Ternary positive electrode material, preparation method and application

Abstract

This invention discloses a ternary cathode material, its preparation method, and its application. The ternary cathode material includes a core matrix and a coating layer. The core matrix comprises a doped nickel-cobalt-manganese layered ternary material, and the coating layer comprises phosphate. The mass percentage of the coating layer in the ternary cathode material is 0.2wt%–5wt%. The ternary cathode material meets the following requirements. This application establishes an average coating layer thickness (d). opt ) and kernel specific surface area (S BET ), theoretical density of the coating layer (ρ) coat ), percentage of target coating mass (C) target The quantitative relationship between the ternary cathode material and the dimensionless morphology factor (φ) is obtained. The coating layer of the ternary cathode material that satisfies this quantitative relationship can effectively suppress interfacial side reactions and enhance structural stability. When this ternary cathode material is applied to lithium-ion batteries, it is beneficial to improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to ternary cathode materials, preparation methods, and applications. Background Technology

[0002] Nickel-cobalt-manganese ternary cathode materials, especially high-nickel ternary cathode materials (LiNixCoyMnzO2, x>0.6), are considered key to achieving high-energy-density power batteries due to their high specific capacity (>200mAh / g). However, during the deep lithium insertion / extraction process, the highly active Ni on the surface... 4+ It catalyzes the decomposition of electrolyte, and at the same time, lattice oxygen is easily precipitated, causing serious interfacial side reactions and irreversible transformation of the bulk structure from layered to spinel / rock salt phase, resulting in rapid decay of cycle life and decrease in thermal stability.

[0003] To address these issues, existing technologies employ surface coating to suppress side reactions and improve cycle performance. However, the coating thickness varies considerably and has low uniformity in existing ternary cathode materials, resulting in poor coverage of the core substrate and consequently unsatisfactory performance.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a ternary cathode material, its preparation method, and its application. When applied to lithium-ion batteries, this ternary cathode material is beneficial for improving the cycle performance of the batteries.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a ternary cathode material, comprising a core matrix and a coating layer, wherein the core matrix comprises a doped nickel-cobalt-manganese layered ternary material, and the coating layer comprises phosphate, wherein the mass percentage of the coating layer in the ternary cathode material is 0.2wt%-5wt%; The ternary cathode material satisfies ; in: d opt The value represents the average thickness of the coating layer, and the unit of the average thickness of the coating layer is nm; S BET The specific surface area of ​​the core matrix is ​​a numerical value, and the unit of the specific surface area of ​​the core matrix is ​​m² / g; ρ coat The theoretical density of the coating material is expressed in g / cm³. C target The target coating layer is expressed as a percentage of its mass, without units. φ satisfies 0 < φ ≤ 1.5, and has no unit.

[0007] In an optional embodiment, the average thickness of the coating layer is 1 nm to 100 nm; And / or, the specific surface area of ​​the core matrix is ​​0.7 m² / g - 1.1 m² / g; And / or, the core matrix includes two or more doping elements.

[0008] In an optional embodiment, the general chemical formula of the core matrix is ​​LiNi. x Co y Mn (1-x-y-α-β-γ) D1 α D2 β D3 γ O2; wherein, D1 is selected from at least one of Zr, Ti, Nb, Ta and W; D2 is selected from at least one of Mg, Ca, Sr and Ba; D3 is selected from at least one of Al, Ga and B; 0.75≤x≤0.92, 0.03≤y≤0.15, 0<α≤0.015, 0<β≤0.015, 0<γ≤0.015, and x+y+α+β+γ<1; And / or, the phosphate is generated in situ on the surface of the core matrix; And / or, the phosphate includes complex phosphates.

[0009] In an optional embodiment, the chemical formula of the composite phosphate is LiuQv(PO4)w, where Q is selected from at least one of Co, Ni, Mn, Fe, Al, Ti and Zr, u>0, v>0 and u, v and w satisfy charge balance; And / or, the complex phosphate is selected from two or more co-solutions of Li3PO4, LiCoPO4 and LiNiPO4, or the complex phosphate is selected from LiCoPO4 or LiNiPO4.

[0010] In an optional embodiment, if the porosity of the coating layer is <5%, the average pore size is <10nm, and the coating coverage of the core substrate surface is ≥95%, then φ is 0.9-1.1. If the porosity of the coating layer is >15%, the average pore size is >30nm, and the surface coating rate of the core substrate is <80%, then φ <0.9. If the porosity of the coating layer is 5%-15%, the average pore size is 10nm-30nm, and the surface coating rate of the core substrate is 80%-95%, then φ is 1.1-1.5.

[0011] Secondly, the present invention provides a method for preparing the ternary cathode material described in the foregoing embodiments, comprising: Under stirring conditions, the pH of the system was controlled to be 9.0-11.5, and phosphate solution and metal ion solution were added to the slurry containing the core matrix, respectively. Then, the slurry was matured to obtain a core matrix coated with an amorphous coating layer. The core matrix coated with the amorphous coating layer is heat-treated to obtain the ternary cathode material.

[0012] In an optional implementation, when d opt When the phosphate concentration C in the phosphate solution is ≤10nm, pre Satisfying 0.005 mol / L ≤ C pre ≤0.020 mol / L; and / or, the phosphate solution addition rate is 0.025*M~0.15*M mL / min; When 10nm <d opt When the phosphate concentration C in the phosphate solution is ≤30nm, pre Satisfying 0.020 mol / L <C pre ≤0.050 mol / L; and / or, the phosphate solution is added at a rate of 0.15*M~0.4*M mL / min; When d opt When the concentration of phosphate ions in the phosphate solution is >30nm, C pre Satisfying 0.050 mol / L <C pre ≤0.100mol / L; and / or, the phosphate solution is added at a rate of 0.4*M~0.75*M mL / min; Where M is the mass of the core matrix in the slurry, and the mass of the core matrix is ​​in grams.

