A three-stage core-shell structure ternary precursor, a positive electrode material, a preparation method and a positive electrode

Abstract

This invention relates to a three-stage core-shell ternary precursor, a cathode material, a preparation method, and a cathode. The preparation method of the three-stage core-shell ternary precursor improves cycle performance and thermal stability while ensuring the capacity of the cathode material by controlling the composition and elemental distribution of the core-shell structure.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a ternary material, particularly a three-segment core-shell structure ternary precursor, cathode material, preparation method, and cathode. Background Technology

[0002] Lithium-ion batteries, as core components for new energy storage and applications, are widely used in electric vehicles, portable electronic devices, and energy storage systems. Among the components of a lithium-ion battery, the performance of the cathode material directly determines key indicators such as energy density, cycle life, and safety performance. Therefore, the development of high-performance cathode materials has always been a research hotspot in the field of lithium-ion batteries.

[0003] High-nickel ternary cathode material (LiNi) x Co y Mn 1-x-y O2 (x≥0.8), with its high nickel content, can provide higher theoretical specific capacity and energy density, meeting the urgent need for long driving range in fields such as electric vehicles, and has become a key research direction for cathode materials in recent years. However, high-nickel ternary cathode materials still face many challenges in practical applications. On the one hand, the nickel element in high-nickel materials is prone to valence state changes (such as Ni...). 2+ Ni 3+ Ni 4+ During charge-discharge cycles, the crystal structure is prone to distortion, leading to cracking of material particles. Electrolyte infiltration further exacerbates side reactions, significantly reducing battery cycle performance. Furthermore, high-nickel ternary cathode materials have poor thermal stability. When the battery is exposed to high temperatures or experiences overcharging, the material is prone to decomposition, releasing oxygen that reacts violently with the electrolyte, causing thermal runaway and seriously threatening battery safety.

[0004] To address the poor cycle performance and thermal stability of high-nickel ternary cathode materials, researchers have implemented various improvement measures. For example, surface coating technology is used to form a protective film on the surface of the material particles to suppress direct contact between the electrolyte and the material, reducing side reactions; or doping modification is employed to introduce other elements to stabilize the material's crystal structure and improve its structural stability. However, simple surface coating or doping modification often fails to simultaneously achieve high capacity, long cycle life, and high thermal stability.

[0005] Core-shell structure design, as a modification strategy with superior overall performance, has gradually attracted researchers' attention. Core-shell structures typically consist of a high-capacity core and a stable outer shell. By rationally designing the composition ratio and structural characteristics of the core and shell, it is hoped that the cycle performance and thermal stability can be significantly improved while ensuring high capacity. For example, a high-nickel-content material can be used as the core to provide high capacity, while a material with lower nickel content and better stability can be used as the shell to enhance cycle and thermal stability. However, current core-shell structure designs still have shortcomings in terms of composition gradient control, shell uniformity, and interfacial compatibility, making it difficult to achieve ideal modification results and limiting the further application of high-nickel ternary cathode materials in high-end fields.

[0006] Therefore, developing a high-nickel ternary cathode material that can precisely control the core-shell structure and achieve a perfect combination of high core capacity and high shell stability is of great practical significance for improving the performance of lithium-ion batteries. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a three-stage core-shell ternary precursor, cathode material, preparation method, and cathode. The preparation method of the three-stage core-shell ternary precursor improves cycle performance and thermal stability while ensuring the capacity of the cathode material by controlling the composition and element distribution of the core-shell structure.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a three-segment core-shell structured ternary precursor, the method comprising the following steps:

[0010] In a protective atmosphere, a first solution, a precipitant solution, and a complexing agent solution are introduced concurrently into the substrate, co-precipitating to the first target particle size. Then, a second solution and a doping solution are introduced concurrently, continuing the co-precipitation reaction to the second target particle size. The introduction of the first solution is stopped, and the co-precipitation reaction continues to the third target particle size. The introduction of the doping solution is stopped, and the co-precipitation reaction continues to the fourth target particle size. Then, a third solution and a doping solution are introduced concurrently, continuing the co-precipitation reaction to the fifth target particle size. The introduction of the second solution is stopped, and the co-precipitation reaction continues to the sixth target particle size. The introduction of the doping solution is stopped, and the co-precipitation reaction continues to the seventh target particle size.

