Yingjin Wei

NASICON-Structured NaTi2(PO4)3@C Nanocomposite as the Low Operation-Voltage Anode Material for High-Performance Sodium-Ion Batteries

NASICON-type structured NaTi2(PO4)3 (NTP) has attracted wide attention as a promising anode material for sodium-ion batteries (SIBs), whereas it still suffer from poor rate capability and cycle stability due to the low electronic conductivity. Herein, the architecture, NTP nanoparticles embedded in the mesoporous carbon matrix, is designed and realized by a facile sol-gel method. Different than the commonly employed potentials of 1.5-3.0 V, the Na(+) storage performance is examined at low operation voltages between 0.01 and 3.0 V. The electrode demonstrates an improved capacity of 208 mAh g(-1), one of the highest capacities in the state-of-the-art titanium-based anode materials. Besides the high working plateau at 2.1 V, another one is observed at approximately 0.4 V for the first time due to further reduction of Ti(3+) to Ti(2+). Remarkably, the anode exhibits superior rate capability, whose capacity and corresponding capacity retention reach 56 mAh g(-1) and 68%, respectively, over 10000 cycles under the high current density of 20 C rate (4 A g(-1)). Worthy of note is that the electrode shows negligible capacity loss as the current densities increase from 50 to 100 C, which enables NTP@C nanocomposite as the prospective anode of SIBs with ultrahigh power density.

Self-assembled large-area Co(OH)(2) nanosheets/ionic liquid modified graphene heterostructures toward enhanced energy storage

Large-area Co(OH)2 nanosheets have been successfully coated with ionic liquid modified graphenevia a general strategy. The advantageous combination of graphene and the 2D structure of the Co(OH)2 nanosheets endows the obtained heterostructures with a remarkable lithium-storage performance, including high reversible capacity and superior cyclic and rate performance.

Carbon and RuO2 binary surface coating for the Li3V2(PO4)3 cathode material for lithium-ion batteries.

RuO2 nanocrystals are successfully impregnated into the surface carbon layer of the Li3V2(PO4)3/C cathode material by the precipitation method. Transmission electron microscopy shows that the RuO2 particles uniformly embed in the surface carbon layer. Cyclic voltammetry and electrochemical impedance spectroscopy indicate that the coexistence of carbon and RuO2 enables high conductivity for both Li ions and electrons and thus stabilizes the interfacial properties of the electrode, facilitates the charge transfer reactions, and improves the Li(+) diffusion in the electrode. As a result, the Li3V2(PO4)3 cathode coated with the binary surface layer shows improved rate capability and cycle stability. Particularly, the material containing 2.4 wt % Ru exhibits the best electrochemical performance and delivers a discharge capacity of 106 mAh g(-1) at the 10 C rate with a capacity retention of 98.4% after 100 cycles.

Na3V2(PO4)3/C composite as the intercalation-type anode material for sodium-ion batteries with superior rate capability and long-cycle life

A Na3V2(PO4)3/C (NVP/C) composite is successfully synthesized by the sol–gel method and examined as the anode material for sodium-ion batteries (SIBs) by means of galvanostatic charge–discharge profiles, cyclic voltammograms, rate performance and cyclic voltammetry comprehensively. The NVP/C electrode delivers a reversible capacity of about 170 mA h g−1 between 3.0 and 0.01 V at a current density of 20 mA g−1 corresponding to three sodium ions insertion/extraction processes. Besides the voltage plateau at 1.57 V, another novel working platform at around 0.28 V is found for the first time in both charging and discharging profiles, possibly owing to the further reduction of vanadium. NVP/C exhibits an excellent rate capability and long-cycle stability with a capacity retention of 62% after 3000 cycles at a high charge rate of 10 C (2 A g−1). Moreover, the intercalation-type Na-ions storage mechanism is proposed on the basis of ex situ X-ray diffraction and high-resolution transmission electron microscopy. Our findings reveal that the NVP/C sample is a promising anode material for SIBs due to its superior rate capability and long cycle life.

Improvements in the Electrochemical Kinetic Properties and Rate Capability of Anatase Titanium Dioxide Nanoparticles by Nitrogen Doping

Pure anatase TiO2 and N-doped TiO2 nanoparticles were prepared by a solvothermal method. X-ray photoelectron spectroscopy showed that the surface of the doped material was dominated by interstitial N, while interstitial and substitutional N coexisted in the material bulk. Both materials showed superior cycle stability. In addition, the N-doped material exhibited much better rate capability than pure TiO2. A discharge capacity of 45 mAh g(-1) was obtained at the 15 C rate, which was 80% higher than that of pure TiO2. The electrochemical kinetic properties of the materials were studied by a galvanostatic intermittent titration technique and electrochemical impedance spectroscopy. The charge-transfer resistance of TiO2 was decreased by N doping. Meanwhile, the minimum lithium diffusion coefficient was increased to 2.14 × 10(-11) cm(2) s(-1), which is 13 times higher than that of pure TiO2. This indicates that the electrochemical kinetic properties of TiO2 were improved by N doping, which substantially improved the specific capacity and rate capability of TiO2.

