 11.5 and the ammonia concentration to 0.4 mol / L. The concentrator is fully refluxed, and the required particle size is achieved through coprecipitation reaction. The feeding is terminated to obtain a precursor slurry.

[0120] (3) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain the precursor.

[0121] (4) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain the positive electrode material Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 4 is that no concentration gradient change is achieved.

[0124] The positive electrode material prepared in this example is Li 1.2 Ni 0.22 Co 0.02 Mn 0.56 O2, its preparation method comprises the following steps:

[0125] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water, and 2 mol / L salt solutions were prepared respectively, wherein the molar ratio of Ni:Co:Mn in the salt solution was 0.27:0.03:0.70; at the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0126] (2) Prepare an alkaline bottom liquid with a pH of 11.3 (sodium hydroxide) and an ammonia concentration of 0.45 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. The solution salt is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through a metering pump respectively for reaction, controlling the pH value to 11.3 and the ammonia concentration to 0.45 mol / L.

[0127] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor. At the same time, the feeding system of the reactor is started, and the pH value is controlled to 11.3, the ammonia concentration to 0.45 mol / L, the reaction time to 30 h, and the concentrator is fully refluxed. The desired particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0128] (4) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain a concentration gradient precursor.

[0129] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 900°C for 12 h. After the reaction, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 1.2 Ni 0.22 Co 0.02 Mn 0.56 O2.

[0130] Comparative Example 4

[0131] The concentration gradient cathode material prepared in this example is Li 1.2 Ni 0.30 Co 0.02 Mn 0.48 O2, its preparation method comprises the following steps:

[0132] (1) Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate were dissolved in deionized water to prepare 2 mol / L solution A and 2 mol / L solution B, respectively. The molar ratio of Ni:Mn in solution A was 0.35:0.65, and the molar ratio of Ni:Co:Mn in solution B was 0.65:0.2:0.15. At the same time, 4 mol / L sodium hydroxide solution was prepared as a precipitant, and 6 mol / L ammonia solution was prepared as a complexing agent.

[0133] (2) Prepare an alkaline bottom liquid with a pH of 11.5 (sodium hydroxide preparation) and an ammonia concentration of 0.4 mol / L in the reactor to cover the bottom stirring paddle. Continue to introduce nitrogen for 20 minutes to remove the dissolved oxygen in the bottom liquid, and keep the reactor sealed and slightly positive pressure. The reactor needs to be protected by inert gas nitrogen throughout the process. The temperature of the reaction system is controlled to be maintained at 55°C by water bath heating, and the stirring speed is 800 rpm. Solution A is evenly pumped into the seed reactor at a rate of 5 L / min through a metering pump. Sodium hydroxide and ammonia water are simultaneously pumped into the seed reactor at a rate of 5 L / min and 0.7 L / min through a metering pump for reaction. At the same time as solution A, solution B is started and pumped into solution A at a flow rate of 1 / 15 of the feed rate to control the pH value to 11.5 and the ammonia concentration to 0.4 mol / L.

[0134] (3) The material does not pass through the overflow port of the seed reactor, and the concentrator is started for full reflux. When the particle size reaches about 3 μm, the concentrated material enters the reactor, and the pH value is controlled to gradually increase from 11.5 to 11.8. The ammonia concentration is increased from 0.4 mol / L to 0.5 mol / L. The reaction time is 30 h, and the concentrator is fully refluxed. The required particle size requirement is achieved through coprecipitation reaction, and the feeding is terminated to obtain a precursor slurry.

[0135] (4) The precursor slurry in the reactor was aged for 6 h, pumped into a centrifuge through a diaphragm pump to achieve solid-liquid separation, and washed with deionized water until the washing clear liquid was neutral. It was then transferred to an oven and dried at 80°C for 24 h to obtain a concentration gradient precursor.

[0136] (5) The obtained precursor was mixed evenly with lithium carbonate in a molar ratio of Li / Me=1:1.5, and pre-sintered at 550°C for 3 h in a tube furnace under a pure oxygen atmosphere, and then kept at 920°C for 12 h. After the reaction was completed, the sintered product was sieved to obtain a concentration gradient positive electrode material Li 12 Ni 030 Co 002 Mn 048 O2.

