Woon Gie Chong

Three-Dimensional Porous Graphene Aerogel Cathode with High Sulfur Loading and Embedded TiO2 Nanoparticles for Advanced Lithium–Sulfur Batteries

Three-dimensional graphene aerogel/TiO2/sulfur (GA/TiO2/S) composites are synthesized through a facile, one-pot hydrothermal route as the cathode for lithium-sulfur batteries. With a high sulfur content of 75.1 wt %, the conductive, highly porous composite electrode delivers a high discharge capacity of 512 mA h/g after 250 cycles at a current rate of 1 C with a low capacity decay of 0.128% per cycle. The excellent capacities and cyclic stability arise from several unique functional features of the cathode. (i) The conductive graphene aerogel framework ameliorates ion/electron transfer while accommodating the volume expansion induced during discharge, and (ii) TiO2 nanoparticles play an important role in restricting the dissolution of polysulfides by chemical bonds with sulfur.

Highly conductive porous graphene/sulfur composite ribbon electrodes for flexible lithium sulfur batteries

Flexible batteries have become an indispensable component of emerging devices, such as wearable, foldable electronics and sensors. Although various flexible batteries have been explored based on one-dimensional and two-dimensional platforms, developing a high energy density electrode with high structural integrity remains challenging. Herein, a scalable, one-pot wet spinning strategy is used to synthesize a flexible porous cathode for lithium-sulfur batteries (LSBs) for the first time, which consists of reduced graphene oxide (rGO), graphene crumples (GCs) and sulfur powders. The electrode structures are tailored using GCs with different dimensions and functional features that are critical to its robustness under mechanical deformation and electrolyte penetration into the battery components. The optimized rGO/GC/S composite ribbon cathodes deliver a high capacity of 524 mA h g-1 after 100 cycles at a current rate of 0.2 C. A shape-conformable battery prototype comprising an rGO/GC/S cathode and a lithium anode demonstrates a stable discharge characteristic under repeated bending/flattening cycles. The LSB prototype supported by an elastomer presents stable discharge behavior with high mechanical robustness against an extension of up to 50%. The above-mentioned findings shed new light on developing sulfur cathodes for flexible, high performance LSBs based on the rational design of graphene structures.

Chemical interactions between red P and functional groups in NiP3/CNT composite anodes for enhanced sodium storage

Red phosphorus has thus far the highest theoretical capacity among all known anode materials for sodium ion batteries (SIBs). However, its low electronic conductivity and large volume expansion during cycles cause rapid capacity fading, leading to poor electrochemical stability. Herein, we report a facile and scalable ball milling approach to synthesize NiP3/carbon nanotube (CNT) composites consisting of NiP3 particles chemically bonded with functionalized CNTs. The conductive CNTs play an important role in stabilizing the composite electrode through an enhanced Na+ diffusion coefficient by two orders of magnitude and six-fold reduction in its charge transfer resistance. The NiP3/CNT composite anode delivers a high initial reversible capacity of 853 mA h g−1 with more than 80% capacity retention after 120 cycles at 200 mA g−1 and an excellent high-rate capacity of 363.8 mA h g−1 after 200 cycles at 1600 mA g−1. The density functional theory (DFT) calculations combined with ab initio molecular dynamics (AIMD) simulations elucidate strong chemical interactions between the red P in NiP3 and the functional groups on CNTs to form P–C and P–O–C bonds by ball milling for the first time. The facile synthesis strategy devised in this study can be applied to other alloy-based composites with relatively low carbon content for use as high performance anodes for SIBs.