A freestanding MoO2‐decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery

Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO₂ nanoparticles (MoO₂‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO₂‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm^?2 (1366 mAh g^?1) in the first cycle at a current density of 0.42 mA cm^?2 and 1006 mAh g^?1 over 150 cycles. Moreover, even at the highest current density (8.4 mA cm^?2), the battery achieved 865 mAh g^?1. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO₂‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO₂‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.     

Electrospun zeolitic imidazolate framework‐derived nitrogen‐doped carbon nanofibers with high performance for lithium‐sulfur batteries

Three‐dimensional (3D) nitrogen‐doped carbon nanofibers (N‐CNFs) which were originating from nitrogen‐containing zeolitic imidazolate framework‐8 (ZIF‐8) were obtained by a combined electrospinning/carbonization technique. The pores uniformly distributed in N‐CNFs result in the improvement of electrical conductivity, increasing of BET surface area (142.82 m² g^?1), and high porosity. The as‐synthesized 3D free‐standing N‐CNFs membrane was applied as the current collector and binder free containing Li₂S₆ catholyte for lithium‐sulfur batteries. As a novel composite cathode, the free‐standing N‐CNFs/Li₂S₆ membrane shows more stable electrochemical behavior than the CNFs/Li₂S₆ membrane, exhibiting a high first‐cycle discharge specific capacity of 1175 mAh g^?1at 0.1 C and keeping discharge specific capacity of 702 mAh g^?1 at higher rate. More importantly, as the sulfur mass in cathodes was increased at 7.11 mg, the N‐CNFs/Li₂S₆ membrane delivered 467 mAh g^?1after 150 cycles at 0.2 C. The excellent electrochemical properties of N‐CNFs/Li₂S₆ membrane can be ascribed to synergistic effects of high porosity and nitrogen‐doping in N‐CNFs from carbonized ZIF‐8, illustrating collective effects of physisorption and chemisorption for lithium polysulfides in discharge‐charge processes.     

Niobium carbide/reduced graphene oxide hybrid porous aerogel as high capacity and long‐life anode material for Li‐ion batteries

Two‐dimensional material MXenes owing to their hydrophilic nature, surface termination, and high conductivity can be used in the energy storage device as an anode material. However, poor ion transfer and less available intercalating sites due to self‐stacking of MXene sheets prevent comprehensive utilization of their electrochemical properties. To resolve this problem, a facile method is introduced in this paper to disperse MXene sheets onto reduced graphene oxide sheets to form a porous structure by enhancing electrostatic interactions between two components, which can facilitate ion movement and provide access of ions to more intercalating sites. This hybrid material delivered a capacity of 357 mAh g^?1 at 0.05 A g^?1 as anode in case of lithium‐ion batteries. Furthermore, the hybrid material showed exceptional stability even after 1000 cycles at 1 A g^?1. Current work offers an easy approach for the synthesis of high‐performance niobium carbide‐based hybrid energy storage materials.     

β‐molybdenum carbide/carbon nanofibers as a shuttle inhibitor for lithium‐sulfur battery with high sulfur loading

We report the synthesis of β‐molybdenum carbide/carbon nanofibers (β‐Mo₂C/CNFs) by electrospinning and annealing process, when exploited as an interlayer in Li‐S batteries, demonstrating significantly improved electrochemical behaviors. The synthesized β‐Mo₂C/CNFs with 3D network structure and high surface area are not only conducive to ion transport and electrolyte penetration but also effectively intercept the shuttle of lithium polysulfide by polar surface interaction. Moreover, the reaction kinetics of the batteries enhanced is due to the presence of β‐Mo₂C, promoting the solid‐state polysulfide conversion reaction in the charge‐discharge process. Compared with the batteries with CNF interlayer and without interlayer, the batteries using a β‐Mo₂C/CNFs interlayer with a sulfur loading of 4.2 mg cm^‐2 delivered excellent electrochemical performance because of a facile redox reaction during cycling. The discharge capacity at the first cycle at 0.7 mA cm^?2 was 1360 mAh g^?1, maintaining a specific capacity of 974 mAh g^?1 after 160 cycles. Furthermore, it showed a high‐rate capacity of 700 mAh g^?1 at 14 mA cm^?2. This work demonstrates the β‐Mo₂C/CNFs as a promising interlayer to exploit Li‐S battery commercialization.     

