Crosslinked ionogels containing inorganic additives for safer lithium metal batteries

Lithium-ion batteries (LIBs) are a well-exploited technology for electrochemical energy storage since the 90s. Unfortunately, LIBs are expected to reach in the next future their theoretical limits in terms of gravimetric and volumetric energy density. Gel polymer electrolytes (GPEs) consisting of a polymer matrix, a lithium salt and a plasticizer are promising electrolytes to increase the energy density and cell safety of lithium metal batteries. Conventional plasticizers utilized are flammable, toxic and unstable at high potential, therefore limiting the use of high-potential cathodes. Ionic liquids (ILs), which are low melting point salts, can be added to polymer matrices to form ionogels (IGs). Compared to conventional plasticizers, ILs own negligible vapour pressure, non-flammability, high thermal and chemical stability and wide electrochemical stability (ESW). However, high Li+ mobility and rate performance are still a challenge due to their high viscosities and transport number, not comparable to conventional electrolytes. In the meantime, Aluminium oxide (Al2O3) is capable to interact with anions through acidic surface groups and should boost Li+ mobility. In this framework, IGs were developed incorporating ILs and Al2O3 nanoparticles upon free radical polymerization in a one-pot preparation method. The polymer backbone was prepared by the thermal reticulation of butyl methacrylate (BMA) with polyethylene glycol diacrylate (PEGDA) as a crosslinking agent. The produced IGs were self-standing with interesting ionic conductivity (10-3 - 10-4 S cm-1 at room temperature) and wide electrochemical stability window (5 - 5.2 V vs. Li+/Li). Testing cells were assembled with lithium metal anode and LFP cathode to evaluate electrochemical performances and safety during galvanostatic cycling under different C-rates. Developed IGs enabled to reach a specific capacity of 120 mAh g-1 at room temperature.