In a paper released past month in Nano Letters, the group describe how they’ve designed a novel “fireproof” strong-condition electrolyte (SSE) for use in lithium-ion batteries. “We deal with the issue of flammability in SSEs by including a fireplace retardant,” claims Jiayu Wan, a postdoctoral researcher in Cui’s lab and co-creator of the paper.
They made use of a flame-retardant material termed decabromodiphenyl ethane, or DBDPE for short. To make their new strong-condition electrolyte, the group to start with designed a thin movie by combining DBDPE with polyimide, a mechanical enforcer.
Utilizing polyimide has numerous benefits, claims Wan. Apart from being “mechanically seriously solid,” it features a large melting place (earning it a lot less most likely that a short circuit will manifest), a solutions-based mostly producing method (which is compatible with how batteries are produced these days), and it’s economical (3M even has movie tapes produced from it).
The hitch, on the other hand, is that polyimide can’t conduct ions. To get all over this snag, Wan and his colleagues extra two various polymers, polyethylene oxide (PEO) and lithium bistrifluoromethanesulfonylimide (LiTFSI), to the combine.
“It’s innovative—they’ve well made use of co-polymers, which is a new way to fix the flammable polymer electrolyte battery issue,” claims Chunsheng Wang, a researcher who reports new battery systems at the College of Maryland.
Sound-condition electrolytes take two main forms. You can make them from ceramics, a material that conducts ions nicely but is exceptionally brittle and success in thick batteries, which have decrease energy density. Or, you can have electrolytes composed of polymers, which are very low cost, lightweight, and versatile. They are also “soft,” that means there is very low resistance together the interface of the electrode and electrolyte, which makes it possible for the electrolyte to conduct ions conveniently.
But polymer electrolytes also have difficulties. “This softness signifies they’re unable to suppress lithium dendrite propagation, so they’re flammable,” claims Wang, referring to the very small needle-like projections that expand from a battery’s anode. Dendrites can end result soon after repeated cycles of charging and discharging when these lithium crystals pierce a battery’s separator, they can get started fires.
“A large amount of individuals consider that for liquid electrolytes, there is no resistance and dendrites can expand via the electrolyte,” claims Wang. “But if you substitute the liquid with a strong, which is mechanically much better, the lithium may perhaps be blocked.”
Their mechanical strength, together with lessened flammability, are just some motives why strong-condition electrolytes have garnered interest amid scientists in the two academia and market. A third reason lies with the truth that they make it possible for batteries to be stacked. “Because the electrolyte doesn’t movement, you can conveniently place them jointly with no wires… which is significant for increasing energy density,” claims Wang.
There is no perfect option, though. “All the various SSEs have some troubles, so you have to harmony them out,” he claims.
It’s a objective that the group at Stanford seems just one move nearer to achieving. Not only is their new strong-condition electrolyte ultrathin (measuring involving ten to twenty five micrometers), it also provides a large particular ability (131 milliampere several hours for every gram, mAh/g, at 1 diploma C), and demonstrates good cycling performance (long lasting 300 cycles at sixty levels C). Crucially, prototype battery cells produced utilizing it proved to get the job done regardless of catching fireplace (in this online video, an LED remains lit even though the battery powering it is on fireplace).
“This was very shocking to us,” claims Stanford’s Wan. “Usually a battery will just explode with a fireplace. But with this just one, not only does it not explode, it nonetheless capabilities.”
Nowadays, the group continues to investigate new components and constructions for use in strong-condition electrolytes, with the aim of improving current density and cell ability. States Wan: “The challenge now is to make the battery cost quicker, have a larger energy density, and to past more time.”