The effect of the binder morphology on the cycling stability of Li-alloy composite electrodes

It is demonstrated that the design of the composite electrode, or more prec isely the morphology and distribution of the binder poly(vinylidine fluorid e) (PVdF) within the composite electrode, has a significant impact on the c ycling performance of Li storage alloy (Sn/SnSb) electrodes. Different bind er morphologies and distributions have been obtained by using different sol vents for the slurry preparation, such as 1-methyl-2-pyrrolidinone (NMP), i n which PVdF is dissolved, yielding electrodes with a homogeneously and fin ely distributed binder, or decane, in which PVdF is only dispersed, yieldin g electrodes in which the original particle morphology of the binder powder is preserved. In constant current cycling tests carried out in an excess o f electrolyte, the electrodes with the 'dispersed' binder show far better c ycling capacities and stabilities than those with the 'dissolved' binder. T his is explained by the different binding strengths, swelling behaviour in the electrolyte, electrode porosities, and possible 'buffer' effects of the compact and the finely distributed binders. (C) 2001 Published by Elsevier Science B.V.