Interface Modulation of Metal Sulfide Anodes for Long-Cycle-Life Sodium-Ion Batteries

Although studies of transition metal sulfides (TMS) as anode materials for sodium-ion batteries are extensively reported, the short cycle life is still a thorny problem that impedes their practical application. In this work, a new capacity fading mechanism of the TMS electrodes is demonstrated; that is, the parasitic reaction between electrolyte anions (i.e., ClO4-) and metal sulfides yields non-conductive and unstable solid-electrolyte interphase (SEI) and meanwhile, corrosively turns metal sulfides into less-active oxides. This knowledge guides the development of an electrochemical strategy to manipulate the anion decomposition and construct a stable interface that prevents extensive parasitic reactions. It is shown that introducing sodium nitrate to the electrolyte radically changes the Na+ solvation structure by populating nitrate ions in the first solvation sheath, generating a stable and conductive SEI layer containing both Na3N and NaF. The optimized interface enables an iron sulfide anode to stably cycle for over 2000 cycles with negligible capacity loss, and a similar enhancement in cycle performance is demonstrated on a number of other metal sulfides. This work discloses metal sulfides' cycling failure mechanism from a unique perspective and highlights the critical importance of manipulating the interface chemistry in sodium-ion batteries.

Automated summary

Although transition metal sulfides (TMS) have been extensively studied as anode materials for sodium-ion batteries, their short cycle life remains a challenge. This study demonstrates a new capacity fading mechanism of TMS electrodes, attributing it to the parasitic reaction between electrolyte anions and metal sulfides. By manipulating the anion decomposition and constructing a stable interface, the researchers achieve significant improvement in cycle performance of various metal sulfides. This work provides a unique perspective on the cycling failure mechanism of metal sulfides and emphasizes the critical importance of interface chemistry in sodium-ion batteries.