Summary The all‐vanadium redox flow battery (VRFB) is emerging as a promising technology for large‐scale energy storage systems due to its scalability and flexibility, high round‐trip efficiency, long durability, and little environmental impact. As the degradation rate of the VRFB components is relatively low, less attention has been paid in terms of VRFB durability in comparison with studies on performance improvement and cost reduction. This paper reviews publications on performance degradation mechanisms and mitigation strategies for VRFBs in an attempt to achieve a systematic understanding of VRFB durability. Durability studies of individual VRFB components, including electrolyte, membrane, electrode, and bipolar plate, are introduced. Various degradation mechanisms at both cell and component levels are examined. Following these, applicable strategies for mitigating degradation of each component are compiled. In addition, this paper summarizes various diagnostic tools to evaluate component degradation, followed by accelerated stress tests and models for aging prediction that can help reduce the duration and cost associated with real lifetime tests. Finally, future research areas on the degradation and accelerated lifetime testing for VRFBs are proposed.

Palladium ͑Pd͒ anode catalyst shows high electrocatalytic oxidation activity under ambient conditions for direct formic acid fuel cell ͑DFAFC͒ operation. However, the highly active Pd is susceptible to significant catalyst poisoning by impurities present in the fuel. In this study, the effect of methyl formate, methanol, and acetic acid impurities on DFAFC performance was investigated. These organic impurities will increase the poisoning rate of the highly active Pd catalyst, resulting in a reduction of fuel cell power output. The impact on performance of various levels of impurities is reported.

Understanding the impact of repeated fast charging of Li-ion batteries, in particular at low temperatures, is critical in view of the worldwide deployment of EV superchargers. In this study, the effects of fast charging using the conventional CCCV protocol on the performances of a high energy cell were investigated. The fast charging capability was confirmed to be negatively affected by low temperatures. The cell was capable of sustaining repeated fast charging at 23 °C without notable performance degradation, but quickly degraded when the charging temperature was decreased. Post-mortem analysis revealed several failure modes, including lithium plating, graphite exfoliation, jelly-roll deformation, active materials crumbling, aluminum corrosion and an abnormal SEI growth on the anode side. A loss of lithium inventory, mainly due to lithium plating and subsequent SEI growth was identified to be the major cause of performance degradation related to repeated fast charging at low temperatures. These results clearly put in evidence that repeated fast charging can cause significant degradations in Li-ion cells, with detrimental consequences in safety, performance and service life. Gaining insights into the failure modes related to repeated fast charging shall guide battery developers towards the optimization of Li-ion cells for EV application.

Redox flow batteries (RFBs) have been studied over the past several decades as a promising candidate for stationary energy storage applications. It is therefore important to understand the reliability of RFBs and the mechanisms that cause degradation with time. Contributions from individual electrodes are difficult to separate especially for long-term cycle testing due to the lack of a stable reference electrode. In our work, the reliability and degradation mechanisms of an all-vanadium RFB were investigated by a stable reference electrode based on the dynamic hydrogen electrode (DHE). The newly developed DHE reference electrode demonstrated high accuracy and long-term stability that enables in situ monitoring of individual electrode signals over hundreds of cycles in a vanadium RFB. This approach enables the full cell degradation to be separated into contributions from the cathode and anode. The cathode and anode were found to play quite different roles in the increase in overpotential of the vanadium RFB during long-term cycling. The anode reaction limited both the charge and discharge capacity over 100 cycles. The negative side also appeared to be the rate limiting factor throughout cycling as determined by EIS measurement. The cathode contributed to the performance degradation as cycling exceeded 50 cycles.

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