High-nickel single-crystal ternary positive electrode modified material and preparation method thereof

Abstract

The application belongs to the technical field of lithium ion battery materials, and particularly relates to a high-nickel single-crystal ternary positive electrode modified material and a preparation method thereof. The method comprises the following steps: after high-nickel single-crystal ternary precursors, lithium hydroxide monohydrate and cerium-tantalum co-doped lithium molybdenum oxyfluoride compounds are ball milled, pre-sintering and high-temperature calcination are performed under an oxygen atmosphere, and single-crystal particle powder is obtained by crushing; then the single-crystal particle powder is mixed with calcium-doped lithium boron phosphorus oxynitride compounds, dried, and then heat treated under a nitrogen atmosphere and sieved. The cerium-tantalum co-doped lithium molybdenum oxyfluoride compounds are prepared by ball milling, drying and step-by-step sintering in a protective powder from lithium carbonate, cerium oxide, tantalum oxide, molybdenum oxide and lithium fluoride; the calcium-doped lithium boron phosphorus oxynitride compounds are prepared by ball milling, step-by-step sintering from lithium carbonate, calcium carbonate, boric acid and ammonium dihydrogen phosphate, and then ball milling and sintering with lithium nitride under nitrogen protection. The application significantly improves the structural stability and electrochemical performance of the high-nickel single-crystal ternary positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a high-nickel single-crystal ternary cathode modification material and its preparation method. Background Technology

[0002] High-nickel single-crystal ternary cathode materials are one of the important cathode materials in the field of lithium-ion batteries. Due to their high specific capacity and relatively good cost advantages, they are widely used in new energy vehicles, energy storage systems, and consumer electronics. With the continuous improvement of market requirements for battery energy density, high nickel content has become the main development direction of ternary cathode materials. Compared with polycrystalline aggregates, single-crystal high-nickel ternary materials have fewer grain boundaries, lower specific surface area, and better mechanical strength, which can effectively alleviate the generation of microcracks during charge and discharge, thereby improving cycle stability and safety performance. However, with the increase of nickel content, the tendency of nickel ions to mix in the material increases, leading to a decrease in structural stability. At the same time, the increase of residual lithium compounds on the surface makes it easy to have side reactions with the electrolyte, causing capacity decay and gas generation problems. Therefore, how to improve the structural stability and interfacial stability of high-nickel single-crystal ternary cathode materials without sacrificing capacity has become a current research hotspot.

[0003] Currently, modification methods for high-nickel single-crystal ternary cathode materials mainly include elemental doping and surface coating. Elemental doping can stabilize the crystal structure at the lattice level, suppressing phase transitions and cation mixing; surface coating can isolate the cathode material from direct contact with the electrolyte, reducing side reactions. However, single modification methods often fail to simultaneously address the dual requirements of bulk and interface stability. While existing doping elements such as aluminum, zirconium, and magnesium can improve stability to some extent, their effect on improving electrochemical performance is limited. Surface coatings such as alumina, titanium oxide, and phosphates often suffer from uneven coating, increased interfacial impedance, or coating detachment during long-term cycling. Furthermore, the sintering process of high-nickel single-crystal materials is sensitive to temperature and atmosphere, and traditional preparation methods struggle to achieve synergistic optimization of doping and coating, resulting in rapid capacity decay even at high temperatures or high voltages. Therefore, developing a modification method that can simultaneously improve both bulk structural stability and interfacial stability, and optimizing its preparation process, is of significant practical importance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a high-nickel single-crystal ternary cathode modification material and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing a high-nickel single-crystal ternary cathode modified material, comprising the following steps:

[0006] S1. By weight, 95-105 parts of high-nickel single-crystal ternary precursor, 45-50 parts of lithium hydroxide monohydrate, and 1.0-2.0 parts of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound are added to a ball mill jar and ball-milled to obtain a mixed powder. The mixed powder is transferred to an alumina crucible, which is then placed in a tube furnace and pre-sintered at 478-482℃ under an oxygen atmosphere. Subsequently, it is calcined at 730-780℃ and cooled to obtain the product. The product is then pulverized to obtain single-crystal particle powder.

[0007] S2. Mix the single crystal powder prepared in step S1 with 2.0-3.0 parts of calcium-doped lithium boron phosphorus oxygen nitrogen compound to obtain a mixed powder; place the mixed powder in a vacuum drying oven and dry it at 118-122℃ to obtain a dried powder; transfer the dried powder to a tube furnace, purge the furnace chamber with nitrogen gas, and then heat it to 348-352℃ under a nitrogen atmosphere, hold it at that temperature, cool it naturally, and sieve it.

