The Dr Jekyll and Mr Hyde of lithium hydride in lithium dendrites and solid-electrolyte interphases

Lithium (Li) hydride (LiH) is widely observed in both the solid electrolyte interphase (S-LiH) and Li dendrites (D-LiH) on Li metal anodes (LMAs). Although considerable research has been devoted to LiH, its role in the LMA remains controversial. In this work, we utilize theoretical calculations to disentangle the chemical components in the solid electrolyte interphase (SEI) and dendrites, systematically analyzing the physicochemical properties of each component. Our results exhibit fundamentally opposite roles for S-LiH and D-LiH: S-LiH enhances cycling stability and suppresses dendrite growth due to its electron-blocking capability, robust Li⁺ conductivity across crystal sizes, and its role as an active stabilizer at the Li/LiH interface. Conversely, D-LiH, with its electronic insulation and extreme brittleness, is identified as the primary cause of capacity decay and anode pulverization. Furthermore, by analyzing electrochemical windows, we explore the thermodynamic mechanisms underpinning the formation, transformation, and decomposition of SEI and dendrite components, providing theoretical explanations for experimental anomalies associated with LiH. Building on these insights, we propose strategies to optimize LiH management, harnessing the advantages of S-LiH while mitigating the adverse impacts of D-LiH. Overall, our work offers a deeper understanding of LiH, laying a foundation for advancing Li battery technologies.