Efficient Fabrication of Hierarchically Porous Graphene-Derived Aerogel and Its Application in Lithium Sulfur Battery

Ultrathin 2D-2D MXene-LDH Interlayer with High Polysulfide Adsorption Ability for Advanced Li-S Batteries

Lithium-sulfur (Li-S) batteries are considered as promising energy storage systems due to the high energy density of 2600 W h kg-1. However, the practical application of Li-S batteries is hindered by the inadequate conductivity of sulfur and Li2S, as well as the shuttle effect caused by polysulfides during the charge-discharge process. Introducing a conductive interlayer between the cathode and the separator to physically resist polysulfides represents an effective and straightforward approach to mitigate the shuttle effect in Li-S batteries. In this paper, an ultrathin (<1 μm) 2D-2D MXene-LDH interlayer with high polysulfide adsorption ability was introduced to Li-S batteries. The synergistic effect between MXene and layered double hydroxide greatly improved the adsorption effect of the interlayers: the conductive Ti3C2Tx MXene chemically adsorbs polysulfides and promotes their fast transfer, and the NiCo-LDH alleviates the restack of MXene and facilitates Li+ diffusion. After inserting the MXene-LDH interlayer, the Li-S batteries exhibit an enhanced specific capacity of 1137.6 mA h g-1 at 0.1 C and retain 622.6 mA h g-1 after 100 cycles. The ultrathin 2D-2D interlayer offers a feasible way for the development of highly efficient and lightweight interlayers in Li-S batteries.

Graphene/Heterojunction Composite Prepared by Carbon Thermal Reduction as a Sulfur Host for Lithium-Sulfur Batteries

An interlayer nanocomposite (CC@rGO) consisting of a graphene heterojunction with CoO and Co₉S₈ was prepared using a simple and low-cost hydrothermal calcination method, which was tested as a cathode sulfur carrier for lithium-sulfur batteries. The CC@rGO composite comprises a spherical heterostructure uniformly distributed between graphene sheet layers, preventing stacking the graphene sheet layer. After the introduction of cobalt heterojunction on a graphene substrate, the Co element content increases the reactive sites of the composite and improves its electrochemical properties to some extent. The composite exhibited good cycling performance with an initial discharge capacity of 847.51 mAh/g at 0.5 C and a capacity decay rate of 0.0448% after 500 cycles, which also kept 452.91 mAh/g at 1 C and in the rate test from 3 C back to 0.1 C maintained 993.27 mAh/g. This article provides insight into the design of cathode materials for lithium-sulfur batteries.

Integration of porous graphitic carbon and carbon fiber framework for ultrahigh sulfur-loading lithium-sulfur battery

A lithium-sulfur battery, a potential next-generation secondary battery, is affected by poor conductivity of sulfur and the dissolution of intermediate polysulfides. Here we report a lithium-sulfur battery with ultrahigh sulfur loading and excellent cycling stability using porous graphitic carbon (PGC) as a high-conductivity carrier of sulfur and carbon fiber with crisscross conductive framework as an electric attachment site of sulfur. PGC is fabricated through a simple and environmentally friendly synthesis process involving high-temperature graphitization in a N₂ atmosphere followed by an annealing process in air. Due to the presence of porous graphitic structure, with C-O termination groups, PGC endows the lithium-sulfur battery system with excellent cycling performance. The lithium-sulfur battery cathode constructed by PGC with a sulfur loading of 2.5 mg cm^-2 still retains a high specific capacity of 734.4 mA h g^-1 after 200 cycles. Meanwhile, an ultrahigh sulfur loading of 12.8 mg cm^-2 for a CR2025 coin cell is achieved, which is the highest sulfur loading reported in the literature for the coin cell. The ultrahigh sulfur loading cell also shows good electrochemical properties, profiting from the mesopores terminated with C-O groups, high specific surface area of 1129.9 m² g^-1 and high-conductivity graphitic structure.

Investigating the Electrocatalysis of a Ti3C2/Carbon Hybrid in Polysulfide Conversion of Lithium-Sulfur Batteries

Despite the fact that lithium-sulfur batteries are regarded as promising next-generation rechargeable battery systems owning to high theoretical specific capacity (1675 mA h g^-1) and energy density (2600 W h kg^-1), several issues such as poor electrical conductivity, sluggish redox kinetics, and severe "shuttle effect" in electrodes still hinder their practical application. MXenes, novel two-dimensional materials with high conductivity, regulable interlayer spacing, and abundant functional groups, are widely applied in energy storage and conversion fields. In this work, a Ti₃C₂/carbon hybrid with expanded interlayer spacing is synthesized by one-step heat treatment in molten potassium hydroxide. The subsequent experiments indicate that the as-prepared Ti₃C₂/carbon hybrid can effectively regulate polysulfide redox conversion and has strong chemisorption interaction to polysulfides. Consequently, the Ti₃C₂/carbon-based sulfur cathode boosts the performance in working lithium-sulfur batteries, in terms of an ultrahigh initial discharge capacity (1668 mA h g^-1 at 0.1 C), an excellent rate performance (520 mA h g^-1 at 5 C), and an outstanding capacity retention of 530 mA h g^-1 after 500 cycles at 1 C with a low capacity fade rate of 0.05% per cycle and stable Coulombic efficiency (nearly 99%). The above results indicate that this composite with high catalytic activity is a potential host material for further high-performance lithium-sulfur batteries.

