Bing Ding

Biomass-derived porous carbon materials with sulfur and nitrogen dual-doping for energy storage

Nowadays, energy shortage is a serious socioeconomic problem. The recovery of biomass can make a very significant contribution in alleviating the burden on already-strained energy resources. Broad beans, which are abundant in amino acids and vitamins, are extensively cultivated worldwide. However, a large quantity of by-product, broad bean shells, remains unused and pollutes the environment from the incinerating and/or uncontrolled decomposition that results. In this paper, we report the synthesis of sulfur and nitrogen dual-doping porous carbon materials, for use as the electrode materials of energy storage devices, produced by carbonizing the shells of broad beans by a chemical activation. The specific capacitance of the as-prepared porous carbon material is as high as 202 F g−1, with a superior cycling performance for electric double layer capacitors at a current density of 0.5 A g−1. Furthermore, it also shows a stable performance for lithium ion batteries and sodium ion batteries, which suggests that it has a promising potential for wide applications in the field of energy storage devices.

Porous nitrogen-doped hollow carbon spheres derived from polyaniline for high performance supercapacitors

Porous nitrogen-doped hollow carbon spheres (PNHCS) had been prepared by pyrolysis of hollow polyaniline spheres (HPS), which were synthesized by the use of sulfonated polystyrene spheres (SPS) as a hard template. PNHCS have a specific surface area of 213 m2 g−1 and a pore volume of 0.24 cm3 g−1. At a current density of 0.5 A g−1, the specific capacitance of the PNHCS prepared is ca. 213 F g−1. The capacity retention after 5000 charge/discharge cycles at a current density of 1 A g−1 is more than 91%. The enhanced electrochemical performance can be attributed to the unique carbon nanostructure and nitrogen-doping of the PNHCS electrodes. The hollow macro-structure plays the role of an “ion-buffering” reservoir. The micropores of the PNHCS enlarge the specific surface area, while the mesopores offer larger channels for liquid electrolyte penetration. Nitrogen groups in the PNHCS not only improve the wettability of the carbon surface, but also enhance the capacitance by addition of a pseudocapacitive redox process.

Sulfur embedded in metal organic framework-derived hierarchically porous carbon nanoplates for high performance lithium–sulfur battery

The wide-scale implementation of lithium–sulfur batteries is limited by their rapid capacity fading, which is induced by the pulverization of the sulfur cathode and dissolution of intermediate polysulfides. Herein, we reported the encapsulation of sulfur (S) into hierarchically porous carbon nanoplates (HPCN) derived from one-step pyrolysis of metal-organic frameworks (MOF-5). HPCN with an average thickness of ca. 50 nm exhibits a three-dimensional (3D) hierarchically porous nanostructure, high specific surface area (1645 m2 g−1) and large pore volume (1.18 cm3 g−1). When evaluated as a cathode for lithium–sulfur batteries, the HPCN–S composite demonstrates high specific capacity and excellent cycling performance. At a current rate of 0.1 C, the initial discharge capacity of HPCN–S is 1177 mA h g−1. Even at a current rate of 0.5 C, it still delivers a discharge capacity of 730 mA h g−1 after 50 cycles and the Coulombic efficiency is up to 97%. The enhanced electrochemical performance of HPCN–S is closely related to its well-defined 3D porous plate nanostructure which not only provides stable electronic and ionic transfer channels, but also plays a key role as a strong absorbent to retain polysulfides and accommodate volume variation during the charge–discharge process.

High performance lithium–sulfur batteries: advances and challenges

The development of high-energy batteries is highly attractive for powering advanced communication equipment and electric vehicles in future. Lithium–sulfur batteries have attracted much attention in recent years due to their low cost, high theoretical specific capacity and energy density. However, lithium–sulfur batteries have not been commercialized because of their intrinsic shortcomings, including the insulation of the active cathode materials, the high solubility of lithium polysulfides in organic liquid electrolytes, and the lithium dendrite in the anode. In this feature article, recent research progress in cathode materials, electrolytes, anode materials, and others is reviewed and commented upon. Some perspectives and directions on future development of lithium–sulfur batteries are pointed out based on knowledge from previous studies and our experience.

Chemically tailoring the nanostructure of graphene nanosheets to confine sulfur for high-performance lithium-sulfur batteries

The commercialization of lithium–sulfur (Li–S) batteries has so far been limited by their rapid capacity fading, which is induced by dissolution of intermediate polysulfides and the pulverization of the sulfur cathode due to volume expansion. Herein, we reported an efficient strategy to confine active sulfur in chemically tailored graphene nanosheets, which were prepared via modified chemical activation of hydrothermal reduced graphene oxide hydrogels. Due to its high specific surface area, large pore volume, controllable size and distribution of nanopores, the two-dimensional (2D) highly porous activated graphene nanosheets (AGNs) were proved to be a promising scaffold to uniformly confine elemental sulfur (S) in their nanopores with high loading. The resultant AGNs/S nanocomposites exhibited a reversible capacity up to 1379 mA h g−1 at 0.2 C as well as remarkable cycling stability, which may contribute to the desirable structural features. The dense nanopores of AGNs, as “micro-reactors” for the electrochemical reactions of sulfur, minimized polysulfide dissolution and shuttling in the electrolyte, and also reserved fast transport of lithium ions to the sequestered sulfur by ensuring good electrolyte penetration. Furthermore, the AGNs with good electronic conductivity allowed good transport of electrons from/to the poorly conducting sulfur for electrochemical reactions at high rates.

