Introduction
As lithium-ion batteries age, their thickness evolves due to internal changes, such as gas generation. These changes arise from cycling stress and aging mechanisms like SEI (solid electrolyte interphase) growth, variations in the porosity of active materials, and lithium plating. The result is volume expansion, which can be measured by observing strain or swelling forces, especially in pouch and prismatic cells.
Properly managing these forces during the design phase is essential to ensure optimal performance, safety, and longevity. TWAICE’s swelling force simulation models address these challenges with precision, offering manufacturers a new lens to optimize battery systems.
What Causes Swelling Force?
Battery cells experience volume changes as a result of:
SEI growth: A necessary protective layer that continues to form throughout the cell's lifecycle.
Active material porosity changes: Alterations in the structure of the electrodes.
Lithium plating: A harmful process where lithium deposits on the anode during charging.
Pouch and prismatic cells, in particular, are designed to operate under a defined pressure, ensuring maximum power output and extended cycle life, especially during the early stages of their lifecycle. Without precise monitoring and management, these forces can lead to accelerated degradation and safety risks.
Finding the Optimal Pressure in Battery Design
Understanding the forces acting within a battery module is critical for balancing performance and aging effects. This is especially relevant for pouch cells, where pressure plays a defining role in determining longevity.
Excessive Pressure: Applying too much pressure can compress the internal components too tightly, accelerating degradation. This can damage the module framing and lead to issues such as lithium plating or internal short circuits caused by high local electrical field strengths.
Insufficient Pressure: Too little pressure allows the cell volume to expand freely, creating excessive space within the module. This flexibility can result in premature aging and reduced performance.
Finding the optimal pressure requires proper stacking within the module, in alignment with manufacturer recommendations. While optimal pressure cannot eliminate swelling, it significantly mitigates its adverse effects over the cell’s lifetime.
Modeling Swelling Force with TWAICE
To address these challenges, TWAICE has developed advanced methods to model and monitor swelling force. During testing, specific pressure is applied using tabs equipped with force sensors placed between the cell and the tabs. These sensors measure the evolution of the cell's thickness over time under various simulated conditions, including different depths of discharge (DoD), varying temperatures, and diverse charging protocols. This approach enables simultaneous monitoring of capacity loss, resistance increase, and pressure evolution, offering comprehensive insights into the cell's mechanical and electrochemical behavior.
With TWAICE’s swelling force modeling capabilities, customers can:
Analyze thickness evolution under different operational conditions.
Determine the optimal pressure required to minimize aging.
Gain deeper insights into how external forces impact the aging process.
Additionally, upon request, we provide and integrate force or strain sensors into test setups, further enhancing the accuracy of the simulations. The data from these sensors is seamlessly integrated into TWAICE’s fitting pipeline, delivering outputs that illustrate the evolution of clamping force or strain over cycles as a function of stress factors.
Conclusion
Swelling force is a critical yet often overlooked aspect of lithium-ion battery design. TWAICE’s pioneering approach to swelling force modeling empower manufacturers to improve long-term performance while mitigating risks and enhance reliability.
Discover how TWAICE’s cutting-edge simulation models can transform your battery development process. Contact us today for a demo or consultation.