Lithium batteries are widely and profoundly applied in different fields (i.e., portable electronic devices and electric vehicles) due to their high energy density and environmental friendliness. However, high-capacity electrode materials become a key to the development of the next generation of high-energy lithium batteries with the increasing demand for extended driving ranges in new energy electric vehicles. The chemical environment in these next-generation high-energy lithium batteries is complex, with intensified electrode/electrolyte interfacial reactions. Among these challenges, some issues such as the volume expansion of high-capacity anode materials and severe side reactions at the interface have a significant negative impact on the cycle life and safety of the battery. Recent studies reveal the presence of significant amounts of lithium hydride (LiH) in the anode of lithium batteries after cycling. However, there is a considerable debate regarding the existence of LiH and its underlying mechanisms. The formation and evolution of LiH, as well as its role in inducing anode failure, remain major research gaps. This review summarizes the fundamental physicochemical properties of LiH based on the existing literature and systematically represents the research work on lithium hydride in non-lithium metal anodes, lithium metal anodes, and non-lithium battery anodes. Furthermore, this review discusses the mechanisms by which LiH induces anode failure and protection, to provide a targeted guidance for the optimization and improvement of high-capacity anode materials, interfaces, and electrolytes, thus facilitating the commercialization of the next generation of high-energy lithium batteries.This review firstly introduced the fundamental physicochemical properties of LiH. As a hydride of metallic lithium, LiH is the lightest ionic compound in nature and exhibits strong alkalinity. Furthermore, this review summarizes the conventional synthesis methods for LiH and the conventional chemical reactions in which it can participate. These related chemical reactions can provide valuable insights and considerations for research on LiH in battery anodes.From the ongoing advancement in the understanding of the interfacial chemistry of battery anodes and advanced characterization techniques, the presence of LiH is confirmed in both non-lithium metal anodes (i.e., graphite, germanium, and silicon) and lithium metal anodes, which serves as a new component of the anode solid electrolyte interphase (SEI) film. However, the existing research mainly focuses on confirming the existence of LiH, while the distribution of LiH in the anode surface/interface or bulk phase, its formation and evolution mechanisms, and its effects on different anode materials remain unclear. In addition to the presence of LiH in lithium battery anodes, related hydrides (such as sodium hydride (NaH), magnesium hydride (MgH₂), etc.) are also identified in non-lithium battery anodes. The formation and decomposition of these hydrides can have significant effects on the performance of the anode materials and even the overall battery performance.Summary and prospectsHigh-capacity anode materials are a preferred option for the development of the next generation of high-energy lithium batteries. However, some issues such as the volume expansion of high-capacity anode materials and severe side reactions at the interface significantly hinder their further development. The discovery of LiH on the anode provides a perspective for investigating the problems related to anode materials and interfacial failure. However, there remains considerable controversy due to the limited scope of the existing research. Firstly, most studies on the physicochemical properties of LiH focus on bulk particles (bulk-LiH), whereas what is generated at the battery anode interface is predominantly in the form of nanoparticles (nano-LiH). It is thus crucial to fully understand the nanoparticle effects of nano-LiH. Also, there is a need for in-depth studies on the formation and decomposition mechanisms of LiH on different anode materials, as well as the various effects and mechanisms by which LiH interacts with these materials. It is important to investigate the reactivity of the nano-sized lithium hydride formed at the anode with various components of the battery, as well as its correlation with battery failure phenomena. A clarification is needed to determine whether LiH accelerates battery failure or failure issues trigger the formation of LiH. Research on these issues can deepen the understanding of LiH and provide valuable insights for the study of hydrides in other battery anodes. Furthermore, the research will offer some targeted strategies for optimizing and improving high-capacity anode materials, interfaces, and electrolytes.