With the move to green energy getting a push, the demand for electric vehicles is surging. However, EVs come with some unique challenges, for example, the time it takes for the lithium-ion battery of an EV to get charged.
It means that enabling fast charging is a dire need when it comes to driving the electrified automotive industry forward while also addressing the inherent challenges with EVs.
In this article, we will compare different fast-charging technologies for the Lithium-ion batteries of EVs.
What is a Lithium-ion Battery?
Lithium-ion batteries are rechargeable secondary batteries. They are made up of A battery is made up of an anode, cathode, separator, electrolyte, and two current collectors (positive and negative). The battery is charged and discharged by lithium ions moving between the negative (anode) and positive (cathode) electrodes emerging in an electrolyte.
This electrolyte in lithium-ion batteries is usually a solution of lithium salt where the solvent can be both organic or inorganic.
During the charging phase, an external power source applies voltage to the battery causing positively charged lithium-ion to travel to the cathode through the electrolyte and vice versa through the separator. The metal anode stores this lithium-ion. On the other hand, the cathode is made of lithium metal oxide. In this process, free lithium-ion is generated in the anode and creates a charge at the anode’s current collector.
Now, during the discharge phase, to let the battery power a device, lithium ions travel to the cathode from the anode, generating a flow of electrons from the anode to the cathode and within the battery. This electron flow induces an electrical current that can be tapped into for powering external devices connected to the battery.
The electrolyte plays a critical role in defining the performance, conductivity, temperature stability, etc., of the battery.
Lithium-ion batteries are widely used in EVs because of their capacity to store high power.
Fast-Charging Principles and Design
Principle
Fast charging with a Lithium-ion battery is achieved by modifying and fortifying the battery structure, optimising battery materials, and holding sway over the charging process.
For example, adopting strategies such as modifying electrode composition, and structure or installing high-capacity electrodes can significantly increase the battery’s charging speed and capacity. Again, to enable high-power charging, you would need a stable and efficient charging power supply – collaborative hardware and software, high-power chargers, etc.
Thermal management and heat dissipation design
Dissipating the large amount of thermal energy (heat) generated during fast charging is critical. It implies that designing the heat dissipation and thermal management system efficiently is critical to ensure the battery doesn’t overheat or get damaged. Cashing in on technologies, such as heat dissipation devices, heat pipes, and liquid cooling can help in this regard.
Common Fast-Charging Methods
High-power Charging
In the high-power charging technique, a high current is delivered to the Lithium-ion battery for reduced charging time, thereby accelerating the charging process.
In the HPC process, the charging station delivers electricity to the vehicle’s battery at a power rating of 100 KW. To ensure this high power level is withstood efficiently, high-end charging stations equipped with advanced technologies such as a combined Charging System (CCS) or CHAdeMO plugs, and liquid-cooled cables are used.
HPC charges the lithium-ion batteries of EVs at a notably high speed, shortening the charging times to about 20 to 30 minutes for an 80% charge.
However, the increased heat generation and capacity fading issues with HPC technology may negatively impact the safety and durability of EV batteries.
Pulse Charging
In this charging technique, bursts of high current are delivered to the battery in a highly controlled manner and with short rest periods. Pulsing the current flow allows for a more optimised charging process that expedites charging times. According to studies, pulse charging can decrease the charging time by around 5–20% with little to no impact on the battery lifecycle.
To ensure no damage is caused to the battery, careful implementation is required. That being said, improper implementation and application of the pulse charging technique can produce temperature variations, mechanical stress, and unequal ion distribution in the Lithium-ion battery of an EV car.
Voltage Boosting
In this process, the charging voltage is increased to speed up the charging process. The higher the charging voltage, the faster the ions move in the battery cell. The result is a significant reduction in charging time. While voltage boosting can augment charging efficacy, it also poses safety risks.
For example, there is a higher chance of causing thermal runaway, overcharging, and other safety issues with increased charging voltage applied to the battery cells.
That being said, proper management of EV batteries, while applying voltage-boosting fast-charging techniques, requires implementing robust battery management systems. Thus, you can automate the monitoring and regulation of voltage levels for controlled battery operation.