[0137] The positive electrode materials described in the above Examples 1 to 4 and Comparative Examples 1 to 4 were respectively made into pole pieces and assembled into liquid lithium-ion batteries as working electrodes for charge and discharge tests. The voltage range was 2.0 to 4.8 V. The first discharge specific capacity and first coulombic efficiency were tested at 0.1C / 0.1C, and the 100-cycle capacity retention and voltage decay were tested at 1C / 1C.

[0138] Table 1 Performance test of lithium ion batteries prepared from positive electrode materials in the embodiments of the present invention and comparative examples

[0139]

[0140] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A concentration gradient manganese-rich cathode material precursor having the chemical formula shown in Formula I: Ni x1 Co x2 Mn y (OH)₂ of formula I; In formula I, x1+x2+y=1, 0<x1≤0.5, 0<x2≤0.5, 0.5≤y≤1; The concentration gradient manganese-rich positive electrode material precursor has a core with uniform composition and a shell with a Mn element concentration that decreases from the inside to the outside. From the inside to the outside, the concentrations of Ni and Co elements in the shell increase gradually, while the concentration of Mn element decreases gradually. The core is composed of Ni and Mn elements with uniform distribution.

2. The method for preparing a concentration gradient manganese-rich cathode material precursor according to claim 1, comprising the following steps: A) adding alkali solution and complexing agent solution into the seed reaction kettle to form a bottom solution; B) Under an inert gas atmosphere, solution A, alkali solution, and complexing agent are continuously introduced into the seed crystal reactor to react; when the material in the seed crystal reactor exceeds the overflow port of the reactor, the concentrated total reflux is started; The solution A is a mixed metal salt solution with low M and high manganese, the M element is Ni, and the molar ratio of the Ni element to the Mn element in the solution A is (0.2-0.45): (0.6-0.8); C) After the particle size reaches 1-3.5 μm, the concentrated material, alkali solution, and complexing agent are introduced into a coprecipitation reactor, and solution B is introduced into a storage tank containing solution A, mixed with solution A, and then continuously introduced into the coprecipitation reactor. The concentration and total reflux are started to carry out a coprecipitation reaction to obtain a precursor slurry; The solution B is a mixed metal salt solution with high M and low manganese, wherein the M elements in the solution B are Ni and Co, and the molar ratio of Ni, Co and Mn elements in the solution B is (0.4-0.7): (0.2-0.3): (0.1-0.3); The molar concentrations of solution A and solution B are the same, and the volume ratio of solution A to solution B is (1-5):1; The feeding rate of solution B in step C) is 1 / 20 to 1 / 5 of the feeding rate of solution A. D) aging the precursor slurry, performing solid-liquid separation, and then drying to obtain a concentration gradient manganese-rich positive electrode material precursor.

3. The preparation method according to claim 2, characterized in that The alkali solution includes one or more of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide and lithium hydroxide, and the concentration of the alkali solution is 0.001-11 mol / L; The complexing agent solution includes one or more of ammonium chloride, ammonium nitrate, ammonium sulfate, citric acid, oxalic acid, ammonia water and ethylenediaminetetraacetic acid, and the concentration of the complexing agent solution is 0.01-10 mol / L.

4. The preparation method according to claim 2, characterized in that In the step B), the pH in the seed crystal reactor is controlled to be 7-12.3, the concentration of the complexing agent is 0.01-1 mol / L, and the temperature is 35-70°C; In the step C), the pH in the coprecipitation reactor is controlled to be 7-12.3, the concentration of the complexing agent is controlled to be 0.01-1 mol / L, and the temperature is controlled to be 35-70°C.

5. A positive electrode material obtained by mixing a positive electrode material precursor with a lithium source and then sintering; The positive electrode material precursor is the concentration gradient manganese-rich positive electrode material precursor according to claim 1 or the concentration gradient manganese-rich positive electrode material precursor prepared by the preparation method according to any one of claims 3 to 4.

6. The positive electrode material according to claim 5, characterized in that The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium oxalate and lithium acetate; The sintering is performed by pre-firing at 300-700° C. for 1-10 hours, then heating to 600-1000° C. and keeping the temperature for 6-24 hours.

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