[0011] After washing, drying and sieving, the three-stage core-shell structured ternary precursor was obtained;

[0012] The first solution is a nickel salt solution;

[0013] The second solution is a nickel-cobalt-manganese mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese is x:y:(1-xy), 0.8≤x≤0.9, 0≤y≤0.1;

[0014] The third solution is a nickel-cobalt-manganese mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese is a:b:(1-ab), a≤0.4, 0≤b≤0.3.

[0015] This invention introduces a high-nickel first solution in the initial stage of the co-precipitation reaction to form a core, providing a high-capacity foundation for the material. As the co-precipitation reaction progresses, a second and third solution with gradually decreasing nickel content are introduced, along with the staged addition of doping solutions, resulting in a gradient core-shell structure with decreasing nickel content from the core to the surface and an orderly distribution of dopant elements. This structure alleviates the volume expansion stress in the high-nickel region during charge-discharge cycles, while the relatively low-nickel outer layer suppresses lattice distortion, reduces particle breakage and interfacial side reactions, thereby improving cycle stability. Furthermore, the synergy between the low-nickel outer layer and the doping elements enhances stability and reduces Li+ degradation at high temperatures. + The risk of structural collapse due to insertion / extraction is significantly reduced, and thermal stability is significantly improved. In addition, the step-like growth of particle size at each stage ensures a smooth transition at the gradient interface, avoids stress concentration, and further enhances cycling performance and thermal stability.

[0016] Optionally, the protective atmosphere may include nitrogen and / or an inert gas; the inert gas may include helium and / or argon.

[0017] Optionally, the nickel salt in the first solution includes any one or a combination of at least two of nickel nitrate, nickel sulfate, or nickel chloride. Typical but non-limiting combinations include a combination of nickel nitrate and nickel sulfate, a combination of nickel sulfate and nickel chloride, a combination of nickel nitrate and nickel chloride, or a combination of nickel nitrate, nickel sulfate, and nickel chloride.

[0018] Optionally, in the second and third solutions, nickel, cobalt, and manganese are provided by nickel salts, cobalt salts, and manganese salts, respectively. Exemplarily, the nickel salt includes any one or at least two combinations of nickel nitrate, nickel sulfate, or nickel chloride. Typical but non-limiting combinations include combinations of nickel nitrate and nickel sulfate, nickel sulfate and nickel chloride, nickel nitrate and nickel chloride, or nickel nitrate, nickel sulfate, and nickel chloride. The cobalt salt includes any one or at least two combinations of cobalt nitrate, cobalt sulfate, or cobalt chloride. Typical but non-limiting combinations include combinations of cobalt nitrate and cobalt sulfate, cobalt sulfate and cobalt chloride, cobalt nitrate and cobalt chloride, or cobalt nitrate, cobalt sulfate, and cobalt chloride. The manganese salt includes any one or at least two combinations of manganese nitrate, manganese sulfate, or manganese chloride. Typical but non-limiting combinations include combinations of manganese nitrate and manganese sulfate, manganese sulfate and manganese chloride, manganese nitrate and manganese chloride, or manganese nitrate, manganese sulfate, and manganese chloride.

[0019] In one embodiment of the present invention, the concentration of the first solution is 2 mol / L to 4 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] In one embodiment of the present invention, the concentration of the second solution is 2 mol / L to 4 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] In one embodiment of the present invention, the concentration of the third solution is 2 mol / L to 4 mol / L, for example, it can be 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] In one embodiment of the present invention, the doping solution includes a zirconium salt solution and a niobium salt solution.