[0013] In an optional embodiment, the mass percentage of the core matrix in the slurry is 5wt%-20wt%; And / or, the heat treatment atmosphere is an oxygen-containing atmosphere, the temperature is 450℃-600℃, and the time is 4h-8h; And / or, it also includes the preparation of the core matrix: sintering a mixture containing a nickel cobalt manganese hydroxide precursor, a lithium source and a dopant to obtain the core matrix.

[0014] In an optional embodiment, the sintering temperature is 700℃-850℃, the sintering time is 12h-20h, and the atmosphere is an oxygen-containing atmosphere.

[0015] Thirdly, the present invention provides a lithium-ion battery comprising the ternary cathode material described in any one of the foregoing embodiments or the ternary cathode material prepared by the method described above.

[0016] The present invention has the following beneficial effects: This application establishes the average thickness of the coating layer (d) opt ) and kernel specific surface area (S BET ), theoretical density of the coating layer (ρ) coat ), percentage of target coating mass (C) target The quantitative relationship between the ternary cathode material and the dimensionless morphology factor (φ) is obtained. The coating layer of the ternary cathode material that satisfies this quantitative relationship can effectively suppress interfacial side reactions and enhance structural stability. When this ternary cathode material is applied to lithium-ion batteries, it is beneficial to improve the cycle performance of the battery. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The images are scanning electron microscope (SEM) images of the kernel matrix before (left) and after (right) coating in Example 1. Figure 2 This is a cross-sectional view of the ternary cathode material prepared in Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] Simply doping ternary cathode materials without coating them, such as using Al, Zr, etc. to stabilize the lattice, cannot solve the surface interface problem.

[0021] Therefore, embodiments of the present invention provide a ternary cathode material, comprising a core matrix and a coating layer. The core matrix comprises a doped nickel-cobalt-manganese layered ternary material, and the coating layer comprises phosphate. The mass percentage of the coating layer in the ternary cathode material is 0.2wt%-5wt%, for example, 0.2wt%, 0.5wt%, 0.8wt%, 1.1wt%, 1.4wt%, 1.7wt%, 2.0wt%, 2.3wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, and 5wt%. The ternary cathode material satisfies ; in: dopt The value represents the average thickness of the coating layer, and the unit of the average thickness of the coating layer is nm; S BET The specific surface area of ​​the core matrix is ​​a numerical value, and the unit of the specific surface area of ​​the core matrix is ​​m² / g; ρ coat The theoretical density of the coating material is expressed in g / cm³. C target The target coating layer is expressed as a percentage of its mass, without units. φ satisfies 0 < φ ≤ 1.5, and has no unit.

[0022] This application establishes the average thickness of the coating layer (d) opt ) and kernel specific surface area (S BET ), theoretical density of the coating layer (ρ) coat ), percentage of target coating mass (C) target The quantitative relationship between the ternary cathode material and the dimensionless morphology factor (φ) is obtained. The coating layer of the ternary cathode material that satisfies this quantitative relationship can effectively suppress interfacial side reactions and enhance structural stability. When this ternary cathode material is applied to lithium-ion batteries, it is beneficial to improve the cycle performance of the battery.

[0023] Among them, C target With a coating size of 0.2wt%-5wt%, it can ensure interface stability while avoiding excessive coating that could lead to reduced activity or obstructed ion transport, thus achieving synergistic optimization of functionality and energy density.

[0024] In an optional embodiment, the average thickness of the coating layer is 1nm-100nm, such as 1nm, 12nm, 23nm, 34nm, 45nm, 56nm, 67nm, 78nm, 89nm, or 100nm; ensuring that the coating layer has both physical isolation capability and lithium-ion penetration feasibility, and taking into account both interface passivation effect and kinetic performance.

[0025] In an optional embodiment, the specific surface area of ​​the core matrix is ​​0.7 m² / g - 1.1 m² / g, for example 0.7 m² / g, 0.80 m² / g, 0.81 m² / g, 0.82 m² / g, 0.83 m² / g, 0.84 m² / g, 0.85 m² / g, 0.86 m² / g, 0.87 m² / g, 0.88 m² / g, 0.89 m² / g, 0.90 m² / g, 1.00 m² / g, 1.10 m² / g, and optionally 0.8 m² / g - 0.9 m² / g. This gives the core a moderate specific surface area, ensuring reactivity while suppressing excessive increase in side reaction area, which is beneficial for coating uniformity and process controllability.

[0026] In an optional embodiment, the core matrix includes two or more doping elements, which enhance the thermal / chemical stability of the bulk structure and alleviate stress concentration and cation mixing during cycling through multi-scale lattice synergistic regulation.

[0027] In an optional embodiment, the general chemical formula of the core matrix is ​​LiNi. x Co y Mn (1-x-y-α-β-γ) D1 α D2 β D3 γ O2; wherein, D1 is selected from at least one of Zr, Ti, Nb, Ta and W; D2 is selected from at least one of Mg, Ca, Sr and Ba; D3 is selected from at least one of Al, Ga and B; 0.75≤x≤0.92, 0.03≤y≤0.15, 0<α≤0.015, 0<β≤0.015, 0<γ≤0.015, and x+y+α+β+γ<1; wherein D1, D2 and D3 respectively play the roles of skeleton reinforcement, interlayer pinning and covalent bonding, improving the overall durability of the material under high voltage.

[0028] In an optional embodiment, the phosphate is generated in situ on the surface of the core matrix, which can achieve chemical bonding and lattice matching with the core surface, significantly improving the bonding force and electrochemical stability of the coating interface and suppressing side reactions. In an optional embodiment, the phosphate includes a composite phosphate, which has better adhesion to the matrix and ionic conductivity than a single phosphate for surface coating. In an optional embodiment, the chemical formula of the composite phosphate is LiuQv(PO4)w, where Q is selected from at least one of Co, Ni, Mn, Fe, Al, Ti and Zr, u>0, v>0 and u, v and w satisfy charge balance; the introduction of transition metal Q into the composite phosphate imparts a certain electronic / ionic mixed conductivity to the coating layer and improves the interfacial charge transfer kinetics.

