P and mo doped ternary positive electrode material, preparation method and battery

Abstract

The application provides a P and Mo doped ternary positive electrode material and a preparation method and a battery. The preparation method comprises the following steps: carrying out a first coprecipitation reaction on a mixed metal source solution, a precipitant solution and a complexing agent solution, then carrying out a second coprecipitation reaction on the mixed metal source solution, the precipitant solution, the complexing agent solution and a phosphorus source solution to obtain a precursor material; the feeding flow rate of the phosphorus source solution is increased in gradient; the precursor material is mixed with a lithium source and sintered to obtain a matrix material, the matrix material is mixed with a molybdenum source, and then heat treatment is carried out under a reducing atmosphere to obtain the P and Mo doped ternary positive electrode material. The preparation method has a double composite structure design of a phosphorus body phase gradient + a molybdenum interface gradient, can effectively remove residual lithium, in-situ construct a uniform composite protective layer, realize the collaborative optimization of residual lithium removal, interface protection and structure stability, and effectively improve the stability of the material.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a P and Mo doped ternary cathode material, its preparation method, and a battery. Background Technology

[0002] High-nickel ternary materials have become the core of power batteries due to their advantages such as high energy density. However, the increase in nickel content has led to a decrease in structural stability and the problem of residual lithium on the surface. Although using large-particle-size high-nickel ternary precursors can optimize tap density, it can cause particle cracking and cycle life degradation due to cation mixing. Furthermore, residual lithium generated by the reaction of excess lithium source with air (such as Li2CO3 and LiOH) can lead to multiple problems such as electrolyte gelation, HF corrosion, and battery swelling, which restricts the application of high-nickel ternary materials.

[0003] Currently, the performance improvement measures for lithium-ion batteries using high-nickel NCM series cathodes mainly fall into two categories: one is to coat the surface of the cathode material and dope it in the bulk phase to improve the stability of the cathode; the other is to use electrolyte additives to improve the stability and film-forming properties of the electrolyte. For example, CN113328069A discloses a lithium phosphate-coated high-nickel cathode material for lithium-ion batteries and its preparation method. It uses lithium dihydrogen phosphate as the coating raw material and generates a fast-ion conductor lithium phosphate coating layer by reacting lithium dihydrogen phosphate with residual alkali (LiOH, Li2CO3) on the surface of the parent material in situ, which can reduce the lithium salt residue on the surface of the parent material. For example, CN119680943A discloses the application of poly-2-acrylamide-2-methylpropanesulfonic acid in removing residual lithium from the surface of high-nickel NCM ternary materials. The cleaning agent with poly-2-acrylamide-2-methylpropanesulfonic acid as the main component is used to clean the residual lithium of high-nickel NCM ternary materials, which can effectively avoid the damage to high-nickel NCM ternary materials caused by existing high-temperature calcination and high-concentration ethanol immersion cleaning treatments.

[0004] However, existing technologies for treating residual lithium on the surface of high-nickel ternary materials have systemic defects, with the core pain points concentrated in the following four aspects: single cleaning processes have poor selectivity, easily damage the surface structure of the material, and result in uneven cleaning and a high rate of secondary lithium generation; single coating technologies are difficult to balance coating density and mass transfer efficiency, resulting in uneven coating layers that are easy to peel off and also sacrifice rate performance; step-by-step processes, due to process fragmentation, can lead to secondary lithium generation, high costs, and rapid decay of interface protection effects; although cutting-edge modification strategies are effective in the laboratory, they have poor compatibility, insufficient stability, and significant cost and production capacity bottlenecks.

[0005] Based on the above research, there is a need to provide a method for preparing ternary cathode materials that can construct a buffer layer, remove residual alkali, and improve the stability of the material. Summary of the Invention

[0006] The purpose of this invention is to provide a P and Mo doped ternary cathode material, its preparation method, and a battery. The preparation method uses a dual composite structure design of phosphorus phase gradient + molybdenum interface gradient to efficiently remove residual lithium while constructing a uniform composite protective layer in situ. This achieves synergistic optimization of residual lithium removal, interface protection, and structural stability, thereby improving the stability of the material.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a P- and Mo-doped ternary cathode material, the method comprising the following steps:

[0009] (1) The mixed metal source solution, precipitant solution and complexing agent solution are passed into the bottom liquid to carry out the first coprecipitation reaction. After the first coprecipitation reaction is completed, the mixed metal source solution, precipitant solution and complexing agent solution and phosphorus source solution are carried out to carry out the second coprecipitation reaction to obtain the precursor material.

