It is hoped that wind and solar energy will one day become major contributors to a future energy grid that has reduced its reliance upon fossil fuels. But one of the biggest problems facing these sectors is the fact that the sun doesn’t always shine and the wind doesn’t always blow. To maintain a consistent energy supply to the grid during such periods we would need a method of storing the energy.
Unfortunately current battery technology is poor and performance degrades quickly, only allowing for several hundred recharge cycles. Advancements would need to be made so that the batteries have a far longer life, can hold much higher levels of energy, and are cheap to produce.
A team of Stanford researchers have recently taken the first steps to producing such a miracle battery. They have used nanoparticles of a crystalline copper hexacyanoferrate to create a high-power, durable, cheap negative-electrode (cathode).
In fact it is so inexpensive to make, so efficient and so durable that it could be used to build batteries big enough for economical, large-scale energy storage on the electrical grid – something researchers have sought for years.
Standard lithium-ion batteries that power most small electronic devices deteriorate with each charge, as the electrodes crystalline structure wears, meaning that the energy storage capacity reduces over time. Due to the precise structure of this cathode it can remain intact, surviving 40,000 cycles of charging and discharging, after which it could still be charged to more than 80 percent of its original charge capacity. The combination of materials that it uses also enables it to recharge and discharge very quickly, and the quicker that a battery can do this, the more power it can release.
Colin Wessells, a graduate student in materials science and engineering who is the lead author of a paper describing the research said, “At a rate of several cycles per day, this electrode would have a good 30 years of useful life on the electrical grid.”
Yi Cui, an associate professor of materials science and engineering, Wessell’s adviser, agreed “That is a breakthrough performance - a battery that will keep running for tens of thousands of cycles and never fail.”
To maximize the benefit of the open structure of their crystalline copper hexacyanoferrate, the Stanford scientists needed to find ions whose size most effectively correlated to the subatomic gaps. Too big and the ions could collide with and damage the crystal structure when they moved in and out of the electrode. Too small and they might become trapped to one side of the open spaces between atoms instead of easily passing through. The right-sized ion turned out to be hydrated potassium.
Wessells explains, “We decided we needed to develop a ‘new chemistry’ if we were going to make low-cost batteries and battery electrodes for the power grid.” So they used a water-based electrolyte, which Wessells described as “basically free compared to the cost of an organic electrolyte” such as is used in lithium ion batteries. They also made the battery’s electrical materials from readily available precursors such as iron, copper, carbon and nitrogen; all of which are extremely inexpensive compared with lithium.
For portable electronic devices the energy density and charge hold time are important, but as the power need increases the size can be larger. For energy grid based batteries the size does not matter as much (they aren’t going to be going anywhere). Instead it’s the cost and the cycle times to replacement that matter. This new cathode promises a better solution to both sectors, personal and industrial. The battery can be produced to power small devices, where it completely out classes current lithium batteries. Or the exact same technology can be produced on a larger scale so that it can be used to store vast levels of energy. “There are no technical challenges to producing this on a big-enough scale.”
The only problem is that the structure of the material means that it can only be used for high voltage cathodes, not the corresponding low voltage anode, without which a battery can’t exist. In fact Wessell and Cui haven’t yet produced a battery; they are still searching for a suitable material from which to make the anode.
Even still, the performance of the new electrode is so superior to existing electrodes that Robert Huggins, an emeritus professor of materials science and engineering told Stanford University News that the electrode “leads to a promising electrochemical solution to the extremely important problem of the large number of sharp drop-offs in the output of wind and solar systems.”
The public always seems to be focused on the large, renewable energy technologies, we don’t realise that a battery that can hold more charge and last for 30 years could be just as important. It is exciting to think of the possibilities available if the major electrolyte chemistries were to have electrode pairs with recharge cycles in the tens of thousands and very fast charge rates. The areas in which batteries could be used would increase vastly, and the cost of many electronic devices would fall, because they could be sold without batteries (a large cost factor). The batteries could also increase the efficiency of renewable energy sources such as wind, solar, hydro, etc. Really, it is not unrealistic to think that such a small invention could radically change the energy and technology world.
By. James Burgess of Oilprice.com