A Modified Water Soluble Binder for Graphite Anode in Li-Ion Battery: Towards a Better Binding Performance

Abstract

In the secondary lithium ion batteries, polymeric binders provide sufficient mechanical strength to the electrodes. The type and amount selection and optimization of the binder may affect the mechanical properties and the electrochemical performance of anodes and may allow significant improvements in the electrochemical capacity, efficiency, charging-discharging rate and cyclic life of battery. Poly(vinylidene difluoride) (PVDF) which is the most widely used binder for Li-ion cells has good electrochemical stability and binding capability but has only solubility in an organic solvent. Poly-methacrylic acid (PMAA) is a water soluble binder which is environmentally friendly has been widely used in industry. However, because of the rigidness of the PMAA polymer, the electrodes go through delamination during production process. We modified the PMAA polymer structure, while maintaining the water solubility, change it to a flexible material. Peel tests show that the graphite laminates using the modified-PMAA material have better binding performance compared to PMAA polymer. Further gain includes improvement of the electrolyte uptake property and improved cell performance for graphite half cells.