Li2NaV2(PO4)3: A novel composite cathode material with high ratio of rhombohedral phase

A novel composite material Li2NaV2(PO4)3/C is developed by utilizing our latest finding to form less stable rhombohedral Li3V2(PO4)3 directly with partial substitution of Li+ to Na+ ions. In the prepared sample, rhombohedral Li3V2(PO4)3 becomes the dominant phase with a proportion of ∼59%, coexistent with monoclinic Li3V2(PO4)3 (10%) and rhombohedral Na3V2(PO4)3 (31%). High-resolution transmission electron microscopy (HRTEM) reveals that different phases coexist in the same primary particles. This characteristic is different from other cathodes, in which the primary particles are single- or poly-crystals. The prepared composite delivers a discharge capacity of 119.1 mAh g−1, of which 93.6% is centralized around 3.7 V vs. Li/Li+, in good agreement with phase's ratio calculated from refinement. The plateaus of monoclinic Li3V2(PO4)3, appeared at 3.6 and 4.1 V vs. Li/Li+, play an additional role of indicator to warn the end of charge and discharge. This kind of electrode materials are particular suitable to build large batteries to power electric vehicles and shape the grid.

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