Tin-carbon-coated aluminum-doped positive electrode precursor as well as preparation method and application thereof

Abstract

The invention provides a tin-carbon-coated aluminum-doped positive electrode precursor as well as a preparation method and application thereof. The positive electrode precursor comprises an aluminum-doped cobalt oxide core and a tin-carbon-coated shell coated outside the aluminum-doped cobalt oxide core. According to the tin-carbon-coated aluminum-doped positive electrode precursor provided by the invention, due to coating of the tin-carbon coating shell, not only is a positive electrode material prepared from the tin-carbon-coated aluminum-doped positive electrode precursor relatively high in electronic conductivity and lithium ion diffusion rate, but also side reaction between the positive electrode material and an electrolyte is effectively prevented; therefore, the battery prepared from the positive electrode material has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a tin-carbon coated and aluminum-doped cathode precursor, and particularly to a tin-carbon coated and aluminum-doped cathode precursor and its preparation method and application. Background Art

[0002] As an electrical energy storage device that can replace fossil energy, lithium-ion batteries have the advantages of high energy density, long service life, and environmental friendliness, and have received extensive attention. At present, lithium-ion batteries are widely used in various fields such as portable electronic devices, electric vehicles, and microchips. However, with the continuous improvement of the battery life requirements of electronic devices and electric vehicles, the research on improving the energy density and preparing battery cathode materials at low cost has become particularly important. Lithium cobalt oxide cathode materials have become the first choice for lithium-ion battery cathode materials in current "3C products" due to their high volumetric energy density. Small-sized portable electronic products have higher requirements for the voltage platform of the cathode material.

[0003] Doping with aluminum element is one of the effective measures to improve the high-voltage electrochemical performance of lithium cobalt oxide, because Al-O has a stronger bond energy than Co-O, which can inhibit the problem of structural collapse caused by phase change during charge and discharge of lithium cobalt oxide.

[0004] In actual preparation, aluminum element is often added in the wet precipitation of cobalt carbonate precursor to achieve the purpose of uniform bulk doping. However, aluminum-doped cobalt carbonate is prone to aluminum precipitation during subsequent heat treatment, and finally a large number of flaky aluminum structures are formed on the surface of the cobalt oxide precursor, which will not only cause uneven distribution of Al and doping failure, but also damage the material structure and cause damage to the battery separator; in addition, after preparing an aluminum-doped cathode precursor from aluminum-doped cobalt carbonate and then preparing a cathode material from the aluminum-doped cathode precursor, since the surface of the cathode material is lithium cobalt oxide material, and the electronic conductivity and lithium ion passing rate of the lithium cobalt oxide material are not high, it will also lead to a decrease in the performance of the battery; in addition, the surface of the cathode material being lithium cobalt oxide material is also prone to side reactions with the hydrolysis product hydrogen fluoride of the electrolyte, resulting in a further decrease in the battery performance.

[0005] CN107611372A discloses a cathode material for a high-capacity and high-voltage lithium battery and a preparation method thereof. In the method, a ternary precursor is stirred with water, then an aluminum sol solution is added dropwise, stirred, filtered, and dried. Then it is mixed with a lithium salt, sintered once, pulverized, and sieved. Then it is added to water and stirred, and a Co salt is added to obtain a cathode material slurry; the cathode material slurry is filtered, washed, and dried to obtain a cathode material powder; finally, the cathode material powder is mixed with a lithium salt and then sintered twice, pulverized, and sieved to prepare a cathode material for a high-capacity and high-voltage lithium-ion battery. By doping Al into the cathode material precursor, this invention can prevent mixed arrangement, improve the initial efficiency, and improve the cycle performance of the material and the stability of the electrolyte at high voltage through lithium cobaltate coating. However, in the sintering process of the ternary precursor after Al doping in this method, aluminum elements are likely to precipitate, thus damaging the structure of the material; in addition, the electron conductivity and lithium-ion passing rate of the cobalt coating layer prepared by this method are not high, which is not conducive to the rate performance of the battery.

[0006] CN109896552A discloses a preparation method of an aluminum-doped lithium-ion cathode material precursor. S1, prepare a mixed solution of a cobalt solution, a liquid caustic solution, and an aluminum-complex solution for standby; S2, add the cobalt solution, ammonia water, and the aluminum-complex solution mixture into the reaction kettle in parallel from one side of the reaction kettle, and add the liquid caustic solution into the reaction kettle in a metered manner from the other side of the reaction kettle; S3, stir and mix the solutions added to the reaction kettle through a spiral stirring impeller, and control the pH value of the solution to be about 12.4; S4, let the mixed solution in the reaction kettle stand still, and filter the supernatant into the aging tank; S5, sinter and batch-mix and demagnetize the aged reactants to obtain a finished aluminum-doped cobalt oxide precursor. However, the lithium cobaltate cathode material obtained by this preparation method is prone to side reactions with the hydrolysis product HF in the electrolyte, thus affecting the performance of the battery; in addition, the residual lithium on the surface of the obtained lithium cobaltate cathode material is also prone to react with water, oxygen, and carbon dioxide, generating lithium compounds that hinder Li + migration on the surface of the lithium cobaltate cathode material.

[0007] The aluminum-doped cathode precursors disclosed in the prior art all have certain defects. There are problems that the electron conductivity and lithium-ion passing rate of the lithium cobaltate cathode material prepared from the aluminum-doped cathode precursor are not high, thus affecting the initial efficiency and cycle performance of the battery; there are also problems that the lithium cobaltate cathode material prepared from the aluminum-doped cathode precursor is prone to side reactions with the electrolyte, thus affecting the electrochemical performance of the battery. Therefore, it is crucial to develop and design a new type of tin-carbon-coated aluminum-doped cathode precursor and its preparation method and application. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a tin-carbon coated aluminum-doped cathode precursor, its preparation method and application. The tin-carbon coated aluminum-doped cathode precursor provided by the present invention, due to the coating of the tin-carbon coating shell, not only enables the cathode material prepared from the tin-carbon coated aluminum-doped cathode precursor to have a high electronic conductivity and lithium ion diffusion rate, but also effectively prevents the side reaction between the cathode material and the electrolyte, thereby enabling the battery prepared from the cathode material to have excellent electrochemical performance.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a tin-carbon coated aluminum-doped cathode precursor, which includes an aluminum-doped cobalt oxide core and a tin-carbon coating shell coated on the outside of the aluminum-doped cobalt oxide core.

