Method and application for surface treatment of lithium-rich cathode material

Abstract

The present application discloses a method for surface treatment of a lithium-rich cathode material and its application. The method of the present application includes subjecting the lithium-rich cathode material to spark plasma sintering to obtain a lithium-rich cathode material with an oxygen vacancy defect layer; the conditions for spark plasma sintering are as follows: under vacuum, applying a pressure of 30-100 MPa, heating to 200-400 °C at a temperature of 20-80 °C and holding for 10-60 minutes. The method of the present application uses spark plasma sintering to induce oxygen vacancy defects on the surface of the lithium-rich cathode material, inhibits the loss of lattice oxygen during charge and discharge processes, promotes the rapid insertion and extraction of lithium ions, stabilizes the lattice structure, and enables the lithium-rich cathode material to have excellent rate performance and cycle stability; in addition, the oxygen vacancies on the surface of the lithium-rich cathode material lower the valence states of some metal elements, generating a spinel-like / rock-salt phase structure, which plays a protective role for the lithium-rich cathode material, reduces the side reactions with the electrolyte, further stabilizes the material structure, and improves the cycle stability.

Description

Technical Field

[0001] This application relates to the field of cathode materials for batteries, and particularly to a method for surface treatment of lithium-rich cathode materials and its applications. Background Art

[0002] In recent years, energy conversion and energy storage devices have witnessed unprecedented rapid development, and the market demand for the new energy vehicle industry has also been increasing day by day. Among them, lithium-ion batteries have become the ideal power source dominating the electric vehicle market due to their advantages such as high energy density and long cycle life. However, the capacities of commercial lithium-ion battery cathode materials such as spinel lithium manganate (LiMn2O4), lithium iron phosphate (LiFePO4), etc. are generally not high. Lithium-rich manganese-based oxide cathode materials have become the most promising next-generation lithium-ion battery cathode materials with a charge-discharge capacity of up to 300 mAh / g. However, lithium-rich manganese-based cathode materials still have problems such as low initial Coulomb efficiency, poor rate performance, severe voltage decay during cycling, and oxygen loss in the high delithiated state, which hinder their further commercial applications.

[0003] During the charge-discharge process, the surface structure and chemical composition of lithium-rich materials will change significantly, ultimately inevitably leading to the attenuation of the electrochemical performance of the materials. Therefore, it is very crucial to modify the surface of lithium-rich oxide particles. Traditional surface coating and doping methods can inhibit surface structure degradation to a certain extent, but with the increase in the number of cycling, the effect is still very limited. In addition, the presence of the coating layer will also hinder the transmission rate of lithium ions on the particle surface, further exacerbating the slow kinetic transmission process of lithium-rich manganese-based materials. Constructing a surface defect layer is an effective means to improve the structural stability of lithium-rich materials. Among them, pre-introducing intrinsic defects such as oxygen vacancies on the surface of lithium-rich particles has received particular attention in recent years. This modification method can effectively alleviate the side reaction between the cathode and the electrolyte, reduce irreversible oxygen loss at high voltages, and effectively improve the electrochemical cycling stability of lithium-rich manganese-based materials.

[0004] Currently, common methods for constructing oxygen vacancies mainly include treatment with reducing gases (H2, CO2, etc.), acids and bases, and organic solvents. However, these chemical methods often have complex processes, long treatment times, high energy consumption, high costs of chemical reagents, and environmental pollution. Moreover, the performance improvement of lithium-rich cathode materials modified by these methods is still very limited, and lithium-rich cathode materials and lithium-ion batteries with long cycle lives cannot be obtained, let alone large-scale commercialization.

[0005] Therefore, how to develop a new pre-constructed oxygen vacancy strategy with a long cycle life and suitable for large-scale commercial production is still an urgent problem to be solved in the technical field of lithium-rich cathode materials. Summary of the Invention

[0006] The objective of this application is to provide a new method for surface treatment of lithium-rich cathode materials and its applications.

