George Ting-Kuo Fey

LiNiVO4: A 4.8 Volt Electrode Material for Lithium Cells

The authors show that the lithium atoms in the inverse spinel, LiNiVO[sub 4], can be electrochemically removed and reinserted in nonaqueous electrochemical cells at about 4.8 V vs. metallic Li. Using in situ x-ray diffraction methods, the authors prove that this is an intercalation reaction. To their knowledge, this is the Li intercalation reaction with the highest voltage known. The isostructural compound LiCoVO[sub 4] also shows reversible lithium intercalation, but only near 4.2 V vs. Li.

Kinetic Characterization of the Electrochemical Intercalation of Lithium Ions into Graphite Electrodes

Lithium intercalated graphites have taken the place of metallic lithium as anodes for secondary lithium batteries. Controlling the anode-electrolyte interface has been a major technical challenge in the development of lithium-ion battery technologies. The interfacial characteristics can be greatly affected by the kinetics of intercalation. However, the kinetics of the electrochemical intercalation of lithium into graphites has not been well analyzed yet. Very few kinetic and interfacial parameters have been reported. In this work, the electrochemical impedance spectroscopy, constant charge step, and galvanostatic pulse polarization techniques were applied to study the kinetics of the intercalation and deintercalation processes of graphite electrodes in a few important lithium battery electrolyte solutions. Based on the proposed equivalent circuit model, we determined the kinetic and interfacial parameters of the intercalation and deintercalation processes. The measured intercalation charge-transfer resistance, exchange current densities, and intercalation capacitance range between 11 and 28 Ω cm 2 , 1.0 and 2.3 mA/cm 2 , and 1.0 and 2.0 μF/cm 2 , respectively, depending on the electrolyte solution compositions. The dependence of these kinetic and interfacial parameters on solvent composition, electrolyte concentration, storage time, and intercalated state is discussed. In addition, the transfer coefficients have been determined. The results suggest that the intercalation/deintercalation process is electrochemically reversible.

New inverse spinel cathode materials for rechargeable lithium batteries

Abstract The synthesis, characterization, and electrochemical properties of LiNi y Co 1 − y VO 4 (0 ≤ y ≤ 1) as the new cathode materials for rechargeable lithium batteries were investigated. A series of LiNi y Co 1 − y VO 4 ( y = 0.1 − 0.9) compounds were synthesized by either a solid-state reaction of LiNi y Co 1 − y O 2 and V 2 O 5 at 800 °C for 12 h or a solution coprecipitation of LiOH · H 2 O, Ni(NO 3 ) 2 · 6H 2 O, Co(NO 3 ) 2 · 6H 2 O and NH 4 VO 3 , followed by heating the precipitate at 500 °C for 48 h. The products from both preparation methods were analyzed by scanning electron microcopy and inductively-coupled plasma-atomic emission spectroscopy. These compounds are inverse spinels based on the results from Rietveld analysis and the fact that the cubic lattice constant a is a linear function of stoichiometry y in LiNi y Co 1 − y VO 4 . Either a 1 M LiC1O 4 -EC + PC (1:1) or 1 M LiBF 4 -EC + PC + DMC (1:1:4) electrolyte can be used as the electrolyte for Li/LiNi y Co 1 − y VO 4 cells up to y = 0.7. The charge and discharge capacity of a Li/1 M LiBF 4 -EC + PC + DMC (1:1:4) /LiNi 0.5 Co 0.5 VO 4 cell were 43.8 and 34.8 mAh/g, respectively, when the cathode material was prepared by the low temperature coprecipitation method.

A new preparation method for a novel high voltage cathode material : LiNiVO4

Abstract A new preparation method for LiNiVO4 has been developed. LiNiVO4 can be readily obtained from the solid state reaction of LiNiO2 and V2O3 or V2O5 at 700 °C for 2 h in air. The quarternary Li-Ni-V-O reaction is strongly dependent on vanadium starting materials, reaction environment atmosphere, reactant stoichiometry and synthesis temperature. Individual particles of LiNiVO4 powders are well-formed crystallites shown clearly by scanning electron microscopy results to be in the shape of an octahedron. Powder X-ray diffraction studies of this crystalline material indicate that LiNiVO4 has an inverse spinel structure different from that of known cathode materials such as LT-LiCoO2 and LiMn2O4. The Li/LiNiVO4 cell can be charged and discharged at about 4.8 V versus metallic Li. To our knowledge, this is the Li intercalation reaction with the highest voltage known.

