Less is More: Trace Amount of a Cyclic Sulfate Electrolyte Additive Enable Ultra-Stable Graphite Anode for High-Performance Potassium-Ion Batteries

Graphite can be successfully used as an anode for potassium-ion batteries (PIBs), while its conversion to KC₈ leads to huge volume expansion, destruction of solid electrolyte interphase (SEI), and thus poor cycling stability. Incorporating additives into electrolytes is an economical and effective way to construct robust SEI for high-performance PIBs. Herein, we developed a series of sulfur-containing additives for PIB graphite anodes, and the impacts of their molecular structure and contents on the SEI are also systematically investigated. Compared with butylene sulfites and 1,3-propane sultone, the 1,3,2-dioxathiolane 2,2-dioxide (DTD) additive endows the graphite electrode (GE) with a higher reversible capacity, and better cycling stability in both the dilute potassium bis(fluorosulfonyl)imide (KFSI)- and potassium hexafluorophosphate (KPF₆)-based carbonate electrolyte, as a result of a thinner and sulfate-enriched SEI. Moreover, the addition of a trace amount (0.2 wt %) DTD to the electrolyte can effectively protect the GE running over 800 cycles at 1 C. Excessive additives in the electrolyte will induce continuous SEI growth and render a rapid capacity fading of the GE. This strategy using the electrolyte additive paves the way for the design of novel PIB electrolytes and thus provides a great opportunity for commercial PIBs.