A TiNb2O7-synergistically modified high-nickel ternary cathode material, its preparation method and application

Abstract

The application provides a TiNb2O7 synergistically modified high-nickel ternary positive electrode material and a preparation method and application thereof. The preparation method of the TiNb2O7 synergistically modified high-nickel ternary positive electrode material is characterized in that: TiNb2O7 with a Wadsley-Roth structure is used, an in-situ self-assembly process of early surface anchoring and later gradient diffusion is used, and a multi-level structure of "surface coating-transition layer doping-core unchanged" is constructed in the particle interior. Ti and Nb elements in the TiNb2O7 diffuse to the bulk phase in the high-temperature crystallization and self-assembly process, and the structure is stabilized from the interior. The TiNb2O7 which is not diffused or partially converted and a lithiumated product thereof remain on the surface to form a protective layer, so that the capacity, stability and rate performance of the high-nickel material are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a TiNb2O7 synergistic modification of a high-nickel ternary cathode material, its preparation method, and its application. Background Technology

[0002] With the trend of upgrading to higher energy density, longer cycle life, and higher safety in the new energy power battery industry, high-nickel ternary cathode materials (especially NCM811 and above high-nickel systems) have become the mainstream choice due to their ultra-high specific capacity. However, their commercial application still faces structural defects and process bottlenecks. Furthermore, due to the excessively high Ni content in high-nickel systems, Li... + with Ni 2+ With similar radii, Li-Ni mixing easily occurs, disrupting the layered lattice order; during charging and discharging, Ni... 3+ / Ni 4+ Phase transitions induce repeated volume deformation, leading to grain boundary cracking, particle pulverization, and a significant decrease in cycle life. Intense interfacial side reactions occur: high-nickel materials have high residual alkali content on their surface, resulting in continuous side reactions with the electrolyte. This leads to excessively high SEI film impedance and electrolyte decomposition producing gas, not only reducing rate performance but also posing a risk of thermal runaway. Ion transport is hindered: grain boundary cracking and interfacial side reaction products block Li... + The transmission channel causes a sharp drop in capacity at high rates, making it impossible to meet the fast charging requirements of power batteries.

[0003] CN113130901A discloses a titanium-doped high-nickel ternary lithium-ion battery cathode material and its preparation method. The preparation method includes the following steps: using aluminum salt and titanium salt as raw materials, AlOOH and TiO(OH)2 are coated onto the surface of a nickel-cobalt binary precursor by hydrolysis, yielding a ternary precursor after hydrolysis; the ternary precursor is then mixed with lithium salt and calcined at high temperature, where AlOOH and TiO(OH)2 respectively generate aluminum and titanium compounds, ultimately obtaining the titanium-doped high-nickel ternary lithium-ion battery cathode material. This preparation method utilizes Al and Ti elements in the shell and bulk phases to stabilize the crystal structure of the material, preventing the dissolution of transition metal ions from the active material during long-term cycling, thereby improving the overall electrochemical performance of the material.

[0004] CN121528888A discloses a high-nickel ternary material with gradient doping of high-valence elements, its preparation method, and a solid-state battery, relating to the field of solid-state battery preparation. The high-nickel ternary material of this technical solution includes high-valence elements, namely Ta, W, Zr, and Nb. Through the gradient doping distribution design of Ta, W, Zr, and Nb elements, this technical solution achieves synergistic optimization of high activity in the core region and high stability in the surface region of the high-nickel ternary material, effectively alleviating problems such as particle breakage, ion mixing, and interfacial impedance, and meeting the needs of solid-state battery cathode materials in high-performance applications.

[0005] Currently, while large-particle-size NCM high-nickel materials offer high energy density, they are prone to cracking and cation mixing during cycling. Existing technologies often employ three approaches: single-element doping, single-surface coating, and stepwise modification. However, each approach has significant drawbacks, making it difficult to achieve a balance between performance, cost, and process. Single-element doping: only improves bulk lattice stability, offers no protection against interfacial side reactions, and improper doping concentration can easily disrupt the layered structure, resulting in significant capacity loss. Single-surface coating: only isolates electrolyte contact, failing to address bulk lattice mixing and volume deformation issues. Grain boundary cracking can still lead to coating layer detachment, resulting in poor modification sustainability. Stepwise modification process: first synthesizing ternary materials, then performing coating / doping treatments, is cumbersome, energy-intensive, and has poor production line adaptability. Multiple heat treatments can easily lead to decreased material crystallinity and significantly increased costs, making large-scale implementation difficult.

