Unraveling the "Gap-Filling" Mechanism of Multiple Charge Carriers in Aqueous Zn-MoS2 Batteries.

The utilization rate of active sites in cathode materials for Zn-based batteries is a key factor determining the reversible capacities. However, a long-neglected issue of the strong electrostatic repulsions among divalent Zn2+ in hosts inevitably causes the squander of some active sites (i.e., gap sites). Herein, we address this conundrum by unraveling the "gap-filling" mechanism of multiple charge carriers in aqueous Zn-MoS2 batteries. The tailored MoS2 /(reduced graphene quantum dots) hybrid features an ultra-large interlayer spacing (2.34 nm), superior electrical conductivity/hydrophilicity, and robust layered structure, demonstrating highly reversible NH4 + /Zn2+ /H+ co-insertion/extraction chemistry in the 1 M ZnSO4 +0.5 M (NH4 )2 SO4 aqueous electrolyte. The NH4 + and H+ ions can act as gap fillers to fully utilize the active sites and screen electrostatic interactions to accelerate the Zn2+ diffusion. Thus, unprecedentedly high rate capability (439.5 and 104.3 mAh g-1 at 0.1 and 30 A g-1 , respectively) and ultra-long cycling life (8000 cycles) are achieved.

Reconstructing Hydrogen Bond Network Enables High Voltage Aqueous Zinc-Ion Supercapacitors.

High-voltage aqueous rechargeable energy storage devices with safety and high specific energy are hopeful candidates for the future energy storage system. However, the electrochemical stability window of aqueous electrolytes is a great challenge. Herein, inspired by density functional theory (DFT), polyethylene glycol (PEG) can interact strongly with water molecules, effectively reconstructing the hydrogen bond network. In addition, N, N-dimethylformamide (DMF) can coordinate with Zn2+ , assisting in the rapid desolvation of Zn2+ and stable plating/stripping process. Remarkably, by introducing PEG400 and DMF as co-solvents into the electrolyte, a wide electrochemical window of 4.27 V can be achieved. The shift in spectra indicate the transformation in the number and strength of hydrogen bonds, verifying the reconstruction of hydrogen bond network, which can largely inhibit the activity of water molecule, according well with the molecular dynamics simulations (MD) and online electrochemical mass spectroscopy (OEMS). Based on this electrolyte, symmetric Zn cells survived up to 5000 h at 1 mA cm-2 , and high voltage aqueous zinc ion supercapacitors assembled with Zn anode and activated carbon cathode achieved 800 cycles at 0.1 A g-1 . This work provides a feasible approach for constructing high-voltage alkali metal ion supercapacitors through reconstruction strategy of hydrogen bond network.

A nitrogen-doped carbon fiber coating embedded in the separator for stable zinc batteries.

A separator modification strategy was proposed by placing nitrogen-doped carbon fibers (NCF700) in the middle of the separator to prevent direct contact between the coating and the rigid zinc metal anode, resulting in coating cracks. The NCF700 coating can homogenize the electric field distribution and increase the transference number of zinc ions. Therefore, the battery assembled with the NCF700 coated separator exhibits superior cycling stability compared to the bare separator.

Regulation of the Electrochemical Plating/Stripping Process for Zn: Multifunctional Effects of N, S-Codoped Carbon Dots.

The aqueous zinc-ion battery is considered as one of the best alternatives to lithium-ion batteries due to its low cost and high safety. However, the inevitable dendrite growth, byproduct formation, and the side reactions have inhibited the application of aqueous zinc-ion batteries. In this work, the electronegative nitrogen and sulfur-codoped carbon dots (NSCDs) are proposed as an electrolyte additive to regulate the uniform distribution of zinc ions and inhibit the growth of dendrites. It was found that only a small amount of NSCD additive (0.2 mg mL-1) exerted a significant influence in electrochemical performance; the symmetrical cell can operate stably for 2000 h with a low voltage hysteresis of 33 mV at the current density of 1 mA cm-2, and a high Coulombic efficiency (CE) of 99.5% can be obtained after 250 cycles.

Natural Stibnite for Lithium-/Sodium-Ion Batteries: Carbon Dots Evoked High Initial Coulombic Efficiency.

HIGHLIGHTS: The chemical process of local oxidation-partial reduction-deep coupling for stibnite reduction of carbon dots (CDs) is revealed by in-situ high-temperature X-ray diffraction. Sb2S3@xCDs anode delivers high initial coulombic efficiency in lithium ion batteries (85.2%) and sodium ion batteries (82.9%), respectively. C-S bond influenced by oxygen-rich carbon matrix can restrain the conversion of sulfur to sulfite, well confirmed by X-ray photoelectron spectroscopy characterization of solid electrolyte interphase layers helped with density functional theory calculations. CDs-induced Sb-O-C bond is proved to effectively regulate the interfacial electronic structure. The application of Sb2S3 with marvelous theoretical capacity for alkali metal-ion batteries is seriously limited by its poor electrical conductivity and low initial coulombic efficiency (ICE). In this work, natural stibnite modified by carbon dots (Sb2S3@xCDs) is elaborately designed with high ICE. Greatly, chemical processes of local oxidation-partial reduction-deep coupling for stibnite reduction of CDs are clearly demonstrated, confirmed with in situ high-temperature X-ray diffraction. More impressively, the ICE for lithium-ion batteries (LIBs) is enhanced to 85%, through the effect of oxygen-rich carbon matrix on C-S bonds which inhibit the conversion of sulfur to sulfite, well supported by X-ray photoelectron spectroscopy characterization of solid electrolyte interphase layers helped with density functional theory calculations. Not than less, it is found that Sb-O-C bonds existed in the interface effectively promote the electronic conductivity and expedite ion transmission by reducing the bandgap and restraining the slip of the dislocation. As a result, the optimal sample delivers a tremendous reversible capacity of 660 mAh g-1 in LIBs at a high current rate of 5 A g-1. This work provides a new methodology for enhancing the electrochemical energy storage performance of metal sulfides, especially for improving the ICE.