Positive electrode precursor, preparation method of positive electrode precursor, positive electrode material and preparation process of positive electrode material

Abstract

The invention provides a positive electrode precursor, a preparation method of the positive electrode precursor, a positive electrode material and a preparation process of the positive electrode material. The positive electrode precursor comprises a phosphorus-doped seed crystal, a phosphorus-doped layer coated outside the phosphorus-doped seed crystal, and a zirconium-rich shell layer coated outside the phosphorus-doped layer, and the mass fraction of doped phosphorus in the phosphorus-doped seed crystal is greater than the mass fraction of doped phosphorus in the phosphorus-doped layer. In the positive electrode precursor provided by the invention, due to introduction of gradient concentration doping of phosphorus, separation of lattice oxygen and mixed arrangement of cations are inhibited, the structural stability of the positive electrode material is enhanced, and the risk that the positive electrode material generates microcracks in the circulation process is reduced; in addition, due to the coating of the zirconium-rich shell layer, not only is the residual alkali reduced, but also the corrosion resistance and the stability of the positive electrode precursor are improved; therefore, the battery prepared from the positive electrode precursor provided by the invention shows relatively high first charge-discharge efficiency and rate capability and excellent cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, relates to a cathode precursor, and particularly relates to a cathode precursor and a preparation method thereof, a cathode material and a preparation process thereof. Background Art

[0002] The new energy industry is undergoing rapid innovation, and electric vehicles and lithium-ion batteries have penetrated into our daily lives. Among the ternary precursor materials, metal oxides represented by nickel cobalt manganese (NCM) and nickel cobalt aluminum (NCA), as the core of the next-generation high-energy density lithium battery materials, their performance may directly determine the cycle life, energy density and safety of the battery. Among them, although the NCM precursor has improved tap density, high-nickel materials are prone to problems such as cracks and cation mixing during the cycling process. In addition, since Li2CO3 and / or LiOH exist on the surface of the NCM precursor, after the cathode material is prepared from the NCM precursor, these residual alkalis are prone to react with the electrolyte to generate HF, which aggravates the capacity attenuation and seriously affects the first charge-discharge efficiency, rate performance and cycle life of the battery prepared from the cathode material.

[0003] CN116639735A discloses a preparation method and application of a quaternary precursor with different structural compactness, nickel-tungsten concentration gradient and in-situ cobalt coating. Among them, the contents of nickel and tungsten gradually increase from the inside to the outside, and cobalt is coated on the surface of the material by a coprecipitation process. The material has a structure of "low-nickel, low-tungsten, low-compactness inner layer - high-nickel, high-tungsten, high-compactness outer layer - cobalt-coated surface" from the inside to the outside, and a certain difference in structural compactness is generated by controlling the concentration and flow rate. The wet method of doping tungsten is used to enhance the structural stability; a stable structure with low nickel in the inner layer and cobalt coating on the surface layer is designed, which provides a buffer space for the volume change during the subsequent charge-discharge process, effectively reducing the generation of microcracks and harmful side reactions. However, the structural stability of this ternary precursor still cannot meet the requirements in practical applications, and there is still a certain risk of cracking during the cycling process, and there is also a risk of side reactions with the electrolyte.

[0004] CN118084081A discloses a ternary cathode material and a preparation method thereof, belonging to the technical field of cathode materials for lithium-ion batteries. (1) Prepare two kinds of Ni, Co, Mn mixed salt solutions, namely solution a and solution b; (2) Continuously add the NCM mixed salt solution a, precipitants and complexing agents into the reaction kettle for co-precipitation reaction respectively. The overflow of the reaction kettle flows to the thickener. When the particle size D50 of the materials in the reaction kettle grows to 2-8 μm, the reaction is paused; (3) Continuously add the NCM mixed salt solution b, precipitants and complexing agents into the reaction kettle to continue the co-precipitation reaction. The overflow of the reaction kettle flows to the thickener. When the particle size D50 of the materials in the reaction kettle grows to 5-15 μm, the reaction is stopped; (4) The materials obtained in step (3) are filtered under pressure, washed and dried to obtain a ternary precursor; (5) The ternary precursor obtained in step (4) is mixed with a lithium salt and subjected to a heating reaction. After the reaction is completed, it is cooled to room temperature, and after crushing and screening, a ternary cathode material is obtained. However, the ternary precursor obtained by this preparation method is prone to problems such as cracks and cation mixing during the cycling process. Moreover, after preparing the cathode material with this ternary precursor, the cathode material is prone to react with the electrolyte to generate HF, resulting in a decline in the electrochemical performance of the battery.

[0005] The NCM cathode precursors disclosed in the prior art all have certain defects. There are problems such as cracks and cation mixing prone to occur during the cycling process, and there is also a problem that the cathode material prepared with the NCM precursor is prone to side reactions with the electrolyte, resulting in the first charge-discharge efficiency, rate performance and cycle stability of the battery prepared with the NCM precursor not meeting the requirements of practical applications. Therefore, it is crucial to develop and design a new type of cathode precursor and its preparation method, cathode material and its preparation process. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a cathode precursor and its preparation method, a cathode material and its preparation process. In the cathode precursor provided by the present invention, due to the introduction of gradient concentration doping of phosphorus, the precipitation of lattice oxygen and cation mixing are inhibited, the structural stability of the cathode material is enhanced, and the risk of generating microcracks in the cathode material during the cycling process is reduced; in addition, due to the coating of the zirconium-rich shell, not only the residual alkali is reduced, but also the corrosion resistance and stability of the cathode precursor are improved; therefore, the battery prepared with the cathode precursor provided in the present invention exhibits high first charge-discharge efficiency and rate performance, and excellent cycle stability.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a cathode precursor, which comprises a phosphorus-doped seed crystal, a phosphorus-doped layer coated on the outside of the phosphorus-doped seed crystal, and a zirconium-rich shell layer coated on the outside of the phosphorus-doped layer;

[0009] The mass fraction of doped phosphorus in the phosphorus-doped seed crystal is greater than that of doped phosphorus in the phosphorus-doped layer.

