Yanjun Zhai

Fabrication of hierarchical porous MnCo2O4 and CoMn2O4 microspheres composed of polyhedral nanoparticles as promising anodes for long-life LIBs

Uniform hierarchical porous MnCo2O4 and CoMn2O4 microspheres (3–6 μm) were fabricated through a solvothermal process followed by a post-annealing treatment. Fascinatingly, these porous MnCo2O4 and CoMn2O4 microspheres are composed of numerous polyhedral nanoparticles with diameters in the range of 200–500 nm. The porous structure is believed to be beneficial for improving the lithium-storage performance of the products, which can effectively buffer the volume expansion during the Li+ insertion/extraction process and shorten the Li+ diffusion lengths. The polyhedral structure can enhance the electrolyte/electrode contact area and increase the number of Li+ insertion/extraction sites. When used as anode materials for lithium-ion batteries, the porous MnCo2O4 and CoMn2O4 microspheres exhibited excellent long-life cycling performance at high rate density. At a current density of 1000 mA g−1, the MnCo2O4 and CoMn2O4 exhibit an initial capacity of 1034 and 1107 mA h g−1 and the capacity is maintained at 740 and 420 mA h g−1 after 1000 cycles. Furthermore, the growth mechanism of porous microspheres is proposed based on many contrast experiments. The relationship between morphology evolution and annealing time is particularly investigated in detail. It is found that the annealing time plays an important role in obtaining products with different morphologies. Through the controlled annealing time, porous microspheres, yolk–shell microspheres and solid microspheres could be selectively obtained.

Hierarchical porous metal ferrite ball-in-ball hollow spheres: General synthesis, formation mechanism, and high performance as anode materials for Li-ion batteries

AbstractHigh yields of CoFe2O4, NiFe2O4 and CdFe2O4 hierarchical porous ball-in-ball hollow spheres have been achieved using hydrothermal synthesis followed by calcination. The mechanism of formation is shown to involve an in situ carbonaceous-template process. Hierarchical porous CoFe2O4 hollow spheres with different numbers of shells can be obtained by altering the synthesis conditions. The electrochemical properties of the resulting CoFe2O4 electrodes have been compared, using different binders. The as-obtained CoFe2O4 and NiFe2O4 have relatively high reversible discharge capacity and good rate retention performance which make them promising materials for use as anode materials in lithium ion batteries.

Facile fabrication of hierarchical porous rose-like NiCo2O4 nanoflake/MnCo2O4 nanoparticle composites with enhanced electrochemical performance for energy storage

The rational design of three-dimensional (3D) hierarchical porous architectures possessing the advantages of improved electrical conductivity and reduced volume change during charge–discharge processes has been proved to be an effective way for enhancing the electrochemical performance of binary metal oxides and related hybrids. Herein, uniform 3D hierarchical porous rose-like NiCo2O4/MnCo2O4 is controllably fabricated through a facile hydrothermal process followed by a subsequent heat treatment, which exhibits high cycling stability (1009 mA h g−1 at 1000 mA g−1 after 600 cycles), high specific capacity and excellent rate capability as anodes for lithium ion batteries. In addition, the NiCo2O4/MnCo2O4 displays an initial specific capacitance of 911.3 F g−1 as a supercapacitor electrode at 5 A g−1. Its excellent electrochemical performances may originate from its unique hierarchical and porous structure, which can buffer the volume expansion and increase the contact area between the electrode and electrolyte. The as-obtained 3D hierarchical porous rose-like NiCo2O4/MnCo2O4 composite exhibits outstanding electrochemical performances, which is a promising candidate for the next-generation energy storage electrodes.

Fabrication of Various V2O5 Hollow Microspheres as Excellent Cathode for Lithium Storage and the Application in Full Cells

Vanadium pentoxide (V2O5) has attracted interesting attention as cathode material for LIBs because of its stable crystal structure and high theoretical specific capacity. However, the low rate performance and poor long-term cycling stability of V2O5 limit its applications. In order to improve its battery performance, various V2O5 hollow microspheres including a yolk-shell structure, double-shell structure, triple-shell structure, and hierarchical hollow superstructures have been selectively prepared. The obtained hierarchical V2O5 hollow microspheres (HVHS) exhibit a high capacity of 123 mAh g(-1) at 20 C (1 C = 147 mA g(-1)) in the range of 2.5-4.0 V, and 73.5 mAh g(-1) can be reached after 3000 cycles. HVHS also display good cycling performance in the range of 2.0-4.0 V. Moreover, the V2O5//Li4Ti5O12 full cell was successfully assembled, which exhibits an excellent performance of 139.5 mAh g(-1) between 1.0 and 2.5 V at a current density of 147 mA g(-1), and a high capacity of 106 mAh g(-1) remained after 100 cycles, indicating the good cycling performance and promising application of the full cell.