[0008] In this invention, the overall synthesis mechanism of the high-nickel single-crystal ternary cathode modified material demonstrates the synergistic effect of bulk doping-induced single crystallization and the construction of a surface ion-conducting layer. During the main reaction stage, the nickel-cobalt-manganese precursor and lithium hydroxide monohydrate undergo profound solid-phase diffusion in an oxygen-rich environment. As the temperature rises to the pre-sintering temperature range, lithium hydroxide melts and wets the precursor particles, and lithium ions begin to intercalate into the transition metal interlayer. At this point, the added cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compound participates in the high-temperature molten salt-assisted growth process. Large ions such as cerium and tantalum can enter the surface layer of the ternary lattice, suppressing the escape of lattice oxygen through strong chemical bonds, while molybdenum and fluorine effectively regulate the crystal plane energy, inducing the material to evolve from a conventional polycrystalline aggregate into regular single-crystal particles. The single-crystal structure significantly reduces the number of grain boundaries, thereby eliminating mechanical stress cracking caused by anisotropic expansion during charging and discharging. In the second-stage modification process, calcium-doped lithium boron phosphorus oxygen nitrogen compounds undergo an in-situ chemical reaction with residual lithium on the surface of single-crystal particles at a relatively low and mild heat treatment temperature. This interface layer formed at a lower temperature not only possesses extremely high flexibility, capable of adapting to minute volume changes in single-crystal particles, but also, by constructing an artificial solid electrolyte interface film, blocks the catalytic pathway of oxidation and decomposition of organic electrolytes by high-valence nickel ions. Through this comprehensive mechanism design, from bulk structural stability to surface chemical protection, the material achieves a significant improvement in structural stability and kinetic performance under high-voltage conditions, fundamentally solving the technical challenges of short cycle life and poor safety of high-nickel materials.

[0009] According to a preferred embodiment of the present invention, in step S1, the temperature is cooled to room temperature.

[0010] According to a preferred embodiment of the present invention, in step S2, the time for holding the temperature at 348-352°C is 3-6 hours.

[0011] According to a preferred embodiment of the present invention, the preparation method of the cerium-tantalum co-doped lithium-molybdenum-oxyfluoride compound includes: A1, adding 14.0-16.0 parts by weight of lithium carbonate, 8.0-9.0 parts by weight of cerium oxide, 21.0-23.0 parts by weight of tantalum oxide, 14.0-15.0 parts by weight of molybdenum oxide and 7.0-8.0 parts by weight of lithium fluoride into a ball mill jar, adding 140-160 parts by weight of anhydrous ethanol, and ball milling to obtain a precursor slurry; A2, drying the precursor slurry at 78-82°C to obtain a powder; transferring the powder into a sealed crucible, burying the crucible in a protective powder composed of lithium carbonate and molybdenum oxide, placing it in a tube furnace, heating to 380-420°C and holding at that temperature under an argon atmosphere, then heating to 720-750°C and holding at that temperature, and then cooling to room temperature to obtain the product; grinding and sieving the product.

[0012] In this invention, the preparation mechanism of cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compound involves a first-stage mixing process where lithium carbonate, cerium oxide, tantalum oxide, molybdenum oxide, and lithium fluoride are subjected to prolonged high-energy ball milling in anhydrous ethanol. Mechanical shearing forces induce numerous lattice defects on the particle surface during this process, significantly reducing the contact resistance of the reactant particles and shortening the diffusion path. During subsequent heating, lithium carbonate decomposes upon reaching the pre-reaction temperature, releasing carbon dioxide and forming an active lithium source. Molybdenum oxide exhibits high volatility at high temperatures; to address this issue, a sealed cap and embedded protective powder strategy are employed. The molybdenum-based vapor generated by the molybdenum oxide and lithium carbonate in the protective powder during heating creates a dynamic equilibrium pressure with the internal environment of the crucible, thereby physically suppressing the loss of molybdenum from the main raw materials and ensuring that the six elements—cerium, tantalum, lithium, molybdenum, oxygen, and fluorine—are strictly integrated according to the preset stoichiometric ratio. When the temperature rises to the high-temperature crystallization reaction range, large-radius cerium ions and high-valence tantalum ions synergistically embed into the molybdenum-oxygen framework. Due to the multivalent nature of cerium ions and the strong chemical bonding of tantalum ions, the structural framework strength of the material can be significantly improved. The introduction of fluorine ions replaces some oxygen atoms in the framework. This anion doping, through charge compensation effect, microscopically modulates the electron distribution, effectively reducing the activation energy of lithium ion migration in such compounds, making it an excellent phase inversion in ion conduction.

[0013] According to a preferred embodiment of the present invention, in step A1, the ball milling time is 6-8 hours.

[0014] According to a preferred embodiment of the present invention, in step A2, the time for holding the temperature at 720-750°C is 10-12 hours.