[0007] This application adopts the following technical solutions:

[0008] On the one hand, this application discloses a method for surface treatment of lithium-rich cathode materials. Among them, the molecular formula of the lithium-rich cathode material is Li 1+x TM 1-x O2, where 0 < x < 0.4, and TM is at least two of Ni, Co, and Mn. The method of this application includes subjecting the lithium-rich cathode material to spark plasma sintering, and thus obtaining a surface-modified lithium-rich cathode material with oxygen vacancy defect layers. The conditions for spark plasma sintering are as follows: under vacuum conditions, applying a pressure of 30 - 100 MPa to the lithium-rich cathode material, and heating it to 200 - 400 °C at a rate of 20 - 80 °C per minute and holding for 10 - 60 minutes.

[0009] It should be noted that this application creatively uses spark plasma sintering at a lower temperature under vacuum conditions to perform surface treatment on the lithium-rich cathode material, thereby introducing a certain number of oxygen vacancy defects on the surface of the lithium-rich material, inhibiting the loss of lattice oxygen during charge and discharge, and further improving the cycle stability of the material. At the same time, the oxygen vacancies provide more possibilities for lithium-ion transport, enhancing the rate performance of the lithium-rich cathode material. Moreover, the oxygen vacancies on the surface of the lithium-rich cathode material lower the valence states of some metal elements, generating a spinel-like / rock-salt phase structure, which plays a protective role for the lithium-rich cathode material, reduces side reactions with the electrolyte, further stabilizes the material structure, and improves the cycle stability.

[0010] It should also be noted that the key of this application lies in performing surface treatment on the prepared lithium-rich cathode material by spark plasma sintering under special conditions. For example, for the lithium-rich cathode material obtained by high-temperature calcination using the solid-phase synthesis method, after cooling to room temperature, spark plasma sintering is carried out. The spark plasma sintering under special conditions of this application means that under a vacuum condition, a pressure of 30 - 100 MPa is applied to the lithium-rich cathode material, and the temperature is raised to 200 - 400 °C at a rate of 20 - 80 °C per minute and held for 10 - 60 minutes. Among them, the vacuum condition is to obtain oxygen defects; by adjusting parameters such as pressure, heating temperature, holding temperature, and holding time, the thickness of the oxygen vacancy defect layer can be adjusted to meet the surface-modified lithium-rich cathode material required for use. For example, the pressure applied to the lithium-rich cathode material can be 30 - 100 MPa, which can be 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, or 100 MPa; the heating rate can be 20 °C / min, 30 °C / min, 40 °C / min, 50 °C / min, 60 °C / min, 70 °C / min, or 80 °C / min; the holding temperature can be 200 °C, 250 °C, 300 °C, 350 °C, or 400 °C; the holding time can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min. Among them, the holding temperature cannot be too high or too low. If the holding temperature is too low, such as lower than 200 °C, it is difficult to form oxygen vacancies that meet the usage requirements; if the temperature is too high, such as higher than 400 °C, it may cause other unknown effects or damage to the crystal structure of some lithium-rich cathode materials.

[0011] In one implementation manner of this application, the lithium-rich cathode material is prepared by the solid-phase synthesis method.

[0012] In one implementation manner of this application, the solid-phase synthesis method specifically includes mixing the source materials evenly and obtaining the lithium-rich cathode material through high-temperature calcination; the conditions for high-temperature calcination are that in an air atmosphere, the evenly mixed source materials are pre-calcined at 400 - 600 °C for 2 - 8 hours, and then sintered at 700 - 900 °C for 6 - 18 hours. Among them, the source materials refer to the materials that provide the source of lithium or TM metal.

[0013] It should be noted that this application creatively combines the solid-phase sintering process with spark plasma sintering to induce the generation of oxygen vacancy defects on the surface of the lithium-rich cathode material. The entire preparation process of the lithium-rich cathode material does not involve chemical reagents, has high safety, and does not generate waste gas or wastewater, which is beneficial to environmental protection.

