Optimization of Voltage Windows for Lithium- Ion Cells and Vanadium Redox Flow Battery: An Experimental Investigation

The battery parameters and their interdependencies playa vital role in the operation and health of the battery system. However, the existing co-relation of these parameters is not properly defined, often neither quantitatively nor qualitatively. Voltage window, an important parameter to ascertain battery operations, refers to the voltage range in which the battery can safely operate while maintaining its performance. A large voltage window can lead to challenges in voltage regulation - design constraints and power management complexity, efficiency variability, thermal management challenges, component stress, battery degradation, BMS complexity, user experience, and many others. Economic design of battery system involves trade-offs between voltage range, capacity (range of SoC operation), and component requirement. In the current research, a quantitative analysis of voltage variation with SoC for three different Li-ion chemistries and vanadium redox flow batteries is analyzed through experimentation. The variations are compared, and a considerable reduction in voltage regulation is observed when the operating SoC range is optimized. It is found that operating the battery in the range of 5%-95% SoC can result in a reduction of the operating voltage range by 36–83 %, depending on the battery type. Operating the battery in the curtailed SoC range also enhances its efficiency.