China's lithium sulfide battery materials research progress or promote electric vehicle progress

Recently, the Zhang Yuegang research group of the Suzhou Institute of Nanotechnology and Nano-Bionics of the Chinese Academy of Sciences independently developed an in-situ scanning/transmission electron microscopy electrochemical chip to realize real-time observation of the charging process of lithium sulfide (Li2S) electrode; fully understand Li2S charging Based on the discharge mechanism, a high-nitrogen-doped graphene-loaded lithium sulfide material was designed as the positive electrode of the battery, and the charge capacity and voltage were controlled significantly.

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The capacity utilization and cycle life of Li2S are published in Advanced Energy Materials.

With the development of society and science and technology, human demand for electrochemical energy storage technology is increasing. The new 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 development of high-capacity lithium-sulfur battery cathode materials is crucial to the development of new energy electric vehicles and portable electronic equipment.

The theoretical capacity of lithium sulfide (Li2S) material is 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 provides the subsequent lithium-discharge reaction. The space protects the electrode structure from damage; it can be assembled with a non-lithium metal anode material (such as silicon, tin, etc.) to effectively avoid the safety hazard caused by problems such as lithium dendrite formation, and is a lithium with great development potential. Sulphur battery cathode material. However, the material has low electron/ion conductivity, and the dissolution of the reaction intermediate polysulfide in the electrolyte causes a shuttle effect and the like, which limits its practical application in lithium-sulfur batteries.

In order to improve the capacity utilization and cycle life of lithium-sulfur batteries, researchers usually fill sulfur into porous materials with high specific surface area and high conductivity (such as carbon nanotubes, porous carbon, graphene and carbon fiber). In the previous research work, Zhang Yuegang's research group found that the introduction of nitrogen-doped functional groups on graphene oxide can not only effectively reduce the dissolution of polysulfides in the electrolyte, but also optimize the distribution of polysulfides in the deposition process (Nano Letters, 2014). , 14, 4821−4827). In order to better improve the capacity utilization and cycle life of Li2S, the team used the in-situ characterization technique to study the Li2S dissolution and redeposition mechanism, and then proposed to regulate the initial activated battery voltage to 3.8 V, and then pass the control voltage (1.7~2.4). V) and charge capacity can effectively prevent the formation of long-chain soluble polysulfide, which allows the electrode to retain a part of the insoluble Li2S as a seed during the charging process, so that the Li2S material can be effectively activated and uniformly redeposited. . In addition, this study effectively increases the wrinkle rate and bending rate of graphene by coating glucose on the surface of graphene oxide before nitriding treatment, thereby providing more support sites for polysulfides; using ammonia in the reaction process. The high-temperature ammonia gas heat treatment method increases the nitrogen doping amount to 12.2%; the high-nitrogen-doped graphene material not only has high conductivity, but also the surface nitrogen functional group can effectively reduce the dissolution of polysulfide and optimize the uniform distribution of Li2S. . The lithium-sulfur battery prepared by using the high-nitrogen-doped graphene-Li2S composite cathode material can maintain a capacity of 318 mA h g-1 after 2000 cycles (1C) (calculated as 457 mA h g- by weight of sulfur element). 1), 3,000 mA h g-1 (360 mA h g-1 by weight of sulfur element) after 3000 cycles (2C) is the longest cycle life reported so far.

For the first time, the research work realized the real-time observation of the charging process of lithium sulfide electrode by using the newly developed in-situ SEM and in-situ TEM chip technology.

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Based on the Li2S charge-discharge mechanism, a new voltage-capacity regulation mechanism was developed, and a new type of high-nitrogen-doped lithium sulfide electrode material was designed, which opened up a broad application for high-energy Li2S-C/Li battery. Application prospects.

The research work has received strong support from the National Natural Science Foundation of China and the Talents Project of the Chinese Academy of Sciences.

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SEM image of in-situ observation of activation process of Li2S material supported on single-layer graphene electrode surface in LiTFSI-DOL/DME electrolyte

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