Coating modification method of ternary positive electrode material, coating modified ternary positive electrode material and application

Abstract

The invention provides a coating modification method of a ternary positive electrode material, a coated modified ternary positive electrode material and application. The coating modification method comprises the following steps: mixing a ternary positive electrode material, a coating source and a composite solvent to obtain mixed slurry; wherein the composite solvent comprises diethylene glycol and water; mixing the mixed slurry and the precipitant solution, and carrying out a co-precipitation reaction to obtain a ternary positive electrode material loaded with a coated precursor; and mixing the ternary positive electrode material loaded with the coated precursor with a lithium source, and calcining to obtain the coated modified ternary positive electrode material. According to the invention, diethylene glycol and water are adopted as a composite solvent, so that a high steric hindrance effect is achieved, growth can be slowed down, coating uniformity is improved, crystal orientation growth of a coating precursor can be regulated and controlled through a directional adsorption effect, a coating layer with a low lithium ion migration energy barrier is formed, and the fast charging performance of the material is improved; the coating layer enables the material to maintain high capacity and enhance the cycling stability at the same time.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for coating modification of ternary cathode materials, coating modified ternary cathode materials, and their applications. Background Technology

[0002] Lithium-ion batteries have been widely used in the energy storage field due to their high energy density, long cycle life, environmental friendliness, and fast charge / discharge capability. As one of the key factors determining battery performance, the characteristics of the cathode material directly affect the overall performance of the battery. Among many candidate materials, nickel-based ternary oxides are considered the most promising cathode materials due to their high energy density and excellent low-temperature and high-temperature tolerance. However, when nickel-based ternary materials operate at high voltages, irreversible structural reconstruction such as rock salt phase formation and lattice oxygen loss easily occur on the surface of the cathode particles, leading to a decline in cycle performance. This phenomenon is mainly driven by two mechanisms: (1) phase transition during charge and discharge; (2) side reactions with the electrolyte. Therefore, developing effective surface modification strategies to suppress structural degradation and maintain interface stability is crucial for improving the practicality of cathode materials.

[0003] The core function of surface modification is to physically isolate the electrolyte from direct contact with the cathode, thereby reducing side reactions. Simultaneously, an ideal modified layer should possess structural stability to suppress phase transitions and mechanical fragmentation on the particle surface. However, the selection of current modification materials still faces significant challenges: an ideal coating must simultaneously satisfy high ionic / electronic conductivity, electrolyte chemical inertness, and mechanical strength. Traditional modification methods, such as metal oxide / fluoride coatings, lithium conductor encapsulation, or conductive polymer deposition, are typically achieved through dry mixing or vapor deposition, but they have obvious limitations: poor coating uniformity, easily leading to increased local interfacial impedance; insufficient adhesion, resulting in detachment and failure after long-term cycling; and limited functionality, making it difficult to balance conductivity and chemical stability. These problems ultimately lead to a difficulty in balancing capacity and stability in modified materials.

[0004] Therefore, how to ensure that cathode materials can maintain both high capacity performance and high cycle stability after surface modification is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for coating modification of ternary cathode materials, the coated modified ternary cathode materials, and their applications. In the process of coating modification of ternary cathode materials, the present invention introduces a combination of diethylene glycol and water as a composite solvent. This solvent exhibits a high steric hindrance effect, which slows down the growth of the coating layer and improves the uniformity of the coating. Furthermore, the ether bonds and hydroxyl groups in the diethylene glycol molecule preferentially adsorb onto specific crystal planes during co-precipitation, allowing diethylene glycol to effectively control the crystal growth orientation of the coating precursor, forming a coating layer with a special structure and a low lithium-ion migration barrier, thus improving the material's fast charge-discharge capability. Moreover, this coating layer is structurally stable under high voltage, significantly inhibiting the oxidative decomposition of the ternary cathode material with the electrolyte at voltages below 4.3V, suppressing manganese dissolution and phase transition, and forming a gradient transition region with gradually changing composition between the coating layer and the ternary cathode material matrix, thereby improving structural stability. In summary, the present invention significantly improves both the long-cycle stability and fast charge-discharge capability of the material while maintaining high capacity. In addition, this coating modification method is simple, low-cost, environmentally friendly, and suitable for large-scale production.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for coating modification of a ternary cathode material, the method comprising the following steps:

[0008] A ternary cathode material, a coating source, and a composite solvent are mixed to obtain a mixed slurry; wherein the composite solvent includes diethylene glycol and water.

[0009] The mixed slurry and precipitant solution are mixed and co-precipitated to obtain a ternary cathode material loaded with the precursor.

[0010] The ternary cathode material with the loaded precursor is mixed with a lithium source and calcined to obtain the coated modified ternary cathode material.

[0011] In the process of coating and modifying ternary cathode materials, this invention introduces a combination of diethylene glycol and water as a composite solvent. This solvent exhibits high steric hindrance, which slows down the growth of the coating layer and improves coating uniformity. Furthermore, the ether bonds and hydroxyl groups in the diethylene glycol molecule preferentially adsorb onto specific crystal planes during co-precipitation, allowing diethylene glycol to effectively control the crystal growth orientation of the coating precursor. This results in a coating layer with a special structure and low lithium-ion migration barrier, improving the material's fast charge-discharge capability. Moreover, this coating layer is structurally stable under high voltage, significantly inhibiting the oxidative decomposition of the ternary cathode material with the electrolyte at voltages below 4.3V. It also suppresses manganese dissolution and phase transition, and forms a gradient transition region with gradually changing composition between the coating layer and the ternary cathode material matrix, further enhancing structural stability. In summary, this invention significantly improves both the long-cycle stability and fast charge-discharge capability of the material while maintaining high capacity. In addition, this coating modification method is simple, low-cost, environmentally friendly, and suitable for large-scale production.