[0010] The feed flow rate gradient of the phosphorus source solution is increased;

[0011] (2) The precursor material and lithium source described in step (1) are mixed and sintered to obtain a matrix material. The matrix material is mixed with a molybdenum source and then heat-treated in a reducing atmosphere to obtain the P and Mo doped ternary cathode material.

[0012] On the one hand, this invention synthesizes precursor materials with increasing phosphorus content from the inside to the outside through a gradient co-precipitation method, so that phosphorus is deeply embedded in the bulk phase from the beginning of material formation, stabilizing lattice oxygen. Thus, through the spatial concentration distribution "from the inside to the outside, from sparse to dense", a stress buffer is constructed while retaining the high specific capacity of the core region, mitigating stress-induced cracks. Furthermore, due to the pre-existing P concentration gradient on the surface layer, the near-surface chemical environment and defect concentration are changed, which can guide and regulate the diffusion depth and distribution of subsequent Mo ions, promoting the formation of a more ideal Mo interface gradient. On the other hand, this invention utilizes gas-phase transport and high-temperature diffusion to induce molybdenum to diffuse from the particle surface to the subsurface in a reducing atmosphere, forming a concentration gradient. Simultaneously, it induces a transformation of the surface structure from layered to spinel phase, resulting in an outermost layer that is primarily composed of a composite interface layer consisting of Li-Mo-O (such as Li2MoO4) and a small amount of Li3PO4. Its main function is to "protect the surface," constructing a spinel buffer layer and removing residual alkali, thereby improving the material's stability. Therefore, the internal P gradient stabilizer phase and the external Mo treatment constructing a spinel protective layer in this invention jointly enhance the material's stability.

[0013] Preferably, in step (1), the particle size D50 of the first coprecipitation reaction particles is D1, and the particle size D50 of the precursor material is D2. The difference between D2 and D1 is 1μm-2.5μm, for example, it can be 1μm, 1.5μm, 2μm or 2.5μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] In this invention, when the particle size D50 of the first co-precipitation reaction reaches D1, phosphorus gradient doping begins. In order to ensure both high-capacity cores and stress reduction in phosphorus gradient doping, the difference between D2 and D1 is preferably within a specific range, thereby further improving the effect of phosphorus gradient doping.

[0015] Preferably, the particle size D50 of the precursor material in step (1) is 3μm-4.5μm, for example, it can be 3μm, 3.5μm, 3.7μm, 4μm or 4.5μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, the initial feed flow rate of the phosphorus source solution in step (1) is 0.1L / h-0.5L / h, for example, it can be 0.2L / h, 0.3L / h, 0.4L / h or 0.5L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.1L / h-0.3L / h.

[0017] Preferably, the rate of increase of the feed flow rate of the phosphorus source solution in step (1) is 0.005L / h-0.1L / h, for example, it can be 0.005L / h, 0.01L / h, 0.02L / h, 0.04L / h, 0.06L / h, 0.08L / h or 0.1L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.005L / h-0.02L / h.

[0018] Preferably, the feed flow rate of the phosphorus source solution in step (1) is increased to 0.15L / h-0.5L / h, for example, it can be 0.15L / h, 0.2L / h, 0.4L / h or 0.5L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the feed flow rate of the mixed metal source solution in step (1) is 3L / h-8L / h, for example, it can be 3L / h, 4L / h, 5L / h, 6L / h, 7L / h or 8L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, the feed flow rate of the precipitant solution in step (1) is 1L / h-3L / h, for example, it can be 1L / h, 1.5L / h, 2L / h, 2.5L / h or 3L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the precipitant solution in step (1) includes a sodium hydroxide solution.

