Lithium-ion Batteries

Overview

A lithium-ion (or li-ion) battery is a rechargeable battery that uses the recombination of Lithium ions with their missing electron to generate electricity, and the reverse of this process to recharge¹.

Lithium-ion batteries can be considered a family of battery technologies including:

1. Traditional lithium-ion
2. Lithium polymer
3. Lithium-iron phosphate

ERROR: tbl-basic-properties REF NOT FOUND shows some of the basic properties of Lithium-ion batteries.

Self Discharge

Lithium-ion batteries have a self-discharge rate which is 10 times less than NiMH batteries².

Charging

The common way to charge a Lithium-ion battery is to follow these steps:

1. The pre-charge stage, which is only applicable if the battery is really flat (less than 2.8V). The battery is charged with a constant-current, usually 10% of current used in the next stage (sometimes called the fast charge).
2. Charge the battery with a constant current (CC), at a rate of around 0.5-1C³.
3. Once the battery reaches a certain voltage (typically 3.9-4.2V), we switch from CC charging to CV charging. We maintain this voltage while the current begins to decrease.
4. Stop charging once the current drops to approximately 0.1C.

1C is the current required to drain the battery in 1 hour, e.g. for a 500mAh battery, 1C is 500mA. Most battery charger ICs will automatically perform the above steps for you.

Pre-charge can also been confused with the pre-charge step that occurs in the manufacturing process after the cells have been filled with electrolytes.

TI’s BQ Range

Texas Instruments sells a large number of battery charger ICs under the prefix BQ. Some are I2C controllable, others are standalone. Some have hot/cold temperature monitoring and others (typically with a J after the numerical code in the part name) have JEITA temperature monitoring.

Four phases:

1. Battery short
2. Pre-conditioning
3. Constant current (CC)
4. Constant voltage (CV)

Richtek RT9481, RT9485

The RT9485 has an on-board MCU.

References