[0006] In view of the inherent defects of existing high-nickel ternary cathode materials, such as severe lattice mixing, poor structural stability, and violent interfacial side reactions, as well as the technical difficulties such as limited effect of single modification, complicated step-by-step modification process, high mass production cost, and difficulty in balancing capacity and safety, there is an urgent need to develop a TiNb2O7 synergistic modification high-nickel ternary cathode material and its preparation method. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a TiNb2O7 synergistic modification of high nickel ternary cathode material, its preparation method and application. The focus is on providing a process scheme for synergistic modification of high nickel ternary cathode material by in-situ gradient doping of TiNb2O7 (TNO) and surface coating. Relying on the unique Wadsley-Roth shear structure of TNO, the bulk lattice stability and interface protection of high nickel ternary material are optimized.

[0008] To achieve this objective, the present invention adopts the following technical solution: One objective of this invention is to provide a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material, the method comprising the following steps: (1) Prepare a mixed ternary salt solution, a precipitant solution, a complexing agent solution, and a TiNb2O7 suspension, wherein the mixed ternary salt solution contains soluble nickel salt, soluble cobalt salt, and soluble manganese salt; (2) The mixed ternary salt solution, the precipitant solution, and the complexing agent solution are injected in parallel into a reactor containing the first bottom liquid to carry out the first coprecipitation reaction. After solid-liquid separation, seed crystals are obtained. (3) The seed crystals are injected into a reaction vessel containing the second base liquid, and the mixed ternary salt solution, the precipitant solution, the complexing agent solution, and the TiNb2O7 suspension are injected to carry out the second coprecipitation reaction. When the target particle size is 3-4 μm away, the injection of the TiNb2O7 suspension is stopped, and the third coprecipitation reaction is carried out until the target particle size is reached. The composite precursor is obtained by solid-liquid separation, washing, and drying in sequence. (4) The lithium source and the composite precursor are mixed evenly, and then subjected to low-temperature pre-calcination, high-temperature crystallization and self-assembly in sequence to obtain TiNb2O7 synergistic modification high-nickel ternary cathode material.

[0009] The key to this invention lies in utilizing Wadsley-Roth structured TiNb2O7 and constructing a multi-level structure of "surface coating - transition layer doping - unchanged core" within the particle through an in-situ self-assembly process of early surface anchoring + later gradient diffusion. During the high-temperature crystallization and self-assembly process, Ti and Nb elements in TiNb2O7 diffuse into the bulk phase, stabilizing the structure from the inside. Undiffused or partially converted TiNb2O7 and its lithiation products remain on the surface, forming a protective layer. This achieves a synergistic improvement in the capacity, stability, and rate performance of high-nickel materials.

[0010] It should be noted that the composite precursor prepared in this invention has a 3-4 μm thick surface layer without Wadsley-Roth structured TiNb₂O₇, allowing for a TiNb₂O₇ doping concentration. During subsequent high-temperature lithiation sintering, Ti and Nb ions from the TiNb₂O₇ doped inside the composite precursor diffuse towards the surface along the concentration gradient. Since the outermost layer is only 3-4 μm thick, these ions can easily penetrate and ultimately reach and accumulate on the surface of the particles. The Ti diffused to the surface... 4+ and Nb 5+ Ions react with excess lithium in the environment to form an extremely thin, uniform, and dense layer of niobium-titanium composite oxide (mainly Li) on the outermost layer of the particle. x TiNb2O7 or similar coating layer.

[0011] It should be noted that in the preparation method of TiNb2O7 synergistic modification of high nickel ternary cathode material of the present invention, when step (3) is limited to 3-4 μm from the target particle size, the injection of the TiNb2O7 suspension is stopped, for example, 3 μm, 3.1 μm, 3.3 μm, 3.5 μm, 3.6 μm, 3.8 μm or 4 μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0012] As a preferred technical solution of the present invention, in step (1), the total concentration of metal ions in the mixed ternary salt solution is 1-3 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0013] Preferably, in step (1), the molar ratio of nickel to the total concentration of metal ions in the mixed ternary salt solution is ≥0.6.