[0023] Optionally, the zirconium salt includes zirconium sulfate.

[0024] Optionally, the niobium salt includes niobium oxalate.

[0025] In one embodiment of the present invention, the concentration of the zirconium salt solution is 0.05 mol / L to 0.15 mol / L, for example, it can be 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L or 0.15 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In one embodiment of the present invention, the concentration of the niobium salt solution is 0.05 mol / L to 0.15 mol / L, for example, it can be 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L or 0.15 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] In one embodiment of the present invention, when the doping solution is introduced, the ratio of the flow rate of the doping solution to the total flow rate of the first solution, the second solution and the third solution is 1:(8 to 12), for example, it can be 1:8, 1:9, 1:10, 1:11 or 1:12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] In one embodiment of the present invention, the temperature of the coprecipitation reaction is 40°C to 80°C, for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] In one embodiment of the present invention, the pH value of the coprecipitation reaction is 10.5 to 11.5, for example, it can be 10.5, 10.8, 11, 11.2 or 11.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] In one embodiment of the present invention, during the coprecipitation reaction, the concentration of the complexing agent in the system is 0.1 mol / L to 0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In one embodiment of the present invention, the stirring speed during the coprecipitation reaction is 200 r / min to 400 r / min, for example, it can be 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] In one embodiment of the present invention, the first target particle size is a median particle size D50 of 2.5 μm to 3.5 μm, for example, it can be 2.5 μm, 3 μm or 3.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In one embodiment of the present invention, the second target particle size is a median particle size D50 of 4.5 μm to 5.5 μm, for example, it can be 4.5 μm, 5 μm or 5.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] In one embodiment of the present invention, the third target particle size is a median particle size D50 of 5.5 μm to 6.5 μm, for example, it can be 5.5 μm, 6 μm or 6.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] In one embodiment of the present invention, the fourth target particle size is a median particle size D50 of 8.5 μm to 9.5 μm, for example, it can be 8.5 μm, 9 μm or 9.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] In one embodiment of the present invention, the fifth target particle size is a median particle size D50 of 9.5 μm to 10.5 μm, for example, it can be 9.5 μm, 10 μm or 10.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] In one embodiment of the present invention, the sixth target particle size is a median particle size D50 of 10.5 μm to 11.5 μm, for example, it can be 10.5 μm, 11 μm or 11.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] In one embodiment of the present invention, the seventh target particle size is a median particle size D50 of 11.5 μm to 12.5 μm, for example, it can be 11.5 μm, 12 μm or 12.5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] In one embodiment of the present invention, the precipitant in the precipitant solution includes sodium hydroxide.

[0040] In one embodiment of the present invention, the complexing agent in the complexing agent solution includes any one or a combination of at least two of ammonia, citric acid, or sodium citrate.

[0041] Secondly, the present invention provides a three-segment core-shell ternary precursor, which is prepared by the preparation method described in the first aspect.

[0042] Thirdly, the present invention provides a method for preparing a cathode material, the method comprising the following steps: mixing a lithium source with the three-stage core-shell structure ternary precursor described in the second aspect, pre-calcining and then calcining to obtain the cathode material.

[0043] In one embodiment of the present invention, the lithium source includes LiOH and / or Li2CO3.

[0044] In one embodiment of the present invention, in order to compensate for the loss on burn-off, the molar ratio of lithium in the lithium source to the three-stage core-shell structure ternary precursor is 1.02:1 to 1.05:1, for example, it can be 1.02:1, 1.03:1, 1.04:1 or 1.05:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Optionally, the preheating temperature is 280℃ to 320℃, for example, it can be 280℃, 290℃, 300℃, 310℃ or 320℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Optionally, the pre-burning time is 2.5h to 3.5h, for example, it can be 2.5h, 3h or 3.5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Optionally, the calcination temperature is 700℃ to 900℃, for example, 700℃, 750℃, 800℃, 850℃ or 900℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Optionally, the calcination time is 10h to 16h, for example, it can be 10h, 12h, 14h, 15h or 16h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Fourthly, the present invention provides a cathode material, which is prepared by the preparation method described in the third aspect.