[0015] According to a preferred embodiment of the present invention, the preparation method of the calcium-doped lithium boron phosphorus oxygen nitrogen compound includes: B1, adding 10.0-12.0 parts by weight of lithium carbonate, 1.5-2.5 parts by weight of calcium carbonate, 3.5-4.5 parts by weight of boric acid, and 2.0-3.0 parts by weight of ammonium dihydrogen phosphate into a ball mill jar, adding 110-130 parts by weight of anhydrous ethanol, ball milling, and drying to obtain powder; placing the powder into a corundum crucible, heating to 298-302°C and holding at that temperature in a muffle furnace under an air atmosphere, then heating to 648-652°C and holding at that temperature, until... Then, after cooling to room temperature, the mixture is ground and sieved under argon protection to obtain the pre-reaction product; B2, in an argon-filled glove box, the pre-reaction product is mixed with 0.8-1.2 parts of lithium nitride and placed into a sealed ball mill jar. Argon is then introduced into the sealed ball mill jar for ball milling; after ball milling, the powder is transferred to a covered boron nitride crucible in the glove box. The covered boron nitride crucible is placed in a tube furnace and heated to 530-570℃ under a nitrogen protective atmosphere. After the reaction is completed, the mixture is cooled to room temperature to obtain the product; the product is then ground and sieved.

[0016] In this invention, the construction mechanism of the calcium-doped lithium boron phosphorus oxynitride compound is essentially to construct a composite oxynitride amorphous structure with ultra-high ionic conductivity. The preparation process consists of two core steps: oxide framework construction and in-situ nitridation. First, lithium carbonate, calcium carbonate, boric acid, and ammonium dihydrogen phosphate undergo a vigorous condensation reaction in air. When heated to the medium-low temperature dehydration range, boric acid and ammonium dihydrogen phosphate undergo dehydration and deammoniation processes, respectively. The generated boron-oxygen and phosphorus-oxygen units, under the induction of lithium and calcium cations, construct a complex polyanionic network by sharing apical oxygen atoms. The incorporation of calcium ions acts as a framework modifier; its larger radius expands the lithium ion transport channels, thereby optimizing the bulk conductivity. After obtaining a stable oxide matrix, lithium nitride is introduced into an argon-protected glove box and subjected to secondary dry ball milling. Mechanical activation energy is used to force the lithium nitride and pre-reacted powder to achieve forced miscibility at the molecular level. After entering the heat treatment stage at the nitriding reaction temperature zone, lithium nitride, acting as an active nitrogen source, carries trivalent nitrogen anions that diffuse into the anion lattice of the oxide via thermal diffusion, partially replacing the original divalent oxygen anions. Because nitrogen atoms have lower electronegativity than oxygen atoms and higher polarizability, the introduction of nitrogen atoms weakens the electrostatic binding of lithium ions to the anion lattice, thus endowing the material with extremely high lithium-ion transport rates even at lower temperatures. This nitrogen-containing compound, as a coating material, can effectively isolate the electrolyte from eroding the positive electrode surface in subsequent processes, mitigating interfacial side reactions.

[0017] According to a preferred embodiment of the present invention, in step B1, the time for holding the temperature at 648-652°C is 8-10 hours.

[0018] According to a preferred embodiment of the present invention, in step B2, the time for holding the temperature at 530-570°C is 5-7 hours.

[0019] A second aspect of the present invention provides a high-nickel single-crystal ternary cathode modified material prepared according to the preparation method of the high-nickel single-crystal ternary cathode modified material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention achieves uniform doping of cerium and tantalum elements in the crystal lattice by introducing a cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compound during the sintering process of high-nickel single-crystal ternary cathode material. Cerium ions have a large ionic radius, which can expand the lithium layer spacing in the layered structure, reduce the lithium ion diffusion barrier, and suppress the migration of nickel ions to lithium sites, thereby effectively alleviating the cation mixing problem commonly found in high-nickel materials. Tantalum ions have a high valence state and strong electronegativity, which can form strong covalent bonds with oxygen atoms, enhance the bonding force between the transition metal layer and the oxygen layer, and significantly improve the thermodynamic stability of the crystal structure in the deep delithiation state. In addition, the introduction of fluorine ions partially replaces the lattice oxygen, further reducing the residual alkali content on the material surface and reducing the gas generation phenomenon caused by the reaction of residual alkali with the electrolyte. Compared with single-doped or unmodified materials, the cathode material prepared by this invention has smaller changes in lattice parameters during long-term cycling, and the phase transition is effectively suppressed. Especially under high-voltage charging, it can still maintain a complete single-crystal structure, avoiding the intergranular cracking problem common in polycrystalline materials.

[0022] (2) Based on bulk doping, this invention further employs calcium-doped lithium boron phosphorus oxynitride compound to coat the surface of single-crystal powder particles. This coating material possesses excellent lithium-ion conductivity and chemical stability, and can form a uniform, dense, and controllable thickness coating layer on the surface of the cathode material. Compared to traditional oxide or phosphate coating layers, calcium-doped lithium boron phosphorus oxynitride compound can not only effectively isolate the cathode material from direct contact with the electrolyte, inhibiting electrolyte decomposition and transition metal dissolution, but its own ionic conductivity does not significantly increase interfacial impedance; on the contrary, it helps to reduce charge transfer resistance. The nitrogen element in the coating layer exists in the form of nitride, which can further react with residual lithium compounds on the surface to generate lithium-ion conductors, achieving in-situ interface repair. By precisely controlling the heat treatment temperature and time of the coating layer, this invention ensures good adhesion between the coating layer and the substrate material, avoiding coating layer detachment and failure during long-term cycling.

