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.     

Freestanding graphitic carbon nitride-based carbon nanotubes hybrid membrane as electrode for lithium/polysulfides batteries

Lithium sulfur batteries have drawled worldwide attention in recent years, which benefit of its high-density energetic, low cost, and environmental benignity. Nevertheless, the shuttle effect of polysulfides and resulting self-discharge lead to capacity fade loss and poor electrochemical performance. Herein, graphitic-carbon nitride/carbon nanotubes (g-C₃N₄/CNTs) hybrid membrane is fabricated by the flow-direct vacuum filtration process. The as-prepared 3-D freestanding g-C₃N₄/CNTs membrane employed as positive current collector containing Li₂S₆ catholyte solution for lithium/polysulfides batteries. The fabricated g-C₃N₄/CNTs provide a physical barriers and chemisorption resist polysulfide shuttling. Moreover, the conductive network constructed by CNTs can empower sulfur to be evenly distributed in the cathode and accelerates electron transport. Thus, to further prove the cooperative effect of g-C₃N₄ and CNTs, the freestanding g-C₃N₄/CNTs/Li₂S₆ electrode exhibits more stable electrochemical performance than CNTs/Li₂S₆ electrode, deliver the first discharge capacity of 876 mAh g⁻¹ at 0.5 C and maintained at 633 mAh g⁻¹ after 300 cycles. The sulfur mass in electrode was increased to 7.11 mg, and the g-C₃N₄/CNTs/Li₂S₆ electrode also possess a high capacity retention of 75.5%. Meanwhile, g-C₃N₄ modified CNTs can not only trap polysulfides by strong adsorption but also effectively inhibit the self-discharge behavior of lithium/polysulfides batteries. As a consequence, the g-C₃N₄/CNTs composites for lithium/polysulfides batteries are indicating an excellent electrochemical stability with a long-term storage without obvious capacity degradation.     

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.     

Preparation and electrochemical properties of lithium–sulfur polymer batteries

The lithium/sulfur (Li–S) batteries consist of a composite cathode, a polymer electrolyte, and a lithium anode. The composite cathode is made from elemental sulfur (or lithium sulfide), carbon black, PEO, LiClO₄, and acetonitrile. The polymer electrolyte is made of gel-type linear poly(ethylene oxide) (PEO) with tetra ethylene glycol dimethyl ether. Cells based on Li₂S or sulfur have open-circuit voltages of about 2.2 and 2.5 V, respectively. The former cell shows two reduction peaks and one oxidation peak. It is suggested that the first reduction peak is caused by the change from polysulfide to short lithium polysulfide, and the second reduction peak by the change from short lithium polysulfide to lithium sulfide (Li₂S, Li₂S₂). The cell based on sulfur has the same reduction mechanism as that of Li₂S, which is caused by the multi process (first and second reduction) of lithium polysulfide. On charge–discharge cycling, the first discharge has a higher capacity than subsequent discharges and the flat discharge voltage is about 2.0 V. As the current load is increased, the discharge capacity decreases. One reason for this fading capacity and low sulfur utilization is the aggregation of sulfur (or polysulfide) with cycling.     

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.     

Graphene–sulfur–Ni(OH)2 sandwich foam composites as free-standing cathodes for high-performance Li–S batteries

Lithium–sulfur (Li–S) batteries are considered as a next-generation energy storage solution thanks to the dramatic increase in their energy density and the accompanying low fabrication cost. Nonetheless, their practical applications have been hampered by critical challenges such as cycling instability, low sulfur utilisation and efficiency. Here, the interfacial growth of Ni(OH)₂-encapsulated sulfur nanoparticles in a reduced graphene oxide free-standing matrix as Li–S cathodes has been highlighted, along with a detailed application investigation of the sandwich foam structure in Li–S batteries. Compared to sulfur composites based solely on a graphene host (S@rGO), this composite foam cathode could provide significant improvements in specific capacity and long-cycle stability with the effective confinement and promoted conversion of lithium polysulfides. Moreover, the sandwich foam composite cathode exhibits a high specific capacity of 1189 mA h g⁻¹ (0.1 C), better rating performance (691 mA h g⁻¹ at 2 C) and remarkable cycling stability, retaining 81% of the initial capacity after 200 cycles of charge–discharge at 0.2 C. Furthermore, Ni(OH)₂ wrapping at the cathode–electrolyte interface offers vastly improved polysulfide shuttle suppression, which provides a new cathode encapsulation method for further developments of advanced Li–S cathodes.     