[0014] It should also be noted that the key of the present application lies in that after obtaining the lithium-rich cathode material by solid-phase high-temperature calcination, surface treatment is carried out by spark plasma sintering; as for the preparation of the lithium-rich cathode material by solid-phase high-temperature calcination, existing solid-phase sintering processes can be referred to. For example, pre-calcination is carried out at 400-600 °C for 2-8 hours, and then sintering is carried out at 700-900 °C for 6-18 hours. Among them, the pre-calcination temperature and time depend on the specific material. For example, it can be 400 °C, 450 °C, 500 °C, 550 °C or 600 °C, and the pre-calcination time can be 2h, 3h, 4h, 5h, 6h, 7h or 8h; the high-temperature calcination temperature also depends on the specific material. For example, it can be 700 °C, 750 °C, 800 °C, 850 °C or 900 °C, and the sintering time can be 6h, 8h, 10h, 12h, 14h, 16h or 18h.

[0015] In one implementation manner of the present application, the source materials are mixed evenly by the ball milling method, that is, the source materials are ball milled and mixed evenly.

[0016] In one implementation manner of the present application, the source material of Li is a lithium salt.

[0017] In one implementation manner of the present application, the lithium salt is at least one of lithium carbonate, lithium hydroxide and lithium acetate.

[0018] In one implementation manner of the present application, the source material of TM is a carbonate or metal hydroxide of TM.

[0019] In one implementation manner of the present application, the lithium-rich cathode material is a lithium-rich manganese-based cathode material.

[0020] In one implementation manner of the present application, the source materials of the lithium-rich manganese-based cathode material are lithium carbonate and nickel cobalt manganese precursor.

[0021] In one implementation manner of the present application, the nickel cobalt manganese precursor is Ni 1 / 6 Co 1 / 6 Mn 2 / 3 CO3 or Ni 1 / 6 Co 1 / 6 Mn 2 / 3 (OH)2.

[0022] It should be noted that for the surface treatment method of the lithium-rich cathode material of the present application, for the lithium-rich manganese-based cathode material, while introducing oxygen vacancy defects by spark plasma sintering, due to charge compensation, a small amount of Mn is generated on the material surface 3+ and the corresponding spinel-like / rock salt phase structure, thereby protecting the particle surface, reducing the side reaction with the electrolyte, further stabilizing the material structure and improving the cycle stability.

[0023] On the other hand, the present application discloses a surface-modified lithium-rich cathode material prepared by the method of the present application.

[0024] Another aspect of the present application discloses an electrode sheet using the surface-modified lithium-rich cathode material of the present application.

[0025] Another aspect of the present application discloses a lithium-ion battery using the surface-modified lithium-rich cathode material of the present application.

[0026] The beneficial effects of the present application are as follows:

[0027] The surface treatment method of the lithium-rich cathode material of the present application uses spark plasma sintering to induce oxygen vacancy defects on the surface of the lithium-rich cathode material, inhibits the loss of lattice oxygen during charge and discharge, promotes the rapid insertion and extraction of lithium ions, stabilizes the lattice structure, and enables the lithium-rich cathode material to have excellent rate performance and cycle stability; moreover, the oxygen vacancies on the surface of the lithium-rich cathode material lower the valence states of some metal elements, generating a spinel-like / rock salt phase structure, which protects the lithium-rich cathode material, reduces side reactions with the electrolyte, further stabilizes the material structure, and improves cycle stability. Description of the Drawings

[0028] Figure 1 is the X-ray diffraction (XRD) pattern of the surface-modified lithium-rich cathode material with an oxygen vacancy defect layer in the experimental group of the embodiments of the present application;

[0029] Figure 2 is the X-ray diffraction (XRD) pattern of the surface-modified lithium-rich cathode material with an oxygen vacancy defect layer in the control group of the embodiments of the present application;

