Functionalized and Surface Coated Fillers as Innovative Strategies for Realizing Li/Na Metal Solid-State Polymer Batteries

Solid-state batteries using alkali metal anodes are the future for next generation of automotive batteries. The development of Li and Na metal solid-state batteries requires efficient electrolytes to improve the performance of the cells in terms of ionic conductivity, electrochemical stability, interfacial compatibility and last but not the least, the mechanical stability for resilience towards dendrite formation that is a prime inhibiting factor for Li metal batteries.<br/>To realize these targets two innovative approaches will be presented. Firstly, Solid Polymer Electrolytes (SPEs) with new functionalized ethyl cellulose bearing a lithium/sodium fluorosulfonylimide group (Ethyl cellulose-LiFSI/NaFSI) is proposed as quasi single ion (Li⁺/Na⁺) conducting polymer electrolyte for all-solid-state lithium and sodium batteries. The functionalization enables a multifunctional strategy taking up the role of Li/Na salt, improving transference number as well as providing mechanical and electrochemical stability. The complex of Li(FSI-ethyl cellulose)/PEO exhibits a Li-ion transference number of t_Li+ = 0.9, and a Na ion transference number of t_Na+ = 0.6 for Na(FSI-ethyl cellulose),which are much higher than those reported for ambipolar LiFSI or NaFSI/PEO SPEs under the same measurement conditions. The generated SPEs showed a high electrochemical and mechanical stability as well as a practical ionic conductivity value of ~10⁻⁴ Scm⁻¹ at 80 °C. All solid-state lithium, sodium and Li/Sulfur cells cycled with quasi single ion conducting hybrid SPE exhibit reversible cycling and good performance at 70 °C, making them promising, environmentally benign and cost-effective candidates for use in advanced energy storage systems.<br/>In the second approach we have shown the surface modification of Ga-substituted Li₇La₃Zr₂O₁₂ (LLZO) with grafted polymers to be an essential strategy for the preparation of ceramic-rich electrolytes. Ceramic-rich polymer membranes with surface-modified LLZO show marked improvements in the quality of the membranes along with improvement of performance, in terms of electrolyte physical and electrochemical properties, as well as coulombic efficiency, interfacial compatibility, and cyclability of Li metal solid-state cells.