Soft composites are critical for soft and flexible materials in energy harvesting, actuators, and multifunctional devices. One emerging approach to create multifunctional composites is through the incorporation of liquid metal (LM) droplets such as eutectic gallium indium (EGaIn) in highly deformable elastomers. The microstructure of such systems is critical to their performance, however, current materials lack control of particle size at diverse volume loadings. Here, we present a fabrication approach to create liquid metalelastomer composites with independently controllable and highly tunable droplet size (100 nm ≦ D ≦ 80 μm) and volume loading (0 ≦ φ ≦ 80%). This is achieved through a combination of shear mixing and sonication of concentrated LM/elastomer emulsions to control droplet size and subsequent dilution and homogenization to tune LM volume loading. These materials are characterized utilizing dielectric spectroscopy supported by analytical modeling which shows a high relative permittivity of 60 (16x the unfilled elastomer) in a composite with φ = 80%, a low tan δ of 0.02, and a significant dependence on φ and minor dependence on droplet size. Temperature response and stability are determined using dielectric spectroscopy through temperature and frequency sweeps and with DSC. These results demonstrate a wide temperature stability of the liquid metal phase (crystallizing <-85 °C for D < 20 μm). Additionally, all composites are electrically insulating across a wide frequency (0.1 Hz-10 MHz) and temperature (-70°C to 100°C) range even up to φ = 80%. We highlight the benefit of LM microstructure control by creating all soft matter stretchable capacitive sensors with tunable sensitivity. These sensors are further integrated into a wearable sensing glove where we identify different objects during grasping motions. This work enables programmable LM composites for soft robotics and stretchable electronics where flexibility and tunable functional response are critical.

All-solid-state sodium batteries (ASSSBs) are promising candidates for grid-scale energy storage. However, there are no commercialized ASSSBs yet, in part due to the lack of a low-cost, simple-to-fabricate solid electrolyte (SE) with electrochemical stability towards Na metal. In this work, we report a family of oxysulfide glass SEs (Na3PS4−xOx, where 0 < x ≤ 0.60) that not only exhibit the highest critical current density among all Na-ion conducting sulfide-based SEs, but also enable high-performance ambient-temperature sodium-sulfur batteries. By forming bridging oxygen units, the Na3PS4−xOx SEs undergo pressure-induced sintering at room temperature, resulting in a fully homogeneous glass structure with robust mechanical properties. Furthermore, the self-passivating solid electrolyte interphase at the Na|SE interface is critical for interface stabilization and reversible Na plating and stripping. The new structural and compositional design strategies presented here provide a new paradigm in the development of safe, low-cost, energy-dense, and long-lifetime ASSSBs.

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.

Metaphosphate glasses such as LiPO3 and NaPO3 are known to incorporate nitrogen in the molten state under NH3 flow to form (Li/Na)PON glasses through the reaction: (Li/Na)PO3 + xNH3 → (Li/Na)PO3−(3x/2)Nx + (3x/2)H2O, by partially replacing two‐coordinated oxygen with two‐ and three‐coordinated nitrogen. After nitridation, the glasses exhibit improved properties such as increased working range, chemical durability, and ionic conductivity. In this study, LiPO3 and NaPO3 glasses were prepared by the conventional melting and casting method and used as base glasses for the ammonolysis procedure. The nitridation processes were carried out by remelting the base glasses at temperatures up to 780°C, under a constant NH3 flow. The effects on the nitrogen content in the resulting (Li/Na)PON glasses caused by different processing times and masses of powder and/or bulk materials were investigated. Nitridation was successfully confirmed by CNHS chemical analyses, Raman spectroscopy, and Differential Scanning Calorimetry. Mass loss measurements after the ammonolysis process and Raman spectroscopy were used to quantify the nitrogen content into the glass structure. A new approach using a specific Raman normalization, (P–N<)/(O–P–O)sym, has been demonstrated as a reliable, simple, and fast way to determine the amounts of N incorporated to metaphosphate glass structures.

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While much of the current research on glassy solid electrolytes (GSEs) has focused on the binary Li 2 S + P 2 S 5 system, compositions with Si are of interest because Si promotes stronger glass formation and allows low-cost melt-quenching (MQ) synthesis under ambient pressure. Another advantage is that they can be formed in homogeneous and continuous glass forms, as a result they are free of grain boundaries. In this work, we have examined the structures and electrochemical properties of bulk glass pieces of sulfide and oxy-sulfide GSE compositions and have also expanded the study by using LiPON glass as a dopant to produce an entirely new class of nitrogen doped mixed oxy-sulfide nitride (MOSN) GSEs. Upon doping with oxygen and nitrogen, the solid electrolyte interface (SEI) is stabilized and the doped MOSN GSE exhibits a critical current density (CCD) of 1.8 mA cm À 2 at 100 °C. We also report on improving the glass quality, the SEI engineering and its limitations, and future plans of improving the electrochemical performance of these homogeneous MQ MOSN GSEs. These fundamental results can help to understand the structures and doping effects of the bulk GSEs, and as such can provide a guide to design improved homogeneous grain-boundary-free GSEs.