Showing papers by "Yong Wang published in 2021"

Nanoengineering of 2D MXene-Based Materials for Energy Storage Applications

Abstract: 2D MXene-based nanomaterials have attracted tremendous attention because of their unique physical/chemical properties and wide range of applications in energy storage, catalysis, electronics, optoelectronics, and photonics. However, MXenes and their derivatives have many inherent limitations in terms of energy storage applications. In order to further improve their performance for practical application, the nanoengineering of these 2D materials is extensively investigated. In this Review, the latest research and progress on 2D MXene-based nanostructures is introduced and discussed, focusing on their preparation methods, properties, and applications for energy storage such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. Finally, the critical challenges and perspectives required to be addressed for the future development of these 2D MXene-based materials for energy storage applications are presented.

The Progress and Prospect of Tunable Organic Molecules for Organic Lithium-Ion Batteries.

Abstract: Compared to inorganic electrodes, organic materials are regarded as promising electrodes for lithium-ion batteries (LIBs) due to the attractive advantages of light elements, molecular-level structural design, fast electron/ion transferring, favorable environmental impacts, and flexible feature, etc. Not only specific capacities but also working potentials of organic electrodes are reasonably tuned by polymerization, electron-donating/withdrawing groups, and multifunctional groups as well as conductive additives, which have attracted intensive attention. However, organic LIBs (OLIBs) are also facing challenges on capacity loss, side reactions, electrode dissolution, low electronic conductivity, and short cycle life, etc. Many strategies have been applied to tackle those challenges, and many inspiring results have been achieved in the last few decades. In this review, we have introduced the basic concepts of LIBs and OLIBs, followed by the typical cathode and anode materials with various physicochemical properties, redox reaction mechanisms, and evolutions of functional groups. Typical charge-discharge behaviors and molecular structures of organic electrodes are displayed. Moreover, effective strategies on addressing problems of organic electrodes are summarized to give some guidance on the synthesis of optimized organic electrodes for practical applications of OLIBs.

Metal-Organic Framework-Derived Nanoconfinements of CoF2 and Mixed-Conducting Wiring for High-Performance Metal Fluoride-Lithium Battery.

Abstract: Metal fluoride (MF) conversion cathodes theoretically show higher gravimetric and volumetric capacities than Ni- or Co-based intercalation oxide cathodes, which makes metal fluoride-lithium batteries promising candidates for next-generation high-energy-density batteries. However, their high-energy characteristics are clouded by low-capacity utilization, large voltage hysteresis, and poor cycling stability of transition MF cathodes. A variety of reasons is responsible for this: poor reaction kinetics, low conductivities, unstable MF/electrolyte interfaces and dissolution of active species upon cycling. Herein, we combine the synthesis of the metal-organic-framework (MOF) with the low-temperature fluorination to prepare MOF-shaped CoF2@C nanocomposites that exhibit confinement of the CoF2 nanoparticles and efficient mixed-conducting wiring in the produced architecture. The ultrasmall CoF2 nanoparticles (5-20 nm on average) are uniformly covered by graphitic carbon walls and embedded in the porous carbon framework. Within the CoF2@C nanocomposite, the cross-linked carbon wall and interconnected nanopores serve as electron- and ion-conducting pathways, respectively, enabling a highly reversible conversion reaction of CoF2. As a result, the produced CoF2@C composite cathodes successfully restrain the above-mentioned challenges and demonstrate high-capacity utilization of ∼500 mAh g-1 at 0.2C, good rate capability (up to 2C), and long-term cycle stability over 400 cycles. Overall, the presented study not only reports on a simple composite design to achieve high-energy characteristics in CoF2-Li batteries but also may provide a general solution for many other metal fluoride-lithium batteries.

Cobalt Coordinated Cyano Covalent-Organic Framework for High-Performance Potassium-Organic Batteries.