Effects of surface lithiated TiO2 nanorods on room-temperature properties of polymer solid electrolytes

Polymer solid electrolyte with high ionic conductivity at room-temperature is most likely to be widely used in solid-state lithium batteries. In this work, the novel surface lithiated TiO₂ nanorods were firstly used as ionic conductor in polymer solid electrolyte. The surface lithiated TiO₂ nanorods-filled polypropylene carbonate polymer composite solid electrolyte (CSE) has an uniform composite structure with a thickness of about 60 μm. The ionic conductivity at room-temperature is 1.21 × 10⁻⁴ S cm⁻¹ and the electrochemical stability window is up to 4.6 V (vs Li⁺/Li). The assembled NCM622/CSE/Li solid-state battery shows a stable cycle performance with a retention capacity of 120 mAh g⁻¹ after 200 cycles at the current density of 0.3 C and a high coulomb efficiency of 99%. Compared with TiO₂ particles, this novel surface lithiated TiO₂ nanorods can provide more continuous ion transport channels and more Lewis acid-base reactive sites, provide a novel way to enhance the lithium ion transport in polymer solid electrolyte.     

High capacity MgH2 composite electrodes for all-solid-state Li-ion battery operating at ambient temperature

MgH₂ with a theoretical capacity of 2036 mAh/g has been studied using LiBH₄ as solid electrolyte with remarkable results. However, LiBH₄ conductivity is reduced drastically from ~10^?3 to ~10^?8 Scm^?1 when operating at temperatures below ~117 °C, due to the crystal structural transition. This change in the conductivity limits the range of operating temperatures of the battery. In order to have all-solid-state lithium ion batteries operating at room temperature, some alternatives were explored in this work. In this study, different batteries compositions were tested for operating temperatures from 30 °C to 120 °C, using LiBH₄, 3LiBH₄·LiI and 80Li₂S–20P₂S₅ to find a workable configuration for all-solid-state lithium-ion battery with MgH₂ as the active material for the working electrode. The cell MgH₂/3LiBH₄·LiI/Acetylene Black carbon | 80Li₂S–20P₂S₅ | Li, shown the best performance with an initial capacity of 1570 mAh/g operating at 30 °C.     

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.     

A thermo-stable poly(propylene carbonate)-based composite separator for lithium-sulfur batteries under elevated temperatures

Lithium-sulfur (Li-S) batteries have a great potential for the future development of energy industry. However, the high-temperature performance of Li-S batteries is still facing great challenge due to the high flammability of the electrolyte, sulfur cathode as well as the separator. The separator modification is an effective method to improve the thermal stability of separator and the electrochemical performance of Li-S batteries under elevated temperatures. However, the reported methods of separator coating are too complicated to be applied in the industrial production. Here, a novel thermo-stable composite separator (M-Celgard-p), in which a layer of silicon dioxide-poly (propylene carbonate) based electrolyte (nano-SiO₂@PPC) with a high ionic-conductivity of 1.03 × 10⁻⁴ S cm⁻¹ is coated on the commercial Celgard-p separator, is prepared by using a simple dipping method. Compared to the Li-S battery assembled with Celgard-p separator, the M-Celgard-p separator combined with a sulfur/polyacrylonitrile (S/PAN) cathode can improve the electrochemical performance of Li-S batteries, especially their high-temperature stability. As a result, the (S/PAN)/M-Celgard-p/Li cell delivers a high specific capacity of 724.7 mAh g⁻¹ at 1.0 A g⁻¹ after 200 cycles and presents a good rate capability of 1408 mAh g⁻¹ at 1.0 A g⁻¹ and 1216 mAh g⁻¹ at 2.0 A g⁻¹. More importantly, the (S/PAN)/M-Celgard-p/Li cell can exhibit a capacity retention ratio of 69.4% after 200 cycles at 60°C. The M-Celgard-p separator with high Li-ion conductivity can not only block the “shuttle-effect” of polysulfides during cycling but also enhance the thermal stability under elevated temperatures. This work presents a simple dipping method to prepare composite separator with excellent thermal stability, which enhance the rate performance and cyclic stability of Li-S batteries under elevated temperatures. We believe this work can provide a new way to develop more reliable Li-S batteries for practical applications.     

Electrochemical performance of all-solid-state lithium secondary batteries improved by the coating of Li2O-TiO2 films on LiCoO2 electrode

All-solid-state lithium secondary batteries using LiCoO₂ particles coated with amorphous Li₂O-TiO₂ films as an active material and Li₂S-P₂S₅ glass-ceramics as a solid electrolyte were fabricated; the electrochemical performance of the batteries was investigated. The interfacial resistance between LiCoO₂ and solid electrolyte was decreased by the coating of Li₂O-TiO₂ films on LiCoO₂ particles. The rate capability of the batteries using the LiCoO₂ coated with Li₂Ti₂O₅ (Li₂O·2TiO₂) film was improved because of the decrease of the interfacial resistance of the batteries. The cycle performance of the all-solid-state batteries under a high cutoff voltage of 4.6 V vs. Li was highly improved by using LiCoO₂ coated with Li₂Ti₂O₅ film. The oxide coatings are effective in suppressing the resistance increase between LiCoO₂ and the solid electrolyte during cycling. The battery with the LiCoO₂ coated with Li₂Ti₂O₅ film showed a large initial discharge capacity of 130 mAh/g and good capacity retention without resistance increase after 50 cycles at the current density of 0.13 mA/cm².     