A novel high specific capacity lithium‐ion capacitor battery with Li+‐doped Ni0.64Al0.64Mn0.56O2 prepared by coprecipitation method as cathode active material

Lithium‐ion capacitor battery is a late‐model energy storage system. It can combine the lithium‐ion battery with the capacitor to ensure that it has a high specific capacity and excellent large‐current discharge performance. In this paper, a novel Li⁺‐doped Ni_0.64Mn_0.64Al_0.56O₂ is synthesized by coprecipitation method and as a capacitor active material with commercialized LiNi_1/3Co_1/3Mn_1/3O₂ in different proportions forms the cathode of the lithium‐ion capacitor batteries. By analyzing the results of physical property characterization, when the mass ratio is 7:3, the crystal size of cathode material is less than 2 μm with uniform porous distribution. And, through electrochemical tests, the cathode has the greatest excellent reversibility, the lowest‐charge resistance, and the fastest‐lithium‐ion diffusion rate. Specific capacity can reach 196.34 mAh g^?1 at 0.5°C and, even at 5°C current density, it also can be 67.63 mAh g^‐1. After 110 times charge and discharge cycles, capacity retention of this cathode material at 5°C still can be over 85%.     

Nanosized Li4Ti5O12/graphene hybrid materials with low polarization for high rate lithium ion batteries

We report a simple strategy to prepare a hybrid of lithium titanate (Li₄Ti₅O₁₂, LTO) nanoparticles well-dispersed on electrical conductive graphene nanosheets as an anode material for high rate lithium ion batteries. Lithium ion transport is facilitated by making pure phase Li₄Ti₅O₁₂ particles in a nanosize to shorten the ion transport path. Electron transport is improved by forming a conductive graphene network throughout the insulating Li₄Ti₅O₁₂ nanoparticles. The charge transfer resistance at the particle/electrolyte interface is reduced from 53.9 Ω to 36.2 Ω and the peak currents measured by a cyclic voltammogram are increased at each scan rate. The difference between charge and discharge plateau potentials becomes much smaller at all discharge rates because of lowered polarization. With 5 wt.% graphene, the hybrid materials deliver a specific capacity of 122 mAh g⁻¹ even at a very high charge/discharge rate of 30 C and exhibit an excellent cycling performance, with the first discharge capacity of 132.2 mAh g⁻¹ and less than 6% discharge capacity loss over 300 cycles at 20 C. The outstanding electrochemical performance and acceptable initial columbic efficiency of the nano-Li₄Ti₅O₁₂/graphene hybrid with 5 wt.% graphene make it a promising anode material for high rate lithium ion batteries.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

Facile synthesis of three‐dimensional graphene networks by magnetron sputtering for supercapacitor electrode

Three‐dimensional (3D) graphene network deposition on Ni foam without any conductive agents and polymer binders was successfully synthesized by radio frequency magnetron sputtering at low temperature. The direct and close contact between graphene and Ni foam is beneficial to the enhanced conductivity of the electrode, as well as the improvement of ion diffusion/transport into the electrode. As a result, the 3D graphene network deposition on Ni foam electrode delivered a high specific capacitance of 122.0 F g⁻¹ at 1.0 A g⁻¹ and excellent cycle stability with capacitance retention of 99.0% after 1000 charge–discharge cycles. The work shows a new way to facile synthesis of 3D graphene network for various applications in the future. Copyright © 2016 John Wiley & Sons, Ltd.     

