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Lithium Ion Battery Knowledge

Source:JYH Technology News Date:2019-09-19

Batteries using lithium-containing materials as electrodes. It is the representative of modern high performance batteries.

 

Introduction of Lithium Ion Battery

 

Lithium-ion batteries are rechargeable batteries, which mainly rely on the movement of lithium ions between positive and negative electrodes. During charging and discharging, Li + is intercalated and de-embedded between the two electrodes. When charging the battery, Li + is detached from the positive electrode and embedded into the negative electrode by electrolyte. The negative electrode is rich in lithium. When discharging, the opposite is true.

 

Lithium-ion batteries are easily confused with the following two types of batteries:

 

(1) Lithium battery: a single substance with lithium.

 

(2) Lithium-ion polymer batteries: Polymers are used to replace liquid organic solvents.

 

Component

 

Steel Shell/Aluminum Shell/Cylinder/Soft Packaging Series:

 

(1) positive electrode, active material general is lithium manganate or lithium cobalt. Now there are lithium nickel cobalt manganate materials, lithium iron phosphate for electric bicycle and electrolytic aluminium foil with thickness of 10-20 microns for conductive collector.

 

(2) Diaphragm, a special composite membrane, allows ions to pass through. But it's an insulator of electrons.

 

(3) Negative electrode, active material is graphite, or carbon with similar graphite structure. Conductive collector uses electrolytic copper foil with thickness of 7-15 microns.
 

(4) Organic electrolyte, a carbonate solvent containing six fluorolithium phosphate is dissolved, and a gel electrolyte is used in the polymer.

 

(5) Battery outer shell, it can be divided into steel shell (which is seldom used nowadays in square shape), aluminium shell, nickel-plated iron shell (used for cylindrical batteries), aluminium plastic film (soft packaging), and battery cap. It is also the positive and negative lead-out end of batteries.

 

                

 

Working State and Efficiency

 

Lithium ion batteries have high energy density and average output voltage. Small self-discharge, good batteries less than 2% per month (recoverable). There is no memory effect. The working temperature range is - 20 ~60 C. The cycle performance is superior, it can charge and discharge quickly, the charging efficiency is up to 100%, and the output power is high. Long service life. It does not contain toxic and harmful substances and is called green battery.

 

Charge

 

Charging is an important step for battery reuse. The charging process of lithium ion batteries can be divided into two stages: constant current fast charging stage and constant voltage current decreasing stage. In the constant current fast charging stage, the battery voltage gradually rises to the standard voltage of the battery. Then it goes to constant voltage stage under the control chip. Voltage does not rise to ensure that it is not overcharged. Current gradually decreases to a set value with the increase of battery power, and finally completes charging. The power statistics chip can sample and calculate the battery power by recording the discharge curve. The discharge curve of lithium-ion batteries will change after many times of use. Although there is no memory effect in lithium-ion batteries, improper charging and discharging will seriously affect the performance of batteries.

 

Discharge

 

If the first charge and discharge time is long enough (usually 3 to 4 hours), the maximum oxidation state (sufficient electricity) of the electrode can be achieved as much as possible. When discharging (or using), the required voltage or until automatic shutdown can be forced to activate the capacity of the battery.

 

Main advantages

 

(1) High voltage: The working voltage of single cell battery is as high as 3.7-3.8V (lithium iron phosphate is 3.2V), which is three times as high as that of Ni-Cd and Ni-H batteries.

 

(2) Higher specific energy: the actual specific energy is about 555 Wh/kg, that is, the material can reach a specific capacity of 150 mAh/g or more (3-4 times Ni-Cd, 2-3 times Ni-MH), which is close to 88% of its theoretical value.

 

(3) Long cycle life: generally more than 500 times, or even more than 1000 times, lithium iron phosphate can reach more than 2000 times. For small current discharge appliances, battery life will multiply the competitiveness of appliances.

 

(4) Good safety performance: no pollution, no memory effect. As the predecessor of Li-ion, lithium batteries are easy to form dendrite short circuit, which reduces their application fields: Li-ion does not contain cadmium, lead, mercury and other elements polluting the environment; a major disadvantage of some technology (such as sintered) Ni-Cd batteries is "memory effect", which seriously restricts the use of batteries, but Li-ion haven't these problems in this regard.

 

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

 

(6) Quick charging and discharging: The capacity of 1C charging for 30 minutes can reach more than 80% of the nominal capacity. And now the capacity of iron phosphate lithium battery can reach 90% of the nominal capacity for 10 minutes.

 

(7) The working temperature range is high, and the working temperature is -25~45 degrees C. With the improvement of electrolyte and cathode, it is expected that the working temperature can be extended to -40~70 degrees C.

 

                      

TypeInfo: Battery Knowledge

Keywords for the information:Lithium Battery