After a holiday season of exploding battery-powered hoverboards, the message is getting out that lithium-ion batteries can have problems, but some cells can cope with overheating and abuse better than others— a perfect opportunity for separator manufacturer Dreamweaver international to show it has a superior shutdown component.
The firm built a series of identical lithium-ion cells (except for their separators) and subjected them to the usual safety tests.
The two most remarkable were a 170 °C hot box and nail penetration.
In the hot box, cells made with conventional separators underwent thermal runaway, bursting the package and venting the electrolyte, while cells made with more thermally stable separators continued to hold their voltage for the full one-hour duration, and still functioned after the test.
The biggest surprises came with the nail penetration test, in which the cells made with a ceramic-coated polyolefin separator underwent immediate thermal runaway, the surface of the cell rising within two minutes to over 100º C. The surface of the cells made with Dreamweaver Gold rose to only 40 ºC, and there was no evidence of electrolyte leakage or smoke.
These cells were then sent to Spectra Power, an independent battery facility, to be disassembled and investigated.
“The most remarkable part of the cell autopsies was that the polyolefin separators in each cell stack were split, cracked, shrunk or burnt around the nail, while the Dreamweaver Gold showed only the physical damage of having a nail driven through the layers,” said Jim Kaschmitter, CEO of the testing laboratory.
“These investigations show that while a shutdown function may be attainable in thermal equilibrium, in a fast, dynamic thermal event, the shutdown often attributed to conventional separators will not uniformly turn the cell off.
“Portions at lower temperatures will still function and can deliver energy to other parts of the cell that will continue to overheat,” said Professor Sungjin Cho of the Joint School of Nanoscience and Nanoengineering in Greensboro, NC.
“As Chief Engineer at two lithium-ion battery companies, I have never seen a cell just do nothing for a half hour after a nail has penetrated the cell. But the cell made with Dreamweaver Gold just sat there. I believe we have found the solution to the lithium ion battery safety problem,” said Carl Hu, former Chief Engineer at Enerdel and International Battery.
