Innovative And Functional Materials For Green And Safe Large-Scale Li/Na-based 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 safe polymer electrolytes and high energy electrodes as well as novel production process thereof. 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 their mixtures. 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, due to the versatile nature of free radical photo-polymerisation multiphase electrode-electrolyte composites are produced [3]. In this process, an appropriate liquid reactive mixture comprising monomers, salts and eventually additives, which constitutes the polymer electrolyte precursor, is drawn into a thin film over the electrode material. Therefore, the liquid reactive mixture can penetrate into the electrode voids to achieve an intimate contact between the electrode/electrolyte surfaces, during film formation. It is then in-situ polymerised to form, in a single step, a self-standing electrode intimately connected to the Li+/Na+-ion conducting electrolyte membrane, with an efficient interpenetration of the two surfaces. By this one-pot process, we are able to optimize the interfacial properties between nanostructured electrodes and polymer electrolytes, thus obtaining high performing electrochemical cells. Lab-scale Li/Na-ion polymer cells are assembled with different nanostructured electrode materials (e.g., LiFePO4, TiO2 nanotubes, Ga2O3 nanorods and graphene-wrapped mixed transition metal oxides) and tested for their long-term cycling ability and rate capability, demonstrating that safe, durable and high energy density devices conceived for green-grid storage and operating at ambient and/or sub-ambient temperatures can be a reality in the near future.