Lithium-ion batteries are rechargeable energy storage devices commonly used in portable electronics, electric vehicles, and renewable energy systems. They operate based on the principles of charging and discharging, which involve the movement of lithium ions between the battery’s electrodes.
Charging Principle:
During the charging process, an external power source is connected to the battery, and a voltage higher than the battery’s current state of charge (SoC) is applied. The charging circuitry controls the flow of current into the battery, regulating the voltage and current levels. Here are the key steps involved in charging a lithium-ion battery:
1. Constant Current (CC) Charging: Initially, the charger applies a constant current to the battery, typically at a higher rate. The current pushes lithium ions from the positive electrode (cathode) to the negative electrode (anode), creating a concentration gradient.
2. Voltage Regulation: As the battery charges and its SoC increases, the charger maintains a constant voltage across the battery terminals. This voltage limit prevents overcharging and protects the battery from damage.
3. Constant Voltage (CV) Charging: In this phase, the charging current gradually decreases while the voltage remains constant. The battery’s SoC continues to rise as lithium ions migrate and intercalate into the anode material (such as graphite).
4. Trickle Charge: Once the battery reaches near-full capacity, the charging current decreases further, providing a small trickle charge to complete the charging process. This helps balance cell voltages and ensures a full charge.
Discharging Principle:
When a lithium-ion battery discharges, it provides electrical energy to power external devices or systems. The following steps outline the discharging process:
1. Opening the Circuit: The battery is connected to a load, initiating the flow of current from the battery’s anode to its cathode through the external circuit.
2. Lithium Ion Movement: During discharge, lithium ions move from the anode (which becomes lithium-depleted) to the cathode. Simultaneously, electrons flow through the external circuit, producing electrical energy.
3. Voltage Decline: As the battery discharges, its voltage gradually decreases. The rate of voltage decline depends on factors such as the load connected and the battery’s capacity.
4. End-of-Discharge Limit: Once the battery voltage drops to a predetermined threshold, known as the end-of-discharge limit, the battery is considered discharged. Discharging the battery beyond this point can lead to over-discharge, potentially damaging the battery or reducing its performance and lifespan.
It’s important to note that lithium-ion batteries incorporate safety features, such as protection circuits, to prevent overcharging, over-discharging, and other potential risks associated with their operation.
