Research Status of Lithium ion Battery Anode Materials
1. Lithium-ion battery charging and discharging works
The real lithium-ion battery was developed by Sony Corporation of Japan in the 1990s.A lithium ion battery is a general term for a battery in which a lithium ion intercalation compound is used as electrode material.
It is mainly composed of positive and negative materials, diaphragm, electrolyte, battery casing and other parts.
When the lithium ion battery is charged and discharged, lithium ions are deintercalated in the positive and negative electrodes, so the lithium ion battery is called a "rocking chair battery".
So how does it work?
During the charging process, lithium ions are generated in the positive electrode of the battery, lithium ions move to the negative electrode through the electrolyte solution, and lithium ions continuously accumulate in the micropores of the negative carbon layer, so the charging capacity of the lithium ion battery is higher and higher.During the discharge process, lithium ions accumulated in the micropores of the negative carbon layer are released, and the electrolyte solution moves back to the positive electrode, and the more lithium ions are removed, the higher the discharge capacity of the lithium ion battery.
2. Research status of anode materials
(1) Carbon anode material
Most of the anode materials produced by lithium-ion batteries in actual life are carbon anode materials. Because of their good conductivity, excellent cycle performance, low cost and good safety performance, carbon anode materials are used in the anode materials of lithium ion batteries. The application rate is very high.
The most widely used anode material for lithium ion batteries is graphite. As a negative electrode material for one of the four major materials of lithium ion batteries, the structure of graphite affects the performance of the battery.
The idealized graphite forms a layered structure in the form of sp2 hybridization, which is beneficial to the extraction and entry of lithium ions, and can form a lithium-graphite intercalation compound with lithium atoms.
The theoretical capacity of graphite can reach 372 mAh / g, the efficiency of charge and discharge can reach more than 90%, and the irreversible capacity is less than 50 mAh / g.
The deintercalation reaction of lithium in graphite mainly occurs between 0-0.25V (relative to Li/Li+), and has a good charge-discharge voltage platform, which has good matching with the provided lithium source positive electrode material, and constitutes the average output of the battery. The high voltage is a negative electrode material for lithium ion batteries with good performance.
(2) Metal oxide anode material
When the metal oxide anode material and the carbon anode material are compared, the metal oxides such as TiO2, CoO, NiO, CuO, FeO, Fe2O3, and Fe3O4 have higher energy density and better safety performance.
The Fe3O4 anode material will be described below as an example.The Fe3O4 anode material has broad development prospects, and the theoretical capacity can reach 926mAh/g. It has the advantages of better conductivity, rich resource sources and green environmental protection.
However, due to the agglomeration phenomenon during the discharge process, the cycle will appear more.
The large volume change leads to poor cycle performance and poor rate performance of the Fe3O4 anode material.
（3）Alloy anode material
The application of alloy anode materials in lithium ion batteries has received wide attention.At present, the most studied alloy anode materials are tin-based and silicon-based materials, and the alloy materials formed by the combination of tin-based and silicon-based materials have the advantages of extremely high energy density, excellent processing performance, and good electrical conductivity.
However, due to the volume expansion of the pole piece during the charge and discharge cycle, the charge and discharge cycle life is short and the performance is deteriorated, so the alloy material is currently difficult to be widely promoted and applied.
The future research direction of alloy materials is mainly to solve the problem of volume expansion of the pole piece, so that the lithium ion battery has superior performance.