| Popis: |
Efficient and effective energy storage technologies are a key element of digital power networks. Batteries offer versatile capabilities, and flow batteries are well suited to large-scale applications due to inherent technical advantages. Their efficiency, capacity and power density, however, is hindered by mass transport limitations. Availability of reactants must be maintained to reduce parasitic overpotentials and maximise electrolyte utilisation. This is a coupled mechanical-electrochemical problem as pressure differentials and associated losses from pumping power must also be considered. This thesis optimises flow battery system performance using computer aided design of cell architecture innovations. Flow-through vanadium redox flow battery cells charging at high state of charge were simulated in COMSOL with two- and three-dimensional multiphysics models developed and validated against published data. Trapezoidal and annular sector shapes, where cell width is reduced towards the outlet, were compared to conventional rectangular geometry. These shapes were employed to increase electrolyte velocity from inlet to outlet, thus improving the delivery of active species as reactants are depleted. The radial design raised the minimum reactant concentration in the cell by 66%, and improved flow uniformity when compared to the trapezoidal design, at the cost of an increased pressure differential. Wedge-shaped cell designs, where the thickness is reduced instead of the width, were then simulated with variable porous electrode compression. Results showed 1% improvement to operating cell voltage. Laboratory experiments demonstrated a 15% higher energy efficiency and extended usable capacity with no parasitic pressure drop increase using this design. Static mixers were then used to address concentration gradients. The redistributing of reactants within the flow frame showed a 60% improvement in minimum V3+ concentration and a corresponding 1% cell voltage improvement by reducing concentration overpotentials. This innovation was then combined with a wedge-shaped cell to take advantage of variable compression with higher flow rate mixed electrolyte at the outlet. Results showed a 2% voltage improvement by addressing concentration overpotential associated with mass transport limitations. This was achieved with a lower pressure drop, demonstrating how mechanical design can optimise flow-through battery cells to reduce losses from pump energy while increasing the availability of active species where required. |