Abstract: Potassium ion batteries (PIBs) are expected to become the next large-scale energy storage candidates due to its low cost and abundant resources. And the covalent organic framework (COF), with designable periodic organic structure and ability to organize redox active groups predictably, has been considering as the promising organic electrode candidate for PIB. Herein, we report the facile synthesis of the cyano-COF with Co coordination via a facile microwave digestion reaction and its application in the high-energy potassium ion batteries for the first time. The obtained COF-Co material exhibits the enhanced π-π accumulation and abundant defects originated from the Co interaction with the two-dimensional layered sheet structure of COF, which are beneficial for its energy-storage application. Adopted as the inorganic-metal boosted organic electrode for PIBs, the COF-Co with Co coordination can promote the formation of the π-K+ interaction, which could lead to the activation of aromatic rings for potassium-ion storage. Besides, the porous two-dimensional layered structure of COF-Co with abundant defects can also promote the shortened diffusion distance of ion/electron with promoted K+ insertion/extraction ability. Enhanced cycling stability with large reversible capacity (371 mAh g-1 after 400 cycles at 100 mA g-1) and good rate properties (105 mAh g-1 at 2000 mA g-1) have been achieved for the COF-Co electrode.

Dendrite-Free and Stable Lithium Metal Battery Achieved by a Model of Stepwise Lithium Deposition and Stripping

Abstract: The uncontrolled formation of lithium (Li) dendrites and the unnecessary consumption of electrolyte during the Li plating/stripping process have been major obstacles in developing safe and stable Li metal batteries. Herein, we report a cucumber-like lithiophilic composite skeleton (CLCS) fabricated through a facile oxidation-immersion-reduction method. The stepwise Li deposition and stripping, determined using in situ Raman spectra during the galvanostatic Li charging/discharging process, promote the formation of a dendrite-free Li metal anode. Furthermore, numerous pyridinic N, pyrrolic N, and CuxN sites with excellent lithiophilicity work synergistically to distribute Li ions and suppress the formation of Li dendrites. Owing to these advantages, cells based on CLCS exhibit a high Coulombic efficiency of 97.3% for 700 cycles and an improved lifespan of 2000 h for symmetric cells. The full cells assembled with LiFePO4 (LFP), SeS2 cathodes and CLCS@Li anodes demonstrate high capacities of 110.1 mAh g−1 after 600 cycles at 0.2 A g−1 in CLCS@Li|LFP and 491.8 mAh g−1 after 500 cycles at 1 A g−1 in CLCS@Li|SeS2. The unique design of CLCS may accelerate the application of Li metal anodes in commercial Li metal batteries. Highlights: 1 A facile method is adopted to obtain cucumber-like lithiophilic composite skeleton.2 Massive lithiophilic sites in cucumber-like lithiophilic composite skeleton can promote and guide uniform Li depositions.3 A unique model of stepwise Li deposition and stripping is determined.

Fluorine/Nitrogen Co-Doped Porous Carbons Derived from Covalent Triazine Frameworks for High-Performance Supercapacitors

Abstract: Porous carbon materials with a synergistically large specific surface area (SBET) and an adjustable structure are urgently needed to meet the demands of high-performance supercapacitors (SCs) and o...

Ultra-small Fe3O4 nanodots encapsulated in layered carbon nanosheets with fast kinetics for lithium/potassium-ion battery anodes

