A positive electrode material, a preparation method thereof, a positive electrode sheet, and a battery

Abstract

The application provides a positive electrode material and a preparation method, a positive electrode sheet and a battery. 3+ and Ti 4+ co-doped lithium cobaltate layer; the phosphorus-based dynamic interface layer is coated on the outside of the gradient heterovalent doping layer; the phosphorus-based dynamic interface layer comprises, from inside to outside, a phosphorus-doped transition layer, an amorphous Li3PO3-LiPO3 layer and a LiF crystalline dispersion layer; the chemical formula of the positive electrode material is LiCoO2@LiCo 1‑x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF; the positive electrode material can greatly prolong the cycle life of the material at high voltage, improve the thermal safety and long-term operation reliability of the material at high voltage full charge, construct a low-impedance and high-efficiency bulk-phase-interface synergistic conduction network, continuously optimize the initial interface impedance in long-term cycling, effectively reduce the first irreversible capacity loss and maintain the interface integrity.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium cobalt oxide (LiCO) has long dominated the cathode material market for consumer lithium-ion batteries due to its high volumetric energy density, excellent electronic conductivity, and high compaction density. It is widely used in space- and weight-sensitive end products such as smartphones, laptops, and wearable devices. Driven by the continuous pursuit of longer battery life and faster charging speeds in current end devices, raising the charging cutoff voltage of LiCO to above 4.6V is a key way to improve energy density. However, when the charging cutoff voltage exceeds 4.6V, deep delithiation of LiCO occurs, leading to a series of serious structural and interface degradation problems, severely restricting its high-voltage, long-cycle stability and safety performance.

[0003] First, at the bulk structure level, deep delithiation leads to Co 3+ Large amounts are oxidized to high-spin Co. 4+ Even Co 4+ δ + (δ>0) The lattice oxygen stability decreases sharply, inducing an irreversible multi-stage phase transition from O3 to H1-3 to O1. This phase transition is accompanied by significant abrupt changes in unit cell parameters (c-axis contraction, a-axis expansion), with an overall unit cell volume change rate exceeding 10%. Stress concentration within the particles leads to microcrack initiation and propagation, causing rapid capacity decay. Secondly, at the electrode / electrolyte interface, highly active Co enriched on the surface under high voltage... 4+ It has strong oxidizing ability, induces the release of lattice oxygen, triggers violent decomposition of electrolyte, generates a high-resistivity, unstable cathode electrolyte interface (CEI) layer, and is accompanied by the dissolution of transition metals, which deteriorates cycle stability and safety.

[0004] To address these challenges, researchers have proposed various modification strategies, primarily including bulk doping and surface coating. However, existing technologies still have significant limitations: Traditional single-doping (uniform valence state) or surface coating (static interface) methods cannot simultaneously address the issues of bulk phase gradient stress and interface dynamic stability. Uniform doping cannot accurately adapt to the surface-bulk phase stress gradient under high pressure, which can easily lead to local structural distortion; static coatings (such as oxides and single phosphates) have problems such as poor bonding with the substrate, high lithium-ion transport impedance, and inability to adapt to changes in interface stress during cycling.

[0005] In recent years, synergistic modification of bulk doping and surface coating has become a research hotspot. However, most dopants are of the same or single valence, lacking synergistic control over lattice charge balance and ion diffusion kinetics. Furthermore, the interface layer is mostly a static, inert structure, making it difficult to achieve "damage self-repair" during cycling. Therefore, overcoming these technical problems and deficiencies has become a key issue that needs to be addressed. Summary of the Invention

[0006] To address the problems of irreversible bulk structure collapse and uncontrolled interfacial side reactions in existing high-voltage lithium cobalt oxide cathode materials when the charging cutoff voltage exceeds 4.6V, this invention provides a cathode material, its preparation method, a cathode sheet, and a battery.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: The first aspect of this invention provides a cathode material comprising a core, a gradient heterovalent doped layer, and a phosphorus-based dynamic interface layer, wherein the core comprises lithium cobalt oxide; the gradient heterovalent doped layer is located on the surface of the core, and the gradient heterovalent doped layer is Al. 3+ and Ti 4+ The co-doped lithium cobalt oxide layer has the chemical composition LiCo. 1-x (Al a Ti b ) x O2; The phosphorus-based dynamic interface layer covers the outside of the gradient heterovalent doped layer; The phosphorus-based dynamic interface layer includes, from the inside out, a phosphorus-doped transition layer, an amorphous Li3PO3-LiPO3 layer, and a LiF crystalline dispersion layer; The phosphorus-doped transition layer and the gradient heterovalent doped layer form a coherent interface; The chemical formula of the positive electrode material is LiCoO2@LiCo 1-x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF, where x satisfies 0.03≤x≤0.09, a+b=1 and a / b=1-2.

[0008] Optionally, in the gradient heterovalent doped layer, the total doping amount of Al and Ti, expressed as a molar fraction of cobalt sites, is 3%–4% on the side closer to the core and 7%–9% on the side closer to the phosphorus-based dynamic interface layer.

[0009] Optionally, the thickness of the phosphorus-based dynamic interface layer is 8-25 nm.

[0010] Optionally, the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2-3:1.

[0011] Optionally, the LiF layer accounts for 30%-70% of the mass percentage of the phosphorus-based dynamic interface layer.

[0012] A second aspect of the present invention provides a method for preparing a cathode material, comprising the following steps: Aluminum source, titanium source and lithium cobalt oxide powder are mixed to form a liquid, and after the first drying and the first sintering, gradient heterovalent doped lithium cobalt oxide is obtained; A gel solution was formed by mixing graded heterovalent doped lithium cobalt oxide with lithium dihydrogen phosphate, followed by a second drying and a second sintering to obtain a phosphorus-coated intermediate. A phosphorus-coated intermediate was electrochemically induced to generate a LiF layer in situ on its surface, thus obtaining a cathode material.

[0013] Optionally, the aluminum source includes one or more of aluminum nitrate and aluminum isopropoxide; and / or, the titanium source includes one or more of tetrabutyl titanate and titanium nitrate.

[0014] Optionally, the first drying is a gradient temperature drying, which includes a first temperature drying, a second temperature drying, and a third temperature drying. The first temperature drying is at a temperature of 50-70℃ and a drying time of 1-2 hours; the second temperature drying is at a temperature of 80-100℃ and a drying time of 1-2 hours; the third temperature drying is at a temperature of 120-140℃ and a drying time of 1-2 hours; and / or, the first sintering temperature is 750-950℃ and the first sintering time is 4-7 hours.

[0015] Optionally, the temperature of the second drying is 120-140℃, and the time of the second drying is 2-4h; and / or, the temperature of the second sintering is 480-580℃, and the time of the second sintering is 2-4h.

[0016] A third aspect of the present invention provides a positive electrode sheet comprising the above-described positive electrode material, or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0017] A fourth aspect of the present invention provides a battery comprising the positive electrode material described above.

