Design and optimization of electrochemical storage and conversion systems

Climate change concerns have pushed nations and supranational bodies to address the challenge of reducing greenhouse gases emissions, with carbon dioxide, primarily linked to the combustion of fossil fuels, being the most significant target. The envisioned energy transition involves a shift toward energy supply systems based on renewable sources and widespread electrification, in particular of the transportation sector. Within this framework, electrochemical storage and conversion systems play an increasingly crucial role. Demand for stationary long-duration energy storage grows with the penetration of renewable energy sources into the energy mix. In addition, battery adoption is the heart of transportation electrification. Although advances in chemistry have introduced various technologies, some of these, even if promising, have been hindered by delays in engineering development and scaling-up processes. This doctoral thesis, conducted at the Electrochemical Energy Storage and Conversion Laboratory (EESCoLab) of the University of Padua, explores various engineering aspects related to electrochemical storage and conversion systems, in particular vanadium redox flow batteries (VRFBs) and lithium-ion batteries. We investigated mixing phenomena in the electrolyte tanks of VRFBs, showing their impact on the performance of industrial-scale systems. In particular, electrolyte stratification near the tank inlets can affect the state of charge of the electrolyte supplied to the stack, thereby influencing the system's deliverable power. The analysis highlighted how such considerations could lead to an optimized redesign of battery tanks. A 3D computational model of a vanadium flow battery cell was developed and validated using COMSOL Multiphysics. This was employed to investigate the performance of a 50 cm^2 interdigitated flow-by configuration, varying the channels number and width. This configuration was demonstrated to offer superior performance compared to the traditional flow-through design under specific operating conditions corresponding to those of industrial-scale stacks. The research also included studies on lithium-ion batteries. A thermal investigation was conducted on a pack of 20 prismatic lithium titanate oxide (LTO) cells. A 3D COMSOL implemented model of this air cooled module was created, incorporating heat exchange conditions for both active and inactive fan states. Subsequently, a reduced-order model was derived to control the temperature of the hottest cell in battery management system (BMS) applications. The characterization of this model was conducted empirically. In addition, electrothermal characterization and modeling of cylindrical lithium-ion cells for automotive racing applications were studied in collaboration with the Formula SAE student team. Through pulse testing, the electrical equivalent circuit of the cells was characterized, while quasi-steady-state thermal tests identified lumped thermal parameters. Validation tests showed a voltage prediction error of less than 20 mV, while surface temperature prediction was in the range of 0.3°C. Finally, the design, construction, and operation of a hybrid diesel/battery-powered vessel prototype for waste removal in Venice was described. This project, carried out in collaboration with Veritas, involved electrifying all propulsion and onboard service systems (excluding the crane), ensuring efficiency and silence while maintaining the same operational capabilities as Veritas's current fleet. Sea trials showed fuel cost savings of 20 % for routes using the range extender and 36 % for fully electric ones.