Stabilizing Lithium Metal Batteries by Anion Modulated Quasi-Solid Polymer Electrolytes

Abstract

Solid polymer electrolyte is considered as a promising strategy for taming lithium metal batteries, but is challenged by poor ionic conductivity, unstable electrolyte/electrode interface and severe dendrite formation, leading to premature battery failure. Herein we design a novel quasi-solid polymer electrolyte (QSPE) by a high donor anion (NO3-) moduated polymerization of poly (1,3-dioxolane) (poly-DOL). The competitive interactions between NO3- and BF3 towards DOL effectively regulates the polymerization behavior of DOL molecules, leading to slightly decreased polymerization degree (~88.8%). The limited but essential DOL residuals within poly-DOL networks not only provides highways for fast ion transport (1.65×10-3 S cm-1 at 25 °C) but also benefits the electrode-electrolyte contact for low interfacial resistance. Specifically, the NO3- modulates the electrolyte solvation structure and leads to a robust inorganic-rich SEI protecting layer on lithium anode. The synertic effect of high ionic conductivity, good interfacial contact and robust SEI enables a dendrite-free lithium anode with stable cycles (>750 h) and ultralow overpotential (<50 mV) for Li|Li cells. The Li|LiFePO4 cells employing such QSPE achieve 73.1 % capacity retention within 500 cycles and stable cycling under 10 mg cm-2 loading. This work provides new insights into the electrolyte microstructure and interfacial properties design for practical cells.

Keywords: quasi-solid polymer electrolyte, lithium metal batteries, solid/electrolyte interface, ionic conductivity, cycling stability