Performance of Commercial LiCoO2 Battery Under Pulse Current Charging Using Varying Duty Cycles

The development of lithium ion battery over the years has been in leaps and bound. Research is still ongoing towards the development of better lithium ion batteries and utilization techniques to power devices and machines of the future

Presently LiCoO₂ is one of the prominent secondary batteries at the moment. The conventional lithium ion battery charging is a two-step process that involves a constant current (CC) charge until the voltage rises to about 4.1V, then constant voltage (CV) charging until the current drops to a desired level. Previous works done by Jun Li Etal shows that with the use of pulse charging the concentration polarization can be eliminated and increase in power transfer rate can be achieved. Pulse charging can also lower charging time, all together leading to higher discharge capacity and longer cycle life¹. In work done by Branko N. popov and his colleagues on optimization of charging protocol for efficient cycling of Li-ion batteries they concluded with reasonable data that the rest period resulted in a slight increase in the capacity of the battery, but the rest period together with short discharge pulse increases the capacity even further because the discharge pulse helps to distribute the active material well throughout electrode² and it might also help create a more even concentration gradient.

We present pulse charging of LiCoO₂using a method of high current pulse charge, followed by a rest period and then a low current pulse discharge as shown in figure 1 this resulted in a charging profile shown in figure 2

The experiment was carried out on a LiCoO₂ battery with a capacity of about 1000mAh using the VersaSTAT 4 equipment. The setup was as followed: 1A charging for 10 seconds followed by a rest period for 1 second and then a discharge of 0.1 for 1second. The voltage limit was set to a maximum of 4.15 and a minimum voltage of 3.0. The discharge after this charging procedure resulted in discharge profile show in figure 3 with a discharge capacity of 548mAh

We also setup a second cycle as followed: 1A charging for 10 seconds followed rest period for 5 second and then a discharge of 0.15 for 5 second. The voltage limit was set to a maximum of 4.15 and a minimum voltage of 3.0 followed by a discharge a 0.5C. For this the resultant discharge capacity was 624mAh as shown in figure 4

This preliminary result shows a wide difference in capacity as the duty cycle is varied which indicates as expected that the rest and discharge period significantly affects the discharge capacity of the battery.The goal of our ongoing research is to establish the optimum duty cycle for charging Li-ion batteries and find dependence of the duty cycle on the structure and physical properties of the electrode and electrolyte. We would also look into the performance of the optimum duty cycle at various temperatures.

References

1. Jun Li, Edward Murphy, Jack Winnick, Paul A. Kohl “the effects of pulse charging on cycling characteristics of commercial lithium-ion batteries “

2. Branko N. Popov, Bala S. Haran, Anand Durairajan and Ralph E. White “Optimization of Charging Protocol for Efficient Cycling of Li-ion Batteries