Fabrication of ultrafine Gd2O3 nanoparticles/carbon aerogel composite as immobilization host for cathode for lithium‐sulfur batteries

Carbon aerogel (CA), possessing abundant pore structures and excellent electrical conductivity, have been utilized as conductive sulfur hosts for lithium‐sulfur (Li‐S) batteries. However, a serious shuttle effect resulted from polysulfide ions has not been effectively suppressed yet due to the weak absorption nature of CA, resulting in rapid decay of capacity as the cycle number increases. Herein, ultrafine (~3 nm) gadolinium oxide (Gd₂O₃) nanoparticles (with upper redox potential of ~ 1.58 V versus Li⁺/Li) are uniformly in‐situ integrated with CA through directly sol‐gel polymerization and high‐temperature carbonization. The Gd₂O₃ modified CA composites (named as Gdx‐CA, where x means molar ratio of Gd₂O₃ nanoparticles to carbon) are incorporated with S. Then, the products (S/Gdx‐CA) are acted as sulfur host materials for Li‐S batteries. The results demonstrate that adding ultrafine Gd₂O₃ nanoparticles can dramatically improve the electrochemical properties of the composite cathodes. The S/Gd2‐CA electrode (loading with 58.9 wt% of S) possesses the best electrochemical properties, including a high initial capacity of 1210 mAh g^?1 and a relatively high capacity of 555 mAh g^?1 after 50 cycles at 0.1 C. It is noteworthy that the performance of long‐term cycle (350 cycles) for the S/Gd2‐CA (317 mAh g^?1 after 100 cycles and 233 mAh g^?1 after 350 cycles at 1 C) is improved significantly than that of S/CA (150 mAh g^?1 after 150 cycles at 1 C). Overall, the enhancement of electrochemical performances can be due to the strong polar nature of the ultrafine Gd₂O₃ nanoparticles, which provide strong adsorption sites to immobilize S and polysulfide. Furthermore, the Gd₂O₃ nanoparticles present a catalytic effect. Our research suggests that adding Gd₂O₃ nanoparticles into S/CA composite cathode is an effective and novelty method for improving the electrochemical performances of Li‐S batteries.     

Nitrogen/sulfur co-doped disordered porous biocarbon as high performance anode materials of lithium/sodium ion batteries

Nitrogen/sulfur co-doped disordered porous biocarbon was facilely synthesized and applied as anode materials for lithium/sodium ion batteries. Benefiting from high nitrogen (3.38 wt%) and sulfur (9.75 wt%) doping, NS_1-1 as anode materials showed a high reversible capacity of 1010.4 mA h g⁻¹ at 0.1 A g⁻¹ in lithium ion batteries. In addition, it also exhibited excellent cycling stability, which can maintain at 412 mAh g^-1 after 1000 cycles at 5 A g⁻¹. As anode materials of sodium ion batteries, NS_1-1 can still reach 745.2 mA h g⁻¹ at 100 mAg^-1 after 100 cycles. At a high current density (5 A g^-1), the reversible capacity is 272.5 mA h g⁻¹ after 1000 cycles, which exhibits excellent electrochemical performance and cycle stability. The preeminent electrochemical performance can be attributed to three effects: (1) the high level of sulfur and nitrogen; (2) the synergic effect of dual-doping heteroatoms; (3) the large quantity of edge defects and abundant micropores and mesopores, providing extra Li/Na storage regions. This disordered porous biocarbon co-doped with nitrogen/sulfur exhibits unique features, which is very suitable for anode materials of lithium/sodium ion batteries.     

Improving lithium‐sulfur battery performance with lignin reinforced MWCNT protection layer

Multi‐walled carbon nanotube (MWCNT) protection layers have previously been used to trap polysulfides and suppress the shuttle effect in lithium sulfur (Li‐S) batteries, leading to significant performance improvement. While the MWCNT is inherently highly conductive and mechanically strong, the cost can be significant and in turn hampered wider application of MWCNT protection layers. Here, we employed lignin, a byproduct during high‐quality bleached paper manufacturing, to replace a portion of MWCNT in the protection layer to reduce cost and enhance surface properties of pristine MWCNT protection layers. We found that the protection layer with 25 wt% lignin leads to the best overall electrochemical performance of Li‐S batteries during charging/discharging at 0.5°C and 1C rate (1C = 1,675 mA g^?1) among various weight‐ratios of lignin/MWCNT, and a low decay rate (0.20% per cycle) and high initial capacity (1342 mA g^?1 and 1437 mA g^?1 for 1C and 0.5C, respectively) are demonstrated. Besides, Li‐S cells with 25 wt% lignin/MWCNT composite protection layer also exhibited great rate capability, of which the specific capacities at 0.1C, 0.5C, 1C, and 2C were 1150, 913, 824, and 637 mAh g^?1, respectively. The enhanced electrochemical stability and performance of Li‐S batteries can be attributed to strengthened polysulfide trapping and improved lithium ion transport with lignin reinforced MWCNT protection layers. We showcased an economic approach to extend cycle life and improve rate capability of Li‐S batteries.     