[0018] According to the cathode material provided by the present invention, the gradient distribution of Al in the gradient heterovalent doped layer of the present invention... 3+ Effectively strengthens the crystal structure and suppresses cell distortion and harmful phase transitions during high-voltage delithiation; Ti 4+The introduced oxygen vacancies optimize local charge balance, reducing lattice oxygen loss and particle microcracks. Simultaneously, the amorphous Li3PO3-LiPO3 in the phosphorus-based dynamic interface layer possesses adaptive reconstruction capabilities, responding to interfacial stress changes during cycling and achieving self-repair of micro-damage. This avoids the performance degradation caused by brittle fracture in traditional static coatings, thus significantly extending the material's cycle life under high voltage. Secondly, Al... 3+ With Ti 4+ The gradient co-doping precisely matches the increasing stress and charge distribution from the inside out during lithium delithiation, preventing element aggregation, effectively widening lithium-ion diffusion channels, and reducing bulk diffusion resistance. The coherent phosphorus-doped transition layer on the interface side reduces lattice mismatch, the amorphous phosphate phase provides a high ion conduction path, and the nanoscale LiF dispersed phase enhances chemical stability without hindering ion migration, collectively constructing a low-impedance, high-efficiency bulk-interface synergistic conduction network. Furthermore, Al... 3+ Stable Co–O framework, Ti 4+ Regulating oxygen vacancy concentration synergistically suppresses oxygen evolution and structural collapse at high temperatures; the LiF crystalline dispersed phase in the phosphorus-based dynamic interface layer effectively passivates surface active sites and significantly inhibits Co. 4+ Dissolution and electrolyte oxidation decomposition reduce gas generation and side reactions, thereby improving the thermal safety and long-term operational reliability of the material under high voltage and full charge conditions. In addition, the amorphous Li3PO3-LiPO3 layer and LiF crystalline dispersion layer of the present invention have chemical inertness, mechanical flexibility and dynamic evolution capability. They not only have low initial interface impedance, but also continuously optimize during long-term cycling, effectively reducing the first irreversible capacity loss and maintaining interface integrity. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The specific capacity of the coin cell at 0.1C corresponds to Embodiment 1 and Comparative Example 8 of the present invention. Detailed Implementation To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0022] In one embodiment, the first aspect of the present invention provides a cathode material comprising a core, a gradient heterovalent doped layer, and a phosphorus-based dynamic interface layer, wherein the core comprises lithium cobalt oxide; the gradient heterovalent doped layer is located on the surface of the core, and the gradient heterovalent doped layer is Al. 3+ and Ti 4+ The co-doped lithium cobalt oxide layer has the chemical composition LiCo. 1-x (Al a Ti b ) x O2; A phosphorus-based dynamic interface layer is coated on the outside of the gradient heterovalent doped layer; The phosphorus-based dynamic interface layer consists of a phosphorus-doped transition layer, an amorphous Li3PO3-LiPO3 layer and a LiF crystalline dispersion layer from the inside to the outside; The phosphorus-doped transition layer and the gradient heterovalent doped layer form a coherent interface; The chemical formula of the cathode material is LiCoO2@LiCo 1-x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF, where x satisfies 0.03≤x≤0.09, a+b=1 and a / b=1-2.

[0023] Specifically, the value of x is any one point value or any two point values ​​from 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 or 0.09; in a preferred embodiment, the value of x is 0.05-0.07.

[0024] When x takes values ​​between 0.03 and 0.09, Al 3+ and Ti 4+ Co-doping can effectively suppress the phase transition and oxygen evolution of lithium cobalt oxide under high pressure, and maintain a high specific capacity. When the value of x is less than 0.03, the doping amount is insufficient, making it difficult to effectively stabilize the surface lattice, which leads to accelerated capacity decay during cycling. When the value of x is greater than 0.09, excessive doping will destroy the layered structure order of LiCoO2, reduce the lithium ion diffusion rate, and cause a significant decrease in initial capacity.

[0025] Specifically, the value of a / b is any one value or a range of any two values ​​from 1, 1.2, 1.4, 1.6, 1.8 or 2; in a preferred embodiment, the value of a / b is 1.2-1.8.

[0026] When the value of a / b is 1-2, Al 3+Provided lattice stability and Ti 4+ The induced oxygen vacancies and lithium-ion diffusion enhancement effects reach a synergistic balance, significantly improving the cycling stability of the material under high voltage above 4.5V. When the value of a / b is less than 1, although the lithium-ion conductivity is improved, the lattice rigidity is insufficient, and structural collapse is likely to occur during deep delithiation. When the value of a / b is greater than 2, although the structural stability is enhanced, the oxygen vacancies are reduced, lithium-ion migration is hindered, and the rate performance deteriorates significantly.

[0027] The gradient distribution of Al in the gradient heterovalent doped layer of the present invention 3+ Effectively strengthens the crystal structure and suppresses cell distortion and harmful phase transitions during high-voltage delithiation; Ti 4+ The introduced oxygen vacancies optimize the local charge balance, reducing lattice oxygen loss and particle microcracks. Meanwhile, the amorphous Li3PO3-LiPO3 in the phosphorus-based dynamic interface layer has adaptive reconstruction capabilities, which can respond to changes in interface stress during cycling and achieve self-repair of micro-damage. This avoids the performance degradation caused by brittle fracture of traditional static coatings, thereby significantly extending the cycle life of the material under high voltage.

[0028] Secondly, Al 3+ With Ti 4+ The gradient co-doping precisely matches the increasing stress and charge distribution from the inside to the outside during the delithiation process, avoiding element aggregation, effectively widening the lithium-ion diffusion channel and reducing the bulk diffusion resistance; the coherent phosphorus-doped transition layer on the interface side reduces lattice mismatch, the amorphous phosphate phase provides a high ion conduction path, and the nanoscale LiF dispersed phase improves chemical stability without hindering ion migration, together constructing a low-impedance, high-efficiency bulk-interface synergistic conduction network.

[0029] Moreover, Al 3+ Stable Co–O framework, Ti 4+ Regulating oxygen vacancy concentration synergistically suppresses oxygen evolution and structural collapse at high temperatures; the LiF crystalline dispersed phase in the phosphorus-based dynamic interface layer effectively passivates surface active sites and significantly inhibits Co. 4+ Dissolution and electrolyte oxidation decomposition reduce gas production and side reactions, thereby improving the thermal safety and long-term operational reliability of the material under high voltage and full charge conditions.

[0030] In addition, the amorphous Li3PO3-LiPO3 layer and the LiF crystalline dispersion layer of the present invention have chemical inertness, mechanical flexibility and dynamic evolution capability. They not only have low initial interface impedance, but also continuously optimize during long-term cycling, effectively reducing the first irreversible capacity loss and maintaining interface integrity.

[0031] In one embodiment, in the gradient heterovalent doped layer, the total doping amount of Al and Ti, expressed as a molar fraction of cobalt sites, is 3%–4% on the side closer to the core and 7%–9% on the side closer to the phosphorus-based dynamic interface layer.

[0032] Specifically, the total doping amount of Al and Ti near the core is any one or a range of any two values ​​from 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, or 4%; in a preferred embodiment, the total doping amount of Al and Ti near the core is 3.2%-3.8%.

[0033] When the total doping amount of Al and Ti is 3%–4% molar fraction near the core, it can provide a moderate lattice anchoring effect while maintaining the high specific capacity of the lithium cobalt oxide core; Al 3+ (Ionic radius 0.053 nm) and Co 3+ (0.054nm) High matching effectively suppresses lattice distortion in the initial delithiation stage, while a small amount of Ti 4+ The introduced oxygen vacancies contribute to local charge balance, and the two work together to achieve an optimized match between the structural stability and electrochemical activity of the core region, while also creating a smooth compositional gradient transition for the heavily doped outer region. When the total doping amount of Al and Ti is less than 3% molar fraction near the core, the doping concentration is insufficient to stabilize the lattice, leading to significant uneven cell shrinkage and micro-stress accumulation in the early stages of high-voltage cycling. This easily induces the O3→H1-3 phase transition, accelerates capacity decay, and weakens the synergistic control ability of the gradient doping layer on the overall structure. When the total doping amount of Al and Ti is greater than 4% molar fraction near the core, the excessively high doping level will over-displace the electrochemically active Co. 3+ The site reduces the reversible specific capacity of the material; at the same time, it destroys the layered order of the core region, increases the lithium-ion migration barrier, weakens the bulk ion diffusion dynamics, and thus offsets the performance advantages brought by the gradient design.

[0034] Specifically, the total doping amount of Al and Ti on the side near the phosphorus-based dynamic interface layer is any one value or a range of any two values ​​from 7%, 7.2%, 7.4%, 7.6%, 7.8%, 8%, 8.2%, 8.4%, 8.6%, 8.8%, or 9%; in a preferred embodiment, the total doping amount of Al and Ti on the side near the phosphorus-based dynamic interface layer is 7.4%-8.6%.

