From the global development of new energy vehicles, their energy sources mainly include lithium-ion batteries, nickel-hydrogen batteries, lead-acid batteries and supercapacitors, most of which are in the form of auxiliary power supplies. The main reason for this is that these battery technologies are not yet fully mature or have significant shortcomings. Compared to conventional vehicles, there are many deviations in terms of cost, power and range. This is also an important reason for limiting the development of new energy vehicles.
Of all battery technologies, the lead-acid battery has the longest history of development. This battery uses metallic lead as the negative electrode and lead oxide as the positive electrode. During the discharge of the battery, lead sulphate is produced at both the positive and negative electrodes. The sulphuric acid is used in the electrolyte solution as both a reactant and a generator of the reaction process. Over the last decade or so, research and development on lead-acid batteries has focused on the application of hybrid electric vehicles.
Nickel-metal hydride batteries
NiMH battery operation is based on the release and absorption of OH- from the nickel oxide anode and the hydrogen metal negative electrode. In the past NiMH batteries were seen as a good interim option in electric vehicles, given the serious safety issues associated with lithium-ion batteries. But their energy density of 50-70Wh/kg does not meet the demand for 150-200Wh/kg energy density in electric vehicles. At the same time the larger component share of nickel in NiMH batteries limits their future price reduction. Therefore, NiMH batteries are not used as a reliable choice.
Lithium-ion batteries are the most used power cell technology in electric vehicles today, thanks to their high energy density and the increased power in a single cell, allowing these batteries to develop smaller masses and densities at competitive prices. Currently, these power cells can be used for electric vehicles for approximately 150 km. lithium-ion batteries have lithium inserted into the electrodes, i.e. the electrode material is the carrier for the lithium ions. Studies have shown an increase in the power (800 to 2000 W/kg) and energy density (100 to 250 Wh/kg) of lithium-ion batteries used in electric vehicles.
If the battery needs to provide both a long period of stored energy and a short burst of power for engine starting or vehicle start-up, the battery design needs to be a compromise solution. More electrodes are used in each cell to increase the total surface area. With this increased current distribution over a larger electrode area, the battery voltage drop can be maintained to meet the system requirements. If the power requirements can be provided by other devices, the battery can use heavier electrodes to achieve energy storage requirements at lower multipliers while achieving better durability. An ideal approach would be for the supercapacitor to provide the pulsed power and the battery to provide only the energy storage. The supercapacitor can be recharged at a lower multiplier in preparation for the next power output, or recharged using braking energy recovery. After charging via the supercapacitor, the battery can operate over a wide range of battery states of charge (SOC) as the power required for starting is already stored in the supercapacitor. Combining batteries and supercapacitors necessarily requires a more complex charging system, as the charging and discharging characteristics of batteries and supercapacitors are significantly different, so their charging cut-off voltages differ considerably. Therefore, some kind of DC/DC converter or switching device may be required to control the 2 devices on the same DC bus.
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