A new biologically inspired battery membrane has enabled a battery with five times the capacity of the industry-standard lithium-ion design to run for the thousands of cycles needed to power an electric car.
A network of aramid nanofibers, recycled from Kevlar, can enable lithium-sulfur batteries to overcome their Achilles heel of cycle life – the number of times it can be charged and discharged – a team from the University of Michigan has shown.
“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 speed, resistance and safety. The challenge today is to make a battery that increases the cycle speed from the previously 10 cycles to hundreds of cycles and meets several other requirements, including cost, “said Nicholas Kotov, a professor at Irving Langmuir Distinguished University of Chemical Sciences and Engineering who led the research.
“Biomimetic construction 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 solve the overall challenges of lithium-sulfur batteries.”
Previously, his team had relied on networks of aramid nanofibers infused with an electrolyte gel to stop one of the main causes of short cycle life: dendrites growing from one electrode to another and piercing the membrane. The toughness of aramid fibers stops the dendrites.
But lithium sulfur batteries have another problem: Small molecules of lithium and sulfur are formed and flow to the lithium, getting stuck and reducing the capacity of the battery. The membrane was needed to allow lithium ions to flow from lithium to sulfur and back – and to block the lithium and sulfur particles, known as lithium polysulfides. This ability is called ion selectivity.
“Inspired by biological ion channels, we designed highways for lithium ions where lithium polysulfides cannot pass tolls,” said Ahmet Emre, a postdoc researcher in chemical engineering and co-author of the paper in Nature Communications.
The lithium ions and lithium polysulfides are similar in size, so it was not enough to block the lithium polysulfides by making small channels. By mimicking pores in biological membranes, UM researchers added an electric charge to the pores in the battery membrane.
They did so by utilizing the lithium polysulfides themselves: they adhered to the aramid nanofibers, and their negative charges repelled the lithium polysulfide ions that continued to form at the sulfur electrode. However, positively charged lithium ions could pass freely.
“Achieving record levels for multiple parameters for multiple material properties is what is needed now for car batteries,” Kotov said. “It’s a bit like gymnastics for the Olympics – you have to be perfect everywhere, including the sustainability of their production.”
As a battery, Kotov says the design is “almost perfect”, with its capacity and efficiency approaching theoretical limits. It can also handle extreme temperatures in cars’ lives, from the heat of charging in full sun to the cold of winter. However, real-world cycle life can be shorter with fast charging, more like 1,000 cycles, he says. This is considered a ten-year lifespan.
Along with the higher capacity, lithium-sulfur batteries have sustainability advantages over other lithium-ion batteries. Sulfur is much more abundant than cobalt of lithium-ion electrodes. In addition, the aramid fibers of the battery membrane can be recycled from old bulletproof vests.
The research was funded by the National Science Foundation and the Department of Defense. The team studied the membrane at the Michigan Center for Materials Characterization. The University of Michigan has patented the membrane, and Kotov is developing a company to bring it to market.
Kotov is also Joseph B. and Florence V. Cejka Professor of Engineering and Professor of Chemical Engineering, Materials Science and Engineering and Macromolecular Science and Engineering.
More information: Study: Multifactorial construction of biomimetic membranes for batteries with several high-performance parameters (DOI: 10.1038 / s41467-021-27861-w)
Originally published by Michigan News, University of Michigan.
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