Multi-element differential distribution co-doped single crystal high-nickel cathode material and preparation method

Abstract

The application discloses a multi-element differential distribution co-doped single-crystal high-nickel positive electrode material and a preparation method and application thereof. The material is doped with a first doping element and a second doping element. The first doping element presents a gradient distribution with an increasing concentration from the inside to the outside in the material particles, and the second doping element presents a substantially uniform distribution in the material particles. The first doping element is an element for strengthening the surface stability of the material, and the second doping element is an element for stabilizing the body phase structure of the material. The material is prepared by taking a lithium salt and a ternary positive electrode material precursor as raw materials, introducing a first doping source and a second doping source, mixing, ball-milling and calcining according to a preset stoichiometric ratio.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to single-crystal high-nickel cathode materials with multi-element differential distribution co-doping, their preparation methods, and applications. Background Technology

[0002] With the rapid development of new energy vehicles and large-scale energy storage industries, the market has placed higher demands on the energy density, cycle life, and safety performance of lithium-ion batteries. High-nickel layered oxide cathode materials, due to their high specific capacity and high energy density, are considered an ideal choice for achieving this goal. Among them, single-crystal materials, by eliminating grain boundaries in polycrystalline aggregates, possess superior structural integrity and have gradually become the focus of industrial and academic research in recent years. However, the inherent structural defects of single-crystal high-nickel cathode materials still severely restrict their practical application. On the one hand, nickel ions (Ni... 2+ ) and lithium ions (Li + The similar radii lead to severe lithium / nickel mixing, with some Ni... 2+ Occupying lithium layer migration channels hinders lithium-ion diffusion; on the other hand, in the deep delithiation state, the material undergoes a drastic H2-H3 phase transition, triggering abrupt changes in lattice parameters and a sharp contraction of the c-axis, generating significant internal stress within the single-crystal particles. This, coupled with enhanced lattice oxygen evolution activity, leads to microcracks within the particles, exacerbated interfacial side reactions, and a decrease in cycle life. Although traditional elemental doping strategies can improve material stability to some extent, uniform doping alone is insufficient to form an effective protective barrier on the material surface, while conventional gradient doping often focuses on the distribution control of a single element, making it difficult to achieve comprehensive optimization of the material from bulk to surface. Especially for single-crystal materials, their grain-boundary-free structure places more precise demands on the distribution morphology and functional synergy of doping elements. Summary of the Invention

[0003] The main objective of this invention is to propose a multi-element differentially distributed co-doped single-crystal high-nickel cathode material and its preparation method, so as to simultaneously and synergistically solve the problems of existing single-crystal high-nickel cathode materials (such as NCM, NCA) due to Li... + / Ni 2+ This addresses the problems of bulk structural instability and severe interfacial side reactions caused by mixed arrangement and H2-H3 phase transition. It overcomes the shortcomings of existing doping techniques that make it difficult to simultaneously optimize the bulk and surface stability of materials, so as to obtain both high specific capacity and long cycle life.

[0004] To achieve the above objectives, the present invention proposes the following technical solution:

[0005] A multi-element differentially distributed co-doped single-crystal high-nickel cathode material is disclosed, wherein the material is doped with a first dopant element and a second dopant element, wherein the first dopant element exhibits a gradient distribution with increasing concentration from the inside to the outside of the material particles, and the second dopant element exhibits a basically uniform distribution in the material particles; the first dopant element is used to enhance the surface stability of the material, and the second dopant element is used to stabilize the bulk structure of the material.

[0006] Furthermore, the first doping element is selected from one of Si, Zr, Hf, and Nb, and the second doping element is selected from one of Ti, Al, Mg, and Ga.

[0007] Furthermore, the single-crystal high-nickel cathode material is formed by the first doping element and the second doping element occupying 1 at% of the transition metal sites in the existing single-crystal high-nickel cathode material; the existing single-crystal high-nickel cathode material is NCM or NCA.

[0008] Furthermore, the single-crystal high-nickel cathode material is LiNi. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2, with a c-axis lattice constant of 14.20 Å, Li + / Ni 2+ The degree of mixing was 0.8%.

