Solid-state batteries utilizing Li metal anodes have the potential to enable improved performance (specific energy >500 Wh/kg, energy density >1,500 Wh/L), safety, recyclability, and potentially lower cost (< $100/kWh) compared to advanced Li-ion systems. 1,2 These improvements are critical for the widespread adoption of electric vehicles and trucks and could create a short haul electric aviation industry. [1][2][3] Expectations for solid-state batteries are high, but there are significant materials and processing challenges to overcome.On May 15 th , 2020, Oak Ridge National Laboratory (ORNL) hosted a 6-hour, national online workshop to discuss recent advances and prominent obstacles to realizing solid-state Li metal batteries. The workshop included more than 30 experts from national laboratories, universities, and companies, all of whom have worked on solid-state batteries for multiple years. The participants' consensus is that, although recent progress on solid-state batteries is exciting, much has yet to be researched, discovered, scaled, and developed. Our goal was to examine the issues and identify the most pressing needs and most significant opportunities. The organizers asked workshop participants to present their views by articulating fundamental knowledge gaps for materials and processing science, mechanical behavior and battery architectures critical to advancing solid-state battery technology. The organizers used this input to set the workshop agenda. The group also considered what would incentivize the adoption of US manufacturing and how to accelerate and focus research attention for the benefit of the US energy, climate, and economic interests. The participants identified pros and cons for sulfide, oxide, and polymerbased solid-state batteries and identified common science gaps among the different chemistries. Addressing these common science gaps may reveal the most promising systems to pursue in the future.

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In a solid-state battery (SSB) system, undesirable electrode−electrolyte interfacial reactions lead to a significant performance degradation. Herein, we performed a systematic study on the chemical stabilities between Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) solid electrolyte and various cathode materials at their adhesion temperatures of 500−900 °C. Quantitative analysis of X-ray diffraction (XRD) data using Rietveld refinement revealed that Li-concentration disparity between LATP and oxide cathode materials (e.g., layered and spinel phases) is the root cause of phase degradation at high temperatures. For example, Li migration from oxide cathodes to LATP produces multiple secondary phases including LiMPO 4 olivine. In contrast, the LiFePO 4 cathode severely reacted with LATP at low temperature (T < 500 °C) and produced an Fe-rich NASICON phase (e.g., Li 3 M 2 (PO 4 ) 3 ). The onset temperature of the phase decomposition varies with chemical compositions and crystal phases of cathodes. Increasing the cathode/electrolyte adhesion temperature offers a trade-off between the specific capacity and cycle life, as exemplified by the LiCoO 2 (LCO) + LATP composite cathodes. The results in this study offer a fundamental understanding of the LATP/cathode reaction mechanism, which will serve as guidance for designing interfaces and controlling the fabrication processes of SSB cells.

The use of nanopillar array electrodes (NAEs) for biosensor applications was explored using a combined experimental and simulation approach to characterize the role of reaction kinetics and mass transport in glucose detection with NAEs. Thin gold electrodes with arrays of vertically standing gold nanopillars were fabricated and their amperometric current responses were measured under bare and functionalized conditions. Results show that the sensing performances of both the bare and functionalized NAEs were affected not only by the presence and variation of the nanoscale structures on the electrodes but also by the reaction kinetics and mass transport of the analyte species involved. These results will shed new light for enhancing the performance of nanostructure based biosensors.

Fabrication of metallic nanopillar array structures and their application as electrodes in electrochemical-based biosensors are discussed in this report. Vertically standing nanopillar array structures were fabricated using an electrodeposition technique and their electrochemical characteristics were evaluated. For possible use in biosensing applications, these standing nanopillars should have sufficient mechanical stability to sustain the capillary forces caused by the nanopillar -liquid interactions in aqueous environment and should provide increased signal response in an electrochemical process. Our results showed that the developed nanopillar arrays were mechanically stable in aqueous environments and the nanostructured electrodes exhibited increased electrochemical response compared with flat electrodes.