Zhonghui Cui

Monodispersed Carbon-Coated Cubic NiP2 Nanoparticles Anchored on Carbon Nanotubes as Ultra-Long-Life Anodes for Reversible Lithium Storage

In search of new electrode materials for lithium-ion batteries, metal phosphides that exhibit desirable properties such as high theoretical capacity, moderate discharge plateau, and relatively low polarization recently have attracted a great deal of attention as anode materials. However, the large volume changes and thus resulting collapse of electrode structure during long-term cycling are still challenges for metal-phosphide-based anodes. Here we report an electrode design strategy to solve these problems. The key to this strategy is to confine the electroactive nanoparticles into flexible conductive hosts (like carbon materials) and meanwhile maintain a monodispersed nature of the electroactive particles within the hosts. Monodispersed carbon-coated cubic NiP2 nanoparticles anchored on carbon nanotubes (NiP2@C-CNTs) as a proof-of-concept were designed and synthesized. Excellent cyclability (more than 1000 cycles) and capacity retention (high capacities of 816 mAh g-1 after 1200 cycles at 1300 mA g-1 and 654.5 mAh g-1 after 1500 cycles at 5000 mA g-1) are characterized, which is among the best performance of the NiP2 anodes and even most of the phosphide-based anodes reported so far. The impressive performance is attributed to the superior structure stability and the enhanced reaction kinetics incurred by our design. Furthermore, a full cell consisting of a NiP2@C-CNTs anode and a LiFePO4 cathode is investigated. It delivers an average discharge capacity of 827 mAh g-1 based on the mass of the NiP2 anode and exhibits a capacity retention of 80.7% over 200 cycles, with an average output of ∼2.32 V. As a proof-of-concept, these results demonstrate the effectiveness of our strategy on improving the electrode performance. We believe that this strategy for construction of high-performance anodes can be extended to other phase-transformation-type materials, which suffer a large volume change upon lithium insertion/extraction.

Field electron emission from individual diamond cone formed by plasma etching

Field electron emission properties of individual diamond cone were investigated using a customized double-probe scanning electron microscope system. The diamond cone was formed by maskless ion sputtering process in bias-assisted hot filament chemical vapor deposition system. The as-formed sharp diamond cone coated with high-sp2-content amorphous carbon exhibited high emission current of about 80μA at an applied voltage of 100V. The field emission was stable and well in consistent with the conventional Fowler-Nordheim emission mechanism, due to a stabilization process in surface work function. It has demonstrated the possibility of using individual diamond cone as a point electron emission source, because of its high field electron emission ability and stable surface state after the process of work function stabilization.

In Situ Fabrication of CoS and NiS Nanomaterials Anchored on Reduced Graphene Oxide for Reversible Lithium Storage

CoS and NiS nanomaterials anchored on reduced graphene oxide (rGO) sheets, synthesized via combination of hydrothermal with sulfidation process, are studied as high-capacity anode materials for the reversible lithium storage. The obtained CoS nanofibers and NiS nanoparticles are uniformly dispersed on rGO sheets without aggregation, forming the sheet-on-sheet composite structure. Such nanoarchitecture can not only facilitate ion/electron transport along the interfaces, but also effectively prevent metal-sulfide nanomaterials aggregation during the lithium reactions. Both the rGO-supported CoS nanofibers (NFs) and NiS nanoparticles (NPs) show superior lithium storage performance. In particular, the CoS NFs-rGO electrodes deliver the discharge capacity as high as 939 mA h g(-1) after the 100th cycle at 100 mA g(-1) with Coulombic efficiency above 98%. This strategy for construction of such composite structure can also synthesize other metal-sulfide-rGO nanomaterials for high-capacity lithium-ion batteries.

