A gradient-doped positive electrode precursor material, a preparation method therefor, and an application thereof

Abstract

This invention provides a gradient-doped cathode precursor material, its preparation method, and its application. The gradient-doped cathode precursor material includes a core and a shell, wherein the core and shell each independently comprise a ternary precursor material, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+ The cathode precursor material of this invention is doped with variable-valence tin through gradient doping, resulting in Sn doping in the core. 4+ Surface doped with Sn 2+ This effectively regulates the charge distribution in the cathode precursor material, which not only improves the stability of the cathode precursor material but also enhances its rate performance.

Description

Technical Field

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

[0002] With the development of electric vehicles, the market is increasingly demanding higher requirements for batteries in terms of high-current charge / discharge capabilities and long cycle life. Battery performance primarily depends on the cathode material, which in turn is strongly correlated with the precursor. Therefore, improving the physicochemical properties and morphology of the precursor is the most convenient way to optimize power batteries. Generally, high-current charge / discharge and long-term high-temperature cycling can cause irreversible damage to battery materials. This is mainly because the structure of the cathode material collapses under these conditions, leading to severe Li / Ni mixing and significantly hindering the lithium-ion intercalation / deintercalation process.

[0003] In the prior art, the cycle life problem is solved by coating the surface, but this causes the side effect of reduced power performance and capacity. For example, CN 115663126A discloses a cathode material and its preparation method, as well as a lithium-ion battery. The cathode material includes a lithium-nickel metal composite oxide and a coating layer. The lithium-nickel metal composite oxide is doped with N' element, which is a metal element. The coating layer is at least partially located on the surface of the lithium-nickel metal composite oxide and includes an organic framework material-inorganic metal compound. This cathode material effectively reduces residual alkali on the material surface and internal Li / Ni cation mixing.

[0004] For example, CN 115520904A discloses a cathode material precursor, its preparation method, and the cathode material. The precursor material comprises a core, an intermediate layer, and a shell layer sequentially bonded radially from the inside out. The materials of the core, intermediate layer, and shell layer all include a nickel-manganese-containing precursor. The precursor of the shell layer is also doped with metal elements. Furthermore, the porosity of the core is lower than that of the intermediate layer, and the porosity of the shell layer is lower than that of the intermediate layer. The cathode material precursor provided has a compact core, a loose and porous intermediate layer, and a dense shell layer, which can enhance the stability of the material structure and shorten the Li-C ratio. + Improving the transport path and reducing Li / Ni mixing can further enhance the stability of the material structure and improve the cycle stability of the cathode material at high temperatures.

[0005] However, although surface coating is the most convenient and effective way to solve material stability and Li / Ni mixing, there are still some problems: (1) Due to the lattice difference between the coating material and the bulk material, the coating material is easy to fall off; (2) The coating material is generally implemented through lithium calcination, and the uniformity of the coating layer is difficult to control accurately.

[0006] Based on the above research, there is a need to provide a gradient-doped cathode precursor material, which can fundamentally solve the problem of decreased stability and electrochemical performance caused by the material structure. Summary of the Invention

[0007] The purpose of this invention is to provide a gradient-doped cathode precursor material, its preparation method, and its application. The cathode precursor material is prepared by gradient doping with variable-valence tin, resulting in Sn doping in the core. 4+ Surface doped with Sn 2+ This effectively regulates the charge distribution in the cathode precursor material, which not only improves the stability of the cathode precursor material but also enhances its rate performance.

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

[0009] In a first aspect, the present invention provides a gradient-doped cathode precursor material, the gradient-doped cathode precursor material comprising a core and a shell, wherein the core and the shell each independently comprise a ternary precursor material, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+ .

[0010] Since the surface layer of the cathode material is in long-term contact with the electrolyte and is often in a highly oxidized state, this invention uses gradient doping to dope the core of the cathode precursor material with Sn. 4+ Sn is doped in the outer shell 2+ This effectively regulates the charge distribution in the precursor material, allowing the doping of the outer shell with low-valence elements to effectively prevent the dissolution of active elements in the material. At the same time, the gradient valence distribution in the material is conducive to electron diffusion, thereby improving the rate performance of the material.

[0011] Preferably, the ternary precursor material includes nickel-cobalt-manganese hydroxide.

