IMPROVING NONUNIFORM UTILIZATION OF LI-ION POUCH CELLS USING TAPERED ELECTRODES THROUGH CALENDERING

Large format lithium-ion pouch cells can have fewer tabs, less packaging material and interconnects, and lower cost but nonuniformmaterial utilization reduces the achievable power and energy densities. The impedance varies across the cell with active material farthest from the tabs having the highest impedance. As a result, these underutilized parts of the cell do not become fully charged or discharged, especially at high current rates, and the energy storage capability of the cell is not fully realized. The current collector thickness can be thickened to increase material utilization, but cost and energy density suffer. In this paper, we propose and simulate linearly tapered electrode coatings to decrease thickness (and increase impedance) in low impedance areas, improving the impedance uniformity and material utilization across the cell. The taper is introduced in the calendering process, by tilting the rollers to change thickness and porosity across the width of the cell. A multiple particle (MP) model is developed and validated in COMSOL to optimize the slope of the taper based on Brute-force algorithm. Higher impedance near the tab balances the higher impedance in the current collector away from the tab. The analysis results show that a 10% linearly tapered positive electrode can improve uniformity by 8 times with 3C charging and increase capacity by 13% with 5C charging.