Ternary cathode materials, their preparation methods and applications

Abstract

This invention provides a ternary cathode material, its preparation method, and its applications. The ternary cathode material has a core-shell structure, including a core and a shell layer covering the surface of the core; the core is a metal-doped ternary cathode material; the chemical formula of the metal-doped ternary cathode material is LiNi. x Co y Mn z Ti p Zr q O2, wherein 0.8≤x≤0.95, 0.02≤y≤0.1, 0.015≤z≤0.06, 0.01≤p≤0.03, 0.005≤q≤0.02, and x+y+z+p+q=1; the shell is a metal oxide. The ternary cathode material of this invention, by simultaneously doping Ti and Zr into a high-nickel ternary cathode as a core, can significantly improve the structural strength and cycle life of the material; simultaneously, the shell can block electrolyte erosion, reduce surface side reactions, and inhibit residual lithium deposition, thereby improving the initial coulombic efficiency and rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode material technology, and more specifically, to a ternary cathode material, its preparation method, and its application. Background Technology

[0002] High-nickel ternary materials, as an important type of cathode material for lithium-ion batteries, have been widely used in electric vehicles and energy storage. With the increasing demand for battery energy density, high-nickel ternary materials (such as NCM or NCA systems with Ni content ≥80%) are gradually becoming the mainstream technology. In existing technologies, high-nickel ternary materials are mainly synthesized through a co-precipitation method to obtain precursors (such as Ni-Co-Mn hydroxide), which are then mixed and sintered with a lithium source. For example, existing technologies use nano-aluminum hydroxide and nano-zirconia as additives to mix with high-nickel precursors and lithium sources to improve the structural stability of the material. Additionally, there are methods to improve electrochemical performance by dissolving soluble cobalt salts and dispersing the high-nickel cathode material. Other existing solutions include vacuum heating treatment to remove residual lithium, using single-crystal technology, or doping modification to optimize material performance.

[0003] However, the aforementioned existing technologies still have significant drawbacks: on the one hand, the high nickel content (Ni≥80%) makes the materials extremely prone to cation mixing, lattice oxygen release, and phase transitions (such as H2 to H3 phase transition) during charge and discharge, which exacerbates the risk of structural collapse and thermal runaway; on the other hand, the alkaline lithium compounds remaining on the surface not only increase the pH value of the material, leading to slurry gelation and battery gas expansion, but also accelerate electrolyte decomposition, reducing the initial coulombic efficiency and rate performance; at the same time, single doping or single coating strategies are difficult to simultaneously take into account the stability of the bulk structure and the stability of the surface interface, making it difficult to improve cycle life and capacity retention, which seriously restricts its application in high-energy-density solid-state batteries. Summary of the Invention

[0004] The main objective of this invention is to provide a ternary cathode material, its preparation method, and its application, in order to solve the problems of low initial coulombic efficiency, poor rate performance, and poor cycle performance caused by the unstable structure and severe residual lithium in existing high-nickel ternary cathode materials.

[0005] To achieve the above objectives, according to one aspect of the present invention, a ternary cathode material is provided. The ternary cathode material has a core-shell structure, including a core and a shell covering the surface of the core. The core material includes a metal-doped ternary cathode material. The chemical formula of the metal-doped ternary cathode material is LiNixCoyMnzTipZrqO2, wherein 0.8≤x≤0.95, 0.02≤y≤0.1, 0.015≤z≤0.06, 0.01≤p≤0.03, 0.005≤q≤0.02, and x+y+z+p+q=1. The shell material includes a metal oxide, which includes one or more of aluminum oxide, cobalt oxide, and niobium pentoxide.

[0006] Furthermore, the core particle size Dv50 is 2~15μm; and / or, the shell thickness is 1~10nm; and / or, the metal oxide is granular, and the metal oxide particle size Dv50 is 5~500nm; and / or, in the metal-doped ternary cathode material, p:q is (0.5~3):1.

[0007] According to another aspect of the present invention, a method for preparing the above-mentioned ternary cathode material is provided, comprising the following steps: Step S1, according to the composition ratio of the metal-doped ternary cathode material in the core, a soluble nickel salt, a soluble cobalt salt, a soluble manganese salt, a titanium dopant, a first zirconium dopant, a complexing agent, a precipitant, a surfactant, and water are mixed to obtain a nickel-cobalt-manganese solution, and a co-precipitation reaction is performed to obtain a first precursor; Step S2, the first precursor, a lithium source, and a second zirconium dopant are mixed to obtain a second precursor; Step S3, the second precursor is sintered to obtain a core; Step S4, the core, a coating metal source, and a solvent are mixed to obtain a coating metal solution, and heat-treated to obtain a ternary cathode material; the coating metal source includes one or more of an aluminum source, a cobalt source, and a niobium source.

[0008] Further, in step S1, the soluble nickel salt includes one or more of NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O; and / or, the soluble cobalt salt includes one or more of CoSO4·7H2O, Co(NO3)2·6H2O, and CoCl2·6H2O; and / or, the soluble manganese salt includes one or more of MnSO4·H2O, Mn(NO3)2·4H2O, and MnCl2·4H2O; and / or, the titanium dopant includes Ti(SO4). 2. One or more of TiOSO4 and Ti(NO3)4; and / or, the first zirconium dopant includes one or more of Zr(NO3)4, ZrO(NO3)2 and Zr(SO4)2; and / or, the complexing agent includes one or more of NH3·H2O, ethylenediamine, triethanolamine and sodium EDTA; and / or, the precipitating agent includes one or more of NaOH, KOH, LiOH, sodium carbonate and sodium bicarbonate; and / or, the surfactant includes one or more of PVP, PEG, CTAB and SDS.

