Electrolyte Engineering for Phosphorus‐Based Anodes in Secondary Ion Batteries: From Liquid Solvation to Solid‐State Interface

Phosphorus anodes offer an ultrahigh theoretical capacity of 2596 mA·h·g⁻¹ for both Li-and Na-ion batteries but suffer from severe volume expansion, unstable interfaces, and intermediate dissolution, which have hindered their practical adoption. Moving beyond conventional electrode material modifications, this review systematically articulates a paradigm shift toward electrolyte engineering as a decisive strategy to address these challenges. We comprehensively analyze the design principles of liquid electrolytes-including weakly solvating electrolytes, localized high-concentration systems, and multi-anion coordination-that enable the construction of robust, anion-derived solid electrolyte interphases (SEI) to suppress polyphosphide shuttling and enhance ion transport. Crucially, we highlight the transition to all-solid-state batteries as a deterministic route to simultaneously overcome interfacial instability and safety concerns, leveraging the mechanical integrity of solid electrolytes to physically constrain volume change. By synergizing electrolyte design with electrode architecture, this review provides a forward-looking framework for developing practical high-energy-density phosphorus-based batteries, accelerating their evolution from laboratory prototypes to commercially viable energy storage systems.