Optimization of LiFePO ₄ nanoparticle suspensions with polyethyleneimine for aqueous processing

Addition of dispersants to aqueous based lithium-ion battery electrode formulations containing LiFePO ₄ is critical to obtaining a stable suspension. The resulting colloidal suspensions enable dramatically improved coating deposition when processing electrodes. This research examines the colloidal chemistry modifications based on polyethyleneimine (PEI) addition and dispersion characterization required to produce high quality electrode formulations and coatings for LiFePO ₄ active cathode material. The isoelectric point, a key parameter in characterizing colloidal dispersion stability, of LiFePO ₄ and super P C45 were determined to be pH = 4.3 and 3.4, respectively. PEI, a cationic surfactant, was found to be an effective dispersant. It is demonstrated that 1.0 wt % and 0.5 wt % PEI were required to stabilize the LiFePO ₄ and super P C45 suspension, respectively. LiFePO ₄ cathode suspensions with 1.5 wt % PEI demonstrated the best dispersibility of all components, as evidenced by viscosity and agglomerate size of the suspensions and elemental distribution within dry cathodes. The addition of PEI significantly improved the LiFePO ₄ performance.