[0035] When the total doping concentration of Al and Ti is 7%–9% molar fraction near the phosphorus-based dynamic interface layer, the structural robustness of the material surface layer can be significantly enhanced: high concentration of Al3+ Strengthening Co-O bonding effectively suppresses surface oxygen precipitation and lattice collapse under high pressure; Ti 4+ Introducing appropriate oxygen vacancies optimizes the surface charge distribution and enhances the lithium-ion insertion / extraction rate. The gradient enrichment of both Al and Ti at the interface precisely matches the increasing stress and charge density from the inside out during high-voltage lithium extraction, providing a stable structural substrate for the overlying phosphorus-based dynamic interface layer and achieving mechanical and electrochemical synergy between the bulk phase and the interface. When the total doping amount of Al and Ti is less than 7% molar fraction near the phosphorus-based dynamic interface layer, the surface doping concentration is insufficient, making it difficult to effectively suppress the drastic contraction and phase transition of the surface lattice under high voltage. This leads to microcracks easily forming on the particle surface, accelerating electrolyte erosion and transition metal dissolution, weakening the adhesion stability of the phosphorus-based interface layer, and consequently causing rapid capacity decay and impedance increase. When the total doping amount of Al and Ti is greater than 9% molar fraction near the phosphorus-based dynamic interface layer, excessive doping will destroy the layered structural order of the LiCoO2 surface layer, forming local impurity phases or cation mixing, hindering lithium-ion migration in the near-surface region. Simultaneously, Al... 3+ An excessively high proportion of oxygen vacancies will reduce the oxygen vacancy concentration, decrease the electron / ion conductivity of the surface layer, and thus worsen the rate performance. Furthermore, the excessive rigidity of the lattice may cause stress mismatch with the flexible phosphorus-based interface layer, inducing interface peeling.

[0036] In one embodiment, the thickness of the phosphorus-based dynamic interface layer is 8-25 nm.

[0037] Specifically, the thickness of the phosphorus-based dynamic interface layer is any one value or a range of any two values ​​selected from 8nm, 10nm, 13nm, 16nm, 19nm, 22nm or 25nm; in a preferred embodiment, the thickness of the phosphorus-based dynamic interface layer is 10-22nm.

[0038] When the thickness of the phosphorus-based dynamic interface layer is 8-25 nm, it can effectively perform multiple functions while ensuring efficient lithium-ion transport: the inner phosphorus-doped transition layer forms a coherent interface with the substrate, ensuring strong adhesion; the middle amorphous Li3PO3-LiPO3 layer has sufficient volume to achieve dynamic reconstruction, adapting to interfacial stress changes during cycling and repairing micro-damage; the outer LiF crystalline dispersed phase is uniformly distributed, effectively passivating the surface and inhibiting electrolyte erosion. This thickness range balances interfacial protection, ion conductivity, and mechanical flexibility, achieving long-term stable electrochemical performance under high voltage. When the thickness of the phosphorus-based dynamic interface layer is less than 8 nm, the interface layer is too thin and it is difficult to form a continuous and effective protective barrier: the amorphous phosphate phase is insufficient to support the dynamic reconstruction function, and microcracks cannot be effectively repaired; the LiF dispersed phase coverage is insufficient and cannot effectively block the electrolyte and highly active Co. 4+Side reactions can exacerbate interfacial side reactions, rapidly increase impedance, and significantly reduce cycle stability. When the thickness of the phosphorus-based dynamic interface layer exceeds 25 nm, the excessively thick interface layer significantly increases the diffusion path and resistance of lithium ions across the interface. Although chemical stability may be further improved, the intrinsic ionic conductivity of the amorphous phase is limited, and an excessively thick coating layer will severely hinder lithium ion transport, leading to deterioration in rate performance and increased polarization. At the same time, the thick layer is prone to internal stress accumulation due to volume changes during cycling, which may induce self-cracking or peeling from the substrate, losing the "dynamic self-healing" advantage and even accelerating performance degradation.

[0039] In one embodiment, the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2-3:1.

[0040] Specifically, the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is any one of the following ratios or a range of any two ratios: 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, or 3:1; in a preferred embodiment, the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2.2-2.8:1.

[0041] When the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2-3:1, optimal synergy between ion conductivity and structural stability can be achieved: Li3PO3 is rich in lithium ions and has high lithium ion conductivity, which is beneficial to improving the interfacial lithium transport kinetics; LiPO3 forms a dense phosphate network framework, providing good mechanical strength and chemical inertness. Within this ratio range, the two form a uniform and flexible amorphous composite phase, which has sufficient dynamic reconstruction capability to adapt to cyclic stress and maintains interfacial integrity, effectively supporting the damage self-healing function. When the molar ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is less than 2:1, the interface layer tends to become rigid, and the glass network becomes excessively cross-linked, leading to increased brittleness and reduced fluidity. This makes it difficult for the material to undergo local rearrangement during cycling to respond to volume changes, weakening its dynamic self-healing ability. At the same time, insufficient lithium-ion concentration leads to a decrease in interfacial ionic conductivity, increasing lithium-ion migration resistance and affecting rate performance. When the molar ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is greater than 3:1, although lithium-ion conductivity is enhanced, the network structure is too loose, significantly reducing mechanical strength and chemical stability. The interface layer is prone to swelling, softening, or even local dissolution under long-term immersion in electrolyte or high voltage, making it difficult to effectively block side reactions. Furthermore, it is prone to plastic deformation or adhesion failure under repeated charge-discharge stress, which in turn reduces the long-term stability of the interface.

[0042] In one embodiment, the LiF layer accounts for 30%-70% of the mass percentage of the phosphorus-based dynamic interface layer.

[0043] Specifically, the mass percentage of the LiF layer in the phosphorus-based dynamic interface layer is any one value or a range of any two values ​​from 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%; in a preferred embodiment, the mass percentage of the LiF layer in the phosphorus-based dynamic interface layer is 45%-60%.

[0044] When the LiF layer accounts for 30%-70% of the mass percentage of the phosphorus-based dynamic interface layer, LiF is uniformly dispersed in the amorphous Li3PO3-LiPO3 matrix in the form of nanocrystals, which can effectively passivate the positive electrode surface, inhibit the oxidative decomposition of the electrolyte, and inhibit Co. 4+ LiF dissolves, improving interfacial chemical stability without forming a continuous, dense insulating film that hinders lithium-ion transport. Simultaneously, LiF synergistically constructs a "rigid-flexible composite" structure with amorphous phosphate, maintaining low interfacial impedance while ensuring interfacial mechanical integrity, achieving long-term stable cycling under high voltage. When the LiF layer accounts for less than 30% of the phosphorus-based dynamic interfacial layer, insufficient LiF coverage fails to effectively prevent direct contact between the highly active surface and the electrolyte, leading to intensified interfacial side reactions, continuous thickening of the CEI film, rapid increase in impedance during cycling, and accelerated capacity decay. When the LiF layer accounts for more than 70% of the phosphorus-based dynamic interfacial layer, excessive aggregation of LiF particles, even forming a continuous phase, significantly increases interfacial ion transport resistance due to its extremely low intrinsic lithium-ion conductivity, deteriorating rate performance. Furthermore, a high proportion of LiF weakens the continuity and dynamic reconstruction capability of the amorphous phosphate matrix, causing the interface to lose its adaptive stress change and micro-damage repair functions, making it prone to brittle cracking during cycling and reducing long-term stability.

