Song Jin

A robust hydrogen evolution catalyst based on crystalline nickel phosphide nanoflakes on three-dimensional graphene/nickel foam: high performance for electrocatalytic hydrogen production from pH 0–14

The design and preparation of highly active catalysts for the hydrogen evolution reaction (HER) is very important for water splitting. Herein, we report a highly active HER catalyst, which is synthesized by loading nanostructured nickel phosphide (Ni2P) on three-dimensional few-layer graphene/nickel foam (G@NF). G@NF was successfully prepared by a chemical vapor deposition process in the presence of methane at high temperature. Compared with nickel phosphide, G@NF, as well as commercial platinum, the Ni2P–G@NF catalyst exhibited very high activity in electrocatalytic H2 production from water (∼7 mV overpotential in alkaline solutions, pH ∼ 14; and ∼30 mV overpotential in acidic solutions, pH ∼ 0). The high catalytic activity of Ni2P–G@NF is attributed to the excellent performance of Ni2P, the large 3D framework which facilitates proton accessibility and electron transfer, and the high surface area.

Covalently Connected Carbon Nanostructures for Current Collectors in Both the Cathode and Anode of Li–S Batteries

A 3D current collector made of covalently connected carbon nanostructures is presented, which can significantly improve battery performance when used as the cathode and/or anode. A Li-S cell assembled using these current collectors, with the cathode loaded with elemental sulfur and the anode loaded with lithium metal, delivers a high-rate capacity of 860 mA h g-1 at 12 C.

The Origin of Improved Electrical Double‐Layer Capacitance by Inclusion of Topological Defects and Dopants in Graphene for Supercapacitors

Low-energy density has long been the major limitation to the application of supercapacitors. Introducing topological defects and dopants in carbon-based electrodes in a supercapacitor improves the performance by maximizing the gravimetric capacitance per mass of the electrode. However, the main mechanisms governing this capacitance improvement are still unclear. We fabricated planar electrodes from CVD-derived single-layer graphene with deliberately introduced topological defects and nitrogen dopants in controlled concentrations and of known configurations, to estimate the influence of these defects on the electrical double-layer (EDL) capacitance. Our experimental study and theoretical calculations show that the increase in EDL capacitance due to either the topological defects or the nitrogen dopants has the same origin, yet these two factors improve the EDL capacitance in different ways. Our work provides a better understanding of the correlation between the atomic-scale structure and the EDL capacitance and presents a new strategy for the development of experimental and theoretical models for understanding the EDL capacitance of carbon electrodes.

High Areal Capacity and Lithium Utilization in Anodes Made of Covalently Connected Graphite Microtubes

Lithium metal is an attractive anode material for rechargeable batteries because of its high theoretical specific capacity of 3860 mA h g-1 and the lowest negative electrochemical potential of -3.040 V versus standard hydrogen electrode. Despite extensive research efforts on tackling the safety concern raised by Li dendrites, inhibited Li dendrite growth is accompanied with decreased areal capacity and Li utilization, which are still lower than expectation for practical use. A scaffold made of covalently connected graphite microtubes is reported, which provides a firm and conductive framework with moderate specific surface area to accommodate Li metal for anodes of Li batteries. The anode presents an areal capacity of 10 mA h cm-2 (practical gravimetric capacity of 913 mA h g-1 ) at a current density of 10 mA cm-2 , with Li utilization of 91%, Coulombic efficiencies of ≈97%, and long lifespan of up to 3000 h. The analysis of structure evolution during charge/discharge shows inhibited lithium dendrite growth and a reversible electrode volume change of ≈9%. It is suggested that an optimized microstructure with moderate electrode/electrolyte interface area is critical to accommodate volume change and inhibit the risks of irreversible Li consumption by side reactions and Li dendrite growth for high-performance Li-metal anodes.

