A negative electrode material, a preparation method therefor, and an application thereof

Abstract

The application relates to the technical field of battery negative electrode materials, and discloses a negative electrode material and a preparation method and application thereof. The negative electrode material comprises a base material and a coating layer coated on the outer surface of the base material. The base material comprises a graphite base and a dopant doped in the graphite base, and the dopant comprises CeO2 and Yb2O3. The coating layer comprises Li4CeO3. The space coupling of the layer-expanding effect of CeO2 and the pinning effect of Yb2O3 improves the capacity of a lithium ion battery, guarantees fast charging, and improves the cycle life of the lithium ion battery. The Li4CeO3 coated on the base material has excellent lithium ion conduction capacity, significantly reduces the energy barrier of lithium ions from the electrolyte into the electrode solid surface, and can improve the interface conduction and the cycle life of the lithium ion battery even at low temperature.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, specifically to an anode material, its preparation method, and its application. Background Technology

[0002] As a high-efficiency energy storage carrier, the performance improvement of batteries is directly related to the technological innovation process of new energy vehicles, energy storage containers, smart grids and portable electronic devices. Taking lithium-ion batteries as an example, their traditional graphite anode has the following defects: (1) Kinetic limitation: The sluggish diffusion kinetics of lithium ions during fast charging leads to insufficient fast charging performance and the risk of lithium plating (the capacity retention rate after 1000 cycles of 5C charging is generally less than 68%), and the performance in low temperature environment deteriorates sharply (the capacity of 0.33C charging at -20℃ is less than 60% of the theoretical value); (2) Structural stability defects: During long-term cycling, the interlayer stress of graphite accumulates (the volume change can reach about 12%), and long-term cycling can easily lead to structural collapse and capacity decay (the capacity retention rate after 1000 cycles of 5C charging is usually less than 85%). Existing modification methods such as silicon-based composites and coating modification have the problem of limited performance improvement. Rare earth elements (such as cerium and lanthanum) have unique electronic structures, and the electronic conductivity and ion diffusion path of graphite can be controlled by doping. However, existing technologies mostly use single rare earth doping, which has insufficient synergistic effect. The preparation process is difficult to achieve uniform modification at the nanoscale, and the performance improvement is one-sided and cannot take into account fast charging, low temperature performance and long life. Summary of the Invention

[0003] This invention provides a negative electrode material to solve the problems of poor fast-charging performance, rapid performance degradation at low temperatures, and short lifespan of existing negative electrode materials.

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

[0005] In a first aspect, the present invention provides a negative electrode material, comprising a matrix material and a coating layer covering the outer surface of the matrix material, wherein the matrix material comprises a graphite matrix and a dopant doped in the graphite matrix, the dopant comprising CeO2 and Yb2O3; and the coating layer comprises Li4CeO3.

[0006] In some alternative embodiments, the molar ratio of CeO2 to Yb2O3 is 1:0.1-0.31.

[0007] In some alternative embodiments, the dopant content is 1wt%-3wt% based on the negative electrode material.

[0008] In some alternative implementations, the thickness of the coating layer is 2nm-8nm.

[0009] In some alternative embodiments, the CeO2 has a particle size of 5nm-10nm.

[0010] In some optional embodiments, the particle size of the Yb2O3 is 2nm-5nm.

[0011] Secondly, the present invention provides a method for preparing the negative electrode material described in the first aspect, comprising the following steps: (1) The cerium salt, ytterbium salt and lithium salt are heated and melted to obtain a molten salt mixture; (2) The molten salt mixture is used as the electrolyte, and graphite is used as the working electrode. It forms a three-electrode electrolytic cell with the reference electrode and the counter electrode for electrolysis. The mixture is then annealed to obtain the final product. The electrolysis step includes a first electrolysis and a second electrolysis; the voltage of the first electrolysis is a negative voltage, and the voltage of the second electrolysis is a positive voltage; The annealing step includes a first annealing, a second annealing, and a third annealing; the temperature of the first annealing is greater than the temperature of the second annealing, which is greater than the temperature of the third annealing.

[0012] In some optional embodiments, the voltage of the first electrolysis is -1.4V to -1.0V, and the current density is 8mA / cm². 2 -12mA / cm 2 The single pulse duration is 5s-15s, the duty cycle is 1:2-4, and the electrolysis time is 50min-70min.

[0013] It should be noted that in this invention, the voltage of the first electrolysis is controlled to be -1.4V to -1.0V to ensure Ce 3+ Can be effectively reduced to Ce 2+ And drive it to embed between graphite layers, preventing the Li from being damaged by excessively low voltage. + Co-intercalation or lithium plating; controlling the single-pulse time of the first electrolysis to 5s-15s to ensure Ce 2+ The interface charge transfer and embedding prevent excessive intercalation or local concentration saturation due to prolonged time.

