Plane Double-Layer Structure of AC@S Cathode Improves Electrochemical Performance for Lithium-Sulfur Battery

Due to the high theoretical specific capacity of lithium-sulfur batteries, it is considered the most promising electrochemical energy storage device for the next generation. However, the development of lithium-sulfur battery has been restricted by its low cycle efficiency and low capacity. We present a Plane double-layer structure of AC@S cathode to improve the electrochemical performance of lithium-sulfur batteries. The battery with this cathode showed good electrochemical performance. The initial discharge capacity of the battery with the structure of AC@S cathode could reach 1,166 mAhg−1 at 0.1 C. After 200 cycles, it still remains a reversible capacity of 793 mAh g−1 with a low fading rate of 0.16% per cycle. Furthermore, the batteries could hold a discharge capacity of 620 mAh g−1 after 200 cycles at a typical 0.5 C rate. The improvement of electrochemical performance is attributed to that the polysulfide produced during charge/discharge can be better concentrated in the cathode by the planar double-layer structure, thus reducing the loss of sulfur

Graphene/Sulfur@Graphene Composite Structure Material for a Lithium-Sulfur Battery Cathode

Graphene/sulfur@graphene composite structure as a cathode material is synthesized with a facile method. Graphene can provide a more efficient conductive network for sulfur and improve the coulombic efficiency of the battery. On the other hand, it may also show the anchoring effect on sulfur, which reduces the loss of sulfur and improves the cycling performance of the battery. Due to the unique structure, the initial discharge capacity of a battery assembled with this structure could reach 1036 mAh g−1 at 0.1 C, and its reversible capacity of 619 mAh g−1 was retained after 200 cycles with a low fading rate of 0.2% per cycle. The battery could hold a discharge capacity of 501 mAh g−1 after 200 cycles at 0.5 C. Thus, the electrochemical performance improved because of the reduction of sulfur loss through polysulfide accumulation at the cathode

Effect of various nitrogen flow ratios on the optical properties of (Hf:N)-DLC films prepared by reactive magnetron sputtering

Hf and N co-doped diamond-like carbon [(Hf:N)-DLC] films were deposited on 316L stainless steel and glass substrates through reactive magnetron sputtering of hafnium and carbon targets at various nitrogen flow ratios (R=N2/[N2+CH4+Ar]). The effects of chemical composition and crystal structure on the optical properties of the (Hf:N)-DLC films were studied. The obtained films consist of uniform HfN nanocrystallines embedded into the DLC matrix. The size of the graphite clusters with sp2 bonds (La) and the ID/IG ratio increase to 2.47 nm and 3.37, respectively, with increasing R. The optical band gap of the films decreases from 2.01 eV to 1.84 eV with increasing R. This finding is consistent with the trends of structural transformations and could be related to the increase in the density of π-bonds due to nitrogen incorporation. This paper reports the influence of nitrogen flow ratio on the correlation among the chemical composition, crystal structure, and optical properties of (Hf:N)-DLC films

High-Performance Lithium-Sulfur Batteries With an IPA/AC Modified Separator

To inhibit the polysulfide-diffusion in lithium sulfur (Li-S) batteries and improve the electrochemical properties, the commercial polypropylene (PP) was decorated by an active carbon (AC) coating with lots of electronegative oxygenic functional group of –OH. Owing to the strong adsorption of AC and the electrostatic repulsion between the –OH and negatively charged polysulfide ions, the Li-S batteries demonstrated a high initial discharge capacity of 1,656 mAh g−1 (approximately 99% utilization of sulfur) and the capacity can still remain at 830 mAh g−1 after 100 cycles at 0.2 C. Moreover, when the rate was increased to 1 C, the batteries could also possess a discharge capacity of 1,143 mAh g−1. The encouraging cycling stability make clear that this facile approach can successfully restrain the shuttle effect of polysulfides and make further progress to the practical application of Li-S batteries

Coordination Supramolecular Network Synergized with Reduced Graphene Oxide Accelerating Redox Kinetics of Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have an ultrahigh specific capacity and low budget. However, their practical application is impeded by the critical issue of sluggish kinetics as well as polysulfide shuttling. Coordination Supramolecular Networks (CSNs) exhibit an excellent charge transport capability and structural dynamic reversibility via their weak bond associations such as hydrogen bonding, π–π stacking, and so on, which provide the possibility to solve the problems existing in Li–S batteries. Herein, we demonstrate the preparation of a 3D structure composite based on Ni-PDA (PDA = pyridine-2, 3-dicarboxylate) CSN with reduced graphene oxide (rGO). FT-IR, XPS, DFT, and electrochemical tests indicate that the Ni-PDA has been introduced into the cathode. The strong affinity of Ni-PDA to polysulfides effectively suppresses their dissolution and diffusion into the electrolyte; meanwhile, the π–π interaction of Ni-PDA with rGO promoted the charge transmission inside the cathode. The synergy of the interactions leads to excellent cycling performance and conversion kinetics in Li–S batteries. The S@Ni-PDA@rGO cell shows a discharge capacity of 1063 mAh g–1 under 0.2 C and obtains a high discharge capacity of 864 mAh g–1 after 100 cycles under 0.5 C with an excellent capacity retention ratio of 100%. This material engineering method can potentially be expanded to other CSN systems, paving an avenue in constructing more efficient and reliable Li–S batteries