A safer, energy-efficient and reliable form of electric car batteries may be at our fingertips.
Our efforts to enter a new age of energy consumption are driven by a need for an environmentally sound, energy-efficient alternative to fossil fuels. Renewable energy has many facets, from solar panels and wind turbines to lithium-ion (Li-ion) batteries. The latter has shown a lot of promise in the last decade by reliably powering everything from laptops and cell phones to Tesla’s electric cars.
However, Li-ion batteries are not without their limitations, chief amongst them the decline in their energy efficiency over time. As more research and development is being invested in new types of electric batteries, one design in particular has generated a lot of buzz: the solid-state battery (SSB). SSBs are currently used in smaller devices such as pacemakers and radio-frequency identification (RFID) devices. That said, countless companies—from start-ups to established car industry giants like Toyota and Volkswagen—are researching means to scale these batteries so they can power larger machines like electric cars and hybrid cars.
“Next-generation batteries, such as solid-state and metal-air batteries, are safer and demonstrate higher performance than lithium-ion batteries,” said Ed Hellwig, safety and quality communications manager at Toyota Motor North America. “We are currently working on the research and development, including the production technology of solid-state batteries, and we have achieved ultra-small battery electric vehicle driving. We are accelerating development aiming for commercialization by the first half of the 2020s.”
Solid-State vs Lithium-Ion Batteries: Key Differences
At their core, both SSBs and Li-ion batteries rely on the transmission of electrons between an anode and a cathode. A standard Li-ion battery is comprised of three layers: a positive cathode, a negative anode and a polymer separator that divides both electrodes. All three layers are submerged in a liquid electrolyte that facilitates the movement of charged particles between the two electrodes. To understand how charged particles are traveling between the electrodes, we must first understand what electrochemical potential is.
In layman’s terms, electrochemical potential pertains to certain metals’ tendency to lose their electrons over a period of time. Lithium in particular has a high electrochemical potential which is why it’s an extremely reactive metal, even when exposed to water and air. Losing its electron renders the lithium into a positively charged lithium-ion (hence the name of the battery) which attracts it to the negatively charged anode. In turn, the discarded lithium electron travels towards the cathode—which is what we call current.
When it comes to SSBs, the key difference is that they eschew the liquid electrolyte polymer for a layer of solid electrolyte (usually polymers or ceramics) which also operates as the separator. Because the electrolyte is solid, it doesn’t need to occupy a larger volume the way the liquid electrolyte does. As a result, SSBs are nearly 50 percent smaller in volume and are also lighter. This stands to play a significant role in the world of electric vehicles (EVs) which have to resort to stacking Li-ion batteries to power the car. In “stacking”, a single EV will have rows of countless interconnected batteries to provide the necessary power for the EV to operate reliably across large distances. As such, “stacking” leads to significant increases in weight. Tesla S, for example, has a battery that weighs a colossal 544 kilograms—more than 25 percent of its total weight!
On top of being smaller and lighter, SSBs are 2.5 times more energy-dense than Li-ion batteries and recharge nearly five times faster. This means that EVs that use SSBs can run for much longer, travel longer distances, and require less time for charging the EV. For many consumers, one of the biggest hurdles in buying an EV is the longer charging time in comparison to refueling with fossil fuels. Tesla, Nissan, Chevrolet and Jaguar EVs, for example, need to be connected to a domestic outlet for around 10 hours for them to be 100 percent recharged. By comparison, SSBs can reach an 80 percent charge in roughly 15 minutes.
Moreover, SSBs suffer less wear and tear even after thousands of recharging cycles. Li-ion batteries start to degrade after just 1000 cycles—which is the reason why, as time goes by, your cell phone needs to be charged more frequently while the quality of how well your phone works also declines. By comparison, even after 5000 cycles, SSBs continue to work at 90 percent efficiency.
Perhaps the most critical drawback of Li-ion batteries is that the liquid electrolytes used in them are flammable. It is the reason behind most instances of burning and even exploding devices in the past few years, especially cell phones and laptops. With SSBs, this issue is circumvented altogether, leading to batteries that are safer, lighter, faster charging and more energy-efficient.
Mass Producing Solid-State Batteries Is Challenging—But Not Impossible
If there is bad news regarding SSBs, it is that they are still in the research and development phase of their lifecycle. Li-ion batteries continue to dominate the world of batteries, and while the public interest in EVs is at an all-time high, scaling SSBs to mass production levels is still a sizable obstacle—chiefly because manufacturing SSBs is extremely cost-prohibitive at larger scales.
One recourse may be additive manufacturing.
Sakuu, a California-based 3D printing start-up, aims to create SSBs via binder jet additive manufacturing for not just EVs but other industries such as aerospace, medical and electronics. Each SSB will be formed by combining metal and ceramic binder jetting. That is, in a single build, the 3D printer will deposit thin layers of lithium to form the electrode and follow it up by depositing thin layers of ceramic to form the solid electrolyte/separator.
Sakuu’s 3D printed batteries are reportedly going to be 50 percent smaller, 30 percent lighter and will have an energy density that is 25 percent more than that of Li-ion batteries. As of right now, Sakuu has successfully created a 3Ah battery. Larger scale batteries for EVs, drones and other electronic devices are expected to be ready by 2022-2023.
“To get the highest energy density batteries, we want to minimize the volume of all the elements that are not adding anything to the performance of the battery,” said Karl Littau, CTO of Sakuu. “That’s the kind of thing that printing really enables.”
California-based QuantumScape and Switzerland-based Blackstone are also looking at 3D printing as the most likely answer to the conundrum of mass-producing SSBs. Like Sakuu, both of these companies are looking at 2022-2023 as the timeline for when their SSB technology can become the new standard-bearer of sustainable, reliable batteries.
