Achieving stable K-storage performance of carbon sphere-confined Sb via electrolyte regulation

Abstract

Potassium-ion batteries (PIBs) have been considered as one of the most promising alternatives to lithium-ion batteries (LIBs) in view of their competitive energy density with significantly reduced product cost. Moreover, alloy-type materials are expected as a high-performance anode of PIBs thanks to their intrinsic chemical stability as well as high theoretical specific capacity. Unfortunately, the serious incompatibility between alloy-type active materials and electrolytes, especially for the formation of unstable solid-electrolyte interfacial (SEI) films, often leads to insufficient cycle life. Herein, the formation mechanism of SEI films in the K-storage systems based on carbon sphere confined Sb anode (Sb@CS) were investigated in commercially available electrolytes. Physical characterizations and theoretical calculation revealed that the solvents in the dilute electrolyte of 0.8 M KPF6/EC + DEC were excessively decomposed on the interface to generate unstable SEI and thus result in inferior K-storage stability. On the contrary, a salt-concentrated electrolyte (3 M KFSI/DME) can generate inorganic-dominated stable SEI due to the preferential decomposition of anions. As a result, the prepared Sb@CS in the matched 3 M KFSI/DME electrolyte delivered a high reversible capacity of 467.8 mA h g−1 after 100 cycles at 100 mA g−1, with a slow capacity decay of 0.19% per cycle from the 10th to the 100th cycle. These findings are of great significance for revealing the interfacial reaction between electrodes and electrolytes as well as improving the stability of Sb-based anode materials for PIBs.