Knowledge of Lithium Ion Batteries

A battery that uses lithium-containing materials as electrodes. It is a typical modern high-performance battery.

Nouns

A lithium-ion battery is a rechargeable battery that functions primarily by relying on the transfer of lithium ions between the positive and negative electrodes. During the charging and discharging processes, Li+ moves back and forth between the two electrodes. When charging the battery, Li+ is desorbed from the cathode and inserted into the anode via the electrolyte, leaving the anode in a lithium -rich state; the reverse is true during discharge.

Lithium-ion batteries are often confused with the following two types of batteries: (1) lithium batteries: a battery in which Li

(1) Lithium battery: lithium elements are present.

(2) Lithium-ion polymer battery: replaces liquid organic solvent with polymer.

Components

Steel shell/aluminum shell/cylindrical/soft package series: (1) Cathode

(1) Cathode - The active material is typically lithium manganese oxide or lithium cobalt oxide, with nickel cobalt lithium manganese oxide materials now emerging, and electric bicycles use lithium iron phosphate with an electrolytic aluminum foil 10 to 20 microns thick. It is used for conductive current collectors.

(2) Separator - a special composite film that allows ions to pass through but is an insulator for electrons.

(3) Anode - The active material is graphite or carbon with a similar graphite structure, and the conductive current collector is an electrolytic copper foil 7 to 15 microns thick.

(4) Organic electrolyte - a carbonate solvent in which lithium hexafluorophosphate is dissolved and a gel electrolyte for polymers.

(5) Battery shells - can be divided into steel shells (now rarely used in rectangular type), aluminum shells, nickel-plated iron shells (used in cylindrical batteries), aluminum plastic film (soft packaging), etc., and batteries. Caps that are also battery shells Positive and negative terminals.

Mechanism of Action

A lithium-ion battery is a lithium-ion battery with a carbon material for the negative electrode and a lithium-containing compound for the positive electrode, consisting only of lithium ions and no metallic lithium. Lithium-ion battery is a generic term for batteries that use lithium-ion interlayer compounds as cathode materials. The charge and discharge process of a lithium-ion battery is a process of lithium ion intercalation and de-intercalation. The process of lithium ion intercalation and de-intercalation involves the intercalation and de-intercalation of electrons corresponding to lithium ions (typically, the cathode is represented by intercalation or de-intercalation, and the anode by insertion or de-intercalation). During the charging and discharging process, lithium ions intercalate/de-intercalate and intercalate/de-intercalate between the positive and negative electrodes. This is vividly referred to as a "rocking chair battery.

Working Conditions and Efficiency

Lithium-ion batteries have high energy density and high average output voltage. Slight self-discharge, good battery, less than 2% per month (recoverable). No memory effect. Wide operating temperature range of -20°C to 60°C. Excellent cycle performance, fast charge/discharge, up to 100% charge efficiency, and high power output. Long lasting. Contains no toxic or harmful substances and is referred to as a green battery.

Charging

Charging is an important step in battery recycling, and the charging process for lithium-ion batteries is divided into two stages: a constant-current fast-charge phase and a constant-voltage current-reduction phase. In the constant-current fast-charge phase, the battery voltage is gradually increased to the battery's standard voltage and then enters a constant-voltage phase under a control chip to ensure that the voltage does not increase again and overcharging does not occur. As the remaining battery charge increases to the set value, the current gradually decreases, eventually completing the charge. The power statistics chip can sample and calculate battery power by recording the discharge curve. The discharge curve changes as the lithium-ion battery is used repeatedly. Although lithium-ion batteries do not have a memory effect, improper charging and discharging can seriously affect battery performance.

Charging Precautions

Excessive charging and discharging of a lithium-ion battery will cause permanent damage to the positive and negative electrodes. Excessive discharge causes the carbon sheet structure of the negative electrode to collapse, and the collapse prevents lithium ions from being inserted during charging; overcharging causes too much lithium ions to be embedded in the carbon structure of the negative electrode, and some lithium ions will not be released.

Charge capacity is charge current x charge time. When the charge control voltage is constant, the higher the charge current (and the faster the charge speed), the smaller the charge capacity. If the battery is charged too fast or the end voltage control point is inappropriate, the battery capacity will be insufficient and, in fact, some electrode active materials in the battery will not react sufficiently to stop charging.

Discharge

The initial charge and discharge, if timed long enough (3-4 hours is generally sufficient), will allow the electrodes to reach the highest possible oxidation state (sufficient charge). Shutdown, the battery capacity can be activated.