[0014] As a preferred technical solution of the present invention, in step (1), the precipitant solution includes a sodium hydroxide solution, and the concentration of the precipitant solution is 3-4 mol / L, such as 3 mol / L, 3.1 mol / L, 3.3 mol / L, 3.5 mol / L, 3.6 mol / L, 3.8 mol / L or 4 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0015] Preferably, in step (1), the complexing agent solution includes ammonia water, and the concentration of the complexing agent solution is 0.5-1 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0016] As a preferred technical solution of the present invention, in step (1), the mass concentration of the TiNb2O7 suspension is 0.5-1.5wt%, for example 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.1wt%, 1.3wt% or 1.5wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0017] As a preferred technical solution of the present invention, in step (2), the pH of the first base liquid is 11.0-11.5, such as 11.0, 11.1, 11.2, 11.3, 11.4 or 11.5, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0018] Preferably, in step (2), the stirring speed of the first coprecipitation reaction is 380-400 rpm, such as 380 rpm, 385 rpm, 390 rpm, 395 rpm or 400 rpm; the pH is controlled at 11.0-11.5, such as 11.0, 11.1, 11.2, 11.3, 11.4 or 11.5; the temperature is controlled at 50-60℃, such as 50℃, 51℃, 53℃, 55℃, 56℃, 58℃ or 60℃; the ammonia concentration is controlled at 0.20-0.30 mol / L, such as 0.20 mol / L, 0.21 mol / L, 0.23 mol / L, 0.25 mol / L, 0.27 mol / L, 0.29 mol / L or 0.30 mol / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0019] Preferably, in step (2), the seed crystal diameter D50 is 3-4 μm, such as 3 μm, 3.1 μm, 3.3 μm, 3.5 μm, 3.6 μm, 3.8 μm or 4 μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0020] As a preferred technical solution of the present invention, in step (3), the amount of seed crystal added is 15-25wt% compared to the second base liquid, such as 15wt%, 16wt%, 18wt%, 20wt%, 21wt%, 23wt% or 25wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0021] Preferably, in step (3), the pH of the second base solution is 10.0-10.5, such as 10.0, 10.1, 10.2, 10.3, 10.4 or 10.5, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0022] Preferably, in step (3), the stirring speed of the second coprecipitation reaction is 300-350 rpm, such as 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm or 350 rpm; the pH is controlled at 10.0-10.5, such as 10.0, 10.1, 10.2, 10.3, 10.4 or 10.5; the temperature is controlled at 50-60℃, such as 50℃, 51℃, 53℃, 55℃, 56℃, 58℃ or 60℃; the ammonia concentration is controlled at 0.10-0.20 mol / L, such as 0.10 mol / L, 0.11 mol / L, 0.13 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L or 0.20 mol / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0023] As a preferred technical solution of the present invention, in step (3), the reaction conditions of the third coprecipitation reaction are consistent with those of the second coprecipitation reaction.

[0024] Preferably, in step (3), the target particle size is 10-15 μm, such as 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0025] Preferably, in the composite precursor described in step (3), the TiNb2O7 doping amount is 0.5-2.5wt%, for example 0.5wt%, 0.8wt%, 1.0wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.4wt%, or 2.5wt%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0026] It should be noted that the TiNb2O7 doping amount described in this invention is 0.5-2.5 wt% relative to the theoretical total mass of the ternary hydroxide corresponding to undoped TiNb2O7.

[0027] As a preferred technical solution of the present invention, in step (4), the lithium source and the composite precursor are mixed evenly according to the Li / (Ni+Co+Mn) molar ratio of 1.03-1.1.

[0028] It should be noted that the Li / (Ni+Co+Mn) molar ratio described in this invention is 1.03-1.1, such as 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09 or 1.1, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0029] It should be noted that the lithium source and the composite precursor are mixed evenly through thorough grinding or mechanical fusion.

