An electrode comprising a space group Pna21 VOPO4 lattice, capable of electrochemical insertion and release of alkali metal ions, e.g., sodium ions. The VOPO4 lattice may be formed by solid phase synthesis of KVOPO4, milled with carbon particles to increase conductivity. A method of forming an electrode is provided, comprising milling a mixture of ammonium metavanadate, ammonium phosphate monobasic, and potassium carbonate; heating the milled mixture to a reaction temperature, and holding the reaction temperature until a solid phase synthesis of KVOPO4 occurs; milling the KVOPO4 together with conductive particles to form a conductive mixture of fine particles; and adding binder material to form a conductive cathode. A sodium ion battery is provided having a conductive NaVOPO4 cathode derived by replacement of potassium in KVOPO4, a sodium ion donor anode, and a sodium ion transport electrolyte. The VOPO4, preferably has a volume greater than 90 Å3 per VOPO4.