Cathode material with core-shell structure, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of battery materials, and discloses a positive electrode material with a core-shell structure, a preparation method of the positive electrode material and a lithium ion battery. The material of the core layer is an LNCM material doped with aluminum, zirconium and niobium, the chemical general formula of the LNCM material is LiNixCoyMnzO2, x + y + z = 1, and 0 lt; x, y, zlt; 1; and the material of the shell layer is a lithium-aluminum-zirconium-niobium composite oxide. The positive electrode material provided by the invention has dual effects of lattice distortion strengthening and interface stabilization, the cycling stability and rate capability of the positive electrode material are remarkably improved while high specific capacity is maintained, and the assembled lithium ion battery can realize high-specific-capacity stable rapid charging and discharging at high rate (such as 1C-5C). Most importantly, an innovative path is provided for low-cost and large-scale modification of the high-nickel ternary positive electrode material, and the method has the capacity of large-scale production.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a core-shell structured cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, high energy density, and long cycle life, have been widely used in the energy storage market. The cathode material is crucial in determining the performance and energy density of lithium-ion batteries. With technological advancements, the performance requirements for lithium-ion batteries are becoming increasingly stringent, with high capacity, long lifespan, high safety, and fast charging capabilities becoming key research areas. In this context, the performance of the cathode material becomes a critical factor limiting the overall performance improvement of lithium-ion batteries.

[0003] However, cathode materials themselves have many problems that urgently need to be solved. High-nickel cathode materials have Li... + / Ni 2+ The high-nickel cathode material suffers from drawbacks such as cation mixing, surface instability, and interfacial side reactions, leading to rapid capacity decay, short cycle life, and poor thermal stability, thus limiting its application in lithium-ion batteries. High-nickel cathode materials readily react with CO2 and H2O in the air, generating Li2CO3 and LiOH on the surface, resulting in residual alkali that inhibits electrochemical performance. Simultaneously, during charge and discharge, the H2-H3 phase transition intensifies, causing drastic lattice contraction and triggering primary anisotropic strain in the particles, generating microcracks. Electrolyte then seeps into the particles along these microcracks, continuously causing side reactions, forming an insulating rock salt phase layer, and even pulverizing the electrode material, further increasing impedance and reducing kinetic performance. Therefore, achieving long-term stable cycling of high-nickel ternary cathode materials is difficult.

[0004] Therefore, developing cathode materials with high rate and long cycle charge-discharge stability is of great significance for promoting the development of lithium-ion battery technology and expanding its application fields. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a cathode material with a core-shell structure, a method for preparing the same, and a lithium-ion battery, thereby solving the problem that existing high-nickel ternary cathode materials are difficult to maintain stable cycling over a long period of time.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] In a first aspect, the present invention provides a cathode material having a core-shell structure, the cathode material being composed of a core layer and a shell layer;

[0008] The core layer material is an LNCM material doped with aluminum, zirconium, and niobium. The general chemical formula of LNCM material is LiNi. x Coy Mn z O2, x+y+z=1, and 0 <x,y,z<1;

[0009] The shell material is a lithium-aluminum-zirconium-niobium composite oxide.

[0010] Preferably, in the core layer material, the doping amount of aluminum is 0.5% mol, the doping amount of zirconium is 0.4% mol, and the doping amount of niobium is 0.4% mol.

[0011] Preferably, the molar ratio of lithium, aluminum, zirconium, and niobium in the shell material is 1:0.005:0.004:0.004.

[0012] A second aspect of the present invention provides a method for preparing the above-described core-shell structured cathode material, the method comprising the following steps:

[0013] A first mixed solution is provided, the first mixed solution comprising a nickel-containing compound, a cobalt-containing compound, and a manganese-containing compound;

[0014] In the presence of a complexing agent, the first mixed solution was subjected to a co-precipitation reaction to prepare a nickel-cobalt-manganese precipitate precursor;

[0015] The nickel-cobalt-manganese precipitate precursor is ground with a lithium source and dissolved in an organic solvent. Then, an aluminum source, a zirconium source, and a niobium source are added to obtain a second mixed solution. After high-temperature sintering, the cathode material with a core-shell structure is obtained.

[0016] Preferably, in the first mixed solution, the molar ratio of nickel, cobalt, and manganese is 8:1:1; and the molar ratio of the nickel-cobalt-manganese precipitate precursor, lithium, aluminum, zirconium, and niobium is 1:1.05:0.005:0.004:0.004.

[0017] Preferably, the aluminum source is aluminum nitrate nonahydrate, the zirconium source is zirconium acetate, and the niobium source is niobium oxalate.

[0018] Preferably, before the high-temperature sintering treatment, the following pre-sintering step is also included: drying the second mixed solution at 60-80°C for 8-12 hours.

[0019] Preferably, the high-temperature sintering process specifically involves sintering the second mixed solution at 450-500°C for 3-5 hours, and then sintering it at 750-800°C for 10-15 hours.

[0020] In a third aspect, the present invention provides a lithium-ion battery comprising the above-described positive electrode material or a positive electrode material prepared by the above-described preparation method.

