Preparation method and application of positive electrode material with optimized surface interface structure

Abstract

The invention relates to a preparation method and application of an optimized surface interface structure of a positive electrode material, lithium oxygen vacancies are accurately constructed on the surface of a layered positive electrode material by using a transient high-temperature pulse Joule heat technology, and the continuous lithium oxygen vacancies promote the surface structure of the positive electrode material to be converted from a layered phase to a spinel phase and a rock salt phase; and finally, a thin, uniform and complete complete coating layer is formed on the surface of the positive electrode material. According to the coating layer formed by the reconstructed and optimized lithium oxygen loss, the surface lithium ion conductivity is remarkably enhanced, and the decomposition of electrolyte on the surface of the positive electrode material and the loss of lattice oxygen are effectively inhibited, so that the integrity of the material is protected. According to the invention, the first coulombic efficiency of the positive electrode material can be greatly improved, and low-capacity attenuation and high-stability long cycle performance can be realized. In addition, the method is simple to operate and short in preparation time, and has the potential of large-scale application.

Description

Technical Field

[0001] The present invention relates to the technical field of modification and preparation of cathode materials for ionic batteries, and particularly to a preparation method for optimizing the surface and interface structure of a cathode material and its application. Background Art

[0002] Ionic batteries have many advantages such as high energy density, long cycle life, low self-discharge, no memory effect, and environmental friendliness. In particular, ionic batteries have been widely used in consumer electronics fields such as smart phones, smart bracelets, digital cameras, and laptop computers, and have huge consumer demands. As a key power source for new energy vehicles, the performance of lithium-ion batteries directly determines important indicators such as the driving range, charging speed, and service life of electric vehicles. On the basis of having been widely applied in the consumer electronics field, lithium-ion batteries are rapidly developing towards high performance, long life, and low cost, and are gradually penetrating into the fields of pure electric, hybrid electric, and range-extended electric vehicles. In addition, it also shows good application prospects in large energy storage systems such as power grid peak regulation, household power distribution, and communication base stations. As one of the core components of lithium-ion batteries, the cathode material plays a crucial role in improving the overall performance of the battery. Improving energy density, enhancing cycle stability, and ensuring safety are challenges common to all types of cathode materials. Especially in the deeply delithiated state, the surface structure of the cathode material is prone to instability, and some lattice oxygen is released in the form of oxygen, while reactive oxygen participates in interfacial side reactions to form an interfacial layer, resulting in irreversible loss of active substances. These phenomena accelerate capacity decay, reduce the initial Coulomb efficiency, increase irreversible capacity, and directly affect the long-term performance and reliability of the battery, so they have become the focus of attention of researchers.

[0003] To overcome these problems, researchers are exploring various modification methods to optimize the performance of cathode materials, such as techniques like ion doping, surface coating, and structure design. Research shows that constructing a protective layer on the surface can effectively regulate and improve the surface structure in the deeply delithiated state. An ideal coating material should be able to promote rapid ion migration and have high chemical stability to resist electrolyte erosion. In addition, good lattice matching between the coating and the substrate is crucial for maintaining the smoothness of lithium-ion diffusion and interface integrity, but it is difficult to achieve in actual operation. Coating layers formed by dry / wet chemistry such as metal oxides, metal fluorides, metal phosphides, and fast ion conductors can prevent direct contact between the cathode material and the electrolyte, thereby alleviating surface instability. However, due to the wetting problem between solids, there are still challenges in precisely controlling the thickness, composition, uniformity, and continuity of the coating layer. Summary of the Invention

[0004] The objective of the present invention is to reconstruct and optimize the surface of the layered oxide cathode material of a lithium-ion battery based on precise control of interfacial lithium oxygen removal, so as to prepare a complete and continuous thin shell layer that matches the bulk material. It aims to solve the problems that the surface structure of the cathode material is prone to become unstable, leading to accelerated capacity decay, reduced initial Coulomb efficiency, and increased irreversible capacity, etc.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method for optimizing the surface and interface structure of a cathode material, comprising the following steps

[0007] (1) Weigh a certain amount of the cathode material, and perform uniform dispersion and drying treatment;

[0008] (2) Uniformly load the cathode material into the interior of a conductive carrier, and process it under certain atmosphere conditions;

[0009] (3) Load the conductive carrier in the conductive carrier heating zone of a Joule heat device, and align the temperature sensor with the middle of the conductive carrier for real-time temperature detection;

[0010] (4) Use a vacuum system and a gas mass flowmeter to control the atmosphere in the reaction chamber of the Joule heat device;

[0011] (5) Start the power supply to perform high-temperature pulsed Joule heat. When applying high-temperature pulses, the working voltage is 10 - 80V, and the working current is 0.5 - 80A; heat up to 300 - 2500 °C; the single-pulse time is 0.001 - 300s.