[0009] Furthermore, in the single-crystal high-nickel cathode material, Si elements are enriched in the near-surface region to enhance surface stability, while Ti elements are uniformly distributed throughout the entire particle bulk phase to stabilize the bulk structure. The two doping elements complement and synergize in terms of spatial distribution and function.

[0010] The present invention also proposes a method for preparing the aforementioned single-crystal high-nickel cathode material, comprising: using lithium salt and ternary cathode material precursor as raw materials, introducing a first doping source and a second doping source, mixing and ball milling according to a preset stoichiometric ratio and calcining to obtain the single-crystal high-nickel cathode material; during the calcination process, the migration barrier of the first doping element contained in the first doping source is higher than the migration barrier of the second doping element contained in the second doping source, so that the first doping element is mainly enriched in the near-surface region of the material particles, and the second doping element is basically uniformly distributed in the bulk phase of the particles.

[0011] Furthermore, the preparation method uses LiOH·H2O and Ni 0.83 Co 0.12 Mn 0.05 Using (OH)₂ precursor as raw material, SiO₂ and TiO₂ are introduced as doping sources, according to Ni… 0.83 Co 0.12 Mn0.05 A mixture of (OH)₂: LiOH·H₂O: SiO₂: TiO₂ in a molar ratio of 1:1.05:0.01:0.01 was ball-milled and then calcined at high temperature to obtain a single-crystal high-nickel cathode material, LiNi. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2.

[0012] Further, the high-temperature calcination includes: first, pre-calcining the mixed ball-milled material in an oxygen atmosphere at a first temperature, and then raising the temperature to a second temperature for high-temperature calcination. More specifically, the first temperature is 450℃~550℃, and the second temperature is 750℃~850℃. Pre-calcination is performed at the first temperature for 4~6 hours, and high-temperature calcination is performed at the second temperature for 10~13 hours.

[0013] The present invention also proposes the application of the aforementioned single-crystal high-nickel cathode material as a cathode material for lithium-ion batteries.

[0014] The present invention also proposes a lithium-ion battery, comprising: a positive electrode, a negative electrode, and an electrolyte, wherein the material of the positive electrode is the aforementioned single-crystal high-nickel positive electrode material.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention constructs a co-doped structure with spatially differentiated distribution of multiple elements by designing a gradient enrichment of the first dopant element (such as Si) in the near-surface region of the particles and a uniform distribution of the second dopant element (such as Ti) in the bulk phase of the particles. The first dopant element, enriched in the near-surface region of the material particles with a gradient distribution (concentration increasing from the inside to the outside), forms strong bonds (such as strong Si-O bonds) with oxygen, thereby forming a stable interface protective layer that effectively blocks the electrolyte from eroding the active material and suppresses interface side reactions. The second dopant element, uniformly doped throughout the bulk phase of the particles, expands the lithium interlayer spacing and stabilizes the lattice oxygen framework by forming strong bonds (such as strong Ti-O bonds), fundamentally suppressing harmful phase transitions during lithium-nickel mixing and charge / discharge processes. Thus, the two co-doped elements complement and synergize in spatial distribution and function, simultaneously improving the bulk structural stability and surface stability of the single-crystal high-nickel cathode material, ultimately obtaining a cathode material with both high specific capacity and long cycle life. Furthermore, this synergistic mechanism of surface protection and bulk stabilization significantly reduces the charge transfer impedance and ohmic impedance of the material, and improves the lithium-ion diffusion coefficient, thereby simultaneously improving the cycle stability (manifested as high capacity retention) and rate performance of the material, ultimately obtaining a single-crystal high-nickel cathode material with both high specific capacity and long cycle life. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the technical route of the embodiments and comparative examples of the present invention.

[0017] Figure 2-1 , Figure 2-2 , Figure 2-3 These are the refined XRD patterns of three samples NCM, Si-NCM, and ST-NCM from the embodiments and comparative examples of this invention.

