“Built‐in Electric Field” Design Enables Rapid Li ⁺ Transport in Polymer Electrolyte

ABSTRACT 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||LiFePO 4 cell delivers a capacity retention of 84% after 5000 cycles at 2C, and Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 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.