[0011] Due to the coating of the tin-carbon coating shell, the tin-carbon coated aluminum-doped cathode precursor provided by the present invention has a high electronic conductivity and lithium ion diffusion rate. The cathode material prepared from the tin-carbon coated aluminum-doped cathode precursor also has a high electronic conductivity and lithium ion diffusion rate, thereby enabling the battery prepared from the cathode material to have a high initial efficiency and excellent cycling performance.

[0012] The tin-carbon coated aluminum-doped cathode precursor provided by the present invention has a tin-carbon coating shell. After the cathode material is prepared from the tin-carbon coated aluminum-doped cathode precursor, the tin-carbon coating shell can effectively prevent the side reaction between the cathode material and the electrolyte, thereby further improving the electrochemical performance of the battery.

[0013] Preferably, based on the mass of the cathode precursor being 100%, the mass fraction of aluminum in the cathode precursor is 0.8 - 2 wt%, for example, it can be 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0014] Preferably, the mass ratio of tin to carbon in the cathode precursor is 1:(0.5 - 1), for example, it can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0015] Preferably, based on the mass of the positive electrode precursor being 100%, the mass fraction of tin in the positive electrode precursor is 0.5 to 5 wt%, for example, it can be 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt% or 5.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] Preferably, based on the mass of the positive electrode precursor being 100%, the mass fraction of carbon in the positive electrode precursor is 0.5 to 5 wt%, for example, it can be 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt% or 5.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the D50 particle size of the aluminum-doped cobalt oxide core is 10 to 20 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] Preferably, the thickness of the tin-carbon coating shell is 0.1 to 0.5 μm, for example, it can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] In a second aspect, the present invention provides a method for preparing the positive electrode precursor described in the first aspect, and the preparation method includes:

[0020] After mixing the aluminum-doped cobalt carbonate core, tin source, carbon source and solvent to obtain a mixed sol, the obtained mixed sol is heat-treated to obtain a positive electrode precursor with a tin-carbon coating on the aluminum-doped one.

[0021] In the preparation method provided by the present invention, by mixing the aluminum-doped cobalt carbonate core with the tin source, carbon source and solvent, an organic colloid containing the tin source is coated on the surface of the aluminum-doped cobalt carbonate core, and a tin-carbon coating shell is formed outside the aluminum-doped cobalt carbonate core during the subsequent heat treatment process, thereby inhibiting the Al segregation that occurs during the heat treatment process of the aluminum-doped cobalt carbonate core, reducing the risk of forming a large number of flaky Al structures on the surface of the cobalt oxide precursor, ensuring the effective doping of aluminum to the cobalt carbonate core, and avoiding the damage to the battery separator caused by the positive electrode material prepared from the positive electrode precursor after Al segregation occurs, thereby improving the performance of the battery.

[0022] In the preparation method provided by the present invention, the organic colloid containing a tin source, which coats the surface of the aluminum-doped cobalt carbonate core, undergoes pyrolysis during the heat treatment. The carbon in the tin-carbon coating shell obtained after pyrolysis can improve the morphology of the aluminum-doped cobalt oxide core formed after the heat treatment of the aluminum-doped cobalt carbonate core and inhibit the cracking of the aluminum-doped cobalt oxide core, thereby further enhancing the performance of the cathode material and the battery prepared from the cathode material.

[0023] Preferably, the method for preparing the aluminum-doped cobalt carbonate core includes:

[0024] Performing a coprecipitation reaction on a first mixed complexing agent solution, a cobalt salt doped with aluminum solution, and a precipitating agent solution to obtain an aluminum-doped cobalt carbonate core.

[0025] Preferably, the first mixing includes: using the complexing agent solution as the bottom liquid, and adding the cobalt salt doped with aluminum solution and the precipitating agent solution into the bottom liquid in a parallel flow manner.

[0026] Preferably, the complexing agent in the complexing agent solution includes any one or at least two combinations of ammonium bicarbonate, ammonia water, or oxalic acid. Typical but non-limiting combinations include the combination of ammonium bicarbonate and ammonia water, the combination of ammonia water and oxalic acid, or the combination of ammonium bicarbonate, ammonia water, and oxalic acid.

[0027] Preferably, the concentration of the complexing agent in the complexing agent solution is 100 - 200 g / L. For example, it can be 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0028] Preferably, the cobalt salt in the cobalt salt doped with aluminum solution includes any one or at least two combinations of cobalt sulfate, cobalt chloride, or cobalt nitrate. Typical but non-limiting combinations include the combination of cobalt sulfate and cobalt chloride, the combination of cobalt chloride and cobalt nitrate, or the combination of cobalt sulfate, cobalt chloride, and cobalt nitrate.

[0029] Preferably, the concentration of the cobalt salt in the cobalt salt doped with aluminum solution is 80 - 150 g / L. For example, it can be 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, 135 g / L, 140 g / L, 145 g / L, or 150 g / L, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0030] Preferably, the aluminum in the cobalt salt-doped aluminum solution exists in the form of aluminum ions, and the mass ratio of aluminum ions to cobalt ions in the cobalt salt-doped aluminum solution is (1-3):100. For example, it can be 1:100, 1.5:100, 2:100, 2.5:100, or 3:100, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0031] Preferably, the precipitant in the precipitant solution includes any one or a combination of at least two of ammonium bicarbonate, sodium carbonate, or sodium bicarbonate. Typical but non-limiting combinations include the combination of ammonium bicarbonate and sodium carbonate, the combination of sodium carbonate and sodium bicarbonate, or the combination of ammonium bicarbonate, sodium carbonate, and sodium bicarbonate.

[0032] Preferably, the concentration of the precipitant in the precipitant solution is 100-200 g / L. For example, it can be 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0033] Preferably, during the coprecipitation reaction, the pH is controlled to be 7.0-8.5. For example, it can be 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, or 8.5, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0034] Preferably, during the coprecipitation reaction, stirring is carried out, and the stirring speed is 100-200 r / min. For example, it can be 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min, or 200 r / min, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0035] Preferably, the method for preparing the aluminum-doped cobalt carbonate core further includes solid-liquid separation, washing, and drying sequentially after the coprecipitation reaction.