[0029] In an optional embodiment, the composite phosphate is selected from two or more co-solutions of Li3PO4, LiCoPO4 and LiNiPO4, or the composite phosphate is selected from LiCoPO4 or LiNiPO4, taking into account high lithium-ion conductivity, electrochemical inertness and interfacial compatibility with the ternary matrix.

[0030] In an optional implementation, if the porosity of the coating layer is <5%, the average pore size is <10nm, and the coating coverage of the core substrate surface is ≥95%, then φ is 0.9-1.1, and the coating layer is smooth and dense. If the porosity of the coating layer is >15%, the average pore size is >30nm, and the coating rate of the core matrix surface is <80%, then φ <0.9. In this case, the coating layer is in the form of sheets, islands, or incomplete coverage. If the porosity of the coating layer is 5%-15%, the average pore size is 10nm-30nm, and the coating rate of the core substrate surface is 80%-95%, then φ is 1.1-1.5. At this time, the coating layer has a rough, porous or interwoven morphology.

[0031] It should be noted that, through extensive experimental research, this application has found that when the porosity, average pore size, and surface coverage of the coating layer satisfy the above three combinations, the coating layer can achieve a better balance between interface protection and ion conduction performance, thereby obtaining better electrochemical cycling stability. Specifically: When the porosity of the coating layer is <5%, the average pore size is <10nm, and the coating rate is ≥95%, the coating layer can form a complete physical barrier, effectively isolating the direct contact between the electrolyte and the core substrate, suppressing interfacial side reactions, and the dense structure is conducive to the rapid conduction of lithium ions. When the porosity of the coating layer is 5%-15%, the average pore size is 10nm-30nm, and the coating rate is 80%-95%, the porous structure provides additional lithium-ion transport channels. At the same time, the rough surface increases the contact area between the coating layer and the electrolyte, which is beneficial to improving the rate performance. When the porosity of the coating layer is >15%, the average pore size is >30nm, and the coating rate is <80%, compared with the case of a coating layer porosity of 5%-15%, an average pore size of 10nm-30nm, and a coating rate of 80%-95%, the continuity of the coating layer decreases, the interfacial side reactions are difficult to suppress effectively, and the cycle performance decreases.

[0032] The three morphologies described above correspond to the optimal performance state (smooth and dense), the suboptimal performance state (rough and porous), and the slightly inferior performance state (sheet-like and island-like) of the coating layer, respectively, clearly demonstrating the correlation between the φ value and the morphology and performance of the coating layer. For other morphology combinations, those skilled in the art can refer to the above rules and determine the corresponding φ value based on the actual porosity, pore size, and coating ratio parameters of the coating layer.

[0033] This invention also provides a method for preparing the ternary cathode material described in the foregoing embodiments, comprising: Under stirring conditions, the pH of the system was controlled to be 9.0-11.5, and phosphate solution and metal ion solution were added to the slurry containing the core matrix, respectively. Then, the slurry was matured to obtain a core matrix coated with an amorphous coating layer. The core matrix coated with the amorphous coating layer is heat-treated to obtain the ternary cathode material.

[0034] Co-precipitation is carried out at pH 9.0–11.5 to synergistically regulate the interfacial reactivity of phosphate and metal ions, causing the composite phosphate precursor to preferentially anchor on the core surface rather than precipitate homogeneously. The ripening process strengthens the interfacial hydrogen bonding and coordination between the precursor and the core, improving the coating uniformity and binding force. Subsequent heat treatment not only achieves the directional transformation from amorphous to crystalline state, but also promotes the diffusion of interfacial atoms to form a stable coating structure with chemical bonding characteristics, taking into account the coating integrity, component uniformity and electrochemical interfacial inertness.

[0035] It should be noted that in order to adjust the pH of the system to 9.0-11.5, a pH adjuster can be introduced into the system. The pH adjuster can be ammonia. Under normal conditions, if the rate of precursor addition increases, the pH should be appropriately increased to accelerate the surface deposition reaction and inhibit homogeneous nucleation.

[0036] In an optional embodiment, the system temperature can be 30-80℃, for example 50-70℃; the curing time can be 30-120min.

[0037] In an alternative embodiment, the slurry can be ultrasonicated in order to ensure that the core matrix is ​​fully dispersed in the slurry.

[0038] In an optional embodiment, before heat treatment of the core substrate covered by the amorphous coating layer, the core substrate covered by the amorphous coating layer may be washed with water, washed with alcohol, and dried.

[0039] In an optional implementation, when d opt When the phosphate concentration C in the phosphate solution is ≤10nm, pre Satisfying 0.005 mol / L ≤ C pre ≤0.020 mol / L, for example 0.005 mol / L, 0.007 mol / L, 0.009 mol / L, 0.011 mol / L, 0.013 mol / L, 0.015 mol / L, 0.017 mol / L, 0.019 mol / L, 0.020 mol / L; in optional embodiments, the phosphate solution addition rate is 0.025*M~0.15*M mL / min, for example 0.025*M mL / min, 0.039*M mL / min, 0.053*M mL / min, 0.067*M mL / min, 0.081*M mL / min, 0.094*M mL / min, 0.108*M mL / min, 0.122*M mL / min, 0.136*M mL / min, 0.150*M mL / min; in ultra-thin coating (d optUnder the target of ≤10 nm, by strictly controlling the upper limit of precursor concentration, supersaturation of the solution is suppressed, effectively inhibiting homogeneous nucleation and ensuring that phosphate preferentially nucleates heterogeneously on the substrate surface and spreads uniformly; the lower limit of concentration ensures sufficient reaction driving force and avoids island-like or discontinuous coverage caused by deposition lag. The dropping acceleration rate is set according to the substrate mass M, achieving linear adaptation between process parameters and material scale, taking into account both the reaction interface renewal rate and local concentration steady state, and stably obtaining nanoscale coatings with precise thickness, dense morphology, and high coverage, supporting d opt The model was reliably implemented from theoretical design to actual fabrication.

