Reversible lithium deposition/dissolution reaction with low polarization through a cross-linked polymer: Geometrical structure effects of the polymer protective layer on lithium metal anodes

A lithium metal anode was coated with a cross-linked PEO-based polymer composed of poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and poly(ethylene glycol) methyl ether acrylate (PEGMA) as a base polymer to suppress electrolyte decomposition and lithium dendrite formation, thereby improving its electrochemical performance. The ca. 10 μm thick polymer membranes with flat and pore-free surface were successfully fabricated on the lithium metal electrode. Physicochemical characteristics of the synthesized polymer membrane such as elastic modulus, electrolyte uptake and mesh size indicate that polymer structure is changed from a linear structure to a bridged network one and increased in its crosslinking density by mixing PEGDA. The PEGDA increased the connectivity of the nanosized cross-linked domains, which led to improvement of the lithium ion transport number in membrane, and polarization and reversibility of deposition/dissolution reaction of lithium. Additionally, no dendrite formation was observed during lithium deposition/dissolution reaction through the bridged network structured polymer membrane. The structure of the PEO-based coating polymer is one of the important factors in the stabilization of the deposition/dissolution reactions of lithium metal anodes, and a bridged-network structure with preferential ion transport capability is more effective to improve these reactions than a straight-chain structure. The nanosized cross-linked domains is formed, and the lithium ion transport number in membrane improved with increasing PEGDA content in the PEO-based polymer membrane. Significant improvement of the reversibility and polarization of deposition/dissolution reaction of lithium metal anode in LiFSI/DME electrolyte solution is achieved by the coating bridged network structure polymer membrane with nanosized domain. Control of the ion transportation by modification of the coated polymer structure is thus an effective way to enhance the deposition/dissolution reactions of lithium metal anodes. • Cross-linked PEO based polymer membrane was used as a coating layer of Li anode. • Polymer structure changed from a linear to bridged network by mixing PEGDA. • Higher Li + transport number was achieved in the bridged structure than straight-chain. • A 0.1:99.9-PEGDA-PEGMA provided stable and least polarization reaction of Li anode. • Decomposition of electrolyte could be suppressed by dense and uniform bridged network.