[0012] In this invention, the ternary cathode material can provide heterogeneous nucleation sites in the coprecipitation reaction, reducing the nucleation barrier and promoting preferential deposition of solute on the crystal nucleus surface.

[0013] In this invention, the composite solvent of diethylene glycol and water functions as follows: 1) It has a high steric hindrance effect, which can slow down the growth kinetics (ion diffusion and crystal growth rate) of the coating layer, resulting in nanoparticles with narrow particle size distribution and uniform morphology, thus improving the coating uniformity; 2) The ether bonds and hydroxyl groups in the diethylene glycol molecule preferentially adsorb onto specific crystal planes of the coating precursor (e.g., the {012} crystal plane of nickel manganese carbonate compounds) during co-precipitation, significantly reducing the surface Gibbs free energy of the crystal plane, inducing preferential growth of carbonate along the {012} direction, and the structure induces the crystal to expand along a specific direction, forming an orthorhombic nanosheet structure coating layer; The sintered product inherits the structural characteristics of the precursor, generating orthorhombic lithium nickel manganese oxide nanosheets, whose surface mainly exposes the {111} crystal plane, and the Li on the {111} crystal plane + The migration barrier is significantly lower than {100}, which significantly improves the lithium-ion diffusion rate and effectively enhances the rate performance and cycle stability of the material.

[0014] In this invention, a ternary cathode material, a coating source, and a composite solvent are mixed to obtain a mixed slurry. Then, the mixed slurry is mixed with a precipitant solution (e.g., sodium carbonate solution) to carry out a co-precipitation reaction, thereby forming a coating precursor on the surface of the ternary cathode material. The active sites on the surface of the ternary cathode material can serve as heterogeneous nucleation nuclei, significantly reducing the nucleation barrier and promoting the directional deposition of reaction products on the surface of the nuclei to form a continuous coating layer, thus avoiding agglomeration caused by homogeneous nucleation.

[0015] Preferably, the ternary cathode material is a nickel-based ternary cathode material with the general chemical formula LiNi.x Co y Mn 1-x-y O2, where x≥0.6, for example, it can be 0.7, 0.8, 0.9 or 0.95, etc., 0<y<0.4, for example, it can be 0.1, 0.2 or 0.3, etc., and 1-xy>0.

[0016] Preferably, the coating source includes nickelates and manganates. Exemplarily, nickelates may be nickel sulfate, nickel nitrate, or nickel acetate, and manganates may be manganese sulfate, manganese nitrate, or manganese acetate.

[0017] Preferably, the transition metal molar ratio of the nickelate and manganate is 1:(3-6.5), for example, it can be 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or 1:6.5, etc.

[0018] Preferably, the mass ratio of diethylene glycol to water is (1.7-3):1, for example, 2.0, 2.5 or 3.0.

[0019] In this invention, a suitable weight ratio can ensure the ion diffusion rate without being too dilute and causing precipitation to be too fast. If the ratio is too low, it can easily lead to limited reaction temperature, metal ion segregation, uneven particle size, and the presence of amorphous regions. If it is too high, it can easily lead to increased viscosity, slow reaction kinetics, and irregular blocky products.

[0020] Preferably, the method for mixing the ternary cathode material, the coating source, and the composite solvent includes:

[0021] The coating source is dissolved in the composite solvent to obtain a coating solution, and then the ternary cathode material is added to the coating solution.

[0022] Preferably, the mass concentration of the coating source in the coating solution is 10-60 g / L, for example, it can be 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L or 60 g / L.

[0023] Preferably, the mass ratio of the ternary cathode material to the coating liquid is 1:(1.5-2.5), for example, it can be 1:1.5, 1:2 or 1:2.5, etc.

[0024] Preferably, the precipitant solution comprises a carbonate solution. For example, it could be a sodium carbonate solution, etc.

[0025] Preferably, the concentration of the precipitant solution is 4-6 mol / L, for example, it can be 4 mol / L, 5 mol / L or 6 mol / L, etc.

[0026] Preferably, during the coprecipitation reaction, the reaction temperature is 20-50℃, for example, 30℃, 40℃ or 50℃, and the reaction time is 0.5-3h, for example, 1h, 2h or 3h.

[0027] Preferably, in the ternary cathode material with the loaded coating precursor, the coating precursor located on the surface of the ternary cathode material is a nickel-manganese carbonate compound with an orthogonal nanosheet structure.

[0028] In this invention, a nickel-manganese carbonate compound with an orthogonal nanosheet structure is used as a coating precursor. During lithium sintering, the sintered product inherits the structural characteristics of the precursor, generating orthogonal lithium nickel manganese oxide (e.g., LiNi). 0.5 Mn 1.5 O2) nanosheets, orthogonal nanosheets with mainly exposed {111} crystal planes on the surface, and Li on the {111} crystal planes + The migration barrier is significantly lower than {100}, which significantly improves the lithium-ion diffusion rate and effectively enhances the rate performance and cycle stability of the material.