[0040] When 10nm <d opt When the phosphate concentration C in the phosphate solution is ≤30nm, pre Satisfying 0.020 mol / L <C pre ≤0.050 mol / L, for example 0.021 mol / L, 0.024 mol / L, 0.027 mol / L, 0.030 mol / L, 0.033 mol / L, 0.036 mol / L, 0.039 mol / L, 0.042 mol / L, 0.045 mol / L, 0.048 mol / L, 0.050 mol / L; in optional embodiments, the phosphate solution is added at a rate of 0.15*M~0.4*M mL / min, for example 0.150*M mL / min, 0.178*M mL / min, 0.206*M mL / min, 0.233*M mL / min, 0.261*M mL / min, 0.289*M mL / min, 0.317*M mL / min, 0.344*M mL / min, 0.372*M The drop rates of 0.400*M mL / min and 0.400*M mL / min are appropriate, ensuring that heterogeneous nucleation dominates on the surface while avoiding insufficient deposition at low concentrations or homogeneous side reactions at high concentrations. The drop rate matches the needs of the reaction interface renewal, allowing sufficient but not excessive contact time between phosphate and metal ions on the substrate surface, promoting continuous growth of the dense layer rather than island accumulation or localized thickening. These two factors work synergistically to ensure that the coating layer maintains good uniformity, continuity, and structural integrity within the medium thickness range, thus stably achieving the interface control target of "thin but not transparent, thick but not obstructive."

[0041] When d opt When the concentration of phosphate ions in the phosphate solution is >30nm, C pre Satisfying 0.050 mol / L <C pre≤0.100 mol / L, for example 0.051 mol / L, 0.056 mol / L, 0.061 mol / L, 0.066 mol / L, 0.071 mol / L, 0.076 mol / L, 0.081 mol / L, 0.086 mol / L, 0.091 mol / L, 0.096 mol / L, 0.100 mol / L; in optional embodiments, the phosphate solution is added at a rate of 0.4*M~0.75*M mL / min, for example 0.400*M mL / min, 0.439*M mL / min, 0.478*M mL / min, 0.517*M mL / min, 0.556*M mL / min, 0.594*M mL / min, 0.633*M mL / min, 0.672*M mL / min, 0.711*M mL / min and 0.750*M mL / min; by increasing the precursor concentration and accelerating the dropping rate, the reactant flux per unit time is enhanced. The higher concentration provides a continuous and stable driving force for surface nucleation and growth, avoiding interlayer porosity or density reduction due to insufficient reaction rate. The appropriate faster dropping rate maintains dynamic interface renewal, inhibits aggregation caused by local supersaturation, and promotes uniform accumulation in the thickness growth direction. The two work synergistically to achieve the goal of thicker coating while ensuring that the thick coating layer has both physical barrier integrity and interfacial bonding stability.

[0042] In the above definition, M is the numerical value of the mass of the core matrix in the slurry, and the mass unit of the core matrix is ​​g.

[0043] In an optional embodiment, the mass percentage of the core matrix in the slurry is 5wt%-20wt%, for example, 5wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%. This ensures that the matrix particles are fully dispersed and stably suspended in the liquid phase, avoiding agglomeration and sedimentation due to excessively high concentration or reduced coating efficiency due to excessively low concentration, thus providing a stable reaction interface basis for uniform in-situ deposition.

[0044] In an optional embodiment, the heat treatment atmosphere is an oxygen-containing atmosphere, the temperature is 450℃-600℃, for example 450℃, 467℃, 483℃, 500℃, 517℃, 533℃, 550℃, 567℃, 583℃, 600℃; the time is 4h-8h, for example 4.0h, 4.4h, 4.8h, 5.2h, 5.6h, 6.0h, 6.4h, 6.8h, 7.2h, 7.6h, 8.0h; this achieves a controllable transformation of amorphous phosphate into a crystalline state, improves the structural stability and ionic conductivity of the coating layer, and avoids high-temperature damage to the core structure or the initiation of side reactions.

[0045] In an optional embodiment, the preparation of the core matrix is ​​also included: sintering a mixture containing a nickel cobalt manganese hydroxide precursor, a lithium source, and a dopant to obtain the core matrix.

[0046] In optional embodiments, the sintering temperature is 700℃-850℃, for example 700℃, 717℃, 733℃, 750℃, 767℃, 783℃, 800℃, 817℃, 833℃, 850℃; the sintering time is 12h-20h, for example 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h; and the atmosphere is an oxygen-containing atmosphere. This ensures that multi-element co-doping is fully incorporated into the crystal lattice, forming a high-nickel layered phase with a uniform structure and ordered cations, providing a physicochemically stable matrix platform for subsequent coating.

[0047] The present invention also provides a lithium-ion battery comprising the ternary cathode material described in any one of the foregoing embodiments or the ternary cathode material prepared by the method described above.

[0048] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0049] Example 1 This embodiment provides a method for preparing a ternary cathode material, wherein the core matrix of the ternary cathode material is Li(NiO). 88 Co0. 09 Mn0. 02 Zr0. 0025 Ti 0.001 Al0. 0025 Mg 0.004 O2, with a LiCoPO4 coating layer, specifically includes the following steps: 1. Raw material: NiO precursor. 88 Co0. 09 Mn0. 03 (OH)2, LiOH·H2O (lithium excess 5%), ZrO2, TiO2, γ-Al2O3 and MgO.

[0050] 2. Primary sintering: Weigh the above raw materials according to the stoichiometric ratio (lithium in 5% excess compared to the theoretical stoichiometric ratio), place them in a planetary ball mill, and ball mill for 4 hours. Place the mixed powder in an oxygen atmosphere furnace, heat to 790℃ at 3℃ / min, hold for 15 hours, and allow to cool naturally. Crush the sintered product and pass it through a 400-mesh sieve to obtain the core matrix powder. BET testing shows that the specific surface area S of this core matrix is... BET It is 0.85 m² / g.

[0051] 3.d opt Application of parameters and guidance on coating process: Set the target coating mass percentage C target =0.01 (i.e., 1.0wt%).

[0052] Given the theoretical density ρ of the coating layer LiCoPO4 coat ≈3.03g / cm³, from Materials Project - Materials Explorer.

