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Preparation of lithium sulfide based on lithium thermal reaction

wallpapers Tech 2021-04-28
Currently, lithium-ion batteries based on topological embedding reactions dominate the market for portable electronics and electric vehicles. However, the energy density of lithium-ion batteries is approaching its limit. In order to pursue higher energy density, researchers begin to focus on battery systems based on conversion reactions. At present, the lithium sulfide cathode and Si cathode pair battery system is considered to be one of the most promising battery systems.
 
Significant achievements have been made in Si cathode, while the development of lithium sulfide cathode materials is relatively lagging behind. This is mainly due to the synthesis of lithium sulfide cathode materials difficult, high melting point, in the air is not stable. Moreover, the activation potential of lithium sulfide cathode material is high, the rate performance is poor, the capacity attenuation is faster. Specifically, the potential in excess of 3.6 V of the lithium sulfide cathode material results in the decomposition of the ether-based electrolyte, resulting in a decrease in capacity. When the upper cutoff voltage is set to 3.6V, less than half of the theoretical capacity can be achieved. Secondly, the insulation properties of lithium sulfide lead to excessive over-potential and low energy efficiency, especially at high current density. Third, similar to the S 8 cathode, the lithium sulfide cathode also has polysulfide (PS) dissolution and produces a shuttle effect. Therefore, new research ideas are needed to prepare high-performance lithium sulfide cathode materials.
 
Li powder reacts with various metal sulfide precursors, Ni, Fe, Cu agglomerate in Li2S/Ni, Li2S/Fe, Li2S/Cu and form extremely ductile metal blocks.TMS is uniformly distributed in Li2S/Co, Li2S/Mn, Li2S/Zn, Li2S/Mo, Li2S/W, Li2S/Ti Li2S matrix. Despite their similar structures, the electrochemical behavior of the two nanocomposites is different. Compared with the original Li2s, the activation potential of Li2s /W, Li2s /Mo and Li2s /Ti decreased significantly due to the formation of the TM-S bond. Compared with pure Li2S, the rate performance and cycle performance of Li2S are also improved significantly.
 
This is mainly due to the enhancement of electron/ion conductivity between TMS and PS, as well as the strong chemisorption. Different from Li2S/W, Li2S/Mo and Li2S/Ti, the introduction of Co, Mn and Zn into the Li2S matrix makes the reversible electrochemical path of Li2S irreversible. That is, Li2s oxidizes only to polysulfides, but not to elemental S, and corresponding metallic sulfides are found in the final product. Therefore, Li2S/Co, Li2S/Mn and Li2S/Zn can be used as pre-lithified rather than active electrode materials. These findings are of guiding significance for the preparation of new Li2S-based cathode materials.

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