原位化学转化法封装硫于分级微-纳炭/碳化钼用于高性能锂硫电池

Encapsulation of sulfur inside micro-nano carbon/molybdenum carbide by in-situ chemical transformation for high-performance Li-S batteries

载体材料作为活性物质硫发生氧化还原反应的反应器,决定了硫正极的电化学性能。因此,通过对载体材料的设计,制备功能性载体材料,可以有效解决锂硫电池的穿梭效应和氧化还原动力学缓慢等问题。采用原位化学转化法将硫封装在空心薄壁C/Mo_(2)C载体的~7 nm空腔中,制备了核壳结构S@C/Mo_(2)C正极材料。纳米级别S@C/Mo_(2)C一次粒子相互连接一起构成微米级二次颗粒,形成了连续的导电网络;纳米级硫核和连续导电网络可以促进锂离子和电子的传输。此外,微孔C/Mo_(2)C壳可以通过物理限域/化学吸附作用减缓多硫化物向外扩散;同时C/Mo_(2)C能有效催化多硫化物的转化,增强氧化还原动力学。基于这些优点,S@C/Mo_(2)C正极材料在0.5 C电流密度时可逆比容量高达1210 mAh g^(-1),且具有较高的倍率性能,3 C时可逆比容量达到780 mAh g^(-1)。此外,该正极材料表现出较好的循环稳定性,300次循环每圈比容量衰减率仅为0.127%。该工作对设计具有高倍率性能和高循环稳定性的硫正极材料具有一定的指导意义。

In lithium-sulfur(Li-S)batteries,the electrochemical properties of the sulfur cathode are determined by the sulfur host,and this controls the shuttle effect and the kinetics,two of the major problems in these batteries.We confined the S in hollow thin-wall C/Mo_(2)C particles smaller than 7 nm across that clustered together to form micrometer-size particles.The conducting network of C/Mo_(2)C shells facilitates lithium-ion and electron transport while acting as a barrier to the outward diffusion of polysulfides.They also improve the redox kinetics because of the catalytic conversion of polysulfides to sulfur.As a result of these features the material achieved a high reversible capacity of 1210 mAh g^(−1) at 0.5 C with a low capacity fade rate of 0.127%per cycle over 300 cycles and a high rate performance(780 mAh g^(−1) at 3.0 C).It is expected that this work will help in the design of sulfur hosts for Li-S batteries with a high rate performance and high cycling stability.