[0053] For the desired interwoven morphology, the porosity is about 5%, the average pore size is about 20 nm, and the coating layer coverage of the core matrix surface is about 90%, the morphology factor φ = 1.1 is taken.

[0054] Substituting the above parameters into d opt Calculation formula:

[0055] The objective of this embodiment is to construct an ultrathin coating layer with an average thickness of approximately 3.5 nm. To achieve this objective, process conditions that suppress rapid precipitation and promote uniform surface nucleation must be employed. Accordingly, this embodiment uses a process system combining a low-concentration (0.015 M) precursor solution with slow titration (1.67 mL / min).

[0056] Preparation and calculation of precursor solution: Total mass of coating layer required:

[0057] Take 0.396g of (NH4)2HPO4 and 0.747g of Co(CH3COO)2 4H2O was dissolved in 200 mL of deionized water to obtain 0.015 mol / L solutions of (NH4)2HPO4 and Co(CH3COO)2.

[0058] 4. Liquid-phase coating: Take 20g of core matrix powder and disperse it in 200mL of deionized water. Sonicate for 30 minutes to ensure thorough dispersion. Under a 60℃ water bath and vigorous stirring, add 0.015mol / L (NH4)2HPO4 solution and 0.015mol / L Co(CH3COO)2 solution dropwise to the suspension using two peristaltic pumps, respectively. Simultaneously, add (5wt%) ammonia to maintain the pH of the system at 10.5±0.2. The titration rate is 1.67mL / min, and the total titration volume is controlled to ensure that the theoretical coating layer mass accounts for 1.0wt% of the final product mass. After the addition is complete, continue aging for 1 hour. Then, centrifuge, wash three times each with deionized water and ethanol, and vacuum dry overnight at 80℃.

[0059] 5. Secondary sintering: The dried powder is placed in a tube furnace and heated to 550°C at a rate of 2°C / min under an oxygen flow. The temperature is held for 5 hours, and then cooled in the furnace to obtain the final product S1, with the morphology as shown. Figure 1 and Figure 2 As shown.

[0060] Characterization of the coating layer: Transmission electron microscopy (TEM) cross-sectional analysis was performed on the S1 sample to measure the actual average thickness d of the coating layer. actual It is 4.2 nm, which is consistent with the theoretically calculated d opt The high degree of agreement (3.5nm) indicates that the coating process is uniform and controllable, verifying the d opt The parameters provide precise guidance for the process. Actual calculations yield φ. actual =0.92 (obtained by substituting the actual average thickness of the coating layer into the above calculation formula), which is basically consistent with the design value of 1.1, verifying the accuracy of the morphology factor.

[0061] Example 2: Thick coating layer The difference between this embodiment and Embodiment 1 is that a thicker coating layer is constructed by adjusting the coating process parameters to verify d. opt Applicability of the model in thick-coverage situations.

[0062] 1. Core substrate preparation: Similar to Example 1, the specific surface area S was obtained. BET =0.85m² / g core matrix powder.

[0063] 2. d opt Parameter application: Set the target coating mass percentage C target =0.05 (i.e., 5.0wt%).

[0064] Theoretical density ρ of the coating layer LiCoPO4 coat ≈3.03g / cm³.

[0065] The morphology of the coating layer is rough, porous, and interwoven, with φ=1.2.

[0066] Calculate d opt :

[0067] According to d opt ≈16.2nm, which belongs to the 10nm range. <d opt For the ≤30nm range, use a medium-concentration precursor solution and a moderate titration rate.

[0068] 3. Preparation of precursor solution: Total mass of the coating layer required: m coat = 0.05 × 20g = 1.0g Prepare a 0.035 mol / L solution of (NH4)2HPO4 and Co(CH3COO)2.

[0069] 4. Liquid phase coating: Take 20g of core matrix powder and disperse it in 200mL of deionized water. Add a 0.035mol / L phosphate and cobalt salt solution dropwise in a 60℃ water bath with stirring. The dropping rate, calculated as M=20g, is 0.25×20=5.0mL / min. Control the pH of the system to 10.5±0.2. After the addition is complete, allow it to mature for 1 hour, then centrifuge, wash, and dry.

[0070] 5. Secondary sintering: Similar to Example 1, sample S2 was obtained by heating at 550°C in an oxygen atmosphere for 5 hours.

[0071] 6. Characterization of the coating layer: TEM cross-sectional analysis showed that the average thickness of the coating layer was approximately 17 nm, consistent with the theoretical calculation of 16.2 nm. The coating layer exhibited a rough, porous, interwoven morphology with a porosity of approximately 12%, an average pore size of approximately 18 nm, and a surface coverage of approximately 88%.

[0072] Example 3: Different coating materials – Li3PO4 coating The difference between this embodiment and Embodiment 1 is that the coating material is changed to Li3PO4, in order to verify d opt The model's applicability to different coating materials.

[0073] 1. Core substrate preparation: Similar to Example 1, the specific surface area S was obtained. BET =0.85m² / g core matrix powder.

[0074] 2. d opt Parameter application: Set the target coating mass percentage C target =0.01 (i.e., 1.0wt%).

[0075] Theoretical density ρ of the coating layer Li3PO4 coat ≈2.54g / cm³.

[0076] The coating layer has a smooth and dense morphology, with φ=1.0.

[0077] Calculate d opt :

[0078] 3. Preparation of precursor solution: Total mass of the coating layer required: m coat = 0.01 × 20g = 0.2g Prepare a 0.015 mol / L (NH4)2HPO4 solution and a 0.015 mol / L LiOH solution (as a lithium source).

[0079] 4. Liquid phase coating: Take 20g of core matrix powder and disperse it in 200mL of deionized water. Add 0.015mol / L (NH4)2HPO4 solution and 0.015mol / L LiOH solution dropwise in a 60℃ water bath with stirring at a dropping rate of 1.67mL / min, controlling the pH of the system at 10.5±0.2. After the addition is complete, allow the mixture to mature for 1 hour, then centrifuge, wash, and dry.

[0080] 5. Secondary sintering: Similar to Example 1, sample S3 was obtained by heating at 550°C in an oxygen atmosphere for 5 hours.

