Jisheng Zhou

Magnetite/graphene nanosheet composites: interfacial interaction and its impact on the durable high-rate performance in lithium-ion batteries

We explore in-depth the interfacial interaction between Fe3O4 nanoparticles and graphene nanosheets as well as its impact on the electrochemical performance of Fe3O4/graphene anode materials for lithium-ion batteries. Fe3O4/graphene hybrid materials are prepared by direct pyrolysis of Fe(NO3)3·9H2O on graphene sheets. The interfacial interaction between Fe3O4 and graphene nanosheets is investigated in detail by thermogravimetric and differential scanning calorimetry analysis, Raman spectrum, X-ray photoelectron energy spectrum and Fourier transform infrared spectroscopy. It was found that Fe3O4 nanoparticles disperse homogeneously on graphene sheets, and form strong covalent bond interactions (Fe–O–C bond) with graphene basal plane. The strong covalent links ensure the high specific capacity and long-period cyclic stability of Fe3O4/graphene hybrid electrodes for lithium-ion batteries at high current density. The capacity keeps as high as 796 mAhg−1 after 200 cycles without any fading in comparison with the first reversible capacity at the current density of 500 mAg−1 (ca. 0.6 C). At 1 Ag−1 (ca. 1.3 C), the reversible capacity attains ca. 550 mAhg−1 and 97% of initial capacity is maintained after 300 cycles. This work reveals an important factor affecting the high-rate and cyclic stability of metal oxide anode, and provides an effective way to the design of new anode materials for lithium-ion batteries.

Hierarchical porous carbon nanosheets and their favorable high-rate performance in lithium ion batteries

Novel hierarchical porous carbon nanosheets (HPCS) with quantities of micropores and mesopores were prepared on a large-scale by using thermoplastic phenolic formaldehyde resin as the carbon source and copper nitrate as the template precursor. The HPCS, possessing a thickness of about 40 nm and the width of several microns, exhibited a high specific capacity and favorable high-rate performance when used as an anode material for lithium ion batteries (LIBs). The reversible capacities were 748 mA h g−1 at a current density of 20 mA g−1 and 460 mA h g−1 even at 1 A g−1, which were much higher than those of traditional porous carbon materials. It also showed superior cyclical stability for only 0.3% capacity loss per cycle under high rate charge-discharge process, suggesting that HPCS should be a promising candidate for anode materials in high-rate LIBs. The roles of various-sized pores in HPCS in Li storage were discussed briefly.

Synthesis and high-rate capability of quadrangular carbon nanotubes with one open end as anode materials for lithium-ion batteries

Novel carbon nanotubes (CNTs) were prepared on a large-scale. Their morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman measurements. It was found that the prepared CNTs possess a quadrangular cross section, as well as one open end and “herringbone”-like walls, so these novel CNTs were named q-CNTs. The unique morphology of q-CNTs implies broad potential applications in many fields, including drug delivery, conductive and high-strength composites, field emission displays and radiation sources, hydrogen storage media, and supercapacitors. When used as the anode materials for lithium-ion batteries, q-CNTs exhibit excellent high-rate performance (a high-reversible capacity of 181 mAh g−1 at the current density of 1000 mA g−1 (ca. 3 C)), which is much higher than that of the common multi-wall carbon nanotubes. This high-rate performance should be attributed to the unique nanostructure of q-CNTs, which results in a high diffusion coefficient for lithium ions in the q-CNTs.

Direct amination of Si nanoparticles for the preparation of Si @ ultrathin SiOx @ graphene nanosheets as high performance lithium-ion battery anodes

NH2-terminated Si nanoparticles with an ultrathin silica shell have been efficiently obtained by a one-step reaction in ammonia–water–ethanol solution. Graphene nanosheet (GNS) encapsulated Si@ultrathin SiOx has been fabricated by self-assembly and thermal treatment. Because of the uniform ultrathin SiOx shell and superior GNS encapsulation structure, this material shows a reversible capacity of 2391.3 mA h g−1, maintaining 1844.9 mA h g−1 after 50 cycles at a current density of 200 mA g−1, and good rate and long cycle performance (∼700 mA h g−1 at 2000 mA g−1 after 350 cycles) as well.

How graphene is exfoliated from graphitic materials: synergistic effect of oxidation and intercalation processes in open, semi-closed, and closed carbon systems

Solution-based oxidation has been widely utilized to prepare graphene oxide or graphene nanoribbons from different carbon precursors, but some details of the exfoliation or unzipping processes still remain elusive. Here, we put forward three graphitic systems for deep understanding of the top-down route. Based on the oxidation-intercalation synergistic effect, the formation mechanisms were proposed.

