Nanocrystals with Aggregate Anionic Structure Enable Ion Transport Decoupling of Chain Segment Movement in Poly(ethylene oxide) Electrolytes

Abstract

Abstract All‐solid‐state polymer electrolytes are promising for lithium batteries, but Li + transport in these electrolytes relies on amorphous chain segment movement, leading to low Li + mobility and poor mechanical strength. Here we propose a novel Li + transport mechanism mediated by PEO 3 :LiBF 4 nanocrystals (NCPB) with the aggregate (AGG) anionic structure, which enables a change from amorphous to crystalline phase dominated ion transport in all‐solid‐state PEO/LiBF 4 electrolyte. Experiments and simulations reveal that the interaction between Li + and F in NCPB with AGG anionic structure simultaneously restricts anion transport and reorients anions within the free volume of NCPB, resulting in a three‐coordination intermediate to facilitate Li + transport. The unique Li + transport mechanism through NCPB makes the PEO/LiBF 4 electrolyte with a high Li + transference number (0.73) and remarkably increased mechanical strength (storage modulus >100 MPa) at 45 °C. As a result, the Li|LiFePO 4 batteries with the ultrathin self‐supported PEO/LiBF 4 electrolyte (10 μm) exhibit significantly improved cycle life (97 % @ 468 cycles) compared to those with PEO/LiTFSI electrolyte (failed @ 68 cycles). This work demonstrates a novel ion transport mechanism for achieving selective and rapid Li + transport.