Achieving stable and reliable assembly of flow battery stacks through equivalent mechanical models

Abstract

The transition to a low-carbon society demands energy conversion and storage devices with high efficiency. Redox flow batteries are promising candidates; however, their stacks' energy efficiency (EE) remains constrained, and one of the main reasons is the sub-optimal assembly force. Inadequate assembly force can elevate contact resistance among components, and heighten ohmic losses. Conversely, excessive assembly force can overly compress porous electrodes, reduce effective permeability and notably elevate pumping loss. Both scenarios adversely impact the stack's energy conversion efficiency. Moreover, insufficient assembly force may lead to seal failure and electrolyte leakage, while excessive force can jeopardize the battery's structural integrity and potentially harm internal components. Furthermore, any modifications to the stack size or assembly materials necessitate a complete repetition of this process, further increasing the complexity and resource demands. Despite its critical significance, the systematic investigation of the impacts of assembly force optimization in flow batteries remains largely neglected within existing research. To overcome these challenges, this study develops an equivalent mechanical model for RFB stacks, facilitating the determination of the optimal assembly force during stack assembly. This optimization accounts for electrochemical performance, sealing integrity, and the structural strength of individual components. Results indicated that maintaining the tightening torque within the calculated range ensured the sealing integrity of the RFB stack. Furthermore, the stack achieved a coulombic efficiency of 95% and an EE of 84% during cycling operations at a current density of 100 mA cm⁻². These findings confirm the effectiveness and practicality of the proposed method for achieving precise and reliable assembly of RFB stacks, ensuring that the battery operates stably while maintaining high EE.