Electric mobility provides opportunity to reduce carbon emissions to the level of the power production itself. The rate of vehicle electrification depends on the performance of batteries, their price level, and how convenient the charging is. Now, battery development and faster charging is improving the outlook.
While electronics are improving at exponential rates – as described by the famous Moore’s law – the batteries supplying them with power are not. They operate in the realm of chemistry, not electronics, and their rate of improvement has been much more modest – about five percent per year.
The evolution of batteries has been an ongoing quest for lighter materials, to improve the power-to-weight ratio. Since the turn of the previous century, energy density has increased six-fold as Lead-acid was commonly replaced by Nickel-metal hydride, in turn giving way to the Lithium-ion batteries dominating the market today. But with Lithium being the lightest solid element in room temperature, a new mechanism of improvement is called for.
Today, Lithium-ion cells have twice the energy density of the first ones brought to the market in the early 1990s, for a tenth of the price. But they are approaching their limit – it has been estimated that energy density can be improved 30 percent more.
Lithium-ion is actually a bundle of various technologies. Their common trait is that Lithium ions travel between the electrodes to release energy – but by substituting the materials in the anode, cathode and electrolyte or arranging them in a different way, batteries end up with essentially different properties.
What lies beyond current Lithium-ion technology? Lithium-air, Zinc-air, Lithium-Sulphur, structural batteries (integrated within a load-bearing structure) and 3D or nano batteries? These are all current topics of research, each with their respective merits and drawbacks. Cheaper materials like Sulphur or Zinc can improve cost-efficiency, but has to be weighed against other important properties like safety, energy density, capacity and charge cycle count.
An idea which seems to have some merit is to replace two-dimensional electrodes with porous, three-dimensional structures. (See ”New Materials Shape the Future” for more about porous materials.) The sponge-like structure provides a much bigger contact area for the chemical reactions, accelerating charge and discharge. One example is a battery developed by a research team in Singapore, where the graphite anode is replaced by a nano-porous Titanium dioxide gel. According to the researchers, this battery can be 70 percent charged in two minutes, with a lifetime exceeding 10 000 cycles. Should such batteries find their way into electric vehicles, both charging speed and battery life would potentially improve 20 times.
Going from liquid electrolyte to a solid ceramic is another way forward. Such batteries would need less protection and cooling, and be easier to handle and stack together. In modular battery designs, such as Tesla’s, these are important benefits.
At the end of April, Tesla announced a new battery pack for home use. The ”PowerWall”, as they call it, will cost $3,500 for 10kW. Intended to be a backup system working in tandem with solar power, it promises to make distributed power production more robust. Beside the modular design, what really is worth noting is the price. This has challenged the market, breeding speculation that batteries are soon to reach to a steep rise in cost-efficiency – and Tesla’s move has been interpreted as an informed bet on that outcome.
Rise of electric cars makes charging an issue
Electric cars and hybrids represent a growing share of the European car fleet. There are about 10 000 plug-in vehicles in Sweden, 4000 being all-electric. (Front-runner Norway, giving out heavy subsidies, has ten times as many.)
While overnight charging at home still is the norm, the growing number of plug-in cars is creating demand for a developed infrastructure of charging stations. The Swedish company Chargestorm is one of many innovators reaping the benefits; the charging posts and control systems developed by the company could be important future exports.
Currently, Sweden has 300 public charging stations, with a little more than 1000 charging posts between them. A minority of these are fast chargers, able to charge in about half an hour instead of the normal 8-10 hours. Tesla (where electricity is payed for in advance and charging stations are free to use) also maintains their own network of ”superchargers” – about 100 posts at 10 stations – able to charge to half capacity in 20 minutes.
The EU is actively pushing to implement large-scale EV charging, and a project is underway to set up 155 fast charging stations – a trans-european charging network covering Germany, Denmark, Sweden and the Netherlands.
Obviously, the speed and availability of charging is a game-changer for the electric vehicle concept. Furthermore, widespread supercharging options would make the performance of battery technology a less critical issue.
In Stockholm, shipping company Green City Ferries, in conjunction with Echandia Marine, initiated traffic in 2014 with the worlds first supercharged electric ferries. Ten minutes of charging – the time needed for passengers to board – gives enough power for an hour in the water. (Read more: ”Stockholm’s ‘super’ charged ferry”). The ferries use a special bipolar NiMH battery, developed by Swedish-American company Nilar and produced in Gävle.
Another Swedish company, Electric Line AB, is attempting to replace or complement car batteries with flywheel energy storage. Flywheels (see also: ”Grid Energy Storage”) have low energy density and are poor long-time storages. On the other hand, they can reduce transformer losses, they can go through many charging cycles without deteriorating – and they can both store and release energy at very high rates. Perhaps, a system combining flywheel and battery storage could achieve very fast charging by initially applying torque to the flywheel, then leaving it to the flywheel to charge the battery while driving.
Another alternative to fast charging could be complete battery swaps – a concept that Tesla has been aiming for. At a battery swap station, the entire discharged battery pack would be removed, and replaced with a fully charged in a matter of minutes. The batteries stock-piled at such stations could potentially be used to implement grid energy storage – and the idea also fits well with the concept of a sustainable circular economy, where selling services rather than products is emphasized.
Wireless, inductive charging is generally slower, but still something that is gaining traction. For smart phones, wireless charging is soon to become the norm – and plug-less electric vehicles may well follow. Volvo have already conducted experiments with the technology. A charging coil could be embedded in the groundwork of a garage, for instance, supplying energy to a vehicle equipped with a receiving coil and parked on the spot. Further in the future, coils in the roadway – perhaps solar-powered – could even charge vehicles while they are driving.
Electric vehicles: more and more feasible
Battery technology is a wide field of research, encompassing chemistry, materials science and engineering. Lithium-ion will surely pass on its crown, and while it remains to be seen what types of batteries will serve as the energy storages of the future, a major transition to electric vehicles is looking more and more feasible – thanks to better batteries, reduced costs, and faster charging.
This article was published in June 2015