Dongming Yin

Metal Organic Frameworks Route to in Situ Insertion of Multiwalled Carbon Nanotubes in Co3O4 Polyhedra as Anode Materials for Lithium-Ion Batteries

Hybridizing nanostructured metal oxides with multiwalled carbon nanotubes (MWCNTs) is highly desirable for the improvement of electrochemical performance of lithium-ion batteries. Here, a facile and scalable strategy to fabricate hierarchical porous MWCNTs/Co3O4 nanocomposites has been reported, with the help of a morphology-maintained annealing treatment of carbon nanotubes inserted metal organic frameworks (MOFs). The designed MWCNTs/Co3O4 integrates the high theoretical capacity of Co3O4 and excellent conductivity as well as strong mechanical/chemical stability of MWCNTs. When tested as anode materials for lithium-ion batteries, the nanocomposite displays a high reversible capacity of 813 mAh g(-1) at a current density of 100 mA g(-1) after 100 charge-discharge cycles. Even at 1000 mA g(-1), a stable capacity as high as 514 mAh g(-1) could be maintained. The improved reversible capacity, excellent cycling stability, and good rate capability of MWCNTs/Co3O4 can be attributed to the hierarchical porous structure and the synergistic effect between Co3O4 and MWCNTs. Furthermore, owing to this versatile strategy, binary metal oxides MWCNTs/ZnCo2O4 could also be synthesized as promising anode materials for advanced lithium-ion batteries.

Core–Shell NiFe2O4@TiO2 Nanorods: An Anode Material with Enhanced Electrochemical Performance for Lithium‐Ion Batteries

Hierarchical porous core-shell NiFe2O4@TiO2 nanorods have been fabricated with the help of hydrothermal synthesis, chemical bath deposition, and a subsequent calcinating process. The nanorods with an average diameter of 48 nm and length of about 300-600 nm turn out have a highly uniform morphology and are composed of nanosized primary particles. Owing to the synergistic effect of individual constituents as well as the hierarchical porous structure, the novel core-shell NiFe2O4@TiO2 nanorods exhibit superior electrochemical performance when evaluated as anode materials for lithium-ion batteries. At the current density of 100 mA g(-1), the composite exhibits a reversible specific capacity of 1034 mAh g(-1) up to 100 charge-discharge cycles, which is much higher than the uncoated NiFe2O4 nanorods. Even when cycled at 2000 mA g(-1), the discharge capacity could still be maintained at 358 mAh g(-1).

Coated/Sandwiched rGO/CoSx Composites Derived from Metal-Organic Frameworks/GO as Advanced Anode Materials for Lithium-Ion Batteries.

Rational composite materials made from transition metal sulfides and reduced graphene oxide (rGO) are highly desirable for designing high-performance lithium-ion batteries (LIBs). Here, rGO-coated or sandwiched CoSx composites are fabricated through facile thermal sulfurization of metal-organic framework/GO precursors. By scrupulously changing the proportion of Co(2+) and organic ligands and the solvent of the reaction system, we can tune the forms of GO as either a coating or a supporting layer. Upon testing as anode materials for LIBs, the as-prepared CoSx -rGO-CoSx and rGO@CoSx composites demonstrate brilliant electrochemical performances such as high initial specific capacities of 1248 and 1320 mA h g(-1) , respectively, at a current density of 100 mA g(-1) , and stable cycling abilities of 670 and 613 mA h g(-1) , respectively, after 100 charge/discharge cycles, as well as superior rate capabilities. The excellent electrical conductivity and porous structure of the CoSx /rGO composites can promote Li(+) transfer and mitigate internal stress during the charge/discharge process, thus significantly improving the electrochemical performance of electrode materials.

Sulfur-impregnated core-shell hierarchical porous carbon for lithium-sulfur batteries.

Core-shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge-discharge process. The as-prepared HPC-sulfur (HPC-S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g(-1) at a current density of 335 mA g(-1) (0.2 C) as a cathode material for lithium-sulfur (Li-S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g(-1) at 6700 mA g(-1) (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g(-1) after 200 cycles.

Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage

Owing to its richer redox reaction and remarkable electrical conductivity, bimetallic nickel cobalt sulfide (NiCo2S4) is considered as an advanced electrode material for energy-storage applications. Herein, nanosized NiCo2S4@C encapsulated in a hollow nitrogen-doped carbon cube (NiCo2S4@D-NC) has been fabricated using a core@shell Ni3[Co(CN)6]2@polydopamine (PDA) nanocube as the precursor. In this composite, the NiCo2S4 nanoparticles coated with conformal carbon layers are homogeneously embedded in a 3D high-conduction carbon shell from PDA. Both the inner and the outer carbon coatings are helpful in increasing the electrical conductivity of the electrode materials and prohibit the polysulfide intermediates from dissolving in the electrolyte. When researched as electrode materials for lithium storage, owing to the unique structure with double layers of nitrogen-doped carbon coating, the as-obtained NiCo2S4@D-NC electrode maintains an excellent specific capacity of 480 mAh g-1 at 100 mA g-1 after 100 cycles. Even after 500 cycles at 500 mA g-1, a reversible capacity of 427 mAh g-1 can be achieved, suggesting an excellent rate capability and an ultralong cycling life. This remarkable lithium storage property indicates its potential application for future lithium-ion batteries.

