## 3 Results and Discussions
### The Influence of Temperature on Battery Performance  
Temperature is an important factor affecting battery performance parameters. Too high or low temperature will affect LIB capacity, charging and discharging efficiency, safety performance and result in battery performance degradation. Figure 5a shows the current change of the LIB in the charging and discharging cycle, and Figure 5b shows the voltage change. For the convenience of statistics, the x-coordinate in the figure represents the time step, and each step is 10 s. That can be seen from the figures, the current and voltage curves of the LIB have the same trend in each working condition. The current and voltage can reach the set rating in each charging and discharging cycle. However, as the cycles progresses, compared with the LIB under extreme conditions, the LIB curves in other conditions shift to the right, which is very similar to Figure 3b. The reason is related to the battery charging and discharging time. Under constant current conditions, the total flux of lithium ions should be roughly similar (both as diffusion in the electrolyte, and total flux into and out of the active material particles), and environmental conditions have little effect on it. However, at lower temperatures, a higher concentration gradient is required to overcome the slower diffusivity to meet the required flux. The higher concentration gradient leads to higher over potential and uneven utilization of electrodes. In turn, this leads to faster reaching of the cut-off voltage when working at lower temperatures. It can be clearly seen in Figure 5a that the LIBs in PCM and PCM-Fin cooling experiments seem to be faster reaching the cutoff voltage than the extreme condition and air cooling experiments in the first discharge cycle when all batteries start at the same state of charge (SOC). On the contrary, a higher temperature of LIB means that a constant current can be provided for a longer period of time. That can be seen in Figure 5b, the voltage drop of LIBs at higher temperature is smaller. In addition, according to Figure 3, it is found that in the constant current charging stage of the battery, the temperature of the battery decreased rapidly in the extreme condition and air cooling experiments, and the temperature is lower  
Figure 4: The temperature changes of LiFePO\({}_{4}\) battery during charging and discharging. than the other cases in a period of time due to the latent heat effect of PCM. It seems that the LIBs under PCM and PCM-Fin cooling conditions can be charged for a longer time in the later cycles than the other cases. Figure 6 shows the current and voltage changes in the LiFePO4 battery during charging and discharging cycles. The current and voltage changes of LiFePO4 LIB have the same trend under four different working conditions. Since the operating temperature of LiFePO4 LIB under four working conditions is higher than the other cases, the current and voltage changes are more similar to the other cases. Figure 5: The current and voltage curves of Sanyo LIB. conditions is around 30-40 \({}^{\circ}\)C, the LIB is in a normal working state and its current and voltage will not change much. Table 4 shows the capacity changes of Sanyo LIB charging and discharging cycles under different working conditions. It is found from the table that the LIB capacity has some changes in each working cycle. The average charging capacity of six cycles is 2414.6 mAh under the extreme conditions, 2399.4 mAh under natural convection, 2397.7 mAh under PCM cooling, and 2403.6 mAh under PCM combined with heat dissipation fins working condition. The average discharging capacity of six cycles  
Figure 6: The current and voltage curves of Sony LIB. is 2412.7 mAh under the extreme conditions, 2398.3 mAh under natural convection, 2398.4 mAh under PCM cooling, and 2383.3 mAh under PCM combined with heat dissipation fins working condition. Table 5 shows the capacity changes of LiFePO4 battery charging and discharging cycles under different working conditions.