A dual-gradient cathode precursor material, its preparation method and application

Abstract

This invention provides a dual-gradient cathode precursor material, its preparation method, and its application. The dual-gradient cathode precursor material includes a gradient core and a gradient shell covering the gradient core. The gradient shell includes an inner surface and an outer surface, with the inner surface close to the gradient core and the outer surface away from the gradient core. The gradient core includes nickel, manganese, and dopant elements, while the gradient shell includes nickel, cobalt, and manganese. From the core of the gradient core to the outer surface of the gradient shell, the nickel content gradually decreases, while the manganese content gradually increases. From the core of the gradient core to its surface, the dopant content gradually decreases. From the inner surface of the gradient shell to its outer surface, the cobalt content gradually increases. The dual-gradient cathode precursor material of this invention, through its dual-gradient design in composition and structure, can significantly improve the structural stability of the material, thereby significantly improving the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a dual-gradient cathode precursor material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries possess advantages such as high operating voltage, high energy density, good rate performance, high safety, long cycle life, low self-discharge, and no memory effect, making them widely used in electric vehicles and mobile devices. The cathode material significantly impacts the electrochemical performance and cost of lithium-ion batteries. High-nickel cathode materials, with their relatively high specific energy and operating voltage, have become the most commercially promising cathode materials. However, the excessively high Ni content in high-nickel materials, while increasing the specific capacity, can also compromise the material's structural stability. The highly active Ni generated during charging... 4+ The reaction with the electrolyte will generate a NiO-like rock salt phase, which will severely damage the structure of the layered material and cause the cathode material structure to collapse.

[0003] Since the precursor of the cathode material is used as the raw material for the preparation of the cathode material, the physicochemical properties and electrochemical performance of the cathode material mainly depend on the morphology, microstructure, particle size and tap density of the precursor. Therefore, it is necessary to improve the composition and structure of the precursor material to improve the problems caused by the excessive Ni content in high-nickel cathode materials. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-gradient cathode precursor material, its preparation method and application. The dual-gradient cathode precursor material, through a dual-gradient design of composition and structure, can significantly improve the structural stability of the material, solve the problems caused by high nickel content, and thus significantly improve the electrochemical performance of the battery.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a dual-gradient cathode precursor material, the dual-gradient cathode precursor material comprising a gradient core and a gradient shell covering the gradient core, the gradient shell comprising an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is far from the gradient core;

[0007] The gradient core includes nickel, manganese, and doping elements, and the gradient shell includes nickel, cobalt, and manganese. From the core of the gradient core to the outer surface of the gradient shell, the content of nickel gradually decreases and the content of manganese gradually increases.

[0008] From the core of the gradient kernel to its surface, the content of doped elements gradually decreases until it stops.

[0009] The cobalt content gradually increases from the inner surface of the gradient shell to the outer surface of the gradient shell.

[0010] The dual-gradient cathode precursor material of this invention contains nickel, manganese, cobalt, and doping elements. On the one hand, in the overall precursor material particles, the content of nickel gradually decreases from the inside to the outside, while the content of manganese gradually increases from the inside to the outside, so that nickel and manganese form a gradient distribution overall. On the other hand, the overall material particles of this invention are divided into a gradient core and a gradient shell on the surface of the gradient core. The doping elements are only gradient-distributed in the gradient core, and the gradient distribution of the doping elements is the same as that of nickel, both of which have a gradually decreasing content. The gradient core forms a cobalt-free nickel-manganese precursor material containing doped elements, thereby effectively improving the stability of the material, reducing lithium-nickel mixing, and solving the problem caused by the high nickel content in the gradient core. The cobalt element of this invention is only gradient-distributed in the gradient shell, making the gradient shell a gradient-distributed nickel-cobalt-manganese precursor material, further improving the structural stability of the material.

[0011] Preferably, the chemical formula of the dual-gradient cathode precursor material is Ni. x Co y Mn z M a (OH)₂, where 0.8 ≤ x < 1, for example, 0.8, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96 or 0.98; 0 < y ≤ 0.2, for example, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17 or 0.2; 0 < z ≤ 0.2, for example, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17 or 0.2; 0 < a ≤ 0.1, for example, 0.01, 0.03, 0.05, 0.07, 0.09 or 0.1; x + y + z + a = 1; and M is a dopant element.

