Evaluating performance and cycle life improvements in the latest generations of prismatic lithium-ion batteries

The last decade has seen an enormous improvement of energy density for lithium-ion battery cells, particularly for automotive grade cells intended for use in electrified vehicles. This has led to vastly improved range for battery electric vehicles as well as for plug-in hybrids. However, the challenge of uncertain battery lifetime remains. The ageing effect due to fast charging is especially difficult to predict due to its non-linear dependence on charge rate, state-of-charge and temperature. We here present results from fast charging (1C and 3C in a 20 % to 80 % SOC-level) of several energy-optimized, prismatic lithium-ion battery cell generations utilizing NMC/graphite chemistry through comparison of capacity retention, resistance and dQ/dV analysis. Considerable improvements are observed throughout cell generations and the results imply that acceptable cycle life can be expected, even under fast charging, when restricting the usage of the available battery capacity. Even though this approach reduces the useable energy density of a battery system, this trade-off could still be acceptable for vehicle applications where conventional overnight charging is not possible. The tested cell format (the VDA PHEV2-standard) has been used for a decade in different electrified vehicles. The ongoing development and improvement of this cell format by several battery cell manufacturers suggests it will continue to be a good choice for future vehicles.