Li-ion battery knowledge

- Mar 09, 2017-

The battery uses the material like lithium as the electrode, which is the representative of the modern high-performance battery. 
Brief Introduction
Li-ion battery is rechargeable; it mainly depends on the moving of Li-ion between cathode and anode. Li+ intercalates and deintercalates between the two electrodes during the period of charging and discharging, back and forth; Li+ takes off from positive when charging, infix the negative through the electrolyte, at this moment, the negative electrode is in the state of rich Li-ion; this situation also works when discharging.
- eLi-ion battery is easy to mix up with below two batteries:
(1)Lithium battery contains elemental lithium.
(2)Li-po battery: using polymer to replace liquid organic solvents.

Steel shell/Aluminum shell/Cylindrical/Soft package series:
(1)Cathode¬——Active material commonly is LiMn2O or LiCoO2, there is Li-NiCoMn material now, electric bicycle uses LiFePo4, conduction current collector uses electrolytic aluminum foil with 10-20μm thickness.
(2)Separator——A special composite membrane, allows ions to pass through, but insulates the electron.
(3)Anode——Active material is graphite or carbon similar to the structure of graphite, conduction current collector uses electrolytic aluminum foil with 7-15μm thickness.
(4)Organic electrolyte——Dissolve carbonate solvent with LiPF, the gelatinous electrolyte is used in Li-po batteries.
(5)Shell——Contains steel shell (rarely used in square type now), Aluminum shell, NP iron shell (used in the cylindrical battery), Al-plastic film (soft package), etc. The battery cap is also the leading terminal of the positive electrode and the negative electrode.

Mechanism of Action
Li-ion battery uses carbon material as the negative electrode, the lithium-containing compound as the positive electrode, lithium metal bar does not exist, but only the li-ion. Lithium-ion battery generally means a lithium-ion infix compound as the cathode material. Charging and discharging process of Li-ion battery are the intercalation and deintercalation processes of li-ion. During the intercalation and deintercalation processes of li-ion, along with the intercalation and deintercalation of electrons equal to li-ion (traditionally, term intercalation or deintercalation is used in cathode, insertion or taking off is used in anode), li-ion intercalates and deintercalates between the two electrodes during the period of charging and discharging, back and forth, so Li-ion battery is vividly called "rocking-chair batteries".

Working Status and Efficiency
The Lithium-ion battery has big energy density; the average output voltage is high. The low self-discharge percentage of a well-made battery is less than 2% per month (recoverable). No memory effect, -20℃~60℃ wide operating temperature range. Excellent recycling performance, charging efficiency up to 100%, long-life using time, high charging and discharging speed and high output power are the features of Lithium-ion battery. It does not contain toxic and hazardous substances, also known as the green battery.

Charging is an important step in re-using the battery, Lithium-ion battery charging process is divided into two stages: fast charging constant current phase and constant voltage current progressive decreasing phase. Constant current fast charging phase, the battery voltage is gradually increased to the standard voltage, then under the control of the chip changes into the constant pressure phase, the voltage will not rise to ensure that no over-charge, current will gradually weaken to the set value along with the rising of the battery power, charge will be finished at last. Power statistics chip can calculate the battery power by recording the discharge curve. After several usages, Lithium-ion battery’s discharge curve will change, although there is no memory effect in Lithium-ion battery, but improper charging and discharging will seriously affect battery performance.

Charging Notes
Lithium-ion battery overcharge and over-discharge will cause permanent damage to the positive and negative. Over-discharging leads anode carbon lamellar structure collapsed, and this collapse will cause the lithium-ion can not be inserted during the process of charging; overcharging makes excessive lithium-ion insert anode carbon structure, causing some of the lithium-ion can be no longer released.
Charging volume equals to the charge current multiplied by charge time, in the case of certain charge control voltage, the greater the charge current (faster charging), the smaller the charge capacity. Battery charging too fast or improper termination voltage control point will also result in insufficient battery capacity. Actually, the battery stops charging when part of the electrode active material has not been fully reached, the situation of charging shortage will be even worse with the number of cycles increased. 

The first time to charge, if time can be longer (usually 3-4 hours is sufficient), you can make the electrode reach the highest oxidation state as much as possible (fully charged), the first time to discharge, the battery is forced into a predetermined time voltage when discharge (or use), or until automatic shutdown, so you can activate the battery capacity smoothly.
But in the normal use of Lithium-ion batteries, you do not need to do so, you can charge at any time, neither fully charged, nor discharged fully before charging. Like the operation of first charging and discharging, just performed 1-2 times every 3-4 months. 

