Degradation of Li3V2(PO4)3-based full-cells containing Li4Ti5O12 or Li3.2V0.8Si0.2O4 anodes modeled by charge-discharge cycling simulations

Li3V2(PO4)3 (LVP) has been considered as a promising cathode material for high-power energy-storage devices because of its high ionic conductivity, good stability, and excellent safety profile. However, LVP-cathode-based devices are infamous for a poor cyclability, due to reductive decomposition of the electrolyte at the counterpart anode during cycling; this is induced by small quantities of vanadium ions that leach from the LVP. To overcome this issue, a deeper understanding of the degradation reaction, which is dependent on the anode reaction potential and the states of charge (SOC), is required. In this study, we constructed two types of LVP-based full-cells (Li4Ti5O12 (LTO)//LVP and Li3.2V0.8Si0.2O4 (LVSiO)//LVP) to investigate the effect of the anode reaction potential on the electrolyte decomposition and cycling performance; the former cell contains a high-reaction-potential anode (1.55 V vs. Li/Li+), while the latter contains a low-reaction-potential anode (0.4–1.3 V vs. Li/Li+). The capacity degradation modes of these full-cells were evaluated using simple charge–discharge cycling simulations based on the coulombic efficiency, capacity decay, and degree of lithium-ion pre-doping of the electrode materials. Simulation studies indicate that the degradation of LTO//LVP is due to the low coulombic efficiency without capacity decay at the LTO anode, whereas the degradation of LVSiO//LVP is due to the low coulombic efficiency with capacity decay at the LVSiO anode. The simulated results were fully supported by experimental and electron microscopic observations. Based on these findings, we mitigated the side reactions arising from leached vanadium-ions using lithium pre-doping and a LiBF4 electrolyte, which resulted in an increase in the capacity retention for both types of full-cells to values of 84–98% after 1000 cycles. These insights provide guidance regarding the degradation modes and potential remedies for increasing the performance of a wide range of battery systems and not just LVP-based systems.