[0036] Preferably, the drying temperature is 80-130 °C. For example, it can be 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, or 130 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the tin source includes any one or a combination of at least two of stannic chloride anhydrous, sodium stannate, or stannous sulfate. Typical but non-limiting combinations include a combination of stannic chloride anhydrous and sodium stannate, a combination of sodium stannate and stannous sulfate, or a combination of stannic chloride anhydrous, sodium stannate, and stannous sulfate.

[0038] Preferably, the carbon source includes pyrrole, resorcinol, and formaldehyde.

[0039] Preferably, the solvent includes water.

[0040] Preferably, the mixing further includes the mixing of a surfactant and a pH regulator.

[0041] Preferably, the surfactant includes any one or a combination of at least two of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, or tetradecyltrimethylammonium bromide. Typical but non-limiting combinations include a combination of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, a combination of cetyltrimethylammonium chloride and tetradecyltrimethylammonium bromide, or a combination of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and tetradecyltrimethylammonium bromide.

[0042] Preferably, the pH regulator includes any one or a combination of at least two of sodium carbonate, potassium carbonate, or ammonium carbonate. Typical but non-limiting combinations include a combination of sodium carbonate and potassium carbonate, a combination of potassium carbonate and ammonium carbonate, or a combination of sodium carbonate, potassium carbonate, and ammonium carbonate.

[0043] Preferably, the mixing includes: secondarily mixing the tin source, carbon source, solvent, surfactant, and pH regulator to obtain a colloidal solution, and tertiarily mixing the aluminum-doped cobalt carbonate core with the obtained colloidal solution to obtain a mixed sol.

[0044] Preferably, the second mixing includes: dissolving the tin source and the surfactant in the solvent to obtain a preliminary mixed solution, and then sequentially adding pyrrole, resorcinol, and a mixture of formaldehyde and the pH regulator to the obtained preliminary mixed solution to obtain a colloidal solution.

[0045] Preferably, the concentration of the tin source in the colloidal solution is 0.1 - 0.5 mol / L. For example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0046] Preferably, the concentration of the surfactant in the glue solution is 0.08 - 0.15 mol / L. For example, it can be 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, or 0.15 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0047] Preferably, the concentration of pyrrole in the glue solution is 1 - 10 g / L. For example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, or 10 g / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0048] Preferably, the concentration of resorcinol in the glue solution is 1 - 10 g / L. For example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, or 10 g / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0049] Preferably, the concentration of formaldehyde in the glue solution is 0.2 - 0.5 mol / L. For example, it can be 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] Preferably, the concentration of the pH regulator in the glue solution is 0.1 - 0.5 mol / L. For example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] Preferably, the mass ratio of the aluminum-doped cobalt carbonate core to the obtained glue solution in the third mixing is 1:(2 - 5). For example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5. However, it is not limited to the listed ratios, and other unlisted values within this range are equally applicable.

[0052] Preferably, the way of the third mixing includes stirring.

[0053] Preferably, the heat treatment includes: subjecting the obtained mixed sol to a polymerization reaction through a first heat treatment, then performing a second heat treatment in a protective atmosphere, and then performing a third heat treatment in an oxygen-containing atmosphere to obtain a cobalt oxide core doped with aluminum coated with tin and carbon, that is, a cathode precursor doped with aluminum and coated with tin and carbon.

[0054] Preferably, the first heat treatment is carried out in an air atmosphere, the temperature of the first heat treatment is 60-90 °C, and the time is 0.5-3 h.

[0055] In the present invention, the temperature of the first heat treatment is 60-90 °C, for example, it can be 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C or 90 °C, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0056] In the present invention, the time of the first heat treatment is 0.5-3 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0057] Preferably, the temperature of the second heat treatment is 500-700 °C, and the time is 2-5 h.

[0058] In the present invention, the temperature of the second heat treatment is 500-700 °C, for example, it can be 500 °C, 550 °C, 600 °C, 650 °C or 700 °C, but is not limited to the listed values, and other unlisted values within this range are equally applicable

[0059] In the present invention, the time of the second heat treatment is 2-5 h, for example, it can be 2 h, 3 h, 4 h or 5 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0060] Preferably, the temperature of the third heat treatment is 600-800 °C, and the time is 0.5-2 h.

[0061] In the present invention, the temperature of the third heat treatment is 600-800 °C, for example, it can be 600 °C, 650 °C, 700 °C, 750 °C or 800 °C, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0062] In the present invention, the time of the third heat treatment is 0.5-2 h, for example, it can be 0.5 h, 1 h, 1.5 h or 2 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0063] As a preferred technical solution of the preparation method of the present invention, the preparation method includes:

[0064] (1) Using ammonium bicarbonate solution with a concentration of 100 - 200 g / L as the bottom solution, a cobalt salt-doped aluminum solution with a cobalt salt concentration of 80 - 150 g / L and a mass ratio of aluminum ions to cobalt ions of (1 - 3):100 is added to the bottom solution in a co-current manner with a precipitant solution having a concentration of 100 - 200 g / L. The pH is controlled to be 7.0 - 8.5 and the mixture is stirred at a speed of 100 - 200 r / min to carry out a co-precipitation reaction. After the co-precipitation reaction, solid-liquid separation and washing are carried out in sequence, and then the obtained solid is dried at 80 - 130 °C to obtain an aluminum-doped cobalt carbonate core;

[0065] (2) Dissolve anhydrous stannous chloride and cetyltrimethylammonium bromide in water to obtain a preliminary mixture solution, and then add pyrrole, resorcinol, and a mixture of formaldehyde and sodium carbonate to the obtained preliminary mixture solution in sequence to obtain a colloidal solution. The concentration of anhydrous stannous chloride in the colloidal solution is 0.1 - 0.5 mol / L, the concentration of cetyltrimethylammonium bromide is 0.08 - 0.15 mol / L, the concentration of pyrrole is 1 - 10 g / L, the concentration of resorcinol is 1 - 10 g / L, the concentration of formaldehyde is 0.2 - 0.5 mol / L, and the concentration of sodium carbonate is 0.1 - 0.5 mol / L;

[0066] (3) Mix the aluminum-doped cobalt carbonate core obtained in step (1) and the colloidal solution obtained in step (2) with a mass ratio of 1:(2 - 5) by stirring to obtain a mixed sol;

[0067] (4) Place the mixed sol obtained in step (3) in an air atmosphere and carry out a heat treatment at 60 - 90 °C for 0.5 - 3 h to cause the mixed sol to carry out a polymerization reaction, and then carry out filtration and drying in sequence to obtain a first intermediate. After filtration and drying, carry out a heat treatment on the obtained first intermediate at 500 - 700 °C for 2 - 5 h in a protective atmosphere to obtain a second intermediate. Then carry out a heat treatment on the obtained second intermediate at 600 - 800 °C for 0.5 - 2 h in an oxygen-containing atmosphere to obtain a tin-carbon-coated aluminum-doped cobalt oxide core, that is, a tin-carbon-coated aluminum-doped cathode precursor.