[0022] Preferably, the feed flow rate of the complexing agent solution in step (1) is 0.5L / h-2L / h, for example, it can be 0.5L / h, 0.8L / h, 1L / h, 1.5L / h or 2L / h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the complexing agent solution in step (1) includes ammonia.

[0024] Preferably, the phosphorus source solution in step (1) includes an ammonium hydrogen phosphate solution.

[0025] Preferably, the concentration of the phosphorus source solution in step (1) is 0.1 mol / L-0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the total metal ion concentration of the mixed metal source solution in step (1) is 1 mol / L-2 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, in the mixed metal source solution of step (1), the molar ratio of nickel ions, cobalt ions and manganese ions is x:y:z, where x > 0.9, for example, it can be 0.91, 0.93, 0.95 or 0.97, z < 0.05, for example, it can be 0.045, 0.04, 0.03, 0.02 or 0.01, and x+y+z=1.

[0028] Preferably, the temperatures of the first coprecipitation reaction and the second coprecipitation reaction in step (1) are independently 50℃-65℃, for example, 50℃, 53℃, 55℃, 60℃ or 65℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the pH of the first coprecipitation reaction and the second coprecipitation reaction in step (1) is 11-12 independently, for example, it can be 11, 11.2, 11.4, 11.6, 11.8 or 12, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, in the system of the first coprecipitation reaction and the second coprecipitation reaction in step (1), the concentration of the complexing agent is independently 0.1 mol / L-0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, in step (1), the stirring speed of the first coprecipitation reaction and the second coprecipitation reaction is independently 300 rpm-400 rpm, for example, it can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm or 400 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the pH of the base solution in step (1) is 10-11, for example, it can be 10, 10.2, 10.4, 10.6, 10.8 or 11, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, in the base liquid of step (1), the concentration of the complexing agent is 0.1 mol / L-0.3 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the ratio of the total molar amount of metal ions in the precursor material to the molar amount of lithium ions in the lithium source in step (2) is 1:(1.02-1.1), for example, it can be 1:1.02, 1:1.04, 1:1.06, 1:1.08 or 1:1.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the lithium source in step (2) includes lithium carbonate and / or lithium hydroxide.

[0036] Preferably, the sintering in step (2) includes pre-firing at 450℃-550℃, for example, 450℃, 470℃, 490℃, 510℃, 530℃ or 550℃, and then calcining at 700℃-800℃, for example, 700℃, 720℃, 740℃, 760℃, 780℃ or 800℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] Preferably, the pre-firing time at 450℃-550℃ is 4h-6h, for example, it can be 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the calcination time at 700℃-800℃ is 7h-10h, for example, it can be 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the amount of molybdenum source added in step (2) is 0.15wt%-0.3wt% of the mass of the matrix material, for example, it can be 0.15wt%, 0.2wt%, 0.23wt%, 0.25wt% or 0.3wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] The present invention preferably adds molybdenum source within a specific range, which ensures effective diffusion, formation of spinel buffer layer and removal of residual alkali, while avoiding excessive addition that would affect the material's capacity.

[0041] Preferably, the molybdenum source in step (2) includes ammonium molybdate.

[0042] Preferably, the heat treatment in a reducing atmosphere in step (2) includes the following steps: first, heat treatment is carried out in an atmosphere containing reducing gas, then the temperature is lowered, and heat treatment is continued in an inert atmosphere.

[0043] This invention first performs heat treatment in an atmosphere containing reducing gas to purify the surface and decompose ammonium molybdate into molybdenum oxide. After cooling, it performs heat treatment in an inert atmosphere to precisely repair the lithium vacancies on the surface through gas-phase lithium replenishment, stabilize the spinel reconstruction layer, and stabilize the formed gradient structure.

[0044] Preferably, the atmosphere containing reducing gas includes inert gas and reducing gas.

[0045] Preferably, the reducing gas includes hydrogen, and the inert gas includes any one or a combination of at least two of argon, helium, or radon.