Bioinspired aerogel based on konjac glucomannan and functionalized carbon nanotube for controlled drug release

In this study, a facile marine bioinspired surface modification approach for carboxyl-functionalized multiwalled carbon nanotube (CCNT) and enhanced interfacial adhesion with the konjac glucomannan (KGM) matrix were illustrated to develop aerogels. Combined with FT-IR, XRD, Raman, TGA, XPS and SEM results, it was indicated that functionalized CCNT (PCCNT) is a reinforcer through hydrogen bond interactions in the aerogel formation process, which could be the main reason for the enhancement. The swelling and vitro release behavior of KGM/PCCNT aerogels were studied under two conditions using the drug 5-fluorouracil (5-FU). The release amount of 5-FU incorporated into KGM/PCCNT4 aerogel was about 48% at pH 1.2 and 62% at pH 6.8 after11 h, respectively. The results showed that the release rate of 5-FU from the KGM/PCCNT4 aerogel using PCCNT could be effectively controlled, suggesting potential applications for it as a drug carrier in targeted delivery in the biomedical filed.

New Insights into the Anchoring Mechanism of Polysulfides inside Nanoporous Covalent Organic Frameworks for Lithium-Sulfur Batteries

The application prospects of lithium-sulfur (Li-S) batteries are constrained by many challenges, especially the shuttle effect of lithium polysulfides (Li₂S _x). Recently, microporous covalent organic framework (COF) materials have been used to anchor electrodes in Li-S batteries, because of their preferable characteristics, such as self-design ability, suitable pore size, and various active groups. To identify the ideal anchoring materials that can effectively restrain the shuttle of Li₂S _x species, the anchoring mechanism between COF materials and Li₂S _x species should be investigated in depth. Therefore, we systematically investigated the anchoring mechanism between specific COF nanomaterials (consisting of boron and oxygen atoms and benzene group) and Li₂S _x ( x = 1, 2, 4, 6, or 8) species on the surface and inside the pore using density functional theory methods with van der Waals interactions. The detailed analysis of the adsorption energy, difference charge density, charge transfer, and atomic density of states can be used to determine that the COF nanomaterials, with the structure of boroxine connecting to benzene groups and boroxine groups not constructed at the corner of the structure, can effectively anchor the Li₂S _x series. Accordingly, this study provides the theoretical basis for the molecular-scale design of ideal anchoring materials, which can be useful to improve the performance of the Li-S batteries.

Functionalization of Graphene Aerogels and their Applications in Energy Storage and Conversion

Functionalized graphene aerogels (GAs) not only own the advantages of the original ones like large specific surface area, three-dimensional porous structures, high specific capacitance and excellent cyclic stability, but also realize the function expansion due to the collective properties endowed via different methods. These characteristics make them advantageous in some promising applications. In this minireview, we focus on the various functionalization methods of GAs and especially their use in the applications of energy storage and conversion like batteries, supercapacitors and fuel cells, etc.

Hierarchically porous graphene for batteries and supercapacitors

Hierarchical porous graphene based materials are explored for their application as electrochemical storage devices due to their large specific surface area, high electrical and thermal conductivity, and excellent specific capacity.

A Honeycomb-like Co@N-C Composite for Ultrahigh Sulfur Loading Li-S Batteries

Because of the high theoretical capacity of 1675 mAh g^-1 and high energy density of 2600 Wh kg^-1, respectively, lithium-sulfur batteries are attracting intense interest. However, it remains an enormous challenge to realize high utilizations and loadings of sulfur in cathodes for the practical applications of Li-S batteries. Herein, we design a quasi-2D Co@N-C composite with honeycomb architecture as a multifunctional sulfur host via a simple sacrificial templates method. The cellular flake with large surface area and honeycomb architecture can encapsulate much more sulfur, leading to high sulfur content (HSC) composites, and by stacking these HSC flakes, a high sulfur loading (HSL) electrode can be realized due to their high layer bulk density. Compared to our previous work in multifunctional Co-N-C composites, the cellular Co@N-C composite displays a distinct enhancement in the sulfur content, sulfur loading, cycle stability, and rate performance. Benefiting from the cellular morphology, a composite with an HSC of 93.6 wt % and an electrode with an HSL of 7.5 mg cm^-2 can be obtained simultaneously, which exhibited excellent rate performance up to 10 C (3.6 mg cm^-2) and great cycling stability.

