Influence of geometrical manufacturing tolerances on lithium-ion battery performance

The manufacture of lithium-ion battery cells consists of multiple production processes, all of which have tolerances that can affect cell performance. For battery packs that contain 100s or 1000s of individual cells, ensuring consistency and minimising variation between cells is important for reliability and lifetime. This study uses a numerical battery model to examine the influence of electrode coating thickness, calendering and electrode cutting tolerance on capacity, energy, resistance and voltage relaxation. Results show that electrode cutting tolerance has the largest affect upon cell performance characteristics, with calendering tolerance predominantly affecting the voltage relaxation period. For the simulated cell, the negative electrode coating tolerance mainly affects the cell capacity and energy, whereas the positive electrode coating tolerance has the most significant effect upon voltage relaxation. Multiple simulations were conducted with random tolerances of a Gaussian distribution applied to all processes simultaneously to represent a production run of 1000 cells. The resulting distribution of cell performance values is compared with manufacture datasheets to determine the expected reject rate for different tolerance SDs. For a reject rate of zero, the maximum tolerance SD must be less than 1% but need not be less than 0.5% for the geometrical parameters considered. Findings show that the electrode slitting, cutting and negative electrode coating tolerances require tighter manufacturing tolerance than calendering and positive electrode coating thickness.