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 gases.
In contrast to many of the other metals that will be needed, copper is hard to substitute. Indeed, one factor likely to increase demand is that it replaces other, often more expensive elements only too well. It is a small-scale example compared to the amounts needed for high-voltage, long-distance cabling, but copper is gradually replacing gold in the bond wires used to connect chips to packages. Also, copper may well start replacing silver in photovoltaic panels.
For these and similar applications, the only realistic option may be to move to nanostructured materials such as graphene, which are today significantly more expensive to manufacture and difficult to use. But carbon brings with it the advantage of far greater abundance and easy sourcing. Breakthroughs in manufacturability would change the picture dramatically.
The periodic table: information is power
This may be a cop-out, but we may be looking at what will drive the next materials age the wrong way. Rather than relying on one key material, perhaps we need a better understanding of all elements so we can find novel ways to combine them. There is a constant tension between identifying the perfect element for the job and one that is both good enough and also easy to source. In the current trade war between the US and China, a potential weapon is access to the rare earths needed for chip-making and magnetics.
China currently produces 80 per cent of the world’s rare earths, including elements such as the neodymium used in magnets and the hafnium needed for the transistors in advanced silicon chips. Even without threats to trade, these elements are hard to mine safely, but better understanding of the interactions between atoms in crystals and molecules could unlock the power of more mundane elements.
For example, a team from Duke University and UC San Diego reckons disorder in crystals could create metal carbides that are harder than diamond but cheaper to produce synthetically. Drills often use tungsten carbide bits because they are strong and heat-resistant, but it may be possible to go to even harder materials. The Duke researchers used computer simulations of interactions between the electrons in various randomly generated lattices to create a shortlist and then had the best candidates and some control samples made in the lab. Their latest effort brings five metals together with carbon in the tongue-twisting alloy: molybdenum niobium tantalum vanadium tungsten carbide.
This kind of work could be exploited on a much wider scale. The US National Institute of Standards and Technology’s Materials Genome Initiative is developing a database of material properties that researchers can feed to machine-learning algorithms to identify novel alternatives.
For three billion years no element has had greater influence on Earth than carbon. It’s not only abundant, but it’s hard to think of an element that is more versatile. As a result, it became the core constituent of life on the planet.
Within a billion years from its first appearance, carbon-based life managed to change the composition of Earth’s atmosphere. Today, it’s having an effect on the atmosphere and climate in a different way. But carbon seems set to enter a new phase as research into its structure unlocks previously unknown properties, some of which are only just beginning to surface.
Something that is drummed into chemistry students from early on is that carbon will always form four stable bonds and that carbon atoms bind to each other readily. Next-door neighbour silicon almost behaves the same way, but not nearly enough. Instead, it only forms stable polymers with oxygen to form the useful but far less versatile silicone.
Carbon’s value comes from the huge amount of variety in how it forms those bonds, thanks to the way that the electrons orbitals reorganise under different conditions. These configurations force the bonds in different directions. They range from the tetrahedral configuration of the sp3 form found in everything from alchohol to diamond through the flattened sp2 of graphene to the highly stressed rod-like configuration of sp1 associated with highly reactive molecules such as acetylene.
Organic molecules mix them together in various configurations but chemists have pushed further into these mixtures, uncovering crystalline forms with novel properties that mix all three symmetries in one substance and which potentially go further than the graphene and nanotubes, based mainly on sp2 carbon, that could act as potential replacements for silicon and copper in electrical circuits.
Xi Zhu of Nanyang Technological University and Min Wang from China’s Southwest University developed an allotrope of carbon that mixes all three forms in a 16-atom cell. It is a crystal that does not just act as a semiconductor. It also has large holes in its matrix that readily absorb gas molecules. The CY carbon crystal is a much more regular crystal than one synthesised in 1997 by Andrei Rode while working at the Australian National University of Canberra. He created a ‘nanofoam’ made of clusters of carbon atoms in a loose 3D web. A litre of this kind of nanofoam weighs less than 20g. This nanofoam is a poor electrical conductor but is attracted to magnets and so provides another potentially exploitable combination of properties.
The tricky part is making these kinds of structures at low cost with the precise degree of control they often need. An alternative form of production is needed to unlock the potential of such materials. But one highly effective method is already in use around us.
Nature has, for the past half-billion years, provided an alternative to the top-down construction that humanity has favoured so far. Over the past decade, synthetic biology has emerged as a discipline that provides humans with a way of managing the bottom-up processes of synthesising almost arbitrarily complex molecules and structures.
One of the enduring mysteries of life is how a single cell, provided with enough food, can multiply and create highly complex forms such as leaves and branches or organs and limbs. The code that informs each cell on what it should do given different environmental signals is clearly stored inside the cell in the form of DNA. But the influences that determine development still lie outside the understanding of current science.
In the near term, this does not matter all that much. The ambitions of most synthetic biology researchers are more down to earth, despite the bold claims some of them make. They are mostly aimed at the production of raw materials that can be incorporated into traditional manufacturing. Proteins rely on just two main structural forms yet have yielded everything from chemical catalysts to teeth and claws. A wide range of materials are on offer with some fairly subtle reprogramming of DNA.
Take spider silk, for example. This is, for its weight and size, an incredibly strong material and can be given other properties, as spiders do, such as high levels of stickiness. One reason why it has not been used industrially up to now is that, unlike silkworms, spiders do not react well to farming: the territorial creatures are too inclined to eat one another.
Bacteria are only too easy to farm and they are far easier to alter genetically in predictable ways. But even they present often surprising problems that need to be worked around. Farmed spider silk was one of the first projects to underline the promise of synthetic biology but it quickly ran into problems that exemplify the challenges researchers have to overcome to make carbon-based manufacture more practical.
A big problem with importing foreign genes into species is that they can easily reject them. If the gene produces chemicals that are poisonous, evolutionary pressure will tend to produce bacteria that do not express the genes or simply remove the offending DNA sequences. Bacteria altered to make spider silk presented a more subtle problem. Ideally, the gene required is a lengthy, repeating sequence that produces a similarly lengthy protein chain. Live bacteria did not accept this repeating sequence and, instead, would only incorporate a much shorter DNA chain.
Rather than alter the bacteria further to try to prevent the mechanisms that lead to the desired DNA being deleted, a team from Washington University in St Louis developed a slightly different recipe for spider silk that would naturally link together the short lumps of protein and, in doing so, create chains that are in the range of those produced by spiders.
As it develops, synthetic biology will most likely not remain a single discipline. Some researchers favour the re-engineering of existing organisms – mainly bacteria and simple creatures – for farming. Others see the long-term aim being the creation of biologically inspired systems that operate at the vat level, possibly using chemistries that do not exist in nature. Researchers in Japan and the US have created synthetic analogues of DNA based on alternatives chemistries, including one based on the amino acids of proteins rather than DNA’s nucleic acids, that may bring with them much more flexibility and the ability to survive harsher industrial conditions. These could, ultimately, be harnessed to create nanofoams and other complex structures more cheaply than today’s synthetic chemistry.
Thanks to the combination of greater understanding of synthetic biology and the structural properties of the element, carbon presents a long-term future for materials science: much more so than lithium or copper. But the diversity of what it offers makes it the strongest contender for development and diversification. Welcome to the Carbon Age.