A positive electrode precursor and its preparation method, positive electrode material and its preparation process

Abstract

The present invention provides a positive electrode precursor and a preparation method thereof, a positive electrode material and a preparation process thereof, wherein the positive electrode precursor 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; the mass fraction of phosphorus doped in the phosphorus-doped seed crystal is greater than the mass fraction of phosphorus doped in the phosphorus-doped layer. In the positive electrode 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 suppressed, the structural stability of the positive electrode material is enhanced, and the risk of microcracks in the positive electrode material during the cycle 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 positive electrode precursor are improved; therefore, the battery prepared with the positive electrode precursor provided by the present invention exhibits higher first charge and discharge efficiency and rate performance, as well as excellent cycle stability.

Description

Technical Field

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

[0002] The new energy industry is undergoing rapid innovation, with electric vehicles and lithium-ion batteries already permeating our daily lives. Among ternary precursor materials, metal oxides, represented by nickel-cobalt-manganese (NCM) and nickel-cobalt-aluminum (NCA), are at the core of next-generation high-energy-density lithium battery materials. Their performance will directly determine the battery's cycle life, energy density, and safety. While NCM precursors improve tap density, high-nickel materials are prone to cracking and cation mixing during cycling. Furthermore, due to the presence of Li2CO3 and / or LiOH on the surface of NCM precursors, when cathode materials are prepared from these NCM precursors, these residual alkalis readily react with the electrolyte to generate HF, exacerbating capacity decay and severely impacting the initial charge and discharge efficiency, rate capability, and cycle life of batteries prepared from these cathode materials.

[0003] CN116639735A discloses a method for preparing a quaternary precursor with structural density differences, nickel-tungsten concentration gradients, and cobalt in-situ coating, and its application. The nickel and tungsten contents tend to gradually increase from the inside to the outside, and cobalt is coated on the surface of the material using a co-precipitation process. The material presents a structure from the inside to the outside of "low nickel, tungsten low density inner layer - high nickel, tungsten high density outer layer - cobalt-coated surface". By controlling the concentration and flow rate, a certain difference in structural density is produced. Wet-doped tungsten modification is used to enhance structural stability; a stable structure with low nickel in the inner layer and cobalt-coated surface is designed to provide a buffer space for volume changes during subsequent charge and discharge processes, effectively reducing the generation of microcracks and harmful side reactions. However, the structural stability of the ternary precursor still cannot meet the needs of practical applications. There is still a certain risk of cracking during the cycle, and there is a risk of side reactions with the electrolyte.

[0004] CN118084081A discloses a ternary positive electrode material and a preparation method thereof, belonging to the technical field of positive electrode materials for lithium ion batteries, comprising the following steps: (1) preparing two mixed salt solutions of Ni, Co and Mn, a and b; (2) continuously adding NCM mixed salt solution a, a precipitant and a complexing agent into a reactor for coprecipitation reaction, wherein the overflow of the reactor flows to a concentrator, and when the particle size D50 of the material in the reactor grows to 2-8 μm, the reaction is suspended; (3) continuously adding NCM mixed salt solution b, a precipitant and a complexing agent into a reactor for coprecipitation reaction, wherein the overflow of the reactor flows to a concentrator, and when the particle size D50 of the material in the reactor grows to 5-15 μm, the reaction is stopped; (4) the material obtained in step (3) is subjected to filter pressing, washing and drying to obtain a ternary precursor; (5) the ternary precursor obtained in step (4) is mixed with lithium salt, subjected to heating reaction, cooled to room temperature after the reaction is completed, crushed and sieved to obtain a ternary positive electrode material. However, the ternary precursor obtained by this preparation method is prone to cracking and cation mixing during the cycle process. Moreover, after the positive electrode material is prepared using the ternary precursor, the positive electrode material easily reacts with the electrolyte to generate HF, thereby causing the electrochemical performance of the battery to deteriorate.