[0010] The cathode precursor provided in the present invention includes a phosphorus-doped seed crystal and a phosphorus-doped layer coated on the outside of the phosphorus-doped seed crystal. Since phosphorus has a relatively strong electronegativity, the introduction of gradient concentration doping of phosphorus can enable oxygen atoms to form a stronger coordination effect with metal ions, adjusting the electronic structure of oxygen in the lattice. This makes the metal ions more stable, reduces the instability of metal ions in the redox reaction, thereby inhibiting the precipitation of lattice oxygen and cation mixing, preventing excessive lattice expansion or contraction of the cathode material prepared from the cathode precursor, enhancing the structural stability of the cathode material, and reducing the risk of microcracks generated in the cathode material during the cycling process.

[0011] The cathode precursor provided in the present invention includes a zirconium-rich shell layer on the outermost layer. Due to the coating of the zirconium-rich shell layer, not only can the residual alkali on the surface of the cathode precursor be effectively reduced, but also zirconium dioxide in the zirconium-rich shell layer has good corrosion resistance and stability. Therefore, the risk of side reactions between the cathode material prepared from the cathode precursor and the electrolyte can be effectively reduced.

[0012] In summary, in the cathode precursor provided by the present invention, due to the introduction of gradient concentration doping of phosphorus, the precipitation of lattice oxygen and cation mixing are inhibited, the structural stability of the cathode material is enhanced, and the risk of microcracks generated in the cathode material during the cycling process is reduced; in addition, due to the coating of the zirconium-rich shell layer, not only the residual alkali is reduced, but also the corrosion resistance and stability of the cathode precursor are improved; therefore, the battery prepared from the cathode precursor provided in the present invention exhibits high first charge-discharge efficiency and rate performance, as well as excellent cycle stability.

[0013] Preferably, the D50 particle size of the phosphorus-doped seed crystal is 2.5 - 3.5 μm, for example, it can be 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm or 3.5 μm, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0014] Preferably, based on the mass of the phosphorus-doped seed crystal as 100%, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5-2.0 wt%, for example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 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 not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0015] Preferably, the thickness of the phosphorus-doped layer is 6-7 μm, for example, it can be 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm or 7.0 μm, but 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 phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1-0.8 wt%, for example, it can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt% or 0.8 wt%, but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the thickness of the zirconium-rich shell layer is 1-2 μm, for example, it can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2.0 μm, but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] In a second aspect, the present invention provides a method for preparing the cathode precursor described in the first aspect, and the preparation method includes:

[0019] (1) The metal mixed salt solution, the precipitant solution, the complexing agent solution and the phosphorus source solution are added into the first bottom liquid in a co-current manner to carry out a co-precipitation reaction to obtain phosphorus-doped seeds;

[0020] (2) The phosphorus-doped seeds obtained in step (1) are added into the second bottom liquid, and then the metal mixed salt solution, the precipitant solution, the complexing agent solution and the phosphorus source solution are added into the second bottom liquid in a co-current manner to carry out a co-precipitation reaction to obtain a solution containing precipitates;

[0021] (3) Add a zirconium source solution to the solution containing the precipitate obtained in step (2) to carry out a precipitation reaction to obtain a cathode precursor;

[0022] In step (1), the flow rate of the phosphorus source solution added in parallel is higher than the flow rate of the phosphorus source solution added in parallel in step (2).

[0023] Preferably, the phosphorus source in the phosphorus source solution in step (1) and step (2) independently includes ammonium dihydrogen phosphate, and the solvent includes water.

[0024] Preferably, the concentrations of the phosphorus source in the phosphorus source solution in step (1) and step (2) are independently 5-20 mmol / L, for example, it can be 5 mmol / L, 6 mmol / L, 7 mmol / L, 8 mmol / L, 9 mmol / L, 10 mmol / L, 11 mmol / L, 12 mmol / L, 13 mmol / L, 14 mmol / L, 15 mmol / L, 16 mmol / L, 17 mmol / L, 18 mmol / L, 19 mmol / L or 20 mmol / L, but are not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0025] Preferably, the flow rate of the phosphorus source solution added in parallel in step (1) is 10-30 mL / min, for example, it can be 10 mL / min, 12 mL / min, 14 mL / min, 15 mL / min, 16 mL / min, 18 mL / min, 20 mL / min, 22 mL / min, 24 mL / min, 25 mL / min, 26 mL / min, 28 mL / min or 30 mL / min, but are not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0026] Preferably, the flow rate of the phosphorus source solution added in parallel in step (2) is 5-15 mL / min, for example, it can be 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 11 mL / min, 12 mL / min, 13 mL / min, 14 mL / min or 15 mL / min, but are not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0027] Preferably, the zirconium source in the zirconium source solution in step (3) independently includes any one or a combination of at least two of zirconium sulfate, zirconium nitrate or zirconium chloride. Typical but non-limiting combinations include a combination of zirconium sulfate and zirconium nitrate, a combination of zirconium nitrate and zirconium chloride, or a combination of zirconium sulfate, zirconium nitrate and zirconium chloride, and the solvent includes water.

[0028] Preferably, the concentration of the zirconium source in the zirconium source solution in step (3) is 20 - 60 mmol / L. For example, it can be 20 mmol / L, 25 mmol / L, 30 mmol / L, 35 mmol / L, 40 mmol / L, 45 mmol / L, 50 mmol / L, 55 mmol / L or 60 mmol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] Preferably, the feeding flow rate of the zirconium source solution in step (3) is 5 - 20 mL / min. For example, it can be 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 12 mL / min, 14 mL / min, 15 mL / min, 16 mL / min, 18 mL / min or 20 mL / min. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] Preferably, the metal salts in the metal mixed salt solution in steps (1) and (2) include nickel salt, manganese salt and cobalt salt, and the solvent includes water.

[0031] Preferably, the total concentration of metal ions in the metal mixed salt solution in steps (1) and (2) is independently 1 - 3 mol / L. For example, it can be 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L or 3.0 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] Preferably, the nickel salt includes any one or a combination of at least two of nickel chloride, nickel sulfate or nickel nitrate. Typical but non - limiting combinations include the combination of nickel chloride and nickel sulfate, the combination of nickel sulfate and nickel nitrate, or the combination of nickel chloride, nickel sulfate and nickel nitrate.

[0033] Preferably, the manganese salt includes any one or a combination of at least two of manganese chloride, manganese sulfate or manganese nitrate. Typical but non - limiting combinations include the combination of manganese chloride and manganese sulfate, the combination of manganese sulfate and manganese nitrate, or the combination of manganese chloride, manganese sulfate and manganese nitrate.

