Mechanistic insights into the impact of electrode areal density on electrochemical and thermal behavior of high-rate lithium-ion batteries

With the widespread application of lithium-ion batteries in electric vehicles, drones, and other fields, the demand for high-rate charge/discharge performance keeps increasing. This study investigates the effects of electrode areal density on a battery's electrochemical and thermal behavior. Four pouch batteries with different electrode areal densities were prepared and tested under 1C, 10C, and 20C. An electrochemical-thermal coupled model was developed, achieving high accuracy with VMREs<1.0 % and TMAEs<1.0 °C. As the areal density increases, the open-circuit voltage rises slightly, whereas the electrolyte voltage loss and the polarization voltage loss increase substantially. During the 20C discharge of the battery with a cathode areal density of 145 g/m2, the polarization voltage loss exhibits a sharp increase following brief fluctuations, while the open-circuit voltage stabilizes after a short drop. Increasing the areal density intensifies the lithium-ion concentration gradient in the electrolyte, resulting in lithium depletion near the cathode-collector interface during ultra-high-rate discharges of thick-electrode batteries. Thermal analysis indicates that ohmic and polarization heat generation increase significantly as the areal density rises, while reaction heat changes slightly. Consequently, total heat generation and average temperature-rise rates scale linearly with the areal density, with the temperature-rise rate increasing more than threefold as the cathode areal density increases from 55 to 145 g/m2. These findings provide a comprehensive understanding of electrochemical and thermal behavior in high-rate batteries, offering strategies for optimizing electrode design.