The lithium–sulfur battery holds a high theoretical energy density, 4–5 times that of today’s lithium-ion batteries, yet its applications have been hindered by poor electronic conductivity of the sulfur cathode and, most importantly, the rapid fading of its capacity due to the formation of soluble polysulfide intermediates (Li2S n , n = 4–8). Despite numerous efforts concerning this issue, combatting sulfur loss remains one of the greatest challenges. Here we show that this problem can be effectively diminished by controlling the sulfur as smaller allotropes. Metastable small sulfur molecules of S2–4 were synthesized in the confined space of a conductive microporous carbon matrix. The confined S2–4 as a new cathode material can totally avoid the unfavorable transition between the commonly used large S8 and S4 2–. Li–S batteries based on this concept exhibit unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior rate capability, which promise a practicable battery with high energy density for applications in portable electronics, electric vehicles, and large-scale energy storage systems.
► Carbon-wrapped sulfur composite was obtained via an in situ sulfur deposition route. ► Sulfur–carbon composite suppresses the shuttle effect during charging. ► Sulfur–carbon composite shows enhanced cyclability and rate capability. ► Sulfur–carbon composite retains structural integrity and low impedance during cycling. An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur at the interspaces between carbon nanoparticles in aqueous solution at room temperature. The product has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, charge–discharge measurements, and electrochemical impedance spectroscopy. The sulfur–carbon composite cathode with 75wt.% active material thus obtained exhibits a remarkably high first discharge capacity of 1116mAhg−1 with good cycle performance, maintaining 777mAhg−1 after 50 cycles. The significantly improved electrochemical performance of the sulfur–carbon composite cathode is attributed to the carbon-wrapped sulfur network structure, which suppresses the loss of active material during charging/discharging and the migration of the polysulfide ions to the anode (i.e., shuttling effect). The integrity of the cathode structure during cycling is reflected in low impedance values observed after cycling. This facile in situ sulfur deposition route represents a low-cost approach to obtain high-performance sulfur–carbon composite cathodes for rechargeable Li–S batteries.
Going into their shell: A novel carbon–sulfur nanocomposite has been synthesized by confining sulfur in double‐shelled “soft” carbon hollow spheres (see figure) with high surface area and porosity. This carbon–sulfur nanocomposite shows outstanding electrochemical performance when evaluated as a cathode material for lithium–sulfur batteries.
A novel vulcanized polyaniline nanotube/sulfur composite was prepared successfully via an in situ vulcanization process by heating a mixture of polyaniline nanotube and sulfur at 280 °C. The electrode could retain a discharge capacity of 837 mAh g−1 after 100 cycles at a 0.1 C rate and manifested 76% capacity retention up to 500 cycles at a 1 C rate.
Binder free vertical aligned (VA) CNT/sulfur composite electrodes with high sulfur loadings up to 70 wt% were synthesized delivering discharge capacities higher than 800 mAh g(-1) of the total composite electrode mass.
A practical route is introduced for synthesizing a sulfur-impregnated graphene composite as a promising cathode material for lithium-sulfur batteries. Sulfur particles with a size of a few microns are successfully grown in the interior spaces between randomly dispersed graphene sheets through a heterogeneous crystal growth mechanism. The proposed route not only enables the control of the particle size of active sulfur but also affords quantitative yields of composite powder in large quantities. We investigate the potential use of the sulfur-impregnated graphene composite as a cathode material owing to its advantages of confining active sulfur, preventing the dissolution of soluble polysulfides, and providing sufficient electrical conduction. A high discharge capacity of 1237 mA h g(-1) during the first cycle and a good cyclic retention of 67% after 50 cycles are attained in a voltage range of 1.8-2.6 V vs. Li/Li+. These results emphasize the importance of tailoring cathode materials for improving the electrochemical properties of lithium-sulfur batteries. Our results provide a basis for further investigations on advanced lithium batteries.
