Extended Segmental Structures Regulate Li + Solvation in 1,3‐Dioxane‐Based Cross‐Linked Polymer Electrolytes for High‐Voltage Lithium Metal Batteries

Cross‐linked polymer electrolytes based on 1,3‐dioxolane (DOL) are attractive for lithium metal batteries, but their application in high‐voltage systems remains limited. 1,3‐dioxane (DOX) has emerged as an effective substitute for DOL in high‐voltage polymer electrolytes, yet the structural origin of its advantage remains unclear. Here, we construct a pair of closely related cross‐linked polymer electrolytes, DOL‐3‐methylglutaric anhydride (MA) and DOX‐MA, within the same anhydride framework to uncover the structural basis of the DOL‐to‐DOX effect. Compared with DOL‐MA, DOX‐MA exhibits more extended segmental structural characteristics, which weaken polymer‐dominated Li + coordination and reconstruct the local solvation environment toward anion‐enriched configurations. This segmental‐structure‐mediated solvation reconstruction further drives the formation of a robust LiF‐rich interphase, thereby enabling faster Li + transport and improved interfacial stability. As a result, DOX‐MA delivers an ionic conductivity of 8.73 × 10 −4 S cm −1 , a Li + transference number of 0.79, and an electrochemical stability window up to 5.3 V. Li||Li symmetric cells exhibit stable cycling for 4000 h with low polarization, and LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)||Li full cells show excellent cycling stability with 89.1% capacity retention at a cutoff voltage of 4.5 V. This work highlights the extended segmental structure as a key factor governing the superior solvation and interfacial behavior of DOX‐based cross‐linked polymer electrolytes.