[0030] Figure 3 is the scanning electron microscope (SEM) image of the surface-modified lithium-rich cathode material with an oxygen vacancy defect layer in the experimental group of the embodiments of the present application;

[0031] Figure 4 is the scanning electron microscope (SEM) image of the surface-modified lithium-rich cathode material with an oxygen vacancy defect layer in the control group of the embodiments of the present application;

[0032] Figure 5 is the X-ray photoelectron spectroscopy (XPS) comparison chart of the lithium-rich manganese-based cathode materials of the lithium batteries in the experimental group and the control group of the embodiments of the present application;

[0033] Figure 6 is the rate performance comparison chart of the lithium-rich manganese-based cathode materials of the lithium batteries in the experimental group and the control group of the embodiments of the present application;

[0034] Figure 7 is the electrochemical cycle stability comparison chart of the lithium-rich manganese-based cathode materials of the lithium batteries in the experimental group and the control group of the embodiments of the present application at a rate of 0.1C to 5C. Detailed Embodiments

[0035] The existing methods for forming oxygen vacancies on the surface of lithium-rich cathode materials are complex in process, time-consuming in treatment, high in energy consumption, high in cost of chemical reagents, and environmentally polluting. More importantly, the rate performance and cyclic stability improvement effects of the lithium-rich cathode materials with oxygen vacancies obtained by the existing methods are relatively poor.

[0036] Spark Plasma Sintering (SPS for short) is a technology for directly passing pulsed current between powder particles for heating and sintering. At present, there have been technical solutions for directly using spark plasma sintering to perform high-temperature calcination on source materials to prepare cathode materials.

[0037] The present application creatively studies and discovers that by using spark plasma sintering to perform low-temperature sintering treatment again on the already prepared lithium-rich cathode materials, such as the lithium-rich cathode materials obtained by high-temperature calcination by the solid-phase method, oxygen vacancy defects can be induced and generated on the surface of the lithium-rich cathode materials, promoting the rapid deintercalation and intercalation of lithium ions, stabilizing the lattice structure, and enabling the lithium-rich cathode materials to have excellent rate performance and cyclic stability. Moreover, low-valence metal elements, such as Mn 3+ and the corresponding spinel-like / rock-salt phase structure are generated on the surface, which plays a protective role for the lithium-rich cathode materials, reduces side reactions with the electrolyte, further stabilizes the material structure, and improves cyclic stability.

[0038] Based on the above research and discovery, the present application creatively proposes a method for surface treatment of lithium-rich cathode materials, including performing spark plasma sintering on the lithium-rich cathode materials, that is, obtaining surface-modified lithium-rich cathode materials with an oxygen vacancy defect layer on the surface; the conditions for spark plasma sintering are that under a vacuum condition, a pressure of 30-100 MPa is applied to the lithium-rich cathode materials, and the temperature is raised to 200-400 °C at a rate of 20-80 °C and held for 10-60 minutes.

[0039] It should be noted that due to its low cost and simple process, the solid-phase synthesis method is widely used in the synthesis of lithium-rich manganese-based cathode materials. However, the lithium-ion diffusion kinetics of the lithium-rich cathode material particles prepared by this method is not very ideal, and the cyclic stability is also relatively poor. Therefore, the present application further uses spark plasma sintering to introduce a certain number of oxygen vacancy defects on the particle surface to modify the material, which can effectively inhibit irreversible lattice oxygen loss and structural distortion during the cycling process and greatly improve cyclic stability. At the same time, the presence of oxygen vacancies is beneficial to the rapid deintercalation and intercalation of lithium ions, and can further improve the rate performance of the lithium-rich material. In addition, due to the charge compensation mechanism, the presence of surface oxygen vacancies will cause the valence state of surface metal elements to become lower, such as resulting in Mn 3+Generated, thus generating an ultrathin spinel-like / rock salt phase structure layer on the surface, which is conducive to acting as a protective layer during cycling, reducing side reactions with the electrolyte, thereby reducing further phase transformation of the material, alleviating the accumulation of lattice strain, and improving the capacity retention rate during long cycling.

