Development of Advanced Multifunctional Polymer Binders for Cathode Materials in Lithium-Ion Batteries

Abstract

Reducing costs and improving environmental friendliness for the manufacturing processes of lithium-ion (Li-ion) battery cells are important goals of today's battery research. Presently, the industry standard polyvinylidene fluoride (PVdF) binder – the glue holding the electrode together – requires a toxic solvent, N-methylpyrrolidone (NMP), during the electrode fabrication processes. Since the purchase and proper disposal of NMP contributes about 13% of the total cost for Li-ion battery production, finding a water-soluble replacement for PVdF would be economically beneficial. The purpose of this research is to develop an effective binder material that uses a water-based solvent, so that currently used toxic solvents can be eliminated, reducing cost and increasing environmental friendliness. Lithiated polyacrylic acid (LiPAA), an alternative binder, uses a water-based solvent and has other desirable properties, such as increased adhesion force, increased cycle life, and decreased capacity fade. LiPAA is not currently a feasible binder, however, because cathodes produced using LiPAA are particularly brittle, which causes cracking during the manufacturing process, leading to reduced cycle life. In order to alleviate this undesirable mechanical behavior, LiPAA will be doped with styrene-butadiene rubber (SBR) and sodium alginate (Na-Alg). We hypothesize that adding these materials to LiPAA will provide the electrode with the desirable electrochemical properties of LiPAA, while mitigating cracking. We applied various compositions of LiPAA, Na-Alg, and SBR binders to a LiNi0.5Mn1.5O4 cathode. We assessed the quality of the coating and microstructure using scanning electron microscopy (SEM). We fabricated cathodes with different binders into coin-type Li-ion battery cells to measure electrochemical performance. We examined the effects of binder composition on the physical and electrochemical properties of cathodes in Li-ion batteries. We found that Na-Alg reduces brittle fracture in the cathodes using LiPAA, where SBR exacerbates it. Increasing the Na-Alg content was found to drastically increase the capacity fade experienced in a full cell.