EEStor's high performance ultracapacitors

Game-changing technology or Much Ado About Nothing?

There have been a lot of rumours flying around the energy sector lately about EEStor, a secretive Texas start-up. True: if EEStor can reach its ambitious goal of replacing the electrochemical battery with high performance ultracapacitors, that would indeed be a major breakthrough in the energy sector. The technology has the potential to radically change transport systems, offset the intermittency problem of some renewable energy power generators, and improve the stability of power grids.

But we’re not that far yet. Most specialists are very sceptical, warning that what EEStor aims at is too good to be true. They have not proven anything yet and some of the technical difficulties seem insurmountable at this point.

Capacitor with high specific energy

The major advantage of ultracapacitors compared to electrochemical batteries is that they can absorb and release power in a very short time and in a virtually endless cycle with little degradation. Their big drawback up to now is that the energy they can store is 25 times less per kilogram than electrochemical batteries. EEStor now claims that it can make a ceramic ultracapacitor with a barium-titanate dielectric that can store 280 watt hours per kilogram. If true, this is more than double the 120 watt hours per kilogram of a lithium-ion battery.

Difficulties to overcome

It has been known for years that barium-titanate powder, if very pure, can have an extremely high permittivity — EEStor cites a permittivity of 18,500 (compared to 20 or 30 for a traditional ultracapacitor dielectric). But before barium-titanate ultracapacitors can be used in cars or devices, a few critical difficulties are still waiting to be solved:

1. Purity. The barium-titanate powder needs to be extremely pure. How will this be done on a mass-production scale?
2. Temperature. The performance of the barium-titanate dielectric is dependent on temperature; it won’t work at low temperatures.
3. Mechanical strength. The ceramic structure is brittle by nature, and will quickly develop microfractures caused by the thermal stress. This will lead to premature failure.
4. Leakage. The system requires a high voltage (3,500 V), however high-voltage capacitors self-discharge quickly. That means that the cars or devices would need to be recharged regularly even if they are not used.
5. Safety. What happens if a car with a 3,500 V energy system crashes?

EEStor has not stated how they propose to overcome these difficulties. But they are claiming to be on track for producing an energy-storage system for electric vehicles weighing less than 50 kilograms, allowing a 300-kilometers driving range, and able to recharge in less than 10 minutes.

If true, it would not be the first time in history that a seemingly impossible technological breakthrough becomes reality, but it also would not be the first time that there has been Much Ado About Nothing for attracting investors to a technological start-up. We will just have to wait and see.