Altering Dendrite Growth Suppression in LiBH ₄ ‐Based Electrolyte for All‐Solid‐State Lithium‐Ion Batteries

ABSTRACT Lithium dendrite growth in solid‐state electrolytes remains a critical challenge for the commercialization of all‐solid‐state Li‐ion batteries. Here, we show that the introduction of controlled amounts of vapor‐grown carbon fibers (VGCFs) into a LiBH 4 ‐based electrolyte can markedly increase the critical current density (CCD) and prolong cycle life, despite the increase of the electronic conductivity. Owing to the lithiation activity and lower surface potential of VGCFs than the LiBH 4 ‐based matrix, lithiation preferentially occurs on VGCFs, and Li dendrites subsequently grow along the lithiated fibers during cycling, rather than as metallic Li deposition and dendrite growth within the LiBH 4 ‐based matrix, which significantly reduces the stress in the electrolyte induced by Li plating. Furthermore, the incorporation of VGCFs highly reinforces the electrolyte. Both effects suppress crack initiation, and no cracks appear even upon electrolyte failure, in sharp contrast to common failure modes generally accompanied by crack formation during dendrite generation. The retarded crack formation and preferential dendrite growth along VGCFs result in a superior CCD of 15.2 mA cm − 2 and prolonged cycling for 2486 h at 0.64 mA cm − 2 . This work reveals that lithiation chemistry, mechanical reinforcement, and electronic activity cooperatively regulate dendrite growth, offering a new strategy for solid‐state electrolyte engineering.