[0034] Preferably, the cobalt salt includes any one or a combination of at least two of cobalt chloride, cobalt sulfate or cobalt nitrate. Typical but non - limiting combinations include the combination of cobalt chloride and cobalt sulfate, the combination of cobalt sulfate and cobalt nitrate, or the combination of cobalt chloride, cobalt sulfate and cobalt nitrate.

[0035] Preferably, the precipitants in the precipitant solutions in steps (1) and (2) independently include any one or a combination of at least two of sodium hydroxide, lithium hydroxide, potassium hydroxide, sodium carbonate, or sodium bicarbonate. Typical but non-limiting combinations include the combination of sodium hydroxide and lithium hydroxide, the combination of lithium hydroxide and potassium hydroxide, the combination of potassium hydroxide and sodium carbonate, the combination of sodium carbonate and sodium bicarbonate, the ternary combination of sodium hydroxide, lithium hydroxide, and potassium hydroxide, or the ternary combination of lithium hydroxide, sodium carbonate, and sodium bicarbonate. The solvents independently include water.

[0036] Preferably, the concentrations of the precipitants in the precipitant solutions in steps (1) and (2) are independently 3 - 4 mol / L. For example, they can be 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.7 mol / L, 3.8 mol / L, 3.9 mol / L, or 4.0 mol / L, but are not limited to the listed values. Other unlisted values within this range are equally applicable.

[0037] Preferably, the complexing agents in the complexing agent solutions in steps (1) and (2) independently include any one or a combination of at least two of ammonia, ammonium bicarbonate, ammonium sulfate, oxalic acid, sodium oxalate, citric acid, sodium citrate, ethylenediaminetetraacetic acid, tartaric acid, sodium tartrate, or sodium hexametaphosphate. Typical but non-limiting combinations include the combination of ammonia and ammonium bicarbonate, the combination of ammonium sulfate and oxalic acid, the combination of citric acid and sodium citrate, the combination of ethylenediaminetetraacetic acid and tartaric acid, the combination of sodium oxalate and sodium tartrate, or the ternary combination of ammonia, citric acid, and sodium hexametaphosphate. The solvents independently include water.

[0038] Preferably, the concentrations of the complexing agents in the complexing agent solutions in steps (1) and (2) are independently 0.5 - 1 mol / L. For example, they can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1.0 mol / L, but are not limited to the listed values. Other unlisted values within this range are equally applicable.

[0039] Preferably, the pH of the first bottom solution in step (1) is 11 - 12, and the complexing agent concentration is 0.2 - 0.3 mol / L.

[0040] The pH of the first bottom solution in step (1) of the present invention is 11 - 12. For example, it can be 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, or 12.0, but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0041] In step (1) of the present invention, the complexing agent concentration of the first bottom solution is 0.2 to 0.3 mol / L. For example, it can be 0.20 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L, 0.25 mol / L, 0.26 mol / L, 0.27 mol / L, 0.28 mol / L, 0.29 mol / L or 0.30 mol / L. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] The first bottom solution described in the present invention is composed of a precipitating agent, a complexing agent and water.

[0043] Preferably, in step (2), the pH of the second bottom solution is 9.5 to 10.5, and the complexing agent concentration is 0.1 to 0.2 mol / L.

[0044] In step (2) of the present invention, the pH of the second bottom solution is 9.5 to 10.5. For example, it can be 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.3, 10.4 or 10.5. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In step (2) of the present invention, the complexing agent concentration of the second bottom solution is 0.1 to 0.2 mol / L. For example, it can be 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L or 0.20 mol / L. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] The second bottom solution described in the present invention is composed of a precipitating agent, a complexing agent and water.

[0047] Preferably, in step (1), during the coprecipitation reaction, the pH is controlled to be 11 to 12, the complexing agent concentration is 0.2 to 0.3 mol / L, and the temperature is 40 to 70 °C.

[0048] In step (1) of the present invention, during the coprecipitation reaction, the pH is controlled to be 11 to 12. For example, it can be 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9 or 12.0. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0049] In step (1) of the present invention, during the coprecipitation reaction, the concentration of the complexing agent is controlled to be 0.2 - 0.3 mol / L. For example, it can be 0.20 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L, 0.25 mol / L, 0.26 mol / L, 0.27 mol / L, 0.28 mol / L, 0.29 mol / L or 0.30 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] In step (1) of the present invention, during the coprecipitation reaction, the temperature is controlled to be 40 - 70 °C. For example, it can be 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C or 70 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] Preferably, during the coprecipitation reaction in step (1), stirring is also carried out at a rotation speed of 350 - 450 rpm. For example, it can be 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm or 450 rpm. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0052] Preferably, after the coprecipitation reaction in step (1), centrifugation and washing are sequentially carried out to obtain phosphorus-doped seeds.

[0053] Preferably, during the coprecipitation reaction in step (2), the pH is controlled to be 9.5 - 10.5, the concentration of the complexing agent is 0.1 - 0.2 mol / L, and the temperature is 40 - 70 °C.

[0054] In step (2) of the present invention, during the coprecipitation reaction, the pH is controlled to be 9.5 - 10.5. For example, it can be 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.3, 10.4 or 10.5. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0055] In step (2) of the present invention, during the coprecipitation reaction, the concentration of the complexing agent is controlled to be 0.1 - 0.2 mol / L. For example, it can be 0.10 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L or 0.20 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0056] In step (2) of the present invention, the temperature during the coprecipitation reaction is controlled at 40-70°C. For example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0057] Preferably, during the coprecipitation reaction in step (2), stirring is also carried out at a rotation speed of 150-250 rpm. For example, it can be 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0058] Preferably, during the precipitation reaction in step (3), the pH is controlled at 8.0-9.0, the concentration of the complexing agent is 0.05-0.15 mol / L, and the temperature is 40-70°C.

[0059] In step (3) of the present invention, the pH during the precipitation reaction is controlled at 8.0-9.0. For example, it can be 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0060] In step (3) of the present invention, the concentration of the complexing agent is 0.05-0.15 mol / L. For example, it can be 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 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, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0061] In step (3) of the present invention, the temperature during the precipitation reaction is controlled at 40-70°C. For example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0062] Preferably, during the precipitation reaction in step (3), stirring is also carried out at a rotation speed of 100 - 200 rpm. For example, it can be 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0063] Preferably, steps (1), (2) and (3) are all carried out in a protective atmosphere.

