Cheap and Easily Processable Polymer Electrolytes for Sodium-based Batteries

The life style of modern civilization is strongly dependent on the use of portable devices, which necessarily require safe and very efficient storage and conversion energy systems. Nowadays, Li-ion batteries (LiBs) represent the most widely used technology in this respect. One of the arduous challenges in this field is the substitution of conventional liquid electrolytes based on organic solvents, which are volatile and hazardous. Solid polymer electrolytes (SPEs) exhibit appealing properties to replace liquid electrolytes. Moreover, research efforts are directed towards alternative systems to LIBs, because lithium is expensive and its resources are geographically constrained. Sodium exhibits suitable electrochemical properties, close to those of lithium, and it is very abundant. These features make Na-based batteries proficient candidates to replace LiBs, particularly when large-scale energy storage is envisaged. Here, we offer an overview of our recent developments on polymer electrolytes for Na-ion batteries. Polymer electrolytes were prepared through different techniques, exploiting both UV-curing and simple casting and various additives to improve specific characteristics (e.g., RTILs, cellulose derivatives, glymes). All samples were thoroughly characterized in the physico-chemical and electrochemical viewpoint. They exhibited excellent ionic conductivity and wide electrochemical stability window, which ensure safe operation at ambient conditions. Electrochemical performances in lab-scale devices are presented, evaluated by means of cycling voltammetry and galvanostatic charge/discharge cycling exploiting different electrode materials (prepared by water-based procedures with green cellulosic binders). Work on Na-ion polymer batteries for moderate temperature application is at an early stage, only lab-scale cells were demonstrated so far. Nevertheless, with the appropriate choice and optimization of electrode/electrolyte materials (and successful combination thereof), the intriguing characteristics of the newly developed SPEs here presented postulates the possibility of their effective implementation in safe, durable and high energy density secondary Na-based polymer devices conceived for green-grid storage and operating at ambient temperatures.