[0029] Preferably, the lithium source includes any one or a combination of at least two of LiNO3, LiCl, LiOH, or Li2CO3. For example, LiOH can be anhydrous lithium hydroxide or lithium hydroxide monohydrate, etc.

[0030] Preferably, the calcination temperature is 500-650℃, for example, 500℃, 550℃, 600℃ or 650℃, and the holding time is 4-6h, for example, 4h, 5h or 6h.

[0031] Preferably, the atmosphere for the calcination treatment is an oxygen-containing atmosphere. For example, it could be oxygen.

[0032] Preferably, the coating modification method includes the following steps:

[0033] (1) Preparation of nickel-based ternary cathode materials, the specific steps include:

[0034] (a) A nickel source (e.g., nickel sulfate, etc.), a cobalt source (e.g., cobalt sulfate, etc.), and a manganese source (e.g., manganese sulfate, etc.) are dissolved in water to obtain a mixed salt solution of transition metals. Then, a precipitant and a complexing agent are added to carry out a co-precipitation reaction. After the reaction is completed, the solution is filtered and washed, and then vacuum dried at a temperature of 110-130°C (e.g., 110°C, 120°C, or 130°C, etc.) for 12-24 h (e.g., 12 h, 18 h, or 24 h, etc.) to obtain a nickel-based ternary precursor.

[0035] (b) The nickel-based ternary precursor and the lithium salt are ball-milled at a molar ratio of 1:(1.02-1.05) (e.g., 1:1.02, 1:1.03, 1:1.04 or 1:1.05, etc.) to obtain a mixture; the ball milling speed is 100-300 rpm (e.g., 100 rpm, 200 rpm or 300 rpm, etc.); the lithium salt includes any one or a combination of at least two of LiNO3, LiCl, LiOH or Li2CO3.

[0036] (c) The mixture is calcined in an oxygen-containing atmosphere at a temperature of 700-1050℃ (e.g., 700℃, 800℃, 900℃, 1000℃ or 1050℃, etc.) for 10-24h (e.g., 10h, 16h, 18h or 24h, etc.) to obtain the nickel-based ternary cathode material.

[0037] (2) Dissolve nickelate and manganate in a composite solvent composed of diethylene glycol and water and stir until homogeneous to obtain a coating solution; the transition metal molar ratio of nickelate and manganate is 1:(3-6.5); the weight ratio of diethylene glycol and water is (1.7-3):1; the mass concentration of the coating source in the coating solution is 10-60 g / L.

[0038] The nickel-based ternary cathode material is added to the coating solution and stirred evenly to obtain a mixed slurry; the mass ratio of the nickel-based ternary cathode material to the coating solution is 1:(1.5-2.5).

[0039] (3) Add a carbonate solution with a concentration of 4-6 mol / L to the mixed slurry and stir evenly. Carry out a co-precipitation reaction at a temperature of 25-50℃ for 0.5-3h to obtain a ternary cathode material coated with nickel-manganese carbonate.

[0040] (4) The nickel-manganese carbonate-coated ternary cathode material is dried, then mixed with lithium salt by ball milling, and calcined at 500-680°C in an oxygen-containing atmosphere for 4-8 hours to obtain spinel-type nickel-manganese lithium oxide-coated ternary cathode material; the lithium salt includes any one or at least two combinations of LiNO3, LiCl, LiOH or Li2CO3; the molar ratio of the transition metal in the nickel-manganese carbonate to the lithium metal in the lithium salt is 2:(1.02-1.05) (for example, it can be 2:1.02, 2:1.03, 2:1.04 or 2:1.05, etc.).

[0041] In a second aspect, the present invention provides a coated modified ternary cathode material, which is prepared by the coating modification method described in the first aspect.

[0042] The modified ternary cathode material includes a matrix material and a coating layer covering the surface of the matrix material. A gradient transition layer is formed between the matrix material and the coating layer, and the gradient transition layer is formed by ion diffusion during the calcination process.

[0043] In this invention, the gradient transition layer formed by ion diffusion during the calcination process ensures a strong bond between the coating layer and the substrate material.

[0044] Preferably, the matrix material has the general chemical formula LiNi. x Co y Mn 1-x-y O2, where x≥0.6, for example, it can be 0.6, 0.7, 0.8, 0.9 or 0.95, etc., 0<y<0.4, for example, it can be 0.1, 0.2 or 0.3, etc., and 1-xy>0.

[0045] Preferably, the matrix material includes secondary particles with a morphology similar to single crystal spheres, which are formed by the aggregation of primary single crystal particles arranged radially.

[0046] Preferably, the coating layer is a spinel-type lithium nickel manganese oxide layer with the general chemical formula LiNi. a Mn 2-a O4, where the value of a ranges from 0.33 to 0.5, for example, it can be 0.33, 0.35, 0.4, 0.45 or 0.5, etc.

[0047] In this invention, the spinel-type lithium nickel manganese oxide layer has an orthorhombic nanosheet structure. The orthorhombic crystal system, through asymmetric lattice distortion, makes Mn 3+ / Mn 4+ The occupied octahedral sites undergo local compression, increasing the Mn-O bond energy and decreasing the Mn bond energy. 3+ Its migration activity can inhibit structural phase transformation and metal Mn dissolution, thereby improving the structural stability of the material.

[0048] Preferably, the gradient transition layer is a transition metal gradient layer formed on the surface by ion self-diffusion during high-temperature sintering.