[0023] (3) This invention organically integrates the two modification steps of bulk doping and surface coating, and optimizes the independent preparation processes of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound and calcium-doped lithium boron phosphorus oxynitride compound, ensuring the high purity, high activity and good dispersibility of the modifiers. Among them, the cerium-tantalum co-doped lithium molybdenum oxyfluoride compound is synthesized by protective powder sintering method, which effectively suppresses the volatilization of fluorine and the loss of lithium at high temperature, and ensures the accuracy of the stoichiometry of doping elements; the calcium-doped lithium boron phosphorus oxynitride compound is synthesized by segmented sintering combined with lithium nitride nitriding treatment, which successfully introduces nitrogen element and forms a nitrogen oxide structure with high ionic conductivity. When the above modifiers are mixed with high-nickel single crystal ternary precursor or single crystal particle powder, uniform distribution is achieved by ball milling and low temperature heat treatment, avoiding local agglomeration or excessive coating. The final high-nickel single crystal ternary cathode modified material has high specific capacity, long cycle life, excellent rate performance and good high temperature stability. In the fully charged thermal runaway test, the thermal decomposition initiation temperature of this material was significantly increased, the heat release was significantly reduced, and the safety performance was effectively improved. In summary, the method provided by this invention is controllable and reproducible, and the prepared cathode material can meet the dual requirements of high-energy-density lithium-ion batteries for structural and interfacial stability, showing broad prospects for industrial application. Detailed Implementation

[0024] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0025] Example 1

[0026] This embodiment provides a method for preparing a high-nickel single-crystal ternary cathode modified material, the steps of which include:

[0027] Step S1: 100g of high-nickel single-crystal ternary precursor (NCM88S type high-nickel single-crystal ternary precursor purchased from Guangdong Fangyuan New Materials Group Co., Ltd.), 47.5g of lithium hydroxide monohydrate, and 1.5g of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound were added to a ball mill jar and ball-milled at 300r / min for 4h to obtain a mixed powder; the mixed powder was transferred to an alumina crucible, and the alumina crucible was placed in a tube furnace. Under an oxygen atmosphere (oxygen flow rate 100mL / min), the temperature was increased to 480℃ at 5℃ / min for pre-sintering for 4h, and then calcined at 755℃ at 5℃ / min for 12h. The mixture was then cooled to room temperature to obtain the product; the product was pulverized to obtain single-crystal particle powder.

[0028] Step S2: Mix the single crystal powder prepared in step S1 with 2.5g of calcium-doped lithium boron phosphorus oxygen nitrogen compound to obtain a mixed powder; place the mixed powder in a vacuum drying oven and dry it at 120℃ for 4h to obtain the dried powder; transfer the dried powder to a tube furnace, purge the furnace chamber with nitrogen gas (flow rate 100mL / min) for 30min, and then heat it to 350℃ at 5℃ / min under a nitrogen atmosphere and hold it for 4.5h. After natural cooling, pass it through a 200-mesh sieve to obtain a high-nickel single crystal ternary cathode modified material.

[0029] Preparation of cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compounds:

[0030] Step A1: Add 15.0g lithium carbonate, 8.5g cerium oxide, 22.0g tantalum oxide, 14.5g molybdenum oxide and 7.5g lithium fluoride into a ball mill jar, add 150g anhydrous ethanol, and ball mill at 300r / min for 7h to obtain precursor slurry;

[0031] Step A2: The precursor slurry is vacuum dried at 80°C to obtain powder; the powder is transferred to a sealed crucible, and the crucible is buried in a protective powder composed of lithium carbonate and molybdenum oxide in a mass ratio of 1:1. The crucible is placed in a tube furnace, and the temperature is increased to 400°C at 5°C / min and held for 2 hours under an argon atmosphere. Then the temperature is increased to 735°C at 5°C / min and held for 11 hours. The temperature is then cooled to room temperature to obtain the product. The product is ground and passed through a 200-mesh sieve.

[0032] Preparation of calcium-doped lithium boron phosphorus oxynitride compounds:

[0033] Step B1: Add 11.0g lithium carbonate, 2.0g calcium carbonate, 4.0g boric acid, and 2.5g ammonium dihydrogen phosphate to a ball mill jar, add 120g anhydrous ethanol, and ball mill at 300r / min for 6h. Dry to obtain powder. Place the powder in a corundum crucible and heat it to 300℃ at 5℃ / min for 2h in a muffle furnace under air atmosphere. Then heat it to 650℃ at 5℃ / min for 9h. Allow it to cool naturally to room temperature, and then grind it through a 200-mesh sieve under argon protection to obtain the pre-reaction product.