Novel one-step gas-phase reaction synthesis of transition metal sulfide nanoparticles embedded in carbon matrices for reversible lithium storage

This report presents a novel one-step method based on the gas-phase reaction between metallocenes and sulfur for synthesizing the nanocomposites of transition metal sulfide nanoparticles embedded in carbon matrices (TMS@C). Various nanocomposites including FeS@C, Cr2S3@C and NiS2@C have been successfully synthesized by using ferrocene, chromocene and nickelocene, respectively. The SEM investigations evidence that the TMS nanoparticles are evenly distributed in the in situ formed carbon matrices, demonstrating that this novel method is an easy way to synthesize homogenous TMS-based nanocomposites with well-controlled nanostructures. As the anodes for lithium ion batteries (LIBs), the as-prepared TMS@C electrodes exhibit excellent rate capability and high reversible capacity. For example, a high reversible capacity of 550 and 480 mA h g−1 can be retained for the FeS@C anode even after 350 cycles at a current density of 0.1 A g−1 and 500 cycles at 0.5 A g−1, respectively. The TEM investigations on the 100th discharged and recharged electrodes demonstrate superior structural stability against repeated lithiation/delithiation of the FeS@C. These impressive results indicate that this novel approach is a promising way to synthesize high-performance TMS electrodes for highly reversible lithium storage.

Reaction pathway and wiring network dependent Li/Na storage of micro-sized conversion anode with mesoporosity and metallic conductivity

Micro-sized or monolithic electrode materials with sufficient mesoporosity and a high intrinsic conductivity are highly desired for high-energy batteries without the trade-off of electrolyte infiltration and accommodation of volume expansion. Here metallic nitrides consisting of mesoporous microparticles were prepared based on a mechanism of solid–solid phase separation and used as conversion anodes for Li and Na storage. Their superior capacity and rate performance during thousands of cycles benefit from the preservation or self-reconstruction of hierarchically conductive wiring networks. The conversion efficiency is also highly dependent on the reaction pathway and product. Exploring more conductive and percolating mass/charge transport networks particularly in a deep sodiation state is a potential solution for activation of Na-driven conversion electrochemistry.

Immobilization of sulfur by constructing three-dimensional nitrogen rich carbons for long life lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have been considered as next-generation rechargeable energy storage systems due to their high theoretical energy densities and low cost; however, the capacity decay resulting from the shuttle of lithium polysulfides (LiPSs) hinders their practical application. Herein, we describe a strategy to synthesize highly pyridinic-N-doped three-dimensional (3D) carbons for the chemisorption of LiPSs, which consist of zeolitic imidazolate framework-8-derived carbon (ZIF-8(C)) coated on the surface of N-doped carbon nanotubes supported by carbon nanosheets (NCNTs–CS–ZIF-8(C)). Using the obtained carbons as sulfur hosts, the S/NCNTs–CS–ZIF-8(C) cathodes show a high sulfur utilization of 86% at 0.1 C, a low capacity decay rate of 0.052% per cycle over 700 cycles at 1 C and impressive cycling life that is 564 mA h g−1 after 700 cycles at 1 C. First principles calculations based on the Vienna Ab-Initio Simulation Package (VASP) reveal that increasing the amount of the pyridinic-N component can enhance the adsorption of LiPSs, which yields effective suppression of the LiPS shuttle.

Job-sharing cathode design for Li–O2 batteries with high energy efficiency enabled by in situ ionic liquid bonding to cover carbon surface defects

