Bio-Based epoxy adhesives as alternative for lithium ion battery binders
Batteries represent the most promising electrical energy storage system for many applications. Especially lithium ion batteries grow in their importance for the portable devices and electric mobility field. The individual constituent parts in such batteries are graphite as anode and lithium metal oxide as cathode material. In addition, carbon black and the binder consisting of polyvinylidene fluoride (PVdF) are added. This polymer is quite expensive and needs to be solved in N-methyl-2-pyrrolidone (NMP), a toxic solvent. This requires numerous expensive efforts for safety regulations. In order to improve the carbon footprint and epoxybased binder system based on renewable raw materials will be developed for the application in lithium ion batteries. The properties this binder have to provide are a good adhesion to ensure the contact between electrode material and collector foil, interaction with the electrolyte for ionic conductivity and compatibility with the active materials for electric conductivity. The starting materials of this investigation are two component adhesive binders of modified conventional epoxides and epoxidized plant oils which were tested with hardeners like fatty amines and anhydrides. The bio-content varies from 20 up to 100%. Furthermore, the new epoxy resins are evaluated in terms of mechanical strength and flexibility, compatibility with the electrolyte solution, processibility and adhesion strength for applications in lithium ion batteries.