[0009] Further, the molar ratio of the first zirconium dopant to the soluble nickel salt is q1:x, 0.004≤q1≤0.019, and the molar ratio of the second zirconium dopant to the first precursor is q2:x, 0.001≤q2≤0.006, and q=q1+q2; and / or, in step S1, the molar concentration of the soluble nickel salt in the nickel-cobalt-manganese solution is 0.8~2mol / L; and / or, the molar ratio of the complexing agent to the soluble nickel salt is... The ratio of precipitant to soluble nickel salt is (0.5~3):1; and / or the molar ratio of precipitant to soluble nickel salt is (1.8~2.3):1; and / or the surfactant accounts for 0.1~5 wt% of the sum of the weights of soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant and first zirconium dopant; and / or the pH of the nickel-cobalt-manganese solution is 10~12; and / or the temperature of the coprecipitation reaction is 50~70℃ and the time is 4~12h.

[0010] Further, in step S2, the lithium source includes one or more of LiOH·H2O, LiOH, and Li2CO3; and / or, the second zirconium dopant includes one or more of ZrO2, Zr(OH)4, and ZrSiO4; and / or, the particle size Dv50 of the second zirconium dopant is 10~500nm; and / or, the molar ratio of lithium source to first precursor is (1.05~1.10):1; and / or, step S2 further includes a step of ball milling the first precursor and lithium source, wherein the ball-to-material ratio is (5~20):1, the speed is 200~800rpm, and the time is 2~4h.

[0011] Further, in step S3, sintering is carried out in an oxidizing atmosphere, which includes oxygen and / or air; and / or, sintering includes a first sintering, a second sintering, and a third sintering performed sequentially; and / or, in step S4, the coating metal source includes one or more of Al(NO3)3, Al2O3, Al(OH)3, Co(OH)2, and Nb2O5; and / or, the solvent includes one or more of ethanol, water, and isopropanol; and / or, the molar ratio of the coating metal source to the core is (0.001~0.02):1; and / or, the heat treatment temperature is 500~700℃, and the time is 1~12h.

[0012] Further, in step S3, the temperature of the first sintering is 400~600℃ and the time is 2~6h; and / or, the temperature of the second sintering is 700~900℃ and the time is 8~16h; and / or, the temperature of the third sintering is 300~500℃, the pressure is -0.07~-0.09MPa, and the time is 8~16h.

[0013] According to another aspect of the present invention, a positive electrode sheet is provided, comprising a positive electrode current collector and a positive electrode material active layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode material active layer comprises the ternary positive electrode material described above.

[0014] According to another aspect of the present invention, a solid-state battery is provided, comprising the above-described positive electrode.

[0015] Applying the technical solution of this invention, the ternary cathode material adopts a core-shell structure design, with the core being LiNi doped with a specific metal. x Co y Mn z Ti p Zr q O2 materials, by simultaneously doping Ti and Zr into high-nickel (0.8≤x≤0.95) ternary cathodes, can effectively enhance the stability of the crystal structure, significantly suppress phase transitions and oxygen release during charge-discharge cycles, thereby significantly improving the structural strength and cycle life of the material. Simultaneously, the metal oxide shell coating the core surface forms a protective barrier, effectively preventing electrolyte erosion of the core, reducing surface side reactions, and significantly suppressing the precipitation of residual lithium compounds, thus greatly improving the initial coulombic efficiency and rate performance. This core-shell structure synergistically optimizes both structural and interfacial stability, enabling high-nickel materials to maintain excellent electrochemical performance even under high-energy-density application conditions. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 The SEM image of the ternary cathode material according to Embodiment 1 of the present invention is shown;

[0018] Figure 2 The SEM image of the ternary cathode material according to Embodiment 1 of the present invention is shown;

[0019] Figure 3 An EDS diagram of element Al in the ternary cathode material according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0021] As described in the background section of this invention, existing technologies suffer from problems such as unstable high-nickel ternary cathode materials, low initial coulombic efficiency, and poor rate and cycle performance due to severe residual lithium. To address these issues, in a typical embodiment of this invention, a ternary cathode material is provided. This ternary cathode material has a core-shell structure, including a core and a shell layer covering the surface of the core. The core material comprises a metal-doped ternary cathode material. The chemical formula of the metal-doped ternary cathode material is LiNi. x Co y Mn z Ti p Zr q O2, wherein 0.8≤x≤0.95, 0.02≤y≤0.1, 0.015≤z≤0.06, 0.01≤p≤0.03, 0.005≤q≤0.02, and x+y+z+p+q=1; the shell material includes metal oxides, which include one or more of aluminum oxide, cobalt oxide, and niobium pentoxide.

[0022] The ternary cathode material of this invention adopts a core-shell structure design, including a core and a shell layer covering the surface of the core. The core is a metal-doped ternary cathode material with the chemical formula LiNi. x Co y Mn z Ti p Zr qO2, by simultaneously doping Ti and Zr into high-nickel (0.8≤x≤0.95) ternary cathodes, can effectively enhance the stability of the crystal structure, significantly suppress phase transitions and oxygen release during charge-discharge cycles, thereby significantly improving the structural strength and cycle life of the material. Simultaneously, the metal oxide shell coating the core surface forms a protective barrier, effectively preventing electrolyte erosion of the core, reducing surface side reactions, and significantly suppressing the precipitation of residual lithium compounds, thus greatly improving the initial coulombic efficiency and rate performance. This core-shell structure synergistically optimizes both structural and interfacial stability, enabling high-nickel materials to maintain excellent electrochemical performance under high energy density applications. Limiting the contents of Co and Mn, and the doping amounts of Ti and Zr within the aforementioned ranges, can further optimize the role of each element in the cathode material, thereby further improving its electrochemical performance.

[0023] In a preferred embodiment, the core particle size Dv50 is 2~15 μm; and / or, the shell thickness is 1~10 nm; and / or, the metal oxide is particulate, and the metal oxide particle size Dv50 is 5~500 nm; and / or, in the metal-doped ternary cathode material, p:q is (0.5~3):1; and / or, 0.02≤p+q≤0.05. In some embodiments, the core particle size Dv50 is 7.5~15 μm. In some embodiments, the ratio of core particle size to shell thickness is (938~14200):1.

