Papers by Keyword: Rate Capability

Abstract: A novel membrane electrode was fabricated by coating conductive slurry (K/Graphene composites as its important component) on copper foil. The membrane electrode, as anode of lithium ion battery, exhibited excellent columbic efficiency and specific capacity of 831 mAh g^-1 after 1000 cycles. The K/Graphene composites presented a multi-layer nanostructure. It provided not only more intercalation space and intercalation sites for Li⁺ during the Li⁺ intercalation/extraction, but also alleviated the agglomeration of dispersed nanocrystals, as well as decreased the electrochemical impedance. The results suggest that the membrane electrode holds great potential as an anode material for LIBs.

Abstract: Thin films of Na_2/3Ni_1/4Mn_3/4O₂ were prepared on stainless steel substrates by pulsed laser deposition technique. X-ray diffraction and Field-emission Scanning Electron Microscope results show that the thin film deposited at 750°C is highly preferred orientation with homogeneous nanoscale particles. Galvanostatic charge/discharge measurement results reveal that the reversible capacity retention is 91% after 30 cycles with a high initial discharge capacity of 175.3 mAhg^-1 at a current density of 13 mAg^-1. It also exhibits excellent rate capability, as the current density increases to 260 mAg^-1, about 80% of its initial capacity can be retained. After the high rate measurement, the NNMO electrode can deliver a discharge capacity of 110.4 mAhg^-1 when the current density was reduced back to 13 mAg^-1.

Abstract: LiFePO₄/C-Ge electrodes were prepared with vacuum thermal evaporation deposition by depositing Ge films on as-prepared LiFePO₄/C electrodes. The effect of Ge film on the electrochemical performances of LiFePO₄/C cells was investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. It was found that Ge-film-surface modified LiFePO₄/C showed excellent electrochemical performances compared to that of the pristine one in terms of cyclability and rate capability. At 60°C, LiFePO₄/C-Ge film exhibited outstanding cyclability with less than 5% capacity fade after 50 cycles while the pristine one suffers 15%. Analysis from the electrochemical measurements showed that the presence of Ge film on the LiFePO₄/C electrode would protect active material from HF generated by the decomposition of LiPF₆ in the electrolyte and stabilize the surface structure of active material during the charge and discharge cycle. Electrochemical impedance spectroscopy (EIS) results indicated that Ge film mainly reduced the charge transfer resistance R_ct of LiFePO₄/C electrode, resulting from the suppression of the solid electrolyte interfacial (SEI) film.

Abstract: The electrochemical properties of hard carbon (HC) have been investigated for use as negative electrode for lithium ion capacitors. The HC electrode was characterized by scanning electron microscope (SEM) method. The HC negative electrode was galvanostatically prelithiated at 0.1C for three cycles between 0.05-2 V. The LIC with activated carbon and HC electrodes was characterized by cyclic voltammetric analysis at the scan rate of 0.1 mV s^-1 with different voltage ranges. The rate capability of the LIC was tested up to 100C and the retention is 54 %. The cycle performance is retained up to 86% at 50C and 80% at 100C even after 10,000 cycles. The results indicate that hard carbon is suitable as negative electrode materials for high power energy applications.

Abstract: Lithium secondary batteries using LiNi_0.5Mn_1.5O₄ (LNMO) films as a cathode material were prepared by pulsed laser deposition on stainless steel substrates. X-ray diffraction and Field-emission Scanning Electron Microscope results show that the film deposited at 750°C exhibits good crystallinity with well-defined grains structure. Galvanostatic charge/discharge measurement results revealed that the reversible capacity maintains 116.8mAhg^-1 after 100 cycles at 0.5C. It also exhibits excellent rate capability, as the rates increase to 5 and 10 C, about 95.4% and 92.3% of its initial capacity at 0.2C can be retained. In additional, thermal stability of the Al₂O₃ coated LNMO thin film cathodes were also explored. The high temperature cyclic performance of LNMO thin film electrode was significantly enhanced by the coating.

