Magnesium-doped core-shell structure precursor, preparation method and positive electrode material

Abstract

The invention relates to a magnesium-doped core-shell structure precursor, a preparation method thereof and a positive electrode material. The magnesium-doped core-shell structure precursor is provided with an inner core and an outer shell coating the inner core, the metal elements in the inner core comprise Ni, Co, Mn and Mg, and the molar ratio of Ni to Co to Mn to Mg is 92: (4-5): (3-4): (0.05-0.2); the metal elements in the shell comprise Ni, Co and Mn, and the molar ratio of Ni to Co to Mn is (50-60): 20: (20-30). According to the magnesium-doped core-shell structure precursor provided by the invention, the composition and the structure of the material are optimized, so that the positive electrode material has excellent performance in the aspects of high energy density, long cycle life and high safety performance, and a new possibility is provided for the application of a lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and relates to a core-shell structured electrode material, in particular to a magnesium-doped core-shell structured precursor, a preparation method thereof, and a cathode material. Background Art

[0002] As an efficient and environmentally friendly energy storage device, lithium-ion batteries have been widely studied and applied in the past few decades. With the continuous growth of the demand for portable electronic products, electric vehicles, and large-scale energy storage systems, the requirements for the performance of lithium-ion batteries are also getting higher and higher. As a key component of lithium-ion batteries, the performance of the cathode material directly affects the energy density, cycle life, safety, and cost of the battery.

[0003] Traditional lithium-ion battery cathode materials such as lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) etc. show excellent performance in some aspects, but there are certain limitations in terms of energy density, cost, and safety. To overcome these limitations, researchers have begun to explore new cathode material systems, among which the ternary cathode materials have attracted much attention due to their high energy density, good cycle stability, and relatively low usage cost.

[0004] Although the ternary cathode materials have obvious advantages in performance, they still face some challenges in practical applications, such as cycle stability, thermal stability, and structural stability at high voltages. Therefore, the development of new ternary cathode materials, their preparation methods, and the corresponding precursors for cathode materials has become a research hotspot in the field of lithium-ion batteries. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a magnesium-doped core-shell structured precursor, its preparation method, and a cathode material. The magnesium-doped core-shell structured precursor provided by the present invention shows excellent performance in terms of high energy density, long cycle life, and high safety performance by optimizing the composition and structure of the material, providing new possibilities for the application of lithium-ion batteries.

[0006] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a magnesium-doped core-shell structured precursor, and the magnesium-doped core-shell structured precursor has a core and a shell covering the core;

[0008] The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:(4 - 5):(3 - 4):(0.05 - 0.2);

[0009] The metal elements in the outer shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is (50 - 60):20:(20 - 30).

[0010] The magnesium-doped core-shell structure precursor provided by the present invention has a core of a nickel-rich ternary precursor doped with Mg and a shell of a manganese-rich ternary precursor; the core meets the requirements of high capacity for electrode materials, but the high nickel content will lead to a decline in the thermal stability and structural stability of the material. The doping of Mg elements in the core can inhibit the cation mixing of nickel and improve the structural stability. At the same time, the introduction of Mg will optimize the lithium-ion diffusion channels and relieve the volume expansion during charge and discharge; the shell can improve the thermal stability of the material and can also act as a protective layer to prevent the high-nickel core from directly contacting the electrolyte, reducing the interfacial side reactions; moreover, in the core-shell structure of the present invention, the compositions of the core and the shell are different, which is beneficial to reducing the interfacial stress and inhibiting the structural cracking during the cycling process.

[0011] Due to the advantages of the magnesium-doped core-shell structure precursor of the present invention, the corresponding cathode material has good structural stability while having high capacity and high energy density.

