Janus waterproof/water-absorbent membrane for lithium-air batteries in humid environments

The ambient humidity poses significant challenges to the practical application of lithium-air batteries. Its intrusion not only seriously corrodes the lithium anode, causing active lithium loss, but also triggers irreversible evolution of discharge products, leading to accumulation of by-products. To address these issues, we have pioneered the design of Janus waterproof/water-absorbent membranes to suppress humidity infiltration. Specifically, a dense polychlorotrifluoroethylene (PCTFE) film with low surface energy is selected as the outer waterproof layer to initially reduce the gas humidity. Then, a porous moisture-sensitive 3A molecular sieve layer is applied as the inner water-absorbent layer to further dehumidify the airflow to obtain a relatively dry environment. Owing to this innovative design, the humidity infiltration is effectively curbed. The lithium anode still exhibits metallic luster with no corrosion spots after cycling for 50 h in 60 % RH air. The discharge product, primarily composed of film-like Li₂O₂, can also be reversibly decomposed. Consequently, the lithium-air battery with Janus membranes can stably cycle for 350 h under hostile condition (60 % RH), about 5 times longer than unprotected battery. We hope this work can provide some inspirations for future design of oxygen-selective membranes.