[0030] Preferably, in step (4), the temperature of the low-temperature preheating is 400-500℃, such as 400℃, 410℃, 430℃, 450℃, 460℃, 480℃ or 500℃, etc.; the heat preservation time is 4-6h, such as 4h, 4.3h, 4.5h, 4.7h, 5h, 5.2h, 5.5h, 5.7h or 6h, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0031] Preferably, in step (4), the low-temperature pre-calcination is carried out in an oxygen atmosphere, which allows the lithium source to melt and penetrate into the composite precursor, while the composite precursor begins to decompose, which is beneficial to the subsequent high-temperature crystallization and self-assembly.

[0032] Preferably, in step (4), the temperature of high-temperature crystallization and self-assembly is 750-850℃, such as 750℃, 770℃, 780℃, 800℃, 810℃, 830℃ or 850℃; the heat preservation time is 10-15h, such as 10h, 11h, 12h, 13h, 14h or 15h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0033] The second objective of this invention is to provide a TiNb2O7 synergistically modified high-nickel ternary cathode material, wherein the TiNb2O7 synergistically modified high-nickel ternary cathode material is prepared by the preparation method described in the first objective and has a multi-level structure of surface coating, transition layer doping, and unchanged core.

[0034] The third objective of this invention is to provide a lithium-ion battery, wherein the lithium-ion battery comprises the TiNb2O7 synergistically modified high-nickel ternary cathode material described in the second objective.

[0035] Compared with existing technical solutions, the present invention has at least the following beneficial effects: (1) The preparation method of TiNb2O7 synergistic modification of high-nickel ternary cathode material provided by the present invention adopts the synergistic modification process of TNO in-situ gradient doping and surface coating, relying on high-valence ion Ti 4+ 、Nb 5+ The lattice pinning effect significantly reduces the degree of Li-Ni mixing.

[0036] (2) The TiNb2O7 synergistic modification of high-nickel ternary cathode material prepared by this invention forms a uniform and dense nanoscale TNO coating layer on the material surface, which isolates the high-nickel cathode from direct contact with the electrolyte, inhibits side reactions caused by residual alkali on the surface, and reduces electrolyte decomposition gas production and the formation of inferior SEI film; moreover, TNO has a three-dimensional lithium-ion transport channel, which ensures interface insulation without hindering Li + Rapid insertion and extraction effectively reduce interfacial charge transfer resistance, improve ion conduction efficiency, and enhance the rate performance and fast charging compatibility of materials.

[0037] (3) The TiNb2O7 synergistic modification high-nickel ternary cathode material prepared by the present invention can effectively suppress lattice oxygen release and improve the thermal stability of the material through the dual mechanism of TNO coating layer and lattice stabilization. Detailed Implementation

[0038] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows: Example 1 This embodiment provides a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material, the preparation method comprising the following steps: (1) Prepare a mixed ternary salt solution with a total metal ion concentration of 1.5 mol / L by mixing nickel chloride, cobalt chloride, and manganese chloride in a molar ratio of Ni:Co:Mn=0.94:0.03:0.03; prepare a sodium hydroxide solution with a concentration of 3.5 mol / L as a precipitant solution; prepare ammonia solution with a concentration of 0.8 mol / L as a complexing agent solution; and prepare a TiNb2O7 suspension with a mass concentration of 1.0 wt%. (2) Fill the reactor with water to half its volume, turn on the stirring speed at 400 rpm, control the temperature at 55°C, and then add ammonia and precipitant solution to prepare the first base solution. The pH of the first base solution is 11.0. After stirring and mixing for 30 min, inject the mixed ternary salt solution, precipitant solution and complexing agent solution into the reactor containing the first base solution in parallel to carry out the first coprecipitation reaction. Control the stirring speed of the first coprecipitation reaction at 400 rpm, the pH at 11.0, the temperature at 55°C, and the ammonia concentration at 0.25 mol / L until the particle size D50 is 3.5 μm. Stop the machine, and obtain seed crystals by centrifugation and washing. (3) The seed crystals are injected into a reactor containing a second base solution, which is ammonia water with a pH of approximately 10.3, and the amount of seed crystals added is 20 wt%. The feed pump of the TiNb2O7 suspension is turned on, and the ratio of the feed rate of the TiNb2O7 suspension to the feed rate of the mixed ternary salt solution is controlled to be 0.1:1 (volume ratio), so as to achieve parallel injection of the mixed ternary salt solution, precipitant solution, complexing agent solution, and TiNb2O7 suspension to carry out the second coprecipitation reaction. The stirring speed was 320 rpm, the pH was controlled at 10.3, the temperature was controlled at 55℃, and the ammonia concentration was controlled at 0.15 mol / L. When the TiNb₂O₇ suspension reached 3.5 μm from the target particle size, the injection was stopped, and the third co-precipitation reaction was carried out until the target particle size of 12 μm was reached. The reaction was then stopped, and the mixture was subjected to solid-liquid separation, washing, and drying to obtain the composite precursor. The TiNb₂O₇ doping content in the composite precursor was 1.6 wt%, as per the target settings. (4) Lithium carbonate and the composite precursor were mechanically fused according to the molar ratio of Li / (Ni+Co+Mn) of 1.08. First, the lithium salt was pre-calcined at 450°C for 5 hours in an oxygen atmosphere to melt and penetrate into the composite precursor. At the same time, the composite precursor began to decompose. Then, the lithium carbonate was kept at 800°C for 12 hours to carry out high-temperature crystallization and self-assembly to obtain TiNb2O7 synergistic modified high-nickel ternary cathode material.

