Green Fabrication of Amorphous FePO4/Carbon Nanotube Electrodes via Electrophoretic Deposition for Sodium-Ion Batteries

The conventional fabrication of electrodes for sodium-ion batteries (SIB) involves mixing of the active material with additives and tape-casting on metallic current collectors. Herein, an electrophoretic deposition (EPD) method has been developed to fabricate composite electrodes without using volatile and toxic solvents as well as binders. The approach is based on the EPD of amorphous FePO4 and multiwall carbon nanotube (MWCNT) from aqueous suspensions. The fabrication of FePO4 suspensions containing MWCNT and the controlled co-deposition of both materials are pivotal for the EPD of composites. Multiple dispersants with different properties are investigated as the charging, dispersing, and film-forming agents. The deposition yield of EPD films is measured under various conditions. The atomic force microscopy analysis, engaged with thermogravimetric tests, provides evidence for the formation of adhesive and conductive FePO4/MWCNT films. The dispersant concentration is optimized in order to achieve high capacity. The composite electrode, prepared by EPD, delivers a discharge capacity of 142.2 mA h g–1 at a current of 10 mA g–1. Another important finding is the possibility to fabricate full-cell SIBs, containing presodiated hard carbon as the anode and a deposited FePO4/MWCNT cathode. The deposited films show adequate capacitance retention as the charge–discharge current increased and stable cycling performance.