[0024] Controlling the core particle size Dv50 within the aforementioned range further promotes uniform particle growth and densification, improving the material's tap density and charge transport efficiency. The set shell thickness is more conducive to forming a continuous, dense, and thin oxide coating structure, which can more effectively prevent direct contact between the electrolyte and active materials, thereby further improving cycle stability. The aforementioned nanoscale metal oxides further promote uniform coverage and high-density adhesion of the coating on the particle surface, enhancing interfacial stability. The better matching of the metal oxide particle size Dv50 with the core makes it easier for the coating to be uniformly dispersed and firmly adhered to the particle surface, reducing interfacial side reactions.

[0025] When the ratio of core particle size to shell thickness falls within the aforementioned range, stress distribution can be further optimized, thereby further suppressing microcrack propagation during charging and discharging and improving the volume stability of the cathode material. Controlling the shell weight percentage within the aforementioned range makes it easier to achieve a balance between coating functionality and active material capacity, further reducing capacity loss due to excessive coating thickness. The synergistic effect of the metal doping element ratio p:q within the aforementioned range can further promote precise control of lattice distortion and improve structural thermal stability. A total metal doping amount satisfying 0.02 ≤ p + q ≤ 0.05 is more conducive to maintaining crystal integrity while further enhancing ion diffusion capabilities, comprehensively improving the overall performance of the material.

[0026] In another typical embodiment of the present invention, a method for preparing the above-mentioned ternary cathode material is also provided, comprising the following steps: Step S1, according to the composition ratio of the metal-doped ternary cathode material in the core, a soluble nickel salt, a soluble cobalt salt, a soluble manganese salt, a titanium dopant, a first zirconium dopant, a complexing agent, a precipitant, a surfactant, and water are mixed to obtain a nickel-cobalt-manganese solution, and a co-precipitation reaction is performed to obtain a first precursor; Step S2, the first precursor, a lithium source, and a second zirconium dopant are mixed to obtain a second precursor; Step S3, the second precursor is sintered to obtain a core; Step S4, the core, a coating metal source, and a solvent are mixed to obtain a coating metal solution, and heat-treated to obtain a ternary cathode material; the coating metal source includes one or more of an aluminum source, a cobalt source, and a niobium source.

[0027] First, according to the composition ratio of the metal-doped ternary cathode material in the core, soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, and first zirconium dopant are mixed, with a molar ratio of x:y:z:p:q1, where q1 is the zirconium content provided by the first zirconium dopant, and 0 < q1 < q. The above raw materials are then mixed with a complexing agent, a precipitant, a surfactant, and water to obtain a nickel-cobalt-manganese solution. The soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, and first zirconium dopant undergo a co-precipitation reaction in the alkaline environment provided by the complexing agent and precipitant, forming a Ni-Co-Mn hydroxide containing partially doped metals, thus obtaining the first precursor.

[0028] Then, the first precursor, lithium source, and second zirconium dopant are mixed. The second zirconium dopant and the first zirconium dopant together provide zirconium element for the metal-doped ternary cathode material. q2 is the zirconium element content provided by the second zirconium dopant, and 0 < q2 < q, and q = q1 + q2. The above raw materials are thoroughly mixed. The secondary doping of Zr enhances the lattice stability and can avoid high-temperature phase transformation during subsequent sintering, forming Ni-Co-Mn hydroxide containing all doped metals, thus obtaining the second precursor.

[0029] The second precursor is sintered. During the sintering process, the Ni-Co-Mn hydroxide containing all the doped metals undergoes crystal phase rearrangement and lithium-ion intercalation reaction in a high-temperature oxygen atmosphere. This results in Ni, Co, Mn and doped elements Ti and Zr forming an ordered layered structure, which promotes the growth of a dense single crystal or near-single crystal core. This effectively suppresses grain boundary defects and oxygen vacancies, resulting in a stable core with consistent crystal orientation. This core has excellent electronic conductivity and lithium-ion diffusion channels, providing a highly active, low-defect substrate for subsequent surface coatings, which is more conducive to achieving a synergistic enhancement effect between the coating and the core.

[0030] Finally, the core, the coating metal source, and the solvent are mixed to obtain a coating metal solution, which allows the coating metal source to fully contact the core surface. Heat treatment is then performed, causing the coating metal to be oxidized in situ on the core surface under heating conditions, forming a metal oxide that coats the core surface, thus obtaining a ternary cathode material.

[0031] This invention introduces titanium and zirconium as dopants, and introduces zirconium in two steps. This allows for phased lattice structure stability during the precursor synthesis and mixing / sintering stages, effectively suppressing cation mixing and oxygen release during the charge / discharge process of the high-nickel system, and improving the crystal structure integrity of the ternary cathode material. Using an independent zirconium source added during the mixing stage promotes its uniform distribution in the grain boundary region during sintering, enhancing grain bonding. Subsequently, coating the surface with a metal oxide precursor and then heat-treating to form a dense alumina coating effectively isolates the electrolyte from direct contact with the active material, reducing surface side reactions and residual lithium formation, and synergistically improving the material's cycle stability and processing safety. This process path effectively avoids the uneven element distribution or coating failure problems that may occur with traditional one-step mixing methods, enabling the material to maintain high capacity output and long cycle life even with high nickel content, making it suitable for the industrial production needs of high-energy-density lithium-ion batteries.

[0032] In a preferred embodiment, in step S1, the soluble nickel salt includes one or more of NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O; and / or, the soluble cobalt salt includes one or more of CoSO4·7H2O, Co(NO3)2·6H2O, and CoCl2·6H2O; and / or, the soluble manganese salt includes one or more of MnSO4·H2O, Mn(NO3)2·4H2O, and MnCl2·4H2O; and / or, the titanium dopant includes one or more of Ti(SO4)2, TiOSO4, and Ti(NO3)4. One or more; and / or, the first zirconium dopant includes one or more of Zr(NO3)4, ZrO(NO3)2 and Zr(SO4)2; and / or, the complexing agent includes one or more of NH3·H2O, ethylenediamine, triethanolamine and sodium EDTA (sodium ethylenediaminetetraacetate); and / or, the precipitating agent includes one or more of NaOH, KOH, LiOH, sodium carbonate and sodium bicarbonate; and / or, the surfactant includes one or more of PVP (polyvinylpyrrolidone), PEG (polyethylene glycol), CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate).

