What is the material for a new age?
What will be the defining material of the next industrial age? In the past hundred years, steel gave way to oil and then silicon as information became the defining power behind industrial development. Will it return to energy, with hydrogen becoming a strong contender as a replacement for petroleum, or will renewables make lithium batteries central to future development? Or will other materials step in to propel industrial evolution further? Here are E&T’s five contenders as the most likely candidate for the next materials age.
Lithium: a high-energy choice
We might already be in the next material age and simply not realise it yet. Lithium emerged as the pre-eminent material for electrical storage two decades ago. But as electric vehicles and grid storage join the list of customers, the quantities required will grow rapidly. In less than five years, the demand for lithium will at least double according to several forecasters, with supply just about keeping pace thanks to the opening of new mines for the mineral spodumene. And the relentless progress of lithium seems unstoppable even though we are likely to see dramatic changes in many of the other materials that go into batteries.
The cathode inside a lithium battery calls for a mixture of cobalt, nickel and manganese. That will change as the result of processes that will govern whatever leads the next material age. R&D is paying careful attention to cutting down on the elements that are expensive and troublesome to source. Cobalt tops that list. Carmaker Volkswagen reckons it will cut cobalt content in its future batteries from around 12 per cent today to 5 per cent within five years, and it is looking to develop cobalt-free batteries.
The anode is less likely to change. There are other elements that could do a better job than graphite but it is hard because it makes the design simpler. In theory, silicon is a better material and, although it takes a lot of energy to purify, has the benefit of abundance. But it suffers from a major problem that does not afflict carbon nearly as badly: the electrodes expand when they capture lithium ions to the point where the solid-state cell bursts. You can avoid this by using complex chemical cocktails and nanostructures but these increase manufacturing cost.
Lithium itself is not necessarily the ideal element for high-density electron storage. That role has been played by cadmium but it suffers from the drawback of being highly toxic. Another option is strontium, which is 20 times more abundant than lithium. But lithium is far lighter, a crucial consideration for products as diverse as smartphones and electric cars, and cheaper to mine.
One continuing problem with lithium is its flammability. Today’s lithium oxides reduce the problem rather than avoid it completely because, if highly reactive pure lithium filaments form through overcharging, the oxygen present in the cell acts as an accelerant. Sulphur is a potential substitute for oxygen but suffers from the same problem as silicon electrodes. It causes the cathode to expand as it acquires lithium ions.
As with silicon electrodes, one option is to resort to a cocktail of elements in the electrolyte. The best candidate so far involves the relatively rare element germanium, which would be difficult to secure in large quantities for industrial and infrastructural-storage batteries. But substitutes may emerge thanks to techniques such as computational chemistry that make sulphur a viable alternative to oxygen.
Another factor that makes lithium’s status as material of the future precarious is that competition for energy storage will come from fuel cells: these can potentially offer far greater energy densities than any battery can offer. For those, hydrogen is an attractive choice.
Hydrogen: the lightweight option
Of all the possible materials of the future, hydrogen has the greatest potential to transform the economy. However, the problem for hydrogen is that it is only a realistic contender if it reaches a position from which it can achieve that transformation.
Hydrogen’s future role depends on structural changes to the way energy is produced and stored. In contrast, lithium’s role will be less important if it’s displaced by fuel cells in the energy infrastructure. But lithium will remain an important material for many other applications. On its own merits, hydrogen is not compelling as a fuel for vehicles. But by making it part of a renewables closed-loop system, it would be easier to bear the infrastructural changes and costs that result from a wholesale conversion to hydrogen.
Hydrogen’s success relies on retooling the transportation infrastructure that currently support today’s oil and methane-intensive energy systems, although the emphasis will shift to localised production and distribution rather than the extensive pipelines and tanker fleets needed for petroleum.
One of the biggest roadblocks to energy generation based almost entirely on renewables is the requirement for energy storage. The grid needs to cache enough energy to ride out slumps in wind or solar production and to be able to support short-term peaks even if nuclear generation is included in the mix. Battery storage seems to be the obvious choice but the cost of manufacture would be likely to prove prohibitive and need to be supplemented by large-scale pumped hydroelectric or mechanical flywheel systems.
Operators of solar and wind generation farms could divert unwanted energy to electrolysis and either dump it into nearby fuel cells to service peak demand from the grid or sell the excess gas as fuel to distributors, who would then supply it to fleets of vehicles.
Hydrogen offers a clean alternative for storage that comes with the added advantage of providing energy that can be much more mobile. By weight, hydrogen’s energy density is around 140MJ/kg. Compare that to 2MJ/kg for an efficient lithium-ion battery. Naturally, there is a catch with hydrogen. To maximise its practical energy density, hydrogen must be liquefied, which greatly increases production and storage costs. One option is to store the gas in highly porous mineral sponges, such as a manganese hydride developed by researchers from the University of New South Wales and Lancaster University. The team claimed their system could make it feasible to store in a car the 5kg of hydrogen needed to support a driving range of 500km.
In 2015, a group of researchers from Stanford University, Imperial College and Western Washington University analysed the cost of creating elemental hydrogen by electrolysis and storage in a scenario where the energy required comes from renewables. The round-trip efficiency of creating and using hydrogen was lower than that of an electrochemical battery. But they calculated the lifetime cost would be lower because the equipment to do the job would work out significantly cheaper and less environmentally destructive. What stands in the way of this is whether society would make the changes that make this conversion possible.
Copper: the second Bronze Age
The main constituent of the metal pots and implements that heralded the beginnings of civilisation during the Bronze Age, copper could be set for a comeback thanks to the way it has crept up on the other contenders from all sides.
It is hard to find an energy-producing or energy-using product that does not use copper in some way or other. And these applications are not necessarily limited to passing electricity. Although it is five times less efficient than diamond, copper acts as an effective conductor of heat. Its much lower cost is why copper is so prevalent in high-grade heatsinks for integrated circuits.
Copper may even find a place in the infrastructure for delivering hydrogen. Copper, as well as aluminium, alloys are not as susceptible to attack by hydrogen gas as other common materials, making it a good choice for piping, though it runs into problems when oxygen is present.
The many applications for copper also lie at the heart of its weakness as the basis for the next materials age. There simply may not be enough to go round. As with lithium, there are potential problems with society becoming increasingly dependent on a single element. Though it is one of the more abundant metals found in the Earth’s crust, a factor that made it so important to early human civilisations, the quantities needed to support a population of eight billion and their demands for electrification could overwhelm our ability to mine and recycle it.
A report that examined four usage scenarios for copper put together by researchers at Yale University’s Center for Industrial Ecology in 2015 estimated demand could easily outstrip supply by 2050. In that time, annual copper usage could almost quadruple.
A big problem posed by much greater use of copper is that, to service this demand, miners will have to move to sites with lower-grade ores, a shift that will in turn increase the energy usage and, without a change in extraction technology itself, carbon dioxide production. It is an ironic turn given that the aim of increased copper usage is to make society less prone to releasing greenhouse ga