A Facilely Synthesized NiCo2S4 with Two Mutually Reinforcing Active Sites for High-Performance Lithium-Sulfur Batteries.

The shuttle effect and slow conversion kinetics of soluble polysulfides hinder the commercial application of lithium-sulfur batteries (LSBs). In this context, we propose a three-dimensional lamellar-stacked nanostructure of nickel cobalt sulfide (D-NiCo2S4) enriched with lattice defects by manipulating the cations in spinel sulfides. It has an obvious synergistic promotion mechanism for the adsorption and catalysis of lithium sulfides. Specifically, Ni3+ on tetrahedral (Td) sites with strong Ni-S covalency anchors LiPSs, whereas Co3+ on octahedral (Oh) sites promotes a highly efficient catalytic conversion of LiPSs, which is confirmed by experimental results and density functional theory (DFT) calculations. Besides, the crystal defects and distortions in the lamellar region could expose more active sites and enhance the redox reaction kinetics of polysulfides. Hence, Li-S batteries with D-NiCo2S4@S as the cathode show outstanding cycle stability; upon cycling at 1 A/g, the battery achieves a high initial specific capacity of 1001.12 and 655.31 mAh g-1 after 1000 cycles (decay rate as low as 0.05% per cycle), as well as a high initial areal capacity of 3.15 mAh cm-2 under high S loading (4.2 mg cm-2). This work provides a viable scheme for designing efficient bimetal sulfide catalysts and furnishes a rational strategy for constructing LSB cathodes with high specific capacity and high area capacity.

Cobalt nanoparticles & nitrogen-doped carbon nanotubes@hollow carbon with high catalytic ability for high-performance lithium sulfur batteries.

Lithium-sulfur (Li-S) battery has been considered as a potential next-era energy storage device. However, its practical application is limited by the volume change of sulfur and the shuttle effect of lithium polysulfides. To effectively overcome these issues, a hollow carbon decorated with cobalt nanoparticles and interconnected by nitrogen doped carbon nanotubes (Co-NCNT@HC) is developed for high-performance Li-S battery. The uniformly distributed nitrogen and cobalt nanoparticles in Co-NCNT@HC are able to enhance the chemical adsorption capability and fasten the transformation speed of the intermediates, thus effectively inhibit the loss of lithium polysulfides. Moreover, the hollow carbon spheres interconnected by carbon nanotubes are structurally stable and electrically conductive. Due to the unique structure, the Li-S battery enhanced by Co-NCNT@HC shows a high initial capacity of 1550 mAh/g at 0.1 A g-1. Even at a high current density of 2.0 A g-1, after 1000 cycles, it still maintains a capacity of 750 mAh/g with a capacity retention of 76.4% (the capacity decay rate is only 0.037% per cycle). This study provides a promising strategy for the development of high-performance Li-S batteries.

A semi-fluid multi-functional binder for a high-performance silicon anode of lithium-ion batteries.

Currently, a variety of binders are developed to inhibit the rapid capacity fading of Si. The Si anodes are mainly enhanced by the chemical bonding effect on the surface of conventional solid-state binders. However, with a huge volume change of silicon, solid binders are easily deactivated. Herein, a semi-fluid binder termed GPC is designed based on a viscoelastic crosslinking network with abundant active sites and self-healing performance. The backbone of the binder network is in situ synthesized using guar gum (GG), polyacrylic acid (PAA), and citric acid (CA). Serving as the flexible joints and the plasticizer of the network, CA small molecules remarkably improve the viscoelasticity of the binder to tolerate the volume change of Si via rearranging particles in the network during cycling. Moreover, CA can form a layer of surface coating on Si to stabilize the SEI for long-term electrochemical performance. As a result, the Si@GPC electrode shows excellent cycling stability and exhibits a superb capacity of 1292 mA h g-1 after 1000 cycles at 2 A g-1. This work illustrates the advantages and prospects of designing semi-fluid binders for high-performance batteries.

An Energy Dissipative Binder for Self-Tuning Silicon Anodes in Lithium-Ion Batteries.

The volume change of the silicon anode seriously affects the electrode integrity and cycle stability. Herein, a binder, GCA13, with energy dissipation function and surface stability effect is proposed to enhance the cycle life and specific capacity. Unlike traditional binders that protect silicon electrodes through long-chain networks, GCA13 introduces citric acid molecules with short-range functions on the long-chain guar gum through weak interconnection. This short-range action is similar to the function of a spring, which can effectively buffer the silicon particle pulverization caused by the volume change. Therefore, the electrode can effectively maintain structural integration with ignorable cracks and alleviated thickness swelling. Thus, the Si@GCA13 anode exhibits a high reversible capacity of 1184 mAh g-1 under 2 A g-1 after 740 cycles with a latter coulombic efficiency of 99.9%. Extraordinarily, benefiting from the superior properties of the GCA13 binder, the electrode shows remarkable cycling stability under low (-15 and 0 °C) and high temperatures (60 °C). The work demonstrates the great potential of this binder design strategy to achieve the overall property promotion of Si anodes for practical application even under harsh service conditions.