High‐performance solid PEO/PPC/LLTO‐nanowires polymer composite electrolyte for solid‐state lithium battery

Solid polymer composite electrolyte (SPCE) with good safety, easy processability, and high ionic conductivity was a promising solution to achieve the development of advanced solid‐state lithium battery. Herein, through electrospinning and subsequent calcination, the Li_0.33La_0.557TiO₃ nanowires (LLTO‐NWs) with high ionic conductivity were synthesized. They were utilized to prepare polymer composite electrolytes which were composed of poly (ethylene oxide) (PEO), poly (propylene carbonate) (PPC), lithium bis (fluorosulfonyl)imide (LiTFSI), and LLTO‐NWs. Their structures, thermal properties, ionic conductivities, ion transference number, electrochemical stability window, as well as their compatibility with lithium metal, were studied. The results displayed that the maximum ionic conductivities of SPCE containing 8 wt.% LLTO‐NWs were 5.66 × 10^?5 S cm^?1 and 4.72 × 10^?4 S cm^?1 at room temperature and 60°C, respectively. The solid‐state LiFePO₄/Li cells assembled with this novel SPCE exhibited an initial reversible discharge capacity of 135 mAh g^?1 and good cycling stability at a charge/discharge current density of 0.5 C at 60°C.     

Flexible supercapacitor based on three‐dimensional cellulose/graphite/polyaniline composite

Fast charge‐discharge rate and high areal capacitance, along with high mechanically stability, are the pre‐requisites for flexible supercapacitors to power flexible electronic devices. In this paper, we have used three‐dimensional polyacrylonitrile graphite foam as flexible current collector for electro‐deposition of polyaniline (PANI) nanowires. The graphite foam with PANI was then used to fabricate symmetric supercapacitor. The fabricated supercapacitor in the three‐electrode system shows a high specific capacitance (C_sp) of 357 F.g^?1 and areal capacitance (C_areal) of 7142 mF.cm^?2 in 1 M H₂SO₄ at current density of 80 mA.cm^?2, while using two‐electrode system, it shows C_sp of 256 F.g^?1 and C_areal of 5120 mF.cm^?2 in 1 M H₂SO₄ at current density of 100 mA.cm^?2. The current density of 100 mA.cm^?2 is up to 10 folds higher than reported current densities of many PANI‐based supercapacitors. The high capacitance can be attributed to the spongy network of PANI‐NWs on three‐dimensional graphite surface which provides an easy path for electrolyte ions in active electrode materials. The developed supercapacitor shows specific energy of 64.8 Whkg^?1 and a specific power of 6.1 kWkg^?1 with a marginally decrease of 1.6% in C_sp after 1000^th cycles, along with coulombic efficiency retention of 87% in polyvinyl alcohol/H₂SO₄ gel electrolyte. This flexible supercapacitor exhibits great potential for energy storage application.     

Enhanced performance of alpha‐Fe2O3 nanoparticles with optimized graphene coated layer as anodes for lithium‐ion batteries

A series of different α‐Fe₂O₃ nanoparticles composites containing different amounts of graphene coatings have been successfully prepared using a simple electrostatic self‐assembly (ESA) method. The structure and electrochemical properties of these α‐Fe₂O₃@graphene composites have been investigated. The α‐Fe₂O₃ nanoparticles composite containing 40 wt% graphene coating exhibits the highest specific capacity (385 mAh g^?1) under 1000 mA g^?1, resulting in superior cycle stability with no downward trend after 500 cycles. These results demonstrate that graphene coatings can be used to enhance the electrochemical properties and morphological stability of α‐Fe₂O₃ nanoparticles as anodic materials for high performance lithium‐ion batteries (LIBs). The low‐energy self‐assembly method employed in the paper has good potential for the broad‐scale preparation of other graphene‐modified materials because of its simplicity and the relatively low temperature conditions.     