[0005] The NCM cathode precursors disclosed in the prior art all have certain drawbacks. They are prone to cracking and cation mixing during cycling. Furthermore, the cathode materials prepared using these precursors are prone to side reactions with the electrolyte, resulting in batteries made using these precursors having initial charge and discharge efficiency, rate capability, and cycle stability that cannot meet the requirements of practical applications. Therefore, the development and design of a new cathode precursor, its preparation method, cathode material, and its preparation process are crucial. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a positive electrode precursor and a preparation method thereof, a positive electrode material and a preparation process thereof. In the positive electrode 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 suppressed, the structural stability of the positive electrode material is enhanced, and the risk of microcracks in the positive electrode material during the cycle 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 positive electrode precursor are improved; therefore, the battery prepared with the positive electrode precursor provided by the present invention exhibits higher first charge and discharge efficiency and rate performance, and excellent cycle stability.

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

[0008] In a first aspect, the present invention provides a positive electrode precursor, comprising 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 phosphorus doped in the phosphorus-doped seed crystal is greater than the mass fraction of phosphorus doped in the phosphorus-doped layer.

[0010] The positive electrode 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 strong negative charge, the introduction of gradient concentration doping of phosphorus can enable oxygen atoms to form a strong coordination effect with metal ions, adjust the electronic structure of oxygen in the lattice, which makes the metal ions more stable and reduces the instability of metal ions in redox reactions, thereby inhibiting the precipitation of lattice oxygen and cation mixing, preventing excessive lattice expansion or contraction of the positive electrode material prepared by the positive electrode precursor, enhancing the structural stability of the positive electrode material, and reducing the risk of microcracks in the positive electrode material during the cycle.

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

[0012] In summary, in the positive electrode 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 suppressed, the structural stability of the positive electrode material is enhanced, and the risk of microcracks in the positive electrode material during the cycle 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 positive electrode precursor are improved; therefore, the battery prepared with the positive electrode precursor provided by the present invention exhibits a higher first charge and discharge efficiency and rate performance, and excellent cycle stability.

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

[0014] Preferably, based on the mass of the phosphorus-doped seed crystal, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5~2.0wt%, for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2.0wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] Preferably, the thickness of the phosphorus-doped layer is 6~7μm, for example, it can be 6.0μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6.6μm, 6.7μm, 6.8μm, 6.9μm or 7.0μm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0016] Preferably, based on the mass of the phosphorus-doped layer as a percentage, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1~0.8wt%, for example, it can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt% or 0.8wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also 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 is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0018] In a second aspect, the present invention provides a method for preparing the positive electrode precursor according to the first aspect, the preparation method comprising:

[0019] (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to a first base solution in parallel to carry out a co-precipitation reaction to obtain phosphorus-doped seed crystals;

[0020] (2) adding the phosphorus-doped seed crystal obtained in step (1) to the second base liquid, and then adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to the second base liquid in parallel to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

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

[0022] The flow rate of the phosphorus source solution added in parallel in step (1) 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 comprises ammonium dihydrogen phosphate, and the solvent comprises water.

[0024] Preferably, the concentration of the phosphorus source in the phosphorus source solution in step (1) and step (2) is independently 5 to 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the addition flow rate of the phosphorus source solution during the parallel addition 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the addition flow rate of the phosphorus source solution during the parallel addition in step (2) is 5 to 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the zirconium source in the zirconium source solution in step (3) independently includes any one of zirconium sulfate, zirconium nitrate or zirconium chloride, or a combination of at least two of them. 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. 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the flow rate of adding the zirconium source solution in step (3) is 5 to 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0031] Preferably, the total concentration of metal ions in the metal mixed salt solution in step (1) and step (2) is independently 1 to 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also 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 a combination of nickel chloride and nickel sulfate, a combination of nickel sulfate and nickel nitrate, or a combination of nickel chloride, nickel sulfate and nickel nitrate.

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

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

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

[0036] Preferably, the concentration of the precipitant in the precipitant solution in step (1) and step (2) is independently 3-4 mol / L, for example, 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0038] Preferably, the concentration of the complexing agent in the complexing agent solution in step (1) and step (2) is independently 0.5-1 mol / L, for example, 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0040] The pH of the first base 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 values ​​not listed within the numerical range are also applicable.

[0041] The concentration of the complexing agent in the first base solution in step (1) of the present invention is 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] In the present invention, the first base liquid consists of a precipitant, a complexing agent and water.

