Influence of carbon black and binder on Li-ion batteries

The electrochemical response of different components such as carbon black (CB), binder, current collector and lithium salt have been examined in a general Li-ion battery context. The influence of these various components, alone and in different combinations, on composite graphite anodes and LiMn2O4 cathodes was addressed. CB electrodes were found to cycle with a reversible capacity of 180 mAh/g between 0.01 and 1.5 V, but with an irreversible capacity of 70%. The effect of adding CB to graphite electrodes was quantified in terms of first-cycle irreversible capacity and reversible capacity. Cyclic voltammetry measurements on CB electrodes were made in the same voltage region using different binders and electrolyte salts. A clear difference could be discerned between using EPDM or PVdF binder; extra reduction reactions were observed for the PVdF binder at 0.35 V. The thermal behaviour of these binders in CB electrodes was also examined in the temperature range 30-300 degreesC. The role of the anion in terms of thermal stability was also quantified from DSC measurements on both CB and graphite electrodes; the starting temperature for exothermal reactions involving SEI-layer reactions is clearly lower (similar to 60 degreesC) for LiBF4 than LiPF6 (similar to 110 degreesC) for both CB and graphite electrodes. Cyclic voltammetry in the cathodic region (3.0-5.5 V) showed oxidation reactions between non-fluorinated binders, CB and LiPF6. These reactions could be avoided by changing to LiBF4. The electrochemical response on using fluorinated and non-fluorinated binders in this voltage region showed clear differences. (C) 2001 Elsevier Science B.V. All rights reserved.