[0040] In summary, the surface treatment method of the lithium-rich cathode material of the present application can form a sufficient amount of oxygen vacancies. On the one hand, the formed oxygen vacancies can inhibit the loss of lattice oxygen during charge and discharge, promote the rapid deintercalation and intercalation of lithium ions, stabilize the lattice structure, and enable the lithium-rich cathode material to have excellent rate performance and cycling stability. On the other hand, the oxygen vacancies on the surface of the lithium-rich cathode material lower the valence states of some metal elements, generating a spinel-like / rock salt phase structure, which plays a protective role for the lithium-rich cathode material, reduces side reactions with the electrolyte, further stabilizes the material structure, and improves the cycling stability.

[0041] The present application will be further described in detail through specific examples below. The following examples are only for further illustration of the present application and should not be construed as limitations on the present application.

[0042] Example

[0043] The lithium-rich cathode material of the lithium-ion battery in this example is a lithium-rich manganese-based cathode material, and its molecular formula is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0044] The Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 preparation method specifically includes the following steps:

[0045] According to the stoichiometric ratio of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, the lithium source and the nickel-cobalt-manganese precursor are mixed. The lithium salt in this example is lithium carbonate, and the nickel-cobalt-manganese precursor is Ni 1 / 6 Co 1 / 6 Mn 2 / 3 CO3. According to Li2CO3:Ni 1 / 6 Co 1 / 6 Mn 2 / 3Add two ingredients into the ball milling jar and take them out after high-energy ball milling for 6 hours. Then, place the well-mixed powder in a porcelain boat and conduct high-temperature calcination in a muffle furnace. The specific solid-phase synthesis steps are as follows: heat the mixed sample at a heating rate of 3 °C per minute to 480 °C, hold for 5 hours, then heat to 850 °C at a heating rate of 3 °C per minute and hold for 12 hours, and finally cool naturally to room temperature. The entire sintering process is carried out in an air atmosphere to obtain the lithium-rich cathode material.

[0046] Then, perform spark plasma sintering on the lithium-rich cathode material. The specific method is as follows: put the prepared lithium-rich cathode material into a mold with a diameter of 10 mm, and then apply a pressure of 60 MPa to the sample through a pressing device. At the same time, quickly heat the sample to 300 °C at a heating rate of 50 °C per minute under vacuum and hold for 30 minutes to obtain the surface-modified lithium-rich cathode material with oxygen vacancy defect layers.

[0047] In this example, XRD diffraction analysis, scanning electron microscopy observation, XPS analysis, rate performance, and electrochemical cycle stability tests were respectively carried out on the finally prepared surface-modified lithium-rich cathode material (marked as the experimental group). At the same time, the lithium-rich cathode material prepared by the solid-phase synthesis step, that is, the lithium-rich cathode material without spark plasma sintering, was used as a control (marked as the control group) for the same tests to compare the influence of spark plasma sintering on the lithium-rich cathode material. Specifically as follows:

[0048] 1. Comparison of structural information

[0049] Characterize and analyze the lithium-ion-rich lithium manganese-based cathode materials of the experimental group and the control group with an X-ray diffractometer (D8-discover type, produced by Bruker Corporation, Germany) to obtain the results as shown in Figure 1 and Figure 2 shown.

[0050] Through Figure 1 and Figure 2 it can be obtained that the diffraction peaks of both the experimental group and the control group are very sharp, indicating that both powders have good crystallinity; there are no impurity peaks in both, and each diffraction peak can correspond one by one to the diffraction peaks of the standard lithium-rich manganese-based material; all diffraction peaks of each sample can be well attributed to the hexagonal layered structure (R-3m space group) and the monoclinic structure (C2 / m space group).

