There is currently an urgent demand for highly efficient energy storage and conversion systems. Due to its high theoretical energy density, low cost, and environmental compatibility, the lithium sulfur (Li–S) battery has become a typical representative of the next generation of electrochemical power sources. Various approaches have been explored to design and prepare sulfur cathode materials to enhance their electrochemical performance. This Research News article summarizes and compares different sulfur materials for Li–S batteries and particularly focuses on the fine structures, electrochemical performance, and electrode reaction mechanisms of pyrolyzed polyacrylo­nitrile sulfur (pPAN@S) and microporous-carbon/small-sulfur composite materials.

Composite materials of porous pyrolyzed polyacrylonitrile–sulfur@graphene nanosheet (pPAN–S@GNS) are fabricated through a bottom-up strategy. Microspherical particles are formed by spray drying of a mixed aqueous colloid of PAN nanoparticles and graphene nanosheets, followed by a simple heat treatment with elemental sulfur. The pPAN–S primary nanoparticles are wrapped homogeneously and loosely within a three-dimensional network of graphene nanosheets (GNS). The hierarchical pPAN–S@GNS composite shows a high reversible capacity of 1449.3 mAh g⁻¹_sulfur or 681.2 mAh g⁻¹_composite in the second cycle; after 300 cycles at a 0.2 C charge/discharge rate the capacity retention is 88.8 % of its initial reversible value. Additionally, the coulombic efficiency (CE) during cycling is near 100 %, apart from in the first cycle, in which CE is 81.1 %. A remarkable capacity of near 700 mAh g⁻¹_sulfur is obtained, even at a high discharge rate of 10 C. The superior performance of pPAN–S@GNS is ascribed to the spherical secondary GNS structure that creates an electronically conductive 3D framework and also reinforces structural stability.

Of the various beyond-lithium-ion batteries, lithium–sulfur (Li-S) batteries were recently reported as possibly being the closest to market. However, its theoretically high energy density makes it potentially hazardous under conditions of abuse. Therefore, addressing the safety issues of Li-S cells is necessary before they can be used in practical applications. Here, we report a concept to build a safe and highly efficient Li-S battery with a flame-inhibiting electrolyte and a sulfur-based composite cathode. The flame retardant not only makes the carbonates nonflammable but also dramatically enhances the electrochemical performance of the sulfur-based composite cathode, without an apparent capacity decline over 750 cycles, and with a capacity greater than 800 mA h⁻¹ g⁻¹(sulfur) at a rate of 10 C.

Of the various beyond-lithium-ion batteries, lithium–sulfur (Li-S) batteries were recently reported as possibly being the closest to market. However, its theoretically high energy density makes it potentially hazardous under conditions of abuse. Therefore, addressing the safety issues of Li-S cells is necessary before they can be used in practical applications. Here, we report a concept to build a safe and highly efficient Li-S battery with a flame-inhibiting electrolyte and a sulfur-based composite cathode. The flame retardant not only makes the carbonates nonflammable but also dramatically enhances the electrochemical performance of the sulfur-based composite cathode, without an apparent capacity decline over 750 cycles, and with a capacity greater than 800 mA h⁻¹ g⁻¹(sulfur) at a rate of 10 C.

As one of the essential components in electrodes, the binder affects the performance of a rechargeable battery. By modifying β-cyclodextrin (β-CD), an appropriate binder for sulfur composite cathodes is identified. Through a partial oxidation reaction in H₂O₂ solution, β-CD is successfully modified to carbonyl-β-cyclodextrin (C-β-CD), which exhibits a water solubility ca. 100 times that of β-CD at room temperature. C-β-CD possesses the typical properties of an aqueous binder: strong bonding strength, high solubility in water, moderate viscosity, and wide electrochemical windows. Sulfur composite cathodes with C-β-CD as the binder demonstrate a high reversible capacity of 694.2 mA h g_(composite)⁻¹ and 1542.7 mA h g_(sulfur)⁻¹, with a sulfur utilization approaching 92.2%. The discharge capacity remains at 1456 mA h g_(sulfur)⁻¹ after 50 cycles, which is much higher than that of the cathode with unmodified β-CD as binder. Combined with its low cost and environmental benignity, C-β-CD is a promising binder for sulfur cathodes in rechargeable lithium batteries with high electrochemical performance.