Enabling Rational SEI Design: Advances in Multimodal Analysis of Lithium Inventory Loss in Liquid-Electrolyte-Based Rechargeable Lithium Batteries

Abstract High-energy-density rechargeable lithium batteries are pivotal for next-generation electric vehicles and urban air mobility; however, their long-term stability is compromised by lithium inventory loss. This review systematically deconstructs the two primary pathways of lithium inventory loss in liquid-electrolyte-based rechargeable lithium batteries: the formation of “dead lithium” (dead Li) and electrolyte consumption during solid electrolyte interphase (SEI) formation. First, we differentiate the formation pathways of dead Li in graphite-based lithium-ion batteries (LIBs) versus lithium-metal batteries (LMBs). We then comprehensively introduce methods for their qualitative and quantitative analyses, ranging from electrochemical diagnostics and high-resolution imaging to chemical quantification techniques like nuclear magnetic resonance and titration gas chromatography. Second, we provide an in-depth discussion on the roles of specific SEI components, specifically inorganic species (e.g., LiF and Li2CO3) and organic matrices, while highlighting advanced spectroscopic and microscopic techniques for their characterization. By bridging state-of-the-art analytical technologies with a component-specific understanding of lithium inventory loss, this review offers strategic insights into diagnosing degradation and guiding the rational design of stable interphases in future battery systems.