Lithium-ion battery is a kind of secondary battery that uses lithium-containing compound as the positive electrode, and realizes charging and discharging through the back-and-forth extraction and insertion of lithium ions between the positive and negative electrodes of the battery during the charging and discharging process. The interior of a lithium-ion battery is mainly composed of a positive electrode, a negative electrode, an electrolyte and a separator.

Lithium-ion batteries work primarily by the movement of lithium ions between the positive and negative electrodes. During the charging and discharging process, Li+ intercalates and deintercalates back and forth between the two electrodes: during charging, Li+ is deintercalated from the positive electrode, intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharge, the opposite is true.

Lithium-ion batteries have many notable features, and their advantages are mainly as follows:

1. High voltage: the working voltage of the single battery is as high as 3.7-3.8V (the lithium iron phosphate is 3.2V, which is 3 times that of the Ni-Cd and Ni-MH batteries.

2. Large specific energy: the actual specific energy that can be achieved is about 555Wh/kg, that is, the material can reach a specific capacity of more than 150mAh/g (3-4 times that of Ni-Cd, 2-3 times that of Ni-MH, close to about 88% of its 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 8000 times. For electrical appliances with low current discharge, the service life of the battery will double the competitiveness of the electrical appliances.

4. Good safety performance: no pollution, no memory effect. As the predecessor of Li-ion, the lithium battery is prone to short-circuit due to the formation of dendrites, which reduces its application fields: Li-ion does not contain cadmium, lead, mercury and other elements that pollute the environment; some processes (such as sintering A major drawback of the Ni-Cd battery of , is the "memory effect", which seriously restricts the use of the battery, but Li-ion does not have this problem at all.

5. Small self-discharge: The self-discharge rate of fully charged Li-ion stored at room temperature for 1 month is about 2%, which is much lower than 25-30% of Ni-Cd and 30-35% of Ni-MH.

6. Fast charging: 1C charging for 30 minutes can reach more than 80% of the nominal capacity, and phosphorus iron batteries can reach 90% of the nominal capacity in 10 minutes.

7. Working temperature: The working temperature is -25~45°C. With the improvement of electrolyte and positive electrode, it is expected to expand to -40~70°C.

Lithium-ion batteries also have some shortcomings, mainly in the following aspects:

1. Aging: Unlike other rechargeable batteries, the capacity of lithium-ion batteries will slowly decline, which is related to the number of uses and temperature. This phenomenon of decay can be expressed as a decrease in capacity or an increase in internal resistance. Because it is related to temperature, it is easier to reflect in electronic products with high operating current. Replacing graphite with lithium titanate appears to increase life.

2. Recovery rate: About 1% of new products from the factory need to be recycled for various reasons.

3. Intolerant of overcharge: When overcharged, the excessively embedded lithium ions will be permanently fixed in the lattice and cannot be released, which can lead to short battery life.

4. Intolerant of over-discharge: During over-discharge, the electrode deintercalates too much lithium ions, which can cause the lattice to collapse, thereby shortening the life.

In recent years, the application range of lithium-ion batteries has become more and more extensive. Lithium batteries are widely used in energy storage power systems such as water, fire, wind and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. At present, lithium batteries have gradually expanded to electric bicycles, electric vehicles and other fields.