Synthesis and characterization of pyrolyzed sugar carbons under nitrogen or argon atmospheres as anode materials for lithium-ion batteries

The pyrolysis of local white sugar was studied at various heat-treatment temperatures in nitrogen and argon atmospheres. The pyrolyzed sugar carbons (PSCs) were characterized by TGA, XRD, SEM, Raman, elemental, and BET surface area analyses. The effects of atmosphere and heat-treatment temperature on the structure, morphology, and cell performance are discussed.

Preparation and characterization of LiNi0.7Co0.2Ti0.05M0.05O2 (M=Mg, Al and Zn) systems as cathode materials for lithium batteries

Abstract The effects of doping with Ti and non-transition metal ions Mg/Al/Zn in LiNi0.8Co0.2O2 on the structural and electrochemical properties were studied. Structural analysis by X-ray diffraction (XRD) revealed that except for the Mg-doped system, there was a high degree of cation mixing, which led to decreases in capacity. However, the systems showed cycling stability. The Mg-doped system had a good capacity of 150 mAh/g over 30 cycles.

The effects of the stoichiometry and synthesis temperature on the preparation of the inverse spinel LiNiVO4 and its performance as a new high voltage cathode material

Abstract The high temperature solid-state reaction between LiNiO2 and V2O3 (or V2O5) in air used to prepare LiNiVO4 has been further studied. This quarternary Li-Ni-V-O reaction is strongly dependent on reaction temperature and lithium stoichiometry in LixNi2 − xO2 and has produced a highly crystalline LiNiVO4 material whose structure has been confirmed to be an inverse spinel by Rietveld analysis with a Bragg R-factor of 1.18 in the absence of crystal orientation preference. The cell performance of LiNiVO4 prepared at various temperatures or by varying x-values in LixNi2 − xO2 has been examined in lithium coin cells and indicated that preparation at low temperatures or when x = 0.89 provided an electrode material with higher cell capacity.

Electrochemical characterization of LixNiyCo1−yO2 electrodes in a 1 M LiPF6 solution of the ethylene carbonate–diethyl carbonate

The electrochemical characteristics of Li x Ni y Co 1-y O 2 (0.5 < y < 0.9) prepared by a co-precipitation method were reported. Slow scan cyclic voltammetry (SSCV) and electrochemical impedance spectroscopy (EIS) were used to investigate the kinetic behavior of the composite electrodes. Kinetic data such as the Tafel slope and the charge-transfer resistance were determined based on the experimental results. An equivalent circuit model was proposed to simulate the impedance spectra and gave a good data fit. The present study also demonstrated that the kinetic data were composition-sensitive to varying lithium content and nickel content in the mixed oxide electrodes.

Effects of surface modification on the electrochemical performance of pyrolyzed sugar carbons as anode materials for lithium-ion batteries

Abstract The surface of pyrolyzed sugar carbons (PSCs) was treated with H2O2, HNO3, or H2SO4 reagents. Surface modification of these materials improved their electrode performance. FTIR, Raman, 13 C NMR, and X-ray diffraction (XRD) spectroscopic techniques were used to characterize structures of the treated and untreated carbons. The charge/discharge capacity, potential profile, and irreversible capacity loss have been investigated. The correlations between cell capacities, H/C ratios, and Raman vibrational modes are discussed.

High-resolution images of ultrafine LiCoO2 powders synthesized by a sol-gel process

Abstract The morphology of ultrafine LiCoO 2 powders prepared by a sol—gel process was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The purity and grain size of LiCoO 2 powders was dependent upon the pH value of the sol—gel process. The grain sizes measured by tapping mode AFM were 68, 74 and 100 nm, for samples made in acidic, neutral and basic media, respectively. Compared with grains synthesized using a solid-state high temperature method, which ranged from 5 to 20 μm, the grains synthesized using a low-temperature sol—gel process were at least 70 times smaller. Only products with small grains made in acidic media displayed a pure LiCoO 2 XRD pattern, implying that growth kinetics were favored in non-acidic media.