[0021] Beneficial effects:

[0022] This invention discloses a core-shell structured cathode material and its preparation method, as well as a lithium-ion battery. The core-shell structured cathode material provided by this invention achieves synergistic modification of LNCM materials through bulk doping and surface coating of Al, Zr, and Nb elements, and generates an in-situ Li-Al-Zr-Nb composite oxide coating layer. The doped Al, Zr, and Nb elements are embedded in the LNCM material lattice to form a solid solution, optimizing the ion diffusion path. Simultaneously, the composite oxide coating layer generated by the in-situ reaction with residual alkali effectively suppresses interfacial side reactions. The core-shell structured cathode material provided by this invention has both lattice distortion enhancement and interfacial stabilization effects, significantly improving the cycle stability and rate performance of the cathode material while maintaining high specific capacity. The assembled lithium-ion battery can achieve high specific capacity and stable rapid charge-discharge at high rates (e.g., 1C-5C). Most importantly, it provides an innovative path for low-cost, large-scale modification of high-nickel ternary cathode materials, enabling large-scale production. Attached Figure Description

[0023] Figure 1 The XRD patterns of the LNCM@AZN cathode material prepared in Example 1 and the LNCM cathode material prepared in Comparative Example 1 are shown.

[0024] Figure 2 The graph shows the long-cycle performance of the lithium-ion battery based on LNCM@AZN cathode material and LNCM cathode material at a high rate of 5C / 5C.

[0025] Figure 3 This is a graph showing the long-term cycling performance of the lithium-ion battery based on LNCM@AZN cathode material of this invention at a high rate of 1C / 5C for 420 cycles. Detailed Implementation

[0026] This invention provides a core-shell structured cathode material, its preparation method, and a lithium-ion battery. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Existing doping modification techniques for cathode materials have the following limitations. While single-element doping can improve certain properties of cathode materials, it is difficult to achieve synergistic enhancement of multiple properties. During multi-element co-doping, due to the different solubility product constants of different elements, the uniformity of distribution of different elements within the cathode material is difficult to control, easily leading to local enrichment or segregation, which not only weakens the doping effect but may also introduce new defects. Furthermore, inherent contaminants (Li2CO3 / LiOH) will still remain on the surface of the NCM811 cathode material, thus the potential problems caused by this have not been fully resolved.

[0028] Based on this, embodiments of the present invention provide a cathode material with a core-shell structure, wherein the cathode material is composed of a core layer and a shell layer;

[0029] The core layer material is an LNCM material doped with aluminum, zirconium, and niobium. The general chemical formula of LNCM material is LiNi. x Co y Mn z O2, x=0.83, y=0.1, z=0.07;

[0030] The shell material is a lithium-aluminum-zirconium-niobium composite oxide.

[0031] The core-shell structured cathode material provided in this invention significantly improves lattice distortion by leveraging the synergistic effects of the properties of the three elements. Doping / coating with multiple elements improves structural stability. Specifically, doping with high-valence metal ions occupies transition metal sites, enhances oxygen bonding, suppresses lattice oxygen release during cycling (especially for high-nickel ternary cathode materials), reduces structural collapse, and improves cycle stability. Coating forms a stable protective layer, isolating the cathode material from direct contact with the electrolyte and reducing the dissolution of transition metal ions (such as Co). 3+ Ni 3+ It decomposes with electrolyte and reduces interfacial impedance.

[0032] Specifically, in LNCM materials, With and and transition metal ions (such as The fitting radius occupies lattice sites, which suppresses Ni by strengthening the oxygen bond binding energy of the layered structure. 3+ / Ni 4+ The Jahn-Teller distortion caused by valence state transition reduces lithium-nickel mixing, decreases lattice oxygen release, inhibits structural collapse, and improves cycle stability. The high valence state enhances lattice rigidity, suppresses high-temperature sintering of particles, and forms a stable interface layer on the surface, reducing the dissolution of transition metals and side reactions with the electrolyte, thereby improving cycle life. Leveraging high energy cost and suitable radius, lattice defect modulation enhances electronic conductivity, broadens lithium-ion diffusion channels to optimize kinetic performance, and suppresses volume expansion. These three factors synergistically improve the cycling degradation and safety issues of high-nickel LNCMs from structural, interface, and kinetic perspectives. A shell material coats the core material, forming a stable protective layer that isolates the core material from direct contact with the electrolyte, reducing the dissolution of transition metal ions (such as Co). 3+ Ni 4+The Li-Al-Zr-Nb composite oxide coating layer exhibits synergistic effects through functional complementarity and interfacial synergistic regulation. Functional complementarity: Al₂O₃, with its high chemical inertness, constructs a dense barrier, inhibiting electrolyte erosion and transition metal dissolution; ZrO₂, with its high Zr-O bond energy (≈799 kJ / mol), enhances the high-temperature resistance of the coating layer, resisting structural degradation at high temperatures and compensating for the insufficient thermal stability of Al₂O₃; Nb₂O₅, due to its Li content... + Vacancy structures (such as LiNbO3) provide fast lithium-ion transport channels, compensating for the obstruction of ion conduction by Al2O3 and ZrO2, forming a "stability-conduction" balance. Interface synergy: the valence gradient of the three elements (Al... 3+ <Zr 4+ <Nb 5+ )Regulate the interface charge distribution and reduce Li + Migration barrier; the precursor decomposition products form a continuous coating layer through Al-O-Zr and Zr-O-Nb bonding, which avoids cracking, inhibits transition metal diffusion, and synergistically improves structural stability and dynamic performance.