[0012] Preferably, the ratio of the particle size D50 of the core to the thickness of the shell is 1:(0.1-1), for example, it can be 1:0.1, 1:0.3, 1:0.5, 1:0.7, 1:0.9 or 1:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] In a second aspect, the present invention provides a method for preparing a gradient-doped cathode precursor material as described in the first aspect, the method comprising the following steps:

[0014] A ternary metal salt solution, a precipitant solution, and a complexing agent solution are mixed and a co-precipitation reaction is carried out to obtain the gradient-doped cathode precursor material.

[0015] The ternary metal salt solution is doped with tin salt;

[0016] The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. At the end of the coprecipitation reaction, the content of oxygen-containing gas in the mixed atmosphere is less than the content of oxygen-containing gas in the mixed atmosphere at the beginning of the coprecipitation reaction.

[0017] This invention achieves regulation of the Sn valence state by controlling the overall oxidation atmosphere of the coprecipitation reaction. At the start of the coprecipitation reaction, a high oxidation state is maintained, resulting in high-valence Sn doping into the core. 4+ Then, the oxidation state of the coprecipitation reaction is lowered so that at the end of the coprecipitation reaction, the content of oxygen-containing gas in the mixed atmosphere is lower than the content of oxygen-containing gas in the mixed atmosphere at the beginning of the coprecipitation reaction, thereby doping the shell with low-valence Sn. 2+ This achieved one-step co-precipitation gradient doping of variable valence tin.

[0018] Preferably, at the start of the coprecipitation reaction, the ratio of the protective gas to the oxygen-containing gas in the mixed atmosphere is 0.05-0.25, for example, it can be 0.05, 0.1, 0.15, 0.2 or 0.25, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] The gas content mentioned in this invention refers to the volume content. The ratio of the protective gas to the oxygen-containing gas in the mixed atmosphere is 0.05-0.25, which means that the volume ratio of the protective gas to the oxygen-containing gas is 0.05-0.5:1. At the beginning of the coprecipitation reaction of this invention, there is a large amount of oxygen-containing gas, maintaining a high oxidation state. However, if the ratio of the protective gas to the oxygen-containing gas is too small at the beginning of the coprecipitation reaction, there will be too much oxygen-containing gas, resulting in excessive oxidation and making it difficult to nucleate and form coprecipitates. If the ratio of the protective gas to the oxygen-containing gas is too large, there will be too little oxygen-containing gas, resulting in no +4 valence Sn inside and losing the modification effect.

[0020] Preferably, at the end of the coprecipitation reaction, the ratio of the protective gas to the oxygen-containing gas in the mixed atmosphere is 0.75-0.95, for example, it can be 0.75, 0.8, 0.85, 0.90 or 0.95, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] When the coprecipitation reaction of this invention is completed, if the ratio of the content of protective gas to oxygen-containing gas is too small, the content of oxygen-containing gas will be too large, and there will be no +2 valence Sn on the surface, thus losing the modification effect. If the ratio of the content of protective gas to oxygen-containing gas is too large, the content of oxygen-containing gas will be too small, which will easily lead to coarse crystals or particle adhesion.

[0022] Preferably, during the coprecipitation reaction, the content of oxygen-containing gas in the mixed atmosphere gradually decreases.

[0023] The content of oxygen-containing gas in the mixed atmosphere of the present invention is gradually reduced until it reaches a ratio of 0.75-0.95 between the content of protective gas and oxygen-containing gas in the mixed atmosphere.

[0024] Preferably, during the coprecipitation reaction, for every 1 μm increase in the particle size D50 of the product, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.05-0.3, for example, it can be 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] For every 1 μm increase in the particle size D50 of the product described in this invention, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.05-0.3. This reflects the rate of change in the degree of oxidation. Controlling the rate of change can control the thickness of the outer shell and the particle size D50 of the core. If the increase in the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is too large, the degree of oxidation will decrease too quickly. If the increase in the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is too small, the degree of oxidation will decrease too slowly. This will also result in an unreasonable ratio of core particle size to outer shell thickness, thereby affecting the performance of the cathode precursor material.

[0026] Preferably, during the coprecipitation reaction, the ratio of the content of the protective gas to the oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.1-0.9. This means that the ratio of the content of the protective gas to the oxygen-containing gas is at least above 0.1, for example, it can be 0.1, 0.15, 0.2, 0.25 or 0.3, and at most below 0.9, for example, it can be 0.9, 0.85, 0.8 or 0.75, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the tin salt comprises a divalent tin salt.

[0028] Preferably, the divalent tin salt includes stannous chloride and / or stannous sulfate.

