A Multifunctional Double-Layer Composite Solid Electrolyte for High-Voltage Lithium Metal Batteries

Composite solid electrolytes, which comprise the flexibility of polymers with mechanical stiffness of inorganic solid electrolytes, are appealing for solid-state battery applications. However, they face challenges in simultaneously suppressing Li dendrite growth from the anode while maintaining high oxidative stability under high voltage. Here, a straightforward and scalable method is proposed by separately incorporating propylene carbonate and lithium hydroxide into a garnet-based polymer membrane; the double-layer composite polymer electrolyte with multifunctional effects is then subsequently formed through mechanically pressing them together. Propylene carbonate enhances the electrolyte’s stability against oxidation during high-voltage charging, contributing to improved battery’s energy density. Meanwhile, the reaction between the lithium hydroxide and lithium salt adjusts the SEI components on the anode side by forming a LiF-rich SEI layer, which improves the battery’s cycling stability. Benefiting from this ingenious design, the LiNi0.6Co0.2Mn0.2O2||Li cells demonstrate remarkable cycling performance for over 70 cycles, retaining 60.6% of their initial capacity at 0.1 C. Furthermore, the Li||Li symmetric cells achieved an outstanding plating and stripping reversibility of approximately 1500 h at 0.2 mA cm–2 with a small overpotential of 28 mV. This design is expected to facilitate the commercialization of electrolytes for high-voltage Li metal batteries.