Li-ion batteries have several advantages when compared with other battery types:
These properties make Li-Ion batteries very popular in modern portable electronic applications. When designing applications with Li-Ion cells, it is important to understand the battery characteristics during charging and discharging, to ensure safe application and best battery life time.
Figure 1 shows several types of Lithium cells, used in different applications, with capacities ranging from 200mAh to 2800Ah. Standard Li-Ion batteries normally use a rigid case, while Li-Polymer batteries often use the flexible foil type or pouch cell case, which reduces size and weight.
Figure 2 shows the typical discharge curves of a 2000mAh Li-Ion battery, from fully charged (4.2V) to fully discharged (3.0V) condition. The discharge rates are expressed as a ratio of battery capacity (C). At high discharge currents, the battery capacity cannot be fully utilized and the battery voltage will drop due to battery internal resistance.
When powering your application from a single Li-Ion cell, the application input range must consider the voltage fluctuation of the battery, which for most Li-Ion batteries ranges from 4.2V fully charged down to 3.0V fully discharged.
Most applications will require some form of voltage regulation. Richtek offers a wide range of LDOs, buck, boost and buck-boost converters that can operate from the typical Li-Ion battery cell voltage range and provide a stable output voltage.
Li-Ion batteries are sensitive to over-discharge, which is why many cells have build-in under-voltage protection circuits that switch off the cell when the cell is discharged below 2.5V. It is recommended to re-charge the battery or disconnect the battery from the system well before this battery internal protection is activated.
When Li-Ion batteries are not used for a prolonged time period, it is better to discharge them to around 40% (~3.7V) to reduce their aging effect.