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.
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