[0012] Optionally, the cathode material in step (1) is Li x MO 2 , where M is one or more of Ni, Co, Mn, Al, Fe.

[0013] Optionally, the morphology of the cathode material in step (1) includes, but is not limited to, polycrystalline structure, single-crystalline structure, core-shell structure.

[0014] Optionally, the dispersion method in step (1) is mechanical ball milling dispersion, manual grinding dispersion with an agate mortar, ultrasonic dispersion, high-speed stirring dispersion.

[0015] Optionally, the drying conditions in step (1) are vacuum drying, the drying temperature is 80 - 100 °C, and the drying time is 10 - 24h.

[0016] Optionally, the cathode material in step (1) can be in powder form or sheet material made by a press.

[0017] Optionally, the conductive carrier in step (2) can be a conductive metal, a conductive polymer, a graphene film, carbon cloth, carbon paper, carbon felt, etc.

[0018] Optionally, the Joule heating device described in step (3) includes an in-built reaction chamber and an open reaction area in the glove box.

[0019] Optionally, the atmosphere described in step (4) is a multi-step treatment including one or more gases selected from, but not limited to, air, vacuum, oxygen, carbon dioxide, argon, and nitrogen.

[0020] Optionally, the temperature sensor described in step (4) is an infrared temperature sensor with a temperature measurement range of 300°C - 2500°C.

[0021] Optionally, the temperature sensor described in step (4) is aligned with the middle of the conductive carrier.

[0022] Optionally, when applying the high-temperature pulse in step (5), the working voltage is 10 - 80V, the working current is 0.5 - 80A; the temperature is raised to 300 - 800°C; and the single-pulse time is 10 - 300s.

[0023] A 100% coated rock salt phase coating layer is formed on the surface of the positive electrode material. The thickness of the coating layer is 0nm - 10nm, and the lithium-oxygen loss of the coating layer is about 20% - 30%.

[0024] The application of a positive electrode material in a lithium-ion battery is obtained by a preparation method for optimizing the surface and interface structure of the positive electrode material.

[0025] The beneficial effects of the present invention: By using the pulsed high-temperature Joule heating technology, the surface and interface structure of the layered oxide positive electrode is reconstructed and optimized by controllable lithium-oxygen removal. Mainly, transient high-temperature pulsed Joule heating technology is used to precisely construct lithium-oxygen vacancies on the surface of the layered positive electrode material; the continuous lithium-oxygen vacancies promote the transformation of the surface structure of the positive electrode material from the layered phase to the spinel phase and the rock salt phase, and finally a thin, uniform, complete, and fully coated layer is formed on the surface of the positive electrode material. The coating layer formed by the reconstructed and optimized lithium-oxygen loss not only significantly enhances the surface lithium-ion conductivity but also effectively inhibits the decomposition of the electrolyte on the surface of the positive electrode material and the loss of lattice oxygen, thereby protecting the integrity of the material. The present invention can greatly improve the initial Coulomb efficiency of the positive electrode material and achieve low capacity decay and high-stability long-cycle performance. In addition, this method is simple to operate and has a short preparation time, and has the potential for large-scale application. Description of the Drawings

[0026] Figure 1 It is a schematic diagram showing the transformation of the surface structure from the layered phase to the spinel phase and then to the rock salt phase induced by the increase in the amount of lithium and oxygen removed in this application;

[0027] Figure 2 It is this application treating single crystal LiNi with 350°C for 25s 08 Co 01 Mn 01O 2 Transmission electron microscopy image;

[0028] Figure 3 This is the transmission electron microscopy image of LiCoO processed at 700 °C for 30 s in this application; 2 Transmission electron microscopy image;

