18650 is the originator of
lithium-ion battery –a standard lithium-ion battery model that Japan
SONY Company set in order to save cost. Among them, 18 means diameter is
18mm, 65 means length is 65mm, 0 means cylindrical battery.
The
common 18650 battery is divided into a lithium ion battery and a
lithium iron phosphate battery. The lithium-ion battery voltage is 3.7V,
the charge cut-off voltage is 4.2v, the lithium iron phosphate battery
has a nominal voltage of 3.2V, the charge cut-off voltage is 3.6v, the
capacity is usually 1200mAh-3350mAh, and the common capacity is
2200mAh-2600mAh.
18650 lithium battery use
The
18650 battery life theory is cyclic charging 1000 times. Due to the
large capacity per unit density, most of them are used in laptop
batteries. In addition, the stability of the 18650 is very good at work.
It is widely used in various electronic fields: it is often used in
high-end glare flashlights. Power, wireless data transmitters, electric
warm clothing, shoes, portable instrumentation, portable lighting
equipment, portable printers, industrial equipment, medical equipment,
etc.
Using voltage to estimate the remaining capacity of the battery has the following instabilities:
1.
The same battery, in the case of the same remaining capacity, the
voltage value changes due to the magnitude of the discharge current.
The higher the discharge current is, the lower the voltage. In the absence of current, the voltage is highest.
2.
The effect of ambient temperature on the battery voltage. The lower the
temperature is, the lower the battery voltage of the same capacity.
3. The effect of cycling on the battery discharge platform,
As
the cycle progresses, the discharge platform of the lithium ion battery
tends to deteriorate. The discharge platform is lowered. Therefore, the
capacity represented by the same voltage also changes accordingly.
4. Different manufacturers, different capacity lithium-ion batteries, the discharge platform is slightly different.
5.
Lithium-ion batteries of different types of electrode materials have
large differences in discharge platforms. The discharge platforms of
cobalt lithium and manganese lithium are completely different.
All of the above will cause voltage fluctuations and voltage differences, making the battery capacity display unstable.
When
using voltage to measure the battery capacity of a mobile phone, it is
impossible to keep the phone in low current standby state all the time.
Temporary losses of large current, such as turning on the backlight,
playing a ringtone, and especially passing through, can quickly reduce
the battery voltage. At this time, the capacity displayed by the mobile
phone has to be reduced more than the actual capacity. When the high
current is removed, the battery voltage goes back up. This will cause
the unreasonable phenomenon that the display of mobile phone capacity
increases instead.
One
useful feature of lithium-ion batteries is that, when they are
discharged, the voltage of the battery decreases with the passage of the
charge and has a fairly steep slope. This gives us another approximate
metering method and the method of taking the battery voltage. It's like
measuring the height of the water in a tank gives you an idea of how
much water is left. But actually the voltage of the lithium battery is
much more complicated than measuring the height of the calm water in the
tank. The voltage used to estimate the residual capacity of a battery
has the following instability: for the same battery, the voltage value
varies with the discharge current under the same residual capacity. The
higher the discharge current is, the lower the voltage. In the absence
of current, the highest voltage; The effect of ambient temperature on
battery voltage, the lower the temperature, the lower the battery
voltage of the same capacity; The influence of the cycle on the
discharge platform of the battery, with the progress of the cycle, the
discharge platform of the lithium ion battery tends to deteriorate.
Discharge platform lowered. So the capacity of the same voltage changes
accordingly; Different manufacturers, different capacity of lithium ion
batteries, the discharge platform slightly different.
Lithium-ion
batteries of different types of electrode materials have large
differences in discharge platform. The discharge platforms of cobalt
lithium batteries and manganese lithium batteries are completely
different. All of the above will cause voltage fluctuations and voltage
differences, making the battery capacity display unstable. When using a
voltage to measure the battery capacity on a mobile phone, it is
impossible for the mobile phone to remain in a standby state with a
small current. Temporary loss of high current, such as turning on the
backlight, ringing the ring, especially through, will cause the battery
voltage to drop quickly. At this point, the capacity displayed by the
phone is reduced more than the actual capacity. When the large current
is removed, the voltage of the battery will rise. This will cause the
unreasonable phenomenon that the capacity display of the mobile phone
will increase instead.
First,
let's talk about the discharge platform of the battery, which means
that the voltage of the battery changes when the fully charged lithium
battery is discharged. The battery has a constant current discharge, and
the battery voltage has to go through three processes, namely, falling,
stabilizing, and then falling. In these three processes, the stable
period is the longest. The longer the stabilization time is, the higher
the discharge platform of the battery. The level of the discharge
platform is closely related to the battery manufacturing process. It is
because the market positioning of each lithium battery manufacturer is
different, the technical process is different, the discharge platform
controlled by it is different, and the quality is very different.
Generally,
18650 lithium batteries have a full voltage of 4.2V. When it is
discharged to 3.7V with a current of 1C and put it for 60 minutes, then
we say that the battery capacity is 2200mAh, during which time according
to the characteristics of the rechargeable battery. , make a picture
below, can better understand the relationship between battery capacity
and voltage and current time and discharge platform
Method
of measuring battery voltage: When the charger detects the battery
voltage while charging, it is considered full when the voltage reaches
the specified voltage value. If the voltage of the lithium battery is
charged to 4.2V, it is considered full. The accuracy of the voltmeter
for detecting voltage should be equal to plus or minus 1% accuracy. The
lithium battery is damaged due to overcharging. If you want to monitor
the battery charge and discharge, there are very mature circuits in the
book for reference. If you just measure it, then it will be easier to
calculate the load resistance according to the capacity, discharge with
the standard discharge current, then detect the voltage, as long as it
can It is sufficient to reach or approach the nominal discharge time.
There
are many shortcomings in the method of measuring the battery voltage,
such as the relationship between the open circuit voltage and the
capacity of the battery produced by different manufacturers. The
advantage is that the design cost is relatively low.
Another
common method of monitoring the remaining capacity is to estimate the
remaining battery capacity in some places where more accurate battery
capacity is required. Estimate the battery life by estimating the
remaining battery capacity by measuring the net charge flowing into/out
of the battery. The total current flowing into/out of the battery is
integrated, that is, the area under the curve in the figure is obtained,
and the obtained net charge number is the remaining capacity. This
method of calculating the battery capacity is currently considered to be
a more accurate method of calculating the battery power. Of course, the
design cost is also relatively high.
The page contains the contents of the machine translation.