[0018] Figure 3 These are SEM images of the embodiments and comparative samples of the present invention.

[0019] Figure 4 These are SEM-EDS images of the embodiments and comparative samples of the present invention.

[0020] Figure 5 This is the XPS spectrum of the ST-NCM sample in an embodiment of the present invention.

[0021] Figure 6-1 The first charge-discharge curve of a battery using NCM sample material from Comparative Example 1 of this invention is shown. Figure 6-2 The first charge-discharge curve of the battery using Si-NCM sample material from Comparative Example 2 of this invention is shown. Figure 6-3 These are the charge-discharge curves of batteries using ST-NCM sample material from Example 1 of this invention.

[0022] Figure 7 The graph shows the cycle performance of batteries using the materials of the embodiments and comparative examples of this invention at a rate of 0.5C.

[0023] Figure 8 The figures show the battery rate performance of the sample materials used in the embodiments and comparative examples of this invention.

[0024] Figure 9 The graph shows the long-cycle performance of batteries using the materials of the embodiments and comparative examples of this invention at a high rate of 5C.

[0025] Figure 10-1 These are the EIS spectra of batteries using the materials from the embodiments and comparative examples of this invention; Figure 10-2 This is the equivalent circuit diagram of a battery.

[0026] Figure 11-1 The diagram shows the lithium-ion diffusion coefficient of batteries using the materials of the embodiments and comparative examples of this invention during the charging process. Figure 11-2 This is a graph showing the lithium-ion diffusion coefficient of batteries using the materials of the embodiments and comparative examples of the present invention during the discharge process. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0028] The core of this invention lies in the doping modification of existing high-nickel cathode materials through a specific preparation process, achieving a spatially differentiated distribution of two doping elements (such as silicon (Si) and titanium (Ti)) within the single-crystal high-nickel cathode material particles. Specifically, the Si element exhibits a gradient distribution with gradually increasing concentration from the inside out, while the Ti element shows a uniform distribution. This enhances the surface stability of the material while stabilizing its bulk structure. The differentiated Si-Ti co-doped single-crystal high-nickel cathode material provided by this invention is LiNi. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2, which is composed of LiOH·H2O and Ni 0.83 Co 0.12 Mn 0.05 Using (OH)₂ precursor as raw material, SiO₂ and TiO₂ are introduced as doping sources, according to Ni… 0.83 Co 0.12 Mn 0.05 The SiO2 : TiO2 : LiOH·H2O : SiO2 : TiO2 is prepared by ball milling and high-temperature calcination of a mixture with a molar ratio of 1 : 1.05 : 0.01 : 0.01. In this preparation process, ball milling of the homogeneous mixture ensures that the doped material retains its single-crystal morphology. The high-temperature calcination is a two-step process: pre-calcination followed by a longer-duration high-temperature calcination. Due to the high bond energy of the Si-O bond, once dissolved on the crystal surface, migration into the bulk phase requires an additional migration energy barrier. Therefore, Si diffuses slowly within the crystal lattice, mainly accumulating on the particle surface and forming a gradient distribution with decreasing concentration from the outside to the inside. Ti, with its ionic radius similar to that of transition metal (TM) sites and a low migration energy barrier, diffuses rapidly within the crystal lattice, occupying TM sites relatively uniformly in the bulk phase. This results in a co-doped structure with spatially differentiated Si-Ti element distribution.

[0029] It should be noted that Si (silicon) can be replaced by other elements such as Zr (zirconium), Hf (hafnium), and Nb (niobium), and Ti (titanium) can be replaced by other elements such as Al (aluminum), Mg (magnesium), and Ga (gallium).

