Daobin Mu

Enhanced Electrochemical Performance of ZnO-Loaded/Porous Carbon Composite as Anode Materials for Lithium Ion Batteries

ZnO-loaded/porous carbon (PC) composites with different ZnO loading amounts are first synthesized via a facile solvothermal method and evaluated for anode materials of lithium ion batteries. The architecture and the electrochemical performance of the as-prepared composites are investigated through structure characterization and galvanostatic charge/discharge test. The ZnO-loaded/PC composites possess a rich porous structure with well-distributed ZnO particles (size range: 30-100 nm) in the PC host. The one with 54 wt % ZnO loading contents exhibits a high reversible capacity of 653.7 mA h g(-1) after 100 cycles. In particular, a capacity of 496.8 mA h g(-1) can be reversibly obtained when cycled at 1000 mA g(-1). The superior lithium storage properties of the composite may be attributed to its nanoporous structure together with an interconnected network. The modified interfacial reaction kinetics of the composite promotes the intercalation/deintercalation of lithium ions and the charge transfer on the electrode. As a result, the enhanced capacity of the composite electrode is achieved, as well as its high rate capability.

New Synthesis of a Foamlike Fe3O4/C Composite via a Self-Expanding Process and Its Electrochemical Performance as Anode Material for Lithium-Ion Batteries

A novel foamlike Fe3O4/C composite is prepared via a sol-gel type method with gelatin as the carbon source and ferric nitrate as the iron source, following a postannealing treatment. Its lithium storage properties as anode material for a lithium-ion battery are thoroughly investigated in this work. With the interaction between ferric nitrate and gelatin, the foamlike architecture is attained through a unique self-expanding process. The Fe3O4/C composite possesses abundant porous structure along with highly dispersed Fe3O4 nanocrystal embedment in the carbon matrix. In the constructed architecture, the 3D porous network property ensures electrolyte accessibility; meanwhile, nanosized Fe3O4 promotes lithiation/delithiation, owing to numerous active sites, large electrolyte contact area, and a short lithium ion diffusion path. As a result, this Fe3O4/C composite electrode demonstrates an excellent cycling stability with a reversible capacity of 1008 mA h g(-1) over 400 cycles at 0.2C (1C = 1000 mA g(-1)), as well as a superior rate performance with reversible capacity of 660 and 580 mA h g(-1) at 3C and 5C, respectively.

Electrospun composite of ZnO/Cu nanocrystals-implanted carbon fibers as an anode material with high rate capability for lithium ion batteries

The paper reports a novel composite with ZnO and Cu nanocrystals implanted into carbon nanofibers (CNFs) and its lithium storage properties, in particular its high rate performance. Fabrication of the fibrous composite is controllably accomplished utilizing an electrospinning approach. The composite electrode exhibits a high reversible capacity of 812 mAxa0hxa0g−1 at a current density of 100 mAxa0g−1 after 50 cycles. Moreover, it shows good rate capability even when cycled at 5000 mAxa0g−1. This can be attributed to the designed nano-fibrous architecture with active material implantation as well as electroconductive Cu introduction. The interconnected particles of ZnO and Cu on the CNFs ensure a good contact in the composite. Moreover, the one-dimensional CNFs act not only as a supporter with good stability, but also provide a shortened transport pathway for Li ions.

Effect of lithium carbonate precipitates on the electrochemical cycling stability of LiCoO2 cathodes at a high voltage

An electrolyte (LiPF6–EC/PC/DEC) containing a lithium carbonate (Li2CO3) additive is used to enable the high cycling stability of a lithium cobalt oxide (LiCoO2) cathode which is charged to 4.5 V for a higher capacity. A capacity as high as 162.8 mA h g−1 (1 C) is maintained after 116 cycles, which is twice as high as the capacity of 88.5 mA h g−1 which was achieved in the Li2CO3 free instance. The interface properties of the electrode are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. It is found that the solid electrolyte interphase (SEI) film tends to be thin and steady, and that the electrolyte decomposition is suppressed with the addition of Li2CO3. A possible mechanism is proposed according to the DFT calculation. The results indicate that the Co4+…CO32− coordination may decrease the oxidizability of Co4+ on the electrode surface so that the electrolyte decomposition could be suppressed.

Enhanced electrochemical performance of LiFePO4 cathode with the addition of fluoroethylene carbonate in electrolyte

The effect of the fluoroethylene carbonate (FEC) addition in electrolyte on LiFePO4 cathode performance was investigated in low-temperature electrolyte LiPF6/EC/PC/EMC (0.14/0.18/0.68). Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests were conducted in this work. In the presence of FEC, the polarization of LiFePO4 electrode decreased both at room and low temperatures. Meanwhile, the exchange current density increased. The rate capability of LiFePO4 electrode was greatly enhanced as well. The morphology of the solid electrolyte interphase (SEI) on LiFePO4 surface was modified with the addition of FEC as confirmed by scanning electron microscopy measurement. A compact film with small impedance was formed on LiFePO4 surface compared to the case of FEC-free. The compositions of the film were analyzed by X-ray photoelectron spectroscopic measurement. The contents of LixPOyFz, LiF, and the carbonate species generated from solvents decomposition were reduced. The modified SEI promoted the migration of lithium ion through the electrode/electrolyte interphase and enhanced the electrochemical performance of the cathode.

