Synthesis and characterization of montmorillonite/polyaniline composites and its usage to modify a commercial separator

Abstract

Composites of montmorillonite (MMT) and polyaniline (PANI) were synthetized through a facile and inexpensive method. Two samples with different MMT:PANI ratios were studied and deeply characterized by XRD, TG, zeta potential, FTIR and XPS measurements. On one hand, the sample with ratio MMT:PANI = 87:13 was an intercalated composite, were polyaniline resides between the inorganic layers of the clay at a regular distance. On the other hand, the sample with ratio MMT:PANI = 12:88 was an exfoliated composite, where the inorganic sheets are immersed in an amorphous polymeric matrix. FTIR and XRD results indicated that in both samples, the emeraldine form of polyaniline was obtained. The composites were used to modify -by dr. blade technique- a commercial separator for lithium-ion batteries (LIBs) with the aim of increasing its wettability, ionic conductivity and electrochemical performance. The three-dimensional and multilayered network structure of the MMT/PANI composites led to an enhancement of the electrolyte uptake capacity (from 32% in bare separator to 137% and 168% for MMT/PANI_87/13 and MMT/PANI_12/88 modified separators, respectively, after 3 h). The presence of the coating membrane also led to an increase of the ionic conductivity by one order of magnitude in the modified separators respect to the unmodified one. These coated and non-coated separators were used to assemble full cells with LiNi1.5Mn0.5O4 as cathode active material. The capacity fade after 200 cycles was 20% lower in the cell with MMT/PANI_12/88 membrane in comparison with the bare separator. The enhancement of the electrochemical performance of the cells with the coated separator suggests that is a promising strategy to be used in LIBs.