[0033] Using the above-mentioned types of soluble nickel salts can further promote the uniform release of nickel ions and further reduce particle agglomeration caused by excessively high local concentrations. Using the above-mentioned types of soluble cobalt salts makes it easier to achieve uniform cobalt distribution in the crystal lattice and improves electronic conductivity. Using the above-mentioned types of soluble manganese salts can further enhance structural stability and suppress the aberrant transformation from layered to spinel phase. Using the above-mentioned types of titanium dopants is more conducive to achieving stable titanium incorporation in the crystal lattice and effectively suppressing phase transitions. Using the above-mentioned types of zirconium dopants can further promote the enrichment of zirconium ions at grain boundaries and enhance the lattice's resistance to deformation. Using the above-mentioned types of complexing agents makes it easier to control the precipitation rate and obtain precursors with uniform morphology. Using the above-mentioned types of precipitants further improves the controllability of the precipitation reaction. Using the above-mentioned types of surfactants makes it easier to control the particle morphology of co-precipitates, is more conducive to achieving single crystallization tendency, and thus significantly improves the structural consistency of the precursor and subsequent sintering activity.

[0034] In a preferred embodiment, the molar ratio of the first zirconium dopant to the soluble nickel salt is q1:x, 0.004≤q1≤0.019, and the molar ratio of the second zirconium dopant to the first precursor is q2:x, 0.001≤q2≤0.006, and q=q1+q2; and / or, in step S1, the molar concentration of the soluble nickel salt in the nickel-cobalt-manganese solution is 0.8~2mol / L; and / or, the molar concentration of the complexing agent to the soluble nickel salt is... The molar ratio of the precipitant to the soluble nickel salt is (0.5~3):1; and / or the molar ratio of the precipitant to the soluble nickel salt is (1.8~2.3):1; and / or the surfactant accounts for 0.1~5 wt% of the sum of the weights of the soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, and first zirconium dopant; and / or the pH of the nickel-cobalt-manganese solution is 10~12; and / or the temperature of the coprecipitation reaction is 50~70℃ and the time is 4~12h.

[0035] Maintaining the molar concentration of soluble nickel salt in the nickel-cobalt-manganese solution within the aforementioned range further promotes uniform nucleation and slow growth of precursor particles, reducing agglomeration caused by excessively high concentrations or morphological irregularities caused by excessively low concentrations. Controlling the molar ratio of the complexing agent to the nickel salt within an appropriate range facilitates the slow release of metal ions, enhancing the controllability of the precipitation process and resulting in precursors with narrower particle size distributions. A more suitable molar ratio of the precipitant to the nickel salt further improves the stability of the precipitation reaction and reduces heterogeneous nucleation phenomena caused by localized supersaturation.

[0036] The aforementioned molar ratio of surfactant to nickel salt is more conducive to adsorption onto the surface of coprecipitate particles, regulating crystal growth direction, inhibiting agglomeration, and guiding the formation of single crystals. Maintaining the pH of the nickel-cobalt-manganese solution within the aforementioned range further promotes precise precipitation of hydroxides and reduces byproduct formation or metal ion residues. Controlling the coprecipitation reaction temperature within the aforementioned range facilitates better matching of reaction kinetics and thermodynamics, improving crystallinity. Extending the reaction time to the aforementioned range further promotes the complete coprecipitation reaction, resulting in a more complete morphology and denser structure of the precipitate, thereby comprehensively improving the overall quality of the precursor and its subsequent sintering activity.

[0037] In a preferred embodiment, in step S2, the lithium source includes one or more of LiOH·H2O, LiOH, and Li2CO3; and / or, the second zirconium dopant includes one or more of ZrO2, Zr(OH)4, and ZrSiO4; and / or, the particle size Dv50 of the second zirconium dopant is 10~500nm; and / or, the molar ratio of lithium source to first precursor is (1.05~1.10):1; and / or, step S2 further includes a step of ball milling the first precursor and lithium source, wherein the ball-to-material ratio is (5~20):1, the speed is 200~800rpm, and the time is 2~4h.

[0038] Using the aforementioned lithium source facilitates a more thorough solid-state reaction between lithium and the precursor at high temperatures, reducing the risk of residual lithium formation. The use of the same zirconium dopant further promotes its uniform dispersion at the grain boundaries, enhancing lattice distortion resistance. Controlling its particle size within the appropriate nanometer range is more conducive to achieving synergistic strengthening of the nanoscale interface, further reducing stress concentration caused by large particles, and further improving the volume stability of the core. In the ball milling process, a reasonable match between the ball-to-material ratio and rotation speed is more conducive to achieving uniform mixing and microstructure activation of the materials, avoiding local agglomeration, improving sintering activity, and making subsequent phase transformation more uniform and efficient.

[0039] Maintaining the molar ratio of lithium source to first precursor within the aforementioned range further enhances the stoichiometric matching of lithium, thus better suppressing cation mixing. Optimizing the molar ratio of second zirconium dopant to precursor (q2:x) facilitates the formation of stable doping sites for zirconium in the crystal lattice, improving structural integrity. The coordinated design of the molar ratio of first to second zirconium dopant (q1:q2) further promotes the gradient distribution of zirconium both in the bulk and on the surface, making it easier to achieve the dual effect of "strong internal structure and stable external structure."

