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31.
In the process of Li+ intercalation-deintercalation, electron removal is accompanied simultaneously. Oxygen was found to compensate electron removal both in theoretical calculations and practical experiments. Chlorine addition to LiNi0.7Co0.3O2 was expected to exchange electrons in that Cl− was easier to lose electrons than O2−. LiNi0.7Co0.3O2−xClx was identified as a pure hexagonal lattice of α-NaFeO2 type by X-ray diffraction. X-ray photoelectron spectroscopy was used to analyze the influence of chlorine substitution on the oxidation state of transition-metal ions. Charge-discharge experiments and cyclic voltammetry confirmed that chlorine addition was an effective way to improve reversible capacity and structural stability in cycles. 相似文献
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This work provides kinetic and transport parameters of Li-ion during its extraction/insertion into thin film LiNi0.5Mn1.5O4 free of binder and conductive additive. Thin films of LiNi0.5Mn1.5O4 (0.2 μm thick) were prepared on electronically conductive gold substrate utilizing the electrostatic spray deposition technique. High purity LiNi0.5Mn1.5O4 thin film electrodes were observed with cyclic voltammetry, to exhibit very sharp peaks, high reversibility, and absence of the 4 V signal related to the Mn3+/Mn4+ redox couple. The electrode subjected to 100 CV cycles of charge/discharge delivered a capacity of 155 mAh g−1 on the first cycle and sustained a good cycling behavior while retaining 91% of the initial capacity after 50 cycles. Kinetics and mass-transport of Li-ion extraction at LiNi0.5Mn1.5O4 thin film electrode were investigated by means of electrochemical impedance spectroscopy. The apparent chemical diffusion coefficient (Dapp) value determined from EIS measurements changed depending on the electrode potential in the range of 10−10-10−12 cm2 s−1. The Dapp profile shows two minimums at the potential values close to the peak potentials of the corresponding cyclic voltammogram. 相似文献
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35.
Spherical lithium manganese oxide spinel was synthesized by an ultrasonic spray pyrolysis method, and has been characterized using X-ray diffraction, scanning electron microscopy, transimission electron microscopy and electrochemical cycling at 3 V regions. The LiMn2O4 powders were composed of about 10 nm-sized primary particles. The delivered discharge capacity of the synthesized nano-material was 125 mAh g−1 between 2.4 and 3.5 V and its retention was about 96% upon 50 cycling. From the high resolution transmission electron microscopic study, it was found that structural transition of the parent material did not occur even after the 50th electrochemical cycling on the 3 V region. It seems that the reversible structural change is possible for nanocrystalline LiMn2O4 as observed by the X-ray diffraction and transition electron microscopic observations. 相似文献
36.
37.
A polymer electrolyte based on microporous poly(vinylidene fluoride-co-hexafluoropropane) (PVdF-HFP) film was studied for use in lithium ion batteries. The microporous PVdF-HFP (Kynar 2801) matrix was prepared from a cast of homogeneous mixture of PVdF-HFP and solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). After evaporation of DMC and EMC, a sold film of the PVdF-HFP and the EC mixture was obtained. EC-rich phase started its formation in the PVdF-HFP/EC film at EC content of about 60 wt.% based on the total weight of PVdF-HFP and EC. The formation of the new phase resulted in the abrupt increase of the porosity of the PVdF-HFP matrix from 32 to 62%. The ionic conductivity of the film soaked in 1 M LiPF6-EC/DMC=1/1 was significantly increased from order of 10−4 S/cm to order of 10−3 S/cm at the EC content of 60 wt.%. Thermal and spectroscopic investigations showed that most of the EC interact with PVdF-HFP with the EC content being below 60 wt.%. MCMB/polymer electrolyte/LiCoO2 cells employing the microporous PVdF-HFP polymer film showed stable charging/discharging characteristics at 1C rate and good rate capability. 相似文献
38.
Spinel compound LiNi0.5Mn1.5O4 was synthesized by a chemical wet method. Mn(NO3)2, Ni(NO3)2·6H2O, NH4HCO3 and LiOH·H2O were used as the starting materials. At first, Mn(NO3)2 and Ni(NO3)2·6H2O reacted with NH4HCO3 to produce a precursor, then the precursor reacted with LiOH·H2O to synthesize product LiNi0.5Mn1.5O4. The product showed a single spinel phase under appropriate calcination conditions, and exhibited a high voltage plateau at about 4.6-4.8 V in the charge/discharge process. The LiNi0.5Mn1.5O4 had a discharge specific capacity of 118 mAh/g at about 4.6 V and 126 mAh/g in total in the first cycle at a discharge current density of 2 mA/cm2. After 50 cycles, the total discharge capacity was above 118 mAh/g. 相似文献
39.
The first use of nickel foam (NF) as electrocatalytic negative electrode in a polysulfide/bromine battery (PSB) is described. The performance of a PSB employing NF and polyacrylonitrile (PAN)-based carbon felt (CF) as negative and positive electrode materials, respectively, was evaluated by constant current charge-discharge tests in a single cell. Charge/discharge curves of the cell, positive and negative electrodes show that the rapid fall in cell voltage is due to the drop of positive potential caused by depletion of Br2 dissolved in the catholyte at the end of discharge. Cell voltage efficiency was limited by the relatively high internal ohmic resistance drop (iR drop). Polarization curves indicated that both NF and CF have excellent catalytic activity for the positive and negative redox reactions of PSB. The average energy efficiency of the single cell designed in this work could be as high as 77.2% at 40 mA cm−2 during 48 charge-discharge cycles. 相似文献
40.