[0029] Figure 4 This is the first charge-discharge curve and cycling performance graph of the single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O 2 and the raw materials assembled into a battery;

[0030] Figure 5 This is the first charge-discharge curve and cycling performance graph of the polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O 2 and the raw materials assembled into a battery;

[0031] Figure 6 This is the transmission electron microscopy image of the polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O 2 processed at 350 °C for 25 s in this application;

[0032] Figure 7 This is the cycling performance graph of the polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O 2 and the raw materials assembled into a battery processed at different temperatures for 25 s in this application;

[0033] Figure 8 This is the cycling performance graph of the polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O 2 and the raw materials assembled into a battery processed at 350 °C for different times in this application;

[0034] Figure 9 This is the first charge-discharge curve and cycling performance graph of the polycrystalline LiNi 0.825 Co 0.115 Mn 0.06 O 2 and the raw materials assembled into a battery processed at 350 °C for 25 s in this application;

[0035] Figure 10 This is the first charge-discharge curve and cycling performance graph of the polycrystalline LiNi 0.9 Co 0.05Mn 0.05 O 2 and the first charge-discharge curve and cycle performance diagram of the battery assembled with the original materials;

[0036] Figure 11 is the LiCoO treated by this application at 700 °C for 30 s 2 and the comparison diagram of the first charge-discharge curve, cycle performance and AC impedance of the battery assembled with the original materials;

[0037] Figure 12 is the first charge-discharge curve diagram of the battery assembled with the lithium-rich manganese treated by this application at 400 °C for 25 s and the original materials. Specific embodiments

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0039] Taking the lithium-ion battery as an example, the embodiments of a preparation method of the present invention for reconstructing and optimizing the surface and interface structure of a layered oxide cathode by controllable lithium-oxygen removal are specifically disclosed with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where the detailed descriptions of well-known matters and the repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art.

[0040] How to achieve a complete thin shell layer that matches and is complete with the bulk material on the surface of the cathode material is the key difficulty and technical point of this application. By using the Joule heat effect to implement highly controllable processing, the layered surface structure can undergo a delithiation and deoxidation process, thereby forming a new coating phase, which has excellent lattice matching with the layered structure oxide.

[0041] The core of this method lies in that by precisely controlling parameters such as current voltage and heating time, the composition and structure of the surface layer can be effectively adjusted, and then a completely thin shell layer that matches and is uniform and complete with the bulk material can be constructed. Transient high-temperature pulsed Joule heating technology is mainly used to precisely construct lithium-oxygen vacancies on the surface of the layered cathode material. The continuous lithium-oxygen vacancies promote the transformation of the surface structure of the cathode material from the layered phase to the spinel phase and the rock salt phase, and finally a thin, uniform and complete completely coated layer is formed on the surface of the cathode material. The coated layer formed by reconstructing and optimizing the lithium-oxygen loss not only significantly enhances the surface lithium ion conductivity, effectively inhibits the decomposition of the electrolyte on the surface of the cathode material and the loss of lattice oxygen, thus protecting the integrity of the material. The present invention can greatly improve the initial Coulomb efficiency of the cathode material, achieve low capacity attenuation and high-stability long-cycle performance. In addition, this method is simple to operate and has a short preparation time, and has the potential for large-scale application.

[0042] Example 1:

[0043] Joule heat treatment:

[0044] (1) Weigh a certain amount of single-crystal NCM811, disperse it evenly and perform a drying treatment;

[0045] (2) Uniformly load the single-crystal NCM811 into the inside of the conductive carrier and treat it under certain atmosphere conditions;

[0046] (3) Load the conductive carrier into the conductive carrier heating zone of the Joule heat equipment, align the temperature sensor with the middle of the conductive carrier for real-time temperature detection, and the temperature is 350 °C;

[0047] (4) Use the vacuum system and the gas mass flowmeter to control the atmosphere in the reaction chamber of the Joule heat equipment to be argon;

[0048] (5) Start the power supply to perform high-temperature pulsed Joule heat for 25 s.

[0049] Example 2: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 350 °C, and the duration is 25 s.

[0050] Example 3: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 300 °C, and the duration is 25 s.

[0051] Example 4: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 400 °C, and the duration is 25 s.

[0052] Example 5: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 500 °C, and the duration is 25 s.