[0049] In this invention, during high-temperature sintering, ions interdiffusion form a gradient transition layer on the surface. The Ni content in the coating layer gradually decreases from the inside to the outside, which effectively alleviates the concentrated stress generated on the positive electrode surface due to volume strain during charging and discharging, inhibits the growth of microcracks, avoids interface cracking, maintains the integrity of the particle structure, and improves the cycle stability of the material.

[0050] Preferably, the particle size Dv50 of the matrix material is 10-15 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0051] Preferably, the thickness of the coating layer is 10-50 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm or 50 nm. It should be noted that the thickness of the coating layer is obtained by direct observation of the material cross-section using a scanning electron microscope (SEM).

[0052] Preferably, based on the total mass of the coated modified ternary cathode material, the mass percentage of the coating layer is 0.5-3%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%. It should be noted that the mass percentage of the coating layer can be measured by comparing the change in the total mass of the material before and after coating.

[0053] Thirdly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the coated modified ternary positive electrode material as described in the second aspect.

[0054] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] In the process of coating and modifying ternary cathode materials, this invention introduces a combination of diethylene glycol and water as a composite solvent. This solvent exhibits high steric hindrance, which slows down the growth of the coating layer and improves coating uniformity. Furthermore, the ether bonds and hydroxyl groups in the diethylene glycol molecule preferentially adsorb onto specific crystal planes during co-precipitation, allowing diethylene glycol to effectively control the crystal growth orientation of the coating precursor. This results in a coating layer with a special structure and low lithium-ion migration barrier, improving the material's fast charge-discharge capability. Moreover, this coating layer is structurally stable under high voltage, significantly inhibiting the oxidative decomposition of the ternary cathode material with the electrolyte at voltages below 4.3V. It also suppresses manganese dissolution and phase transition, and forms a gradient transition region with gradually changing composition between the coating layer and the ternary cathode material matrix, further enhancing structural stability. In summary, this invention significantly improves both the long-cycle stability and fast charge-discharge capability of the material while maintaining high capacity. In addition, this coating modification method is simple, low-cost, environmentally friendly, and suitable for large-scale production. Attached Figure Description

[0057] Figure 1 This is a scanning electron microscope image of the coated and modified ternary cathode material provided in Example 1 of this invention.

[0058] Figure 2 This is a scanning electron microscope image of the ternary cathode material provided in Comparative Example 1 of this invention.

[0059] Figure 3 This is a comparison chart of the cycle performance curves provided in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0060] 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.

[0061] Example 1

[0062] This embodiment provides a coating modification method for ternary cathode materials, the coating modification method comprising the following steps:

[0063] (1) Preparation of chemical formula with general chemical formula LiNi 0.9 Co 0.05 Mn 0.05 The specific steps for using O2 in nickel-based ternary cathode materials include:

[0064] (a) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in deionized water in a molar ratio of Ni:Co:Mn=90:5:5 to prepare 6 L of 2 mol / L mixed transition metal salt solution; 7.2 L of 2 mol / L ammonia solution and 5 L of 5 mol / L NaOH solution were prepared.

[0065] The transition metal mixed salt solution was continuously injected into a batch reactor along with ammonia and NaOH solution at a flow rate of 0.3 L / h using a peristaltic pump. The reaction temperature was controlled at 60°C, and the pH of the reaction system was 11.15. The co-precipitation reaction was carried out under a nitrogen atmosphere. After the reaction, the mixture was allowed to stand and age until the particle size Dv50 of the product particles was 10 μm. Then, it was filtered and washed successively with deionized water and anhydrous ethanol. Finally, it was vacuum dried in a vacuum oven at 120°C for 18 h to obtain a nickel-based ternary precursor with the chemical formula Ni. 0.9 Co 0.05 Mn 0.05 (OH)2.

[0066] (b) The nickel-based ternary precursor and LiOH·H2O were placed in a ball mill jar at a molar ratio of 1:1.04 and ball milled at a speed of 150 rpm to obtain a mixture.

[0067] (c) The mixture is calcined in an oxygen atmosphere at a temperature of 800°C for 15 hours, and then passed through a 400-mesh sieve to obtain the nickel-based ternary cathode material.

[0068] (2) Dissolve 6.02g of anhydrous nickel acetate and 23.42g of anhydrous manganese acetate in a composite solvent (1000g) composed of diethylene glycol and water and stir for 30min to obtain a coating solution; the transition metal molar ratio of the anhydrous nickel acetate and anhydrous manganese acetate is 1:4; the weight ratio of the diethylene glycol and water is 7:3; the total mass concentration of the anhydrous nickel acetate and anhydrous manganese acetate in the coating solution is 29.44g / L.

[0069] The nickel-based ternary cathode material is added to the coating solution and magnetically stirred until homogeneous to obtain a mixed slurry; the mass ratio of the nickel-based ternary cathode material to the coating solution is 1:2.03.

[0070] (3) Add 100L of sodium carbonate solution with a concentration of 5mol / L to the mixed slurry and stir for 5min to mix evenly. Then carry out a co-precipitation reaction at 40℃ for 1h to obtain a ternary cathode material coated with nickel manganese carbonate; the nickel manganese carbonate has an orthogonal nanosheet structure.

