Poly (ethylene oxide) based solid polymer electrolyte improved by multifunctional additives of poly (acrylamide) and LiI

Solid polymer electrolyte (SPE) as core component of all-solid-state lithium metal battery (ASSLMB) has regained tremendous concerns due to its good flexibility and low cost. However, low ionic conductivity , unstable interphase and unsatisfying cycling stability hinder its practical application in ASSLMB. Herein, we designed a PEO-based SPE (PEO/20PAM/LiI) via adding optimum content of poly (acrylamide) (PAM) and 2 wt% LiI to address above issues. The amide groups (-(C = O)-(N H)) in PAM could effectively facilitate the decomposition of LiTFSI due to the strong coordination of C = O/Li + and N H/TFSI − , significantly releasing more “Free Li + ”. The C = O group also weakens the coordination of Li + /ether oxygen and assists Li + transfer along the PEO chains, providing an efficient transmission pathway for Li + . Furthermore, LiI could facilitate the uniform Li + deposition at the electrode-electrolyte interface and stimulate the formation of stable interfacial layer, restraining the generation of lithium dendrites . The obtained PEO/20PAM/LiI exhibits high ionic conductivity (2.75 × 10 −4 S cm −1 , 35 °C), outstanding mechanical strength (0.55 MPa) and wide electrochemical window (∼ 5 V). The assembled Li symmetric battery could endure high critical current density (CCD, 1.8 mA cm −2 ) and perform Li plating/stripping steadily over 1600 h at 0.1 mA cm −2 at 35 °C. Meanwhile, LiFePO 4 (LFP)/Li ASSLMB with this SPE displays preeminent cycling stability over 250 cycles with high capacity retention (97.3%) and high coulombic efficiency (99.9%) at 0.3 C at 35 °C. This rational design strategy shows great potential in simultaneously realizing high ionic conductivity and good interfacial stability for ASSLMB.