Tailoring Highly Ion‐Conductive and Stabled PVDF‐Based Solid Electrolyte via Surface Coordination Chemistry

Abstract The composite solid‐state electrolyte, composed of polyvinylidene fluoride (PVDF) polymer and garnet, exhibits great promising in solid‐state batteries. However, the dehydrofluorination of PVDF induced by the garnet narrows its voltage window and deteriorates the electrode‐electrolyte interface, inhibits ion transport. Here, a coordination interphase is constructed on garnet fillers via in situ polymerization of cyanoethyl cellulose (CEC) to stabilize the organic/inorganic interface. La atoms in garnet coordinating with C≡N groups of CEC, creating a Lewis basic environment that facilitates the linking of adjacent C≡N groups to form conjugated C═N sequences, thereby forming a 5‐nm ultrathin polycyanethyl cellulose (PCEC) layer on the garnet surface. The interaction between PCEC and garnet triggers the strong Li + ion adsorption, thus producing a fast Li + ion migration pathway through the garnet/PCEC interface. Consequently, the composite electrolyte demonstrates a high room‐temperature ionic conductivity of 5.6 × 10 −4 S cm −1 , a high cutoff voltage of up to 4.8 V versus Li + /Li, and excellent stability against lithium metal. Using this electrolyte, a practical 560 mAh Li|LiNi 0.9 Co 0.05 Mn 0.05 O 2 solid‐state lithium metal pouch cell achieves superior weight and volume energy densities of up to 408 Wh kg −1 and 733 Wh L −1 , respectively.