Ultrahigh-nickel ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a super-high-nickel ternary positive electrode material, a preparation method thereof and a lithium ion battery. The super-high-nickel ternary positive electrode material comprises an inner core and a lithium metal oxide coating layer coated on the surface of the inner core; the chemical general formula of the inner core is LiNi (1‑x‑y‑z) Co x Mn y M z O2, 0.9≤(1-x-y-z)<1, 0.01≤x<0.1, 0.01≤y<0.1, 0.001≤z≤0.03; M is a bulk doping element; the lithium metal oxide coating layer contains a doping element A, and the doping concentration of the doping element A increases gradually along the radial direction from the inner surface to the outer surface of the lithium metal oxide coating layer. The application can effectively eliminate or reduce the interface mismatch and stress concentration between the lithium metal oxide coating layer and the inner core, realize smooth transition of the physical and chemical properties from the bulk to the coating layer, and significantly improve the bulk structure reversibility, interface chemical stability and environmental resistance of the material.

Description

Technical Field

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

[0002] Ultra-high nickel cathode materials (such as LiNiO2 and its derivatives) are key to next-generation high-energy-density lithium-ion batteries due to their high specific capacity. However, they suffer from severe structural degradation problems in the deep delithiation state: (1) Bulk structural instability: a harmful phase transition occurs from hexagonal phase (H1 / H2 / H3) to monoclinic phase (M), accompanied by severe lattice distortion and anisotropic volume shrinkage, leading to particle cracking; (2) Violent interfacial side reactions: high-activity Ni 4+ (3) High environmental sensitivity: residual lithium on the surface (Li2CO3 / LiOH) is prone to react with H2O and CO2 in the air, which deteriorates the processing and electrochemical performance.

[0003] To address these issues, the industry generally adopts a synergistic modification strategy of "bulk doping + surface coating". For example, the technique disclosed by Hou et al. (doi.org / 10.1002 / anie.202521113) uses Zr bulk doping to stabilize the lattice, while using a uniform Li3NbO4 layer for surface coating to isolate the electrolyte. This strategy improves the material performance to some extent.

[0004] While the aforementioned "bulk doping + uniform coating" strategy is effective, it still has inherent limitations: 1) Interface stress concentration: The uniform coating layer and the substrate material have abrupt changes in physical properties (such as lattice constant, coefficient of thermal expansion, etc.). During the long-term volume change caused by lithium-ion insertion / extraction, this abrupt interface is prone to become a stress concentration point, inducing coating layer cracking or peeling off from the substrate, leading to protection failure. 2) Ion transport barrier: The clear interface between the uniform coating layer and the substrate may constitute an additional interface barrier for lithium-ion diffusion, especially at high rates. 3) Limited protection function: Existing coating layers mostly focus on a single function (such as ion conduction or physical barrier), making it difficult to achieve multi-level, progressive protection from the bulk phase to the surface.

[0005] Therefore, how to eliminate or reduce the interfacial mismatch and stress concentration between the coating layer and the substrate, and achieve a smooth transition of physicochemical properties from the bulk phase to the surface, so as to more durablely and effectively improve the reversibility of the bulk structure, interfacial chemical stability and environmental tolerance of ultra-high nickel cathode materials, is an urgent technical problem to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an ultra-high nickel ternary cathode material, its preparation method, and a lithium-ion battery. This invention, by doping the core with bulk dopant elements while simultaneously increasing the dopant element A in the lithium metal oxide coating layer radially from the inside out, effectively eliminates or mitigates interfacial mismatch and stress concentration between the lithium metal oxide coating layer and the core. This achieves a smooth transition of physicochemical properties from the bulk phase to the coating layer, providing a smoother "slope-like" channel for lithium ions to cross the interface, rather than a "step-like" barrier. This results in a more durable and effective improvement in the bulk structural reversibility, interfacial chemical stability, and environmental tolerance of the ultra-high nickel ternary cathode material. Fundamentally, this enhances the long-term structural integrity and interfacial stability of the ultra-high nickel ternary cathode material under extreme operating conditions, ultimately significantly improving the cycle performance, rate performance, and safety performance of the cathode material.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides an ultra-high nickel ternary cathode material, the ultra-high nickel ternary cathode material comprising a core and a lithium metal oxide coating layer covering the surface of the core.

[0008] The general chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 0.9≤(1-xyz)<1, 0.01≤x<0.1, 0.01≤y<0.1, 0.001≤z≤0.03; M is a bulk doping element; the lithium metal oxide coating layer contains doping element A, and the doping concentration of doping element A increases in a gradient from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

[0009] This invention effectively eliminates or reduces interfacial mismatch and stress concentration between the lithium metal oxide coating and the core by doping the bulk phase with a dopant element while simultaneously increasing the dopant element A in the lithium metal oxide coating from the inside to the outside in a radial gradient. This achieves a smooth transition of physicochemical properties from the bulk phase to the coating, providing a smoother "slope-like" channel for lithium ions to cross the interface rather than a "step-like" barrier. This results in a more durable and effective improvement in the reversibility of the bulk structure, interfacial chemical stability, and environmental tolerance of the ultra-high nickel ternary cathode material. It fundamentally improves the long-term structural integrity and interfacial stability of the ultra-high nickel ternary cathode material under extreme operating conditions, ultimately significantly improving the cycle performance, rate performance, and safety performance of the cathode material.