[0053] Example 6: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 350 °C, and the duration is 15 s.

[0054] Example 7: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 350 °C, and the duration is 60 s.

[0055] Example 8: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 350 °C, and the duration is 120 s.

[0056] Example 9: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 350 °C, and the duration is 300 s.

[0057] Example 10: The same as Example 1, except that the cathode material is polycrystalline Ni825, the treatment temperature is 350 °C, and the duration is 25 s.

[0058] Example 11: The same as Example 1, except that the cathode material is polycrystalline Ni90, the treatment temperature is 350 °C, and the duration is 25 s.

[0059] Example 12: The same as Example 1, except that the cathode material is LiCoO 2 , the treatment temperature is 700 °C, and the duration is 30 s.

[0060] Example 13: The same as Example 1, except that the cathode material is Li-rich, the treatment temperature is 400 °C, and the duration is 25 s.

[0061] Comparative Example 1: The original single-crystal NCM811 without Joule heat treatment.

[0062] Comparative Example 2: The original polycrystalline NCM811 without Joule heat treatment.

[0063] Comparative Example 3: The same as Example 1, except that the cathode material is polycrystalline NCM811, the treatment temperature is 600 °C, and the duration is 25 s.

[0064] Comparative Example 4: The original polycrystalline Ni825 without Joule heat treatment.

[0065] Comparative Example 5: The original polycrystalline Ni90 without Joule heat treatment.

[0066] Comparative Example 6: The original LiCoO without Joule heat treatment 2 .

[0067] Comparative Example 7: As-prepared Li-rich without Joule heat treatment.

[0068] Tests and results:

[0069] We made cathode sheets from the cathode materials after treatment in Examples 1-13 and the cathode materials in Comparative Examples 1-7 respectively, assembled them into coin cells for testing:

[0070] Preparation of cathode sheets and battery assembly:

[0071] (1) Weigh the cathode material, binder, and conductive agent according to a certain mass ratio;

[0072] (2) Put the weighed chemicals into a stirring box, add two zirconium beads with a diameter D = 3 mm, and place the stirring box in a Thinky stirrer to stir at a speed of 600 rmp for 30 min;

[0073] (3) Spread the stirred slurry evenly on carbon-coated aluminum foil with a 50-μm scraper;

[0074] (4) Place it in an oven at 120 °C and dry for 12 h, then cut it into 11-mm round pieces with a punching machine;

[0075] (5) After weighing, assemble it into a CR2032 coin cell in a glove box;

[0076] Test results of Example 1 and Comparative Example 1:

[0077] Figure 4 Show the first-cycle charge-discharge curves and cycling performance graphs of coin cells assembled with the single-crystal NCM811 material subjected to 350 °C - 25 s Joule heat treatment prepared in Example 1 of the present invention and the as-prepared single-crystal NCM811 material without Joule heat treatment in Comparative Example 1. The test conditions are 0.1C, the charge-discharge voltage range is 2.7 - 4.3 V, and the test temperature is 26 °C. The cycling test conditions are 1C, the charge-discharge voltage range is 2.7 - 4.3 V, and the test temperature is 26 °C.

[0078] Figure 4 -a:

[0079] Abscissa (Specific Capacity, mAh / g): Represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 250 mAh / g.

[0080] Ordinate (Voltage, V): Represents the voltage of the battery, with the unit of V, ranging from 0 to 4.5 V.

[0081] Figure 4 -b:

[0082] Abscissa (Cycle Number): Represents the number of cycles of the battery, ranging from 0 to 100 cycles.

[0083] Left ordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 200 mAh / g.

[0084] Right ordinate (Coulombic Efficiency, %): Represents the coulombic efficiency of the battery, ranging from 0% to 100%.

[0085] Compared with Comparative Example 1, after 25 s of Joule heat treatment at 350 °C in Example 1, the initial coulombic efficiency of the battery increased from 85.29% to 88.34%. The capacity retention rate after 100 cycles at 1 C increased from 83.91% to 93.71%.

