New Amorphous Oxy-Sulfide Solid Electrolyte Material: Anion Exchange, Electrochemical Properties, and Lithium Dendrite Suppression via In Situ Interfacial Modification.

Glassy sulfide materials have been considered as promising candidates for solid-state electrolytes (SSEs) in lithium and sodium metal (LM and SM) batteries. While much of the current research on lithium glassy SSEs (GSSEs) has focused on the pure sulfide binary Li2S + P2S5 system, we have expanded these efforts by examining mixed-glass-former (MGF) compositions which have mixtures of glass formers, such as P and Si, which allow melt-quenching synthesis under ambient pressure and therefore the use of grain-boundary-free SSEs. We have doped these MGF compositions with oxygen to improve the chemical, electrochemical, and thermal properties of these glasses. In this work, we report on the short-range order (SRO), namely atomic-level, structures of Li2S + SiS2 + P2O5 MGF mixed oxy-sulfide glasses and, for the first time, study the critical current density (CCD) of these Si-doped oxy-sulfide GSSEs in LM symmetric cells. The samples were synthesized by planetary ball milling (PBM), and it was observed that a certain minimum milling time was necessary to achieve a final SRO structure. To address the short-circuiting lithium dendrite (LD) problems that were observed in these GSSEs, we demonstrate a simple and novel strategy for these Si-doped oxy-sulfide GSSEs to engineer the LM-GSSE interface by forming an in situ interlayer via heat treatment. Stable cycling to ∼1200 h at a capacity of 2 mAh·cm-2 per discharge/charge cycle under a current density of 1 mA·cm-2 is achieved. These results indicate that these MGF oxy-sulfide GSSEs combined with an optimized interfacial modification may find use in LM, and by extrapolation, SM, batteries.

Lithium Thiosilicophosphate Glassy Solid Electrolytes Synthesized by High-Energy Ball-Milling and Melt-Quenching: Improved Suppression of Lithium Dendrite Growth by Si Doping.

Due to the volatility of P2S5, the ambient pressure synthesis of Li2S + P2S5 (LPS) has been limited to planetary ball-milling (PBM). To utilize PBM of LPS to generate a solid electrolyte (SE), the as-synthesized powder sample must be pressed into pellets, and as such the presence of as-pressed grain boundaries in the SE cannot be avoided. To eliminate the grain boundaries, LPS doped with SiS2 has been studied because SiS2 lowers the vapor pressure of the melt and promotes strong glass formation, which in combination allows for greater ease in synthesis. In this work, we have examined the structures and electrochemical properties of lithium thiosilicophosphate 0.6Li2S + 0.4[xSiS2 + 1.5(1 - x)PS5/2], 0 ≤ x ≤ 1, glassy solid electrolytes (GSEs) prepared by both PBM and melt-quenching (MQ). It is shown that the critical current density improved after incorporating SiS2, reaching 1.5 mA/cm2 for the x = 0.8 composition. However, the interfacial reaction of MQ GSE with lithium metal introduced microcracks, which shows that further research is needed to explore and develop more stable GSE compositions. These fundamental results can help to understand the interface reaction and formation and as such can provide a guide to design improved homogeneous GSEs with SiS2 as a glass former, which have no grain boundaries and thereby may help suppress lithium dendrite formation.

Long hydrophilic-and-cationic polymers: a different pathway toward preferential activity against bacterial over mammalian membranes.

We show that simply converting the hydrophobic moiety of an antimicrobial peptide (AMP) or synthetic mimic of AMPs (SMAMP) into a hydrophilic one could be a different pathway toward membrane-active antimicrobials preferentially acting against bacteria over host cells. Our biostatistical analysis on natural AMPs indicated that shorter AMPs tend to be more hydrophobic, and the hydrophilic-and-cationic mutants of a long AMP experimentally demonstrated certain membrane activity against bacteria. To isolate the effects of antimicrobials' hydrophobicity and systematically examine whether hydrophilic-and-cationic mutants could inherit the membrane activity of their parent AMPs/SMAMPs, we constructed a minimal prototypical system based on methacrylate-based polymer SMAMPs and compared the antibacterial membrane activity and hemolytic toxicity of analogues with and without the hydrophobic moiety. Antibacterial assays showed that the hydrophobic moiety of polymer SMAMPs consistently promoted the antibacterial activity but diminished in effectiveness for long polymers, and the resultant long hydrophilic-and-cationic polymers were also membrane active against bacteria. What distinguished these long mutants from their parent SMAMPs were their drastically reduced hemolytic toxicities and, as a result, strikingly enhanced selectivity. Similar toxicity reduction was observed with the hydrophilic-and-cationic mutants of long AMPs. Taken together, our results suggest that long hydrophilic-and-cationic polymers could offer preferential membrane activity against bacteria over host cells, which may have implications in future antimicrobial development.