Lifen Xiao

Sodium ion insertion in hollow carbon nanowires for battery applications.

Hollow carbon nanowires (HCNWs) were prepared through pyrolyzation of a hollow polyaniline nanowire precursor. The HCNWs used as anode material for Na-ion batteries deliver a high reversible capacity of 251 mAh g(-1) and 82.2% capacity retention over 400 charge-discharge cycles between 1.2 and 0.01 V (vs Na(+)/Na) at a constant current of 50 mA g(-1) (0.2 C). Excellent cycling stability is also observed at an even higher charge-discharge rate. A high reversible capacity of 149 mAh g(-1) also can be obtained at a current rate of 500 mA g(-1) (2C). The good Na-ion insertion property is attributed to the short diffusion distance in the HCNWs and the large interlayer distance (0.37 nm) between the graphitic sheets, which agrees with the interlayered distance predicted by theoretical calculations to enable Na-ion insertion in carbon materials.

A Soft Approach to Encapsulate Sulfur: Polyaniline Nanotubes for Lithium‐Sulfur Batteries with Long Cycle Life

A novel vulcanized polyaniline nanotube/sulfur composite was prepared successfully via an in situ vulcanization process by heating a mixture of polyaniline nanotube and sulfur at 280 °C. The electrode could retain a discharge capacity of 837 mAh g(-1) after 100 cycles at a 0.1 C rate and manifested 76% capacity retention up to 500 cycles at a 1 C rate.

Reversible Sodium Ion Insertion in Single Crystalline Manganese Oxide Nanowires with Long Cycle Life

Single crystalline Na4Mn9O18 nanowires were synthesized via pyrolysis of polyacrylate salt precursors prepared by in-situ polymerization of the metal salts and acrylate acid, followed by calcinations at an appropriate temperature to achieve good crystalline structure and uniform nanowire morphology with an average diameter of 50 nm. The Na4Mn9O18 nanowires have shown a high, reversible, and near theoretical sodium ion insertion capacity (128 mA h g-1 at 0.1C), excellent long cyclability (77% capacity retention for 1000 cycles at 0.5 C), along with good rate capability. Good capacity and charge-discharge stability are also observed for full cell experiments using a pyrolyzed carbon as the anode, therefore demonstrating the potential of these materials for sodium-ion batteries for large scale energy storage. Furthermore, this research shows that a good crystallinity and small particles are required to enhance the Na-ion diffusion and increase the stability of the electrode materials for long charge-discharge cycles.

Hierarchical carbon framework wrapped Na3V2(PO4)3 as a superior high-rate and extended lifespan cathode for sodium-ion batteries.

Hierarchical carbon framework wrapped Na3 V2 (PO4 )3 (HCF-NVP) is successfully synthesized through chemical vapor deposition on pure Na3 V2 (PO4 )3 particles. Electrochemical experiments show that the HCF-NVP electrode can deliver a large reversible capacity (115 mA h g(-1) at 0.2 C), superior high-rate rate capability (38 mA h g(-1) at 500 C), and ultra-long cycling stability (54% capacity retention after 20 000 cycles).

Mesoporous Amorphous FePO4 Nanospheres as High-Performance Cathode Material for Sodium-Ion Batteries

FePO4 nanospheres are synthesized successfully through a simple chemically induced precipitation method. The nanospheres present a mesoporous amorphous structure. Electrochemical experiments show that the FePO4/C electrode demonstrates a high initial discharging capacity of 151 mAh g(-1) at 20 mA g(-1), stable cyclablilty (94% capacity retention ratio over 160 cycles), as well as high rate capability (44 mAh g(-1) at 1000 mA g(-1)) for Na-ion storage. The superior electrochemical performance of the FePO4/C nanocomposite is due to its particular mesoporous amorphous structure and close contact with the carbon framework, which significantly improve the ionic and electronic transport and intercalation kinetics of Na ions.

Clewlike ZnV2O4 Hollow Spheres: Nonaqueous Sol–Gel Synthesis, Formation Mechanism, and Lithium Storage Properties

