Electric planes could be the future of aviation. In theory, they will be much quieter, cheaper, and cleaner than the planes we have today. Electric planes with a 1,000 km range on a single charge could be used for half of all commercial aircraft flights today, cutting global aviation’s carbon emissions by about 15%.
It’s the same story with electric cars. An electric car isn’t simply a pollution free version but, a better car: Its electric motor makes little noise and provides lightning-fast response to the driver’s decisions. Charging an electric car costs much less than paying for an equivalent amount of fossil fuels. Electric cars can be built with a fraction of moving parts, which makes them cheaper to maintain.
So what’s the challenge? It’s because batteries are expensive, making the upfront cost of an electric car much higher than a similar oil-powered model. Similarly, current batteries don’t pack in enough energy by weight or volume to power passenger aircrafts. We still need fundamental breakthroughs in battery technology before that becomes a reality.
Scientists still don’t fully understand many of the fundamentals of what exactly happens inside these devices. What we do know is that there are, essentially, three problems to solve in order for batteries to truly transform our lives yet again: power, energy, and safety.
Lithium-ion battery and the power challenge
A battery strong enough to launch and keep aloft a commercial jet for 1,000 km requires a lot of energy to be released in very little time, especially during takeoff. So it’s not just about having lots of energy stored but also having the ability to extract that energy very quickly.
Every battery has two electrodes: a cathode and an anode. Most anodes of lithium-ion batteries are made of graphite, but cathodes are made of various materials, depending on what the battery will be used for. Below, you can see how different cathode materials change the way battery types perform on six measures.
The most cutting-edge battery chemistry we currently have is lithium-ion. Most experts agree that no other chemistry is going to disrupt lithium-ion for at least another decade or more. A lithium-ion battery has two electrodes (cathode and anode) with a separator (a material that conducts ions but not electrons, designed to prevent shorting) in the middle and an electrolyte (usually liquid) to enable the flow of lithium ions back and forth between the electrodes. When a battery is charging, the ions travel from the cathode to the anode; when the battery is powering something, the ions move in the opposite direction.
The battery’s power capacity is determined by, essentially, how fast this process happens. But it’s not so simple to turn up the speed. Drawing lithium-ions out of the cathode loaf too quickly can cause the slices to develop flaws and eventually break down. It’s one reason why the longer we use our smartphone, laptop, or electric car, the worse their battery life gets. Every charge and discharge causes the loaf to weaken that little bit.
Various companies are working on solutions to the problem. One idea is to replace layered electrodes with something structurally stronger. For example, the 100-year-old Swiss battery company Leclanché is working on a technology that uses lithium iron phosphate (LFP), which has an “olivine” structure, as the cathode, and lithium titanate oxide (LTO), which has a “spinel” structure, as the anode. These structures are better at handling the flow of lithium ions in and out of the material.
Leclanché currently uses its battery cells in autonomous warehouse forklifts, which can be charged to 100% in nine minutes. For comparison, the best Tesla supercharger can charge a Tesla car battery to about 50% in 10 minutes.
Efforts like Leclanché’s show it’s possible to tinker with battery chemistry to increase their power. Still, nobody has yet built a battery powerful enough to rapidly deliver the energy needed for a commercial plane to defeat gravity. Startups are looking to build smaller planes (seating up to 12 people), which could fly on relatively lower power-dense batteries, or electric hybrid planes, where jet fuel does the hard lifting and batteries do the coasting. But there’s really no company working in this space anywhere near commercialization. Further, the kind of technological leap required for an all-electric commercial plane will likely take decades.
The Energy Challenge
The Tesla Model 3, the company’s most affordable model, starts at $35,000. It runs on a 50 kWh battery, which costs approximately $8,750, or 25% of the total car price. According to Bloomberg New Energy Finance, the average global cost for lithium-ion batteries in 2018 was about $175 per kWh—down from nearly $1,200 per kWh in 2010.
The US Department of Energy calculates that once battery costs fall below $125 per kWh, owning and operating an electric car will be cheaper than an oil-powered car in most parts of the world. It doesn’t mean electric vehicles will win over oil-powered vehicles in all niches and domains, but it’s a tipping point where people will start to prefer electric cars simply because they will make more economical sense in most cases.
One way to get there is to increase the energy density of batteries—to cram more kWh into a battery pack without lowering its price. Battery chemist can do that, in theory, by increasing the energy density of either the cathode or the anode, or both.
The most energy-dense cathode on the way to commercial availability is NMC 811 (each digit in the number represents the ratio of nickel, manganese, and cobalt, respectively, in the mix). It’s not yet perfect. The biggest problem is that it can only withstand a relatively small number of charge-discharge life cycles before it stops working. But experts predict that industry R&D should solve the problems of the NMC 811 within the next five years. When that happens, batteries using NMC 811 will have higher energy density by 10% or more.
Graphite has been and remains far and away the dominant anode material. It’s cheap, reliable, and relatively energy dense, especially compared to current cathode materials. But it’s fairly weak when stacked up against other potential anode materials, like silicon and lithium. Silicon, for example, is theoretically much better at absorbing lithium ions as graphite. That’s why a number of battery companies are trying to spray some silicon in with the graphite in their anode designs.
A bigger step would be to develop a commercially viable anode made completely from silicon. But the element has traits that make this difficult. When graphite absorbs lithium ions, its volume does not change much. A silicon anode, however, swells to four times its original volume in the same scenario. Unfortunately, you can’t just make the casing bigger to accommodate that swelling, because the expansion breaks apart what’s called the “solid electrolyte interphase,” or SEI, of the silicon anode.
Over the last decade, a few Silicon Valley startups have been working to solve this problem. For example, Sila Nano’s approach is to encase silicon atoms inside a nano-sized shell with lots of empty room inside. That way, the SEI is formed on the outside of the shell and the expansion of silicon atoms happens inside it without shattering the SEI after each charge-discharge cycle. The company, valued at $350 million, says its technology will power devices as soon as 2020.
The Safety Challenge
All the molecular tinkering done to pack more energy in batteries can come at the cost of safety. Ever since its invention, the lithium-ion battery has caused headaches because of how often it catches fire.
Today’s lithium-ion batteries still have inherent risks, because they almost always use flammable liquids as the electrolyte. It’s one of nature’s unfortunate (for us humans) quirks that liquids able to easily transport ions also tend to have a lower threshold to catching fire. One solution is to use solid electrolytes. But that means other compromises. A battery design can easily include a liquid electrolyte that’s in contact with every bit of the electrodes—making it able to efficiently transfer ions. It’s much harder with solids.
So far, the commercial use of lithium-ion batteries with solid electrolytes has been limited to low-power applications, such as for internet-connected sensors. The efforts to scale up solid-state batteries—that is, containing no liquid electrolyte—can be broadly classified into two categories: solid polymers at high temperatures and ceramics at room temperature.
Keeping the Balance
Batteries are already big business, and the market for them keeps growing. All that money attracts a lot of entrepreneurs with even more ideas. But battery startups are difficult bets—they fizzle even more often than software companies, which are known for their high failure rate. That’s because innovation in material sciences is hard.
So far battery chemists have found that, when they try to improve one trait (say energy density), they have to compromise on some other trait (say safety). That kind of balancing act has meant the progress on each front has been slow and fraught with problems. But with more eyes on the problem the chances of success go up. The potential of batteries remains huge, but given the challenges ahead, it’s better to look at every claim about new batteries with a good dose of analysis.
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