[0046] Preferably, in the atmosphere containing reducing gas, the volume percentage of reducing gas is 20 vol%-40 vol%, for example, it can be 20 vol%, 25 vol%, 30 vol%, 35 vol% or 40 vol%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the heat treatment in an atmosphere containing a reducing gas includes first holding the temperature at 250℃-350℃, for example, 250℃, 270℃, 290℃, 310℃, 330℃, or 350℃, for 0.8h-1.5h, for example, 0.8h, 1h, 1.2h, 1.4h, or 1.5h, and then raising the temperature to 650℃-750℃, for example, 650℃, 670℃, 690℃, 710℃, 730℃, or 750℃, and holding the temperature for 4h-6h, for example, 4h, 4.5h, 5h, 5.5h, or 6h, but not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0048] Preferably, the temperature at which the heat treatment is continued in the inert atmosphere is 450℃-550℃, for example, 450℃, 470℃, 490℃, 510℃, 530℃ or 550℃, and the holding time is 2h-4h, for example, 2h, 2.5h, 3h, 3.5h or 4h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] In a second aspect, the present invention provides a P- and Mo-doped ternary cathode material, which is prepared by the preparation method described in the first aspect.

[0050] Preferably, the P and Mo-doped ternary cathode material is graded doped with phosphorus, and its surface includes a composite interface layer comprising lithium molybdate compound and lithium phosphate compound.

[0051] Thirdly, the present invention provides a battery comprising a ternary cathode material doped with P and Mo as described in the second aspect.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) This invention synthesizes precursor materials with increasing phosphorus content from the inside to the outside through gradient co-precipitation method, so that phosphorus is deeply embedded in the bulk phase from the beginning of material formation, stabilizing lattice oxygen. Thus, through the spatial concentration distribution of "from the inside to the outside and from sparse to dense", stress buffer is constructed while retaining the high specific capacity of the core region, which reduces stress-induced cracks. Furthermore, due to the pre-existing P concentration gradient on the surface layer, the near-surface chemical environment and defect concentration are changed, which can guide and regulate the diffusion depth and distribution of subsequent Mo ions, and promote the formation of a more ideal Mo interface gradient.

[0054] (2) In this invention, molybdenum is diffused from the particle surface to the subsurface in a reducing atmosphere through gas phase transport and high temperature diffusion to form a concentration gradient. At the same time, the surface structure is induced to change from layered to spinel phase, so that the outermost layer is mainly composed of Li-Mo-O (such as Li2MoO4) and a small amount of Li3PO4 composite interface layer. Its main function is to "protect the surface", construct a spinel buffer layer and remove residual alkali, and improve the stability of the material. Therefore, the internal P gradient stabilizes the bulk phase and the external Mo treatment constructs a spinel protective layer, which together improves the stability of the material. Detailed Implementation

[0055] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0056] Example 1

[0057] This embodiment provides a method for preparing a P- and Mo-doped ternary cathode material, the method comprising the following steps:

[0058] (1) Prepare a mixed metal source solution with a nickel ion, cobalt ion and manganese ion molar ratio of 0.92:0.05:0.03 and a total metal ion concentration of 1.5 mol / L, and prepare a 0.2 mol / L ammonium hydrogen phosphate solution;

[0059] Water was added to the reactor until it reached half its volume. The stirring speed was turned on at 400 rpm, and the temperature was controlled at 50°C. Ammonia and sodium hydroxide solution were then added to prepare a bottom solution with a pH of 11 and an ammonia concentration of 0.2 mol / L. After stirring and mixing for 30 min, the mixed metal source solution, sodium hydroxide solution, and ammonia solution were fed into the bottom solution at a flow rate of 5 L / h, 2 L / h, and 1 L / h, respectively, to carry out the first coprecipitation reaction. The temperature of the first coprecipitation reaction was controlled at 50°C, the pH was in the range of 11-11.5, the ammonia concentration was 0.3 mol / L, and the stirring speed was 400 rpm.

