Electrolyte design for robust gradient solid-electrolyte interfaces to enable high-performance silicon anodes for pouch batteries

Abstract

Silicon (Si) anodes has emerged as an ideal anode for the next generation of lithium-ion batteries owing to its high specific capacity. Nevertheless, Si particles undergo large volume expansion during cycling, inducing the continuous fragmentation/re-formation of the solid-electrolyte interphase (SEI) layer, which leads to rapid capacity decay and low Coulombic efficiency in EC-based carbonate electrolytes. Herein, a weakly solvating electrolyte with boric acid tris(hexafluoroisopropyl) ester (BTHE), 2,2,2-trifluoroethyl methyl carbonate (FDEC), and fluoroethylene carbonate (FEC) is developed to build a stable SEI. BTHE is introduced as a functional additive, which is induce anion and fluorinated solvent to form a gradient rigid–soft coupling SEI layer. In contrast to other anion-derived interfaces, weakly solvating electrolyte has been proven to construct a highly robust and stable –CF3-rich-organic outer layer and LiF-rich inner layer SEI on the Si anodes, resulting in approximately 99.9 % ultra-high Coulombic efficiency and ultra-high areal capacity (∼8.1 mAh cm−2). Beyond proof of concept, a 2.68 Ah Si||LiNi0.8Mn0.1Co0.1O2 pouch cell has an impressive 84.3 % capacity retention after 1000 cycles and could work normally at temperatures ranging from −30 °C to 100 °C based on this electrolyte, representing a pioneering report in pouch cells incorporating Si anodes.