Effects of Mechanical Properties of Elastomeric Electrolytes for Stable Operation of Lithium Metal Batteries

Abstract

The mechanical properties of polymer electrolytes are critical for the stable operation of lithium metal batteries (LMBs), as they accommodate volume changes of the lithium (Li) metal anode, suppress dendrite formation, and maintain interfacial stability. Here, we present a systematic investigation into the role of the mechanical characteristics of fluorinated elastomeric electrolytes (FEEs) in enabling stable cycling of LMBs at ambient and low temperatures. The FEEs consist of bicontinuous elastomer and plastic crystal phases, allowing independent control of mechanical properties by adjusting the crosslinking density of the elastomer phase. Concurrently, FEEs retain the fast ion transport properties of the plastic crystal phase, exhibiting high ionic conductivity of ≈1.1 and ≈0.24 mS cm⁻¹ at 25 and −10 °C, respectively. The optimized FEE demonstrates balanced toughness (140.6 kJ m⁻³) and adhesion energy (31.4 J m⁻²), along with elastic recovery characteristic, enabling a Li|| LiNi_0.8Co_0.1Mn_0.1O₂ full cell to deliver a high initial discharge capacity (153 mAh g⁻¹) with 76% capacity retention after 150 cycles at −10 °C. In contrast, lightly crosslinked FEEs undergo irreversible plastic deformation and loss of interfacial contact, while excessively crosslinked systems suffer from low toughness and are prone to fracture, both resulting in poor cycling performance.