[0064] As a preferred technical solution of the preparation method described in the present invention, the preparation method includes:

[0065] (1) In a protective atmosphere, an aqueous metal mixed salt solution with a total metal ion concentration of 1 - 3 mol / L, an aqueous precipitant solution with a concentration of 3 - 4 mol / L, an aqueous complexing agent solution with a concentration of 0.5 - 1 mol / L, and an aqueous ammonium dihydrogen phosphate solution with a concentration of 5 - 20 mmol / L are added in parallel flow to a first bottom solution (composed of a precipitant, a complexing agent and water) with a pH of 11 - 12 and a complexing agent concentration of 0.2 - 0.3 mol / L. When adding in parallel flow, the addition flow rate of the aqueous ammonium dihydrogen phosphate solution is 10 - 30 mL / min. Control the pH to be 11 - 12, the complexing agent concentration to be 0.2 - 0.3 mol / L, the temperature to be 40 - 70°C, and stir at a rotation speed of 350 - 450 rpm to carry out a coprecipitation reaction, and then carry out centrifugation and washing in sequence to obtain phosphorus-doped seeds;

[0066] (2) In a protective atmosphere, the phosphorus-doped seeds obtained in step (1) are added to a second bottom solution with a pH of 9.5 - 10.5 and a complexing agent concentration of 0.1 - 0.2 mol / L, and then an aqueous metal mixed salt solution with a total metal ion concentration of 1 - 3 mol / L, an aqueous precipitant solution with a concentration of 3 - 4 mol / L, an aqueous complexing agent solution with a concentration of 0.5 - 1 mol / L, and an aqueous ammonium dihydrogen phosphate solution with a concentration of 5 - 20 mmol / L are added in parallel flow to the second bottom solution. When adding in parallel flow, the addition flow rate of the aqueous ammonium dihydrogen phosphate solution is 5 - 15 mL / min. Control the pH to be 9.5 - 10.5, the complexing agent concentration to be 0.1 - 0.2 mol / L, the temperature to be 40 - 70°C, and stir at a rotation speed of 150 - 250 rpm to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

[0067] (3) In a protective atmosphere, a zirconium source solution with a concentration of 20 - 60 mmol / L is added to the solution containing the precipitate obtained in step (2) at a flow rate of 5 - 20 mL / min, controlling the pH to be 8.0 - 9.0, the complexing agent concentration to be 0.05 - 0.15 mol / L, and the temperature to be 40 - 70 °C, and a precipitation reaction is carried out to obtain a cathode precursor.

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

[0069] In a fourth aspect, the present invention provides a preparation process for the cathode material described in the third aspect, and the preparation process includes:

[0070] The cathode precursor described in the first aspect is pre-oxidized by heating to obtain a precursor hydroxy-oxide; then the obtained precursor hydroxy-oxide is mixed with a lithium source and sintered to obtain the cathode material.

[0071] In the preparation process provided by the present invention, pre-oxidation is carried out by heating before sintering. Since the lattice oxygen arrangement of the precursor hydroxy-oxide obtained after pre-oxidation is more ordered, it is easier to form a layered structure (R-3m space group) during calcination. Therefore, cation mixing (Ni ²+ occupying the lithium ion site) can be further reduced, thereby improving the crystal structure of the obtained cathode material and enhancing the cycle stability of the battery prepared from the obtained cathode material.

[0072] Preferably, the heating temperature is 200 - 300 °C, the time is 2 - 6 h, and it is carried out in a protective atmosphere.

[0073] In the present invention, the heating temperature is 200 - 300 °C, for example, it can be 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C or 300 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0074] In the present invention, the heating time is 2 - 6 h, for example, it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0075] Preferably, the lithium source includes any one or at least two combinations of lithium hydroxide, lithium carbonate or lithium nitrate. Typical but non-limiting combinations include the combination of lithium hydroxide and lithium carbonate, the combination of lithium carbonate and lithium nitrate, the combination of lithium hydroxide and lithium nitrate, or the combination of lithium hydroxide, lithium carbonate and lithium nitrate.

[0076] Preferably, the molar ratio of the precursor hydroxyoxide to the lithium source in the mixing is 1:(1.05 - 1.2). For example, it can be 1:1.05, 1:1.08, 1:1.10, 1:1.12, 1:1.15, 1:1.18, or 1:1.20. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0077] Preferably, the sintering temperature is 650 - 850 °C, and the time is 8 - 14 h.

[0078] In the present invention, the sintering temperature is 650 - 850 °C. For example, it can be 650 °C, 670 °C, 690 °C, 700 °C, 720 °C, 740 °C, 760 °C, 780 °C, 800 °C, 820 °C, 840 °C, or 850 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0079] In the present invention, the sintering time is 8 - 14 h. For example, it can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, or 14 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0080] The numerical ranges described in the present invention include not only the point values exemplified above, but also any point values between the above - mentioned numerical ranges that are not exemplified. Due to space limitations and for the sake of simplicity, the specific point values included in the described ranges are not exhaustively listed in the present invention.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] (1) In the cathode precursor provided by the present invention, due to the introduction of gradient - concentration doping of phosphorus, the precipitation of lattice oxygen and cation mixing are inhibited, the structural stability of the cathode material is enhanced, and the risk of micro - cracks generated in the cathode material during the cycling process is reduced. In addition, due to the coating of the zirconium - rich shell, not only the residual alkali is reduced, but also the corrosion resistance and stability of the cathode precursor are improved. Therefore, the battery prepared from the cathode precursor provided in the present invention exhibits a high first - charge - discharge efficiency and rate performance, as well as excellent cycle stability.

[0083] (2) In the preparation process provided by the present invention, pre - oxidation is carried out by heating before sintering. Since the lattice oxygen arrangement of the precursor hydroxyoxide obtained after pre - oxidation is more ordered, it is easier to form a layered structure (R - 3m space group) during calcination. Therefore, cation mixing (Ni ²+ occupying lithium - ion sites) can be further reduced, thereby improving the crystal structure of the obtained cathode material and enhancing the cycle stability of the battery prepared from the obtained cathode material. Detailed embodiments

[0084] The technical solution 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 on the present invention.

[0085] Example 1

[0086] This example provides a cathode precursor, which includes a phosphorus-doped seed crystal with a D50 particle size of 3.0 μm, a phosphorus-doped layer with a thickness of 6.5 μm coated on the outside of the phosphorus-doped seed crystal, and a zirconium-rich shell layer with a thickness of 1.5 μm coated on the outside of the phosphorus-doped layer;

[0087] The mass fraction of doped phosphorus in the phosphorus-doped seed crystal is greater than that in the phosphorus-doped layer; based on the mass of the phosphorus-doped seed crystal as 100%, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 1.25 wt%; based on the mass of the phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.45 wt%.