3D free-standing nitrogen-doped reduced graphene oxide aerogel as anode material for sodium ion batteries with enhanced sodium storage

Sodium ion batteries have drawn extensive attentions for large-scale energy storage to replace lithium ion batteries primarily due to the natural abundance of sodium resource and low cost, but their energy density and electrochemical performance are hindered by the sluggish diffusion kinetics of sodium ion. Herein, free-standing nitrogen-doped graphene aerogel has been fabricated via hydrothermal reaction as the potential anode material for sodium ion batteries. The three dimensional porous network structure of the graphene aerogel provides sufficient interstitial space for sodium ion accommodation, allowing fast and reversible ion intercalation/de-intercalation. The nitrogen doping could introduce defects on the graphene sheets, making the feasible transport of large-sized sodium ion. Benefiting from the effective structure and nitrogen doping, the obtained material demonstrates high reversible capacities, good cycling performance (287.9 mA h g⁻¹ after 200 cycles at a current density of 100 mA g⁻¹), especially superior rate capability (151.9 mA h g⁻¹ at a high current density of 5 A g⁻¹).

Highly Conductive Porous Transition Metal Dichalcogenides via Water Steam Etching for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries show significant advantages for next-generation energy storage systems owing to their high energy density and cost effectiveness. The main challenge in the development of long-life and high-performance Li-S batteries is to simultaneously facilitate the redox kinetics of sulfur species and suppress the shuttle effect of polysulfides. In this contribution, we present a general and green water-steam-etched approach for the fabrication of H- and O-incorporated porous TiS₂ (HOPT). The conductivity, porosity, chemisorptive capability, and electrocatalytic activity of HOPT are enhanced significantly when compared with those of raw TiS₂. The synthetic method can be expanded to the fabrication of other highly conductive transition metal dichalcogenides such as porous NbS₂ and CoS₂. The as-obtained HOPT can serve as both a substitute of conductive agents and an additive of interlayer materials. The optimal electrode delivers discharge capacities of 950 mA h g^-1 after 300 cycles at 0.5 C and 374 mA h g^-1 after 1000 cycles at 10 C. Impressively, an unprecedented reversible capacity of 172 mA h g^-1 is achieved after 2500 cycles at 30 C, and the average capacity fading rate per cycle is as low as 0.015%. Importantly, four half-cells based on this electrode in series could drive 60 light-emitting diode indicator modules (the nominal power 3 W) after 20 s of charging. The instantaneous current and power of this device on reaching 275 A g^-1 and 2611 W g^-1, respectively, indicate outstanding high-power discharge performance and potential applications in electric vehicles and other large-scale energy storage systems.

Ultrathin Cobaltosic Oxide Nanosheets as an Effective Sulfur Encapsulation Matrix with Strong Affinity Toward Polysulfides

Two-dimensional ultrathin cobaltosic oxide nanosheets with numerous geometrical holes were synthesized by the hydrothermal method, and further used as an effective encapsulation matrix for sulfur and polysulfides in lithium-sulfur batteries. The cobaltosic oxide/sulfur nanosheet composite electrode exhibits high Coulombic efficiency (99%), a suppressed shuttle effect, and a reversible capacity of 656 mA h g^-1 at 0.2 C after 200 cycles, with small capacity fading of 0.219% per cycle, whereas its carbon-sulfur electrode counterpart only retains a capacity of 386 mA h g^-1 after 100 cycles. The improved performance is attributed to the strong chemical interaction between polysulfides and cobaltosic oxide, and its facile ionic transport and enhanced reaction kinetics, which can effectively control the diffusion of polysulfides and keep them within the cathode region, leading to good electrochemical stability.

Role of Graphene Oxide Liquid Crystals in Hydrothermal Reduction and Supercapacitor Performance

The formation of liquid crystal (LC) phases in graphene oxide (GO) aqueous solution is utilized to develop high-performance supercapacitors. To investigate the effect of LC formation on the properties of subsequently reduced GO (rGO), we compare films prepared through blade-coating of viscous LC-GO solution and ultrasonic spray-coating of diluted GO aqueous dispersion. After hydrothermal reduction under identical conditions, the films show different morphology, oxygen content, and specific capacitance. Trapped water in the LC GO film plays a role in preventing restacking of sheets and facilitating the removal of oxygenated groups during the reduction process. In device architectures with either liquid or polymer electrolyte, the specific capacitance of the blade-coated film is twice as high as that of the spray-coated one. For a blade-coated film with mass loading of 0.115 mg/cm(2), the specific capacitance reaches 286 F/g in aqueous electrolyte and 263 F/g in gelled electrolyte, respectively. This study suggests a route to pilot-scale production of high-performance graphene supercapacitors through blade-coated LC-GO films.

Synergistically enhanced activity of graphene quantum dots/graphene hydrogel composites: a novel all-carbon hybrid electrocatalyst for metal/air batteries

Primary zinc/air batteries could be the next generation of energy storage devices because of their high power density and high safety. Graphene quantum dots nested in the graphene hydrogel have been proposed as excellent all-carbon hybrid oxygen reduction reaction (ORR) catalysts, indicative of their great potential in primary zinc/air batteries.