High performance cathode with sufficiently high areal sulfur loading is still a major challenge for practical Li/S batteries. Herein, we propose a 3D nanocarbon architecture with robust electrical ...“highway” network for high sulfur mass loading and efficient sulfur utilization. The structure is constructed by “welding” highly conductive nitrogen-doped graphene (NG) and nitrogen-doped carbon nanotubes (NCNT) together through in-situ polymeric crosslinking and nitrogen-doped carbon shell (NCS) formation. The highly sulfur-absorptive NCS provides strong physical and chemical confinements to sulfur and polysulfides, which is confirmed by in-situ Raman and electrochemical analysis. At a moderate sulfur loading, the NG-NCNT@NCS@S cathode exhibits a high initial discharge capacity of 1421mAhg−1, excellent rate performance of 750mAhg−1 at 2C and 465mAhg−1 at 5C, and a capacity fading rate as low as 0.037% per cycle at 2C for 1400 cycles. At high areal sulfur loading up to 10.2mgcm−2, the cathode retains a high areal capacity of 5.43mAhcm−2 after 150 cycles at a high current rate (1C). A large areal cathode (77 × 50mm2) with sulfur loading of 8.5mgcm−2 delivers a record-high capacity of 9.04mAhcm−2 at 0.1C, demonstrating its great potential for practical application in Li/S batteries.
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•Carbon nanotubes and graphene nanosheets are “welded” by N-doped carbon shells.•The 3D carbon network is highly conductive, robust, and flexible.•In-situ optical analysis shows the network is effective in trapping polysulfides.•A cathode of high sulfur loading can deliver high capacities event at high rates.
Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt Mg(THF)6AlCl42 was synthesized ...and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm−1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.
Simple but effective: A simple magnesium salt Mg(THF)6AlCl42 can be used as a magnesium electrolyte that possesses a highly reversible Mg cycling efficiency, good anodic stability, and good ionic conductivity. Mg/S batteries containing the electrolyte could be cycled over 20 cycles, thus indicating electrochemically reversible conversion of sulfur into MgS.
Non‐nucleophilic electrolytes that can reversibly plate/strip Mg are essential for realizing high‐performance rechargeable Mg/S batteries. In contrast to organometallic electrolytes, all‐inorganic ...electrolytes based on MgCl2‐AlCl3 complexes are more cost‐effective and hold better stability to air and moisture. A recently developed electrolyte that contains tetrahydrofuran solvated divalent Mg cation, Mg·6THFAlCl42, has exhibited decent compatibility with the sulfur cathode. However, it suffers a large overpotential and short cycle life, which hinders its applications in Mg/S batteries. Here, an efficient plating/stripping of Mg is realized successfully by using LiCl to dissolve MgCl2 from the electrolyte/electrode interface. As a result, the overpotential of Mg plating/stripping is remarkably reduced to 140/140 mV at a current density of 500 µA cm−2. Both experiments and density functional theory (DFT) calculations reveal that the LiCl‐assisted solubilization of MgCl2 facilitates the exposure of fresh surface on the Mg anode. Utilizing such an LiCl‐activation strategy, Mg/S full batteries with a significantly extended cycle life of over 500 cycles, as well as coulombic efficiency close to 100%, are achieved successfully. This work demonstrates the role of LiCl‐assisted interface activation on extending the cycle‐life Mg/S batteries with all‐inorganic electrolytes.
The electrolyte–electrode interface of an Mg anode could be passivated by the formation of low‐solubility species such as MgCl2. Here, it is found that an LiCl additive could effectively boost the interfacial property by forming soluble intermediate species such as Mg2(µ‐Cl)3·6THF+ and LiCl2·2THF−, which is critical to sustain a fresh Mg surface for Mg/S batteries with long cycle life.
