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 gen eral Li-ion battery context. The influence of these various components, alo ne 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 cap acity of 70%. The effect of adding CB to graphite electrodes was quantified in terms of first-cycle irreversible capacity and reversible capacity. Cyc lic voltammetry measurements on CB electrodes were made in the same voltage region using different binders and electrolyte salts. A clear difference c ould be discerned between using EPDM or PVdF binder; extra reduction reacti ons were observed for the PVdF binder at 0.35 V. The thermal behaviour of t hese 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 s tarting 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 th e cathodic region (3.0-5.5 V) showed oxidation reactions between non-fluori nated binders, CB and LiPF6. These reactions could be avoided by changing t o LiBF4. The electrochemical response on using fluorinated and non-fluorina ted binders in this voltage region showed clear differences. (C) 2001 Elsev ier Science B.V. All rights reserved.