The difficult achievement of high round-trip energy efficiency or low charge overpotential has retarded Li–O2(air) batteries in real applications. Although much effort has been focused on exploring novel catalysts, their potential effects are usually counteracted by a quick passivation of the electrode as a consequence of side reactions, which likely contribute to the widely observed high-voltage reversibility (e.g. >4 V). Here, we report a job-sharing design of a carbon-based cathode, Ru-IL (ionic liquid)–CNT (carbon nanotube), with fine Ru nanodots anchored on the IL-decorated CNT surface. The subnanometer IL cation linker is crucial to seal carbon surface defects without sacrificing Li+/e− charge transfer and therefore efficiently suppresses the occurrence of side reactions. This charged decoration guarantees that Ru functions as the microstructure promoter to stabilize highly disordered Li2O2. It enables achievement of high energy efficiency (80–84%) Li–O2 batteries characterized by a substantial charge plateau with an extremely low overpotential of 0.18 V. Even by using the mode of voltage cut-off, a reversible capacity around 800–1000 mA h g−1 is maintained for more than 100 cycles. When the reversible capacity is limited to 500 mA h g−1, the cycling number can reach up to at least 240 cycles. The disentangled CNT networks, loose precipitation of nanostructured products and high donor number electrolytes allow thick electrode fabrication (8 mg cm−2), leading to a high areal capacity of 3.6–7.6 mA h cm−2. Our results indicate a defect-inspired strategy to bury undesired defect sites in the original electrode framework and to electrochemically synthesize the stable defect-rich Li2O2 product.

Rapid Development and Critical Issues of Secondary Lithium-air Batteries: Rapid Development and Critical Issues of Secondary Lithium-air Batteries

Rechargeable lithium-air batteries have been the focus in recent years, owing to their great potential for achieving super-high specific energy density. Many researchers have carried out investigations on crucial issues such as reaction mechanism, cycle life, overpotential, rate capability, and significant progresses have been made. Based on these efforts, in combination with our own experience, this paper summarizes recent development of secondary lithium-air batteries, and our opinions on the critical scientific issues which are urgently required to solve in view of real application.

Controllable synthesis of hollow copper oxide encapsulated into N-doped carbon nanosheets as high-stability anodes for lithium-ion batteries

Copper oxide is one of the promising anode materials for lithium-ion batteries (LIBs) due to its high energy density. However, it suffers from fast capacity fading and poor cycling stability, arising from the low electrical conductivity and the large volume expansion. Herein, we report a chemical vapor and solid deposition strategy for the synthesis of hollow copper nanoparticles supported by N-doped carbon nanosheets (Cu@NCSs) on Cu foil, adopting a polymer as the carbon source. After successive oxidation treatment, the construction of hollow copper oxide encapsulated into N-doped carbon nanosheets (CuO@NCSs) is achieved. The resulting products are used as anodes in LIBs, displaying a capacity of 688 mA h g−1 over 1000 cycles at 2 A g−1 and a capacity of 400 mA h g−1 at 4 A g−1. Such superior performance is attributed to the well-designed hollow CuO@NCS composites, which not only improve the electrical conductivity of electrode materials, but also allow easy penetration of electrolyte and mitigation of the volume expansion.

Formation of self-limited, stable and conductive interfaces between garnet electrolytes and lithium anodes for reversible lithium cycling in solid-state batteries

Solid-state batteries (SSBs) have already attracted significant attention due to their potential to offer high energy density and excellent safety as compared to the currently used lithium-ion batteries with liquid electrolytes. The use of a lithium anode in SSBs is extremely important to realize these advantages. Starting from the synthesis of a highly conductive cubic garnet solid electrolyte (Li6.375La3Zr1.375Nb0.625O12, LLZNO) using Nb as a structure stabilizer, in this study, we demonstrated the resolution of interfacial problems between the garnet electrolyte and lithium anode and the integration of the lithium anode into garnet-based SSBs by modifying the as-synthesized LLZNO with a Sn thin film. Due to the Sn modification, the interfacial resistances between the garnet electrolyte and the lithium anode decreased approximately 20 times to only 46.6 Ω cm2. The fast and reversible lithium plating/stripping under high current densities and the excellent battery performance of Li/Sn-LLZNO/LiFePO4 full cells were achieved. This improvement is ascribed to the formation of a Li–Sn alloy interlayer, which severs as a self-limited stable and conductive interface, bridging the garnet electrolyte and the lithium anode and enabling fast and stable lithium transport. As a proof-of-concept, this effective surface modification method will offer inspirations to researchers for overcoming the interfacial problems and promoting the development of high-performance SSBs.