[0051] 2. Particle morphology characterization

[0052] Characterize the micro-morphology of the lithium-rich manganese-based cathode materials of the experimental group and the control group with a scanning electron microscope (ZEISS SUPRA55) to obtain the SEM images at a magnification of 50,000 times, respectively as shown in Figure 3 andFigure 4 as shown

[0053] It was found through observation that both the experimental group and the control group exhibited the typical morphological characteristics of lithium-rich manganese-based cathode materials, which were regular polyhedral structures. There was no obvious difference in the particle shape, and the particle sizes were basically the same.

[0054] 3. Characterization of oxygen vacancy defects

[0055] The O 1s peaks of the lithium-rich manganese-based cathode materials of the experimental group and the control group were characterized by X-ray photoelectron spectroscopy (XPS, ESCALab220I-XL). The specific results are as Figure 5 shown

[0056] Figure 5 In, the peak at 531.1 eV represents carbonate, and there is not much difference in the peaks of the samples before and after modification at this position; the peak at 528.9 eV corresponds to lattice oxygen. It can be clearly seen that the peak intensity of the experimental group after modification is much smaller than that of the control group at this position, indicating that the covalency of oxygen and transition metals is weaker; thus, it can be seen that lattice oxygen loss occurred in the experimental group after surface modification treatment, that is, oxygen vacancy defects were obtained in the structure.

[0057] 4. Comparison of electrochemical performance

[0058] The two lithium-rich manganese-based cathode materials in the experimental group and the control group were assembled into batteries for electrochemical performance test characterization. Here, the specific assembly process is introduced taking the experimental group as an example, and the control group is the same. The specific assembly steps are as follows:

[0059] (1) Preparation of the positive electrode sheet

[0060] The lithium-rich manganese-based cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, conductive carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in a mortar according to a mass ratio of 8:1:1, and then transferred to a beaker. Then, N-methylpyrrolidone (NMP) was added for dispersion, and the mass ratio of PVDF to NMP added was 1:25. After the beaker was placed on a magnetic stirrer and stirred thoroughly for 3 hours, it was evenly coated on the aluminum foil. Then, the aluminum foil was transferred to a blast drying oven at 80 °C and dried. After drying for two hours, it was cut into circular pieces with a diameter of 10 mm. Subsequently, the cut electrode sheets were transferred to a vacuum drying oven at 110 °C and dried for 20 hours for standby.

[0061] (2) Preparation of the battery negative electrode

[0062] The battery negative electrode was a commercially available lithium sheet with a diameter of 14 mm from AVIC Lithium Battery Co., Ltd.

[0063] (3) Button cell assembly

[0064] The CR2032 button cell was assembled in a glove box filled with argon. The electrolyte in this example was 1 mol / L LiPF6 dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1. The separator used was Celgard 2400 polypropylene membrane. The assembly order from top to bottom was the positive electrode case, the positive electrode plate, the separator, the negative electrode, the steel sheet, the spring sheet, and the negative electrode case. After assembly, it was left standing for 6 hours for standby use.

[0065] (4) Battery performance test

[0066] The electrochemical test of the battery was carried out using a Neware electrochemical test system. Here, the button cell was placed on the Neware electrochemical test channel, and the measured voltage range was 2.0V - 4.8V. The cycle stability and rate performance of the battery were compared and tested.

[0067] Comparison of cycle stability:

[0068] The button cells assembled with the lithium-rich manganese-based cathode materials of the experimental group and the control group were subjected to charge and discharge cycle tests in the voltage range of 2.0 - 4.8V at a charge and discharge rate of 1C (current density of 250 mA / g), and the number of cycles was 150. The results are as Figure 6 shown.

[0069] Figure 6 The results showed that the discharge specific capacity of the experimental group decreased from 184.5 mAh / g in the first cycle to 181.7 mAh / g after 150 cycles, and the capacity retention rate was as high as 98.5%. While in the control group, during the 150-cycle process, the discharge specific capacity decreased from 175.0 mAh / g in the first cycle to 121.8 mAh / g, and the capacity retention rate was only 69.6%. From the above comparison, it can be seen that the lithium-rich manganese-based cathode material of the experimental group had a significant improvement in cycle stability after the surface modification treatment by spark plasma sintering, and the capacity retention rate was much higher than that of the control group.

