An Ultra‐Stable Electrode‐Solid Electrolyte Composite for High‐Performance All‐Solid‐State Li‐Ion Batteries

Abstract The low ionic and electronic conductivity between current solid electrolytes and high‐capacity anodes limits the long‐term cycling performance of all‐solid‐state lithium‐ion batteries (ASSLIBs). Herein, this work reports the fabrication of an ultra‐stable electrode‐solid electrolyte composite for high‐performance ASSLIBs enabled by the homogeneous coverage of ultrathin Mg(BH 4 ) 2 layers on the surface of each MgH 2 nanoparticle that are uniformly distributed on graphene. The initial discharge process of Mg(BH 4 ) 2 layers results in uniform coverage of MgH 2 nanoparticle with both LiBH 4 as the solid electrolyte and Li 2 B 6 with even higher Li ion conductivity than LiBH 4 . Consequently, the Li ion conductivity of graphene‐supported MgH 2 nanoparticles covered with ultrathin Mg(BH 4 ) 2 layers is two orders of magnitude higher than that without Mg(BH 4 ) 2 layers. Moreover, the thus‐formed inactive Li 2 B 6 with strong adsorption capability toward LiBH 4 , acts as a stabilizing framework, which, coupled with the structural support role of graphene, alleviates the volume change of MgH 2 nanoparticles and facilitates the intimate contact between LiBH 4 and individual MgH 2 nanoparticles, leading to the formation of uniform stable interfaces with high ionic and electronic conductivity on each MgH 2 nanoparticles. Hence, an ultrahigh specific capacity of 800 mAh g −1 is achieved for MgH 2 at 2 A g −1 after 350 cycles.