[0014] In some alternative embodiments, the voltage of the second electrolysis is 0.6V-1.0V, and the current density is 2mA / cm². 2 -5mA / cm 2 The single pulse duration is 5s-30s, the duty cycle is 1:2-4, and the electrolysis time is 50min-70min.

[0015] It should be noted that in this invention, the voltage of the second electrolysis is controlled to be 0.6V-1.0V to ensure Yb 3+It can be effectively reduced to metallic Yb and deposited, preventing the molten salt from being oxidized due to excessive voltage; the single pulse time of the second electrolysis is controlled to be 5s-30s to ensure that metallic Yb can complete nucleation and growth at the defect site, preventing excessive deposition of metallic Yb.

[0016] In some optional embodiments, the first annealing temperature is 600℃-700℃, the time is 20min-40min, the heating rate is 7℃ / min-13℃ / min, and the annealing atmosphere is a mixture of inert gas and hydrogen.

[0017] In some optional embodiments, the second annealing temperature is 400℃-500℃, the time is 50min-70min, the cooling rate is 3℃ / min-7℃ / min, and the annealing atmosphere is an inert gas.

[0018] It should be noted that the lithium salt remaining after the first annealing reacts with the unavoidable trace amounts of moisture in the environment to form LiOH. During the second annealing, LiOH decomposes to form Li2O and reacts with trace amounts of CO2 in the atmosphere to produce Li2CO3. Therefore, in the second annealing stage, the residual lithium source in the system that can participate in the reaction has naturally transformed into Li2O and / or Li2CO3, which are thermodynamically stable products under high-temperature solid-state chemistry.

[0019] From a thermodynamic perspective, the formation of nanocrystals is indeed spontaneous. However, in this invention, by adjusting the gradient, multiple kinetic constraints are imposed on the spontaneous process, causing the grain growth to automatically stop or slow down drastically when the optimal nanoscale size is reached, thus precisely controlling the CeO2 particle size to 5nm-10nm and the Yb2O3 cluster size to the range of 2nm-5nm.

[0020] Furthermore, although the atmosphere of the second annealing in this invention is an inert atmosphere, trace amounts of oxygen-containing impurities (such as Li2CO3 and H2O) remaining in the precursor, trace amounts of oxygen adsorbed by the graphite and molten salt from the environment (the N2 / H2 atmosphere of the first annealing), and pre-intercalated Ce 2+ and surface-deposited Yb 3+ A reaction occurs, Ce 2+ The graphite is transformed into CeO2 nanocrystals, and the metallic Yb is transformed into Yb2O3 clusters. If an active atmosphere such as oxygen is used, the edges of the graphite bulk will be oxidized, the rare earth elements will be deeply oxidized, the nanoscale dispersion will be destroyed, and the subsequent in-situ generation of Li4CeO3 will not be possible.

[0021] In some optional embodiments, the third annealing temperature is 250℃-350℃, the time is 100min-140min, the cooling rate is 1℃ / min-3℃ / min, and the annealing atmosphere is vacuum.

[0022] In some alternative embodiments, the mass ratio of the cerium salt, the ytterbium salt, and the lithium salt is 1:0.2-0.8:5.2-7.2.

[0023] In some alternative embodiments, the cerium salt includes at least one of cerium chloride, cerium fluoride, cerium bromide, and cerium iodide.

[0024] In some alternative embodiments, the ytterbium salt includes at least one of ytterbium chloride, ytterbium fluoride, ytterbium bromide, and ytterbium iodide.

[0025] In some alternative embodiments, the lithium salt includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide.

[0026] In some alternative implementations, an acid pickling step is also included after annealing.

[0027] Furthermore, in the acidic step, the acidic reagent includes phosphoric acid and / or citric acid.

[0028] Thirdly, the present invention provides an application of the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect in a battery.

[0029] It should be noted that the cerium salt and ytterbium salt of the present invention can use waste phosphor containing CeCl3 and YbCl3 as rare earth source, which can reduce costs.

[0030] Furthermore, the pretreatment of waste phosphors includes the following steps: Pretreatment of waste phosphors (NaYF4:Yb, Er, CeMgAl) 11 O 19 :Tb 3+ The phosphor was then processed by a jaw crusher to a particle size ≤100μm, and the 45μm-75μm particles were separated by a vibrating sieve, with a proportion >85%. Afterwards, it was acid-leached in a mixed solution of 6mol / L HCl and 10vol% H2O2 to remove impurities, with a mass ratio of phosphor to the mixed solution of 1:8. The mixture was shaken in a water bath at 80℃ for 120 min, centrifuged, and then subjected to a three-stage countercurrent extraction in a kerosene solution of 20vol% 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507), an extraction ratio O / A of 1:2, and a pH of 2.5, yielding Ce with a recovery rate >95%. 3+ and Yb 3+ The rare earth concentrate was finally mixed with NH4Cl, Ce 3+ and Yb 3+ The total molar number and the molar ratio of NH4Cl were 1:3. The mixture was calcined at 300℃ for 2 hours to obtain CeCl3 / YbCl3 mixed powder.

