Multimodal Characterization of the Morphology and Functional Interfaces in Composite Electrodes for Li–S Batteries by Li Ion and Electron Beams

We report the characterization of multiscale 3D structural architectures of novel poly­[sulfur-<i>random</i>-(1,3-diisopropenylbenzene)] copolymer-based cathodes for high-energy-density Li–S batteries capable of realizing discharge capacities >1000 mAh/g and long cycling lifetimes >500 cycles. Hierarchical morphologies and interfacial structures have been investigated by a combination of focused Li ion beam (LiFIB) and analytical electron microscopy in relation to the electrochemical performance and physicomechanical stability of the cathodes. Charge-free surface topography and composition-sensitive imaging of the electrodes was performed using recently introduced low-energy scanning LiFIB with Li⁺ probe sizes of a few tens of nanometers at 5 keV energy and 1 pA probe current. Furthermore, we demonstrate that LiFIB has the ability to inject a certain number of Li cations into the material with nanoscale precision, potentially enabling control of the state of discharge in the selected area. We show that chemical modification of the cathodes by replacing the elemental sulfur with organosulfur copolymers significantly improves its structural integrity and compositional homogeneity down to the sub-5-nm length scale, resulting in the creation of (a) robust functional interfaces and percolated conductive pathways involving graphitic-like outer shells of aggregated nanocarbons and (b) extended micro- and mesoscale porosities required for effective ion transport

Improving the Charge Conductance of Elemental Sulfur via Tandem Inverse Vulcanization and Electropolymerization

The synthesis of polymeric materials using elemental sulfur (S₈) as the chemical feedstock has recently been developed using a process termed inverse vulcanization. The preparation of chemically stable sulfur copolymers was previously prepared by the inverse vulcanization of S₈ and 1,3-diisopropenylbenzene (DIB); however, the development of synthetic methods to introduce new chemical functionality into this novel class of polymers remains an important challenge. In this report the introduction of polythiophene segments into poly­(sulfur-<i>random</i>-1,3-diisopropenylbenzene) is achieved by the inverse vulcanization of S₈ with a styrenic functional 3,4-propylenedioxythiophene (ProDOT-Sty) and DIB, followed by electropolymerization of ProDOT side chains. This methodology demonstrates for the first time a facile approach to introduce new functionality into sulfur and high sulfur content polymers, while specifically enhancing the charge conductivity of these intrinsically highly resistive materials

Colloidal Polymers from Dipolar Assembly of Cobalt-Tipped CdSe@CdS Nanorods

The synthesis of a modular colloidal polymer system based on the dipolar assembly of CdSe@CdS nanorods functionalized with a single cobalt nanoparticle “tip” (CoNP-tip) is reported. These heterostructured nanorods spontaneously self-assembled <i>via</i> magnetic dipolar associations of the cobalt domains. In these assemblies, CdSe@CdS nanorods were carried as densely grafted side chain groups along the dipolar NP chain to form bottlebrush-type colloidal polymers. Nanorod side chains strongly affected the conformation of individual colloidal polymer bottlebrush chains and the morphology of thin films. Dipolar CoNP-tipped nanorods were then used as “colloidal monomers” to form mesoscopic assemblies reminiscent of traditional copolymers possessing segmented and statistical compositions. Investigation of the phase behavior of colloidal polymer blends revealed the formation of mesoscopic phase separated morphologies from segmented colloidal copolymers. These studies demonstrated the ability to control colloidal polymer composition and morphology in a manner observed for classical polymer systems by synthetic control of heterostructured nanorod structure and harnessing interparticle dipolar associations

Inverse Vulcanization of Elemental Sulfur to Prepare Polymeric Electrode Materials for Li–S Batteries

Sulfur-rich copolymers based on poly­(sulfur-<i>random-</i>1,3-diisopropenylbenzene) (poly­(S-<i>r</i>-DIB)) were synthesized via inverse vulcanization to create cathode materials for lithium–sulfur battery applications. These materials exhibit enhanced capacity retention (1005 mAh/g at 100 cycles) and battery lifetimes over 500 cycles at a C/10 rate. These poly­(S-<i>r</i>-DIB) copolymers represent a new class of polymeric electrode materials that exhibit one of the highest charge capacities reported, particularly after extended charge–discharge cycling in Li–S batteries