[0012] The metal elements in the core of the present invention include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:(4 - 5):(3 - 4):(0.05 - 0.2). Further, based on the total molar parts of Ni, Co, and Mn being 100 parts, the molar parts of Mg are 0.05 - 0.2 parts. For example, it can be 0.05 parts, 0.1 parts, 0.12 parts, 0.15 parts, 0.18 parts, or 0.2 parts, but not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0013] The metal elements in the outer shell of the present invention include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is (50 - 60):20:(20 - 30). Further, based on the total molar parts of Ni, Co, and Mn being 100 parts, the molar parts of Ni are 50 - 60 parts, and the molar parts of Mn are 20 - 30 parts.

[0014] Preferably, the median particle size D50 of the core is 8 μm - 10 μm. For example, it can be 8 μm, 9 μm, or 10 μm, but not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0015] Preferably, the median particle size D50 of the magnesium-doped core-shell structure precursor is 10 μm - 12 μm. For example, it can be 10 μm, 11 μm, or 12 μm, but not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0016] Second aspect, the present invention provides a method for preparing the magnesium-doped core-shell structure precursor described in the first aspect, and the preparation method includes the following steps:

[0017] A core with a median particle size D50 of 8 μm - 10 μm is prepared by coprecipitation reaction; then the coprecipitation reaction is continued to obtain the magnesium-doped core-shell structure precursor with a median particle size D50 of 10 μm - 12 μm.

[0018] Preferably, the preparation method includes:

[0019] (1) Mix the first metal salt solution, the precipitant solution and the complexing agent solution in the bottom liquid, and carry out coprecipitation reaction until a core with a median particle size D50 of 8 μm - 10 μm is obtained;

[0020] (2) Replace the first metal salt solution with the second metal salt solution, change the feeding rates of the precipitant solution and the complexing agent solution to maintain the conditions of the coprecipitation reaction unchanged, and continue the coprecipitation reaction to obtain the magnesium-doped core-shell structure precursor with a median particle size D50 of 10 μm - 12 μm;

[0021] The metal elements in the first metal salt solution include Ni, Co, Mn and Mg;

[0022] The metal elements in the second metal salt solution include Ni, Co and Mn.

[0023] Preferably, the total metal ion concentration in the first metal salt solution is 1 mol / L - 2.5 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L or 2.5 mol / L, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0024] Preferably, the metal salt in the first metal salt solution is sulfate.

[0025] Preferably, the total metal ion concentration in the second metal salt solution is 1 mol / L - 2.5 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L or 2.5 mol / L, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0026] Preferably, the metal salt in the second metal salt solution is sulfate.

[0027] Preferably, the precipitant solution is a sodium hydroxide solution with a mass concentration of 30 wt% - 35 wt%. For example, it can be 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt% or 35 wt%, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the complexing agent solution is ammonia water with a mass concentration of 10 wt% - 20 wt%. For example, it can be 10 wt%, 12 wt%, 15 wt%, 18 wt% or 20 wt%, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0029] The bottom solution of the present invention is prepared from water, a precipitant and a complexing agent.

[0030] Preferably, the pH value of the bottom solution is 11.2 - 12. For example, it can be 11.2, 11.4, 11.5, 11.8 or 12, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0031] Preferably, the ammonia concentration in the bottom solution is 4 g / L - 12 g / L. For example, it can be 4 g / L, 5 g / L, 8 g / L, 10 g / L or 12 g / L, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the temperature of the bottom solution is 40°C - 80°C. For example, it can be 40°C, 50°C, 60°C, 70°C or 80°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0033] Preferably, the temperature of the coprecipitation reaction is 40°C - 80°C. For example, it can be 40°C, 50°C, 60°C, 70°C or 80°C, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable;

[0034] Preferably, the pH value of the coprecipitation reaction is 10 - 11. For example, it can be 10, 10.2, 10.5, 10.8 or 11, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable;

[0035] Preferably, the ammonia concentration of the coprecipitation reaction is 4 g / L - 10 g / L. For example, it can be 4 g / L, 5 g / L, 8 g / L, 9 g / L or 10 g / L, but is not limited to the listed values. The other unlisted values within the numerical range are equally applicable.

