There is a lot of hype in and around energy storage and in particular around lithium-ion batteries which are becoming more widespread thanks to their increasing use in consumer goods and electric and hybrid motor vehicles. However, lithium-ion batteries are still too expensive for many applications and we will not see exponential growth in the electric vehicle market until we see cost parity with the internal combustion engined car. That said there are other storage technologies such as ultracapacitors (or supercapacitors as they are also known) which may be used in conjunction with lithium-ion batteries to not only bring down costs but also improve performance.
Lithium-ion batteries offer higher energy density than all other forms of commercially available rechargeable batteries which is critical for increasing the range of a car or the amount of talk-time you have on your mobile phone. However, that high amount of energy comes at a cost and that is lower power density which means that those batteries are not good at giving short bursts of power. But, they are perfect for providing a continuous release of energy.
Ultracapacitors on the other hand can instantaneously release all of their energy, meaning they have a very high power density. Ultracapacitors can deliver sharp bursts of energy for short periods, as well as charge or quickly capture excess energy that may be otherwise lost. This is why they are increasingly being used in automobiles for stop-start systems such as the Peugeot 308 . Whatsmore ultracapacitors are able to fully charge and discharge up to a 1m times (as against 5-10,000 for the average lithium-ion battery) without any degradation in performance. They are also not as sensitive as batteries to extreme cold or hot weather. However, ultracapacitors do suffer in that they have poor energy density meaning they don’t provide power for a long period of time. But that is why it makes sense to couple them with lithium-ion batteries. The advantages would be significant.
By combining lithium-ion batteries with ultracapacitors for instance in an electric car you could have lots of energy (increased range of the car) and lots of power (acceleration). In addition, the use of ultracapacitors could significantly expand the lifetime of the lithium-ion battery as it would not need to be used for providing the fast bursts of power which degrade the chemicals of the battery and decrease its lifetime. The use of ultracapacitors would also allow faster charging and enable kinetic energy recover systems (KERS) which could improve the efficiency of not only cars but also other type of combustion engine. Finally, the combination of lithium-ion batteries with supercapacitors would also enable a simpler design and thus lower cost of the battery system as lithium-ion battery systems are normally overbuilt to enable higher power density. This all begs the question why ultracapacitors and lithium-ion batteries are not already being combined together into one power system?
One of the issues is that both ultracapacitors and lithium-ion batteries, although they have been around for decades, have been rather niche market until recently. Costs improvements particularly in lithium-ion batteries is changing all that and we are now seeing them used in a wide range of applications from backup power to grid balancing to electric cars. But combining them with ultracapacitors is something that engineers have not got around to yet. It is also complex and difficult to integrate them both into one power system as a battery stores energy chemically, while the ultracapacitor is an electrical device that stores the energy in an electrostatic field between two electrodes.
That all said we are now seeing ultracapacitors and lithium-ion hybrid solutions in stationery storage applications and going forward we will see them used together in automobiles, trains, and other industrial applications. In addition, we will see them used alongside conventional power generators such as diesel gensets and turbines to reduce the need for costly ramp ups and ramp downs which will not only prolong the generator’s system life but also reduce maintenance costs, carbon emissions and fuel usage. In a nutshell, hybrid ultracapacitor and lithium-ion systems are coming your way…