It used to be that there was only one market that was heavily investing in lithium batteries and that was ‘consumer electronics’. Now, transportation is a growing market and they are looking to replicate this success by investing in these lithium-based batteries.
That said, these batteries have their fair share of troubles, such as fire risk and they stop working at -20 degrees Celsius. As a result, engineers at the University of California San Diego have disclosed that they created new electrolytes from liquefied gas which will allow lithium batteries to run at temperatures as low as -60 degrees Celsius. Additionally, this new electrolyte will enable electrochemical capacitors to run at -80 degrees Celsius (their current temperature limit is -40 degrees). The new technology not only allows the batteries to work in low temperatures, but performance in room temperature is still maintained. Essentially, the new electrolyte chemistry developed by engineers at UC San Diego has the potential to increase energy density and better the safety of lithium batteries and electrochemical capacitors.
The newly developed technology could enable electric vehicles traveling in cold climates to travel further on one single charge. This will assuage range anxiety during the winter, often seen in locations such as Boston. In addition, this technology could be used to powercraft in the bitter cold, such as high atmosphere WiFi drones or weather balloons.
Following the release of the news, investors are now wondering how these lithium batteries and electrochemical capacitors can be so resistant to the cold. To answer simply, the electrolytes in the batteries and capacitors are made from liquefied gas solvents. These solvents are gases that are liquefied under tame pressures, thus making them more immune to freezing than traditional liquid electrolytes. In regards to the new lithium battery electrolyte, these were made using liquefied fluoromethane gas. On the other side of the equation, the electrochemical capacitor electrolyte was made using liquefied difluoromethane gas.
“Deep de-carbonization hinges on the breakthroughs in energy storage technologies. Better batteries are needed to make electric cars with improved performance-to-cost ratios,” says Shirley Meng, the leading author of the study and a nanoengineering professor at the UC San Diego Jacobs School of Engineering. “And once the temperature range for batteries, ultra-capacitors and their hybrids is widened, these electrochemical energy storage technologies can be adopted in many more emerging markets. This work shows a promising pathway and I think the success of this unconventional approach can inspire more scientists and researchers to explore the unknown territories in this research area.”
Elaborating further, Cyrus Rustomji, who is a postdoctoral researcher in Meng’s group, says, “It is generally agreed upon that the electrolyte is the primary bottleneck to improve performance for the next generation energy storage devices. Liquid-based electrolytes have been thoroughly researched and many are now turning their focus to solid state electrolytes. We have taken the opposite, albeit risky, approach and explored the use of gas based electrolytes.”
As of right now, the researchers at UC San Diego hold the title of being the first to explore gas-based electrolytes for electrochemical energy storage devices. Talk about having an impressive resume, right?
Not only does this technology help to solve the issues surrounding lithium batteries, but they could also be used in the future to help power spacecraft for interplanetary missions. “Mars rovers have a low temperature specification that most existing batteries cannot meet,” says Rustomji, “our new battery technology can meet these specs without adding expensive and heavy heating elements.”
When brainstorming the project, the UC San Diego team concluded that gases have the ability to make them work well at temperatures where traditional liquid electrolytes would freeze, thus leading to low viscosity. According to Rustomji, “low viscosity leads to high ion mobility, which means high conductivity for the battery or capacitor, even in the extreme cold.”
The researchers initially looked at a number of possible gas contenders but decided to focus on two new electrolytes. The first was based on liquefied fluoromethane for lithium batteries, while the other was based on liquefied difluoromethane for the electrochemical capacitors.
Mentioned previously, these new electrolytes will help make lithium batteries much safer as they alleviate the ‘thermal runaway’ problem. This is when a lithium battery gets hot enough that it sets off a toxic chain of chemical reactions, thus heating up the battery even more. However, with these new electrolytes, the battery will not be able to self-heat at temperatures that are higher than room temperature. Why? Because electrolytes lose the ability to dissolve salts at extreme temperatures, therefore the battery loses energy and stops working.
“This is a natural shutdown mechanism that prevents the battery from overheating.” says Rustomji. He also noted that this mechanism can be reversed. “As soon as the battery gets too hot, it shuts down. But as it cools back down, it starts working again. That’s uncommon in conventional batteries.”
That’s one small step for man, one giant leap for lithium-batteries
Finally, Meng, Rustomji and the entire team of researchers at UC San Diego have created an electrolyte that works with the lithium metal anode. Lithium isn’t just the name of a Nirvana song, it’s also thought to be the ultimate anode material as it is lighter and can store more charge than any existing anodes. The problem here is that lithium metal reacts with traditional liquid electrolytes. These reactions will cause the lithium metal to have a decreased Coulombic efficiency, which means that it can only go through a limited number of charge and discharge rounds before it completely stops working. Furthermore, with repeated charge and discharge rounds, lithium can compile at certain spots on the electrode. This results in dendrites which spear parts of the battery and cause it to short-circuit and fail.
Other firms have tried to solve these issues by using low viscosity electrolytes, applying high mechanical pressure on the electrode, and using fluorinated electrolyte additives to create the perfect chemical makeup on the surface of a lithium metal electrode. All good ideas, but the new liquefied gas electrolytes created by the UC San Diego team is the best option as it combines all three ideas. The interphase formed on the electrode by the research team is an extremely uniform and dendrite free surface, which allows for a Coulombic efficiency of more than 97% and improved battery energy. Furthermore, this is the first time that an electrolyte has had a high performance on lithium metal and cathode materials. This, in turn, could allow for an increase in the long-term energy density of batteries.
What does the future entail?
Advancing forward, researchers are now focused on improving the energy density and cyclability of lithium batteries and electrochemical capacitors. Asides from that, researchers want to make lithium batteries and electrochemical capacitors function in even colder temperatures (down to -100 degrees Celsius). As mentioned, this work could help develop technology to power spacecrafts that are going to explore planets such as Saturn and Jupiter.
All in all, this is fantastic news if you are interested in lithium investing or the electric vehicle industry.
Featured Image: jacobsschool.ucsd.edu
