Polyethylene Glycol Dimethyl Ether-Plasticized Poly(vinylidene difluoride)-Based Polymer Electrolytes Inhibit Dendrite Growth and Enable Stable Cycling for Lithium-Metal Batteries

The conventional poly(vinylidene difluoride) (PVDF) polymer backbone in the lithium battery system shows poor compatibility with polyethylene glycol dimethyl ether (PEGDME) and results in the PVDF matrix separating from the PEGDME. It reacts with the lithium metal anode, forming an uneven passivation layer that causes battery capacity to decay. Here, poly(ethylene oxide) (PEO)-modified PVDF (mPVDF) was used as a polymer matrix to prepare freestanding quasi-solid-state polymer electrolytes with a PEGDME plasticizer (mQSPEs) to minimize battery deterioration. The PEO-mPVDF skeleton incorporated with an adequate amount of PEGDME reaches an ionic conductivity of 10–3 S cm–1 and simultaneously exhibits excellent compatibility with the lithium metal anode. The differential scanning calorimetry and thermogravimetric analysis show that the mPVDF backbone exhibits strong interactions with the polymer matrix and PEGDME, which has higher glass transition temperature (Tg) and decomposition temperature (Td) compared to the original PVDF backbone. Optical microscopy images show that the PEGDME stays in the mPVDF matrix without separation. The modified polymer matrix successfully prevents the degradation of PEGDME at the lithium metal anode, leading to long-term stability of mQSPEs with lithium metal.