[0040] In a preferred embodiment, in step S3, sintering is carried out in an oxidizing atmosphere, which includes oxygen and / or air; and / or, sintering includes a first sintering, a second sintering, and a third sintering performed sequentially; and / or, in step S4, the coating metal source includes one or more of Al(NO3)3, Al2O3, Al(OH)3, Co(OH)2, and Nb2O5; and / or, the solvent includes one or more of ethanol, water, and isopropanol; and / or, the molar ratio of the coating metal source to the core is (0.001~0.02):1; and / or, the heat treatment temperature is 500~700℃, and the time is 1~3h.

[0041] Sintering is carried out in an oxidizing atmosphere, which further promotes the repair of oxygen vacancies in the crystal lattice and inhibits structural collapse caused by the reduction of high-valence nickel, thus providing a better foundation for maintaining the integrity of the layered structure. The sintering process employs segmented first, second, and third sintering stages. Segmented sintering further slows down the crystallization rate, which is more conducive to improving the controllability of phase transformation, further reducing the formation of microcracks caused by sudden thermal stress changes, and improving volume stability. The selection of the aforementioned types of coating metal sources facilitates the uniform adsorption of aluminum precursors on the core surface, thereby making it easier to form a continuous and dense oxide layer.

[0042] Using the aforementioned solvents can further improve the dispersibility of the coating precursor and reduce uneven coating caused by agglomeration. A properly controlled molar ratio of the coating metal source to the core is more conducive to forming a coating with nanoscale thickness, effectively blocking electrolyte penetration without significantly hindering lithium-ion transport. Controlling the heat treatment conditions within the aforementioned range can further promote the full oxidation reaction of the aluminum source, while further reducing excessive sintering or surface reconstruction of the core, making it easier for the coating to form a strong interfacial bond with the bulk lattice, synergistically improving cycle stability and interfacial compatibility.

[0043] In a preferred embodiment, in step S3, the temperature of the first sintering is 400~600℃ and the time is 2~6h; and / or, the temperature of the second sintering is 700~900℃ and the time is 8~16h; and / or, the temperature of the third sintering is 300~500℃, the pressure is -0.07~-0.09MPa, and the time is 8~16h.

[0044] The first sintering under the aforementioned conditions can further promote the gentle removal of residual moisture and organic matter in the precursor, avoiding particle breakage or loose structure caused by violent volatilization, and is more conducive to maintaining the integrity of the particle morphology. The second sintering under the aforementioned conditions can further improve the lattice insertion efficiency of lithium ions and transition metals, promote the ordered growth of layered structures, and make it easier to reduce the defect density inside the crystal and grow the grains appropriately without excessive densification.

[0045] The third sintering, conducted under the aforementioned vacuum environment, further promotes the thermal decomposition and volatilization of surface lithium compounds, significantly reduces the surface alkalinity of the material, and is more conducive to improving slurry dispersibility and battery processing safety. This vacuum delithiation stage, in conjunction with the preceding segmented high-temperature sintering, forms a gradient synergy, further reducing oxygen loss and surface reconstruction phenomena caused by traditional single high-temperature treatment. This allows the material to maintain a stable bulk structure while forming a more stable surface chemical environment, further reducing side reactions between the cathode material and the electrolyte, thereby significantly enhancing the overall electrochemical compatibility and long-term cycle reliability of the material.

[0046] In another typical embodiment of the present invention, a positive electrode sheet is also provided, comprising a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector, wherein the positive electrode material active layer comprises the aforementioned ternary positive electrode material. Because the positive electrode material active layer of the positive electrode sheet comprises a ternary positive electrode material, the rate performance and cycle performance of the positive electrode sheet are significantly improved.

[0047] Because the positive electrode material active layer of the cathode sheet includes ternary cathode material, its high nickel content imparts high specific capacity, and the synergistic enhancement of structural stability by composite doping significantly improves the energy density and cycle durability of the cathode sheet. Simultaneously, the surface nano-oxide coating effectively suppresses side reactions and interfacial impedance growth in the electrolyte, which is more conducive to maintaining the chemical stability of the electrode-electrolyte interface, thereby further improving rate performance and safety performance. Furthermore, the deep removal of residual lithium significantly reduces the surface alkalinity of the material, making it easier for the slurry to maintain good rheological properties during coating, reducing the risk of bubbles and powder shedding, thus optimizing the overall processing performance of the cathode sheet.

[0048] In another typical embodiment of the present invention, a solid-state battery is also provided, including the above-described positive electrode. Due to the inclusion of the positive electrode, the processing performance, rate performance, and cycle performance of the solid-state battery of the present invention are significantly improved.

[0049] In typical, but not limiting, metal-doped ternary cathode materials, the p:q ratio is 0.5:1, 0.8:1, 1.1:1, 1.3:1, 1.6:1, 1.9:1, 2.2:1, 2.4:1, 2.7:1, 3.0:1, or any two of these values. The molar ratio of the first zirconium dopant to the soluble nickel salt is q1:x, where q1 is 0.004, 0.006, 0.007, 0.009, 0.011, 0.012, 0.014, 0.016, 0.017, 0.019, or any two of these values. The molar ratio of the second zirconium dopant to the first precursor is q2:x, where q2 is 0.001≤q2≤0.006 and q=q1+q2; and / or, a range of values ​​consisting of 0.001, 0.002, 0.003, 0.004, 0.005, 0.006 or any two of these values.

[0050] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0051] Example 1

[0052] Step S1: Soluble nickel salt (NiSO4·6H2O), soluble cobalt salt (CoSO4·7H2O), soluble manganese salt (MnSO4·H2O), titanium dopant (Ti(SO4)2), and first zirconium dopant (Zr(NO3)4) are mixed with water in a molar ratio of x:y:z:p:q1. Then, a complexing agent (NH3·H2O), a precipitant (NaOH), and a surfactant (PVP) are added to obtain the molar concentration of the soluble nickel salt. A nickel-cobalt-manganese solution with a concentration of 1.5 mol / L was subjected to a co-precipitation reaction at pH 11.0 and a temperature of 60 °C for 8 h to obtain the first precursor. The molar ratio of the complexing agent to the soluble nickel salt was 1.5:1, the molar ratio of the precipitant to the soluble nickel salt was 2.0:1, and the surfactant accounted for 2.5 wt% of the sum of the weights of the soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, and the first zirconium dopant. The values ​​of x, y, z, p, and q1 are shown in Table 1.

