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Analysis of Charging and Discharging Mechanism of Lithium Battery

Author: Source: Datetime: 2016-10-27 14:24:47

The most important three steps of lithium battery charging:


The first step: to determine the voltage <3V, the first pre-charge, 0.05C current;


The second step: to determine the 3V


The third step: to determine the voltage> 4.2V, constant voltage charge, the voltage is 4.20V, the current decreases with increasing voltage until full.

1, brief description lithium battery and working principle


Lithium-ion battery since its inception in 1990, because of its excellent performance has been rapid development, and widely used in society. Lithium-ion batteries to other unparalleled advantages of the battery quickly occupied many areas, as we all know mobile phones, laptops, small cameras, solar powered portable generator and so on.


At present the basic principle of lithium battery is recognized as the so-called "rocking chair theory." Lithium battery discharge and discharge is not through the traditional way to achieve the transfer of electrons, but by lithium ions in the layer of crystal material in and out, the energy change. In the case of normal charge and discharge, the lithium ion out of the general cause only layer spacing changes, and will not cause damage to the crystal structure, so from the discharge in terms of reflection, lithium-ion battery is an ideal reversible battery. Lithium-ion battery in the positive and negative poles in and out, just as a rocking chair in the positive and negative shake to shake, so it was the lithium-ion battery image called rocking chair battery.


We often say that the advantages of lithium-ion battery is for the traditional nickel-cadmium batteries (Ni / Cd) and nickel-metal hydride batteries (Ni / MH) in terms of. With a working voltage high specific energy cycle life long self-discharge rate without memory effect and so on.


2, lithium battery in the daily use of the common sense


(1), the error: "battery activation, the first three charge 12 hours or more"


For lithium battery "activation", many say is: charge time must be more than 12 hours, repeated three times in order to activate the battery. This "charge the first three times to charge more than 12 hours," saying, apparently from the nickel batteries (such as nickel-cadmium and nickel-hydrogen) continue down the argument. So this argument can be said that the beginning is misinformation. After a sample survey, we can see a considerable number of people confused the two battery charging method. While for lifepo4 batteries, the charge method is different.


Lithium batteries and nickel batteries charge and discharge characteristics are very different, all the serious technical information reviewed have stressed overcharge and over discharge will lithium batteries, especially the liquid lithium-ion battery caused great harm. Therefore, the best charge in accordance with standard time and standard methods of charging, in particular, do not carry more than 12 hours of super-long charge. Typically, the instructions on the phone description of the charging method is suitable for the phone's standard charging method.


(2), not a long time to charge the battery fully used up re-charge


Lithium-ion battery cell phone or charger will automatically stop charging after the battery is full, there is no nickel-powered charger called 10 hours continuous "trickle" charge. If the lithium battery in full, on the charger is also no longer charged.


Abnormal time charge and full use of empty power will cause overcharge and over-discharge, the lithium-ion battery will cause permanent damage to the positive and negative, from the molecular level, over-discharge will lead to excessive release of lithium-negative carbon electrode Layer structure collapse, over-charging will be too much lithium-ion hard stuffed into the negative carbon structure, which makes some of the lithium-ion can no longer be released.


(3), battery life


On the lithium-ion battery charge and discharge cycle of the test table, on the cycle life of the data are listed below (DOD is the discharge depth of the English abbreviation):


Cycle life (10% DOD):> 1000 times

Cycle life (100% DOD):> 200 times


Can be seen from the above data, the number of chargeable and discharge depth, 10% DOD cycle life than 100% DOD to be much longer. Of course, if converted to the actual charge of the relative total capacity of 10% * 1000 = 100,100% * 200 = 200, the latter fully charge or discharge or to be better. But the lithium battery life is mainly reflected in the charge and discharge cycle, the cycle is an absolute concept, the last use of 30% of the electricity, full of electricity, the next use of 70% of the electricity, and full of electricity, this happens to be a charge cycle. So still follow the inventor of the slogan of lithium batteries, "that is, that is, that is, that is, charge and use" method of using lithium batteries.


(4), regular depth of charge and discharge for battery calibration


Lithium-ion batteries are generally with a management chip and charge control chip. For example, the lifepo4 battery pack with BMS in solar power systems. The management chip has a series of registers, there are capacity, temperature, ID, charge status, the number of discharge and other values. These values will gradually change in use. Use the instructions in the "use of a month or so should be fully charged once" approach should be the main role is to amend the value of these registers inappropriate.

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