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.

中文翻译：

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具有多电子功能的富锂聚阴离子材料，具有高工作电压：用于锂离子电池的Li ₅ V ₂ PO ₄ F ₈

与作为阴极材料的普通氧化物相比，聚阴离子化合物具有相对较低的能量密度。我们首次报道了富锂的氟磷酸盐化合物Li ₅ V ₂ PO ₄ F ₈，该化合物具有高的能量密度，这既来自钒的多电子反应，又来自于氟诱导的高电压。所开发的材料具有新的晶体结构，该结构具有角共享八面体VO ₂ F ₄和四面体PO ₄的坚固的三维框架三维锂离子扩散路径，可以促进锂离子的（脱）嵌入。当利用两个电子时，其理论容量为285 mAh / g。实际上，它在V ³⁺ / V ⁴⁺氧化还原反应中显示出最高的氧化还原电压，约为4.4 V（vs Li / Li +），可逆容量为111 mAh / g。仅在第一次充电时，它才会显示V ⁴⁺ / V ⁵⁺的活性氧化还原反应电压约为4.9 V（vs Li / Li +），充电容量为228 mAh / g。此外，钒不足相在高达2C的充放电速率下均显示出稳定的容量保持率和良好的倍率性能。此处报道的发现富含锂和氟的磷酸盐化合物的发现引入了一种新的阴极材料系列，并且有望进行进一步的探索和优化来释放该系列的全部潜力。