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Correct charge method

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Lithium battery

Lithium batteries such as mobile phones and notebook computers are used as secondary batteries, which can be charged multiple times and are convenient to use. However, there are many opinions and even misunderstandings regarding the charging method of lithium batteries.

So, how to charge the new lithium battery correctly? Xixi has sorted out the commonly used mobile phone lithium battery charging methods. Of course, you must know why. The correct use of lithium batteries is inseparable from the understanding of the charging and discharging process of lithium batteries.

1. Correct charging method for lithium battery

  • Regardless of whether the lithium battery is used or not, the “shelf life” is 3 years, and it decays quickly after about 400-500 times. It depends on whether you use it for 3 years or the number of times you charge it first.

  • In addition to being afraid of low power, lithium batteries are also afraid of overheating, especially when charging. If your mobile phone case has poor heat dissipation and heats up while charging, it is best to remove the case while charging.

  • Shallow charge and shallow discharge are ideal, that is, charging and discharging do not reach 100% of the maximum capacity of the battery, that is, the charging and discharging cannot be completed. When the battery is 10%-90%, it can be charged normally, and it can be pulled out after it is fully charged. Do not use the phone for a long time during the charging process, which can make it live the longest.
  • It is not recommended to play with the mobile phone while charging. It should be safer when the battery is half-charged (ie about 50%). If the temperature inside the battery is relatively high when the battery is full, the heat will be generated when playing the mobile phone. If the battery becomes larger, the battery temperature will have a certain impact on the life.

2. Detailed explanation of lithium battery charging process

The most suitable charging process for lithium-ion batteries can be divided into four stages: trickle charging, constant current charging, constant voltage charging and charging termination.

Lithium battery
  • Stage 1: trickle charge-trickle charge is used to pre-charge the fully discharged battery cell (recovery charge). When the battery voltage is lower than about 3V, first charge the battery with a constant current of maximum 0.1C.

  • Phase 2: Constant current charging-when the battery voltage rises above the trickle charge threshold, increase the charging current for constant current charging. The current for constant current charging is between 0.2C and 1.0C. The current during constant current charging is not required to be very accurate, and quasi-constant current is also acceptable. In the linear charger design, the current often rises as the battery voltage rises to minimize the heat dissipation problem on the pass transistor.
    Constant current charging greater than 1C will not shorten the entire charging cycle time, so this approach is not advisable. When charging with a higher current, the battery voltage will rise faster due to the overvoltage of the electrode reaction and the voltage rise on the internal impedance of the battery. The constant current charging phase will become shorter, but since the time of the constant voltage charging phase below will increase accordingly, the total charging cycle time will not be shortened.

  • Phase 3: Constant voltage charging-When the battery voltage rises to 4.2V, the constant current charging ends and the constant voltage charging phase begins. To maximize performance, the voltage regulation tolerance should be better than +1%.

  • Stage 4: Charge termination-Unlike nickel batteries, continuous trickle charging of lithium-ion batteries is not recommended. Continuous trickle charge will cause the plate plating effect of metal lithium. This will make the battery unstable and may cause a sudden automatic quick disassembly.

There is two typical lithium battery charging termination methods: using the minimum charging current to determine or using a timer. 

The minimum current method monitors the charging current in the constant voltage charging stage and terminates charging when the charging current decreases to the range of 0.02C to 0.07C. The second method starts timing at the beginning of the constant voltage charging phase, and terminates the charging process after two hours of continuous charging.

The above four-stage charging method takes about 2.5 to 3 hours to complete the fully discharged battery. Advanced chargers also adopt more safety measures. For example, if the battery temperature exceeds the specified window (usually 0°C to 45°C), then charging will be suspended.

It can also be seen from the lithium battery charging curve that we can not only use the lithium battery correctly according to the characteristics of each stage, but also better protect the lithium battery and avoid improper operation that may damage the lithium battery.

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2 thoughts on “Correct charge method”

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