Engineering a better battery – is Lithium the answer?
Author : J GALE
by Steve Mackay PhD, Technical Director: IDC Technologies
The only way to reach the limits of the possible is to go beyond them into the impossible. Arthur C. Clarke’s suggestion is particularly apt for battery technology.
As engineering professionals we are required on a daily basis to stretch ourselves in so many different ways - engineering skills/know-how/designs/installation works/costs. But what is amazing is the one area that is critical to all of us and yet still lurches along with only small improvements is battery technology. This is despite the technology being around since the early 1800's, thanks to Volta. A quick review follows of batteries concluded with a more detailed discussion on the promising Lithium route.
Batteries 101
Essentially a battery is made up of one or more cells, each with a negative and positive electrode, kept apart by conductive electrolyte that allows ions to travel between them.
Rechargeable batteries make up two-thirds of the world battery market (56 billion dollars). The first rechargeable battery (lead-acid) was invented by Plante in 1859 and is still much used today. In the early 1900's an electric car was a common sight, but they could not compete, on range, with the noxious, petrol driven ones. Nickel Cadmium batteries arrived in the 1900's and were used where more power was required.
Lead acid and nickel-cadmium cells still dominate the market today as they are more cost effective even though they can't store as much energy, per weight, as the newer technologies. Something the author is very familiar with having struggled through the jungles of Africa carrying these in a military backpack for radio communications. Nickel-metal hydride batteries have been in the market place since 1989 and store about twice as much energy as a lead-acid battery for a given weight.
Lithium-ion is composed of the lightest metal and can thus store more energy than other metals (more on this later). Modern phones and laptops are using cobalt oxide as the positive electrode, but as it is so reactive it is not suitable for hybrid or electric vehicles. Manganese can be used, but this stores less energy and has a shorter life. Instead of cobalt oxide, iron phosphate is cheaper, safer and more environmentally friendly. It is not easy to predict which lithium ion will prevail.
Lithium and more lithium
As we all know, lithium-ion batteries have been up there in driving the portability revolution. Rechargeable lithium-ion batteries hold more charge in a lighter package (as lithium is the lightest metal – hydrogen is not a metal) and have dramatically improved the performance of phones to small electric aircraft. But they do have one drawback – they charge and discharge too rapidly (and the resultant heat can damage the battery or cause a fire). So they need constant monitoring and control by a built-in electronic circuit to avoid this problem.
Admittedly, our experience with lithium batteries for notebook computers hasn't been all that fantastic. A substantial number of them fail or don't really work after two to three years of use; causing some angst whilst waiting for delayed flights and eagerly seeking out a power point to run one’s computer. But this new approach is claimed to be different….
Construction and operation
The basic construction elements of lithium-ion batteries are individual cells. Each cell comprises two electrodes separated by electrolyte (a gel). When the battery is being charged, the lithium ions migrate from the positive electrode (lithium material) to the negative electrode (carbon) through the gel. When the battery is providing the power, the process is reversed.
Generally, the positive electrodes are made from lithium iron phosphate but an innovative company (Corvus in Vancouver in good old Canada) use lithium nickel manganese cobalt, because it can provide a greater power density (by more than 20% on conventional lithium iron phosphate). Each cell is placed into 6.2kWh modules, which can be placed together to store an unbelievable MWh. Using some nifty electronics, these 6.2kWh modules can be charged from zero to full in as little as 30 minutes; and able to be discharged in 6 minutes. Corvus claim 3000 charging cycles based on a 100% depth of discharge (till completely flat) – perhaps many more if the depth of discharge is only 80%, say. Although, being cynical about claims like this, one would need to see this demonstrated in a real application.
Prices and applications
Naturally, these modules are still fiendishly expensive (esp. compared to the other more usual batteries). £5700 against £4600 for a standard lithium iron phosphate one. The suggestion is to use these mega batteries in applications such as diesel engines which idle for long periods of time where these batteries could provide the necessary power. Thus resulting in a ferocious reduction in carbon dioxide (and burnt fuel) emissions. Or alternatively replace diesel engines with electric motors powered by batteries due to the increased efficiencies. And also as an application in electric cars - a recent one with a lithium battery traveled 600km from Munich to Berlin. Renewable energy sources such as from wind and solar are highly variable. Battery technologies that decrease the cost per watt of renewable energy would be a boon.
Intriguingly (as China is really going gangbusters with renewable energy technologies), the Chinese have ordered a 2.2 MWh lithium battery from these Canadians for back-up to a coal-fired power station.
Finally, lithium is not a rare element. It is produced in countries such as Chile, Australia and China; and hopefully recyclable; so seemingly inexhaustible supplies.
Perhaps we need to devote more resources and thought to this critical research - as Albert Einstein remarked: "It's not that I'm so smart; it's just that I stay with problems longer". Batteries need the same attention and improvement as computer chips – as most of us know - the latter have doubled their performance, every two years, for decades now.
References
Thanks to the Economist for interesting reading
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