Studies On The Technological Design And Performance Of Lithium-ion Power Battery Pack For Electric Bicycles

As the power source, high power and high energy battery pack is one of the key components of the electric bicycles, and the performance of the batteries have important effect on the prospect of the electric bicycles. Lithium-ion batteries are considered as the most promising batteries with much of advantages like high voltage, high specific energy, good cycle performance and no pollution to circumstances, etc. Due to the production technology, the difference among single batteries exists inevitably. More critically, the difference of their performance will be enlarged during use. As a result, a vicious circle shows up, makes the difference larger and larger, and has a serious influence on battery performance and cycle life. According to single batteries cycle life character, this paper studies the battery consistency, ameliorates the effect of sub-matching, structural-designing and management system, hoping to control and reduce the battery difference, let battery output its maxinlum performance.Firstly, the consistency of single cells and batteries pack were studied respectively. The LiFePO4/C power batteries were used in experiment, the model was IFP186596with8Ah nominal capacity. Ambient temperature and charge-discharge rate were the external factors which affect the consistency of the battery. However, the more critical internal factors which caused by the deterioration of battery consistency were differences of the battery capacity fading rate. Experimental results show that solving the consistency problem of battery pack using battery selected and assembled with the battery initial performance were not only necessity but also limitations.Secondly, the impact and the performance of the36V/8Ah battery pack for electric bicycle which using on different charge-discharge conditions were studied. Capacity fade and inconsistent of the battery pack degree with the increase with the depth of the charge and discharge and the tendency was expanding, in practical application, long-term depth discharge of the battery pack should be avoided. Equalizing charge and pulse charge and discharge can effectively improve the cycle life and consistency of the battery pack. Discharge of simulated operating conditions more accurately reflect the actual application of the battery pack, compared to the cycle under constant current conditions, the attenuation of the battery pack is more pronounced.Finally, as the view of the heat generation and dissipation, connection optimized design of36V/8Ah battery pack which using for electric bicycle were studied. The pole piece of the experimental battery winding way, the heat capacity of the direction parallel to the pole piece was greater than the direction of the vertical pole piece. Therefore, the direction of the battery outer surface parallel to the pole piece was designed to direct contact with air conducive to the battery pack, which the overall temperature equilibrium and simulation experiments had been verified.Based on the above analysis, it’s a system engineering to improve the cycle life of the battery pack, from the production of the battery to and management control.