Qizhen Zhu

Nitrogen-Rich Mesoporous Carbon as Anode Material for High-Performance Sodium-Ion Batteries.

Nitrogen-rich carbon with interconnected mesoporous structure has been simply prepared via a nano-CaCO3 template method, using polyaniline as carbon and nitrogen precursors. The preparation process includes in situ polymerization of aniline in a nano-CaCO3 aqueous solution, carbonization of the composites and removal of the template with diluted hydrochloric acid. Nitrogen sorption shows the carbon-enriched mesopores with a specific surface area of 113 m(2) g(-1). The X-ray photoelectron spectroscopy (XPS) analysis indicates that the carbon has a high nitrogen content of 7.78 at. %, in the forms of pyridinic and pyrrolic, as well as graphitic nitrogen. The nitrogen-rich mesoporous carbon shows a high reversible capacity of 338 mAh g(-1) at a current density of 30 mA g(-1), and good rate performance as well as ultralong cycling durability (110.7 mAh g(-1) at a current density of 500 mA g(-1) over 800 cycles). The excellent sodium storage performance of the nitrogen-rich mesoporous carbon is attributed to its disordered structure with large interlayer distance, interconnected porosity, and the enriched nitrogen heteroatoms.

Facile synthesis of nitrogen-doped, hierarchical porous carbons with a high surface area: the activation effect of a nano-ZnO template

Hierarchical porous carbons have recently attracted much attention due to their unique features in practical applications, but suffer from the complex and costly synthesis procedure. In this work, a simple but very effective method was proposed to synthesize nitrogen-doped, hierarchical porous carbons with a high surface area by one-step pyrolysis of nano-ZnO/gelatin composites. During pyrolysis, zinc oxide nanoparticles act as not only a hard template to create mesopores, but also an activating agent to create micropores as well as enlarge the pore sizes of the mesopores, making the carbon possess a developed hierarchical porous structure with a high BET surface area of 2412 m2 g−1 and a large pore volume of 3.436 cm3 g−1. The activation effect of nano-ZnO was investigated by thermogravimetric analysis, carbon yield, nitrogen adsorption–desorption measurements, SEM, TEM and so on. The pyrolysis temperature has an important influence on the properties of the carbon materials. Both the BET surface area and pore volume increase dramatically with the pyrolysis temperature. Being used as an electrode material for supercapacitors, the developed hierarchical porous structure endows the carbon with superior rate capability.

A hollow carbon foam with ultra-high sulfur loading for an integrated cathode of lithium–sulfur batteries

Lithium–sulfur batteries are promising energy storage system with high energy density, however, for many years, the difficulty in combining good cycling performance and high sulfur loading have impeded their practical application. In this study, an ultra-light flexible carbon foam (MFC) with a 3D interconnected hollow network was prepared through a special heating program from melamine–formaldehyde foam. The MFC can be used as an efficient host material to achieve both ultra-high sulphur loading and good electrochemical performance in lithium–sulphur batteries. Without a conductive additive and a binder, the sulphur loading in the MFC-based cathode could easily reach up to 75%. The MFC contains a high content of N and O strongly absorbing the polysulfides and has a flexible and sparse skeleton accommodating large volume change during electrochemical reactions. To further improve the performance of the eletrode, GO or rGO was used to decorate the MFC skeleton. The MFC-based electrodes with 75% sulfur loading have excellent cycling performance. The initial capacity of the MFC–S, MFC–GO–S and MFC–rGO–S, based on the mass of the whole electrodes, are 1010.7 mA h g−1, 1183.1 mA h g−1 and 1134.6 mA h g−1 at 0.1C, respectively. After the inevitable capacity fading in the first few cycles, the capacity retention is over 95% after 100 cycles compared with the 20th cycle. These results indicate that the carbon foam is an excellent choice for high sulphur loading Li–S batteries.

Microorganism-moulded pomegranate-like Na3V2(PO4)3/C nanocomposite for advanced sodium-ion batteries

Na3V2(PO4)3 (NVP) with a NASICON crystal structure is a promising cathode material for sodium-ion batteries; however, it has a low rate performance due to its poor electric conductivity. Herein, pomegranate-like NVP/C composites were proposed and prepared via a simple and cost-efficient method using yeast as the mould. Owing to the strong adsorption ability of yeast, high tolerance to extreme conditions and high nitrogen and phosphorus content, a hierarchically structured material composed by NVP particles embedded within a N-/P-doped carbon framework was formed in situ. In the NVP/C composites, the nanoscaled NVP grains coated by carbon, derived from the cytoplasm, and micron-sized carbon capsules, which resulted from the carbonization of the sturdy cell walls, were formed to further accommodate dozens of the carbon-coated NVP grains, resulting in a pomegranate-like architecture. This unique structure and the N-/P-doped carbon framework can provide superior electrochemical kinetics and stability, with efficient electron pathways, and can also buffer volume changes during Na+ insertion/extraction. As a result, the NVP/C composites exhibit a good rate performance (113.9 mA h g−1 at 10C) and an outstanding long-term cycling stability (capacity retention of around 74.7% after 10 000 cycles). The properties of the pomegranate-like structure moulded by yeast microorganisms are remarkable and the NVP/C composite is believed to be a promising electrode material for sodium-ion batteries.

