Mastering the use and maintenance techniques of lithium-ion batteries can
extend the service life of lithium-ion batteries and maintain the excellent
performance of the battery.
Lithium-ion battery discharge
Discharge stop voltage: The rated voltage of lithium-ion battery is 3.6V
(some products are 3.7V), and the discharge stop voltage is 2.5-2.75V (the
battery factory gives the operating voltage plan or the stop discharge voltage,
each parameter is slightly different ). The discharge termination voltage of the
battery should not be less than 2.5 (n is in series
Number of batteries), continuous discharge below the discharge stop voltage
is called over-discharge. Over-discharge will shorten the battery life, and in
severe cases, it will cause battery failure. When the battery is not in use, the
battery should be charged until it retains 20% of its capacity, and then stored
in moisture-proof packaging. The voltage should be checked once every 3 to 6
months and charged to ensure that the battery voltage is within the safe voltage
value (above 3V).
Discharge current: Lithium-ion batteries are not suitable for high-current
discharge. When excessive current is discharged, a higher internal temperature
will occur and energy will be lost, reducing the battery life.
During the discharge time, if there are no protective components in the
battery, overheating will occur and damage the battery. Therefore, the maximum
discharge current given by the battery production factory should not exceed the
maximum discharge current given in the product characteristics table during
use.
Discharge temperature: The discharge curves at different temperatures are
different. At different temperatures, the discharge voltage and discharge time
of lithium-ion batteries are also different.
The battery should be discharged (operated) within the temperature range of
-20°C to +60°C.
Lithium-ion battery charging
What should be noted when using lithium batteries is that the battery
enters a dormant state after being left for a period of time. At this time, the
capacity is lower than the normal value and the use time is also shortened.
However, lithium batteries are very easy to activate. As long as 3-5 normal
charge and discharge cycles are used, the battery can be activated and restored
to normal capacity. Due to the characteristics of lithium batteries, they have
almost no memory effect. Therefore, the new lithium battery in the user's mobile
phone does not require special methods and equipment during the activation
process.
To charge lithium-ion batteries, a dedicated lithium-ion battery charger
should be used. Lithium-ion battery charging adopts the "constant
current/constant voltage" method. Constant current charging is performed first,
and when it is close to the cut-off voltage, it is changed to constant voltage
charging. For example, a battery with a capacity of 800mA.h has a charging
voltage of 4.2V. The battery is
800mA (charge rate 1C) constant current charging. At the beginning, the
battery voltage rises with a large slope. When the battery voltage is close to
4.2V, it changes to
4.2V constant voltage charging, the lithium battery current gradually
decreases, and the voltage does not change much. When the charging current drops
to 1/10C (about 80mA), it is considered that the battery is close to the
charger.
When the battery is full, charging can be stopped (some chargers start a
timer after reaching 10C and complete charging after a certain period of time).
Do not use rechargeable nickel-cadmium batteries
Use electrical appliances (three-cell nickel-cadmium batteries) to charge
lithium-ion batteries (although the rated voltage is the same, 3.6V). Due to the
different charging methods, it is easy to cause overcharge.
Charging voltage: The charging stop voltage when fully charged is related
to the battery negative electrode material. Coke is 4.1V, while graphite is
4.2V. They are generally called 4.1V lithium-ion batteries and 4.2V lithium-ion
batteries. When charging, please note that 4.1V batteries cannot be charged with
a 4.2V charger, otherwise there will be a risk of overcharging.
(4.1V and 4.2V chargers use different charger ICs). Lithium-ion batteries
have very high charging requirements and require sophisticated charging circuits
to ensure charging safety. The tolerance of the charging voltage accuracy is ±1%
of the additional value (for example, when charging a 4.2V lithium-ion battery,
the tolerance is
±0.042V), overvoltage charging will cause permanent damage to the
lithium-ion battery.
Charging current: Lithium-ion battery charging current should be based on
the battery manufacturer's recommendations and requires a current-limiting
circuit to prevent overcurrent (overheating). The commonly used charging rate is
0.25~1C, and the recommended charging current is 0.5C (C is the capacity of the
battery, such as a battery with a nominal capacity of 1500mA.h.
Charging current 0.5*1500=750mA). When charging with high current, it is
often necessary to detect the battery temperature to prevent battery damage or
explosion due to overheating.
Charging temperature: When charging the battery, its ambient temperature
cannot exceed the temperature plan listed in the product characteristics table.
The battery should be in the temperature range of 0~45℃
Charge in a safe environment, away from high temperature (above 60℃) and
low temperature (-20℃) environments.
