Novel cellulose-based composite polymer electrolytes for green, efficient and durable Na-ion batteries

The mobile world depends on lithium-ion batteries – the ultimate rechargeable energy store at present. Modern Li-ion batteries hold more than twice as much energy by weight as the first commercial versions sold by Sony in 1991 - and are ten times cheaper. But they are nearing their limit. As the world's lightest metal, lithium provides a huge weight advantage. But some researchers argue that the next generation of secondary batteries should switch to heavier elements such as sodium. Resulting energy storage systems could never fit in a car, and cannot beat Li-ion on measures such as energy stored per unit weight. But when it comes to storing energy for the electricity grid - or other non-portable applications - size does not matter. Instead of a small, light battery that packs a powerful punch, what people need is a battery that cheaply bottles and releases small-to-large amounts of electricity without much maintenance. In this work, innovative biocomposite quasi-solid polymer electrolytes specifically conceived and developed for Na-ion secondary cell, based on mixture of polyethylene oxide (PEO) and carboxymethyl cellulose (CMC) or, eventually, nanoscale microfibrillated cellulose fibres (NFCs) and containing supporting sodium salt are prepared. This is the first ever report where the useful aspects of bio-derived Na-conducting electrolyte components are unravelled and required parameters are thoroughly investigated. Moreover, the performances of lab scale quasi-solid devices are presented, evaluated by means of cycling voltammetry and galvanostatic charge/discharge cycling. We also present the preliminary durability tests of the devices inherited by different PEO vs. CMC or NFC ratios, as well as the cell response upon various temperatures and current ranges. So far, work on Na-ion polymer batteries for moderate temperature application is at an early stage, only small battery cells in the lab are demonstrated, nevertheless with the appropriate choice and development of materials to be used for the electrodes as well as the electrolyte, low-cost and long-life Na ion polymer batteries would be promising for applications in next-generation of large-scale energy storage system in the near term.