Electrochemical synthesis of a lithium-rich rock-salt-type oxide Li5W2O7 with reversible deintercalation properties.

Starting from the ribbon structure Li2W2O7, the lithium-rich phase Li5W2O7 with an ordered rock-salt-type structure has been synthesized, through a topotactic irreversible reaction, using both electrochemistry and soft chemistry. In contrast to Li2W2O7, the lithium-rich oxide Li5W2O7 shows reversible deintercalation properties of two lithium molecules per formula unit: a stable reversible capacity of 110 mAh/g at 1.70 V is maintained after 10 cycles. The exploration of the lithium mobility in this system shows that Li2W2O7 is a cationic conductor with σ = 4.10(-4) S/cm at 400 °C and Ea = 0.5 eV.