Hongyu Dong

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.

Architecture design of nitrogen-doped 3D bubble-like porous graphene for high performance sodium ion batteries

N-Doped 3D bubble-like porous graphene was synthesized via a simple template directed method using polystyrene nanospheres as a template and low-cost industrial melamine as the nitrogen source. The as-synthesized N-3DPGX possessed a high specific surface area, uniform and controllable porous structure and high nitrogen doping content. Benefiting from these features, the as-obtained N-3DPG4 as an anode for sodium ion batteries delivered a high specific capacity of 310 mA h g−1 after 500 cycles at a current density of 0.2 A g−1, and also excellent rate capability as high as 169 mA h g−1 at 10 A g−1. This simple synthetic method, unique porous structure and outstanding electrochemical performance demonstrated that N-3DPG is a promising candidate for application in sodium ion batteries for large-scale electrochemical energy storage.

A particle–carbon matrix architecture for long-term cycle stability of ZnFe2O4 anode

ZnFe2O4/C with a unique compound structure was in situ synthesized through a facile one-step route using glycine as complexing agent and carbon source. ZnFe2O4 nanoparticles are embedded in a carbon matrix to form submicron particles. The carbon matrix in the composite material is divided into surface carbon and inner carbon, not only facilitates the electronic conduction, but also inhibits the aggregation of ZnFe2O4 nanoparticles, which largely accommodates the mechanical stresses caused by the volume change of ZnFe2O4 during charge/discharge process. ZnFe2O4/C could maintain their integrity and provide excellent properties. The obtained ZnFe2O4/C has a specific capacity of 2055 mA h g−1 at 1000 mA g−1 and a capacity retention of 54% with the current density increasing from 100 to 5000 mA g−1. The excellent performance is derived from the unique compound structure and this facile fabrication method also has good prospects in synthesizing other materials.

Excellent oxygen evolution reaction of NiO with a layered nanosphere structure as the cathode of lithium–oxygen batteries

A layered nanosphere structured NiO catalyst was successfully synthesized by a simple and efficient hydrothermal method as a cathode material for lithium–oxygen (Li–O2) batteries. Cyclic voltammetry (CV), dual electrode voltammetry (DECV) and chronoamperometry (CA) by rotating ring-disk electrode (RRDE) were carried out to investigate the catalytic activity of this catalyst for the oxygen evolution reaction (OER). The results revealed that the layered nanosphere NiO exhibited excellent electrochemical performance, stability and a typical four-electron reaction as a cathode electrocatalyst for rechargeable nonaqueous Li–O2 batteries. The overpotential of the NiO is only up to 0.61 V. X-ray photoelectron spectroscopy (XPS) characterization shows that the Li2O2 and Li2CO3 formed during the discharge process and decomposed after charging. Moreover, the cut-off voltage of discharging is about 2.0 V in the NiO-based Li–O2 batteries, while the specific capacity is up to 3040 mA h g−1. There is no obvious performance decline of the battery after 50 cycles at a current density of 0.1 mA cm−2 with a superior limited specific capacity of 800 mA h g−1. Herein, the layered nanosphere structured NiO catalyst is considered a promising cathode electrocatalyst for Li–O2 batteries.

In situ synthesis of metal embedded nitrogen doped carbon nanotubes as an electrocatalyst for the oxygen reduction reaction with high activity and stability

In this work, a Co–N doped carbon nanotube (CNT) catalyst was fabricated via a simple pyrolysis approach and the effects of solvothermal processing on the catalytic activity of the as-prepared material were investigated in detail. The results show that after solvothermal processing (Co-NC) the catalyst has a more homogeneous anemone structure, a higher nitrogen content, a larger BET surface area and a higher degree of graphitization compared to the catalyst produced after non-solvothermal processing (Co-MA). The results of electrochemical tests indicate that Co-NC, compared to commercial 20% Pt/C and Co-MA, has an improved mass transfer process and sufficient active site exposure, which brings about superb oxygen reduction electrocatalytic activity, a higher reduction potential (−0.2 V vs. Ag/AgCl), a limiting diffusion current (5.44 mA cm−2) and excellent stability in 0.1 M KOH solution.

A novel modified PP separator by grafting PAN for high-performance lithium–sulfur batteries

A novel modified separator was synthesized with an ultraviolet irradiated polypropylene (PP) membrane and acrylonitrile monomers by a solution grafting reaction. It was demonstrated that polyacrylonitrile (PAN) was grafted on the PP separator surface by analyzing the results of FESEM, ATR–FTIR and XPS. The thermostability and wettability of the PAN-grafted PP (PP-g-PAN) separator were enhanced. Then, Li–S batteries were assembled using the modified separators. The cycling and rate capacity performance is improved clearly because of the higher liquid uptake, smaller porous size, better polysulfides absorption effect and interfacial affinity of the grafted separator. The modified separator can hinder the movement of Li2Sx effectively to prevent the shuttle effect of a Li–S battery. Therefore, this efficient method has great potential to be applied to the modification of other kinds of polymer membranes.

Biomimetic Synthesis of Polydopamine Coated ZnFe2O4 Composites as Anode Materials for Lithium-Ion Batteries

Metal oxides as anode materials for lithium storage suffer from poor cycling stability due to their conversion mechanisms. Here, we report an efficient biomimetic method to fabricate a conformal coating of conductive polymer on ZnFe2O4 nanoparticles, which shows outstanding electrochemical performance as anode material for lithium storage. Polydopamine (PDA) film, a bionic ionic permeable film, was successfully coated on the surfaces of ZnFe2O4 particles by the self-polymerization of dopamine in the presence of an alkaline buffer solution. The thickness of PDA coating layer was tunable by controlling the reaction time, and the obtained ZnFe2O4/PDA sample with 8 nm coating layer exhibited an outstanding electrochemical performance in terms of cycling stability and rate capability. ZnFe2O4/PDA composites delivered an initial discharge capacity of 2079 mAh g–1 at 1 A g–1 and showed a minimum capacity decay after 150 cycles. Importantly, the coating layer improved the rate capability of composites compared to that of its counterpart, the bare ZnFe2O4 particle materials. The outstanding electrochemical performance was because of the buffering and protective effects of the PDA coating layer, which could be a general protection strategy for electrode materials in lithium-ion batteries.