[0068] In the third aspect, the present invention provides a cathode material, which is prepared from the cathode precursor described in the first aspect.

[0069] In the fourth aspect, the present invention provides a lithium battery, which includes the cathode material described in the third aspect.

[0070] The numerical ranges described in the present invention not only include the specific point values exemplified above, but also include any arbitrary point values between the above numerical ranges not exemplified. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) For the tin-carbon-coated aluminum-doped cathode precursor provided by the present invention, due to the coating of the tin-carbon coating shell, the tin-carbon-coated aluminum-doped cathode precursor has a high electronic conductivity and a high lithium-ion diffusion rate. The cathode material prepared from the tin-carbon-coated aluminum-doped cathode precursor also has a high electronic conductivity and a high lithium-ion diffusion rate, so that the battery prepared from the cathode material has a high initial efficiency and excellent cycling performance;

[0073] (2) The tin-carbon-coated aluminum-doped cathode precursor provided by the present invention has a tin-carbon coating shell. After the cathode material is prepared from the tin-carbon-coated aluminum-doped cathode precursor, the tin-carbon coating shell can effectively prevent the side reaction between the cathode material and the electrolyte, thereby further improving the electrochemical performance of the battery;

[0074] (3) In the preparation method provided by the present invention, by mixing the aluminum-doped cobalt carbonate core with the tin source, the carbon source and the solvent, the surface of the aluminum-doped cobalt carbonate core is coated with an organic colloid containing the tin source, and a tin-carbon coating shell is formed outside the aluminum-doped cobalt carbonate core during the subsequent heat treatment process, thereby inhibiting the Al segregation that occurs during the heat treatment of the aluminum-doped cobalt carbonate core, reducing the risk of forming a large number of flaky Al structures on the surface of the cobalt oxide precursor, ensuring the effective doping of aluminum to the cobalt carbonate core, and avoiding the damage to the battery separator caused by the cathode material prepared from the cathode precursor after Al segregation, thereby improving the performance of the battery;

[0075] (4) In the preparation method provided by the present invention, the organic colloid containing the tin source coated on the surface of the aluminum-doped cobalt carbonate core undergoes pyrolysis during the heat treatment process. The carbon in the tin-carbon coating shell obtained after pyrolysis can improve the morphology of the aluminum-doped cobalt oxide core formed after the heat treatment of the aluminum-doped cobalt carbonate core and inhibit the cracking of the aluminum-doped cobalt oxide core, thereby further improving the performance of the cathode material and the battery prepared from the cathode material. Description of the Drawings

[0076] Figure 1 is the SEM image of the tin-carbon-coated aluminum-doped cathode precursor provided in Example 1.

[0077] Figure 2 is the SEM image of the aluminum-doped cathode precursor provided in Comparative Example 1. Detailed Embodiments

[0078] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0079] Example 1

[0080] This embodiment provides a tin-carbon-coated aluminum-doped positive electrode precursor, which includes an aluminum-doped cobalt oxide core with a D50 particle size of 15 μm and a tin-carbon coating shell with a thickness of 0.3 μm coating the aluminum-doped cobalt oxide core.

[0081] Based on the mass of the positive electrode precursor, the mass fraction of aluminum in the positive electrode precursor is 1.4 wt %, the mass ratio of tin to carbon is 1:0.75, the mass fraction of tin is 2.75 wt %, and the mass fraction of carbon is 2.06 wt %.

[0082] The preparation method of the positive electrode precursor is:

[0083] (1) Using an ammonium bicarbonate aqueous solution with a concentration of 150 g / L as a base liquid, a cobalt salt-doped aluminum aqueous solution with a cobalt sulfate concentration of 120 g / L and a mass ratio of aluminum ions to cobalt ions of 2:100 and an ammonium bicarbonate aqueous solution with a concentration of 150 g / L are added to the base liquid in parallel, the pH is controlled to 8.0 and the stirring speed is 150 r / min to perform a coprecipitation reaction; after the coprecipitation reaction, solid-liquid separation and washing are performed in sequence, and the obtained solid is dried at 105° C. to obtain an aluminum-doped cobalt carbonate core;

[0084] (2) dissolving anhydrous tin chloride and cetyltrimethylammonium bromide in water to obtain a primary mixed solution, and then sequentially adding pyrrole, resorcinol, and a mixture of formaldehyde and sodium carbonate to the obtained primary mixed solution to obtain a glue solution, wherein the concentration of anhydrous tin chloride in the glue solution is 0.3 mol / L, the concentration of cetyltrimethylammonium bromide is 0.12 mol / L, the concentration of pyrrole is 1-10 g / L, the concentration of resorcinol is 1-10 g / L, the concentration of formaldehyde is 0.35 mol / L, and the concentration of sodium carbonate is 0.3 mol / L;

[0085] (3) mixing the aluminum-doped cobalt carbonate cores obtained in step (1) and the colloid obtained in step (2) at a mass ratio of 1:3.5 by stirring to obtain a mixed sol;

[0086] (4) placing the mixed sol obtained in step (3) in an air atmosphere, and subjecting the mixed sol to a polymerization reaction by heat treatment at 75°C for 1.5 hours, and then filtering and drying in sequence to obtain a first intermediate; then heat treating the obtained first intermediate at 600°C for 3.5 hours in an argon atmosphere to obtain a second intermediate; then heat treating the obtained second intermediate at 700°C for 1.2 hours in an air atmosphere to obtain a tin-carbon-coated aluminum-doped cobalt oxide core, i.e., a tin-carbon-coated aluminum-doped positive electrode precursor.