Abstract: Iron oxides are regarded as promising anodes for both lithium-ion batteries (LIBs) and potassium-ion batteries (KIBs) due to their high theoretical capacity, abundant reserves, and low cost, but they are also facing great challenges due to the sluggish reaction kinetics, low electronic conductivity, huge volume change, and unstable electrode interphases. Moreover, iron oxides are normally prepared at high temperature, forming large particles because of Ostwald ripening, and exhibiting low electronic/ionic conductivity and unfavorable mechanical stability. To address those issues, herein, we have synthesized ultra-small Fe3O4 nanodots encapsulated in layered carbon nanosheets (Fe3O4@LCS), using the coordination interaction between catechol and Fe3+, demonstrating fast reaction kinetics, high capacity, and typical capacitive-controlled electrochemical behaviors. Such Fe3O4@LCS nanocomposites were derived from coordination compounds with layered structures via van der Waals's force. Fe3O4@LCS-500 (annealed at 500 °C) nanocomposites have displayed attractive features of ultra-small particle size (∼5 nm), high surface area, mesoporous and layered feature. When used as anodes, Fe3O4@LCS-500 nanocomposites delivered exceptional electrochemical performances of high reversible capacity, excellent cycle stability and rate performance for both LIBs and KIBs. Such exceptional performances are highly associated with features of Fe3O4@LCS-500 nanocomposites in shortening Li/K ion diffusion length, fast reaction kinetics, high electronic/ionic conductivity, and robust electrode interphase stability.

Imine-Induced Metal-Organic and Covalent Organic Coexisting Framework with Superior Li-Storage Properties and Activation Mechanism

Abstract: Due to the adjustable structure and the broad application prospects in energy and other fields, the exploration of porous organic materials [metal-organic polymers (MOPs), covalent organic frameworks (COFs), etc.] has attracted extensive attention. In this work, an imine-induced metal-organic and covalent organic coexisting framework (Co-MOP@COF) hybrid was designed based on the combination between the amino units from the organic ligands of Co-MOP and the aldehyde groups from COF. The obtained Co-MOP@COF hybrid with layer-decorated microsphere morphology exhibited good electrochemical cycling performance (a large reversible capacity of 1020 mAh g-1 after 150 cycles at 100 mA g-1 and a reversible capacity of 396 mAh g-1 at 500 mA g-1 ) as the anode for Li-ion batteries. The coexisting framework structure endowed the Co-MOP@COF hybrid with more surface area exposed in the exfoliated COF structure, which provided rapid Li-ion diffusion, better electrolyte infiltration, and effective activation of functional groups. Therefore, the Co-MOP@COF hybrid material achieved an enhanced Li storage mechanism involving multi-electron redox reactions, related to the CoII center and organic groups (C=C groups of benzene rings and C=N groups), and furthermore improved electrochemical performance.

Two-dimensional imine-based covalent–organic-framework derived nitrogen-doped porous carbon nanosheets for high-performance lithium–sulfur batteries

Abstract: Lithium–sulfur batteries are attracting more attention due to their high theoretical capacity and energy density. However, they have the problems of short cycling performance, low sulfur loading and shuttle effect; in order to overcome these problems, more efforts have been devoted to the exploration of effective host materials for sulfur confinement. Herein, we report a facile approach for the synthesis of nitrogen-doped porous carbon (NPC) nanosheets, derived from imine-based covalent organic frameworks (COFs), as the host material. In situ nitrogen doping is very uniform due to the inherited nitrogen element distributed uniformly in the COF skeleton. Sulfur-loaded NPC composites can achieve a high sulfur loading amount of 71.8% and enhanced lithium–sulfur battery performance, in terms of a high initial discharge capacity (1398 mA h g−1 at 0.1C) and good cycling properties (reversible capacity of 833 mA h g−1 after 250 cycles). The existence of nitrogen doped carbon nanosheets with a high surface area and controlled porosity can lead to effective immobilization of the polysulfides and simultaneous improvement of the reaction kinetics of the sulfur species. This design strategy provides an extended method for fabricating high performance cathodes for lithium–sulfur batteries.

Unusual Inside–Outside Li Deposition within Three-Dimensional Honeycomb-like Hierarchical Nitrogen-Doped Framework for a Dendrite-Free Lithium Metal Anode

Abstract: Lithium (Li) metal batteries have attracted massive research interest as candidates for a high energy density system. However, the instability and dendrite issue of Li metal have substantially hind...