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Basic concepts and parameters of lithium polymer batteries
2022-11-15
Lithium polymer battery, English LI-polymer, referred to as LIPO, is a new type of battery with high energy density and large discharge current. At the same time, lithium batteries are relatively fragile to use, and are extremely sensitive to overcharge and overdischarge. You should be familiar with their performance during use. The charging and discharging process of lithium polymer batteries is the process of intercalation and deintercalation of lithium ions. During charging, lithium ions are detached from the negative electrode and inserted into the positive electrode, while during discharge, lithium ions are separated from the positive electrode and inserted into the negative electrode. Once the lithium polymer battery is discharged and the voltage is too low or the charging voltage is too high, the structure of the positive and negative electrodes will collapse, resulting in irreversible damage to the lithium polymer battery.
The main parameters
Discharge cut-off voltage 2.75V
The minimum voltage for safe discharge of the battery cell. Continuing to discharge below this voltage will cause damage to the battery performance.
Charge cut-off voltage 4.20V
The highest voltage for safe charging of the battery cell. Continuing to charge above this voltage will damage the battery performance.
Standard voltage 3.7V
The standard nominal voltage of the cell is also the parameter we use when calculating the voltage.
Storage voltage 3.85V
The voltage suitable for long-term storage, lithium batteries have the characteristics of low self-discharge, but there will still be partial self-discharge during long-term storage, resulting in a voltage drop, so it should be stored at a voltage higher than 3.7V.
S number
When we call the voltage of the battery, we usually call it S, and S is the number of batteries connected in series. For example, a 12S lithium battery actually means that 12 cells are connected in series. The standard voltage of a lithium battery is 3.7V. Its voltage is 3.7*12=44.4V.
S refers to the number of batteries in series.
P number
P refers to the number of batteries connected in parallel. For example, 3S1P means that the batteries are not connected in parallel; while for 3S2P, the battery is actually composed of 6 batteries connected in series.
Internal resistance
Ohmic internal resistance mainly refers to the composition of electrode material, electrolyte, diaphragm resistance and contact resistance of various parts, which is related to the size, structure and assembly of the battery. The internal resistance of the battery is very small, and we generally define it in units of milliohms. The smaller the internal resistance, the stronger the discharge capacity of the battery, and the weaker the discharge capacity of the battery with the larger the internal resistance.
C number
battery discharge rate
capacity
The capacity of the battery is expressed in Mah or Ah, which means that the battery continues to discharge at a certain current for 1 hour.
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