High capacity Li-ion battery anodes: Impact of crystallite size, surface chemistry and PEG-coating

Battery electrodes are complex mesoscale systems comprised of an active material, conductive agent, current collector, and polymeric binder. Previous work showed that introduction of poly [3-(potassium-4-butanoate) thiophene] (PPBT) as a binder component coupled with a polyethylene glycol (PEG) surface coating on magnetite (Fe3O4) nanoparticles enhanced electron and ion transport in the high capacity anode system. Here, the impact of Fe3O4 crystallite size (10 nm vs. 20 nm) and surface chemistry were explored to evaluate their effects on interfacial interactions within the composite PEG/PPBT based electrodes and resultant battery performance. The Fe3O4 synthesis methods inevitably lead to differences in surface chemistry. For instance, the Fe3O4 particles synthesized using ammonium hydroxide appeared more dispersed, and afforded improved rate capability performance. Notably, chemical interactions between the active nanoparticles and PPBT binder were only seen with particles synthesized using triethylamine. Capacity retention and cycling performance were unaffected. This study provides fundamental insights into the significant impact of active material synthesis on the design and fabrication of composite battery electrodes.