Due to fluctuation in power produced by renewable energy sources such as wind and solar power, energy storage devices are in-separable component of the renewable energy power plant. Energy storage devices like rechargeable batteries stores the surplus amount of the energy produced by renewables and delivers back to the grid when in demand.  However, most battery technologies suffer from limited cyclability, poor scalability in terms of power and energy especially when power modules of several hundred kilowatt and energy on a scale of MW-h to GW-h are needed.

Vanadium redox flow batteries (VRFB) are attractive in this respect as it employs highly stable and durable liquid electrolyte for generating the power. This allows scaling up the batteries independently of nominal power and energy storage capacity. When higher power is required, the area of the electrode can be increased and when higher energy storage capacity is required, the amount of the liquid electrolyte can be increased. 

VRFB uses vanadium species (V²⁺, V³⁺, V⁴⁺ and V⁵⁺) dissolved in an electrolyte. Because of the limited solubility of V⁵⁺ species in the catholyte, presently the volumetric energy density of the electrolyte is limited. Addition of specific additives into the electrolyte improves the V⁵⁺solubilty. Albeit this comes with a disadvantage of possible side reactions lowering the electrochemical efficiency. These side reactions strongly depend on the additive concentration, temperature and state of charge (V⁵⁺ concentration).

The rate of side reactions with respect to V⁵⁺ and additive concentration is up to now not well studied in literature. In this Master thesis work, experiments will give an insight for optimal electrolyte formulation which is crucial for large scale VRFB batteries. Mainly two types of experiments are carried out at various formulations of additives in the electrolyte. Firstly, the solubility of vanadium species (mainly V⁵⁺) as function of temperature and additive concentration will be investigated. Second, at optimal formulations of electrolyte the VRFB electrochemical performance will be evaluated at lab bench scale.