Lithium-ion rechargeable cells with polyacenic semiconductor (PAS) and LiCoO2 electrodes

Polyacenic semiconductor (PAS), heat-treated at 700°C, has a lithium intercalation capacity as high as 438 mAh g⁻¹ which is higher than the theoretical capacity of 372 mAh g⁻¹ for graphite. The electrochemical behaviour of PAS is examined by studying Li/PAS and Li/graphite cells. In a PAS or graphite anode, three reactions are distinguished: (i) reaction of lithium with the Teflon binder; (ii) decomposition of electrolyte, and (iii) intercalation of Li⁺ ions. Two laboratory cells with liquid organic electrolyte or polymer electrolyte and PAS as the anode demonstrate that PAS is a promising anode material for lithium-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.     

Improve redox activity and cycling stability of the lithium-sulfur batteries via in situ formation of a sponge-like separator modification layer

The electronic nonconductivity of S and shuttle effect of soluble polysulfides are two fundamental issues that limit the application of lithium-sulfur (Li-S) batteries. Regarding these issues, herein, a sponge-like Ketjen black (KB)-triphenylphosphine sulfide (TPS) multifunctional modification layer was proposed to coat the separator of the advanced Li-S batteries. The layer was formed by an in situ spontaneous reaction between triphenylphosphine (TPP) of the conventional KB-TPP layer and Li₂S₆ solution. This functional layer can ensure a high e⁻ and Li⁺ conductivity while inhibiting the diffusion of soluble polysulfides. As a result, the redox activity, rate capability, and cycling stability of the batteries are significantly enhanced. Comparing with the discharge capacities at 2C for the PE separator, introducing the KB-TPS functional layer was beneficial for the capacity retentions of the cells, since the capacity increased from 16.1% to 66.6% at the same C-rate. A capacity degeneration rate of 0.045% per cycle was obtained for the cell with an S area density of 3.6 mg cm⁻². This work is a step forward in the exploration of advanced Li-S batteries, being a valuable reference for the study of related systems.     

Improving electrochemical properties and structural stability of lithium manganese silicates as cathode materials for lithium ion batteries via introducing lithium excess

The serious capacity decay caused by structural amorphization is still a major issue for polyanion-type lithium manganese silicates (Li₂MnSiO₄) as cathode material for lithium ion batteries. In this work, a new strategy for alleviating the structural instability via the introduction of excess lithium into the host crystal lattice is provided. A comprehensive study demonstrates that the required energy for the extraction/insertion of lithium ions into host crystal lattice was decreased as a result of changed local environment of cations in the compound after the excess lithium occupancy in lattice. Importantly, it was found that Li-rich samples deliver higher reversible capacity and increased average potential than pristine sample, indicating the improved energy density of polyanion-type Li_{2 + 2x}Mn_{1 − x}SiO₄/C_. Additionally, the structure of Li2.2 sample was kept intact, while the Li2.0 sample was transformed to amorphous state at 200 mA h g⁻¹ during the initial charging process by controlling the charge cut-off potential. As expected, the introduction of a certain amount of excess lithium into Li₂MnSiO₄ is explored as a route to achieving increased capacity with more movable lithium, while maintaining its structural stability and cyclic stability.     

N-Doped graphene embellished with Co9S8 enable advanced sulfur cathode for high-performance lithium-sulfur batteries

Lithium-sulfur batteries have drawn widespread attention as favorable energy storage systems. However, the low conductivity of S gives rise to a poor specific capacity. Moreover, the shuttle effect of soluble lithium polysulfides (LiPS) causes a rapid performance deterioration in Li-S systems. Herein, Co₉S₈ implanted on N-doped graphene (Co₉S₈-NG) is proposed to support S in cathodes. The N-doped graphene substantially enhanced the electronic conductivity of the S-based cathode. Meanwhile, Co₉S₈ with a high polarity not only effectively immobilized the LiPS species through chemical binding but also considerably catalyzed the LiPS electrochemical conversion, ultimately suppressing its shuttle effect. As expect, the cathode with the Co₉S₈-NG composite demonstrated high specific capacities of 1051.5 and 564.6 mA h g⁻¹ at 0.2 and 2 C, respectively. Moreover, a satisfactory cycling stability was displayed at 1 C for 400 cycles, with an average capacity fading of 0.085% per cycle. Therefore, Co₉S₈-NG was exhibited to improve the cathode performance in numerous aspects and can be regarded as a potential host material to improve the overall performance of Li-S batteries.     