[0071] (4) The nickel-manganese carbonate-coated ternary cathode material is vacuum dried at 60°C for 6 hours, and then the nickel-manganese carbonate-coated ternary cathode material is ball-milled and mixed evenly with LiOH·H2O. Subsequently, it is calcined at 580°C in an oxygen atmosphere for 5 hours to obtain spinel-type nickel-manganese lithium oxide-coated ternary cathode material; wherein, the molar ratio of the transition metal in the nickel-manganese carbonate to the lithium metal in the LiOH·H2O is 2:1.04.

[0072] This embodiment also provides a coated modified ternary cathode material, which is prepared by the coating modification method described above.

[0073] The modified ternary cathode material includes a matrix material and a coating layer covering the surface of the matrix material. A gradient transition layer is formed between the matrix material and the coating layer, and the gradient transition layer is formed by ion diffusion during the calcination process.

[0074] The chemical formula of the matrix material is LiNi. 0.9 Co 0.05 Mn 0.05 O2; the matrix material includes secondary particles with a spherical morphology, which are aggregated from primary single-crystal particles arranged radially; the particle size Dv50 of the matrix material is 12 μm; the coating layer is a spinel-type lithium nickel manganese oxide layer with a thickness of 15 nm and the chemical formula LiNi. 0.5 Mn 1.5 O4; Based on the total mass of the modified ternary cathode material, the mass ratio of the coating layer is 2.4%.

[0075] Figure 1 The image shows a scanning electron microscope (SEM) image of the modified ternary cathode material provided in this embodiment. As can be seen from the image, the surface of the ternary spherical particles is coated with a layer of white substance, indicating that the coating has been uniformly covered on the surface of the spherical particles.

[0076] Example 2

[0077] This embodiment provides a coating modification method for ternary cathode materials, the coating modification method comprising the following steps:

[0078] (1) Preparation of chemical formula with general chemical formula LiNi 0.9 Co 0.05 Mn 0.05 The specific steps for using O2 in nickel-based ternary cathode materials include:

[0079] (a) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in deionized water in a molar ratio of Ni:Co:Mn=90:5:5 to prepare 6 L of 2 mol / L mixed transition metal salt solution; 7.2 L of 2 mol / L ammonia solution and 5 L of 5 mol / L NaOH solution were prepared.

[0080] The transition metal mixed salt solution was continuously injected into a batch reactor along with ammonia and NaOH solution at a flow rate of 0.3 L / h using a peristaltic pump. The reaction temperature was controlled at 60°C, and the pH of the reaction system was 11.15. The co-precipitation reaction was carried out under a nitrogen atmosphere. After the reaction, the mixture was allowed to stand and age until the particle size Dv50 of the product particles was 10 μm. Then, it was filtered and washed successively with deionized water and anhydrous ethanol. Finally, it was vacuum dried in a vacuum oven at 120°C for 18 h to obtain a nickel-based ternary precursor with the chemical formula Ni. 0.9 Co 0.05 Mn 0.05 (OH)2.

[0081] (b) The nickel-based ternary precursor and LiOH·H2O were placed in a ball mill jar at a molar ratio of 1:1.04 and ball milled at a speed of 150 rpm to obtain a mixture.

[0082] (c) The mixture is calcined in an oxygen atmosphere at a temperature of 800°C for 15 hours, and then passed through a 400-mesh sieve to obtain the nickel-based ternary cathode material.

[0083] (2) Dissolve 4.21g of anhydrous nickel acetate and 25.76g of anhydrous manganese acetate in a composite solvent (1000g) composed of diethylene glycol and water and stir for 30min to obtain a coating solution; the transition metal molar ratio of the anhydrous nickel acetate and anhydrous manganese acetate is 1:6.25; the weight ratio of the diethylene glycol and water is 7:3; the total mass concentration of the anhydrous nickel acetate and anhydrous manganese acetate in the coating solution is 29.97g / L.

[0084] The nickel-based ternary cathode material is added to the coating solution and magnetically stirred until homogeneous to obtain a mixed slurry; the mass ratio of the nickel-based ternary cathode material to the coating solution is 1:2.03.

[0085] (3) Add 100L of sodium carbonate solution with a concentration of 5mol / L to the mixed slurry and stir for 5min to mix evenly. Then carry out a co-precipitation reaction at 40℃ for 1h to obtain a ternary cathode material coated with nickel manganese carbonate; the nickel manganese carbonate has an orthogonal nanosheet structure.

[0086] (4) The nickel-manganese carbonate-coated ternary cathode material was vacuum dried at 60°C for 6 hours, and then the nickel-manganese carbonate-coated ternary cathode material was ball-milled and mixed evenly with LiOH·H2O. Subsequently, it was calcined at 580°C in an oxygen atmosphere for 5 hours to obtain spinel nickel-manganese lithium oxide-coated ternary cathode material; wherein the molar ratio of the transition metal in the nickel-manganese carbonate to the lithium metal in the LiOH·H2O was 2:1.04.

[0087] This embodiment also provides a coated modified ternary cathode material, which is prepared by the coating modification method described above.

[0088] The modified ternary cathode material includes a matrix material and a coating layer covering the surface of the matrix material. A gradient transition layer is formed between the matrix material and the coating layer, and the gradient transition layer is formed by ion diffusion during the calcination process.

[0089] The chemical formula of the matrix material is LiNi. 0.9 Co 0.05 Mn 0.05 O2; the matrix material includes secondary particles with a spherical morphology, which are aggregated from primary single-crystal particles arranged radially; the particle size Dv50 of the matrix material is 12 μm; the coating layer is a spinel-type lithium nickel manganese oxide layer with a thickness of 15 nm and the chemical formula LiNi. 0.35 Mn 1.65 O4; Based on the total mass of the modified ternary cathode material, the mass ratio of the coating layer is 2.4%.