[0087] Example 2

[0088] This embodiment provides a tin-carbon coated aluminum-doped cathode precursor. The cathode precursor includes an aluminum-doped cobalt oxide core with a D50 particle size of 10 μm, and a tin-carbon coating shell with a thickness of 0.1 μm coated on the outside of the aluminum-doped cobalt oxide core.

[0089] Based on the mass of the cathode precursor as 100%, the mass fraction of aluminum in the cathode precursor is 0.8 wt%, the mass ratio of tin to carbon is 1:0.5, the mass fraction of tin is 1 wt%, and the mass fraction of carbon is 0.5 wt%.

[0090] The preparation method of the cathode precursor is as follows:

[0091] (1) Using an ammonium bicarbonate aqueous solution with a concentration of 100 g / L as the bottom liquid, a cobalt salt doped with aluminum aqueous solution with a cobalt sulfate concentration of 80 g / L and a mass ratio of aluminum ions to cobalt ions of 1:100 is added to the bottom liquid in a co-current manner with an ammonium bicarbonate aqueous solution with a concentration of 100 g / L. The pH is controlled at 7.5 and stirred at a rotation speed of 200 r / min to carry out a co-precipitation reaction; after the co-precipitation reaction, solid-liquid separation and washing are carried out in sequence, and then the obtained solid is dried at 130 °C to obtain an aluminum-doped cobalt carbonate core.

[0092] (2) Dissolve anhydrous tin chloride and cetyltrimethylammonium bromide in water to obtain a primary mixture, and then add pyrrole, resorcinol, and a mixture of formaldehyde and sodium carbonate to the obtained primary mixture in sequence to obtain a colloidal solution. The concentration of anhydrous tin chloride in the colloidal solution is 0.1 mol / L, the concentration of cetyltrimethylammonium bromide is 0.08 mol / L, the concentration of pyrrole is 1 g / L, the concentration of resorcinol is 1 g / L, the concentration of formaldehyde is 0.5 mol / L, and the concentration of sodium carbonate is 0.5 mol / L.

[0093] (3) Mix the aluminum-doped cobalt carbonate core obtained in step (1) and the colloidal solution obtained in step (2) with a mass ratio of 1:2 by stirring to obtain a mixed sol.

[0094] (4) Place the mixed sol obtained in step (3) in an air atmosphere, and carry out a heat treatment at 90 °C for 0.5 h to make the mixed sol carry out a polymerization reaction, and then carry out filtration and drying in sequence to obtain a first intermediate; then in an argon atmosphere, carry out a heat treatment on the obtained first intermediate at 500 °C for 5 h to obtain a second intermediate; then in an air atmosphere, carry out a heat treatment on the obtained second intermediate at 800 °C for 0.5 h to obtain a tin-carbon coated aluminum-doped cobalt oxide core, that is, a tin-carbon coated aluminum-doped cathode precursor.

[0095] Example 3

[0096] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. The cathode precursor includes an aluminum-doped cobalt oxide core with a D50 particle size of 20 μm, and a tin-carbon coating shell with a thickness of 0.5 μm coated on the outside of the aluminum-doped cobalt oxide core.

[0097] Based on the mass of the cathode precursor as 100%, the mass fraction of aluminum in the cathode precursor is 2 wt%, the mass ratio of tin to carbon is 1:1, the mass fraction of tin is 5 wt%, and the mass fraction of carbon is 5 wt%.

[0098] The preparation method of the cathode precursor is as follows:

[0099] (1) Using an ammonium bicarbonate aqueous solution with a concentration of 200 g / L as the bottom liquid, a cobalt salt-doped aluminum aqueous solution with a cobalt salt concentration of 150 g / L and a mass ratio of aluminum ions to cobalt ions of 3:100 is added to the bottom liquid in a parallel flow manner with an ammonium bicarbonate aqueous solution with a concentration of 200 g / L. The pH is controlled to be 8.5 and stirred at a rotation speed of 100 r / min to carry out a coprecipitation reaction; after the coprecipitation reaction, solid-liquid separation and washing are carried out in sequence, and then the obtained solid is dried at 80 °C to obtain an aluminum-doped cobalt carbonate core;

[0100] (2) Dissolve anhydrous tin chloride and cetyltrimethylammonium bromide in water to obtain a preliminary mixture, and then add pyrrole, resorcinol, and a mixture of formaldehyde and sodium carbonate to the obtained preliminary mixture in sequence to obtain a colloidal solution. The concentration of anhydrous tin chloride in the colloidal solution is 0.5 mol / L, the concentration of cetyltrimethylammonium bromide is 0.15 mol / L, the concentration of pyrrole is 10 g / L, the concentration of resorcinol is 10 g / L, the concentration of formaldehyde is 0.2 mol / L, and the concentration of sodium carbonate is 0.1 mol / L;

[0101] (3) Mix the aluminum-doped cobalt carbonate core obtained in step (1) and the colloidal solution obtained in step (2) with a mass ratio of 1:5 by stirring to obtain a mixed sol;

[0102] (4) Place the mixed sol obtained in step (3) in an air atmosphere, carry out a heat treatment at 60 °C for 3 h to cause the mixed sol to carry out a polymerization reaction, and then carry out filtration and drying in sequence to obtain a first intermediate; then in a nitrogen atmosphere, carry out a heat treatment on the obtained first intermediate at 700 °C for 2 h to obtain a second intermediate; then in an air atmosphere, carry out a heat treatment on the obtained second intermediate at 600 °C for 2 h to obtain a tin-carbon-coated aluminum-doped cobalt oxide core, that is, a tin-carbon-coated aluminum-doped cathode precursor.

[0103] Example 4

[0104] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that the mass fraction of aluminum is 0.3 wt%, that is, in step (1) of the preparation method of the cathode precursor, the mass ratio of aluminum ions to cobalt ions in the cobalt salt-doped aluminum solution is 0.5:100, the rest are the same as in Example 3.

[0105] Example 5

[0106] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that the mass fraction of aluminum is 3.7 wt%, that is, in step (1) of the preparation method of the cathode precursor, the mass ratio of aluminum ions to cobalt ions in the cobalt salt-doped aluminum solution is 4:100, the rest are the same as in Example 3.

