A Breakthrough Improvement to Lithium Sulfur Batteries

American Institute of Physics researchers have looked to lithium sulfur batteries because of sulfur’s high theoretical capacity and energy density to develop higher capacity batteries.

Lithium ion batteries aren’t keeping up with energy demands from higher power electronic devices, electric vehicles and smart electric grids. To develop higher capacity batteries, researchers have looked to lithium sulfur batteries because of sulfur’s high theoretical capacity and energy density.

There are still several problems to solve before lithium sulfur batteries can be put into practical applications. The biggest is the shuttling effect that occurs during cycling. This effect causes the diffusion of polysulfides from the cathode, creating capacity loss. It also consumes a lot of fresh lithium and electrolytes, and reduces battery performance.

To solve this problem and improve lithium sulfur battery performance, the researchers created a sandwich-structured electrode using a novel material that traps polysulfides and increases the reaction kinetics.

Another is sulfur’s intrinsically low electrical conductivity and the rapid capacity decay caused by polysulfides escaping from the cathode.

To solve the shuttling problem and improve lithium sulfur battery performance, the authors of the paper published in APL Materials, created a sandwich-structured electrode using a novel material that traps polysulfides and increases the reaction kinetics.

ZIF-67 is a metal-organic framework (MOF) constructed from metal ions or metal clusters and organic ligands. It holds great promise in gas storage and separation, catalysis and energy storage. MOF-derived materials are also attractive in energy storage due to their robust structure, porous surface and high conductivity.

A sandwich-structured electrode with sulfur immobilized in between PZ67 layers, as a PZ67/S/PZ67 build, improves the practical energy density of the lithium sulfur battery to three to five times higher than that of lithium ion batteries. The PZ67 is composed of polar materials, and the porous carbon showed a synergistic effect in the chemical interaction, served as a physical barrier, offered a high conductivity to prohibit the polysulfide shuttling effect and enhanced the batteries’ cycling performance.

Author of the paper Siwu Li said, “The porous PZ67 can not only absorb the polysulfides to form a confinement, it can also improve the kinetics of the actual active materials’ reaction during the battery cycling. That means it may also improve the discharge voltage of the battery, and that is a big contribution to improving the energy density of the batteries.”

Li also noted that the sandwich-structured electrode that confines soluble polysulfides could be useful for anyone working to confine soluble materials. His team plans to continue their work in order to scale up the process of fabricating the hybrid electrode using a hot pressing procedure. They also plan to address instabilities on the anode side of lithium sulfur batteries, possibly by adding a protective layer.

This is quite good news for the consumer hoping for more battery capacity or simply a smaller unit with equivalent energy. While the press release isn’t saying how expensive or complex construction might be, one wouldn’t be surprised to read the cost and complexity are not far away from today’s products. The wild card is the PZ67, which isn’t a commercial quantity item, but could be, and that will tell the marketability tale.

The story for lithium sulfur batteries isn’t over, lacking an answer for the anode, but this team sure looks to have good answers for a far better battery solution.