Optimization of multicomponent aqueous suspensions of lithium iron phosphate (LiFePO₄) nanoparticles and carbon black for lithium-ion battery cathodes

Addition of polyethyleneimine (PEI) to aqueous LiFePO₄ nanoparticle suspensions improves stability and reduces agglomerate size, which is beneficial to lithium-ion battery cathode manufacturing. This research examines the effect of both PEI concentration and molecular weight (MW) on dispersing LiFePO₄ and Super P C45 in multicomponent aqueous suspensions. It is demonstrated that the optimal conditions for obtaining stable suspensions with minimal agglomerate size are 1.5wt% PEI with MW=2000gmol^-1 and 5.0wt% PEI with MW=10,000gmol^-1 for LiFePO₄ and Super P C45, respectively. The mixing sequence also affects rheological properties of these suspensions. It is found that dispersing the LiFePO₄ and Super P C45 separately yielded suspensions with superior properties (Newtonian rheological behavior, smaller agglomerate size, improved settling, etc.). In particular, dispersing the LiFePO₄ prior to the Super P C45 when making the final multicomponent suspension is found to be beneficial, which was evidenced by higher half-cell discharge capacity.