Electrochemical properties of beta-LiVOPO4 prepared by carbothermal reduction

The electroactive lithium vanadyl phosphate phase, beta-LiVOPO4 [Pnma, a=7.446(4) Angstrom, b=6.278(4) Angstrom, and c=7.165 (4) Angstrom] has been synthesized by a two-stage method involving a novel carbothermal reduction (CTR) reaction. The vanadium (V) precursor compound, alpha-VOPO4.xH(2)O was initially precipitated as thin platelets from an aqueous solution containing V2O5 and phosphoric acid. In the subsequent carbothermal reduction step, the anhydrous alpha-VOPO4 was reacted with lithium carbonate and high-surface-area carbon to yield the single-phase beta-LiVOPO4 product. The beta-LiVOPO4 material was characterized using a combination of X-ray diffraction, constant current cycling, and electrochemical voltage spectroscopy. Preliminary electrochemical evaluation determined a reversible specific capacity of up to 135 mAh/g, equivalent to the cycling of x=0.85 in Li1-xVOPO4. The symmetrical nature of the differential capacity data confirmed the energetic reversibility of the insertion reactions, although features consistent with the presence of irreversible cell reactions could also be detected. Constant current cycling at C/20 and C/40 indicated the longer term stability of the lithium insertion reactions evidenced by minimal capacity fade over the first 30 charge-discharge cycles. For certain low-rate lithium-ion applications we believe that the CTR beta-LiVOPO4 material may represent a candidate replacement for the commercially successful cathode active materials LiCoO2 and LiMn2O4. (C) 2004 The Electrochemical Society.