[0060] (2) After the first coprecipitation reaction reaches the particle size D50 of D1, the mixed metal source solution, sodium hydroxide solution, ammonia water, and ammonium hydrogen phosphate solution are continuously fed into the reactor at a feed flow rate of 5 L / h, 2 L / h, 1 L / h, and 0.2 L / h to carry out the second coprecipitation reaction. The temperature of the second coprecipitation reaction is controlled at 50℃, the pH is in the range of 11-11.5, the ammonia concentration is 0.3 mol / L, and the rotation speed is 400 rpm to obtain a precursor material with a particle size D50 of 3.5 μm. The difference between the particle size D50 and D1 of the precursor material is 2 μm.

[0061] The feed flow rate of the ammonium hydrogen phosphate solution increases linearly at a rate of 0.01 L / h; it then increases uniformly from 0.2 L / h to 0.4 L / h and ends.

[0062] (3) Grind and mix the precursor material and LiOH·H2O thoroughly in a mortar. The ratio of the total molar amount of metal ions in the precursor material to the molar amount of lithium ions in LiOH·H2O is 1:1.05. After mixing, pre-calcine the resulting mixture at 500°C for 5 hours in an oxygen atmosphere, then sinter at 750°C for 10 hours, and then allow it to cool naturally to obtain the matrix material.

[0063] (4) The matrix material and ammonium molybdate are ball-milled and mixed in a ball mill, wherein the amount of ammonium molybdate added is 0.2 wt% of the mass of the matrix material. Then, the temperature is raised from room temperature to 300°C in a mixture of argon and hydrogen (hydrogen content is 30 vol%) and held for 1 hour. Then, the temperature is raised to 700°C and held for 5 hours. Finally, the temperature is held at 500°C in an argon atmosphere for 3 hours to obtain the P and Mo doped ternary cathode material.

[0064] Example 2

[0065] This embodiment provides a method for preparing a P- and Mo-doped ternary cathode material, the method comprising the following steps:

[0066] (1) Prepare a mixed metal source solution with a nickel ion, cobalt ion and manganese ion molar ratio of 0.94:0.03:0.03 and a total metal ion concentration of 2 mol / L, and prepare a 0.5 mol / L ammonium hydrogen phosphate solution;

[0067] Water was added to the reactor until it reached half its volume. The stirring speed was turned on at 300 rpm, and the temperature was controlled at 60°C. Ammonia and sodium hydroxide solution were then added to prepare a bottom solution with a pH of 10 and an ammonia concentration of 0.3 mol / L. After stirring and mixing for 30 min, the mixed metal source solution, sodium hydroxide solution, and ammonia solution were fed into the bottom solution at a flow rate of 8 L / h, 1 L / h, and 2 L / h, respectively, to carry out the first coprecipitation reaction. The temperature of the first coprecipitation reaction was controlled at 60°C, the pH was in the range of 11.0-11.5, the ammonia concentration was 0.5 mol / L, and the stirring speed was 300 rpm.

[0068] (2) After the first coprecipitation reaction reaches the particle size D50 of D1, the mixed metal source solution, sodium hydroxide solution, ammonia solution, and ammonium hydrogen phosphate solution are continuously fed into the reactor at a feed flow rate of 8 L / h, 1 L / h, 2 L / h, and 0.3 L / h, respectively, to carry out the second coprecipitation reaction. The temperature of the second coprecipitation reaction is controlled at 60℃, the pH is in the range of 11.0-11.5, the ammonia concentration is 0.5 mol / L, and the rotation speed is 300 rpm, to obtain a precursor material with a particle size D50 of 4.5 μm. The difference between the particle size D50 and D1 of the precursor material is 2.5 μm.

[0069] The feed flow rate of the ammonium hydrogen phosphate solution increases linearly at a rate of 0.02 L / h; and then increases uniformly at a rate of 0.3 L / h to 0.5 L / h.

[0070] (3) Grind and mix the precursor material and LiOH·H2O thoroughly in a mortar. The ratio of the total molar amount of metal ions in the precursor material to the molar amount of lithium ions in LiOH·H2O is 1:1.1. After mixing, pre-calcine the resulting mixture at 450°C for 6 hours in an oxygen atmosphere, then sinter it at 800°C for 7 hours, and then allow it to cool naturally to obtain the matrix material.

