Atomically Intimate Solid Electrolyte/Electrode Contact Capable of Surviving Long-Term Cycling with Repeated Phase Transitions.

The electrode-electrolyte contact issue within the composite electrode layer is a grand challenge for all-solid-state Li batteries. In order to achieve cycling performances comparable to Li-ion batteries based on liquid electrolyte, the aforementioned solid-solid contact not only needs to be sufficiently thorough but also must tolerate repeated cycling. Simultaneously meeting both requirements is rather challenging. Here, we discover that epitaxy may effectively overcome such bottlenecks even when the electrode undergoes repeated phase transitions during cycling. Through epitaxial growth, the perovskite LiLaTiO solid electrolyte was found capable of forming atomically intimate contact with both the spinel LiTiO and rock-salt LiTiO. In contrast to conventional expectations, such epitaxial interfaces can also survive repeated spinel-to-rock-salt phase transitions. Consequently, the LiTiO-LiLaTiO composite electrode based on epitaxial solid-solid contact delivers not only a rate capability comparable to that of the surry-cast one with solid-liquid contact but also an excellent long-term cycling stability.