A Mechanical Strength-Enhanced Polymer Coating with Anion-Phobic and Solvent-Phobic Capability for Advanced Lithium Metal Anodes

Lithium (Li) metal is considered an attractive anode for high-energy Li secondary batteries, but it suffers from a short cycle life and serious safety hazards due to its high reactivity and dendritic growth. A potential approach is to construct a stable artificial SEI film. Herein, we report a polymer coating that is composed of LiTFSI and PVDF-HFP, which is spread onto the Li foil (25 μm) by the blade coating method (abbreviated as Li-PH@Li). During drying, LiTFSI reacts with Li metal to form LiF that is distributed evenly in the coating layer, thus improving the mechanical strength of the coating. In addition, the coating layer could selectively transport the Li-ions and delay the transport of solvent and PF6–, alleviating the side reaction between Li metal and electrolyte. Therefore, a dense Li deposition layer is obtained during a long cycle. Consequently, the Li-PH@Li||LFP coin cell with a low N/P ratio (3:1) could maintain 355 cycles at 0.5 C (0.79 mA cm–2), while only 240 cycles for the bare Li||LFP cell. Moreover, a lean Li-PH@Li||LFP pouch cell, whose N/P ratio is 1.9:1, can also sustain more than 200 cycles. This work paves a new approach to protect Li metal anodes for high-performance Li metal batteries.