A Quasi-Solid-State Flexible Fiber-Shaped Li-CO₂ Battery with Low Overpotential and High Energy Efficiency

The rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO₂ battery was recently proposed as a novel and promising candidate for next-generation energy-storage systems. However, the current Li-CO₂ batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO₂ batteries for wearable electronics have been reported so far. Herein, a quasi-solid-state flexible fiber-shaped Li-CO₂ battery with low overpotential and high energy efficiency, by employing ultrafine Mo₂ C nanoparticles anchored on a carbon nanotube (CNT) cloth freestanding hybrid film as the cathode, is demonstrated. Due to the synergistic effects of the CNT substrate and Mo₂ C catalyst, it achieves a low charge potential below 3.4 V, a high energy efficiency of ≈80%, and can be reversibly discharged and charged for 40 cycles. Experimental results and theoretical simulation show that the intermediate discharge product Li₂ C₂ O₄ stabilized by Mo₂ C via coordinative electrons transfer should be responsible for the reduction of overpotential. The as-fabricated quasi-solid-state flexible fiber-shaped Li-CO₂ battery can also keep working normally even under various deformation conditions, giving it great potential of becoming an advanced energy accessory for wearable electronics.