[0012] Preferably, M includes any one or a combination of at least two of Nb, Mo, or Ta.

[0013] The doping elements in the gradient kernel described in this invention are selected from high-valence elements such as Nb, Mo, or Ta. After doping, high-valence elements may accumulate along the crystal boundary, which can play a role in fixing and protecting the crystal, thereby improving the crystal structure strength, strengthening the microstructure, and increasing the crystallinity of the material. Therefore, the performance of the precursor material can be maximized.

[0014] Preferably, in the dual-gradient cathode precursor material, the molar ratio of nickel in the gradient core to nickel in the gradient shell is (0.7-0.95):(0.05-0.3), for example, it can be 0.7:0.3, 0.8:0.2, 0.9:0.1, or 0.95:0.05, but is not limited to the listed values; other unlisted values ​​within the range are also applicable. Gradient core, gradient shell

[0015] In the dual-gradient cathode precursor material of the present invention, the nickel content of the gradient core and the gradient shell is within a specific range, which can further enhance the combination effect of the gradient core and the gradient shell, promote the gradient distribution effect, and thus further improve the electrochemical performance of the material.

[0016] Secondly, the present invention provides a method for preparing a dual-gradient cathode precursor material as described in the first aspect, the method comprising the following steps:

[0017] A co-precipitation reaction is carried out on a high-nickel manganese solution, a medium-low nickel manganese solution, a dopant source solution, a precipitant solution, and a complexing agent solution to obtain a gradient core. Then, the dopant source solution is replaced with a cobalt source solution, and the co-precipitation reaction is continued to coat the surface of the gradient core with a gradient shell to obtain the dual-gradient cathode precursor material.

[0018] During the coprecipitation reaction, the flow rate of the high-nickel manganese solution gradually decreases, while the flow rate of the medium-low-nickel manganese solution gradually increases. When preparing the gradient core, the flow rate of the dopant source solution gradually decreases until the gradient core is obtained and then pauses. When preparing the gradient shell, the flow rate of the cobalt source solution gradually increases.

[0019] This invention employs a high-nickel manganese solution and a medium-low nickel manganese solution as feedstocks, and controls the feed flow rate to gradually reduce the nickel content and gradually increase the manganese content in the particles. Furthermore, after obtaining the gradient core through the co-precipitation reaction, the dopant source solution is replaced with a cobalt source solution to continue the co-precipitation reaction, thereby obtaining a gradient shell on the surface of the gradient core. Therefore, this invention can obtain the dual-gradient cathode precursor material through only one co-precipitation reaction.

[0020] Preferably, in the manganese-containing high-nickel solution, the molar ratio of manganese ions to nickel ions is (0-0.2):(0.8-1), but does not include 0:(0.8-1). For example, it can be 0.02:0.98, 0.05:0.95, 0.1:0.9 or 0.2:0.8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the total metal ion concentration in the manganese-containing high-nickel solution is 1.0-3.0 mol / L, for example, it can be 1.0 mol / L, 2.0 mol / L or 3.0 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, in the manganese-containing low-nickel solution, the molar ratio of manganese ions to nickel ions is (0.05-0.5):(0.5-0.85), for example, it can be 0.15:0.85, 0.25:0.75, 0.35:0.65 or 0.5:0.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the total metal ion concentration in the manganese-containing low-nickel solution is 1.0-3.0 mol / L, for example, it can be 1.0 mol / L, 2.0 mol / L or 3.0 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the pH of the coprecipitation reaction is 9-11.5, for example, 9, 10, 11 or 11.5, and the ammonia concentration is 0.1-10 g / L, for example, 0.1 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L or 10 g / L, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the process involves passing a high-nickel manganese solution, a medium-low nickel manganese solution, a dopant source solution, a precipitant solution, and a complexing agent solution into the base solution to perform a co-precipitation reaction.

