Lithium-ion Full Cell Manufacturing Process Training-- electrolyte Section 1

1.Lithium-ion battery electrolyte

Lithium-ion battery electrolysis is a mixture of organic solvents and lithium salts, plus functional additives. The electrolyte itself is electrically neutral, and conducts ions but not electrons in the battery, and it is one of the important components to ensure the normal operation of lithium-ion batteries

 

1.1.Role of Electrolyte

Lithium-ion battery electrolyte is an important medium responsible for the shuttle of lithium

ions in the positive and negative electrodes;  

Good electrochemical stability over a wide range of voltages;

Good electrochemical and chemical stability over a wide range of temperatures;

Good ion transmission performance;

It can form a good interface at the positive and negative electrodes to ensure the normal

operation of the battery cell performance.

2.Common composition of electrolyte

2.1.Solvents

1.EC: Polar solvent, dissolves lithium salt and has film-forming effect, is an essential component.

2.DMC: weakly polar solvent, low viscosity, conducive to the increase of conductivity, mostly used for rate type and electrolyte requiring good wettability.

3.EMC: Easy to decompose into DMC and DEC in small amounts, and is mostly used in aluminum shell batteries with EC.

4.DEC: High boiling point, mixed with EC and PC, mostly used for high-temperature electrolyte.

5.PC: Polar solvent with high boiling point, used for high-temperature storage electrolyte, but poor compatibility with natural graphite.

2.2.Lithium salts

LiPF6：good conductivity, outstanding chemical and electrochemical stability, disadvantage is slightly poor thermal stability and easy hydrolysis, is the main salt in the current commercial application of formulations.

 

2.3.Common additives

1.VC：Vinylene carbonate, containing unsaturated double bonds, is chemically more reactive than PC and EC, and can break the double bonds at higher decomposition potentials than PC and EC during discharge, forming a network of macromolecules involved in the formation of the SEI layer. Its usage is generally no more than 2%, which can effectively reduce the first capacity loss of lithium-ion batteries, improve the stability of the SEI layer at high temperatures, and increase the cycle life.

2.FEC: Fluoroethylene carbonate, FEC has one more -F substituent group than EC, and this group has a strong ability to absorb electrons, so it can be explained that at higher potentials, FEC can undergo reductive decomposition reactions. The circulation efficiency and safety performance of the electrolyte in the electrolyte formed by fluorocarbonate are also improved.

2.4.Additives

1.PS: 1,3-propanesulfonolactone, a high-temperature additive, can form an effective protective film at the cathode, so that the reactivity between the cathode and the electrolyte is reduced, and the high-temperature performance of the battery cell can be well improved.

 

2.From the data, it is clear that VC and FEC are beneficial to the cell cycle, while PS alone does not bring beneficial help to the cycle.

 

 

3. Physicochemical properties and test

methods of electrolytes

These five indicators are the basic requirements of the industry for electrolyte!

 

3.1. HF and moisture of the electrolyte

1. When LiPF6 is dissociated directly in the aqueous solution, the change of HF is relatively constant.