Development of Standardized Battery Pack for Next-Generation PHEVs in Considering the Effect of External Pressure on Lithium-Ion Pouch Cells

The performance and marketability of eco-friendly vehicles highly depend on their high-voltage battery system. Lithium-ion pouch cells have advantages of high energy density and cost-effectiveness than other types of batteries. However, due to their low mechanical stability, their characteristics are strongly influenced by external conditions. Especially, external pressure on pouch cell is a crucial factor for the performance, life cycle, and structural safety of battery pack. Therefore, optimizing pressure level has been a critical consideration in designing battery pack structures for lithium-ion pouch cell. In this work, we developed an optimized structure of the battery module and pack to apply appropriate pressure on pouch cells. They also include a standardization strategy to meet the varied demand in capacity and power for automotive application. The footprint of cell is standardized, and the thickness of cell is varied according to the capacity of a cell which is determined by the number of electrodes and thickness of active materials. The module and pack structures comprise standard and unique parts. The standard parts hold a cell to ensure structural stability and the unique parts are designed to absorb varied thickness of a cell, respectively. We have studied characteristics of cells according to the applied pressure to define optimum point. Thickness changes, evolved pressure, and capacity of a cell have been measured under varying external pressures. Pack level numerical simulations and tests are performed to verify the performance, life cycle, and safety. According to the test results, the developed cell and pack meet the specific requirements. The optimized pressure level has been studied, and the standardization strategy for cell and pack is developed. By adopting the proposed design, it is expected that performance and price compatibility of the battery system can be improved.