[0107] Example 6

[0108] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor, except that the mass ratio of tin to carbon is 1:2;

[0109] That is, in step (2) of the preparation method of the cathode precursor, the concentration of anhydrous tin chloride in the glue solution is 0.5 mol / L, the concentration of pyrrole is 20 g / L, the concentration of resorcinol is 20 g / L, the concentration of formaldehyde is 0.4 mol / L, and in step (3) of the preparation method of the cathode precursor, the mass ratio of the aluminum-doped cobalt carbonate core to the glue solution is 1:5. The rest are the same as in Example 3.

[0110] Example 7

[0111] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor, except that the mass ratio of tin to carbon is 1:0.2;

[0112] That is, in step (2) of the preparation method of the cathode precursor, the concentration of anhydrous tin chloride in the glue solution is 0.5 mol / L, the concentration of pyrrole is 2 g / L, the concentration of resorcinol is 2 g / L, the concentration of formaldehyde is 0.04 mol / L, and in step (3) of the preparation method of the cathode precursor, the mass ratio of the aluminum-doped cobalt carbonate core to the glue solution is 1:5. The rest are the same as in Example 3.

[0113] Example 8

[0114] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor, except that the thickness of the tin-carbon coating shell is 0.05 μm;

[0115] That is, in step (3) of the preparation method of the cathode precursor, the mass ratio of the aluminum-doped cobalt carbonate core to the glue solution is 1:0.5. The rest are the same as in Example 3.

[0116] Example 9

[0117] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor, except that the thickness of the tin-carbon coating shell is 1 μm;

[0118] That is, in step (3) of the method for preparing the cathode precursor, the mass ratio of the aluminum-doped cobalt carbonate core to the colloidal solution is 1:10, and the rest are the same as in Example 3.

[0119] Example 10

[0120] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that in step (3) of the method for preparing the cathode precursor, the temperature for the polymerization reaction of the mixed sol is 50 °C, the rest are the same as in Example 3.

[0121] Example 11

[0122] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that in step (3) of the method for preparing the cathode precursor, the temperature for the polymerization reaction of the mixed sol is 100 °C, the rest are the same as in Example 3.

[0123] Example 12

[0124] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that in step (3) of the method for preparing the cathode precursor, the temperature for heat-treating the obtained first intermediate is 400 °C, the rest are the same as in Example 3.

[0125] Example 13

[0126] This embodiment provides a tin-carbon-coated aluminum-doped cathode precursor. Except that in step (3) of the method for preparing the cathode precursor, the temperature for heat-treating the obtained first intermediate is 800 °C, the rest are the same as in Example 3.

[0127] Comparative Example 1

[0128] This comparative example provides an aluminum-doped cathode precursor. Except that the tin-carbon coating shell outside the aluminum-doped cobalt oxide core is omitted, that is, steps (2), (3), and (4) of the method for preparing the cathode precursor are omitted, and the aluminum-doped cobalt carbonate core obtained in step (1) is heat-treated at 800 °C to obtain an aluminum-doped cathode precursor, the rest are the same as in Example 3.

[0129] Comparative Example 2

[0130] This comparative example provides a tin-coated aluminum-doped cathode precursor. Except that the tin-carbon coating shell outside the aluminum-doped cobalt oxide core is replaced with a tin shell, that is, the mixture of pyrrole, resorcinol, and formaldehyde and sodium carbonate added in step (2) of the method for preparing the cathode precursor is omitted, the rest are the same as in Example 3.

[0131] Comparative Example 3

[0132] This comparative example provides a carbon-coated aluminum-doped cathode precursor. Except that the tin-carbon coating shell covering the outside of the aluminum-doped cobalt oxide core is replaced with a carbon shell, that is, anhydrous stannous chloride added in step (2) of the preparation method of the cathode precursor is omitted, the rest are the same as in Example 3.

[0133] The tin-carbon-coated aluminum-doped cathode precursor provided in Example 1 and the aluminum-doped cathode precursor provided in Comparative Example 1 were tested with a scanning electron microscope, and the SEM image of the tin-carbon-coated aluminum-doped cathode precursor provided in Example 1 is as Figure 1 shown; the SEM image of the aluminum-doped cathode precursor provided in Comparative Example 1 is as Figure 2 shown.

[0134] The cathode materials were prepared using the cathode precursors provided in the above examples and comparative examples. The method for preparing the cathode materials is as follows: The cathode precursor and lithium carbonate were uniformly mixed according to a molar ratio of lithium in lithium carbonate to metal ions in the cathode precursor of 1:1.05, and then placed in a tube furnace for sintering. The sintering atmosphere was pure oxygen, and pre-sintering was carried out at 400 °C for 4 h. After pre-sintering, it was naturally cooled to room temperature, the sample was taken out, simply ground, and then high-temperature sintering was continued. Then, calcination was carried out at 800 °C for 15 h. After calcination, it was naturally cooled to room temperature, and the sample was ground and sieved to obtain the cathode material.

[0135] The prepared cathode material was used to prepare a lithium-ion battery: The obtained cathode material, conductive carbon black SP (TIMCAL), and polyvinylidene fluoride PVDF (HSV900) were mixed according to a mass ratio of 90:5:5. The solvent was N-methylpyrrolidone, and the mixture was stirred into a slurry. The obtained slurry was uniformly coated on aluminum foil with a doctor blade having a coating gap of 100 μm; after coating, it was first dried by blowing, then roll-pressed and cut into circular electrode sheets, and then vacuum-dried at 120 °C and the weight of the electrode sheets was measured to obtain the positive electrode sheets of the button half-cell; the negative electrode was a metal lithium sheet, the separator was a PP microporous membrane, and the electrolyte was a lithium battery basic electrolyte. The positive electrode sheet, metal lithium sheet, separator, and electrolyte were assembled to obtain a button cell.

[0136] The obtained button cells were charged and discharged at 0.1C / 0.1C, and charge-discharge tests were carried out in a voltage window of 2.8 - 4.3V. The first charge-discharge efficiency (1C / 0.1C discharge capacity ratio), 0.1C rate performance, and capacity retention rate after 100 cycles at 1C of the button cells are shown in Table 1.

