Basic knowledge of lithium battery

Lithium-ion batteries are rechargeable batteries that rely on lithium ions moving between positive and negative electrodes. In the charging and discharging process, Li+ is embedded and disembedded back and forth between the two electrodes: when charging the battery, Li+ is disembedded from the positive electrode, through the electrolyte into the negative electrode, the negative electrode is in a lithium rich state; The opposite is true when discharging.

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

(1) Lithium battery: there is lithium elemental.

(2) Lithium ion polymer batteries: replace liquid organic solvents with polymers.

Part of the

Steel shell/aluminum shell/cylinder/flexible packaging series:

(1) anode - the active substance is generally lithium manganese or lithium cobalt manganese, and now there is a nickel cobalt manganese lithium material, electric bicycle with lithium iron phosphate, conductive fluid collection using thickness of 10-20 micron electrolytic aluminum foil.

(2) Diaphragm -- a special composite membrane that allows ions to pass through but acts as an insulator for electrons.

(3) Anode -- the active substance is graphite, or carbon with a similar graphite structure, and the conductive collector uses electrolytic copper foil with a thickness of 7-15 microns.

(4) Organic electrolyte -- carbonate solvent with lithium hexafluorophosphate dissolved, polymer gel electrolyte is used.

(5) battery shell - divided into steel shell (now square type rarely used), aluminum shell, nickel-plated iron shell (cylindrical battery use), aluminum plastic film (soft packaging), and the battery cap, is also the positive and negative end of the battery.

Mechanism of action

Lithium ion battery with carbon material as the negative electrode, lithium containing compound as the positive electrode, there is no metal lithium, only lithium ions, this is lithium ion battery. Lithium ion battery is the general name of battery with lithium ion embedded compound as cathode material. The charging and discharging process of lithium ion battery is the embedding and de-embedding process of lithium ion. The embedding and de-embedding of lithium ions are accompanied by the embedding and de-embedding of equivalent electrons with lithium ions (traditionally, the positive electrode is represented by embedding or de-embedding, while the negative electrode is represented by inserting or de-inserting). In the charging and discharging process, lithium ions are embedded/de-embedded and inserted/de-inserted between the positive and negative poles, which is vividly called "rocking chair battery".

Working status and efficiency

Lithium ion batteries have high energy density and high average output voltage. Self discharge small, good battery, below 2% per month (recoverable). No memory effect. The wide operating temperature range is -20℃ ~ 60℃. Excellent cycle performance, fast charging and discharging, charging efficiency up to 100%, and large output power. Long service life. It does not contain toxic and harmful substances and is called green battery.

charging

Charging is an important step for battery reuse. The charging process of lithium ion battery is divided into two stages: constant current fast charging stage and constant voltage current decline stage. Constant current fast charge stage, the battery voltage gradually increased to the standard voltage of the battery, then under the control chip into the constant voltage stage, the voltage is no longer increased to ensure not overcharge, the current is gradually weakened to the set value with the rise of the battery quantity, and the final completion of charging. The battery charge can be calculated by sampling the discharge curve. After repeated use, the discharge curve of lithium ion battery will change. Although there is no memory effect of lithium ion battery, improper charge and discharge will seriously affect the performance of the battery.

Precautions for Charging

Overcharging and discharging of lithium-ion batteries can cause permanent damage to the anode and cathode. Excessive discharge leads to the collapse of the cathode carbon lamellar structure, and the collapse will cause the lithium ion cannot be inserted in the charging process. Overcharging causes too many lithium ions to embed in the negative carbon structure, and some of them can no longer be released.

The charging quantity is equal to the charging current times the charging time. In the case of a certain charging control voltage, the higher the charging current (the faster the charging speed), the lower the charging quantity. Excessive charging speed and improper termination voltage control point of the battery will also cause insufficient capacity of the battery. In fact, part of the active substance of the electrode of the battery will stop charging without sufficient reaction. This phenomenon of insufficient charging will be aggravated with the increase of the number of cycles.