[0029] Preferably, the concentration of divalent tin ions in the ternary metal salt solution is 0.5-20 g / L, for example, it can be 0.5 g / L, 5 g / L, 10 g / L, 15 g / L or 20 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the total metal ion concentration in the ternary metal salt solution is 80-120 g / L, for example, it can be 80 g / L, 100 g / L or 120 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The ternary metal salt solution of the present invention includes nickel ions, cobalt ions and manganese ions, and the corresponding metal salt includes any one or a combination of at least two of sulfate, nitrate or chloride.

[0032] Preferably, the concentration of the precipitant solution is 200-400 g / L, for example, it can be 200 g / L, 300 g / L or 400 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the concentration of the complexing agent solution is 10-20 wt%, for example, it can be 10 wt%, 15 wt% or 20 wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the precipitant solution comprises any one or a combination of at least two of sodium hydroxide, sodium carbonate, or ammonium bicarbonate.

[0035] Preferably, the complexing agent solution comprises any one or a combination of at least two of ammonia, oxalic acid, or citric acid.

[0036] Preferably, the temperature of the coprecipitation reaction is 40-60℃, for example, 40℃, 50℃ or 60℃, and the pH is maintained in the range of 8-12. This means that the lowest pH of the coprecipitation reaction is above 8, for example, 8, 8.5 or 9, and the highest pH is below 12, for example, 12, 11.5 or 11, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, after the coprecipitation reaction is completed, aging, solid-liquid separation, washing and drying steps are also performed.

[0038] Preferably, the aging time is 2-18 hours, for example, 2 hours, 5 hours, 10 hours, 15 hours or 18 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the protective gas includes nitrogen and / or an inert gas, wherein the inert gas includes any one or a combination of at least two of helium, argon, or krypton, and the oxygen-containing gas includes air.

[0040] In this invention, a ternary metal salt solution, a precipitant solution, and a complexing agent solution are simultaneously introduced into a base liquid for a co-precipitation reaction. The base liquid includes the complexing agent solution and the precipitant solution, and the base liquid occupies 1 / 4 to 1 / 2 of the total volume of the reaction vessel. For example, it can be 1 / 4, 1 / 3, or 1 / 2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0042] A ternary metal salt solution, a precipitant solution, and a complexing agent solution are mixed to carry out a coprecipitation reaction. The temperature of the coprecipitation reaction is 40-60℃, and the pH is maintained in the range of 8-12. After the coprecipitation reaction is completed, the coprecipitation reaction slurry is aged for 2-18 hours, and then solid-liquid separation, washing, and drying are performed to obtain the gradient-doped cathode precursor material.

[0043] The ternary metal salt solution is doped with tin salt, including divalent tin salt. The total metal ion concentration in the ternary metal salt solution is 80-120 g / L, and the concentration of divalent tin ions is 0.5-20 g / L. The concentration of the precipitant solution is 200-400 g / L, and the concentration of the complexing agent solution is 10-20 wt%.

[0044] The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.1-0.9. For every 1 μm increase in the particle size D50 of the product particles of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.05-0.3, until the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.75-0.95.

[0045] Thirdly, the present invention provides a cathode material, which is obtained by mixing and sintering a lithium source and a cathode precursor material with gradient doping as described in the first aspect.

[0046] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode material as described in the third aspect.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] This invention achieves core doping of the cathode precursor material with Sn through gradient doping of variable valence tin. 4+ Sn is doped in the outer shell 2 + This effectively regulates the charge distribution in the precursor material, allowing the doping of the outer shell with low-valence elements to effectively prevent the dissolution of active elements in the material. At the same time, the gradient valence distribution in the material is conducive to electron diffusion, thereby improving the rate performance of the material. Attached Figure Description

[0049] Figure 1 This is a diagram showing the charge distribution of Sn in the gradient-doped cathode precursor material described in Embodiment 1 of the present invention.

[0050] Figure 2 This is a scanning electron microscope image of the gradient-doped cathode precursor material described in Embodiment 1 of the present invention at a magnification of 20,000. Detailed Implementation

[0051] 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.

[0052] Example 1

[0053] This embodiment provides a gradient-doped cathode precursor material, which includes a core and a shell. The core and shell each independently comprise nickel-cobalt-manganese hydroxide, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+ The ratio of the core particle size D50 to the shell thickness is 1:0.5.

