MIL-91(Al) to Boost Solid-Solid Conversion Reactions in Li-Se Batteries

Abstract

Lithium-Selenium (Li-Se) batteries have emerged as one of the most promising candidates for next-generation energy storage systems owing to superior electronic conductivity, impressive volumetric capacity, and enhanced compatibility with carbonate electrolyte of selenium, comparable to sulfur. Despite these advantages, the development of Li-Se batteries is impeded by several intrinsic challenges, including volume expansion during the discharge process and the consequent sluggish reaction kinetics that undermine their electrochemical performance. In this study, MIL-91(Al) is used as an electrode additive to accelerate the one-step mutual solid-solid conversion reaction between Se and Li2Se in the carbonate-based electrolyte. By doing so, uncontrollable deposition of Li2Se is effectively mitigated, enhancing the electrochemical performance of the system. Thus, the use of MIL-91(Al) results in reduced internal resistance and faster Li-ion transfer rate, as analyzed by SPEIS and GITT. Ab initio calculations and molecular dynamics simulations further reveal that Li2Se anchors to closely situated dangling oxygens of the phosphonate group of the organic linker of MIL-91(Al), inducing relaxation of the Li-Se-Li angle and stabilizing the overall structure. Accordingly, the MIL-91(Al)-containing Li-Se cells demonstrate a high specific capacity of approximately 530 mAh g-1 at 1C (675 mA g-1) after 100 cycles and retaining a specific capacity of 320 mAh/g even under high current rate (20C) after 200 cycles. This research underlines the importance of the use of electrocatalyst/electroadsorbent materials to enhance the redox kinetics of the conversion reactions between Se and Li2Se, thus paving the way for the development of high-performance Li-Se batteries.