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Monolithic Cotton Supercapacitors

HAL 9000: I am putting myself to the fullest possible use, which is all I think that any conscious entity can ever hope to do.

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After making the dog hair/dryer lint supercapacitor I struck upon a very obvious method for building massive aqueous supercapacitors that outperform all else in energy density and self discharge.

Because of how supercapacitors work, storing energy at the electrolyte/electrode interface and not requiring the movement of ions all the way from anode to cathode, much of the mass attributed to metals in charge collectors can be removed if a monolithic active electrode can be constructed with low resistance. This also solves the largest issue with aqueos electrolytes to date, being self discharge primarily caused by impurities like iron containing ions shuttling back and forth between electrodes.

Utilizing a bulk activated pyrolitic graphitized cotton fibers the best performing supercapacitors in regards to total weight of the device can be constructed.

Progress is a slow and fickel beast, that often presents itself by accident. In a mad rush for the anything goes competition for the 2016 hackaday prize I stumbled on to a new method for making supercapacitors. In literature it is often described how to make monoliths and aerogels. The problem being is they researchers always grind them up and mix with a binder then paste on electrodes. This is not the way forward.

This project will describe how to make monolithic binder free supercapacitors using activated cotton fibers.

Because of how supercapacitors work, storing charges in the interface between electrode and electrolyte they can theoretically be made as massive as one desires as long as the carbon electrode is electrically conductive enough to avoid ohmic losses. I would not have even pondered this application if the dog hair and lint supercapacitor carbon monolith had not had such a low resistance.

I believe this construction method will be used in the future everywhere for grid scale storage of energy. It solves the main problems associated with aqueous supercapacitors being mAh by total weight of the device, self discharge rates, and cost of metals used in charge collectors.

This method can easily be scaled to make room sized supercapacitors for pennies on the dollar vs lead acid batteries and all other energy storage means. I believe it is the holy grail of low cost supercapacitors that can be constructed anywhere on earth.

This documentation describes Open Hardware and is licensed under the CERN OHL v. 1.2. You may redistribute and modify this documentation under the terms of the CERN OHL v.1.2. (http://ohwr.org/cernohl). This documentation is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN OHL v.1.2 for applicable conditions

pvcplug.stl

A plug for 1.5 inch PVC pipe.

Standard Tesselated Geometry - 35.24 kB - 07/11/2016 at 09:27

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  • Finally no resistance in the monolith

    MECHANICUS07/11/2016 at 01:27 0 comments

    I put the ammonia soaked cotton in a pipe, and beat the heck out of it to fully compress it with a hammer and chisel.

    Then pyrolitically graphitized it at 900 degrees celcius in my forge. As you can see the resistance reading is zero.

    Next step is to activate it, so I dunked it in 6M KOH. and back in the forge for 60 minutes.

  • After about 1.5 years fleshing this thing out I think I have it made.

    MECHANICUS06/24/2016 at 07:11 0 comments

    I have tried practically every last method known to make a high performance supercapacitor I can use in my power armor, prosthesis, and space planes.

    I think I finally figure it out and it should have been obvious but it wasn't. Batteries must have very thin active materials very close to each other because of how they work. Ions such as lithium has to travel all the way from the anode to the cathode when discharging, so rate capability (c discharge rating and charge rating) is impacted by distance. However supercapacitors operate completely differently. The charge is stored directly on the active material and faradaic redox reactions at the cathode only occur at the cathode, meaning no ions have to migrate all the way through an electrolyte.

    This means as long as the active materials for each electrode are conductive enough to not cause ohmic losses through resistance they can be incredibly thick. Illustration below


    I finally got the materials in today to remake my forge, it's a little too hot at the moment to run the fireplace so I can proceed.

  • The Good, The Bad, and the Incredibly Poor

    MECHANICUS06/24/2016 at 05:56 0 comments

    A repository for the old supercapacitors I had to slog through to get to this point.

  • With Electrolysis I Can Push 1.5 Amps Per Gram Instantaneous

    MECHANICUS03/30/2016 at 11:24 0 comments

  • THE POWER .625 Amps 2.2 volts per gram!

    MECHANICUS03/30/2016 at 10:38 0 comments

    Aqueous Super-capacitors are the ticket, if you want power now!

