Semi-Interpenetrating Network Electrolytes Utilizing Ester-Functionalized Low Tg Polysiloxanes in Lithium-Metal Batteries

Solid polymer electrolytes (SPE) obtained from polyesters are viable alternatives to polyethylene oxide-based materials, especially for room-temperature applications. In SPEs, the ion conduction is dependent on the polymer segmental mobility and is thus facilitated by low glass transition temperature (Tg). Here, the study synthesizes an ester-funtionalized polysiloxane-based polymer electrolyte with an exceptionally low Tg of −76 °C, resulting in a high ionic conductivity of 2.6 × 10⁻⁵ S cm⁻¹ at room temperature and a lithium transference number of 0.72. However, the low Tg and consequently low mechanical stability require reinforcement to promote the formation of stable lithium-electrolyte interfaces in lithium plating stripping experiments and stable battery cycling in lithium-metal batteries (LMBs). For this, the SPE is incorporated into a network structure to yield a semi-interpenetrating network electrolyte (SPE20-SIPN) which results in significantly improved storage modulus by three orders of magnitude and ionic conductivity is maintained upon crosslinking. The SPE20-SIPN exhibits stable cycling for up to 50 cycles with fluctuation (voltage noise) in some of the cells. A combination of crosslinking and nanoparticle addition (SPE20-N10-SIPN) overcomes the voltage noise and results in high coulombic efficiencies and high capacity retention above 80% for 200 cycles in solvent-free, all-solid-state LMBs at 30 °C.