Songtao Lu

Three-dimensional sulfur/graphene multifunctional hybrid sponges for lithium-sulfur batteries with large areal mass loading.

In this communication, we introduce the concept of three dimensional (3D) battery electrodes to enhance the capacity per footprint area for lithium-sulfur battery. In such a battery, 3D electrode of sulfur embedded into porous graphene sponges (S-GS) was directly used as the cathode with large areal mass loading of sulfur (12 mg cm−2), approximately 6–12 times larger than that of most reports. The graphene sponges (GS) worked as a framework that can provide high electronic conductive network, abilities to absorb the polysulfides intermediate, and meanwhile mechanical support to accommodate the volume changes during charge and discharge. As a result, the S-GS electrode with 80 wt.% sulfur can deliver an extremely high areal specific capacitance of 6.0 mAh cm−2 of the 11th cycle, and maintain 4.2 mAh cm−2 after 300 charge−discharge cycles at a rate of 0.1C, representing an extremely low decay rate (0.08% per cycle after 300 cycles), which could be the highest areal specific capacity with comparable cycle stability among the rechargeable Li/S batteries reported ever.

Graphene/Co9S8 nanocomposite paper as a binder-free and free-standing anode for lithium-ion batteries

Flexible lithium ion batteries with high energy density have recently received tremendous interest due to their potential applications in flexible electronic devices. Herein, we report a simple high energy ball-milling technique together with vacuum filtration to fabricate a highly flexible, conductive, robust and free-standing RGO/Co9S8 nanocomposite paper with high conductivity (121 S cm−1), tensile strength (50.4 MPa) and Youngs modulus (3.5 GPa) which can be directly used as a free-standing anode for flexible LIBs without binders, conducting agents and metallic current collectors. The free-standing RGO/Co9S8 anode with a high mass active material loading of 66.7 wt% Co9S8 can deliver a high specific capacity of 1415 mA h gCo9S8−1 (944 mA h gelectrode−1) and maintain 573 mA h gCo9S8−1 (382.2 mA h gelectrode−1) after 500 cycles at a current density of 1C (1C = 545 mA g−1). More importantly, the rate capability was improved by introducing RGO. The RGO/Co9S8 anode exhibited impressive capacities of 1096.70 mA h gCo9S8−1 with a capacity recuperability of 69.4% as the current returned to 0.1C. These results demonstrate that the well designed nanocomposite is of great potential as an anode for flexible LIBs. As far as we know, such improved electrochemical performance can be attributed to the nanosized Co9S8 particles with a diameter of ∼25 nm homogeneously dispersed on the surface of high conductive graphene sheets that can be obtained owing to the milling impact stress, which enhances surface electrochemical reactivity and shortens the transport length of lithium ions and electrons. Whats more, the large specific surface area of the graphene sheet enables the uniform distribution of Co9S8 and offers better ability to accommodate volume expansion/shrinkage of Co9S8 during repeated charge/discharge cycles.

3D graphene framework supported Li2S coated with ultra-thin Al2O3 films: binder-free cathodes for high-performance lithium sulfur batteries

Lithium sulfide (Li2S) has drawn special attention as a promising cathode material for emerging energy storage systems due to its high theoretical specific capacity and great compatibility with lithium metal-free anodes. However, Li2S cathodes urgently require a solution to increase their poor electrical conductivity and to suppress the dissolution of long-chain polysulfide (Li2Sn, 4 ≤ n ≤ 8) species into electrolyte. To this end, we report a free-standing Al2O3–Li2S–graphene oxide sponge (GS) composite cathode, in which ultrathin Al2O3 films are preferentially coated on Li2S by an atomic layer deposition (ALD) technique. As a result, a combination of high electron conductivity (from GS) and strong binding with Li2Sn (from ultrathin Al2O3 films) was designed for cathodes. The newly developed Al2O3–Li2S–GS cathodes are able to deliver a highly reversible capacity of 736 mA h gLi2S−1 (427 mA h gcathode−1) at 0.2C, which is much higher than that of corresponding cathodes without Al2O3 (59%). Also, the long-term cycling stability of Al2O3–Li2S–GS cathodes was demonstrated up to 300 cycles at 0.5C with an excellent capacity retention of 88%. In addition, combined with density functional theory calculations, the promotional mechanism of ultrathin Al2O3 films was elucidated using extensive characterization. The ultra-thin Al2O3 film with optimal thickness not only acts as a physical barrier to Li2S nanoparticles, but provides a strong binding interaction to suppress Li2Sn species dissolution.

Binder-free cathodes based on sulfur–carbon nanofibers composites for lithium–sulfur batteries

Binder-free S-FCNF composite films with sulfur coated uniformly on the surface of FCNFs were used as cathodes for lithium–sulfur batteries. Such cathodes have both high sulfur content (78 wt%) and large areal mass loading (8 mg cm−2), and they can deliver a high areal specific capacity of 1.87 mA h cm−2 (234 mA h gelectrode−1) after 100 cycles at 0.1 C.

A Sheet-like Carbon Matrix Hosted Sulfur as Cathode for High-performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are a promising candidate of next generation energy storage systems owing to its high theoretical capacity and energy density. However, to date, its commercial application was hindered by the inherent problems of sulfur cathode. Additionally, with the rapid decline of non-renewable resources and active appeal of green chemistry, the intensive research of new electrode materials was conducted worldwide. We have obtained a sheet-like carbon material (shaddock peel carbon sheets SPCS) from organic waste shaddock peel, which can be used as the conductive carbon matrix for sulfur-based cathodes. Furthermore, the raw materials are low-cost, truly green and recyclable. As a result, the sulfur cathode made with SPCS (SPCS-S), can deliver a high reversible capacity of 722.5 mAh g−1 at 0.2 C after 100 cycles with capacity recuperability of ~90%, demonstrating that the SPCS-S hybrid is of great potential as the cathode for rechargeable Li-S batteries. The high electrochemical performance of SPCS-S hybrid could be attributed to the sheet-like carbon network with large surface area and high conductivity of the SPCS, in which the carbon sheets enable the uniform distribution of sulfur, better ability to trap the soluble polysulfides and accommodate volume expansion/shrinkage of sulfur during repeated charge/discharge cycles.

Improving the performance of Li–S batteries by reinforced PPy wrapping over acetylene black-coated sulfur

A strategy of reinforced PPy wrapping over an acetylene black-coated sulfur composite (PPy–AB/S) was designed for synthesizing cathode materials of Li–S batteries with improved performance. It was found that the resulting PPy–AB/S cathodes were able to maintain 630 mA h g−1 even after 200 charge–discharge cycles at a rate of 0.5 C.

A Convenient Method for Manufacturing TiO2 Electrodes on Titanium Substrates

Thin titanium dioxide films were successfully prepared on titanium plates in ammonium sulfate solution with the micro-plasma oxidation method. The thin TiO2 films were sensitized with a cis-RuL2(SCN)2·2H2O (L = cis-2, -bipyridine-4, -dicarboxlic acid) ruthenium complex, and implemented into a dye sensitized solar cell configuration. The influence of current density on the surface structure and photoelectric performance of the TiO2 films was investigated. The results show that the thin TiO2 films are porous, and the dye-sensitized solar cell based on the film prepared at 14 A/dm2 has exhibited higher overall light-to-electricity conversion efficiencies of 0.095% under the illumination at 40 mW/cm2.