[0031] The technical solution of this invention has the following advantages: 1. The negative electrode material provided by this invention includes a matrix material and a coating layer covering the outer surface of the matrix material. The matrix material includes a graphite matrix and dopants doped in the graphite matrix, wherein the dopants include CeO2 and Yb2O3; the coating layer includes Li4CeO3. CeO2 mainly expands the interlayer spacing and improves fast charging performance. CeO2 contains abundant oxygen vacancies, which can provide lithium storage sites and increase the capacity of lithium-ion batteries. At the same time, it can stabilize ion diffusion channels. Even if the graphite layer undergoes slight thermal shrinkage at low temperatures, the expanded interlayer spacing of the graphite can still remain unobstructed. Combined with the additional surface diffusion paths provided by the oxygen vacancies in CeO2 nanocrystals, it jointly ensures the bulk transport capability of lithium ions at low temperatures. However, excessive embedding will weaken the stability of the graphite structure, leading to structural collapse in the later stages of cycling. Yb2O3 has a strong pinning effect, which increases the grain boundary migration barrier, inhibits grain boundary cracking and interlayer slip, stabilizes the interlayer structure of graphite, reduces interface impedance, and ensures fast charging. Even at low temperatures, it can still provide... Effective suppression of lattice distortion and stress concentration caused by anisotropic shrinkage of graphite lattice at low temperatures maintains the structural integrity required for lithium-ion intercalation; however, the ionic radius is relatively small, the layer expansion effect is limited, and the contribution to capacity improvement is small; the layer expansion of CeO2 and the pinning effect of Yb2O3 are spatially coupled, which not only improves the capacity of lithium-ion batteries and ensures fast charging, but also improves the cycle life of lithium-ion batteries. Coating Li4CeO3 on the substrate material, the Li4CeO3 coating layer is a fast ion conductor with excellent lithium-ion conductivity, which significantly reduces the energy barrier for lithium ions to enter the electrode solid surface from the electrolyte. Even at low temperatures, it can improve interfacial conduction and improve the cycle life of lithium-ion batteries.

[0032] 2. The method for preparing the negative electrode material provided by the present invention includes the following steps: heating and melting cerium salt, ytterbium salt, and lithium salt to obtain a molten salt mixture; using the molten salt mixture as an electrolyte, electrolyzing it in a three-electrode electrolytic cell with graphite as the working electrode, a reference electrode, and a counter electrode, and then annealing the resulting material. The present invention embeds Ce and Yb into graphite through electrolysis, specifically: Ce... 3+ Ce is reduced to Ce on the surface of the graphite working electrode. 2+ Due to Ce 2+ The ionic radius matches the interlayer channel size of the graphite. Driven by an electric field, it embeds itself into the interlayer of graphite, expanding the interlayer spacing to 0.342 nm, forming a pre-expanded layer structure, thus increasing the interlayer spacing and improving fast charging performance. 3+ The metal is reduced to metallic Yb and deposited on high-energy sites such as the edges, defects, and grain boundaries of graphite particles, forming pre-pinning points that stabilize the graphite interlayer structure, reduce interfacial impedance, and improve kinetics. This effectively suppresses the relative slippage and expansion between graphite layers during charging and discharging, thereby improving fast-charging performance and cycle life. After annealing, Ce... 2+The lithium is converted into CeO2 nanocrystals, which contain abundant oxygen vacancies that can provide lithium storage sites, thus improving capacity. Metallic Yb is converted into Yb2O3 clusters, while the remaining lithium compounds react with Ce... 2+ The formation of a Li4CeO3 coating layer enhances interfacial conductivity, thereby improving the cycle life of lithium-ion batteries.

[0033] 3. The method for preparing the negative electrode material provided by the present invention controls the voltage of the first electrolysis to be -1.4V to -1.0V, Ce 3+ Ce is reduced to Ce on the surface of the graphite working electrode. 2+ Due to Ce 2+ The ionic radius matches the interlayer channel size of the graphite, and under the drive of an electric field, it is embedded into the interlayer of graphite, expanding the interlayer spacing to 0.342 nm, forming a pre-expanded layer structure, and improving the capacity of the lithium-ion battery; then a second electrolysis is performed at 0.6V-1.0V, Yb 3+ Under a relatively positive potential, it is reduced to metallic Yb and deposited on high-energy sites such as the edges, defects and grain boundaries of graphite particles, forming pre-pinning points, reducing interface impedance and ensuring fast charging.

