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The Knowledge of Lithium Batteries 2018-02-19

What are the advantages of lithium secondary battery?

1.High energy density

2.High working voltage

3.No memory effect

4.Long cycle life

5.No pollution

6.Light weight

7.low Self-discharge

What are the advantages of lithium polymer battery?

1. No battery leakage, the battery does not contain liquid electrolyte inside, instead, its colloidal solids;

2. Can be made of thin battery: 3.6V400mAh capacity, its thickness can be 0.5mm;

3 the batteries can be designed into a variety of shapes;

4 batteries can be bent: the maximum polymer battery can be bent around 900;

5. Can be made of  high voltage battery:the liquid electrolyte battery can only be made batteries in series to get high voltage, while there is no liquid in the polymer battery itself, so it can be made into  multi-layer in a single module to achieve high voltage;

6. The capacity will be twice the size of the same lithium-ion battery.

IEC standard lithium battery cycle life test:

The battery can be discharged form 0.2C to 3.0V

1.1C constant current and constant voltage when charging to 4.2V cut-off current 20mA, then put aside for 1 hour, last to discharge from 0.2C to 3.0V (one cycle);

After repeated 500 cycles,the capacity should be more than 60% of the initial capacity;

The national standard is that lithium battery standard charge retention test:

The battery should be discharged form 0.2C to 3.0V at 25 ℃. Kepp the the constant current constant voltage at 1C, and charge to 4.2V, the cut-off current 10mA. Stored the battery for 28 days at a temperature of 20 + _5 ,and then discharge from 0.2C to 2.75V to count the discharge capacity.

What is and how much is the self-discharge rate of secondary battery  ?

Self-discharge, also known as charge-holding capacity, which refers to at the state of open circuit, the capacity ability that the battery can storage under certain environmental conditions. In general, self-discharge is mainly affected by the manufacturing process, materials, storage conditions, self-discharge is one of the main parameters to measure the performance of the battery. Generally, the lower the battery temperature is, the lower the self-discharge rate is. However, it should be noted that too low or too high temperatures may cause the battery to be damaged and can not be used.

Compared to other rechargeable battery systems, self-discharge rates for solar cells containing liquid electrolyte are significantly lower at about 25% at about 10% / month.

What is the internal resistance of the battery, how to measure it?

Internal resistance refers to the resistance of battery when the current flowing through battery when working, which are generally divided into AC internal resistance and DC internal resistance. The internal resistance of the rechargeable battery is very small,  due to electrode capacity polarization when measured DC resistance , which will result in polarization resistance, so itits true value can not measured, while measured the exchange resistance can be immune to the impact of polarization resistance, we can get the value.

AC resistance test method is: use the characteristic that the battery is equivalent to an active resistance,give it a 1000HZ, 50mA constant current, sampling the the voltage, rectifting accurately measure the resistance from these process.

What is battery internal pressure, how much is the normal internal pressure generally ?

The internal pressure of the battery is due to the pressure generated by the gas generated during charging and discharging. Mainly affected by the battery material,manufacturing process, structure and other factors. In general, battery internal pressure are maintained at normal levels, the battery pressure may be increased in the case of overcharge or over discharge,

If the composite reaction speed is lower than the decomposition reaction speed, the gas will be too late to be consumed,then it will cause the increasing battery pressure.

What is the internal pressure test?

Lithium battery pressure test: (UL standard)

Simulate the battery at an altitude of 15240m (low pressure at11.6kPa), test if battery leakage or drum.

How does ambient temperature affect battery performance?

Among all the environmental factors, the temperature has the greatest effect on the charge-discharge performance of the battery. The electrochemical reaction at the electrode / electrolyte interface is related to the ambient temperature, and the electrode / electrolyte interface is regarded as the heart of the battery. If the temperature drops, the reaction rate of the electrode also drops. Assuming that the battery voltage is kept constant, the discharge current decreases and the battery power output also drops. If the temperature rise, the battery output power will rise, the temperature also affects the electrolyte transmission speed,which will accelerate when the temperature rise, the transmission temperature drops,the transmission slows, the battery charge and discharge performance will be affected. But the temperature is too high and is more than 45, which will destroy the chemical balance within the battery, leading to side effects.

Methods of controling the battery overcharge

In order to prevent the battery from overcharging, it is necessary to control the charging end point. When the battery is full, there will be some special information available to judge whether the charging reaches the end point. There are generally six ways to prevent the battery from being overcharged:

1. Peak voltage control: by detecting the peak voltage of the battery to determine the end of charging;

2.dT / dt control: by detecting the battery peak temperature change rate to determine the end of charging;

3.T control: When the battery is fully charged, the difference between the temperature and the ambient temperature will reach the maximum;

4.-V control: when the battery is fully charged and reaches to a peak voltage, the voltage will drop to a certain value;

5. Timing control: By setting a certain charging time to control the charging end, generally, filled the battery into the nominal capacity of 130% that the time required;

6. TCO Control: Consideration should be given to the safety and characteristics of the battery. Charging should be avoided at high temperatures (except for high temperature batteries), so charging should be stopped when the battery temperature is increased by 60℃.

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