The report on the CMC as a binder in the evaluation for an electric double layer capacitor
Yamagata University
Faculty of Engineering /
Department of Chemistry and Chemical Engineering
Kohei Nakajima
Introduction
Insulator is not only prevents leakage of high voltage power lines and the like, electrically there are also important features. One of the major applications of the insulator is used as a dielectric. That is, in the insulator, the electrons are strongly bound by the nucleus of the element. However, by applying an electric field from the outside, the relative displacement between the nuclei and electrons occurs, and polarization. The polarized layer is called an electric double layer, is applied as a laminate capacitor or capacitor batteries. In the manufacture of lithium secondary batteries, the slurry are kneaded cell reaction active material and a carbon material with a binder to create an electrode by applying aluminum foil. Lithium cobalt oxide to be used as a battery reaction active material, since deterioration due to overcharging is concerned, PVDF has been used as a binder. However, since the PVDF has a high processing cost, there is a problem that not a few adverse effects on the environment, In place of PVDF, a polymer material such as styrene-butadiene rubber and acrylic and dispersed in water, an attempt to use as a binder have been made. Also, when using such a water-dispersed binder, it is necessary to control the rheology of when applying the slurry to an aluminum foil. Therefore, thickening agents such as carboxymethyl cellulose has been added to the slurry in order to improve the coating properties. In this report, and at the same time to evaluate the coating properties for the various CMC, performs the electrochemical measurement, and the CMC that does not degrade the battery performance and intended to seek an ideal slurry designs that thickener.
Theory and Method
I will use the Mitsubishi aluminum (1N99) as aluminum foil, was designed a slurry containing only carbon material. I represent the composition of the adjusted slurry in Table 1. I weighed about 5.0mg of thickener using the even balance, water about 500mg, the carbon nanotubes of approximately 10mg is added, Sufficiently kneaded and adjusted the slurry in addition to SBR dispersion of 20~30mg. The adjusted slurry is then coated and dried on an aluminum foil cut into 1.0cm × 4.0cm, I was evaluated for its slurry application performance.
When charging and discharging test in a lithium ion secondary battery close to real, it is necessary to a variety of designs. To the created electrode, as an electric double layer capacitor for evaluation, was assembled in the cell. Cell, in soy sauce refers that was purchased at 100 yen shop, was attached to the working electrode and the counter electrode. I put a 0.5wt% ammonium adipate aqueous solution as an electrolyte solution. In this way, the battery-powered shown below, was assembled EDLC evaluation cell. I examined the polarization resistance and impact of the capacitance thickener had using cyclic voltammetry. In addition, as a condition, sweep range of CV is 0V ~ 1.0V, sweep speed was 100mV / sec.
Table.1 Thickening agent name and the composition of the slurry
|
Thickening agent name |
Mass /mg |
H2O*2 |
CNT /mg |
SBR dispersion *3 /mg |
|
WSCA-90 |
4.0 |
10 drop |
11 |
80 |
|
CMC-Li |
7.0 |
10 drop |
11 |
29 |
|
Cellulose acetate L-50 |
6.0 |
20 drop |
22 |
26 |
|
JERUNA QH300 |
6.0 |
10 drop |
10 |
1 drop |
|
HEC DAICEL SE850 |
6.0 |
10 drop |
11 |
1 drop |
|
HEC DAICEL SE400 |
5.0 |
10 drop |
10 |
1 drop |
|
CMC DAICEL 1260 |
5.0 |
10 drop |
16 |
29 |
|
CMC DAICEL 1220 |
6.0 |
10 drop |
10 |
1 drop |
|
CMC DAICEL 1190 |
5.0 |
10 drop |
10 |
1 drop |
|
CMC DAICEL 2200 |
7.0 |
10 drop |
10 |
1 drop |
*2 Water was about 500mg in 10 drops.
*3 SBR dispersion was about 20~30mg per droplet.
Results
The state of each CMC in charge of when it is applied to the slurry during adjustment and Al, further coating amount of CNT are shown below.
CMC Daicel 1260 , first was fairly loosely , and continue to stir went increased viscosity, finally were also relatively loose .The coating amount of CNT was 4.7mg.
HEC Daicel SE850, the viscosity as time passes and the paint went increasing. The coating amount of CNT was 2.9mg.
I have observed the coating state of all of the slurry after drying. CMC DAICEL1260, JERUNA QH300, CMC-Li, CMC DAICEL1220, HEC DAICEL SE850, CMC DAICEL1190, this order coating unevenness was less in.
