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A novel porous sulfur/carbon nanocomposite was prepared as the cathode material for lithium-sulfur batteries. The porous nanostructure of the composite is beneficial for enhancing the cycle life by accommodating the volume expansion of sulfur particles and adsorbing the polysulfide produced during the electrochemical reaction. The resulting nanocomposite shows a high capacity of 1039 mA h g À1 at 1C (1C ¼ 1675 mA g À1 ) in the first cycle and the reversible capacity remains high at up to 1023 mA h g À1 even after 70 cycles.

Chitosan with abundant of hydroxyl and amine groups as an additive for cathode and separator has been proved to be an effective polysulfide trap agent in lithium-sulfur batteries. Compared with common sulfur cathode, the cathode with chitosan shows enhanced initial discharge capacity from 950 to 1145 mAh g -1 at C/10. The reversible specific capacity after 100 cycles increases from 508 mAh g -1 to 680 mAh g -1 and 473 to 646 mAh g -1 at rates of C/2 and 1C, respectively. In addition, batteries with separators that are coated with carbon/chitosan layer can exhibit high discharge capacity of 830 mAh g -1 at C/2 after 100 cycles and 675 mAh g -1 at 1C after 200 cycles with the capacity fading as low as 0.11% per cycle. These studies demonstrate the benefits of using chitosan for not only lithium-sulfur batteries but also potentially other sulfur-based battery applications.

Harnessing biomass to fabricate electronic devices has lately drawn significant research attention because it not only represents a promising strategy for making materials but is also beneficial for the sustainable development of technologies.

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Lithium–sulfur batteries have been considered as one of the most promising energy storage devices due to their high theoretical capacity and low cost. They go through complicated multistep electrochemical reactions from solid (sulfur)–liquid (soluble polysulfide) to liquid (soluble polysulfide)–solid (Li2S) during the discharge process. Actually, during this process, the transition from liquid phase (Li2S4) to solid phase (Li2S) at 2.1 V plateau is a difficult step with sluggish kinetics, thus leading to low sulfur utilization and discharge capacity. To promote the transition processes and enhance the sulfur utilization, CoS2@multichannel carbon nanofiber composites (CoS2@MCNFs) serving as sulfur host were successfully synthesized. Herein, CoS2 catalysts are proven to be beneficial not only for enhancing the phase-transition kinetics but also for adsorbing soluble polysulfide. Besides, unlike other carbon materials, MCNFs have plenty of hollow channels and thus enhance sulfur loading and conductivity. Accordingly, the discharge capacity increases 32% more than that of electrode without CoS2. And a very low capacity fade rate of 0.03% per cycle (over 450 cycles) is obtained at a 0.5C rate. This work has opened up new ideas for enhancing sulfur utilization for high sulfur-loading electrode.

The file includes experimental details, Figure S1-S11. EXPERIMENTAL SECTONPreparation of CoSe 2 @N-CA. All chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. All were of analytical grade and required no further treatment prior to processing. Typically, 9.1 mM resorcinol, 1.5 mL furfuraldehyde, and 0.26 mM hexamethylenetetramine were were dissolved in 6.7 mL ethanol and stirred for 10 min. Then 10 mM Co(Ac) 2 were added in the above solution and stirred for 40 min at 45 °C to produce a uniform solution. The obtained solution was poured into a sealed penicillin bottle. After 7 days standing at 80 °C, the solution was eventually became a gel of a dark brown color. The resulting gel was taken out of the bottle and dried at 100 °C for 5 h. Next, the gel was annealed at 500 °C for 2 h under an argon atmosphere and in this process the transition metal compounds were reduced and transformed into Co@N-CA. The obtained Co@N-CAwas mixed with selenium powders in a mass ratio of 1:1 and annealed in a vacuum tube at 400 °C for 2 h. Materials Characterization. The crystalline phases and phase purity of the asobtained CoSe 2 @N-CAwere identified by X-ray diffraction (XRD) (Philips X'pert PRO SUPER X-ray diffractometer), Raman spectroscopy (LabRamHR, JY Company, France), and X-ray photoelectron spectroscopy (XPS). The morphologies of the materials were analyzed by Field-emission scanning electron microscopy (FESEM) (SU8220, HITACHI, Japan), transmission electron microscopy(TEM) (JEM-2100F, JEOL, Japan)and high resolution TEM (HRTEM).Electrochemical Measurements. The electrodes were fabricated by mixing active material, acetylene black, carboxyl methyl cellulose (CMC), and styrene butadiene rubber (SBR) with a weight ratio of 80:10:5:5 in deionized water dispersant. The viscous slurry was coated on Cu foil and dried at 80 °C overnight. Coin cells for SIBs were assembled such that the CoSe 2 @N-CA was considered the working electrode and metallic sodium sheet as the counter anode. Glass fibers were used as the