P-040

Nadežda Traškina

nadezda.traskina@ftmc.lt

Linas Vilčiauskas, Jurgis Pilipavičius

Center for Physical Sciences and Technology (FTMC), Lithuania

EVA-based binder for aqueous composite Na-ion insertion batteries

Aqueous sodium ion batteries with great capacity and cycle life characteristics are a combination of comprehensive cell design, electrolyte chemistry and precisely selected electrode composition. Electrochemical performance of electrodes can be tailored by varying active material, conductive additive and the binding polymer properties as well as the ratio of abovementioned materials. Despite being generally overlooked, a suitable polymeric binder plays a crucial role in the preparation of high-performance electrodes. Currently, most state-of-the-art aqueous battery electrodes are processed using fluorine-containing polyvinylidene fluoride (PVDF). Despite the undeniable advantages such as great mechanical properties oxidation-reduction resistance, this market-dominating binder is associated with a number of safety and environmental red flags. The most concerns arise due to organic solvents such as the highly toxic N-methyl-2-pyrrolidone (NMP) being present in electrode formulations. Moreover, fluorinated carbohydrates, such as PVDF, have been a target of ever-expanding regulations due to their persistence, bioaccumulation and potential health risk. Such compounds are favoured in manufacturing due to their durability and well-functioning properties. However, recently the EU Chemicals Agency (ECHA) published the draft proposal for an EU-wide restriction on their production and uses, starting a much-needed process to restrict these ‘forever chemicals’ found in water, food, homes, and nearly all our bodies. Under the Chemicals Strategy for Sustainability, the European Commission committed to phase out the use of per- and polyfluoroalkyl substances (PFAS), unless their use is essential – a commitment that should be turned into action through the development of this restriction. This, once again, emphasises, that switching to a greener binder alternative is required in order to smoothly transition research advances into production lines. The discovery and development of suitable anode and cathode binding materials appears to be a quiet challenging task as there is an impressive list of requirements for a potential binder. Among the properties that have to be taken into consideration are: solubility in safe solvents and no/minimal swelling after curing, electrochemical stability, moderate flexibility, good binding properties at high solid contents and, in perfect scenario, adhesion to metal substrates in non-aqueous media. One of the potential alternatives to PVDF, ethylene vinyl acetate (EVA), and its aqueous dispersions comply with most of the requirements. Their physical and chemical qualities can be altered by tuning the ratio between two copolymers- ethylene and vinyl acetate. Moreover, crosslinking polymers with suitable crosslinking agents can completely change materials properties, thus, allowing noncomplicated polymers such as polyvinyl acetate to exhibit new qualities, which are so desirable for binders.