[0053] Step S2: The first precursor, lithium source (LiOH·H2O), and second zirconium dopant (ZrO2, particle size 50nm) are mixed to obtain a mixture, wherein the molar ratio of lithium source to first precursor is 1.08:1, and the molar ratio of second zirconium dopant to first precursor is q2:x=0.003:x; the mixture is ball-milled at a ball-to-material ratio of 10:1, a speed of 500rpm, and a time of 3h to obtain the second precursor.

[0054] Step S3: Under an oxygen atmosphere, the second precursor is sintered at 500°C for 4 hours to remove moisture, then sintered at 800°C for 12 hours. After cooling to room temperature, it is heated to 400°C under a vacuum of -0.08MPa and sintered for 12 hours to remove residual lithium, thus obtaining the core.

[0055] Step S4: The coated metal source (Al(NO3)3) and the core are dissolved in a solvent (ethanol, 100 mL) at a molar ratio of 0.01:1 to obtain a coated metal solution. The solution is then heat-treated at 600℃ for 6 h to obtain a ternary cathode material.

[0056] Example 2

[0057] The difference from Example 1 is that,

[0058] In step S1, the values ​​of x, y, z, p, and q1 are different, as detailed in Table 1;

[0059] In step S2, the value of q2 varies, as detailed in Table 1;

[0060] In step S4, the molar ratio of the coating metal source (Al(NO3)3) to the core is 0.001:1.

[0061] Example 3

[0062] The difference from Example 1 is that,

[0063] In step S1, the values ​​of x, y, z, p, and q1 are different, as detailed in Table 1;

[0064] In step S2, the value of q2 varies, as detailed in Table 1;

[0065] In step S4, the molar ratio of the core to the coating metal source (Al(NO3)3) is 0.02:1.

[0066] Example 4

[0067] The difference from Example 1 is that,

[0068] In step S1, the soluble nickel salt is Ni(NO3)2·6H2O, the soluble cobalt salt is Co(NO3)2·6H2O, the soluble manganese salt is Mn(NO3)2·4H2O, the titanium dopant is Ti(NO3)4, the first zirconium dopant is ZrO(NO3)2, the complexing agent is ethylenediamine, the precipitant is sodium carbonate, and the surfactant is PEG; the values ​​of x, y, z, p, and q1 are different, as detailed in Table 1.

[0069] In step S2, the value of q2 varies, as shown in Table 1.

[0070] Example 5

[0071] The difference from Example 1 is that,

[0072] In step S1, the soluble nickel salt is NiCl2·6H2O, the soluble cobalt salt is CoCl2·6H2O, the soluble manganese salt is MnCl2·4H2O, the titanium dopant is TiOSO4, the first zirconium dopant is Zr(SO4)2, the complexing agent is sodium EDTA, the precipitant is sodium bicarbonate, and the surfactant is CTAB; the values ​​of x, y, z, p, and q1 are different, as detailed in Table 1.

[0073] In step S2, the value of q2 varies, as shown in Table 1.

[0074] Example 6

[0075] The difference from Example 1 is that,

[0076] In step S1, the values ​​of x, y, z, p, and q1 are different, as detailed in Table 1;

[0077] In step S2, the value of q2 varies, as shown in Table 1.

[0078] Example 7

[0079] The difference from Example 1 is that,

[0080] In step S1, triethanolamine is used as the complexing agent, LiOH is used as the precipitant, and SDS is used as the surfactant. The amount of water added is adjusted so that the molar concentration of soluble nickel salt in the nickel-cobalt-manganese solution is 0.8 mol / L. The amounts of complexing agent and precipitant added are adjusted so that the molar ratio of complexing agent to soluble nickel salt is 0.5:1 and the molar ratio of precipitant to soluble nickel salt is 1.8:1.

[0081] In step S2, the lithium source is Li2CO3, the second zirconium dopant is Zr(OH)4, the particle size Dv50 of the second zirconium dopant is 10nm, and the amount of lithium source added is adjusted so that the molar ratio of lithium source to first precursor is 1.05:1; the ball-to-material ratio of ball milling is 5:1, the speed is 200rpm, and the time is 4h.

[0082] Example 8

[0083] The difference from Example 1 is that,

[0084] In step S1, the amount of water added is adjusted so that the molar concentration of soluble nickel salt in the nickel-cobalt-manganese solution is 2 mol / L; the amount of complexing agent and precipitant added is adjusted so that the molar ratio of complexing agent to soluble nickel salt is 3:1 and the molar ratio of precipitant to soluble nickel salt is 2.3:1.

[0085] In step S2, the second zirconium dopant is ZrSiO4, and the particle size Dv50 of the second zirconium dopant is 500 nm. The amount of lithium source added is adjusted so that the molar ratio of lithium source to first precursor is 1.1:1. The ball-to-material ratio of ball milling is 20:1, the speed is 800 rpm, and the time is 2 h.

[0086] Example 9

[0087] The difference from Example 1 is that,

[0088] In step S1, the amount of surfactant added is adjusted so that the surfactant accounts for 0.1 wt% of the sum of the weights of the soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, and first zirconium dopant; the amount of precipitant added is adjusted so that the pH value of the nickel-cobalt-manganese solution is 10; the temperature of the coprecipitation reaction is 50℃ and the time is 12h.

[0089] In step S3, the second precursor is sintered for 6 hours at 400°C in an air atmosphere, then sintered for 16 hours at 700°C, cooled to room temperature, heated to 300°C under a vacuum of -0.07MPa, and sintered for 16 hours.

[0090] In step S4, the coating metal source is Co(OH)2, the solvent is isopropanol, and the heat treatment temperature is 500℃ for 12 hours.