[0050] Fifthly, the present invention provides a positive electrode, the positive electrode comprising the positive electrode material described in the fourth aspect.

[0051] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] This invention introduces a high-nickel first solution in the initial stage of the co-precipitation reaction to form a core, providing a high-capacity foundation for the material. As the co-precipitation reaction progresses, a second and third solution with gradually decreasing nickel content are introduced, along with the staged addition of doping solutions, resulting in a gradient core-shell structure with decreasing nickel content from the core to the surface and an orderly distribution of dopant elements. This structure alleviates the volume expansion stress in the high-nickel region during charge-discharge cycles, while the relatively low-nickel outer layer suppresses lattice distortion, reduces particle breakage and interfacial side reactions, thereby improving cycle stability. Furthermore, the synergy between the low-nickel outer layer and the doping elements enhances stability and reduces Li+ degradation at high temperatures. + The risk of structural collapse due to insertion / extraction is significantly reduced, and thermal stability is significantly improved. In addition, the step-like growth of particle size at each stage ensures a smooth transition at the gradient interface, avoids stress concentration, and further enhances cycling performance and thermal stability. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Example 1

[0056] This embodiment provides a method for preparing a three-segment core-shell structured ternary precursor, the method comprising the following steps:

[0057] (1) Prepare the first solution, the second solution, the third solution, the zirconium salt solution, and the niobium salt solution;

[0058] The first solution is a 2 mol / L nickel sulfate solution;

[0059] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0060] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0061] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0062] (2) A bottom liquid is set in the reactor with a pH of 11.2, an ammonia concentration of 0.3 mol / L, and a temperature of 70°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 300 r / min;

[0063] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3 μm; then the second solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 5 μm; the first solution is stopped, and the co-precipitation reaction continues until D50 reaches 6 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9 μm; then the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 10 μm; the second solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 11 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12 μm;

[0064] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:9.

[0065] The coprecipitation reaction was carried out at a temperature of 60℃, a pH of 11, and an ammonia concentration of 0.3 mol / L.

[0066] (4) After washing, drying and sieving, a three-stage core-shell structured ternary precursor is obtained.

[0067] Example 2

[0068] This embodiment provides a method for preparing a three-segment core-shell structured ternary precursor, the method comprising the following steps:

[0069] (1) Prepare the first solution, the second solution, the third solution, the zirconium salt solution, and the niobium salt solution;

[0070] The first solution is a 3 mol / L nickel sulfate solution;

[0071] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 3 mol / L.

[0072] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 3 mol / L.

[0073] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0074] (2) A bottom liquid is set in the reactor with a pH of 11, an ammonia concentration of 0.1 mol / L, and a temperature of 40°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 200 r / min;

[0075] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 2.5 μm; then the second solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 4.5 μm; the first solution is stopped, and the co-precipitation reaction continues until D50 reaches 5.5 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 8.5 μm; then the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 9.5 μm; the second solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 10.5 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 11.5 μm;

[0076] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:12.

[0077] The coprecipitation reaction was carried out at a temperature of 40℃, a pH of 10.5, and an ammonia concentration of 0.1 mol / L.

[0078] (4) After washing, drying and sieving, a three-stage core-shell structured ternary precursor is obtained.

[0079] Example 3

[0080] This embodiment provides a method for preparing a three-segment core-shell structured ternary precursor, the method comprising the following steps:

[0081] (1) Prepare the first solution, the second solution, the third solution, the zirconium salt solution, and the niobium salt solution;

[0082] The first solution is a 4 mol / L nickel sulfate solution;

[0083] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 4 mol / L.