[0045] In one embodiment, a second aspect of the present invention provides a method for preparing a cathode material, comprising the following steps: S1. A mixture of aluminum source, titanium source and lithium cobalt oxide powder is prepared, and after the first drying and the first sintering, a graded heterovalent doped lithium cobalt oxide is obtained; S2. Gradient heterovalent doped lithium cobalt oxide is mixed with lithium dihydrogen phosphate to form a gel liquid, which is then dried and sintered a second time to obtain a phosphorus-coated intermediate; S3. Phosphorus-coated intermediates are electrochemically induced to generate a LiF layer in situ on their surface to obtain the cathode material.

[0046] Specifically, in step S1, an aluminum source, a titanium source, and lithium cobalt oxide powder are mixed to form a solution, which is then dried and sintered for the first time to obtain graded heterovalent doped lithium cobalt oxide, including the following steps: S11. Mix lithium cobalt oxide powder with solvent and ultrasonically disperse for 40-60 min to obtain suspension A; S12. Mix the aluminum source, titanium source and solvent, add dispersant, and stir until homogeneous to obtain solution B; S13. Add solution B to suspension A at a rate of 0.8~1.2 drops / second, stir and react at 55~75℃ for 3~5h, then dry for the first time to obtain precursor powder; sinter the precursor powder for the first time and cool naturally to obtain graded anisovalent doped lithium cobalt oxide. The solvent is selected from one or more of ethanol, isopropanol, deionized water, and acetone. The dispersant is selected from one or more of polypropylene glycol 600, polyvinylpyrrolidone (PVP), citric acid, and sodium dodecylbenzene sulfonate (SDBS); The dispersant accounts for 0.8% to 1.5% of the total mass of the aluminum and titanium sources; Specifically, in step S2, graded heterovalent doped lithium cobalt oxide is mixed with lithium dihydrogen phosphate to form a gel solution, which is then dried a second time and sintered a second time to obtain a phosphorus-coated intermediate, including the following steps: Gradient anisovalent doped lithium cobalt oxide was dispersed in deionized water, and lithium dihydrogen phosphate (2% to 6% of the mass of the gradient doped lithium cobalt oxide) was added. After ultrasonic dispersion for 30 to 50 minutes, the mixture was stirred at 40 to 60°C until a gel was formed. After a second drying and a second sintering, a phosphorus-coated intermediate was obtained. The amount of lithium dihydrogen phosphate added accounts for 2% to 6% of the total mass of graded heterovalent doped lithium cobalt oxide.

[0047] Specifically, in step S3, a LiF layer is generated in situ on the surface of the phosphorus-coated intermediate through electrochemical induction to obtain the cathode material, including the following steps: A phosphorus-based coating intermediate was mixed with a conductive agent and a binder, coated onto aluminum foil, dried, and then assembled with lithium foil, electrolyte, and separator to form a half-cell. Constant current and constant voltage pre-cycle activation was employed: voltage range 3.0–4.7V, current density 0.1C, 4–6 cycles. During pre-cycle, LiPF6 in the electrolyte reacted in situ with the phosphorus-based pre-interface layer to generate LiF, while Li3PO3 and LiPO3 underwent dynamic reconstruction, ultimately forming a phosphorus-based dynamic interface layer, yielding the cathode material.

[0048] The cathode material prepared by the above method achieves synergistic breakthroughs in key performance dimensions such as high voltage, fast charging, long life and high safety, and is particularly suitable for high energy density lithium-ion batteries for high-end consumer electronics.

[0049] In one embodiment, the aluminum source includes one or more of aluminum nitrate and aluminum isopropoxide; and / or, the titanium source includes one or more of tetrabutyl titanate and titanium nitrate.

[0050] Using one or more of aluminum nitrate, aluminum isopropoxide, tetrabutyl titanate, or titanium nitrate as the aluminum and titanium sources not only ensures the Al 3+ With Ti 4+ The good solubility and reactivity of the precursor in solution also significantly improve the uniformity and controllability of the gradient heterovalent doped layer, thereby achieving high-precision gradient doping, improving doping uniformity and interfacial bonding strength.

[0051] In one embodiment, the first drying is a gradient temperature drying, which includes a first temperature drying, a second temperature drying, and a third temperature drying. The first temperature drying is at a temperature of 50-70°C and a drying time of 1-2 hours; the second temperature drying is at a temperature of 80-100°C and a drying time of 1-2 hours; the third temperature drying is at a temperature of 120-140°C and a drying time of 1-2 hours; and / or, the first sintering temperature is 750-950°C and the first sintering time is 4-7 hours.

[0052] By employing the above-mentioned gradient temperature drying and high-temperature sintering process, Al can be effectively achieved. 3+ With Ti 4+ Uniform distribution and controllable diffusion on the surface of lithium cobalt oxide yield a doped layer with a complete structure and precise compositional gradient. First, a three-stage gradient drying process (50–70℃ → 80–100℃ → 120–140℃) allows the solvent (e.g., ethanol) to evaporate slowly and in stages, avoiding the "coffee ring effect" or uneven aggregation of metal precursors on the particle surface caused by rapid drying. This process promotes the formation of an initial concentration gradient between the aluminum and titanium sources from the outside in, laying the foundation for a smooth bulk doping gradient during subsequent sintering. Second, the gradient heating effectively alleviates the abrupt change in capillary stress during drying, reducing hard agglomeration and surface cracking of micron-sized lithium cobalt oxide particles, ensuring the dispersibility and reactivity of the precursor powder, and facilitating grain densification and coherent interfacial growth during subsequent sintering. Furthermore, under air atmosphere sintering conditions of 750–950℃ for 4–7 hours, Al… 3+ With Ti 4+ Sufficient energy is obtained to diffuse from the particle surface to the interior, but the diffusion depth is controlled within tens of nanometers due to time and temperature windows. Combined with the initial gradient distribution of the precursor, a heterovalent doping profile is finally formed that continuously increases from the core side (3%–4%) to the interface side (7%–9%), which not only enhances surface stability but also retains the high capacity characteristics of the core.

[0053] In one embodiment, the temperature of the second drying is 120-140°C and the time of the second drying is 2-4 hours; and / or, the temperature of the second sintering is 480-580°C and the time of the second sintering is 2-4 hours.

[0054] First, drying at 120–140℃ for 2–4 hours effectively removes moisture and residual solvent from the gel, while preventing localized crystallization or cracking of lithium dihydrogen phosphate caused by sudden temperature increases. This gentle drying process helps form a continuous, dense phosphate gel coating layer that uniformly covers the surface of the graded heterovalent doped lithium cobalt oxide particles. Second, the low-temperature sintering window of 480–580℃ promotes the decomposition of lithium dihydrogen phosphate to generate an active phosphate phase, while also allowing a small amount of P... 5+ Ions diffuse moderately into the surface lattice of lithium cobalt oxide, forming a phosphorus-doped transition layer. This transition layer and the inner gradient doped layer form a coherent or semi-coherent interface due to good lattice matching, significantly enhancing the interfacial bonding strength and preventing the coating layer from peeling off during subsequent cycles. Moreover, the sintering temperature is controlled below 580℃, which is far lower than the crystallization temperature of the lithium phosphate system (usually >650℃), effectively suppressing the precipitation of Li3PO3 / LiPO3 crystalline phase and ensuring that the coating layer is dominated by the amorphous glass phase. This amorphous structure has good flexibility and atomic-level fluidity, providing a structural basis for stress adaptation and damage self-repair in subsequent electrochemical cycles.

[0055] In one embodiment, a third aspect of the present invention provides a positive electrode sheet comprising the above-described positive electrode material, or a positive electrode material prepared by the above-described method for preparing the positive electrode material.

[0056] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including a positive electrode material, a positive electrode conductive agent and a positive electrode binder; In some embodiments, the positive electrode conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0057] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0058] In some embodiments, the type of positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as lanthanum, stainless steel, lanthanum plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.

[0059] In one embodiment, a fourth aspect of the present invention provides a battery comprising the above-described positive electrode material.

