第一性原理对氮掺杂石墨烯作为锂-空电池阴极材料还原氧分子的机理研究

采用第一性原理,研究了不同浓度的氮掺杂石墨烯还原氧分子的机理.结果表明,掺杂氮原子以后,氧分子的吸附能增大,获得的电荷增多,O-O键长变长,说明氮掺杂石墨烯增强了对氧分子的还原能力.进一步分析发现,氧分子吸附之后,氮原子和氧分子均从碳原子上获得电荷,氮原子同时也向氧分子转移电荷,从而使氧分子与基底的相互作用增强.另外,通过对比不同浓度的氮原子掺杂,发现3.13 at%的氮原子掺杂比例对氧分子的还原性能最好.

α-MnO_2 nanoneedle-based hollow microspheres coated with Pd nanoparticles as a novel catalyst for rechargeable lithium-air batteries

The hollow α-MnO2 nanoneedle-based microspheres coated with Pd nanoparticles were reported as a novel catalyst for rechargeable lithium-air batteries. The hollow microspheres are composed ofα-MnO2 nanoneedles. Pd nanoparticles are deposited on the hollow microspheres through an aqueous-solution reduction of PdCl2 with NaBH4 at room temperature. The results of TEM, XRD, and EDS show that the Pd nanoparticles are coated on the surface ofα-MnO2 nanoneedles uniformly and the mass fraction of Pd in the Pd-coated α-MnO2 catalyst is about 8.88%. Compared with the counterpart of the hollow α-MnO2 catalyst, the hollow Pd-coated α-MnO2 catalyst improves the energy conversion efficiency and the charge-discharge cycling performance of the air electrode. The initial specific discharge capacity of an air electrode composed of Super P carbon and the as-prepared Pd-coatedα-MnO2 catalyst is 1220 mA＆#183;h/g （based on the total electrode mass） at a current density of 0.1 mA/cm2, and the capacity retention rate is about 47.3% after 13 charge-discharge cycles. The results of charge-discharge cycling tests demonstrate that this novel Pd-coatedα-MnO2 catalyst with a hierarchical core-shell structure is a promising catalyst for the lithium-air battery.

Effect of Magnetic Field on Properties of AuPt Particles Magneto- electrodeposited on Carbon Paper

AuPt nano particles are bi-functional catalysts for Oxygen Reduction Reaction （ORR） and Oxygen Evolution Reaction （OER） that were taken place on air electrodes in lithium air batteries. Magnetic field has been applied during electrodeposition for the preparation of AuPt particles. With the increase of the magnetic flux density under constant current density, the grain size decreases from - 1μm to 200nm and the activity of the AuPt catalyst increases. The magnetic field oriented vertical to the electric field has a promotion effect on increasing the catalytic ability of AuPt/carbon electrode. By pulse plating, the grain size decreases to about 100nm. By adjusting parameters of the electric field and the magnetic field, controllable in-situ preparation of AuPt catalyst with various morphology and catalytic activity could be achieved.

Preparation and electrochemical performance of hollow-spherical polypyrrole/V_2O_5 composite

In order to improve the lower practical capacity and bad cyclability of crystalline V2O5（c-V2O5）,the vanadium oxide（V2O5） and polypyrrole（PPy） hybrid with hollow-spherical（HS） structure was studied.HS nanocomposite comprised of conductive polypyrrole and vanadium pentoxide（PPy/V2O5） was synthesized by polymerization of pyrrole monomer（Py） in the hollow-microspherical V2O5 host.This novel hybrid was characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and tested as the cathode material for lithium-ion batteries（LIB） by galvanostatic cell cycling and electrochemical impedance spectroscopy（EIS）.The hollow-spherical polypyrrole/vanadium oxide（HS-PPy/V2O5） composites,in which PPy molecules are intercalated between the layers of V2O5,exhibit slight reduced capacity and substantially improve cyclability and electrochemical activity compared with the pure HS-V2O5.

Amorphous CoSnO_3@rGO nanocomposite as an efficient cathode catalyst for long-life Li-O_2 batteries

An amorphous CoSnO3@rGO nanocomposite fabricated using a surfactant‐assisted assembly method combined with thermal treatment served as a catalyst for non‐aqueous lithium‐oxygen(Li‐O2)batteries.In contrast to the specific surface area of the bare CoSnO3 nanoboxes(104.3 m2 g–1),the specific surface area of the CoSnO3@rGO nanocomposite increased to approximately 195.8 m2 g–1 and the electronic conductivity also improved.The increased specific surface area provided more space for the deposition of Li2O2,while the improved electronic conductivity accelerated the decomposition of Li2O2.Compared to bare CoSnO3,the overpotential reduced by approximately 20 and 60 mV at current densities of 100 and 500 mA g?1 when CoSnO3@rGO was used as the catalyst.A Li‐O2 battery using a CoSnO3@rGO nanocomposite as the cathode catalyst cycled indicated a superior cyclic stability of approximately 130 cycles at a current density of 200 mA g–1 with a limited capacity of 1000 mAh g–1,which is 25 cycles more than that of the bare amorphous CoSnO3 nanoboxes.

Solvation structure and dynamics of Li and LiO_(2)and their transformation in non-aqueous organic electrolyte solvents from first-principles simulations

Density functional theory calculations together with ab initio molecular dynamics(AIMD)simulations have been used to study the solvation,diffusion and transformation of Li^(+)and LiO_(2)upon O_(2)reduction in three organic electrolytes.These processes are critical for the performance of Li-air batteries.Apart from studying the structure of the solvation shells in detail,AIMD simulations have been used to derive the diffusivity and together with the Blue Moon ensemble approach to explore LiO_(2)formation from Li^(+)and O_(2)−and the subsequent disproportionation of 2LiO_(2)into Li_(2)O_(2)+O_(2).By comparing the results of the simulations to gas phase calculations,the impact of electrolytes on these reactions is assessed which turns out to be more pronounced for the ionic species involved in these reactions.

