Charge and discharge characteristics of lithium-ion batteries

Charge and discharge characteristics of lithium-ion batteries

With the development of lithium-ion battery technology, the market share is increasing. From consumer electronics to the new energy storage field,

regardless of changes in product application or material system optimization, the fundamental characteristics of lithium-ion battery charging and discharging have not changed.

All lithium battery charging and discharging characteristics still follow a similar step curve.

Characteristics of lithium batteries:

Lithium-ion batteries currently have one of the highest energy densities and single-cell voltages. They do not require trickle float charging when the battery is fully charged.

Unlike lead-acid and nickel-metal hydride batteries, lithium-ion batteries do not experience memory effect. This means that lithium-ion batteries do not remember the remaining charge before each full depletion.

Therefore, lithium-ion batteries generally adopt a special charging mode called constant current and constant voltage (CC-CV) charging.

The charging curves of lithium-ion batteries are adjusted automatically based on the temperature and voltage level of the battery cells.

(Please note that lithium batteries should be charged with a special charger designed for lithium-ion batteries, not lead-acid battery chargers.)

Charging steps of a lithium battery:

Stage 1: Trickle Charge

If the voltage of the Li-ion battery is below the trickle to pre-charge voltage threshold (below 2V/cell),the IC (Integrated Circuit) will charge the battery with a trickle charge current of 90-100mA (adjustable).

The trickle charge stage is typically used when the cell voltage is very low (around 2.1V). In this state, the battery pack is usually already protected due to deep discharge or overcurrent.

The charger's IC will provide a small current to activate the battery and trigger the IC to close its MOSFETs, reconnecting the battery.

Trickle charging usually lasts only a few seconds. If the battery pack is not reconnected within a certain period of time, it indicates that the battery is damaged.

Stage 2: Pre-Charge

Once the battery pack is activated and connected, it enters the Pre-Charge stage. During Pre-Charge, the charger's IC will charge the depleted battery with a small current,

typically 0.1C, causing the voltage to rise slowly. The purpose is to safely charge the battery with a small current to prevent damage until its voltage reaches a higher level.

Stage 3: Constant Current Charging (CC)

The constant current (CC) charging stage, also known as the fast charging stage, starts when the battery voltage reaches 2.9-3V (adjustable).

In this stage, a current ranging from 0.2C to 3C (depending on the specific battery) can be used for charging.

The rapid charging stage continues until the battery is almost full, and then it transitions to the constant voltage charging stage.

Stage 4: Constant Voltage Charging (CV)

Typically, When the lithium-ion battery voltage exceeds 4.1V (adjustable), it enters the constant voltage charging stage.

The charging IC monitors the battery voltage level, and once the battery reaches the specified constant voltage charging voltage,

the charging mode switches to constant voltage charging.

Stage 5: Charging Cut-off (Stop)

Typically, in the constant voltage charging stage, when the current flowing into the battery drops below 0.1C, the charger IC immediately stops charging.

This indicates that the battery is fully charged, and the charging process is complete.