Sulfurized polyacrylonitrile (SPAN) represents a class of sulfur-bonded polymers, which have shown thousands of stable cycles as a cathode in lithium−sulfur batteries. However, the exact molecular structure and its electrochemical reaction mechanism remain unclear. Most significantly, SPAN shows an over 25% 1st cycle irreversible capacity loss before exhibiting perfect reversibility for subsequent cycles. Here, with a SPAN thinfilm platform and an array of analytical tools, we show that the SPAN capacity loss is associated with intramolecular dehydrogenation along with the loss of sulfur. This results in an increase in the aromaticity of the structure, which is corroborated by a >100× increase in electronic conductivity. We also discovered that the conductive carbon additive in the cathode is instrumental in driving the reaction to completion. Based on the proposed mechanism, we have developed a synthesis procedure to eliminate more than 50% of the irreversible capacity loss. Our insights into the reaction mechanism provide a blueprint for the design of highperformance sulfurized polymer cathode materials.

Solid-state lithium batteries are uniquely suited for operation at elevated to even high temperatures (>100 °C). Under these conditions, however, oxide cathode materials are unstable with high-conductivity sulfide-based electrolytes while elemental sulfur suffers from poor utilization due to its insulating nature. Here, we developed an ionic liquid mediated synthesis procedure for polythiocynogen (poly-SCN) and applied it as a sulfur-rich cathode. The material, with uniform, submicrometer particle size and a > 55 wt % sulfur loading, exhibits good thermal stability of over 200 °C. A specific capacity of over 800 mAh g–1 at 100 °C is realized when poly-SCN is used as a cathode in an all-solid-state battery (ASSB). Mechanistic studies show that during discharge, both C–S and S–S bonds in poly-SCN are cleaved along with the formation of Li2S. During charge, the re-formation of poly-SCN structure is observed. The scalable synthesis procedure, high thermal stability, high sulfur loading, and high capacity make poly-SCN a promising candidate for high temperature solid state batteries.

The pore architecture of nanoporous copper (NP-Cu) plays a vital role in its technological applications. The synthesis of NP-Cu by the conversion reaction has been reported, where an ionic Cu precursor (salt or oxide) is chemically reduced with n-butyllithium to form a Cu metal nanocomposite, from which the Li-containing product is removed to form NP-Cu. Anions in the Cu compound precursors significantly affect the size of Cu in the nanocomposite due to the effect of lithium salt on Cu diffusion. Thermal annealing of the nanocomposites reveals that the activation energy for diffusion correlates with the melting point of the lithium salt, which is used as a proxy for their tendencies of forming defects, indicating that Cu diffusion takes place through the bulk phase of the salt rather than the Cu/salt interfaces. This experimentally observed behavior is consistent with the results from density functional theory calculations. Further, doping the lithium salt with Mg 2+ increases the defect concentration and facilitates enhanced Cu diffusion. The choice of anion in the Cu salt precursor thus provides an effective tool to enable control of the nanoscale size of Cu and the resultant NP porosity.

We herein report the development of the sputtering process for the fabrication of low-temperature thin film solid oxide fuel cells (TF-SOFCs) supported by anodized aluminum oxide (AAO). The process development has been conducted for each component, anode, electrolyte, electrolyte/cathode interlayer, and cathode to scale up the cell from 1cm x 1cm to 15 cm x 15 cm. In order to fabricate a uniform thin film regardless of the size of AAO, sputtering conditions such as power, pressure, angle, target-to-substrate distance (TSD), and time have been developed. The recipe for the anode and cathode has aimed at a porous structure with nano-grains for high reactivity. In contrast, the recipe for the electrolyte has been optimized for thickness uniformity and high density. With these sputtering recipes TF-SOFCs with the required microstructure and thickness uniformity have been successfully fabricated on 15 cm x 15 cm AAO substrates.