[0081] 6. Characterization of the coating layer: TEM cross-sectional analysis showed that the average thickness of the coating layer was approximately 4.3 nm, consistent with the theoretical calculation of 4.6 nm. The coating layer was smooth and dense, with a porosity of approximately 3%, an average pore size of approximately 5 nm, and a surface coverage of approximately 96%.

[0082] Example 4: Different coating morphologies—island-like discontinuous coating The difference between this embodiment and Embodiment 1 is that an island-like discontinuous coating layer morphology is constructed by adjusting the coating process parameters (lowering the pH value) to verify d. opt The applicability of the model to different morphologies and the effect of adjusting the φ value.

[0083] 1. Core substrate preparation: Similar to Example 1, the specific surface area S was obtained. BET =0.85m² / g core matrix powder.

[0084] 2. d opt Parameter application: Set the target coating mass percentage C target =0.01 (i.e., 1.0wt%).

[0085] Theoretical density ρ of the coating layer LiCoPO4 coat ≈3.03g / cm³.

[0086] The desired effect is to form an island-like discontinuous coating layer, with φ=0.7.

[0087] Calculate d opt :

[0088] 3. Preparation of precursor solution: Similar to Example 1, a 0.015 mol / L solution of (NH4)2HPO4 and Co(CH3COO)2 was prepared.

[0089] 4. Liquid phase coating: Take 20g of core matrix powder and disperse it in 200mL of deionized water. Add a 0.015mol / L phosphate and cobalt salt solution dropwise in a 60℃ water bath with stirring at a rate of 1.67mL / min, controlling the pH of the system at 8.5±0.2 (lower than the pH value in Example 1). After the addition is complete, allow it to mature for 1 hour, then centrifuge, wash, and dry.

[0090] 5. Secondary sintering: Similar to Example 1, sample S4 was obtained by heating at 550°C in an oxygen atmosphere for 5 hours.

[0091] 6. Characterization of the coating layer: TEM cross-sectional analysis showed that the coating layer was distributed in an island-like, discontinuous pattern, with an average thickness of approximately 5.3 nm, consistent with the theoretical calculation of 5.5 nm. The porosity of the coating layer was approximately 22%, the average pore size was approximately 45 nm, and the surface coverage was approximately 65%.

[0092] Comparative Example 1: The main difference between this comparative example and Example 1 is that no coating was performed, resulting in a core matrix powder, which is denoted as sample C1.

[0093] Comparative Example 2: The main difference between this comparative example and Example 1 is that ZrO2, TiO2, γ-Al2O3, and MgO were not added to the raw materials. The remaining steps are exactly the same as in Example 1, and sample C2 is obtained.

[0094] Comparative Example 3: The main difference between this comparative example and Example 1 is that in step 3, the coating agent is replaced with an equimolar amount of tetraethyl orthosilicate (TEOS), and SiO2 is coated using the sol-gel method. The specific steps include: mixing tetraethyl orthosilicate (TEOS) with anhydrous ethanol and deionized water at a volume ratio of 1:5:2, adjusting the pH to 4.5-5.0 with dilute hydrochloric acid, and hydrolyzing in a 40°C water bath for 30 minutes. Then, 20g of the core matrix powder is added, and the reaction is continued for 2 hours. After the reaction, the powder is centrifuged, washed three times with anhydrous ethanol, and vacuum dried overnight at 80°C. The dried powder is placed in a muffle furnace, heated to 550°C at a rate of 2°C / min, held at this temperature in air for 5 hours, and then cooled with the furnace to obtain sample C3.

[0095] Comparative Example 4: The main difference between this comparative example and Example 1 is that in step 3, a high-concentration (0.15 mol / L) solution of (NH4)2HPO4 and Co(CH3COO)2 was prepared; and the dropping rate in step 3 was 13.3 mL / min. The total titration volume was controlled so that the theoretical coating layer mass accounted for 1.0 wt% of the final product mass. The calculated φ... actual =0.185.

[0096] Comparative Example 5: The main difference between this comparative example and Example 1 is that in step 2, the sintering temperature and precursor particle size are adjusted simultaneously to prepare a high-nickel ternary material matrix with a specific surface area of ​​1.5 m² / g.

[0097] Comparative Example 6: The main difference between this comparative example and Example 1 is that in step 3, a high-concentration (0.03 mol / L) solution of (NH4)2HPO4 and Co(CH3COO)2 is prepared; and in step 3, the titration rate is 0.835 mL / min. The calculated φ... actual =0.43.

[0098] Some parameters in the above embodiments and comparative examples were recorded, and some product performance was tested. The test methods are as follows, and the test results are shown in Table 1.

[0099] S BET The specific surface area was determined using a specific surface area analyzer via nitrogen adsorption-desorption isotherm (BET method).

[0100] Average thickness of coating layer: The cross-sectional morphology of the coating layer was observed under high magnification of TEM. 20-50 different particles were randomly selected for measurement. The coating layer thickness was measured at 5-10 different locations for each particle. The arithmetic mean of all measurements was calculated.

[0101] The initial discharge specific capacity test method included: using the prepared positive electrode material as the working electrode, lithium metal sheet as the counter / reference electrode, Celgard 2400 as the separator, and a 1.0 M LiPF6 EC / DMC / EMC (volume ratio 1:1:1) solution (containing 2 wt% VC additive) as the electrolyte, and assembling a CR2032 coin cell in an argon-protected glove box. Test conditions: After the battery was left to stand at 25°C for 12 hours, charge-discharge tests were performed at a rate of 0.1C (1C = 200 mA / g), with a voltage window of 2.8 V - 4.3 V (vs. Li). + / Li). The initial discharge specific capacity is taken as the discharge capacity value of the first cycle.

[0102] The test method for 500-cycle capacity retention includes: after the initial charge-discharge test, the battery undergoes long-term cycle testing at a 1C rate and a voltage window of 2.8 V - 4.3 V. The calculation method is: 500-cycle capacity retention = (discharge capacity of the 500th cycle / discharge capacity of the 1st cycle) × 100%. The test temperature is 25°C.