[0034] 4. The method for preparing the negative electrode material provided by the present invention controls the temperature of the first annealing to be 600℃-700℃, thereby reducing the Ce that may be oxidized during the electrochemical process. 4+ Restore to Ce 2+ This ensures that all Ce participates in subsequent oxidation in the +2 oxidation state, avoiding Ce... 4+ The structural disruption prepares the site for the next step of uniform oxidation. The second annealing temperature is controlled at 400℃-500℃ to allow the pre-embedded Ce to... 2+ Reacting with surface-deposited Yb restricts oxide grain growth and leads to the formation of Ce clusters. 2+The graphite is transformed into CeO2 nanocrystals of 5nm-10nm, and metallic Yb is transformed into Yb2O3 clusters of 2nm-5nm. At the same time, during the annealing stage at 400℃-500℃, the Ce enriched on the surface reacts with the lithium compounds (such as Li2O or Li2CO3) remaining in the molten salt to generate Li4CeO3. The Ce concentration is the highest in the graphite surface area, so the reaction occurs preferentially on the surface. The generated Li4CeO3 is a fast ion conductor. It forms a dense, continuous coating layer on the outer surface that is chemically bonded to the substrate. It grows from the inside out in situ, rather than being physically attached. The third annealing temperature is 250℃-350℃, which is much lower than the temperature at which CeO2 and Yb2O3 grow significantly (greater than 600℃). At the same time, the vacuum environment eliminates the gaseous medium for material transport, greatly inhibiting the "Ostwald ripening" of nanoparticles, making the CeO2 and Yb2O3 structural dimensions stable. Under vacuum and thermal energy drive, atoms at the interface between the Li4CeO3 coating layer and the graphite matrix undergo short-range diffusion, forming stronger chemical bonds (such as CO-Ce), making the structure more stable. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 These are X-ray diffraction patterns of the artificial graphite (a) of the present invention and the negative electrode material (b) prepared in Example 1; Figure 2 These are the Raman spectra of the artificial graphite (a) of the present invention and the negative electrode material (b) prepared in Example 1; Figure 3 The images show the scanning transmission electron microscope-energy dispersive X-ray spectra of the negative electrode material prepared in Example 1 of this invention; wherein, (a) is a scanning transmission electron microscope image of the negative electrode material prepared in Example 1; (b) C element; (c) Ce element; (d) Yb element; (e) O element; (f) Li element; Figure 4 This is a high-resolution transmission electron microscope image of the negative electrode material prepared in Example 1 of the present invention. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0038] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0039] In this invention, high-resolution transmission electron microscopy (TEM) is used to test the particle size of CeO2 and Y2O3. The specific method includes: uniformly dispersing the negative electrode material powder in an ethanol solution, then dropping it onto a copper grid with a microgrid, and drying it. Then, a JEM-2100 & X-Max80 TEM instrument is used to test the material. First, the entire grid is rapidly scanned at low magnification to locate the target area. Then, a thin area of ​​the target area is moved to the center of the optical axis for precise focusing. Switching to high-magnification TEM mode (10nm, 5nm), the condenser aperture and beam deflector are adjusted to ensure the beam spot is centered and uniform on the sample. The sample is confirmed to be stable under electron beam irradiation, and image acquisition is performed. The acquired images are subjected to a fast Fourier transform to measure the interplanar spacing, determining whether it is CeO2 or Yb2O3 crystal. The particle size of CeO2 and / or Y2O3 is then determined based on the scale markings on the image.

[0040] In this invention, inductively coupled plasma (ICP) is used to test the content of CeO2 and Yb2O3. The Ce / Yb elemental content is detected after acid hydrolysis of the sample. The specific testing method is as follows: 50 mg of negative electrode material and 5 mL of aqua regia (HNO3 and HCl volume ratio 1:3) are microwave digested (200℃, 30 min) to dissolve the CeO2 and Yb2O3 doped in the graphite. The digested mixture is then diluted to 100 mL with ultrapure water and vacuum filtered through a 0.22 μm filter membrane. The filtrate is then subjected to ICP detection, and the emission intensities of Ce and Yb are measured at wavelengths of 413.765 nm and 328.937 nm, respectively. A standard curve is plotted using cerium oxide and ytterbium oxide standards processed simultaneously with the sample. The linear correlation coefficient is ≥0.9999, and the concentrations of Ce and Yb in 100 mL are measured. Ce and C Yb By reverse-engineering the mass fractions of CeO2 and Yb2O3, we can determine the mass fractions of CeO2 and Yb2O3 in the negative electrode material.

