Pulsed Current Based Fast Charging Methods for Li-Ion Battery

Abstract

The increasing rate of greenhouse gas emissions from conventional cars and its impact on global warming in the recent years has led to the technological advancements in the evolution of electric vehicles. Developing fast charging methods for Li-ion batteries is one such technological advancement and soon it will be imperative to promote the usage of electric vehicles in increased numbers. However, fast charging of Li-ion battery accelerates aging mechanisms [1] and triggers thermal runaway condition. As a result, this study investigates pulsed current based fast charging methods employed on C/NMC batteries. Pulses of current at low frequency (mHz) [2] and high frequency (KHz) are used with an extended pulse current period, thanks to higher voltage limit based on ohmic drop compensation [3]. The findings of the experimental investigation clearly establishes that a compromise has to be found between relaxation period and temperature in order to achieve fast charging. For instance, on one hand, a 2C current pulse with an on duration of 3s and relaxation duration of 1s allows to save 45% of recharging time when compared with standard constant current-constant voltage charging (CC-CV) at 0.5C as shown in the figure below. On the other hand, the temperature variation does not exceed 20°C beyond ambient which is lower than that of its counterpart CC-CV at 2C. Hence, the experimental investigation successfully opens the doors to implement fast charging methods on C/NMC batteries by limiting the temperature rise, there by arresting the ageing of batteries and thermal runaway condition.Keyword: Li-ion, Fast charging, Current pulse, Ohmic drop compensation, Temperature, Thermal runaway. Figure 1