Implementing an Air Suction Effect Induction Strategy to Create Super Thermally Insulating and Superelastic SiC Aerogels.

Silicon carbide (SiC) aerogels are promising thermal insulators that are lightweight and possess high thermal stability. However, their application is hindered by their brittleness. Herein, an air suction effect induction (ASEI) strategy is proposed to fabricate a super thermally insulating SiC aerogel (STISA). The ASEI strategy exploits the air suction effect to subtly regulate the directional flow of the SiO gas, which can induce directional growth and assembly of SiC nanowires to form a directional lamellar structure. The sintering time is significantly reduced by >90%. Significant improvements in the compression and elasticity performance of the STISA are achieved upon the formation of a directional lamellar structure through the ASEI strategy. Moreover, the lamellar structure endows the STISA with an ultralow thermal conductivity of 0.019 W m-1 K-1 . The ASEI strategy paves the way for structural design of advanced ceramic aerogels for super thermal insulation.

Mechanically Strong and Tailorable Polyimide Aerogels Prepared with Novel Silicone Polymer Crosslinkers.

Polyimide (PI) aerogels were prepared using self-designed silicone polymer cross-linkers with multi-amino from low-cost silane coupling agents to replace conventional small-molecule cross-linkers. The long-chain structure of silicone polymers provides more crosslinking points than small-molecule cross-linkers, thus improving the mechanical properties of polyimide. To investigate the effects of amino content and degree of polymerization on the properties of silicone polymers, the different silicone polymers and their cross-linked PI aerogels were prepared. The obtained PI aerogels exhibit densities as low as 0.106 g/cm3 and specific surface areas as high as 314 m2/g, and the maximum Young's modulus of aerogel is up to 20.9 MPa when using (T-20) as cross-linkers. The cross-linkers were an alternative to expensive small molecule cross-linkers, which can improve the mechanical properties and reduce the cost of PI aerogels.

Improvement of the Thermal Insulation Performance of Silica Aerogel by Proper Heat Treatment: Microporous Structures Changes and Pyrolysis Mechanism.

A simple heat treatment method was used to optimize the three-dimensional network structure of the hydrophobic aerogel, and during the heat treatment process at 200-1000 °C, the thermal conductivity of the aerogel reached the lowest to 0.02240 W/m·K between 250 °C and 300 °C, which was mainly due to the optimization of microstructure and pyrolysis of surface groups. Further Fluent heat-transfer simulation also confirmed the above results. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to finely measure the pyrolysis process of aerogels, and the pyrolysis process of aerogel was divided into four stages. (I) Until 419 °C, as the temperature continued to rise, surface methyl groups were oxidized to form hydroxyl. (II) As the temperature reached to 232 °C, the oxidation proceeded. In addition, inside the aerogel, because of lacking oxygen, the reaction produced CH4 and C-Si bonds would form. (III) After 283 °C, Si-OH groups began to condense to form Si-O-Si, which optimized the three-dimensional network structures to be beneficial to improve the thermal insulation performance of silica aerogel. (IV) When it reached 547 °C, the chemical reaction was terminated, and all the primary particles gradually fused into secondary particles and sintered to form clusters.

Mechanically strong polyimide aerogels cross-linked with low-cost polymers.

Polyimide aerogels were prepared using low-cost polymers with different structure capped polyamide oligomers serving as cross-linking agents. To investigate the effects of the anhydride density on cross-linker chain units and side groups of cross-linkers on their properties and microstructures, two kinds of polymers from maleic anhydride, endic anhydride, and styrene were prepared by simple radical polymerization. The polyimide aerogels exhibit densities as low as 0.087 g cm-3 and specific surface areas as high as 456 m2 g-1. And the maximum modulus of the aerogel is up to 21.3 MPa. These cross-linkers are alternatives to expensive small molecule cross-linkers, therefore reducing the cost of PI aerogels.

"Robust-Soft" Anisotropic Nanofibrillated Cellulose Aerogels with Superior Mechanical, Flame-Retardant, and Thermal Insulating Properties.

Advanced thermal insulation materials with low thermal conductivity and robustness derived from regenerative resources are badly needed for building energy conservation. Among them, nanofibrillated cellulose aerogels have huge application potential in the field of thermal insulation materials, but it is still a challenge to prepare cellulose aerogels of excellent comprehensive properties in a simple way. Herein, we demonstrate a unidirectional freeze-drying strategy to develop a novel "robust-soft" anisotropic nanofibrillated cellulose aerogel (NFC-Si-T) by integrating nanofibrillated cellulose (NFC) and Si-O-Si bonding networks under the catalytic dehydration of p-toluenesulfonic acid (TsOH). The anisotropic structure endows the NFC-Si-T with high flexibility that can be easily bent or even tied with a knot, and in addition, it possesses high Young's modulus (1-3.66 MPa) that can resist the compression weight of 10,000 times of its own weight without deformation. Furthermore, the NFC-Si-T aerogels exhibit anisotropic thermal insulation performances with a low average thermal conductivity (0.028-0.049 W m-1 K-1). More importantly, the limited oxygen index of the NFC-Si-T reaches up to 42.6-51%, showing excellent flame-retardant performance. Therefore, the "robust-soft" anisotropic NFC-Si-T aerogels can be used as an advanced thermal insulation material for building thermal insulation applications.