[0034] Step B2: In an argon-filled glove box, the pre-reaction product was mixed with 1.0 g of lithium nitride and placed into a sealed ball mill jar. Argon gas was introduced into the sealed ball mill jar, and the mixture was ball-milled at 300 r / min for 4 h. After ball milling, the powder was transferred to a covered boron nitride crucible in the glove box. The covered boron nitride crucible was placed in a tube furnace, and the temperature was increased to 550 °C at 5 °C / min and held for 6 h under a nitrogen protective atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain the product. The product was then ground through a 200-mesh sieve.

[0035] Example 2

[0036] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a high-nickel single-crystal ternary cathode modified material, the steps of which include:

[0037] Step S1: Add 95g of high-nickel single-crystal ternary precursor, 45g of lithium hydroxide monohydrate, and 1.0g of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound to a ball mill jar and ball mill at 300r / min for 4h to obtain a mixed powder; transfer the mixed powder to an alumina crucible, place the alumina crucible in a tube furnace, and pre-sinter at 478℃ for 4h under an oxygen atmosphere (oxygen flow rate 100mL / min) at a temperature of 5℃ / min, followed by high-temperature calcination at 730℃ for 12h at a temperature of 5℃ / min, and cool to room temperature to obtain the product; pulverize the product to obtain single-crystal particle powder;

[0038] Step S2: Mix the single crystal powder prepared in step S1 with 2.0 g of calcium-doped lithium boron phosphorus oxygen nitrogen compound to obtain a mixed powder; place the mixed powder in a vacuum drying oven and dry it at 118 °C for 4 h to obtain the dried powder; transfer the dried powder to a tube furnace, purge the furnace chamber with nitrogen gas (flow rate 100 mL / min) for 30 min, and then heat it to 348 °C at 5 °C / min under a nitrogen atmosphere and hold it for 3 h, cool it naturally, and pass it through a 200-mesh sieve to obtain a high-nickel single crystal ternary cathode modified material.

[0039] Preparation of cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compounds:

[0040] Step A1: Add 14.0g lithium carbonate, 8.0g cerium oxide, 21.0g tantalum oxide, 14.0g molybdenum oxide and 7.0g lithium fluoride into a ball mill jar, add 140g anhydrous ethanol, and ball mill at 300r / min for 6h to obtain precursor slurry;

[0041] Step A2: The precursor slurry is vacuum dried at 78°C to obtain powder; the powder is transferred to a sealed crucible, and the crucible is buried in a protective powder composed of lithium carbonate and molybdenum oxide in a mass ratio of 1:1. The crucible is placed in a tube furnace, and under an argon atmosphere, the temperature is increased to 380°C at 5°C / min and held for 2 hours. Then, the temperature is increased to 720°C at 5°C / min and held for 10 hours. The temperature is then cooled to room temperature to obtain the product. The product is ground and passed through a 200-mesh sieve.

[0042] Preparation of calcium-doped lithium boron phosphorus oxynitride compounds:

[0043] Step B1: Add 10.0g lithium carbonate, 1.5g calcium carbonate, 3.5g boric acid, and 2.0g ammonium dihydrogen phosphate to a ball mill jar, add 110g anhydrous ethanol, and ball mill at 300r / min for 6h. Dry to obtain powder. Place the powder in a corundum crucible and heat it to 298℃ at 5℃ / min for 2h in a muffle furnace under air atmosphere. Then heat it to 648℃ at 5℃ / min for 8h. Allow it to cool naturally to room temperature, and then grind it through a 200-mesh sieve under argon protection to obtain the pre-reaction product.

[0044] Step B2: In an argon-filled glove box, the pre-reaction product was mixed with 0.8 g of lithium nitride and placed into a sealed ball mill jar. Argon gas was introduced into the sealed ball mill jar, and the mixture was ball-milled at 300 r / min for 4 h. After ball milling, the powder was transferred to a covered boron nitride crucible in the glove box. The covered boron nitride crucible was placed in a tube furnace, and the temperature was increased to 530 °C at 5 °C / min and held for 5 h under a nitrogen protective atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain the product. The product was then ground through a 200-mesh sieve.

[0045] Example 3

[0046] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a high-nickel single-crystal ternary cathode modified material, the steps of which include:

[0047] Step S1: Add 105g of high-nickel single-crystal ternary precursor, 50g of lithium hydroxide monohydrate, and 2.0g of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound to a ball mill jar and ball mill at 300r / min for 4h to obtain a mixed powder; transfer the mixed powder to an alumina crucible, place the alumina crucible in a tube furnace, and pre-sinter at 482℃ for 4h under an oxygen atmosphere (oxygen flow rate 100mL / min) at a temperature of 5℃ / min, followed by high-temperature calcination at 780℃ for 12h at a temperature of 5℃ / min, and cool to room temperature to obtain the product; pulverize the product to obtain single-crystal particle powder;

[0048] Step S2: Mix the single crystal powder prepared in step S1 with 3.0 g of calcium-doped lithium boron phosphorus oxygen nitrogen compound to obtain a mixed powder; place the mixed powder in a vacuum drying oven and dry it at 122℃ for 4 h to obtain the dried powder; transfer the dried powder to a tube furnace, purge the furnace chamber with nitrogen gas (flow rate 100 mL / min) for 30 min, and then heat it to 352℃ at 5℃ / min under a nitrogen atmosphere and hold it for 6 h, cool it naturally, and pass it through a 200-mesh sieve to obtain a high-nickel single crystal ternary cathode modified material.