[0090] Example 3

[0091] This embodiment provides a coating modification method for ternary cathode materials, the coating modification method comprising the following steps:

[0092] (1) Preparation of chemical formula with general chemical formula LiNi 0.9 Co 0.05 Mn 0.05 The specific steps for using O2 in nickel-based ternary cathode materials include:

[0093] (a) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in deionized water in a molar ratio of Ni:Co:Mn=90:5:5 to prepare 6 L of 2 mol / L mixed transition metal salt solution; 7.2 L of 2 mol / L ammonia solution and 5 L of 5 mol / L NaOH solution were prepared.

[0094] The transition metal mixed salt solution was continuously injected into a batch reactor along with ammonia and NaOH solution at a flow rate of 0.3 L / h using a peristaltic pump. The reaction temperature was controlled at 60°C, and the pH of the reaction system was 11.15. The co-precipitation reaction was carried out under a nitrogen atmosphere. After the reaction, the mixture was allowed to stand and age until the particle size Dv50 of the product particles was 10 μm. Then, it was filtered and washed successively with deionized water and anhydrous ethanol. Finally, it was vacuum dried in a vacuum oven at 120°C for 18 h to obtain a nickel-based ternary precursor with the chemical formula Ni. 0.9 Co 0.05 Mn 0.05 (OH)2.

[0095] (b) The nickel-based ternary precursor and LiOH·H2O were placed in a ball mill jar at a molar ratio of 1:1.04 and ball milled at a speed of 150 rpm to obtain a mixture.

[0096] (c) The mixture is calcined in an oxygen atmosphere at a temperature of 800°C for 15 hours, and then passed through a 400-mesh sieve to obtain the nickel-based ternary cathode material.

[0097] (2) Dissolve 4.82g of anhydrous nickel acetate and 24.98g of anhydrous manganese acetate in a composite solvent (1000g) composed of diethylene glycol and water and stir for 30min to obtain a coating solution; the transition metal molar ratio of the anhydrous nickel acetate and anhydrous manganese acetate is 1:5.3; the weight ratio of the diethylene glycol and water is 7:3; the total mass concentration of the anhydrous nickel acetate and anhydrous manganese acetate in the coating solution is 29.8g / L.

[0098] The nickel-based ternary cathode material is added to the coating solution and magnetically stirred until homogeneous to obtain a mixed slurry; the mass ratio of the nickel-based ternary cathode material to the coating solution is 1:2.03.

[0099] (3) Add 100L of sodium carbonate solution with a concentration of 5mol / L to the mixed slurry and stir for 5min to mix evenly. Then carry out a co-precipitation reaction at 40℃ for 1h to obtain a ternary cathode material coated with nickel manganese carbonate; the nickel manganese carbonate has an orthogonal nanosheet structure.

[0100] (4) The nickel-manganese carbonate-coated ternary cathode material is vacuum dried at 60°C for 6 hours, and then the nickel-manganese carbonate-coated ternary cathode material is ball-milled and mixed evenly with LiOH·H2O. Subsequently, it is calcined at 580°C in an oxygen atmosphere for 5 hours to obtain spinel-type nickel-manganese lithium oxide-coated ternary cathode material; wherein, the molar ratio of the transition metal in the nickel-manganese carbonate to the lithium metal in the LiOH·H2O is 2:1.04.

[0101] This embodiment also provides a coated and modified ternary cathode material, wherein the coated and modified ternary cathode material...

[0102] The cathode material was prepared using the coating modification method described above.

[0103] The modified ternary cathode material includes a matrix material and a coating layer covering the surface of the matrix material. A gradient transition layer is formed between the matrix material and the coating layer, and the gradient transition layer is formed by ion diffusion during the calcination process.

[0104] The chemical formula of the matrix material is LiNi. 0.9 Co 0.05 Mn 0.05 O2; the matrix material includes secondary particles with a spherical morphology, which are aggregated from primary single-crystal particles arranged radially; the particle size Dv50 of the matrix material is 12 μm; the coating layer is a spinel-type lithium nickel manganese oxide layer with a thickness of 15 nm and the chemical formula LiNi. 0.4 Mn 1.6 O4; Based on the total mass of the modified ternary cathode material, the mass ratio of the coating layer is 2.4%.

[0105] Example 4

[0106] The difference between this embodiment and Embodiment 1 is that the weight ratio of diethylene glycol to water in the composite solvent is 1:1.

[0107] The remaining preparation methods and parameters are consistent with those in Example 1.

[0108] Example 5

[0109] The difference between this embodiment and Embodiment 1 is that the weight ratio of diethylene glycol to water in the composite solvent is 4:1.

[0110] The remaining preparation methods and parameters are consistent with those in Example 1.

[0111] Example 6

[0112] The difference between this embodiment and Embodiment 1 is that the mass ratio of the ternary cathode material to the coating liquid is 1:3.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Example 7

[0115] The difference between this embodiment and Embodiment 1 is that the mass ratio of the ternary cathode material to the coating liquid is 1:1.