Enhanced electrochemical performance in lithium ion batteries of a hollow spherical lithium-rich cathode material synthesized by a molten salt method

A high voltage layered Li1.2Ni0.16Co0.08Mn0.56O2 cathode material with a hollow spherical structure has been synthesized by molten-salt method in a NaCI flux. Characterization by X-ray diffraction and scanning electron microscopy confirmed its structure and proved that the as-prepared powder is constituted of small, homogenously sized hollow spheres （1-1.5 μm）. The material exhibited enhanced rate capability and high first cycle efficiency due to the good dispersion of secondary particles. Galvanostatic cycling at different temperatures （20, 40, and 60 ℃） and a current rate of 2 C （500 mA.g-1） showed no significant capacity fade.

Rational synthesis of SnS_2@C hollow microspheres with superior stability for lithium-ion batteries

Tin-based nanomaterials have been extensively explored as high-capacity anode materials for lithium ion batteries（LIBs）. However,the large volume changes upon repeated cycling always cause the pulverization of the electrode materials. Herein,we report the fabrication of uniform SnS_2@C hollow microspheres from hydrothermally prepared SnO_2@C hollow microspheres by a solid-state sulfurization process. The as-prepared hollow SnS_2@C microspheres with unique carbon shell,as electrodes in LIBs,exhibit high reversible capacity of 814 mA h g^（-1） at a current density of 100 mA g^（-1）,good cycling performance（783 mA h g^（-1） for 200 cycles maintained with an average degradation rate of 0.02% per cycle） and remarkable rate capability（reversible capabilities of 433 mA h g^（-1）at 2C）. The hollow space could serve as extra space for volume expansion during the charge-discharge cycling,while the carbon shell can ensure the structural integrity of the microspheres. The preeminent electrochemical performances of the SnS_2@C electrodes demonstrate their promising application as anode materials in the next-generation LIBs.

SnO_2 hollow spheres:Polymer bead-templated hydrothermal synthesis and their electrochemical properties for lithium storage

SnO2 hollow spheres have been synthesized via a facile hydrothermal method using sulfonated polystyrene beads as a template followed by a calcination process in air.X-ray diffraction,scanning electron microscopy,and transmission electron microscopy show that the as-obtained SnO2 hollow spheres have a wall thickness of about 50 nm,and consist of nanosized SnO2 particles with a mean diameter of about 15 nm.Electrochemical measurements indicate that the SnO2 hollow spheres exhibit improved electrochemical performance in terms of specific capacity and rate capability in comparison with commercial SnO2 when used as anode materials for lithium-ion batteries.The enhanced performance may be attributed to the spherical and hollow structure,as well as the building blocks of SnO2 nanoparticles.

In situ construction of amorphous hierarchical iron oxyhydroxide nanotubes via selective dissolution-regrowth strategy for enhanced lithium storage

The low-cost and high-capacity metal oxides/oxyhydroxides possess great merits as anodes for lithium-ion batteries(LIBs)with high energy density.However,their commercialization is greatly hindered by insufficient rate capability and cyclability.Rational regulations of metal oxides/oxyhydroxides with hollow geometry and disordered atomic frameworks represent efficient ways to improve their electrochemical properties.Herein,we propose a fast alkalietching method to realize the in-situ fabrication of iron oxyhydroxide with one-dimensional(1D)hierarchical hollow nanostructure and amorphous atomic structure from the iron vanadate nanowires.Benefiting from the improved electron/ion kinetics and efficient buffer ability for the volumetric change during the electro-cycles both in nanoscale and atomic level,the graphene-modified amorphous hierarchical FeOOH nanotubes(FeOOH-NTs)display high rate capability(~650 mA h g^−1 at 2000 mA g^−1)and superior long-term cycling stability(463 mA h g^−1 after 1800 cycles),which represents the best cycling performance among the reported FeOOH-based materials.More importantly,the selective dissolutionregrowth mechanism is demonstrated based on the time tracking of the whole transition process,in which the dissolution of FeVO4 and the in-situ selective re-nucleation of FeOOH during the formation of FeOOH-NTs play the key roles.The present strategy is also a general method to prepare various metal(such as Fe,Mn,Co,and Cu)oxides/oxyhydroxides with 1D hierarchical nanostructures.

Hollow and hierarchical Na_2Li_2Ti_6O_(14) microspheres with high electrochemical performance as anode material for lithium-ion battery

Relying on a solvent thermal method, spherical Na2Li2Ti6O14 was synthesized. All samples prepared by this method are hollow and hierarchical structures with the size of about 2-3 μtm, which are assembled by many primary nanoparticles （-300nm）. Particle morphology analysis shows that with the increase of temperature, the porosity increases and the hollow structure becomes more obvious. Na2Li2Ti6Ol4 obtained at 800℃ exhibits the best electro- chemical performance among all samples. Charge-discharge results show that Na2Li2Ti6O14 prepared at 800℃ can delivers a reversible capacity of 220.1, 181.7, 161.6, 144.2, 118.1 and 97.2 mA h g-1 at 50, 140, 280, 560, 1400, 2800 mA g-1. How- ever, Na2Li2Ti6O4-bulk only delivers a reversible capacity of 187, 125.3, 108.3, 88.7, 69.2 and 54.8 mA h g-1 at the same current densities. The high electrochemical performances of the as-prepared materials can be attributed to the distinctive hollow and hierarchical spheres, which could effectively reduce the diffusion distance of Li ions, increase the con- tact area between electrodes and electrolyte, and buffer the volume changes during Li ion intercalation/deintercalation processes.