Zhaoxia Cao

MOF-Derived Cobalt-Doped ZnO@C Composites as a High-Performance Anode Material for Lithium-Ion Batteries

Cobalt (Co)-doped MOF-5s (Co-MOF-5s) were first synthesized by a secondary growth method, followed by a heat treatment to yield Co-doped ZnO coated with carbon (CZO@C). Compared with carbon-coated ZnO (ZnO@C), the doping of Co increased the graphitization degree of the carbon on the surface of CZO@C nanoparticles and enhanced the conductivity of the material. The electrochemical properties of the materials were characterized by galvanostatic discharge/charge tests. It was found that the as-synthesized CZO@C composites enabled a reversible capacity of 725 mA h g(-1) up to the 50th cycle at a current density of 100 mA g(-1), which was higher than that of ZnO@C composites (335 mA h g(-1)).

First-principles and experimental study of nitrogen/sulfur co-doped carbon nanosheets as anodes for rechargeable sodium ion batteries

Heteroatom doped carbon materials have recently demonstrated an outstanding sodium storage ability and are being considered as the most promising candidate as anodes for sodium ion batteries. However, there is limited understanding of the relationship between structural and electronic properties and electrochemical storage capacity. First-principles calculations on a doped graphene cluster propose that N, S co-doping can promote the electronegativity, adsorption capacity of Na atoms and diffusion of Na+ ions on graphene sheets, especially for the sample consisting of more pyridinic-N, while excessive O atoms may alleviate these. All these features render N, S co-doped carbon as a superior anode for sodium ion batteries. Therefore, the N, S co-doped carbon nanosheets are fabricated via a simple thermal treatment method using gelatin as the carbon source and thiourea as the N and S precursor. The optimized product (mgelatin : mthiourea = 1 : 10) results in a superb cycling capacity of 300 mA h g−1 after 500 cycles, with a coulombic efficiency of ∼100%. This study provides a facile and reliable route to prepare co-doped carbon with enhanced sodium storage properties.

In situ synthesis of flexible elastic N-doped carbon foam as a carbon current collector and interlayer for high-performance lithium sulfur batteries

A flexible elastic N-doped carbon foam (NCF) has been successfully synthesized in situ via direct carbonization/pyrolysis of polyurethane foam, which is a facile, cost-effective and environmentally friendly method. Due to its uniform three-dimensional connected structure, its reasonable composition with N doping and its high electronic conductivity, the NCF can function as both a three-dimensional current collector and a carbon interlayer for lithium sulfur batteries. As a typical model, cathodes consisting of NCF and CNT/S were prepared. The resulting batteries deliver a large reversible capacity of 1124 mA h g−1 at 0.5C and retain a high specific capacity of 902.8 mA h g−1 after 100 cycles, with a coulombic efficiency of 98.6% throughout the cycles. Furthermore, a discharge capacity of 691.8 mA h g−1 is still attainable when the rate is increased to 2.0C. The excellent cycling performance and rate capability are contributed to the uniform flexible elastic, conductive 3D framework and good porosity, and may have great significance for large-scale commercial applications of Li–S batteries.

Submicron peanut-like MnCO3 as an anode material for lithium ion batteries

Submicron peanut-like MnCO3 is prepared by a facile homogeneous precipitation and delivers better electrochemical performance as an anode material for lithium ion battery. The physical characterization reveals that the peanut-like MnCO3 is composed of irregular nanoparticles, which results in a large surface area. As a contrast, square MnCO3 is obtained with structural directing agents. Submicron peanut-like MnCO3 delivers a reversible specific capacity of 700 mA h g−1 at 233 mA g−1 (1C = 466 mA g−1) after 140 cycles. The discharge capacities at 46, 93, 233, 466, 932, and 2330 mA g−1 are 1047, 1038, 881, 843, 750 and 410 mA h g−1, respectively, and a recovery capacity of 1100 mA h g−1 after 60 cycles could still be obtained. It also displays a discharge capacity of 618 mA h g−1 at high current density of 932 mA g−1 after 80 cycles. The advanced performance can be attributed to the unique morphology, facile electron and Li+ transportation at the electrode/electrolyte interface and self-accommodation of the large volume change during discharge/charge.

A novel sulfur/carbon composite for low cost lithium–sulfur batteries with high cycling stability

The lithium sulfur (Li–S) battery is a promising electrochemical system for the next generation high density rechargeable batteries having a theoretical energy density of ∼2600 W h kg−1. In spite of the intrinsic advantages, Li–S batteries currently are confronted with a variety of problems such as low specific capacity and short cycle life. In this work, a novel sulfur/carbon composite was prepared using coconut shell carbon as raw material for Li–S batteries. The structure of the composite could accommodate the volume expansion of sulfur particles and trap the dissolved polysulfide produced during the electrochemical reaction. Therefore, the composite based cell demonstrates a high initial capacity of 878 mA h g−1 at a rate of 0.1 C, and excellent cycling stability, in which a reversible capacity of 774 mA h g−1 was maintained even after 50 cycles.

