Electrolyte additives unlock the potential of lithium-sulfur batteries

Lithium-ion (Li-ion) batteries are an integral a part of society, from cellphones and laptops to electrical autos. Whereas Li-ion batteries have been a serious success up to now, scientists worldwide are racing to design even higher “beyond Li-ion” batteries within the shift towards a extra electrified world. Business Li-ion batteries are much less energy-dense than different batteries and depend on comparatively costly substances, comparable to cobalt and nickel compounds, that are additionally closely depending on weak provide chains.

One of many extra promising options to Li-ion batteries are lithium-sulfur (Li-S) batteries, which have an anode of lithium steel and a cathode of sulfur. This electrode pairing guarantees two to 3 occasions larger power densities and lowered prices, whereas additionally utilizing Earth-abundant sources.

However these batteries don’t come with out their very own challenges, together with a brief life cycle because of the undesirable migration of polysulfide ions and the uneven distribution and incidence of chemical reactions inside the system.

By creating an revolutionary additive for the electrolyte, researchers on the U.S. Division of Vitality’s (DOE) Argonne Nationwide Laboratory are making progress towards addressing these issues which are limiting the widespread adoption of Li-S batteries.

Their analysis is published within the journal Joule.

In Li-ion batteries, lithium ions are saved within the areas between layers of the cathode materials and transfer forwards and backwards between the cathode and anode throughout charging and discharging.

Li-S batteries, nonetheless, depend on a unique course of. In these cells, lithium ions transfer between the cathode and anode through a chemical response. Elemental sulfur from the cathode is transformed into polysulfide compounds—composed of sulfur atom chains—a few of which might dissolve within the electrolyte.

Due to this solubility, a “shuttling” impact happens, the place the polysulfides journey forwards and backwards between the cathode and the anode. This shuttling ends in lack of materials from the sulfur cathode as a result of it’s deposited on the anode, which limits the general battery cycle life and efficiency.

Quite a few methods have been proposed to mitigate polysulfide shuttling and different challenges. One such technique, utilizing an additive within the electrolyte, has lengthy been regarded as incompatible as a consequence of chemical reactivity with the sulfur cathode and different battery elements.

Argonne chemist Guiliang Xu and his group have created a brand new class of additive and located that such components can truly enhance battery efficiency. By controlling the way in which the additive reacts with sulfur compounds, researchers are higher in a position to create an interface between the cathode and electrolyte that’s essential to facilitate straightforward transport of lithium ions.

“The additive, called a Lewis acid additive, is a salt that reacts with the polysulfide compounds, forming a film over the entire electrode,” Xu mentioned. “The key is to have a minor reaction to form the film, without a continuous reaction that consumes the material and reduces energy density.”

The additive types a movie on each the anode and the cathode, suppressing the shuttle impact, enhancing the soundness of the cell and selling an ion transport “highway” all through the electrode. This electrolyte design additionally minimizes sulfur dissolution and enhances response homogeneity, enabling using components that had been beforehand thought of incompatible.

To validate the idea, the researchers in contrast their electrolyte with the additive to a standard electrolyte utilized in Li-S batteries. They noticed a big discount in polysulfide formation. The brand new electrolyte confirmed very low dissolution of polysulfides, which was confirmed with X-ray methods.

Additional, they tracked the response conduct throughout battery charging and discharging. These experiments made use of Argonne’s Superior Photon Supply (APS) and Brookhaven Nationwide Laboratory’s Nationwide Synchrotron Gentle Supply II, each DOE Workplace of Science person services, which confirmed that the electrolyte design minimized the dissolution and formation of polysulfides.

“Synchrotron techniques provide powerful tools for characterizing battery materials,” mentioned Tianyi Li, a beamline scientist on the APS. “By using X-ray diffraction, X-ray absorption spectroscopy and X-ray fluorescence microscopy at the APS, it was confirmed that the new interface design effectively mitigates well-known issues including polysulfide shuttle. More importantly, this interface enhances ion transfer, which helps to reduce reaction heterogeneities.”

Xu added, “With further optimization and development of sulfur electrodes, we believe Li-S batteries can achieve higher energy density and better overall performance, contributing to their commercial adoption.”

One other main problem for Li-S batteries is the soundness of the lithium steel—it reacts simply and poses security considerations. Xu and his group are engaged on creating higher electrolytes to stabilize the lithium steel and cut back the flammability of the electrolyteguaranteeing the security of Li-S batteries.

On the APS, Beamline 20-BM was used for X-ray absorption spectroscopy to probe the solubility of polysulfide. Beamline 17-BM was used for X-ray diffraction imaging to discover the homogeneity or heterogeneity of your entire cell. Beamline 2-ID was used for X-ray fluorescence mapping to substantiate solubility of the electrode materials and to watch the migration of sulfur in typical electrolytes.

Different contributors to this work embrace Chen Zhao, Heonjae Jeong, Inhui Hwang, Yang Wang, Jianming Bai, Luxi Li, Shiyuan Zhou, Chi Cheung Su, Wenqian Xu, Zhenzhen Yang, Manar Almazrouei, Cheng-Jun Solar, Lei Cheng and Khalil Amine .