[0088] The preparation method of the cathode precursor is as follows:

[0089] (1) In an argon atmosphere, an aqueous metal mixed salt solution with a total metal ion concentration of 2 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate with a molar ratio of nickel ions, manganese ions and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 3.5 mol / L, an aqueous ammonia solution with a concentration of 0.75 mol / L and an aqueous ammonium dihydrogen phosphate solution with a concentration of 12.5 mmol / L are co-fed into a first bottom liquid with a pH of 11.5 and an ammonia concentration of 0.25 mol / L (composed of sodium hydroxide, ammonia and water). When co-feeding, the feeding flow rate of the aqueous ammonium dihydrogen phosphate solution is 20 mL / min, the pH is controlled at 11.5, the ammonia concentration is 0.25 mol / L, the temperature is 55 °C, and stirring is carried out at a speed of 400 rpm to carry out a coprecipitation reaction, and then centrifugation and washing are carried out in sequence to obtain a phosphorus-doped seed crystal;

[0090] (2) In an argon atmosphere, the phosphorus-doped seeds obtained in step (1) are added to a second bottom solution with a pH of 10 and an ammonia concentration of 0.15 mol / L. Then, an aqueous metal mixed salt solution with a total metal ion concentration of 2 mol / L (composed of nickel sulfate, manganese sulfate, and cobalt sulfate with a molar ratio of nickel ions, manganese ions, and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 3.5 mol / L, an aqueous ammonia solution with a concentration of 0.75 mol / L, and an aqueous ammonium dihydrogen phosphate solution with a concentration of 12.5 mmol / L are added to the second bottom solution in a co-current manner. When adding in a co-current manner, the addition flow rate of the aqueous ammonium dihydrogen phosphate solution is 10 mL / min. Control the pH to be 10, the ammonia concentration to be 0.15 mol / L, and the temperature to be 55 °C, and stir at a rotation speed of 200 rpm to carry out a co-precipitation reaction to obtain a solution containing a precipitate;

[0091] (3) In an argon atmosphere, an aqueous zirconium sulfate solution with a concentration of 40 mmol / L is added to the solution containing sodium hydroxide obtained in step (2) at a flow rate of 12.5 mL / min. Control the pH to be 8.5, the ammonia concentration to be 0.1 mol / L, and the temperature to be 55 °C to carry out a precipitation reaction to obtain a positive electrode precursor.

[0092] This example also provides a positive electrode material, and the preparation process of the positive electrode material is as follows:

[0093] The positive electrode precursor provided in this example is pre-oxidized by heating at 250 °C for 4 h to obtain a precursor hydroxy-oxide; then, the obtained precursor hydroxy-oxide is mixed with lithium hydroxide and sintered at 750 °C for 11 h to obtain the positive electrode material.

[0094] Example 2

[0095] This example provides a positive electrode precursor, and the positive electrode precursor includes phosphorus-doped seeds with a D50 particle size of 2.5 μm, a phosphorus-doped layer with a thickness of 7 μm coated outside the phosphorus-doped seeds, and a zirconium-rich shell layer with a thickness of 2 μm coated outside the phosphorus-doped layer;

[0096] The mass fraction of doped phosphorus in the phosphorus-doped seeds is greater than the mass fraction of doped phosphorus in the phosphorus-doped layer; based on the mass of the phosphorus-doped seeds as 100%, the mass fraction of phosphorus in the phosphorus-doped seeds is 2.0 wt%; based on the mass of the phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.8 wt%.

[0097] The preparation method of the positive electrode precursor is as follows:

[0098] (1) In a nitrogen atmosphere, an aqueous metal mixed salt solution with a total metal ion concentration of 1 mol / L (composed of nickel sulfate, manganese sulfate, and cobalt sulfate with a molar ratio of nickel ions, manganese ions, and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 3 mol / L, an aqueous ammonia solution with a concentration of 0.5 mol / L, and an aqueous ammonium dihydrogen phosphate solution with a concentration of 20 mmol / L were fed in parallel into a first bottom liquid with a pH of 11 and an ammonia concentration of 0.2 mol / L (composed of sodium hydroxide, ammonia, and water). When fed in parallel, the feeding flow rate of the aqueous ammonium dihydrogen phosphate solution was 30 mL / min. The pH was controlled at 11, the ammonia concentration was 0.2 mol / L, the temperature was 40 °C, and stirring was carried out at a rotation speed of 450 rpm to carry out a coprecipitation reaction. Then, centrifugation and washing were carried out in sequence to obtain a phosphorus-doped seed crystal;

[0099] (2) In a nitrogen atmosphere, the phosphorus-doped seed crystal obtained in step (1) was added to a second bottom liquid with a pH of 9.5 and an ammonia concentration of 0.2 mol / L. Then, an aqueous metal mixed salt solution with a total metal ion concentration of 3 mol / L (composed of nickel sulfate, manganese sulfate, and cobalt sulfate with a molar ratio of nickel ions, manganese ions, and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 4 mol / L, an aqueous ammonia solution with a concentration of 1 mol / L, and an aqueous ammonium dihydrogen phosphate solution with a concentration of 20 mmol / L were fed in parallel into the second bottom liquid. When fed in parallel, the feeding flow rate of the aqueous ammonium dihydrogen phosphate solution was 15 mL / min. The pH was controlled at 9.5, the ammonia concentration was 0.2 mol / L, the temperature was 40 °C, and stirring was carried out at a rotation speed of 250 rpm to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

[0100] (3) In a nitrogen atmosphere, an aqueous zirconium nitrate solution with a concentration of 20 mmol / L was added to the solution containing the precipitate obtained in step (2) at a flow rate of 20 mL / min. The pH was controlled at 8.0, the ammonia concentration was 0.15 mol / L, and the temperature was 40 °C to carry out a precipitation reaction to obtain a cathode precursor.

[0101] This example also provides a cathode material, and the preparation process of the cathode material is as follows:

[0102] The cathode precursor provided in this example was pre-oxidized by heating at 300 °C for 2 h to obtain a precursor hydroxyoxide; then, the obtained precursor hydroxyoxide was mixed with lithium hydroxide and sintered at 650 °C for 14 h to obtain the cathode material.