[0030] Example 1

[0031] like Figure 1 As shown, in Embodiment 1 of the present invention, Ni 0.83 Co 0.12 Mn0.05 (OH)₂ is used as a precursor, lithium salt LiOH·H₂O is added, and SiO₂ and TiO₂ are introduced as dopant sources (preferably nano-sized powders), according to Ni 0.83 Co 0.12 Mn 0.05 The mixture of (OH)2:LiOH·H2O:SiO2:TiO2 in a molar ratio of 1:1.05:0.01:0.01 was homogeneous and then ball-milled. After ball milling, the mixture was pre-calcined at 500℃ for 5 hours in an oxygen atmosphere, followed by high-temperature calcination at 800℃ for 12 hours, ultimately forming the target product LiNi with good crystallinity. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2 (denoted as ST-NCM) simultaneously achieved co-doping of 1 at% Si and 1 at% Ti. In the ball milling step, the ball-to-material ratio was controlled at 20:1, the rotation speed was about 300 r / min, and the effective ball milling time was about 1.5h (to prevent local overheating of the equipment, a mode of 5 minutes forward rotation / 5 minutes stop / 5 minutes reverse rotation / 5 minutes stop was adopted, so the effective ball milling time was 1.5h, and the actual ball milling time was 3h).

[0032] It should be noted that the temperature and time of the calcination process in the above embodiments are merely exemplary, and those skilled in the art can make appropriate adjustments. For example, the pre-calcination temperature can be selected within the range of 450℃ to 550℃, and the calcination time is not limited to 5 hours, but can be between 4 and 6 hours. Furthermore, the high-temperature calcination after pre-calcination is not limited to 800℃, but can be selected within the range of 750℃ to 850℃, and the calcination time is not limited to 12 hours, but can be between 10 and 13 hours.

[0033] Comparative Example 1

[0034] like Figure 1 As shown, this comparative example uses Ni 0.83 Co 0.12 Mn 0.05 (OH)₂ is used as a precursor, and lithium salt LiOH·H₂O is added, according to Ni 0.83 Co 0.12 Mn 0.05 The mixture was homogeneous with (OH)₂ and LiOH·H₂O at a molar ratio of 1:1.05, and then the same ball milling and calcination process as in Example 1 was used to obtain single-crystal LiNi material. 0.83 Co 0.12 Mn 0.05 O2 (denoted as NCM).

[0035] Comparative Example 2

[0036] This comparative example uses Ni 0.83 Co 0.12 Mn 0.05 (OH)₂ is used as a precursor, lithium salt LiOH·H₂O is added, and SiO₂ is introduced as a dopant source, according to Ni 0.83 Co 0.12 Mn 0.05 The mixture of (OH)2: LiOH·H2O: SiO2 in a molar ratio of 1:1.05:0.01 was homogeneous, and then the same ball milling and calcination process as in Example 1 was used to obtain single-crystal LiNi material. 0.82 Co 0.12 Mn 0.05 Si 0.01 O2 (denoted as Si-NCM) enables the replacement of 1 at% of transition metal sites in the material with Si.

[0037] The crystal structures of the three samples obtained above were analyzed using a Bruker D8 Advance X-ray diffractometer (XRD). A Cu Kα radiation source (wavelength λ = 0.15406 nm) was used, with operating parameters set to 45 kV tube voltage and 40 mA tube current. The scanning range was set to 10°–80° (2θ), and the scanning rate was 2° / min. The refined XRD patterns of the three samples (NCM, Si-NCM, and ST-NCM) are shown below. Figure 2-1 , Figure 2-2 , Figure 2-3 Detailed crystal structure information was obtained through refinement using GSAS II software. All diffraction peaks conformed to the typical α-NaFeO2 layered structure characteristics and belonged to the R-3m space group. Notably, no obvious impurity phase diffraction peaks were observed in the diffraction patterns of any samples, indicating that the introduction of doping elements did not change the basic crystal structure of the material (it remains a single crystal) and was successfully dissolved in the lattice without inducing phase separation. The XRD refinement results are shown in Table 1. After Si-Ti dual-element co-doping, the lithium-nickel mixing degree in the material was significantly improved, decreasing from 2.0% in the undoped sample to 0.8%. Simultaneously, the refinement data showed a slight increase in the c-axis lattice constant c (Å), a structural change that confirms the effective widening of lithium-ion transport channels in the layered material. The increased interlayer spacing helps to lower the lithium-ion migration barrier, providing a favorable structural basis for improving the material's rate performance and cycle stability.