Porous Nitrogen‐Doped Carbon Nanotubes Derived from Tubular Polypyrrole for Energy‐Storage Applications

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m(2)  g(-1)) and a large pore volume (1.28 cm(3)  g(-1)) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5 A g(-1), PNCNT presents a high specific capacitance of 210 F g(-1), as well as excellent cycling stability at a current density of 2 A g(-1). When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mA h g(-1) at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mA h g(-1). The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution.

Hierarchically Porous Carbon Encapsulating Sulfur as a Superior Cathode Material for High Performance Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are deemed to be a promising energy storage device for next-generation high energy power system. However, insulation of S and dissolution of lithium polysulfides in the electrolyte lead to low utilization of sulfur and poor cycling performance, which seriously hamper the rapid development of Li-S batteries. Herein, we reported that encapsulating sulfur into hierarchically porous carbon (HPC) derived from the soluble starch with a template of needle-like nanosized Mg(OH)2. HPC has a relatively high specific surface area of 902.5 m(2) g(-1) and large total pore volume of 2.60 cm(3) g(-1), resulting that a weight percent of sulfur in S/HPC is up to 84 wt %. When evaluated as cathodes for Li-S batteries, the S/HPC composite has a high discharge capacity of 1249 mAh g(-1) in the first cycle and a Coulombic efficiency as high as 94% with stable cycling over prolonged 100 charge/discharge cycles at a high current density of 1675 mA g(-1). The superior electrochemical performance of S/HPC is closely related to its unique structure, exhibiting the graphitic structure with a high developed porosity framework of macropores in combination with mesopores and micropores. Such nanostructure could shorten the transport pathway for both ions and electrons during prolonged cycling.

Biomass derived carbon for energy storage devices

Electrochemical energy storage devices are becoming increasingly more important for reducing fossil fuel energy consumption in transportation and for the widespread deployment of intermittent renewable energy. The applications of different energy storage devices in specific situations are all primarily reliant on the electrode materials, especially carbon materials. Biomass-derived carbon materials are receiving extensive attention as electrode materials for energy storage devices because of their tunable physical/chemical properties, environmental concern, and economic value. In this review, recent developments in the biomass-derived carbon materials and the properties controlling the mechanism behind their operation are presented and discussed. Moreover, progress on the applications of biomass-derived carbon materials as electrodes for energy storage devices is summarized, including electrochemical capacitors, lithium–sulfur batteries, lithium-ion batteries, and sodium-ion batteries. The effects of the pore structure, surface properties, and graphitic degree on the electrochemical performance are discussed in detail, which will guide further rational design of the biomass-derived carbon materials for energy storage devices.

Prussian blue analogues: a new class of anode materials for lithium ion batteries

Metal–organic frameworks (MOFs) have attracted extensive interest in the context of energy storage due to their high surface areas, controllable structures and excellent electrochemical properties. In particular, Prussian blue analogues (PBAs) have recently gained attention as a new class of cathode materials for rechargeable batteries. However, the anode properties of the host framework have been very limited. Herein, we demonstrate that nanoparticles of cobalt hexacyanocobaltate and manganese hexacyanocobaltate, typical Prussian blue analogues with the chemical formula M3II[CoIII(CN)6]2·nH2O (M = Co, Mn), can be operated as novel battery anodes in an organic liquid-carbonate electrolyte. The Co3[Co(CN)6]2 material exhibits a clear electrochemical activity in the voltage range of 0.01–3 V vs. Li/Li+ with a reversible capacity of 299.1 mA h g−1. Furthermore, superior rate capability (as the current density increases from 20 to 2000 mA g−1, the capacity retains about 34%) could be achieved, attributing to the small particle sizes and rapid transport of Li+ ions through large channels in the open-framework. We believe that this work provides a new insight into the electrochemical properties of PBAs and opens new perspectives to develop anode materials for rechargeable batteries.

Absorption mechanism of carbon-nanotube paper-titanium dioxide as a multifunctional barrier material for lithium-sulfur batteries

Lithium-sulfur batteries attract much interest as energy storage devices for their low cost, high specific capacity, and energy density. However, the insulating properties of sulfur and high solubility of lithium polysulfides decrease the utilization of active materials by the battery resulting in poor cycling performance. Herein, we design a multifunctional carbon-nanotube paper/titanium-dioxide barrier which effectively reduces active material loss and suppresses the diffusion of lithium polysulfides to the anode, thereby improving the cycling stability of lithium-sulfur batteries. Using this barrier, an activated carbon/sulfur cathode with 70% sulfur content delivers stable cycling performance and high Coulombic efficiency (∼99%) over 250 cycles at a current rate of 0.5 C. The improved electrochemical performance is attributed to the synergistic effects of the carbon nanotube paper and titanium dioxide, involving the physical barrier, chemical adsorption from the binding formation of Ti-S and S-O, and other interactions unique to the titanium dioxide and sulfur species.