Lithium batteries necessitate a charging algorithm that upholds a constant current constant voltage (CCCV) during the charging process. In other words, a Li-Ion battery should be charged by a fixed current level, usually 1 to 1.5 amperes, until it hits its concluding voltage.
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Lithium is one of the most important metal resources that we have today. It is used for making Lithium-ion batteries for operating almost all portable electronic devices we see around. With a focus on clean fuel and advanced technologies, Li-ion batteries have also found their place in Electric Vehicles and drones. Just between 2021-2022, the global consumption of Li-ion batteries has increased to 41%, a reason why Elon Musk has called it the ‘new oil’.
Lithium-ion batteries are known for their high energy density, lower weight, and rechargeable properties, making them suitable for various electronic devices like Laptops and Mobile Phones to Electric Vehicles and Drones. However, the Li-ion battery is sensitive to voltage or current fluctuations, so efficient charging is paramount. A good and efficient charging setup for the battery ensures operational safety, longevity, and high performance.
Li-ion Battery Charging and Discharging Chemistry
Like any other battery, a lithium or Li-ion battery comprises an anode, a cathode, a separator, an electrolyte, and two current collectors – positive and negative. While the battery is discharging, it provides an output electric current used for running the application in which it is being used. While charging a lithium battery, the battery is supplied through an external voltage source.
During discharge, the anode releases Li-ions to the Cathode. This causes a flow of electrons from the anode to the cathode, and thus, there is a flow of current when a device is connected externally through the current collectors. On the other hand, when the battery is plugged in through an appropriate voltage source, the opposite happens, i.e., the Li-ions flow from the cathode to the anode, and the battery is thus charged back.
Inside a Li-ion battery, an Oxidation-Reduction (Redox) reaction occurs during the charge and discharge cycle.
Reduction Reaction: The reduction reaction takes place at the cathode. There is Cobalt Oxide, which combines with the Lithium ions to form Lithium-Cobalt Oxide.
Oxidation Reaction: takes place at the anode. The graphite intercalation compound LiC6 forms graphite (C6) and lithium ions there.
Complete Reaction:
Methods of charging Li-ion batteries
The following are the methods of Lithium battery charging.
- Constant Current (CCCV) Charging
- Fast Charging
- Smart Charging
Constant Current (CCCV) Charging:
As the Li-ion battery begins to charge after a discharge phase, it is typically supplied with constant current source charging. This ensures not only the safe operating voltage of the battery but also the fast charging of the battery in the initial phase. The lithium battery charging mechanism switches to constant voltage mode as the battery reaches capacity. This ensures that the voltage remains constant while the current from the source to the battery decreases gradually to near zero as the battery tends to full charge.
Fast Charging:
Most Li-ion battery applications need fast charging, like Electric Vehicles or mobile phones. Fast charging needs a higher level of voltage and current, which can hasten the charging process by supplying higher power per unit of time. However, Li-ion batteries are sensitive to voltage and current levels. Hence, a proper charging mechanism is important for the safe and sound operation of the battery. This also ensures the longevity of the battery.
Smart Charging:
There are critical systems where Li-ion batteries are used and are charged using intelligent technologies like BMS (Battery Management System). These innovative systems use algorithms like Battery Temperature, Voltage, and charge level to regulate the battery charging procedure accordingly. This ensures the battery’s safety and the system’s efficient working.
Challenges in charging Li-ion batteries
At the onset, Li-ion batteries are undoubtedly one of the most essential and promising energy storage devices that can be charged back after use. However, there are challenges with the charging and operation of the battery, which are as follows.
Thermal runaway:
Li-ion batteries generate heat while charging. With the demand for faster-charging technologies, the voltage and current are increasing, further aggravating the heat generation problem. Excessive heat generation may lead to thermal runaway of the battery and safety issues for the application and the operator. An efficient heat management system is thus required for the safe and sound operation of the battery.
Overcharging:
Overcharging may cause irreversible damage to the Li-ion batteries. It is important to take care of the charging levels and timely shutdown of the charging circuit. Various overcharging safety control mechanisms are used in the charger circuit to avoid overcharging risk, avoid heat generation, and ensure battery life.
Wearing and Degradation:
With multiple charging and discharging cycles, the Li-ion batteries wear out fairly quickly due to the chemical reaction within them. The result is that they must be replaced with a new one within 2-3 years of usage, which can get expensive. Thus, controlling the rate of wearing and degradation is important to increase battery life. Avoiding faulty charging mechanisms, safe charging limits, and controlled voltage and current charging ensure the battery’s longevity.
Extreme reactivity of the Lithium:
Li-ion batteries have a separator between the anode and the cathode electrodes, which avoids their contact. But if this separator breaks due to any physical damage or an external short-circuit, both the electrodes can come in contact, which may lead to flames and fumes as Lithium is highly reactive. Thus, the Li-ion batteries must be handled carefully and with all available safety procedures.
Tips for Charging Lithium Battery for a longer lifespan
Tip 1- Understand the battery
Lithium-ion batteries are composed of a positive electrode and a negative electrode. During the charging process, the electrons flow out of the battery through the electrical current while ions shift from one electrode to another. This creates a dynamic exchange where both electrodes seem to be “breathing” in and out, accurately exchanging ions.
