Bimetallic MOF-derived CNTs-grafted carbon nanocages as sulfur host for high-performance lithium–sulfur batteries

Synergistic effect of porous carbon shell confinement and catalytic conversion of nickel nanoparticle cores for improved lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are some of the most promising energy storage systems to break the ceiling of Li-ion batteries. However, the notorious shuttle effect and slow redox kinetics give rise to low sulfur utilization and discharge capacity, poor rate performance, and fast capacity decay. It is proved that the reasonable design of the electrocatalyst is one of the important ways to improve the electrochemical performance of LSBs. Here, a core-shell structure with gradient adsorption capacity for reactants and sulfur products was designed. The Ni nanoparticles core coated with graphite carbon shell was prepared by one-step pyrolysis of Ni-MOF precursors. The design takes advantage of the principle that the adsorption capacity decreases from the core to the shell, and the Ni core with strong adsorption capacity is easy to attract and capture soluble lithium polysulfide (LiPS) during the discharge/charging process. This trapping mechanism prevents the diffusion of LiPSs to the outer shell and effectively inhibits the shuttle effect. In addition, the Ni nanoparticles within the porous carbon, as the active center, expose most of the inherent active sites to the surface area, thus achieving a rapid transformation of LiPSs, significantly reducing the reaction polarization, and improving the cyclic stability and reaction kinetics of LSB. Therefore, the S/Ni@PC composites exhibited excellent cycle stability (a capacity of 417.4 mA h g-1 for 500 cycles at 1C with a fading rate of 0.11%) and outstanding rate performance (1014.6 mA h g-1 at 2C). This study provides a promising design solution of Ni nanoparticles embedded in porous carbon for high-performance, safe and reliable LSB.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

In Situ Anchoring Anion-Rich and Multi-Cavity NiS2 Nanoparticles on NCNTs for Advanced Magnesium-Ion Batteries

Magnesium (Mg)-ion batteries with low cost and good safety characteristics has attracted a great deal of attention recently. However, the high polarity and the slow diffusion of Mg²⁺ in the cathode material limit the development of practical Mg cathode materials. In this paper, an anion-rich electrode material, NiS₂ , and its composite with Ni-based carbon nanotubes (NiS₂ /NCNTs) are explored as the cathode materials for Mg-ion batteries. These NiS₂ /NCNTs with excellent Mg²⁺ storage property is synthesized by a simple in situ growth of NiS₂ nanoparticles on NCNTs. NiS₂ with both a large regular cavity structure and abundant sulfur-sulfur (SS) bonds with high electronegativity can provide a large number of active sites and unobstructed transport paths for the insertion-disinsertion of Mg²⁺ . With the aid of 3D NCNTs skeleton as the transport channel of the electron, the NiS₂ /NCNTs exhibit a high capacity of 244.5 mAh g^-1 at 50 mA g^-1 and an outstanding rate performance (94.7 mAh g^-1 at 1000 mA g^-1 ). It achieves capacitance retention of 58% after 2000 cycles at 200 mA g^-1 . Through theoretical density functional theory (DFT) calculations and a series of systematic ex situ characterizations, the magnesiation/demagnesiation mechanisms of NiS₂ and NiS₂ /NCNTs and are elucidated for fundamental understanding.

Simultaneously enhancing redox kinetics and inhibiting the polysulfide shuttle effect using MOF-derived CoSe hollow sphere structures for advanced Li-S batteries

Lithium-sulfur (Li-S) batteries generally suffer from a serious "shuttle effect" during the charging/discharging process, resulting in the loss of active components and sluggish redox reaction kinetics that hinder the cycle life and rate performance of the battery. To address this, CoSe/C hollow structures (CoSe/C HSs) were prepared via a simple hydrothermal strategy and used as a sulfur host for Li-S batteries. The battery with CoSe/C HSs exhibited a high initial specific discharge capacity of 1405 mA h g-1 with a coulombic efficiency of 99.8% at 0.1C. Additionally, S@CoSe/C HS cathodes with a high sulfur loading of 5.1 mg cm-2 delivered a considerable specific discharge capacity of 1256.1 mA h g-1 and maintained a high capacity of 1120 mA h g-1 after 100 cycles with a capacity decay rate of 0.11% per cycle at 0.1C. The unique raspberry-like structure of CoSe/C HSs prevents polysulfides from escaping the cathode host via both physical containment and the formation of Co-S and Se-Li chemical bonds, and it also enhances the polysulfide redox kinetics. Furthermore, the peculiar raspberry-like structure can withstand volume changes during charging/discharging to better protect the cathode.

Disassembly of lignocellulose into cellulose, hemicellulose, and lignin for preparation of porous carbon materials with enhanced performances

Lignocellulose is the primary component of many biomasses, including corn straw. Herein, lignocellulose in corn straw was disassembled into the individual polymers, cellulose, hemicellulose, and lignin via a mild and facile method. Subsequently, three porous carbon materials were prepared by carbonization and chemical activation of cellulose (PCCC), hemicellulose (PCHC), and lignin (PCLC). The three materials showed higher specific surface areas (2565.7, 2996.1, and 2590.3 m² g^-1) and higher porosities (1.4261, 1.5876, and 1.2406 cm³ g^-1) than that of PCCS, a porous carbon material derived from raw corn straw (1993 m² g^-1 and 1.19 cm³ g^-1). Of note, PCCC and PCHC exhibited higher adsorption (1025.5 and 950.1 mg g^-1) of brilliant green (BG), than PCCS (876.7 mg g^-1). Besides, the BG adsorption capacities of the designed materials were higher than that of most adsorbents, and 2-2.5 times higher than that of graphite oxide (416.7 mg g^-1). These study results indicate that the disassembly of lignocellulosic biomass into cellulose, hemicellulose, and lignin is an effective strategy for preparing various porous carbon materials with enhanced performances.