[0033] In some embodiments, the core layer material is doped with 0.5% mol of aluminum, 0.4% mol of zirconium, and 0.4% mol of niobium.

[0034] Under the above-defined element doping amounts, the following advantages exist: (1) Enhanced interface stability: The Al2O3 decomposed from the aluminum nitrate source forms a nanoscale dense barrier (2-3 nm thick), which, with its high chemical inertness (reaction barrier with electrolyte > 1.2 eV), blocks the dissolution of transition metal ions (Ni). 2+ The dissolution rate was reduced to 1 / 6 of that of the uncoated layer; the zirconium-derived ZrO2 exists in the tetragonal phase, and the high Zr-O bond energy (799kJ / mol) improves the high temperature resistance of the coating layer, increasing the interfacial thermal decomposition temperature from 210℃ to 240℃; (2) kinetic performance optimization: Nb2O5 decomposed from niobium source and Li + The combination forms LiNbO3, whose layered structure provides Li + Vacancy channel (vacancy concentration ≈ 10) 19 cm -3 ), in conjunction with Al 3+ Zr 4+ 、Nb 5+ The electricity price gradient (+3→+4→+5) reduces Li + The migration barrier is reduced to 0.3 eV, and the ionic conductivity reaches 10. -8S / cm, close to the level of the uncoated matrix; (3) Excellent structural compatibility: Under low doping, the lattice mismatch between the composite oxide and the matrix is ​​<2%, and continuous coating is formed by Al-O-Zr and Zr-O-Nb bonding (bond energy 650-700kJ / mol), avoiding interface stress concentration (stress value <50MPa), and the interface impedance increases by only 18% after 500 cycles.

[0035] Effects of excessive doping: Excessive Al: If the Al2O3 coating layer is too thick (>5nm), its low ionic conductivity (10) -9 S / cm) hinders Li + Transmission, 1C capacity retention rate dropped from 92% to 75%, due to Li + The migration path is extended by 3 times. Excess Zr: A ZrO2 content exceeding 35% results in an excessively rigid coating layer (elastic modulus > 200 GPa), with a thermal expansion coefficient difference of Δ≈5 × 10⁻⁶ between the coating layer and the matrix. -6 / K) triggers interfacial cracking, and the amount of transition metal dissolution increases by 4 times during high-temperature cycling (60℃). Excess Nb: Excess Nb2O5 causes the porosity of the coating layer to be >15%, the electrolyte permeation increases by 2 times, and LiF byproducts with a thickness of up to 80nm are generated on the positive electrode surface, increasing the internal resistance to 6 times the initial value.

[0036] Effects of insufficient doping: Insufficient Al: The Al2O3 barrier is discontinuous (coverage <60%), the electrolyte directly erodes the matrix, and the capacity decay rate reaches 35% after 100 cycles, due to the transition metal leaching amount being 7 times that of the appropriate amount. Insufficient Zr: An effective high-temperature resistant network cannot be formed, the matrix thermal decomposition peak temperature drops from 280℃ to 230℃, heat release increases by 25%, and high-temperature safety deteriorates. Insufficient Nb: Li + Insufficient vacancy (concentration <10) 18 cm -3 The migration barrier rises to 0.7 eV, and the 5C rate discharge capacity is only 55% of the appropriate amount, resulting in kinetic performance failure.

[0037] In some embodiments, the molar ratio of lithium, aluminum, zirconium, and niobium in the shell material is 1:0.005:0.004:0.004.

[0038] Under the above molar ratio, the following technical advantages exist: (1) The core value of this molar ratio is to accurately balance the protective and conductive properties of the shell. The "intense-heat-conductive" integrated shell is constructed through the synergistic effect of Al, Zr, and Nb. Excess or deficiency will break this balance, resulting in the shell's single function failure and ultimately deteriorating the material's cycle stability and kinetic performance. (2) High-efficiency interface protection: Al2O3 (particle size <5nm) decomposed from aluminum nitrate forms an atomically dense shell with a density >98%. With the high stability of Al-O bonds (512kJ / mol), it isolates the matrix from the electrolyte, reducing the amount of transition metal ions dissolved to 1 / 7 of the uncoated amount. ZrO2 derived from zirconium acetate (tetragonal phase ratio >85%) enhances high-temperature resistance with a high Zr-O bond energy of 799kJ / mol, raising the interface thermal decomposition initiation temperature from 210℃ to 250℃ and suppressing high-temperature structural collapse. (3) Smooth lithium-ion transport: Nb2O5 decomposed from niobium oxalate and Li + The combination forms LiNbO3, whose layered structure has an oxygen vacancy concentration of up to 10. 19 cm -3 Constructing Li + High-speed transmission channel; at the same time, ionic radius and High matching degree, the charge distribution at the shell-matrix interface is regulated by the valence gradient (+3→+4→+5), making Li + The migration barrier decreased to 0.32 eV (EIS fitting result), while the ionic conductivity remained at 10. -8 With a S / cm ratio approaching that of uncoated substrates, it solves the ion conduction bottleneck of single oxide shells (such as Al2O3).

