Batteries are critical for military missions. Modern soldiers are equipped with night- vision goggles, radios, smartphones, GPS, infrared sights, a laptop all of which depend on batteries to power them. Some of the missions the soldiers perform can take weeks, rather than days, without any ability to recharge; therefore he carries many spare batteries.
Army forces may be required to conduct sustained operations in temperatures as low as -65° Fahrenheit (F).The cold has been identified as an enemy of military forces and equipment since the beginning of recorded history. When employed in a cold region, a force actually faces two enemies–the tactical enemy and the environment that also aggressively attacks and can destroy equipment and men. Under such conditions, personnel are subject to decreased efficiency and cold casualties, equipment is prone to breakdowns, supply problems are increased, and operations are restricted and complicated by the environment.
On cold winter days, electric vehicles can lose half their driving range due to poor battery performance. At –40 °C, lithium-ion batteries retain just 12% of their capacity. So in the Arctic, at high altitudes, and in space, rechargeable batteries must be insulated and heated, or non-rechargeable batteries or supercapacitors must be used instead. But they tend to be very bulky because of the heating system and large amount of insulation they need to function properly at sub-zero temperatures. Such measures are neither physically nor economically viable for applications like smartphones, cameras, laptops or electric cars. Scientist are developing new battery technologies capable of working in ultra-low temperatures of Arctic, at high altitudes, and in space.
The colder it gets, the slower the metabolism of the chemical reaction inside the battery. The battery drains faster as a result. Lithium-ion batteries work poorly in extreme cold because their electrolyte solvents become viscous or even freeze, which hampers the movement of lithium ions between the anode and cathode during charging and use. Also when it’s cold, the ions can’t make their way inside the graphite anode—a process called intercalation. Instead, the lithium ions plate the electrode’s surface with flammable lithium metal.
“Lithium-ion batteries suffer so badly in freezing temperatures because they have very little internal resistance,” says Hanumant Singh, an electrical engineer at Northeastern University who builds cold-weather robots for places like Antarctica and Greenland. Less resistance means these batteries generate less waste energy as heat (a good thing in more mild climes). But the absence of waste heat also means they’re more vulnerable when temperatures plummet.
Such deficiencies are particularly pronounced in devices like smartphones, which are designed to sit mostly inactive for long periods of time throughout the day. Their batteries never draw enough current to heat themselves. But vehicles like drones and electric cars, which demand very high power for shorter periods of time, can generate enough warmth to keep the batteries going, just at a greatly reduced level of performance.
Now researchers have designed a new lithium-ion battery that still works at –70 °C. Such batteries could improve the performance of electric cars in winter, and help power high-altitude machinery, space stations, and planetary rovers (Joule 2018, DOI: 10.1016/j.joule.2018.01.017).
Rechargeable battery weathers extreme cold conditions
To make a rechargeable battery that would operate safely and maintain performance in the extreme cold, Yongyao Xia, a physical chemist at Fudan University, selected ethyl acetate as a cold-tolerant electrolyte solvent. Ethyl acetate’s freezing point is –84 °C, and it doesn’t become viscous when it’s cold. A previous paper showed that ethyl acetate could be used in a lithium-ion battery, but those researchers didn’t explore its use at low temperatures. So Xia gave it a try. But when his team combined the solvent with conventional electrodes, the battery still performed poorly at low temperatures.
Xia’s group next combined the solvent with electrodes made of organic materials instead of the conventional inorganic ones. When the battery charges, the polyimide anode material undergoes a reaction that allows lithium ions to bind to it, while counter anions absorb onto a polytriphenylamine cathode. When the battery discharges, the reaction goes in reverse, lithium ions get released, and the anions desorb. The resulting organic battery works from 50 °C down to –70 °C. And at –70 °C, the battery maintains 70% of its room-temperature storage capacity.
Maintaining performance over such a wide temperature range is impressive, says Shirley Meng, a materials scientist at the University of California, San Diego. However, the Fudan battery works at only 1.2 V, which is a relatively low voltage, she says.
Xia says his group is further tailoring the electrolyte and electrode materials to improve performance.
