Multielectron-capable Li-rich polyanion material with high operating voltage: Li5V2PO4F8 for Li-ion batteries
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Date
2019-12-13
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Publisher
American Chemical Society
Abstract
Polyanion compounds have relatively low energy density compared to plain oxides as cathode materials. We for the first time report on a Li-rich fluorophosphate compound, Li5V2PO4F8, that can have high energy density originating from both the multielectron reaction of vanadium and high voltage induced by a fluorine. The developed material has a new crystal structure that has a robust three-dimensional framework of corner-sharing octahedra VO2F4 with tetrahedra PO4 and three-dimensional lithium ion diffusion pathways, which can facilitate the (de)intercalation of lithium ions. Its theoretical capacity is 285 mAh/g when two electrons are exploited. Practically, it shows the highest redox voltage, ∼4.4 V (vs Li/Li+), among V3+/V4+ redox reactions, with 111 mAh/g of reversible capacity. Only in the first charge does it show an active redox reaction of the V4+/V5+ at ∼4.9 V (vs Li/Li+) with 228 mAh/g of charge capacity. Moreover, the vanadium-deficient phase shows stable capacity retention and good rate capability at both charging and discharging rates up to the 2C rate. The discovery of the lithium- and fluorine-rich phosphate compounds reported here introduces a new family of cathode materials, and further exploration and optimization can be expected to unlock the full potential of this family. © 2019 American Chemical Society
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Keywords
Crystal structure, Vanadium, Lithium, Redox reactions, Radioisotope batteries, Oxides
Citation
Kim, M., Avdeev, M., & Kang, B. (2019). Multielectron-capable Li-rich polyanion material with high operating voltage: Li5V2PO4F8 for Li-ion batteries. ACS Energy Letters, 5(2), 403-410. doi:10.1021/acsenergylett.9b02451