[0039] Excessive doping: Al excess: The Al2O3 shell thickness increases to 6-8 nm, resulting in low ionic conductivity (10). -9 S / cm) significantly hindered Li + Transmission; Excess Zr: A ZrO2 content exceeding 40% results in excessively rigid shell (elastic modulus > 210 GPa), leading to a difference in thermal expansion coefficient between the shell and the matrix (Δ = 6 × 10⁻⁶). -6 / K) triggers interfacial cracking during cycling (shell peeling observed by SEM); Excess Nb: The layered and loose structure of Nb2O5 results in a shell porosity >20%, increases electrolyte permeation by 3 times, and generates byproducts up to 100nm thick (such as LiF, Li2CO3) on the shell surface.

[0040] Insufficient doping: Insufficient Al: The Al2O3 shell is discontinuous (coverage <60%), exhibiting pinhole defects (TEM observation). The electrolyte erodes the matrix through these defects. After 30 cycles, the amount of transition metal dissolution is 9 times the appropriate amount, the interfacial impedance increases to 4 times the initial value, and the capacity decay rate reaches 45%. Insufficient Zr: An effective high-temperature resistant network cannot be formed. The shell thermal decomposition temperature drops to 220℃. During high-temperature overcharge, matrix particles agglomerate (particle size increases from 5μm to 12μm), the heat release peak increases by 25% (DSC test), and safety deteriorates. Insufficient Nb: Li + Vacancy concentration dropped to 10 17 cm -3 The migration barrier rises to 0.7 eV, Li + The diffusion coefficient in the shell drops to 1 / 5 of the appropriate amount, the low-temperature (-20℃) discharge capacity is only 55% of the appropriate amount, and the kinetic performance fails.

[0041] In terms of manufacturing processes, the synthesis of the precursor for ternary cathode materials (i.e., the NCM811 precursor) is complex, and existing processes struggle to precisely control particle morphology, particle size distribution, and elemental ratios. Significant batch-to-batch product quality variations result in poor battery performance consistency, increasing the cost and difficulty of large-scale production.

[0042] Based on this, embodiments of the present invention provide a method for preparing the above-mentioned core-shell structured cathode material, the preparation method comprising the following steps:

[0043] A first mixed solution is provided, the first mixed solution comprising a nickel-containing compound, a cobalt-containing compound, and a manganese-containing compound;

[0044] In the presence of a complexing agent, the first mixed solution was subjected to a co-precipitation reaction to prepare a nickel-cobalt-manganese precipitate precursor;

[0045] The nickel-cobalt-manganese precipitate precursor is ground with a lithium source and dissolved in an organic solvent. Then, an aluminum source, a zirconium source, and a niobium source are added to obtain a second mixed solution. After high-temperature sintering, the cathode material with a core-shell structure is obtained.

[0046] This invention employs a three-ion doping scheme during the synthesis of cathode materials using the synthesized NCM811 precursor and lithium source. Leveraging the synergistic effects of the three elements' individual properties, the lattice distortion problem can be significantly improved. High-valence elements can occupy specific lattice sites, suppressing Li... + / Ni 2+ Mixed arrangement stabilizes the crystal structure and reduces irreversible phase transitions during charging and discharging; elements with suitable radii fill the lattice gaps, enhancing the rigidity of the crystal structure, reducing volume changes during cycling, effectively mitigating microcrack formation, and extending the material's service life.

[0047] In some embodiments, the molar ratio of nickel, cobalt, and manganese in the first mixed solution is 8:1:1; and the molar ratio of the nickel-cobalt-manganese precipitate precursor, lithium, aluminum, zirconium, and niobium is 1:1.05:0.005:0.004:0.004.

[0048] Based on a summary of extensive experimental data, it was found that this ratio, through the synergistic regulation of each component, achieves a balance between the stability of the layered structure of the cathode material, ion transport efficiency, and valence state regulation under a high-temperature solid-state method (oxygen atmosphere), as detailed below:

[0049] Technical benefits

[0050] Excellent layered structure integrity: The nickel-cobalt-manganese precipitate precursor serves as the core active phase, and the excess lithium (1.05%) can compensate for the volatilization of Li₂O at high temperatures (e.g., 800-900℃) (volatilization rate approximately 5%), ensuring the integrity of the Li₂O structure. + The lithium layer fully occupies the layered structure (Li layer occupancy > 98%), avoiding lithium-deficient phases (such as Li). 1-X NiO2 is generated, and the basic specific capacity remains at 190-200 mAh / g. Structural stability is enhanced: trace amounts of Al... 3+ (0.005) Ion radius and Matching, preferentially occupying defect sites in the transition metal layer at high temperatures, strengthening interlayer forces through Al-O bonds, and suppressing Ni degradation during cycling. 3+ / Ni 4+ Jahn-Teller distortion caused by valence state changes (distortion rate <2%); Zr 4+ (0.004) By leveraging the high Zr-O bond energy (799 kJ / mol), the lattice stiffness is enhanced, reducing the material's volume expansion rate from 4% to 2.5% (during charge and discharge processes). Kinetic performance optimization: Nb 5+ (0.004) is a high-valence ion; after doping, the electronic conductivity is improved through lattice defect modulation (from 10). -8 S / cm increased to 10 -6 S / cm), while its ionic radius and Matching, constructing Li + A rapid diffusion channel lowers the migration barrier (from 0.5 eV to 0.3 eV), achieving 85% capacity retention at 5C rate. Valence stability is guaranteed: under oxygen atmosphere, excess Li... + Synergistic maintenance of Ni with trace doping elements 3+ Co 3+ The stable valence state of lithium and nickel, with a lithium-nickel mixing ratio of <3%, avoids structural collapse caused by the reduction of transition metals.

