Simplified calculation of the area specific impedance for battery design

Battery design is a critical aspect of material and system development that leads to the commercialization of effective electrochemical energy storage systems. Successful modeling of battery designs relies upon accurate calculation of the area specific impedance (ASI). A simplified calculation of the ASI is presented that accounts for physical limitations without performing computationally expensive calculations. The limiting currents for transport within the electrolyte and within the intercalation materials are implemented into a linear form of the Butler–Volmer equation to calculate the interfacial impedance. Lithium-ion batteries are then designed to examine the effect of power to energy ratio on battery dimensions. A large ASI is shown to be detrimental to battery design regardless if the increase in impedance results from mass transport limitations or a reduction in electrochemical active area due to small electrode loadings. The smaller electrochemical active area does not increase the voltage losses of a battery when a constant C-rate is maintained. However, the higher ASI values from low electrode loadings require a larger separator and current collector area resulting in a greater battery volume and weight to achieve similar energy and power requirements when compared to a system with a lower ASI.

Research highlights▶ A simple expression for the ASI can include active area and limiting currents. ▶ A higher ASI does not always increase the polarization of the electrochemical cell. ▶ A higher ASI lowers power and energy density of the battery regardless of the origin.