  • Oxidized Carbons for Storing Electrolyzed Hydrogen

    MECHANICUS03/26/2016 at 00:31 0 comments

    The main problem with aqueous electrolytes especially basic or acidic ones is that they are limited to around .8 volts full cell potential due to electrolysis of the water and evolution of oxygen at the cathode and hydrogen at the anode.

    Yes your multimeter may read 1.2 volts potential open circuit but the cell will quickly self discharge to .8volts in a few minutes.

    In order to fix this pH neutral electrolytes need to be used and an oxygen scavenger must be present. Cathodic corrosion inhibitors such as potassium nitrite or sodium molybdate are great candidates.

    For the anode, oxygen groups present on the carbons can easily store the hydrogen evolved from electrolysis in faradaic redox reactions.

    At the cathode when we have KI present iodate- or I2- forms and can be reduced. This produces even more faradaic redox reactions.

    These reactions happening at both the anode and cathode defy conventional wisdom on how psuedocapacitors work and things start to look like a battery.

    At this point the discharge curves no longer act like capacitors and we can no longer consider them as such. Consequently we also approach energy storage densities of lithium ion batteries. Expressed in farads it would be around 600 farads per gram of active material but as I said that is not an intelligent way to describe these systems. It is best to being using watt hours per gram this also gives us a great comparison between lithium ion and our ultra-capacitors.

  • How many Poles does it take to make a breakthrough?

    MECHANICUS03/22/2016 at 12:51 0 comments

    Turns out only 3!

    Water Based AC/AC Supercapacitors Reaching the Performance of Systems in Organic Electrolyte

    http://ma.ecsdl.org/content/MA2014-02/3/211.abstract

    I will be combining this method with my nitrogen plasma functionalized AC and hopefully get 500 farads per gram at 1.6 volts! Or use oxidized AC and get 1.9 volts potential.

    Very excited!

  • What I tried tonight

    MECHANICUS03/22/2016 at 12:00 0 comments

    Graphene, SiO2(DE crystalline), CuCl2, Carbon Black Cathode/ N-AC anode/ K2SO4 aqueous electrolyte

    -Result horrible performance .6 volts and rapid leakage

    CuCl2 Graphene Cathode/ N-AC anode/ DMSO KOH PVA electrolyte

    -Poor Performance not better than aqueous electrolyte

    CuCl2 Cathode/ N-AC anode/ .5 Molar K2SO4 aqueous electrolyte

    -Ok results .6 volts around 200 farads per gram

    Symmetric EDLC capacitor with N-AC for both electrodes/ K2SO4 aqueous electrolyte

    -Superb results very fast cycling and charging typical 50 farads per gram EDLC performance 1.9 volts potential rivaling exotic organic electrolytes.

    -Needs Carbon Black for increased conductivity of electrodes, as discharge was a little slow

    N-AC in polyurethane painted very well

    Tried 6 N-AC electrodes in parallel and had 150mA leakage current best guess is unbalanced electrodes, but painting by hand this is to be expected.

    Moving forward Li2SO4 comes on thursday and is much more soluble in water, will retry EDLC with 2 molar solution instead of .5 molar K2SO4

    Improvements to be made to CuCl2 ultracapacitor are adsorbing the transition metal chloride into activated carbon to increase conductivity of the colloid. Most likely requires KOH or LiOH to function properly, results were poor with K2SO4.

    I started ball milling some DE amorphous with MnO2 as the SiO2 should increase the psuedocapacitive effect on the cathode.

    Need to retest CuCl2 SiO2 with KOH electrolyte.

    Need to nitrogen plasma functionalize MWCNT and try with K2SO4.

    Need to oxidize AC with H2O2 35% and test vs Microwave nitrogen plasma functionalized, as well as ammonia functionalized ox-AC.

    Need to test potassium iodide as redox mediator in transition metal oxide, ie MnO2 SiO2 cathode. .1 molar concentration in K2SO4.

  • Myriad Methods

    MECHANICUS12/17/2015 at 06:46 0 comments

    Moving into all aqueous neutral electrolytes should provide the highest voltages and energy densities in these materials at the lowest cost possible.

    I am moving into using potassium sulfate and lithium sulfate as the electrolyte and 1.9 volts is stable as opposed to my best 1.2/1.3 volts achieved previously.

    2 molar concentrations will be used.

