Deep eutectic solvent-assisted phase separation for polyurea-based polymer electrolytes

Solid polymer electrolytes (SPEs) as core components for next-generation lithium metal batteries have attracted great interests in terms of improving the safety and energy density. It is worth noting that the transport of lithium ions in SPEs requires the assistance of segmental motion, and on the contrary the mechanical robustness of polymers originates from the restricted segmental motion. Therefore, it is very challenging to balance fast ion transport and enhanced mechanical robustness of SPEs. To overcome above trade-off, here, we report a class of three-dimensional interconnected polyurea-based electrolytes with enhanced phase separation structure with the assistance of a deep eutectic solvent (DES). The DES selectively plasticizes the soft segment in polyurea and increases its chain motion, while induces further aggregation of the hard segment in polyurea and forms enhanced dynamically physical cross-linking network due to polarity incompatibility. The gel polyurea-based electrolytes (GPUEs) with a phase separation structure achieve decoupling of mechanical properties and ionic conductivity, showing a combination of superior mechanical strength (3.2 MPa) and high ionic conductivity (1.5 × 10−4 S cm−1, 30 °C). Moreover, the Li|GPUEs|LiFePO4 coin cell shows a satisfactory initial discharge specific capacity (higher than 150 mAh g−1 at 1 C), and the capacity retention is higher than 80% after 500 cycles.