Micro- and Nanocrystalline Inverse Spinel LiCoVO₄ for Intercalation Pseudocapacitive Li⁺ Storage with Ultrahigh Energy Density and Long-Term Cycling

Intercalation pseudocapacitance has been recognized as a new type of charge storage mechanism in crystalline metal oxides, wherein Li⁺ intercalation is not limited to surface structures, instead extended to the bulk crystalline framework of the material. This may possibly narrow the performance gap between pseudocapacitors and batteries. Hitherto, very few crystalline materials have been found to exhibit such an intrinsic capacitive property. Here, we report for the first time that the inverse spinel LiCoVO₄ exhibits intercalation pseudocapacitive Li⁺ storage property in aqueous electrolyte. Micro- and nanocrystalline LiCoVO₄ were synthesized via conventional solid-state reaction and hydrothermal reaction followed by calcination, respectively. In particular, nanocrystalline LiCoVO₄ demonstrated better Li⁺ intercalation benefited from its small crystallite size with highly exposed Li⁺ selective crystallographic pathways toward electrolyte. The LiCoVO₄ nanocrystals demonstrated excellent capacitive performance, including high specific capacitance (929.58 F g^–1 at 1 A g^–1) and cycling stability. Moreover, asymmetric hybrid cells were assembled using nanocrystalline LiCoVO₄ and MWCNT as the positive and negative electrode, respectively. The hybrid cells exhibited an unprecedented energy density (148.75 Wh kg^–1 at a power density of 264.6 W kg^–1) and superior cycling stability (94% capacitance retention after 5000 cycles).