[0036] The present invention does not impose excessive restrictions on the flow rates of the first metal salt solution, the second metal salt solution, the precipitant solution, and the complexing agent solution during the coprecipitation reaction, as long as the ammonia concentration condition and the pH value condition for the coprecipitation reaction can be met.

[0037] In a third aspect, the present invention provides a cathode material, which is prepared from the magnesium-doped core-shell structure precursor described in the first aspect; or, is prepared from the magnesium-doped core-shell structure precursor prepared by the preparation method described in the second aspect.

[0038] Exemplarily, the preparation method of the cathode material includes: mixing a lithium source with the magnesium-doped core-shell structure precursor, and performing sintering under an oxygen-containing atmosphere condition to obtain the cathode material.

[0039] Preferably, the lithium source includes lithium hydroxide.

[0040] Preferably, the sintering temperature is 500°C - 800°C, for example, it can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0041] Preferably, the sintering time is 6h - 10h, for example, it can be 6h, 7h, 8h, 9h, or 10h, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0042] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The magnesium-doped core-shell structure precursor provided by the present invention has a core of a nickel-rich ternary precursor doped with Mg and a shell of a manganese-rich ternary precursor; the core meets the high-capacity requirements of the electrode material, but the high nickel content will lead to a decrease in the thermal stability and structural stability of the material. The doping of Mg element in the core can inhibit the cation mixing of nickel, improve the structural stability, and at the same time, the introduction of Mg will optimize the lithium-ion diffusion channel and relieve the volume expansion during charge and discharge; the shell can improve the thermal stability of the material, and can also act as a protective layer to prevent the high-nickel core from directly contacting the electrolyte, reducing the interfacial side reaction; moreover, in the core-shell structure of the present invention, the compositions of the core and the shell are different, which is beneficial to reducing the interfacial stress and inhibiting the structural cracking during the cycling process. Detailed Embodiments

[0045] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0046] Example 1

[0047] This example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0048] The metal elements in the core include Ni, Co, Mn and Mg, and the molar ratio of Ni, Co, Mn, Mg is 92:4:4:0.2; the metal elements in the shell include Ni, Co and Mn, and the molar ratio of Ni, Co, Mn is 50:20:50;

[0049] The preparation method of the magnesium-doped core-shell structure precursor includes the following steps:

[0050] (1) Use water, sodium hydroxide and ammonia water to prepare a bottom solution with a pH value of 11.5, an ammonia concentration of 8 g / L and a temperature of 60 °C; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water solution with a mass concentration of 15 wt%; use nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, Mg of 92:4:4:0.2 and a total metal ion concentration of 2 mol / L; use nickel sulfate, cobalt sulfate and manganese sulfate to prepare a second metal salt solution with a molar ratio of Ni, Co, Mn of 50:20:50 and a total metal ion concentration of 2 mol / L;

[0051] (2) Add the first metal salt solution, sodium hydroxide solution and ammonia water into the bottom solution in parallel flow. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are used for co-precipitation reaction, so that the co-precipitation reaction is carried out under the conditions of a temperature of 60 °C, a pH value of 10.5 and an ammonia concentration of 7 g / L, and the co-precipitation reaction is carried out until a core with a median particle size D50 of 9 μm is obtained;

[0052] (3) Replace the first metal salt solution with the second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the co-precipitation reaction, and continue the co-precipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 11 μm is obtained.