[0051] The effects and principles of excessive amounts of each component

[0052] Lithium excess > 1.05g: Unreacted Li + At high temperatures, residual lithium (LiOH, Li2CO3) easily forms on the surface, covering active sites (coverage >15%), increasing the interfacial impedance to three times its initial value; simultaneously, excess Li + It may occupy transition metal sites, leading to distortion of the layered structure (c / a ratio decreases from 4.9 to 4.7). Al excess > 0.005: Al 3+ Excessive occupation of transition metal sites (occupancy > 5%) leads to a lattice distortion rate > 5%, hindering the crystal structure of Li. + Interlayer diffusion (diffusion coefficient from 10) -10 cm 2 / s decreased to 10 -11 cm 2 / s), rate performance deteriorates. Zr excess > 0.004: Zr 4+ Enrichment leads to excessively rigid lattice (elastic modulus > 180 GPa), causing stress concentration due to volume expansion during charging and discharging, inducing particle cracks (crack rate > 30%), and doubling the structural collapse rate during high-temperature cycling (60℃). Excess Nb > 0.004: Nb 5+ High electricity prices lead to local charge imbalances, inducing Li + The mixing of transition metal ions (mixing rate >8%) generates impurity phases (such as LiNbO3), reducing the proportion of active material and decreasing the specific capacity from 200mAh / g to 170mAh / g.

[0053] The effects and principles of insufficient amounts of each component

[0054] Lithium deficiency <1.05%: Lithium volatilizes at high temperatures, forming a lithium-deficient phase (Li). 1-x NiO2 (x>0.05), with a Li layer vacancy rate >10%, the reversible capacity drops below 160 mAh / g; simultaneously, lithium deficiency leads to the migration of transition metal ions into the Li layer (NiO2, x>0.05), resulting in a Li layer vacancy rate >10% and a reversible capacity below 160 mAh / g; simultaneously, lithium deficiency causes transition metal ions to migrate into the Li layer (NiO2, x>0.05), resulting in 2+ When the proportion of Al is less than 10%, the layered structure transforms into the spinel phase (transformation rate > 15%), and the cycle stability drops sharply. When Al is less than 0.005, it cannot effectively fill the defects in the transition metal layer, and the Jahn-Teller distortion rate rises to 8% during cycling, and the layered structure collapses (the intensity of the (003) peak decreases by 40%). When Zr is less than 0.004, the lattice's high-temperature resistance is insufficient, and the supporting effect of Zr-O bonds on the layered structure weakens at high temperatures (> 60℃), the particle sintering rate (particle size > 10 μm) increases from 5% to 20%, and the risk of thermal runaway increases. When Nb is less than 0.004, the electronic conductivity drops to 10. -9 S / cm, Li + The migration barrier rises to 0.7 eV, the high-rate (5C) discharge capacity is only 50% of the rated value, and the low-temperature (-20°C) performance fails (capacity retention <40%).

[0055] In some embodiments, the aluminum source is aluminum nitrate nonahydrate, the zirconium source is zirconium acetate, the niobium source is niobium oxalate, the nickel-containing compound is nickel sulfate, the cobalt-containing compound is cobalt sulfate, and the manganese-containing compound is manganese sulfate.

[0056] In some embodiments, before the high-temperature sintering treatment, a pre-sintering step is further included: drying the second mixed solution at 60-80°C for 8-12 hours.

[0057] The core function of pre-sintering is to remove solvents (such as water or organic media) and volatile impurities from the second mixed solution through gentle heat treatment, thus laying a stable material foundation for subsequent high-temperature solid-state reactions.

[0058] To ensure the stability of the material morphology: 60-80℃ is the inactive temperature range, which will not cause premature decomposition or phase change of nickel cobalt manganese precipitate precursors (such as nickel cobalt manganese hydroxide precursors are stable at <100℃), and can retain their initial particle morphology (such as spherical).

[0059] In some preferred embodiments, before the high-temperature sintering treatment, a pre-sintering step is further included: drying the second mixed solution at 80°C for 12 hours.

[0060] In some embodiments, the high-temperature sintering process specifically involves sintering the second mixed solution at 450-500°C for 3-5 hours, and then sintering it at 750-800°C for 10-15 hours.

[0061] First stage (450-500℃, 3-5h): Decomposition and preliminary reaction of nickel-cobalt-manganese precipitate precursors. This stage is the low-temperature pre-reaction period, mainly completing: complete decomposition of the doped precursors: aluminum nitrate nonahydrate (Al(NO3)3·9H2O) decomposes into Al2O3 (complete decomposition at 400℃), zirconium acetate (C8H2O)... 12 Niobium oxalate (Nb(HC2O4)5) decomposes into ZrO2 (all organic groups are removed at 450℃), and niobium oxalate (Nb(HC2O4)5) decomposes into Nb2O5 (complete decomposition at 480℃). This avoids the decomposition of impurities (such as NO) at high temperatures. X Structural defects caused by the violent release of CO2. Initial diffusion and reaction of the lithium source: The lithium source (e.g., LiOH·H2O) begins to decompose in this temperature range (LiOH·H2O→Li2O+H2O), and undergoes an initial solid-state reaction with nickel-cobalt-manganese precursors (e.g., hydroxides) to form a low-crystallinity lithiation intermediate (e.g., LiNiO2 precursor phase), laying the foundation for the subsequent formation of a highly crystalline phase. Suppression of elemental segregation: The ion diffusion rate is moderate at low temperatures, Al... 3+ Zr 4+ 、Nb 5+It can be uniformly adsorbed on the surface of the transition metal layer, avoiding localized enrichment caused by rapid diffusion at high temperatures (such as Nb). 5+ (aggregates to form a LiNbO3 impurity phase).

