Elastomeric Electrolyte With Selective Tuning of Ion Transport Pathway for Low‐Temperature and High‐Voltage Lithium Metal Batteries

ABSTRACT We demonstrate an elastomeric electrolyte enabling stable operation of lithium (Li) metal batteries (LMBs) across a wide temperature range, including −20°C. The electrolyte forms a bicontinuous structure composed of an elastomeric polymer matrix and plastic crystal domains through polymerization‐induced phase separation. This bicontinuous structure allows selective tuning of Li + transport characteristics through the plastic crystal phase without compromising the mechanical strain (∼300%) of the elastomeric electrolyte, which is essential for accommodating Li metal volume fluctuations and suppressing dendrite growth. Combined experimental and simulation studies reveal that the reorientational dynamics of the succinonitrile (SN) plastic crystals are enhanced by molecular interactions with a structurally similar dinitrile compound, adiponitrile (ADN). With an optimized SN/ADN‐based plastic crystal phase, the elastomeric electrolyte exhibits significantly enhanced ionic conductivity (0.17 mS cm − 1 ) and Li + transference number (0.65) at −20°C compared to the pure SN phase, due to the enhanced Li + hopping. As a result, the elastomeric electrolyte with superior Li + transport properties and mechanical integrity achieves outstanding electrochemical performance in solid‐state LMBs at −20°C, delivering a high discharge capacity of 154 mAh g − 1 and 90% capacity retention after 100 cycles at a high cut‐off voltage of 4.5 V.