Double-gradient positive electrode precursor material and preparation method and application thereof

Abstract

The invention provides a double-gradient positive electrode precursor material and a preparation method and application thereof.The double-gradient positive electrode precursor material comprises a gradient inner core and a gradient shell wrapping the gradient inner core, the gradient shell comprises an inner surface and an outer surface, the inner surface is close to the gradient inner core, and the outer surface is far away from the gradient inner core; the gradient inner core comprises a nickel element, a manganese element and a doping element, the gradient shell comprises a nickel element, a cobalt element and a manganese element, and the content of the nickel element is gradually reduced and the content of the manganese element is gradually increased from the core of the gradient inner core to the outer surface of the gradient shell; the content of the doped elements is gradually reduced from the core of the gradient core to the surface of the gradient core; and the content of the cobalt element is gradually increased from the inner surface of the gradient shell to the outer surface of the gradient shell. According to the double-gradient positive electrode precursor material, through composition and structure double-gradient design, the structural stability of the material can be remarkably improved, so that the electrochemical performance of a battery is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a dual-gradient positive electrode precursor material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, high energy density, good rate performance, high safety, long cycle life, low self-discharge and no memory effect. They are widely used in electric vehicles and mobile devices. The positive electrode material has a great influence on the electrochemical performance and cost of lithium-ion batteries. High-nickel positive electrode materials have relatively high specific energy and operating voltage, making them the most commercially promising positive electrode materials. However, the excessive Ni content in high-nickel materials will not only increase the gram capacity of the material, but also destroy the structural stability of the material. The highly active Ni generated during the charging process 4+ The reaction with the electrolyte will generate a NiO-like rock salt phase, which seriously damages the structure of the layered material and causes the collapse of the positive electrode material structure.

[0003] Since the cathode material precursor is 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 structure of the precursor material to improve the problems caused by excessive Ni content in high-nickel cathode materials. Summary of the invention

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

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a dual-gradient positive electrode precursor material, the dual-gradient positive electrode 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 away from the gradient core;

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

[0008] From the core of the gradient core to the surface of the gradient core, the content of the doping element gradually decreases until it stops;

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

[0010] The dual-gradient positive electrode precursor material described in the present invention contains nickel, manganese, cobalt and doping elements. On the one hand, in the overall precursor material particles, the content of nickel element gradually decreases from the inside to the outside, and the content of manganese element gradually increases from the inside to the outside, so that nickel and manganese form a gradient distribution on the whole; on the other hand, the overall material particles of the present invention are divided into a gradient core and a gradient shell on the surface of the gradient core, wherein the doping element is gradient distributed only in the gradient core, and the doping element is the same as the nickel element in gradient distribution, and the content of both gradually decreases, forming a gradient distribution of cobalt-free nickel-manganese precursor material containing doping elements in the gradient core, 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, and the cobalt element of the present invention is gradient distributed only in the gradient shell, so that the gradient shell is 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, wherein 0.8≤x<1, for example, it can be 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, it can be 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17 or 0.2, 0<z≤0.2, for example, it can be 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17 or 0.2, 0<a≤0.1, for example, it can be 0.01, 0.03, 0.05, 0.07, 0.09 or 0.1, x+y+z+a=1, and M is a doping element.

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

[0013] The doping elements in the gradient core of the present invention are selected from high-valent elements Nb, Mo or Ta. After doping, the high-valent elements may accumulate along the crystal boundaries, play a role in fixing and protecting the crystals, thereby improving the strength of the crystal structure, strengthening the microstructure, and improving the crystallinity of the material. Therefore, the performance of the precursor material can be maximized.

[0014] Preferably, in the dual-gradient positive electrode 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 it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. Gradient core gradient shell

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

[0016] In a second aspect, the present invention provides a method for preparing the dual gradient positive electrode precursor material as described in the first aspect, the preparation method comprising the following steps:

[0017] A manganese-containing high-nickel solution, a manganese-containing medium-low nickel solution, a doping element source solution, a precipitant solution and a complexing agent solution are subjected to a coprecipitation reaction to obtain a gradient core, and then the doping element source solution is replaced with a cobalt source solution, and the coprecipitation reaction is continued to coat the gradient core surface with a gradient shell to obtain the dual-gradient positive electrode precursor material;

[0018] During the coprecipitation reaction, the flow rate of the manganese-containing high-nickel solution gradually decreases, the flow rate of the manganese-containing medium-low nickel solution gradually increases, the flow rate of the doping element source solution gradually decreases when preparing the gradient core until the gradient core is obtained, and the flow rate of the cobalt source solution gradually increases when preparing the gradient shell.