[0086] Test results of Example 2 and Comparative Example 2:

[0087] Figure 5 Show the initial charge-discharge curves and cycling performance graphs of the coin cells assembled with the polycrystalline NCM811 material subjected to 350 °C - 25 s Joule heat treatment prepared in Example 2 of the present invention and the original polycrystalline NCM811 material without Joule heat treatment in Comparative Example 2. The test conditions were 0.1 C, the charge-discharge voltage range was 2.7 - 4.3 V, and the test temperature was 26 °C. The cycling test conditions were 1 C, the charge-discharge voltage range was 2.7 - 4.3 V, and the test temperature was 26 °C.

[0088] Figure 5 -a:

[0089] Abscissa (Specific Capacity, mAh / g): Represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 250 mAh / g.

[0090] Ordinate (Voltage, V): Represents the voltage of the battery, with the unit of V, ranging from 0 to 4.5 V.

[0091] Figure 5 -b:

[0092] Abscissa (Cycle Number): Represents the number of cycles of the battery, ranging from 0 to 500 cycles.

[0093] Left ordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 200 mAh / g.

[0094] Right vertical coordinate (Coulombic Efficiency, %): Represents the Coulombic efficiency of the battery, ranging from 0% to 100%.

[0095] Compared with Comparative Example 2, after Joule heat treatment at 350 °C for 25 s in Example 2, the initial Coulombic efficiency of the battery increased from 89.6% to 95.2%. The capacity retention rate after 500 cycles at 1C increased from 65.19% to 93.56%.

[0096] Test results of Examples 3, 4, 5 and Comparative Example 3:

[0097] Figure 7 Show the first charge-discharge curves and cycle performance graphs of coin cells assembled with the polycrystalline NCM811 materials prepared in Examples 3, 4, 5 and Comparative Examples 2, 3 of the present invention. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7 - 4.3 V, and the test temperature was 26 °C.

[0098] Horizontal coordinate (Cycle Number): Represents the number of cycles of the battery, ranging from 0 to 200 cycles.

[0099] Left vertical coordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 200 mAh / g.

[0100] Right vertical coordinate (Coulombic Efficiency, %): Represents the Coulombic efficiency of the battery, ranging from 0% to 100%.

[0101] Compared with Comparative Example 2, after Joule heat treatment at 300 °C, 400 °C, 500 °C for 25 s in Examples 3, 4, 5, the capacity retention rate after 200 cycles at 1C increased from the original 80.32% to 88.32%, 92.26%, 85.41% in sequence. While after Joule heat treatment at 600 °C for 25 s in Comparative Example 3, compared with Comparative Example 2, the capacity retention rate after 200 cycles at 1C decreased from the original 80.32% to 68.08%. It can be seen that the performance of Examples 3, 4, 5 is improved, and the performance of Comparative Example 3 is not improved.

[0102] Test results of Examples 6, 7, 8, 9:

[0103] Figure 8 Show the first charge-discharge curves and cycle performance graphs of coin cells assembled with the polycrystalline NCM811 materials prepared in Examples 6, 7, 8, 9 and Comparative Example 2 of the present invention. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7 - 4.3 V, and the test temperature was 26 °C.

[0104] Abscissa (Cycle Number): Represents the number of cycles of the battery, ranging from 0 to 200 cycles.

[0105] Left ordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 200 mAh / g.

[0106] Right ordinate (Coulombic Efficiency, %): Represents the coulombic efficiency of the battery, ranging from 0% to 100%.

[0107] Compared with Comparative Example 2, after Joule heat treatment at 350 °C for 15 s, 60 s, 120 s, and 300 s in Examples 6, 7, 8, and 9, the capacity retention rates of cycling 200 circles at a current rate of 1C increased from 80.32% to 89.24%, 90.03%, 92.75%, and 90.72% in sequence.

[0108] Test results of Example 10 and Comparative Example 4:

[0109] Figure 9 Show the first charge-discharge curve and cycling performance graph of a coin cell assembled with the Ni825 material subjected to Joule heat treatment at 350 °C for 25 s prepared in Example 10 of the present invention and the as-received polycrystalline Ni825 material without Joule heat treatment in Comparative Example 4. The test conditions for the first cycle are 0.1C, the charge-discharge voltage range is 2.7 - 4.3V, and the test temperature is 26 °C. The test conditions for cycling are 1C, the charge-discharge voltage range is 2.7 - 4.3V, and the test temperature is 26 °C.

[0110] Figure 9 -a:

[0111] Abscissa (Specific Capacity, mAh / g): Represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 250 mAh / g.

