Comparative safety analysis of current and next-generation battery technologies

The global transition to sustainable energy systems demands high-performance batteries, yet the inherent safety limitations of lithium-ion batteries (LIBs)—particularly thermal runaway driven by flammable liquid electrolytes—pose critical barriers to widespread adoption in safety-critical applications. This review conducts a comprehensive, evidence-based comparative safety assessment of three pivotal battery technologies: incumbent LIBs, emerging sodium-ion batteries (SIBs), and solid-state batteries (SSBs). We establish a detailed safety baseline for LIBs, examining failure mechanisms under thermal, electrical, and mechanical abuse conditions, including thermal runaway progression (T 1 , T 2 , T 3 ), gas evolution profiles, and cell-to-cell propagation dynamics. SIBs demonstrate significant safety improvements through higher thermal runaway initiation temperatures (220–260 °C vs. 170–220 °C for NMC LIBs), reduced heat release rates, lower hydrogen content in off-gases (30 % vs. 42 % for LFP), and transformative zero-volt transport capability. SSBs, particularly oxide-based variants, represent a paradigm shift by eliminating flammable liquid electrolytes, achieving exceptional thermal stability (T 2 > 600 °C), minimal gas evolution (<0.5 L/Ah), and dramatically slower propagation rates (0.3–0.9 °C/min vs. 9–11 °C/min for high-Ni NMCs). However, application-specific safety rankings reveal critical nuances: LFP's superior thermal stability is offset by severe HF toxicity (3000–8000 ppm), while sulfide SSBs present conditional H 2 S risks upon moisture exposure. This analysis demonstrates the evolution from 'engineered safety'—relying on external protective systems—towards 'intrinsic safety' integrated into core battery chemistry and architecture, providing actionable guidance for technology selection across diverse deployment scenarios from electric vehicles to grid-scale energy storage. • Battery safety rankings are not universal but highly application-scenario dependent. • Sodium-ion batteries show superior toxicity profiles and safe zero-volt transport. • Oxide solid-state batteries eliminate flammable electrolytes for intrinsic safety. • LFP batteries emit high HF levels, challenging their "safest chemistry" perception. • Sulfide solid-state batteries might pose H 2 S toxicity risks upon moisture exposure.