Safe bidirectional pulse heating method for the lithium-ion battery pack on a high-power electric motorcycle

The charging ability at low temperatures affects the convenience and safety of electric vehicles in winter. Unlike electric cars, electric motorcycles generally do not carry high-efficiency external heating device such as heat pumps owing to strict limits on their weight and volume. This study focuses on the applicability of bidirectional pulse heating to improving the low temperature charging ability of a high-power electric motorcycle, which is also the first vehicle-used bidirectional pulse heating case. A simplified thermoelectrical model of the battery pack is proposed for onboard calculation, and a reference electrode is used to determine conservative boundary values for the bidirectional pulse and fast charging current to protect the battery cells from lithium plating and ensure the safety of the motorcycle. A map is established indicating the best preheating temperature, based on which the heating rate of the battery pack can reach 6.8 °C/min at 0 °C. The bidirectional pulse heating is tested on the electric motorcycle during winter season in Beijing, and the experimental results show that the temperature of the battery pack increases as expected. The proposed method will be applied on the motorcycle and improve with battery aging data in the future.