Follow analysis of voltage inconsistency in 45-kWh cylindrical lithium-ion battery pack of electric vehicles

Voltage inconsistency (VI) is a major phenomenon usually appeared in cylindrical lithium-ion battery systems in Electric Vehicles (EV) after a long cycling, substantially lead to a decreasing cycle life. Analyzed manner for VI should be close to the actual operation with the application of the battery. In this study, a 45-kWh electric vehicle battery pack in the EV after operated 49,000 km was selected and performed multiple investigation encompassing system-level powertrain characterization, module-level analysis, and cell-level electrochemical diagnostics. After characterization of the vehicle system, multiple abnormal phenomena were identified: a system alarm fault occurred, the maximum dynamic VI between modules reached 348 mV, the ohmic internal resistance of the single cell rose from 2.21 mΩ to 4.03 mΩ, and disassembled cell inspection revealed that the anode thickness increased from 130.00 μm to 167.10 μm. The progressive expansion forces narrowed electrolyte permeation channels in the central regions of the cylindrical batteries, which led to insufficient Li + intercalation in electrode sheet centers and Li plating at the electrode edges. These mechanisms collectively contribute to dynamic VI development. VI evolution during cyclic aging directly impacts battery service life and capacity utilization. By leveraging empirical data from field-operated battery packs, this work elucidates the mechanistic origins of dynamic voltage inconsistency, thereby establishing a foundation for diagnostic methodologies in battery system anomaly detection.