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Analysis of common terms for lithium batteries-Semco University

Analysis of common terms for lithium batteries
Introduction

Energy density, self-discharge rate, cut-off voltage, battery internal resistance… This series of lithium electricity parameters and technical terms are confusing for many people who have just come into contact with lithium batteries. So, what do these common terms for lithium batteries mean? Let’s follow the editor to learn about it.

1. Battery Capacity:

The capacity of the battery is determined by the number of active substances in the battery, usually expressed in mAh or Ah.

2. Charging And Discharging Magnification:

It means how much current it is charged and discharged. Generally, it is calculated by a multiple of the nominal capacity of the battery, which is called a few C. Taking a battery with a capacity of 1500mAh as an example, it is stipulated that 1C = 1500mAh. If discharged at 2C, that is, a current discharge is 3000mA, the battery test is generally based on 0.5C.

3. Charging Cut-Off Voltage:

When fully charged, the active substance on the plate has reached a saturation state. At this time, the voltage is called the charging cut-off voltage. Ternary lithium is generally set at 4.2V, and lithium iron phosphate is generally set at 3.65V.

4. Discharge Cut-Off Voltage:

After the lithium battery is discharged to a certain voltage, it is not appropriate to continue to discharge, otherwise, it will cause irreversible loss of part of the lithium battery power, and serious cases will completely damage the battery. Ternary lithium is generally set at 2.75V, and lithium iron phosphate is generally set at 2.5V.

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5. Nominal Voltage:

The potential difference between the positive and negative electrodes of the battery is called the Nominal voltage of the battery. The Nominal voltage is determined by the electrode potential of the plate material and the concentration of the internal electrolyte. Ternary lithium is usually labeled 3.6V or 3.7V, and lithium iron phosphate batteries are usually labeled 3.2V. Internal pressure: The internal pressure of the battery is the pressure caused by the internal accumulation of moisture and organic solution in the battery during the charging and discharging process. It is affected by battery materials, manufacturing process, battery structure, and other factors.

6. Internal Resistance:

Resistance to the battery when it is working, the current flows through the inside of the battery. It is generally divided into AC internal resistance (ACR) and DC internal resistance (DCR).

7. Cycle Life:

After a complete charge and discharge, it is called a cycle. IEC (International Electrotechnical Commission) standard: a single battery is discharged to 3.0V at 0.2C, 1C constant current is charged to 4.2V, and the cut-off current is 20MA. After being shelved for 1 hour, it is discharged to 3.0V (one cycle) at 0.2C. After 500 repeated cycles, the capacity should be 60 of the initial capacity. More than %. That is to say, the cycle life of lithium batteries is 500 times. The national standard stipulates that after 300 cycles, the capacity should be maintained at 70%; if it is lower than 60% of the initial capacity, scrapping should generally be considered.

8. Self-Discharge Rate:

The rate of loss of capacity during storage, the reduced capacity as a proportion of the battery capacity, expressed as a percentage of the capacity decrease per unit time. The self-discharge rate of general lithium batteries is 2%-9%/month. The lower the self-discharge rate, the better the storage performance. The impact of ambient temperature is great, and too high a temperature will accelerate self-discharge.

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9. SOC (State of Charge):

A charge state, also known as a residual charge, represents the ratio of the remaining capacity of the battery after being used for a period of time or for a long time to the capacity of its fully charged state, which is often expressed as a percentage.

The value range is 0~1, which means that the battery is fully discharged when SOC = 0, and when SOC = 1 means that the battery is fully charged.
DOD (Depth of Discharge): The discharge depth of the battery. When the battery is full,
Its DOD is 0, and its DOD is 1 after full discharge. Therefore, under normal circumstances,
The DOD of the battery is a value between 0 and 1, and the relationship between DOD and SOC is DOD+SOC=1.

10. Energy Density:

The energy released per unit volume or mass, usually using volume energy density (Wh/L) or mass-energy density (Wh/Kg).

Conclusion

Familiar with and mastering the common terms of lithium batteries knowledge is compulsory for beginners. It is conducive to establishing the basic concepts of lithium electric products and the normal development of daily work.

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