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

[0044] The pH of the second base solution in step (2) of the present invention is 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] The concentration of the complexing agent in the second base solution in step (2) of the present invention is 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] The second base liquid in the present invention consists of a precipitant, a complexing agent and water.

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

[0048] During the coprecipitation reaction in step (1) of the present invention, the pH is controlled to be 11-12, for example, 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, and other values ​​not listed within the numerical range are also applicable.

[0049] During the coprecipitation reaction in step (1) of the present invention, 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, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] The temperature of the coprecipitation reaction in step (1) of the present invention is controlled to be 40-70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0051] Preferably, the coprecipitation reaction in step (1) is accompanied by stirring at a speed of 350 to 450 rpm, for example, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm or 450 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the coprecipitation reaction in step (1) further includes centrifugation and washing to obtain phosphorus-doped seed crystals.

[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] During the coprecipitation reaction in step (2) of the present invention, 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, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] During the coprecipitation reaction in step (2) of the present invention, 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, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] The temperature of the coprecipitation reaction in step (2) of the present invention is controlled to be 40-70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0057] Preferably, the coprecipitation reaction in step (2) is accompanied by stirring at a speed of 150 to 250 rpm, for example, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] Preferably, during the precipitation reaction in step (3), the pH is controlled to be 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] During the precipitation reaction in step (3) of the present invention, the pH is controlled to be 8.0-9.0, for example, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] The concentration of the complexing agent in step (3) of the present invention is 0.05-0.15 mol / L, for example, 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] The precipitation reaction in step (3) of the present invention is carried out at a temperature of 40-70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0062] Preferably, the precipitation reaction in step (3) is accompanied by stirring at a speed of 100 to 200 rpm, for example, 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm or 200 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

[0065] (1) In a protective atmosphere, a metal mixed salt aqueous solution with a total metal ion concentration of 1-3 mol / L, a precipitant aqueous solution with a concentration of 3-4 mol / L, a complexing agent aqueous solution with a concentration of 0.5-1 mol / L, and an ammonium dihydrogen phosphate aqueous solution with a concentration of 5-20 mmol / L are added in parallel 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. The addition rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition is 10-30 mL / min. The pH is controlled to be 11-12, the complexing agent concentration is 0.2-0.3 mol / L, the temperature is 40-70°C, and the solution is stirred at a speed of 350-450 rpm to carry out a co-precipitation reaction, followed by centrifugation and washing to obtain phosphorus-doped seed crystals;

[0066] (2) in a protective atmosphere, adding the phosphorus-doped seed crystal obtained in step (1) to a second base liquid having a pH of 9.5-10.5 and a complexing agent concentration of 0.1-0.2 mol / L, and then adding a metal mixed salt aqueous solution having a total metal ion concentration of 1-3 mol / L, a precipitant aqueous solution having a concentration of 3-4 mol / L, a complexing agent aqueous solution having a concentration of 0.5-1 mol / L, and an ammonium dihydrogen phosphate aqueous solution having a concentration of 5-20 mmol / L to the second base liquid in parallel, wherein the ammonium dihydrogen phosphate aqueous solution is added at a flow rate of 5-15 mL / min, the pH is controlled to be 9.5-10.5, the complexing agent concentration is 0.1-0.2 mol / L, the temperature is 40-70° C., and the mixture is stirred at a 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 having a concentration of 20 to 60 mmol / L is added to the solution containing the precipitate obtained in step (2) at a flow rate of 5 to 20 mL / min, the pH is controlled to be 8.0 to 9.0, the complexing agent concentration is controlled to be 0.05 to 0.15 mol / L, and the temperature is controlled to be 40 to 70°C to carry out a precipitation reaction to obtain a positive electrode precursor.

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

[0069] In a fourth aspect, the present invention provides a process for preparing the positive electrode material according to the third aspect, the process comprising:

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

[0071] In the preparation process provided by the present invention, pre-oxidation is performed by heating before sintering. Since the lattice oxygen arrangement of the precursor oxyhydroxide obtained after pre-oxidation is more orderly, it is easier to form a layered structure (R-3m space group) during calcination, thereby further reducing the cation mixing (Ni ²+ occupying lithium ion sites), thereby improving the crystal structure of the obtained positive electrode material and enhancing the cycle stability of the battery prepared with the obtained positive electrode material.

