Selective sodium(I) capture by olivine FePO4@C electrode in pseudocapacitive deionization: Mechanism and application

For the first time, a carbon coated olivine phase iron phosphate (O-FePO4@C) composite was developed by electrochemical delithiation of olivine phase LiFePO4@C composite as a pseudocapacitive electrode to explore the selective desalting behavior towards Na+, Mg2+, and Ca2+ ions.

Significantly, this work also offered a new strategy for the recycling of waste lithium iron phosphate batteries, which is killing two birds with one stone. Batch experiments reflected both excellent electrosorption capacity (61.3 mg g-1 for Na+) at 1.2 V and good cycling stability of the O-FePO4@C electrode. Cyclic voltammetry (CV) and X-ray diffraction (XRD) combined with density functional theory (DFT) simulation revealed that the electrosorption mechanism of O-FePO4@C is derived from ion intercalation for Na+ and Mg2+, and electrical double layers (EDLs) adsorption for Ca2+, respectively, which exhibited outstandingly selective sodium(I) electrosorption ability.