New Battery Technology | Fast Recharge Batteries
Of all the criticisms of electric vehicles, probably the most commonly-heard is that their batteries take too long to recharge – after all, limited range wouldn’t be such a big deal if the cars could be juiced up while out and about, in just a few minutes. Well, while no one is promising anything, new fast recharge batteries developed at the University of Illinois, Urbana-Champaign do indeed look like they might be a step very much in the right direction. They are said to offer all the advantages of capacitors and batteries, in one unit.
Lithium-ion batteries have risen to prominence as the preferred battery system for handheld electronics, hybrid cars, and grid storage in recent years. Despite the fact that a growing number of vehicle makers are launching electrified cars, range anxiety and the time it takes to refuel the batteries remain a major concern. High currents, which are used to speed up the charging phase, have been known to minimise energy efficiency and trigger capacity and power fade. Fast charging is a multiscale challenge, so understanding and improving fast charging efficiency requires insights from the atomic to the device level.
Consumers’ apprehension towards electric cars is largely due to range fear (EVs). EVs must be able to recharge easily anywhere in any weather, much like gasoline cars, in order to be fully compatible with gasoline vehicles. However, none of today’s electric vehicles allow rapid charging in cold or even moderate temperatures due to the possibility of lithium plating, which causes metallic lithium to form in the battery, reducing battery life and even posing a safety risk.
Lithium-ion batteries have risen to prominence as the preferred battery system for handheld electronics, hybrid cars, and grid storage in recent years. Despite the fact that a growing number of vehicle makers are launching electrified cars, range anxiety and the time it takes to refuel the fast recharge batteries remain a major concern. High currents, which are used to speed up the charging phase, have been known to minimise energy efficiency and trigger capacity and power fade. Fast charging is a multiscale challenge, so understanding and improving fast charging efficiency requires insights from the atomic to the device level.
“This system that we have gives you capacitor-like power with battery-like energy,” said U Illinois’ Paul Braun, a professor of materials science and engineering. “Most capacitors store very little energy. They can release it very fast, but they can’t hold much. Most batteries store a reasonably large amount of energy, but they can’t provide or receive energy rapidly. This does both.”
The speed at which conventional batteries are able to charge or discharge can be dramatically increased by changing the form of their active material into a thin film, but such films have typically lacked the volume to be able to store a significant amount of energy. In the case of Braun’s batteries, however, that thin film has been formed into a three-dimensional structure, thus increasing its storage capacity.
Fast recharge batteries equipped with the 3D film have been demonstrated to work normally in electrical devices, while being able to charge and discharge 10 to 100 times faster than their conventional counterparts.
To make the three-dimensional thin film, the researchers coated a surface with nano scale spheres, which self-assembled into a lattice-like arrangement. The spaces between and around the spheres were then coated with metal, after which the spheres were melted or dissolved away, leaving the metal as a framework of empty pores. Electro polishing was then used to enlarge the pores and open up the framework, after which it was coated with a layer of the active material – both lithium-ion and nickel metal hydride batteries were created.
The system utilizes processes already used on a large scale, so it would reportedly be easy to scale up. It could also be used with any type of battery, not just Li-ion and NiMH.
The implications for electric vehicles are particularly exciting. “If you had the ability to charge rapidly, instead of taking hours to charge the vehicle you could potentially have vehicles that would charge in similar times as needed to refuel a car with gasoline,” Braun said. “If you had five-minute charge capability, you would think of this the same way you do an internal combustion engine. You would just pull up to a charging station and fill up.”
Braun and his team believe that the fast recharge batteries technology could be used not only for making electric cars more viable, but also for allowing phones or laptops to be able to recharge in seconds or minutes. It could also result in high-power lasers or defibrillators that don’t need to warm up before or between pulses.
It is very difficult to work with electrodes batteries and/or low temperatures (below 0 degree Celsius). When comparing the slightly lower energy density (180 Wh/kg versus 220 Wh/kg) and corresponding cost penalty ($196 kWh1 versus $103 kWh1) due to the increased ratio of cell deadweight content (which does not contribute to charge storage) versus active material, the downside of thin film battery charging becomes clear. With power density, there is currently a trade-off between energy density and quality. Fundamentally, all of the issues around XFC (at the EV level) can be boiled down to a single issue.