Layer-Spacing-Enlarged MoS2 Superstructural Nanotubes with Further Enhanced Catalysis and Immobilization for Li-S Batteries.

A layer-spacing-enlarged MoS2 nanotube (LE-MoS2) consisting of hierarchical superstructural nanosheets (-MoS2-carbon layer-MoS2-) was fabricated and served as the sulfur host. The (002) lattice plane of LE-MoS2 is greatly expanded to 1.04 nm and 67.7% higher than that of the conventional 2H-MoS2. Benefitting from the layer-spacing-enlarged hierarchical superstructure of LE-MoS2, the catalytic effect on the S(s)-Li2Sx (soluble, x > 6)-Li2Sy (soluble, y > 2)-Li2S(s) phase transformation kinetics and immobilizing effect on the soluble Li2Sy in Li-S batteries are both further enhanced and demonstrated by in situ X-ray adsorption near-edge structure spectroscopy and first-principles calculations. The formation of hierarchical superstructural nanosheets was carefully investigated by customized synchrotron vacuum ultraviolet photoionization mass spectrometry.

Cagelike CoSe2@N-Doped Carbon Aerogels with Pseudocapacitive Properties as Advanced Materials for Sodium-Ion Batteries with Excellent Rate Performance and Cyclic Stability.

Electrochemical conversion reaction based electrodes offer a high sodium storage capacity in rechargeable batteries by utilizing the variable valence states of transition metals. Thus, transition metal chalcogenides (TMCs) as such materials have been intensively investigated in recent years to explore the possibilities of practical application in rechargeable sodium-ion batteries; however, it is hindered by poor rate performance and a high-cost preparation method. In addition, some issues in regards to conversion reactions remain poorly understood, including incomplete reversible reaction processes, polarization, and hysteresis. Herein, a novel cagelike CoSe2@N-doped carbon aerogels hybrid composite was designed and prepared by a facile and high-efficiency sol-gel technology. Benefiting from the surface engineering optimization, high charge transfer, and low-energy diffusion barrier, the CoSe2@N-doped carbon aerogels exhibit a high pseudocapacitive property. Most importantly, the CoSe2 anode has been carefully investigated at different discharge/charge states by X-ray absorption near edge spectroscopy technologies and density functional theory (DFT) simulations, which deeply reveal the capacity fading mechanism and phase transition behavior.

Dual-Functional Multichannel Carbon Framework Embedded with CoS2 Nanoparticles: Promoting the Phase Transformation for High-Loading Li-S Batteries.

Lithium-sulfur batteries have been considered as one of the most promising energy storage devices due to their high theoretical capacity and low cost. They go through complicated multistep electrochemical reactions from solid (sulfur)-liquid (soluble polysulfide) to liquid (soluble polysulfide)-solid (Li2S) during the discharge process. Actually, during this process, the transition from liquid phase (Li2S4) to solid phase (Li2S) at 2.1 V plateau is a difficult step with sluggish kinetics, thus leading to low sulfur utilization and discharge capacity. To promote the transition processes and enhance the sulfur utilization, CoS2@multichannel carbon nanofiber composites (CoS2@MCNFs) serving as sulfur host were successfully synthesized. Herein, CoS2 catalysts are proven to be beneficial not only for enhancing the phase-transition kinetics but also for adsorbing soluble polysulfide. Besides, unlike other carbon materials, MCNFs have plenty of hollow channels and thus enhance sulfur loading and conductivity. Accordingly, the discharge capacity increases 32% more than that of electrode without CoS2. And a very low capacity fade rate of 0.03% per cycle (over 450 cycles) is obtained at a 0.5C rate. This work has opened up new ideas for enhancing sulfur utilization for high sulfur-loading electrode.

A long life sodium-selenium cathode by encapsulating selenium into N-doped interconnected carbon aerogels.

Selenium cathodes have attracted a great deal of attention due to their much higher electronic conductivity compared to sulfur cathodes and similar volumetric capacity to them. However, selenium cathodes still suffer from rapid capacity fading because of low utilization of active materials, high volume changes and the shuttle effect of polyselenides. Herein, we prepared selenium-carbon aerogel composites as cathodes for sodium-selenium batteries by infiltrating selenium into the microporous structure of N-doped interconnected carbon aerogels (Se@NCAs). The carbon matrix could effectively accommodate the volume change of Se during cycling and alleviate the shuttle effect of polyselenides. The Se@NCA cathode exhibits an excellent discharge capacity (600 mA h g-1 after 50 cycles at 0.1 A g-1) and a superior rate capability (430 mA h g-1 at 2 A g-1) for Na-Se batteries. In addition, it also shows a superior long cycling life of 407 mA h g-1 at a current density of 0.5 A g-1 after 800 cycles with only 0.04% capacity decline per cycle.

