Enabling Long-Cycle Li–S Batteries at −20 °C via Activation of Li2S Redox Kinetics with Co and Mo2C Nanospheres

As a potential high-safety and high-energy-density technology, lithium sulfide has been extensively studied as a cathode material for lithium–sulfur batteries under room temperature conditions. However, limited by its intrinsic characteristics of low electronic conductivity and high activation energy barrier, conventional Li2S cathodes struggle to overcome the activation energy barrier at low temperatures, resulting in scarce research on their application below zero. Specifically, studies on operation at −20 °C are nearly nonexistent. Herein, a synergistic strategy combining molybdenum carbide support adsorption and cobalt metal catalysis is proposed for low-temperature performance investigation. Via a lithiation reaction, Li2S@MoC–Co nanocomposites are fabricated by in situ synthesizing Li2S nanoparticles, introducing MoC as the support, and incorporating Co metal. When assembled into batteries with Li2S@MoC–Co as the cathode and metallic lithium as the anode, the activation energy barrier is reduced to 2.41 V at room temperature, exhibiting excellent electrochemical performance. A high initial discharge capacity of 1100 mAh g–1 is achieved at 0.1 C, and a discharge capacity of 430 mAh g–1 is retained after 200 cycles at 0.5 C. Even at −20 °C, Li2S is almost fully activated during the first charging cycle, delivering a discharge capacity of 360 mAh g–1 at 0.05 C. Moreover, a capacity retention rate of 92% is maintained after 300 cycles at 0.5 C. This work realizes high output and high-capacity retention of Li2S at −20 °C, providing a new paradigm for the development of low-temperature Li2S-based batteries.