[0026] Preferably, the pH of the base solution is 9-12, for example, 9, 10, 11 or 12, and the ammonia concentration is 0.1-5 g / L, for example, 0.1 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L or 5 g / L, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the temperature of the coprecipitation reaction is 30-80℃, for example, it can be 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the concentration of the precipitant solution is 9-12 mol / L, for example, it can be 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the precipitant solution comprises sodium hydroxide or potassium hydroxide.

[0030] Preferably, the concentration of the complexing agent solution is 6-10 mol / L, for example, it can be 6 mol / L, 8 mol / L or 10 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the complexing agent solution comprises ammonia.

[0032] Preferably, the coprecipitation reaction is carried out in a protective gas, which includes nitrogen and / or argon.

[0033] Preferably, after the coprecipitation reaction is completed, aging, solid-liquid separation, washing and drying are also performed.

[0034] In a second aspect, the present invention provides a cathode material, which is obtained by mixing and sintering a lithium source and a dual-gradient cathode precursor material as described in the first aspect.

[0035] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode material as described in the second aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The dual-gradient cathode precursor material of this invention achieves a gradient distribution of nickel and manganese by gradually decreasing the nickel content from the inside out and gradually increasing the manganese content from the inside out. Furthermore, the material particles are divided into a gradient core and a gradient shell on the surface of the gradient core. Doping elements are only distributed in the gradient core, and their gradient distribution is the same as that of nickel, with both gradually decreasing in content. This creates a gradient-distributed, cobalt-free nickel-manganese precursor material containing doped elements within the gradient core, effectively improving material stability, reducing lithium-nickel mixing, and solving the problem caused by high nickel content in the gradient core. Additionally, the cobalt element is only distributed in the gradient shell, making the gradient shell a gradient-distributed nickel-cobalt-manganese precursor material, further enhancing the structural stability of the material. Attached Figure Description

[0038] Figure 1 This is a SEM image of the dual-gradient cathode precursor material described in Embodiment 1 of the present invention. Detailed Implementation

[0039] 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.

[0040] Example 1

[0041] This embodiment provides a dual-gradient cathode precursor material, the chemical formula of which is Ni. 0.8 Co 0.05 Mn 0.1 Nb 0.05 (OH)2, the dual-gradient cathode precursor material includes a gradient core and a gradient shell with a nickel content molar ratio of 0.85:0.15, where the gradient core is coated with a gradient shell and the gradient shell is coated with a gradient shell.

[0042] The gradient shell includes an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is far from the gradient core; from the core of the gradient core to the outer surface of the gradient shell, the content of nickel gradually decreases and the content of manganese gradually increases; from the core of the gradient core to the surface of the gradient core, the content of Nb gradually decreases; from the inner surface of the gradient shell to the outer surface of the gradient shell, the content of cobalt gradually increases.

[0043] The preparation method of the dual-gradient cathode precursor material includes the following steps:

[0044] According to the formulation, under a nitrogen atmosphere, a high-nickel manganese solution, a medium-low nickel manganese solution, an Nb source solution (sodium niobate solution), a sodium hydroxide solution, and ammonia water were introduced into a base solution (pH 11, ammonia concentration 2 g / L). A co-precipitation reaction was carried out at 50°C, a pH range of 9.8-10.5, and an ammonia concentration of 3-4 g / L. Then, the dopant source solution was replaced with a cobalt source solution (cobalt sulfate solution), and the co-precipitation reaction continued. After aging, solid-liquid separation, washing, and drying, the dual-gradient cathode precursor material was obtained. The SEM image of the dual-gradient cathode precursor material is shown below. Figure 1 As shown;

[0045] During the coprecipitation reaction, the flow rate of the high-nickel manganese solution gradually decreases, the flow rate of the medium-low nickel manganese solution gradually increases, the flow rate of the dopant source solution gradually decreases, and the flow rate of the cobalt source solution gradually increases.

[0046] The manganese-containing high-nickel solution has a manganese ion to nickel ion molar ratio of 0.05:0.95 and a total metal ion concentration of 2 mol / L; the manganese-containing medium-low-nickel solution has a nickel-manganese molar ratio of 0.7:0.3 and a total metal ion concentration of 2 mol / L; the sodium hydroxide solution has a concentration of 10 mol / L and the ammonia solution has a concentration of 5 mol / L.

