To all Experts,
I bought some labgrade AC and put it on some grafoil using some pva. When I used znso4 as electrolyte. I charged the whole thing at 1.6 v. It took about 2 hours to reach 1.6-1.8 volts. But when I set the multimeter on current and tried a direct short, there was no current at all.. only 1-2 ma.
If I charge it at 3.5 v, it is able to run my 10 ma motor for about 40 minutes after a 10 min charge. But the anode is expanding. Can someone help me understand why the supercp is not charging at 1.6v?
Can you explain a little better what you are doing there. How can you charge with 1.6V while achieving 1.8V? What is your setup? Grafoil may not suitable, often activated carbon is used.
Is this an aqueous system? 3.5 V is well above the breakdown voltage of water, you could just be making a H2+O2 fuel cell, which would explain why you don't see anything at lower voltage. Is your system open, can you see bubbles?
What is your charge profile? You should use a CCCP charge profile and monitor current and voltage if you can. If there is large polarization then the cell voltage will jump to 1.6 V with very little capacity during charge. Self-discharge could be another issue. Let the capacitor sit after charging and measure OCV.
Start your initial charge profile using a V1-secured (low-V) value: V1=0.5V.
If you do not get near the same charge (>50%) in discharge phase then you have to make a better SC electrode (interfaces). Charging more than V1 (e.g. 1.6V or 1.8V) is, just, a waste of your time, if the initial V1-test fails.
I am so sorry guys. Totally missed on getting back on time.
@ Christoph
Actually, I guess so because it is ZnSo4's potential that I can reach 1.8. The grafoil is the current collector for the activated carbon in my supercap
@ Zachary
Yes. This is an aqueous system. Although I bought the AC off a lab supply stores, I am not sure if it has a good surface area. The setup is some grafoil with some AC on it. This is a symmetric supercap with a paper tower with some electrolyte in it. Can you tell me more about cccp. Cant find anything on google
@ ioannis:
Thats a great idea. I tried again with some Graphene and had better results. But not as good as in the flooded cell. I was able to run a motor for 10 minutes @ charge of 1.8v. I guess I need better active materials
@Mukund Vadrev:
When the initial charge profile, using low-V (V1=0.5V) value(s), WE-test is good, then you can VN-broaden (repeating N-times), this profile test. So, if you extend, now, the low-V value to a new(er) value of the VN-upper limit (VN=V1 + N*Vstep), using very small[1] steps, say a compromised step value of Vstep=0.1V, you can hit better your target. However, you must stop this (stepwise-VN) test, when you find the maximum capacity, for this (particular) WE configuration.
In other words, this (stepwise-VN, slow) way test, might get you faster[2], towards what you want[3].
1. Maybe the last (good WE-test) VN is much lower than 1.8V, your (motor, fast) test.
2. "slow and steady can get better results than going a faster pace towards your goal" like ... the Rabbit and Turtle Race, story, lesson. http://www.web-esl.com/advreadings/rabbitturtle.htm , https://www.youtube.com/watch?v=0BON0VxgThc
3. Higher (WE) capacity, running your motor for more time.
What kind of multi-meter are you using? Have you used this multi-meter for such a reading in the past? What is the resistance of the leads you are using?
I suggest you use an oscilloscope in single shot mode. However you will also need a switch and a small resistor. Through the oscilloscope you will be recording the voltage drop across the resistor. Then current will be the voltage divided by the resistance you have used.
Let me know if you need more information.
Mukund Vadrev, CCCP stands for constant current constant potential. I believe it is a standard method of charging commercial batteries, like your cell phone. In brief, you start with a controlled positive current, when it reaches a designated voltage it will hold that voltage until current drops below a threshold value.
In general, the slower you charge or discharge a battery/capacitor, the closer you will achieve theoretical capacity. If you charge/discharge too quickly there are polarization effects that will create resistance, so your device reaches its maximum or minimum voltage sooner (which means less than ideal capacity). An example of this is the kinetic restrictions of ion diffusion in intercalation batteries. Ions can only move so fast inside a material, and if your current is too high then ion diffusion cannot keep up, and that creates a polarization. Double layer capacitors avoid this kinetic problem because all charge is stored on the surface of the electrode (that is why you want high surface area, for increased capacity) near the electrolyte.
It seems that you are testing your capacitors/batteries by short circuiting them through a motor or multimeter. If you want to characterize your devices I think it would be wise to invest in some sort of electrochemical tester or potentiostat that can control and measure current/voltage. Alternatively, you could put some resistors in series with your multimeters to control current, perhaps make your own feedback circuit to maintain constant current as your device changes voltage.
Ok so I succeed in charging it. Turns out my powesupply had some rust issues. I used some elmers glue with some AC on some Grafoil. Turns out @3.5v in a flooded cell, intercalation probably is happening to a high degree and giving a high surface area expanded 3d graphite electrode. And it would charge really quickly ~2 mins to full charge.
I need to look for a new binder and better current collectors
I am able to run a tiny CD player motor for about 25 minutes 2cm x 2cm
Mukund Vadrev, you should find a better way to measure the performance of your device, instead of running it through a motor. The motor draws high current, which could change the performance of your devices. It would be best if you found a way to control current and measure voltage.
Absolutely. I will also try charging my cap at different voltages successively to try simulate the scan rate. I realized capacitance is higher at smaller scan rates