Insight into the Capacity Fading Mechanism of Amorphous Se₂S₅ Confined in Micro/Mesoporous Carbon Matrix in Ether-Based Electrolytes

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 Se₂S₅ confined in micro/mesoporous carbon (Se₂S₅/MPC) cathode was investigated by in situ X-ray near edge absorption spectroscopy (XANES) and theoretical calculations. The Se₂S₅/MPC composite was synthesized by a modified vaporization-condensation method to ensure a good encapsulation of Se₂S₅ 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 (Li₂Se_n) with carbon host is in an order of Li₂Se₆ > Li₂Se₄ > Li₂Se. 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.