# Improved Performance of Li-ion Polymer Batteries Through Improved Pulse Charging Algorithm
## 3 The Impact of Pulse Charging Parameters on Cycle Life of Lipo Batteries  
The impact of using a pulse charging algorithm, specifically the pulse charger parameters, on the cycle life of a LiPo battery was investigated [37]. Similar to Section 2, the parameters investigated were duty cycle, frequency, and the ambient temperature at which the battery was charged. The parameter levels were similarly set as: Duty cycle of 20%, 50%, and 80%, ambient temperature of 0 \({}^{\circ}\)C, 23 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C, and frequency at which the pulse charger was operated at 0.1 kHz, 1 kHz, 6 kHz, 12 kHz, 50 kHz, and 100 kHz. Using these parameters, a 36-row sized orthogonal array was constructed and experiments conducted in accordance with this DoE. It was observed that the inherent battery impedance increased as the charge and discharge cycles increased for both pulse charged and CC-CV charged batteries. As the battery is subjected to an increasing number of charge and discharge cycles, various side chemical reactions occur, which can affect the battery impedance. Across temperature, LiPo batteries charged at 0 \({}^{\circ}\)C using the standard CC-CV algorithm had lower battery impedance compared to those that were pulse charged. A similar trend was also observed at 45 \({}^{\circ}\)C. However, at 23 \({}^{\circ}\)C, both batteries subjected to pulse charging and CC-CV charging has similar impedance values. When analyzing the factors that impacted battery impedance, a LiPo battery pulse charged at a duty cycle of 50%, had lower impedance compared to that pulsed at duty cycles of 20% and 80% after 400 charge and discharge cycles.  
When determining which factors affected battery cycle life, it was observed that the cycle life of the battery increased when the battery was pulsed at the frequency at which its impedance was minimum (in this case, 12 kHz) and at a 50% duty cycle. These two parameters had the greatest impact on the cycle life of the battery. A 50% duty cycle meant equal time allocated to anode and cathode reversal while charging at the lowest impedance meant highest conversion of input energy into stored energy. Ambient temperature, 23 \({}^{\circ}\)C, also enhanced battery cycle life when compared to charging the battery at 0 \({}^{\circ}\)C and 45 \({}^{\circ}\)C. Charging the LiPo battery at frequencies below that which the minimum impedance occurred resulted in a shorter cycle life, while charging at the higher frequencies still resulted in shorter cycle life when compared to the optimal charging frequency. The pulse charging of a LiPo battery at the optimal parameters, i.e., 50% duty cycle, 12 kHz (frequency at which minimum battery impedance occurred), and 23 \({}^{\circ}\)C, resulted in an additional 100 cycles when compared with a battery charged using the standard CC-CV charging algorithm. Figure 7 summarizes the remaining capacity of batteries that were subjected to pulse charging using optimal parameters as compared to those using standard CC-CV charging. Pulse charging using the right charging parameters could enhance the cycle life of batteries, ensuring that batteries are seldomly replaced, resulting in overall cost reduction and environmental burden. It was also deduced that in some circumstances, e.g., under extreme temperatures, CC-CV can be used in order to improve battery impedance and ensure longer cycle life. This leads to the potential for the implementation of a temperature dependent algorithm selection.  
A comparison of this work was made with other state-of-the-art pulse charging techniques. This is summarized in Table 1. The impact of the proposed pulse charging algorithms on the cycle life of batteries are not evaluated in most previous works. It is important to evaluate the benefits of proposed pulse charging algorithms across both charge time and cycle life to prevent frequent replacement of batteries, which is something this work evaluates.