[0072] Preferably, the heating temperature is 200-300° C., the heating time is 2-6 hours, and the heating is performed in a protective atmosphere.

[0073] The heating temperature in the present invention 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 values ​​not listed within the numerical range are also applicable.

[0074] The heating time in the present invention is 2 to 6 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

[0076] Preferably, the molar ratio of the precursor oxyhydroxide to the lithium source in the mixture 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0078] The sintering temperature in the present invention 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, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0079] The sintering time in the present invention is 8 to 14 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours or 14 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0080] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

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

[0082] (1) In the positive electrode precursor provided by the present invention, the introduction of gradient concentration doping of phosphorus inhibits the precipitation of lattice oxygen and cation mixing, thereby enhancing the structural stability of the positive electrode material and reducing the risk of microcracks in the positive electrode material during the cycle. 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 positive electrode precursor are improved. Therefore, the battery prepared with the positive electrode precursor provided by the present invention exhibits high first charge and 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 performed by heating before sintering. Since the lattice oxygen arrangement of the precursor oxyhydroxide obtained after pre-oxidation is more orderly, it is easier to form a layered structure (R-3m space group) during calcination, thereby further reducing the cation mixing (Ni ²+ occupying lithium ion sites), thereby improving the crystal structure of the obtained positive electrode material and enhancing the cycle stability of the battery prepared with the obtained positive electrode material. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0085] Example 1

[0086] This embodiment provides a positive electrode precursor, comprising 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 phosphorus doped in the phosphorus-doped seed crystal is greater than the mass fraction of phosphorus doped in the phosphorus-doped layer; based on the mass of the phosphorus-doped seed crystal, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 1.25 wt %; based on the mass of the phosphorus-doped layer, the mass fraction of phosphorus in the phosphorus-doped layer is 0.45 wt %.

[0088] The preparation method of the positive electrode precursor is:

[0089] (1) In an argon atmosphere, a metal mixed salt aqueous 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 ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution with a concentration of 3.5 mol / L, an ammonia aqueous solution with a concentration of 0.75 mol / L and an ammonium dihydrogen phosphate aqueous solution with a concentration of 12.5 mmol / L were added in parallel to a first bottom liquid (composed of sodium hydroxide, ammonia and water) with a pH of 11.5 and an ammonia concentration of 0.25 mol / L. The addition rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition was 20 mL / min. The pH was controlled to be 11.5, the ammonia concentration to be 0.25 mol / L, the temperature to be 55°C, and the solution was stirred at a speed of 400 rpm to carry out a coprecipitation reaction, and then centrifuged and washed in sequence to obtain phosphorus-doped seed crystals;

[0090] (2) In an argon atmosphere, the phosphorus-doped seed crystal obtained in step (1) is added to a second base liquid having a pH of 10 and an ammonia concentration of 0.15 mol / L, and then a metal mixed salt aqueous solution having a total metal ion concentration of 2 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate in a molar ratio of nickel ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution having a concentration of 3.5 mol / L, an ammonia aqueous solution having a concentration of 0.75 mol / L and an ammonium dihydrogen phosphate aqueous solution having a concentration of 12.5 mmol / L are added to the second base liquid in parallel, the flow rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition is 10 mL / min, the pH is controlled to be 10, the ammonia concentration is 0.15 mol / L, the temperature is controlled to be 55° C., and the mixture is stirred at a speed of 200 rpm to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

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

[0092] This embodiment 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 embodiment is pre-oxidized by heating at 250° C. for 4 hours to obtain a precursor hydroxyl oxide; the obtained precursor hydroxyl oxide is then mixed with lithium hydroxide and sintered at 750° C. for 11 hours to obtain the positive electrode material.

