LiMn2O4-based composites processed by a chemical-route: Microstructural, electrical, electrochemical, and mechanical characterization

Composites of positive electrodes for rechargeable lithium batteries have been prepared from LiMn2O4 as electrochemically active material, carbon black (CB) as good electronic conductor, and polyvinylidenefluoride (PVDF) as binder. The composites having different contents in LiMn2O4 and CB, and nearly the same content in PVDF have been processed by a route that is currently used. The microstructure of the composites, as followed by scanning electron microscopy (SEM), is heterogeneous showing extended regions of PVDF–CB, and clusters of LiMn2O4. The electrical conductivity shows a sharp increase at the CB content of 3 vol.% (2 wt.%) in accordance with a percolation process. The capacity shows also a sharp increase at that content. A maximum in capacity at ca. 10 wt.% of CB is observed when the overall weight of the composite is taken into account. Both features, sharp increase in capacity and maximum of capacity, have been found in discharge experiments made at different currents. The composites show an elastic behavior up to a stress of ca. 6 MPa. Above this, the composites breaks down through a crack that propagates slowly according to a ductile behavior. The microstructure as well as the electrical, electrochemical, and mechanical properties of the composites are compared with those reported on composites having the same three components but processed by a different route.