[0039] Example 2 This embodiment provides a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material, the preparation method comprising the following steps: (1) Prepare a mixed ternary salt solution with a total metal ion concentration of 1 mol / L by mixing nickel chloride, cobalt chloride, and manganese chloride in a molar ratio of Ni:Co:Mn=0.94:0.03:0.03; prepare a sodium hydroxide solution with a concentration of 3 mol / L as a precipitant solution; prepare ammonia water with a concentration of 0.5 mol / L as a complexing agent solution; prepare a TiNb2O7 suspension with a mass concentration of 0.5 wt%. (2) Fill the reactor with water to half its volume, turn on the stirring speed to 380 rpm, control the temperature at 55°C, and then add ammonia and precipitant solution to prepare the first base solution. The pH of the first base solution is 11.5. After stirring and mixing for 30 min, inject the mixed ternary salt solution, precipitant solution and complexing agent solution into the reactor containing the first base solution in parallel to carry out the first coprecipitation reaction. Control the stirring speed of the first coprecipitation reaction to 400 rpm, the pH to 11.5, the temperature to 50°C, and the ammonia concentration to 0.20 mol / L until the particle size D50 is 3 μm. Stop the machine, and obtain seed crystals by centrifugation and washing. (3) The seed crystals are injected into a reactor containing a second base solution, which is ammonia water with a pH of approximately 10.0, and the seed crystal addition amount is 15wt%. The feed pump of the TiNb2O7 suspension is turned on to achieve parallel injection of the mixed ternary salt solution, precipitant solution, complexing agent solution, and TiNb2O7 suspension to carry out the second coprecipitation reaction. The stirring speed of the second coprecipitation reaction is 300rpm, the pH is controlled at 10.0, the temperature is controlled at 50℃, and the ammonia concentration is controlled at 0.10mol / L. When the target particle size is 3μm away, the injection of the TiNb2O7 suspension is stopped, and the third coprecipitation reaction is carried out until the target particle size of 12μm is reached. The reactor is then stopped, and the mixture is sequentially subjected to solid-liquid separation, washing, and drying to obtain the composite precursor. The TiNb2O7 doping amount in the composite precursor is 0.5wt% according to the target setting. (4) Lithium carbonate and the composite precursor were mechanically fused according to the molar ratio of Li / (Ni+Co+Mn) of 1.08. First, the lithium salt was pre-calcined at 450°C for 5 hours in an oxygen atmosphere to melt and penetrate into the composite precursor. At the same time, the composite precursor began to decompose. Then, the lithium carbonate was kept at 800°C for 12 hours to carry out high-temperature crystallization and self-assembly to obtain TiNb2O7 synergistic modified high-nickel ternary cathode material.

