Operando Structural and Electrochemical Investigation of Li1.5V₃O₈ Nanorods in Li-ion Batteries

We report facile solvothermal synthesis of submicron (sub-micrometer)-sized rod-like Li 1.5 V 3 O 8 crystals using a mixture of ethylene glycol/water as the reacting media. The crystal structure and morphology of the resulting compound were characterized by Rietveld refinement, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and thermal analysis (TG/DTA). Rietveld analysis confirms monoclinic Li 1.5 V 3 O 8 crystals with P 2 1 /m symmetry having a monodispersed ∼5 μm long and ∼500 nm thick rod-like morphology. As the cathode in Li-ion batteries (LIBs), Li 1.5 V 3 O 8 nanorods deliver a reversible discharge capacity of ∼239 mAh g –1 in the voltage window of 2.0–4.0 V (vs Li/Li + ) at a 0.1 C rate after 50 cycles. Li 1.5 V 3 O 8 nanorods retain an impressive discharge capacity of ∼161 mAh g –1 after 250 cycles at a 1 C rate. Operando (in-situ) XRD investigation of Li 1.5 V 3 O 8 during electrochemical (dis)charging confirms the phase transformations from a Li-poor α-phase (Li 1 ) via a Li-rich α-phase (Li 2.5 ) to a β-phase (Li 4 ). Low-temperature performance evaluation of the Li 1.5 V 3 O 8 cathode exhibits less than 50% of the discharge capacity achieved at 25 °C. Evaluation of dis(charge) behavior over different temperatures suggests that charge transfer resistance ( R ct ) plays a crucial role in determining Li-ion diffusivity vis-à-vis specific capacity at low-temperature.