"Built-in Electric Field" Design Enables Rapid Li⁺ Transport in Polymer Electrolyte

Polymer electrolytes hold great promise for lithium metal batteries owing to their low-cost, facile processability, and superior electrode compatibility, yet are hindered by intrinsically low ionic conductivity due to their strong Li⁺-polymer interaction. Inspired by the built-in electric field (BIEF) concept, we propose a novel strategy of creating a continuous BIEF to uniformly weaken Li^+-polymer interactions, thereby achieving a consistently low energy barrier for Li⁺ transport. Specifically, continuous metal Lewis acidic sites (positive side) are introduced along the ether oxygen (-O-) sites (negative side) of the polymer chain, inducing charge redistribution and establishing a directional BIEF. This field reduces the electron density around the -O- groups, significantly attenuating Li⁺-polymer interactions. The resulting electrolyte achieves an ultrahigh ionic conductivity of 1.14 mS cm^-1 and a Li⁺ transference number of 0.78 at 25°C. Remarkably, Li||Li cell shows exceptional cycling stability for over 6000 h. Moreover, Li||LiFePO₄ cell delivers a capacity retention of 84% after 5000 cycles at 2C, and Li||LiNi_0.5Co_0.2Mn_0.3O₂ cell maintains 80% capacity after 500 cycles at 1C. This work pioneers a general BIEF-based paradigm for designing high-performance polymer electrolytes, offering a promising avenue toward advanced quasi-solid-state batteries.