[0041] In this invention, the thickness of the coating layer is tested using a high-resolution transmission electron microscope (TEM), comprising the following steps: The negative electrode material powder is uniformly dispersed in an ethanol solution, then dropped onto a copper grid with a microgrid, and dried. A JEM-2100 & X-Max80 TEM instrument is then used to test the material. First, the entire grid is rapidly scanned at low magnification to locate the target area. Then, a thin area of ​​the target region is moved to the center of the optical axis for precise focusing. The TEM is switched to high-magnification mode (10nm, 5nm), and the condenser aperture and beam deflector are adjusted to ensure the beam spot is centered and uniform on the sample. The sample is confirmed to be stable under electron beam irradiation. Image acquisition is performed, and the coating layer thickness is determined based on the scale readings on the image.

[0042] Example 1 This embodiment provides a method for preparing a negative electrode material, including the following steps: (1) LiCl powder and CeCl3 / YbCl3 mixed powder (CeCl3 and YbCl3 in a mass ratio of 1:0.5) were mixed in an alumina crucible at a mass ratio of 4:1. Ar and H2 in a volume ratio of 95:5 were introduced and the temperature was raised to 450℃ at 5℃ / min and held for 1h to prepare molten salt. (2) Artificial graphite was extruded to form a graphite working electrode (100×50×3mm), which was then assembled into a three-electrode system with a nickel mesh counter electrode and a CeO2 reference electrode, and 250g of molten salt was injected. The distance between the working electrode and the counter electrode was 15±0.5mm, and the distance between the working electrode and the reference electrode was 8±0.3mm. The three-electrode system was connected to a potentiostat (Princeton PARSTAT 4000+) for electrochemical doping. The initial pulse voltage was -1.2V and the current density was 10mA / cm. 2 A single pulse of 10 seconds was applied with a duty cycle of 1:3, for a total electrolysis time of 60 minutes. Then, the pulse voltage was 0.8V and the current density was 3mA / cm². 2 A single pulse was applied for 30 seconds at a duty cycle of 1:3, with a total processing time of 60 minutes, to obtain a molten salt electrochemically doped graphite electrode. The electrode was then ground and pulverized, placed in a tube furnace, and heated to 650°C at a rate of 10°C / min under an atmosphere of N2 and H2 in a volume ratio of 95:5, and held for 30 minutes. Then, it was cooled to 450°C at a rate of 5°C / min under an Ar atmosphere and held for 60 minutes. Finally, it was cooled to 300°C under a vacuum at a rate of 2°C / min and held for 120 minutes before being cooled to room temperature. (3) The annealed powder was soaked in a mixed solution of 0.5 mol / L H3PO4 and 0.1 mol / L citric acid (pH=3.2), ultrasonically dispersed at 60℃ (40 kHz, 300 W) for 20 min, washed with deionized water until neutral, vacuum filtered, and vacuum freeze-dried to obtain the negative electrode material; wherein, in the negative electrode material, the particle sizes of CeO2 and Yb2O3 are 8 nm and 3 nm, respectively, the contents of CeO2 and Yb2O3 are 1.33% and 0.67 wt%, respectively, the molar ratio of CeO2 and Yb2O3 is 1:0.22; the thickness of the coating layer is 5 nm.

[0043] Example 2 This embodiment provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that the mass ratio of CeCl3 to YbCl3 is 1:0.2. In the negative electrode material, the particle sizes of CeO2 and Yb2O3 are 9 nm and 2 nm, respectively, the contents of CeO2 and Yb2O3 are 1.34 wt% and 0.4 wt%, respectively, the molar ratio of CeO2 to Yb2O3 is 1:0.13, and the thickness of the coating layer is 4 nm.

[0044] Example 3 This embodiment provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that the mass ratio of CeCl3 to YbCl3 is 1:0.8. In the negative electrode material, the particle sizes of CeO2 and Yb2O3 are 6 nm and 5 nm, respectively, the contents of CeO2 and Yb2O3 are 1.35 wt% and 0.95 wt%, respectively, and the molar ratio of CeO2 to Yb2O3 is 1:0.31; the thickness of the coating layer is 6 nm.