[0047] Example 2

[0048] This embodiment provides a dual-gradient cathode precursor material, the chemical formula of which is Ni.0.9 Co 0.02 Mn 0.05 Ta 0.03 (OH)2, the dual-gradient cathode precursor material includes a gradient core and a gradient shell with a nickel content molar ratio of 0.95:0.05, where the gradient core is coated with nickel and the gradient shell is coated with nickel.

[0049] The gradient shell includes an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is far from the gradient core; from the core of the gradient core to the outer surface of the gradient shell, the content of nickel gradually decreases and the content of manganese gradually increases; from the core of the gradient core to the surface of the gradient core, the content of Ta gradually decreases; from the inner surface of the gradient shell to the outer surface of the gradient shell, the content of cobalt gradually increases.

[0050] The preparation method of the dual-gradient cathode precursor material includes the following steps:

[0051] According to the formula, under a nitrogen atmosphere, a high-nickel manganese solution, a medium-low nickel manganese solution, a Ta source solution (sodium tantalate solution), a sodium hydroxide solution, and ammonia water are introduced into a base solution (the pH of the base solution is 12, and the ammonia concentration is 3 g / L). A co-precipitation reaction is carried out at 40°C, a pH of 10-10.8, and an ammonia concentration of 3.8-5.2 g / L. Then, the dopant source solution is replaced with a cobalt source solution (cobalt sulfate solution), and the co-precipitation reaction continues. After aging, solid-liquid separation, washing, and drying, the dual-gradient cathode precursor material is obtained.

[0052] During the coprecipitation reaction, the flow rate of the high-nickel manganese solution gradually decreases, the flow rate of the medium-low nickel manganese solution gradually increases, the flow rate of the dopant source solution gradually decreases, and the flow rate of the cobalt source solution gradually increases.

[0053] The manganese-containing high-nickel solution has a manganese ion to nickel ion molar ratio of 0.02:0.98 and a total metal ion concentration of 2.4 mol / L; the manganese-containing medium-low-nickel solution has a nickel-manganese molar ratio of 0.8:0.2 and a total metal ion concentration of 1.0 mol / L; the sodium hydroxide solution has a concentration of 12 mol / L and the ammonia solution has a concentration of 10 mol / L.

[0054] Example 3

[0055] This embodiment provides a dual-gradient cathode precursor material, the chemical formula of which is Ni. 0.8 Co 0.05 Mn 0.1 Nb 0.05(OH)2, the dual-gradient cathode precursor material includes a gradient core and a gradient shell, wherein the molar ratio of nickel content in the gradient core to nickel content in the gradient shell is 0.80:0.20.

[0056] The gradient shell includes an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is far from the gradient core; from the core of the gradient core to the outer surface of the gradient shell, the content of nickel gradually decreases and the content of manganese gradually increases; from the core of the gradient core to the surface of the gradient core, the content of Nb gradually decreases; from the inner surface of the gradient shell to the outer surface of the gradient shell, the content of cobalt gradually increases.

[0057] The preparation method of the dual-gradient cathode precursor material includes the following steps:

[0058] According to the formula, under a nitrogen atmosphere, a high-nickel manganese solution, a medium-low nickel manganese solution, an Nb source solution (sodium niobate solution), a sodium hydroxide solution, and ammonia water are introduced into a base solution (the pH of the base solution is 11, and the ammonia concentration is 2 g / L). A co-precipitation reaction is carried out at 60°C, pH 11, and an ammonia concentration of 2 g / L. Then, the dopant source solution is replaced with a cobalt source solution (cobalt sulfate solution), and the co-precipitation reaction continues. After aging, solid-liquid separation, washing, and drying, the dual-gradient cathode precursor material is obtained.

[0059] During the coprecipitation reaction, the flow rate of the high-nickel manganese solution gradually decreases, the flow rate of the medium-low nickel manganese solution gradually increases, the flow rate of the dopant source solution gradually decreases, and the flow rate of the cobalt source solution gradually increases.

