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)-(NH)) in PAM could effectively facilitate the decomposition of LiTFSI due to the strong coordination of C = O/Li+ and NH/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, LiFePO4 (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.