Terrence Xu

Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Composites For High-Performance Lithium-Sulfur Battery Cathodes

Despite the high theoretical capacity of lithium-sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g(-1) after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer-sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm(-2)) with a high sulfur loading of approximately 5 mg cm(-2), which is ideal for practical applications of the lithium-sulfur batteries.

Mesoporous carbon-carbon nanotube-sulfur composite microspheres for high-areal-capacity lithium-sulfur battery cathodes.

Lithium-sulfur (Li-S) batteries offer theoretical energy density much higher than that of lithium-ion batteries, but their development faces significant challenges. Mesoporous carbon-sulfur composite microspheres are successfully synthesized by combining emulsion polymerization and the evaporation-induced self-assembly (EISA) process. Such materials not only exhibit high sulfur-specific capacity and excellent retention as Li-S cathodes but also afford much improved tap density, sulfur content, and areal capacity necessary for practical development of high-energy-density Li-S batteries. In addition, when incorporated with carbon nanotubes (CNTs) to form mesoporous carbon-CNT-sulfur composite microspheres, the material demonstrated superb battery performance even at a high current density of 2.8 mA/cm(2), with a reversible capacity over 700 mAh/g after 200 cycles.

Micro-sized silicon–carbon composites composed of carbon-coated sub-10 nm Si primary particles as high-performance anode materials for lithium-ion batteries

We report the synthesis of micro-sized silicon–carbon (Si–C) composites, which simultaneously possess primary sub-10 nm Si particles and secondary micro-sized aggregation coated with carbon. Because of this unique structure, the as-synthesized Si–C composite anode can deliver excellent cycling stability with a high reversible specific capacity (∼1600 mA h g−1) within 150 cycles at 400 mA g−1. Moreover, a high volumetric capacity of ∼1088 mA h cm−3 was demonstrated by using this composite cathode, which is 5 times higher than that of commercially available nano-silicon based anodes.

Polyanthraquinone as a Reliable Organic Electrode for Stable and Fast Lithium Storage

In spite of recent progress, there is still a lack of reliable organic electrodes for Li storage with high comprehensive performance, especially in terms of long-term cycling stability. Herein, we report an ideal polymer electrode based on anthraquinone, namely, polyanthraquinone (PAQ), or specifically, poly(1,4-anthraquinone) (P14AQ) and poly(1,5-anthraquinone) (P15AQ). As a lithium-storage cathode, P14AQ showed exceptional performance, including reversible capacity almost equal to the theoretical value (260 mA h g(-1); >257 mA h g(-1) for AQ), a very small voltage gap between the charge and discharge curves (2.18-2.14=0.04 V), stable cycling performance (99.4% capacity retention after 1000 cycles), and fast-discharge/charge ability (release of 69% of the low-rate capacity or 64% of the energy in just 2 min). Exploration of the structure-performance relationship between P14AQ and related materials also provided us with deeper understanding for the design of organic electrodes.

Bis(2,2,2-trifluoroethyl) ether as an electrolyte co-solvent for mitigating self-discharge in lithium-sulfur batteries.

Lithium-sulfur batteries suffer from severe self-discharge because of polysulfide dissolution and side reaction. In this work, a novel electrolyte containing bis(2,2,2-trifluoroethyl) ether (BTFE) was used to mitigate self-discharge of Li-S cells having both low- and high-sulfur-loading sulfur cathodes. This electrolyte meaningfully decreased self-discharge at elevated temperature, though differences in behavior of cells with high- and low-sulfur-loading were also noted. Further investigation showed that this effect likely stems from the formation of a more robust protective film on the anode surface.

Flexible freestanding sandwich-structured sulfur cathode with superior performance for lithium–sulfur batteries

Flexible freestanding sandwich-structured sulfur cathodes are developed for lithium–sulfur batteries, which exhibit excellent cycling stability and rate capability. Moreover, a high areal capacity of ∼4 mA h cm−2 is demonstrated based on this new cathode configuration with high sulfur loading (∼4 mg S cm−2).

Porous spherical carbon/sulfur nanocomposites by aerosol-assisted synthesis: the effect of pore structure and morphology on their electrochemical performance as lithium/sulfur battery cathodes.

Porous spherical carbons (PSCs) with tunable pore structure (pore volume, pore size, and surface area) were prepared by an aerosol-assisted process. PSC/sulfur composites (PSC/S, S: ca.59 wt %) were then made and characterized as cathodes in lithium/sulfur batteries. The relationships between the electrochemical performance of PSC/S composites and their pore structure and particle morphology were systematically investigated. PSC/S composite cathodes with large pore volume (>2.81 cm(3)/g) and pore size (>5.10 nm) were found to exhibit superior electrochemical performance, likely due to better mass transport in the cathode. In addition, compared with irregularly shaped carbon/sulfur composite, the spherical shaped PSC/S composite showed better performance due to better electrical contact among the particles.