Improving the electrochemical performance of lithium metal batteries with hollow shell microspheres and polypyrrole vapor phase-coated LiV₃O₈ cathodes

New hollow shell structured lithium trivanadate (LiV₃O₈) microspheres were synthesized by a spray drying method, and the effect of a vapor-phase-polypyrrole coating on the surface of this active material was studied. A thin and uniform coating layer could form by a simple vapor-phase-polymerization (VPP) method. The polypyrrole coating layer not only compensates for the low conductivity of the active material but also prevents its direct contact with the electrolyte and reduces vanadium dissolution. The LiV₃O₈ morphology and presence of the coating layer were confirmed using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The electrochemical performance was analyzed using a battery testing system and impedance spectroscopy. The cycle performance of the Li-powder/polypyrrole-VPP-coated hollow shell LiV₃O₈ cell showed a higher capacity and greater capacity retention (LiV₃O₈: 160.80 mA h g⁻¹, 62.31%; coated LiV₃O₈: 206.55 mA h g⁻¹, 82.02%) in the range of 1.8–4.0 V at a 0.2 C-rate, even after 200 cycles. The rate capability at various current densities was also high. Further, it had a low charge transfer resistance, which remained low even after many cycles. Thus, the combined effect of hollow-shell-structure and polypyrrole-VPP coating, led LiV₃O₈ to its improved electrochemical performance.