(Invited) Disordered Rock-Salt Li3+XV2O5: A High-Rate Anode for Lithium-Ion Batteries

Abstract

Rechargeable lithium-ion batteries with high energy density that can be safely charged and discharged at high rates are desirable for electrified transportation and other applications. However, the sub-optimal intercalation potentials of current anodes result in a trade-off between energy density, power and safety. Here we report that disordered rock salt Li3+x V2O5 can be used as a fast-charging anode that can reversibly cycle two lithium ions at an average voltage of about 0.6 volts versus a Li/Li+ reference electrode. The increased potential compared to graphite reduces the likelihood of lithium metal plating if proper charging controls are used, alleviating a major safety concern (short-circuiting related to Li dendrite growth). In addition, a lithium-ion battery with a disordered rock salt Li3V2O5 anode yields a cell voltage much higher than does a battery using a commercial fast-charging lithium titanate anode or other intercalation anode candidates (Li3VO4 and LiV0.5Ti0.5S2). DFT calculations reveal that lithium is displaced from stable octahedral sites to less stable tetrahedral sites, resulting in a suppression of the voltage. The crystal structure is well maintained throughout the process with a maximum volume change of 5.9%. This gives rise to exceptional cycling stability, with negligible capacity decay after 6000 cycles. Further, the material is shown to have exceptional rate capabilities, delivering over 40 per cent of its capacity in 20 seconds. Theoretical calculations unveil unique lithium redistribution mechanisms that are responsible for the high rate capability. At the beginning of Li insertion into Li3V2O5, diffusion of Li takes place by a concerted t-o-t mechanism where tetrahedral Li pushes its neighboring octahedral Li to another tetrahedral sites. At the end of the insertion process, direct tetrahedron to tetrahedron (t-t) diffusion is preferred. Both of these mechanism feature low activation energy values which result in rapid lithium diffusion and exceptional rate capabilities. This low-potential, high-rate intercalation reaction can be used to identify other metal oxide anodes for fast-charging, long-life lithium-ion batteries.