Polymer Electrolytes for Green, Safe and Robust All-Solid Na-ion Batteries

The modern life style that we are enjoying depends on energy storage systems in which the role of Li-ion batteries (LiBs) is peerless. However, state-of-the-art LiBs are approaching the verge of possible technological imagination, particularly in terms of energy density. Some researchers argue that next-gen secondary batteries should switch to heavier elements such as sodium. Indeed, when it comes to gigantic energy storage systems for the electricity grid and/or other non-portable applications where size does not matter, Na-based systems can be an effective and intelligent choice. Nevertheless, research on NiBs’ components is at the very beginning, particularly for what concerns the electrolyte, where standard organic liquid electrolytes are mainly used. Unfortunately, their flammable nature jeopardizes the safety of these large scale systems, which in case of failure may lead to thermal runaways. In this work, an overview is provided on quasi-solid polymer electrolytes specifically conceived and developed for Na-ion secondary cells, based on polyethylene oxide (PEO), acrylates/methacrylates and/or mixtures thereof. Eventually, pyranose ring based natural additives and/or low volatile plasticizers are added along with supporting sodium salts to improve specifically defined characteristics. All the sample are thoroughly characterized in the physic-chemical and electrochemical viewpoint. The performances in lab scale devices are presented, evaluated by means of cycling voltammetry and galvanostatic charge/discharge cycling exploiting different electrode materials (prepred by water-based procedures exploiting carboxymethylcellulose as binder). We also present preliminary aging resistance tests of the devices inherited by different solid electrolytes, as well as the cell response upon various temperatures and current regimes. So far, work on Na-ion polymer batteries for moderate temperature application is at an early stage, only lab-scale small battery cells are demonstrated. Nevertheless, with the appropriate choice and development of electrode/electrolyte materials, the overall characteristics of the SPEs here developed 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 and/or sub-ambient temperatures.