[0094] Example 2

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

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

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

[0098] (1) In a nitrogen atmosphere, a metal mixed salt aqueous 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 ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution with a concentration of 3 mol / L, an ammonia aqueous solution with a concentration of 0.5 mol / L and an ammonium dihydrogen phosphate aqueous solution with a concentration of 20 mmol / L were added in parallel to a first bottom liquid (composed of sodium hydroxide, ammonia and water) with a pH of 11 and an ammonia concentration of 0.2 mol / L. The addition rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition was 30 mL / min. The pH was controlled to be 11, the ammonia concentration to be 0.2 mol / L, the temperature to be 40°C, and the solution was stirred at a speed of 450 rpm to carry out a coprecipitation reaction, and then centrifuged and washed in sequence to obtain phosphorus-doped seed crystals;

[0099] (2) In a nitrogen atmosphere, the phosphorus-doped seed crystal obtained in step (1) is added to a second base liquid having a pH of 9.5 and an ammonia concentration of 0.2 mol / L, and then a metal mixed salt aqueous solution having a total metal ion concentration of 3 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate in a molar ratio of nickel ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution having a concentration of 4 mol / L, an ammonia aqueous solution having a concentration of 1 mol / L and an ammonium dihydrogen phosphate aqueous solution having a concentration of 20 mmol / L are added in parallel to the second base liquid, the flow rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition is 15 mL / min, the pH is controlled to be 9.5, the ammonia concentration is 0.2 mol / L, the temperature is 40°C, and the mixture is stirred at a speed of 250 rpm to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

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

[0101] This embodiment also provides a positive electrode material, and the preparation process of the positive electrode material is as follows:

[0102] The positive electrode precursor provided in this embodiment is pre-oxidized by heating at 300° C. for 2 hours to obtain a precursor oxyhydroxide; the obtained precursor oxyhydroxide is then mixed with lithium hydroxide and sintered at 650° C. for 14 hours to obtain the positive electrode material.

[0103] Example 3

[0104] This embodiment provides a positive electrode precursor, comprising 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 phosphorus doped in the phosphorus-doped seed crystal is greater than the mass fraction of phosphorus doped in the phosphorus-doped layer; based on the mass of the phosphorus-doped seed crystal, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5 wt %; based on the mass of the phosphorus-doped layer, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1 wt %.

[0106] The preparation method of the positive electrode precursor is:

[0107] (1) In an argon atmosphere, a metal mixed salt aqueous 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 ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution with a concentration of 4 mol / L, an ammonia aqueous solution with a concentration of 1 mol / L and an ammonium dihydrogen phosphate aqueous solution with a concentration of 5 mmol / L were added in parallel to a first bottom liquid (composed of sodium hydroxide, ammonia and water) with a pH of 12 and an ammonia concentration of 0.3 mol / L. The addition rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition was 20 mL / min. The pH was controlled to be 12, the ammonia concentration to be 0.3 mol / L, the temperature to be 70°C, and the solution was stirred at a speed of 350 rpm to carry out a coprecipitation reaction, and then centrifuged and washed in sequence to obtain phosphorus-doped seed crystals;

[0108] (2) In an argon atmosphere, the phosphorus-doped seed crystal obtained in step (1) is added to a second base liquid having a pH of 10.5 and an ammonia concentration of 0.1 mol / L, and then a metal mixed salt aqueous solution having a total metal ion concentration of 1 mol / L (composed of nickel sulfate, manganese sulfate and cobalt sulfate in a molar ratio of nickel ion, manganese ion and cobalt ion of 0.96:0.02:0.02), a sodium hydroxide aqueous solution having a concentration of 3 mol / L, an ammonia aqueous solution having a concentration of 0.5 mol / L and an ammonium dihydrogen phosphate aqueous solution having a concentration of 5 mmol / L are added to the second base liquid in parallel, the flow rate of the ammonium dihydrogen phosphate aqueous solution during the parallel addition is 5 mL / min, the pH is controlled to be 10.5, the ammonia concentration is 0.1 mol / L, the temperature is 70°C, and the mixture is stirred at a speed of 150 rpm to carry out a coprecipitation reaction to obtain a solution containing a precipitate;

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

[0110] This embodiment 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 embodiment is pre-oxidized by heating at 200° C. for 6 hours to obtain a precursor oxyhydroxide; the obtained precursor oxyhydroxide is then mixed with lithium hydroxide and sintered at 850° C. for 8 hours to obtain the positive electrode material.