Chinese scientists create tiny battery capable of working in ultra-low temperatures
Chinese researchers say they have found a way to produce a tiny, lightweight lithium battery for use in mobile phones and electric cars that can hold up to 80 per cent of its charge in temperatures as low as minus 40 degrees Celsius.
The breakthrough came by using a combination of a new material called hard carbon along with lithium vanadium phosphate, the team from the Dalian Institute of Chemical Physics said in a paper published in this month’s edition of the scientific journal Nano Energy.“Our goal is to develop an all-season battery that is low-cost but high-safety for consumer products,” said Song Zihan, its lead author.It was an unprecedented approach, but “we proved it works”, he said.
The idea of a battery that can withstand extreme cold is not new, and they are already in use in space and in the Arctic and Antarctic.
The trick, Song said, was replacing the soft graphite in normal lithium batteries with hard carbon. Graphite is a good conductor and often used for the anode at the bottom of a battery, where electrons are generated. But the performance of graphite drops as the mercury slides.
Song said that hard carbon was a new material that had attracted a lot of research interest in recent years, and compared with graphite, it had a much higher tolerance for the cold. That was because of its highly irregular and “almost messy” structure, comprising layers of carbon atoms that are interconnected with each other, he said. However, hard carbon also caused a rapid depletion of the lithium ions that served as an agent carrying the electric flow in battery, he said.
In the past, researchers have tried adding lithium powders or flakes to improve battery life, but the approach has proven costly and dangerous, mostly because pure lithium is highly reactive. So Song and his colleagues used a composite material called lithium vanadium phosphate as the positive cathode on top of the battery.
The composite was capable of providing enough extra lithium ions for the hard carbon’s need without increasing the risk of fire or explosion, and it was cheap, he said. “The pairing of hard carbon and lithium vanadium phosphate worked a charm,” Song said. But the technology is still a long way from being commercially viable.
The battery Song’s team made is far too small for any real-life applications, and enlarging it would require some “innovative engineering solutions”, he said. Another scientist involved in the project said the team was working with battery manufacturers to see if the technology could be commercialised.
A water-based, fire-proof battery
Lithium-ion batteries have the potential to deliver enormous amounts of energy, but that power often comes at the cost of safety. When lithium-ion batteries get punctured or become overheated, they can cause deadly fires that even water can’t extinguish. For the Army, a battery that can power high-energy electronic devices while withstanding extreme abuse would be vital for enhancing Soldier capability and survivability in the modern battlefield.
Traditional lithium-ion batteries catch fire because the electrolyte in the battery is oftentimes a flammable organic compound that is sensitive to temperature, he said. When these batteries become damaged, they can generate significant amounts of heat and ignite a fire with the electrolyte as the fuel.
Army researchers and their partners at the University of Maryland and Johns Hopkins Applied Physics Laboratory have developed a new, water-based and fire-proof battery.
These aqueous lithium-ion batteries replace the highly flammable electrolyte in lithium-ion batteries, using a nonflammable, water-based solvent–and also using a lithium salt that is not heat-sensitive, allowing for batteries to be stored and used at a much broader range of temperatures. Cresce and the team first collaborated with scientists at the University of Maryland to study the properties of a new class of aqueous electrolytes known as water-in-salt electrolytes and published their findings in the journal Science
“If the battery’s temperature in storage happens to spike to 150 degrees Fahrenheit, the battery won’t cease to operate,” Cresce said. “In fact, it’ll probably still operate the same. Most importantly, it will not sustain a flame, so any damage to the battery will result in, at worst, a battery that doesn’t deliver anymore voltage.”
“Our project addresses the risk by allowing high-energy or high-power batteries to be put on the Soldier with no risk of the batteries catching on fire,” said Dr. Arthur von Wald Cresce, an Army materials engineer. “We’re hoping that by designing safety into the battery, this concern goes away and Soldiers can use their batteries as they please.”
This research, part of the laboratory’s Center for Research in Extreme Batteries, began in late 2014 with the goal to promote research collaboration the lab and partners in industry and academia.