[0103] Example 3

[0104] This embodiment provides a cathode precursor, which includes a phosphorus-doped seed crystal with a D50 particle size of 3.5 μm, a phosphorus-doped layer with a thickness of 6 μm coated on the outside of the phosphorus-doped seed crystal, and a zirconium-rich shell layer with a thickness of 1 μm coated on the outside of the phosphorus-doped layer;

[0105] The mass fraction of doped phosphorus in the phosphorus-doped seed crystal is greater than that in the phosphorus-doped layer; based on the mass of the phosphorus-doped seed crystal as 100%, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5 wt%; based on the mass of the phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1 wt%.

[0106] The preparation method of the cathode precursor is as follows:

[0107] (1) In an argon atmosphere, an aqueous metal mixed salt solution with a total metal ion concentration of 3 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate with a molar ratio of nickel ions, manganese ions and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 4 mol / L, an aqueous ammonia solution with a concentration of 1 mol / L and an aqueous ammonium dihydrogen phosphate solution with a concentration of 5 mmol / L are co-fed into a first bottom liquid with a pH of 12 and an ammonia concentration of 0.3 mol / L (composed of sodium hydroxide, ammonia and water). When co-feeding, the feeding flow rate of the aqueous ammonium dihydrogen phosphate solution is 20 mL / min, the pH is controlled at 12, the ammonia concentration is 0.3 mol / L, the temperature is 70 °C, and stirring is carried out at a rotation speed of 350 rpm to carry out a co-precipitation reaction, and then centrifugation and washing are carried out in sequence to obtain phosphorus-doped seed crystals;

[0108] (2) In an argon atmosphere, the phosphorus-doped seed crystals obtained in step (1) are added to a second bottom liquid with a pH of 10.5 and an ammonia concentration of 0.1 mol / L, and then an aqueous metal mixed salt solution with a total metal ion concentration of 1 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate with a molar ratio of nickel ions, manganese ions and cobalt ions of 0.96:0.02:0.02), an aqueous sodium hydroxide solution with a concentration of 3 mol / L, an aqueous ammonia solution with a concentration of 0.5 mol / L and an aqueous ammonium dihydrogen phosphate solution with a concentration of 5 mmol / L are co-fed into the second bottom liquid. When co-feeding, the feeding flow rate of the aqueous ammonium dihydrogen phosphate solution is 5 mL / min, the pH is controlled at 10.5, the ammonia concentration is 0.1 mol / L, the temperature is 70 °C, and stirring is carried out at a rotation speed of 150 rpm to carry out a co-precipitation reaction to obtain a solution containing precipitates;

[0109] (3) In an argon atmosphere, an aqueous zirconium chloride solution with a concentration of 60 mmol / L was added to the solution containing the precipitate obtained in step (2) at a flow rate of 5 mL / min, controlling the pH to 9.0, the ammonia concentration to 0.05 mol / L, and the temperature to 70 °C to conduct a precipitation reaction to obtain a positive electrode precursor.

[0110] This example also provides a positive electrode material, and the preparation process of the positive electrode material is as follows:

[0111] The positive electrode precursor provided in this example was pre-oxidized by heating at 200 °C for 6 h to obtain a precursor hydroxyoxide; then the obtained precursor hydroxyoxide was mixed with lithium hydroxide and sintered at 850 °C for 8 h to obtain the positive electrode material.

[0112] Example 4

[0113] This example provides a positive electrode precursor, which is the same as that in Example 3 except that the thickness of the phosphorus-doped layer is 5 μm.

[0114] This example also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that in Example 3.

[0115] Example 5

[0116] This example provides a positive electrode precursor, which is the same as that in Example 3 except that the thickness of the phosphorus-doped layer is 8 μm.

[0117] This example also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that in Example 3.

[0118] Example 6

[0119] This example provides a positive electrode precursor, which is the same as that in Example 3 except that the thickness of the zirconium-rich shell layer is 0.5 μm.

[0120] This example also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that in Example 3.

[0121] Example 7

[0122] This example provides a positive electrode precursor, which is the same as that in Example 3 except that the thickness of the zirconium-rich shell layer is 3 μm.

[0123] This example also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that in Example 3.

[0124] Example 8

[0125] This embodiment provides a cathode precursor. Except that, taking the mass of the phosphorus-doped seed as 100%, the mass fraction of phosphorus in the phosphorus-doped seed is 0.2 wt%, that is, the feeding rate of the aqueous ammonium dihydrogen phosphate solution in step (1) of the preparation method of the cathode precursor is 4 mL / min, the rest are the same as in Embodiment 3.

[0126] This embodiment also provides a cathode material, and the preparation process of the cathode material is the same as that in Embodiment 3.

[0127] Example 9

[0128] This embodiment provides a cathode precursor. Except that, taking the mass of the phosphorus-doped seed as 100%, the mass fraction of phosphorus in the phosphorus-doped seed is 2.5 wt%, that is, the feeding rate of the aqueous ammonium dihydrogen phosphate solution in step (1) of the preparation method of the cathode precursor is 50 mL / min, the rest are the same as in Embodiment 3.

[0129] This embodiment also provides a cathode material, and the preparation process of the cathode material is the same as that in Embodiment 3.

[0130] Example 10

[0131] This embodiment provides a cathode precursor, and the cathode precursor is the same as that in Embodiment 3.

[0132] This embodiment also provides a cathode material. Except that, in the preparation process of the cathode material, when pre-oxidizing the cathode precursor provided in this embodiment, the heating temperature is 150 °C, the rest are the same as in Embodiment 3.

[0133] Example 11

[0134] This embodiment provides a cathode precursor, and the cathode precursor is the same as that in Embodiment 3.

[0135] This embodiment also provides a cathode material. Except that, in the preparation process of the cathode material, when pre-oxidizing the cathode precursor provided in this embodiment, the heating temperature is 400 °C, the rest are the same as in Embodiment 3.

[0136] Comparative Example 1

[0137] This comparative example provides a cathode precursor. Except that the phosphorus-doped layer in the cathode precursor is omitted, and the D50 particle size of the phosphorus-doped seed is 9.5 μm, that is, step (2) of the preparation method of the cathode precursor is omitted, and the time of the co-precipitation reaction in step (1) is extended so that the D50 particle size of the phosphorus-doped seed in this comparative example is the same as the D50 particle size of the precipitate obtained in step (2) of the preparation method provided in Embodiment 3, the rest are the same as in Embodiment 3.