[0103] The testing methods for DSC peak temperature include: Sample preparation: Disassemble the cycled positive electrode battery in a glove box, remove the positive electrode sheet, wash thoroughly with DMC solvent to remove residual electrolyte, and scrape off the positive electrode material powder after drying.

[0104] Test conditions: Using a differential scanning calorimeter, approximately 2-5 mg of the above powder was mixed with an equal mass of fresh electrolyte (1.0 M LiPF6 EC / DMC / EMC (volume ratio 1:1:1) solution) in a high-pressure sealed crucible. The temperature was increased at a rate of 5°C / min or 10°C / min, and the temperature was scanned within the range of room temperature to 400°C.

[0105] The porosity and average pore size of the coating were determined by nitrogen adsorption-desorption isotherms (BET / BJH method).

[0106] Table 1

[0107] In Example 1, based on kernel base S BET (0.85 m² / g) and the target coating amount (1.0 wt%), as well as the approximate morphology of the target coating layer, were used to calculate... The thickness was approximately 3.5 nm, which guided the preparation of the coating precursor solution. Characterization of the prepared ternary cathode material confirmed that the actual coating thickness was approximately 3.5 nm. The estimated values ​​are consistent, and the coating layer is uniform and dense. Examples 2-4 also confirm that for different coating layer thicknesses, coating layer proportions, coating layer materials, and coating layer morphologies, as long as the requirements of this application are met, the coating layer can achieve the desired results. The conditions all exhibit good cyclic performance, and this can guide the preparation of coating precursor solutions.

[0108] A comparison of Example 1 and Comparative Example 1 shows that the presence of the LiCoPO4 coating significantly improves cycling performance. In contrast to Example 1 and Comparative Example 3, even with doping, an inappropriate coating composition can lead to a decrease in cycling performance instead of an increase.

[0109] Comparing Example 1 and Comparative Example 2, for a co-doped core matrix (S1) with a stable bulk structure, under the condition that... Under certain conditions, it exhibits superior overall performance, indicating that bulk reinforcement is a prerequisite for the coating layer to function effectively.

[0110] Comparative Example 4 used a high concentration of 0.15 mol / L (exceeding the d... opt The ≤10nm range requires a concentration of 0.005~0.020mol / L (7.5 times the upper limit), and a rapid titration of 0.5h (equivalent to a titration rate of approximately 13.3mL / min, exceeding the upper limit of 3.0mL / min by more than 4 times). This results in an extremely uneven coating layer with severe local aggregation and a very wide thickness distribution (2-40nm). Furthermore, electron microscopy revealed a large number of free nanoparticles (homogeneous nucleation products in the solution). Calculations show that φ... actual The value was 0.185, far lower than the theoretical design value of 1.1. Under these process conditions, the supersaturation of the solution increased sharply, and homogeneous nucleation became dominant. This resulted in a large amount of phosphate nucleating in the solution rather than depositing on the substrate surface, ultimately forming a highly heterogeneous coating layer with severe local agglomeration.

[0111] The coating layer of the ternary cathode material prepared in Comparative Example 5 is very sparse and discontinuous, exhibiting a distinct island-like distribution, with an average thickness of only about 1.76 nm and low coverage. Its φ... actual The specific surface area is approximately 1.25, but due to the excessively high specific surface area of ​​the core matrix (1.50 m² / g), under the same target coating amount (1.0 wt%) and coating process conditions, the actual coating layer formed is too thin and discontinuous, failing to effectively cover the more active sites brought about by the high specific surface area, thus leading to poor product performance. This also proves that for core matrices with different specific surface areas, using a fixed "empirical coating amount" and a fixed "empirical process" is ineffective. The model of this invention introduces S... BET It can automatically calculate the theoretical thickness d to adapt to different substrates. opt And can be based on d opt Adjusting the process (e.g., for higher S) BETTo achieve effective coverage of the matrix, fine-tuning of concentration or reaction time may be necessary to achieve the target coating effect, which is something that traditional empirical methods cannot achieve.

[0112] Comparative Example 6 used a high concentration (0.03 mol / L). Although the titration rate (0.835 mL / min, approximately half that of Example 1) was within the limits of this invention, this titration rate, relative to the high concentration of phosphate solution, led to unstable local supersaturation, insufficient deposition in some areas, and slow aggregation in others, resulting in poor product cycle performance. Calculate φ. actual The actual coating thickness (9.0 nm) was approximately 0.431, which is far lower than the theoretical design value of φ=1.1. At the same time, the actual coating thickness (9.0 nm) was significantly higher than the theoretical expectation (approximately 3.5 nm), and the thickness distribution was wide (3-15 nm) with high porosity (21.3%). This indicates that the lack of coordination between titration rate and concentration will cause the coating morphology to deviate from the expectation, thereby reducing the product performance.

[0113] "In this application" The model not only enables the coating process to move from "experience-based exploration" to "quantitative design," ensuring the achievement of the target coating effect and reproducibility, but more importantly, by quantitatively linking the coating thickness with the physical properties of the core matrix and the target performance, it provides a core tool for achieving precise synergistic enhancement of the "bulk phase-interface," making it highly practical.

[0114] Compared with the prior art, this application has the following significant advantages: (1) The S of the quantitative correlation kernel in this application BET C target d opt During the materials design phase, the obtained core S can be used as a basis. BET and the preset C target (e.g., 1.0 wt%), directly calculate d opt This guides the precise formulation of precursor concentrations in the coating process.

[0115] (2) D1 elements in this application (such as Zr) 4+ Ti 4+ ) stabilizes lattice oxygen through strong MO bonds, inhibiting oxygen loss; D2 elements (such as Mg²⁺) + It can effectively occupy lithium sites and suppress Li+ / Ni² + Cation mixing; D3 elements (such as Al³) + This enhances the structural stability of the material. The three elements work synergistically to strengthen the bulk structure at the atomic level. The outer lithium-ion conductive phosphate coating not only acts as a physical barrier to prevent electrolyte corrosion, but its own rapid lithium-ion conduction characteristics also ensure efficient ion transport at the interface, achieving a synergistic effect of "internal stability and external smooth flow."

