The global demand for fossil fuels continues to rise, but their supply is finite, and their consumption has led to significant environmental issues, such as greenhouse gas emissions and global warming. To mitigate these effects, transitioning to renewable energy sources is essential. However, one challenge with renewable energy is its intermittent nature, which makes it difficult to provide a stable electricity supply that matches fluctuating demands. Therefore, energy from renewables must be stored efficiently for controlled release into the grid.
Traditional battery technologies like lead-acid and lithium-ion batteries have limitations when it comes to large-scale renewable energy storage. Lead-acid batteries suffer from low energy efficiency and present toxic risks, while lithium-ion batteries, which rely on scarce lithium, underperform during deep discharge cycles. These shortcomings make conventional batteries unsuitable for large-scale applications in renewable energy storage.
Redox flow batteries (RFBs) present a promising solution to these storage issues. They offer high energy efficiency, long cycle life, and low maintenance costs. RFBs also allow for flexibility and scalability due to their unique design, which separates the active materials from the electrochemical cell. This separation enables active substances to be pumped into the cell as needed, depending on energy demands, providing better control over energy management.
Redox Flow Batteries (RFB) come in different types, categorized by the active species they use, the solvent type (either aqueous or nonaqueous), and the physical state of the active materials (liquid, solid, or gas). One of the most recognized types of redox flow batteries is the vanadium redox flow battery (VRFB), which operates using vanadium ions in an electrolyte solution of sulfuric acid. In this system, vanadium ions in different oxidation states facilitate the electrochemical reactions necessary to store and release energy.
VRFBs offer several advantages. Beside the mentioned benefits of RFBs, vanadium ions do not cause contamination when they diffuse across the membrane, and any ion crossover that occurs is naturally corrected during battery operation. VRFBs also exhibit relatively low levels of gas evolution during rapid charge cycles, which enhances efficiency, and the electrolyte can potentially be recycled for use in other applications. Efficiency levels for VRFBs in controlled conditions typically range between 70% and 90%.
However, VRFBs also face challenges. They require precise thermal regulation to maintain an operating temperature between 10 °C and 40 °C to prevent the thermal precipitation of vanadium species, which could compromise performance. The high oxidation potential of V⁵⁺ ions can degrade the ion exchange membranes and the positive electrode. Gas evolution at the electrodes can damage the system and reduce its efficiency, as it depletes the battery's charge and reduces the surface area of the electrodes. Other drawbacks include the high costs of VRFB technology, the limited energy density achievable with the electrolyte, and the potential for degradation due to the sulfuric acid and vanadium ions in the system.
Improving the performance of VRFBs will require advancements in the composition of the electrolyte and the development of more durable materials for membranes, electrodes, and other components. Additionally, reducing resistive and parasitic losses within the battery stack is critical to maintaining high efficiency and ensuring the commercial viability of VRFB technology.
BatCAT (Battery Cell Assembly Twin) contributes to advancements in redox flow battery technologies, including VRFB. The project is aligned with the rigorous study and optimization of VRFBs through advanced modelling and simulation techniques.
Creating a digital twin for battery manufacturing that integrates data-driven and physics-based methods enables BatCAT to refine the design and operation of VRFBs systematically.
Their efforts directly contribute to ensuring that VRFBs can offer the best energy storage solutions, not only in terms of technical efficiency but also by accounting for real-world conditions like resource availability, cost control, and environmental sustainability.
Amirhossein Aghabarari,
BatCAT, NMBU
2024