1School of Materials Science and Engineering, Clemson University, 2Center for Optical Materials Science and Engineering Technologies, Clemson University
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Kayyar, A., Huang, J., Samiee, M., Luo, J. Construction and Testing of Coin Cells of Lithium Ion Batteries. J. Vis. Exp. (66), e4104, doi:10.3791/4104 (2012).
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 materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 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.
1. Preparation of a Working Electrode
2. Preparation of Electrolyte
3. Preparation of a Counter Electrode (Lithium foil in this case)
4. Coin Cell Assembly
5. Coin Cell Testing
Weight of the electrode disc with the current collector =WEO
Weight of the uncoated current collector disc of the same diameter =WCC
Weight of electrode material, WEM, is given by
Weight of active material in the electrode, WAM, is given by
Theoretical capacity for the electrode disc, CED, is given by
where C is the theoretical specific capacity of the active material.
6. Representative Results
As an example, a coin cell was constructed using LiCoO2 as the active material for the working electrode. After construction, the cell was tested at C/5 rate. The obtained profile is shown in Figure 3. The voltage window was set to be between 3 and 4.3 V for this coin cell. The capacity was 155 mAh/g for the first charge cycle and 140 mAh/g for the first discharge cycle.
Figure 1. Flow chart of the coin cell construction procedure. First, a working electrode is prepared from the powder of the active material. Then, a counter electrode is prepared from a clean lithium foil and the separators are punched out. Finally, a cell is assembled inside an argon glovebox.
Figure 2. Schematic of a coin cell assembly process showing all the components in the order that they are placed inside the coin cell case.
Figure 3. Representative results obtained from a coin cell constructed using a working electrode made from LiCoO2 and a lithium foil counter electrode. The plot shows the first charge and first discharge curves for the coin cell that was charged and discharged at C/5 rate.
Figure 4. Comparison of good and bad coatings after they have been dried. A cracked coating typically results from slurry that has excess NMP and a porous coating typically results from slurry that has insufficient NMP.
Figure 5. Comparison of a well crimped coin cell and a badly crimped coin cell, along with an un-crimped cell. Typically, a badly crimped coin cell splits open after a few hours in ambient due to the swelling of lithium foil after reaction with moisture.
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 appropriate number of spacers to be used depends on the thickness of the lithium foil electrode and the height of the cell. This number can be varied in order to obtain a sufficiently close packed cell. After the cells are assembled, they are crimped to obtain a tight seal. It is critical that the cell is crimped well since both the lithium electrode and the electrolyte are sensitive to moisture. Figure 5 shows a comparison of a badly crimped cell and a well crimped cell, along with an un-crimped cell.
No conflicts of interest declared.
We gratefully acknowledge the support from the Ceramics program in Division of Materials Research of the U.S. National Science Foundation, under the grant no. DMR-1006515 (program manager, Dr. Lynnette D. Madsen).
|1-Methyl-2-pyrrolidinone, 99.5%||Alfa Aesar||31903|
|Carbon black, acetylene, 99.9+%||Alfa Aesar||39724|
|LiPF6 in EC:DMC:DEC||MTI Corporation||EQ-Be-LiPF6|
|Analog Vortex Mixer||VWR||58816-121|
|Coin cell case||MTI Corporation||EQ-CR2032-CASE-304|
|Spring and spacer||MTI Corporation||EQ-CR20SprSpa-304|
|Battery tester||Arbin Instruments||BT2143|