[0049] Preparation of cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compounds:

[0050] Step A1: Add 16.0g lithium carbonate, 9.0g cerium oxide, 23.0g tantalum oxide, 15.0g molybdenum oxide and 8.0g lithium fluoride into a ball mill jar, add 160g anhydrous ethanol, and ball mill at 300r / min for 8h to obtain precursor slurry;

[0051] Step A2: The precursor slurry is vacuum dried at 82℃ to obtain powder; the powder is transferred to a sealed crucible, and the crucible is buried in a protective powder composed of lithium carbonate and molybdenum oxide in a mass ratio of 1:1. The crucible is placed in a tube furnace, and under an argon atmosphere, the temperature is increased to 420℃ at 5℃ / min and held for 2 hours. Then, the temperature is increased to 750℃ at 5℃ / min and held for 12 hours. The temperature is then cooled to room temperature to obtain the product. The product is ground and passed through a 200-mesh sieve.

[0052] Preparation of calcium-doped lithium boron phosphorus oxynitride compounds:

[0053] Step B1: Add 12.0g lithium carbonate, 2.5g calcium carbonate, 4.5g boric acid, and 3.0g ammonium dihydrogen phosphate to a ball mill jar, add 130g anhydrous ethanol, and ball mill at 300r / min for 6h. Dry to obtain powder. Place the powder in a corundum crucible and heat it to 302℃ at 5℃ / min for 2h in a muffle furnace under air atmosphere. Then heat it to 652℃ at 5℃ / min for 10h. Allow it to cool naturally to room temperature, and then grind it through a 200-mesh sieve under argon protection to obtain the pre-reaction product.

[0054] Step B2: In an argon-filled glove box, the pre-reaction product was mixed with 1.2g of lithium nitride and placed into a sealed ball mill jar. Argon gas was introduced into the sealed ball mill jar, and the mixture was ball-milled at 300r / min for 4h. After ball milling, the powder was transferred to a covered boron nitride crucible in the glove box. The covered boron nitride crucible was placed in a tube furnace, and the temperature was increased to 570℃ at 5℃ / min and held for 7h under a nitrogen protective atmosphere. After the reaction was completed, the mixture was cooled to room temperature to obtain the product. The product was then ground through a 200-mesh sieve.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that no cerium-tantalum co-doped lithium molybdenum oxyfluoride compound is added in step S1, while the remaining steps and all parameters are the same as in Example 1.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that no calcium-doped lithium boron phosphorus oxynitride compound is added in step S2, while the remaining steps and all parameters are the same as in Example 1.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 1 is that no cerium-tantalum co-doped lithium molybdenum oxyfluorine compound is added in step S1, and no calcium-doped lithium boron phosphorus oxynitrogen compound is added in step S2. All other steps and parameters are the same as in Example 1.

[0061] According to relevant national and industry standards, the performance of the high-nickel single-crystal ternary cathode modification materials provided in the above embodiments and comparative examples was tested. The test methods are as follows:

[0062] Initial discharge specific capacity and initial coulombic efficiency tests: The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1, respectively. N-methylpyrrolidone was added and stirred into a uniform slurry, which was then coated onto aluminum foil. After vacuum drying at 120°C for 12 hours, the mixture was cut into 12mm diameter discs as positive electrode sheets. Using lithium metal sheets as negative electrodes and Celgard 2400 as separators, and with 1 mol / L LiPF6 dissolved in ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1) as the electrolyte, CR2032 coin cells were assembled in an argon glove box. Constant current charge-discharge tests were performed at 25°C using a battery testing system. The charging rate was 0.1C (1C = 200mA / g), the charging cutoff voltage was 4.3V, the discharging rate was 0.1C, and the discharging cutoff voltage was 2.8V. Record the initial discharge specific capacity (mAh / g) and initial coulombic efficiency (%, i.e., initial discharge specific capacity / initial charge specific capacity × 100%). Three parallel cells were tested in each group, and the average value was taken.

[0063] Capacity retention test after 100 cycles at 1C: Using the same CR2032 coin cells as described above, the cells were charged at a constant current rate of 1C to 4.3V at 25℃, and then discharged at a constant current rate of 1C to 2.8V, repeating this cycle 100 times. The discharge specific capacity of the first cycle and the discharge specific capacity of the 100th cycle were recorded. Capacity retention rate (%) = (discharge specific capacity of the 100th cycle / discharge specific capacity of the first cycle) × 100%. Three parallel cells were tested in each group, and the average value was taken.