[0040] Example 3 This embodiment provides a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material, the preparation method comprising the following steps: (1) Prepare a mixed ternary salt solution with a total metal ion concentration of 3 mol / L by mixing nickel chloride, cobalt chloride and manganese chloride in a molar ratio of Ni:Co:Mn=0.94:0.03:0.03; prepare a sodium hydroxide solution with a concentration of 4 mol / L as a precipitant solution; prepare ammonia water with a concentration of 1 mol / L as a complexing agent solution; prepare a TiNb2O7 suspension with a mass concentration of 1.5 wt%. (2) Fill the reactor with water to half its volume, turn on the stirring speed at 400 rpm, control the temperature at 55°C, and then add ammonia and precipitant solution to prepare the first base solution. The pH of the first base solution is 11.5. After stirring and mixing for 30 min, inject the mixed ternary salt solution, precipitant solution and complexing agent solution into the reactor containing the first base solution in parallel to carry out the first coprecipitation reaction. Control the stirring speed of the first coprecipitation reaction at 400 rpm, the pH at 11.5, the temperature at 60°C, and the ammonia concentration at 0.30 mol / L until the particle size D50 is 4 μm. Stop the machine, and obtain seed crystals by centrifugation and washing. (3) The seed crystals are injected into a reactor containing a second base solution, which is ammonia water with a pH of about 10.5, and the seed crystals are added at a rate of 25 wt%. The feed pump of the TiNb2O7 suspension is turned on to achieve parallel injection of the mixed ternary salt solution, precipitant solution, complexing agent solution, and TiNb2O7 suspension to carry out the second coprecipitation reaction. The stirring speed of the second coprecipitation reaction is 350 rpm, the pH is controlled at 10.5, the temperature is controlled at 60℃, and the ammonia concentration is controlled at 0.20 mol / L. When the target particle size is 4 μm away, the injection of the TiNb2O7 suspension is stopped, and the third coprecipitation reaction is carried out until the target particle size of 12 μm is reached. The reactor is then stopped, and the mixture is subjected to solid-liquid separation, washing, and drying to obtain the composite precursor. The TiNb2O7 doping amount in the composite precursor is 2.5 wt%, according to the target setting. (4) Lithium carbonate and the composite precursor were mechanically fused according to the molar ratio of Li / (Ni+Co+Mn) of 1.08. First, the lithium salt was pre-calcined at 450°C for 5 hours in an oxygen atmosphere to melt and penetrate into the composite precursor. At the same time, the composite precursor began to decompose. Then, the lithium carbonate was kept at 800°C for 12 hours to carry out high-temperature crystallization and self-assembly to obtain TiNb2O7 synergistic modified high-nickel ternary cathode material.

[0041] Example 4 This embodiment provides a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material. Compared with Embodiment 1, the only difference is that the mass concentration of the TiNb2O7 suspension is adjusted so that, according to the target setting, the TiNb2O7 doping amount in the composite precursor is 0.3wt%.

[0042] Example 5 This embodiment provides a method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material. Compared with Embodiment 1, the only difference is that the mass concentration of the TiNb2O7 suspension is adjusted so that, according to the target setting, the TiNb2O7 doping amount in the composite precursor is 2.8 wt%.

[0043] Comparative Example 1 This comparative example provides a method for preparing a high-nickel ternary cathode material. The only difference from Example 1 is that the TiNb2O7 suspension is completely omitted, that is, TiNb2O7 doping is not performed.

[0044] Comparative Example 2 This comparative example provides a method for preparing a high-nickel ternary cathode material. Compared with Example 1, the only difference is that the third coprecipitation reaction is directly omitted. That is, the TiNb2O7 suspension is injected in parallel with other raw materials to carry out the second coprecipitation reaction until the target particle size of 12μm is reached. Then the process is stopped, and the composite precursor is obtained by sequential solid-liquid separation, washing, and drying.

[0045] Comparative Example 3 This comparative example provides a method for preparing a high-nickel ternary cathode material. Compared with Example 1, the only difference is that in step (3), when the TiNb2O7 suspension is 6 μm away from the target particle size, the injection is stopped and the third coprecipitation reaction is carried out. When the target particle size of 12 μm is reached, the process is stopped, and the composite precursor is obtained by solid-liquid separation, washing, and drying in sequence.

[0046] Particle testing: The precursors prepared in the above examples and comparative examples were tested for tap density and particle strength, respectively. Specifically, the tap density was tested according to the national standard GBT-21354-2008, and the particle strength was tested using a micro compression testing machine (MCT).