[0071] (4) The matrix material and ammonium molybdate are ball-milled and mixed in a ball mill, wherein the amount of ammonium molybdate added is 0.3 wt% of the mass of the matrix material. Then, the temperature is raised from room temperature to 250°C in a mixture of argon and hydrogen (hydrogen content is 40 vol%) and held for 1.5 h. Then, the temperature is raised to 750°C and held for 4 h. Finally, the temperature is held at 550°C for 2 h in an argon atmosphere to obtain the P and Mo doped ternary cathode material.

[0072] Example 3

[0073] This embodiment provides a method for preparing a P- and Mo-doped ternary cathode material, the method comprising the following steps:

[0074] (1) Prepare a mixed metal source solution with a nickel ion, cobalt ion and manganese ion molar ratio of 0.92:0.05:0.03 and a total metal ion concentration of 1 mol / L, and prepare a 0.1 mol / L ammonium hydrogen phosphate solution;

[0075] Water was added to the reactor until it reached half its volume. The stirring speed was turned on at 400 rpm, and the temperature was controlled at 65°C. Ammonia and sodium hydroxide solution were then added to prepare a bottom solution with a pH of 11 and an ammonia concentration of 0.1 mol / L. After stirring and mixing for 30 min, the mixed metal source solution, sodium hydroxide solution, and ammonia solution were fed into the bottom solution at a flow rate of 3 L / h, 3 L / h, and 0.5 L / h, respectively, to carry out the first coprecipitation reaction. The temperature of the first coprecipitation reaction was controlled at 65°C, the pH was in the range of 11.5-12, the ammonia concentration was 0.1 mol / L, and the stirring speed was 400 rpm.

[0076] (2) After the first coprecipitation reaction reaches the particle size D50 of D1, the mixed metal source solution, sodium hydroxide solution, ammonia water, and ammonium hydrogen phosphate solution are continuously fed into the reactor at a feed flow rate of 3 L / h, 3 L / h, 0.5 L / h, and 0.1 L / h, respectively, to carry out the second coprecipitation reaction. The temperature of the second coprecipitation reaction is controlled at 65℃, the pH is 11.5-12, the ammonia concentration is 0.1 mol / L, and the rotation speed is 400 rpm, to obtain a precursor material with a particle size D50 of 3 μm. The difference between the particle size D50 and D1 of the precursor material is 1 μm.

[0077] The feed flow rate of the ammonium hydrogen phosphate solution increases linearly at a rate of 0.005 L / h; and then increases uniformly at a rate of 0.1 L / h to 0.15 L / h.

[0078] (3) Grind and mix the precursor material and LiOH·H2O thoroughly in a mortar. The ratio of the total molar amount of metal ions in the precursor material to the molar amount of lithium ions in LiOH·H2O is 1:1.02. After mixing, pre-calcine the resulting mixture at 550°C for 4 hours in an oxygen atmosphere, then sinter at 700°C for 10 hours, and then allow it to cool naturally to obtain the matrix material.

[0079] (4) The matrix material and ammonium molybdate are ball-milled and mixed in a ball mill, wherein the amount of ammonium molybdate added is 0.15 wt% of the mass of the matrix material. Then, the temperature is raised from room temperature to 350°C in a mixture of argon and hydrogen (hydrogen content is 20 vol%) and held for 0.8 h. Then, the temperature is raised to 650°C and held for 6 h. Finally, the temperature is held at 450°C in an argon atmosphere for 4 h to obtain the P and Mo doped ternary cathode material.

[0080] Example 4

[0081] This embodiment provides a method for preparing a P and Mo doped ternary cathode material. Except for step (4), in which the amount of ammonium molybdate added is 0.02 wt% of the mass of the matrix material, the preparation method is the same as in Example 1.

[0082] Example 5

[0083] This embodiment provides a method for preparing a P and Mo doped ternary cathode material. Except for step (4), in which the amount of ammonium molybdate added is 0.5 wt% of the mass of the matrix material, the preparation method is the same as in Example 1.