[0060] The manganese-containing high-nickel solution has a manganese ion to nickel ion molar ratio of 0.1:0.9 and a total metal ion concentration of 2.6 mol / L; the manganese-containing medium-low-nickel solution has a nickel-manganese molar ratio of 0.65:0.35 and a total metal ion concentration of 3.0 mol / L; the sodium hydroxide solution has a concentration of 9 mol / L and the ammonia solution has a concentration of 5 mol / L.

[0061] Example 4

[0062] This embodiment provides a dual-gradient cathode precursor material, which is the same as that in Embodiment 1 except that Nb is replaced with Al in equimolar amounts.

[0063] Example 5

[0064] This embodiment provides a dual-gradient cathode precursor material, which is the same as that in Example 1 except that Nb is replaced with Mg in equal molar amounts.

[0065] Example 6

[0066] This embodiment provides a dual-gradient cathode precursor material. Except for the molar ratio of nickel content in the gradient core to nickel content in the gradient shell being 0.75:0.25, which allows the molecular formula of the dual-gradient cathode precursor material to adapt to the gradient shell, the rest of the dual-gradient cathode precursor material is the same as in Embodiment 1.

[0067] Example 7

[0068] This embodiment provides a dual-gradient cathode precursor material. Except for the molar ratio of nickel content in the gradient core to nickel content in the gradient shell being 0.99:0.01, which allows the molecular formula of the dual-gradient cathode precursor material to adapt to the gradient shell, the rest of the dual-gradient cathode precursor material is the same as in Embodiment 1.

[0069] Comparative Example 1

[0070] This comparative example provides a cathode precursor material. The dual-gradient cathode precursor material is the same as in Example 1, except that the Nb source solution is not introduced in its preparation method, the cobalt source solution is continuously introduced during the co-precipitation reaction so that the obtained dual-gradient cathode precursor material does not contain Nb, and the cobalt content gradually increases from the particle core to the outer surface.

[0071] Comparative Example 2

[0072] This comparative example provides a cathode precursor material. The dual-gradient cathode precursor material is the same as in Example 1, except that the Nb source solution is not replaced with a cobalt source solution in its preparation method, so that the obtained dual-gradient cathode precursor material does not contain Co, and the Nb content gradually decreases from the particle core to the outer surface.

[0073] Comparative Example 3

[0074] This comparative example provides a cathode precursor material. Except for the fact that the contents of nickel, cobalt, manganese and Nb do not change in a gradient, and the flow rate of the solution does not change in the preparation method, the cathode precursor material is the same as that in Example 1.

[0075] The cathode precursor materials obtained in the above examples and comparative examples were mixed with lithium hydroxide, then heated at 400°C for 4 hours, and then heated at 800°C for 8 hours to obtain the cathode material, which was then used to prepare a cathode sheet. This sheet was then combined with a lithium sheet, a polyethylene separator, and a lithium hexafluorophosphate electrolyte to prepare a battery. The 0.1C discharge specific capacity and the capacity retention rate after 100 cycles were then tested. The test results are shown in Table 1.

[0076] Table 1

[0077]

[0078] As can be seen from the table above:

[0079] As shown in Example 1 and Comparative Examples 1-3, the cathode precursor material of the present invention is a dual-gradient material, wherein the doping element and the Co element cooperate to achieve dual gradients, effectively improving the stability of the material, reducing lithium-nickel mixing, and improving the electrochemical performance of the battery. As shown in Example 1 and Examples 4-5, the doping element in the gradient core of the present invention is preferably a high-valence element such as Nb, Mo, or Ta, which can achieve crystal boundary accumulation. Unlike the doping mechanism of Al and Mg, it can further improve the electrochemical performance of the precursor material. As shown in Example 1 and Examples 6-7, in the dual-gradient doping of the present invention, the contents of the gradient core and the gradient shell need to be matched to promote the effect of dual-gradient doping, thereby further improving the electrochemical performance of the precursor material.

[0080] In summary, this invention provides a dual-gradient cathode precursor material, its preparation method, and its application. The dual-gradient cathode precursor material, through a dual-gradient design of composition and structure, can significantly improve the structural stability of the material, solve the problems caused by high nickel content, and thus significantly improve the electrochemical performance of the battery.

