Thin polymer electrolyte with MXene functional layer for uniform Li⁺ deposition in all-solid-state lithium battery

Solid polymer electrolyte (SPE) shows great potential for all-solid-state batteries because of the inherent safety and flexibility; however, the unfavourable Li⁺ deposition and large thickness hamper its development and application. Herein, a laminar MXene functional layer‒thin SPE layer‒cathode integration (MXene-PEO-LFP) is designed and fabricated. The MXene functional layer formed by stacking rigid MXene nanosheets imparts higher compressive strength relative to PEO electrolyte layer. And the abundant negatively-charged groups on MXene functional layer effectively repel anions and attract cations to adjust the charge distribution behavior at electrolyte–anode interface. Furthermore, the functional layer with rich lithiophilic groups and outstanding electronic conductivity results in low Li nucleation overpotential and nucleation energy barrier. In consequence, the cell assembled with MXene-PEO-LFP, where the PEO electrolyte layer is only 12 μm, much thinner than most solid electrolytes, exhibits uniform, dendrite-free Li⁺ deposition and excellent cycling stability. High capacity (142.8 mAh g^-1), stable operation of 140 cycles (capacity decay per cycle, 0.065%), and low polarization potential (0.5 C) are obtained in this Li|MXene-PEO-LFP cell, which is superior to most PEO-based electrolytes under identical condition. This integrated design may provide a strategy for the large-scale application of thin polymer electrolytes in all-solid-state battery.