Nitrogen-Doped Hollow Carbon Nanospheres for High-Performance Li-Ion Batteries

N-doped carbon materials is of particular attraction for anodes of lithium-ion batteries (LIBs) because of their high surface areas, superior electrical conductivity, and excellent mechanical strength, which can store energy by adsorption/desorption of Li+ at the interfaces between the electrolyte and electrode. By directly carbonization of zeolitic imidazolate framework-8 nanospheres synthesized by an emulsion-based interfacial reaction, we obtained N-doped hollow carbon nanospheres with tunable shell thickness (20 nm to solid sphere) and different N dopant concentrations (3.9 to 21.7 at %). The optimized anode material possessed a shell thickness of 20 nm and contained 16.6 at % N dopants that were predominately pyridinic and pyrrolic. The anode delivered a specific capacity of 2053 mA h g-1 at 100 mA g-1 and 879 mA h g-1 at 5 A g-1 for 1000 cycles, implying a superior cycling stability. The improved electrochemical performance can be ascribed to (1) the Li+ adsorption dominated energy storage mechanism prevents the volume change of the electrode materials, (2) the hollow nanostructure assembled by the nanometer-sized primary particles prevents the agglomeration of the nanoparticles and favors for Li+ diffusion, (3) the optimized N dopant concentration and configuration facilitate the adsorption of Li+; and (4) the graphitic carbon nanostructure ensures a good electrical conductivity.

Atom-Thick Interlayer Made of CVD-Grown Graphene Film on Separator for Advanced Lithium–Sulfur Batteries

Lithium-sulfur batteries are widely seen as a promising next-generation energy-storage system owing to their ultrahigh energy density. Although extensive research efforts have tackled poor cycling performance and self-discharge, battery stability has been improved at the expense of energy density. We have developed an interlayer consisting of two-layer chemical vapor deposition (CVD)-grown graphene supported by a conventional polypropylene (PP) separator. Unlike interlayers made of discrete nano-/microstructures that increase the thickness and weight of the separator, the CVD-graphene is an intact film with an area of 5 × 60 cm2 and has a thickness of ∼0.6 nm and areal density of ∼0.15 μg cm-2, which are negligible to those of the PP separator. The CVD-graphene on PP separator is the thinnest and lightest interlayer to date and is able to suppress the shuttling of polysulfides and enhance the utilization of sulfur, leading to concurrently improved specific capacity, rate capability, and cycle stability and suppressed self-discharge when assembled with cathodes consisting of different sulfur/carbon composites and electrolytes either with or without LiNO3 additive.

Robust Expandable Carbon Nanotube Scaffold for Ultrahigh‐Capacity Lithium‐Metal Anodes

There has been a renewed interest in using lithium (Li) metal as an anode material for rechargeable batteries owing to its high theoretical capacity of 3860 mA h g-1 . Despite extensive research, modifications to effectively inhibit Li dendrite growth still result in decreased Li loading and Li utilization. As a result, real capacities are often lower than values expected, if the total mass of the electrode is taken into consideration. Herein, a lightweight yet mechanically robust carbon nanotube (CNT) paper is demonstrated as a freestanding framework to accommodate Li metal with a Li mass fraction of 80.7 wt%. The highly conductive network made of sp2-hybridized carbon effectively inhibits formation of Li dendrites and affords a favorable coulombic efficiency of >97.5%. Moreover, the Li/CNT electrode retains practical areal and gravimetric capacities of 10 mA h cm-2 and 2830 mA h g-1 (vs the mass of electrode), respectively, with 90.9% Li utilization for 1000 cycles at a current density of 10 mA cm-2 . It is demonstrated that the robust and expandable nature is a distinguishing feature of the CNT paper as compared to other 3D scaffolds, and is a key factor that leads to the improved electrochemical performance of the Li/CNT anodes.

Advanced 3D Current Collectors for Lithium-Based Batteries

Li-based batteries are a hot research topic because they are the most popular energy storage system for high energy-density devices. As an important component of the battery, the current collectors in both cathode and anode should be well designed. Herein, the design of 3D current collectors for Li-based batteries is considered, including 3D metal-based and carbon-based current collectors. The progress in nanotechnology provides appropriate 3D current collectors characterized by highly efficient morphologies and architectures. In particular, 3D current collectors with different morphology are classified. Critical factors of current collectors that affect the electrochemical performance of Li-based batteries are comprehensively debated. Finally, conclusion and perspectives of the future research in this field are discussed.