Li Ion batteries: Difference between revisions
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The standard charging voltage for most 18650 Li-ion batteries is 4.20 V ± 0.05 V. But slight charge and discharge will improve the battery reliablity and life cycles. | The standard charging voltage for most 18650 Li-ion batteries is 4.20 V ± 0.05 V. But slight charge and discharge will improve the battery reliablity and life cycles. | ||
Slow charging is best (reduces stress and lengthens cell life.). Charge at less than 1 C current whenever possible, and at less than 0.5 C for resuscitating depleted cells. | |||
=== Reviving over discharged batteries === | |||
'''Step 1.''' If voltage is under 2.5V, give a batterie a brief pre-charge before full charging: | |||
* Set power supply to 3.7V and 500mA current limit. | |||
* Connect discharged cell and charge for 2-5 minutes. | |||
* Check voltage again. Stop when voltage reaches 3.0V. | |||
* This small pre-charge brings the cell voltage up enough for normal charging. | |||
'''Step 2.''' Charge depleted cells at 0.5 C or lower (slower is better). Then capacity test cycles to check cell health. Healthy 18650 cells should be: | |||
* 2300+ mAh capacity | |||
* <150-200 mΩ internal resistance | |||
* <2%/month self-discharge | |||
== 21700 cells == | == 21700 cells == | ||
== Spot welding == | == Spot welding == | ||
Revision as of 10:45, 10 August 2025
Introduction
1865 / 18650 cells
Diameter is 18 mm and length 65.0 mm.
Voltage
Note that the chemistry changes and thus these value might be a bit different. Be careful.
- Discharge cutoff voltage (the low voltage limit) is around 2.0V to 2.5V
- Over discharged < 2.5 V
- Discharged 3 V
- Nominal voltage is (usual) 3.6 V or 3.7 V.
- Full charge voltage is 4.2 V, which is the maximum voltage
Chemistry:
- Lithium Cobalt Oxide (LiCoO2): nominal voltage of 3.6V and is known for its high energy density.
- Lithium Manganese Oxide (LiMn2O4): a nominal voltage of 3.7V and offer thermal stability compared to LiCoO2
- Lithium Nickel Manganese Cobalt Oxide (NMC): a nominal voltage of 3.6V or 3.7V and provide a good balance of energy density and power capability.
- Lithium Iron Phosphate (LiFePO4): a nominal voltage of about 3.2V with excellent safety characteristics and long cycle life.
Over the upper limit (maximum voltage) battery will cause electrolyte breakdown and thermal runaway.
Below the lower Limit the battery’s chemistry may change irreversibly.
State of charge (SOC) and maximum voltage relation.
Charging
The standard charging voltage for most 18650 Li-ion batteries is 4.20 V ± 0.05 V. But slight charge and discharge will improve the battery reliablity and life cycles.
Slow charging is best (reduces stress and lengthens cell life.). Charge at less than 1 C current whenever possible, and at less than 0.5 C for resuscitating depleted cells.
Reviving over discharged batteries
Step 1. If voltage is under 2.5V, give a batterie a brief pre-charge before full charging:
- Set power supply to 3.7V and 500mA current limit.
- Connect discharged cell and charge for 2-5 minutes.
- Check voltage again. Stop when voltage reaches 3.0V.
- This small pre-charge brings the cell voltage up enough for normal charging.
Step 2. Charge depleted cells at 0.5 C or lower (slower is better). Then capacity test cycles to check cell health. Healthy 18650 cells should be:
- 2300+ mAh capacity
- <150-200 mΩ internal resistance
- <2%/month self-discharge
