Aiping Hu

Facile synthesis of 3D plum candy-like ZnCo2O4 microspheres as a high-performance anode for lithium ion batteries

In this paper, 3D plum candy-like ZnCo2O4 microspheres (3D plum candy-like ZCO MSs) with nanoscale building blocks were synthesized by an ultrasonic spray pyrolysis technology and evaluated as anode materials for high-performance lithium ion batteries (LIBs). The uniform ZnCo2O4 microspheres exhibit plum candy-like architectures and are built from a large amount of interconnected nanoparticles with a diameter of approximately 38 nm. Owing to the unique hierarchical porous structure, the 3D plum candy-like ZCO MSs exhibit many advantageous properties such as their ability to facilitate the transport of Li+ and electrolytes by shortening the diffusion ways, to accommodate the mechanical stress and volume change associated with the Li+ insertion/extraction processes, and to improve the contact area between electrode and electrolyte, which are beneficial to improve the electrochemical performance. As a consequence, the ZnCo2O4 nanomaterials exhibit excellent cycling performance with a discharge capacity of 1030 mA h g−1 after 110 cycles at 200 mA g−1 and superior rate capability (769 mA h g−1 at 2000 mA g−1). In virtue of the simple synthesis method and excellent electrochemical performance, 3D porous ZCO MSs have huge potential as anode materials for the next-generation LIBs.

Molybdenum disulfide nanosheet embedded three-dimensional vertically aligned carbon nanotube arrays for extremely-excellent cycling stability lithium-ion anodes

Molybdenum disulfide (MoS2) nanosheets embedded in three-dimensional (3D) vertically aligned carbon nanotube arrays (VACNTs) have been fabricated via a simple nebulization-assisted hydrothermal method. The MoS2/VACNTs possess a highly ordered and uniformly oriented 3D structure with MoS2 nanosheets adhering strictly to the surface of VACNTs. When evaluated as lithium-ion anode materials, so-obtained MoS2/VACNTs composites containing 52 wt% MoS2 exhibit superb electrochemical performances, including high capacity (1078 mA h g−1 at 100 mA g−1 after 1st cycle), good rate capability (789 mA h g−1 at 2000 mA g−1 after 20 cycles), and extremely-excellent cycling stability, for the MoS2/VACNTs electrode can still deliver a discharge capacity of 512 mA h g−1 after 1000 cycles at 5000 mA g−1, compared with pristine MoS2 (negligible discharge capacity at the 70th cycle). Such high electrical properties can mainly be attributed to the unique well-directed pore-morphology which provides low-resistant shortest diffusion pathways upon the high-conductive VACNTs to accelerate ion/electron movement. Moreover, the elastic spare-space inside/outside VACNTs as a buffer factor effectively restrains large volumetric change from MoS2 during the charge/discharge process. It can be determined that such a structure is attractive to achieve extremely-excellent cycling stability lithium-ion anodes.

Controllable graphene coated mesoporous carbon/sulfur composite for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are attractive for the next generation of rechargeable batteries due to their high energy density, but several problems have hindered their widespread practical realization. Mesoporous carbon/sulfur (CMK-3/S) composites, controllably coated with graphene sheets via the functionalization of the CMK-3 surface with the assistance of a bridging agent (L-lysine and PEG), are presented here. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the graphene could be coated uniformly and tightly on the surface of mesoporous carbon/sulfur (RGO@CMK-3/S) particles in the presence of L-lysine. In this unique “double-carbon” structure, the abundant pore structure and graphene coating layers serve to accommodate the large volume expansion of the sulfur nanoparticles during discharge, preventing the dissolution of polysulfide intermediates from the cathode, and improving the sulfur nanoparticles’ electrical conductivity. Galvanostatic charge–discharge tests indicated that the RGO@CMK-3/S composite prepared using L-lysine exhibited high and stable specific capacities of up to ∼720 mA h g−1 over more than 100 cycles at 0.5C, and an excellent rate capability of 660 mA h g−1 at a rate of 2C, representing a promising cathode material for rechargeable lithium batteries.

Alignment and structural control of nitrogen-doped carbon nanotubes by utilizing precursor concentration effect

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a simple ultrasonic spray pyrolysis method. The precursor concentration effect was examined to effectively control alignment, open tip and diameter of the NCNTs by changing xylene/cyclohexylamine ratio. The structure and morphology of the resultant NCNTs were characterized by scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy. The degree of alignment and the diameter of the NCNTs increased as the xylene/cyclohexylamine precursor mixture was changed from 0 to 35% cyclohexylamine. This precursor composition also caused a large number of open-ended nanotubes to form with graphite layers inside the cavities of the NCNTs. However, further increase cyclohexylamine content in the precursor reduced the degree of alignment and diameter of the NCNTs. We demonstrate control over the NCNT alignment and diameter, along with the formation of open-ended nanotube tips, and propose a growth mechanism to understand how these properties are interlinked.