Chemical Analysis
Overview: As all other chemical batteries, Lithium-ion battery is combined by three parts: cathode, the anode, and electrolyte. Electrode material can be intercalated (inserted) / deintercalated (escaped) by lithium-ion.
Cathode: cathode material, as described above, has many options to choose, but the mainstream product often uses lithium-iron phosphate. The contrasts of different cathode material are listed below: 

Cathode Material

Average Output Voltage

Energy Density













Cathode reaction: Li-ion intercalates when discharging, deintercalates when charging.
Charging: LiFePO4 → Li1-xFePO4 + xLi + xe Discharging: Li1-xFePO4 + xLi + xe → LiFePO4
Anode: Anode material often uses graphite. The new study found titanate can be a better material.
Anode reaction: Li-ion inserts when discharging, escapes when charging.
Charging: xLi + xe + 6C → LixC6 Discharging: LixC6 → xLi + xe + 6C

Electrolyte solution
Solute: often used lithium salt such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4). Solvent: because the voltage of the battery is much higher than the decomposition voltage of water, the Lithium-ion batteries often use an organic solvent, such as diethyl ether, ethylene carbonate, propylene carbonate, and diethyl carbonate. The organic solvent often destroyed the structure of graphite when it’s charged, as a consequence, the graphite will be exfoliated, and form a solid electrolyte membrane (solid electrolyte interphase, SEI) on the surface, that leads to the formation of the electrode passivation. The organic solvent also brought flammable, explosive and other security issues.

The main advantage
(1) High voltage: the voltage of a single battery is 3.7-3.8V (lithium iron phosphate is 3.2V), that’s 3 times more than NiMH battery and NiCd battery.
(2) High energy ratio: the energy ratio could reach about 555Wh / kg at present, the energy ratio of material could reach 150mAh / g or more (3-4 times than Ni-Cd, 2-3 times than Ni-MH), it is close to about 88% of its theoretical value.
(3) Long cycle life: in general, the cycle life is more than 500 times or even more than 1000 times, lithium iron phosphate battery could be used more than 2000 times. For electrical with small discharge current, battery cycle life will double its competitiveness.
(4) Better security: pollution-free, no memory effect. Formerly known as Li-ion lithium batteries, because lithium metal is easy to form dendrite and leads to short circuit, that limited its application areas; Li-ion battery does not contain cadmium, lead, mercury, and others which will pollute the environment; some processes (such as sintered) of Ni-Cd battery exist a big problem "memory effect" which seriously constrained the using of battery, but Li-ion battery does not have this problem.
(5) Low self-discharge: when it’s preserved at room temperature for a month, the self-discharge of a fully charged Li-ion battery is about 2%, that’s much lower than the Ni-Cd of 25-30%, NiMH of 30-35%.
(6) Fast charge and discharge: the capacity will reach more than 80% of nominal capacity when it’s charged with 1C for 30 minutes, now phosphorus iron battery could reach 90% of nominal capacity when charged for 10 minutes.
(7) Operating temperature range: operating temperature range is -25~45°C, with the improvement of electrolyte and positive, expected to widen to -40~70°C. 

Use of Li-ion battery
(1) How to charge for new battery
When using Li-ion battery, we should note that the capacity will be lower than its normal capacity when it’s preserved for a period of time, and the time of using will be shortened. However, it’s easy to be activated and recover normal capacity after 3-5 times charging. As the characteristics of Li-ion battery, it is almost no memory effect. Therefore, it needn’t any special devices and methods when the users activate their new mobile with Li-ion battery.
For the problem of activating the Li-ion battery, many people say that it must charge more than 12 hours, and repeat three times to activate the battery. Obviously, it inherited from the nickel battery (such as NiCd battery and NiMH battery). 
Therefore, this is miscommunication. It has a great difference between Li-ion battery and nickel battery in charging and discharging. I can clearly tell all of you that over-discharging and over-charging is bad for lithium battery, especially for lithium liquid ion battery based on the serious date that I read . Therefore, the best way to charge is following the standard time and way, especially, don’t charge too long like 12h (it’s ok when show charging is full).
In addition, Li-ion battery and the charger will automatically stop after the battery is fully charged; there is no trickle charge for 10 hours, which occurs in nickel battery. In other words, if the electric energy of your Li-ion battery is full, it’s no point to charge more time. And we can not guarantee the protection circuit characteristics never change and the quality of safety battery’s charge and discharge, so your battery will be long-term at the brink of danger. This is another reason we against to long charge. These issues also fit the situation for over discharging the Li-ion battery. 