[0045] Example 4 This embodiment provides a method for preparing a negative electrode material, including the following steps: (1) Lithium iodide powder and CeCl3 / YbCl3 mixed powder (CeCl3 and YbCl3 in a mass ratio of 1:0.5) were mixed in an alumina crucible at a mass ratio of 5.2:1.5, and Ar and H2 in a volume ratio of 95:5 were introduced. The temperature was raised to 450℃ at 5℃ / min and held for 1h to prepare molten salt. (2) Artificial graphite was extruded to form a graphite working electrode (100×50×3mm), which was then assembled into a three-electrode system with a nickel mesh counter electrode and a CeO2 reference electrode, and 150g of molten salt was injected. The distance between the working electrode and the counter electrode was 15±0.5mm, and the distance between the working electrode and the reference electrode was 8±0.3mm. The three-electrode system was connected to a potentiostat (Princeton PARSTAT 4000+) for electrochemical doping. The initial pulse voltage was -1V and the current density was 8mA / cm. 2A single pulse of 5 seconds was applied with a duty cycle of 1:2, for a total electrolysis time of 70 minutes. Then, the pulse voltage was 0.6V and the current density was 5mA / cm². 2 A single pulse was applied for 5 seconds at a duty cycle of 1:4, with a total processing time of 50 minutes, to obtain a molten salt electrochemically doped graphite electrode. The electrode was then ground and pulverized and placed in a tube furnace. Under an atmosphere of N2 and H2 volume ratio of 95:5, the temperature was increased to 700℃ at 7℃ / min and held for 20 minutes. Then, under an Ar atmosphere, the temperature was decreased to 400℃ at 3℃ / min and held for 70 minutes. Finally, under a vacuum, the temperature was decreased to 250℃ at 3℃ / min and held for 140 minutes before being cooled to room temperature. (3) The annealed powder was soaked in a mixed solution of 0.5 mol / L H3PO4 and 0.1 mol / L citric acid (pH=3.2), ultrasonically dispersed at 60℃ (40 kHz, 300 W) for 20 min, washed with deionized water until neutral, vacuum filtered, and vacuum freeze-dried to obtain the negative electrode material; wherein, in the negative electrode material, the particle sizes of CeO2 and Yb2O3 are 7 nm and 3 nm, respectively, the contents of CeO2 and Yb2O3 are 0.66 wt% and 0.39 wt%, respectively, the molar ratio of CeO2 and Yb2O3 is 1:0.26; the thickness of the coating layer is 3 nm.

[0046] Example 5 This embodiment provides a method for preparing a negative electrode material, including the following steps: (1) Lithium fluoride powder and CeCl3 / YbCl3 mixed powder (CeCl3 and YbCl3 in a mass ratio of 1:0.5) were mixed in an alumina crucible at a mass ratio of 7.2:1.5. Ar and H2 in a volume ratio of 95:5 were introduced and the temperature was raised to 450℃ at 5℃ / min and held for 1h to prepare molten salt. (2) Artificial graphite was extruded to form a graphite working electrode (100×50×3mm), which was then assembled into a three-electrode system with a nickel mesh counter electrode and a CeO2 reference electrode, and 350g of molten salt was injected. The distance between the working electrode and the counter electrode was 15±0.5mm, and the distance between the working electrode and the reference electrode was 8±0.3mm. The three-electrode system was connected to a potentiostat (Princeton PARSTAT 4000+) for electrochemical doping. The initial pulse voltage was -1.4V and the current density was 12mA / cm. 2 A single pulse of 15s was applied with a duty cycle of 1:4, for a total electrolysis time of 50 minutes. Then, the pulse voltage was 1V and the current density was 2mA / cm². 2A single pulse was applied for 10 seconds at a duty cycle of 1:2, with a total processing time of 70 minutes, to obtain a molten salt electrochemically doped graphite electrode. The electrode was then ground and pulverized and placed in a tube furnace. Under an atmosphere of N2 and H2 volume ratio of 95:5, the temperature was increased to 600℃ at 13℃ / min and held for 40 minutes. Then, under an Ar atmosphere, the temperature was decreased to 500℃ at 7℃ / min and held for 50 minutes. Finally, under a vacuum, the temperature was decreased to 350℃ at 1℃ / min and held for 100 minutes before being cooled to room temperature. (3) The annealed powder was soaked in a mixed solution of 0.5 mol / L H3PO4 and 0.1 mol / L citric acid (pH=3.2), ultrasonically dispersed at 60℃ (40 kHz, 300 W) for 20 min, washed with deionized water until neutral, vacuum filtered, and vacuum freeze-dried to obtain the negative electrode material; wherein, in the negative electrode material, the particle sizes of CeO2 and Yb2O3 are 7 nm and 4 nm, respectively, the contents of CeO2 and Yb2O3 are 1.96 wt% and 0.98 wt%, respectively, the molar ratio of CeO2 and Yb2O3 is 1:0.22; the thickness of the coating layer is 7 nm.

[0047] Comparative Example 1 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that in step (1), the CeCl3 / YbCl3 mixed powder is replaced with the same mass of CeCl3.

[0048] Comparative Example 2 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that in step (1), the CeCl3 / YbCl3 mixed powder is replaced with the same mass of YbCl3.

[0049] Comparative Example 3 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that in step (1), the addition of LiCl powder is omitted.