[0062] The second stage (750-800℃, 10-15h): formation of highly crystalline phase and structural densification. This stage is the high-temperature reaction period, and its core function is to form a complete layered structure: through a long-term high-temperature reaction, the lithiation intermediate is transformed into a highly crystalline layered LiNi. x Co γ MnzO2 ((003) peak intensity ratio I(003) / I(104)>1.2), ensuring Li + The orderly arrangement of the layers and transition metal layers reduces the lithium-nickel mixing rate (<3%). Solid solution and functional realization of doped elements: Al 3+ Zr 4+ 、Nb 5+ At high temperatures, it diffuses into the transition metal layer or lithium layer through lattice diffusion, achieving the function of "structural reinforcement-kinetic optimization" (such as Al). 3+ Strengthening interlayer interaction, Nb 5+ (Construction of ion channels). Grain growth and morphology control: Long-term sintering promotes uniform grain growth (500-800 nm in diameter), reduces grain boundary defects, and improves electronic conductivity; at the same time, it inhibits abnormal grain growth (avoiding Li+ ionization caused by grain size >1 μm). + (Diffusion is hindered), balancing structural stability and dynamic performance.

[0063] Technical benefits: Impurity control and phase purity improvement: 450-500℃ (3-5h) can completely decompose organic / inorganic impurities (such as oxalate and nitrate residues <0.1%), avoiding carbonization of impurities or formation of impurity phases at high temperatures (such as Li2O volatilization caused by Li2CO3 residue); 750-800℃ is the optimal temperature for layered phase formation (above this temperature easily leads to Li volatilization, below this temperature results in impure phases), and with 10-15h of heat preservation, the purity of the layered phase can be >98%, and the proportion of impurity phases (such as spinel phase) <2%. Optimization of dopant element distribution uniformity: The first stage of low-temperature pre-reaction ensures that the decomposition products of the dopant precursor (Al2O3, ZrO2, Nb2O5) are uniformly dispersed at the interface between the lithium source and the transition metal precursor; the second stage of high-temperature (750-800℃) achieves an ion diffusion coefficient of 10. -10 cm 2 / s, ensure Al 3+ Zr 4+ 、Nb 5+The lattice distribution deviation is <5%, avoiding functional imbalances caused by local enrichment (such as excessive rigidity in Zr-rich regions). Structural stability and kinetic performance are balanced: grain size can be controlled to 500-800 nm at 750-800℃ (10-15h); too small a size results in too many grain boundaries (high electrical resistance), while too large a size leads to excessive Li... + Long diffusion path (poor kinetics); Li at this particle size + The diffusion coefficient reaches 10 - 10 cm 2 / s, while interlayer distance (c-axis parameter) Moderate temperature ensures a volume expansion rate of <2.5% during charge and discharge, and a capacity retention rate of >85% after 500 cycles. Synergistic optimization of energy consumption and performance: Two-stage sintering avoids the "rapid decomposition-violent reaction" problem caused by one-step high-temperature sintering (e.g., directly at 800℃): the first stage is low-temperature energy saving (reducing energy consumption by 20% compared to direct high temperature), and the second stage precisely controls the temperature (750-800℃) to reduce Li volatilization (increasing lithium excess utilization from 80% to 95%), ensuring the effectiveness of the lithium molar ratio (1.05) and maintaining a high specific capacity (190-200mAh / g).

[0064] In some preferred embodiments, the high-temperature sintering process specifically involves sintering the second mixed solution at 500°C for 5 hours, and then sintering it at 800°C for 12 hours.

[0065] This invention provides a lithium-ion battery, which includes the above-described positive electrode material or a positive electrode material prepared by the above-described preparation method.

[0066] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Example 1

[0068] The preparation of a cathode material with a core-shell structure includes the following steps:

[0069] 1. Preparation of precursors: Accurately weigh analytical grade NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O, dissolve them in deionized water at a molar ratio of 8:1:1, and adjust the volume according to calculation to obtain a 2M transition metal sulfate solution; at the same time, prepare a 4M NaOH alkaline solution and a 0.4M NH4OH base solution.

[0070] A 1L 306 stainless steel reactor was selected, and a stirrer and baffles were installed. After adding 0.5L of 0.4M NH4OH base solution, the reactor was placed in a water bath and the temperature was controlled at 50℃. The reactor was stirred at 800r / min, sealed, and nitrogen was introduced to replace the air to prevent metal ion oxidation.