[0010] In this invention, the doping concentration of dopant element A increases in a radial gradient from the inner surface to the outer surface of the lithium metal oxide coating. The innermost layer of the lithium metal oxide coating can achieve a close match with the crystal structure and chemical properties of the core material, effectively reducing interfacial energy, suppressing interfacial side reactions, and enhancing interfacial bonding strength. The intermediate transition layer of the lithium metal oxide coating can achieve a smooth transition of ion conduction and stress transfer. The outermost layer of the lithium metal oxide coating can provide optimal chemical inertness, effectively isolating electrolyte and air erosion.

[0011] In this invention, 0.9 ≤ (1-xyz) < 1, for example, it can be 0.9, 0.92, 0.94, 0.96, or 0.98, etc. 0.01 ≤ x < 0.1, for example, it can be 0.01, 0.03, 0.05, 0.07, or 0.09, etc. 0.01 ≤ y < 0.1, for example, it can be 0.01, 0.03, 0.05, 0.07, or 0.09, etc. 0.001 ≤ z ≤ 0.03, for example, it can be 0.001, 0.01, 0.02, or 0.03, etc. A suitable doping amount of the bulk dopant element M can significantly improve the structural stability of the material without sacrificing capacity. On the one hand, a suitable amount of dopant element (such as Zr) 4+ Introducing the dopant into the crystal lattice can suppress lattice collapse and cation mixing under high delithiation states. On the other hand, controlling the doping amount to within 3% can avoid capacity loss caused by excessive inert elements. At the same time, an appropriate doping amount provides a good bulk phase basis for the design of buffer element B in the subsequent gradient coating layer, enabling buffer element B to form a stable chemical bond with the bulk phase and achieve a smooth transition from the bulk phase to the surface.

[0012] Preferably, the particle size D50 of the kernel is 2-15 μm, for example, it can be 2 μm, 5 μm, 7 μm, 10 μm, 12 μm or 15 μm, and is more preferably 3-10 μm.

[0013] Preferably, the bulk doping element includes any one or a combination of at least two of Al, Zr, Ti, Ta, W, Mg, or Y.

[0014] Preferably, in the core, the bulk dopant element M is uniformly distributed in the crystal lattice.

[0015] In this invention, the dispersed bulk dopant elements can suppress local stress concentration and delay lattice distortion and microcrack formation during charge and discharge. This distribution provides a coherent and low-resistance transport channel for the bulk diffusion of lithium ions. Together with the lithium metal oxide coating layer on the core surface, it achieves integrated control of structure and performance from the bulk phase to the interface, significantly improving the structural durability and electrochemical stability of the material under long cycles and high rates.

[0016] Preferably, 0.005≤z≤0.02, for example, it can be 0.005, 0.01, 0.015 or 0.02, etc.

[0017] Preferably, the thickness of the lithium metal oxide coating layer is 2-50 nm, for example, it can be 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, and is preferably 5-20 nm.

[0018] In this invention, an appropriate coating thickness can provide sufficient physical barrier function without significantly increasing lithium-ion diffusion resistance. If the thickness is too thin (<2nm), it is difficult to completely cover the substrate surface and cannot effectively prevent electrolyte erosion; if the thickness is too thick (>50nm), it will prolong the lithium-ion diffusion path, increase interfacial resistance, and lead to a decrease in rate performance. Therefore, controlling the thickness within the range of 5-20nm achieves the optimal balance between interfacial protection and ion transport, ensuring both the integrity of the coating layer and maintaining the rapid passage capability of lithium ions.

[0019] Preferably, the doping element A includes any one or a combination of at least two of Nb, Ta, W, Ti, Si, or B.

[0020] Preferably, the gradient increase is either a continuous increase or a segmented increase.

[0021] In this invention, the continuous incremental approach can achieve a smooth transition of the physicochemical properties of the coating layer, reducing the barrier to lithium-ion transport across the interface and the accumulation of internal stress.

[0022] In this invention, the segmented incremental method can be, for example, setting at least two sublayers with different doping concentrations to form a segmented continuous change. This method maintains the advantages of gradient functional design while being more controllable and repeatable in terms of process.

[0023] Preferably, in the lithium metal oxide coating layer, the doping amount of doping element A is 0.01-2wt%, for example, it can be 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, or 2wt%, etc.

[0024] In this invention, an appropriate doping amount can ensure the integrity and functionality of the coating layer while avoiding dilution of the active material due to excessive doping. When the doping amount is too low (<0.01wt%), the coating layer is difficult to form a continuous and uniform protective layer, resulting in limited isolation effect against the electrolyte. When the doping amount is too high (>2.0wt%), although the coating layer is denser, the specific capacity of the material is sacrificed due to excessive inert components, and it may also affect the precise control of the gradient structure. Therefore, controlling the doping amount within the range of 0.05-1.0wt% achieves an optimal balance between interface stability and capacity retention.

[0025] Preferably, the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is ≥1.5, for example, it can be 1.5, 2, 4, 6, 8, 10, 15 or 20, etc., preferably ≥2, and more preferably 2-10.

