Li3-xNaxV2(PO4)3 (0≤x≤3): Possible anode materials for rechargeable lithium-ion batteries

• Li3-xNaxV2(PO4)3 (0 ≤ x ≤ 3) series are firstly evaluated as anode materials.
• Li3-xNaxV2(PO4)3 anodes show lithium storage activity in 1.0–3.0 V.
• The lithium storage capability of different Li3-xNaxV2(PO4)3 is compared.
• Structural reversibility of Li3-xNaxV2(PO4)3 is studied by in-situ XRD.

In this paper, a series of Li3-xNaxV2(PO4)3 (0 ≤ x ≤ 3) are prepared by a solid state reaction and systematically evaluated as anode materials for lithium-ion batteries. Structural analysis shows that the phase structure of Li3-xNaxV2(PO4)3 changes along with the evolution of Na content. Charge-discharge tests exhibit that Li3V2(PO4)3 shows the highest initial charge specific capacity as high as 88.3 mAh g−1 among all the seven samples, and the reversible capacity is kept at 68.3 mAh g−1 after 45 cycles, corresponding to 77.3% of the initial charge capacity. With increasing of Na content in Li3-xNaxV2(PO4)3, the as-obtained sample show poorer lithium storage capability than Li3V2(PO4)3. As a result, Na3V2(PO4)3 shows the inferior cycling performance than other Li3-xNaxV2(PO4)3. It can only deliver a reversible capacity of 20.9 mAh g−1 after 45 cycles, corresponding to 45.9% of the initial charge capacity. In-situ X-ray diffraction observations demonstrate that the poor electrochemical property of Na3V2(PO4)3 anode is due to the irreversible structural evolution during charge-discharge process. Therefore, reducing the Na3V2(PO4)3 phase in as-obtained sample is a feasible route to improve the lithium storage capability of Li3-xNaxV2(PO4)3.

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