[0060] In some embodiments, the battery includes the above-described positive electrode, negative electrode, separator, and electrolyte; In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0061] In some embodiments, the negative electrode active material includes one or more of graphite, silicon-carbon composite materials, or lithium metal materials; the negative electrode active material is preferably designed in conjunction with the positive electrode and functionalized electrolyte to maximize the overall performance of the battery.

[0062] In some embodiments, the negative electrode conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0063] In some embodiments, the negative electrode binder includes at least one of styrene-butadiene latex and CMC.

[0064] In some embodiments, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be at least one of copper foil, copper alloy foil, lanthanum foil, stainless steel foil, titanium foil, foamed lanthanum, foamed copper, or composite current collector; in some preferred embodiments, the negative electrode current collector includes copper foil.

[0065] In some embodiments, the diaphragm is a porous polymer film selected from polyethylene (PE), polypropylene (PP) single-layer film, or PE / PP / PE three-layer composite film. Preferably, the diaphragm surface may be coated with a ceramic or polymer coating to improve thermal stability and electrolyte wettability.

[0066] In some embodiments, the electrolyte includes lithium salt, organic solvent, and additives; In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium difluorophosphate, or lithium tetrafluoroborate; preferably, the lithium salt is lithium hexafluorophosphate. In some embodiments, the organic solvent includes two or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); preferably, the organic solvent is a mixed solvent composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) in a volume ratio of 4:5:1. In some embodiments, the additives include one or more of fluoroethylene carbonate (FEC), 1,3-propane sulpholol (PS), vinyl sulfate (DTD), lithium difluorophosphate (LiDFP), tris(trimethylsilane) phosphate (TMSPa), or vinylene carbonate (VC); wherein, FEC not only participates in the construction of the negative electrode SEI as a film-forming additive, but can also serve as a fluorine source to generate LiF in situ on the positive electrode surface, thereby synergistically improving the interface stability; In some preferred embodiments, the electrolyte is 1 mol / L LiPF6 dissolved in a mixed solvent of EC:EMC:FEC (volume ratio 4:5:1), which is used to match the high-voltage lithium cobalt oxide cathode and graphite anode system to achieve synergistic optimization of high voltage stability, fast charging performance and cycle life.

[0067] The above-mentioned negative electrode, positive electrode and separator are assembled into a cell by stacking or winding in a "positive-separator-negative" manner, electrolyte is injected, and after formation, aging and capacity testing, it is packaged in an aluminum-plastic film soft pack, steel shell or aluminum shell to obtain a lithium-ion battery.

[0068] The battery of the present invention can be used in consumer electronics (such as smartphones and laptops), electric vehicles (such as electric vehicles and electric bicycles), and energy storage systems (such as grid energy storage and home energy storage).

[0069] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0070] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0071] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0072] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0073] Table 1. Design of cathode materials for Examples 1-21 and Comparative Examples 1-9; Example 1 This embodiment illustrates the cathode material and battery disclosed in this invention; it includes the following operational steps: Cathode material preparation: Preparation of gradient heterovalent doped precursor: 10 g of lithium cobalt oxide was dispersed in 120 mL of ethanol and sonicated for 50 min to obtain suspension A; 0.42 g of aluminum nitrate and 0.35 g of tetrabutyl titanate (a / b = 1.2) were dissolved in 30 mL of ethanol, and 0.12 g of polypropylene glycol 600 was added and stirred to obtain solution B; solution B was added dropwise to A at 1 drop / second, stirred at 65 °C for 4 h, gradient dried (60 °C → 90 °C → 130 °C, 1.5 h each), and sintered at 850 °C for 5 h to obtain LiCoO2@LiCo 1-0.06 (Al 0.55 Ti 0.45 ) 0.06 O2; Construction of phosphorus-based pre-interface layer: 5g LiCoO2@LiCo 1-0.06 (Al 0.55 Ti 0.45 ) 0.06 O2 was dispersed in 60 mL of water, 0.25 g of LiH2PO4 was added, and the mixture was sonicated for 40 min and stirred at 50 °C to form a gel. The gel was dried at 130 °C for 3 h and sintered at 530 °C for 3 h to obtain the intermediate. 3. Electrochemical-induced modification: An electrode was prepared by mixing intermediates, conductive carbon black, and PVDF in a ratio of 85:10:5. This electrode was then assembled with a lithium sheet and a 1M LiPF6 / EC+EMC+FEC (4:5:1) electrolyte to form a half-cell. After pre-cycling at 3.0~4.7V / 0.1C for 5 cycles, the target material LiCoO2@LiCo was obtained. 1-x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF; wherein, the total molar fraction of Al and Ti doping near the core is 3.5%, and the total molar fraction of Al and Ti doping near the phosphorus-based dynamic interface layer is 8.5%; the thickness of the phosphorus-based dynamic interface layer is 16 nm, the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2.5:1, and the LiF layer accounts for 50% of the mass percentage of the phosphorus-based dynamic interface layer.

[0074] Preparation of positive electrode: The positive electrode material LiCoO2@LiCo 1-x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF was mixed with conductive carbon black and PVDF at a mass ratio of 85:10:5 and uniformly prepared into a slurry using N-methylpyrrolidone (NMP) as a solvent. This slurry was then uniformly coated onto an aluminum foil current collector and vacuum-dried at 80℃ for 12 hours. The resulting product was then rolled to a compaction density of 4.2±0.1 g / cm³. 3 The positive electrode sheet was thus produced.

[0075] Preparation of negative electrode: A negative electrode slurry is prepared by mixing graphite, the negative electrode material, and SBR, the binder, in a ratio of 98:2. The negative electrode slurry is then coated onto the copper foil of the negative electrode current collector on a coating machine. After drying, rolling, die-cutting and other processes, the negative electrode sheet is obtained.

[0076] Electrolyte preparation: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) in a mass ratio of 4:5:1 to obtain an electrolyte with a concentration of 1 mol / L.

[0077] Celgard 2400 membrane was used as the diaphragm; Battery manufacturing: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrodes are then wound into a battery cell. The battery cell is placed into a pre-formed battery casing, and the electrolyte is injected into the baked and dried battery cell. After vacuum sealing, settling, and formation processes, the battery is obtained.

[0078] Example 2-21 Examples 2-21 illustrate the cathode material and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: The parameters of the cathode material shown in Table 1 are used.

[0079] Comparative Examples 1-9 Comparative Examples 1-9 are used to illustrate the cathode material and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being: The parameters of the cathode material shown in Table 1 are used.

[0080] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-21 and Comparative Examples 1-9: 1. Volumetric Energy Density (Wh / L) Test Method: Test the discharge specific capacity C (mAh / g) of the positive electrode at 3.0–4.65V and 1C rate, and calculate the volumetric energy density using the following formula: Volumetric energy density = C × compaction density × 3.7 / 1000; Unit: Wh / L.

[0081] 2.0.1C First Discharge Specific Capacity (mAh / g) and First Charge-Discharge Efficiency (%) Test Method: The prepared positive electrode sheet was used as the working electrode, the lithium metal sheet was used as the counter electrode and reference electrode, the Celgard 2400 polypropylene microporous membrane was used as the separator, and the electrolyte was 1M LiPF6 dissolved in a mixed solvent of EC:DMC:FEC (volume ratio 3:6:1). The CR2032 coin cell was assembled in an argon atmosphere glove box. At room temperature, a constant current charge-discharge tester was used to perform the first charge-discharge cycle at a current density of 0.1C within a voltage range of 3.0–4.65V. The first discharge specific capacity and the first discharge specific capacity were recorded, in mAh / g. The first charge-discharge efficiency was calculated using the following formula: First charge / discharge efficiency = (First discharge specific capacity / First charge specific capacity) × 100% 3.10C rate discharge specific capacity (mAh / g) test method: The half cell is first activated at 0.1C for 3 cycles, and then charged at 0.1C and discharged at 10C within the range of 3.0–4.65V. The discharge specific capacity after stable cycling is recorded, which is the 10C rate discharge specific capacity, in mAh / g.

