Preparation method and application of positive electrode material surface interface structure optimization

Abstract

The application relates to a preparation method and application of a positive electrode material surface interface structure optimization, and utilizes a transient high-temperature pulse joule heat technology to accurately construct lithium oxygen vacancies on the surface of a layered positive electrode material. The continuous lithium oxygen vacancies promote the transformation of the positive electrode material surface structure from a layered phase to a spinel phase and a rock salt phase, and finally form a thin, uniform and complete complete coating layer on the surface of the positive electrode material. The coating layer formed by the reconstruction and optimization of lithium oxygen loss not only significantly enhances the surface lithium ion conductivity, 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 application can greatly improve the first coulomb efficiency of the positive electrode material, realizes low capacity attenuation and high-stability long cycle performance. In addition, the method is simple in operation, short in preparation time and has the potential for large-scale application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modification and preparation of positive electrode materials of ion batteries, and particularly relates to a preparation method for optimizing the surface and interface structure of positive electrode materials and application thereof. BACKGROUND

[0002] Ion batteries have many advantages such as high energy density, long cycle life, small self-discharge, no memory effect and environmental friendliness, and especially ion batteries have been widely used in consumer electronics such as smart phones, smart bracelets, digital cameras and notebook computers, and have huge consumer demand. As a key power source for new energy vehicles, the performance of lithium ion batteries directly determines important indicators such as driving range, charging speed and service life of electric vehicles. On the basis of having achieved wide application in the field of consumer electronics, 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 extended range electric vehicles. In addition, it also shows good application prospects in large-scale 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 positive electrode material plays a crucial role in improving the overall performance of the battery. Improving energy density, improving cycle stability and ensuring safety are common challenges faced by all types of positive electrode materials. Especially in the deep delithiation state, the surface structure of the positive electrode material is easy to be unstable, part of the lattice oxygen is released in the form of oxygen, and active oxygen participates in the interface side reaction to form an interface layer, resulting in irreversible loss of active material. These phenomena accelerate the capacity decay, reduce the initial coulombic efficiency, increase the irreversible capacity, and directly affect the long-term performance and reliability of the battery, so it has become the focus of researchers.

[0003] In order to overcome these problems, researchers are exploring various modification methods to optimize the performance of positive electrode materials, such as ion doping, surface coating and structure design technologies. Studies have shown that by constructing a protective layer on the surface, the surface structure in the deep delithiation state can be effectively adjusted and improved. The ideal coating material should be able to promote rapid ion migration and have high chemical stability to resist electrolyte corrosion. In addition, good lattice matching between the coating and the substrate is crucial for maintaining the smoothness of lithium ion diffusion and the integrity of the interface, but it is difficult to achieve in actual operation. The coating layer formed by dry / wet chemical method such as metal oxide, metal fluoride, metal phosphide and fast ion conductor can prevent direct contact between the positive electrode material and the electrolyte, thereby alleviating the 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

[0004] The purpose of the present application is to reconstruct and optimize the surface of lithium ion battery layered oxide cathode material based on accurate control of lithium-oxygen removal, to prepare a complete thin shell layer that matches and is completely continuous with the bulk material. It aims to solve the problem that the surface structure of the cathode material is easy to become unstable, leading to accelerated capacity attenuation, reduced first coulomb efficiency and increased irreversible capacity, etc.

[0005] The technical solutions adopted by the present application are as follows:

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

[0007] (1) A certain amount of cathode material is weighed and uniformly dispersed and dried;

[0008] (2) The cathode material is uniformly loaded into the conductive carrier and treated under certain atmosphere conditions;

[0009] (3) The conductive carrier is loaded in the conductive carrier heating zone of the joule heat device, and the temperature sensor is aimed at the middle of the conductive carrier for real-time temperature detection;

[0010] (4) The atmosphere in the reaction chamber of the joule heat device is regulated by a vacuum system and a gas mass flow meter;

[0011] (5) Start the power supply to perform high-temperature pulse joule heat, and the working voltage is 10-80V and the working current is 0.5-80A during high-temperature pulse; the temperature is raised to 300-2500℃; the single pulse time is 0.001-300s.

[0012] Optionally, the cathode material in step (1) is Li x MO2, M is one or more of Ni, Co, Mn, Al, and Fe.

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

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

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

[0016] Optionally, the cathode material in step (1) can be a powder or a sheet-shaped 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 heat device in step (3) includes an internal reaction cavity and an open reaction area in a glove box.

