Rechargeable high‐energy lithium–sulfur batteries suffer from rapid capacity decay and poor rate capability due to intrinsically intermediate polysulfides' shuttle effect and sluggish redox kinetics. To tackle these problems simultaneously, a layer‐by‐layer electrode structure is designed, each layer of which consists of ultrafine CoS 2 ‐nanoparticle‐embedded porous carbon evenly grown on both sides of reduced graphene oxide (rGO). The CoS 2 nanoparticles derived from metal–organic frameworks (MOFs) have an average size of ≈10 nm and can facilitate the conversion between Li 2 S 6 and Li 2 S 2 /Li 2 S in the liquid electrolyte by a catalytic effect, leading to improved polysulfide redox kinetics. In addition, the interconnected conductive frameworks with hierarchical pore structure afford fast ion and electron transport and provide sufficient space to confine polysulfides. As a result, the layer‐by‐layer electrodes exhibit good rate capabilities with 1180.7 and 700 mAh g −1 at 1.0 and 5.0 C, respectively, and maintain an impressive cycling stability with a low capacity decay of 0.033% per cycle within ultralong 1000 cycles at 5.0 C. Even with a high sulfur loading of 3.0 mg cm −2 , the electrodes still show high rate performance and stable cycling stability over 300 cycles.
Formation of supramolecular ionic liquid (IL) gels (ionogels) induced by low-molecular-mass gelators (LMMGs) is an efficient strategy to confine ILs, and the negligible influence of LMMGs on the electrochemical properties of ILs makes ionogels ideal quasisolid electrochemical materials. Furthermore, the stimuli-responsive and self-healing characters of the supramolecular gel can be utilized for the potential development of smart electrochemical materials. However, the poor mechanical properties of supramolecular ionogels reported so far limit their practical applications. Herein, we investigated a series of efficient d-gluconic acetal-based gelators (Gn, PG16, and B8) that can harden a wide variety of ILs at low concentrations. It was shown that both alkyl chain length and the number of hydrogen bonding sites of a certain gelator, as well as the nature of the IL anion, significantly influenced the gelation abilities. The resulting ionogels were thermally reversible, and most of them were stable at room temperature. Interestingly, a PG16-based supramolecular ionogel showed rapid self-healing properties upon mechanical damage. Furthermore, the PG16-based ionogel demonstrated unprecedented performances including the favorable ionic conductivity, excellent mechanical strength, and enhanced viscoelasticity, which make it a great self-healing electrochemical material. The ionogel formation mechanism was proposed based on the analysis of Fourier transform infrared, HNMR, and X-ray diffraction, indicating that a combination of hydrogen bonding, π-π stacking, and interactions between alkyl chains was responsible for the self-assembly of gelators in ILs. Overall, our present studies on exploring the structure-property relationship of gelators for the formation of practically useful supramolecular ionogels shed light for future development of more functionalized ionogels.
The amorphous metal boride materials are attractive catalyst for advanced lithium sulfur batteries, but their catalytic mechanism remains unclear. Herein, 2D amorphous Mo-doped cobalt boride (Co 7 Mo 3 B) is designed for the first time as bidirectional sulfur catalysis by rapid chemical reduction. The atom cluster structure of Co 7 Mo 3 B is revealed by theoretical calculation. Electron paramagnetic resonance test further confirms that Co 7 Mo 3 B has interstitial compound structure characteristics. Experimental results show that the porous 2D nanosheets structure and the interaction of Mo, B, Co atoms contribute to enhanced conductivity, high long-chain lithium polysulfides affinity, and reversible Li 2 S nucleation and dissociation, thus accelerating LiPSs reduction and Li 2 S oxidation kinetics. In addition, the interstitial Co 7 Mo 3 B enables intercalation of Li and B during chargingdischarging while keeping the structure stable. As a result, the S cathode with Co 7 Mo 3 B catalyst delivers good life (1000 cycles at 5 C), superior rate performance (10 C). Even at high sulfur areal loading of 6.79 mg cm -2 and electrolyte/sulfur ratio of 5 μL mg -1 , the Co 7 Mo 3 B/S composite cathode still exhibits good areal capacity and capacity retention rate.
Self-healing ionogel is a promising smart material because of its high conductivity and reliable stimuli responsiveness upon mechanical damage. However, self-healing ionogels possessing rapid, complete recovery properties and multifunctionality are still limited. Herein, we designed a new d-gluconic acetal-based gelator (PB8) bearing a urea group in the alkyl side chain. Interestingly, the balance between hydrophilicity and hydrophobicity of the molecule is achieved. Thus, PB8 could form transparent ionogels because of its excellent affinity to ionic liquids (ILs), which exhibited appropriate mechanical strength, high viscoelasticity, and efficient self-healing properties. The presence of synergistic effects from hydrogen bonding, π–π stacking, and interactions between the urea-containing side chains was responsible for the self-assembly of gelators in ILs and the self-healing property mainly related to the side chains of PB8. Interestingly, the transparent PB8-IL4 ionogel possessed high conductivity and mechanical strength, moldable and injectable properties, and rapid and complete self-healing characteristics (complete recovery within 14 min), which showed excellent performance as a smart ionic conductor. Furthermore, the self-healing PB8-based ionogels with anticorrosion properties are a remarkable lubricating material in the steel–steel contact and exhibited excellent lubricating performances. Overall, an efficient PB8-based ionogel with self-healing properties has been developed for potential use both as a smart electrical conductor and as a high-performance lubricating material. The unique structure of PB8 bearing a urea group in the side chain is found to be responsible for the multifunctional ionogel formation.
A novel two-component organogel system based on acid-base interaction showed flexibility, high-transparency and self-healing properties with enhanced viscoelasticity. Meanwhile, the two-component gelator displayed room-temperature phase selective gelation of aromatic solvents from aromatic solvents/water mixtures in powder form and excellent dye removal ability.
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