[0026] In this invention, controlling the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to satisfy a specific ratio with the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer ensures the formation of an effective concentration gradient structure in the coating layer. When this ratio is ≥1.5, it indicates that element A has undergone significant enrichment from the inside out, forming a dense protective "armor" on the outermost layer, while the inner layer maintains properties similar to the substrate, achieving a smooth transition of physicochemical properties. If the ratio is too small (<1.5), the gradient characteristics are not obvious, the coating layer is nearly uniformly distributed, and the problem of interface stress concentration cannot be effectively alleviated; on the other hand, if the ratio is too large (>10), the gradient change is too drastic, which may generate new stress mismatch at the interface. Therefore, it is preferable to control the ratio within the range of 2-10 to achieve the best balance between maximizing the gradient effect and interface compatibility.

[0027] Preferably, the lithium metal oxide coating layer further contains a buffer element B, which may be the same as or different from the bulk dopant element.

[0028] In this invention, when the type of buffer element B is the same as that of the bulk dopant element, a "seamless bridge" from bulk doping to surface coating can be achieved, which strengthens the matching between the core and the coating layer and eliminates the interface mismatch and stress concentration between the coating layer and the core.

[0029] In this invention, when the type of buffer element B is different from that of the bulk dopant element, the main function of buffer element B is closer to "smoothing the transition," and its main function is to be compatible with the physicochemical properties of lithium metal oxides. For example, the selected element B (such as Ti or Al) and element M (Zr) have similar ionic radii, charge numbers, and coordination chemistry, both of which can stabilize the crystal lattice, and their oxides (such as TiO2, Al2O3) have good chemical compatibility with the oxides of the core and dopant element A (such as Li3NbO4).

[0030] Preferably, the buffer element B includes any one or a combination of at least two of Zr, Al, Ti, Ce, Fe, or Sn.

[0031] Preferably, in the lithium metal oxide coating layer, the ratio of the total doping amount of doping element A to the total doping amount of buffer element B is 1:(0.1-10), for example, it can be 1:0.1, 1:0.5, 1:1, 1:3, 1:5, 1:7, 1:9 or 1:10, etc., preferably 1:(0.2-5).

[0032] In this invention, a suitable ratio ensures that A and B form a dual concentration gradient with opposite directions. When the A:B ratio is in the range of 1:(0.1-10), both have sufficient content to participate in gradient formation. If the A content is too high (ratio > 1:0.1), the decreasing gradient of B is difficult to manifest, and the interfacial buffering effect is insufficient. If the B content is too high (ratio < 1:10), the enrichment degree of A on the outermost layer is insufficient, and the ability to isolate the electrolyte decreases. Therefore, when the ratio is controlled in the range of 1:0.5 to 1:2, the contents of A and B are comparable, which is most conducive to the spontaneous formation of a regular reverse gradient structure (A high on the outside and low on the inside, B high on the inside and low on the outside) through competitive diffusion during sintering, thereby achieving a synergistic effect of interfacial stress buffering and chemical protection.

[0033] Preferably, the doping concentration of the buffer element B decreases in a radial gradient from the inner surface to the outer surface of the lithium metal oxide coating.

[0034] In this invention, the doping concentration distribution of buffer element B ensures that the innermost layer (rich in buffer element B) of the lithium metal oxide coating layer is highly compatible with the bulk lattice, thus guaranteeing strong bonding and serving as a structural buffer band.

[0035] Preferably, the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is ≥1.5, for example, it can be 1.5, 2, 4, 6, 8, 10, 15, 20, 25 or 30, etc., preferably ≥2, and more preferably 2-20.

[0036] In this invention, controlling the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer to satisfy a specific ratio with the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer ensures that element B is enriched near the substrate, thus playing a role in interface buffering and stress transition. When this ratio is ≥1.5, it indicates that element B has been significantly enriched from the outside to the inside, forming a transition region highly compatible with the bulk lattice on the inner side of the coating layer, acting as a "buffer pad" to absorb and disperse stress caused by volume changes. If the ratio is too small (<1.5), the enrichment of element B at the interface is insufficient, and the stress buffering effect is limited; on the other hand, if the ratio is too large (>20), the content of B at the interface is too high, which may lead to a decrease in the lithium-ion conductivity of the inner layer of the coating layer. Therefore, controlling the ratio within the range of 2-20 can achieve the best balance between stress buffering effect and ion transport capability, ensuring that the gradient coating layer maintains structural integrity during long-term cycling.

[0037] Secondly, the present invention provides a method for preparing an ultra-high nickel ternary cathode material as described in the first aspect, the method comprising the following steps: The core precursor is obtained by mixing an ultra-high nickel ternary cathode material precursor, a lithium source, and a compound containing bulk dopants; the coating layer precursor is obtained by mixing a compound containing dopant element A with a lithium source.

[0038] The coating precursor is loaded onto the surface of the core precursor to form a precursor complex.

[0039] The precursor composite is subjected to temperature-controlled sintering in an oxygen-containing atmosphere to obtain the ultra-high nickel ternary cathode material.

[0040] The ultra-high nickel ternary cathode material comprises a core and a lithium metal oxide coating layer covering the surface of the core. The chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 0.9≤(1-xyz)<1, 0.01≤x<0.1, 0.01≤y<0.1, 0.001≤z≤0.03; the doping concentration of the dopant element A increases in a gradient from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

[0041] The preparation process provided by this invention can achieve the in-situ directional diffusion of dopant element A through "diffusion kinetic control" in a single temperature-controlled sintering process, thereby realizing the self-formation of gradient structure in the metal oxide coating layer. This process is simple and efficient, requires no multiple coatings or post-processing, and is suitable for mass production.

