Humidity-triggered autothermal regulation of lithium-ion batteries via liquid metal-PCM composites for enhanced cold-environment performance

Low-temperature operation degrades lithium-ion battery (LIB) performance and safety. We report a humidity-responsive composite that combines eutectic gallium-indium-coated aluminum (LM@Al), active carbon, and phase-change microcapsules (PCMs) to enable rapid, controllable preheating and sustained thermal buffering without the need for external electronics. LM@Al releases exothermic heat through Al-water redox while liquid metal forms a catalytic, thermally conductive shell; activated carbon accelerates moisture transport; and PCM absorbs peak heat, prolonging insulation. SEM-EDX confirms core-shell LM@Al particles and LM microdroplet formation during reaction. Systematic tests on 18,650 cells identify an optimal composition (LM:Al:PCM = 10:1:2 with 10% fixed active carbon) and a 3 mm composite thickness, achieving heating rates of up to 4.9 °C/min and a safe peak temperature of 29 °C at an ambient temperature range of −10 to 0 °C. Humidity control strategies tune heat release to match discharge rates, balancing rapid preheating and material consumption. At extreme −20 °C, performance is limited by water freezing. The continuous 90% RH supply approach converts pulsed humidity-triggered heat into uniform, mild thermal output, improving low-temperature discharge capacity and mitigating capacity fade, offering a promising passive BTMS solution for cold-climate battery applications. Future work should address challenges related to scale-up, long-term cycling, and integration.