Stanford Team Develops Fireproof Solid State Electrolyte

By Battery Power Staff

February 7, 2020 | A team of researchers from Stanford University has developed a fireproof, ultralightweight polymer-polymer solid-state electrolyte. The solution could provide increased energy densities while improving safety for lithium-ion batteries. The work was published online this week in ACS Nano Letters (DOI: 10.1021/acs.nanolett.9b04815).

Battery damage in a lithium-ion battery—for example, if it is overcharged or from lithium dendrite formation—can cause liquid electrolytes to catch fire. Scientists have experimented with a variety of solutions, such as adding fire retardants to the electrolyte, or replacing the soft and flammable separator and electrolyte with a solid-state electrolyte (SSE). However, SSEs have their own limitations, they can be brittle, heavy, and still flammable. Yi Cui and colleagues wanted to design a safer alternative.

The Stanford team developed an SSE composed of a porous mechanical support (a polyimide film), fire-retardant additive (decabromodiphenyl ethane, DBDPE), and polymer electrolyte (polyethylene oxide/lithium bis[trifluoromethanesulfonyl]imide). The researchers say this is the first ultralightweight polymer-based SSE that is fireproof.

“The mechanism for the fireproof property of DBDPE was suggested to be the free-radical scavenging reaction,” the authors write. “DBDPE can degrade to generate Bromo free radicals (Br•) upon heating. The highly reactive radicals H• and OH• emitted by the burning electrolyte can be captured by Br•, weakening or terminating combustion chain branching reactions. Moreover, the gas phase product such as HBr, H2O, and Br2 released in a free- radical scavenging reaction limits the heat and mass transfer. These gas products dilute the concentration of oxygen between the heat source and electrolyte, thus retarding the self- sustaining combustion.”

In flame tests, the SSE without the fire retardant DBDPE “combusted violently” when a flame was applied. The solid state electrolyte with DBDPE “twisted because of the extreme heat but did not catch fire.” The team reports that a battery made with the SSE continued to function well even when it was exposed to flames.

In addition, the new SSE provided an energy density and performance at least comparable to conventional lithium-ion batteries.

The solid-state electrolyte was both fireproof and lightweight “with an excellent electrochemical performance,” the authors write in their paper. “The proposed polymer−polymer composite SSE configuration represents a universal and promising route to make high energy density and safe lithium batteries.”