Post Li-ion batteries: back to the future?

Abstract While Lithium-ion batteries dominate the current market, their widespread large-scale application can be limited by concerns regarding sustainability, cost and supply risk. This perspective evaluates emerging post-Li-ion chemistries, categorized by electrolyte type: aqueous, organic liquid, and solid-state, defining the concepts and describing the state-of-the art, with special emphasis in near-term manufacturable options. Aqueous electrolytes offer inherent non-flammability and high ionic conductivity but are fundamentally limited by the narrow thermodynamic stability window of water. Research in this area focuses on zinc-metal anodes, which face challenges related to dendritic growth and corrosion, and aqueous M-ion (Li ⁺ , Na ⁺ ) systems, which suffer from electrode active material degradation and limited operation voltages. Organic liquid electrolytes enable wider electrochemical windows. Sodium-ion batteries (SIBs) have emerged as credible ‘drop-in’ alternative, and though differences in Na ⁺ solvation and (solid electrolyte interphase) stability remain critical factors, market-ready cells are being developed and progressively entering early commercial applications. Potassium-ion batteries (KIBs) offer potential but are still in a very early stage of development. Technologies utilizing multivalent charge carriers (Mg ²⁺ , Ca ²⁺ , Al ³⁺ ) using metal anodes hold promise of high energy densities, yet practical developments are also limited. Room-temperature Solid-state batteries could bring in safety and energy density, but bottlenecks remain related to the chemical and mechanical instability of solid–solid interfaces. Overall, post-Li-ion battery research is characterized by a broad and dynamic landscape of technologies with very different maturity levels. Ongoing advances are progressively defining realistic application spaces while also revealing new roadblocks in the development. Rather than converging on a single successor, future energy storage is likely to rely on a diversified portfolio of complementary technologies tailored to specific applications whose viability will ultimately depend on a number of factors. A comparative technology assessment with minimum validation criteria and a critical roadmap that distinguishes near-term complementary technologies from conditional, niche and exploratory concepts is provided.