Wenquan Lu

Characterization of a commercial size cylindrical Li-ion cell with a reference electrode

A method of monitoring the performance of the cell components was developed to study the cycling behavior of the commercial size rechargeable lithium-ion cells. A lithium reference electrode was placed into the center of a full commercial cylindrical cell in an effort to monitor the electrochemical behavior of the cell and its component electrodes during cycling. This technique allowed the resolution of measured voltage into component cathode and anode voltages and hence the resolution of the total area-specific impedance (ASI) into cathode and anode ASI. The cathode was found to be the electrode limiting the power and capacity of the Li-ion cell. Further investigations also revealed that the increase in the cathode ASI is a main cause of power and energy degradation of the cell during cycling.

Thermal investigations of transitional metal oxide cathodes in Li-ion cells

Abstract Accelerating rate and differential scanning calorimeters were used to investigate the thermal behavior of LiCoO2 and LiNi0.8Co0.2O2 cathodes in fully charged Li-ion cells. The heat flow for LiNi0.8Co0.2O2 was observed to be three times higher than that for LiCoO2. The net heat transferred out of the cell fabricated with a LiNi0.8Co0.2O2 cathode was found to be 51% higher than the net heat transferred out of the cell fabricated with LiCoO2. Although LiNi0.8Co0.2O2 was found to be thermally less stable than LiCoO2, the electrochemical performance of the LiNi0.8Co0.2O2 cathode under high power discharge was found superior to LiCoO2.

Electrochemical and thermal behavior of copper coated type MAG-20 natural graphite

Abstract Natural graphite powders, type MAG-20, were modified by electroless deposition of copper onto the graphite surface. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the modified graphite showed that almost all the copper covered the edge plane of graphite particles and the copper content increased from 6 to 17 at.% depending upon the plating time. Thermal gravimetric analysis (TGA) confirmed the copper composition obtained using EDS. TGA carried out under oxygen atmosphere showed that the combustion temperature decreased by 200xa0°C for a copper content from 0 to 16 at.%. Cycling the modified graphite at a C/10 rate showed that the initial large irreversible capacity typically present in untreated natural graphite was significantly reduced when the modified graphite contained 6–17 at.% copper coatings. A differential scanning calorimetry (DSC) comparison between fully lithiated copper coated MAG-20 with fully lithiated MCMB showed that the major exothermic peak for the MAG-20 modified graphite is lower in magnitude and is shifted to higher temperatures. However, both MAG-20 and MCMB types of lithiated graphite gave the same amount of total heat generation up to 350xa0°C.

Electrochemical and thermal behaviour of LiNi0.8Co0.2O2 cathode in sealed 18650 Li-ion cells

The electrochemical performance of LiNi0.8Co0.2O2 cathodes in Li ion cells was investigated under static and dynamic load conditions, which prevail in ‘electric and hybrid vehicles’ using ‘constant current constant voltage and ‘hybrid pulse power characteristic’ procedures.The thermal properties of this cathode were investigated using the differential scanning calorimetric and accelerated rate calorimetric techniques. The cell fabricated with a LiNi0.8Co0.2O2 cathode showed excellent power performance. The specific energy produced by the 18650 cell was 90 Wh kg−1 at 100 W kg−1 power level.

An electrochemical double layer capacitor based on nanocrystalline lead ruthenate pyrochlore

Lead ruthenate pyrochlore Pb2Ru2O7−x was synthesized as a new electrode material for aqueous-electrolyte electrochemical capacitors. The material was characterized using X-ray diffraction, thermogravimetric analysis, BET area analysis, and cyclic voltammetry. Redox processes significantly improve the capacitance of the materials compared to the conventional double layer capacitors. For materials heated at low temperatures, the redox processes merge smoothly resulting in an excellent capacitive behavior. The capacitors built with the lead-ruthenate electrodes show an excellent electrochemical performance under constant-power discharge.

Electrochemical performance of carbon materials derived from paper mill sludge

Abstract A pure, high surface area and cost-effective carbon-based material with possible application in electrochemical processes was synthesized from industrial sludge. Surface characterization included N2-adsorption isotherm data and mathematical models such as the DR equation, and BJH methods. The extent of the purity was assessed from thermogravimetric analysis (TGA). The electrochemical properties, i.e. the potential use as electrode in Li ion batteries, were evaluated using conventional electrochemical testing such as charge/discharge cycling and impedance spectroscopy. The results of the data analysis were promising and indicated that paper mill sludge can be successfully used to produce a pure carbon for potential use in electrochemical applications.