[0064] 5C Rate Capacity Retention Test: Using the same CR2032 coin cells as described above, charge and discharge tests were conducted sequentially at 0.2C, 0.5C, 1C, 2C, and 5C rates at 25℃, with 5 cycles at each rate. The charge and discharge rates were the same, and the voltage range was 2.8-4.3V. The specific capacity of the 5th discharge at 0.2C and the specific capacity of the 5th discharge at 5C were recorded. The 5C rate capacity retention rate (%) = (5C rate discharge specific capacity / 0.2C rate discharge specific capacity) × 100%. Three parallel cells were tested in each group, and the average value was taken.

[0065] Charge transfer resistance test after cycling: The battery (maintaining 50% state of charge) after 100 cycles at 1C was disassembled, the positive electrode was removed, and cleaned and dried with dimethyl carbonate. It was then reassembled into a symmetrical battery (positive electrode | electrolyte | positive electrode). AC impedance testing was performed using an electrochemical workstation with a frequency range of 0.01Hz to 100kHz and an AC amplitude of 5mV. The charge transfer resistance (unit: Ω) was obtained through equivalent circuit fitting. Three parallel batteries were tested in each group, and the average value was taken.

[0066] Thermal decomposition onset temperature test: The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into CR2032 coin cells. They were charged to 4.3V at 0.1C at 25℃ using the method described above, and then kept at a constant voltage until the current dropped to 0.01C, resulting in a fully charged positive electrode. The cells were disassembled in an argon glove box, the positive electrode was removed, and the positive electrode material powder was scraped off. Thermal analysis was performed using a thermogravimetric-differential scanning calorimeter. 3-5 mg of powder was weighed and placed in an sealed aluminum crucible under a nitrogen atmosphere. The heating rate was 10℃ / min, and the temperature range was from room temperature to 500℃. The onset temperature of the exothermic peak (unit: ℃) was recorded, i.e., the thermal decomposition onset temperature. Three parallel samples were tested in each group, and the average value was taken.

[0067] The performance test data above are shown in Table 1.

[0068] Table 1 Performance Test Results

[0069]

[0070] As can be seen from the above, Examples 1-3 significantly solve the following technical problems compared to Comparative Examples 1-3:

[0071] First, the initial discharge specific capacity of Comparative Example 3 (without any modifier) ​​was only 200.3 mAh / g, and the initial coulombic efficiency was only 83.5%, while the initial discharge specific capacity of Examples 1-3 reached 204.2-208.1 mAh / g, and the initial coulombic efficiency was improved to 89.2-89.8%. This indicates that the synergistic effect of cerium-tantalum co-doped lithium molybdenum oxyfluorine compound and calcium-doped lithium boron phosphorus oxynitrogen compound effectively suppressed the residual alkali and cation mixing on the surface of high-nickel materials, and reduced irreversible capacity loss.

[0072] Secondly, the capacity retention rate of Comparative Example 3 after 100 cycles of 1C was only 81.5%, while that of Comparative Example 1 (coated but undoped) was 88.6% and that of Comparative Example 2 (doped but uncoated) was 86.9%. However, Examples 1-3 all reached 93.5-94.6%, indicating that simultaneous bulk cerium-tantalum doping and surface calcium doping with lithium boron phosphorus oxygen nitrogen coating can significantly stabilize the crystal structure and protect the interface, thereby greatly extending the cycle life.

[0073] Third, the 5C rate capacity retention rate of Comparative Example 3 was only 73.2%, Comparative Example 1 was 80.3%, Comparative Example 2 was 78.9%, while Examples 1-3 reached 85.1-87.2%, indicating that cerium-tantalum doping increased the lithium layer spacing and reduced the lithium-ion diffusion barrier. At the same time, the calcium-doped lithium boron phosphorus oxygen nitrogen coating layer has good ionic conductivity, which synergistically reduced polarization at high rates.

[0074] Fourth, the charge transfer resistance of Comparative Example 3 after cycling was as high as 118.2Ω, compared to 89.5Ω in Comparative Example 1 and 94.6Ω in Comparative Example 2, while that of Examples 1-3 was only 56.9-61.7Ω. This confirms that the combined action of the two modifiers can effectively suppress the accumulation of interfacial byproducts during cycling and maintain low interfacial impedance.

[0075] Fifth, the thermal decomposition initiation temperature of Comparative Example 3 was only 201.8℃, compared to 219.7℃ in Comparative Example 1 and 215.3℃ in Comparative Example 2, while that of Examples 1-3 increased to 235.4-240.2℃. This indicates that cerium-tantalum doping enhances the stability of lattice oxygen, and the calcium-doped lithium-boron-phosphorus-oxygen-nitrogen coating isolates the electrolyte from direct contact with the positive electrode surface, thereby significantly improving the thermal safety of the material.

