In-situ constructing of dual bifunctional interfacial layers of garnet-type Li6.4La3Zr1.4Ta0.6O12 solid electrolyte towards long-cycle stability for flexible solid metal lithium batteries

Lithium metal batteries are used widely because of their high security and high energy density. However, the solid electrolytes and electrodes have incompatible interfaces, and the lithium anode is also hindered by dendrite growth. Herein, a bifunctional stable electrode interface layer is constructed by in-situ polymerization of polyester-based monomers and organic solvent, revealing the strong correlation between cathode electrolyte interphase (CEI) on cathode and solid electrolyte interface (SEI) on Li metal anode. The sandwich-like composite electrolyte prepared with garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO) active fillers and polymer electrolyte composed of (poly(ethylene glycol) dimethyl ether (PEGDME), trimethylolpropane trimethyllacrylate (TMPTMA), 1,6-hexanediol diacrylate (HDDA)(named as P(PF)1TH) exhibits excellent flexibility, wide electrochemical window, and good thermal stability. Moreover, P(PF)1TH-10%LLZTO electrolyte has satisfactory ionic conductivity (1.42 × 10−3) at 50 °C and high Li+ transference number (0.547) at 25 °C, and symmetrical Li|P(PF)1TH-10%LLZTO|Li cells can run stably for more than 1000 h at 0.1 mA cm−2 at 50 °C. The assembled LiFePO4(LEP)|P(PF)1TH-10%LLZTO |Li cell shows high discharge capacity of 139.9/122.8 mAh g−1 with capacity retain of 90.64%/97.96% after 200 cycles at 1C/2C. This work introduces a dual functional interface layer between electrolyte and electrode through in-situ polymerization, which brings a new idea for electrode interface compatibility.