With the rapid development of new energy vehicle technology and sales, the technical requirements for lithium batteries are also gradually increasing. At this stage, the use of new positive and negative materials and new battery structure design can improve the energy density. For example, high nickel ternary lithium positive electrode, silicon-containing negative electrode, CTB and CTC integration technology.
In addition, lithium battery lithium supplementation technology is also an important way to improve energy density. During the first charging of the lithium battery, the electrolyte reacts on the surface of the graphite anode to form a solid electrolyte interface membrane (SEI membrane), which consumes a large amount of lithium precipitated from the positive electrode, resulting in the attenuation of the capacity and energy density of the lithium battery.
Therefore, in order to offset the irreversible lithium loss caused by the formation of the SEI membrane on the battery and maintain the total capacity and energy density of the battery, researchers developed a lithium supplementation technology.
Lithium replenishment technology
Lithium replenishment technology is also called pre-lithiumisation or lithium embedding technology, which adds lithium to the battery before the lithium battery works to achieve the purpose of replenishing lithium ions. Common lithium supplementation technologies include positive lithium supplementation and negative lithium supplementation.
The electrochemical method is usually used to supplement the positive electrode of lithium. By adding materials to the positive electrode of the lithium-ion battery, the battery releases active lithium through material decomposition during the charging process, so as to make up for the positive irreversible lithium loss caused by the formation of the SEI film.
Negative lithium supplementation is a key development of technical direction at present, including self-precharge lithium supplementation (lithium foil lithium supplementation), physical lithium supplementation, chemical lithium supplementation and electrochemical lithium supplementation.
Lithium foil lithium supplement technology
Lithium foil lithium supplementation is a lithium supplementation technology using the principle of self-precipitation. Because the potential of lithium metal is the lowest among all electrode materials, coupled with the existence of potential difference, in the case of electrolyte, the anode material is in direct contact with the lithium foil material of the metal, and the lithium ion will follow the electrons after thermodynamic reaction.
Lithium powder lithium supplement technology
Lithium powder lithium supplementation is a commonly used chemical lithium supplementation method. Its principle is to use low-potential lithium-containing chemical reagents (also known as lithium supplementation agents) to chemically react with negative electrode materials to replenish the negative electrodes. The technology of lithium powder lithium supplementation was proposed by the American FMC Company. At the same time, this company was also the first to develop stable lithium powder, which was added to the negative electrode through spraying or homogenization.
Electrochemical lithium supplement technology
Electrochemical lithium replenishment is done by introducing lithium metal and the negative electrode to form a pair of electrodes, and then uses the electrochemical principle to control the charge and discharge depth to complete the negative electrode lithium replenishment. However, this method is more complicated, involving the disassembly and assembly of batteries, and the technology of each manufacturer is different.
For example, Tesla’s patent applies lithium metal or a mixture containing lithium powder to the negative electrode surface, and then realizes the negative electrode lithium supplementation through electrochemistry.
In fact, in contrast, positive lithium supplementation is relatively simple. Why does the industry have to study more troublesome and complex negative lithium supplementation technology.
This is because the stability of materials such as additives in cathode lithium supplementation technology is poor, which is easy to affect battery performance and bring safety hazards. Some material decomposition products are incompatible with cathode materials. This has also led to difficulties in the selection of additive materials in positive lithium supplementation technology.
Lithium supplementation technology is becoming a key technical means, which plays a key role in improving the energy density and cycle life of lithium batteries. However, the negative lithium supplementation technology will become the direction of focus on research to improve the stability of the process and the safety of production.
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