The high-power lithium-ion power batteries currently used in electric bicycles are basically composed of multiple single batteries in series and parallel. In its application process, the main problem with lithium power batteries is that the discreteness between individual cells is large, which affects the safety and service life of the entire battery pack.

　　Therefore, we believe that the ideal lithium-power battery pack management should be aimed at the safety and service life of the battery pack. The requirement of this kind of control is: not only can manage and protect each single cell in the battery pack, but also keep the voltage of each battery balanced and consistent when discharging, as if many glasses of water balance out on the same horizontal line. flow. When charging, it is necessary to ensure that all the batteries in the battery pack are charged uniformly on the same voltage line until all the batteries are fully charged, just like many cups. Although the capacity is different, when filling water at the same flow rate, ensure that Every cup is overflowing.

　　To sum up, during the use of the lithium battery for electric bicycles, it is necessary to always keep the battery overcharged, overcharged, non-heating, and have a long life, especially for safe use. This requires that the battery pack must have the function of balancing and protecting each single battery.

　　Fourth, the classification of lithium batteries for electric bicycles

　　 Lithium batteries for electric bicycles can be roughly divided into three categories: lithium manganese batteries, ternary material batteries and lithium iron phosphate batteries.

　　Lithium manganese oxide battery: To solve the high temperature performance of lithium manganese oxide battery, the positive electrode material, battery structure design and electrolyte formula of the battery must be improved. In Japan and South Korea, modified lithium manganese oxide is used. When the modified lithium manganese oxide battery is stored at 65°C for one week, the capacity only drops to 99%.

　　Ternary material battery: Cobalt, nickel, manganese ternary materials are used as cathode materials for lithium batteries, which overcome the shortcomings of poor high-temperature performance of lithium manganate and increase the specific energy of the battery.

　　 Lithium iron phosphate battery: Since 2002, the United States and Canada have begun to develop lithium iron phosphate batteries, which have become a new type of power lithium battery with great development prospects. Long life, 2000 cycles of 1C charge and discharge at room temperature.

　　Advantages of lithium iron phosphate battery: high safety. The binding force of the phosphate chemical bond is relatively strong, and the structure is stable; it is environmentally friendly and does not contain any heavy metals; it is non-toxic (SGS certified), non-polluting; fast charging, lithium iron phosphate batteries can be quickly charged and discharged with high current 5～10C; High current discharge performance is good; 10～50C high current and high power discharge.

　　Disadvantages of lithium iron phosphate batteries: low temperature performance is inferior to other cathode materials such as lithium manganate. The cell voltage of a lithium iron phosphate battery is 3.2V. A 36V battery pack requires 12 single cells in series. The life of a single lithium iron phosphate battery currently exceeds 2000 times, but the life of a battery pack may only be 500 times.