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

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

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

[0022] Optionally, the high-temperature pulse in step (5) is applied with a working voltage of 10-80V and a working current of 0.5-80A, the temperature is raised to 300-800℃, 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 0-10nm, and the lithium-oxygen loss of the coating layer is about 20%-30%.

[0024] A preparation method of a positive electrode material surface interface structure optimization application of the positive electrode material in a lithium ion battery.

[0025] The present application has the following beneficial effects: by using pulse high-temperature Joule heat technology, the surface interface structure of the layered oxide positive electrode is reconstructed and optimized through controllable lithium-oxygen removal, and the lithium-oxygen vacancy is precisely constructed on the surface of the layered positive electrode material mainly by using transient high-temperature pulse Joule heat technology; the continuous lithium-oxygen vacancy promotes 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 and complete coating 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, effectively inhibits the decomposition of the electrolyte and the loss of the lattice oxygen on the surface of the positive electrode material, thereby protecting the integrity of the material. The present application can greatly improve the first coulomb efficiency of the positive electrode material, and realize low capacity attenuation and high stable long cycle performance. In addition, the method is simple to operate and short in preparation time, and has the potential for large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the present application for increasing the amount of delithiation and deoxygenation to induce the transformation of the surface structure from the layered phase to the spinel phase to the rock salt phase;

[0027] Figure 2 is an electron microscope image of the single crystal LiNi 08 Co 01 Mn 01 O2 treated at 350℃ for 25s in the present application;

[0028] Figure 3 is an electron micrograph of LiCoO2 treated at 700°C for 30 s of the present application;

[0029] Figure 4 is a first cycle charge-discharge curve and cycle performance graph of a battery assembled from single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 and the original material treated at 350°C for 25 s of the present application;

[0030] Figure 5 is a first cycle charge-discharge curve and cycle performance graph of a battery assembled from polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 and the original material treated at 350°C for 25 s of the present application;

[0031] Figure 6 is an electron micrograph of polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 treated at 350°C for 25 s of the present application;

[0032] Figure 7 is a cycle performance graph of a battery assembled from polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 and the original material treated at different temperatures for 25 s of the present application;

[0033] Figure 8 is a cycle performance graph of a battery assembled from polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 and the original material treated at 350°C for different times of the present application;

[0034] Figure 9 is a first cycle charge-discharge curve and cycle performance graph of a battery assembled from polycrystalline LiNi 0.825 Co 0.115 Mn 0.06 O2 and the original material treated at 350°C for 25 s of the present application;

[0035] Figure 10 is a first cycle charge-discharge curve and cycle performance graph of a battery assembled from polycrystalline LiNi 0.9 Co 0.05 Mn 0.05 O2 and the original material treated at 350°C for 25 s of the present application;

[0036] Figure 11is the first circle charge-discharge curve and cycle performance and AC impedance comparison chart of the battery assembled by LiCoO2 treated at 700℃ for 30s and the original material in the application;

[0037] Figure 12 is the first circle charge-discharge curve chart of the battery assembled by lithium-rich manganese treated at 400℃ for 25s and the original material in the application. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in a clear and complete manner with reference to the drawings in the embodiments of the present application. The described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0039] With lithium ion batteries as examples, an embodiment of a preparation method for reconstructing and optimizing the surface interfacial structure of a layered oxide positive electrode by controllable lithium-oxygen removal is specifically disclosed with reference to the drawings. However, unnecessary detailed descriptions will be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures will be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by a person of ordinary skill in the art.

[0040] How to realize a complete thin shell layer that matches the bulk material on the surface of the positive electrode material is a key difficulty and technical point of the present application. Through highly controllable treatment by utilizing the Joule heating effect, the layered surface structure can undergo a delithiation and deoxygenation process, thereby forming a new coating phase that has excellent lattice matching with the layered structure oxide.

[0041] The core of this method is that by precisely controlling the current, voltage, and heating time and other parameters, the composition and structure of the surface layer can be effectively adjusted, and a complete thin shell layer that matches the bulk material and is uniform and complete can be constructed. The lithium-oxygen vacancies are precisely constructed on the surface of the layered positive electrode material mainly by using the transient high-temperature pulse Joule heating technology. The continuous lithium-oxygen vacancies promote the transformation of the positive electrode material surface structure from the layered phase to the spinel phase and the rock salt phase, and finally a thin and uniform and complete coating 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, effectively inhibits the decomposition of the electrolyte and the loss of the lattice oxygen on the surface of the positive electrode material, thereby protecting the integrity of the material. The present application can greatly improve the first coulomb efficiency of the positive electrode material, realize low capacity attenuation, and high stable long cycle performance. In addition, the method is simple to operate and short in preparation time, and has the potential for large-scale application.

