Asymmetrically modified polyzwitterionic polymer electrolytes for dendrite-free and high voltage lithium metal...

Solid electrolytes suitable for compatibility with high voltage cathodes are desired to increase the energy density of solid lithium metal batteries. However, because of their limited internal energy gap, single-phase polymer or ceramic examples cannot exhibit both strong electrochemical stability and reasonable lithium compatibility. Herein, a novel in-situ construction asymmetric interface modified polyzwitterionic gel polymer electrolyte (AMPE) is proposed. It is composed of a cathode-compatibility layer (CCL) and lithium-compatible layer (LCL). The zwitterionic polymers in AMPE can restrain the motion of anions to prevent space charge formation caused by local anion depletion, and meanwhile promote the dissociation of lithium salts and regulate Li⁺ distribution in the vicinity of anode. The CCL exhibits superior suitability for high-voltage cathodes with the introduction of PAN. Meanwhile, the FEC in LCL could reduce side reactions between cyanide groups and lithium anodes, achieving dendrite free lithium metal batteries. As a result, AMPE exhibits improved ionic conductivity of 2.86 × 10^-4 S cm^-1, high Li⁺ transference number of 0.60 and wide electrochemical stability window of 5.19 V. Li/AMPE/Li batteries stably cycle over 4000 h at 0.1 mA cm^-2 and over 1200 h at 0.2 mA cm^-2, respectively. The Li/AMPE/LiFePO₄ and Li/AMPE/LiNi_0.8Co_0.1Mn_0.1O₂ batteries exhibit excellent cycle ability and cycle reversibility, Li/AMPE/LiFePO₄ batteries stably cycle over 2000 cycles at 1C and Li/AMPE/NCM811 batteries stably cycle over 480 cycles at 0.5C, respectively.