Electricity is the movement and acceleration of electrons at a certain rate. The simplest way to store electricity is to directly store electrons. Capacitors can do this, which is why you can “upload” and “download” electrical energy so quickly in capacitors.
Because of their energetic nature, capacitors can only hold very few electrons. An example of this is to try to store hydrogen in a high pressure tank.
A new type of capacitor was invented around 1971. It was trade-named “supercapacitor”, but its technical name, the “electrochemical dual layer capacitor” (or EDLC), is what it is known for. Although it can store more electrons than regular capacitors but is a little slower, it can also store them in a smaller amount.
Supercapacitors have a specific-energy around 6-10 Wh/kg, and at least 10kW/kg of specific-power. The supercapacitor costs 4X more than typical Li-ion battery (120-250Wh/kg) and is not compatible with mobile platforms. Supercapacitors have a longer cycle life than Li-ion batteries, which can last between 500 and 2000 cycles.
Li-ion batteries use ion-exchange as a means of producing electrical energy. However, this chemical reaction is too slow for them to store all the vehicle’s braking energy. A typical EV’s Li-ion powerpack stores only 20% of the braking energy. Supercapacitors are used to store more of the brake energy and release it to accelerate the EV. This helps reduce the degradation of Li-ion batteries due to high charges and discharges.
To increase supercapacitors’ specific-energy, and/or energy density, significant R&D is underway. Newer materials can be used to achieve supercapacitors that produce 50 Wh/kg. Lab tests have shown this. Researchers are working to increase the supercapacitors’ power output to 150 Wh/kg, which would be comparable with today’s Lithium batteries.
Supercapacitors are more energy-efficient than conventional batteries. EVs equipped with supercapacitors can only be charged before you use the EV. Then, try to run out of energy in a few days. A hybrid power pack that combines supercapacitors and Li-ion cells will allow an EV to accelerate quickly, recover most of its brake regen energy, and do a quick recharge to get another 30-50 mile. This will maximize the battery’s cycle life and let the supercapacitors do the heavy-power work.
Because supercapacitors can store energy at extremely fast rates and have a longer life span, solar and wind farms will become more feasible. Supercapacitors will become cheaper as new materials become more affordable. In the future, energy storage costs for supercapacitors will be lower at US$100/kWh.
Supercapacitors won’t take up more space than Lithium-ion battery because of their energy density. An EV can still travel between 200 and 250 miles on a 5-minute charge, even at 150 Wh/kg. This assumes that the charging facility also uses the supercapacitor to charge it.