[0084] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 4 mol / L.

[0085] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0086] (2) A bottom liquid is set in the reactor with a pH of 11.5, an ammonia concentration of 0.5 mol / L, and a temperature of 80℃; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 400 r / min;

[0087] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3.5 μm; then the second solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 5.5 μm; the first solution is stopped, and the co-precipitation reaction continues until D50 reaches 6.5 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9.5 μm; then the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 10.5 μm; the second solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 11.5 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12.5 μm;

[0088] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:8.

[0089] The coprecipitation reaction was carried out at a temperature of 80℃, a pH of 11.5, and an ammonia concentration of 0.5 mol / L.

[0090] (4) After washing, drying and sieving, a three-stage core-shell structured ternary precursor is obtained.

[0091] Example 4

[0092] This embodiment provides a method for preparing a three-stage core-shell structured ternary precursor. Except for changing the flow rate of the precipitant solution to make the pH value of the coprecipitation reaction 10, the rest is the same as in Example 1.

[0093] Example 5

[0094] This embodiment provides a method for preparing a three-stage core-shell structured ternary precursor. Except for changing the flow rate of the precipitant solution to make the pH value of the coprecipitation reaction 12, the rest is the same as in Example 1.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing a core-shell structured ternary precursor, the method comprising the following steps:

[0097] (1) Prepare the first solution, the third solution, the zirconium salt solution and the niobium salt solution;

[0098] The first solution is a 2 mol / L nickel sulfate solution;

[0099] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0100] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0101] (2) A bottom liquid is set in the reactor with a pH of 11.2, an ammonia concentration of 0.3 mol / L, and a temperature of 70°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 300 r / min;

[0102] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3 μm; then zirconium salt solution and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 6 μm; the introduction of zirconium salt solution and niobium salt solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9 μm; then the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 10 μm; the introduction of the first solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 11 μm; the introduction of zirconium salt solution and niobium salt solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12 μm;

[0103] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first and third solutions is 1:9.

[0104] The coprecipitation reaction was carried out at a temperature of 60℃, a pH of 11, and an ammonia concentration of 0.3 mol / L.

[0105] (4) After washing, drying and sieving, a core-shell structured ternary precursor is obtained.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing a core-shell structured ternary precursor, the method comprising the following steps:

[0108] (1) Prepare the first solution, the second solution, the zirconium salt solution and the niobium salt solution;

[0109] The first solution is a 2 mol / L nickel sulfate solution;

[0110] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0111] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0112] (2) A bottom liquid is set in the reactor with a pH of 11.2, an ammonia concentration of 0.3 mol / L, and a temperature of 70°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 300 r / min;

[0113] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution) and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3 μm; then the second solution, zirconium salt solution and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 5 μm; the first solution is stopped, and the co-precipitation reaction continues until D50 reaches 6 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9 μm; then the zirconium salt solution and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 11 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12 μm;

[0114] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution and the second solution is 1:9;

[0115] The coprecipitation reaction was carried out at a temperature of 60℃, a pH of 11, and an ammonia concentration of 0.3 mol / L.

[0116] (4) After washing, drying and sieving, a core-shell structured ternary precursor is obtained.

[0117] Comparative Example 3

[0118] This comparative example provides a method for preparing a core-shell structured ternary precursor, the method comprising the following steps:

[0119] (1) Prepare the first solution, the second solution, the third solution, the zirconium salt solution, and the niobium salt solution;

[0120] The first solution is a 2 mol / L nickel sulfate solution;

[0121] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0122] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0123] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0124] (2) A bottom liquid is set in the reactor with a pH of 11.2, an ammonia concentration of 0.3 mol / L, and a temperature of 70°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 300 r / min;

[0125] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3 μm; then the first solution is stopped, and the second solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 6 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9 μm; then the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 10 μm; the second solution is stopped, and the co-precipitation reaction continues until the particle size D50 reaches 11 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12 μm;

[0126] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:9.