[0038] Table 1

[0039]

[0040] The microstructure of the three synthesized sample materials was observed using a HITACHI S-4800 field emission scanning electron microscope (SEM), and the surface elemental distribution was characterized using an Oxford Ultim Max 65 energy dispersive spectroscopy (EDS) system. The characterization results are as follows: Figure 3 As shown, the ST-NCM material exhibits a well-dispersed single-crystal morphology with no obvious amorphous deposits or nanoscale secondary agglomerations, confirming the material's highly crystalline single-crystal characteristics. Through Figure 4 The EDS surface scan analysis shown indicates that Ni, Co, Mn, Si, Ti, and O elements exhibit continuous and uniform spatial distribution characteristics on the material surface.

[0041] The elemental depth distribution of the material was analyzed using a PHI 5000 VersaProbe II X-ray photoelectron spectroscopy (XPS). By controlling the Ar ion sputtering time (0 s, 60 s, 120 s), signal evolution patterns from the surface to the bulk phase were obtained. The XPS depth profile clearly revealed the differential elemental distribution between Si and Ti. Figure 5 As shown, the signal intensity of the Si 2p characteristic peak decreases with increasing etching depth (Figure a), while the signal intensity of the Ti 2p characteristic peak remains stable throughout the etching process without significant fluctuations (Figure b). This confirms the core design of this invention: Si doping is enriched in the near-surface region in a gradient form with increasing concentration from the inside out, while Ti doping is uniformly distributed throughout the bulk phase of the particle. This differentially distributed Si-Ti co-doping forms a complementary and synergistic configuration in space.

[0042] Based on the characterization and analysis results of XRD, SEM and XPS, it can be confirmed that the present invention constructs a spatially differentiated element doping structure according to the multi-scale stabilization design principle of single-crystal high-nickel cathode material. Specifically, it is reflected in: (1) through the gradient enrichment of Si elements in the near-surface region of the particles, a stable interface protective layer is formed by strong Si-O bonds, which effectively blocks the electrolyte from eroding the active material and suppresses interface side reactions; (2) by using Ti elements for uniform doping in the bulk phase of the material, the lithium interlayer spacing is expanded, promoting lithium ion transport. At the same time, the strong Ti-O bonds stabilize the lattice oxygen framework, which essentially suppresses the harmful phase transitions during lithium-nickel mixing and charging and discharging. This synergistic mechanism of surface protection and bulk stability jointly ensures the structural integrity and continuous stability of the electrochemical performance of the material during long-term cycling.

[0043] To verify the actual electrochemical performance of the synthesized material in lithium-ion batteries, the ST-NCM cathode material with a differentiated Si-Ti doped structure, as characterized and confirmed in the aforementioned embodiments of the present invention, was fabricated as a working electrode and battery assembly was performed. The specific steps are as follows:

[0044] First, electrode sheets were prepared using a slurry coating method. The positive electrode active material ST-NCM, acetylene black conductive agent, and polyvinylidene fluoride (PVDF, Solef 5130) binder were ground and mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent was added to adjust the slurry viscosity, and the mixture was continuously stirred until a uniform slurry was obtained. The slurry was then uniformly coated onto the surface of an aluminum foil current collector using a doctor blade, controlling the areal density of the active material to be 2-3 mg·cm³. -2 The coated electrode was placed in a vacuum drying oven at 120°C for 12 hours. Finally, the electrode was punched into a circular positive electrode with a diameter of 12 mm.

[0045] Then, the positive electrode was transferred to an argon-filled glove box (LABstar MBRAUN, Germany) to assemble CR2032 coin cells. A lithium metal sheet was used as the negative electrode, and a Celgard PP2400 porous membrane was used as the separator. The electrolyte system consisted of 1 M LiPF6 dissolved in a mixed solvent of EMC / DEC / FEC (volume ratio 1:1:1). The following components were added sequentially: negative electrode shell, spring plate, gasket, lithium sheet, 35 μL electrolyte, separator, 35 μL electrolyte, positive electrode, gasket, and positive electrode shell. The assembled battery was then handled with insulated tweezers and sealed using a coin cell sealing machine. After static aging, the sealed batteries underwent electrochemical performance testing.