[0054] The preparation method of gradient-doped cathode precursor materials includes the following steps:

[0055] A ternary metal salt solution with a total metal ion concentration of 90 g / L, a sodium hydroxide solution with a concentration of 400 g / L, and an oxalic acid solution with a concentration of 15 wt% were co-flowed into the base liquid to carry out a coprecipitation reaction. The temperature of the coprecipitation reaction was 50 °C, and the pH was maintained in the range of 8-12. After the coprecipitation reaction was completed, the coprecipitation reaction slurry was aged for 6 hours, and then solid-liquid separation, washing, and drying were performed to obtain the gradient-doped cathode precursor material.

[0056] The ternary metal salt solution includes nickel sulfate, cobalt sulfate, manganese sulfate, and divalent tin salt, wherein the divalent tin salt is stannous chloride, and the concentration of divalent tin ions in the ternary metal salt solution is 5 g / L; the bottom solution includes water, oxalic acid, and sodium hydroxide, and the bottom solution occupies 1 / 2 of the total volume of the reaction vessel;

[0057] The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. At the beginning of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.1. At the end of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.8. During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is in the range of 0.1-0.9, and as the reaction proceeds, the content of oxygen-containing gas gradually decreases until the ratio of the content of protective gas to oxygen-containing gas is 0.9.

[0058] For every 1 μm increase in the particle size D50 of the product from the coprecipitation reaction, the ratio of the protective gas to the oxygen-containing gas in the mixed atmosphere increases by 0.15; the protective gas is nitrogen, and the oxygen-containing gas is air.

[0059] In the gradient-doped cathode precursor material described in this embodiment, the charge distribution state diagram of Sn is as follows: Figure 1 As shown, the scanning electron microscope image at 20,000x magnification is as follows. Figure 2 As shown.

[0060] Example 2

[0061] This embodiment provides a gradient-doped cathode precursor material, which includes a core and a shell. The core and shell each independently comprise nickel-cobalt-manganese hydroxide, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+

[0062] The ratio of the kernel's particle size D50 to the shell's thickness is 1:0.1;

[0063] The preparation method of gradient-doped cathode precursor materials includes the following steps:

[0064] A ternary metal salt solution with a total metal ion concentration of 120 g / L, a sodium hydroxide solution with a concentration of 200 g / L, and an oxalic acid solution with a concentration of 20 wt% were co-flowed into the base liquid to carry out a coprecipitation reaction. The temperature of the coprecipitation reaction was 60 °C, and the pH was maintained in the range of 8-12. After the coprecipitation reaction was completed, the coprecipitation reaction slurry was aged for 18 h, and then solid-liquid separation, washing, and drying were performed to obtain the gradient-doped cathode precursor material.

[0065] The ternary metal salt solution includes nickel sulfate, cobalt sulfate, manganese sulfate, and divalent tin salt, wherein the divalent tin salt is stannous sulfate, and the concentration of divalent tin ions in the ternary metal salt solution is 20 g / L; the bottom solution includes water, oxalic acid, and sodium hydroxide, and the bottom solution occupies 1 / 2 of the total volume of the reaction vessel;

[0066] The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. At the beginning of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.05. At the end of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.75. During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.05-0.75. As the reaction proceeds, the content of oxygen-containing gas gradually decreases until the ratio of the content of protective gas to oxygen-containing gas is 0.75.

[0067] For every 1 μm increase in the particle size D50 of the product from the coprecipitation reaction, the ratio of the content of the protective gas to the oxygen-containing gas in the mixed atmosphere increases by 0.05; the protective gas is nitrogen, and the oxygen-containing gas is air.

[0068] Example 3

[0069] This embodiment provides a gradient-doped cathode precursor material, which includes a core and a shell. The core and shell each independently comprise nickel-cobalt-manganese hydroxide, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+

[0070] The ratio of the kernel's particle size D50 to the shell's thickness is 1:1;

[0071] The preparation method of gradient-doped cathode precursor materials includes the following steps:

[0072] A ternary metal salt solution with a total metal ion concentration of 80 g / L, a sodium hydroxide solution with a concentration of 400 g / L, and an oxalic acid solution with a concentration of 20 wt% were co-flowed into the base liquid to carry out a coprecipitation reaction. The temperature of the coprecipitation reaction was 40 °C, and the pH was maintained in the range of 8-12. After the coprecipitation reaction was completed, the coprecipitation reaction slurry was aged for 2 hours, and then solid-liquid separation, washing, and drying were performed to obtain the gradient-doped cathode precursor material.