[0082] 4.5C Cycle 100 Cycle Capacity Retention Rate (%) Test Method: The assembled CR2032 coin cell (positive electrode as working electrode, lithium metal sheet as counter electrode, Celgard 2400 separator, 1M LiPF6 / EC:DMC:FEC (3:6:1, v / v) electrolyte) was aged at room temperature (25±2℃). Then, it was activated by three cycles at 0.1C in the voltage range of 3.0–4.65V to stabilize the electrode / electrolyte interface. Then, it was charged and discharged at 5C for 100 cycles at constant current.

[0083] Calculate the capacity retention rate using the following formula: Capacity retention rate = (Discharge capacity at 100th cycle / Discharge capacity at 1st cycle) × 100%; 5. Initial decomposition temperature (°C, DSC) test method: After the positive electrode material is completely delithiated under a high voltage of 4.65V, the battery is disassembled, the electrode is washed with dimethyl carbonate (DMC), and the positive electrode powder is scraped off after vacuum drying.

[0084] Using a differential scanning calorimeter (DSC) under a nitrogen atmosphere, the temperature was increased from room temperature to 400℃ at a rate of 10℃ / min. The temperature corresponding to the first obvious endothermic / exothermic inflection point of the curve was recorded, which is the initial decomposition temperature.

[0085] 6.200℃ Mass Loss (%TGA) Test Method: Take the above-mentioned completely delithiated cathode powder, and use a thermogravimetric analyzer (TGA) under a nitrogen atmosphere to heat to 200℃ at a rate of 10℃ / min and hold for 10 min. Record the percentage change in mass. 7. Lithium-ion diffusion coefficient test method: Calculated using electrochemical impedance spectroscopy (EIS) combined with potentiostatic step (GITT) or cyclic voltammetry (CV).

[0086] Test conditions: Open circuit potential, frequency range 10 6 Hz–10 -2 Hz, amplitude 5mV.

[0087] The impedance parameters are obtained by fitting an equivalent circuit, and the lithium-ion diffusion coefficient DLi is calculated using the Randles-Sevcik formula or the GITT diffusion formula. + Unit: ×10 -10 cm 2 / s.

[0088] The test results are shown in Table 2.

[0089] Table 2 Battery Electrochemical Performance Comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that when x ranges from 0.03 to 0.09, the material exhibits excellent comprehensive electrochemical performance: volumetric energy density of 772–798 Wh / L, initial discharge specific capacity of 179.5–185.1 mAh / g at 0.1C, initial charge / discharge efficiency of 92.1–93.2%, discharge specific capacity of 135.7–142.3 mAh / g at 10C rate, capacity retention of 96.2–97.1% after 100 cycles at 5C, mass loss of only 1.9–2.3% at 200℃, and lithium-ion diffusion coefficient of 8.2–8.8 × 10⁻⁶. -10 cm 2 / s. Al 3+ and Ti 4+Co-doping effectively suppresses phase transition and oxygen evolution in lithium cobalt oxide under high voltage while maintaining a high specific capacity. When the value of x is less than 0.03 (e.g., in Comparative Example 1, x=0.02), the material performance deteriorates significantly: the volumetric energy density drops to 720Wh / L, the initial charge-discharge efficiency is only 88.3%, the 5C cycle capacity retention is only 85.2%, the mass loss at 200℃ increases to 4.5%, and the lithium-ion diffusion coefficient is only 4.2×10⁻⁶. -10 cm 2 / s. Insufficient doping makes it difficult to effectively stabilize the surface lattice, leading to accelerated capacity decay during cycling. When the value of x is greater than 0.09 (e.g., in Comparative Example 2, x=0.1), the material performance also declines: volumetric energy density 742Wh / L, initial charge-discharge efficiency 90.1%, 5C cycle capacity retention 90.5%, mass loss at 200℃ 3.3%, and lithium-ion diffusion coefficient 6.1×10 -10 cm 2 Excessive doping disrupts the ordered layered structure of LiCoO2, reduces the lithium-ion diffusion rate, and causes a significant decrease in initial capacity.

[0090] Comparing Example 1 and Comparative Examples 5-7, it can be seen that when the gradient heterovalent doped layer is Al 3+ and Ti 4+ The material exhibits optimal performance with co-doped lithium cobalt oxide layers: volumetric energy density of 785 Wh / L, initial charge-discharge efficiency of 92.6%, 5C cycle capacity retention of 96.8%, mass loss at 200℃ of 2.1%, and lithium-ion diffusion coefficient of 8.5 × 10⁻⁶. -10 cm 2 / s. Al 3+ With Ti 4+ The synergistic effect can simultaneously improve structural stability and ion transport efficiency; when the gradient heterovalent doped layer is only Al 3+ When a lithium cobalt oxide layer is doped (Comparative Example 5), the performance decreases significantly: volumetric energy density 728 Wh / L, initial charge-discharge efficiency 89.2%, 5C cycle capacity retention 88.1%, mass loss at 200℃ 4.2%, and lithium-ion diffusion coefficient 5.2 × 10⁻⁶. -10 cm 2 / s; Single Al 3+ While doping can stabilize the crystal lattice, it lacks Ti. 4+ The induced oxygen vacancies and ion diffusion enhancement effect limit rate and cycling performance. When the gradient heterovalent doped layer is only Ti... 4+ With the addition of a doped lithium cobalt oxide layer (Comparative Example 6), performance deteriorates further: volumetric energy density 732 Wh / L, initial charge-discharge efficiency 89.4%, 5C cycle capacity retention 88.5%, mass loss at 200℃ 4.1%, and lithium-ion diffusion coefficient 5.4 × 10⁻⁶. -10 cm 2 / s. Single Ti 4+ Doping easily induces local structural distortions, leading to a double decrease in initial capacity and cycle stability. The worst performance is observed when no gradient heterovalent doped layer is present (Comparative Example 7): volumetric energy density 727 Wh / L, initial charge / discharge efficiency 88.2%, 5C cycle capacity retention only 88%, mass loss at 200℃ 3.4%, and lithium-ion diffusion coefficient only 6 × 10⁻⁶. -10 cm 2 Undoped lithium cobalt oxide is prone to irreversible phase transition and oxygen release under high pressure, leading to severe capacity decay and interfacial side reactions.

[0091] Comparing Examples 1, 4-5, and 3-4, it can be seen that the material performance is optimal when the a / b ratio is 1-2: volumetric energy density 778–792 Wh / L, initial charge / discharge efficiency 92.4%–92.9%, 10C rate discharge specific capacity 137.1–140.2 mAh / g, 5C cycle capacity retention 96.5%–97.3%, 200℃ mass loss 2%–2.2%, and lithium-ion diffusion coefficient 8.3–8.6 × 10⁻⁶. -10 cm 2 / s. Al 3+ Provided lattice stability and Ti 4+ The induced oxygen vacancy and lithium-ion diffusion enhancement effects achieve a synergistic balance, significantly improving the material's cycle stability under high voltages above 4.5V. When the a / b value is less than 1 (e.g., in Comparative Example 3, a / b = 0.5), performance declines: volumetric energy density 735Wh / L, initial charge / discharge efficiency 89.7%, 10C rate discharge specific capacity 121.3mAh / g, 5C cycle capacity retention 89.2%, 200℃ mass loss 3.8%, and lithium-ion diffusion coefficient 5.8 × 10⁻⁶. - 10 cm 2 / s. Although the lithium-ion conductivity is improved, the lattice rigidity is insufficient, making it prone to structural collapse during deep delithiation. When the a / b value is greater than 2 (e.g., in Example 5, a / b=2; in Comparative Example 4, a / b=2.5), the performance deteriorates: volumetric energy density 730Wh / L, initial charge / discharge efficiency 89.5%, 10C rate discharge specific capacity 120.1mAh / g, 5C cycle capacity retention 88.7%, 200℃ mass loss 4%, and lithium-ion diffusion coefficient 5.5×10 -10 cm 2 / s. Although the structural stability is enhanced, the reduction of oxygen vacancies hinders lithium-ion migration, resulting in a significant deterioration in rate performance.

