Electrochemical Intercalation of Li into Heteropoly 12 Molybdophosphoric Acid Ion-exchanged with Cs.

Electrochemical Li intercalation properties in 12-molybdophosphoric and 12-tangstophosphoric acids were investigated. It was found that both 12-molybdophosphoric and 12-tangstophosphoric acids exhibit fairly large capacity for the Li intercalation. Flat potential of 12-tangstophosphoric acids was 0.5V, which could be used for the anode of Li ion battery. 12-molybdophosphoric acid exhibits the flat potential of 1.5 V, although cycle stability is not high. XRD measurement shows the formation of Li2MoO4 after the intercalation of Li. Therefore electrochemical Li intercalation occurs by redox between Mo6+ and Mo4+ and so the theoretical Li intercalation capacity in 12-molybdophosphoric acid is 373mAh/g. Ion-exchanging H+ in 12-molybdophosphoric acid to Cs+ is effective to improve the cycle stability and capacity of ca. 200 mAh/g is sustained after 10 cycles. De-intercalation potential of 4.0V is newly appeared by substitution of Mo in 12-molybdophosphoric acid with V although the capacity is still not large. Therefore, substitution of V is effective for increasing the Li intercalation potential.