[0076] In summary, this invention successfully solves the key technical problems of poor cycle stability, insufficient rate performance, rapid impedance growth, and low thermal safety of high-nickel single-crystal ternary cathode materials through synergistic modification of bulk cerium-tantalum co-doping and surface calcium-doped lithium boron phosphorus oxygen nitrogen coating.

Claims

1. A method for preparing a high-nickel single-crystal ternary cathode modified material, characterized in that the steps include: include: S1. By weight, 95-105 parts of high-nickel single-crystal ternary precursor, 45-50 parts of lithium hydroxide monohydrate, and 1.0-2.0 parts of cerium-tantalum co-doped lithium molybdenum oxyfluoride compound are added to a ball mill jar and ball-milled to obtain a mixed powder. The mixed powder is transferred to an alumina crucible, which is then placed in a tube furnace and pre-sintered at 478-482℃ under an oxygen atmosphere. Subsequently, it is calcined at 730-780℃ and cooled to obtain the product. The product is then pulverized to obtain single-crystal particle powder. S2. Mix the single crystal powder prepared in step S1 with 2.0-3.0 parts of calcium-doped lithium boron phosphorus oxygen nitrogen compound to obtain a mixed powder; place the mixed powder in a vacuum drying oven and dry it at 118-122℃ to obtain a dried powder; transfer the dried powder to a tube furnace, purge the furnace chamber with nitrogen gas, and then heat it to 348-352℃ under a nitrogen atmosphere, hold it at that temperature, cool it naturally, and sieve it.

2. The preparation method of the high-nickel single-crystal ternary cathode modified material according to claim 1, characterized in that, In step S1, the temperature is cooled to room temperature.

3. The preparation method of the high-nickel single-crystal ternary cathode modified material according to claim 1, characterized in that, In step S2, the temperature is raised to 348-352℃ and held for 3-6 hours.

4. The preparation method of the high-nickel single-crystal ternary cathode modified material according to claim 1, characterized in that, The preparation method of the cerium-tantalum co-doped lithium-molybdenum-oxyfluorine compound includes: A1, adding 14.0-16.0 parts by weight of lithium carbonate, 8.0-9.0 parts by weight of cerium oxide, 21.0-23.0 parts by weight of tantalum oxide, 14.0-15.0 parts by weight of molybdenum oxide and 7.0-8.0 parts by weight of lithium fluoride into a ball mill jar, adding 140-160 parts by weight of anhydrous ethanol, and ball milling to obtain a precursor slurry; A2, drying the precursor slurry at 78-82℃ to obtain a powder; transferring the powder into a sealed crucible, burying the crucible in a protective powder composed of lithium carbonate and molybdenum oxide, placing it in a tube furnace, heating to 380-420℃ and holding under an argon atmosphere, then heating to 720-750℃ and holding, and then cooling to room temperature to obtain the product; grinding and sieving the product.

5. The preparation method of the high-nickel single-crystal ternary cathode modified material according to claim 4, characterized in that, In step A1, the ball milling time is 6-8 hours.

6. The method for preparing the high-nickel single-crystal ternary cathode modified material according to claim 4, characterized in that, In step A2, the temperature is raised to 720-750℃ and held for 10-12 hours.

7. The method for preparing the high-nickel single-crystal ternary cathode modified material according to claim 1, characterized in that, The preparation method of the calcium-doped lithium boron phosphorus oxynitride compound includes: B1, adding 10.0-12.0 parts by weight of lithium carbonate, 1.5-2.5 parts by weight of calcium carbonate, 3.5-4.5 parts by weight of boric acid, and 2.0-3.0 parts by weight of ammonium dihydrogen phosphate into a ball mill jar, adding 110-130 parts by weight of anhydrous ethanol, ball milling, and drying to obtain powder; placing the powder into a corundum crucible, heating to 298-302℃ and holding at that temperature in a muffle furnace under an air atmosphere, then heating to 648-652℃ and holding at that temperature, and naturally cooling to room temperature. Then, under argon protection, the mixture is ground and sieved to obtain the pre-reaction product; B2, in an argon-filled glove box, the pre-reaction product is mixed with 0.8-1.2 parts of lithium nitride and placed into a sealed ball mill jar. Argon is then introduced into the sealed ball mill jar for ball milling; after ball milling, the powder is transferred to a covered boron nitride crucible in the glove box. The covered boron nitride crucible is placed in a tube furnace and heated to 530-570℃ under a nitrogen protective atmosphere. After the reaction is completed, the mixture is cooled to room temperature to obtain the product; the product is then ground and sieved.

8. The method for preparing the high-nickel single-crystal ternary cathode modified material according to claim 7, characterized in that, In step B1, the temperature is raised to 648-652℃ and held for 8-10 hours.

9. The method for preparing the high-nickel single-crystal ternary cathode modified material according to claim 7, characterized in that, In step B2, the temperature is raised to 530-570℃ and held for 5-7 hours.

10. A high-nickel single-crystal ternary cathode modification material, characterized in that, The high-nickel single-crystal ternary cathode modified material is prepared by the method described in any one of claims 1-9.

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