[0073] The ternary metal salt solution includes nickel sulfate, cobalt sulfate, manganese sulfate, and divalent tin salt, wherein the divalent tin salt is stannous chloride, and the concentration of divalent tin ions in the ternary metal salt solution is 1 g / L; the bottom solution includes water, oxalic acid, and sodium hydroxide, and the bottom solution occupies 1 / 4 of the total volume of the reaction vessel;

[0074] The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. At the beginning of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.25. At the end of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.95. During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.25-0.95. As the reaction proceeds, the content of oxygen-containing gas gradually decreases until the ratio of the content of protective gas to oxygen-containing gas is 0.95.

[0075] For every 1 μm increase in the particle size D50 of the product from the coprecipitation reaction, the ratio of the content of the protective gas to the oxygen-containing gas in the mixed atmosphere increases by 0.3; the protective gas is nitrogen, and the oxygen-containing gas is air.

[0076] Example 4

[0077] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is 0.01 at the beginning of the co-precipitation reaction, and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.01-0.9 during the co-precipitation reaction to make the obtained gradient-doped cathode precursor material adaptable to changes, the rest is the same as in Example 1.

[0078] Example 5

[0079] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is 0.35 at the beginning of the co-precipitation reaction, and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.35-0.9 during the co-precipitation reaction to make the obtained gradient-doped cathode precursor material adaptable to changes, the rest is the same as in Example 1.

[0080] Example 6

[0081] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is 0.65 at the end of the co-precipitation reaction, and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.1-0.65 to make the obtained gradient-doped cathode precursor material adaptable to changes, the rest is the same as in Example 1.

[0082] Example 7

[0083] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is 0.99 at the end of the co-precipitation reaction, and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.1-0.99 to make the obtained gradient-doped cathode precursor material adaptable to changes, the rest is the same as in Example 1.

[0084] Example 8

[0085] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the particle size D50 of the coprecipitation reaction product increases by 1 μm and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.03 to make the obtained gradient-doped cathode precursor material adaptable, the rest is the same as in Example 1.

[0086] Example 9

[0087] This embodiment provides a gradient-doped cathode precursor material. Except for the preparation method, in which the particle size D50 of the co-precipitation reaction product increases by 1 μm and the ratio of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.4 to make the gradient-doped cathode precursor material adaptable, the rest is the same as in Example 1.

[0088] Comparative Example 1

[0089] This comparative example provides a cathode precursor material in which, except for the preparation method, the ratio of protective gas to oxygen-containing gas in the mixed atmosphere during the co-precipitation reaction is consistently 0.1, ensuring that the cathode precursor material is doped only with Sn. 4+ Except for the above, everything else is the same as in Example 1.

[0090] Comparative Example 2

[0091] This comparative example provides a cathode precursor material in which, except for the preparation method, the ratio of protective gas to oxygen-containing gas in the mixed atmosphere during the co-precipitation reaction is consistently 0.9, ensuring that the cathode precursor material is doped only with Sn. 2+ Except for the above, everything else is the same as in Example 1.

[0092] The positive electrode precursor materials obtained in the above embodiments and comparative examples are mixed with lithium hydroxide and sintered to obtain positive electrode materials. The positive electrode materials are prepared into positive electrode sheets, which are then used to prepare batteries with lithium sheets, lithium hexafluorophosphate electrolyte, and polyethylene separators. Electrochemical performance is tested at 25°C, with charge-discharge conditions of 100 cycles at 0.1C / 0.2C and 50 cycles at 0.5C / 0.5C for rate testing.

[0093] The test results are shown in Table 1:

[0094] Table 1

[0095] Cycle retention rate (%) Ratio capacity retention rate (%) Example 1 98 95 Example 2 97 95 Example 3 98 94 Example 4 94 94 Example 5 95 92 Example 6 95 93 Example 7 95 92 Example 8 95 92 Example 9 94 94 Comparative Example 1 91 92 Comparative Example 2 92 91

[0096] As can be seen from Table 1:

[0097] The precursor material obtained by this invention exhibits excellent electrochemical performance. As shown in Example 1 and Comparative Examples 1-2, the gradient doping of variable valence tin in this invention facilitates electron diffusion and avoids the dissolution of active elements on the material surface, thereby improving battery performance. As shown in Examples 1 and 4-9, the ratio of protective gas to oxygen-containing gas content at the beginning and end of co-precipitation, as well as the increase in the ratio, affects the Sn content in the material. 4+and Sn 2+ The distribution and content of these substances affect battery performance.

