A Lithium-Ion Battery That Works Even When It’s on Fire

In a paper printed last thirty day period in Nano Letters, the staff explain how they’ve developed a novel “fireproof” reliable-state electrolyte (SSE) for use in lithium-ion batteries. “We deal with the difficulty of flammability in SSEs by incorporating a hearth retardant,” states Jiayu Wan, a postdoctoral researcher in Cui’s lab and co-writer of the paper. 

They employed a flame-retardant content named decabromodiphenyl ethane, or DBDPE for quick. To make their new reliable-state electrolyte, the staff very first developed a slender movie by combining DBDPE with polyimide, a mechanical enforcer. 

Employing polyimide has several positive aspects, states Wan. Apart from staying “mechanically seriously powerful,” it boasts a large melting place (producing it significantly less very likely that a quick circuit will manifest), a answers-centered production system (that is compatible with how batteries are designed today), and it’s inexpensive (3M even has movie tapes designed from it).

The hitch, however, is that polyimide cannot conduct ions. To get about this snag, Wan and his colleagues extra two unique polymers, polyethylene oxide (PEO) and lithium bistrifluoromethanesulfonylimide (LiTFSI), to the blend.

“It’s innovative—they’ve neatly employed co-polymers, which is a new way to resolve the flammable polymer electrolyte battery difficulty,” states Chunsheng Wang, a researcher who scientific studies new battery systems at the University of Maryland.

Stable-state electrolytes acquire two major kinds. You can make them from ceramics, a content that conducts ions well but is incredibly brittle and benefits in thick batteries, which have reduce electrical power density. Or, you can have electrolytes composed of polymers, which are small expense, light-weight, and flexible. They’re also “soft,” indicating there is small resistance along the interface of the electrode and electrolyte, which lets the electrolyte to conduct ions conveniently.

But polymer electrolytes also have troubles. “This softness usually means they’re not able to suppress lithium dendrite propagation, so they’re flammable,” states Wang, referring to the small needle-like projections that grow from a battery’s anode. Dendrites can outcome just after recurring cycles of charging and discharging when these lithium crystals pierce a battery’s separator, they can begin fires.

“A great deal of persons think that for liquid electrolytes, there is no resistance and dendrites can grow by means of the electrolyte,” states Wang. “But if you switch the liquid with a reliable, which is mechanically much better, the lithium might be blocked.”

Their mechanical toughness, along with minimized flammability, are just some reasons why reliable-state electrolytes have garnered fascination between scientists in both equally academia and market. A 3rd motive lies with the point that they allow batteries to be stacked. “Because the electrolyte does not circulation, you can conveniently put them together with no wires… which is significant for escalating electrical power density,” states Wang.

There is no great possibility, though. “All the unique SSEs have some troubles, so you have to stability them out,” he states.

It’s a intention that the staff at Stanford appears just one action nearer to reaching. Not only is their new reliable-state electrolyte ultrathin (measuring amongst ten to 25 micrometers), it also provides a large distinct capability (131 milliampere several hours for every gram, mAh/g, at one diploma C), and demonstrates good biking overall performance (long lasting three hundred cycles at sixty levels C). Crucially, prototype battery cells designed applying it proved to operate inspite of catching hearth (in this video clip, an LED stays lit even though the battery powering it is on hearth).

“This was very surprising to us,” states Stanford’s Wan. “Usually a battery will just explode with a hearth. But with this just one, not only does it not explode, it however capabilities.” 

These days, the staff continues to discover new products and constructions for use in reliable-state electrolytes, with the purpose of maximizing recent density and cell capability. States Wan: “The problem now is to make the battery charge more quickly, have a bigger electrical power density, and to last longer.”