[0091] Example 10

[0092] The difference from Example 1 is that,

[0093] In step S1, the amount of surfactant added is adjusted so that the surfactant accounts for 5 wt% of the sum of the weights of the soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant and first zirconium dopant; the amount of precipitant added is adjusted so that the pH value of the nickel-cobalt-manganese solution is 12; the temperature of the coprecipitation reaction is 70℃ and the time is 4h.

[0094] In step S3, the second precursor is sintered for 2 hours at 600°C in an air atmosphere, then sintered for 8 hours at 900°C, cooled to room temperature, heated to 500°C under a vacuum of -0.09MPa, and sintered for 8 hours.

[0095] In step S4, the coating metal source is Nb2O5, the solvent is water, and the heat treatment temperature is 700℃ for 1 hour.

[0096] Comparative Example 1

[0097] The existing high-nickel NCM ternary material has the chemical formula LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0098] Comparative Example 2

[0099] The difference from Example 1 is that step S4 is omitted, and the core is obtained as a ternary cathode material.

[0100] Comparative Example 3

[0101] The difference from Example 1 is that in step S2, no second zirconium dopant is added, and the first precursor is mixed with the lithium source to obtain the second precursor.

[0102] Performance testing:

[0103] The ternary cathode materials prepared in the above embodiments and comparative examples were analyzed and tested as follows, and the results are shown in Tables 2 and 3.

[0104] 1. Material particle size Dv50: The material particle size Dv50 is determined using a laser particle size analyzer. The sample is dispersed in anhydrous ethanol and tested after ultrasonic dispersion. The particle size corresponding to a cumulative volume distribution of 50% is taken as Dv50.

[0105] 2. Shell thickness: The shell thickness was measured using a high-resolution transmission electron microscope (HRTEM). At least 20 locations were randomly selected on the surface of different particles to measure the coating thickness, and the average value was taken as the shell thickness.

[0106] Artificial graphite, carbon black, and PVDF were mixed in a weight ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to serve as the negative electrode of a lithium-ion battery. The separator was a polypropylene microporous membrane, and the electrolyte was a 1 mol / L LiPF6 solution with an electrolyte solvent ratio of EC:DMC:EMC = 1:1:1 (v / v / v). The positive electrode sheet from the embodiments and comparative examples of this invention was assembled with the above components to form a 3Ah pouch battery.

[0107] 3. Initial discharge specific capacity: After the battery has been left to stand at 25℃ for 12 hours, a first charge-discharge test is performed at a rate of 0.1C. The charging cutoff voltage is 4.3V, and the discharging cutoff voltage is 2.8V. Record the initial discharge capacity and calculate the initial discharge specific capacity based on the mass of the positive electrode active material.

[0108] 4. Battery Cycle Performance: After the battery was left to stand at 25℃ for 12 hours, it underwent three activation cycles at a 0.1C rate. Subsequently, constant current and constant voltage charging and discharging cycle tests were performed at a 0.5C rate within a voltage range of 2.8V to 4.3V. The discharge capacity at the 500th and 1000th cycles were recorded, and the corresponding capacity retention rates were calculated. 500-cycle retention rate = Discharge capacity at the 500th cycle ÷ Initial discharge capacity; 1000-cycle retention rate = Discharge capacity at the 1000th cycle ÷ Initial discharge capacity.

[0109] 5. Battery Rate Performance: After the battery was left to stand at 25℃ for 12 hours, it was first activated by three charge-discharge cycles at a 0.1C current. Then, charge-discharge tests were conducted at 0.2C and 2C rates. The charging method was constant current and constant voltage charging to 4.3V, with a cutoff current of 0.05C; the discharge cutoff voltage was 2.8V. The discharge capacity was recorded, and the capacity retention rate at 2C rate was calculated using the discharge capacity at 0.2C rate as the baseline. 2C rate capacity retention rate = (2C discharge capacity / 0.2C discharge capacity) × 100%.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] Table 3

[0115]

[0116] SEM image of the ternary cathode material in Embodiment 1 of the present invention is shown below. Figure 1 As shown, the ternary cathode material has a particle size of 9.5 μm and a distinct coating layer on its surface. The SEM image and corresponding EDS image of the ternary cathode material in Example 1 of this invention are shown below. Figure 2 and Figure 3 As shown, the Al element is uniformly distributed on the particle surface, indicating that the Al element coating was successful.

[0117] As can be seen, Comparative Example 1, due to the lack of Ti and Zr doping and alumina coating treatment, is prone to cation mixing, lattice oxygen release, and H2-H3 phase transition during charge and discharge, resulting in decreased crystal structure stability. At the same time, the material surface is in direct contact with the electrolyte, which exacerbates side reactions and further leads to rapid capacity decay during cycling. Therefore, its initial discharge capacity, rate performance, and cycle retention rate are the lowest.

[0118] Although Comparative Example 2 underwent Ti and Zr doping modification, it did not undergo alumina coating treatment, resulting in a lack of an effective protective layer on the material surface. This made it easy for the electrolyte to undergo side reactions with the active material, leading to a continuous increase in interfacial impedance and an intensified reaction between residual lithium and the electrolyte. Consequently, its rate performance and cycle performance were significantly lower than those of the embodiments of the present invention.

[0119] Although Comparative Example 3 was doped with Ti and Zr and coated with alumina, the one-time addition of Zr to the precursor system resulted in uneven distribution of zirconium elements inside the particles and at the grain boundaries, making it difficult to fully exert the effects of lattice stabilization and grain boundary strengthening. In contrast, the present invention adopts a two-step method to introduce zirconium elements, which makes the zirconium elements form a more reasonable distribution in the bulk phase and grain boundary regions. This can effectively suppress structural degradation and microcrack propagation during cycling. Therefore, its cycling performance, especially the long-cycle retention rate, is significantly better than that of Comparative Example 3.