We have investigated the chemical bonding and electronic structure of a graphene oxide-sulfur (GO-S) nanocomposite by X-ray Photoelectron Spectroscopy (XPS), Near-edge X-ray Absorption Fine Structure (NEXAFS), and X-ray Emission Spectroscopy (XES). The nanocomposite, synthesized by a chemical reaction-deposition approach followed by low temperature thermal treatment, is composed of a thin and uniform sulfur film anchored on a graphene oxide (GO) sheet. The GO is partially reduced during the chemical synthesis process, resulting in the appearance of a C-H bond and an increase in the ordering of GO sheets. The moderate chemical interactions between sulfur and GO can preserve the intrinsic electronic structure of GO, and on the other hand, immobilize the sulfur on the GO sheets, which should be responsible for the excellent electrochemical performance of the lithium-sulfur cells by using the GO-S nanocomposite as the cathode material.
Realization of a ubiquitous clean energy future depends critically on the efficient storage and utilization of renewable energies. Lithium-ion batteries are appealing in this regard, but low-cost, abundant, safe, high energy-density electrode materials need to be developed to adopt them. Here we present a sulfur-multi-wall carbon nanotube (MWCNT) composite cathode with high-rate cyclability by a facile binder/current collector-free fabrication process. The composite cathode exhibits high capacities of 1352 mAh g(-1) at 1C rate and 1012 mAh g(-1) at 4C rate. Due to the self-weaving behavior of MWCNTs, extra cell components such as binders and current collectors are rendered unnecessary, thereby streamlining the electrode manufacturing process and decreasing the cell weight. While the highly conductive MWCNTs improve the active material utilization at high rates, the absorption ability of the cathode framework localizes the electrolyte and suppresses the migration of soluble polysulfides. The cathode design and facile synthesis enhance the feasibility of practical high rate Li-S batteries.
In this paper we report a novel lithium-sulfur cell, which is characteristic of a unique combination of carbon nanofibers–sulfur cathode and gel polymer electrolyte (GPE). In particular, the carbon nanofibers for the cathode and the poly(acrylonitrile)/poly(methyl methacrylate) (PAN/PMMA) membrane for the GPE are prepared by electrospinning technique. The GPE consists of electrospun PAN/PMMA membrane and 1 mol kg−1 lithium bis(trifluoromethylsulfonyl)imide in N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PPR14TFSI) and poly (ethylene glycol) dimethyl ether (PEGDME). The membrane and cell performances are investigated by scanning electron spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. It is found that the cell using the GPE based on PAN/PMMA membrane and PPR14TFSI-PEGDME (1:1) exhibits the largest discharge capacity and the best cycle durability. The discharge capacity of this cell remains at 760 mA h g−1 after 50 cycles. This new sulfur/electrolyte system combines the advantages of the carbon nanofibers that provide an effective conduction path and network-like structure, and the GPE that suppresses the dissolution of the intermediate products generated during the discharge process. The ratio of PPR14TFSI to PEGDME affects the ionic conductivity of the GPE, the stability of the sulfur electrode and the compatibility of lithium electrode with the GPE. ► Fibrous PAN/PMMA membrane and carbon nanofibers were prepared by electrospinning technique. ► Improved performances of GPE based on PAN/PMMA incorporating with IL PPR14TFSI by adding PEGDME. ► Improved Li-sulfur battery performance by combining use of CNFs-S electrode and GPE with IL.
A sulfur–polypyrrole composite consisting of orthorhombic bipyramidal sulfur particles (63.3 wt %) coated with a polypyrrole nanolayer has been synthesized by a low-cost, scalable, environmentally benign process and investigated as a cathode material for Li-ion batteries. Cathodes containing the sulfur–polypyrrole composite have been evaluated in half cells by cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The sulfur–polypyrrole composite cathode shows better electrochemical stability, cyclability, and rate capability than pristine sulfur as the polypyrrole coating acts as a conductive matrix for electron transfer while prohibiting lithium polysulfide dissolution. At C/5 rate, the sulfur–polypyrrole composite cathode exhibits ∼200 mAh/g higher capacity than the pristine sulfur after 50 cycles. At C/2 and 1C rates, the composite shows significantly better capacity retention than the pristine sulfur over 100 cycles.