[0046] To verify the material properties of the embodiments of the present invention, the cathode materials NCM and Si-NCM of Comparative Examples 1 and 2 were also fabricated into working electrodes and assembled into batteries according to the above steps for comparative testing.

[0047] The electrochemical performance of the three assembled coin cells was tested using a multi-channel battery testing system (LAND CT 2001 A, China), with a voltage range of 2.8–4.3 V (relative to Li). + / Li).

[0048] like Figures 6-1 to 6-3 As shown in the charge-discharge curves, the initial discharge specific capacity of the NCM material at 0.2 C rate is 187.0 mAh / g, while that of the Si-NCM material is 195.1 mAh / g. In comparison, the ST-NCM material with differentiated Si and Ti co-doping exhibits a higher reversible capacity, reaching an initial discharge specific capacity of 197.7 mAh / g. After three activation cycles at 0.2 C rate, long-term cycling tests were conducted at 0.5 C rate. Figure 7As shown, the ST-NCM material retained a capacity of 87.39% after 200 cycles, while the Si-NCM material retained 80.68%, and the NCM material retained only 67.63% of its initial capacity. This indicates that the differentiated Si-Ti co-doping strategy can significantly improve the structural stability of the material during charge-discharge cycling, thus giving it excellent long cycle life. Furthermore, rate testing results at different current densities further confirm the excellent kinetic performance of this material. Figure 8 As shown, ST-NCM materials exhibit higher capacity at different charge / discharge rates from 0.1 C to 5 C, indicating that they have fast and stable lithium-ion migration channels.

[0049] More importantly, ST-NCM materials also exhibit excellent cycling stability at high rates of 5 C. For example... Figure 9 As shown, the NCM material retains only 63.41% of its capacity after 500 cycles, while the ST-NCM material retains as much as 92.09%. This result fully demonstrates that the differentiated Si-Ti co-doping strategy can not only optimize performance at low rates, but also significantly enhance the structural stability of the material under extreme operating conditions.

[0050] Electrochemical impedance spectroscopy (EIS) of the materials was tested using a multi-channel Biologic VMP3 electrochemical workstation with a voltage amplitude of 5 mV and a frequency range of 10 mHz–100 kHz. Figure 10-1 As shown, compared with NCM and Si-NCM materials, ST-NCM materials exhibit significantly reduced electrochemical impedance. Figure 10-2 The equivalent circuit fitting shown (where CPE1 is a constant-phase element, typically representing the double-layer capacitance at the electrode-electrolyte interface in a battery; Z) w The solid-state diffusion impedance of lithium ions within the bulk phase of the electrode material is used to obtain the ohmic resistance (R0) of batteries assembled from the three materials respectively. s ), charge transfer resistance (R) ct Key parameters such as R0 of ST-NCM material are shown in Table 2. s The value is 0.580 Ω, lower than 0.823 Ω for NCM materials and 0.645 Ω for Si-NCM materials, indicating that its electrode has a more efficient electron conduction network. Meanwhile, the R0 of ST-NCM materials... ct The value (64.28 Ω) is significantly lower than that of NCM material (171.3 Ω) and Si-NCM material (145.4 Ω), indicating that the Si-Ti co-doping strategy can significantly reduce the charge transfer impedance at the electrode / electrolyte interface, thereby significantly improving the kinetics of lithium ion insertion / extraction at the interface.

[0051] Table 2. EIS fitting results for the three materials

[0052]

[0053] The lithium-ion diffusion coefficient of the material was analyzed using intermittent galvanostatic titration (GITT). Tests were conducted at a 0.1 C rate within a voltage window of 2.8–4.3 V, with each 20-minute galvanostatic pulse applied, followed by a 3-hour settling period to allow the system to reach quasi-equilibrium. Figure 11-1 (Charging process) and Figure 11-2 As shown in the discharge process, the lithium-ion diffusion coefficient of ST-NCM material is consistently higher than that of undoped NCM material during charge and discharge. This indicates that the Si-Ti co-doping strategy effectively widens the lithium layer spacing, providing a more optimized diffusion path for lithium-ion migration, thus improving the ion transport kinetics of the material and ultimately enhancing its rate performance.