Ultrafast lithium storage in TiO2–bronze nanowires/N-doped graphene nanocomposites

A TiO2–bronze/N-doped graphene nanocomposite (TiO2–B/NG) is prepared by a facile hydrothermal combined with hydrazine monohydrate vapor reduction method. The material exhibits macro- and meso-porosity with a high specific surface area of 163.4 m2 g−1. X-Ray photoelectron spectroscopy confirms the successful doping of nitrogen in the graphene sheets. In addition, the TiO2–B nanowires are substantially bonded to the NG sheets. Cyclic voltammetry and electrochemical impedance spectroscopy show that the N-doped graphene improves the electron and Li ion transport in the electrode which results in better electrochemical kinetics than that of the pristine TiO2–B nanowires. As a result, the charge transfer resistance of the TiO2–B/NG electrode is significantly reduced. In addition, the lithium diffusion coefficient of TiO2–B/NG increases by about five times with respect to that of pristine TiO2–B. The TiO2–B/NG composite exhibits a remarkably enhanced electrochemical performance compared to that of TiO2–B. It shows a discharge capacity of 220.7 mA h g−1 at the 10C rate with a capacity retention of 96% after 1000 cycles. In addition, it can deliver a discharge capacity of 101.6 mA h g−1 at an ultra high rate of 100C, indicating its great potential for use in high power lithium ion batteries.

Recent advances in IV–VI semiconductor nanocrystals: synthesis, mechanism, and applications

This review is focused on the recent developments of the synthesis, mechanism and applications of IV–VI semiconductor nanocrystals (NCs), including germanium-, tin- and lead-based chalcogenides NCs. First of all, we systematically introduce a series of investigations on the preparation with controllable size and shape via a wide variety of methods. Corresponding growth mechanisms are also discussed. Moreover, the promising potential of IV–VI semiconductor NCs as building blocks with respect to energy, sensors and catalysis is highlighted. For the purpose of enhancing the performance to satisfy the practical applications, tailored nanocomposites by combining noble metals or graphene etc. are further developed. Finally, we present some concluding remarks and perspectives for future developments. We hope this article can provide researchers with the key snapshots of the recent advances and the future challenges, thus achieving a great progress in IV–VI semiconductor NCs.

Shape and size controlled synthesis and properties of colloidal IV–VI SnSe nanocrystals

Colloidal IV–VI SnSe nanocrystals with small and uniform size distribution were synthesized by a facile and phosphine-free method. Simple Sn6O4(OH)4 was introduced as a tin precursor to synthesize the SnSe nanocrystals. By changing the reaction temperature and Sn/Se molar ratio, SnSe nanocrystals with different shapes and sizes were achieved. The influence of reaction temperature and Sn/Se molar ratio to the shape and size of SnSe nanocrystals has been discussed detail. Similar to other IV–VI tin chalcogenides, SnSe shows potential as energy storage material. The performance of SnSe nanocrystals as an anode material for lithium ion batteries has been investigated. A mechanism for SnSe as anode material has been proposed based on its performance. The influence of the shape and size of the SnSe nanocrystals on the performance of lithium ion batteries has been discussed in detail.

Sodium vanadium titanium phosphate electrode for symmetric sodium-ion batteries with high power and long lifespan

Sodium-ion batteries operating at ambient temperature hold great promise for use in grid energy storage owing to their significant cost advantages. However, challenges remain in the development of suitable electrode materials to enable long lifespan and high rate capability. Here we report a sodium super-ionic conductor structured electrode, sodium vanadium titanium phosphate, which delivers a high specific capacity of 147u2009mAu2009hu2009g−1 at a rate of 0.1 C and excellent capacity retentions at high rates. A symmetric sodium-ion full cell demonstrates a superior rate capability with a specific capacity of about 49u2009mAu2009hu2009g−1 at 20 C rate and ultralong lifetime over 10,000 cycles. Furthermore, in situ synchrotron diffraction and X-ray absorption spectroscopy measurement are carried out to unravel the underlying sodium storage mechanism and charge compensation behaviour. Our results suggest the potential application of symmetric batteries for electrochemical energy storage given the superior rate capability and long cycle life.

LiFe(MoO4)2 as a Novel Anode Material for Lithium-Ion Batteries

Polycrystalline LiFe(MoO4)2 is successfully synthesized by solid-state reaction and examined as anode material for lithium-ion batteries in terms of galvanostatic charge-discharge cycling, cyclic voltammograms (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). The LiFe(MoO4)2 electrode delivers a high capacity of 1034 mAh g(-1) at a current density of 56 mA g(-1) between 3 and 0.01 V, indicating that nearly 15 Li(+) ions are involved in the electrochemical cycling. LiFe(MoO4)2 also exhibits a stable capacity of 580 mAh g(-1) after experiencing irreversible capacity loss in the first several cycles. Moreover, the Li-ion storage mechanism for LiFe(MoO4)2 is suggested on the basis of the ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) at different insertion/extraction depths. A successive structural transition from triclinic structure to cubic structure is observed, and the tetrahedral coordination of Mo by oxygen in LiFe(MoO4)2 changes to octahedral coordination in Li2MoO3, correspondingly. When being discharged to 0.01 V, the active electrode is likely to be composed of Fe and Mo metal particles and amorphous Li2O due to the multielectron conversion reaction. The insights obtained from this study will benefit the design of new anode materials for lithium-ion batteries.