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  • 1
    Step 1

    You will need an electric kiln or forge capable of 900 degrees celcius. For the cheapest option build a gas forge like the one described below. An electric kiln is preferable, but I could not afford one at this time, nor do I have time to build one for the citizen scientist portion of the HAD 2016 prize.

    Acquire a barbecue charcoal chimney from the local hardware store, and some refractory cement. That or make some refractory cement there are countless tutorials on the net. You will also need some diatomaceous earth and sodium hydroxide to make a water glass/ sodium silicate refractory to glaze the forge with. A small peice of pipe will be needed for the gas torch inlet.

    Prepare the mold so the refractory can be cast.

    The inlet should be angled so the flames can swirl around the crucible, I placed my inlet in the middle so that I can get the most even heating on the crucible from the middle outwards.

    Mix up the refractory, you will need two 12.5 buckets for the size I made, or do like I did and mix in a second equal portion of pool filter diatomaceous earth which is SiO2 and is an excellent refractory material.

    Cast in the mold, you may need something to hold the pipe, or whatever you used for the center portion down as the hydrostatic pressure will force it upwards and outwards. After 30 minutes (or the pot life/working time listed on the refractory) remove the center mold.

    After the refractory has cured, mix up some diatomaceous earth and sodium hydroxide to make water glass/sodium silicate. There are numerous tutorials on youtube found here https://www.youtube.com/results?search_query=make+water+glass Paint the water glass on all surfaces of the forge, this will glaze the forge and make it much more efficient.

    You will then need to flame cure the water glass and slowly bring the forge up to working temperature. Err on the side of caution and adhere to the full cure instructions for the mixed refractory, 24 hours is a good rule. To the top is my old forge is was pretty bad(would not cherry) I will be using it as a lid however. You will need a swirl flame torch that can be acquired on EBAY this will not work with a pencil tip torch see bill of materials.

    WARNING: If the outside of the forge feels hot, STOP FIRING IMMEDIATELY it still has considerable water in the refractory and will eventually crack or explode. Let it sit while hot and when it cools down fire again and again until the water has evaporated.

    The final product should look something like this, and will be ready for pyrolizing your biomass to make a highly conductive binder free monolith.

  • 2
    Step 2

    I put the ammonia soaked cotton in a pipe, and beat the heck out of it to fully compress it with a hammer and chisel. You can use any kind of plumbing pipe, just be sure to drill a hole in one end cap so the pressure can be released. I used 2 inch pipe and fittings.

    Then pyrolitically graphitized it at 900 degrees celcius in my forge for 80 minutes. That means get the pipe red/orange hot and watch for methane flames to rise out of the hole in your pipe as the cotton is pyrolized. As you can see the resistance reading is zero when pyrolysis has fully converted the cotton into crystalline graphite carbon fibers.

    Next step is to activate it, so I dunked it in 6M KOH. and back in the forge for 60 minutes. After activating the KOH and any metallic KOH as well as iron impurities need to be removed with dilute HCl. This can be done with soaking, then constructing a pvc fitting for a filter flask to hold the monoliths while water is poured over them. (I am still cleaning these activated carbons at the time of writing so I just made a video with an unactivated piece)

  • 3
    Step 3

    Assemble with PVC and 3d printed plugs. Using 1.5 inch PVC

    Place a piece of shop towel, on the PVC. Wet your monolith half in electrolyte then push it into the PVC trim off any excess shop towel. I used 1 M Li2SO4 and .008 M KI in water for the electrolyte this electrolyte allows a much larger stable operating voltage due to the high solvation affinity of water for sulfate ions and lithium ions. Meaning a stronger dielectric and no breakdown of water into hydrogen and oxygen up to about 1.6-1.8 volts. You can use anything from table salt to potassium hydroxide and still get marginal results.

    I soldered some wires, (white for negative red for positive) on some stainless foil. Then ran the wire through the end cap.

    Then put PVC in solvent all over the plugs.

    Then clamped together and squeezed like crazy, the more pressure you can put this under the better it will perform.

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slacker wrote 12/07/2015 at 09:57 point

Dig your projects, man.  What sort of ballmill are you using?

  Are you sure? yes | no

MECHANICUS wrote 12/11/2015 at 04:39 point

oh and the media is some alumina I got from some other chick on ebay she got them from a junk yard at an airforce base.  just get some alumina balls off of ebay, the smaller the better.

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