Electrolyte Reagents for Lithium-Ion Batteries

By: Dr. Koji Abe, Advanced Energy Materials R&D Center, Chemicals Company, UBE Industries, Ltd.

Introduction

In recent years, the applications of lithium-ion batteries (LIBs) have expanded beyond the traditional use as a power source for mobile devices such as smartphones, tablets, etc. to electric vehicle (EV) battery systems and power storage. The greatest advantages of LIBs are their high operating voltage of 4 V and high energy density per unit volume and mass. The main components of LIB are the cathode, anode, separator and electrolyte. Although cathode and anode materials have been extensively investigated, the research on electrolytes drew little attention until the launch of Purelyte® functional electrolytes in 19971,2,3,4. The subsequent intensification of research into electrolytes and their additives has been a major driving force behind the technological progress made with LIBs, currently one of the core elements of LIB technology. In order to help researchers working on LIBs, Sigma-Aldrich® has recently launched a variety of battery grade ready-to-use electrolytes (Tables 1 & 2) from UBE Industries, Ltd.

 

Table 1: Battery grade electrolytes (H2O <15ppm; HF < 50 ppm; APHA < 50) with 1.0M LiPF6 concentration for lithium-ion batteries
 

Product Name Product Number
1.0M LiPF6 in EC/DMC=50/50 (v/v) 746711
1.0M LiPF6 in EC/EMC=50/50 (v/v) 746738
1.0M LiPF6 in EC/DEC=50/50 (v/v) 746746
1.0M LiPF6 in DMC 746754
1.0M LiPF6 in EMC 746762
1.0M LiPF6 in DEC 746770
1.0M LiPF6 in PC 746789

 

Table 2: Battery grade electrolytes (H2O <15ppm; HF < 50 ppm; APHA < 50) with a high LiPF6 concentration

Product Name Product Number
2.0M LiPF6 in EC/DMC=50/50 (v/v) 809357
2.0M LiPF6 in EC/EMC=50/50 (v/v) 809365
2.0M LiPF6 in EC/DEC=50/50 (v/v) 809349
2.0M LiPF6 in DMC 809411
2.0M LiPF6 in EMC 809403
2.0M LiPF6 in DEC 809543
2.0M LiPF6 in PC 809470

Battery grade electrolytes

About 15 years ago, most electrolytes used in LIBs were of low purity. In fact, owing to an increase in the HF concentration resulting from the reaction between the moisture and LiPF6 in the electrolytes over time, some of those electrolytes would change color to a reddish brown during storage. However, the use of transparent, high-purity electrolytes, has become the industry standard as they remain chemically stable and do not show a change in HF concentration over a long period of time (Figure 1)5.

Comparison of the time dependence of HF concentration in a high-purity electrolyte and a regular electrolyte

Figure 1. Comparison of the time dependence of HF concentration in a high-purity electrolyte and a regular electrolyte. The change in HF concentration causes a change in color in regular electrolytes.

The use of high quality battery grade reagents and solvents such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. form the basis of high quality functional electrolytes offered by Sigma-Aldrich®.

Solvents and additives

In addition to high quality electrolytes, the battery grade solvents and additives are also important for lithium-ion battery researchers. These battery grade solvents (Table 3) are used to adjust the concentration of battery grade electrolytes (for representative examples see Figures 3), and as a cleaning solvent for various types of battery analysis. In LIBs, the additives (Table 4) are used for battery performance improvement, such as protection of anode or cathode, overcharge protection and suppression of metal elution. The role of different additives in LIBs is summarized in Table 46-13.