Synergistic effect of sulfur on electrochemical performances of carbon‐coated vanadium pentoxide cathode materials with polyvinyl alcohol as carbon source for lithium‐ion batteries

Vanadium pentoxide (V₂O₅) is a common cathode material for lithium‐ion battery, but its low electronic and ionic conductivity seriously affect its electrochemical performances. In this paper, a type of carbon‐coated V₂O₅ and S composite cathode material with PVA as the carbon source is utilized to lithium‐ion batteries. X‐ray diffraction and Raman test results illustrate that sulfur can make the V₂O₅ lose part of oxygen atoms and become nonstoichiometric vanadium oxide (V₂O_5‐x). Electrochemical test results show that sulfur can provide a considerable proportion of the specific capacity of the whole cathode. This illustrates that the synergistic effect of sulfur can optimize the structure of vanadium pentoxide in order to increase more electron transfer channels, and at the same time, it also can provide additional specific capacity for the whole cathode. When the ratio of V₂O₅ and sulfur is 1:3, the discharge specific capacity can reach 923.02, 688.37, and 592.70 mAh g^?1 at 80, 160, and 320‐mA g^?1 current density, respectively, and after 100 times charge and discharge cycles at 320‐mA g^?1 current density, the capacity retention rate can achieve to more than 60%.     

Magnetic tubular carbon nanofibers as anode electrodes for high‐performance lithium‐ion batteries

Novel magnetic tubular carbon nanofibers (MTCFs) are prepared through the combination technique of hypercrosslinking, control extraction, and carbonization. The diameter of MTCFs is mainly concentrated between 90 and 120 nm, and the average tube diameter is about 30 nm. A trace amount of Fe₃O₄ exists inside the MTCFs with a particle size of 3 nm, which is formed by in situ conversion of the catalyst (FeCl₃) for the hypercrosslinking reaction. The MTCFs with high surface area (448.74 m² g^?1) and porous wall are used as anode material for lithium‐ion batteries. The electrochemical properties of MTCFs are compared, and tubular carbon nanofibers (TCFs) prepared by the complete extraction. Electrochemical analysis shows that the introduction of Fe₃O₄ nanoparticles makes MTCFs have higher reversible capacity and better rate performance. MTCFs exhibit high reversible specific capacity of 1011.7 mAh g^?1 after 150 cycles at current density of 100 mA g^?1. Even at high current density of 3000 mA g^?1, a remarkable reversible capacity of 270.0 mAh g^?1 is still delivered. Thus, the novel MTCFs show potential application value in anode material for high‐performance lithium‐ion battery.     

Hierarchical Zn1.67Mn1.33O4/graphene nanoaggregates as new anode material for lithium‐ion batteries

Cubic spinel type Zn_1.67Mn_1.33O₄ porous sub‐micro spheres were synthesized by the calcination of solvothermally prepared Zn_xMn_1 ? xCO₃ precursor powders and evaluated as new anode materials for Li‐ion batteries for the first time. Each sphere exhibited aggregated morphology, constructed entirely from nanoparticles with a primary particle size of 11 nm. Electrochemical investigations and ex‐situ transmission electron microscopy analyses revealed that the reaction mechanism of obtained Zn_1.67Mn_1.33O₄ nanoaggregates is the combined conversion and alloying reaction, similar to that of ZnMn₂O₄ systems. In favor of the uniform porous sphere structure, these resulting Zn_1.67Mn_1.33O₄ nanoaggregates enabled the mitigation of volume change upon cycling. In addition, graphene composites with Zn_1.67Mn_1.33O₄ nanoaggregates were fabricated to improve electrical conductivity, simply by adding graphenes during solvothermal reaction for the formation of Zn_xMn_1 ? xCO₃ precursors. Zn_1.67Mn_1.33O₄/graphene composites showed a capacity of 670 mA h g^?1 higher than that of pure Zn_1.67Mn_1.33O₄ (518 mA h g^?1) after 200 cycle at a current density of 100 mA g^?1.     

