Daxian Cao

Honeycomb-like carbon nanoflakes as a host for SnO2 nanoparticles allowing enhanced lithium storage performance

While possessing potential advantages as electrodes for lithium-ion batteries, SnO2@carbon composites have been suffering from one common drawback – aggregation of Sn particles during the repeated alloying–dealloying cycles and the resulting pulverization issue. We combat this issue through the fabrication of honeycomb-like SnO2@carbon nanoflakes (SnO2@CNFs) that are able to confine SnO2 nanoparticles within well-separated carbon cavities, so that the Li–Sn alloying–dealloying reaction occurs in the independent microreactors thus avoiding aggregation of Sn metal particles formed. The SnO2 particle size, loading amount and the coverage density are controlled by adjusting the weight ratio between the tin precursor and the CNF. Transmission electron microscopy confirms that the highly graphitic honeycomb-like CNF matrix efficiently buffers and accommodates volume changes of the Li–Sn alloy. Used as anode materials for lithium-ion batteries, the SnO2@CNFs with 66.0 wt% SnO2 display the highest lithium storage capacity, delivering a discharge capacity of 940 mA h g−1 after 150 cycles at 200 mA g−1. For the long-term and high-rate applications, the SnO2@CNFs with 41.5 wt% SnO2 show the best electrochemical performance, delivering a discharge capacity of 400 mA h g−1 at 1 A g−1 after 500 cycles.

A Hierarchical Phosphorus Nanobarbed Nanowire Hybrid: Its Structure and Electrochemical Properties

Nanostructured phosphorus-carbon composites are promising materials for Li-ion and Na-ion battery anodes. A hierarchical phosphorus hybrid, SiC@graphene@P, has been synthesized by the chemical vapor deposition of phosphorus on the surfaces of barbed nanowires, where the barbs are vertically grown graphene nanosheets and the cores are SiC nanowires. A temperature-gradient vaporization-condensation method has been used to remove the unhybridized phosphorus particles formed by homogeneous nucleation. The vertically grown barb shaped graphene nanosheets and a high concentration of edge carbon atoms induced a fibrous red phosphorus (f-RP) growth with its {001} planes in parallel to {002} planes of nanographene sheets and led to a strong interpenetrated interface interaction between phosphorus and the surfaces of graphene nanosheets. This hybridization has been demonstrated to significantly enhance the electrochemical performances of phosphorus.

Nanocarved MoS2-MoO2 Hybrids Fabricated Using in Situ Grown MoS2 as Nanomasks

The morphology and hybridization of nanostructures are crucial to achieve properties for various applications. An in situ grown three-dimensional (3D) MoS2 nanomask has been adopted to control the morphology and hybridization of molybdenum compounds. The in situ generated MoS2 mask on MoO3 nanobelt surfaces allowed us to fabricate a 3D c-MoO2@MoS2 hybrid nanostructure, in which c-MoO2 is a carved MoO2 nanobelt with a well-distributed hole pattern. The nanomasks have been controlled by adjusting the alignments of MoS2. The exposed MoO2 surfaces of c-MoO2@MoS2 were further sulfurated to give cw-MoO2@MoS2, in which all surfaces of MoO2 are wrapped by a few layers of MoS2. The structure synergistically enhanced the electrochemical performances of MoO2 and MoS2, especially at high current rates. Reversible capacities of 1418 and 295 mAh/g after 115 and 300 cycles still remained for the cw-MoO2@MoS2 anodes at current rates of 1 and 10 A/g, respectively.

Binding SnO2 nanoparticles onto carbon nanotubes with assistance of amorphous MoO3 towards enhanced lithium storage performance

We report the synthesis of a novel SnO2/MoO3/carbon nanotubes (CNTs) hybrid (denote as SMC) via hydrothermally treating aqueous SnCl4-Na2MoO4-CNTs suspension. The hydrolysis of SnCl4 promotes the precipitation of Na2MoO4, resulting in the simultaneous coprecipitation of the amorphous MoO3 and SnO2 nanoparticles which attach onto the CNTs (Note that no MoOx is produced in the absence of SnCl4). When used as anode materials for lithium ion batteries (LIBs), the as-prepared SMC hybrid delivers a high reversible capacities of 1032 and 887mAh/g after 50 cycles at current densities of 200 and 500mA/g, respectively, and still retains a reversible capacity of 496mAh/g even after 200 cycles at a higher rate of 2A/g, which shows much better lithium storage performance than that of the counterpart hybrid of SnO2/CNTs (denote as SC, with only 569mAh/g after 50 cycles at 200mA/g). The enhanced electrochemical performance of SMC can be attributed to a synergistic effect, namely, MoO3 not only confines SnO2 nanoparticles onto the CNTs but also brings additional lithium storage capacity, while the flexible conductive CNT networks facilitate the charge transfer and electrolyte diffusion.

Pyrolytic synthesis of MoO 3 nanoplates within foam-like carbon nanoflakes for enhanced lithium ion storage

MoO3 as electrode material for lithium ion batteries (LIBs) suffers from the poor ionic and electronic conductivity, while hybridizing nanostructured MoO3 with carbon-based materials is regarded as an efficient strategy. Herein, we report the facile synthesis of MoO3 nanoplates within foam-like carbon nanoflakes (CNFs) via the pyrolysis of molybdenum 2-ethtlhexanoate (C48H90MoO12) at a low temperature of 300 °C under ambient atmosphere. Mixing C48H90MoO12 with the highly porous foam-like CNFs allows the sufficient pyrolysis of Mo precursor, which can readily crystallize into MoO3 with plate morphology. The loading amount of MoO3 within CNFs can be easily and precisely controlled by adjusting the relative amount of C48H90MoO12/CNFs, while the plate morphology of MoO3 can be well preserved. The structural characteristics as well as the formation mechanism are investigated. When used as anode material for LIBs, optimized MoO3/CNFs displays superior lithium storage performance, delivering a high discharge capacity of 791 mA h/g after 100 cycles at 500 mA/g and even ∼600 mA h/g at a high rate of 2000 mA/g. Moreover, the present pyrolysis synthetic strategy can be generally applied for low-cost and large-scale fabrication of various MoO3/carbon nanocomposites, which demonstrates great potential in the development of high-performance electrodes for electrochemical energy-storage.