If a lithium-ion battery is overcharged, overdischarged or overcurrent
during the charging or discharging process, it will cause damage to the battery
or reduce its service life. Open for this
It emits various protection components and protection circuits composed of
protection ICs, which are installed in the battery or battery pack to provide
complete protection for the battery. But
Overcharge and overdischarge should be avoided as much as possible during
use. For example, when the mobile phone battery is charging, it should be
separated from the charger in time when it is almost full.
Leave. When the discharge depth is shallow, the cycle life will be
significantly improved. Therefore, when using it, do not wait until a low
battery signal appears on your phone before charging it.
Please do not continue to use it when this signal appears, although there
is still some residual capacity available for use when this signal appears.
storage and shipping
Lithium-ion batteries can be stored in a clean, dry, and ventilated
environment with a temperature of -5 to 35°C and a relative humidity of no more
than 75%. They should be prevented from corrosion.
If it comes into contact with sexual substances, keep away from fire and
heat sources. Do not place it in direct sunlight. Do not disassemble the battery
at will. If the battery is stored for a long time, the battery
The capacity should be maintained at 30% to 50% of the nominal capacity. It
is recommended that the stored batteries be charged every 6 months.
Batteries should be packed into boxes for transportation. During
transportation, they should avoid violent vibration, impact or squeezing, and
avoid exposure to sunlight and rain. Automobiles can be used.
Cars, trains, ships, airplanes and other means of transportation are used
for transportation.
short circuit
Regarding the safety issues of lithium-ion batteries, friends, please pay
attention. Lithium-ion batteries are prone to short circuits during
charging.
Although most lithium-ion batteries have protection circuits against short
circuits and explosion-proof wires. But in many cases, this circuit works in
various situations,
It doesn't necessarily work. The effect of explosion-proof wires is also
very limited.
overcharge
All lithium-ion batteries, including polymer lithium-ion batteries, lithium
iron batteries, etc., are very afraid of overcharging.
If the lithium-ion battery is charged for too long, the possibility of
explosion will increase.
The chemical properties of lithium are very active and easy to burn. When
the battery is charged and discharged, the temperature inside the battery
continues to rise, and the gas generated during the activation process
expands.
expansion, causing the internal pressure of the battery to increase. When
the pressure reaches a certain level, if the outer shell is damaged, it will
rupture, causing leakage, fire, or even explosion.
Therefore, we must pay great attention to safety when using lithium-ion
batteries.
Charge
Charging is an important process for repeated use of batteries. The
charging process of lithium-ion batteries is divided into two stages: constant
current fast charging stage and constant voltage current decreasing stage.
part. In the constant current fast charging stage, the battery voltage
gradually rises to the battery's standard voltage, and then switches to the
constant voltage stage under the control chip, and the voltage no longer
rises.
High to ensure that it will not be overcharged, the current will gradually
weaken to the set value as the battery power increases, and charging will
eventually be completed. Power calculation chip pass
By recording the discharge curve, the battery capacity can be calculated by
sampling. After repeated use of lithium-ion batteries, the discharge curve will
change.
Although the battery does not have a memory effect, improper charging and
discharging will seriously affect the battery performance.
Charging precautions
Excessive charging and discharging of lithium-ion batteries will cause
permanent damage to the positive and negative electrodes. Excessive discharge
causes the negative electrode carbon sheet structure to collapse, and the
collapse will cause
During the charging process, lithium ions cannot penetrate; overcharging
causes too many lithium ions to be embedded in the carbon structure of the
negative electrode, causing some of the lithium ions to no longer be able to
penetrate.
The law is released.
The charging capacity is equal to the charging current multiplied by the
charging time. When the charging control voltage is certain, the larger the
charging current (the faster the charging speed), the higher the charging
speed.
The smaller the amount of electricity. Excessive battery charging speed and
improper stop voltage control point will also cause insufficient battery
capacity. In fact, part of the battery's power
The extremely active material stops charging without sufficient reaction,
and this phenomenon of insufficient charging intensifies as the number of cycles
increases.
discharge
For the first charge and discharge, if the time can be longer (usually 3-4
hours is enough), then the electrode can reach the highest oxidation state as
much as possible (enough to
(electricity), when discharging (or using), it is forced to the specified
voltage, or until it automatically shuts down, which can activate the battery
usage capacity.
However, in the daily use of lithium-ion batteries, there is no need to do
this. It can be charged at any time as needed. It is not necessary to be fully
charged when charging.
Stop, no need to discharge first. Operations like initial charge and
discharge only need to be performed 1-2 times every 3-4 months.
