Regulating the Interfacial Solvation Environment by a Pyran-Based Polymer for High-Areal-Capacity and Low-Temperature-Endurable Magnesium Metal Batteries

Regulating the artificial solid electrolyte interphase (SEI) and interfacial solvation structure of the electrolyte is crucial for developing rechargeable magnesium batteries (RMBs) with long cycling life, high current density tolerance, and fast ion transport capability operated under extreme environments, such as low temperatures. Herein, an effective strategy using oligomeric poly(3,4-dihydro-2H-pyran) (polyDHP) is proposed to modulate the interfacial solvation structure of RMBs, with the construction of an artificial SEI with rapid Mg-ion conductivity. The steric hindrance of polyDHP and its electrostatic interaction with Mg2+ reduce the solvent molecules in the first solvation shell, allowing polyDHP molecules to participate in coordination, thus lowering the desolvation energy barrier of Mg2+ and facilitating their deposition and stripping. Furthermore, due to the glass transition behavior, oligomeric polyDHP exhibits a more ordered structure with more continuous internal ion transport channels at −20 °C, therefore enabling stable RMB operation at lower temperatures for the first time. The corresponding Mg symmetric cells display a much lower overpotential (400 mV) and excellent cycling stability at both room temperature (over 5000 h at 5 mA cm–2 and 10 mA h cm–2) and a low temperature of −20 °C (over 1300 h at 3 mA cm–2 and 3 mA h cm–2). This strategy supports the stable cycling of CuS∥Mg full cells for over 200 cycles at −20 °C. This work reveals the importance of regulating the interfacial solvation structure, promoting the realistic applications of RMBs under extreme conditions.