Biobased polymer electrolytes for sustainable potassium batteries

Rechargeable batteries are a key technology in the world rush toward the energy transition. Li-ion batteries (LIBs) have reached unprecedent targets of performance and safety, nevertheless it is not logical to think that the LIB technology only is able to bear the world electrification, given the lithium scarcity (0.0017 wt% in the Earth crust) and its uneven distribution. It is therefore not surprising the increasing attention coming from the research community on potassium-based batteries. Potassium is abundant on Earth (2.09 wt%), evenly distributed, characterized by a very low standard equilibrium potential (-2.93 V vs. SHE with respect to -3.09 V vs. SHE of Li+/Li) and Lewis acidity (smaller solvated ions and thus faster conduction) [2]. K-ion batteries (KIBs) already proved to have all the requirements for large stationary storage systems. In this scenario and keeping in mind the sustainability of this technology, our groups work on the design, synthesis and characterization of fully biobased polymers for KIB electrolytes. In this contribution two gel polymer electrolytes are proposed. Primary, the first biosorced electrolyte successfully used in a KIB system is a lignin-based membrane resulted by crosslinking of pre-oxidized Kraft lignin matrix with PEGDGE [1]. Once the membrane is activated by soaking liquid electrolyte, the as obtained gel polymer electrolyte has been fully characterized showing suitable ionic conductivity exceeding 10-3 S cm-1, excellent chemical compatibility and tremendous ability at suppressing the growth of metal dendrites. The second electrolyte proposed for potential potassium-based application was crosslinked via ring-opening reaction of a cardanol-epoxidized resin with a cyclic succinic anhydride as curing agents. The samples showed excellent mechanical and thermal stability, a high electrolyte uptake ability, impressive electrochemical stability and outstanding ionic conductivities (up to 10-2 S cm-1).