Jiarui He

Three-dimensional CNT/graphene–sulfur hybrid sponges with high sulfur loading as superior-capacity cathodes for lithium–sulfur batteries

A facile method is presented to synthesize three-dimensional carbon nanotube/graphene–sulfur (3DCGS) sponge with a high sulfur loading of 80.1%. In the well-designed 3D architecture, the two-dimensional graphene nanosheets function as the 3D porous backbone and the one-dimensional (1D) highly conductive carbon nanotubes (CNTs) can not only significantly enhance the conductivity, but also effectively tune the mesoporous structure. Compared to the three-dimensional graphene–sulfur (3DGS) sponge without CNTs, the conductivity of 3DCGS is enhanced by 324.7%; most importantly, compared to the monomodal mesopores (with a size of 3.5 nm) formed in the 3DG, bimodal mesopores (with sizes of 3.5 and 32.1 nm) were formed in 3DCG; the bimodal mesopores, especially the newly formed 32.1 nm mesopores, provide abundant electrochemical nanoreactors, accommodate plenty of sulfur and polysulfides, and facilitate charge transportation and electrolyte penetration. The significantly enhanced conductivity and the unique bimodal-mesopore structure in 3DCGS result in its superior electrochemical performance. The reversible discharge capacity for sulfur is 1217 mA h g−1; the corresponding capacity for the whole electrode (including the 3DCGS, the conductive additive and the binder) is 877.4 mA h ge−1, which is the highest ever reported. In addition, the capacity decay is as low as 0.08% per cycle, and the high-rate capacity up to 4C is as large as 653.4 mA h g−1. The 3DCGS sponge with high sulfur loading is promising as a superior-capacity cathode for lithium–sulfur batteries.

From Metal–Organic Framework to Li2S@C–Co–N Nanoporous Architecture: A High-Capacity Cathode for Lithium–Sulfur Batteries

Owing to the high theoretical specific capacity (1166 mAh g-1), lithium sulfide (Li2S) has been considered as a promising cathode material for Li-S batteries. However, the polysulfide dissolution and low electronic conductivity of Li2S limit its further application in next-generation Li-S batteries. In this report, a nanoporous Li2S@C-Co-N cathode is synthesized by liquid infiltration-evaporation of ultrafine Li2S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) derived from metal-organic frameworks. The obtained Li2S@C-Co-N architecture remarkably immobilizes Li2S within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C-Co-N and Li2S nanoparticles, the Li2S@C-Co-N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g-1 after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g-1 at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li-S batteries.

Three-Dimensional Hierarchical Reduced Graphene Oxide/Tellurium Nanowires: A High-Performance Freestanding Cathode for Li–Te Batteries

Three-dimensional aerogel with ultrathin tellurium nanowires (TeNWs) wrapped homogeneously by reduced graphene oxide (rGO) is realized via a facile hydrothermal method. Featured with high conductivity and large flexibility, the rGO constructs a conductive three-dimensional (3D) backbone with rich porosity and leads to a free-standing, binder-free cathode for lithium-tellurium (Li-Te) batteries with excellent electrochemical performances. The cathode shows a high initial capacity of 2611 mAh cm(-3) at 0.2 C, a high retention of 88% after 200 cycles, and a high-rate capacity of 1083 mAh cm(-3) at 10 C. In particular, the 3D aerogel cathode delivers a capacity of 1685 mAh cm(-3) at 1 C after 500 cycles, showing pronounced long-cycle performance at high current density. The performances are attributed to the well-defined flexible 3D architecture with high porosity and conductivity network, which offers highly efficient channels for electron transfer and ionic diffusion while compromising volume expansion of Te in charge/discharge. Owing to such advantageous properties, the reported 3D rGO/tellurium nanowire (3DGT) aerogel presents promising application potentials as a high-performance cathode for Li-Te batteries.

Pure thiophene-sulfur doped reduced graphene oxide: synthesis, structure, and electrical properties

Here we propose, for the first time, a new and green ethanol-thermal reaction method to synthesize high-quality and pure thiophene-sulfur doped reduced graphene oxide (rGO), which establishes an excellent platform for studying sulfur (S) doping effects on the physical/chemical properties of this material. We have quantitatively demonstrated that the conductivity enhancement of thiophene-S doped rGO is not only caused by the more effective reduction induced by S doping, but also by the doped S atoms, themselves. Furthermore, we demonstrate that the S doping is more effective in enhancing conductivity of rGO than nitrogen (N) doping due to its stronger electron donor ability. Finally, the dye-sensitized solar cell (DSCC) employing the S-doped rGO/TiO2 photoanode exhibits much better performance than undoped rGO/TiO2, N-doped rGO/TiO2 and TiO2 photoanodes. It therefore seems promising for thiophene-S doped rGO to be widely used in electronic and optoelectronic devices.

Synthesis and electrochemical properties of graphene-modified LiCo1/3Ni1/3Mn1/3O2 cathodes for lithium ion batteries

High-quality, reduced graphene oxide (RGO) homogeneously coated LiCo1/3Ni1/3Mn1/3O2 (NCM) was synthesized by ultrasonically mixing/stirring GO and NCM in water and then thermal reduction of GO to RGO. The composite NCM cathode shows much higher specific capacity, better cycling stability and high rate performance after being wrapped by RGO, which is attributed to the much lower electrochemical impedance for the electrode due to the presence of RGO. It is promising for RGO modified NCM to be used as an excellent cathode.

