Bifunctional Separator with Ultra-Lightweight MnO2 Coating for Highly Stable Lithium-Sulfur Batteries.

The severe shuttling behavior in the discharging-charging process largely hampers the commercialization of lithium-sulfur (Li-S) batteries. Herein, we design a bifunctional separator with an ultra-lightweight MnO2 coating to establish strong chemical adsorption barriers for shuttling effect alleviation. The double-sided polar MnO2 layers not only trap the lithium polysulfides through extraordinary chemical bonding but also ensure the uniform Li+ flux on the lithium anode and inhibit the side reaction, resulting in homogeneous plating and stripping to avoid corrosion of the Li anode. Consequently, the assembled Li-S battery with the MnO2-modified separator retains a capacity of 665 mA h g-1 at 1 C after 1000 cycles at the areal sulfur loading of 2.5 mg cm-2, corresponding to only 0.028% capacity decay per cycle. Notably, the areal loading of ultra-lightweight MnO2 coating is as low as 0.007 mg cm-2, facilitating the achievement of a high energy density of Li-S batteries. This work reveals that the polar metal oxide-modified separator can effectively inhibit the shuttle effect and protect the Li anode for high-performance Li-S batteries.

Phase Conversion Accelerating "Zn-Escape" Effect in ZnSe-CFs Heterostructure for High Performance Sodium-Ion Half/Full Batteries.

Sodium-ion batteries (SIBs) are considered as a promising large-scale energy storage system owing to the abundant and low-cost sodium resources. However, their practical application still needs to overcome some problems like slow redox kinetics and poor capacity retention rate. Here, a high-performance ZnSe/carbon fibers (ZnSe-CFs) anode is demonstrated with high electrons/Na+ transport efficiency for sodium-ion half/full batteries by engineering ZnSe/C heterostructure. The electrochemical behavior of the ZnSe-CFs heterostructure anode is deeply studied via in situ characterizations and theoretical calculations. Phase conversion is revealed to accelerate the "Zn-escape" effect for the formation of robust solid electrolyte interphase (SEI). This leads to the ZnSe-CFs delivering a superior rate performance of 206 mAh g-1 at 1500 mA g-1 for half battery and an initial discharge capacity of 197.4 mAh g-1 at a current density of 1 A g-1 for full battery. The work here heralds a promising strategy to synthesize advanced heterostructured anodes for SIBs, and provides the guidance for a better understanding of phase conversion anodes.

Adsorption-Catalysis-Conversion of Polysulfides in Sandwiched Ultrathin Ni(OH)2 -PANI for Stable Lithium-Sulfur Batteries.

Strong adsorption and catalysis for lithium polysulfides (LiPSs) are critical toward the electrochemical stability of Li-S batteries. Herein, a hollow sandwiched nanoparticle is put forward to enhance the adsorption-catalysis-conversion dynamic of sulfur species. The outer ultrathin Ni(OH)2 nanosheets not only confine LiPSs via both physical encapsulation and chemical adsorption, but also promote redox kinetics and accelerate the conversion of sulfur species, which is revealed by experiments and theoretical calculations. Meanwhile, the inner hollow polyaniline soft core provides a strong chemical bonding to LiPSs after vulcanization, which can chemically adsorpt LiPSs, and synergistically confine the shuttle effect. Moreover, the Ni(OH)2 nanosheets with a large specific area can enhance the wettability of electrolyte, and the flexible hollow sandwiched structure can accommodate the volume expansion, promoting sulfur utilization and structural stability. The obtained cathode exhibits excellent electrochemical performance with an initial discharge capacity of 1173 mAh g-1 and a small capacity decay of 0.08% per cycle even after 500 cycles at 0.2 C, among the best results of Ni(OH)2 -based materials for Li-S batteries. It is believed that the combination of adsorption-catalysis-conversion will shed a light on the development of cathode materials for stable Li-S batteries.

Gradient selenium-doping regulating interfacial charge transfer in zinc sulfide/carbon anode for stable lithium storage.

Metal sulfides have attracted much attentions as anode materials for lithium-ion batteries (LIBs) because of the high theoretical capacity. However, the poor electronic conductivity and large volume variation usually give rise to the rapid capacity decay and undesirable rate performance, severely hampering their practical application. Herein, a gradient selenium-doped hollow sandwich structured zinc sulfide/carbon (ZnS/C) composite (Se-HSZC) is designed and fabricated as long life-span and stable anode material for LIBs. The gradient Se-doping enhances the interfacial charge transfer in Se-HSZC, while the unique double carbon shell sandwich structure further greatly reduces the volume expansion and ensures the electron fast transportation. Consequently, the Se-HSZC anode presents outstanding rate capability (654 mAh g-1 at 2 A g-1) with remarkable reversible capacity (567 mAh g-1 after 1500 cycles at 4 A g-1) for the half battery. In particular, a reversible capacity of 457 mAh g-1 at 0.5 A g-1 is achieved after 50 cycles for the full battery with LiNi0.6Co0.2Mn0.2O2 as cathode. This work offers a promising design route of novel metal sulfides nanostructures for high performance LIBs.

