What Are The Excellent Properties Of high Concentration Electrolytes?

The electrolyte is the key material of the lithium battery, which has a significant impact on the battery's performance such as rate, capacity, cycle life, applicable temperature and safety. The electrolyte is generally composed of lithium salts, solvents and additives. When the concentration of lithium salts in the electrolyte is increased to more than 3 mol / L, the coordination number of solvent molecules and Li + will be reduced to 1 ~ 2, and there is almost no solution Free solvent molecules, lithium salts usually exist in the form of aggregates AGGs and contact ion pairs CIPs. Then a high concentration electrolyte be constituted.

The high concentration electrolyte has many excellent performances as the following :

(1) Prevent graphite peeling

The solvent electrolyte containing ethylene carbonate can form a stable SEI film containing lithium fluoride on the surface of the graphite negative electrode, avoiding the co-intercalation of Li + solvent compounds in the graphite layer, but EC has the disadvantages of high viscosity and high melting point, which affects the low temperature performance and rapidity of the battery Charge and discharge performance. By increasing the lithium salt concentration in the electrolyte, the graphite electrode can have good compatibility in electrolytes that do not contain ethylene carbonate solvents.

(2) Improve rate performance

Yamada et al. Found that the high-concentration (3.6 mol / L) LiFSA / DME (1,2-dimethoxyethane) electrolyte has a good interface film to promote Li + insertion / extraction reaction, and Li + The higher the concentration, the larger the number of Li + migration compared to the dilute concentration of LiFSI / DME electrolyte, which is beneficial to improve the rate performance of the battery.

(3) Suppression of aluminum foil corrosion

Sulfoimide lithium salts (such as LiFSI, LiTFSI, etc.) have high ionic conductivity, and high thermal and electrochemical stability. However, the Al corrosion problem of this type of lithium salt electrolyte is serious. The researchers found that a high concentration of sulfonimide lithium salt electrolyte can inhibit the corrosion of Al foil.

(4) Promote the formation of SEI film, inhibit lithium dendrites and contribute to the long-term stable circulation of metallic lithium.

Studies have shown that increasing the lithium salt concentration of the electrolyte can form a stable SEI film on the surface of Li metal, improving electrode stability and battery coulombic efficiency.

In summary, the high-concentration electrolyte makes it have a wider electrochemical window and better safety by changing the solvation state of lithium ions.