Li salt initiated in-situ polymerized solid polymer electrolyte: new insights via in-situ electrochemical impedance spectroscopy

Favorable interface is essential for the implementation of high energy density and high safety solid-state lithium metal battery (SSLMB). The in-situ transformation of electrolyte from liquid to solid-state is of great significance for the compatibility of interface. Herein, an in-situ polymerized glycerin triglycidyl ether (PGTE) solid polymer electrolyte (SPE) featuring excellent ion transfer capability, superior interfacial compatibility and cross-linked structure is developed by the initiation of optimal LiDFOB following cationic catalytic mechanism. Ionic conductivity of 4.16 × 10^-4 S cm⁻¹ is achieved at 60 °C due to the superiority of oxyethylene repeating units (C–C-O/C-O-C), and a discharge capacity of 135.2 mAhg⁻¹ is obtained after 200 cycles at 0.2C for LiFePO₄(LFP)/PGTE/Li battery. More importantly, as a Li salt initiated SPE, the in-situ polymerization process of PGTE is firstly investigated via ex-situ FT-IR, the ring opening catalytic activity of Lewis acid on epoxide is evaluated and the order of LiDFOB＞LiPF₆＞AlCl₃ is revealed. Furthermore, the effect of in-situ prepared SPE on electrode/electrolyte interface is innovatively explored using in-situ electrochemical impedance spectroscopy (EIS). The stable interfacial passivation layer is generated at platform voltage and the maximum value of average diffusion coefficient is also obtained at the plateau.