[0019] The present invention adopts a manganese-containing high-nickel solution and a manganese-containing medium-low nickel solution for feeding and controls the feed flow rate, so that the content of nickel in the particles can be gradually reduced and the content of manganese can be gradually increased. In addition, after the gradient inner core is obtained by the coprecipitation reaction, the doping element source solution is replaced with a cobalt source solution to continue the coprecipitation reaction, so that a gradient outer shell can be obtained on the surface of the gradient inner core. Therefore, the present invention can obtain the dual-gradient positive electrode precursor material through only a one-step coprecipitation 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, and other unlisted values ​​within the numerical 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, 1.0 mol / L, 2.0 mol / L or 3.0 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, in the manganese-containing medium-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, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the total metal ion concentration in the manganese-containing medium-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, and other unlisted values ​​within the numerical 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the manganese-containing high-nickel solution, the manganese-containing medium-low nickel solution, the doping element source solution, the precipitant solution and the complexing agent solution are introduced into the base solution to carry out 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 is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the coprecipitation reaction temperature is 30-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the concentration of the precipitant solution is 9-12 mol / L, for example, 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical 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, 6 mol / L, 8 mol / L or 10 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

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

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

[0035] In a third aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises 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 positive electrode precursor material of the present invention gradually reduces the content of nickel from the inside to the outside and gradually increases the content of manganese from the inside to the outside, so that nickel and manganese form a gradient distribution on the whole; and the overall material particles of the invention are divided into a gradient core and a gradient shell on the surface of the gradient core, wherein the doping element is gradient distributed only in the gradient core, and the doping element is the same as the nickel element in gradient distribution, and the content of both is gradually reduced, and a gradient-distributed cobalt-free nickel-manganese precursor material containing doping elements is formed in the gradient core, 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, and the cobalt element of the present invention is gradient distributed only in the gradient shell, so that the gradient shell is a gradient-distributed nickel-cobalt-manganese precursor material, further improving the structural stability of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a SEM image of the dual-gradient positive electrode precursor material described in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Example 1

[0041] This embodiment provides a dual-gradient positive electrode 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 positive electrode precursor material includes a gradient core and a nickel content of the gradient core and a nickel content of the gradient shell covering the gradient core, the molar ratio of which is 0.85:0.15 gradient shell gradient core gradient shell;

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

[0043] The preparation method of the dual gradient positive electrode precursor material comprises the following steps:

[0044] According to the formula, in a nitrogen atmosphere, a manganese-containing high-nickel solution, a manganese-containing medium-low nickel solution, a Nb source solution (sodium niobate solution), a sodium hydroxide solution and ammonia water are introduced into a base liquid (the pH of the base liquid is 11 and the ammonia concentration is 2 g / L), and a coprecipitation reaction is carried out at 50° C., a pH range of 9.8-10.5 and an ammonia concentration of 3-4 g / L. Then, the doping element source solution is replaced with a cobalt source solution (cobalt sulfate solution), and the coprecipitation reaction is continued. After aging, solid-liquid separation, washing and drying, the dual-gradient positive electrode precursor material is obtained. The SEM image of the dual-gradient positive electrode precursor material is as shown in Figure 1 As shown;

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

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

[0047] Example 2

[0048] This embodiment provides a dual-gradient positive electrode precursor material, the chemical formula of which is Ni0.9 Co 0.02 Mn 0.05 Ta 0.03 (OH)2, the dual gradient positive electrode precursor material includes a gradient core and a nickel content of the gradient core and a nickel content of the gradient shell covering the gradient core, the molar ratio of which is 0.95:0.05 gradient shell gradient core gradient shell;

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

[0050] The preparation method of the dual gradient positive electrode precursor material comprises the following steps:

[0051] According to the formula, in a nitrogen atmosphere, a manganese-containing high-nickel solution, a manganese-containing medium-low nickel solution, a Ta source solution (sodium tantalate solution), a sodium hydroxide solution and ammonia water are introduced into a base liquid (the pH of the base liquid is 12 and the ammonia concentration is 3 g / L), and a coprecipitation reaction is carried out at 40° C., a pH of 10-10.8 and an ammonia concentration of 3.8-5.2 g / L, and then the doping element source solution is replaced with a cobalt source solution (cobalt sulfate solution), and the coprecipitation reaction is continued, and then aging, solid-liquid separation, washing and drying are carried out to obtain the dual-gradient positive electrode precursor material;

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

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

[0054] Example 3

[0055] This embodiment provides a dual-gradient positive electrode 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 positive electrode precursor material includes a gradient core and a nickel content of the gradient core and a nickel content of the gradient shell covering the gradient core, the molar ratio of which is 0.80:0.20 gradient shell gradient core gradient shell;

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

[0057] The preparation method of the dual gradient positive electrode precursor material comprises the following steps:

[0058] According to the formula, in a nitrogen atmosphere, a manganese-containing high-nickel solution, a manganese-containing medium-low nickel solution, a 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), and a coprecipitation reaction is carried out at 60° C., a pH of 11 and an ammonia concentration of 2 g / L, and then the doping element source solution is replaced with a cobalt source solution (cobalt sulfate solution), and the coprecipitation reaction is continued, and then aging, solid-liquid separation, washing and drying are carried out to obtain the dual-gradient positive electrode precursor material;

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

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

[0061] Example 4

[0062] This embodiment provides a dual-gradient positive electrode precursor material, which is the same as that of Embodiment 1 except that Nb is replaced by Al in equal moles.

[0063] Example 5

[0064] This embodiment provides a dual-gradient positive electrode precursor material, which is the same as that of Embodiment 1 except that Nb is replaced by Mg in equal moles.

[0065] Example 6

[0066] The present embodiment provides a dual-gradient positive electrode precursor material, which is the same as that of Embodiment 1 except that the molar ratio of the nickel content of the gradient inner core to the nickel content of the gradient outer shell is 0.75:0.25, so that the molecular formula of the dual-gradient positive electrode precursor material can be adaptively changed to the gradient outer shell.

[0067] Example 7

[0068] The present embodiment provides a dual-gradient positive electrode precursor material, which is the same as that of Embodiment 1 except that the molar ratio of the nickel content of the gradient inner core to the nickel content of the gradient outer shell is 0.99:0.01, so that the molecular formula of the dual-gradient positive electrode precursor material can be adaptively changed to the gradient outer shell.

[0069] Comparative Example 1

[0070] This comparative example provides a positive electrode precursor material. The dual-gradient positive electrode precursor material is the same as Example 1 except that in its preparation method, no Nb source solution is introduced, and the cobalt source solution is always introduced during the co-precipitation reaction, so that the obtained dual-gradient positive electrode precursor material does not contain Nb, and the content of cobalt element gradually increases from the core to the outer surface of the particle.

[0071] Comparative Example 2

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

[0073] Comparative Example 3

[0074] This comparative example provides a positive electrode precursor material, which is the same as Example 1 except that the nickel content, the content of the cobalt element, the manganese element and the Nb element do not change gradually, and in the preparation method, the flow rate of the solution does not change.

[0075] The positive electrode precursor material obtained in the above embodiments and comparative examples was mixed with lithium hydroxide, and then kept at 400°C for 4 hours, and then kept at 800°C for 8 hours to obtain a positive electrode material to prepare a positive electrode sheet, and then prepared into a battery with a lithium sheet, a polyethylene separator and a lithium hexafluorophosphate electrolyte, and then tested the 0.1C discharge specific capacity and the capacity retention rate of 100 cycles. The test results are shown in Table 1:

[0076] Table 1

[0077]

[0078] From the above table we can see that:

[0079] It can be seen from Example 1 and Comparative Examples 1-3 that the positive electrode precursor material of the present invention is a dual gradient material, in which the doping element and the Co element cooperate with each other to realize a dual gradient, effectively improving the stability of the material, reducing the lithium-nickel mixing, and improving the electrochemical performance of the battery; It can be seen from Example 1 and Examples 4-5 that the preferred doping elements in the gradient core of the present invention are high-valent elements such as Nb, Mo or Ta, which can achieve crystal boundary accumulation, which is different from the Al and Mg doping mechanism and can further improve the electrochemical performance of the precursor material; It can be seen from Example 1 and Examples 6-7 that in the dual gradient doping of the present invention, the contents of the gradient core and the gradient shell need to be matched with each other to promote the effect of dual gradient doping, thereby further improving the electrochemical performance of the precursor material.

[0080] In summary, the present invention provides a dual-gradient positive electrode precursor material and a preparation method and application thereof. The dual-gradient positive electrode precursor material can significantly improve the structural stability of the material through a dual-gradient design of composition and structure, 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 implementation mode 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 those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A dual-gradient cathode precursor material, characterized in that: The dual-gradient positive electrode precursor material comprises a gradient core and a gradient shell covering the gradient core, wherein the gradient shell comprises an inner surface and an outer surface, wherein the inner surface is close to the gradient core and the outer surface is far away from the gradient core; The gradient inner core comprises nickel, manganese and doping elements, and the gradient outer shell comprises nickel, cobalt and manganese. From the core of the gradient inner core to the outer surface of the gradient outer 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 the doping element gradually decreases until it stops; The content of cobalt element 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, wherein 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 doping element; Preferably, the M includes any one of Nb, Mo or Ta, or a combination of at least two of them.

3. The dual gradient cathode precursor material according to claim 1 or 2, characterized in that: In the dual-gradient positive electrode 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).

4. A method for preparing a dual gradient cathode precursor material as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: A manganese-containing high-nickel solution, a manganese-containing medium-low nickel solution, a doping element source solution, a precipitant solution and a complexing agent solution are subjected to a coprecipitation reaction to obtain a gradient core, and then the doping element source solution is replaced with a cobalt source solution, and the coprecipitation reaction is continued to coat the gradient core surface with a gradient shell to obtain the dual-gradient positive electrode precursor material; During the coprecipitation reaction, the flow rate of the manganese-containing high-nickel solution gradually decreases, the flow rate of the manganese-containing medium-low nickel solution gradually increases, the flow rate of the doping element source solution gradually decreases when preparing the gradient core until the gradient core is obtained, and the flow rate of the cobalt source solution gradually increases when preparing the gradient shell.

5. The preparation method according to claim 4, 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); Preferably, the total metal ion concentration in the manganese-containing high-nickel solution is 1.0-3.0 mol / L; Preferably, in the manganese-containing medium-low nickel solution, the molar ratio of manganese ions to nickel ions is (0.05-0.5):(0.5-0.85); Preferably, the total metal ion concentration in the manganese-containing medium-low nickel solution is 1.0-3.0 mol / L.

6. The preparation method according to claim 4 or 5, characterized in that: The pH of the coprecipitation reaction is 9-11.5, and the ammonia concentration is 0.1-10 g / L; Preferably, the manganese-containing high-nickel solution, the manganese-containing medium-low nickel solution, the doping element source solution, the precipitant solution and the complexing agent solution are introduced into the base solution to carry out a coprecipitation reaction; Preferably, the pH of the base solution is 9-12, and the ammonia concentration is 0.1-5 g / L.

7. The preparation method according to claim 4 or 5, characterized in that: The temperature of the coprecipitation reaction is 30-80°C; Preferably, the concentration of the precipitant solution is 9-12 mol / L; Preferably, the concentration of the complexing agent solution is 6-10 mol / L.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The coprecipitation reaction is carried out in a protective gas, wherein the protective gas comprises nitrogen and / or argon; Preferably, after the coprecipitation reaction is completed, aging, solid-liquid separation, washing and drying are further performed.

9. A positive electrode material, characterized in that: The positive electrode material is obtained by mixing and sintering a lithium source and a dual-gradient positive electrode precursor material as described in any one of claims 1 to 3.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material as claimed in claim 8.

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