[0081] 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 dual-gradient cathode precursor material, characterized in that, The dual-gradient cathode precursor material includes a gradient core and a gradient shell covering the gradient core. The gradient shell includes an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is away from the gradient core. The gradient core includes nickel, manganese, and doping elements. The doping elements include any one or a combination of at least two of Nb, Mo, or Ta. The gradient shell includes nickel, cobalt, and manganese. From the core of the gradient core to the outer surface of the gradient shell, the content of nickel gradually decreases and the content of manganese gradually increases. From the core of the gradient kernel to its surface, the content of doped elements gradually decreases until it stops. The cobalt content gradually increases from the inner surface of the gradient shell to the outer surface of the gradient shell.

2. The dual-gradient cathode precursor material according to claim 1, characterized in that, The chemical formula of the dual-gradient cathode precursor material is Ni. x Co y Mn z M a (OH)2, where 0.8≤x<1, 0<y≤0.2, 0<z≤0.2, 0<a≤0.1, x+y+z+a=1, and M is a dopant element.

3. The dual-gradient cathode precursor material according to claim 2, characterized in that, The M includes any one or a combination of at least two of Nb, Mo, or Ta.

4. The dual-gradient cathode precursor material according to claim 1, characterized in that, In the dual-gradient cathode precursor material, the molar ratio of nickel in the gradient core to nickel in the gradient shell is (0.7-0.95):(0.05-0.3).

5. A method for preparing a dual-gradient cathode precursor material as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: A co-precipitation reaction is carried out on a high-nickel manganese solution, a medium-low nickel manganese solution, a dopant source solution, a precipitant solution, and a complexing agent solution to obtain a gradient core. Then, the dopant source solution is replaced with a cobalt source solution, and the co-precipitation reaction is continued to coat the surface of the gradient core with a gradient shell to obtain the dual-gradient cathode precursor material. During the coprecipitation reaction, the flow rate of the high-nickel manganese solution gradually decreases, while the flow rate of the medium-low-nickel manganese solution gradually increases. When preparing the gradient core, the flow rate of the dopant source solution gradually decreases until the gradient core is obtained and then pauses. When preparing the gradient shell, the flow rate of the cobalt source solution gradually increases.

6. The preparation method according to claim 5, characterized in that, In the manganese-containing high-nickel solution, the molar ratio of manganese ions to nickel ions is (0-0.2):(0.8-1), but does not include 0:(0.8-1).

7. The preparation method according to claim 5, characterized in that, The total metal ion concentration in the manganese-containing high-nickel solution is 1.0-3.0 mol / L.

8. The preparation method according to claim 5, characterized in that, In the manganese-containing low-nickel solution, the molar ratio of manganese ions to nickel ions is (0.05-0.5):(0.5-0.85).

9. The preparation method according to claim 5, characterized in that, The total metal ion concentration in the manganese-containing low-nickel solution is 1.0-3.0 mol / L.

10. The preparation method according to claim 5, characterized in that, The pH of the coprecipitation reaction is 9-11.5, and the ammonia concentration is 0.1-10 g / L.

11. The preparation method according to claim 5, characterized in that, The process involves passing a high-nickel manganese solution, a medium-low nickel manganese solution, a doped element source solution, a precipitant solution, and a complexing agent solution into the base liquid to carry out a co-precipitation reaction.

12. The preparation method according to claim 11, characterized in that, The pH of the substrate solution is 9-12, and the ammonia concentration is 0.1-5 g / L.

13. The preparation method according to claim 11, characterized in that, The temperature for the coprecipitation reaction is 30-80℃.

14. The preparation method according to claim 11, characterized in that, The concentration of the precipitant solution is 9-12 mol / L.

15. The preparation method according to claim 11, characterized in that, The concentration of the complexing agent solution is 6-10 mol / L.

16. The preparation method according to claim 11, characterized in that, The coprecipitation reaction is carried out in a protective gas, which includes nitrogen and / or argon.

17. The preparation method according to claim 11, characterized in that, After the coprecipitation reaction was completed, aging, solid-liquid separation, washing, and drying were carried out.

18. A positive electrode material, characterized in that, The cathode material is obtained by mixing and sintering a lithium source and a dual-gradient cathode precursor material as described in any one of claims 1-4.

19. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in claim 18.

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