[0070] Comparison of rate performance:

[0071] According to the same electrochemical test method, the rate performance of the lithium-rich manganese-based cathode materials of the experimental group and the control group was tested. Using the Neware test system, the voltage range was 2.0V to 4.8V, and the experimental group and the control group were subjected to charge and discharge tests at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C respectively. The results are as Figure 7 shown.

[0072] Figure 7The results show that the discharge specific capacity of the oxygen vacancy-rich lithium-rich manganese-based material modified by spark plasma sintering is higher than that of the unmodified control group of lithium-rich manganese-based materials at each rate. Moreover, as the test rate gradually increases, the difference in discharge specific capacity between the experimental group and the control group gradually increases. At the same time, it is found that even at a high rate of 5C, the experimental group can still maintain a discharge specific capacity of 128 mAh / g, which is better than 113 mAh / g of the control group. This is mainly due to the oxygen vacancy defects on the surface of the modified material, which are beneficial to the rapid transmission of lithium ions and effectively promote the fast charge-discharge ability of the material.

[0073] The above content is a further detailed description of the present application in combination with specific implementation manners, and it cannot be determined that the specific implementation of the present application is only limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, without departing from the concept of the present application, several simple deductions or substitutions can still be made.

Claims

1. A method for surface treatment of a lithium-rich cathode material, characterized in that: The molecular formula of the lithium-rich cathode material is Li 1+x TM 1-x O2, where 0 < x < 0.4, and TM is at least two of Ni, Co, and Mn; The method includes subjecting the lithium-rich cathode material to spark plasma sintering to obtain a surface-modified lithium-rich cathode material with an oxygen vacancy defect layer; The conditions for the spark plasma sintering are as follows: under a vacuum condition, applying a pressure of 30 - 100 MPa to the lithium-rich cathode material, and heating at a heating rate of 20 - 80 °C / min to 200 - 400 °C and holding for 10 - 60 minutes.

2. The method according to claim 1, characterized in that: The lithium-rich cathode material is prepared by a solid-phase synthesis method.

3. The method according to claim 2, wherein: The solid-phase synthesis method includes mixing the source materials evenly and obtaining the lithium-rich cathode material through high-temperature calcination; The conditions for the high-temperature calcination are as follows: in an air atmosphere, first pre-calcining the evenly mixed source materials at 400 - 600 °C for 2 - 8 hours, and then sintering at 700 - 900 °C for 6 - 18 hours.

4. The method according to claim 3, wherein: The mixing of the source materials evenly is carried out by a ball milling method.

5. The method according to claim 3, characterized in that: Among the source materials, the source material of Li is a lithium salt.

6. The method according to claim 5, wherein: The lithium salt is at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

7. The method according to claim 3, wherein: Among the source materials, the source material of TM is a carbonate or metal hydroxide of TM.

8. The method according to any one of claims 1 to 7, characterized in that: The lithium-rich cathode material is a lithium-rich manganese-based cathode material.

9. The method according to claim 8, wherein: The source materials of the lithium-rich manganese-based cathode material are lithium carbonate and nickel cobalt manganese precursor.

10. The method according to claim 9, wherein: The nickel-cobalt-manganese precursor is Ni 1 / 6 Co 1 / 6 Mn 2 / 3 CO3 or Ni 1 / 6Co 1 / 6 Mn 2 / 3 (OH)2 11. A surface-modified lithium-rich cathode material prepared by the method according to any one of claims 1 - 10.

12. An electrode sheet using the surface-modified lithium-rich cathode material according to claim 11.

13. A lithium-ion battery using the surface-modified lithium-rich cathode material according to claim 11.

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