[0116] (3) The cathode material prepared in this application can maintain a capacity retention of up to 93.2% after 500 cycles at a voltage range of 2.8-4.3V (vs. Li+ / Li) and a 1C rate, which is far superior to the comparative example. At the same time, the thermal runaway initiation temperature of the material can be increased by more than 15°C compared with the comparative example, and the safety is significantly enhanced.

[0117] (4) The preparation method of this application has strong universality: based on mature solid-phase sintering and liquid-phase precipitation technology, the process parameter window is wide, the reproducibility is good, the coating is uniform and the thickness is controllable, and it is easy to achieve large-scale production.

[0118] (5) This application pioneers a new paradigm for quantitative and predictable coating process design: the d proposed in this invention opt The design-control system, for the first time, transforms the coating process from an experience-based "black box" operation into a predictable, controllable, and optimizable "white box" engineering approach based on physical models. This system not only precisely guides material proportioning but, more importantly, proactively designs matching process systems (such as concentration and drip rate) according to the target thickness. It also quantitatively evaluates the product to guide iterative optimization, fundamentally solving the core technical challenge of controlling the uniformity and repeatability of high-nickel material coatings. This has significant guiding value for industrialization.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A ternary cathode material, characterized in that, The cathode material comprises a core substrate and a coating layer. The core substrate consists of a doped nickel-cobalt-manganese layered ternary material, and the coating layer consists of phosphate. The mass percentage of the coating layer in the ternary cathode material is 0.2 wt%-5 wt%. The ternary cathode material satisfies ; in: d opt The value represents the average thickness of the coating layer, and the unit of the average thickness of the coating layer is nm; S BET The specific surface area of ​​the core matrix is ​​a numerical value, and the unit of the specific surface area of ​​the core matrix is ​​m² / g; ρ coat The theoretical density of the coating material is expressed in g / cm³. C target The target coating layer is expressed as a percentage of its mass, without units. φ satisfies 0 < φ ≤ 1.5, and has no unit.

2. The ternary cathode material according to claim 1, characterized in that, The average thickness of the coating layer is 1nm-100nm; And / or, the specific surface area of ​​the core matrix is ​​0.7 m² / g - 1.1 m² / g; And / or, the core matrix includes two or more doping elements.

3. The ternary cathode material according to claim 1, characterized in that, The general chemical formula of the core matrix is ​​LiNi. x Co y Mn (1-x-y-α-β-γ) D1 α D2 β D3 γ O2; wherein, D1 is selected from at least one of Zr, Ti, Nb, Ta and W; D2 is selected from at least one of Mg, Ca, Sr and Ba; D3 is selected from at least one of Al, Ga and B; 0.75≤x≤0.92, 0.03≤y≤0.15, 0<α≤0.015, 0<β≤0.015, 0<γ≤0.015, and x+y+α+β+γ<1; And / or, the phosphate is generated in situ on the surface of the core matrix; And / or, the phosphate includes complex phosphates.

4. The ternary cathode material according to claim 3, characterized in that, The chemical formula of the complex phosphate is LiuQv(PO4)w, where Q is selected from at least one of Co, Ni, Mn, Fe, Al, Ti and Zr, u>0, v>0 and u, v and w satisfy charge balance; And / or, the complex phosphate is selected from two or more co-solutions of Li3PO4, LiCoPO4 and LiNiPO4, or the complex phosphate is selected from LiCoPO4 or LiNiPO4.

5. The ternary cathode material according to claim 1, characterized in that, If the porosity of the coating layer is <5%, the average pore size is <10nm, and the coating coverage of the core substrate is ≥95%, then φ is 0.9-1.

1. If the porosity of the coating layer is >15%, the average pore size is >30nm, and the surface coating rate of the core substrate is <80%, then φ <0.

9. If the porosity of the coating layer is 5%-15%, the average pore size is 10nm-30nm, and the surface coating rate of the core substrate is 80%-95%, then φ is 1.1-1.

5.

6. A method for preparing a ternary cathode material according to any one of claims 1-5, characterized in that, include: Under stirring conditions, the pH of the system was controlled to be 9.0-11.5, and phosphate solution and metal ion solution were added to the slurry containing the core matrix, respectively. Then, the slurry was matured to obtain a core matrix coated with an amorphous coating layer. The core matrix coated with the amorphous coating layer is heat-treated to obtain the ternary cathode material.

7. The method for preparing the ternary cathode material according to claim 6, characterized in that, When d opt When the phosphate concentration C in the phosphate solution is ≤10nm, pre Satisfying 0.005 mol / L ≤ C pre ≤0.020 mol / L; and / or, the phosphate solution addition rate is 0.025*M~0.15*M mL / min; When 10nm <d opt When the phosphate concentration C in the phosphate solution is ≤30nm, pre Satisfying 0.020 mol / L <C pre ≤0.050 mol / L; and / or, the phosphate solution is added at a rate of 0.15*M~0.4*M mL / min; When d opt When the concentration of phosphate ions in the phosphate solution is >30nm, C pre Satisfying 0.050 mol / L <C pre ≤0.100mol / L; and / or, the phosphate solution is added at a rate of 0.4*M~0.75*M mL / min; Where M is the mass of the core matrix in the slurry, and the mass of the core matrix is ​​in grams.

8. The method for preparing the ternary cathode material according to claim 6, characterized in that, The mass percentage of the core matrix in the slurry is 5wt%-20wt%; And / or, the heat treatment atmosphere is an oxygen-containing atmosphere, the temperature is 450℃-600℃, and the time is 4h-8h; And / or, it also includes the preparation of the core matrix: sintering a mixture containing a nickel cobalt manganese hydroxide precursor, a lithium source and a dopant to obtain the core matrix.

9. The method for preparing the ternary cathode material according to claim 8, characterized in that, The sintering temperature is 700℃-850℃, the time is 12h-20h, and the atmosphere is an oxygen-containing atmosphere.

10. A lithium-ion battery, characterized in that, Includes the ternary cathode material as described in any one of claims 1-5.

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