Lithium-ion and Li-ion batteries offer an excellent level of performance. To gain the best from them, they must be charged correctly.
Lithium-ion charge/discharge chemistry
In very basic terms, the charge and discharge of a lithium-ion battery are relatively easy to explain.
When the lithium-ion cell or battery is discharging it provides current to an external circuit. Internally the anode releases lithium ions in an oxidation process which passes to the cathode. The electrons from the ions that have been created flow in the opposite direction, flowing out into the electrical or electronic circuit that is being powered. The ions and electrons then reform at the cathode.
Electronic conditions for lithium-ion battery charging
In terms of the electronics for the process, charging lithium-ion batteries is very different to charging Ni-Cads or NiMH batteries. It is not possible to use the same electronic circuits to charge them for a variety of reasons.
The charging lithium-ion batteries is voltage-dependent rather than current based. In this way, the charging of lithium-ion batteries is more akin to that of lead-acid batteries.
Charging lithium-ion batteries can be split into two main stages:
Constant current charge: In the first stage of charging a li-ion battery or cell, the charge current is controlled. Typically this will be between 0.5 and 1.0 C. (NB: for a 2 000 mAh battery the charge rate would be 2 000 mA for a charge rate of C).
For consumer-based LCO cells and batteries, a charge rate of a maximum of 0.8C is recommended.
Saturation charge: After a time the voltage peaks at around 4.2 Volts for an LCO cell. At this point, the cell or battery must enter a second stage of charging known as the saturation charge. A constant voltage of 4.2 volts is maintained and the current will steadily fall.
The end of the charge cycle is reached when the current falls to around 10% of the rated current. The charge time may be around two hours for this stage depends upon the type of cell and the manufacturer, etc.
Lithium-ion battery charging precautions
In view of the amount of energy stored in lithium-ion batteries and the nature of their chemistry, etc., it is necessary to ensure that the batteries are charged in the appropriate manner and with the appropriate charger and equipment.
Li-ion charge-discharge cycles
The lifetime of lithium-ion cells and batteries is often given in terms of the number of charge-discharge cycles they can accommodate before their charge retention capacity falls.
The charging and discharging of lithium-ion batteries is key to their operation and long-term performance. Typically battery management chips are incorporated into the battery packs. This manages the charging and discharging of the Li-ion battery.
In this way, the user can plug the battery into a charger and leave it to charge in the knowledge that it does not have to be unplugged after a certain time. The battery management chip will also ensure the battery is not discharged too far. The issue is to ensure that the battery management understands the exact state of the battery charge.