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Comparative Example 1

[0118] The difference between this comparative example and Example 1 is that steps (2), (3) and (4) are not performed, and the nickel-based ternary cathode material obtained in step (1) is used as the final ternary cathode material.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Figure 2 The image shows a scanning electron microscope (SEM) image of the ternary cathode material provided in this comparative example. As can be seen from the image, the secondary particles exhibit a near-spherical morphology and are formed by multiple primary particles tightly packed together through grain boundaries. This indicates that the sintering process was properly controlled, resulting in sufficient grain growth and a dense structure.

[0121] Figure 3 The comparison graphs of the cycle performance curves of Example 1 and Comparative Example 1 measured at 2.8-4.3V and 1C are shown. The results show that the cycle performance of the coated modified ternary cathode material is significantly improved. This is attributed to the fact that the coating layer prepared by the special process is relatively stable under high voltage. After coating, it can prevent the ternary cathode material from undergoing oxidative decomposition with the electrolyte at less than 4.3V. At the same time, a gradient transition layer is formed, which ensures a strong bond between the coating layer and the matrix material, avoids the generation of microcracks, and improves the cycle stability of the material.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 1 is that steps (2), (3), and (4) are omitted, and instead the following steps are performed after step (1):

[0124] 507.36g of nickel-based ternary cathode material, 6.02g of nickel acetate, 23.42g of manganese acetate and 2.97g of LiOH·H2O were ball-milled and mixed evenly, and then calcined at 580℃ for 5h in an oxygen atmosphere to obtain the coated ternary cathode material.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Comparative Example 3

[0127] The difference between this comparative example and Example 1 is that diethylene glycol is replaced with ethylene glycol in the composite solvent.

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Performance testing

[0130] The ternary cathode materials provided in the above embodiments and comparative examples were mixed with polyvinylidene fluoride and acetylene black at a mass ratio of 8:1:1 to form a slurry, which was then coated on aluminum foil to obtain a cathode sheet; lithium sheet was used as the anode sheet; lithium hexafluorophosphate was used as the solute in the electrolyte, and the solvent was a combination of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1; the separator was a polypropylene separator; and a CR2032 coin cell was assembled.

[0131] The charge-discharge performance of the CR2032 button cell was tested: under constant current conditions, charge-discharge cycles were performed at a rate of 0.1C, and the 0.1C charge-discharge specific capacity was measured; under constant current conditions, charge-discharge cycles were performed at a rate of 0.3C, and the 0.3C charge-discharge specific capacity was measured.

[0132] Cyclic performance testing was performed on the CR2032 coin cell: Under constant current conditions, charge and discharge cycles were performed at a 1C rate within a voltage range of 2.8V to 4.3V for 80 cycles. The discharge capacity of the 80th cycle was recorded, and the capacity retention rate relative to the first discharge capacity was calculated.

[0133] The results are shown in Table 1.

[0134] Table 1

[0135]

[0136] analyze:

[0137] As shown in Table 1, the capacity of the coated and modified ternary cathode material prepared by the coating modification method provided by this invention is improved. This is attributed to the spinel-type coating layer mainly exposing the {111} crystal plane, while the Li on the {111} crystal plane... +The migration barrier is significantly lower than {100}, which significantly reduces the lithium-ion migration barrier, increases the diffusion rate of lithium ions, effectively improves the material's fast charge and discharge capability, and enhances the material's electrochemical performance.

[0138] As can be seen from the comparison between Example 1 and Examples 4-5, if the weight ratio of diethylene glycol to water in the composite solvent is too small, the insufficient amount of diethylene glycol will lead to limited reaction, metal ion segregation, and thus uncontrolled reaction products and uneven particle size. If the weight ratio of diethylene glycol to water in the composite solvent is too large, the excessive amount of diethylene glycol will lead to increased viscosity, slow reaction kinetics, and irregular blocky product.

[0139] A comparison of Examples 1 and 6-7 shows that if the mass ratio of the ternary cathode material to the coating solution is too small, i.e., the amount of coating solution used is too large, the lithium-ion diffusion path will be aggravated, which will easily lead to a concentration gradient in the liquid and cause local precipitation, resulting in uncontrolled product formation and reduced coating uniformity. If the mass ratio of the ternary cathode material to the coating solution is too large, i.e., the amount of coating solution used is too small, local high-concentration areas will form, leading to uncontrolled nucleation rate, uncontrolled particle size, easy formation of agglomerates, and reduced coating effect.

[0140] As can be seen from the comparison between Example 1 and Comparative Example 1, if the nickel-based ternary cathode material obtained in step (1) is used as the final ternary cathode material, it cannot have long life and fast charge and discharge capabilities.

[0141] As can be seen from the comparison between Example 1 and Comparative Example 2, if nickel acetate, manganese acetate and LiOH·H2O are directly mixed and calcined on the basis of the nickel-based ternary cathode material obtained in step (1) to obtain the coated ternary cathode material, the coating product is uncontrolled and the coating uniformity is poor, resulting in a small improvement in the electrical performance of the material.

[0142] As can be seen from the comparison between Example 1 and Comparative Example 3, if diethylene glycol is replaced with ethylene glycol in the composite solvent, the steric hindrance effect of diethylene glycol is lacking, and agglomerates are easily formed.

[0143] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for coating and modifying a ternary cathode material, characterized in that, The coating modification method includes the following steps: A ternary cathode material, a coating source, and a composite solvent are mixed to obtain a mixed slurry; wherein the composite solvent includes diethylene glycol and water. The mixed slurry and the precipitant solution are mixed and co-precipitated to obtain a ternary cathode material loaded with the precursor. The ternary cathode material with the loaded precursor is mixed with a lithium source and calcined to obtain the coated modified ternary cathode material.