Melamine-based polymer networks enabled N, O, S Co-doped defect-rich hierarchically porous carbon nanobelts for stable and long-cycle Li-ion and Li-Se batteries.

Li-Se battery is a promising energy storage candidate owing to its high theoretical volumetric capacity and safe operating condition. In this work, for the first time, we report using the whole organic Melamine-based porous polymer networks (MPNs) as a precursor to synthesize a N, O, S co-doped hierarchically porous carbon nanobelts (HPCNBs) for both Li-ion and Li-Se battery. The N, O, S co-doping resulting in the defect-rich HPCNBs provides fast transport channels for electrolyte, electrons and ions, but also effectively relieve volume change. When used for Li-ion battery, it exhibits an advanced lithium storage performance with a capacity of 345 mAh g-1 at 500 mA g-1 after 150 cycles and a superior rate capacity of 281 mAh g-1 even at 2000 mA g-1. Further density function theory calculations reveal that the carbon atoms adjacent to the doping sites are electron-rich and more effective to anchor active species in Li-Se battery. With the hierarchically porous channels and the strong dual physical-chemical confinement for Li2Se, the Se@ HPCNBs composite delivers an ultra-stable cycle performance even at 2 C after 1000 cycles. Our work here suggests that introduce of heteroatoms and defects in graphite-like anodes is an effective way to improve the electrochemical performance.

Molybdenum disulfide quantum dots directing zinc indium sulfide heterostructures for enhanced visible light hydrogen production.

Photocatalytic hydrogen (H2) production based on semiconductors is important to utilize solar light for clean energy and environment. Herein, we report a visible light responsive heterostructure, designed and constructed by molybdenum disulfide quantum dots (MoS2-QDs) in-situ seeds-directing growth and self-assemble of zinc indium sulfide (ZnIn2S4) nanosheet to ensure their full contact through a simple one-step solvothermal method for highly improved visible light H2 production. The MoS2-QDs in-situ seeds-directing ZnIn2S4 heterostructure not only builds heterojunctions between MoS2 and ZnIn2S4 to spatially separate the photogenerated electrons and holes, but also serves as the active sites trapping photogenerated electrons to facilitate H2 evolution. As a result, MoS2-QDs/ZnIn2S4 exhibits high photocatalytic activity for H2 production, and the optimized 2 wt% MoS2-QDs/ZnIn2S4 (2MoS2-QDs/ZnIn2S4) heterostructure exhibits the highest H2 evolution rate of 7152 umol·h-1·g-1 under visible light, ∼9 times of pure ZnIn2S4. Our strategy here could shed some lights on developing noble-metal free heterostructures for highly efficient photocatalytic H2 production.

MOF-derived nitrogen-doped core-shell hierarchical porous carbon confining selenium for advanced lithium-selenium batteries.

The lithium-selenium (Li-Se) battery has attracted growing interest recently due to its high energy density and theoretical capacity. However, the shuttle effect and volume change during cycling severely hinder its further application. In this work, we report a metal-organic framework (MOF)-derived nitrogen-doped core-shell hierarchical porous carbon (N-CSHPC) with interconnected meso/micropores to effectively confine Se for high-performance Li-Se batteries. The micropores were located at the ZIF-8-derived core and the ZIF-67-derived shell, while mesopores appeared at the core-shell interface after the pyrolysis of the core-shell ZIF-8@ZIF-67 precursor. Such a special hierarchical porous structure effectively confined selenium and polyselenides to prevent their dissolution from the pores and also alleviated the volume change. In particular, in situ nitrogen doping, which afforded N-CSHPC, not only improved the electrical conductivity of Se but also provided strong chemical adsorption on Li2Se, as confirmed by density functional theory calculations. On the basis of dual-physical confinement and strong chemisorption, Se/N-CSHPC-II (molar ratio of Co source to Zn source of 1.0 in the core-shell ZIF-8@ZIF-67 precursor) exhibited reversible capacities of up to 555 mA h g-1 after 150 cycles at 0.2 C and 462 mA h g-1 after 200 cycles at 0.5 C and even a discharge capacity of 432 mA h g-1 after 200 cycles at 1 C. Our demonstration here suggests that the carefully designed Se/C composite can improve the reversible capacity and cycling stability of Se cathodes for Li-Se batteries.