Android battery (I): Basic Principles of Lithium Battery

Keywords: Android battery shutdown ChargingAndroidboot. Mode
Charger

Platform information:
Kernel: linux2.6/linux3.0
System: Android/android4.0
Platform: s5pv310 (samsungexynos 4210)

Author: xubin341719 (You are welcome to reprint it. Please note the author)

Correct the mistakes and learn and make progress together !!

The battery's position in electronic products is not required. However, the battery interface is relatively simple. There are only two cables: the positive and negative poles. This is widely known for primary school students. However, when using electronic products, there are still a lot of battery-related things.

This article introduces three aspects:

Android battery (I): Basic Principles of Lithium Battery

Android battery (2): Charging Process for Android shutdown and display of charging Screen

Android battery (III): Android battery system

Android battery (4): Battery meter (max17040) Driver Analysis

Android battery (5): Analysis of the battery charging IC (pm2301) Driver

The three most important steps for battery charging are as follows:

Step 1:Determine the voltage <3 V, pre-charge first, 0.05c current;

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

Step 3:Determine the voltage> 4.2 V, constant voltage charging, the voltage is 4.20 V, the current decreases with the increase of the voltage until full.

I. Lithium Battery

1. Briefly describe lithium battery and working principle

Since its advent in 1990, lithium-ion batteries have developed rapidly and are widely used in society due to their excellent performance. Lithium-ion battery has quickly occupied many fields, such as mobile phones, laptops, and small cameras, with incomparable advantages in other electric pools.

Currently, the basic principle of lithium battery is the so-called "rocking chair theory ". The charge-discharge of lithium batteries does not transfer electrons in the traditional way, but changes in energy by entering and exiting the lithium ion in the crystal of the layer. Under normal charge discharge, the entry and exit of lithium ion generally only changes the layer spacing, but does not damage the crystal structure. Therefore, in terms of charge discharge, lithium-ion battery is an ideal reversible battery. During the charge discharge, the lithium ion enters and exits at the positive and negative ends of the battery, just as the rocking chair shakes between the positive and negative ends. Therefore, some people refer to the lithium ion battery image as the rocking chair battery.

We often say that the superiority of lithium-ion batteries is for traditional Ni/CD and Ni/MH batteries.
It has advantages such as low self-discharge rate and non-memory effect with high voltage to energy ratio and long cycle life.

2. Knowledge about routine use of Lithium Battery
(1) misunderstanding: "The battery is activated, and the first three times are charged for more than 12 hours"

Many sayings about the "activation" problem of lithium battery are that the charging time must be over 12 hours, and the battery must be retried three times to activate the battery. This "charge for the first three times is charged for more than 12 hours" is obviously a continuation of the statement from the nickel battery (such as nickel-cadmium and nickel-Mh. Therefore, it can be said that it was a false positive at the beginning. After sampling, we can see that a considerable number of people confuse the two battery charging methods.

The charging and discharging characteristics of lithium battery and nickel battery are very different, all the serious official technical materials that have been reviewed emphasize that charge and discharge will cause great damage to lithium batteries, especially liquid lithium-ion batteries. Therefore, it is best to charge according to the standard time and standard method, especially do not charge over 12 hours. Generally, the charging method described in the mobile phone manual is a standard charging method suitable for the mobile phone.

(2) charge for a long period of time, fully use of the battery and re-charge

The cell phone or charger of a lithium battery will automatically stop charging after the battery is full, and there is no such thing as a "streaming" charge that lasts for more than 10 hours. If the lithium battery is fully filled, it will not be charged if it is placed on the charger.

Ultra-long charging and full use of empty power will cause excessive charging and over-discharge, which will permanently damage the positive and negative sides of the lithium-ion battery. From the molecular level, excessive discharge will lead to excessive release of lithium ion in the negative carbon electrode and collapse its layered structure. Excessive charging will hard pack too many lithium ions into the carbon structure of the negative electrode, and some of the lithium ions can no longer be released.

(3) battery life

The following table lists the cycle life data (DOD is short for discharge depth) of the lithium-ion battery charge-discharge cycle experiment table ):
Cycle Life (10% DOD):> 1000 times
Cycle Life (100% DOD):> 200 times
From the above data, we can see that the number of recharges is related to the discharge depth. The cycle life of 10% DOD is much longer than that of 100% DOD. Of course, if it is equivalent to the actual total charge capacity of 10% * 1000 = 100,100% * 200 = 200, it is better to fully charge and discharge the latter. However, the life of a lithium battery is mainly reflected in the charging and discharging cycle. This cycle is an absolute concept. The last time 30% of the power was used, the power was fully charged, and the next time 70% of the power was used, the power was fully charged, this is just a charging cycle. Therefore, the lithium battery is still used in accordance with the lithium battery inventor's slogan "out-of-the-box, out-of-the-box.

(4) battery calibration with regular deep charge/discharge

Lithium-ion battery generally comes with a management chip and a charging control chip. The management chip has a series of registers, including capacity, temperature, ID, charging status, discharge times, and other values. These values gradually change in use. The main function of the "one month or so should be fully filled" method in the instruction should be to correct the improper values in these registers.

 

2. lithium battery charging is a limited pressure flow mode

The process is completed in three steps:

Step 1: Determine the voltage <3 V, and perform pre-charging first. The current is 0.05c;

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

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

In fact, today I am not familiar with this. I checked it online and learned the above as common sense.
When charging starts, check the voltage of the battery to be charged first. If the voltage is lower than 3 V, pre-charge the battery first. The charging current is 1/10 of the set current, which is usually about 0.05c. After the voltage rises to 3 V, it enters the standard charging process. The standard charging process is: Constant Current charging with set current. When the battery voltage rises to 4.20v, constant voltage charging is changed to keep the charging voltage as 4.20 v. At this point, the charging current gradually drops. When the current drops to 1/10 of the Set charging current, the charging ends.
Generally, the charging current of lithium battery is set between 0.2C and 1C. The larger the current, the faster the charging, and the greater the heat of the battery. In addition, excessive current is charged, and the capacity is insufficient because the electrochemical reaction inside the battery takes time. Just like beer, if it is too fast, it will produce bubbles, but it will not be satisfied.
Term explanation: charge-discharge current is generally referred to as C, and C is the value corresponding to the battery capacity. Generally, the battery capacity is expressed as AH and Mah. For example, the battery capacity of M8 is 1200 Mah, and the corresponding C is 1200mA. 0.2C is equal to 240mA.
The following figure shows a typical Charging Curve for a lithium battery:

3. Discharge of lithium battery. For battery, normal use is the discharge process.
Lithium battery discharge only requires a few points:

1. The discharge current cannot be too large. Excessive Current leads to internal heat of the battery, which may cause permanent damage;

2. Never discharge too much! The lithium battery is most afraid of excessive discharge. Once the discharge voltage is lower than 2.7 V, the battery may be decommissioned.
Below is a typical discharge curve of a typical lithium battery:

The typical discharge curve shows that the larger the battery discharge current, the smaller the discharge capacity, and the faster the voltage drop.
Therefore, after the battery is working at a high load, the voltage will rise after the reduction of the load, that is, the "back-to-power" phenomenon.

 

Let's look at a figure. This discharge curve stops during the discharge process and shows "power-Back ".