2. The coating modification method according to claim 1, characterized in that, The ternary cathode material is a nickel-based ternary cathode material with the general chemical formula LiNi. x Co y Mn 1-x-y O2, where x≥0.6, 0<y<0.4, 1-xy>0; And / or, the coating source includes nickelates and manganates; The transition metal molar ratio of the nickelate and manganate is 1:(3-6.5); And / or, the mass ratio of the diethylene glycol to water is (1.7-3):

1.

3. The coating modification method according to claim 1 or 2, characterized in that, The method for mixing the ternary cathode material, the coating source, and the composite solvent includes: The coating source is dissolved in the composite solvent to obtain a coating solution, and then the ternary cathode material is added to the coating solution; And / or, the mass concentration of the coating source in the coating solution is 10-60 g / L; And / or, the mass ratio of the ternary cathode material to the coating liquid is 1:(1.5-2.5).

4. The coating modification method according to any one of claims 1-3, characterized in that, The precipitant solution includes a carbonate solution; And / or, the concentration of the precipitant solution is 4-6 mol / L; And / or, during the coprecipitation reaction, the reaction temperature is 25-50℃ and the reaction time is 0.5-3h; And / or, in the ternary cathode material with the loaded coating precursor, the coating precursor located on the surface of the ternary cathode material is a nickel-manganese carbonate compound with an orthogonal nanosheet structure.

5. The coating modification method according to any one of claims 1-4, characterized in that, The lithium source includes any one or a combination of at least two of LiNO3, LiCl, LiOH or Li2CO3; And / or, the calcination treatment is carried out at a temperature of 500-650℃ and a holding time of 4-6h; And / or, the atmosphere for the calcination treatment is an oxygen-containing atmosphere.

6. The coating modification method according to any one of claims 1-5, characterized in that, The coating modification method includes the following steps: (1) Preparation of nickel-based ternary cathode materials, the specific steps include: (a) Dissolve nickel, cobalt and manganese sources in water to obtain a mixed salt solution of transition metals, then add precipitant and complexing agent to carry out coprecipitation reaction. After the reaction is completed, filter and wash, and then vacuum dry at 110-130℃ for 12-24h to obtain nickel-based ternary precursor. (b) The nickel-based ternary precursor and the lithium salt are ball-milled at a molar ratio of 1:(1.02-1.05) to obtain a mixture; the ball milling speed is 100-300 rpm; the lithium salt includes any one or a combination of at least two of LiNO3, LiCl, LiOH or Li2CO3; (c) The mixture is calcined in an oxygen-containing atmosphere at a temperature of 700-1050°C for 10-24 hours to obtain the nickel-based ternary cathode material; (2) Dissolve nickelate and manganate in a composite solvent composed of diethylene glycol and water and stir until homogeneous to obtain a coating solution; the transition metal molar ratio of nickelate and manganate is 1:(3-6.5); the weight ratio of diethylene glycol and water is (1.7-3):1; the mass concentration of the coating source in the coating solution is 10-60 g / L; The nickel-based ternary cathode material is added to the coating solution and stirred until homogeneous to obtain a mixed slurry; the mass ratio of the nickel-based ternary cathode material to the coating solution is 1:(1.5-2.5); (3) Add a carbonate solution with a concentration of 4-6 mol / L to the mixed slurry and stir evenly. Carry out a co-precipitation reaction at a temperature of 25-50℃ for 0.5-3h to obtain a ternary cathode material coated with nickel-manganese carbonate. (4) The nickel-manganese carbonate-coated ternary cathode material is dried, then mixed with lithium salt by ball milling, and calcined at 500-680℃ in an oxygen-containing atmosphere for 4-8 hours to obtain spinel-type nickel-manganese lithium oxide-coated ternary cathode material; the lithium salt includes any one or a combination of at least two of LiNO3, LiCl, LiOH or Li2CO3; the molar ratio of the transition metal in the nickel-manganese carbonate to the lithium metal in the lithium salt is 2:(1.02-1.05).

7. A coated and modified ternary cathode material, characterized in that, The coated and modified ternary cathode material is prepared by the coating and modification method as described in any one of claims 1-6; The modified ternary cathode material includes a matrix material and a coating layer covering the surface of the matrix material. A gradient transition layer is formed between the matrix material and the coating layer, and the gradient transition layer is formed by ion diffusion during the calcination process.

8. The coated modified ternary cathode material according to claim 7, characterized in that, The chemical formula of the matrix material is LiNi. x Co y Mn 1-x-y O2, where x≥0.6, 0<y<0.4, 1-xy>0; And / or, the matrix material includes secondary particles with a morphology similar to single crystal spheres, which are aggregated from primary single crystal particles arranged radially; And / or, the coating layer is a spinel-type lithium nickel manganese oxide layer with the general chemical formula LiNi. a Mn 2-a O4, where the value of a ranges from 0.33 to 0.

5.

9. The coated modified ternary cathode material according to claim 7 or 8, characterized in that, The particle size Dv50 of the matrix material is 10-15 μm; And / or, the thickness of the coating layer is 10-50 nm; And / or, based on the total mass of the coated modified ternary cathode material, the mass percentage of the coating layer is 0.5-3%.

10. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes the coated modified ternary positive electrode material as described in any one of claims 7-9.

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