A typical discharge end voltage for lithium-ion Li-ion batteries is 3 V per cell. And 2.5 V is the cut-off voltage, interrupting the process of further discharge.
Charge fully discharged lithium-ion Li-ion rechargeable batteries, three-stage charging method to put the batteries in working condition.
However, in practice, it happens that such batteries can be completely discharged when the voltage is below 2.5 V per cell. This usually occurs when they are stored for a long time without recharging. In this case, manufacturers of lithium-ion Li-ion batteries recommend a three-stage method of charging them to put them into working condition..
Not all chargers can charge lithium-ion batteries discharged to less than 2.5 V per cell. First you need to raise the voltage on the battery to a level sufficient to start the charger. After that, a small current charge is needed to restore its capacity.
Particular caution should be exercised when lithium-ion Li-ion batteries are restored to life, which have had a long interruption in use and were stored in a state of deep or complete discharge..
Recommendations for charging fully discharged lithium-ion Li-ion batteries.
As an example, we give recommendations for charging a fully discharged lithium-ion battery used to power old Siemens 45 series mobile phones (S45, ME45). These phones use a 840 mAh lithium-ion battery. The role of the temperature sensor in it is performed by a thermistor with a resistance of 22 kOhm at f = 25 degrees.
In general, the power management of a cell phone is provided by a dedicated microchip (ASIC). The manufacturer – Siemens – clearly defined that the lower voltage limit to which the battery can be discharged is 3.2 V. Why not 2.5 V, as mentioned above? Because only with a voltage of at least 3.2 V, the operation of a mobile phone is guaranteed. The voltage of a fully charged battery is 4.2 V.
In the event that a deep discharge of the battery has occurred, charging it as usual – in 2-3 hours – will fail. Recovery charge must be performed in three stages:
1. Battery charge current of 20 mA to a voltage of 2.8 V.
2. Charge current of 50 mA to a voltage of 3.2 V.
3. Normal charge up to 4.2 V.
When the battery is completely discharged, the charge process is controlled by a specialized (custom) ASIC chip type DO8296B. Moreover, in this case, its power source in the first two stages of the charge is the charger. And on the third – the battery itself.
Each chain of parallel-connected lithium-ion batteries must have its own means of monitoring their condition. The more elements are connected in series in the battery, the more perfect should be its protection circuit. In commercial applications, the number of batteries in a battery should not exceed four.
Based on the book Battery.