[0042] For example, the lithium source can be lithium carbonate or lithium hydroxide monohydrate, etc.

[0043] Preferably, the method for loading the coating precursor onto the surface of the core precursor includes any one of wet impregnation, spray coating, or atomic layer deposition.

[0044] Preferably, the oxygen partial pressure in the oxygen-containing atmosphere is 0.6-1 atm, for example, it can be 0.6 atm, 0.7 atm, 0.8 atm, 0.9 atm or 1 atm, etc.

[0045] This invention, by controlling the oxygen partial pressure, can drive the dopant element A to slowly diffuse inward from the surface, while simultaneously driving some lithium and transition metal ions in the core to diffuse outward, while the buffer element B is distributed in the transition region.

[0046] Preferably, the temperature-controlled sintering step includes: The initial reaction is carried out at a first temperature, and then the temperature is increased to a second temperature at a heating rate of 1-3℃ / min (e.g., 1℃ / min, 2℃ / min, or 3℃ / min, etc.) to carry out the crystallization reaction.

[0047] Preferably, the first temperature is 300-500℃, for example, it can be 300℃, 400℃ or 500℃, and the heat preservation time is 4-6h, for example, it can be 4h, 5h or 6h.

[0048] Preferably, the second temperature is 700-800℃, for example, 700℃, 750℃ or 800℃, and the heat preservation time is 13-18h, for example, 13h, 15h or 18h.

[0049] Through the aforementioned temperature-controlled sintering process, this invention drives the dopant element A to slowly diffuse inward from the surface, while simultaneously driving some lithium and transition metal ions in the core to diffuse outward, while the buffer element B is distributed in the transition region. Furthermore, by precisely controlling the diffusion time and temperature, a lithium metal oxide coating layer with the aforementioned gradient structure is ultimately formed in situ on the core surface.

[0050] Preferably, the raw materials for preparing the coating layer precursor also include a compound containing buffer element B.

[0051] Preferably, the preparation method includes the following steps: (1) The ultra-high nickel ternary cathode material precursor, lithium source and compound containing bulk doped elements are mixed in stoichiometric ratio to obtain the core precursor.

[0052] The chemical formula of the ultra-high nickel ternary cathode material precursor is Ni. (1-a-b) Co a Mn b(OH)2, 0.9≤(1-ab)<1 (e.g., it can be 0.9, 0.92, 0.94, 0.96 or 0.98, etc.), 0.01≤a<0.1 (e.g., it can be 0.01, 0.03, 0.05, 0.07 or 0.09, etc.), 0.01≤b<0.1 (e.g., it can be 0.01, 0.03, 0.05, 0.07 or 0.09, etc.); the compound containing the bulk doped element includes any one or a combination of at least two of Al salt, Zr salt, Ti salt, Ta salt, W salt, Mg salt or Y salt.

[0053] A compound containing dopant element A, a compound containing buffer element B, and a lithium source are mixed to obtain a coating precursor.

[0054] Wherein, the compound containing dopant element A includes any one or a combination of at least two of Nb salt, Ta salt, W salt, Ti salt, Si salt or B salt; the compound containing buffer element B includes any one or a combination of at least two of Zr salt, Al salt, Ti salt, Ce salt, Fe salt or Sn salt.

[0055] (2) The coating layer precursor is loaded onto the surface of the core precursor by any one of wet impregnation, spray coating or atomic layer deposition to form a precursor complex.

[0056] (3) The precursor composite is subjected to programmed temperature-controlled sintering in an oxygen-containing atmosphere with an oxygen partial pressure of 0.6-1 atm, the steps of which include: A preliminary reaction is carried out at a first temperature of 300-500℃ for 4-6 hours, and then the temperature is increased to a second temperature of 700-800℃ at a heating rate of 1-3℃ / min for 13-18 hours to obtain the sintered product.

[0057] (4) Cool the sintered product, grind and sieve it to obtain ultra-high nickel ternary cathode material.

[0058] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode sheet, the positive electrode sheet comprising the ultra-high nickel ternary positive electrode material as described in the first aspect.

[0059] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects: This invention effectively eliminates or reduces interfacial mismatch and stress concentration between the lithium metal oxide coating and the core by doping the bulk phase with a dopant element while simultaneously increasing the dopant element A in the lithium metal oxide coating from the inside to the outside in a radial gradient. This achieves a smooth transition of physicochemical properties from the bulk phase to the coating, providing a smoother "slope-like" channel for lithium ions to cross the interface rather than a "step-like" barrier. This results in a more durable and effective improvement in the reversibility of the bulk structure, interfacial chemical stability, and environmental tolerance of the ultra-high nickel ternary cathode material. It fundamentally improves the long-term structural integrity and interfacial stability of the ultra-high nickel ternary cathode material under extreme operating conditions, ultimately significantly improving the cycle performance, rate performance, and safety performance of the cathode material. Detailed Implementation

[0061] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0062] Example 1 This embodiment provides an ultra-high nickel ternary cathode material, which includes a core and a lithium metal oxide coating layer covering the surface of the core.

