Analytical Multimode Scanning and Transmission Electron Imaging and Tomography of Multiscale Structural Architectures of Sulfur Copolymer Based Composite Cathodes for Next Generation High Energy Density Li S Batteries
Abstract Poly[sulfur random (1,3 diisopropenylbenzene) copolymers synthesized via inverse vulcanization represent an emerging class of electrochemically active polymers recently used in cathodes for Li S batteries, capable of realizing enhanced capacity retention (1,005 mAh/g at 100 cycles) and lifetimes of over 500 cycles. The composite cathodes are organized in complex hierarchical three dimensional (3D) architectures, which contain several components and are challenging to understand and characterize using any single technique. Here, multimode analytical scanning and transmission electron microscopies and energy dispersive X ray/electron energy loss spectroscopies coupled with multivariate statistical analysis and tomography were applied to explore origins of the cathode enhanced capacity retention. The surface topography, morphology, bonding, and compositions of the cathodes created by combining sulfur copolymers with varying 1,3 diisopropenylbenzene content and conductive carbons have been investigated at multiple scales in relation to the electrochemical performance and physico mechanical stability. We demonstrate that replacing the elemental sulfur with organosulfur copolymers improves the compositional homogeneity and compatibility between carbons and sulfur containing domains down to sub 5 nm length scales resulting in (a) intimate wetting of nanocarbons by the copolymers at interfaces; (b) the creation of 3D percolation networks of conductive pathways involving graphitic like outer shells of aggregated carbons; (c) concomitant improvements in the stability with preserved meso and nanoscale porosities required for efficient charge transport.
Microscopy and Microanalysis