[0042] Embodiment 1:

[0043] Joule heat treatment:

[0044] (1) A certain amount of single-crystal NCM811 is uniformly dispersed and dried;

[0045] (2) The single-crystal NCM811 is uniformly loaded into the conductive carrier, and treated under certain atmosphere conditions;

[0046] (3) The conductive carrier is loaded into the conductive carrier heating zone of the joule heat device, and the temperature sensor is aimed at the middle of the conductive carrier for real-time temperature detection, and the temperature is 350℃;

[0047] (4) The atmosphere in the reaction chamber of the joule heat device is controlled to be argon by using a vacuum system and a gas mass flow meter;

[0048] (5) Start the power supply to perform high-temperature pulse joule heat, and the time is 25s.

[0049] Example 2: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 350℃, and the duration is 25s.

[0050] Example 3: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 300℃, and the duration is 25s.

[0051] Example 4: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 400℃, and the duration is 25s.

[0052] Example 5: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 500℃, and the duration is 25s.

[0053] Example 6: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 350℃, and the duration is 15s.

[0054] Example 7: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 350℃, and the duration is 60s.

[0055] Example 8: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 350℃, and the duration is 120s.

[0056] Example 9: The same as example 1, except that the positive electrode material is polycrystalline NCM811, the treatment temperature is 350℃, and the duration is 300s.

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

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

[0059] Example 12: Same as Example 1, except that the cathode material is LiCoO2, the treatment temperature is 700°C, and the duration is 30s.

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

[0061] Comparative Example 1: Raw monocrystalline NCM811 without Joule heat treatment.

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

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

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

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

[0066] Comparative Example 6: Raw LiCoO2 without Joule heat treatment.

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

[0068] Test and Results:

[0069] We made cathode sheets from the cathode materials treated in Examples 1-13 and the cathode materials of Comparative Examples 1-7, respectively, and assembled button cells to test them:

[0070] Preparation of Cathode Sheets and Assembly of Batteries:

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

[0072] (2) We put the weighed materials into a stirring box, added two zirconium beads with a diameter D = 3 mm, and placed the stirring box into a Thinky stirrer to stir at a speed of 600 rpm for 30 min;

[0073] (3) We evenly coated the stirred slurry on a carbon-coated aluminum foil with a 50 μm doctor blade.

[0074] (4) Put into oven 120℃ and dry for 12h, and cut into 11mm round pieces by a puncher;

[0075] (5) After weighing, put into a glove box and assemble into CR2032 button cell;

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

[0077] Figure 4 The first cycle charge-discharge curves and cycle performance of button cells assembled using the 350℃-25s joule heat treated monocrystalline NCM811 material of Example 1 and the original monocrystalline NCM811 material of Comparative Example 1 without joule heat treatment are shown. The test conditions are 0.1C, the charge-discharge voltage range is 2.7-4.3V, and the test temperature is 26℃. The cycle test conditions are 1C, the charge-discharge voltage range is 2.7-4.3V, and the test temperature is 26℃.

[0078] Figure 4 -a in:

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

[0080] Vertical axis (Voltage, V): represents the voltage of the battery, with a unit of V, ranging from 0 to 4.5V.

[0081] Figure 4 -b in:

[0082] Horizontal axis (Cycle Number, cycle times): represents the cycle times of the battery, ranging from 0 to 100 cycles.

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

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

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

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

[0087] Figure 5The first cycle charge-discharge curves and cycle performance of the button cells assembled using the 350℃-25s joule heat treated polycrystalline NCM811 material prepared in Example 2 of the present application and the original polycrystalline NCM811 material without joule heat treatment of Comparative Example 2 are shown. The test conditions are 0.1C, the charge-discharge voltage range is 2.7-4.3V, and the test temperature is 26℃. The cycle test conditions are 1C, the charge-discharge voltage range is 2.7-4.3V, and the test temperature is 26℃.

[0088] Figure 5 -a in:

[0089] Horizontal axis (Specific Capacity, mAh / g): represents the specific capacity of the battery, with units of mAh / g, ranging from 0 to 250 mAh / g.

[0090] Vertical axis (Voltage, V): represents the voltage of the battery, with units of V, ranging from 0 to 4.5V.