[0063] The general chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 1-xyz=0.92, x=0.04, y=0.03, z=0.01; M is Zr; the particle size D50 of the core is 5μm; in the core, the bulk dopant element M is uniformly distributed in the lattice; the thickness of the lithium metal oxide coating layer is 25nm; the lithium metal oxide coating layer contains dopant element A and buffer element B, wherein dopant element A is Nb and buffer element B is Zr; the doping concentration of dopant element A increases gradually from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction, and the gradient increase is continuous; the doping concentration of buffer element B decreases gradually from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

[0064] In the lithium metal oxide coating layer, the doping amount of dopant element A is 0.2 wt%; the ratio of the total doping amount of dopant element A to the total doping amount of buffer element B is 1:0.8; the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is 4; and the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is 5.

[0065] This embodiment also provides a method for preparing the above-mentioned ultra-high nickel ternary cathode material, the method comprising the following steps; (1) Commercial ultra-high nickel ternary cathode material precursor, LiOH·H2O (5% lithium excess) and ZrO(NO3)2 are mixed evenly in a high-speed mixer according to the stoichiometric ratio to obtain the core precursor.

[0066] The chemical formula of the commercial ultra-high nickel ternary cathode material precursor is Ni. 0.92 Co 0.05 Mn 0.03 (OH)2.

[0067] Nb(C2H5O)5, ZrO(NO3)2 and LiOH·H2O were dissolved together in anhydrous ethanol to obtain a solution containing the coating layer precursor.

[0068] (2) The core precursor is dispersed in ethanol, and then the solution containing the coating layer precursor is slowly added dropwise under stirring. After the addition is complete, the stirring is continued and the solvent is evaporated. The coating layer precursor is loaded on the surface of the core precursor to obtain the precursor complex.

[0069] (3) The precursor composite is subjected to programmed temperature-controlled sintering in an oxygen-containing atmosphere with an oxygen partial pressure of 0.8 atm, the steps of which include: The initial reaction was carried out at 450℃ for 5 hours with a heating rate of 5℃ / min, and then the temperature was increased to 750℃ for 15 hours with a heating rate of 2℃ / min to obtain the sintered product.

[0070] (4) The sintered product is naturally cooled and then ground through a 400-mesh sieve to obtain an ultra-high nickel ternary cathode material.

[0071] EDS line scan of the ultra-high nickel ternary cathode material provided in this embodiment shows that the Nb signal intensity continuously increases from the inside of the particle to the surface, while the Zr signal intensity continuously decreases, proving the increasing gradient of Nb and the decreasing gradient of Zr.

[0072] Example 2 This embodiment provides an ultra-high nickel ternary cathode material, which includes a core and a lithium metal oxide coating layer covering the surface of the core.

[0073] The general chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 1-xyz=0.92, x=0.04, y=0.03, z=0.01; M is Zr; the particle size D50 of the core is 4μm; in the core, the bulk dopant element M is dispersedly distributed; the thickness of the lithium metal oxide coating layer is 10nm; the lithium metal oxide coating layer contains dopant element A and buffer element B, wherein dopant element A is Ta and buffer element B is Al; the doping concentration of dopant element A increases radially from the inner surface to the outer surface of the lithium metal oxide coating layer in a continuous increasing manner; the doping concentration of buffer element B decreases radially from the inner surface to the outer surface of the lithium metal oxide coating layer.

[0074] In the lithium metal oxide coating layer, the doping amount of dopant element A is 0.15 wt%; the ratio of the total doping amount of dopant element A to the total doping amount of buffer element B is 1:1; the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is 2; the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is 2.

[0075] This embodiment also provides a method for preparing the above-mentioned ultra-high nickel ternary cathode material, the method comprising the following steps; (1) Commercial ultra-high nickel ternary cathode material precursor, LiOH·H2O (5% lithium excess) and ZrO(NO3)2 are mixed evenly in a high-speed mixer according to the stoichiometric ratio to obtain the core precursor.

[0076] The chemical formula of the commercial ultra-high nickel ternary cathode material precursor is Ni. 0.92 Co 0.05 Mn 0.03 (OH)2.

[0077] Ta(C2H5O)5, Al(NO3)3·9H2O and LiOH·H2O were dissolved together in anhydrous ethanol to obtain a solution containing the coating layer precursor.

[0078] (2) The core precursor is dispersed in ethanol, and then the solution containing the coating layer precursor is slowly added dropwise under stirring. After the addition is complete, the stirring is continued and the solvent is evaporated. The coating layer precursor is loaded on the surface of the core precursor to obtain the precursor complex.

[0079] (3) The precursor composite is subjected to programmed temperature-controlled sintering in an oxygen-containing atmosphere with an oxygen partial pressure of 0.8 atm, the steps of which include: The initial reaction was carried out at 300℃ for 6 hours with a heating rate of 5℃ / min, and then the temperature was increased to 700℃ for 18 hours with a heating rate of 1℃ / min to obtain the sintered product.

[0080] (4) The sintered product is naturally cooled and then ground through a 400-mesh sieve to obtain an ultra-high nickel ternary cathode material.

[0081] Example 3 This embodiment provides an ultra-high nickel ternary cathode material, which includes a core and a lithium metal oxide coating layer covering the surface of the core.