Lithium/sulfur (Li/S) battery is a promising next-generation energy storage system owing to its high theoretical energy density. However, for practical use there remains some key problems to be ...solved, such as low active material utilization and rapid capacity fading, especially at high areal sulfur loadings. Here, we report a facile one-pot method to prepare porous three-dimensional nitrogen, sulfur-codoped graphene through hydrothermal reduction of graphene oxide with multi-ion mixture modulation. We show solid evidence that the results of multi-ion mixture modulation can not only improve the surface affinity of the nanocarbons to polysulfides, but also alter their assembling manner and render the resultant 3D network a more favorable pore morphology for accommodating and confining sulfur. It also had an excellent rate performance and cycling stability, showing an initial capacity of 1304 mA h g−1 at 0.05C, 613 mA h g−1 at 5C and maintaining a reversible capacity of 462 mA h g−1 after 1500 cycles at 2C with capacity fading as low as 0.028% per cycle. Moreover, a high areal capacity of 5.1 mA h cm−2 at 0.2C is achieved at an areal sulfur loading of 6.3 mg cm−2, which are the best values reported so far for dual-doped sulfur cathodes.
•3D porous NSG is synthesized under ammonia and sulfide ion modulation.•The surface chemistry and pore morphology of NSG is simultaneously optimized.•The S@NSG cathode exhibits long cycle life and high capacity.
A hybrid material of carbon coated Fe3O4 (Fe3O4@C) is synthesized by chemical vapor deposition method using Fe2O3 as starting material and acetylene as carbon source. The obtained material is Fe3O4 ...spheres of ∼400nm coated by thin carbon layer with a thickness of ∼10nm. As an anode material for lithium ion batteries, Fe3O4@C shows an improved electrochemical performance in the reversible capacity and cycling stability, together with excellent rate capability. The performance is much better than the results obtained from bare Fe2O3 and commercial Fe3O4 of the same size. In addition to the comparison of electrochemical impedance spectra of the Fe2O3, Fe3O4 and Fe3O4@C electrodes before and after 50 charge/discharge cycles, a surface contrast of the three electrodes before and after cycling is systematically investigated to explore the influence of carbon layer on the electrochemical performance of the Fe3O4 spheres.
Transition metal chalcogenides such as FeS
2
are promising electrode materials for energy storage. However, poor rate performance and low cycling stability hinder the practical application of FeS
2
...cathode in secondary batteries. In this study, highly pure pyrite FeS
2
nanocrystals (NCs) with octahedral shape and 200–300 nm size have been synthesized via a facile and environmentally benign approach based on a surfactant-free aqueous reaction. Combined with a compatible ether electrolyte, the prepared FeS
2
NCs, despite their dimension far beyond the quantum confined regime, could achieve high utilization and reversibility as a cathode active material due to the well-defined crystal structure and the uncapped rough surfaces. Furthermore, we find that the last charging voltage step of FeS
2
only contributes a minor capacity but caused severe capacity fading due to the formation of soluble polysulfides. By suppressing this step through setting a proper upper cut-off voltage, the cycle life of the Li/FeS
2
cell is dramatically improved. The Li/FeS
2
cell running over a voltage window of 1.0–2.4 V at 1C delivers an initial capacity of 486.1 mA h g
−1
, slightly lower than that running over 1.0–3.0 V (561.1 mA h g
−1
), but outperforms the latter substantially after 500 cycles (367 mA h g
−1
vs 315 mA h g
−1
), corresponding to a capacity decay rate as low as 0.048% per cycle. Our results provide a meaningful approach for the development of not only the advanced FeS
2
material for long-life rechargeable batteries, but also other transition metal chalcogenide nanomaterials for a variety of potential applications.
