Layered Li-rich vanadium phosphate Li9V3(P2O7)3(PO4)2: cathode and anode materials for lithium-ion batteries

In this paper, we have prepared the carbon-coated Li9V3(P2O7)3(PO4)2 (LVPP/C) composite via a simple carbon thermal reduction and its lithium inserted-extracted mechanism are systematically investigated. LVPP/C cathode can keep a reversible capacity of 100.6 mAhg−1, 98.7% of the initial discharge capacity, after 50 cycles within 2.5 V-4.6 V, while an obviously capacity-fading is observed within 2.5 V-4.8 V. Meanwhile, the LVPP/C anode delivers a well rate capability and, a reversible capacity of 94.5 mAhg−1 (1.0-2.5 V) can still be retained after 60 cycles, ranging from 0.1C to 2C and finally in 0.1C succession. A good preservation of the LVPP structure is observed during the discharge-charge process by in-situ XRD and an intercalation reaction mechanism is also confirmed for LVPP/C anode here for the first time. At last, a novel symmetrical full battery by using LVPP/C as both cathode and anode simultaneously has been successfully assembled. The investigation shows that this symmetrical cell, with an average voltage of 2.5 V, can deliver a reversible capacity of 59.8 mAhg−1 after 30 cycles at 0.1C.