A Radical Mediator Layer on Composite Solid Polymer Electrolyte for Uniform Lithium Deposition

Uneven diffusion and gradual accumulation of lithium under electric fields lead to the formation of lithium dendrite, which impedes the practical applications of all-solid-state lithium metal batteries. To achieve even deposition of Li⁺, a free radical polymer (PTMA), poly (2,2,6,6-tetramethylpiperidinyloxy meth-acrylate), serving as Li⁺ transport and deposition mediator layer in Polyethylene oxide-Li₇La₃Zr₂O₁₂ (PEO-LLZO) composite solid polymer electrolytes is employed. During the transporting process, Li⁺ is anchored by the O^· site of PTMA, hopping along PTMA chains until deposited onto the Li metal anode. This Li⁺ transport route is confirmed by the displacement of PTMA-⁶Li with PTMA-⁷Li and ⁶Li-tracing NMR. The DFT calculation confirms Li⁺ is more energetically preferred to coordinate with PTMA than directly deposited onto the lithium electrode, the atomic Li deposition furtherly occurs since the lower adsorption energy of Li on the Li (001) slab than Li⁺. Therefore, the deposition of Li⁺ avoids the influence of the electric field with the assistance of the PTMA mediator layer, and a molecular scale Li⁺ deposition is achieved since each unit of PTMA acts as an active site of lithium transition and deposition. Consequently, lithium symmetrical battery shows stable cycles 4000 h at 0.1 mA cm^-2 and 60 °C. The LiFePO₄/Li batteries show excellent cyclic and rate performance.