The light harvesting efficiency of an acceptor dye can be enhanced by judicious choice and/or design of donor materials in the Förster resonance energy transfer (FRET) based dye-sensitized solar ...cells (DSSCs). In this work, we explore graphene quantum dots (GQDs) as energy relay antennas for the high power conversion efficiency Ru-based N719 acceptor dyes. The absorption, emission, and time decay spectral results evidence the existence of the FRET, the radiative energy transfer (RET), and a synergistic interaction between GQDs and N719 dye. The FRET efficiency is measured to be 27%. The GQDs co-sensitized DSSC achieves an efficiency (ƞ) of 7.96% with a Jsc of 16.54 mAcm−2, which is 30% higher than that of a N719-based DSSC. GQDs also reduce the charge recombination, which results in an increased open-circuit voltage up to 770 mV. The incident photon-to-current conversion efficiency and UV–Vis absorption measurement reveal that the enhanced absorption of the GQDs antennas is responsible for the improved Jsc in the whole UV–Visible region, while the RET/FRET and the synergistic effect contribute to the significant increase of Jsc in the UV region.
•Graphene quantum dot acts as good energy donors for acceptor N719 dye.•Graphene quantum dot exhibits a weak molecular interaction with N719 dye.•Light absorption of N719 is increased via Förster resonance energy transfer.•The enhanced light absorption improves photocurrent density by 30%.•Cosensitization of graphene quantum dot improves charge collection efficiency.
Abstract
Non‐nucleophilic electrolytes that can reversibly plate/strip Mg are essential for realizing high‐performance rechargeable Mg/S batteries. In contrast to organometallic electrolytes, ...all‐inorganic electrolytes based on MgCl
2
‐AlCl
3
complexes are more cost‐effective and hold better stability to air and moisture. A recently developed electrolyte that contains tetrahydrofuran solvated divalent Mg cation, Mg·6THFAlCl
4
2
, has exhibited decent compatibility with the sulfur cathode. However, it suffers a large overpotential and short cycle life, which hinders its applications in Mg/S batteries. Here, an efficient plating/stripping of Mg is realized successfully by using LiCl to dissolve MgCl
2
from the electrolyte/electrode interface. As a result, the overpotential of Mg plating/stripping is remarkably reduced to 140/140 mV at a current density of 500 µA cm
−2
. Both experiments and density functional theory (DFT) calculations reveal that the LiCl‐assisted solubilization of MgCl
2
facilitates the exposure of fresh surface on the Mg anode. Utilizing such an LiCl‐activation strategy, Mg/S full batteries with a significantly extended cycle life of over 500 cycles, as well as coulombic efficiency close to 100%, are achieved successfully. This work demonstrates the role of LiCl‐assisted interface activation on extending the cycle‐life Mg/S batteries with all‐inorganic electrolytes.
Transition metal chalcogenides such as FeS.sub.2 are promising electrode materials for energy storage. However, poor rate performance and low cycling stability hinder the practical application of ...FeS.sub.2 cathode in secondary batteries. In this study, highly pure pyrite FeS.sub.2 nanocrystals (NCs) with octahedral shape and 200-300 nm size have been synthesized via a facile and environmentally benign approach based on a surfactant-free aqueous reaction. Combined with a compatible ether electrolyte, the prepared FeS.sub.2 NCs, despite their dimension far beyond the quantum confined regime, could achieve high utilization and reversibility as a cathode active material due to the well-defined crystal structure and the uncapped rough surfaces. Furthermore, we find that the last charging voltage step of FeS.sub.2 only contributes a minor capacity but caused severe capacity fading due to the formation of soluble polysulfides. By suppressing this step through setting a proper upper cut-off voltage, the cycle life of the Li/FeS.sub.2 cell is dramatically improved. The Li/FeS.sub.2 cell running over a voltage window of 1.0-2.4 V at 1C delivers an initial capacity of 486.1 mA h g.sup.-1, slightly lower than that running over 1.0-3.0 V (561.1 mA h g.sup.-1), but outperforms the latter substantially after 500 cycles (367 mA h g.sup.-1 vs 315 mA h g.sup.-1), corresponding to a capacity decay rate as low as 0.048% per cycle. Our results provide a meaningful approach for the development of not only the advanced FeS.sub.2 material for long-life rechargeable batteries, but also other transition metal chalcogenide nanomaterials for a variety of potential applications.
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