Transport kinetics, thermodynamics and thermal stability of the electrode materials for lithium ion batteries.

摘要

A structural model to calculate the electrochemical interface area for a composite graphite electrode is described. A new equation using the model predicted area to calculate chemical diffusion coefficient ( DLi+ ) eliminates the effects from fabrication such as active mass ( mB) and geometric area (SGeo). The chemical diffusion coefficient values calculated for graphite electrodes of different thicknesses and porosities using the new equation are almost same as expected. The values of DLi+ in the graphite vary between 10-11.9 and 10 -9.9 cm2/s over the course of the lithium deintercalation in the graphite samples.; The electrochemical performances and power abilities of several natural graphite and artificial graphite samples were investigated as anode materials in lithium-ion batteries. All artificial graphite samples showed well-ordered graphitized structures and good reversible capacities. Irreversible capacity is related with crystallite size, particle size, and treatment of sample. The capacity decreases with an increase of the current in the intercalation process; while it is independent of the current in the deintercalation process. The reason is the chemical diffusion coefficient in deintercalation process is one or two orders of magnitude greater than that in the intercalation process.; Electrochemical performances of the natural graphite (Mag-10)/Li half-cell, LiNi0.8Co0.15Al0.05O2/Li half-cell, and LiNi0.8Co0.15Al0.05O2/Mag-10 full-cell are discussed in terms of reversible and irreversible capacity. Heat rate profiles of these cells cycled at various current levels are studied in terms of reversible and irreversible heat generation. The agreement between experiment data and calculated results is quite good at low and moderate current levels (≤C/5). The quantitative heat contributions of the cathode and anode to the overall cell heat generation are also determined.; Differential scanning calorimeter (DSC) is used in this study to evaluate the thermal runaway potential of high power lithium ion cells. The activation energies and enthalpies are calculated from the DSC traces for the specific exothermic reactions occurring at various temperatures for the lithiated anode and the delithiated cathode materials in the presence of the organic carbonate electrolyte. These findings provide insight into which components of the lithium-ion cell are most responsible for the thermal runaway condition.