[0112] Ordinate (Voltage, V): Represents the voltage of the battery, with the unit of V, ranging from 0 to 4.5V.

[0113] Figure 9 -b:

[0114] Abscissa (Cycle Number, cycle times): Represents the number of cycles of the battery, ranging from 0 to 200 cycles.

[0115] Left ordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 200 mAh / g.

[0116] Right vertical coordinate (Coulombic Efficiency, %): Represents the Coulombic efficiency of the battery, ranging from 0% to 100%.

[0117] Compared with Comparative Example 4, after the Joule heat treatment of Example 10 at 350 °C for 25 s, the initial Coulombic efficiency of the battery increased from 87.54% to 92.11%. The capacity retention rate after 200 cycles at 1C increased from 69.18% to 83.82%.

[0118] Test results of Example 11 and Comparative Example 5:

[0119] Figure 10 Shows the initial charge-discharge curve and cycle performance graph of a coin cell assembled with the Ni90 material subjected to Joule heat treatment at 350 °C for 25 s prepared in Example 11 of the present invention and the original polycrystalline Ni90 material without Joule heat treatment of Comparative Example 5. The initial test conditions were 0.1C, the charge-discharge voltage range was 2.7 - 4.3V, and the test temperature was 26 °C. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7 - 4.3V, and the test temperature was 26 °C.

[0120] Figure 10 - In -a:

[0121] Horizontal coordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 275 mAh / g.

[0122] Vertical coordinate (Voltage, V): Represents the voltage of the battery, with the unit of V, ranging from 0 to 4.5V.

[0123] Figure 10 - In -b:

[0124] Horizontal coordinate (Cycle Number, number of cycles): Represents the number of cycles of the battery, ranging from 0 to 80 cycles.

[0125] Left vertical coordinate (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 240 mAh / g.

[0126] Right vertical coordinate (Coulombic Efficiency, %): Represents the Coulombic efficiency of the battery, ranging from 0% to 100%.

[0127] Compared with Comparative Example 5, after the Joule heat treatment of Example 11 at 350 °C for 25 s, the initial Coulombic efficiency of the battery increased from 83.32% to 90.18%. The capacity retention rate after 80 cycles at 1C increased from 85.54% to 89.81%.

[0128] Test results of Example 12 and Comparative Example 6:

[0129] Figure 11 Show the first charge-discharge curve, cycling performance and AC impedance diagram of the coin cells assembled with the LiC O O 2 material prepared in Example 12 of the present invention under 700 °C - 30 s Joule heat treatment and the original LiC O O 2 material without Joule heat treatment in Comparative Example 6. The first cycle test conditions are 0.1C, the charge-discharge voltage range is 3 - 4.65V, and the test temperature is 26 °C. The cycling test conditions are 0.5C, the charge-discharge voltage range is 3 - 4.65V, and the test temperature is 26 °C.

[0130] Figure 11 -a:

[0131] Horizontal axis (Specific Capacity, mAh / g): Represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 250 mAh / g.

[0132] Vertical axis (Voltage, V): Represents the voltage of the battery, with the unit of V, ranging from 0 to 4.8V.

[0133] Figure 11 -b:

[0134] Horizontal axis (Cycle Number): Represents the number of cycles of the battery, ranging from 0 to 200 cycles.

[0135] Left vertical axis (Specific Capacity, mAh / g): Represents the specific capacity of the battery, ranging from 0 to 220 mAh / g.

[0136] Right vertical axis (Coulombic Efficiency, %): Represents the coulombic efficiency of the battery, ranging from 0% to 100%.

[0137] Figure 11 -c:

[0138] Horizontal axis (Z'): Represents the real part of the impedance, ranging from 0 to 200 ohm.

[0139] Vertical axis (Z”): Represents the imaginary part of the impedance, ranging from 0 to 200 ohm.

[0140] Figure 11 -d:

[0141] Horizontal axis (Z'): Represents the real part of the impedance, ranging from 0 to 70 ohm.

[0142] Vertical coordinate (Z"): represents the imaginary part of impedance, ranging from 0 to 70 ohm.

[0143] Compared with Comparative Example 6, after the Joule heat treatment of the battery at 700 °C for 30 s in Example 12, the initial Coulomb efficiency of the battery increased from 83.37% to 94.11%. The capacity retention rate after 200 cycles at 1C increased from 68.89% to 95.11%. The impedance of the battery also decreased significantly.