[0137] Table 1

[0138]

[0139]

[0140] From Table 1 and Figure 1 and Figure 2 it can be obtained that:

[0141] (1) After preparing the cathode material from the cathode precursor provided in Examples 1 to 3, the battery prepared from the cathode material exhibits a high first charge-discharge efficiency, high rate performance, and excellent cycle stability;

[0142] (2) By comparing Example 3 with Examples 4 and 5, it can be seen that the mass fraction of aluminum in the cathode precursor provided by the present invention affects the performance of the cathode precursor and the battery; when the mass fraction of aluminum in the cathode precursor is 0.8-2 wt%, the cathode precursor and the battery exhibit better performance. This is because after aluminum doping, the strong Al-O bond can inhibit the lattice oxygen precipitation and phase change of lithium cobaltate at high voltage, improving the stability of the electrode material at high voltage; if the doping amount of aluminum is too low, the improvement effect is poor, and if the doping amount of aluminum is too high, it will cause segregation of Al inside the particles, resulting in deterioration of the electrochemical performance of the battery;

[0143] (3) By comparing Example 3 with Examples 6 and 7, it can be seen that the mass ratio of tin to carbon in the cathode precursor provided by the present invention affects the performance of the cathode precursor and the battery; when the mass ratio of tin to carbon is 1:(0.5-1), the cathode precursor and the battery exhibit better performance. This is because when the mass ratio of tin to carbon is 1:(0.5-1), carbon and tin have good combination, and the synergistic effect between tin and carbon can enhance the lithium ion diffusion rate of the composite material, thus improving the rate performance of the battery;

[0144] (4) By comparing Example 3 with Examples 8 and 9, it can be seen that the thickness of the tin-carbon coating shell in the cathode precursor provided by the present invention affects the performance of the cathode precursor and the battery; when the thickness of the tin-carbon coating shell is 0.1-0.5 μm, the cathode precursor and the battery exhibit better performance. This is because when the thickness of the coating shell is too thick, it is not conducive to the rapid transmission of ions, and when the thickness of the tin-carbon coating shell is too thin, it is difficult to play a protective role;

[0145] (5) It can be seen from the comparison between Example 3 and Examples 10 and 11 that in the preparation method of the cathode precursor provided by the present invention, the temperature at which the mixed sol undergoes a polymerization reaction affects the performance of the cathode precursor and the battery; when the temperature is 60-90 °C, the cathode precursor and the battery exhibit better performance. This is because within this temperature range, the sol polymerization is slow and uniform, which can tightly connect the polymer with the core and improve the electronic conductivity of the material; when the temperature is too low, the reaction time is long, which is not conducive to ensuring the efficiency of industrial production; while when the temperature is too high, the reaction will be violent, resulting in problems such as particle agglomeration and adhesion and uneven thickness of the protective layer;

[0146] (6) It can be seen from the comparison between Example 3 and Examples 12 and 13 that in the preparation method of the cathode precursor provided by the present invention, the temperature for heat-treating the obtained first intermediate affects the performance of the cathode precursor and the battery; when the temperature is 500-700 °C, the cathode precursor and the battery exhibit better performance. This is because at this temperature, effective colloidal carbonization can be achieved to form a tight shell layer, and tin can also be evenly distributed in the shell layer; when the temperature is too low, the colloidal carbonization is incomplete; when the temperature is too high, it is easy to cause uneven shrinkage of the core-shell and the appearance of cavities;

[0147] (7) It can be seen from the comparison between Example 3 and Comparative Examples 1-3 that for the tin-carbon-coated aluminum-doped cathode precursor provided by the present invention, due to the coating of the tin-carbon coating shell, the tin-carbon-coated aluminum-doped cathode precursor has a high electronic conductivity and a high lithium-ion diffusion rate. The cathode material prepared from the tin-carbon-coated aluminum-doped cathode precursor also has a high electronic conductivity and a high lithium-ion diffusion rate, so that the battery prepared from the cathode material has a high initial efficiency and excellent cycling performance;

[0148] The tin-carbon-coated aluminum-doped cathode precursor provided by the present invention has a tin-carbon coating shell. After the cathode material is prepared from the tin-carbon-coated aluminum-doped cathode precursor, the tin-carbon coating shell can effectively prevent side reactions between the cathode material and the electrolyte, thereby further improving the electrochemical performance of the battery;

[0149] In the preparation method provided by the present invention, by mixing the aluminum-doped cobalt carbonate core with a tin source, a carbon source and a solvent, an organic colloid containing the tin source is coated on the surface of the aluminum-doped cobalt carbonate core, and a tin-carbon coating shell is formed outside the aluminum-doped cobalt carbonate core during the subsequent heat treatment process, thereby inhibiting the Al segregation that occurs during the heat treatment process of the aluminum-doped cobalt carbonate core, reducing the risk of forming a large number of flaky Al structures on the surface of the cobalt oxide precursor, ensuring the effective doping of aluminum into the cobalt carbonate core, and avoiding the damage to the battery separator caused by the cathode material prepared from the cathode precursor after Al segregation, thereby improving the performance of the battery;

[0150] In the preparation method provided by the present invention, during the heat treatment, the organic colloid containing a tin source and coated on the surface of the aluminum-doped cobalt carbonate core undergoes pyrolysis. The carbon in the tin-carbon coating shell obtained after pyrolysis can improve the morphology of the aluminum-doped cobalt oxide core formed after the heat treatment of the aluminum-doped cobalt carbonate core and inhibit the cracking of the aluminum-doped cobalt oxide core, thereby further improving the performance of the cathode material and the battery prepared from the cathode material.

[0151] The above are only specific embodiments 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 fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A tin-carbon coated aluminum-doped cathode precursor, characterized in that The positive electrode precursor includes an aluminum-doped cobalt oxide core and a tin-carbon coated shell covering the outside of the aluminum-doped cobalt oxide core.

2. The cathode precursor according to claim 1, wherein Based on the mass of the positive electrode precursor as 100%, the mass fraction of aluminum in the positive electrode precursor is 0.8 - 2 wt%. Preferably, the mass ratio of tin to carbon in the positive electrode precursor is 1:(0.5 - 1). Based on the mass of the positive electrode precursor as 100%, the mass fraction of tin in the positive electrode precursor is 0.5 - 5 wt%. Preferably, based on the mass of the positive electrode precursor as 100%, the mass fraction of carbon in the positive electrode precursor is 0.5 - 5 wt%.