 

Table 3: Battery grade solvents (purity > 99%, H2O < 10 ppm, Acid Value < 10 ppm)

Solvent EC PC DMC EMC DEC FEC
CAS No. 96-49-1 108-32-7 616-38-6 623-53-0 105-58-8 114435-02-8
Product Number 809950 809969 809942 809934 900018 -
Structure

 

Table 4: Battery grade additives (purity > 99.5%, H2O < 100 ppm, acid content < 200 ppm)

Name Vinylene carbonate 1,3-Propane sultone 2-Propynyl methanesulfonate Cyclohexylbenzene t-Amyl benzene Adiponitrile
CAS No. 872-36-6 1120-71-4 16156-58-4 827-52-1 2049-95-8 111-69-3
Function Protection of Anode Protection of Cathode Protection of Anode Overcharge prevention Overcharge prevention Suppression of metal elution
Product Number 809977 809985 809993 810002 900001 900020
Structure

 

Preparation of customized battery grade electrolyte solutions

Customized electrolyte compositions are often required by researchers. Accordingly, Sigma-Aldrich® standard electrolytes can easily be mixed to produce the desired composition by mixing specified amounts of the standard electrolyte (Tables 1 & 2) and/or solvents (Table 3) under an anhydrous atmosphere. Schematics for preparing some of the customized electrolyte compositions are shown in Figures 3-4. It should be noted that the exposure of the LiPF6-based electrolytes to moisture triggers the decomposition of LiPF6 which leads to the generation of HF and deterioration of the electrolytes. Therefore an anhydrous condition is mandatory for making the aforementioned adjustments.

The steps for adjusting the composition are as follows:

  1. Determine the solvent composition to be prepared.
  2. Unseal the package containing the corresponding reagent under an anhydrous atmosphere (e.g. in a glove box).
  3. Weigh the required amount of reagent and adjust it in a metal, plastic, or other non-glass container.

electrolyte compositions

Figure 2. Examples of preparing customized electrolyte compositions (1.0M LiPF6 concentration) using the reagents from Table 1.

Adjustment of LiPF6 concentration

Schematics illustrating the preparation of additional electrolyte formulations

Figure 3: Schematics illustrating the preparation of additional electrolyte formulations (adjustment of LiPF6 concentration)

 

Schematics illustrating the preparation of an electrolyte containing an additive

Figure 4. Schematics illustrating the preparation of an electrolyte containing an additive

 

References

  1. Yoshitake, H. Battery and Power Supply in Techno-Frontier Symposium, Makuhari, Chiba, April 14-16, 1999.
  2. Yoshitake, H. Functional Electrolytes, In Lithium-ion secondary batteries. Yoshio, M., Kozawa, A., Eds,; Nikkan Kogyo Shimbun Ltd.: Tokyo, Japan, 2000; Chapter 5.
  3. Yoshitake, H., Functional Electrolytes Specially Designed for Lithium-ion Batteries, In Lithium-ion batteries.Yoshio, M., Bradd, R. J., Kozawa, A., Eds,; Springer Science + Business Media, LLC: New York, 2009; Chapter 19.
  4. Abe, K. Nonaqueous Electrolytes and Advances in Additives, In Electrolytes for Lithium and Lithium-ion Batteries; Springer Science + Business Media: New York, 2014; Chapter 3.
  5. Hamamoto, T; Hitaka, A.; Abe, K.; Ueno, Y.; Ohira, N.; Watanabe, M., Electrolyte solution for lithium secondary battery. U.S. Patent 6,045,945, 1998
  6. Hamamoto, T., Hitaka, A., Nakata, Y., Abe, K., JP Patent 3,627,754, 1999
  7. Hamamoto, T., Ueki, A., Abe, K., Takai, T., US Patent 6,413,678, 2000
  8. Hamamoto, T., Hitaka, A., Nakada, Y., Abe, K., US Patent 6,033,809, 2000
  9. Hamamoto, T., Abe, K., Takai, T., Matsumori, Y., Ito, A., US Patent 6,479,191, 2000
  10. Takahashi, M., Yasutake, Z., Abe, K., Ueki, A., Hamamoto, T., US Patent 6,632,572, 2000
  11. Abe, K., Matsumori, Y., Ueki, A., US Patent 7,294,436, 2002
  12. Hamamoto, T., Ueki, A., Abe, K., Miyoshi, K., US Patent 7,981,552, 2002
  13. Hamamoto, T., Abe, K., Ushigoe, Y., Matsumori, Y., US Patent 6,881,522, 2002