[0084] Example 6

[0085] This embodiment provides a method for preparing a P and Mo doped ternary cathode material. Except for the difference of 0.5 μm between the particle size D50 and D1 of the precursor material in step (2), the preparation method is the same as in Example 1.

[0086] Example 7

[0087] This embodiment provides a method for preparing a P and Mo doped ternary cathode material. Except for the difference of 3 μm between the particle size D50 and D1 of the precursor material in step (2), the preparation method is the same as in Example 1.

[0088] Example 8

[0089] This embodiment provides a method for preparing a P and Mo doped ternary cathode material. Except for step (4), which involves heat treatment in a mixture of argon and hydrogen, and then holding the material at 500°C for 3 hours in an argon atmosphere, the preparation method is the same as in Example 1.

[0090] Comparative Example 1

[0091] This comparative example provides a method for preparing a P and Mo doped ternary cathode material. Except for the constant feed flow rate of the ammonium hydrogen phosphate solution in step (2), the preparation method is the same as that in Example 1.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing a P and Mo doped ternary cathode material. Except for step (4), in which the mixture obtained by ball milling is kept at 500°C for 3 hours in a pure argon atmosphere, the preparation method is the same as in Example 1.

[0094] The P and Mo doped ternary cathode materials obtained in the above examples and comparative examples were used to prepare cathode sheets, which were then combined with lithium sheets, polypropylene separators, and lithium hexafluorophosphate electrolyte to prepare lithium-ion batteries. The electrochemical performance of the lithium-ion batteries was tested under the following conditions: at 25°C, the prepared lithium-ion batteries were activated by constant current charge-discharge cycles at a rate of 0.1C for 3 cycles within a voltage range of 2.8-4.5V to obtain the discharge specific capacity at a rate of 1C. Then, 500 constant current charge-discharge cycles were performed at a rate of 1C, and the initial discharge specific capacity and the capacity retention rate after 500 cycles were recorded.

[0095] The test results are shown in Table 1 below:

[0096] Table 1

[0097]

[0098] As can be seen from Table 1 above:

[0099] As shown in Examples 1-3 and Comparative Example 1, the gradient doping of phosphorus in the precursor of the present invention not only ensures the high capacity of the precursor core but also constructs a stress buffer and guides the subsequent diffusion of molybdenum, thereby simultaneously ensuring the battery's capacity and cycle performance. As shown in Examples 1-3 and Comparative Example 2, the heat treatment in a reducing atmosphere during the coating of the molybdenum source promotes molybdenum diffusion, purifies the surface, and facilitates the construction of a spinel buffer layer, thus effectively improving the material's stability and the battery's electrochemical performance. As shown in Examples 1 and Examples 4-5, the amount of molybdenum source added affects... The construction of the composite interface layer in this invention affects the stability of the material, and the preferred addition amount is within a specific range. As can be seen from Examples 1 and 6-7, when phosphorus is doped in the precursor, the timing of introducing the phosphorus source affects the gradient distribution of phosphorus, thereby affecting the gradient doping effect. Preferably, the difference between the particle size D50 of the precursor material and the particle size D50 of the particles obtained from the first coprecipitation reaction is within a specific range. As can be seen from Examples 1 and 8, this invention preferably performs heat treatment in an atmosphere containing a reducing gas, then cools down, and switches to an inert atmosphere to continue heat treatment, which can further improve the stability of the material.

[0100] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a P and Mo-doped ternary cathode material, characterized in that, The preparation method includes the following steps: (1) The mixed metal source solution, precipitant solution and complexing agent solution are passed into the bottom liquid to carry out the first coprecipitation reaction. After the first coprecipitation reaction is completed, the mixed metal source solution, precipitant solution and complexing agent solution and phosphorus source solution are carried out to carry out the second coprecipitation reaction to obtain the precursor material. The feed flow rate gradient of the phosphorus source solution is increased; (2) The precursor material and lithium source described in step (1) are mixed and sintered to obtain a matrix material. The matrix material is mixed with a molybdenum source and then heat-treated in a reducing atmosphere to obtain the P and Mo doped ternary cathode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size D50 of the first coprecipitation reaction is D1, the particle size D50 of the precursor material is D2, and the difference between D2 and D1 is 1μm-2.5μm; Preferably, the particle size D50 of the precursor material in step (1) is 3μm-4.5μm.