(2) When the battery should be charged for normal using
Often to see this argument, because the number of charging and discharging is limited, so it should be possible to run out the electric energy of phone battery, and then recharge it. In fact, the cycle life of Li-ion battery has nothing to do with this. The following can be exemplified on a Lithium-ion battery charge and discharge cycle test table, about the data of cycle life is listed below:
Cycle life (10% DOD) :> 1000 times
Cycle life (100% DOD) :> 200 times
DOD is the depth of discharge abbreviation. From the table, discharge time is related to the depth of charge, 10% DOD cycle life is much longer than the 100% DOD. Of course, if equivalent to the relative total capacity of the actual charge: 10% * 1000 = 100, 100% * 200 = 200, the latter is better in completely charge and discharge, but the statement of previous net friend must be amended: In normal case, you should have reserved in the principle that recharging after ran out of the electric energy of battery, but if the capacity of your battery is not enough for you to use for all daytime next day, you should charge in time. Also, it doesn’t a matter if you would like to charge your battery with your charger in office.
Run out of the electric energy of your battery then charge, which is one way to recover the battery. And as people said that charge for a long time, there is another widespread view that running out of the electric energy as much as possible. This is really just a practice on nickel batteries; the purpose is to avoid the memory effect. Unfortunately, it also spread over Li-ion battery. There ever were some samples that some people don’t charge for their phone and keep using until the phone automatically shutdown, even though the warning of lower energy occurred before. The result is that their phone has no reaction in starting up after charged, and then they had to have their phone repaired. In fact, this is due to the over-discharge of battery and lead to brownout, so that it hasn’t normal charging and condition to start up.
Personal recommendation is that don’t charge your phone battery too often or charge until the battery runs out all electric energy. It has no effect on the battery when we charge the battery, even though the electric energy doesn’t run out. It’s better to charge your battery for 2-3 hours every time. It doesn’t have to charge fully. We should have fully charged 1-2 times (normal charging time) and fully discharged 1-2 times for our battery every 3-4 months.
The battery should be kept in cool and dry place if you won’t use it for a long time. It’s better for battery with half full state ( the full state is 70-80% of capacity, if 4 grids stand for full energy on your phone, then 3 grids is best). It’s dangerous to preserve your battery with full energy, that’s also harmful to the battery. The battery will be destroyed if it has no energy. And we should check the battery whether it needs a charge every 3-6 months.
Li-ion battery could be divided into liquid lithium-ion batteries and lithium ion polymer batteries by electrolyte, polymer lithium ion battery electrolyte is a colloid, and it will not flow, so there is no leakage, more secure. 

Instruction of maintenance
Do not exceed the maximum charging voltage when charging; do not go under the minimum operating voltage when discharging.
Whatever the voltage of Li-ion battery must be higher than the minimum operating voltage, low voltage and over-discharge or self-discharge will lead to decomposition of the active material of lithium ion, which may be impossible to recover.
Any overcharge of Li-ion battery could damage the performance of the battery, even explosion. It’s necessary to avoid overcharging for Li-ion battery.
Do not always deep discharge, deep charging. However, after the experience of about 30 per charge cycle, electricity detection chip will automatically perform a deep discharge, deep charge, to accurately assess the status of the battery.
Avoid high temperatures, which will shorten the life of the battery, even an explosion. If the conditions permit, it could be stored in the refrigerator. If you are using an AC laptop, please unplug the Li-ion battery bar, so that it won’t be affected by the heat of the computer.
Avoid frozen, but the freezing point of most Li-ion battery electrolyte is -40 ℃, so it is not easy to freeze.
Please save 40% to 60% of the amount of capacity if you won’t use the battery for a long time. When the electric energy is too low, it may lead to over-discharge due to self-discharge.
Since the Li-ion battery will natural aging, although it isn’t working, so we should purchase the right quantity of battery according to actual requirements, it’s not wise to buy too many.

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