[0082] The general chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 1-xyz=0.92, x=0.04, y=0.03, z=0.01; M is Zr; the particle size D50 of the core is 6μm; in the core, the bulk dopant element M is dispersedly distributed; the thickness of the lithium metal oxide coating layer is 50nm; the lithium metal oxide coating layer contains dopant element A and buffer element B, wherein dopant element A is W and buffer element B is Ti; the doping concentration of dopant element A increases gradually from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction, and the gradient increase is continuous; the doping concentration of buffer element B decreases gradually from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

[0083] In the lithium metal oxide coating layer, the doping amount of dopant element A is 0.3 wt%; the ratio of the total doping amount of dopant element A to the total doping amount of buffer element B is 1:1.2; the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is 10; and the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is 20.

[0084] This embodiment also provides a method for preparing the above-mentioned ultra-high nickel ternary cathode material, the method comprising the following steps; (1) Commercial ultra-high nickel ternary cathode material precursor, LiOH·H2O (5% lithium excess) and ZrO(NO3)2 are mixed evenly in a high-speed mixer according to the stoichiometric ratio to obtain the core precursor.

[0085] The chemical formula of the commercial ultra-high nickel ternary cathode material precursor is Ni. 0.92 Co 0.05 Mn 0.03 (OH)2.

[0086] W(C2H5O)5, Ti(C4H9O)4 and LiOH·H2O were dissolved together in anhydrous ethanol to obtain a solution containing the coating layer precursor.

[0087] (2) The core precursor is dispersed in ethanol, and then the solution containing the coating layer precursor is slowly added dropwise under stirring. After the addition is complete, the stirring is continued and the solvent is evaporated. The coating layer precursor is loaded on the surface of the core precursor to obtain the precursor complex.

[0088] (3) The precursor composite is subjected to programmed temperature-controlled sintering in an oxygen-containing atmosphere with an oxygen partial pressure of 1 atm, the steps of which include: The initial reaction was carried out at 500℃ for 4 hours with a heating rate of 5℃ / min, and then the temperature was increased to 800℃ for 13 hours with a heating rate of 3℃ / min to obtain the sintered product.

[0089] (4) The sintered product is naturally cooled and then ground through a 400-mesh sieve to obtain an ultra-high nickel ternary cathode material.

[0090] Example 4 The difference between this embodiment and Embodiment 1 is that the doping concentration of the dopant element A increases in a radial direction from the inner surface to the outer surface of the lithium metal oxide coating layer. The gradient increase is segmented, that is, it is a continuous segmented change consisting of two sub-layers with different concentrations. The atomic percentage concentration of dopant element A in the first sub-layer (inner layer) is 3 at%, and the atomic percentage concentration of dopant element A in the second sub-layer (outer layer) varies from 8 at%.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Example 5 The difference between this embodiment and Embodiment 1 is that the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is 1.2.

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Example 6 The difference between this embodiment and Embodiment 1 is that the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is 12.

[0095] The remaining preparation methods and parameters are consistent with those in Example 1.

[0096] Example 7 The difference between this embodiment and Embodiment 1 is that the lithium metal oxide coating layer does not contain buffer element B.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Example 8 The difference between this embodiment and Embodiment 1 is that in the lithium metal oxide coating layer, the ratio of the total doping amount of doping element A to the total doping amount of buffer element B is 1:15.

[0099] The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Example 9 The difference between this embodiment and Embodiment 1 is that the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is 1.2.

[0101] The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Example 10 The difference between this embodiment and Embodiment 1 is that the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is 22.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 11 The difference between this embodiment and Embodiment 1 is that the oxygen partial pressure in the oxygen-containing atmosphere is 0.4 atm.

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] Example 12 The difference between this embodiment and Embodiment 1 is that the oxygen partial pressure in the oxygen-containing atmosphere is 1.2 atm.

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

[0108] Example 13 The difference between this embodiment and Embodiment 1 is that the heating rate when the temperature is increased from 450°C to 750°C is 5°C / min.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Comparative Example 1 The difference between this comparative example and Example 1 is that the doping element A in the lithium metal oxide coating layer is evenly distributed, so the solution containing the coating layer precursor is prepared by the following method: dissolving the Li3NbO4 precursor and ZrO(NO3)2 together in anhydrous ethanol to obtain the solution containing the coating layer precursor.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Comparative Example 2 The difference between this comparative example and Example 1 is that the lithium metal oxide coating layer is not provided.

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

[0114] Performance testing The ultra-high nickel ternary cathode material provided in the above embodiments and comparative examples was mixed with conductive carbon black and binder PVDF at a mass ratio of 8:1:1 and added to N-methylpyrrolidone to form a slurry. This slurry was coated onto an aluminum foil current collector, and after drying, rolling, and cutting, it was made into a cathode sheet. A lithium metal sheet was used as the anode sheet. A polypropylene microporous membrane (Celgard 2400) was selected as the separator. The electrolyte was a solution containing 1 mol / L LiPF6, and the solvent consisted of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:1:1. The cells were assembled according to conventional processes to obtain a 2032 coin cell.

[0115] Electrochemical performance tests were performed on the 2032 coin cell, including: 1) Initial discharge specific capacity, test conditions include: 0.1C, 2.8-4.6V.

[0116] 2) Cycle retention rate, test conditions include: 1C, 2.8-4.6V, 25℃, 500 cycles.

