Construction and Testing of Coin Cells of Lithium Ion Batteries

Summary

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

Abstract

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles¹ or even electrical grid stabilization systems². All these applications simulate a dramatic increase in the research and development of battery materials^3-7, including new materials^3,8, doping⁹, nanostructuring^10-13, coatings or surface modifications^14-17 and novel binders¹⁸. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage.

In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.

In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO₂ working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials¹⁴. Third, better binders (other than PVDF) have also developed and used¹⁸. Finally, other types of electrolytes (instead of LiPF₆) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes⁷.

Protocol

1. Preparation of a Working Electrode

1. Prepare a mixture of ~6 wt. % polyvinylidene fluoride (PVDF) binder in N-methyl-2-pyrrolidone (NMP).
2. Weigh 80 wt. % active material (LiCoO₂ in this case) and 10 wt. % C black (acetylene, 99.9+ %) and then mix them in a vortex for 1 min.
3. Add NMP-binder mixture such that the binder constitutes 10 wt. % of the total weight of the mixture.
4. Transfer the above mixture into a small glass vial and mix in the vortex mixer at maximum rpm for about 30 min. Two zirconia balls of 5 mm diameter can be used as media for better mixing. If needed, add more NMP in order to obtain slurry of requir....

Discussion

In our experience, the most critical step in the preparation of the working electrode is making good slurries with consistency. As shown in Figure 4, excess NMP in the slurry can result in a cracked coating, while insufficient NMP can result in a porous coating. In the work presented here, CR2032 coin cell cases that are 20 mm in diameter are used. It should be noted that coin cell cases of different sizes can be used, where the electrode sizes should be varied accordingly. During cell assembly, the appr.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Poly(vinylidene fluoride)	Sigma-Aldrich	182702
1-Methyl-2-pyrrolidinone, 99.5%	Alfa Aesar	31903
LiCoO2	Alfa Aesar	42090
Carbon black, acetylene, 99.9+%	Alfa Aesar	39724
LiPF6 in EC:DMC:DEC	MTI Corporation	EQ-Be-LiPF6
Celgard separator	Celgard	C480
Analog Vortex Mixer	VWR	58816-121
Vacuum oven
Vacuum pump
Hydraulic press
Coin cell case	MTI Corporation	EQ-CR2032-CASE-304
Spring and spacer	MTI Corporation	EQ-CR20SprSpa-304
Glovebox	mBraun	UNILAB
Battery tester	Arbin Instruments	BT2143