Capacity-increasing robust porous SiO2/Si/graphene/C microspheres as an anode for Li-ion batteries

Robust porous SiO2/Si/graphene/C microspheres have been successfully synthesized by a simple two-step process of ultrasonic spraying and partial magnesiothermic reduction. The 3-D porous microspheres consist of Si/SiO2 nanoparticles (around 5–10 nm) covered by a layer of carbon and connected by graphene. We explored the electrochemical properties of the porous microspheres as an anode for lithium ion batteries (LIBs). In SiO2/Si/graphene/C microspheres, numerous pores could leave enough room for volume expansion and contraction of silicon during lithiation and delithiation, and provide large space voids for electrolyte reserves. Meanwhile, graphene plays a role in reinforcing the porous structure. The prepared sample shows superior cyclability with a discharge capacity of 1104.9 mA h g−1 in the second cycle and 1141.6 mA h g−1 over 200 cycles at a current density of 0.1 mA cm−2. The capacity retention is more than 100%, making it very promising as a future LIBs anode.

Compact-Nanobox Engineering of Transition Metal Oxides with Enhanced Initial Coulombic Efficiency for Lithium-Ion Battery Anodes

A novel strategy is proposed to construct a compact-nanobox (CNB) structure composed of irregular nanograins (average diameter ≈ 10 nm), aiming to confine the electrode-electrolyte contact area and enhance initial Coulombic efficiency (ICE) of transition metal oxide (TMO) anodes. To demonstrate the validity of this attempt, CoO-CNB is taken as an example which is synthesized via a carbothermic reduction method. Benefiting from the compact configuration, electrolyte can only contact the outer surface of the nanobox, keeping the inner CoO nanograins untouched. Therefore, the solid electrolyte interphase (SEI) formation is reduced. Furthermore, the internal cavity leaves enough room for volume variation upon lithiation and delithiation, resulting in superior mechanical stability of the CNB structure and less generation of fresh SEI. Consequently, the SEI remains stable and spatially confined without degradation, and hence, the CoO-CNB electrode delivers an enhanced ICE of 82.2%, which is among the highest values reported for TMO-based anodes in lithium-ion batteries. In addition, the CoO-CNB electrode also demonstrates excellent cyclability with a reversible capacity of 811.6 mA h g-1 (90.4% capacity retention after 100 cycles). These findings open up a new way to design high-ICE electrodes and boost the practical application of TMO anodes.

Graphitic carbon-wrapped NiO embedded three dimensional nitrogen doped aligned carbon nanotube arrays with long cycle life for lithium ion batteries

In this work, a three-dimensional nitrogen doped aligned carbon nanotube array (NACNTs)@NiO@graphitic carbon composite was fabricated by an effective strategy involving nebulized ethanol assisted infiltration, In this structure, the NiO nanoparticles were wrapped by graphitic carbon layers and NiO@graphitic carbon core–shell nanoparticles adhered strictly to the surface of NACNTs to form a highly ordered 3D structure. When this composite was used as an anode for lithium ion batteries, the well-ordered pore of its NACNTs can facilitate the electrolyte to penetrate and improve electronic conductivity. At the same time, the graphitic layers can promote the stability of a solid electrolyte interface film. Therefore, the NACNTs@NiO@graphitic carbon composite containing 68.1 wt% NiO delivers excellent capacity retention of 91.6% after 200 cycles at 0.2C.

Synthesis and characterisation of γ-Fe2O3 nanowire arrays via a versatile, simple and low-cost method

γ-Fe2O3 nanowire arrays embedded in anodic alumina template were fabricated by an improved sol–gel method. The morphologies, structures and magnetic behaviour of the as-prepared products were investigated by X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy and magnetic hysteresis analysis. The results show that arrayed γ-Fe2O3 polycrystalline nanowires with an average diameter about 40 nm and an average length about 0.5 µm were prepared. A number of superparamagnetic nanoneedles grew along the nanowires. The ordered one-dimensional arrays weaken the superparamagnetic effect. In addition, a possible formation mechanism about nanowires is proposed. The charge factor, gravity effect and molecular heat movement impelled the Fe sols filling into the pores of the template. γ-Fe2O3 nanowire arrays look forward to the applications of magnetic recording in the future.