A Facile Molten‐Salt Route for Large‐Scale Synthesis of NiFe2O4 Nanoplates with Enhanced Lithium Storage Capability

Binary metal oxides have been deemed as a promising class of electrode materials for high-performance lithium ion batteries owing to their higher conductivity and electrochemical activity than corresponding monometal oxides. Here, NiFe2O4 nanoplates consisting of nanosized building blocks have been successfully fabricated by a facile, large-scale NaCl and KCl molten-salt route, and the changes in the morphology of NiFe2O4 as a function of the molten-salt amount have been systemically investigated. The results indicate that the molten-salt amount mainly influences the diameter and thickness of the NiFe2O4 nanoplates as well as the morphology of the nanosized building blocks. Cyclic voltammetry (CV) and galvanostatic charge-discharge measurements have been conducted to evaluate the lithium storage properties of the NiFe2O4 nanoplates prepared with a Ni(NO3)2/Fe(NO3)3/KCl/NaCl molar ratio of 1:2:20:60. A high reversible capacity of 888 mAh g(-1) is delivered over 100 cycles at a current density of 100 mA g(-1). Even at a current density of 5000 mA g(-1) , the discharge capacity could still reach 173 mAh g(-1). Such excellent electrochemical performances of the NiFe2O4 nanoplates are contributed to the short Li(+) diffusion distance of the nanosized building blocks and the synergetic effect of the Ni(2+) and Fe(3+) ions.

A Core–Shell Fe/Fe2O3 Nanowire as a High‐Performance Anode Material for Lithium‐Ion Batteries

The preparation of novel one-dimensional core-shell Fe/Fe2 O3 nanowires as anodes for high-performance lithium-ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe2 O3 shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core-shell Fe/Fe2 O3 nanowire maintains an excellent reversible capacity of over 767 mA h g(-1) at 500 mA g(-1) after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g(-1) , a stable capacity as high as 538 mA h g(-1) could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large-scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high-performance LIBs.

Yolk@Shell or Concave Cubic NiO–Co3O4@C Nanocomposites Derived from Metal–Organic Frameworks for Advanced Lithium-Ion Battery Anodes

Novel hybrid metal oxides with advanced architectures are extensively pursued to achieve synergetic properties with respect to improved lithium-ion storage properties. Here, rationally designed yolk@shell or concave NiO-Co3O4@C (YNCC or CNCC) nanocubes have been fabricated by the simple and versatile thermolysis-induced transformation of metal-organic frameworks (MOFs), aimed at simultaneously addressing the capacity fade and conductivity deficiency of metal oxides. The as-prepared nanocomposites with plentiful hierarchical pores integrate the distinct functionalities of the ternary components: NiO and Co3O4 as the major active materials can guarantee high capacity, while carbon can improve the conductivity and accommodate volume changes. Benefitting from the intrinsic material and architecture features, the YNCC and CNCC nanocomposites deliver excellent electrochemical performances with high reversible specific capacity, superior cycling stability (803 and 870 mAh g-1 at 100 mA g-1 after 100 cycles), and good rate capability (339 and 398 mAh g-1 at 2 A g-1) as anode materials for lithium-ion batteries.

A general strategy for coating metal–organic frameworks on diverse components and architectures

Forming a uniform metal–organic framework (MOF) nanocoating is still a famed challenge in the construction of core@shell composites. Here, a facile and versatile strategy that enables a surfactant-modified core to be wrapped up by a compact ZIF-8 shell has been reported. There is no limitation of the composition, dimension, size and shape of the core components, which can be CNTs, metal/non-metal oxides, organics and MOFs with dimensions ranging from one-dimensional (1D) nanowires to three-dimensional (3D) hollow spheres, and sizes from dozens of nanometers to several micrometers. The hybridization of various core components with a ZIF-8 shell offers the opportunity to achieve collective properties and create novel functions that are not available in individual building blocks. As a proof-of-concept application, the CNTs@ZIF-8 (Zn, Co) and Ni(OH)2@ZIF-8 (Zn, Co) derived CNTs@ZnCo2O4 and NiO@ZnCo2O4 composites manifest strong ability to improve the electrochemical performances as anode materials for lithium-ion batteries (LIBs). It is expected that the as-fabricated core@shell composites may cater to the various demands from applications in catalysis, sensing and energy storage.

Enhanced electrochemical performance by a three-dimensional interconnected porous nitrogen-doped graphene/carbonized polypyrrole composite for lithium–sulfur batteries

Three-dimensional interconnected porous nitrogen-doped graphene/carbonized polypyrrole nanotube (N-GP/CPN) materials have been fabricated via carbonization and chemical activation of polypyrrole-functionalized graphene nanosheets with KOH. The obtained N-GP/CPN with high surface, abundant nanopores and nitrogen doping can serve as conductive substrates for hosting a high content of sulfur and can effectively impede the dissolution of polysulfides. The N-GP/CPN-S composite exhibits excellent electrochemical performance as the cathode material for lithium–sulfur (Li–S) batteries, including a high initial discharge capacity of 1128 mA h g−1 at 0.5C, a notable cycling stability with a high stable capacity of 726 mA h g−1 and an ultraslow decay rate of 0.07% per cycle as long as 500 cycles. Moreover, the N-GP/CPN-S cathode also exhibits good rate capacity, showing a high reversible stable capacity of 687 mA h g−1 at 4C.