[0091] Figure 5 -b in:

[0092] Horizontal axis (Cycle Number, cycle number): represents the cycle number of the battery, ranging from 0 to 500 cycles.

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

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

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

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

[0097] Figure 7 The first cycle charge-discharge curves and cycle performance of the button cells assembled using the polycrystalline NCM811 materials prepared in Example 3, 4, 5 and Comparative Example 2, 3 of the present application are shown. The cycle test conditions are 1C, the charge-discharge voltage range is 2.7-4.3V, and the test temperature is 26℃.

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

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

[0100] Right ordinate (Coulombic Efficiency, %): indicates the coulombic efficiency of the battery, ranging from 0% to 100%.

[0101] Compared with Comparative Example 2, the capacity retention rates of Examples 3, 4, and 5 after joule heat treatment at 300°C, 400°C, and 500°C for 25s were increased from the original 80.32% to 88.32%, 92.26%, and 85.41%, respectively, at 1C rate after 200 cycles. Comparative Example 3 after joule heat treatment at 600°C for 25s had a capacity retention rate of 68.08% after 200 cycles at 1C rate, which was lower than that of Comparative Example 2. Therefore, the performance of Examples 3, 4, and 5 was improved, while the performance of Comparative Example 3 was not improved.

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

[0103] Figure 8 The first cycle charge-discharge curves and cycle performance of the polycrystalline NCM811 material prepared using Examples 6, 7, 8, and 9 and Comparative Example 2 and assembled into button cells are shown. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7-4.3V, and the test temperature was 26°C.

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

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

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

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

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

[0109] Figure 9The first cycle charge-discharge curves and cycle performance of button cells assembled using the 350℃-25s joule heat treated Ni825 material prepared in Example 10 of the present application and the original polycrystalline Ni825 material of Comparative Example 4 without joule heat treatment are shown. The first cycle test conditions were 0.1C, the charge-discharge voltage range was 2.7-4.3V, and the test temperature was 26℃. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7-4.3V, and the test temperature was 26℃.

[0110] Figure 9 - in a:

[0111] Horizontal axis (Specific Capacity, mAh / g): represents the specific capacity of the battery, in mAh / g, ranging from 0 to 250 mAh / g.

[0112] Vertical axis (Voltage, V): represents the voltage of the battery, in V, ranging from 0 to 4.5V.

[0113] Figure 9 - in b:

[0114] Horizontal axis (Cycle Number, cycle number): represents the cycle number of the battery, ranging from 0 to 200 cycles.

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

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

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

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

[0119] Figure 10 The first cycle charge-discharge curves and cycle performance of button cells assembled using the 350℃-25s joule heat treated Ni90 material prepared in Example 11 of the present application and the original polycrystalline Ni90 material of Comparative Example 5 without joule heat treatment are shown. The first cycle test conditions were 0.1C, the charge-discharge voltage range was 2.7-4.3V, and the test temperature was 26℃. The cycle test conditions were 1C, the charge-discharge voltage range was 2.7-4.3V, and the test temperature was 26℃.

[0120] Figure 10 -a in:

[0121] Horizontal axis (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 axis (Voltage, V): represents the voltage of the battery, with the unit of V, ranging from 0 to 4.5 V.

[0123] Figure 10 -b in:

[0124] Horizontal axis (Cycle Number, cycle times): represents the cycle times of the battery, ranging from 0 to 80 cycles.

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

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

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

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

[0129] Figure 11 The first cycle charge-discharge curves and cycle performance of the button cells assembled from the LiC O O2 material prepared in Example 12 of the present application and the original LiC O O2 material of Comparative Example 6 without joule heat treatment are shown. The first cycle test conditions were 0.1C, the charge-discharge voltage range was 3-4.65V, and the test temperature was 26°C. The cycle test conditions were 0.5C, the charge-discharge voltage range was 3-4.65V, and the test temperature was 26°C.

[0130] Figure 11 -a in:

[0131] Horizontal axis (Specific Capacity, mAh / g): represents the specific capacity of the battery, with the unit of mAh / g, ranging from 0 to 275 mAh / g.

[0132] Voltage (V): represents the voltage of the battery, in V, ranging from 0 to 4.8 V.

[0133] Figure 11 in -b:

[0134] Cycle Number: represents the cycle number of the battery, ranging from 0 to 200 cycles.

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

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

[0137] Figure 11 in -c:

[0138] Z': represents the real part of the impedance, ranging from 0 to 200 ohm.

[0139] Z": represents the imaginary part of the impedance, ranging from 0 to 200 ohm.

