What happens to an e-bike battery if winter comes? Liu Yang, Vice General Manager of LEV Battery Business Unit at Phylion, knows exactly what to do.

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Expert blog by: Liu Yang, Vice General Manager of LEV Battery Business Unit, Phylion

It is well known that the range of e-bike is obviously reduced under low temperature in winter. It is mainly due to the reason of decrease of battery capacity and charging and discharging efficiency caused by low temperature etc..

1. The harm of low-temperature charging and discharging to the battery

It is difficult or even impossible for e-bike to charge normally at low temperatures. Under such circumstance, battery charging has a certain risk. As the temperature decreases, the dynamic characteristics of graphite anode become worse and worse. During charging, the electrochemical polarization of graphite anode increases significantly. The lithium metal precipitated easily forms lithium dendrites, breaks through the diaphragm and leads to short circuit between the positive and negative electrodes.

Discharge at low temperature also affects battery capacity. At low temperature, the activity of cathode materials decreases, resulting in a decrease in the number of lithium ions that can move to bring discharge current. Besides capacity, open-circuit voltage of batteries decreases as the temperature drops. Therefore, the energy of battery will be reduced substantially.

2. Decrease of charging and discharging efficiency

At low temperature, the SEI of negative electrode of lithium-ion batteries becomes thicker and the conduction rate of lithium ions in SEI decreases with the increase of SEI impedance. Finally, the charging and discharging efficiency of lithium-ion batteries decreases with the formation of polarization at low temperature.

3. Internal side effects of lithium-ion batteries

At low temperature, the performance of lithium-ion batteries deteriorates seriously, and some side effects occur during the charging and discharging process of lithium-ion batteries. These side effects are mainly the irreversible reaction between lithium ion and electrolyte, which will cause the capacity degradation of lithium batteries and further deteriorate the performance of batteries.

Battery Protection Scheme under Low Temperature

While in the face of the limited use of lithium batteries at low temperature, the strategy is heating while charging, which has obvious effect on improving the discharge capacity and long-term life of lithium batteries.

Before charging or using lithium batteries at low temperature, BMS control is used to heat both ends of the batteries to ensure that the batteries can be charged and discharged normally. BMS monitors the temperature of the battery in real time and continues to heat once the temperature drops to the preset value.

At present, this technology has been applied to the actual project. This technology not only ensures the safety of E-bike during charging, but also guarantees the capacity of the battery at low temperature to ensure the mileage of the vehicle and the cycle life of the battery. It has practical significance for the normal use of E-bike in cold environment.