[0047] Electrical performance testing: The positive electrode materials prepared in the above examples and comparative examples were mixed with conductive carbon black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, respectively. A positive electrode slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a solvent and uniformly coated onto an aluminum foil current collector, controlling the active material surface loading to be 4.5 ± 0.2 mg / cm³. 2 CR2032 coin cells were assembled in a glove box filled with dry argon gas, using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1.0M LiPF6 (ethylene carbonate: methyl ethyl carbonate = 3:7, w / w) with 2wt% vinylene carbonate (VC) added as the electrolyte. Activation was performed by three constant-current charge-discharge cycles at 0.1C. The initial discharge specific capacity was measured at 1C, and the initial discharge specific capacity and capacity retention after 500 cycles were recorded. Subsequently, under the same charging regime, after 500 cycles, a discharge test was conducted at 6C. The 6C capacity retention was calculated using the following formula: (6C discharge specific capacity / 1C discharge specific capacity) × 100%. All electrochemical tests were performed at a constant temperature of 25°C.

[0048] The test results are summarized in Table 1.

[0049] Table 1 As shown in Table 1, and as demonstrated in Examples 1-3, the TiNb2O7 synergistic modification of the high-nickel ternary cathode material prepared by this invention forms a uniform and dense nanoscale TNO coating layer on the material surface. This isolates the high-nickel cathode from direct contact with the electrolyte, suppresses side reactions caused by residual alkali on the surface, reduces electrolyte decomposition gas generation and the formation of inferior SEI film, and achieves a precursor tap density ≥ 2.19 g / cm³. 3 The precursor particles have a strength ≥45.2 MPa; moreover, TNO possesses a three-dimensional lithium-ion transport channel, ensuring interface insulation without hindering Li-ion transport. + Rapid insertion and extraction effectively reduces interfacial charge transfer impedance, improves ion conduction efficiency, and enhances the material's rate performance and fast charging compatibility. The initial discharge specific capacity measured at 1C rate is ≥216.5mAh / g, and the capacity retention rate at 6C cycles is ≥85.6%.

[0050] As shown in Example 4, if the TiNb2O7 doping amount in the composite precursor is reduced to 0.3wt%, the strength of the precursor particles will decrease significantly, reaching only 41.3MPa. As shown in Example 5, if the TiNb2O7 doping amount in the composite precursor is increased to 2.8wt%, although the strength of the precursor particles will be enhanced, the first discharge specific capacity measured at 1C rate will decrease to 210.8mAh / g.

[0051] As shown in Comparative Example 1, without TiNb2O7 doping, the precursor tap density decreases significantly, reaching only 2.08 g / cm³. 3 Furthermore, the precursor particle strength decreases significantly, reaching only 32.5 MPa, and the 6C cycle capacity retention also decreases significantly, reaching only 68.4%. As shown in Comparative Example 2, if the outermost layer of the composite precursor does not have an undoped TiNb₂O₇ diffusion layer, not only will the precursor particle strength decrease to only 38.9 MPa, but the 6C cycle capacity retention will also decrease to only 75.3%. As shown in Comparative Example 3, if the outermost layer of the composite precursor has a large undoped TiNb₂O₇ diffusion layer (12 μm), not only will the precursor particle strength decrease to only 41.2 MPa, but the 6C cycle capacity retention will also decrease to only 78.6%.

[0052] The key to the preparation method of TiNb2O7 synergistic modification of high-nickel ternary cathode material of the present invention lies in utilizing TiNb2O7 with Wadsley-Roth structure. Through an in-situ self-assembly process of early surface anchoring and later gradient diffusion, a multi-level structure of "surface coating - transition layer doping - unchanged core" is constructed inside the particle. In this process, Ti and Nb elements in TiNb2O7 diffuse into the bulk phase during high-temperature crystallization and self-assembly, stabilizing the structure from the inside. The undiffused or partially converted TiNb2O7 and its lithiation products remain on the surface, forming a protective layer. This achieves a synergistic improvement in the capacity, stability and rate performance of the high-nickel material. Furthermore, the composite precursor prepared by this invention has a surface layer of 3-4 μm thickness that is not doped with Wadsley-Roth structured TiNb2O7, allowing for the formation of a TiNb2O7 doping concentration. During the subsequent high-temperature lithiation sintering process, the Ti and Nb ions in the TiNb2O7 doped inside the composite precursor will diffuse towards the surface along the concentration gradient. Since the outermost layer is only 3-4 μm thick, these ions can easily pass through and eventually reach and accumulate on the outermost surface of the particles; the Ti diffused to the surface... 4+ and Nb 5+ Ions react with excess lithium in the environment to form an extremely thin, uniform, and dense layer of niobium-titanium composite oxide (mainly Li) on the outermost layer of the particle. x TiNb2O7 or similar coating layer.

