Positron Annihilation Spectroscopy as a Diagnostic Tool for Probing the First‐Cycle Defect Evolution in Magnesium–Sulfur Battery Electrodes

Abstract

Magnesium–sulfur batteries are elusive candidates for the post‐lithium‐ion battery. Their critical challenge for commercialization is rapid capacity fading due to polysulfide shuttle dissolution and slow kinetics during cycling. Insight into the free volumes, morphology, and structural evolution of the sulfur cathode in an Mg/S battery results in a deep understanding of the electrochemical reaction mechanism to further engineer an efficient electrode. In this work, a sulfur cathode with silicon carbide and graphene‐based material S_SiC_GNP is designed and characterized. The full cell based on the Mg anode and S_SiC cathode achieves a high initial discharge capacity of ≈600 mAh g−1 with short cycle life. Positron annihilation spectroscopy (PAL), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS) combined with a scanning electron microscope are used to investigate defect states, free volume interconnectivity/morphology, and structure evolution of sulfur electrode at different electrochemical states. The results show growth in the free volumes and Mg2+ content upon discharge and shrinking upon recharge, while sulfur content is deficient upon demagnesiation. This work provides deep insight and an effective strategy helping to engineer an efficient cathodic material.

Life Aging Effect as a Conditioning Process that Regulates the Performance of the Halogen-Free Mg Electrolyte

“…EDS data coincide well with XRD data, confirming the conversion reaction between magnesium ions and sulfur atoms. Figure e shows SEM-EDS mapping for S 0 with uniform deposition of S particles on the surface of the carbon flakes, which confirms that the microwave-assisted cathode preparation method is a powerful tool for designing promising sulfur-based cathodes . After discharge (S 1 ), the SEM-EDS mapping shows a homogeneous distribution of Mg and S in the background and microstick surface morphology in the front of the image, Figure e.…”

“…Figure 7e shows SEM-EDS mapping for S 0 with uniform deposition of S particles on the surface of the carbon flakes, which confirms that the microwave-assisted cathode preparation method is a powerful tool for designing promising sulfur-based cathodes. 30 After discharge (S 1 ), the SEM-EDS mapping shows a homogeneous distribution of Mg and S in the background and microstick surface morphology in the front of the image, Figure 7e. After the charge, the image displays smooth surface morphology with a homogeneous distribution of Mg and S. 2 for the fresh one due to the peroxide process of the ether solvent.…”

Advances and Challenges in Electrolyte Development for Magnesium–Sulfur Batteries: A Comprehensive Review

“…Therefore, it is highly desirable to develop novel and safe systems and materials based on Mg 2+ /Mg metal conversion chemistry with a higher energy density, where anode dendrite growth can be effectively suppressed [ 35 , 36 , 37 ]. Sulfur is one of the most promising candidates for conversion cathodes because of its high theoretical capacity (1672 mAh g −1 ) and volumetric capacity (3459 mAh mL −1 ), as well as its reserve abundance [ 38 , 39 , 40 , 41 ]. Sulfur cathodes have been well developed in Li-S battery systems.…”