Self-Assembled Coral-like Hierarchical Architecture Constructed by NiSe2 Nanocrystals with Comparable Hydrogen-Evolution Performance of Precious Platinum Catalyst

For the first time, self-assembled coral-like hierarchical architecture constructed by NiSe2 nanocrystals has been synthesized via a facile one-pot DMF-solvothermal method. Compared with hydrothermally synthesized NiSe2 (H-NiSe2), the DMF-solvothermally synthesized nanocrystalline NiSe2 (DNC-NiSe2) exhibits superior performance of hydrogen evolution reaction (HER): it has a very low onset overpotential of ∼136 mV (vs RHE), a very high cathode current density of 40 mA/cm2 at ∼200 mV (vs RHE), and an excellent long-term stability; most importantly, it delivers an ultrasmall Tafel slope of 29.4 mV dec-1, which is the lowest ever reported for NiSe2-based catalysts, and even lower than that of precious platinum (Pt) catalyst (30.8 mV dec-1). The superior HER performance of DNC-NiSe2 is attributed to the unique self-assembled coral-like network, which is a benefit to form abundant active sites and facilitates the charge transportation due to the inherent high conductivity of NiSe2 nanocrystals. The DNC-NiSe2 is promising to be a viable alternative to precious metal catalysts for hydrogen evolution.

Three-dimensional CoS2/RGO hierarchical architecture as superior-capability anode for lithium ion batteries

For the first time, a three-dimensional hierarchical architecture of CoS2/reduced graphene oxide (3DCG) with CoS2 particles uniformly anchored on the graphene network has been synthesized by a facile hydrothermal method. The 3DCG anode exhibits superior electrochemical performances: it delivers a high reversible specific capacity of 1499 mA h g−1 and remains 1245 mA h g−1 after 150 cycles at a current density of 100 mA g−1, which is the highest ever reported for CoS2-based materials; the rate capability remains 306 mA h g−1 even at 4000 mA g−1. The excellent performance can be attributed to the unique 3D porous structure, in which the reduced graphene oxide (RGO) network can guarantee the high conductivity of the composite, accommodate the volume change of CoS2 particles during cycling, and shorten the diffusion lengths for lithium ions. The 3DCG composite can be a promising anode candidate for high-performance lithium-ion batteries.

Tellurium-Impregnated Porous Cobalt-Doped Carbon Polyhedra as Superior Cathodes for Lithium–Tellurium Batteries

Lithium-tellurium (Li-Te) batteries are attractive for energy storage owing to their high theoretical volumetric capacity of 2621 mAh cm-3. In this work, highly nanoporous cobalt and nitrogen codoped carbon polyhedra (C-Co-N) derived from a metal-organic framework (MOF) is synthesized and employed as tellurium host for Li-Te batteries. The Te@C-Co-N cathode with a high Te loading of 77.2 wt % exhibits record-breaking electrochemical performances including an ultrahigh initial capacity of 2615.2 mAh cm-3 approaching the theoretical capacity of Te (2621 mAh cm-3), a superior cycling stability with a high capacity retention of 93.6%, a ∼99% Columbic efficiency after 800 cycles as well as rate capacities of 2160, 1327.6, and 894.8 mAh cm-3 at 4, 10, and 20 C, respectively. The redox chemistry of tellurium is revealed by in operando Raman spectroscopic analysis and density functional theory simulations. The results illustrate that the performances are attributed to the highly conductive C-Co-N matrix with an advantageous structure of abundant micropores, which provides highly efficient channels for electron transfer and ionic diffusion as well as sufficient surface area to efficiently host tellurium while mitigating polytelluride dissolution and suppressing volume expansion.

Partially reduced graphene oxide based FRET on fiber-optic interferometer for biochemical detection

An all-fiber graphene oxide (GO) based ‘FRET on Fiber’ concept is proposed and applied in biochemical detections. This method is of both good selectivity and high sensitivity, with detection limits of 1.2 nM, 1.3 μM and 1 pM, for metal ion, dopamine and single-stranded DNA (ssDNA), respectively.

Facile fabrication of RGO wrapped LiMn2O4 nanorods as a cathode with enhanced specific capacity

A facile method with ethanol assisted dispersion combined with a magnetic stirrer to prepare reduced graphene oxide (RGO) wrapped LiMn2O4 nanorods (LNs) is presented. The results show that compared to LNs, a LNs/RGO cathode for lithium-ion batteries (LIBs) exhibits much smaller impedance and much better electrochemical performance. After coating with RGO, the initial discharge capacity can be increased from 118.9 to 143.5 mA h g−1 at 0.2C which can retain 139.2 mA h g−1 after 50 cycles; the rate discharge capacities of LNs/RGO can reach 99.5, 82.1, 56 mA h g−1 at 10, 20, 30C, respectively. The significant performance enhancement can be attributed to the synergetic effect of the LiMn2O4 nanorods matrix and the conductive graphene wrapping layers. The excellent electrochemical properties make LNs/RGO a promising cathode material for high-performance LIBs. In addition, the facile synthesis route enables mass production and can be extended to prepare other graphene wrapped anode or cathode electrodes for LIBs.