[0053] Example 2

[0054] This example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0055] The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:4:4:0.2; the metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 50:20:50;

[0056] The preparation method of the magnesium-doped core-shell structure precursor includes the following steps:

[0057] (1) Prepare a bottom solution with a pH value of 11.2, an ammonia concentration of 4 g / L, and a temperature of 40 °C using water, sodium hydroxide, and ammonia; prepare a sodium hydroxide solution with a mass concentration of 30 wt%; prepare an ammonia water solution with a mass concentration of 10 wt%; use nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, and Mg of 92:4:4:0.2 and a total metal ion concentration of 1 mol / L; use nickel sulfate, cobalt sulfate, and manganese sulfate to prepare a second metal salt solution with a molar ratio of Ni, Co, Mn of 50:20:50 and a total metal ion concentration of 1 mol / L;

[0058] (2) The first metal salt solution, sodium hydroxide solution, and ammonia water are added to the bottom solution in a co-current manner. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a co-precipitation reaction, so that the co-precipitation reaction is carried out under the conditions of a temperature of 40 °C, a pH value of 10, and an ammonia concentration of 4 g / L, and the co-precipitation reaction is carried out until a core with a median particle size D50 of 8 μm is obtained;

[0059] (3) Replace the first metal salt solution with the second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the co-precipitation reaction, and continue the co-precipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 10 μm is obtained.

[0060] Example 3

[0061] This example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0062] The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:4:4:0.2; the metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, Mn is 50:20:50;

[0063] The preparation method of the magnesium-doped core-shell structure precursor includes the following steps:

[0064] (1) Prepare a bottom solution with a pH of 12, an ammonia concentration of 12 g / L, and a temperature of 80 °C using water, sodium hydroxide, and ammonia water; prepare a sodium hydroxide solution with a mass concentration of 35 wt%; prepare an ammonia water solution with a mass concentration of 20 wt%; prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, and Mg of 92:4:4:0.2 and a total metal ion concentration of 2.5 mol / L using nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate; prepare a second metal salt solution with a molar ratio of Ni, Co, and Mn of 50:20:50 and a total metal ion concentration of 2.5 mol / L using nickel sulfate, cobalt sulfate, and manganese sulfate;

[0065] (2) Add the first metal salt solution, sodium hydroxide solution, and ammonia water to the bottom solution in parallel flow. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are used for coprecipitation reaction, so that the coprecipitation reaction is carried out at a temperature of 80 °C, a pH of 11, and an ammonia concentration of 10 g / L until a core with a median particle size D50 of 10 μm is obtained;

[0066] (3) Replace the first metal salt solution with the second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the coprecipitation reaction, and continue the coprecipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 12 μm is obtained.

[0067] Example 4

[0068] This example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0069] The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:5:3:0.2; the metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 60:20:20;

[0070] The preparation method of the magnesium-doped core-shell structure precursor includes the following steps:

[0071] (1) Prepare a bottom solution with a pH of 11.5, an ammonia concentration of 8 g / L, and a temperature of 60 °C using water, sodium hydroxide, and ammonia water; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water solution with a mass concentration of 15 wt%; prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, and Mg of 92:5:3:0.2 and a total metal ion concentration of 2 mol / L using nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate; prepare a second metal salt solution with a molar ratio of Ni, Co, and Mn of 60:20:20 and a total metal ion concentration of 2 mol / L using nickel sulfate, cobalt sulfate, and manganese sulfate;

[0072] (2) In the bottom solution, a first metal salt solution, a sodium hydroxide solution, and ammonia water are added in parallel flow. The flow rate of the first metal salt solution is 20 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a coprecipitation reaction, so that the coprecipitation reaction is carried out under the conditions of a temperature of 60 °C, a pH value of 10.5, and an ammonia concentration of 7 g / L until a core with a median particle size D50 of 9 μm is obtained;

[0073] (3) Replace the first metal salt solution with a second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the coprecipitation reaction, and continue the coprecipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 11 μm is obtained.