However, in normal use of a lithium-ion battery, it does not need to be recharged and can be recharged whenever needed. There is no need to fully charge or first discharge the battery. Operations such as charging and discharging for the first time need only be performed once or twice every three to four months in succession.

Chemical Analysis

Overview: Like all chemical batteries, lithium ion batteries are composed of three parts: a cathode, an anode, and an electrolyte. The electrode materials are all lithium ions that can be intercalated (inserted)/de-intercalated.

Cathode: cathode material, as mentioned above, there are many optional cathode materials, the current mainstream products mainly use lithium iron phosphate. Comparison of different cathode materials:.

Cathode Material

Average output voltage

Energy Density

LiCoO2

3.7V

140mAh/g

LiMn2O4

3.7V

100mAh/g

LiFePO4

3.2V

130mAh/g

Li2FePO4F

3.6V

115mAh/g

Cathode reaction: Lithium ions are inserted during discharge and released during charging. Charging: LiFePO4 → Li1-xFePO4+xLi+xe Discharging: Li1-xFePO4+xLi+xe → LiFePO4

 

Anode: The anode material is primarily graphite. New research has found that titanate may be a better material.

 

Anode reaction: lithium ions are desorbed during discharge and inserted during charging. During charging: xLi+xe+6C→LixC6 During discharge: LixC6→xLi+xe+6C

 

Electrolyte liquid

Solute: Lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4) are often used. Solvents: Organic solvents such as ether, ethylene carbonate, propylene carbonate, and diethyl carbonate are often used in lithium-ion batteries because the battery's operating voltage is much higher than the decomposition voltage of water. Organic solvents often destroy the graphite structure during charging, causing it to delaminate and form a solid electrolyte film (solid electrolyte interface, SEI) on its surface, resulting in passivation of the electrodes. Organic solvents also pose safety issues such as flammability and explosions.

 

Main Advantages

 

(1) High voltage: The operating voltage of a single battery is as high as 3.7 to 3.8V (3.2V for lithium iron phosphate), three times higher than Ni-Cd and Ni-H batteries.

 

(2) High specific energy: The actual specific energy that can be achieved today is about 555Wh/kg. This means that the specific capacity of the material is 150mAh/g (3 to 4 times that of Ni-Cd and 2 to 3 times that of Ni-MH), close to about 88% of the theoretical value.

 

(3) Long cycle life: Generally, it can reach more than 500 times, even more than 1000 times, and lithium iron phosphate can reach more than 2000 times. For low current discharge appliances, the service life of the battery doubles the competitiveness of the appliance.

 

(4) Good safety performance: no pollution, no memory effect. Lithium battery, the predecessor of lithium-ion, is prone to short circuit due to metallic lithium forming dendrites, thus reducing its application field. Lithium ion does not contain elements such as cadmium, lead, and mercury, which pollute the environment. Some processes (e.g., sintering types) Nicad batteries have a major drawback called "memory effect," which greatly limits the use of the battery, but lithium-ion batteries do not have this problem at all.

 

(5) Small amount of self-discharge: The self-discharge rate of a fully charged Li-ion after one month of storage at room temperature is about 2%, much lower than 25-30% and 30-35% for Ni-Cd Ni and MH.

 

(6) Fast charging and discharging: a 30-minute charge at 1C can reach more than 80% of nominal capacity, and iron phosphorus batteries can now be charged to 90% of nominal capacity in 10 minutes.

 

(7) High operating temperature range: operating temperature is -25~45C, but with the improvement of electrolyte and cathode, it is expected to be used up to -40~70C.

 

Use of lithium-ion batteries

 

(1) How to charge a new battery

 

When using lithium batteries, please note that after a certain period of time, the batteries will enter a dormant state, resulting in a lower capacity than normal and a shorter usage time. However, lithium batteries are easy to start up and after 3 to 5 cycles of normal charging and discharging, the battery can be started up and returned to normal capacity. Due to the nature of the lithium battery itself, there is little memory effect. Therefore, a new lithium battery in a user's cell phone does not require any special methods or equipment during the activation process.

 

As for the "activation" of the lithium-ion battery, as many people say, to activate the battery, if this is done three times, the charge time requires at least 12 hours. This "12+ hours for the first three charges" is obviously a continuation of nickel batteries (nickel cadmium, nickel metal hydride, etc.). Therefore, this type of statement is misinformation from the beginning. I can clearly tell you that all serious formal technical information I have checked stresses that the charging and discharging characteristics of lithium and nickel batteries are very different and that overcharging and overdischarging affect lithium batteries, especially liquid lithium batteries . . cause a lot of damage. Therefore, it is recommended to charge according to standard times and standard methods. In particular, do not charge the batteries for more than 12 hours (the charger can only fully charge them).