[0098] In summary, this invention provides a gradient-doped cathode precursor material, its preparation method, and its application. The cathode precursor material is prepared by gradient doping with variable-valence tin, resulting in Sn doping in the core. 4+ Surface doped with Sn 2+ This effectively regulates the charge distribution in the cathode precursor material, which not only improves the stability of the cathode precursor material but also enhances its rate performance.

[0099] 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 gradient-doped cathode precursor material, characterized in that, The gradient-doped cathode precursor material includes a core and a shell, wherein the core and shell each independently comprise a ternary precursor material, and the core is doped with Sn. 4+ The outer shell is doped with Sn. 2+ .

2. The gradient-doped cathode precursor material according to claim 1, characterized in that, The ternary precursor material includes nickel-cobalt-manganese hydroxide.

3. The gradient-doped cathode precursor material according to claim 1, characterized in that, The ratio of the kernel's particle size D50 to the shell's thickness is 1:(0.1-1).

4. A method for preparing a gradient-doped cathode precursor material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: A ternary metal salt solution, a precipitant solution, and a complexing agent solution are mixed and a co-precipitation reaction is carried out to obtain the gradient-doped cathode precursor material. The ternary metal salt solution is doped with tin salt; The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. At the end of the coprecipitation reaction, the content of oxygen-containing gas in the mixed atmosphere is less than the content of oxygen-containing gas in the mixed atmosphere at the beginning of the coprecipitation reaction.

5. The preparation method according to claim 4, characterized in that, At the start of the coprecipitation reaction, the ratio of the protective gas to the oxygen-containing gas in the mixed atmosphere is 0.05-0.

25.

6. The preparation method according to claim 5, characterized in that, At the end of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.75-0.

95.

7. The preparation method according to claim 4, characterized in that, During the coprecipitation reaction, the content of oxygen-containing gas in the mixed atmosphere gradually decreases.

8. The preparation method according to claim 4, characterized in that, During the coprecipitation reaction, for every 1 μm increase in the particle size D50 of the product, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.05-0.

3.

9. The preparation method according to claim 4, characterized in that, During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is maintained within the range of 0.1-0.

9.

10. The preparation method according to claim 4, characterized in that, The tin salts include divalent tin salts.

11. The preparation method according to claim 10, characterized in that, The divalent tin salts include stannous chloride and / or stannous sulfate.

12. The preparation method according to claim 4, characterized in that, In the ternary metal salt solution, the concentration of divalent tin ions is 0.5-20 g / L.

13. The preparation method according to claim 4, characterized in that, The total metal ion concentration in the ternary metal salt solution is 80-120 g / L.

14. The preparation method according to claim 4, characterized in that, The concentration of the precipitant solution is 200-400 g / L.

15. The preparation method according to claim 4, characterized in that, The concentration of the complexing agent solution is 10-20 wt%.

16. The preparation method according to claim 4, characterized in that, The coprecipitation reaction is carried out at a temperature of 40-60℃ and the pH is maintained in the range of 8-12.

17. The preparation method according to claim 4, characterized in that, After the coprecipitation reaction was completed, aging, solid-liquid separation, washing and drying steps were also performed.

18. The preparation method according to claim 17, characterized in that, The aging time is 2-18 hours.

19. The preparation method according to claim 4, characterized in that, The preparation method includes the following steps: A ternary metal salt solution, a precipitant solution, and a complexing agent solution are mixed to carry out a coprecipitation reaction. The temperature of the coprecipitation reaction is 40-60℃, and the pH is maintained in the range of 8-12. After the coprecipitation reaction is completed, the coprecipitation reaction slurry is aged for 2-18 hours, and then solid-liquid separation, washing, and drying are performed to obtain the gradient-doped cathode precursor material. The ternary metal salt solution is doped with tin salt, including divalent tin salt. The total metal ion concentration in the ternary metal salt solution is 80-120 g / L, and the concentration of divalent tin ions is 0.5-20 g / L. The concentration of the precipitant solution is 200-400 g / L, and the concentration of the complexing agent solution is 10-20 wt%. The coprecipitation reaction is carried out in a mixed atmosphere of protective gas and oxygen-containing gas. During the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is maintained in the range of 0.1-0.

9. For every 1 μm increase in the particle size D50 of the product of the coprecipitation reaction, the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere increases by 0.05-0.3, until the ratio of the content of protective gas to oxygen-containing gas in the mixed atmosphere is 0.75-0.

95.

20. A positive electrode material, characterized in that, The cathode material is obtained by mixing and sintering a lithium source and a cathode precursor material with gradient doping as described in any one of claims 1-3.

21. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in claim 20.

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