[0092] Comparing Examples 1 and 6-9, it can be seen that when the total molar fraction of Al and Ti doping near the core is 3%–4%, and the molar fraction of Al and Ti doping near the phosphorus-based dynamic interface layer is 7%–9%, ​​the material performance is optimal: volumetric energy density 785–802 Wh / L, initial charge / discharge efficiency 92.6%–93.5%, 10C rate discharge specific capacity 138.5–143.5 mAh / g, 5C cycle capacity retention 96–96.8%, 200℃ mass loss 1.8–2.1%, and lithium-ion diffusion coefficient 8.5–9 × 10⁻⁶. -10 cm 2 Gradient doping achieves layered protection of "core stability - interface enhancement," balancing bulk structural integrity and interface stability. When the total doping amount of Al and Ti is less than 3% molar fraction near the core or greater than 9% near the phosphorus-based dynamic interface layer, performance decreases slightly: volumetric energy density 775 Wh / L, initial charge / discharge efficiency 92.2%, 10C rate discharge specific capacity 136.8 mAh / g, 5C cycle capacity retention 96.4%, 200℃ mass loss 2.2%, and lithium-ion diffusion coefficient 8.4 × 10⁻⁶. -10 cm 2 Gradient imbalance leads to insufficient bulk or interfacial stability, resulting in slight degradation in cycle and rate performance. Significant performance degradation occurs when the total Al and Ti doping concentration is greater than 4% near the core or less than 7% near the phosphorus-based dynamic interface layer: volumetric energy density 770 Wh / L, initial charge / discharge efficiency 92%, 10C rate discharge specific capacity 135.2 mAh / g, 5C cycle capacity retention 96.9%, 200℃ mass loss 2.3%, and lithium-ion diffusion coefficient 8.1 × 10⁻⁶. -10 cm 2 Excessive doping disrupts the bulk layered structure, or insufficient doping at the interface leads to protection failure, resulting in a decrease in capacity and stability.

[0093] Comparing Examples 1 and 10-13, it can be seen that when the thickness of the phosphorus-based dynamic interface layer is 8-25 nm, the material performance is optimal: volumetric energy density 780–785 Wh / L, initial charge / discharge efficiency 92.5%–92.7%, 10C rate discharge specific capacity 137.9–138.8 mAh / g, 5C cycle capacity retention 96.3–96.8%, 200℃ mass loss 2%–2.1%, and lithium-ion diffusion coefficient 8.5–8.7 × 10⁻⁶. -10 cm 2 / s. While ensuring efficient lithium-ion transport, it effectively performs multiple functions: the inner phosphorus-doped transition layer forms a coherent interface with the substrate, ensuring strong adhesion; the middle amorphous Li3PO3-LiPO3 layer has sufficient volume to achieve dynamic reconstruction, adapting to interfacial stress changes during cycling and repairing micro-damage; the outer LiF crystalline dispersed phase is uniformly distributed, effectively passivating the surface and inhibiting electrolyte erosion. This thickness range balances interfacial protection, ion conductivity, and mechanical flexibility, achieving long-term stable electrochemical performance under high voltage; when the thickness of the phosphorus-based dynamic interface layer is less than 8nm, the performance slightly decreases: volumetric energy density 776Wh / L, initial charge / discharge efficiency 92.3%, 10C rate discharge specific capacity 136.9mAh / g, 5C cycle capacity retention 96.7%, 200℃ mass loss 2.2%, lithium-ion diffusion coefficient 8.5×10 -10 cm 2 / s. The interface layer is too thin, making it difficult to form a continuous and effective protective barrier: the amorphous phosphate phase is insufficient to support the dynamic reconstruction function, and microcracks cannot be effectively repaired; the LiF dispersed phase coverage is insufficient, and it cannot effectively block the electrolyte from the highly active Co. 4+ Side reactions exacerbate interfacial side reactions, leading to a rapid increase in impedance and a significant decrease in cycle stability. When the thickness of the phosphorus-based dynamic interface layer exceeds 25 nm, performance deteriorates significantly: volumetric energy density 778 Wh / L, initial charge-discharge efficiency 92.1%, 10C rate discharge specific capacity 136.4 mAh / g, 5C cycle capacity retention 95.9%, 2% mass loss at 200℃, and lithium-ion diffusion coefficient 8.4 × 10⁻⁶. -10 cm 2 / s. An excessively thick interface layer significantly increases the diffusion path and resistance of lithium ions migrating across the interface; although chemical stability may be further improved, the intrinsic ionic conductivity of the amorphous phase is limited, and an excessively thick coating layer will severely hinder lithium ion transport, leading to deterioration of rate performance and increased polarization; at the same time, the thick layer is prone to internal stress accumulation due to volume changes during cycling, which may induce self-cracking or peeling from the substrate, losing the "dynamic self-healing" advantage, and even accelerating performance degradation.

[0094] Comparing Examples 1 and 14-17, it can be seen that when the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2-3:1, the material performance is optimal: volumetric energy density 783–788 Wh / L, initial charge / discharge efficiency 92.6%–92.8%, 10C rate discharge specific capacity 138.1–139.5 Ah / g, 5C cycle capacity retention 96.4–96.8%, mass loss at 200℃ 2%–2.1%, and lithium-ion diffusion coefficient 8.5–8.8 × 10⁻⁶. -10 cm 2 / s. Optimal synergy between ion conductivity and structural stability can be achieved: Li3PO3 is rich in lithium ions and has high lithium-ion conductivity, which is beneficial for improving interfacial lithium transport kinetics; LiPO3 forms a dense phosphate network framework, providing good mechanical strength and chemical inertness. Within this ratio range, the two form a uniform and flexible amorphous composite phase, possessing sufficient dynamic reconfiguration capability to adapt to cyclic stress while maintaining interfacial integrity, effectively supporting damage self-healing function. When the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is less than 2:1, performance declines: volumetric energy density 782Wh / L, initial charge / discharge efficiency 91.8%, 10C rate discharge specific capacity 137.2mAh / g, 5C cycle capacity retention 95.9%, 200℃ mass loss 1.9%, lithium-ion diffusion coefficient 8.9×10 - 10 cm 2 / s. The interface layer tends to become rigid, and the glass network is excessively cross-linked, leading to increased material brittleness and reduced fluidity. This makes it difficult for local rearrangement to occur during cycling in response to volume changes, weakening the dynamic self-healing ability. Simultaneously, insufficient lithium-ion concentration reduces interfacial ionic conductivity, increasing lithium-ion migration resistance and affecting rate performance. When the molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is greater than 3:1, performance deteriorates: volumetric energy density 779Wh / L, initial charge / discharge efficiency 92.4%, 10C rate discharge specific capacity 137.5mAh / g, 5C cycle capacity retention 97%, 200℃ mass loss 2.2%, and lithium-ion diffusion coefficient 8.4×10⁻⁶. -10 cm 2 Although lithium-ion conductivity is enhanced, the network structure is too loose, resulting in a significant reduction in mechanical strength and chemical stability. The interface layer is prone to swelling, softening, or even local dissolution under long-term immersion in electrolyte or high voltage, making it difficult to effectively block side reactions. Furthermore, it is prone to plastic deformation or adhesion failure under repeated charge-discharge stress, which in turn reduces the long-term stability of the interface.