3. The cathode precursor according to claim 1 or 2, characterized in that, The D50 particle size of the aluminum-doped cobalt oxide core is 10 - 20 μm. Preferably, the thickness of the tin-carbon coated shell is 0.1 - 0.5 μm.

4. A method for preparing the cathode precursor according to any one of claims 1 to 3, characterized in that, The preparation method includes: Mixing an aluminum-doped cobalt carbonate core, a tin source, a carbon source, and a solvent to obtain a mixed sol, and performing heat treatment on the obtained mixed sol to obtain a positive electrode precursor with a tin-carbon coated aluminum-doped structure.

5. The preparation method according to claim 4, characterized in that, The method for preparing the aluminum-doped cobalt carbonate core includes: Mixing a first complexing agent solution, a cobalt salt doped with aluminum solution, and a precipitating agent solution, and performing a coprecipitation reaction to obtain an aluminum-doped cobalt carbonate core. Preferably, the aluminum in the cobalt salt doped with aluminum solution exists in the form of aluminum ions, and the mass ratio of aluminum ions to cobalt ions in the cobalt salt doped with aluminum solution is (1 - 3):

100. Preferably, the pH is controlled to be 7.0 - 8.0 during the coprecipitation reaction.

6. The preparation method according to claim 4 or 5, characterized in that, The tin source includes any one or a combination of at least two of anhydrous tin chloride, sodium stannate, or stannous sulfate. Preferably, the carbon source includes pyrrole, resorcinol, and formaldehyde. Preferably, the solvent includes water. Preferably, the mixing further includes mixing a surfactant and a pH regulator. Preferably, the mixing includes: performing a second mixing on the tin source, the carbon source, the solvent, the surfactant, and the pH regulator to obtain a colloidal solution, and performing a third mixing on the aluminum-doped cobalt carbonate core and the obtained colloidal solution to obtain a mixed sol. Preferably, the concentration of the tin source in the colloidal solution is 0.1 - 0.5 mol / L. Preferably, the concentration of the surfactant in the colloidal solution is 0.08 - 0.15 mol / L. Preferably, the concentration of pyrrole in the colloidal solution is 1 - 10 g / L. Preferably, the concentration of resorcinol in the colloidal solution is 1 - 10 g / L. Preferably, the concentration of formaldehyde in the colloidal solution is 0.2 - 0.5 mol / L. Preferably, the concentration of the pH regulator in the colloidal solution is 0.1 - 0.5 mol / L. Preferably, the mass ratio of the aluminum-doped cobalt carbonate core to the obtained colloidal solution in the third mixing is 1:(2 - 5).

7. The preparation method according to any one of claims 4 to 6, characterized in that The heat treatment includes: subjecting the obtained mixed sol to a polymerization reaction through a first heat treatment, then performing a second heat treatment in a protective atmosphere, and then performing a third heat treatment in an oxygen-containing atmosphere to obtain a tin-carbon coated aluminum-doped cobalt oxide core, that is, a positive electrode precursor with a tin-carbon coated aluminum-doped structure. Preferably, the first heat treatment is performed in an air atmosphere, the temperature of the first heat treatment is 60 - 90 °C, and the time is 0.5 - 3 h. Preferably, the temperature of the second heat treatment is 500 - 700 °C, and the time is 2 - 5 h. Preferably, the temperature of the third heat treatment is 600 - 800 °C, and the time is 0.5 - 2 h.

8. The preparation method according to any one of claims 4 to 7, characterized in that, The preparation method includes: (1) Using an ammonium bicarbonate solution with a concentration of 100 - 200 g / L as the bottom liquid, a cobalt salt-doped aluminum solution with a cobalt salt concentration of 80 - 150 g / L and a mass ratio of aluminum ions to cobalt ions of (1 - 3):100 is added to the bottom liquid in a co-current manner with a precipitant solution with a concentration of 100 - 200 g / L. The pH is controlled to be 7.0 - 8.5, and the mixture is stirred at a rotation speed of 100 - 200 r / min for a coprecipitation reaction; after the coprecipitation reaction, solid-liquid separation and washing are carried out in sequence, and then the obtained solid is dried at 80 - 130 °C to obtain an aluminum-doped cobalt carbonate core; (2) Dissolving anhydrous tin chloride and cetyltrimethylammonium bromide in water to obtain a preliminary mixture, and then successively adding pyrrole, resorcinol, and a mixture of formaldehyde and sodium carbonate to the obtained preliminary mixture to obtain a colloidal solution. The concentration of anhydrous tin chloride in the colloidal solution is 0.1 - 0.5 mol / L, the concentration of cetyltrimethylammonium bromide is 0.08 - 0.15 mol / L, the concentration of pyrrole is 1 - 10 g / L, the concentration of resorcinol is 1 - 10 g / L, the concentration of formaldehyde is 0.2 - 0.5 mol / L, and the concentration of sodium carbonate is 0.1 - 0.5 mol / L; (3) Mixing the aluminum-doped cobalt carbonate core obtained in step (1) and the colloidal solution obtained in step (2) with a mass ratio of 1:(2 - 5) by stirring to obtain a mixed sol; (4) Placing the mixed sol obtained in step (3) in an air atmosphere, carrying out a heat treatment at 60 - 90 °C for 0.5 - 3 h to cause the mixed sol to undergo a polymerization reaction, and then successively carrying out filtration and drying to obtain a first intermediate; then, in a protective atmosphere, carrying out a heat treatment on the obtained first intermediate at 500 - 700 °C for 2 - 5 h to obtain a second intermediate; then, in an oxygen-containing atmosphere, carrying out a heat treatment on the obtained second intermediate at 600 - 800 °C for 0.5 - 2 h to obtain a tin-carbon-coated aluminum-doped cobalt oxide core, that is, a tin-carbon-coated aluminum-doped cathode precursor.

9. A cathode material, characterized in that, The cathode material is prepared from the cathode precursor according to any one of claims 1 - 3.

10. A lithium battery, characterized in that, The lithium battery includes the cathode material according to claim 9.

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