[0140] Figure 11 in -d:

[0141] Z': represents the real part of the impedance, ranging from 0 to 70 ohm.

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

[0143] Compared with Comparative Example 6, the coulombic efficiency of the battery in Example 12 increased from 83.37% to 94.11% after 700℃ joule heat treatment for 30s. The capacity retention rate after 200 cycles at 1C rate 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 The first cycle charge-discharge curve of the coin cell battery assembled using the 400℃-25s joule heat treated Li-rich material prepared in Example 13 of the present application and the original Li-rich material of Comparative Example 7 without joule heat treatment is shown. The first cycle test condition is 0.05C, the charge-discharge voltage range is 2-4.8V, and the test temperature is 26℃.

[0146] Figure 12 in -e:

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

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

[0149] Compared with Comparative Example 7, the first cycle coulombic efficiency of the battery of Example 13 increased from 72.45% to 90.69% after 25 s of joule heat treatment at 400°C.

[0150] In the figures, Jxxx°C represents the data of the present application, and the material name represents the original data.

[0151] In summary, the present application provides a method for preparing a complete thin shell layer that matches and is uniform and complete with the bulk material by reconstructing and optimizing the interfacial structure of the layered oxide positive electrode through controllable lithium-oxygen removal. The surface structure of the positive electrode material is more stable, and the capacity retention rate and the first coulombic efficiency are significantly improved.

[0152] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solutions and concepts of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A preparation method of positive electrode material surface interface structure optimization, characterized in that, The method comprises the following steps: (1) a certain amount of positive electrode material is weighed and uniformly dispersed and dried; (2) the positive electrode material is uniformly loaded into the conductive carrier, and the conductive carrier is treated under a certain atmosphere; (3) the conductive carrier in step (1) is loaded into the conductive carrier heating zone of the joule heat device, and a temperature sensor is used to detect the temperature in real time; (4) the atmosphere in the reaction chamber of the joule heat device is controlled by a vacuum system and a gas mass flow meter; (5) a power supply is started to perform high-temperature pulse joule heat, and a working voltage of 10-80 V and a working current of 0.5-80 A are applied during high-temperature pulse; the temperature is raised to 300-2500 ℃; and the single pulse time is 0.001-300 s. The optimized positive electrode material forms a coated rock salt phase coating layer on the surface, and the coating layer has lithium-oxygen loss.

2. The preparation method of the positive electrode material surface interface structure optimization according to claim 1, characterized in that, The positive electrode material in step (1) is Li x MO2, M being one or several of Ni, Co, Mn, Al, Fe.

3. The preparation method of the positive electrode material surface interface structure optimization according to claim 1 or 2, characterized in that, The morphology of the positive electrode material in step (1) includes but is not limited to polycrystalline structure, single crystal structure, core-shell structure, radial structure, porous structure, hollow structure and nanostructure.

4. The preparation method of the positive electrode material surface interface structure optimization according to claim 1, characterized in that, The dispersion method in step (1) is manual dispersion by agate mortar, mechanical ball milling dispersion, ultrasonic dispersion and high-speed stirring dispersion; and the drying condition in step (1) is vacuum drying, the drying temperature is 80-100 ℃, and the drying time is 10-24 h.

5. The method of claim 1, wherein the method is characterized by: The positive electrode material in step (2) is powder or sheet material made by a pressure machine.

6. The method of claim 1, wherein the method is characterized by: The conductive carrier in step (2) is a conductive metal, a conductive polymer, a graphene film, a carbon cloth, a carbon paper or a carbon felt; and the atmosphere in step (2) is a multi-step treatment including but not limited to one or more gases selected from the group consisting of air, vacuum, oxygen, carbon dioxide, argon and nitrogen.

7. The method of claim 1, wherein the method further comprises: The temperature sensor in step (3) is aligned with the middle of the conductive carrier.

8. The preparation method of the positive electrode material surface interface structure optimization according to claim 1, characterized in that, In step (5), the working voltage applied during high-temperature pulse is 10-80 V, the working current is 0.5-80 A, the temperature is raised to 300-800 ℃, and the single pulse time is 10-300 s.

9. The positive electrode material obtained by the preparation method according to any one of claims 1-8, wherein 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 greater than 0 nm and less than or equal to 10 nm, and the lithium-oxygen loss of the coating layer is 20%-30%.

10. The positive electrode material obtained by the preparation method according to any one of claims 1-8 or the positive electrode material of claim 9, wherein the positive electrode material is applied in a lithium ion battery.

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