Important method of pre-lithiation
1. Negative electrode advance formation method
Let the negative electrode be formed separately, and then assemble with the positive electrode after the SEI film is formed on the negative electrode to prevent the loss of lithium ions on the positive electrode by formation, and greatly improve the first-time efficiency and capacity of the full battery. The advantage of this pre-lithiation method is that it can simulate the normal formation process to the greatest extent, and at the same time ensure that the formation effect of the SEI film is similar to that of lithium-ion batteries. big.
2. Negative electrode spraying lithium powder method
A stable metal lithium powder particle is produced, the inner layer of the particle is metal lithium, and the outer layer is a protective layer with good lithium ion conductivity and electronic conductivity; during the pre-lithiation process, the lithium powder is first dispersed in the In the organic solvent, the dispersion is then sprayed on the negative electrode sheet, and then the residual organic solvent on the negative electrode sheet is dried, so that the pre-lithiated negative electrode sheet is obtained.
During formation, the lithium powder sprayed on the negative electrode will be consumed in the formation of the SEI film, thereby retaining the lithium ions deintercalated from the positive electrode to the maximum extent, and improving the capacity of the lithium-ion battery. The disadvantage of using this pre-lithiation method is safety. It is difficult to guarantee, and the cost of material and equipment transformation is relatively high.
3. Negative three-layer electrode method
Compared with the normal copper foil, the copper foil of the three-layer electrode method is coated with the metal lithium powder required for later formation. In order to protect the lithium powder from reacting with the air, a protective layer is applied; the negative electrode is directly coated on the protective layer. layer.
When the cell is filled with liquid, the protective layer will be dissolved in the electrolyte, so that the metal lithium is in contact with the negative electrode, and the lithium ions consumed by the formation of the SEI film are supplemented by metal lithium powder. The conditions are not strict, but the stability of the protective layer in the pole piece unwinding, rolling, cutting and other stations is a great challenge to the research and development of electrode materials. The guarantee of the adhesion of the negative electrode material after the metal lithium powder is formed and disappeared Quite difficult.
4. Positive lithium-rich material method
When the first effect of the negative electrode is lower than that of the positive electrode, too many lithium ions will be lost to the negative electrode during formation, resulting in the effective space of the positive electrode being unable to be filled with lithium ions after discharge, resulting in a waste of lithium intercalation space in the positive electrode; if a small amount of lithium ions are added to the positive electrode The lithium-rich material with high gram capacity can supply more lithium ions for the formation of the SEI film during formation, and there is no need to worry that the lithium-rich material cannot intercalate lithium again during discharge.
2. Lithium-ion battery pre-lithiation technology
The common pre-lithiation method is negative electrode lithium supplementation, such as lithium foil lithium supplementation, lithium powder lithium supplementation, etc., which are currently key pre-lithiation processes; in addition, lithium silicide powder and electrolytic lithium salt solution are used for pre-lithiation. Lithium technology.
1. Lithium supplementation with lithium foil
Lithium foil lithium supplementation is a technology that uses the self-discharge mechanism to supplement lithium. The potential of metal lithium is the lowest among all electrode materials. Due to the existence of potential difference, when the negative electrode material is in contact with metal lithium foil, electrons spontaneously move to the negative electrode, accompanied by the intercalation of Li+ in the negative electrode.
2. Stabilized lithium metal powder (SLMP)
Compared with adding in the slurry mixing process, it is simpler and easier to directly load SLMP onto the dry negative electrode surface. Use SLMP to pre-lithiate the silicon-carbon nanotube negative electrode. Drop 3% SLMP/toluene solution on the surface of the silicon-carbon nanotube negative electrode. After the toluene solvent is volatilized, perform tableting, activation, and pre-lithiation After that, the initial irreversible capacity of the negative electrode decreased by 20% to 40%.
3. Lithium silicide powder
The size of the nano-lithium silicide powder is small, which is more conducive to the dispersion in the negative electrode; in addition, it is already in an expanded state, and the volume change during the cycle will not affect the structure of the entire electrode.
4. Lithium supplementation by electrolysis of lithium salt solution
Silicon is supplemented with lithium by electrolyzing Li2SO4 aqueous solution in an electrolytic cell. The sacrificial electrode is a copper wire immersed in Li2SO4. Whether lithium foil, SLMP or lithium silicide powder is used to supplement lithium, the use of metal lithium is involved. Lithium metal is expensive, highly active, difficult to operate, and requires high costs for storage and transportation for protection.
With the in-depth research of lithium-ion battery materials, the improvement of manufacturing level, and the improvement of market requirements for battery performance, the traditional ideas of replacing electrode materials and developing new electrolytes to improve the performance of lithium-ion batteries have been very limited. The emergence of pre-lithiation technology provides an effective solution to improve the performance of lithium-ion batteries, especially in terms of improving irreversible capacity loss and increasing energy density, and injects new vitality into the development of lithium-ion battery technology.