Here, I show all of CMC of capacitance obtained from the cyclic voltammogram in the table.2, the polarization resistance, capacitance per CNT coating amount 1mg.
Table.2 capacitance, the polarization resistance, capacitance per CNT coating amount 1mg
|
Thickener name |
Capacitance /mF |
Polarization resistance /kΩ |
Coating amount of CNT /mg |
Capacitance / Coating amount of CNT mg/mF |
|
CMC-Li |
0.57 |
18 |
4.4 |
0.13 |
|
JERUNA QH300 |
0.90 |
22 |
3.1 |
0.29 |
|
HEC DAICEL SE850 |
0.62 |
12 |
2.9 |
0.21 |
|
CMC DAICEL 1260 |
1.10 |
3 |
4.7 |
0.23 |
|
CMC DAICEL 1220 |
0.55 |
10 |
4.0 |
0.14 |
|
CMC DAICEL 1190 |
0.25 |
13 |
8.4 |
0.03 |
|
Cellulose acetate L-50 |
0.95 |
7 |
8.6 |
0.11 |
|
CMC DAICEL 2200 |
1.08 |
2 |
5.9 |
0.18 |
|
WSCA90 |
0.50 |
8 |
1.3 |
0.38 |
|
HEC DAICEL SE400 |
0.25 |
38 |
2.7 |
0.09 |
In addition, I show each rank of capacitance, Polarization resistance, capacitance per CNT coating amount 1mg in the table.3.
Table.3 Each rank of capacitance, polarization resistance, capacitance per CNT coating amount 1mg
|
Rank |
Capacitance |
Polarization resistance |
Capacitance per CNT coating amount 1mg |
|
1 |
CMC DAICEL 1260 |
CMC DAICEL 2200 |
WSCA90 |
|
2 |
CMC DAICEL 2200 |
CMC DAICEL 1260 |
JERUNA QH300 |
|
3 |
Cellulose acetate L-50 |
Cellulose acetate L-50 |
CMC DAICEL 1260 |
|
4 |
JERUNA QH300 |
WSCA90 |
HEC DAICEL SE850 |
|
5 |
HEC DAICEL SE850 |
CMC DAICEL 1220 |
CMC DAICEL 2200 |
|
6 |
CMC-Li |
HEC DAICEL SE850 |
CMC DAICEL 1220 |
|
7 |
CMC DAICEL 1220 |
CMC DAICEL 1190 |
CMC-Li |
|
8 |
WSCA90 |
CMC-Li |
Cellulose acetate L-50 |
|
9 |
HEC DAICEL SE400 |
JERUNA QH300 |
HEC DAICEL SE400 |
|
10 |
CMC DAICEL 1190 |
HEC DAICEL SE400 |
CMC DAICEL 1190 |
I shows the correlation between the capacitance and the CNT coating amount in Fig.1.
Fig.1 Correlation of capacitance and CNT coating amount
Conclusion
Capacitance is a quantity indicating whether the insulated conductors, such as capacitors, how much charge is stored. It can be said that this number is a better capacitor larger. However, if you look at the Table 2, they've occurred and until 0.25μF~1.10μF, is a big difference. Since it is unlikely that the take is a difference of up to here by the performance of CMC, I first was discussed other elements. The composition of the slurry, as shown in Table 1, because all CNT concentration is approximately equal, large errors such as reverse the results cannot be confirmed here. However, there occurs a significant difference also CNT coating amount in Table 2. So, I examined the correlation between the two numbers of the capacitance and the CNT coating amount. As shown in Figure 1, it was found that there is a correlation with the exception of one type of CMC. In other words, I can be seen that the capacitance is approximately proportional to the CNT coating amount. In other words, the capacitance per CNT coating amount 1mg is appropriate to compare the performance of each CMC. If we check each rank are shown in Table 3, measured value and the CNT coating amount capacitance per 1mg became completely different results.
Then, I describe the polarization resistance. That the polarization resistance is small, is that electricity flows easily. However, there is also disadvantage likely to rust out the metal. Therefore, in evaluating the industrial capacitors, it cannot be said categorically and this value is better the smaller. Here, it is assumed that it is better small in order to consider the evaluation of CMC only.
From Table 3, three of the CMC, CMC Daicel 2200, CMC Daicel 1260, WSCA90 that with a color, polarization resistance, for with any of the values of capacitance per CNT coating amount 1mg also has a relatively good result .
References
Masakatsu Nomura and Teruo Suzuka (2004), “Latest industrial chemistry”
Kazuya Kobayashi and Shozo Yamashita (2004), “Industrial technology foundation”
Akiya Kozawa (1990), “Modern electrochemical”