Electrochemical Sodium Insertion into the 3D-framework of Na_3M_2(PO_4)_3 (M=Fe, V)

Abstract

Insertion of sodium into phosphates Na_3M_2 (PO_4)_3 (M=Fe, V) were investigated electrochemically to determine the usefulness as the possible cathodes for sodium batteries. The discharge curves show that sodium ion can be accommodated into these hosts. Specific charges of up to 45mAhg^<-1> and 140mAhg^<-1> were obtained for Na/Na_3Fe_2 (PO_4)_3 and Na/Na_3V_2(PO_4)_3 cells with liquid organic electrolytes at room temperature, respectively. Intercalation processes under constant current densities of 0.1mAcm^<-2> were reversible within the range of composition 3.0<x<3.4 for Na_xFe_2 (PO_4)_3 and 1.2<x<3.8 for Na_xV_2 (PO_4)_3.