文摘
In contrast to the stable cycle performance of space confined Se-based cathodes for lithium batteries in carbonate-based electrolytes, their common capacity fading in ether-based electrolytes has been paid less attention and not yet well-addressed so far. In this work, the lithiation/delithiation of amorphous Se<sub>2sub>S<sub>5sub> confined in micro/mesoporous carbon (Se<sub>2sub>S<sub>5sub>/MPC) cathode was investigated by in situ X-ray near edge absorption spectroscopy (XANES) and theoretical calculations. The Se<sub>2sub>S<sub>5sub>/MPC composite was synthesized by a modified vaporization–condensation method to ensure a good encapsulation of Se<sub>2sub>S<sub>5sub> into the pores of MPC host. In situ XANES results illustrated that the lithiation/delithiation reversibility of Se component was gradually decreased in ether-based electrolytes, leading to an aggravated formation of long-chain polyselenides during cycling and further capacity decay. Moreover, ab initio calculations revealed that the binding energy of polyselenides (Li<sub>2sub>Se<sub>nsub>) with carbon host is in an order of Li<sub>2sub>Se<sub>6sub> > Li<sub>2sub>Se<sub>4sub> > Li<sub>2sub>Se. The insights into the failure mechanism of Se-based cathode gain in this work are expected to serve as a guide for future design on high performance Se-based cathodes.