Interfaces and interphases in batteries

Lithium-ion battery (LIB) is the most popular electrochemical device ever invented in the history of mankind. It is also the first-ever battery that operates on dual-intercalation chemistries, and the very first battery that relies on interphases on both electrodes to ensure reversibility of the cell chemistries. Although it was the commercial success of LIBs that highlighted the importance of interphases, its occurrence far predated the birth of LIBs, and its existence goes far beyond the scope of lithium-based battery chemistries. This perspective intends to shed light on the evolution of our knowledge about interfaces and interphases in batteries. As two intimately intertwined components in electrochemical devices, interface has been thoroughly described in classical electrochemistry, while interphase still presents many unanswered questions to us. The efforts of understanding and eventually tailor-designing the latter will hold the key to enable the next generation battery chemistries.