[0074] Example 5

[0075] This example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0076] The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:4:4:0.05; the metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 50:20:50;

[0077] The preparation method of the magnesium-doped core-shell structure precursor includes the following steps:

[0078] (1) Prepare a bottom solution with a pH value of 11.5, an ammonia concentration of 8 g / L, and a temperature of 60 °C using water, sodium hydroxide, and ammonia water; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water with a mass concentration of 15 wt%; use nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, and Mg of 92:4:4:0.05 and a total metal ion concentration of 2 mol / L; use nickel sulfate, cobalt sulfate, and manganese sulfate to prepare a second metal salt solution with a molar ratio of Ni, Co, and Mn of 50:20:50 and a total metal ion concentration of 2 mol / L;

[0079] (2) In the bottom solution, a first metal salt solution, a sodium hydroxide solution, and ammonia water are added in parallel flow. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a coprecipitation reaction, so that the coprecipitation reaction is carried out under the conditions of a temperature of 60 °C, a pH value of 10.5, and an ammonia concentration of 7 g / L until a core with a median particle size D50 of 9 μm is obtained;

[0080] (3) Replace the first metal salt solution with a second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the coprecipitation reaction, and continue the coprecipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 11 μm is obtained.

[0081] Comparative Example 1

[0082] This comparative example provides a core-shell structure precursor having a core and a shell coating the core;

[0083] The metal elements in the core include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 92:4:4; the metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 50:20:50;

[0084] The preparation method of the core-shell structure precursor includes the following steps:

[0085] (1) Prepare a bottom solution with a pH value of 11.5, an ammonia concentration of 8 g / L, and a temperature of 60 °C using water, sodium hydroxide, and ammonia; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water solution with a mass concentration of 15 wt%; use nickel sulfate, cobalt sulfate, and manganese sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, and Mn of 92:4:4 and a total metal ion concentration of 2 mol / L; use nickel sulfate, cobalt sulfate, and manganese sulfate to prepare a second metal salt solution with a molar ratio of Ni, Co, and Mn of 50:20:50 and a total metal ion concentration of 2 mol / L;

[0086] (2) Add the first metal salt solution, sodium hydroxide solution, and ammonia water into the bottom solution in a co-current manner. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a co-precipitation reaction, so that the co-precipitation reaction is carried out at a temperature of 60 °C, a pH value of 10.5, and an ammonia concentration of 7 g / L until a core with a median particle size D50 of 9 μm is obtained;

[0087] (3) Replace the first metal salt solution with the second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the co-precipitation reaction, and continue the co-precipitation reaction until a core-shell structure precursor with a median particle size D50 of 11 μm is obtained.

[0088] Comparative Example 2

[0089] This comparative example provides a magnesium-doped core-shell structure precursor having a core and a shell coating the core. Except that the molar ratio of Ni, Co, Mn, and Mg in the core is 92:4:4:0.4 and the molar ratio of Ni, Co, Mn, and Mg in the first metal salt solution is correspondingly adjusted, the rest are the same as in Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides a magnesium-doped precursor, the metal elements of which include Ni, Co, Mn and Mg, and the molar ratio of Ni, Co, Mn, Mg is 92:4:4:0.2;

[0092] The preparation method of the magnesium-doped precursor comprises the following steps:

[0093] (1) Prepare a bottom solution with a pH value of 11.5, an ammonia concentration of 8 g / L and a temperature of 60 °C using water, sodium hydroxide and ammonia water; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water with a mass concentration of 15 wt%; use nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, Mn, Mg of 92:4:4:0.2 and a total metal ion concentration of 2 mol / L;

[0094] (2) The first metal salt solution, sodium hydroxide solution and ammonia water are added to the bottom solution in parallel flow. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a co-precipitation reaction, so that the co-precipitation reaction is carried out at a temperature of 60 °C, a pH value of 10.5 and an ammonia concentration of 7 g / L until a magnesium-doped precursor with a median particle size D50 of 11 μm is obtained.

