Investigating the Origin of the Enhanced Sodium Storage Capacity of Transition Metal Sulfide Anodes in Ether‐Based Electrolytes
Xucai Yin, Yang Ren, Shu Guo, Baoyu Sun, Libin Wu, Chunyu Du, Jiajun Wang, Gepin Yin, Hua Huo
Abstract
Abstract Although ether‐based electrolytes have gradually been identified as a vital factor to achieving the excellent electrochemical performance observed in transition metal sulfide (TMS) anodes in sodium‐ion batteries (SIBs), there is still a lack of a fundamental understanding about the origin of the positive effect of ether‐based electrolytes on TMS anodes. Herein, a microspherical CoS 2 anode has been taken as a representative of TMS. It has been demonstrated that the sodiation process involves not only a traditional conversion reaction taking place between solid‐state CoS 2 and Na 2 S, but also a solid–liquid phase conversion process between active materials and soluble sodium polysulfide (Na 2 S n , 2 < n < 8). More importantly, it is first revealed that the long‐term stability and the reversibility of CoS 2 anode are mainly due to the solid–liquid conversion behavior, which makes bulk CoS 2 gradually develop into a stable porous structure with fast Na + transport kinetics and small stress/strain during cycling. Consequently, the CoS 2 electrode delivers remarkable long‐cycle life with an ultrahigh capacity retention rate of 94.8% even after 1500 cycles at 2 A g −1 (only 2.13 mAh g −1 fading per 100 cycles) and high volumetric capacity of 949 mAh cm −3 at a high active material loading of 3.3 mg cm −2 .