[0095] Comparing Examples 1 and 18-21, it can be seen that when the LiF layer accounts for 30%-70% of the mass percentage of the phosphorus-based dynamic interface layer, the material performance is optimal: volumetric energy density 781–785 Wh / L, initial charge / discharge efficiency 92.5–92.7%, 10C rate discharge specific capacity 137.8–138.6 mAh / g, 5C cycle capacity retention 96.7%-96.8%, 200℃ mass loss 2.1%, and lithium-ion diffusion coefficient 8.5–8.7 × 10⁻⁶. -10 cm 2 / s. LiF is uniformly dispersed in the form of nanocrystals in the amorphous Li3PO3-LiPO3 matrix, which can effectively passivate the positive electrode surface, inhibit the oxidative decomposition of the electrolyte, and Co. 4+ Dissolution enhances interfacial chemical stability without forming a continuous, dense insulating film that hinders lithium-ion transport. Simultaneously, LiF synergistically constructs a "rigid-flexible composite" structure with amorphous phosphate, maintaining low interfacial impedance while ensuring interfacial mechanical integrity, achieving long-term stable cycling under high voltage. When the LiF layer accounts for less than 30% of the phosphorus-based dynamic interface layer by mass, performance slightly decreases: volumetric energy density 779 Wh / L, initial charge / discharge efficiency 91.8%, 10C rate discharge specific capacity 136.1 mAh / g, 5C cycle capacity retention 95.5%, 2% mass loss at 200℃, and lithium-ion diffusion coefficient 8.8 × 10⁻⁶. -10 cm 2 Insufficient LiF coverage fails to effectively prevent direct contact between the highly active surface and the electrolyte, leading to intensified interfacial side reactions, continuous thickening of the CEI film, rapid increase in impedance during cycling, and accelerated capacity decay. When the LiF layer accounts for more than 70% of the mass percentage of the phosphorus-based dynamic interface layer, performance deteriorates significantly: volumetric energy density 777 Wh / L, initial charge-discharge efficiency 92.3%, 10C rate discharge specific capacity 137.2 mAh / g, 5C cycle capacity retention 97.1%, 200℃ mass loss 2.2%, and lithium-ion diffusion coefficient 8.3 × 10⁻⁶. -10 cm 2 / s. Excessive aggregation of LiF particles, even forming a continuous phase, significantly increases interfacial ion transport resistance due to the extremely low intrinsic lithium-ion conductivity, thus deteriorating rate performance. At the same time, a high proportion of LiF weakens the continuity and dynamic reconstruction capability of the amorphous phosphate matrix, causing the interface to lose its adaptive stress change and micro-damage repair function, making it prone to brittle cracking during cycling and reducing long-term stability.

[0096] Comparing Example 1 and Comparative Examples 8-9, it can be seen that when the cathode material includes a phosphorus-based dynamic interface layer (containing Li3PO3 and an amorphous LiPO3 layer and a crystalline dispersed phase of LiF), the performance is optimal: volumetric energy density 785 Wh / L, initial charge-discharge efficiency 92.6%, 10C rate discharge specific capacity 138.5 mAh / g, 5C cycle capacity retention 96.8%, 200℃ mass loss 2.1%, and lithium-ion diffusion coefficient 8.5 × 10⁻⁶. -10 cm 2 / s. A complete interface layer can simultaneously achieve structural protection, ion transport, and dynamic self-healing, maximizing electrochemical stability under high voltage.

[0097] When the cathode material does not include a phosphorus-based dynamic interface layer, the performance declines significantly: volumetric energy density 725 Wh / L, initial charge / discharge efficiency 88.9%, 10C rate discharge specific capacity 116.7 mAh / g, 5C cycle capacity retention 87.3%, 200℃ mass loss 4.3%, and lithium-ion diffusion coefficient 4.9 × 10⁻⁶. -10 cm 2 / s. Without an interface layer to protect the cathode surface, it is directly exposed to the high-voltage electrolyte, which can easily trigger violent side reactions, oxygen release, and structural collapse, leading to a sharp decline in capacity and cycle performance.

[0098] When the phosphorus-based dynamic interface layer does not include the LiF crystalline dispersion layer, the performance decreases significantly: volumetric energy density 738 Wh / L, initial charge / discharge efficiency 89.8%, 10C rate discharge specific capacity 123.2 mAh / g, 5C cycle capacity retention 89.8%, 200℃ mass loss 3.6%, and lithium-ion diffusion coefficient 5.9 × 10⁻⁶. -10 cm 2 / s. Without the passivation effect of LiF, the interface layer cannot effectively inhibit electrolyte oxidation and Co. 4+ Dissolution exacerbates side reactions and significantly reduces cycle stability and thermal stability.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cathode material, characterized in that: The cathode material comprises a core, a gradient heterovalent doped layer, and a phosphorus-based dynamic interface layer. The core comprises lithium cobalt oxide. The gradient heterovalent doped layer is located on the surface of the core and is Al. 3+ and Ti 4+ The co-doped lithium cobalt oxide layer has the chemical composition LiCo. 1-x (Al a Ti b ) x O2; The phosphorus-based dynamic interface layer covers the outside of the gradient heterovalent doped layer; The phosphorus-based dynamic interface layer includes, from the inside out, a phosphorus-doped transition layer, an amorphous Li3PO3-LiPO3 layer, and a LiF crystalline dispersion layer; The phosphorus-doped transition layer and the gradient heterovalent doped layer form a coherent interface; The chemical formula of the positive electrode material is LiCoO2@LiCo 1-x (Al a Ti b ) x O2@Li3PO3-LiPO3-LiF, where x satisfies 0.03≤x≤0.09, a+b=1 and a / b=1-2.

2. The cathode material according to claim 1, characterized in that: In the gradient heterovalent doped layer, the total doping amount of Al and Ti, expressed as a molar fraction of cobalt sites, is 3%–4% on the side closer to the core and 7%–9% on the side closer to the phosphorus-based dynamic interface layer.

3. The cathode material according to claim 1, characterized in that: The thickness of the phosphorus-based dynamic interface layer is 8-25 nm.

4. The cathode material according to claim 1, characterized in that: The molar mass ratio of Li3PO3 to LiPO3 in the Li3PO3-LiPO3 layer is 2-3:

1.

5. The cathode material according to claim 1, characterized in that: The LiF layer accounts for 30%-70% of the mass percentage of the phosphorus-based dynamic interface layer.

6. The method for preparing the cathode material according to any one of claims 1-5, characterized in that: Includes the following steps: Aluminum source, titanium source and lithium cobalt oxide powder are mixed to form a liquid, and after the first drying and the first sintering, gradient heterovalent doped lithium cobalt oxide is obtained; A gel solution was formed by mixing graded heterovalent doped lithium cobalt oxide with lithium dihydrogen phosphate, followed by a second drying and a second sintering to obtain a phosphorus-coated intermediate. A phosphorus-coated intermediate was electrochemically induced to generate a LiF layer in situ on its surface, thus obtaining a cathode material.

7. The method for preparing the cathode material according to claim 6, characterized in that: The aluminum source includes one or more of aluminum nitrate and aluminum isopropoxide; and / or, the titanium source includes one or more of tetrabutyl titanate and titanium nitrate.

8. The method for preparing the cathode material according to claim 6, characterized in that: The first drying process is a gradient temperature drying process, which includes a first temperature drying, a second temperature drying, and a third temperature drying. The first temperature drying is performed at a temperature of 50-70℃ for 1-2 hours; the second temperature drying is performed at a temperature of 80-100℃ for 1-2 hours; the third temperature drying is performed at a temperature of 120-140℃ for 1-2 hours; and / or, the first sintering temperature is 750-950℃ for 4-7 hours.

9. The method for preparing the cathode material according to claim 6, characterized in that: The second drying temperature is 120-140℃, and the second drying time is 2-4h; and / or, the second sintering temperature is 480-580℃, and the second sintering time is 2-4h.

10. A positive electrode plate, characterized in that: This includes the cathode material as described in any one of claims 1-5, or the cathode material prepared by the method described in any one of claims 6-9.

11. A battery, characterized in that: Including the cathode material as described in claim 10.

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