Hollow ZnV(2)O(4) microspheres with a clewlike feature were synthesized by reacting zinc nitrate hexahydrate and ammonium metavanadate in benzyl alcohol at 180 degrees C for the first time. GC-MS analysis revealed that the organic reactions that occurred in this study were rather different from those in benzyl alcohol based nonaqueous sol-gel systems with metal alkoxides, acetylacetonates, and acetates as the precursors. Time-dependent experiments revealed that the growth mechanism of the clewlike ZnV(2)O(4) hollow microspheres might involve a unique multistep pathway. First, the generation and self-assembly of ZnO nanosheets into metastable hierarchical microspheres as well as the generation of VO(2) particles took place quickly. Then, clewlike ZnV(2)O(4) hollow spheres were gradually produced by means of a repeating reaction-dissolution (RD) process. In this process, the outside ZnO nanosheets of hierarchical microspheres would first react with neighboring vanadium ions and benzyl alcohol and also serve as the secondary nucleation sites for the subsequently formed ZnV(2)O(4) nanocrystals. With the reaction proceeding, the interior ZnO would dissolve and then spontaneously diffuse outwards to nucleate as ZnO nanocrystals on the preformed ZnV(2)O(4) nanowires. These renascent ZnO nanocrystals would further react with VO(2) and benzyl alcohol, ultimately resulting in the final formation of a hollow spatial structure. The lithium storage ability of clewlike ZnV(2)O(4) hollow microspheres was studied. When cycled at 50 mA g(-1) in the voltage range of 0.01-3 V, this peculiarly structured ZnV(2)O(4) electrode delivered an initial reversible capacity of 548 mAh g(-1) and exhibited almost stable cycling performance to maintain a capacity of 524 mAh g(-1) over 50 cycles. This attractive lithium storage performance suggests that the resulting clewlike ZnV(2)O(4) hollow spheres are promising for lithium-ion batteries.

Electrochemical properties and morphological evolution of pitaya-like Sb@C microspheres as high-performance anode for sodium ion batteries

Pitaya-like Sb@C microspheres are prepared successfully by facile aerosol spray drying synthesis. Structural and morphological characterizations reveal that the Sb@C microspheres have a uniform pitaya-like structure, with well crystallized Sb nanoparticles embedded homogeneously in the carbon matrix. The Sb@C microsphere electrodes exhibit high Na storage capacity of 655 mA h g−1 at C/15 with excellent cyclability (93% of capacity retention over 100 cycles), as well as remarkable rate capability. Also, the morphological evolution of the Sb@C microspheres is unravelled to account for its excellent electrochemical performance, caused by maintenance of the pitaya-like configuration during cycling. This structural stability guarantees tight contact of Sb with carbon buffer, as well as uniform distribution of Sb to balance the localized mechanical stress, ensuring excellent electrochemical performance. The structural design and synthetic method reported in this work may provide an effective way to stabilize electrochemical performance of Na-storable alloy materials and therefore provide a new prospect for creation of cycle-stable alloy anodes for high capacity Na-ion batteries.

A tin(II) sulfide–carbon anode material based on combined conversion and alloying reactions for sodium-ion batteries

A tin(II) sulfide–carbon (SnS–C) nanocomposite is prepared by a simple high-energy mechanical milling method. XRD, SEM and TEM characterizations show that the nanocomposite is composed of well crystallized SnS nanoparticles with a size of about 15 nm, which are dispersed uniformly in the conductive carbon matrix. The SnS–C electrode exhibits a high Na storage capacity (568 mA h g−1 at 20 mA g−1) and excellent cycling stability (97.8% capacity retention over 80 cycles) as well as high-rate capability. Ex situ XRD result confirms a sequential conversion and alloying–dealloying reaction mechanism of the SnS–C electrode during the Na uptaking and extraction cycles. The superior electrochemical performance of the electrodes can be attributed to the small crystalline size of SnS and good carbon coating, which facilitate electrochemical utilization and maintain the structural integrity.

Surface-Modified Graphite as an Improved Intercalating Anode for Lithium-Ion Batteries

A simple approach to improve the initial charge/discharge behavior of natural graphite is described. Graphite modified by adsorption or adhesion of polydimethylsiloxane is used as an intercalating anode for lithium-ion batteries. The modified graphite electrode shows ∼14% reduction in the first irreversible capacity while the reversible capacity remains unchanged in comparison with a bare graphite electrode. In addition, the chemical modification also improves the cycling performance of the graphite electrode.

Molecular structures of polymer/sulfur composites for lithium–sulfur batteries with long cycle life

Vulcanized polyaniline/sulfur (SPANI/S) nanostructures were investigated for Li–S battery applications, but the detailed molecular structures of such composites have not been fully illustrated. In this paper, we synthesize SPANI/S composites with different S content in a nanorod configuration. FTIR, Raman, XPS, XRD, SEM and elemental analysis methods are used to characterize the molecular structure of the materials. We provide clear evidence that a portion of S was grafted on PANI during heating and connected the PANI chains with disulfide bonds to form a crosslinked network and the rest of S was encapsulated within it. Polysulfides and elementary S nanoparticles are physically trapped inside the polymer network and are not chemically bound to the polymer. The performance of the composites is further improved by reducing the particle size. After 200 cycles, a capacity retention rate of 80.4, 80.5, 87.6, and 90.0% is observed at 0.1, 0.2, 0.5 and 1 C respectively in the SPANI/S composite with 55% S content.