Sn–Co nanoalloys embedded in porous N-doped carbon microboxes as a stable anode material for lithium-ion batteries

For improving the capacity and stability of Sn-based anode materials, a novel Sn–Co nanoalloy embedded in porous N-doped carbon was synthesized using the metal–organic framework ZIF-67 as both the template and carbon source, and SnCl4 as the tin source through carbonization. This composite shows the shape of a microbox with the diameter of about 2 μm in which about 10 nm of Sn–Co nanoalloy particles were uniformly embedded. When used as the anode material for lithium-ion batteries, it exhibits a high capacity of 945 mA h g−1, and 86.6% capacity retention after 100 cycles at 100 mA g−1 as well as an excellent rate capacity of 472 mA h g−1 at a high current density of 2 A g−1. The superior electrochemical performance can be ascribed to the well-dispersed, nano-sized alloy and the buffering effect of porous N-doped carbon coating. Moreover, the uniform particles remain intact upon cycling which gives the material enhanced electrochemical stability.

Diffusion of Metal in a Confined Nanospace of Carbon Nanotubes Induced by Air Oxidation

Air oxidation can result in the motion of metal confined in carbon nanotubes (CNTs). This can also be utilized to tailor various hybrid nanostructures. By controllable air-oxidation, as-prepared metal@CNT nanorods (a) can be converted first to core-shell-void nanorods (b), then to metal/metal oxide@CNT nanotubes (c), and finally to mesoporous metal oxide nanotubes (d). The metal/metal oxide@CNT nanotubes and mesoporous metal oxide nanotubes are expected to find many applications, such as in lithium ion batteries, catalysis, magnetic drug delivery, and gas sensing.

A universal strategy to prepare porous graphene films: binder-free anodes for high-rate lithium-ion and sodium-ion batteries

Porous graphene films (PGFs) were developed by introducing defects and extra edges into graphene using GO and a metal salt (ferric nitrate) as sources via a facile filtration method together with a thermal reduction and subsequent removal of the metal. The pore size and density could be controlled by simply adjusting the amount of ferric nitrate. When used as an anode for lithium ion batteries, PGF-1 showed a high reversible capacity, improved cycling stability, and ultra-high rate performance (971, 298, and 163 mA h g−1 at the rates of 10, 30, and 50 A g−1 after 10 000 cycles). When used as an anode for sodium ion batteries, PGF-1 showed a reversible capacity of 195 mA h g−1 at 50 mA g−1 after 50 cycles. Even at a high rate of 1000 mA g−1, the reversible capacity can still remain at 111 mA h g−1 after 1000 cycles. The excellent performance should be attributed to the special porous structure of the PGF. On one hand, plenty of defects within the PGF provided extra reaction sites for lithium and sodium ion storage. On the other hand, the porous structure of the PGF resulted in fast diffusion and transfer of lithium/sodium ions and electrons throughout the electrodes.

Carbon-Nanotube-Encapsulated FeF2 Nanorods for High-Performance Lithium-Ion Cathode Materials

Application of iron fluoride, a promising candidate of cathode materials for lithium ion batteries, is being hindered by its poor electrochemical performance caused by low electronic conductivity and large volume change. Design of carbon-encapsulated transitional metal compounds (including fluoride, oxide, sulfide, etc.) structure is one of the most effective strategies in improving their lithium-ion storage performance. In this work, we successfully synthesize for the first time carbon-nanotube-encapsulated FeF2 nanorods via a facile in situ co-pyrolysis of ferrocene and NH4F. This kind of core/shell carbon nanotube/FeF2 nanorod exhibits better cyclic stability and rate-performance used as cathode materials. Better electrochemical performance of the nanorods should be attributed to the protection of the carbon shell because, experimentally, it is observed that outer carbon shells suffer from high internal stress during Li-ion insertion but efficiently keep the nanorods in the one-dimensional morphology and make nanorods a good electrical contact with the conductive carbon black. This work not only prepares high-performance core/shell carbon/iron fluoride cathode materials, but should also open a facile pathway for design of various novel nanostructures of other metal fluoride/carbon core/shell structures for future lithium-ion batteries.

Branched carbon-encapsulated MnS core/shell nanochains prepared via oriented attachment for lithium-ion storage

Novel branched carbon encapsulated MnS (MnS@C) nanochains were prepared by an in situ co-pyrolysis method. The morphology and structure of the MnS@C nanochains were mainly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). It was found that the prepared MnS@C nanochains possess interesting branched structures, which are constructed by interconnected MnS@C nanoparticles with a diameter of ca. 200–400 nm. More interestingly, the MnS@C nanoparticles have novel “pomegranate-like” structures, in which inner cores are not made of whole nanoparticles but composed of many MnS nanoparticles. The formation mechanism of MnS@C should be attributed to an Oriented Attachment (OA) mechanism by investigating various intermediate products obtained by controlling the reaction conditions. The branched MnS@C nanochains after annealing (MnS@C-800) demonstrated perfect cycling stability and long cycle life when used as anode materials for lithium-ion batteries (LIBs). At a current density of 50 mA g−1, the stable specific capacity is around 545 mA h g−1 while the pure MnS anode experiences a drastic drop quickly to 300 mA h g−1 at the initial few cycles. At 500 mA g−1, the reversible specific capacity is ca. 318 mA h g−1 at the initial cycle and is maintained at ca. 200 mA h g−1 after 800 cycles.