[0138] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0139] Comparative Example 2

[0140] This comparative example provides a cathode precursor. Except that the phosphorus-doped seed crystal is replaced by a non-phosphorus-doped seed crystal, that is, the aqueous ammonium dihydrogen phosphate solution added in step (1) of the preparation method of the cathode precursor is omitted, the rest are the same as those of Example 3.

[0141] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0142] Comparative Example 3

[0143] This comparative example provides a cathode precursor. Except that the phosphorus-doped layer is replaced by a non-phosphorus-doped intermediate layer, that is, the aqueous ammonium dihydrogen phosphate solution added in step (2) of the preparation method of the cathode precursor is omitted, the rest are the same as those of Example 3.

[0144] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0145] Comparative Example 4

[0146] This comparative example provides a cathode precursor. Except that the phosphorus-doped seed crystal is replaced by a non-phosphorus-doped seed crystal and the phosphorus-doped layer is replaced by a non-phosphorus-doped intermediate layer, that is, the aqueous ammonium dihydrogen phosphate solutions added in steps (1) and (2) of the preparation method of the cathode precursor are omitted, the rest are the same as those of Example 3.

[0147] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0148] Comparative Example 5

[0149] This comparative example provides a cathode precursor. Except that the mass fraction of phosphorus doped in the phosphorus-doped seed crystal is less than the mass fraction of phosphorus doped in the phosphorus-doped layer; based on the mass of the phosphorus-doped seed crystal as 100%, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5 wt%; based on the mass of the phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.8 wt%;

[0150] That is, the addition flow rate of the aqueous ammonium dihydrogen phosphate solution in step (1) of the preparation method of the cathode precursor is 20 mL / min, and the addition flow rate of the aqueous ammonium dihydrogen phosphate solution in step (2) is 40 mL / min, and the rest are the same as those of Example 3.

[0151] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0152] Comparative Example 6

[0153] This comparative example provides a cathode precursor. Except for omitting the zirconium-rich shell layer coated on the outside of the phosphorus-doped layer, that is, omitting step (3) of the preparation method of the cathode precursor, and extending the time of the coprecipitation reaction in step (2), so that the D50 particle size of the precipitate obtained in step (2) in this comparative example is the same as the D50 particle size of the cathode precursor obtained in step (3) of Example 3, the rest are the same as Example 3.

[0154] This comparative example also provides a cathode material, and the preparation process of the cathode material is the same as that of Example 3.

[0155] Using the cathode materials provided in the above examples and comparative examples to prepare a battery, the method for preparing the battery is as follows: Mix the cathode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) in a mass ratio of 90:5:5, use N-methylpyrrolidone as the solvent, mix and stir into a slurry, and evenly coat the obtained slurry on the aluminum foil with a doctor blade with a coating gap of 100 um; After coating, first dry with hot air, then roll and cut into circular electrode sheets, and then vacuum dry at 120 °C and weigh the electrode sheets to obtain the positive electrode sheets of the coin half-cell; The negative electrode is a metal lithium sheet, the separator is a PP microporous membrane, and the electrolyte is a lithium battery basic electrolyte. Assemble the positive electrode sheet, metal lithium sheet, separator and electrolyte to obtain a button battery;

[0156] Perform electrochemical performance tests on the obtained coin batteries. The battery tests use a battery test system (BlueTEC CT2001A, Wuhan, China). First, activate 3 times at a rate of 0.1C / 2.7~4.3V, and then perform electrochemical performance tests on the activated coin batteries under the conditions of 2.7~4.3V@0.1C / 1C. The first charge-discharge efficiency (1C / 0.1C discharge capacity ratio), 0.1C first discharge specific capacity, and capacity retention rate after 100 cycles at 1C of the coin battery are shown in Table 1.

[0157] Table 1

[0158]

[0159] It can be seen from Table 1 that:

[0160] (1) The batteries prepared with the cathode materials provided in Examples 1 to 3 show high first charge-discharge efficiency, high first discharge specific capacity and excellent cycle stability;

[0161] (2) It can be seen from the comparison between Example 3 and Examples 4 and 5 that the thickness of the phosphorus-doped layer in the positive electrode precursor of the present invention affects the performance of the positive electrode precursor, the positive electrode material and the battery; when the thickness of the phosphorus-doped layer is 6-7 μm, the positive electrode precursor, the positive electrode material and the battery have better performance. This is because when the thickness of the phosphorus-doped layer is 6-7 μm, a mechanical property gradient transition is formed among the phosphorus-doped seeds, the phosphorus-doped layer and the zirconium-rich shell layer, which improves the stability of the positive electrode material prepared from the positive electrode precursor and avoids and slows down the cracking of the whole material during the cycling process; in addition, when the thickness of the phosphorus-doped layer is 6-7 μm, the main oxygen active sites of the phosphorus-doped layer can be covered, and within this thickness range, the thickness of the phosphorus-doped layer is also beneficial to inhibiting oxygen evolution;

[0162] (3) It can be seen from the comparison between Example 3 and Examples 6 and 7 that the thickness of the zirconium-rich shell layer in the positive electrode precursor of the present invention affects the performance of the positive electrode precursor, the positive electrode material and the battery; when the thickness of the zirconium-rich shell layer is 1-2 μm, the positive electrode precursor, the positive electrode material and the battery have better performance. This is because when the thickness of the zirconium-rich shell layer is 1-2 μm, the 1-2 μm zirconium-rich shell layer and the 6-7 μm phosphorus-doped layer form a rigid-flexible composite structure, which can play the role of buffering stress to the greatest extent; when the thickness of the zirconium-rich shell layer is too thin (<1 μm), it cannot effectively resist the volume expansion of the phosphorus-doped seeds, and the particles are relatively easy to crack after cycling; when the thickness of the zirconium-rich shell layer is too thick (>2 μm): the rigidity of the zirconium-rich shell layer is too strong, which easily leads to interface stress concentration and thus causes shell layer peeling;

[0163] (4) It can be seen from the comparison between Example 3 and Examples 8 and 9 that the mass fraction of phosphorus in the phosphorus-doped seeds of the present invention affects the performance of the positive electrode precursor, the positive electrode material and the battery; taking the mass of the phosphorus-doped seeds as 100%, when the mass fraction of phosphorus in the phosphorus-doped seeds is 0.5-2.0 wt%, the positive electrode precursor, the positive electrode material and the battery have better performance. This is because the phosphorus-doped seeds with a phosphorus mass fraction of 0.5-2.0 wt% can form continuous Li3PO4 fast ion channels, and at the same time, P 50 replaces O 2- to form strong P-O bonds, stabilize the lattice in the positive electrode precursor, inhibit the loss of lattice oxygen, and thus improve the performance of the positive electrode material prepared from the positive electrode precursor;

[0164] (5) By comparing Example 3 with Examples 10 and 11, it can be seen that in the preparation process of the cathode material of the present invention, the heating temperature during the pre-oxidation of the cathode precursor provided in this example will affect the performance of the cathode precursor, cathode material and battery; when the heating temperature during pre-oxidation is 200~300°C, the cathode precursor, cathode material and battery have better performance. This is because by controlling the heating temperature during pre-oxidation to 200~300°C, it helps to form an ordered layered structure, enhance lithium ion transport, and thus improve the electrochemical performance of the cathode material prepared from the cathode precursor.