 

Furthermore, a lithium battery or charger will automatically stop charging when the battery is fully charged, and there is no so-called "trickle" charging, which lasts more than 10 hours with a nickel charger. In other words, if a lithium battery is fully charged, it will be wasted on the charger. In addition, the characteristics of the battery's charge/discharge protection circuitry never change and its quality cannot be guaranteed to be perfect. Thus, the battery will be at risk for a long period of time. This is another reason against long-time charging.

 

Yet another aspect that cannot be ignored is that lithium batteries are also not suitable for over-discharge, and over-discharge is also harmful to lithium batteries.

 

(2) When to start charging during normal use

 

Although we often see this saying because cell phone batteries need to be charged as much as possible because of the limited number of times they can be charged and discharged, it actually has nothing to do with the life of the lithium battery. Below is an example of an experimental table on charge and discharge cycles for lithium-ion batteries. The data on cycle life is as follows

 

Cycle life (10%DOD): >1000 cycles

 

Cycle life (100%DOD):>200 cycles

 

In this table, DOD is an abbreviation for Depth of Discharge. From the table, we can see that the charging time is related to the depth of discharge and that the cycle life of 10% DOD is much longer than that of 100% DOD. Of course, in terms of the relative total capacity of the actual charge, 10%*1000=100, 100%*200=200, the latter full charge and discharge is still superior, but the previous netizen's statement needs to be corrected. Under certain circumstances, charging should be reserved and done according to the principle of charging when the battery is depleted, but if the battery is expected to last less than a day on the second day, charging should begin on the second day. Whether or not to bring the charger into the office is another matter.

 

The principle of recharging a battery's remaining charge is not to take you to extremes. As common a saying as long recharging is, "use up as much of the battery as possible." This practice is actually only practiced with nickel batteries; the goal is to avoid the memory effect, but unfortunately it is also widespread with lithium batteries. In one case, after a cell phone displayed a low battery warning, the user continued to use the phone without recharging it until it automatically turned off. As a result, the cell phone in this instance did not respond during the subsequent charging and activation and had to be sent to customer service for repair. This is actually due to low battery voltage caused by over-discharge, which is not a normal charging and starting condition.

Personally, I recommend that you do not overcharge or under-power your phone's lithium-ion battery. Charging the battery before it is depleted will not damage the battery. It is recommended to charge the battery within 2 to 3 hours. It is also not necessary to fully charge the battery. However, lithium batteries should be fully charged once or twice (normal charge time) and discharged every 3-4 months.

 

Lithium batteries that have not been used for a long time should be stored in a cool, dry place. It is recommended to use them in a half-charged state. Storage with a fully charged battery is dangerous and will damage the battery; storage without charging will damage the battery. Check every 3 to 6 months to see if the battery should be recharged.

 

Lithium-ion batteries can be divided into liquid lithium-ion batteries and polymer lithium-ion batteries according to their electrolyte. The electrolyte in a polymer Li-ion battery is colloidal and does not flow, so there is no leakage problem and it is safer.

 

Maintenance Procedure

 

The maximum charge voltage must not be exceeded when charging and must not fall below the minimum operating voltage when discharging.

 

Lithium-ion batteries should always be kept above the minimum operating voltage. Low-voltage over-discharge or self-discharge reactions can cause decomposition and destruction of the lithium ion active material, which may not be reversible.

 

Overcharging a lithium ion battery can severely damage battery performance or cause an explosion. Lithium ion batteries should not be overcharged during the charging process.

 

Do not perform frequent deep discharges or deep charges. However, after approximately 30 charge cycles, the power detection chip will automatically perform deep discharge and deep charge to accurately assess the condition of the battery.

 

Avoid high temperatures, which can shorten service life in mild cases and cause explosions in severe cases. Store in a refrigerator if possible. If the notebook computer is using AC power, unplug the lithium-ion battery strip to avoid being affected by the heat generated by the computer.

 

Avoid freezing. However, the freezing point of most lithium-ion battery electrolytes is -40°C (-40°F), and they do not freeze easily.

 

If the battery will not be used for a long period of time, store it with a 40%~60% charge. Low battery charge may cause over-discharge due to self-discharge.

 

Lithium-ion batteries naturally degrade if not used, and should be purchased according to actual needs; over-purchasing is not recommended.