Influence of Metal Impurities or Additives in the Electrolyte of a Vanadium Redox Flow Battery

As one of the most attractive large-capacity energy storage systems, vanadium redox flow batteries have many advantages such as a rapid response, long service life, environment-friendliness, and non-flammability. However, the high cost of the vanadium electrolyte has hindered the broad market penetration. The price of the vanadium electrolyte can be significantly reduced if a cost-competitive technology for producing the electrolyte from recycled V 2 O 5 may be used. Accordingly, the effects of the impurities in the recycled V 2 O 5 on the performance of vanadium redox flow batteries (VRFBs) must be understood. However, there have been very few published studies on the effects of these electrolyte impurities. In order to establish a reliable electrolyte specification for VRFB developers, we analyzed the influence of a wide range of potential metal impurities or additives on the electrochemical activity, diffusion of vanadium ions, and battery performance of these systems. The investigated impurities include Li + , Na + , K + , Mg 2+ , Cr 3+ , Mn 2+ , Fe 2+ /F 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , and Mo 6+ ions. Most of the metal ions affected the V 2+ /V 3+ redox reaction rather than the VO 2+ /VO 2 + redox reaction. On the basis of our findings, we suggest detailed specifications that may be used to manage the quality of the vanadium electrolyte.