The price of lithium has climbed steeply in recent weeks. Citibank believes demand will be 64% higher in the coming 5 years. Lithium is the ubiquitous energy storage element consumed in ever greater quantities with each new generation of mobile phones and the arrival of electric cars by many manufacturers led by Tesla. Tesla also market their Power Wall battery, made in a new lithium battery ‘mega factory’. They are all looking for additional lithium supplies suggesting that the price of the metal will continue to be firm, but lithium has some real competition ahead.
In the formula for energy contained in a capacitor:
E = (0.5 x C) x v2
Energy (Joules) = ½ x Capacitance (Farads) x voltage squared
With regard to this formula we see companies obtaining significant increases in capacitor energy density either by an increasing capacitance or by increasing the voltage.
UK based Dr. Robert Murray Smith, chairman of Edison Power, a private US company, has been making a series of congenial and easy to understand informational videos that are available on YouTube that show something fascinating; the emergence of graphene as a component of batteries and capacitors. This is just beginning to shake up the electrical component market. Graphene is safe. A baby can swallow it without consequence since it’s just carbon. It can be composted. It doesn’t heat up and is extremely common. If capacitors obtain higher energy storage, then the lithium ion battery industry could easily have a lot of stranded lithium assets within a few years. Why?
Capacitors have always been the envy of batteries for a couple of very good reasons. They are very fast to charge and discharge. Some have dry electrolytes which means that they can cycle almost infinitely but even wet electrolytes can make it to 100,000 cycles. These characteristics are a just a dream for chemical batteries which are often limited to fewer than 1,000 cycles and have a very slow charge and discharge times of many hours. Up until this point though, chemical batteries have taken the lead in terms of energy capacity. Battery construction is all about volumes of chemicals while capacitors are about the huge, charge holding surface area of the electrodes. Activated carbon from an organic source such as coconuts will offer 1,500 square meters per gram but other forms of carbon including graphene, offer up to 3,000 square meters per gram of valuable, electron sheltering, surface area, the equivalent of 11.5 tennis courts. Such high surface areas are also able to be further improved by nanotechnology. The path to further improvements in such high capacitance is to find solutions to challenges such as inhibiting electric fields generated within the capacitor, a common issue in microchip design.
Improvements today have allowed the energy density of supercapacitors to reach 131 Watt hours per kilogram, four times the previous level and 65% of the 200 Wh/kg offered by lithium ion. Dr. Lu Wu of Gwangju Institute of Science and Technology, in South Korea has generated a form of graphene that lets him store the full equivalent of lithium ion batteries.
A good metaphor is an open-top glass vase and a normal bottle, say a wine bottle, with a thin neck, both full of water. The vase is like the capacitor. When it’s tipped over, all the water comes out immediately and you can fill it up fast too. In electrical terms, all the available stored energy comes out all at once, the equivalent of a high power rating. The bottle on the other hand, is like the battery. When tipped the water comes out of its neck at a limited rate and it takes much longer to empty. The same is true of filling it up or recharging it again.
For example, on a cold morning, you may have difficulty starting your car. The cold, lead acid battery can’t provide enough energy all at once, to turn over the starter motor. If you attach a supercapacitor to the cold battery for a few minutes though, you can charge up the capacitor and then use it to discharge this electricity much faster, and start the engine. Another example is where the battery and capacitor work together combining their capabilities. A bus might need a lot of power when it’s accelerating, but batteries can only partially help. Super-capacitors already charged from the battery though, can dump enough energy on that electric motor to make sure acceleration goes without a hitch.
Many electric vehicles have regenerative breaking, where the turning wheels spin the motor(s) in reverse, creating resistance that slows the vehicle. The motors generate electricity which can be very economically saved in the batteries. If the bus has regenerative braking, its lithium ion batteries will be unable to absorb the charge fast enough. Luckily, capacitors can rapidly absorb all the electrical energy from the brakes first and then feed it at an appropriate rate to the lithium-ion batteries. This teaming up of battery and capacitor is only a temporary phenomenon however.
The arrival on the scene of graphene has caused capacitors to suddenly have a significant amount of energy density instead of simply power. This is a key distinction. Until this point, a chemical battery had energy but not power while the capacitor has power but not energy. This relationship is now undergoing rapid transformation.
Since first writing this blog, I have met with CEO Stephen Voller of Zap & Go from Oxford, UK, who have another graphene offering and are on the verge of commercialization with a working energy storage to charge your phone. Also I have found another grid smoothing company in Europe as well as a Spanish group called Graphenano who are making strong claims that are still waiting to be verified. Edison Power, affiliated with earlier mentioned Sunvault, is the second case and has increased the capacitance using graphene with its large surface area. The result is that you also obtain an elevated energy storage level.
Combining both high capacitance with high voltage has been elusive to date. An example of a company that has increased the voltage component of the formula is Eestor, a Texas based capacitor company headed up by CEO, Ian Clifford. They have managed to combine a very high functioning dielectric, barium titanate, between electric plates operating at very high voltages. Eestor’s voltages are as high as 3,500 volts, meaning that the capacitors have a significant amount of energy capacity, rivaling the lithium-ion battery. Even a single, 1 Farad capacitance at 3,500 volts means the capacitor holds 1.7 kilowatt hours of electrical energy. These particular, disruptive capacitors are intended to address the demand/supply, grid smoothing market and will have few competitors.
It’s clear that in this environment, a safe, cheap, fast charging and discharging, electrical energy storage device (EESD) that can cycle endlessly has huge advantages. Maybe lithium’s days are numbered?