[0095] Comparative Example 4

[0096] This comparative example provides a magnesium-doped core-shell structure precursor, which has a core and a shell covering the core;

[0097] The metal elements in the core include Ni, Co and Mn, and the molar ratio of Ni, Co, Mn is 92:4:4; the metal elements in the shell include Ni, Co, Mn and Mg, and the molar ratio of Ni, Co, Mn, Mg is 50:20:50:0.2;

[0098] The preparation method of the magnesium-doped core-shell structure precursor comprises the following steps:

[0099] (1) Prepare a bottom solution with a pH value of 11.5, an ammonia concentration of 8 g / L and a temperature of 60 °C using water, sodium hydroxide and ammonia water; prepare a sodium hydroxide solution with a mass concentration of 32 wt%; prepare an ammonia water with a mass concentration of 15 wt%; use nickel sulfate, cobalt sulfate and manganese sulfate to prepare a first metal salt solution with a molar ratio of Ni, Co, Mn of 92:4:4 and a total metal ion concentration of 2 mol / L; use nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate to prepare a second metal salt solution with a molar ratio of Ni, Co, Mn, Mg of 50:20:50:0.2 and a total metal ion concentration of 2 mol / L;

[0100] (2) The first metal salt solution, sodium hydroxide solution and ammonia water are added in parallel flow to the bottom liquid. The flow rate of the first metal salt solution is 60 L / h, and the flow rates of the sodium hydroxide solution and ammonia water are subjected to a co-precipitation reaction, so that the co-precipitation reaction is carried out under the conditions of a temperature of 60 °C, a pH value of 10.5, and an ammonia concentration of 7 g / L until a core with a median particle size D50 of 9 μm is obtained;

[0101] (3) Replace the first metal salt solution with the second metal salt solution, adjust the flow rates of the sodium hydroxide solution and ammonia water to maintain the conditions of the co-precipitation reaction, and continue the co-precipitation reaction until a magnesium-doped core-shell structure precursor with a median particle size D50 of 11 μm is obtained.

[0102] Performance characterization

[0103] The precursors obtained in the above examples and comparative examples are respectively mixed with lithium hydroxide according to a molar ratio of 1:1.05, and then sintered at 650 °C for 8 h to obtain the corresponding cathode materials.

[0104] The obtained cathode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) are mixed according to a mass ratio of 90:5:5. The solvent is N-methylpyrrolidone, and the mixture is stirred into a slurry. The obtained slurry is evenly coated on an aluminum foil with a doctor blade having a coating gap of 100 μm; after coating, it is first dried by blowing, then rolled and cut into a circular electrode sheet, and then vacuum dried at 120 °C and the weight of the electrode sheet is weighed to obtain a cathode electrode sheet for a button half-cell; the negative electrode is a metal lithium sheet, the separator is a PP microporous membrane, and the electrolyte is a basic electrolyte for lithium batteries. The cathode electrode sheet, metal lithium sheet, separator and electrolyte are assembled to obtain a button cell; the electrochemical performance is tested at a rate of 0.1C in the voltage range of 2.8V - 4.3V, and the obtained results are shown in Table 1.

[0105] Table 1

[0106]

[0107] As can be seen from Table 1, the magnesium-doped core-shell structure precursor provided by the present invention has good electrochemical performance, its initial discharge specific capacity is above 190.5 mAh / g, and the cycle capacity retention rate can reach above 90.3%.

[0108] It can be seen from the comparison between Comparative Example 1 and Example 1 that when Mg doping is not carried out in the core, both the discharge specific capacity and the cycle capacity retention rate decrease significantly; it can be seen from the comparison between Comparative Example 2 and Example 1 that when the Mg doping amount is too high, it is also not conducive to improving the discharge specific capacity and the cycle capacity retention rate of the obtained magnesium-doped core-shell structure precursor; it can be seen from the comparison between Comparative Example 3 and Example 1 that when the obtained magnesium-doped precursor does not have a core-shell structure, it is not conducive to improving the discharge specific capacity and the cycle capacity retention rate of the obtained magnesium-doped core-shell structure precursor; it can be seen from the comparison between Comparative Example 4 and Example 1 that when Mg is doped in the shell, it is also not conducive to improving the discharge specific capacity and the cycle capacity retention rate of the obtained magnesium-doped core-shell structure precursor.