[0112] Example 4

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

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

[0115] Example 5

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

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

[0118] Example 6

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

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

[0121] Example 7

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

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

[0124] Example 8

[0125] This embodiment provides a positive electrode precursor, which is the same as Example 3 except that the mass fraction of phosphorus in the phosphorus-doped seed crystals is 0.2 wt %, that is, the addition flow rate of the ammonium dihydrogen phosphate aqueous solution in step (1) of the preparation method of the positive electrode precursor is 4 mL / min.

[0126] This embodiment also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that of Example 3.

[0127] Example 9

[0128] This embodiment provides a positive electrode precursor, which is the same as Example 3 except that the mass fraction of phosphorus in the phosphorus-doped seed crystals is 2.5 wt %, that is, the addition flow rate of the ammonium dihydrogen phosphate aqueous solution in step (1) of the preparation method of the positive electrode precursor is 50 mL / min.

[0129] This embodiment also provides a positive electrode material, and the preparation process of the positive electrode material is the same as that of Example 3.

[0130] Example 10

[0131] This embodiment provides a positive electrode precursor, which is the same as that of Example 3.

[0132] This embodiment further provides a positive electrode material, which is the same as that of Example 3 except that the heating temperature for pre-oxidation of the positive electrode precursor provided in this embodiment is 150° C. in the preparation process of the positive electrode material.

[0133] Example 11

[0134] This embodiment provides a positive electrode precursor, which is the same as that of Example 3.

[0135] This embodiment further provides a positive electrode material, which is the same as that of Example 3 except that the heating temperature for pre-oxidation of the positive electrode precursor provided in this embodiment is 400° C. in the preparation process of the positive electrode material.

[0136] Comparative Example 1

[0137] This comparative example provides a positive electrode precursor, which is the same as Example 3 except that the phosphorus-doped layer in the positive electrode precursor is omitted and the D50 particle size of the phosphorus-doped seed crystal is 9.5 μm, that is, step (2) of the preparation method of the positive electrode 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 crystal 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 Example 3.

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

[0139] Comparative Example 2

[0140] This comparative example provides a positive electrode precursor, which is the same as Example 3 except that the phosphorus-doped seed crystals are replaced with non-phosphorus-doped seed crystals, that is, the addition of the ammonium dihydrogen phosphate aqueous solution in step (1) of the preparation method of the positive electrode precursor is omitted.

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

[0142] Comparative Example 3

[0143] This comparative example provides a positive electrode precursor, which is the same as Example 3 except that the phosphorus-doped layer is replaced by an intermediate layer that is not doped with phosphorus, that is, the addition of the ammonium dihydrogen phosphate aqueous solution in step (2) of the preparation method of the positive electrode precursor is omitted.

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

[0145] Comparative Example 4

[0146] This comparative example provides a positive electrode precursor, which is the same as Example 3 except that the phosphorus-doped seed crystals are replaced by non-phosphorus-doped seed crystals, and the phosphorus-doped layer is replaced by a non-phosphorus-doped intermediate layer, that is, the addition of the ammonium dihydrogen phosphate aqueous solution in step (1) and step (2) of the preparation method of the positive electrode precursor is omitted.

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

[0148] Comparative Example 5

[0149] This comparative example provides a positive electrode 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, the mass fraction of phosphorus in the phosphorus-doped seed crystal is 0.5wt%; based on the mass of the phosphorus-doped layer, the mass fraction of phosphorus in the phosphorus-doped layer is 0.8wt%;

[0150] That is, the preparation method of the positive electrode precursor is the same as Example 3 except that the flow rate of adding the ammonium dihydrogen phosphate aqueous solution in step (1) is 20 mL / min, and the flow rate of adding the ammonium dihydrogen phosphate aqueous solution in step (2) is 40 mL / min.

