In-Built Polymer-in-Solvent and Solvent-in-Polymer Electrolytes for High-Voltage Lithium Metal Batteries

Summary All-solid-state electrolytes are widely understood to be required for energy-dense storage/conversion devices. Persistent problems associated with low ionic conductivity, poor charge transport across explicit and implicit interfaces, and inferior chemical stability continue to pose significant barriers to progress. Here, we synthesize and study a series of gel (or “quasi-solid-state”) electrolytes that can overcome many of the known limitations of their all-solid-state analogs. We discover that in two physical states, solvent-in-polymer (SIP) and polymer-in-solvent (PIS), the electrolytes offer exceptional ion-transport and stability characteristics. In both states, crystallization of the polymer component and thermodynamic activity of the solvent are lowered, allowing the electrolytes to achieve attractive combinations of ion transport, thermal, and electrochemical stability. Moreover, the SIP-PIS electrolytes can be in situ polymerized inside an electrochemical cell, resulting in fast kinetics for LiNi0.8Mn0.1Co0.1O2 cathode with areal capacity of 2.5 mAh/cm2 and long-term stability toward lithium metal anode over 1,200 h.