[0050] Comparative Example 4 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that the voltage of the first electrolysis and the second electrolysis is 0.8V.

[0051] Comparative Example 5 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that the voltage of the first electrolysis and the second electrolysis is both -1.2V.

[0052] Comparative Example 6 This comparative example provides a method for preparing a negative electrode material, which is basically the same as the steps in Example 1, except that the annealing temperature is 650℃, the holding time is 210min, and the annealing atmosphere is a N2 and H2 atmosphere with a volume ratio of 95:5.

[0053] X-ray diffraction (XRD) tests were performed on the artificial graphite of Example 1 and the negative electrode material prepared in Example 1, see [see details]. Figure 1 As shown. From Figure 1 It can be seen that the peak position of the (002) crystal plane of the negative electrode material is shifted to the left compared to the peak position of the (002) crystal plane of the graphite in Example 1. The interlayer spacing of the d(002) crystal plane of the graphite is 0.3354 nm, while the interlayer spacing of the d(002) crystal plane of the negative electrode material increases to 0.342 nm, proving that Ce 2+ The effective embedding of [agent] and the formation of CeO2 contribute to the layer expansion of the d(002) crystal plane, thereby increasing the interlayer spacing of the d(002) crystal plane in the negative electrode material. This can improve fast charging performance and simultaneously enhance the Li [material's] efficiency. + The volume change of the graphite unit during the insertion process provides additional buffer space, effectively mitigating the lattice expansion caused by insertion / extraction and improving cycle life.

[0054] Raman spectroscopy was performed on the artificial graphite of Example 1 and the negative electrode material prepared in Example 1, see [link to Raman spectroscopy]. Figure 2 As shown. From Figure 2 It can be seen that the ID / IG ratio of graphite is 0.18, and the intensity of the D peak of the anode material is significantly enhanced, with the ID / IG ratio increasing to 0.3. This indicates that the anode material is transformed from highly ordered graphite to a "functionalized defective carbon composite material", which can provide additional lithium storage sites to increase capacity, create multidimensional ion channels to improve fast charging performance and low-temperature performance.

[0055] The negative electrode material prepared in Example 1 was subjected to scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) testing, see [see details]. Figure 3 As shown. From Figure 3 The graphite exhibits a bulk morphology, with uniform distribution of C, Ce, Yb, O, and Li elements, indicating successful CeO2 and Yb2O3 doping of the graphite. High-resolution transmission electron microscopy (HR-TEM) was used to analyze the anode material prepared in Example 1. Figure 4 As shown. From Figure 4 The obvious lattice stripes and Li4CeO3 composition at the edges of the graphite indicate that the graphite surface is coated with Li4CeO3. The interlayer spacing of the graphite d(002) crystal plane becomes 0.342 nm, indicating that the anode material has been successfully prepared.

[0056] In addition, to investigate the electrochemical performance of the negative electrode material of this invention as a negative electrode in a lithium-ion battery, the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-6, the conductive agent (Super P conductive carbon black), and the binder (PVDF) were mixed at a mass ratio of 8:1:1 to prepare electrode sheets (12 mm diameter discs). Artificial graphite was used as a lithium-ion battery negative electrode as a control group. PP separators were selected, and LiPF6 and vinylene carbonate (VC) (LiPF6 concentration of 1 mol / L and VC mass percentage of 3%) were added to an equal volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the electrolyte. Button half-cells (Li sheet negative electrode, 14 mm diameter) were assembled and, after standing for 10 h, the electrochemical performance was tested using Wuhan Landian testing instruments.

[0057] High-rate cycle performance testing: Room temperature rate performance: Batteries assembled in Examples 1-5 and Comparative Examples 1-6 were tested at 0.33C and 5C constant current charge-discharge rates (test temperature 25℃, test voltage range 0.005V-1.5V). The ratio of 5C capacity to initial 0.33C capacity after 10, 100, and 500 cycles, as well as the capacity retention rate after 1000 cycles at 5C, were compared. Low-temperature performance: 0.33C constant current charge-discharge test (test temperature -20℃, test voltage range 0.005V-1.5V) was conducted. The capacity at 0.33C rate and the capacity retention rate after 200 cycles at 1C rate were compared. The results are shown in Table 1.

[0058] Table 1. Cycle performance test results of button batteries prepared in each embodiment and comparative example.

