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 Li_0.33La_0.56TiO₃solid electrolyte was found capable of forming atomically intimate contact with both the spinel Li₄Ti₅O₁₂and rock-salt Li₇Ti₅O₁₂. In contrast to conventional expectations, such epitaxial interfaces can also survive repeated spinel-to-rock-salt phase transitions. Consequently, the Li₄Ti₅O₁₂-Li_0.33La_0.56TiO₃composite 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.