Improvement of the electrochemical properties of Li-ion batteries based on a holistic binder concept for aqueous electrode slurries

Lithium-ion batteries show great potential for applications as stationary energy storage devices and/or in electric vehicles. A secondary lithium-ion battery essentially consists of four components: two electrodes, an electrolyte and a separator. The electrodes provide the structure in which the lithium ions can be stored. To produce electrodes, the starting materials are first mixed together and processed into a homogeneous paste, known as a slurry. This contains active material and non-electroactive additives - carbon to improve conductivity and polymers as thickeners, dispersants and binders. Despite the enormous research activities in the field of Li-ion batteries, the actual contribution of these polymers to cell performance is still unclear.

Based on systematic investigations into the flow behavior of the pastes, the adhesion and cohesion of the dried layers, as well as their electrochemical properties, this research project aims to develop a binder concept that provides electrode layers with good electrochemical properties, high cycle stability and long battery life. In view of the ecological requirements of modern lithium-ion batteries, the electrode slurries are formulated as aqueous suspensions containing established active materials and a combination of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as polymer additives.  In addition, an innovative coating concept will be developed based on the application of two layers with different mechanical and microstructural properties in order to achieve high adhesion and cohesion with a reduced polymer concentration. One focus will be on investigating the influence of the polymers on the cycle life of the cells. In addition to the established graphite anodes, new concepts with graphite/silicon mixtures as the active material will also be investigated with regard to suitable polymer additives.