Plasma membranes of biological cells inspire a new separator for a practical lithium-sulfur battery

December 16, 2022

(Nanowerk reflectors) Lithium-sulfur (Li-S) batteries are compelling candidates for next-generation energy storage devices: sulfur is plentiful, cheap, and sustainable. Thanks to sulfur’s multi-step reactions, it also has a higher theoretical energy density than found in current lithium-ion battery technology. However, the reaction intermediates, called polysulfides, exhibit poor reaction kinetics and tend to dissolve in the electrolyte. Furthermore, they deposit on the surface and passivate all battery components, especially the separator and the anode, thus “killing” the battery.

Consequently, the ability to tune the complex polysulfide chemistry is a key challenge to achieving a practical lithium-sulfur battery with high cycle life and minimal electrolyte weight.

“The holy grail in battery research is to improve reaction kinetics and maximize energy density,” Petar Jovanović, a researcher in Monash University’s Department of Mechanical and Aerospace Engineering, tells Nanowerk. “It’s an ongoing battle. In Li-S batteries, the key is to improve the slow reaction kinetics and keep the soluble polysulfides from leaking out of the cathode. But this has to be done extremely efficiently.”

By mimicking a biological cell plasma membrane—the membrane that separates the inside of the cell from the outside environment and regulates the transport of materials into and out of the cell—Jovanović and his co-researchers demonstrated that a graphene oxide membrane reduced in 2D can adjust these polysulfides. They exploit the excellent monovalent Li+ transport properties of a single liquid elastic polymer (EPL) to construct an rGO-based laminar composite membrane, termed EPL-rGO. Schematic depicting the analogy between a plasma membrane and the EPL-rGO membrane Schematic depicting the analogy between a plasma membrane and the EPL-rGO membrane. (Reprinted from doi:10.1016/j.xcrp.2022.101186 under the CC BY-NC-ND 4.0 license)

This separator’s efficiency in controlling polysulfide chemistry and its sub-micron thickness minimizes the amount of electrolyte needed, which allows for lightweight, high energy density batteries.

“This allowed us to make more realistic batteries, demonstrating excellent performance even at high cycling speeds,” notes Jovanović, first author of a paper on this work. “We have also produced prototype pouch cells, which are ranked among the longest-lived Li-S pouches in the literature.”

The team reported the findings in Cell reports. Physical sciences (“Mimicking a cell plasma membrane to adjust dynamic polysulfide chemistry for a practical lithium-sulfur battery”). Double sided cathode bag cell Double-sided cathode bag cell (5 × 3 cm). (Reprinted from doi:10.1016/j.xcrp.2022.101186 under the CC BY-NC-ND 4.0 license)

Dr. Adds Mahdokht Shaibani, co-author of this work, adds: ‘As far as we can ascertain, our work demonstrates the first reported lithium-sulfur pouch cell using permselective membranes, indicating the enormous efforts required to design this critical component of the lithium-battery at the sulfur on a large scale and reliably.”

So far, permselective membranes have been explored in the literature at largely impractical parameters: very low active material loads and high electrolyte volumes mean that these batteries have only ever demonstrated low energy densities. The main reason for this is that Li+ the transport of ions is severely limited, which means that the reactions are slow and the polysulfides tend to accumulate on the membrane surface.

Increasing the transport speed of Li+ ions with lithium-philic coordination sites and keeping the membrane surface electrochemically active compared to polysulfides, the team was able to dramatically reduce electrolyte volumes and increase the sulfur loading.

Consequently, by imparting ion-selective channels, enzyme activity, and adhesion properties, the team’s EPL-rGO membrane can accelerate the transport of the desired ions (Li+) while blocking others (polysulfides) and decomposing them enzymatically, i.e. they act as redox mediators. The bioadhesion afforded by protein incorporation also allows a stable membrane to be coated on the 250 nm thick separator. comparison of permselective membrane separators between button cells Comparison of permselective membrane separators between button cells assembled with a sulfur loading of 3.2 mg cm-2. (Reprinted from doi:10.1016/j.xcrp.2022.101186 under the CC BY-NC-ND 4.0 license)

The superior performance of this new membrane achieves excellent capacity and long cycle life while maintaining the challenging capacity-related electrolyte volume (E/C ratio) of ≤5 µL mAh-1thus surpassing the vast majority of best-in-class Li-S batteries in the literature.

Furthermore, the design approach of a reactive permselective membrane can be broadly applied to a number of 2D materials and biopolymers, opening opportunities for future developments to further optimize and control nanochannels, improve reaction kinetics, and extend sulfur cycle life. – based batteries.

“We are excited because the ion selectivity of our membranes also offers them the potential to be used in flow battery applications, such as vanadium flow batteries, and other separation processes such as water purification,” Jovanović points out.

He adds that the scalability, reliability and low cost of the manufacturing process mean the membrane is ready to be tested and further optimized at the bag cell level. Furthermore, the advantage of this membrane design means that different 2D materials and biopolymers can be studied to further improve the performance. Of
Michael is the author of three Royal Society of Chemistry books: Nano-Society: Pushing the Boundaries of Technology, Nanotechnology: The Future is Tiny and Nanoengineering: The Skills and Tools Making Technology Invisible Copyright ©


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