A composite dielectric membrane with low dielectric loss for dendrite-free lithium deposition in lithium metal batteries

Abstract

Dielectric materials capable of generating a counteracting electric field at the interface to diminish electric field gradients show promise in facilitating uniform lithium deposition and preventing dendrite formation in lithium metal batteries. However, the significant obstacle is achieving a balance between the dielectric constant and dielectric loss, which effectively reduces the electric field gradients while maintaining a low resistance and overpotential. Herein, we fabricate an organic–inorganic composite membrane with an asymmetrical porous structure that strikes an optimal balance between the dielectric constant and loss. Specifically, the inorganic LiNbO₃ imparts a high dielectric constant and superior Li⁺ conductivity, while the incorporation of organic PVDF substantially lowers the overall dielectric loss of the membrane. The unique asymmetrical porous structure, transitioning from loose to dense, reduces the leakage current density and enhances Li⁺ transport compared to a uniformly dense structure. It also ensures a uniform Li⁺ flux for smooth deposition by the dense side. The Li–Cu half cell shows an average coulombic efficiency of 98.3% over 500 cycles, and the full cell with high-loading LiFePO₄ (12 mg cm⁻²) maintains a high capacity retention of 78% after 400 cycles. This work opens up new avenues for developing efficient and durable lithium metal batteries.