[0120] In summary, this invention achieves a simultaneous improvement in bulk structural stability and surface interface stability through the synergistic design of Ti and Zr co-doping, two-step introduction of zirconium, and surface alumina coating. This results in a ternary cathode material that possesses both high initial discharge capacity, excellent rate performance, and long-term cycle stability.

[0121] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the present 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 ternary cathode material has a core-shell structure, including a core and a shell covering the surface of the core; The core material includes a metal-doped ternary cathode material; the chemical formula of the metal-doped ternary cathode material is LiNi. x Co y Mn z Ti p Zr q O2, where 0.8≤x≤0.95, 0.02≤y≤0.1, 0.015≤z≤0.06, 0.01≤p≤0.03, 0.005≤q≤0.02, and x+y+z+p+q=1; The shell material includes metal oxides, which include one or more of aluminum oxide, cobalt oxide, and niobium pentoxide.

2. The ternary cathode material according to claim 1, characterized in that, The kernel's particle size Dv50 is 2~15μm; and / or, The thickness of the shell layer is 1~10 nm; and / or, The metal oxide is in particulate form, and the particle size Dv50 of the metal oxide is 5~500 nm; and / or, In the metal-doped ternary cathode material, the p:q ratio is (0.5~3):

1.

3. The method for preparing the ternary cathode material according to claim 1 or 2, characterized in that, Includes the following steps: Step S1: According to the composition ratio of the metal-doped ternary cathode material in the core, soluble nickel salt, soluble cobalt salt, soluble manganese salt, titanium dopant, first zirconium dopant, complexing agent, precipitant, surfactant and water are mixed to obtain a nickel-cobalt-manganese solution, and a co-precipitation reaction is carried out to obtain the first precursor. Step S2: Mix the first precursor, the lithium source, and the second zirconium dopant to obtain the second precursor; Step S3: Sinter the second precursor to obtain the core; Step S4: Mix the core, the coating metal source, and the solvent to obtain a coating metal solution, and perform heat treatment to obtain the ternary cathode material; the coating metal source includes one or more of aluminum source, cobalt source, and niobium source.

4. The method for preparing the ternary cathode material according to claim 3, characterized in that, In step S1 The soluble nickel salt includes one or more of NiSO4·6H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O; and / or, The soluble cobalt salt includes one or more of CoSO4·7H2O, Co(NO3)2·6H2O, and CoCl2·6H2O; and / or, The soluble manganese salt includes one or more of MnSO4·H2O, Mn(NO3)2·4H2O, and MnCl2·4H2O; and / or, The titanium dopant includes one or more of Ti(SO4)2, TiOSO4, and Ti(NO3)4; and / or, The first zirconium dopant includes one or more of Zr(NO3)4, ZrO(NO3)2, and Zr(SO4)2; and / or, The complexing agent includes one or more of NH3·H2O, ethylenediamine, triethanolamine, and sodium EDTA; and / or, The precipitant includes one or more of NaOH, KOH, LiOH, sodium carbonate, and sodium bicarbonate; and / or, The surfactant includes one or more of PVP, PEG, CTAB, and SDS.

5. The method for preparing the ternary cathode material according to claim 3, characterized in that, The molar ratio of the first zirconium dopant to the soluble nickel salt is q1:x, 0.004 ≤ q1 ≤ 0.019; the molar ratio of the second zirconium dopant to the first precursor is q2:x, 0.001 ≤ q2 ≤ 0.006, and q = q1 + q2; and / or, In step S1 In the nickel-cobalt-manganese solution, the molar concentration of the soluble nickel salt is 0.8~2 mol / L; and / or, The molar ratio of the complexing agent to the soluble nickel salt is (0.5~3):1; and / or, The molar ratio of the precipitant to the soluble nickel salt is (1.8~2.3):1; and / or, The surfactant comprises 0.1 to 5 wt% of the sum of the weights of the soluble nickel salt, the soluble cobalt salt, the soluble manganese salt, the titanium dopant, and the first zirconium dopant; and / or, The pH value of the nickel-cobalt-manganese solution is 10-12; and / or, The coprecipitation reaction is carried out at a temperature of 50-70°C for 4-12 hours.

6. The method for preparing the ternary cathode material according to claim 3, characterized in that, In step S2 The lithium source includes one or more of LiOH·H2O, LiOH, and Li2CO3; and / or, The second zirconium dopant includes one or more of ZrO2, Zr(OH)4, and ZrSiO4; and / or, The particle size Dv50 of the second zirconium dopant is 10~500 nm; and / or, The molar ratio of the lithium source to the first precursor is (1.05~1.10):1; and / or, Step S2 further includes a step of ball milling the first precursor, the lithium source and the second zirconium dopant, wherein the ball-to-material ratio of the ball milling is (5~20):1, the speed is 200~800 rpm and the time is 2~4 h.

7. The method for preparing the ternary cathode material according to claim 3, characterized in that, In step S3 The sintering is carried out in an oxidizing atmosphere, which includes oxygen and / or air; and / or, The sintering includes a first sintering, a second sintering, and a third sintering performed sequentially; and / or, In step S4 The coating metal source includes one or more of Al(NO3)3, Al2O3, Al(OH)3, Co(OH)2, and Nb2O5; and / or, The solvent includes one or more of ethanol, water, and isopropanol; and / or, The molar ratio of the coating metal source to the core is (0.001~0.02):1; and / or, The heat treatment is performed at a temperature of 500~700℃ for 1~12 hours.

8. The method for preparing the ternary cathode material according to claim 7, characterized in that, In step S3 The first sintering temperature is 400~600℃, and the time is 2~6h; and / or, The second sintering temperature is 700~900℃, and the time is 8~16h; and / or, The third sintering temperature is 300~500℃, the pressure is -0.07~-0.09MPa, and the time is 8~16h.

9. A positive electrode sheet, comprising a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector, characterized in that, The active layer of the cathode material includes the ternary cathode material as described in claim 1 or 2.

10. A solid-state battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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