Stepwise Intercalation-Conversion-Intercalation Sodiation Mechanism in CuInS₂Prompting Sodium Storage Performance

The low charge storage in intercalation-type reaction and the large volume change induced by conversion/alloying reactions greatly limit the practical selection of anodes in sodium-ion batteries (SIBs). Herein, CuInS2 as SIBs anode with an unusual stepwise intercalation-conversion-intercalation reaction mechanism is developed. This mechanism effectively arouses the synergies between conversion and intercalation reactions, thus alleviating the shortcomings of conventional anode materials with either low capacity or severe performance decay. Especially, unlike most of the bimetallic sulfides that usually undergo conversion/alloying dominant reactions, the indium species in CuInS2 control a reversible Na+ intercalation-extraction reaction, which can excite a stepwise and complementary reaction to stabilize performance. As a result, the CuInS2 displays better electrochemical performances as compared with the conversion-type Cu2S. This work is a milestone in the development of high-performance anodes with an appropriate working mechanism and provides significant insights for exploring appropriate anodes in alkali-ion batteries.