One-dimensional manganese borate hydroxide nanorods and the corresponding manganese oxyborate nanorods as promising anodes for lithium ion batteries

Novel manganese and boron containing nanomaterials have been investigated for applications in rechargeable lithium ion batteries (LIBs) in recent years owing since they are more environmentally-benign and more abundant in nature than the materials currently employed. In this study, one-dimensional (1D) Mn3B7O13OH nanorods and MnBO2OH nanorod bundles were controllably fabricated by using NH4HB4O7 and Mn(NO3)2 as reagents via a hydrothermal or solvothermal process, respectively, without any surfactants or templates at 220 °C. It is interesting to find that both materials are transformed into Mn2OBO3 nanorods/nanorod bundles by subsequent calcination. The formation processes of the above 1D borate containing products were investigated and the as-obtained four kinds of borates were studied as novel anode materials. It was found that the Mn2OBO3 nanorods displayed the best performance among the four borates, delivering an initial discharge capacitiy of 1,172 mAh·g−1 at 100 mA·g−1, and 724 mAh·g−1 could be retained after 120 cycles. A full battery composed of a Mn2OBO3 nanorod anode and a commercial LiFePO4 (or LiCoO2) cathode has also been assembled for the first time, which delivered an initial discharge capacity of 949 mAh·g−1 (779 mAh·g−1 for LiCoO2). The excellent cycle and rate performances of the products reveal their potential applications as anodes for LIBs.

Rationally designed hierarchical MnO2@NiO nanostructures for improved lithium ion storage

The design of hierarchical nanostructures to be used as anodes (involving higher rate capabilities and better cycle lives) and meet further lithium ion battery applications has attracted wide attention. Herein, a hierarchical MnO2@NiO core–shell nanostructure with a MnO2 nanorod as the core and NiO flakes as the shell has been synthesized by combining a hydrothermal treatment and an annealing process. MnO2 nanorods serve as a high theoretical capacity (1233 mA h g−1) material, and they allow efficient electrical and ionic transport owing to their one-dimensional structure. The porous NiO flakes used as the shell would enlarge the contact area across the electrode/electrolyte, and can also serve as volume spacers between neighboring MnO2 nanorods to maintain electrolyte penetration as well as reducing the aggregation during Li+ insertion/extraction. As a result, the MnO2@NiO core–shell structure exhibits improved cycling stability (939 mA h g−1 after 200 cycles at a current density of 1 A g−1) and outstanding rate performance, suggesting that the synergetic effect and characteristics of the core–shell nanostructure would benefit the electrochemical performance of lithium ion batteries.

Mn3O4@C core–shell composites as an improved anode for advanced lithium ion batteries

Rationally designed nanocomposites with effective surface modification are important to improve the electrochemical performance of Li-ion batteries. Carbon coatings as an economical and practically feasible approach, which would provide good conductivity and promote Li-ion diffusion, leading to improved electrochemical performance. Mn3O4@C core–shell nanorods were prepared using the synchronous reduction and decomposition of acetylene. The resulting Mn3O4@C core–shell nanorods possess a one dimensional shape, porous structure and uniform carbon layer (∼3 nm), which result in electrochemical stability. When tested as anodes, they deliver a specific capacity of 765 mA h g−1 after 100 cycles at a current density of 500 mA g−1, which is considerably higher than pure Mn3O4 nanorods. Even at a current density of 2 A g−1, the Mn3O4@C core–shell nanorods can maintain 380 mA h g−1. Their excellent lithium storage performance can be ascribed to the uniform carbon coating layer as well as their unique one dimensional porous structure.

Co-pyrolysis synthesis of Fe3BO6 nanorods as high performance anodes for lithium-ion batteries

The high capacity, negligible toxicity, environmentally benign nature and abundant reserves (low cost of elements contained) of the Fe3BO6 nanomaterial enable it to be a highly promising anode material for lithium-ion batteries. In this study, Fe3BO6 nanorods encapsulated in graphite (defined as “Fe3BO6@C”) core–shell like composites have been produced in situ firstly via a co-pyrolysis approach in a stainless-steel autoclave. After subsequent calcinations, Fe3BO6 nanorods with diameters in the range of 20–50 nm were obtained with high yield, which display a first discharge capacity of 1192 mA h g−1 (with a coulombic efficiency of 70%). It is found that at the current density of 100 mA g−1, the specific capacity of the Fe3BO6 nanorods can remain at 873.2 mA h g−1 after 100 cycles; it is worth noting that their specific capacity can still remain at 710 mA h g−1 even if the current density was set at 1000 mA g−1, indicating the excellent cycle stability and promising applications of the as-obtained Fe3BO6 nanorods utilized as anode material at high power field.