Abstract: Carbon-coated, bismuth-doped, lithium iron phosphates, LiFe_1xBi_xPO₄ (0x0.05), have been synthesized by a solid-state reaction method. From the optimization, the carbon-coated LiFe_0.95Bi_0.05PO₄ phase showed superior performances in terms of phase purity and high discharge capacity. The structural, morphological, and electrochemical properties were studied and compared to carbon-coated, LiFePO₄. The Li/LiFe_0.95Bi_0.05PO₄ with carbon coating cell delivered an initial discharge capacity of 145 mAh/g and was 30 mAh/g higher than the Li/LiFePO₄ with carbon coating cell. Cyclic voltammetry revealed excellent reversibility of the LiFe_0.95Bi_0.05PO₄ with carbon coating material. High rate capability studies were also performed and showed a capacity retention over 93% during the cycling. It was concluded that substituted Bi ion play an important role in enhancing battery performance of the LiFePO₄ material through improving the kinetics of the lithium insertion/extraction reaction on the electrode.

Abstract: A Fe-site doped lithium phosphate LiFe0.99La0.01PO4 as cathode material for lithium ion battery was synthesized by solid-state reaction. The crystalline structure, morphology of particles and electrochemical performances of the sample were investigated by X-ray diffraction, scanning electron microscopy, charge-discharge test and cyclic voltammetry. The results show that the small LiFe0.99La0.01PO4 particles are simple pure olive-type phase structure with uniformly distribution of gain size. The LiFe0.99La0.01PO4 obtained has proper electrochemical capacity, good cycle ability and rate performances. Such an excellent electrochemical characteristic should be partially related to the enhanced electronic conductivities and probably the better mobility of Li ion in the crystal of the doped sample.

Abstract: A mixed lithium phosphate LiMn0.6Fe0.4PO4 as cathode material for lithium ion battery was synthesized by solid-state reaction. The crystalline structure, morphology of particles and electrochemical performances of the sample were investigated by X-ray diffraction, scanning electron microscopy, charge-discharge test and cyclic voltammetry. The results show that the small LiMn0.6Fe0.4PO4 particles are simple pure olive-type phase structure with uniformly distribution of gain size. The LiMn0.6Fe0.4PO4 obtained has a high electrochemical capacity, good cycle ability and excellent stability under high temperature. However, the capacity loss corresponding to 4.0V plateau at high rate, which had been proved by various electrochemical tests, is the main obstacle to its practical application.

Abstract: Li(Ni_1/3Co_1/3Mn_1/3)O₂ material with high rate capability was synthesized by a novel gel-combustion method using polyvinylpyrrolidone as a polymer chelating agent and a fuel. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to study the structure, morphology and element distribution of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ material. XRD analysis showed that all samples were α-NaFeO₂ structure and Li(Ni_1/3Co_1/3Mn_1/3)O₂ prepared at 900 °C had the highest c/a of 4.977 indicating the highest layered-ness. EDS scan demonstrated that the precursor was homogeneous. SEM images indicated all samples were well crystallized. Charge and discharge tests showed all samples had good rate capability. Among them, Li(Ni_1/3Co_1/3Mn_1/3)O₂ prepared at 900 °C had the highest capacity and the best rate capability. It delivered 162.1 mAh•g⁻¹ at 0.25 C between 2.5 and 4.3 V and the capacity retention was about 81% compared to that of 0.25C rate.

Abstract: Well-aligned TiO₂ nanotube arrays were fabricated from anodization by a subsequent heat treatment. Rate performance and electrochemical properties of TiO₂ nanotube arrays were studied intensively. The electrode exhibits excellent rate capabilities at various rates with an average coulombic efficiency reaching 95.6%. It is obvious that TiO₂ nanotube array possesses high rate capability and excellent cycling stability.