[0117] 3) Rate performance, test conditions include: 25℃, constant current charge and discharge test at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C, 2.8-4.6V, record capacity retention rate = 5C discharge capacity / 0.1C discharge capacity.

[0118] 4) High-temperature cycling performance, test conditions include: 1C, 2.8-4.6V, 60℃, 200 cycles, record capacity retention.

[0119] The test results are shown in Table 1.

[0120] Table 1 analyze: As shown in Table 1, this invention, by doping bulk dopant elements into the core while simultaneously increasing the dopant element A in the lithium metal oxide coating layer radially from the inside to the outside, effectively eliminates or mitigates interfacial mismatch and stress concentration between the lithium metal oxide coating layer and the core. This achieves a smooth transition of physicochemical properties from the bulk phase to the coating layer, providing a smoother "slope-like" channel for lithium ions to cross the interface rather than a "step-like" barrier. This results in a more durable and effective improvement in the reversibility of the bulk structure, interfacial chemical stability, and environmental tolerance of the ultra-high nickel ternary cathode material. Fundamentally, this enhances the long-term structural integrity and interfacial stability of the ultra-high nickel ternary cathode material under extreme conditions, ultimately significantly improving the cycle performance (capacity retention up to 88.5%), rate performance, and safety performance (capacity retention up to 85.2% at high temperatures). Furthermore, the initial discharge specific capacity data shows that the coating layer has minimal impact on the initial capacity, proving that Li... + The passage is clear.

[0121] A comparison of Examples 1 and 5-6 shows that if the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is too small, the gradient characteristics are not obvious, the coating layer is nearly uniformly distributed, and it cannot effectively alleviate the stress concentration at the interface, resulting in a decrease in cycle stability. If the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is too large, the gradient change is too drastic, which may generate new stress mismatch at the interface and may also affect the lattice matching degree between the coating layer and the substrate, resulting in a decrease in rate performance.

[0122] As can be seen from the comparison between Example 1 and Example 7, if the lithium metal oxide coating does not contain buffer element B, the coating lacks a stress buffer layer and cannot effectively absorb and disperse the interfacial stress caused by volume changes, resulting in a significant decrease in cycle stability. At the same time, the bonding force between the coating and the substrate is weakened, and it is easy to peel off after long-term cycling.

[0123] As can be seen from the comparison between Example 1 and Example 8, if the ratio of the total doping amount of doping element A to the total doping amount of buffer element B in the lithium metal oxide coating layer is too small, that is, if the doping amount of buffer element B is too large, the content of doping elements in the outer coating layer is insufficient, and a dense protective layer cannot be formed, resulting in a decrease in the ability to isolate the electrolyte and poor cycle performance.

[0124] A comparison of Examples 1 and 9-10 shows that if the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is too small, the enrichment degree of element B near the substrate side is insufficient, the interface buffering effect is weakened, and the stress caused by lattice mismatch cannot be effectively relieved, resulting in a decrease in cycling and high-temperature performance. If the ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating layer to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating layer is too large, element B is over-enriched at the interface, which may lead to a decrease in the lithium-ion conductivity of the inner layer of the coating layer, hindering lithium-ion transport and affecting rate performance.

[0125] A comparison of Example 1 and Examples 11-12 shows that if the oxygen partial pressure in the oxygen-containing atmosphere is too low, the oxidation atmosphere is insufficient, the diffusion driving force of dopant element A is weakened, and the gradient structure is not fully formed, resulting in performance close to that of Example 7 without buffer element B. If the oxygen partial pressure in the oxygen-containing atmosphere is too high, although a gradient structure can be formed, the excessive oxygen partial pressure will increase the process cost and may lead to excessive surface oxidation, resulting in a slight decrease in performance, but still better than the comparative example.

[0126] A comparison of Example 1 and Example 13 shows that if the heating rate is too high during the process of heating from the initial reaction stage to the crystallization reaction stage, the diffusion time of dopant element A and buffer element B is insufficient, and the competitive diffusion cannot be fully realized to form a regular gradient structure, resulting in an incomplete gradient and a decrease in cycle and rate performance.

[0127] As can be seen from the comparison between Example 1 and Comparative Example 1, if the dopant element A in the coating layer does not have a gradient structure, there is an obvious abrupt change in properties at the interface, which cannot buffer the volume change stress during cycling, resulting in cycling performance, rate performance and high temperature performance being significantly lower than the protection scheme of the present invention.

[0128] As can be seen from the comparison between Example 1 and Comparative Example 2, if the lithium metal oxide coating layer is not provided, the highly active core is directly exposed to the electrolyte, resulting in severe side reactions, serious dissolution of transition metals, particle cracking during cycling, leading to a sharp decline in cycling performance and rapid failure at high temperatures.

