Recent progress on passive cooling strategies for Li-ion battery of electric vehicles

The battery is a vital component of an electric vehicle (EV), and an inadequate thermal management can lead to excessive temperature rise, non-uniform heating, and safety risks. This work presents a comprehensive evaluation of passive battery thermal management solutions for lithium-ion batteries under low to moderate operating conditions, with particular emphasis on phase change materials (PCMs) and PCM-heat pipe integration. Through critical review and comparative synthesis of recent experimental and modeling studies, the influence of pure, composite, and nano-enhanced phase change materials (NEPCMs), as well as different heat pipe configurations, is systematically assessed under varying discharge rates. Key performance indicators include maximum temperature, temperature uniformity (ΔT), system weight, and safety metrics such as flame retardancy. Results indicate that composite and NEPCMs can effectively maintain cell temperatures below 45 °C and ΔT < 5 °C at low to moderate discharge rates (typically 1C-3C); however, these thermal benefits are often accompanied by reductions in latent heat, shifts in melting temperature, and increased system weight. At higher C-rates, PCM-assisted heat pipe configurations demonstrate superior temperature control and improved thermal uniformity, though secondary cooling strategies may be required to ensure long-term reliability. The incorporation of flame-retardant PCM formulations is identified as critical for mitigating thermal runaway risks. By explicitly correlating passive cooling performance with discharge-rate-dependent thermal benchmarks, this review establishes practical selection guidelines for passive battery thermal management systems, offering actionable insights for improving EV battery pack reliability, lifespan, and safety. • At high C-rates, PCMs and HPs maintain battery pack temperature below 45 °C with ΔT < 5 °C. • Effective BTMS using PCM and HPs requires secondary cooling systems for enhanced performance. • Additives boost thermal conductivity of CPCMs but reduce latent heat capacity and melting temperature. • Flame-retardant properties of PCMs are crucial in EV battery applications to prevent thermal runaway.