[0059] As shown in Table 1, the cerium-ytterbium dual rare earth gradient doped graphite anode material of the present invention exhibits significantly improved fast-charging and cycle performance compared to the original graphite. In Comparative Example 1, the anode material lacks Yb doping, resulting in poor pinning effect and the inability of CeO2 and Yb2O3 to spatially couple, leading to lower lithium-ion battery capacity, poor fast-charging performance, and reduced cycle life. In Comparative Example 2, the anode material lacks Ce doping and a Li4CeO3 coating layer, resulting in fewer lithium storage sites, preventing the expansion of graphite interlayer spacing, and the inability of CeO2 and Yb2O3 to spatially couple, further contributing to lower lithium-ion battery capacity, poor fast-charging performance, and reduced cycle life. In Comparative Example 3, the anode material lacks LiCl powder, preventing the formation of a Li4CeO3 coating layer and hindering interfacial conductivity, resulting in poor cycle life. In Comparative Example 4, both the first and second electrolytic voltages are 0.8V, and no Ce is added. 2+The absence of Ce doping and Li4CeO3 coating in the negative electrode material, embedded between graphite layers, results in lower capacity, poor fast-charging performance, and reduced cycle life of the lithium-ion battery. In Comparative Example 5, the voltages of the first and second electrolytic cells are both -1.2V, and Yb is not deposited in the graphite. The lack of Yb doping in the negative electrode material leads to lower capacity, poor fast-charging performance, and reduced cycle life of the lithium-ion battery. In Comparative Example 6, the annealing temperature is 650 min and the holding time is 210 min. The negative electrode material cannot form a Li4CeO3 coating layer, which cannot improve interfacial conductivity, resulting in poor fast-charging performance and reduced cycle life of the lithium-ion battery.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A negative electrode material, comprising a matrix material and a coating layer covering the outer surface of the matrix material, characterized in that, The matrix material includes a graphite matrix and dopants doped in the graphite matrix, the dopants including CeO2 and Yb2O3; the coating layer includes Li4CeO3.

2. The negative electrode material according to claim 1, characterized in that, The molar ratio of CeO2 to Yb2O3 is 1:0.1-0.

31.

3. The negative electrode material according to claim 1 or 2, characterized in that, Based on the negative electrode material, the content of the dopant is 1wt%-3wt%.

4. The negative electrode material according to claim 1, characterized in that, The thickness of the coating layer is 2nm-8nm; And / or, the CeO2 has a particle size of 5nm-10nm; And / or, the particle size of the Yb2O3 is 2nm-5nm.

5. A method for preparing the negative electrode material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) The cerium salt, ytterbium salt and lithium salt are heated and melted to obtain a molten salt mixture; (2) The molten salt mixture is used as the electrolyte, and graphite is used as the working electrode. It forms a three-electrode electrolytic cell with the reference electrode and the counter electrode for electrolysis. The mixture is then annealed to obtain the final product. The electrolysis step includes a first electrolysis and a second electrolysis; the voltage of the first electrolysis is a negative voltage, and the voltage of the second electrolysis is a positive voltage; The annealing step includes a first annealing, a second annealing, and a third annealing; the temperature of the first annealing is greater than the temperature of the second annealing, which is greater than the temperature of the third annealing.

6. The method for preparing the negative electrode material according to claim 5, characterized in that, The voltage of the first electrolysis is -1.4V to -1.0V, and the current density is 8mA / cm². 2 -12mA / cm 2 The single pulse duration is 5s-15s, the duty cycle is 1:2-4, and the electrolysis time is 50min-70min; And / or, the voltage of the second electrolysis is 0.6V-1.0V, and the current density is 2mA / cm². 2 -5mA / cm 2 The single pulse duration is 5s-30s, the duty cycle is 1:2-4, and the electrolysis time is 50min-70min.

7. The method for preparing the negative electrode material according to claim 5, characterized in that, The first annealing temperature is 600℃-700℃, the time is 20min-40min, the heating rate is 7℃ / min-13℃ / min, and the annealing atmosphere is a mixture of inert gas and hydrogen. And / or, the temperature of the second annealing is 400℃-500℃, the time is 50min-70min, the cooling rate is 3℃ / min-7℃ / min, and the annealing atmosphere is an inert gas; And / or, the third annealing temperature is 250℃-350℃, the time is 100min-140min, the cooling rate is 1℃ / min-3℃ / min, and the annealing atmosphere is vacuum.

8. The method for preparing the negative electrode material according to claim 5, characterized in that, The mass ratio of the cerium salt, the ytterbium salt, and the lithium salt is 1:0.2-0.8:5.2-7.

2.

9. The method for preparing the negative electrode material according to claim 5 or 8, characterized in that, The cerium salt includes at least one of cerium chloride, cerium fluoride, cerium bromide, and cerium iodide; And / or, the ytterbium salt includes at least one of ytterbium chloride, ytterbium fluoride, ytterbium bromide, and ytterbium iodide; And / or, the lithium salt includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide; And / or, after annealing, there is also a pickling step.

10. The application of the negative electrode material according to any one of claims 1-4 or the negative electrode material prepared by the preparation method according to any one of claims 5-9 in a battery.

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