[0144] Test results of Example 13 and Comparative Example 7:

[0145] Figure 12 Shows the initial charge-discharge curve of a coin cell assembled with the Li-rich material prepared by Joule heat treatment at 400 °C for 25 s in Example 13 of the present invention and the original Li-rich material without Joule heat treatment in Comparative Example 7. The initial test conditions were 0.05C, the charge-discharge voltage range was 2 - 4.8V, and the test temperature was 26 °C.

[0146] Figure 12 In:

[0147] Horizontal coordinate (Specific Capacity, mAh / g): represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 350 mAh / g.

[0148] Vertical coordinate (Voltage, V): represents the voltage of the battery, with the unit of V, ranging from 0 to 5V.

[0149] Compared with Comparative Example 7, after the Joule heat treatment of the battery at 400 °C for 25 s in Example 13, the initial Coulomb efficiency of the battery increased from 72.45% to 90.69%.

[0150] In the attached drawings, the data of the present application are represented by Jxxx °C, and the original data are represented by the material name.

[0151] In summary, the present invention provides a method for preparing a complete thin shell layer that matches and is uniform and complete with the bulk material by controllable lithium-oxygen removal reconstruction and optimization of the surface and interface structure of the layered oxide cathode. The surface structure of the cathode material is made more stable, and the capacity retention rate and the initial Coulomb efficiency have been significantly improved.

[0152] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a cathode material with optimized surface and interface structure, characterized in that: The following steps are involved: (1) Weigh a certain amount of positive electrode material, disperse it evenly, and dry it; (2) The positive electrode material is uniformly loaded into the conductive carrier and treated under certain atmosphere conditions; (3) loading the conductive carrier in step (1) into a conductive carrier heating zone of a Joule heating device, and detecting the temperature in real time using a temperature sensor; (4) Using a vacuum system and a gas mass flow meter to control the atmosphere in the reaction chamber of the Joule heating device; (5) Start the power supply to perform high-temperature pulse Joule heating. During the high-temperature pulse, the working voltage applied is 10 to 80 V, and the working current is 0.5 to 80 A. The temperature is raised to 300 to 2500° C. The single pulse time is 0.001 to 300 s.

2. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: The positive electrode material in step (1) is Li x MO2, M is one or more of Ni, Co, Mn, Al, and Fe.

3. A method for preparing a cathode material with optimized surface and interface structure according to claim 1 or 2, characterized in that: The morphology of the positive electrode material described in step (1) includes, but is not limited to, a polycrystalline structure, a single crystal structure, a core-shell structure, a radial structure, a porous structure, a hollow structure, and a nanostructure.

4. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: The dispersion method described in step (1) is agate mortar hand grinding dispersion, mechanical ball milling dispersion, ultrasonic dispersion, and high-speed stirring dispersion; the drying condition described in step (1) is vacuum drying, the drying temperature is 80-100° C., and the drying time is 10-24 hours.

5. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: The positive electrode material in step (2) may be a powder or a sheet material made by a press.

6. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: The conductive carrier described in step (2) can be a conductive metal, a conductive high polymer, a graphene film, a carbon cloth, a carbon paper or a carbon felt; the atmosphere described in step (2) is a multi-step treatment of one or more gases including but not limited to air, vacuum, oxygen, carbon dioxide, argon and nitrogen.

7. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: The temperature sensor in step (3) should be aligned with the middle of the conductive carrier.

8. The method for preparing a cathode material with optimized surface and interface structure according to claim 1, characterized in that: In the step (5), the working voltage applied during the high temperature pulse is 10 to 80 V, the working current is 0.5 to 80 A; the temperature is raised to 300 to 800° C.; and the single pulse time is 10 to 300 s.

9. The positive electrode material obtained by the preparation method according to any one of claims 1 to 8 has a 100% rock salt phase coating layer formed on its surface, the thickness of the coating layer is 0nm-10nm, and the lithium oxygen loss of the coating layer is about 20%-30%.

10. Use of the positive electrode material obtained according to the preparation method according to any one of claims 1 to 8 or the positive electrode material according to claim 9 in a lithium ion battery.

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