“Fast-charging” mechanism of Li3VO4 from the perspective of material science for lithium-ion battery

"Fast-charging" lithium-ion batteries enjoy extensive attention as energy storage devices for portable electronic devices and new energy vehicles. Regrettably, high safety could not be effectively ensured while the batteries undergo fast-charging process. Li3VO4 could be recognized as a high-safety "fast-charging" anode material considering its appropriate Li-insertion voltage and fast kinetic characteristics. Currently, notwithstanding the fact that Li3VO4 has been extensively investigated as an anode material for lithium-ion batteries and the encouraging research results have been accomplished, the distinction between ion diffusion mechanisms during fast-charging and slow-charging has not been well elucidated. Unlike previous reports, Li+ fast/slow diffusion mechanisms in Li3VO4 are investigated in detail in this work. Specifically, Li+ tends to diffuse along path a due to rather fast Li-insertion/deinsertion processes. Correspondingly, Li+ undergoes diffusion along path a and path b during slow-charging. Unlike the conventional view that Li+ prefers to diffuse along path a under all conditions. Additionally, the lattice changes of Li+ insertion into different sites are predicted. The findings could facilitate to comprehend the mechanism of doping, nanosizing, and other modification methods, and the fast-charging issue could be addressed in a targeted way. For instance, the optimal fast diffusion paths are modified at both atomic and lattice scales, inducing that Li+ could be inserted into the lattice of material faster during fast-charging and the power densities could be increased. Accordingly, understanding the fast diffusion mechanism of Li+ in Li3VO4 is crucial to addressing the "fast-charging" of these materials. Unfortunately, the inferior electronic conductivity restricts its Li-storage capacity in "fast-charging" devices. Herein, a Li3VO4 based anode material is prepared thorough a one-step hydrothermal method and liquid-phase dispersion technique in the existence of polyvinyl pyrrolidone, which demonstrates exceptional discharging and charging specific capacities, maintaining 273 mAh g−1 at 0.1 A g−1. It also presents considerably higher "fast-charging" performance even at 1.0–4.0 A g−1. Electrochemical kinetic studies indicate that the thin coating could improve the conductivity of Li3VO4. The Li-insertion sites and diffusion paths during fast-charging and slow-charging processes are predicted computationally. And the in-situ XRD is adopted to insight into the structural changes of composites during Li-insertion/deinsertion processes. The data furnishes a theoretical basis for comprehending the fast lithium storage mechanism of Li3VO4 and offers a new method for searching for "fast-charging" anode materials.