When a battery supplies current, electrons move from the anode to the cathode outside the battery. If you recharge the battery by supplying current, the electrons are sent back to the anode, and the lithium ions re-intercalate themselves in the cathode. This entire process of charging and discharging is called a cycle, which determines the life of the battery. The number of cycles depends on the manufacturing process, the chemical components, and usage.
The capacity of a rechargeable battery is measured in ampere-hours (Ah). For instance, a battery capacity of 5.6 Ah can deliver 5.6 A for an hour at 25°C over a cycle.
The capacity of the battery is affected by the following parameters.
- The charging, discharging, and operating temperature.
- The C rate of the Battery- The C rate is the charging and discharging rate of the battery. Charge and discharge currents are typically expressed in fractions or multiples of the C rate: A C charge/discharge refers to charging or discharging a battery in one hour. A C/3 charge/discharge takes three hours, while a 3C charge/discharge takes only 20 minutes.
- Multiple cycles– Due to physical and chemical degradation of the electrodes and electrolyte, the battery loses capacity over time.
- The voltage level that reflects the charge level: A battery at 4.2V is fully charged, while a voltage of 2.7V indicates complete discharge (cut-off).
Tip 2: Follow the CCCV Charging Process
Charging a lithium-ion battery is a complex process that demands careful consideration. The charger you choose is crucial in determining the lifespan of your battery. Using the wrong charger or plugging it into an unsuitable power supply can lead to safety hazards. It’s imperative to choose a charger specifically designed for lithium-ion batteries and set the parameters accurately to ensure the battery’s longevity.
Proper lithium-ion battery charging involves Constant Current (CC) charging and Constant Voltage (CV) charging. Firstly, a CC charging raises the voltage to the end-of-charge voltage level. CV charging is initiated after reaching the targeted voltage level, causing the current to decrease gradually. When the current drops too low, the charging process is completed, and the charger must be disconnected.
Tip 3: Carefully design your Battery Management System(BMS)
Li-Ion cells are commonly used in various applications, but it is crucial to pair them with electronics. The Battery Management System (BMS) is a vital electronic component that ensures the safety of the battery. It has safety features that stop the discharge or charge process to prevent the battery from over or Undervoltage. The BMS continuously monitors the temperature and disconnects the battery to avoid overheating.
The Battery Management System (BMS) can optimize the charge distribution among the cells in a battery pack, which is called balancing. When cells are connected in series in a battery, they tend to age at different rates over time. This can lead to the oldest cell in the pack deteriorating faster than the others. As the battery pack’s lifespan depends on the oldest cell, a reliable balancing system can greatly enhance the battery’s overall lifespan.
The Battery Management System (BMS) can be customized according to your needs. Some BMS models can show you the State of Charge and the State of Health of your battery. For instance, if the State of Health is 80%, the battery’s capacity has reduced by 20% since the beginning of its life. This information is useful because a 30% loss of the original capacity indicates that the battery is reaching the end of its chemical life and needs to be replaced soon.
Tip 4: Lower the Battery charging C rate
When the lithium-ion battery is charged slowly, such as C/2, C/5, or lower, the lithium ions can easily fit into the graphite sheets without harming the electrodes. However, the intercalation process becomes more difficult when the charging rate increases. At high charging rates, the lithium ions cannot properly penetrate the electrode and instead accumulate on its surface, which leads to premature battery aging.
Fast charging rates up to 10C are possible for mobile and EV batteries but require specialized electrode constructions and may limit battery lifespan.
It is crucial to consider the required charging time, speed, and battery aging. Although a C/60 charging rate is more beneficial for the electrodes, it may not always be feasible for all applications due to the lengthy 60-hour charging time. A faster 3C charging time (20 minutes) is achievable but may also hasten the battery’s aging. Therefore. The charging rate of the battery must be restricted to C or less to guarantee the best possible battery life.
Tip 5: Control the charging temperature
Most lithium-ion batteries use graphite in one of their electrodes. When the battery is charged at an elevated temperature, the graphite sheets in the electrode start to separate, leading to a permanent loss of capacity in the battery. This problem can worsen at higher charging rates, as the charging current increases the battery’s temperature and accelerates the separation of the graphite sheets.
When a high voltage is combined with high temperature, the electrochemistry within a cell produces gases that hasten the aging of the battery. Also, high temperatures may cause the cell to expand, posing safety risks if the battery casing or device is not designed to accommodate such changes. It is crucial to adhere to the limits specified by the battery manufacturer and avoid, for instance, leaving a cell fully charged for an extended period in an overheated car during the summer months.
If the battery lacks necessary safeguards, a temperature above 130°C can cause thermal runaway due to overcharge, over-discharge, or overtemperature.
Li-ion batteries have specific temperature limits for charging. Most can’t withstand temperatures above 60°C and are recommended to be charged at a maximum of 45°C under a C/2 charge rate.
It is difficult to charge most batteries below 0°C due to the contraction of electrode sheets and the decrease in electronic conductivity of the electrolyte. This makes it challenging for ions to intercalate in the graphite, and it may cause the formation of lithium deposits, which can lead to a permanent loss in capacity. To address this issue, some manufacturers recommend charging batteries at a slow rate (C/20) when operating below 0°C.
Despite all these challenges, Lithium-ion batteries are one of the most popular and safest for various applications. Research is going on to make these batteries more robust, reliable, safe, and efficient. For example, researchers have created a liquid electrolyte that turns into a solid when it is hit. This will help keep batteries from heating up or catching fire if damaged. With their increased demand, these batteries will be safer, last longer, and have reduced costs.