How thermally stable are vanadium cathode Li-ion cells?

Abstract

Vanadium-based cathode materials are promising candidates for next-generation high energy batteries, as they are capable of enabling multi-electron redox reactions to host more than one Li⁺ ion per vanadium atom. This work examined two vanadium cathodes (ζ-V₂O₅ and ε-VOPO₄) with respect to their electrochemical performance and thermal behaviors and compared the results with those of two commercial cathodes, LiFePO₄ (LFP) and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811). The two vanadium materials delivered much higher capacities (∼300 mA h g⁻¹ at C/20) than LFP and NMC811 as expected. They also presented comparable cycling and rate performance. Thermal evaluations on the charged samples in the presence of LP30 electrolyte by ex situ ARC and DSC measurements showed that they are significantly more stable than NMC811 and are comparable with LFP. Much larger heat generation was detected for both vanadium materials during normal charge and discharge through in operando thermal monitoring of the coin cells during cycling, which is ascribed to their complex reaction mechanism and huge polarization between charge and discharge. This did not harm their electrochemical performance and revealed that the increase in heat with cycling is similar to and even better than that of the NMC811 cathode.