With the development of society and science and technology, mankind's demand for electrochemical energy storage technology is increasing. The emerging energy storage system, lithium-sulfur battery, has the advantages of high theoretical capacity, low cost, and environmental friendliness, and has attracted the attention of researchers at home and abroad. . The research and development of high-capacity cathode materials for lithium-sulfur batteries is crucial for the development of new energy vehicles and portable electronic devices. Lithium sulfide (Li2S) material has a theoretical capacity of up to 1166 mA h g-1, which is several times that of other transition metal oxides and phosphates; the volume shrinkage that occurs during the first delithiation charging process can provide a subsequent lithium intercalation reaction The space protects the electrode structure from damage; it can be assembled with non-lithium metal anode materials (such as silicon, tin, etc.) to effectively avoid potential safety hazards caused by lithium dendrite formation and is a potential lithium Sulfur battery cathode material. However, the low electron/ion conductivity of the material, the dissolution of the polysulfide in the reaction solution in the reaction solution initiate the shuttle effect and other issues, which limits its practical application in lithium-sulfur batteries. Recently, the research group Zhang Yuegang of the Suzhou Institute of Nanotechnology and Nano-Bionics, Chinese Academy of Sciences independently researched and developed an in-situ scanning/transmission electron microscopy electrochemical chip to achieve real-time observation of the charging process of lithium sulfide electrodes. The mechanism of charge and discharge of Li2S is fully understood. Based on the design of high-nitrogen-doped graphene-loaded lithium sulfide materials as the battery cathode, and through the control of charge capacity and voltage, significantly improve the Li2S capacity utilization and cycle life, related results were published in the Advanced Energy Materials magazine. To increase the capacity utilization and cycle life of lithium-sulfur batteries, researchers generally fill sulfur into porous materials with high specific surface area and high electrical conductivity (such as carbon nanotubes, porous carbon, graphene, and carbon fibers). Zhang Yuegang's research group found in the previous research work that the introduction of nitrogen-doped functional groups on graphene oxide can not only effectively reduce the dissolution of polysulfide in the electrolyte, but also optimize the distribution of polysulfide in the deposition process (Nano Letters, 2014 , 14, 4821−4827). To better improve capacity utilization and cycle life of Li2S, the team used in-situ characterization techniques to study the mechanism of Li2S dissolution and redeposition, and then proposed to regulate the initial activated cell voltage to 3.8V and then control voltage (1.7~2.4). V) and charge capacity can effectively prevent the formation of long-chain soluble polysulfide, the charge-discharge regulation method allows the electrode to retain a part of the insoluble Li2S as a seed during charging, so that the Li2S material can be effectively activated and uniformly redeposited. . In addition, this study covers the surface of graphene oxide coated with glucose before nitriding, effectively increasing the wrinkle and bending rate of graphene, thereby providing more loading sites for polysulfide; using ammonia during the reaction process. The method of heat treatment with high-temperature ammonia gas makes the nitrogen doping amount increase to 12.2%. The highly nitrogen-doped graphene material not only has high conductivity, but also has a surface nitrogen functional group that can effectively reduce the polysulfide dissolution and optimize the uniform distribution of Li2S. . The lithium-sulfur battery prepared by using the high-nitrogen-doped graphene-Li2S composite positive electrode material can still maintain a capacity of 318 mA h g-1 after being circulated for 2000 cycles (1C) (converted to 457 mA h g-by weight of sulfur element). 1) It can maintain 256 mA h g-1 after 3,000 cycles (2C) cycle (converted to 368 mA h g-1 by sulfur element weight), which is the longest cycle life reported so far. The research work for the first time using the newly developed in-situ scanning electron microscope and in-situ TEM chip technology to realize the real-time observation of the lithium sulfide electrode charging process, and based on the study of Li2S charge and discharge mechanism, the development of a new voltage - capacity control Mechanism, a new type of high-nitrogen doped electrode material loaded with lithium sulfide is designed, which opens up a broad application prospect for the application of high-energy Li2S-C/Li batteries. The research work has received strong support from the National Natural Science Foundation of China and the 1,000-member project of the Chinese Academy of Sciences.
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