[0127] The coprecipitation reaction was carried out at a temperature of 60℃, a pH of 11, and an ammonia concentration of 0.3 mol / L.

[0128] (4) After washing, drying and sieving, a core-shell structured ternary precursor is obtained.

[0129] Comparative Example 4

[0130] This comparative example provides a method for preparing a three-stage core-shell structured ternary precursor, the method comprising the following steps:

[0131] (1) Prepare the first solution, the second solution, the third solution, the zirconium salt solution, and the niobium salt solution;

[0132] The first solution is a 2 mol / L nickel sulfate solution;

[0133] The second solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 86:7:7 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0134] The third solution is a mixture of nickel sulfate, cobalt sulfate and manganese sulfate, with a molar ratio of nickel, cobalt and manganese of 4:3:3 and a total concentration of nickel sulfate, cobalt sulfate and manganese sulfate of 2 mol / L.

[0135] The zirconium salt solution is a 0.1 mol / L zirconium sulfate solution; the niobium salt solution is a 0.1 mol / L nickel oxalate solution.

[0136] (2) A bottom liquid is set in the reactor with a pH of 11.2, an ammonia concentration of 0.3 mol / L, and a temperature of 70°C; nitrogen gas is introduced into the reactor and stirred continuously at a stirring speed of 300 r / min;

[0137] (3) The first solution, precipitant solution (2 mol / L sodium hydroxide solution), and complexing agent solution (ammonia) are introduced into the bottom solution in parallel to co-precipitate until the particle size D50 reaches 3 μm; then the second solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 5 μm; the first solution is stopped, and the co-precipitation reaction continues until D50 reaches 6 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 9 μm; then the second solution is stopped, and the third solution, zirconium salt solution, and niobium salt solution are introduced in parallel to continue the co-precipitation reaction until the particle size D50 reaches 11 μm; the zirconium salt solution and niobium salt solution are stopped, and the co-precipitation reaction continues until the particle size D50 reaches 12 μm;

[0138] When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:9.

[0139] The coprecipitation reaction was carried out at a temperature of 60℃, a pH of 11, and an ammonia concentration of 0.3 mol / L.

[0140] (4) After washing, drying and sieving, a three-stage core-shell structured ternary precursor is obtained.

[0141] Performance Characterization

[0142] The precursors prepared in the above examples and comparative examples were mixed with LiOH, with a molar ratio of LiOH to precursor of 1.03:1. The mixture was then heated to 300°C for 3 hours for pre-calcination, followed by further heating to 800°C and holding for 15 hours before being cooled in the furnace to obtain the cathode material.

[0143] The positive electrode material, polyvinylidene fluoride, and acetylene black were mixed in a mass ratio of 80:10:10, NMP (N-methylpyrrolidone) was added, and the mixture was stirred to form a slurry. This slurry was then coated onto aluminum foil, dried, and used as the positive electrode. A lithium sheet was used as the negative electrode to assemble a CR2025 coin cell. The electrochemical performance of the battery was tested at 2.8V to 4.3V, and the results are shown in Table 1.

[0144] Table 1

[0145]

[0146]

[0147] In summary, this invention introduces a high-nickel first solution in the initial stage of the co-precipitation reaction to form a core, providing a high-capacity foundation for the material. As the co-precipitation reaction progresses, a second and third solution with gradually decreasing nickel content are introduced, along with the staged addition of doping solutions, resulting in a gradient core-shell structure with decreasing nickel content from the core to the surface and an orderly distribution of dopant elements. This structure can alleviate the volume expansion stress in the high-nickel region during charge-discharge cycles, while the relatively low-nickel outer layer can suppress lattice distortion, reduce particle breakage and interfacial side reactions, thereby improving cycle stability. Furthermore, the synergy between the low-nickel outer layer and the doping elements enhances stability and reduces the Li+ content at high temperatures. + The risk of structural collapse due to insertion / extraction is significantly reduced, and thermal stability is significantly improved. In addition, the step-like growth of particle size at each stage ensures a smooth transition at the gradient interface, avoids stress concentration, and further enhances cycling performance and thermal stability.