All solid state lithium ion rechargeable batteries using NASICON structured electrolyte

Abstract

NASICON (Sodium super ionic conductor) structured Li_1·5Al_0·5Ge_1·5(PO₄)₃ (LAGP) solid electrolyte is synthesized through a solid state reaction. The total conductivity of the LAGP electrolyte is 7×10^?5 S cm^?1 with a potential window larger than 6 V. All solid state lithium batteries are fabricated using LiMn₂O₄ as a cathode, LAGP as an electrolyte and lithium metal as an anode. The LiMn₂O₄/LAGP/Li cell can deliver a capacity of about 80 mAh g^?1 in the first discharge cycle and increases gradually with charge/discharge cycles, indicating that LAGP can be used as a promising electrolyte for lithium rechargeable batteries.     

Constructing light-weight polar boron-doped carbon nitride nanosheets with increased active sites and conductivity for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are highly attractive as one of the most promising energy storage systems owing to their superior theoretical capacity, low cost and environmental compatibility. Nevertheless, the low utilization of active materials and detrimental shuttle reactions severely inhibit the practical application of Li-S batteries. Herein, a lightweight 2D boron doped g-C₃N₄ nanosheets (BCN) with abundant active sites and increased conductivity prepared by a facile route is introduced onto commercial separators to achieve high performance Li-S batteries. The prepared BCN displays a 2D thin layer nanosheet structure with a thickness of ～2.5 nm. The boron doping not only can increase surface area and improve electrical conductivity, but also chemically anchor more polysulfides due to the formed B-N bond, which can effectively minimize the shuttling of polysulfides through the synergistic effect of physical yield and chemical confinement. As a result, the assembled Li-S batteries employing BCN separators with multifunction display large discharge capacity of 1197 mAh g⁻¹, high sulfur utilization and outstanding durability with a capacity decay rate of 0.09% per cycle at 1 C after 500 cycles, which are also supported by the density functional theory simulation. Additionally, the alleviated self-discharge behavior and good areal capacity (up to 6.4 mAh cm⁻²) at a high sulfur loading of the cell are also demonstrated. The exploration of BCN modified separator furnishes a viable way to construct high energy density and long lifespan Li-S batteries.     

Fabrication of CoFe/N-doped mesoporous carbon hybrids from Prussian blue analogous as high performance cathodes for lithium-sulfur batteries

CoFe/N-doped mesoporous carbon hybrids are synthesized by a simple pyrolysis of Prussian blue analogue (PBA) and melamine, in which the structure is rationally designed by controlling the weight ratio of PBA/melamine and annealing temperature. By applying the composite as the cathode material for lithium-sulfur batteries, it demonstrates outstanding electrochemical performances including a high reversible capacity (1315 mAh g⁻¹ at 0.2 C), excellent rate capability (724 and 496 mAh g⁻¹ at 2 and 5 C rates, respectively) and superior cycling stability (528 and 367 mAh g⁻¹ at 2 and 5C after 500 cycles, respectively). The synergetic effect of the mesoporous carbon matrix, uniform sized CoFe nanoparticles and N heteroatoms simultaneously contributes to the confinement of sulfur species. The presence of abundant mesopores and micropores can physically confine sulfur species. The formed CoFe-N_x moieties can not only improve the electronic conductivity of the as-prepared composites, but also offer highly effective active sites for chemical absorption and catalytic transformation of polysulfides to suppress any shuttle effect. In addition, the mesoporous structure can effectively alleviate the volume changes resulted from charge–discharge process. The strategy developed in this work proposes an alternative way to obtain N-doped mesoporous carbon matrix modified with CoFe nanoparticles for high performance cathode materials of lithium-sulfur batteries.     

Gallium (III) sulfide as an active material in lithium secondary batteries

In an attempt to identify an active material for use in lithium secondary batteries with high energy density, we investigated the electrochemical properties of gallium (III) sulfide (Ga₂S₃) at 30 °C. Ga₂S₃ shows two sloping plateaus in the potential range between 0.01 V and 2.0 V vs. (Li/Li⁺). The specific capacity of the Ga₂S₃ electrode in the first delithiation is ca. 920 mAh g⁻¹, which corresponds to 81% of the theoretical capacity (assuming a 10-electron reaction). The capacity in the 10th cycle is 63% of the initial capacity. Ex situ X-ray diffraction and X-ray absorption fine structure analyses revealed that the reaction of the Ga₂S₃ electrode proceeds in two steps: Ga₂S₃ + 6Li⁺ + 6e⁻ ? 2Ga + 3Li₂S and Ga + xLi⁺ + xe⁻ ? Li_xGa.