Creative utilization of natural nanocomposites: nitrogen-rich mesoporous carbon for a high-performance sodium ion battery

A resource-abundant, low-cost and high-performance anode is indispensable to the future success of sodium ion batteries (SIBs) for applications in large-scale energy storage. Animal byproducts are naturally pre-organized organic/inorganic nanocomposite materials composed of collagen and nanominerals. Making the best use of these natural nanocomposites is a good choice to develop carbon anodes for SIBs. Here, using shrimp skin as an example, we demonstrated a simple preparation of nitrogen-rich mesoporous carbon materials from natural nanocomposites and used these carbon materials for developing high-performance SIBs. Collagen was used as a nitrogen-rich precursor of the carbon, while the nanominerals, distributed evenly in the collagen matrix, acted as a hard template to create mesopores. The shrimp skin was subjected to direct pyrolysis under an inert atmosphere followed by removal of minerals, and was hence easily transformed into nitrogen-rich mesoporous carbons subsequently shown to serve as high-performance sodium storage materials. In this way, we turned “trash” into “treasure”. The unique microstructure of the nitrogen-rich mesoporous carbon resulted in its exhibiting outstanding performances as anodes for SIBs. The reversible sodium storage capacity reached as high as 434.6 mA h g−1 at 30 mA g−1 with excellent cycle durability and rate capability. These results indicated the creative utilization of the natural nanocomposites to be a facile, sustainable strategy for the synthesis of high-performance sodium storage materials.

Self‐Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self-assembly of transition metal oxide (TMO) nanostructures, including TiO2 nanorods and SnO2 nanowires, on MXene (Ti3 C2 ) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO2 /MXene and SnO2 /MXene heterostructures exhibit superior high-rate performance, making them promising high-power and high-energy anode materials for lithium-ion batteries.

A floral variant of mesoporous carbon as an anode material for high performance sodium and lithium ion batteries

The floral variant of mesoporous carbon was simply prepared by direct pyrolysis of zinc citrate followed by washing with dilute hydrochloric acid. The unique floral microstructure endows the carbon with ultrahigh reversible capacity, excellent cycle stability and superior rate performance as an anode material for both sodium ion batteries and lithium ion batteries. The floral variant of mesoporous carbon exhibits a reversible sodium storage capacity as high as 438.5 mA h g−1 at a current density of 30 mA g−1 and retains a value of 68.7 mA h g−1 at an enhanced current density of 10 A g−1. Moreover, the floral mesoporous carbon can deliver a tremendous reversible capacity up to 1370 mA h g−1 at 50 mA g−1 as an anode for lithium ion batteries. It can output a high reversible capacity of 222 mA h g−1 even when being charged and discharged at 50 A g−1. Based on the astounding capacity and rate performance, the floral variant of mesoporous carbon can be regarded as one of the most promising anode materials for both sodium-ion and lithium-ion batteries.

Three-Dimensional Carbon Current Collector Promises Small Sulfur Molecule Cathode with High Areal Loading for Lithium–Sulfur Batteries

With the high energy density of 2600 W h kg-1, lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems. However, the serious capacity fading resulting from the shuttle effect hinders its commercial application. Encapsulating small S2-4 molecules into the pores of ultramicroporous carbon (UMC) can eliminate the dissolved polysulfides, thus completely inhibiting the shuttle effect. Nevertheless, the sulfur loading of S2-4/UMC is usually not higher than 1 mg cm-2 because of the limited pore volume of UMC, which is a great challenge for small sulfur cathode. In this paper, by applying ultralight 3D melamine formaldehyde-based carbon foam (MFC) as a current collector, we dramatically enhanced the areal sulfur loading of the S2-4 electrode with good electrochemical performances. The 3D skeleton of MFC can hold massive S2-4/UMC composites and act as a conductive network for the fast transfer of electrons and Li+ ions. Furthermore, it can serve as an electrolyte reservoir to make a sufficient contact between S2-4 and electrolyte, enhancing the utilization of S2-4. With the MFC current collector, the S2-4 electrode reaches an areal sulfur loading of 4.2 mg cm-2 and performs a capacity of 839.8 mA h g-1 as well as a capacity retention of 82.5% after 100 cycles. The 3D MFC current collector provides a new insight for the application of Li-S batteries with high areal small sulfur loading and excellent cycle stability.

Organic salt-derived nitrogen-rich, hierarchical porous carbon for ultrafast supercapacitors

Nitrogen-rich, hierarchical porous carbons with high surface area were simply prepared by direct pyrolysis of a nitrogen-containing organic salt, i.e. ethylenediaminetetraacetic acid calcium disodium salt (EDTANa2Ca), as electrode materials for supercapacitors. Besides micropores originating from the elimination of some small molecular substances, the template effects of nano-CaO and nano-Na2CO3 particles (the intermediate products derived from EDTANa2Ca) created some meso/macropores, resulting in a developed hierarchical porous structure. As the pyrolysis temperature increases from 600 °C to 850 °C, the nitrogen content decreases from 10.8 at% to 1.48 at%, whereas both the BET surface area and the pore volume increase dramatically. The BET surface area and pore volume of the carbon prepared at 850 °C reach as high as 2015 m2 g−1 and 1.74 cm3 g−1, respectively, and the meso/macropores account for about 70% of the total pore volume. The developed hierarchical porous structure enables the carbon to exhibit excellent rate capability. It can endure an ultrafast scan rate of 5000 mV s−1 and an ultrahigh charge/discharge current up to 200 A g−1 with a capacitance of 115 F g−1 in 6 mol L−1 KOH.