Uncovering the Effect of Crystallinity on the Pseudocapacitive Behavior of Li⁺ Storage on Disordered Rock-Salt Vanadium Oxide.

Abstract

Lithium-rich disordered rock-salt (DRS) materials exhibit potential for fast-charging Li-ion batteries and capacitors, primarily arising from their pseudocapacitive Li⁺ charge-storage behavior in a low-potential region (<1.0 V versus Li/Li⁺). This behavior originates from a three-dimensional (3D) Li⁺-percolation diffusion network, a mechanism defined as percolation pseudocapacitance. However, the relationship between the structural characteristics and pseudocapacitive behaviors remains unclear. Here, we design a series of DRS-Li₃V₂O₅ with different degrees of crystallinity through adjusting the crystallization of V₂O₅ precursors. We show that DRS-Li₃V₂O₅ with a lower degree of crystallinity exhibits quasi-rectangular cyclic voltammetry (CV) curves and sloped galvanostatic charge/discharge (GCD) profiles, characteristic of surface redox pseudocapacitance. On the contrary, DRS-Li₃V₂O₅ with a higher degree of crystallinity shows a couple of redox peaks with a small voltage offset observed in CV curves and approximately plateau-like GCD profiles, which are characteristic of intercalation pseudocapacitance. Besides, a lower degree of crystallinity leads to a higher specific capacity at a low rate but a poorer rate capability at a high rate, whereas a higher degree of crystallinity leads to a higher pseudocapacitive contribution and a longer cycling lifespan. We propose that a higher degree of crystallinity can promote the formation of a more integrated percolation network on DRS electrodes, which provides faster 3D Li⁺ transport pathways.