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

[0152] Comparative Example 6

[0153] This comparative example provides a positive electrode precursor, which is the same as Example 3 except that the zirconium-rich shell layer covering the outside of the phosphorus-doped layer is omitted, that is, step (3) of the preparation method of the positive electrode precursor is omitted, and the time of the co-precipitation reaction in step (2) is extended so that the D50 particle size of the precipitate obtained in step (2) of this comparative example is the same as the D50 particle size of the positive electrode precursor obtained in step (3) of Example 3.

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

[0155] A battery was prepared using the positive electrode materials provided in the above embodiments and comparative examples. The method for preparing the battery was as follows: the positive electrode material, conductive carbon black SP (TIMCAL) and polyvinylidene fluoride PVDF (HSV900) were mixed in a mass ratio of 90:5:5, N-methylpyrrolidone was used as the solvent, and the mixture was stirred into a slurry. The resulting slurry was evenly coated on an aluminum foil with a scraper with a coating gap of 100 μm; after coating, it was first blown dry, then rolled and cut into circular electrode sheets, and then vacuum dried at 120° C. and weighed to obtain a button half-cell positive electrode sheet; a metal lithium sheet was selected as the negative electrode, a PP microporous membrane was selected as the diaphragm, and a lithium battery basic electrolyte was selected as the electrolyte. The positive electrode sheet, the metal lithium sheet, the diaphragm and the electrolyte were assembled to obtain a button battery;

[0156] The obtained button cells were subjected to electrochemical performance tests. The battery test system (Blue Power CT2001A, Wuhan, China) was used for the battery test. First, the cells were activated three times at a rate of 0.1C / 2.7-4.3V. Then, the activated button cells were subjected to electrochemical performance tests at 2.7-4.3V@0.1C / 1C. The first charge and discharge efficiency (1C / 0.1C discharge capacity ratio), the first discharge capacity at 0.1C, and the capacity retention rate after 100 cycles at 1C were shown in Table 1.

[0157] Table 1

[0158]

[0159] From Table 1, we can get:

[0160] (1) The batteries prepared using the muscle-enhancing materials provided in Examples 1 to 3 exhibited high initial charge and discharge efficiency, high initial discharge specific capacity, and excellent cycle stability;

[0161] (2) By comparing Example 3 with Examples 4 and 5, it can be seen 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 6~7μm, 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 6~7μm, the phosphorus-doped seed crystal, the phosphorus-doped layer and the zirconium-rich shell form a mechanical property gradient transition, which improves the stability of the positive electrode material prepared from the positive electrode precursor and avoids and slows down the cracking of the entire material during the cycle process; in addition, the thickness of the phosphorus-doped layer is 6~7μm, which can cover the main oxygen active sites of the phosphorus-doped layer. The thickness of the phosphorus-doped layer within this thickness range is also conducive to inhibiting oxygen precipitation;

[0162] (3) By comparing Example 3 with Examples 6 and 7, it can be seen that the thickness of the zirconium-rich shell 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 is 1~2μm, 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 is 1~2μm, the 1~2μm zirconium-rich shell and the 6~7μm phosphorus-doped layer form a rigid-flexible composite structure, which can maximize the role of buffering stress; when the thickness of the zirconium-rich shell is too thin (<1μm), it cannot effectively resist the volume expansion of the phosphorus-doped seed crystal, and the particles are more likely to crack after cycling; when the thickness of the zirconium-rich shell is too thick (>2μm): the rigidity of the zirconium-rich shell is too strong, which easily leads to interface stress concentration, thereby causing shell peeling;

[0163] (4) By comparing Example 3 with Examples 8 and 9, it can be seen that the mass fraction of phosphorus in the phosphorus-doped seed crystals 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 seed crystals as 100%, when the mass fraction of phosphorus in the phosphorus-doped seed crystals is 0.5-2.0wt%, the positive electrode precursor, the positive electrode material and the battery have better performance. This is because the phosphorus-doped seed crystals with a phosphorus mass fraction of 0.5-2.0wt% can form a continuous Li3PO4 fast ion channel, and P 50 Replace O 2- Forming strong PO bonds, stabilizing the lattice in the cathode precursor, inhibiting lattice oxygen loss, and thus improving the performance of the cathode material prepared from the cathode precursor;