[0148] The applicant declares that the above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a three-stage core-shell structure ternary precursor, characterized in that, The preparation method includes the following steps: In a protective atmosphere, a first solution, a precipitant solution, and a complexing agent solution are introduced concurrently into the base solution for co-precipitation until the median particle size D50 reaches 2.5 μm to 3.5 μm. Then, a second solution and a doping solution are introduced concurrently, and the co-precipitation reaction continues until the median particle size D50 reaches 4.5 μm to 5.5 μm. The introduction of the first solution is stopped, and the co-precipitation reaction continues until the median particle size D50 reaches 5.5 μm to 6.5 μm. The introduction of the doping solution is stopped, and the co-precipitation reaction continues until the median particle size D50 reaches 8.5 μm to 9.5 μm. Then, a third solution and a doping solution are introduced concurrently, and the co-precipitation reaction continues until the median particle size D50 reaches 9.5 μm to 10.5 μm. The introduction of the second solution is stopped, and the co-precipitation reaction continues until the median particle size D50 reaches 10.5 μm to 11.5 μm. The introduction of the doping solution is stopped, and the co-precipitation reaction continues until the median particle size D50 reaches 11.5 μm to 12.5 μm. After washing, drying and sieving, the three-segment core-shell structured ternary precursor was obtained; The first solution is a nickel salt solution; The concentration of the first solution is 2 mol / L to 4 mol / L; The second solution is a nickel-cobalt-manganese mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese is x:y:(1-xy), 0.8≤x≤0.9, 0≤y≤0.1; the concentration of the second solution is 2mol / L~4mol / L; The third solution is a nickel-cobalt-manganese mixed salt solution, wherein the molar ratio of nickel, cobalt and manganese is a:b:(1-ab), a≤0.4, 0≤b≤0.3; the concentration of the third solution is 2mol / L~4mol / L; The doping solution includes a zirconium salt solution and a niobium salt solution, wherein the concentration of the zirconium salt solution is 0.05 mol / L to 0.15 mol / L, and the concentration of the niobium salt solution is 0.05 mol / L to 0.15 mol / L. When the doped solution is introduced, the ratio of the flow rate of the doped solution to the total flow rate of the first solution, the second solution, and the third solution is 1:(8~12).

2. The production method according to claim 1, characterized by, The temperature of the coprecipitation reaction is 40℃~80℃.

3. The preparation method according to claim 1, characterized in that, The pH value of the coprecipitation reaction is 10.5~11.

5.

4. The preparation method according to claim 1, characterized in that, During the coprecipitation reaction, the concentration of the complexing agent in the system is 0.1 mol / L to 0.5 mol / L.

5. The preparation method according to claim 1, characterized in that, The stirring speed during the coprecipitation reaction is 200 r / min to 400 r / min.

6. The method of claim 1, wherein, The precipitant in the precipitant solution includes sodium hydroxide.

7. The preparation method according to claim 1, characterized in that, The complexing agent in the complexing agent solution includes any one or a combination of at least two of ammonia, citric acid, or sodium citrate.

8. A three-stage core-shell structure ternary precursor, characterized in that, The three-segment core-shell ternary precursor is prepared by the preparation method described in any one of claims 1 to 7.

9. A method for producing a positive electrode material, characterized by, The preparation method includes the following steps: mixing a lithium source with the three-stage core-shell structure ternary precursor of claim 8, pre-calcining and then calcining to obtain the cathode material.

10. A positive electrode material, characterized in that, The cathode material is prepared by the preparation method described in claim 9.

11. A positive electrode, characterized by comprising: The positive electrode comprises the positive electrode material as described in claim 10.

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