Innovative and functional materials for green and safe Na-ion large-scale energy storage

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 in energy density. Some researchers argue that next-gen secondary batteries should switch to heavier elements such as Na. 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-ion batteries (NiB) can be an intelligent choice. Nevertheless, research on NiBs' components is at the very beginning, and it is necessary to develop novel types of materials, both novel high energy electrodes and stable and safe polymer electrolytes. In this work, an overview is provided on both truly solid and 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. Both standard casting and smart photopolymerization techniques have been explored. Moreover, the most recent results regarding novel nanostructured negative electrodes, comprising TiO2 nanotubes, Ga2O3 nanorods and graphene-supported metal oxides will be presented. 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. The results about Ga2O3 nanorods and TiO2 nanotubes, along with the appropriate choice and development of novel polymer electrolytes, demonstrate that 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 can be a reality in the near futur