[0129] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high-nickel ternary cathode material, characterized in that, The ultra-high nickel ternary cathode material includes a core and a lithium metal oxide coating layer covering the surface of the core; The general chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 0.9≤(1-xyz)<1, 0.01≤x<0.1, 0.01≤y<0.1, 0.001≤z≤0.03; M is a bulk doping element; the lithium metal oxide coating layer contains doping element A, and the doping concentration of doping element A increases in a gradient from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

2. The ultra-high nickel ternary cathode material according to claim 1, characterized in that, The particle size D50 of the core is 2-15 μm, preferably 3-10 μm; And / or, the bulk doping element includes any one or a combination of at least two of Al, Zr, Ti, Ta, W, Mg or Y; And / or, in the core, the bulk dopant element M is uniformly distributed in the crystal lattice; And / or, 0.005≤z≤0.02; And / or, the thickness of the lithium metal oxide coating is 2-50 nm; And / or, the doping element A includes any one or a combination of at least two of Nb, Ta, W, Ti, Si or B; And / or, the gradient increase method is either continuous increase or segmented increase.

3. The ultra-high nickel ternary cathode material according to claim 2, characterized in that, In the lithium metal oxide coating layer, the doping amount of element A is 0.01-2 wt%; And / or, the ratio of the atomic percentage concentration of dopant element A on the outer surface of the lithium metal oxide coating layer to the atomic percentage concentration of dopant element A on the inner surface of the lithium metal oxide coating layer is ≥1.

5.

4. The ultra-high nickel ternary cathode material according to claim 3, characterized in that, The lithium metal oxide coating layer also contains a buffer element B, which may be the same as or different from the bulk doping element. The buffer element B includes any one or a combination of at least two of Zr, Al, Ti, Ce, Fe, or Sn; In the lithium metal oxide coating layer, the ratio of the total doping amount of doping element A to the total doping amount of buffer element B is 1:(0.1-10), preferably 1:(0.2-5).

5. The ultra-high nickel ternary cathode material according to claim 4, characterized in that, The doping concentration of the buffer element B decreases in a radial direction from the inner surface to the outer surface of the lithium metal oxide coating. The ratio of the atomic percentage concentration of buffer element B on the inner surface of the lithium metal oxide coating to the atomic percentage concentration of buffer element B on the outer surface of the lithium metal oxide coating is ≥1.

5.

6. A method for preparing an ultra-high nickel ternary cathode material as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A core precursor is obtained by mixing an ultra-high nickel ternary cathode material precursor, a lithium source, and a compound containing bulk doped elements; a coating layer precursor is obtained by mixing a compound containing doped element A with a lithium source. The coating precursor is loaded onto the surface of the core precursor to form a precursor complex. The precursor composite was subjected to temperature-controlled sintering in an oxygen-containing atmosphere to obtain the ultra-high nickel ternary cathode material. The ultra-high nickel ternary cathode material comprises a core and a lithium metal oxide coating layer covering the surface of the core. The chemical formula of the core is LiNi. (1-x-y-z) Co x Mn y M z O2, 0.9≤(1-xyz)<1, 0.01≤x<0.1, 0.01≤y<0.1, 0.001≤z≤0.03; the doping concentration of the dopant element A increases in a gradient from the inner surface to the outer surface of the lithium metal oxide coating layer in the radial direction.

7. The preparation method according to claim 6, characterized in that, The method of loading the coating layer precursor onto the surface of the core precursor includes any one of wet impregnation, spray coating or atomic layer deposition. And / or, the oxygen partial pressure in the oxygen-containing atmosphere is 0.6-1 atm; And / or, the temperature-controlled sintering step includes: The initial reaction is carried out at the first temperature, and then the temperature is increased to the second temperature at a heating rate of 1-3℃ / min to carry out the crystallization reaction; The first temperature is 300-500℃, and the holding time is 4-6 hours; The second temperature is 700-800℃, and the holding time is 13-18h.

8. The preparation method according to claim 6, characterized in that, The raw materials for preparing the coating layer precursor also include compounds containing buffer element B.

9. The preparation method according to claim 6, characterized in that, The preparation method includes the following steps: (1) The ultra-high nickel ternary cathode material precursor, lithium source and compound containing bulk doped elements are mixed in stoichiometric ratio to obtain the core precursor; The chemical formula of the ultra-high nickel ternary cathode material precursor is Ni. (1-a-b) Co a Mn b (OH)2, 0.9≤(1-ab)<1, 0.01≤a<0.1, 0.01≤b<0.1; the compound containing bulk doped elements includes any one or a combination of at least two of Al salt, Zr salt, Ti salt, Ta salt, W salt, Mg salt or Y salt; A compound containing doped element A, a compound containing buffer element B, and a lithium source are mixed to obtain a coating layer precursor. Wherein, the compound containing doped element A includes any one or a combination of at least two of Nb salt, Ta salt, W salt, Ti salt, Si salt or B salt; the compound containing buffer element B includes any one or a combination of at least two of Zr salt, Al salt, Ti salt, Ce salt, Fe salt or Sn salt. (2) The coating layer precursor is loaded onto the surface of the core precursor by any one of wet impregnation, spray coating or atomic layer deposition to form a precursor complex; (3) The precursor composite is subjected to programmed temperature-controlled sintering in an oxygen-containing atmosphere with an oxygen partial pressure of 0.6-1 atm, the steps of which include: A preliminary reaction is carried out at a first temperature of 300-500℃ for 4-6 hours, and then the temperature is increased to a second temperature of 700-800℃ at a heating rate of 1-3℃ / min for 13-18 hours to obtain a sintered product. (4) Cool the sintered product, grind and sieve it to obtain ultra-high nickel ternary cathode material.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet, which includes the ultra-high nickel ternary positive electrode material as described in any one of claims 1-5.

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