From the perspective of the development of global new energy vehicles, its power sources mainly include lithium-ion batteries, nickel-metal hydride batteries, lead-acid batteries, and supercapacitors. Most of the supercapacitors appear in the form of auxiliary power sources. The main reason is that these battery technologies are not fully mature or have obvious shortcomings. Compared with traditional vehicles, there are many gaps in terms of cost, power and cruising range. This is also an important reason for restricting the development of new energy vehicles.
Lead-acid batteries
Among all battery technologies, lead-acid batteries have the longest development history. The battery uses metallic lead as the negative electrode and lead oxide as the positive electrode. During the discharge process of the battery, lead sulfate will be generated at the positive and negative poles. The sulfuric acid in the electrolyte solution is not only a reactant of the reaction process, but also a product of the reaction process. In the past decade or so, the research and development of lead-acid batteries has mainly focused on the application of hybrid electric vehicles.
NiMH battery
NiMH batteries work based on the release and absorption of OH- at the nickel oxide anode and the hydrogen metal anode. In the past, nickel-metal hydride batteries were seen as a good temporary option in electric vehicles, given the serious safety concerns of lithium-ion batteries. However, its energy density of 50~70Wh/kg cannot meet the energy density requirement of 150~200Wh/kg for electric vehicles. At the same time, the large proportion of nickel in nickel-metal hydride batteries limits its future price reduction. Therefore, NiMH batteries are not considered a reliable choice.
Lithium Ion Battery
Lithium-ion batteries are the most used power battery technology in electric vehicles today, thanks to their high energy density and increased power in a single cell, allowing this type of battery to develop smaller mass and density. Currently, these power batteries can power electric vehicles for about 150km. Lithium is inserted into the electrodes of lithium-ion batteries, that is, the electrode material is the carrier of lithium ions. Studies have shown an increase in both power (800-2000W/kg) and energy density (100-250Wh/kg) of lithium-ion batteries used in electric vehicles.
Super capacitor
If the battery needs to provide both long-term storage energy and short-term pulse power for engine start or vehicle launch, the battery design needs to adopt a compromise solution. More electrodes are required in each cell to increase the total surface area. This increased current is distributed over a larger electrode area, keeping the battery voltage drop within the system requirements. If the power requirements can be supplied by other devices, the battery can use heavier electrodes to achieve better durability while meeting the energy storage requirements at low rates. An ideal approach would be to provide pulsed power from a supercapacitor, with batteries only providing energy storage. The supercapacitor can be recharged at a lower rate in preparation for the next power output, or recharged with braking energy recovery. After charging through the supercapacitor, the battery can operate over a wide range of battery state of charge (SOC) because the power required for cranking is already stored in the supercapacitor. Combining batteries and supercapacitors will inevitably require a more complex charging system, because the charging and discharging characteristics of batteries and supercapacitors are significantly different, so their charge cut-off voltages are quite different. Therefore, some kind of DC/DC converter or switching device may be required to control 2 devices on the same DC bus.