Density Functional Theory Research into the Reduction Mechanism for the Solvent/Additive in a Sodium-Ion Battery.

The solid-electrolyte interface (SEI) film in a sodium-ion battery is closely related to capacity fading and cycling stability of the battery. However, there are few studies on the SEI film of sodium-ion batteries and the mechanism of SEI film formation is unclear. The mechanism for the reduction of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), ethylene sulfite (ES), 1,3-propylene sulfite (PS), and fluorinated ethylene carbonate (FEC) is studied by DFT. The reaction activation energies, Gibbs free energies, enthalpies, and structures of the transition states are calculated. It is indicated that VC, ES, and PS additives in the electrolyte are all easier to form organic components in the anode SEI film by one-electron reduction. The priority of one-electron reduction to produce organic SEI components is in the order of VC>PC>EC; two-electron reduction to produce the inorganic Na2 CO3 component is different and follows the order of EC>PC>VC. Two-electron reduction for sulfites ES and PS to form inorganic Na2 SO3 is harder than that of carbonate ester reduction. It is also suggested that the one- and two-electron reductive decomposition pathway for FEC is more feasible to produce inorganic NaF components.

Suppression of lithium dendrite growth by introducing a low reduction potential complex cation in the electrolyte

A low reduction potential complex cation (LRPCC) N-methyl-N-butylpiperidinium was introduced to the LiPF6/EC/DEC electrolyte to investigate its effect on the interface properties of a lithium anode. The reduction of N-methyl-N-butylpiperidinium LRPCC is analyzed by density functional theory (DFT) calculations using the Gaussian 09 package. Lithium dendrites and fractured metal Li are examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The solid electrolyte interface (SEI) film of the metal Li surface is analyzed by X-ray photoelectron spectroscopy (XPS). It is indicated that the LUMO energy level of the LRPCC is higher than lithium ions one. It exhibits a better electrostatic shield around the initial protuberances, reducing the growth of the Li dendrites. The shield effect could play a role even at a higher current density and a wider electrostatic repulsion shield owing to the stronger reduction resistance ability and the higher concentration of the LRPCC. It is demonstrated that there is an interaction among Li dendrites, dead Li and the SEI film. It is shown that the electrolyte containing the complex ion can effectively enhance the coulombic efficiency of Li deposition as well.

The heat generation rate of nickel-metal hydride battery during charging/discharging

The heat generation rate of nickel-metal hydride battery is investigated during charging/discharging in this study. The heat capacity of 8xa0Ah cylindrical Ni-MH battery is measured using a large-scale calorimeter. An accelerating rate calorimeter is employed to provide an adiabatic environment for the battery. The generation rates of reaction heat, polarization heat, and combination heat are calculated through curve fitting. Results show that there exits a linear relationship between each generation rate of the three heat items and the charging/discharging currents. It is suggested that the ohm internal resistance of the battery needs to be as low as possible for reducing the ohm heat. In addition, it is better to avoid overcharging in the higher rate of 5 C for battery safety.

Lithium–air and lithium–copper batteries based on a polymer stabilized interface between two immiscible electrolytic solutions (ITIES)

We propose and demonstrate the direct application of immiscible aqueous/organic interfaces in lithium–air and lithium–copper batteries. Therefore, the two half-reactions are separated in their respectively favourable electrolytic environments without using any other membranes. In order to prevent water and oxygen from interrupting the reaction in organic phases, we add poly(methyl methacrylate) (PMMA) to propylene carbonate (PC) and investigate its concentration effects using Pt ultramicroelectrodes (UMEs). Pt UMEs provide us the sensitive measure of water contamination as well as the diffusion property of oxygen in the polymer electrolytes. By studying the discharge profiles under various electrolytic conditions, we demonstrate that these batteries are of longer discharge time and higher specific capacity when the polymer electrolyte contains about 10 to 20% of PMMA.

A three-dimensional network structure Si/C anode for Li-ion batteries

A three-dimensional (3D) network structure Si/C anode with large pores is fabricated by using gelatin-PVA as carbon source. Silicon particles are embedded in the 3D network carbon skeleton. Gaussian calculation and FTIR test are employed to analyze the role of molecules interaction in forming the 3D network structure. The modified Si/C anode exhibits a reversible capacity of 830xa0mAxa0hxa0g−1 after 100 cycles at 400xa0mAxa0g−1, and a capacity of 810xa0mAxa0hxa0g−1 at 1.6xa0Axa0g−1 and 521xa0mAxa0hxa0g−1 at 3.2xa0Axa0g−1. The 3D network structure with large pores benefits the electrolyte penetration, and the carbon coating layer avoids the direct contact of silicon particles with the electrolyte. The carbon layer can also help buffer the volume expansion of silicon, which is good to the cycling stability. All these aspects contribute to the enhanced electrochemical performance of the Si anode.