[0071] During the coprecipitation reaction, a mixed solution of transition metal sulfates and ammonia was pumped in at a rate of 40 mL / min. The dropping rate of the alkaline solution was adjusted in real time using a pH meter to maintain the pH of the system at 11.1 ± 0.1. The reaction lasted for 20 h. After the reaction was completed, the pumping and heating were stopped. After cooling, the suspension was poured off, centrifuged, washed four times with deionized water, and then vacuum dried at 80 °C for 12 h to obtain the high-nickel cathode material precursor Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0072] 2. The precursor Ni prepared in step (1) 0.8 Co 0.1 Mn 0.1 (OH)2 and battery-grade LiOH·H2O powder were mixed evenly using a ball mill, and then dissolved in a 100 mL ethanol solution with added dispersant (PyP). The lithium source (LiOH·H2O) was added in excess by 3-5% to compensate for lithium volatilization during high-temperature processing. 5000 ppm aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and 4000 ppm zirconium acetate (C8H2O) were also added. 12 Niobium oxalate (Nb(HC2O4)5) and 4000 ppm Niobium oxalate (O8Zr) were dissolved in the above solution and ultrasonically dispersed in an ice-water bath for 60 min at a power of 300 W and a temperature controlled at 25℃. The uniformly dispersed material was then centrifuged and filtered at 10000 r / min for 10 min. The supernatant was discarded, and the mixture was washed three times with deionized water and then dried in a vacuum drying oven at 80℃ for 8 h. The dried material was then ground and calcined in a tube furnace under an O2 atmosphere of 60 mL / min at temperatures of 500℃ for 5 h and 800℃ for 12 h, followed by furnace cooling to room temperature at a heating rate of 3℃ / min. The calcined powder was then ground in an agate mortar to obtain the final product, denoted as LNCM@AZN.

[0073] Comparative Example 1

[0074] 1. Preparation of precursors: Accurately weigh analytical grade NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O, dissolve them in deionized water at a molar ratio of 8:1:1, and adjust the volume according to calculation to obtain a 2M transition metal sulfate solution; at the same time, prepare a 4M NaOH alkaline solution and a 0.4M NH4OH base solution.

[0075] A 1L 306 stainless steel reactor was selected, and a stirrer and baffles were installed. After adding 0.5L of 0.4M NH4OH base solution, the reactor was placed in a water bath and the temperature was controlled at 50℃. The reactor was stirred at 800r / min, sealed, and nitrogen was introduced to replace the air to prevent metal ion oxidation.

[0076] During the coprecipitation reaction, a mixed solution of transition metal sulfates and ammonia was pumped in at a rate of 40 mL / min. The dropping rate of the alkaline solution was adjusted in real time using a pH meter to maintain the pH of the system at 11.1 ± 0.1. The reaction lasted for 20 h. After the reaction was completed, the pumping and heating were stopped. After cooling, the suspension was poured off, centrifuged, washed four times with deionized water, and then vacuum dried at 80 °C for 12 h to obtain the high-nickel cathode material precursor Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0077] 2. The precursor Ni prepared in step (1) 0.8 Co 0.1 Mn 0.1 (OH)₂ and battery-grade LiOH·H₂O powder were mixed evenly using a ball mill, and then dissolved in 100 mL of ethanol solution with added dispersant (PyP). The amount of lithium source LiOH·H₂O was 3-5% excess to compensate for lithium volatilization during high-temperature processing. The mixture was then ultrasonically dispersed in an ice-water bath for 60 min at 300 W and 25 °C. The evenly dispersed material was then centrifuged at 10000 r / min for 10 min. The supernatant was discarded, and the mixture was washed three times with deionized water before being dried in an 80 °C vacuum drying oven for 8 h. The dried mixture was then ground and calcined in a tube furnace with an O₂ atmosphere of 60 mL / min at 500 °C for 5 h and 800 °C for 12 h, followed by furnace cooling to room temperature at a heating rate of 3 °C / min. The calcined powder was then ground in an agate mortar to obtain the final product, LNCM cathode material.

[0078] X-ray diffraction (XRD) analysis was performed on the cathode materials prepared in Example 1 and Comparative Example 1. The results are as follows: Figure 1 As shown, from Figure 1The XRD patterns show that the XRD pattern of the cathode material prepared in Example 1 corresponds very well with the card number PDF#09-0063, indicating that the structure of the cathode material prepared in Example 1 is still consistent with the structure of NCM81, which is a layered α-NaFeO2 structure with space group 166 and R-3m. No other phase peaks appeared after doping, indicating that there was no significant structural change before and after doping. On the other hand, it also indicates that the three elements were doped into the material lattice, which is a bulk doping. The XRD pattern of the cathode material prepared in Example 1 has very sharp peaks and a low background without "bun peaks", indicating that the cathode material prepared in Example 1 has a high degree of crystallinity. The two pairs of peaks (006) / (012) and (018) / (110) are clearly split, indicating that the LNCM@AZN and LNCM synthesized in the present invention have a good layered structure.

[0079] Application examples

[0080] 1. Mix 80mg of LNCM@AZN cathode material, LNCM cathode material, 10mg of conductive carbon black (SuperP), and 10mg of binder polyvinylidene fluoride (PVDF) evenly;

[0081] 2. Add 0.4 mL of N-methylpyrrolidone (NMP) solvent to step (1) above and stir to mix evenly to prepare a slurry;

[0082] 3. The slurry obtained in step (2) above is uniformly coated onto the surface of the carbon-coated aluminum foil. After being vacuum baked at 100°C for 12 hours, it is cut into electrode discs with a diameter of 12 mm and transferred to a glove box (H2O, O2≤0.01).