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

[0165] (6) By comparing Example 3 with Comparative Examples 1 to 6, it can be seen that in the positive electrode precursor provided by the present invention, due to the introduction of the gradient concentration doping of phosphorus, the precipitation of lattice oxygen and cation mixing are suppressed, the structural stability of the positive electrode material is enhanced, and the risk of microcracks in the positive electrode material during the cycle 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 positive electrode precursor are improved; therefore, the battery prepared by the positive electrode precursor provided by the present invention shows a higher first charge and discharge efficiency and rate performance, and excellent cycle stability; in the preparation process provided by the present invention, pre-oxidation is performed by heating before sintering. Since the lattice oxygen arrangement of the precursor hydroxy oxide obtained after pre-oxidation is more orderly, it is easier to form a layered structure (R-3m space group) during calcination, thereby further reducing the cation mixing (Ni ²+ occupying lithium ion sites), thereby improving the crystal structure of the obtained positive electrode material and enhancing the cycle stability of the battery prepared with the obtained positive electrode material.

[0166] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily 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 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; The mass fraction of phosphorus doped in the phosphorus-doped seed crystal is greater than the mass fraction of phosphorus doped in the phosphorus-doped layer; The thickness of the phosphorus-doped layer is 6-7 μm; based on the mass of the phosphorus-doped layer, the mass fraction of phosphorus in the phosphorus-doped layer is 0.1-0.8 wt %; 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 %; The method for preparing the positive electrode precursor includes: (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to a first base solution in parallel to carry out a co-precipitation reaction to obtain phosphorus-doped seed crystals; (2) adding the phosphorus-doped seed crystal obtained in step (1) to the second base liquid, and then adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to the second base liquid in parallel to carry out a coprecipitation reaction to obtain a solution containing a precipitate; (3) adding a zirconium source solution to the solution containing the precipitate obtained in step (2) to carry out a precipitation reaction to obtain a positive electrode precursor; The metal salts in the metal mixed salt solutions in step (1) and step (2) include nickel salts, manganese salts and cobalt salts.

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

3. A method for preparing the positive electrode precursor according to claim 1 or 2, characterized in that: The preparation method comprises: (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to a first base solution in parallel to carry out a co-precipitation reaction to obtain phosphorus-doped seed crystals; (2) adding the phosphorus-doped seed crystal obtained in step (1) to the second base liquid, and then adding a metal mixed salt solution, a precipitant solution, a complexing agent solution and a phosphorus source solution to the second base liquid in parallel to carry out a coprecipitation reaction to obtain a solution containing a precipitate; (3) adding a zirconium source solution to the solution containing the precipitate obtained in step (2) to carry out a precipitation reaction to obtain a positive electrode precursor; The flow rate of the phosphorus source solution added in parallel in step (1) is higher than the flow rate of the phosphorus source solution added in parallel in step (2); The metal salts in the metal mixed salt solutions in step (1) and step (2) include nickel salts, manganese salts and cobalt salts.

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

5. The preparation method according to claim 3, characterized in that The solvent in the metal mixed salt solution in step (1) and step (2) includes water; The total concentration of metal ions in the metal mixed salt solutions in step (1) and step (2) is independently 1 to 3 mol / L; During the coprecipitation reaction in step (1), the pH is controlled to be 11-12, the concentration of the complexing agent 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 concentration of the complexing agent 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 concentration of the complexing agent is controlled to be 0.05-0.15 mol / L, and the temperature is controlled to be 40-70°C.

6. A positive electrode material, characterized in that The positive electrode material is prepared from the positive electrode precursor according to claim 1 or 2.

7. A process for preparing the positive electrode material according to claim 6, characterized in that: The preparation process comprises: The positive electrode precursor according to claim 1 or 2 is pre-oxidized by heating to obtain a precursor oxyhydroxide; the obtained precursor oxyhydroxide is then mixed with a lithium source and sintered to obtain the positive electrode material.

8. The preparation process according to claim 7, characterized in that: The heating temperature is 200-300° C., the time is 2-6 hours, and it is carried out in a protective atmosphere; The molar ratio of the precursor oxyhydroxide to the lithium source in the mixture is 1:(1.05-1.2); The sintering temperature is 650-850° C., and the sintering time is 8-14 hours.

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