[0109] In summary, for the magnesium-doped core-shell structure precursor provided by the present invention, the core is a nickel-rich ternary precursor doped with Mg, and the shell is a manganese-rich ternary precursor; the core meets the requirements of high capacity of the electrode material, but the high nickel content will lead to a decrease in the thermal stability and structural stability of the material. The doping of Mg element in the core can inhibit the cation mixing of nickel, improve the structural stability. At the same time, the introduction of Mg will optimize the lithium ion diffusion channel and relieve the volume expansion during charge and discharge; the shell can improve the thermal stability of the material and can also be used as a protective layer to prevent the high-nickel core from directly contacting the electrolyte, reducing the interfacial side reaction; moreover, in the core-shell structure of the present invention, the compositions of the core and the shell are different, which is conducive to reducing the interfacial stress and inhibiting the structural cracking during the cycling process.

[0110] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A magnesium-doped core-shell structure precursor, characterized in that, The magnesium-doped core-shell structure precursor has a core and a shell coating the core; The metal elements in the core include Ni, Co, Mn, and Mg, and the molar ratio of Ni, Co, Mn, and Mg is 92:(4-5):(3-4):(0.05-0.2); The metal elements in the shell include Ni, Co, and Mn, and the molar ratio of Ni, Co, Mn is (50-60):20:(20-30).

2. The preparation method of the magnesium-doped core-shell structure precursor according to claim 1, characterized in that, The preparation method includes the following steps: A core with a median particle size D50 of 8 μm - 10 μm is prepared by coprecipitation reaction; then the coprecipitation reaction is continued to obtain the magnesium-doped core-shell structure precursor with a median particle size D50 of 10 μm - 12 μm.

3. The preparation method according to claim 2, wherein The preparation method includes: (1) Mix a first metal salt solution, a precipitant solution, and a complexing agent solution in the bottom liquid, and carry out coprecipitation reaction until a core with a median particle size D50 of 8 μm - 10 μm is obtained; (2) Replace the first metal salt solution with a second metal salt solution, change the feeding rates of the precipitant solution and the complexing agent solution to maintain the coprecipitation reaction conditions unchanged, and continue the coprecipitation reaction to obtain the magnesium-doped core-shell structure precursor with a median particle size D50 of 10 μm - 12 μm; The metal elements in the first metal salt solution include Ni, Co, Mn, and Mg; The metal elements in the second metal salt solution include Ni, Co, and Mn.

4. The preparation method according to claim 3, characterized in that, The total metal ion concentration in the first metal salt solution is 1 mol / L - 2.5 mol / L.

5. The preparation method according to claim 3, characterized in that, The total metal ion concentration in the second metal salt solution is 1 mol / L - 2.5 mol / L.

6. The preparation method according to claim 3, characterized in that, The precipitant solution is a sodium hydroxide solution with a mass concentration of 30 wt% - 35 wt%.

7. The preparation method according to claim 3, characterized in that, The complexing agent solution is an ammonia water solution with a mass concentration of 10 wt% - 20 wt%.

8. The preparation method according to claim 3, characterized in that The pH value of the bottom liquid is 11.2 - 12; and / or, the ammonia concentration in the bottom liquid is 4 g / L - 12 g / L; and / or, the temperature of the bottom liquid is 40 °C - 80 °C.

9. The preparation method according to claim 3 or 4, characterized in that, The temperature of the coprecipitation reaction is 40 °C - 80 °C; and / or, the pH value of the coprecipitation reaction is 10 - 11; and / or, the ammonia concentration of the coprecipitation reaction is 4 g / L - 10 g / L.

10. A cathode material, characterized in that, The cathode material is prepared from the magnesium-doped core-shell structure precursor described in claim 1; or is prepared from the magnesium-doped core-shell structure precursor prepared by the preparation method described in any one of claims 2 - 9.

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