Oxygen- and dendrite-resistant ultra-dry polymer electrolytes for solid-state Li–O₂ batteries

Utilizing polymer electrolytes in Li–O₂ batteries could effectively solve safety issues caused by flammable liquid electrolytes. However, the effect of polymer matrixes and additional liquid electrolytes on the cycle performance of Li–O₂ batteries is still not clear. Herein, free-standing, Li-ion conducting ultra-dry polymer electrolytes (UDPEs) without additional liquid electrolytes are synthesized by a simple tape-casting and vacuum-drying method. The long-term cycle performance (over 800 ​h) of the UDPE-based symmetric Li–Li cells in O₂ atmosphere demonstrates that the UDPEs significantly resist O₂ crossover and Li dendrite penetration. Moreover, side reactions caused by the degradation of liquid electrolytes can be alleviated and a stable LiF-containing solid electrolyte interface is formed between the UDPEs and Li metal. Meanwhile, the cycle life of the UDPE-based catalyst-free Li–O₂ batteries under a high current density of 0.4 ​mA ​cm^-2 is improved by more than twofold in comparison with that of the liquid electrolyte-based Li–O₂ batteries. The replacement of liquid electrolytes by UDPEs does not change the fundamental reaction of the solid-state Li–O₂ batteries, which is still the formation and decomposition of typical Li₂O₂ crystals. The outstanding comprehensive performance of UDPEs may trigger further studies towards multifunctional polymer electrolytes in Li–O₂ batteries and even other alkali metal-based O₂ (air) batteries.