Jens Groot

Impact of Periodic Current Pulses on Li-Ion Battery Performance

Pulse charging and pulse discharging have been reported by many authors in the literature to improve the performance of various secondary electrochemical cells. Only a few authors mentioned the effects of such charge and discharge method on lithium-ion batteries. The overall objective of this work is to experimentally investigate the impact of certain current pulse profiles on the electrical performance of Li-ion batteries. The results highlight a detrimental impact of periodic pulses on the cell performance compared to profiles with constant current.

Impedance spectroscopy characterisation of automotive NMC/graphite Li-ion cells aged with realistic PHEV load profile

The ageing behaviour of Li-ion cells in automotive applications is known to be strongly non-linear with respect to operating conditions. In addition, it has a profound impact on performance, cost and reliability of the target vehicle. The work presented in this paper concerns automotive type NMC/graphite Li-ion battery cells aged under realistic and accelerated conditions, analyzed using electrochemical impedance spectroscopy and with the implementation of an electric equivalent circuit model. Two cycle life tests were performed at +22°C and +45°C surrounding temperature, with reference performance tests performed at ±0°C, +22°C and +45°C. The duty cycle applied is derived from speed samples of real-world city driving characteristics for electric passenger cars with fast charging at 2C-rate. Results show that despite a significant decrease in capacity, a decrease in charge transfer resistance can be observed during the first stages of aging which may be correlated to an increased double layer capacitance. Also, an increase in peak power at low temperatures is observed.

Energy storage system optimisation of a plug-in HEV

This paper deals with the optimisation of the energy storage system of a parallel hybrid plug-in car. The objective is to study how the electric driving range is influenced by factors such as package volume and auxiliary power consumption. Simulation and optimisation are used to find the most cost effective battery arrangement for specified electric driving range, volume, power and lifetime requirements. Two battery technologies, NiMH and Li-ion, are included in the simplified case study. The result indicates that the battery cost and size are highly dependent on the required electric driving range. It is found that a 3±5km electric driving range is possible with a minor cost increase. An electric driving range of 15±25km is possible, but results in a more bulky, and much more costly, battery system. It is important to point out that the results are not general. The electric driving range can be significantly extended by decreasing the roll and/or the air resistance.

Impact of periodic current pulses on Li-ion batteries lifetime in vehicular application

Using the hybrid electric vehicle application as a reference, the possible impact of periodic current pulses on lithium ion secondary battery cycle life was evaluated. Several profile types, with and without pulses, were evaluated in a comparative study on cycle life of commercial graphite/LiFePO4 batteries. Results are presented, compared and analysed. Contrary to the well-known results on lead-acid batteries and to results in previously published work, there is no indication that periodic pulses could enhance the cycle life of Li-ion batteries. On the contrary, certain pulse patterns have been identified to be detrimental to Li-ion batteries.