A review with 132 references. Societal and regulatory pressures are pushing industry towards more sustainable energy sources, such as solar and wind power, while the growing popularity of portable cordless electronic devices continues. These trends necessitate the ability to store large amounts of power efficiently in rechargeable batteries that should also be affordable and long-lasting. Lithium-sulfur (Li-S) batteries have recently gained renewed interest for their potential low cost and high energy density, potentially over 2600 Wh kg⁻¹. The current review will detail the most recent advances in early 2020. The focus will be on reports published since the last review on Li-S batteries. This review is meant to be helpful for beginners as well as useful for those doing research in the field, and will delineate some of the cutting-edge adaptations of many avenues that are being pursued to improve the performance and safety of Li-S batteries.

Sulfur cements have drawn significant attention as binders because sulfur is a byproduct of fossil fuel refining. Sulfur cements that can be formed by the vulcanization of elemental sulfur and plant-derived olefins such as terpenoids are particularly promising from a sustainability standpoint. A range of terpenoid–sulfur cements have shown compressional and flexural properties exceeding those of some commercial structural mineral cements. Pozzolans such as fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBFS) and abundant clay resources such as metakaolin (MK) are attractive fines for addition to binders. Herein, we report 10 composites prepared by a combination of sulfur, terpenoids (geraniol or citronellol), and these pozzolans. This study reveals the extent to which the addition of the pozzolan fines to the sulfur–terpenoid cements influences their mechanical properties and chemical resistance. The sulfur–terpenoid composites CitS and GerS were prepared by the reaction of 90 wt% sulfur and 10 wt% citronellol or geraniol oil, respectively. The density of the composites fell within the range of 1800–1900 kg/m³ and after 24 h submersion in water at room temperature, none of the materials absorbed more than 0.7 wt% water. The compressional strength of the as-prepared materials ranged from 9.1–23.2 MPa, and the percentage of compressional strength retained after acid challenge (submersion in 0.1 M H₂SO₄ for 24 h) ranged from 80–100%. Incorporating pozzolan fines into the already strong CitS (18.8 MPa) had negligible effects on its compressional strength within the statistical error of the measurement. CitS-SF and CitS-MK had slightly higher compressive strengths of 20.4 MPa and 23.2 MPa, respectively. CitS-GGBFS and CitS-FA resulted in slightly lower compressive strengths of 17.0 MPa and 15.8 MPa, respectively. In contrast, the compressional strength of initially softer GerS (11.7 MPa) benefited greatly after incorporating hard mineral fines. All GerS derivatives had higher compressive strengths than GerS, with GerS-MK having the highest compressive strength of 19.8 MPa. The compressional strengths of several of the composites compare favorably to those required by traditional mineral cements for residential building foundations (17 MPa), whereas such mineral products disintegrate upon similar acid challenge.

High sulfur-content materials (HSMs) formed via inverse vulcanization of elemental sulfur with animal fats and/or plant oils can exhibit remarkable mechanical strength and chemical resistance, sometimes superior to commercial building products. Adding pozzolan fine materials—fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBFS), or metakaolin (MK)—can further improve HSM mechanical properties and stability. Herein, we detail nine materials comprised of rancidified chicken fat, elemental sulfur, and canola or sunflower oil (to yield CFS or GFS, respectively) and, with or without FA, SF, GGBFS, or MK. The base HSMs, CFS₉₀ or GFS₉₀, contained 90 wt% sulfur, 5 wt% chicken fat, and 5 wt% canola or sunflower oil, respectively. For each HSM/fine combination, the resulting material was prepared using a 95:5 mass input ratio of HSM/fine. No material exhibited water uptake >0.2 wt% after immersion in water for 24 h, significantly lower than the 28 wt% observed with ordinary Portland cement (OPC). Impressively, CFS₉₀, GFS₉₀, and all HSM/fine combinations exhibited compressive strength values 15% to 55% greater than OPC. After immersion in 0.5 M H₂SO₄, CFS₉₀, GFS_90, and its derivatives retained 90% to 171% of the initial strength of OPC, whereas OPC disintegrated under these conditions. CFS₉₀, GFS₉₀, and its derivatives collectively show promise as sustainable materials and materials with superior performance versus concrete.

The unique properties and sustainability advantages of sulfur polymer cement have led to efforts to use them as alternatives to traditional Portland cement. The current study explores the impact of environmental stresses on the strength development of polymer composite SunBG₉₀, a material composed of animal and plant fats/oils vulcanized with 90 wt. % sulfur. The environmental stresses investigated include low temperature (−25 °C), high temperature (40 °C), and submersion in water, hexanes, or aqueous solutions containing strong electrolyte, strong acid, or strong base. Samples were analyzed for the extent to which exposure to these stresses influenced the thermo-morphological properties and the compressional strength of the materials compared to identical materials allowed to develop strength at room temperature. Differential scanning calorimetry (DSC) analysis revealed distinct thermos-morphological transitions in stressed samples and the notable formation of metastable γ-sulfur in hexane-exposed specimens. Powder X-ray diffraction confirmed that the crystalline domains identified by DSC were primarily γ-sulfur, with ~5% contribution of γ-sulfur in hexane-exposed samples. Compressive strength testing revealed high strength retention other than aging at elevated temperatures, which led to ~50% loss of strength. These findings reveal influences on the strength development of SunBG₉₀, lending important insight into possible use as an alternative to OPC.