Redox flow battery liquid electrolyte flows

Based on the occurrence of phase transition, redox flow batteries can be classified as a true system or a hybrid system. In a true system, active species dissolve in the electrolytes all the time, and no second phase other than liquid is formed on the electrode. For a hybrid system, at least one kind of active species is insoluble solid or gas. In the next chapter, we will introduce different types of redox flow batteries using this method. 

Zhang DP, Liu QH, Shi XS, Li YD. Tetrabutylammonium hexafluorophosphate and l-ethyl-3-methyl imidazohum hexafluorophosphate ionic liquids as supporting electrolytes for non-aqueous vanadium redox flow batteries. J Power Sources 2012 203 201-5. 

In redox flow batteries, the chemical compounds responsible for energy storage are liquid and remain in solution in the electrolyte. This mode of operation enables us to circumvent the limitation of conventional electrochemical batteries wherein electrochemical reactions create solid compounds which are stored directly in the electrodes where they are formed. The mass that it is possible to accumulate locally is therefore necessarily limited by the volume and mass of the electrodes, which sets a maximum capacity. 

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