[0053] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0054] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0056] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a TiNb2O7 synergistically modified high-nickel ternary cathode material, characterized in that, The preparation method includes the following steps: (1) Prepare a mixed ternary salt solution, a precipitant solution, a complexing agent solution, and a TiNb2O7 suspension, wherein the mixed ternary salt solution contains soluble nickel salt, soluble cobalt salt, and soluble manganese salt; (2) The mixed ternary salt solution, the precipitant solution, and the complexing agent solution are injected in parallel into a reactor containing the first bottom liquid to carry out the first coprecipitation reaction. After solid-liquid separation, seed crystals are obtained. (3) The seed crystals are injected into a reaction vessel containing the second base liquid, and the mixed ternary salt solution, the precipitant solution, the complexing agent solution, and the TiNb2O7 suspension are injected to carry out the second coprecipitation reaction. When the target particle size is 3-4 μm away, the injection of the TiNb2O7 suspension is stopped, and the third coprecipitation reaction is carried out until the target particle size is reached. The composite precursor is obtained by solid-liquid separation, washing, and drying in sequence. (4) The lithium source and the composite precursor are mixed evenly, and then subjected to low-temperature pre-calcination, high-temperature crystallization and self-assembly in sequence to obtain TiNb2O7 synergistic modification high-nickel ternary cathode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the total concentration of metal ions in the mixed ternary salt solution is 1-3 mol / L; Preferably, in step (1), the molar ratio of nickel to the total concentration of metal ions in the mixed ternary salt solution is ≥0.

6.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the precipitant solution includes a sodium hydroxide solution, and the concentration of the precipitant solution is 3-4 mol / L; Preferably, in step (1), the complexing agent solution includes ammonia water, and the concentration of the complexing agent solution is 0.5-1 mol / L.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (1), the mass concentration of the TiNb2O7 suspension is 0.5-1.5wt%.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the pH of the first base solution is 11.0-11.5; Preferably, in step (2), the stirring speed of the first coprecipitation reaction is 380-400 rpm, the pH is controlled at 11.0-11.5, the temperature is controlled at 50-60℃, and the ammonia concentration is controlled at 0.20-0.30 mol / L.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (3), the amount of seed crystals added is 15-25 wt% compared to the second substrate solution; Preferably, in step (3), the pH of the second base solution is 10.0-10.5; Preferably, in step (3), the stirring speed of the second coprecipitation reaction is 300-350 rpm, the pH is controlled at 10.0-10.5, the temperature is controlled at 50-60℃, and the ammonia concentration is controlled at 0.10-0.20 mol / L.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (3), the reaction conditions for the third coprecipitation reaction are consistent with those for the second coprecipitation reaction; Preferably, in step (3), the target particle size is 10-15 μm; Preferably, in the composite precursor described in step (3), the TiNb2O7 doping amount is 0.5-2.5wt%.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the lithium source and the composite precursor are mixed evenly according to a Li / (Ni+Co+Mn) molar ratio of 1.03-1.1; Preferably, in step (4), the temperature of the low-temperature preheating is 400-500℃, and the holding time is 4-6h; Preferably, in step (4), the low-temperature pre-firing is carried out in an oxygen atmosphere; Preferably, in step (4), the temperature of high-temperature crystallization and self-assembly is 750-850℃, and the heat preservation time is 10-15h.

9. A TiNb2O7 synergistic modification of a high-nickel ternary cathode material, characterized in that, The TiNb2O7 synergistically modified high-nickel ternary cathode material is prepared by the preparation method described in any one of claims 1-8, and has a multi-level structure of surface coating, transition layer doping, and unchanged core.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the TiNb2O7 synergistically modified high-nickel ternary cathode material as described in claim 9.

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