Bio-inspired synthesis of ordered N/P dual-doped porous carbon and its use as anode for sodium-ion batteries.

Carbonaceous materials are one of the most promising anode materials for sodium-ion batteries, because of their abundance, stability, and safe usage. However, the practical application of carbon materials is hindered by poor specific capacity and low initial Coulombic efficiency. The design of porous structure and doping with heteroatoms are two simple and effective methods to promote the sodium storage performance. Herein, the N, P co-doped porous carbon materials are fabricated using renewable and biodegradable gelatin as carbon and nitrogen resource, phosphoric acid as phosphorus precursor and polystyrene nanospheres as a template. The product can deliver a reversible capacity of 230 mA h g-1 at a current density of 0.2 A g-1 , and even a high capacity of 113 mA h g-1 at 10 Ag-1 . The enhanced sodium storage performance is attributed to the synergistic effect of the porosity and the dual-doping of nitrogen and phosphorus.

Facile synthesis of Fe2O3/MWCNT composites with improved cycling stability

In this study, Fe2O3/multi-walled carbon nanotube (Fe2O3/MWCNT) composites were synthesized via vacuum solution absorption and subsequent calcination treatment. The amount of Fe2O3 and MWCNT components, crystalline structure, morphology and electrochemical performance of the as-prepared material were characterized by thermo-gravimetric (TG) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method, energy dispersive spectrometry (EDS) and charge–discharge tests. Results show that Fe2O3 nano-particles, with a diameter of about 23 nm, loaded in the void space in the intertwined MWCNT matrix or on the MWCNT homogeneously. The as-obtained Fe2O3/MWCNT composites have a relatively small BET surface area, pore size and pore volume compared to that of pure MWCNT. Electrochemical measurements show that the Fe2O3/MWCNT composites exhibit a high reversible capacity of 1026 mA h g−1 after 50 cycles at a charge–discharge rate of 0.2 C. The improved performance may be ascribed to the nano-sized Fe2O3 with a faster Li+ diffusion coefficient which can release the volume expansion effectively. On the other hand, the MWCNT can act as a buffering matrix and electron conductors in the composites.

Carbonized non-woven fabric films as adsorbing interlayers to enhance electrochemical performance of lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries with an effective adsorbing interlayer, high capacity and long cycle life have been fabricated using a simple method by placing an interlayer between the sulfur cathode and the separator. The interlayer with optimized porosity, electrolyte uptake and electrical conductivity can facilitate the use of pure sulfur (with a sulfur content of 70%) as a highly reversible cathode, which was made of carbonized non-woven fabrics (Mind Act Upon Mind™ Skincare Wipes) modified with Ketjenblack. A high capacity of 1486 mA h g−1 at a rate of 0.1C (1C = 1675 mA g−1) in the first cycle was obtained, and the reversible capacity remains high, up to 858 mA h g−1, even after 100 cycles.

Activated clay of nest structure encapsulated sulfur cathodes for lithium–sulfur batteries

Activated clay (AC) with a nest-like structure and a large surface area was employed to support sulfur as the cathode for lithium–sulfur batteries. The special structure may have a similar effect to small filter screens for entrapping sulfur and restricting the diffusion of polysulfides during cycling. A high capacity of 959.6 mA h g−1 was achieved at a rate of 0.1 C in the first cycle for the AC/S composite with a sulfur content of 57 wt% and the reversible capacity remained high at up to 700.9 mA h g−1 even after 50 cycles.

Sulfur grown around carbon nanotubes as a cathode material for Li/S battery

Sulfur/multi-walled carbon nanotubes (MWCNTs) composites have been successfully prepared by an in situ growth strategy as a cathode material for lithium/sulfur battery. The microstructure and morphology of the sulfur/MWCNTs composites are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). From the results, it is found that the nano-sulfur (shell) grows around the MWCNTs (core) and is well-dispersed over the whole surface of the MWCNTs. Tested by coin type cells, the composite materials exhibited the sulfur utilization approaching to 78% for the first cycle, the capacity retention closing to 84% after 100 cycles at various rates. The excellent electrochemical performance could be attributed to the nano-size sulfur and the homogeneous distribution of sulfur on MWCNTs matrix, resulting from this novel in situ growth method, which not only enhances the reactive activity of sulfur during charge–discharge processes but also provides stable electrical and ionic transfer channels.