1. Lithium battery

1. Briefly describe the lithium battery and its working principle

Since its inception in 1990, it has developed rapidly due to its excellent performance and has been widely used in society. Lithium-ion batteries have quickly occupied many fields with the incomparable advantages of other batteries, such as well-known mobile phones, notebook computers, small cameras, etc.

The currently accepted basic principle of lithium batteries is the so-called "rocking chair theory". The charge and discharge of the lithium battery are not realized by the transfer of electrons in the traditional way. Still, the energy change occurs through the entry and exit of lithium ions in the crystal of the layered material. Under standard charge and discharge conditions, the entry and exit of lithium ions generally only cause changes in the interlayer spacing without causing damage to the crystal structure. Therefore, lithium-ion batteries are ideal reversible batteries from the perspective of charge and discharge. When charging and discharging, lithium ions go back and forth between the positive and negative electrodes of the battery, just like a rocking chair which is rocking between the positive and negative electrodes. Therefore, some people call the lithium-ion battery a rocking chair battery.

The advantages of lithium-ion batteries that we often say are for traditional nickel-cadmium batteries (Ni/Cd) and nickel-metal hydride batteries (Ni/MH). It has the advantages of high working voltage, high specific energy, significant cycle life, long self-discharge rate and no memory effect.

2. Common sense in the daily use of lithium batteries

(1) Misunderstanding: "The battery is activated, and the first three charges are more than 12 hours."

There are many sayings for the "activation" of lithium batteries: the charging time must be more than 12 hours, and it must be repeated three times to activate the battery. This statement that "the first three charges should be charged for more than 12 hours" continues the message from nickel batteries (such as nickel-cadmium and nickel-metal hydride). Therefore, this statement can be said to be misrepresented from the beginning. After a sample survey, it can be seen that a considerable number of people confuse the charging methods of the two batteries.

Lithium and nickel batteries' charging and discharging characteristics are very different, and all the formal severe technical documents I have reviewed emphasize that overcharge and over-discharge can cause massive damage to lithium batteries, predominantly liquid lithium-ion batteries. Therefore, it is best to charge according to the standard time and method, significantly not to charge for more than 12 hours. Usually, the charging method described in the mobile phone manual is the common charging method suitable for the mobile phone.

2) It is not beneficial to charge for a long time, and the battery is ultimately used up and then charged

Lithium-ion battery mobile phones or chargers will automatically stop charging after the battery is fully charged. There is no so-called "trickle" charging for more than 10 hours for nickel battery chargers. If the lithium battery is fully charged, it will not be charged when placed on the charger.

Over-charging and over-discharging will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. From a molecular point of view, over-discharging will cause the negative electrode carbon to release lithium ions excessively and make its layer structure collapses. Overcharging will force so many lithium ions into the negative carbon structure that some of them can no longer be released.

(3) battery life

Regarding the experimental table of charge and discharge cycles of lithium-ion batteries, the data on cycle life are listed as follows (DOD is the English abbreviation of the depth of discharge):

Cycle life (10% DOD): >1000 times

Cycle life (100% DOD): > 200 times

It can be seen from the above data that the number of rechargeable times is related to the depth of discharge, and the cycle life at 10% DOD is much longer than that at 100% DOD. Of course, if the total capacity of actual charging is 10%*1000=100, 100%*200=200, the latter's full charge and discharge are still better. However, the life of a lithium battery is mainly reflected in the charge and discharge cycle. This cycle is an absolute concept. The last time it used 30% of the power, it was fully charged, and the next time it used 70% of the administration, it was fully charged again. This is just a charge. Cycle. Therefore, the lithium battery is still used by the slogan of the inventor of the lithium battery, "charge and use as soon as you use it".

(4) Regular deep charge and discharge for battery calibration

Lithium-ion batteries generally have a management chip and a charge control chip. There are a series of registers in the management chip, which store the values of capacity, temperature, ID, charging state, and discharge times. These values will gradually change during use. The primary function of the "full charge and discharge once a month or so" instruction manual should be to correct the improper values in these registers.

2. The charging method of the lithium battery is the voltage-limited cross-current method

It is mainly completed in three steps:

Step 1: To judge the voltage < 3V, pre-charge should be carried out first, 0.05C current;

Step 2: Judging 3V<voltage<4.2V, constant current charging 0.2C~1C current;

Step 3: Judging the voltage > 4.2V, constant voltage charging, the voltage is 4.20V, the current decreases with the increase of the voltage until it is fully charged.

Today, I don't understand this point a bit. I checked it on the Internet, and then I understood it as common sense.

When charging starts, the battery's voltage to be charged should be detected first. If the voltage is lower than 3V, pre-charging should be performed first. The charging current is 1/10 of the set current, generally about 0.05C. After the voltage rises to 3V, it enters the standard charging process. The normal charging process is constant current charging with the set current. When the battery voltage increases to 4.20V, it is changed to continuous voltage charging, and the charging voltage is kept at 4.20V. The charging current gradually decreases at this time, and when the current decreases to 1/10 of the set charging current, the charging ends.

Generally, the charging current of lithium batteries is set between 0.2C and 1C. The higher the current, the faster the charging, and the greater the battery heat. Moreover, if the current is too large for charging, the capacity is not total because the electrochemical reaction inside the battery takes time. Like pouring beer, if you run it too fast, it will produce foam and become dissatisfied.

Terminology explanation: The charge and discharge current is generally referred to by C, which is the value corresponding to the battery capacity. The battery capacity is usually expressed in Ah and mAh. For example, the battery capacity of the M8 is 1200mAh, and the corresponding C is 1200mA. 0.2C is equal to 240mA.

The following is a typical charging curve for lithium batteries:

3. The discharge of lithium battery, for the storm, the normal use is the discharge process

There are only a few points to pay attention to when discharging lithium batteries:

1. The discharge current should not be too large. Excessive current will cause internal heating of the battery, which may cause permanent damage;

2. Never over-discharge! Lithium batteries are most afraid of over-discharge. The battery may be scrapped once the discharge voltage is lower than 2.7V.

The following is a typical discharge curve of a general lithium battery:

It can be seen from the typical discharge curve diagram that the larger the battery discharge current, the smaller the discharge capacity and the faster the voltage drop.