Carbon Based Battery Research

I am currently exploring carbon based supercapacitors to replace batteries is Electric vehicles. The purpose is not to have a major breakthrough and develop a battery that is better then existing lithium polymer batteries, but to develop a battery that has a decent energy storage, is environmentally friendly and is inexpensive to make.

Currently for EV's people tend to gravitate between 2 types of batteries, namely lead acid and lithium polymer or lithium ion. People choose Lead acid batteries because they are common and proven over the last century. Easy to maintain and hard to damage. Well understood, and most importantly, quite inexpensive. However, they require maintenance, are bulky and heavy, are made with toxic and corrosive materials and can spill (I am mainly talking about flooded lead acid batteries, like a car battery. I know there are other more expensive lead acid formats). The second type of battery is a lithium battery of some sort. Lithium batteries have an amazing energy density and are usually in smaller cells so the battery packs can be better shaped to accommodate the space being used. They also offer fairly high charge and discharge rates. However, they are expensive and you can damage a cell if they are overcharged or over discharged. Damaged cells can be dangerous, to the point of explosion. Because of this they require a BMS to take care of charging and discharge state. They are also not environmentally friendly and need to be recycled with care. They do last about 5x longer then lead acid batteries. There are other batteries in between, all used with varying success and all have some combinations of the disadvantages, with not much gain.

I am researching a battery, or supercapacitor that uses a dual carbon electrode and a non-aqueous ionic solution as an electrolyte. The batteries energy density should fall between a lead acid battery and current lithium batteries. The components are environmentally friendly (in fact, except for the aluminum you can ingest the components) and can be thrown away or recycled with ease as there is nothing toxic. They can be damaged from overcharging, but the result is degraded life and storage. The can be discharge to 0 volts without damaging the cell. The cells can also handle extreme charge and discharge current without damage. You can short the cell without damaging it. A damaged cell will not catch fire and is in fact fire retardant and do not produce heat when charging or discharging. Lastly, their lifespan is 4-5x longer then lithium and the cost much less to make.

The proposed cells do not come close to the energy density of current lithium cells, however I believe they are a better choice for a number of reasons, the sum of which I’m basing my decision.

1)The cells and batteries can be manufactured in the specific size of the space needed. Most vehicles when converted to electric have 2 major spaces for batteries, the place where the gas tank was and usually the engine compartment. These batters can be made to better use this space then lithium or Lead Acid batteries. In addition they do not require a BMS or any heating or cooling which saves on space and weight and is a less complex system. Also these batteries can be made to fit other places, for example, In my vehicle design I’m planning to put a floor/skid plate under the vehicle for aerodynamic reasons… but I can fill the space above this with cells made to fit that space. In fact, since there is no risk of fire in an accident I can place cell packs in between the frame, in the door panels, even in the roof lining and under the seat. Basically, where ever there is space. The cells have no heavy metals so their weight is less and I estimate we could almost double the capacity that we can do with lithium and more then double the lead acid capacity

2) The cells are super capacitors, they can charge and discharge almost instantaneously. The other components wont allow this but it does mean I don’t have to worry about heat and how much current is being discharged when pushing the electric motor. The batteries will give anything the motor takes. It also means we can charge via DC at a high rate. The charger I’m planning to use can charge at 30-40kw and I plan to have dual chargers, meaning I should be able to charge from empty to full in around 20-30min depending on the capacity of the batteries. The cells will also charge in cold weather and do not require cooling. Even though I get leas storage per same size cell as lithium I believe I can safely put more cells in the vehicle to make up for the difference.

3) Unlike chemical batteries currently used which will only operate in a small voltage band (1.8v-2.3v for lead acid cells and 3.2v-4.2v for lithium) these batteries can discharge down to 0 without damaging the battery so I’m hoping for an operating voltage between 4.2v-1v. It can go lower but under 0.5v there is not enough energy to drive the motor. The electronics, especially the inverter, is designed to work from 12v to 600v. I am limiting the higher voltage in our vehicle to 425v as that is the most the charging system can do without major redesign. With a much greater voltage range per cell of 4.25v-1v we should be able to use more stored energy from the cell then chemical batteries

4) Cost. I’m estimating that these batteries will be around 10% of the cost of lithium and up to 50% of lead acid batteries. So as long as we can fit them we can purchase more batteries to make up for the lower density (and it will probably still be far less). Reason 1 above states why this may be feasible. Also the batteries will have many more cycles meaning they have a longer life, so they wont have to be replaced. They may outlive the vehicle they are put in.

Remember that currently this is only a proposed idea based on a number of months research and I am just now getting into testing these ideas. Dual carbon batteries are not new and there have been extensive research and builds using different components with good success. However, most research and money has gone into trying to get the most energy density and not into new batteries that compete with existing and proven batteries, and its obvious why funding goes that way. I’m interested in an average, but inexpensive and flexible storage solution that will work well on electric vehicle. Other applications I can see use is power walls and larger UPS systems where space is available but batteries for those systems can be cost prohibitive.

As I’ve said, this technology isn’t new. Carbon batteries were used before the common alkaline batteries we use now. Other battery technology like this has seen some use over the last decade or two. I encountered a company that did saltwater batteries for power storage at home or industrial applications. They were large but worked. Their design I don’t think was efficient but it was a carbon anode or cathode (zinc I think was the other electrode) with a cotton separator and salt water as the electrolyte. They did have expected limitations. Mainly the voltage per cell had to be under 2.1v or you would start electrolysis in the water and they couldn’t handle high current as the water would heat up and that would cause issues. Ill see if I can find a link.

My thought process has taken me through much research and I came to some simple conclusions. First the electrolyte can not use water as a solvent. I’m hoping to have a top voltage of 4.25v but if water were used, electrolysis occurs at 2.1v creating hydrogen and oxygen. Not only do you start loosing your solvent but you create explosive gases and depending on what material you use the oxygen produced can drastically advance oxidization on your anode and cathode. I have to find a solution that could handle higher voltage. Testing will tell if I am correct.

I’m planning on making different types of batteries with different components and test them against what I have envisioned. The best one will win. Initially I do want to test a battery with distilled water and NaCl (salt) as the electrolyte. I also want to test out polyvinyl ethanol which I can produce and which is used as solid electrolyte in current manufactured capacitors. Ill be testing different ratios and quantities with the membrane and electrodes being the same.

The next set of testing once I finish with the components and make my decision, will be the separators. I’m thinking of trying tracing paper, regular paper, paper towel and shop towel. All these have been used as separators but I’m not sure which is better. If I think up another separator, I will test that too.

Lastly, I need to know what configuration will give the best storage. Do I use very large electrodes with only 1 or 2 electrodes in parallel or do I use many small electrodes (over 20) in parallel. Of course for comparison reasons the total surface area for the electrodes on each test would be the same.

Ill be keeping a blog of how the testing is proceeding and the results. I am also thinking of doing a video blog as well. I’m hoping that at the end everything will come together with half decent results that may be used as a commercially viable product or offering.

Thought Id include 2 youtube videos of Robert Murray-Smith in the UK with FWG who has been doing reasearch for batteries and capacitors for years. In the 2 videos he explains the Dual carbon system they are using and the second one shows the voltage difference. He is using salt water as he says but the results are impressive. As I said, Im not the first person to do this.