Internal short circuit protection
Due to the influence of many factors such as material system and
manufacturing process, lithium-ion batteries are at risk of internal short
circuit. Although lithium-ion batteries are
They have passed strict aging and self-discharge selections before leaving
the factory. However, due to process failures and other unpredictable
application factors, there are still some problems.
A certain probability of failure leads to internal short circuit during
use. Regarding power batteries, there are hundreds or even tens of thousands of
lithium-ion batteries in the battery pack.
section, which greatly increases the probability of internal short-circuit
in the battery pack. Due to the huge energy contained inside the power battery
pack, the occurrence of internal short circuit can easily be induced.
Vicious accidents, resulting in casualties and property losses.
For parallel-connected lithium-ion power battery modules, when one or
several batteries are short-circuited, the other batteries in the battery module
will discharge it.
The energy of the battery pack will cause the temperature of the internal
battery to rise rapidly, which can easily induce thermal runaway and eventually
cause the battery to catch fire and explode.
Although the conventional temperature measurement can tell the IC to cut
off the main circuit when the battery heats up, it cannot prevent the continuous
discharge inside the parallel battery module.
Moreover, due to the cutoff of the main circuit, all the energy of the
battery module is concentrated on the internal short-circuited battery, which
increases the probability of thermal runaway.
The ideal plan is to cut off the connection loop between this battery and
other batteries in the module when it is found that a certain battery is
short-circuited and heated up. like
As shown in Figure 2, when TEPPTC or MHP-TA series products are assembled
on a single battery, the TE protection device can effectively block when an
internal short circuit occurs.
Internally short-circuited battery communicates with other batteries in the
module to prevent serious accidents. Regarding power battery packs with a large
number of single cells, when assembling
There are high requirements for the commonality of the internal resistance
of the battery and the device. However, due to its internal bimetallic
structure, the MHP-TA has very good commonality of the device resistance and can
be used very efficiently.
The earth meets the requirements regarding the internal resistance of the
battery.
The system composition of lithium-ion power batteries and the actual road
conditions are complex, so the protection of passive components is
essential.
Lithium battery advantages
1) High voltage
The operating voltage of a single battery is as high as 3.7-3.8V (lithium
iron phosphate is 3.2V), which is three times that of Ni-Cd and Ni-MH
batteries.
2) Greater than energy
The actual specific energy that can be achieved is about 555Wh/kg, that is,
the material can achieve a specific capacity of more than 150mAh/g (3--4 times
that of Ni-Cd, 2--3
Times that of Ni-MH), which is close to about 88% of its theoretical
value.
3) Long cycle life
Generally, it can reach more than 500 times, or even more than 1,000 times,
and lithium iron phosphate can reach more than 2,000 times. Regarding electrical
appliances that discharge small currents, electricity
The service life of the pool will double the competitiveness of the
appliance.
4) Good safety function
No pollution, no recall effect. As the predecessor of Li-ion
New lithium-ion battery
Lithium batteries, because metallic lithium can easily form dendrites and
cause short circuits, which reduces its application areas: Li-ion does not
contain cadmium, lead, mercury and other environmentally polluting
chemicals.
Element: A major drawback of Ni-Cd batteries with some processes (such as
sintered type) is the "memory effect", which severely restricts the use of
batteries, but Liion does not have this problem at all.
5) Small self-discharge
The self-discharge rate of fully charged Li-ion after one month of storage
at room temperature is about 2%, which is much lower than Ni-Cd's 25-30% and
Ni-MH's 30-
35%.
6) Fast charging
The capacity of 1C charging can reach more than 80% of the nominal capacity
in 30 minutes, and the iron phosphorus battery can be charged to 90% of the
nominal capacity in 10 minutes.
7) Operating temperature
The operating temperature is -25~45°C. With the improvement of electrolyte
and positive electrode, it is hoped to be expanded to -40~70°C.
Disadvantages of lithium batteries
1) Aging
Unlike other rechargeable batteries, the capacity of lithium-ion batteries
will slowly decline, related to the number of uses and temperature. This
phenomenon of decline
It can be indicated by a decrease in capacity or an increase in internal
resistance.
Because it is related to temperature, it is easier to perform in electronic
products with high operating current. Replacing graphite with lithium titanate
seems to extend life. store
The relationship between temperature and the rate of permanent loss of
capacity:
2) Recovery rate
About 1% of new products leaving the factory need to be recalled for
various reasons.
3) Intolerant to overcharging
When overcharging, excessively embedded lithium ions will be permanently
fixed in the crystal lattice and cannot be released again, which can lead to
short battery life.
4) Intolerance to over-discharge
During over-discharge, too many lithium ions are deintercalated from the
electrode, which can cause the crystal lattice to collapse, thus shortening the
service life.
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