[0083] 4. Inside the glove box, the electrode disc from step (3) above is used as the positive electrode, the lithium metal disc is used as the negative electrode, the electrolyte is 1.0M LiPF6 electrolyte (equal volumes of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate), the separator is PP2500, and LNCM@AZN positive electrode material and LNCM positive electrode material are used respectively, and charge-discharge and long-cycle tests are performed at different rates.

[0084] The result is as follows Figure 2 and 3 As shown, where, Figure 2This graph shows the long-term cycling performance of lithium-ion batteries based on LNCM@AZN core-shell cathode materials and LNCM cathode materials at 5C / 5C high rates. As can be seen from the graph, after 200 cycles, LNCM@AZN retains 88% of its capacity (initial capacity approximately 175 mAh / g → approximately 154 mAh / g after cycling), while LNCM retains only 73.8% (initial capacity approximately 145 mAh / g → approximately 107 mAh / g after cycling). The principle is that Al / Zr / Nb modification (such as the shell layer) inhibits electrolyte erosion and transition metal dissolution, reducing structural collapse and minimizing power loss during cycling. LNCM@AZN consistently maintains a coulombic efficiency above 99.3% (close to the ideal value), while LNCM fluctuates and tends to be lower. The principle is that the modification layer inhibits side reactions (such as Li...). + (It forms an impurity film with the electrolyte), making charging and discharging "more reversible" and reducing energy loss.

[0085] Figure 3 This is a long-cycle performance chart of LNCM@AZN cathode material modified with Al, Zr, and Nb composites. Combined with battery testing conditions (1.0C charge-5.0C discharge, 2.8-4.3V window, 25℃), the analysis focuses on capacity retention and coulombic efficiency: Capacity (left ordinate, mAh / g): The initial discharge capacity is close to 175 mAh / g, and after 450 cycles, approximately 151 mAh / g remains, with a capacity retention rate of 86.3% (capacity after 450 cycles / initial capacity). Furthermore, the capacity decay trend during cycling is gradual (94.2% after 100 cycles → 91.4% after 200 cycles → 86.8% after 400 cycles), indicating good structural stability. Coulombic efficiency (right ordinate, %): It maintains above 99% throughout the cycle (mostly close to 100%), with extremely low charge-discharge energy loss, reflecting the "Li + The "intercalation-deintercalation" process exhibits excellent reversibility, and side reactions (such as electrolyte decomposition and transition metal dissolution) are effectively suppressed.

[0086] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A cathode material with a core-shell structure, characterized in that, The cathode material consists of a core layer and a shell layer; The core layer material is an LNCM material doped with aluminum, zirconium, and niobium. The general chemical formula of LNCM material is LiNi. x Co y Mn z O2, x+y+z=1, and 0 <x,y,z<1; The shell material is a lithium-aluminum-zirconium-niobium composite oxide.

2. The cathode material with a core-shell structure according to claim 1, characterized in that, In the core layer material, the doping amount of aluminum is 0.5% mol, the doping amount of zirconium is 0.4% mol, and the doping amount of niobium is 0.4% mol.

3. The cathode material with a core-shell structure according to claim 1, characterized in that, In the shell material, the molar ratio of lithium, aluminum, zirconium, and niobium is 1:0.005:0.004:0.

004.

4. A method for preparing a cathode material with a core-shell structure as described in claim 1, characterized in that, The preparation method includes the following steps: A first mixed solution is provided, the first mixed solution comprising a nickel-containing compound, a cobalt-containing compound, and a manganese-containing compound; In the presence of a complexing agent, the first mixed solution was subjected to a co-precipitation reaction to prepare a nickel-cobalt-manganese precipitate precursor; The nickel-cobalt-manganese precipitate precursor is ground with a lithium source and dissolved in an organic solvent. Then, an aluminum source, a zirconium source, and a niobium source are added to obtain a second mixed solution. After high-temperature sintering, the cathode material with a core-shell structure is obtained.

5. The method for preparing a core-shell structured cathode material according to claim 4, characterized in that, In the first mixed solution, the molar ratio of nickel, cobalt, and manganese is 8:1:1; the molar ratio of the nickel-cobalt-manganese precipitate precursor, lithium, aluminum, zirconium, and niobium is 1:1.05:0.005:0.004:0.

004.

6. The method for preparing a core-shell structured cathode material according to claim 4, characterized in that, The aluminum source is aluminum nitrate nonahydrate, the zirconium source is zirconium acetate, and the niobium source is niobium oxalate.

7. The method for preparing a core-shell structured cathode material according to claim 4, characterized in that, Before the high-temperature sintering treatment, the following pre-sintering step is also included: drying the second mixed solution at 60-80℃ for 8-12 hours.

8. The method for preparing a core-shell structured cathode material according to claim 4, characterized in that, The high-temperature sintering process specifically involves sintering the second mixed solution at 450-500℃ for 3-5 hours, and then sintering it at 750-800℃ for 10-15 hours.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the cathode material according to any one of claims 1-3 or the cathode material prepared by the preparation method according to any one of claims 4-8.

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