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.

Bi-doped carbon dots for a stable lithium metal anode.

Bi-doped carbon dots (Bi-CDs) with rich polar groups and good compatibility were employed as co-deposition electrolyte additives to homogenize Li+ flux for dendrite-free Li deposition. High coulombic efficiency (99.0%) and long-term stability (800 h) with reduced overpotential (∼15 mV) were achieved after introducing Bi-CDs in conventional electrolyte for high-performance Li-S batteries.

Carbon Dots-Regulated Pomegranate-Like Metal Oxide Composites: From Growth Mechanism to Lithium Storage.

Carbon dots (CDs) are considered as excellent structural regulator for metal oxides (MOs) due to their abundant functional groups, superior dispersibility, and ultrasmall size (<10 nm). Herein, a new approach is proposed to construct porous pomegranate-like MOs/CDs composite based on the CDs-induced in situ growth mechanism of ion adsorption-multipoint surface nucleation-crosslinking agglomeration. The proposed methodology is successfully applied to prepare SnO2 /CDs, Cu2 O/CDs, and Fe2 O3 /CDs composites, respectively, demonstrating its universality to metal oxides. Taking SnO2 /CDs composite as a case study for anode material in lithium-ion batteries, it exhibits high lithium storage capacity, excellent cycling stability, and a special feature of capacity increase upon cycling. This study provides a new idea for the design of metal oxides materials tuned by CDs and broadens the application of CDs in the field of material synthesis.

Heterogeneous Interface Design for Enhanced Sodium Storage: Sb Quantum Dots Confined by Functional Carbon.

Antimony (Sb) is considered a promising anode material for sodium-ion batteries due to its high specific capacity and moderate working potential. However, the non-negligible volume variation leads to the rapid decay of capacity, which hinders the practical application of Sb anode materials. Here, an economical and scalable route with high yield is proposed to obtain Sb ultrafine nanocrystals embedded in a porous carbon skeleton. Notably, the synergetic effect of the heterogeneous structure is maximized by inducing the interfacial coupling SbOC and creating buffering space for the volume effect of Sb. The high-entropy phase interface creates the doping site breaking the periodicity of atoms and alters the electronic structure, also bridging the slip of intergranular defects. Thus, the electronic conductivity and phase interface structural stability are reinforced. The mechanism of accelerating electron migration at the heterogeneous phase interface is visualized through the density functional theory method, and the mass/charge-transfer kinetics is analyzed via the calculation of surface-induced capacitive contribution.

Carbon Dots Evoked Li Ion Dynamics for Solid State Battery.

Solid composite electrolyte-based Li battery is viewed as one of the most competitive system for the next generation batteries; however, it is still restricted by sluggish ion diffusion. Fast ion transport is a characteristic of the polyethylene oxide (PEO) amorphous phase, and the mobility of Li+ is restrained by the coordination interaction within PEO and Li+ . Herein, the design of applying functionalized carbon dots (CDs) with abundant surface features as fillers is proposed. High ionic conductivity is achieved in the CD-based composite electrolytes resulting from enhanced ion migration ability of polymer segments and mobility of Li+ . Specially, the optimum effect with nitrogen and sulfur co-doped carbon dots (NS-CD) is a consequence of strong interaction between edge-nitrogen/sulfur in NS-CD and Li+ . Solid-state nuclear magnetic resonance results confirm that more mobile Li+ is generated. Moreover, it is observed that lithium dendrite is suppressed compared to PEO electrolyte associated with reinforced mechanical properties and high transference number. The corresponding all-solid-state batteries, with the cathode of LiFePO4 or high voltage NCM523, exhibit long cycling life and excellent rate performances. It is a novel strategy to achieve high ionic conductivity composite electrolyte with uniform lithium deposition and provides a new direction to the mechanism of fast Li+ movement.

Structure and Interface Modification of Carbon Dots for Electrochemical Energy Application.

Carbon dots (CDs) as new nanomaterials have attracted much attention in recent years due to their unique characteristics. Notably, structure and interface modification (carbon core, edge, defects, and functional groups) of CDs have been considered as valid methods to regulate their properties, which contain electron transfer effect, electrochemical activity, fluorescence luminescent, and so on. Additionally, CDs with ultrasmall size, excellent dispersibility, high specific surface area, and abundant functional groups can guarantee positive and extraordinary effects in electrical energy storage and conversion. Therefore, CDs are used to couple with other materials by constructing a special interface structure to enhance their properties. Here, diverse structural and interfacial modifications of CDs with various heteroatoms and synergy effects are systematically analyzed. And not only several main syntheses of CDs-based composites (CDs/X) are summarized but also the merit and demerit of CDs/X in electrical energy storage are discussed. Finally, the applications of CDs/X in energy storage devices (supercapacitors, batteries) and electrocatalysts for practical applications are discussed. This review mainly provides a comprehensive summary and future prospect for synthesis, modification, and electrochemical applications of CDs.

High Sulfur-Doped Hard Carbon with Advanced Potassium Storage Capacity via a Molten Salt Method.

Owing to the slight volume expansion after potassiation, hard carbon is regarded as a promising anode material for potassium-ion batteries (PIBs). Heteroatom doping (such as sulfur or nitrogen) is a common method to modify hard carbon for high K-storage capacity and long cycling performance. High sulfur-doped hard carbon with a sulfur content of 25.8 wt % is prepared by calcining glucose in molten salt (K2SO4@LiCl/KCl). It exhibits high specific capacities of 361.4 mA h g-1 during the 1st cycle and 317.7 mA h g-1 during the 100th cycle at 0.05 A g-1. The high capacity arises from the K-S reaction behavior, which is demonstrated by the cyclic voltammetry test and galvanostatic intermittent titration technique. This work is an effective application of the molten salt method for PIBs, furnishing an understanding to K-storage behaviors of hard carbon- with high sulfur content.