Surface modification of LiNi0.5Co0.2Mn0.3O2 cathode materials with Li2O‐B2O3‐LiBr for lithium‐ion batteries

LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode material suffers from phase transformation and electrochemical performance degradation as its main drawbacks, which are strongly dependent on the surface state of NCM523. Herein, an effective surface modification approach was demonstrated; namely, the fast lithium‐ion conductor (Li₂O‐B₂O₃‐LiBr) was coated on NCM523. The Li₂O‐B₂O₃‐LiBr coating layer as a protecting shell can prevent NCM523 particles from corrosion by the acidic electrolyte, leading to a superior discharge capacity, rate capability, and cycling stability. At room temperature, the Li₂O‐B₂O₃‐LiBr–coated NCM523 exhibited an excellent capacity retention of 87.7% after 100 cycles at the rate of 1 C, which is remarkably better than that (29.8%) without the uncoated layer. Furthermore, the coating layer also increased the discharge capacity of NCM523 cathode material from 68.7 to 117.0 mAh g^?1 at 5 C. Those can be attributed to the reduction in the electrode polarization and improvement in the electrode conductivity, which was supported by electrochemical impedance spectroscopy and cyclic voltammetry measurements.     

A novel titania nanorods‐filled composite solid electrolyte with improved room temperature performance for solid‐state Li‐ion battery

Solid‐state batteries (SSBs) with room temperature (RT) performances had been one of the most promising technologies for energy storage. To achieve a chemical stable and high ionic conductive solid electrolyte, herein, a titania (TiO₂) (B) nanorods‐filled poly(propylene carbonate) (PPC)‐based organic/inorganic composite solid electrolyte (CSE) was prepared for the first time. It was found that by using TiO₂(B) nanorods, the ionic conductivity of the CSE membrane could be improved to 1.52 × 10^?4 S/cm, the electrochemical stable window was more than 4.6 V, and the tensile strength reaches 27 MPa with a strain less than 6%. The CSE was applied for SSB and showed excellent room temperature electrochemical performances. At 25°C, the LiFePO₄/CSE/Li SSB with 3%TiO₂‐filled CSE had the first cycle specific discharge capacity of 162 mAh/g with a capacity retention of 93% after 100 cycles at 0.3C. While the NCM622/CSE/Li SSB with 3%TiO₂‐filled CSE had the first specific discharge capacity of 165 mAh/g with a capacity retention of 88% after 100 cycles at 0.3C. The enhancement effect of TiO₂(B) nanorods could be ascribed that the rod‐like fillers provide more continuous Li‐ion transport path compared with nano particles, and the surface porosity and composition of TiO₂(B) nanorods could also improve the interfacial contact and Lewis acid‐base reaction sites between polymer and fillers. The TiO₂(B) nanorods‐filled CSE with high chemical stability, potential window, and ionic conductivity was promising to meet the requirements of SSBs.     

Sulfur encapsulated in nitrogen-doped graphene aerogel as a cathode material for high performance lithium-sulfur batteries

Lithium-sulfur batteries are considered to be an ideal high-performance rechargeable lithium battery. However, some problems have seriously hindered the practical application of lithium-sulfur batteries. A simple one-step hydrothermal method has been applied to design nitrogen-doped graphene aerogel (N-GA) with three different nitrogen sources. Subsequently, sulfur was encapsulated in N-GA by chemical deposition method to synthesize sulfur encapsulated in N-GA (N-GA/S) composites. Among them, the N-GA1/S composite with sulfur content reaching 75.5 wt% has a discharge specific capacity of 723.9 mAh g^?1 after 100 cycles at 0.7 C, and the capacity retention rate is up to 87.4% while the coulombic efficiency still remains 98%. The outstanding electrochemical performance is owing to the good coating of sulfur by nitrogen-doped graphene aerogel, the improvement of the conductivity of the graphene skeleton by nitrogen doping, and the strong adsorption capacity of the doped nitrogen atom to lithium polysulfide. The graphene skeleton also helps to reduce the volume effect while charging and discharging. Furthermore, the proportion of pyridinic-N in N-GA1/S composites is higher than that in the two other composites, and it has a better adsorption capacity for lithium polysulfide.