Nanoflower-like N-doped C/CoS2 as high-performance anode materials for Na-ion batteries.

Novel nanoflower-like N-doped C/CoS2 spheres assembled from 2D wrinkled CoS2 nanosheets were synthesized through a facile one-pot solvothermal method followed by sulfurization. Ascribed to the optimized 3D nanostructure and rational surface engineering, the unique hierarchical structure of the nanoflower-like C/CoS2 composites showed an excellent sodium ion storage capacity accompanied by high specific capacity, superior rate performance and long-term cycling stability. Specifically, the conductive interconnected wrinkled nanosheets create a number of mesoporous structures and thus can greatly release the mechanical stress caused by Na+ insertion/extraction. Besides, it was observed from the experiments that many extra defect vacancies and Na+ storage sites are introduced by the nitrogen doping process. It was also observed that the crosslinked 2D nanosheets can effectively reduce the diffusion lengths of sodium ions and electrons, resulting in an outstanding rate performance (>700 mA h g-1 at 1 A g-1 and 458 mA h g-1 at even 10 A g-1) and extraordinary cycling stability (698 mA h g-1 at 1 A g-1 after 500 cycles). The results provide a facile approach to fabricate promising anode materials for high-performance sodium-ion batteries (SIBs).

Facile construction of the aerogel/geopolymer composite with ultra-low thermal conductivity and high mechanical performance.

In this work, we have successfully prepared a lightweight, highly hydrophobic and superb thermal insulating aerogel/geopolymer composite by a sol-gel immersion method. After silica aerogel was impregnated, the composite exhibited nano-porous structures. Moreover, scanning electron microscopy observations revealed that the aerogel particles were tightly anchored on the geopolymer surface. With several excellent properties (bulk density: 306.5 g cm-3, thermal conductivity: 0.0480 W m-1 K-1 and maximum compressive strength: 0.79 MPa) the as-prepared composite shows great potential to be applied in the thermal insulation field.

Double-Morphology CoS2 Anchored on N-Doped Multichannel Carbon Nanofibers as High-Performance Anode Materials for Na-Ion Batteries.

Na-ion batteries (NIBs) have attracted increasing attention given the fact that sodium is relatively more plentiful and affordable than lithium for sustainable and large-scale energy storage systems. However, the shortage of electrode materials with outstanding comprehensive properties has limited the practical implementations of NIBs. Among all the discovered anode materials, transition-metal sulfide has been proven as one of the most competitive and promising ones due to its excellent redox reversibility and relatively high theoretical capacity. In this study, double-morphology N-doped CoS2/multichannel carbon nanofibers composites (CoS2/MCNFs) are precisely designed, which overcome common issues such as the poor cycling life and inferior rate performance of CoS2 electrodes. The conductive 3D interconnected multichannel nanostructure of CoS2/MCNFs provides efficient buffer zones for the release of mechanical stresses from Na+ ions intercalation/deintercalation. The synergy of the diverse structural features enables a robust frame and a rapid electrochemical reaction in CoS2/MCNFs anode, resulting in an impressive long-term cycling life of 900 cycles with a capacity of 620 mAh g-1 at 1 A g-1 (86.4% theoretical capacity) and a surprisingly high-power output. The proposed design in this study provides a rational and novel thought for fabricating electrode materials.

CoS2 Nanoparticles Wrapping on Flexible Freestanding Multichannel Carbon Nanofibers with High Performance for Na-Ion Batteries.

Exploration for stable and high-powered electrode materials is significant due to the growing demand for energy storage and also challengeable to the development and application of Na-ion batteries (NIBs). Among all promising electrode materials for NIBs, transition-mental sulfides have been identified as potential candidates owing to their distinct physics-chemistry characteristics. In this work, CoS2 nanomaterials anchored into multichannel carbon nanofibers (MCNFs), synthesized via a facile solvothermal method with a sulfidation process, are studied as flexible free-standing electrode materials for NIBs. CoS2 nanoparticles uniformly distributed in the vertical and horizontal multichannel networks. Such nanoarchitecture can not only support space for volume expansion of CoS2 during discharge/charge process, but also facilitate ion/electron transport along the interfaces. In particular, the CoS2@MCNF electrode delivers an impressively high specific capacity (537.5 mAh g-1 at 0.1 A g-1), extraordinarily long-term cycling stability (315.7 mAh g-1 at at 1 A g-1 after 1000 cycles), and excellent rate capacity (537.5 mAh g-1 at 0.1 A g-1 and 201.9 mAh g-1 at 10 A g-1) for sodium storage. Free-standing CoS2@MCNF composites with mechanical flexibility provide a promising electrode material for high-powered NIBs and flexible cells.