3. The preparation method according to claim 1 or 2, characterized in that, The initial feed flow rate of the phosphorus source solution in step (1) is 0.1 L / h-0.5 L / h, preferably 0.1 L / h-0.3 L / h; Preferably, the rate of increase of the feed flow rate of the phosphorus source solution in step (1) is 0.005 L / h-0.1 L / h, and more preferably 0.005 L / h-0.02 L / h; Preferably, the feed flow rate of the mixed metal source solution in step (1) is 3L / h-8L / h; Preferably, the feed flow rate of the precipitant solution in step (1) is 1L / h-3L / h; Preferably, the feed flow rate of the complexing agent solution in step (1) is 0.5L / h-2L / h.

4. The preparation method according to claim 1 or 2, characterized in that, The phosphorus source solution in step (1) includes an ammonium hydrogen phosphate solution; Preferably, the concentration of the phosphorus source solution in step (1) is 0.1 mol / L to 0.5 mol / L; Preferably, the total metal ion concentration of the mixed metal source solution in step (1) is 1 mol / L-2 mol / L; Preferably, in the mixed metal source solution of step (1), the molar ratio of nickel ions, cobalt ions and manganese ions is x:y:z, where x>0.9, z<0.05, and x+y+z=1.

5. The preparation method according to claim 1 or 2, characterized in that, In step (1), the temperatures of the first coprecipitation reaction and the second coprecipitation reaction are independently 50℃-65℃; Preferably, in step (1), the pH of the first coprecipitation reaction and the second coprecipitation reaction are independently 11-12; Preferably, in the system of the first coprecipitation reaction and the second coprecipitation reaction in step (1), the concentration of the complexing agent is independently 0.1 mol / L-0.5 mol / L.

6. The preparation method according to claim 1 or 2, characterized in that, In step (1), the stirring speeds for the first coprecipitation reaction and the second coprecipitation reaction are independently 300 rpm to 400 rpm; Preferably, the pH of the base solution in step (1) is 10-11; Preferably, in the base liquid of step (1), the concentration of the complexing agent is 0.1 mol / L-0.3 mol / L.

7. The preparation method according to claim 1 or 2, characterized in that, The ratio of the total molar amount of metal ions in the precursor material to the molar amount of lithium ions in the lithium source in step (2) is 1:(1.02-1.1); Preferably, the sintering in step (2) includes pre-firing at 450℃-550℃ and then calcining at 700℃-800℃; Preferably, the pre-firing time at 450℃-550℃ is 4h-6h; Preferably, the calcination time at 700℃-800℃ is 7h-10h.

8. The preparation method according to claim 1 or 2, characterized in that, The amount of molybdenum source added in step (2) is 0.15wt%-0.3wt% of the mass of the matrix material; Preferably, the heat treatment in a reducing atmosphere described in step (2) includes the following steps: first, heat treatment is performed in an atmosphere containing reducing gas, then the temperature is lowered, and heat treatment is continued in an inert atmosphere; Preferably, the atmosphere containing reducing gas includes an inert gas and a reducing gas; Preferably, in the atmosphere containing reducing gas, the volume percentage of reducing gas is 20 vol%-40 vol%. Preferably, the heat treatment in an atmosphere containing reducing gas includes holding at 250℃-350℃ for 0.8h-1.5h, then raising the temperature to 650℃-750℃ and holding for 4h-6h. Preferably, the temperature at which the heat treatment is continued in the inert atmosphere is 450℃-550℃, and the holding time is 2h-4h.

9. A P- and Mo-doped ternary cathode material, characterized in that, The P and Mo doped ternary cathode material is prepared by the preparation method described in any one of claims 1-8.

10. A battery, characterized in that, The battery comprises a P- and Mo-doped ternary cathode material as described in claim 9.

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