Claims

1. A single-crystal high-nickel cathode material with multi-element differential distribution co-doping, characterized in that: The material is doped with a first dopant element Si and a second dopant element Ti. The first dopant element exhibits a gradient distribution with increasing concentration from the inside to the outside of the material particles, while the second dopant element exhibits a basically uniform distribution. The gradient distribution is due to the high bond energy of Si-O bonds during calcination. Once dissolved on the crystal lattice surface, additional migration energy barriers are required for further migration into the bulk phase. Therefore, Si diffuses slowly within the crystal lattice and is mainly enriched on the particle surface, forming a gradient distribution with increasing concentration from the inside to the outside. The first dopant element is used to enhance the surface stability of the material, and the second dopant element is used to stabilize the bulk structure of the material.

2. The single-crystal high-nickel cathode material as described in claim 1, characterized in that: The single-crystal high-nickel cathode material is formed by the first doping element and the second doping element occupying 1 at% of the transition metal sites in the existing single-crystal high-nickel cathode material; the existing single-crystal high-nickel cathode material is NCM or NCA.

3. The single-crystal high-nickel cathode material as described in claim 2, characterized in that: The single-crystal high-nickel cathode material is LiNi. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2, with a c-axis lattice constant of 14.20 Å, Li + / Ni 2+ The degree of mixing was 0.8%.

4. The method for preparing the single-crystal high-nickel cathode material according to any one of claims 1-3, characterized in that, include: Using lithium salt and ternary cathode material precursor as raw materials, a first doping source and a second doping source are introduced, mixed and ball-milled according to a preset stoichiometric ratio, and then calcined to obtain the single-crystal high-nickel cathode material. During the calcination process, the migration barrier of the first doping element contained in the first doping source is higher than that of the second doping element contained in the second doping source, so that the first doping element is mainly enriched in the near-surface region of the material particles, and the second doping element is basically uniformly distributed in the bulk phase of the particles. The first doping element is Si, and the second doping element is Ti. Since the Si-O bond energy is high, once it is dissolved on the crystal lattice surface, it requires an additional migration barrier to migrate into the bulk phase. Therefore, the diffusion of Si in the crystal lattice is relatively slow, so it is mainly enriched in the particle surface layer, forming a gradient distribution with increasing concentration from the inside to the outside.

5. The preparation method according to claim 4, characterized in that, Specifically, it includes: With LiOH·H2O and Ni 0.83 Co 0.12 Mn 0.05 Using (OH)₂ precursor as raw material, SiO₂ and TiO₂ are introduced as doping sources, according to Ni… 0.83 Co 0.12 Mn 0.05 A mixture of (OH)₂ : LiOH·H₂O : SiO₂ : TiO₂ in a molar ratio of 1 : 1.05 : 0.01 : 0.01 was ball-milled and then calcined at high temperature to obtain a single-crystal high-nickel cathode material, LiNi. 0.81 Co 0.12 Mn 0.05 Si 0.01 Ti 0.01 O2.

6. The preparation method according to claim 5, characterized in that, The high-temperature calcination includes: first, pre-calcining the mixed ball-milled material in an oxygen atmosphere at a first temperature, and then raising the temperature to a second temperature for high-temperature calcination.

7. The preparation method according to claim 6, characterized in that: The first temperature is 450℃~550℃, and the second temperature is 750℃~850℃.

8. The application of the single-crystal high-nickel cathode material as described in any one of claims 1-3, characterized in that, Used as a positive electrode material in lithium-ion batteries.

9. A lithium-ion battery, characterized in that, include: A positive electrode, a negative electrode, and an electrolyte, wherein the material of the positive electrode is the single-crystal high-nickel positive electrode material according to any one of claims 1-3.

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