Facilitating Charge Reactions in Al-S Batteries with Redox Mediators

Locally Concentrated Ionic Liquid Electrolytes for Wide-Temperature-Range Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries are promising energy storage devices due to their high theoretical capacity, low cost, and high safety. However, the high viscosity and inferior ion transport of conventionally used ionic liquid electrolytes (ILEs) limit the kinetics of Al-S batteries, especially at sub-zero temperatures. Herein, locally concentrated ionic liquid electrolytes (LCILE) formed via diluting the ILEs with non-solvating 1,2-difluorobenzene (dFBn) co-solvent are proposed for wide-temperature-range Al-S batteries. The addition of dFBn effectively promotes the fluidity and ionic conductivity without affecting the AlCl4 - /Al2 Cl7 - equilibrium, which preserves the reversible stripping/plating of aluminum and further promotes the overall kinetics of Al-S batteries. As a result, Al-S cells employing the LCILE exhibit higher specific capacity, better cyclability, and lower polarization with respect to the neat ILE in a wide temperature range from -20 to 40 °C. For instance, Al-S batteries employing the LCILE sustain a remarkable capacity of 507 mAh g-1 after 300 cycles at 20 °C, while only 229 mAh g-1 is delivered with the dFBn-free electrolyte under the same condition. This work demonstrates the favorable use of LCILEs for wide-temperature Al-S batteries.

Three-Dimensional Nitrogen-Doped Carbonaceous Networks Anchored with Cobalt as Separator Modification Layers for Low-Polarization and Long-Lifespan Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries have attracted extensive interest due to their high theoretical energy density, inherent safety, and low cost. However, severe polarization and poor cycling performance significantly limit the development of Al-S batteries. Herein, three-dimensional (3D) nitrogen-doped carbonaceous networks anchored with cobalt (Co@CMel-ZIF) is proposed as a separator modification layer to mitigate these issues, prepared via carbonizations of a mixture of ZIF-7, melamine, and CoCl2. It exhibits a 3D network structure with a moderate surface area and high average pore diameter, which is demonstrated to be effective in adsorbing the aluminum polysulfides and hindering the mobility of polysulfides across the separator for enhanced cyclic stability of Al-S batteries. Meanwhile, Co@CMel-ZIF are characterized by abundant catalytic pyridinic-N and Co-Nx active sites that effectively eliminate the barrier of sulfides' conversion and thereby facilitate the polarization reduction. As a result, Al-S cells based on the separator modified with Co@CMel-ZIF exhibit a low voltage polarization of 0.47 V under the current density of 50 mA g-1 at 20 °C and a high discharge specific capacity of 503 mAh g-1 after 150 cycles. In contrast, the cell employing a bare separator exhibits a polarization of 1.01 V and a discharge capacity of 300 mAh g-1 after 70 cycles under the same conditions. This work demonstrates that modifying the separators is a promising strategy to mitigate the high polarization and poor cyclability of Al-S batteries.

Polyoxometalates@Metal-Organic Frameworks Derived Bimetallic Co/Mo2 C Nanoparticles Embedded in Carbon Nanotube-Interwoven Hierarchically Porous Carbon Polyhedron Composite as a High-Efficiency Electrocatalyst for Al-S Batteries

Al-S battery (ASB) is a promising energy storage device, notable for its safety, crustal abundance, and high theoretical energy density. However, its development faces challenges due to slow reaction kinetics and poor reversibility. The creation of a multifunctional cathode material that can both adsorb polysulfides and accelerate their conversion is key to advancing ASB. Herein, a composite composed of polyoxometalate nanohybridization-derived Mo2 C and N-doped carbon nanotube-interwoven polyhedrons (Co/Mo2 C@NCNHP) is proposed for the first time as an electrochemical catalyst in the sulfur cathode. This composite improves the utilization and conductivity of sulfur within the cathode. DFT calculations and experimental results indicate that Co enables the chemisorption of polysulfides while Mo2 C catalyzes the reduction reaction of long-chain polysulfides. X-ray photoelectron spectroscopy (XPS) and in situ UV analysis reveal the different intermediates of Al polysulfide species in Co/Mo2 C@NCNHP during discharging/charging. As a cathode material for ASB, Co/Mo2 C@NCNHP@S composite can deliver a discharge-charge voltage hysteresis of 0.75 V with a specific capacity of 370 mAh g-1 after 200 cycles at 1A g-1 .

ZnSe/SnSe2 hollow microcubes as cathode for high performance aluminum ion batteries

Advances in cathode material design and understanding of intercalation mechanisms are necessary to improve the overall performance of aluminum ion batteries. Therefore, we designed ZnSe/SnSe₂ hollow microcubes with heterojunction structure as a cathode material for aluminum ion batteries. ZnSe/SnSe₂ hollow microcubes with an average size of about1.4 µm were prepared by selenization of ZnSn(OH)₆ microcubes successfully. The shell thickness of ZnSe/SnSe₂ hollow microcubes is about 250 nm. On one hand, the hollow cubic structure can effectively alleviate the volume effect, provide shorter ion diffusion paths, and increase the contact area with the electrolyte. On the other hand, ZnSe/SnSe₂ heterojunction structure can establish a built-in electric field to facilitate ion transport. The synergistic effect of the two leads to the improved electrochemical performance of ZnSe/SnSe₂ as the cathode of aluminum ion batteries. The material delivered a reversible capacity of 124 mAh/g after 150 cycles at a current density of 100 mA/g. Meanwhile, coulombic efficiency remained above 98% in almost all cycles. In addition, the electrochemical reaction mechanism and kinetic process of Al³⁺ and ZnSe/SnSe₂ were studied.

Advances and challenges of aluminum-sulfur batteries

The search for cost-effective stationary energy storage systems has led to a surge of reports on novel post-Li-ion batteries composed entirely of earth-abundant chemical elements. Among the plethora of contenders in the 'beyond lithium' domain, the aluminum-sulfur (Al-S) batteries have attracted considerable attention in recent years due to their low cost and high theoretical volumetric and gravimetric energy densities (3177 Wh L^-1 and 1392 Wh kg^-1). In this work, we offer an overview of historical and present research pursuits in the development of Al-S batteries with particular emphasis on their fundamental problem-the dissolution of polysulfides. We examine both experimental and computational approaches to tailor the chemical interactions between the sulfur host materials and polysulfides, and conclude with our view on research directions that could be pursued further.

A Zn-S aqueous primary battery with high energy and flat discharge plateau

We demonstrate a disposable aqueous primary battery chemistry that comprises environmentally benign materials of the sulfur cathode and Zn anode in a 1 M ZnCl₂ aqueous electrolyte. The Zn-S battery shows a high energy density of 1083.3 Wh kg^-1 for sulphur with a flat discharge voltage plateau around 0.7 V. When operating at a high mass loading of 8.3 mg cm^-2 for sulfur in the cathode, the battery exhibits a very high areal capacity of 11.4 mA h cm^-2 and areal energy of 7.7 mW h cm^-2.