Scientists at the University of Michigan have used recycled Kevlar to create a membrane that solves the biggest challenges of lithium-sulfur batteries.
Lithium-sulfur batteries offer several times the capacity of lithium-ion batteries – up to five times more – but they have a trade-off that makes them unviable.
That trade-off is instability in the cathode, where the cathodes balloon in size during charging, creating extreme degradation. The biggest challenge facing researchers is finding an appropriate cathode that won’t degrade.
The team at the University of Michigan have potentially solved the problem, creating a membrane made from a network of aramid nanofibers, recycled from Kevlar, that protects the battery from degradation over multiple cycles.
The membrane allows lithium ions to flow to the lithium electrode, but it restricts lithium polysulfides which damage the battery. This process is called ion selectivity.
The strength of the Kevlar fibres also stops spiky dendrites growing from the electrode from damaging the membrane, keeping it intact.
There are a number of reports claiming several hundred cycles for lithium-sulfur batteries, but it is achieved at the expense of other parameters—capacity, charging rate, resilience and safety. The challenge nowadays is to make a battery that increases the cycling rate from the former 10 cycles to hundreds of cycles and satisfies multiple other requirements including cost.”
“Biomimetic engineering of these batteries integrated two scales—molecular and nanoscale. For the first time, we integrated ionic selectivity of cell membranes and toughness of cartilage. Our integrated system approach enabled us to address the overarching challenges of lithium-sulfur batteries.”Nicholas Kotov, University Professor of Chemical Sciences and Engineering.
Despite the promise of lithium-sulfur batteries, there are several competing technologies that are equally interesting. These include graphene sodium-ion and graphene aluminium-ion, as well as solid-state batteries.
Source: University of Michigan.