[0165] (6) By comparing Example 3 with Comparative Examples 1~6, it can be seen that in the cathode precursor provided by the present invention, due to the introduction of gradient concentration doping of phosphorus, the precipitation of lattice oxygen and cation mixing are inhibited, the structural stability of the cathode material is enhanced, and the risk of microcracks generated in the cathode material during the cycling process is reduced; in addition, due to the coating of the zirconium-rich shell layer, not only the residual alkali is reduced, but also the corrosion resistance and stability of the cathode precursor are improved; therefore, the battery prepared from the cathode precursor provided in the present invention exhibits a high first charge-discharge efficiency and rate performance, as well as excellent cycle stability; in the preparation process provided by the present invention, pre-oxidation is carried out by heating before sintering. Since the lattice oxygen arrangement of the precursor hydroxyoxide obtained after pre-oxidation is more ordered, it is easier to form a layered structure (R-3m space group) during calcination, so it can further reduce cation mixing (Ni ²+ occupying lithium ion sites), thereby improving the crystal structure of the obtained cathode material and enhancing the cycle stability of the battery prepared from the obtained cathode material.

[0166] The above is only the specific implementation manner 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 disclosure scope of the present invention.

Claims

1. A cathode precursor, characterized in that, The positive electrode precursor includes a phosphorus-doped seed crystal, a phosphorus-doped layer coating the outside of the phosphorus-doped seed crystal, and a zirconium-rich shell layer coating the outside of the phosphorus-doped layer; The mass fraction of doped phosphorus in the phosphorus-doped seed crystal is greater than the mass fraction of doped phosphorus in the phosphorus-doped layer.

2. The cathode precursor according to claim 1, characterized in that, The D50 particle size of the phosphorus-doped seed crystal is 2.5 - 3.5 μm; Based on the mass of the phosphorus-doped seed crystal as 100%, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5 - 2.0 wt%.

3. The cathode precursor according to claim 1, characterized in that, The thickness of the phosphorus-doped layer is 6 - 7 μm; Based on the mass of the phosphorus-doped layer as 100%, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1 - 0.8 wt%.

4. The cathode precursor according to claim 1, characterized in that, The thickness of the zirconium-rich shell layer is 1 - 2 μm.

5. A method for preparing the cathode precursor according to any one of claims 1 to 4, characterized in that The preparation method includes: (1) A metal mixed salt solution, a precipitant solution, a complexing agent solution, and a phosphorus source solution are added in parallel flow to a first bottom liquid for coprecipitation reaction to obtain a phosphorus-doped seed crystal; (2) The phosphorus-doped seed crystal obtained in step (1) is added to a second bottom liquid, and then a metal mixed salt solution, a precipitant solution, a complexing agent solution, and a phosphorus source solution are added in parallel flow to the second bottom liquid for coprecipitation reaction to obtain a solution containing precipitates; (3) A zirconium source solution is added to the solution containing precipitates obtained in step (2) for precipitation reaction to obtain a positive electrode precursor; The flow rate of the parallel addition of the phosphorus source solution in step (1) is higher than the flow rate of the parallel addition of the phosphorus source solution in step (2).

6. The preparation method according to claim 5, characterized in that The phosphorus source in the phosphorus source solution in steps (1) and (2) independently includes ammonium dihydrogen phosphate, and the solvent is water; The concentrations of the phosphorus source in the phosphorus source solution in steps (1) and (2) are independently 5 - 20 mmol / L; The addition flow rate of the phosphorus source solution during parallel addition in step (1) is 10 - 30 mL / min; The addition flow rate of the phosphorus source solution during parallel addition in step (2) is 5 - 15 mL / min; The concentration of the zirconium source in the zirconium source solution in step (3) is 20 - 60 mmol / L; The addition flow rate of the zirconium source solution in step (3) is 5 - 20 mL / min.

7. The preparation method according to claim 5, characterized in that The metal salts in the metal mixed salt solution in steps (1) and (2) include nickel salt, manganese salt, and cobalt salt, and the solvent is water; The total concentration of metal ions in the metal mixed salt solution in steps (1) and (2) is independently 1 - 3 mol / L; During the coprecipitation reaction in step (1), the pH is controlled to be 11 - 12, the complexing agent concentration is 0.2 - 0.3 mol / L, and the temperature is 40 - 70 °C; During the coprecipitation reaction in step (2), the pH is controlled to be 9.5 - 10.5, the complexing agent concentration is 0.1 - 0.2 mol / L, and the temperature is 40 - 70 °C; During the precipitation reaction in step (3), the pH is controlled to be 8.0 - 9.0, the complexing agent concentration is 0.05 - 0.15 mol / L, and the temperature is 40 - 70 °C.

8. A cathode material, characterized in that, The positive electrode material is prepared from the positive electrode precursor according to any one of claims 1 - 4.

9. The preparation process of the cathode material according to claim 8, characterized in that, The preparation process includes: The cathode precursor described in any one of claims 1 to 4 is pre-oxidized by heating to obtain a precursor hydroxyoxide; then the obtained precursor hydroxyoxide is mixed with a lithium source and sintered to obtain the cathode material.

10. The preparation process according to claim 9, characterized in that, The temperature of the heating is 200 to 300 °C, the time is 2 to 6 h, and it is carried out in a protective atmosphere; In the mixing, the molar ratio of the precursor hydroxyoxide to the lithium source is 1:(1.05 to 1.2); The temperature of the sintering is 650 to 850 °C, and the time is 8 to 14 h.

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