Lithium-ion Full Cell Manufacturing Process Training-- electrolyte Section(II)

1.Expression of the formula

 

1.1.The yellow part is the main electrolyte formulation for the experiment in this article, let's translate into the table below

 

 

1.2.So how to configure the electrolyte exactly?

 

 

From the figure above, it can be observed that the industrial prefers to use mass ratio expressions, which is significantly different from the volume ratio expressions commonly used in academic circles. This is largely due to the following reasons: 1. Industry is based on quality control unit in the production of electrolyte; 2. The volume of solvents is a function of temperature, and it is greatly affected by environmental temperature in practical use, making it unsuitable for large-scale industrial applications!

1.3.The solvent mass expression method has the following differences:

Addition method: when the laboratory test group is continued, in the case of the control group, the method of adding additional additives, this method is easy to compare and simple to operate when actually doing experiments, the disadvantage is that when you add the method, the actual mass fraction of the additives is diluted because the additives you add are diluted, which has little effect when the additives are small,but when the amount of additives is large, the impact on the mass fraction is obvious.

Internal addition: the quality of additives in each group of the experiment is certain, when you set it to 2%, the actual formula is 2%, which affects the mass proportion of the solvent. This kind of method, in the actual experiment, is troublesome to configure, and each recipe has to be specially configured. The advantage is that the mass fraction of the combination ratio of the additives is constant, and it is easy to explain the mass ratio expression to the customer, so it is not easy to misunderstand.

 

1.4.So how to configure the electrolyte exactly?

 

Through the above explanation, you should understand the deviation of industry and academia in the understanding of formula expressions. It is particularly emphasized here that the industry will not use the method of "constant volume" volume to configure an electrolyte with a certain molar concentration of lithium salt.

Back to the configuration steps in this case: (Control Group)

1.Find the density of EC and DEC.

2.According to the volume ratio of 1:2, the mass ratio is calculated to be ~40.4:59.6.

3.1M lithium salt at 12.5% wt.

4.The mass-to-mass ratio formula for the Control group is shown on the right

5.The additive group is set to 1 in the control group, and the corresponding amount of additives is (additive).

 

2.Analysis of electrolyte discoloration

2.1.We mentioned it in the previous lecture Recommendations for sample-level electrolyte

storage:

1.The best storage conditions for conventional electrolyte: in the glove box (≤

5ppm),temperature ≤ 24°C;
2. Storage container selection: aluminum bottle, steel cylinder, fluorinated bottle, glass container is not recommended;
3. Special type of electrolyte: under closed conditions, the recommended storage temperature is below 20°C.
4. The meaning of special types of electrolytes: high content of EC (such as formula EC content above 40% volume ratio) Electrolyte: high content of DMC (such as formula DMC content above 40% volume ratio) Electrolyte:high content of FEC (such as formula FEC content above 5% mass ratio) Electrolyte:high lithium salt solubility, lithium salt > 1.20M, electrolyte containing DTD and other special additives.

2.2.From the suggestions, we can know that the main factors affecting the discoloration of

electrolyte are:

1. LiPF6

2. Type and content of additives

3. Storage environment (container, temperature, etc.)
The factors involved in the problem of discoloration are mainly the above three categories, which mainly affect the generation of pigments brought about by transesterification reaction, lithium salt catalytic decomposition, solvent catalytic decomposition, and ultimately affect the color of the electrolyte?

2.3.Here we would like to share with you some of our experimental results, so that you

can have a certain feeling about the electrolyte discoloration：

50℃,10d,blank experiment, no LiPF6 was added, and the colors of the four groups did not

change