Solid state electrolyte systems boasting Li + conductivity of >10 mS cm −1 at room temperature have opened the potential for developing a solid state battery with power and energy densities that are competitive with conventional liquid electrolyte systems. The primary focus of this review is twofold. First, differences in Li penetration resistance in solid state systems are discussed, and kinetic limitations of the solid state interface are highlighted. Second, technological challenges associated with processing such systems in relevant form factors are elucidated, and architectures needed for cell level devices in the context of product development are reviewed. Specific research vectors that provide high value to advancing solid state batteries are outlined and discussed. Solid state battery systems are of great interest because of potential benefits in gravimetric and volumetric energy density, operable temperature range, and safety in comparison to traditional liquid electrolyte based systems. However, unresolved fundamental issues remain in the quest to fully understand the behavior of all-solid batteries, especially in the area of electrochemical interfaces.1 There are also a number of significant engineering challenges that require methodical effort to enable a tangible product. Some transitions from academic laboratories to entrepreneurial efforts attempting to overcome these challenges remain unsuccessful in efforts to bring a product to the market.2,3 Vital parameters that require robust understanding from a product development standpoint are material cost, cell lifetime and shelf life, cell energy density on a volumetric and gravimetric basis, operable capabilities for given temperature conditions, and safety. The advantage of energy density remains to be realized in solid state electrolytes (SSEs) since most studies to date utilize thick SSEs or cathodes with low active loading compared to liquid counterparts. 4,5 Furthermore, the desire to use SSEs in conjunction with Li metal anodes requires understanding and managing the morphology of Li metal plating, which can impact volumetric energy density. Operation at both higher and lower temperature compared to conventional technologies is a significant potential advantage of SSE systems. However, reports of solid state cells achieving parity with traditional systems at room temperature or any other temperature do not currently exist. The safety, specifically decreased flammability, of SSE systems is another potential advantage but requires ongoing validation and study.6 Unlike current liquid electrolyte systems, 7 the manufacturability and material component costs of SSEs have not been well characterized, and thus the value of these features will need to be weighed accordingly with any added cost. Operating lifetime of SSEs capturing intrinsic materials parameters such as voltage stability, 8 as well as catastrophic failure modes such as shorting, 9 have been briefly investigated, but in the absence of high energy density electrode formulations and appli...

We study the temperature dependence of dielectric constant (K) and spontaneous polarization (Ps) in the range of −95–200°C. Cubic (C)-tetragonal (T) and T-orthorhombic (O) transitions are observed at 264 and 25°C, respectively. The Curie–Weiss temperature of C-T transition is 249°C, indicating it is first order. X-ray data indicate T-O phase coexistence at 25°C. A singularity in Ps at 25°C and a T-O phase coexistence spanning 25–31°C was observed, wherein Ps increases from 17×10−2C∕m2 at 31°Cto23×10−2C∕m2 25°C. The transition at 25°C appears diffusionless and polymorphic with martensite start and finish temperatures of 31 and 25°C, respectively. The maximum in d33 is 345pC∕N and is attributed to the instability at 25°C, where Ps and K show singularity.

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The rare-earth nickelates (RNiO 3 ) exhibit interesting phenomena such as unusual antiferromagnetic order at wavevector q = (½, 0, ½) and a tunable insulator-metal transition that are subjects of active research. Here we present temperature-dependent transport measurements of the resistivity, magnetoresistance, Seebeck coefficient, and Hall coefficient (R H ) of epitaxial SmNiO 3 thin films with varying oxygen stoichiometry. We find that from room temperature through the high temperature insulator-metal transition, the Hall coefficient is hole-like and the Seebeck coefficient is electron-like. At low temperature the Néel transition induces a crossover in the sign of R H to electron-like, similar to the effects of spin density wave formation in metallic systems but here arising in an insulating phase ~200 K below the insulator-metal transition. We propose that antiferromagnetism can be stabilized by bandstructure even in insulating phases of correlated oxides, such as RNiO 3 , that fall between the limits of strong and weak electron correlation.3

Thin film micro-solid oxide fuel cells (mSOFCs) utilizing nanoporous ruthenium (Ru) anodes were fabricated and investigated for direct methane operation for the first time. The mSOFCs consist of 8 mol % yttria-stabilized zirconia (YSZ) thin film electrolytes, porous platinum (Pt) cathodes and porous Ru anodes, fabricated on silicon platforms by physical vapor deposition. The fuel cells, tested with methane as the fuel and air as the oxidant, exhibited an open circuit voltage (OCV) of 0.71 V and a peak power density of 450 mW cm À2 at 500 C without visually detectable carbon deposition. Structural investigations revealed that the morphology evolution in nanoporous Ru anodes was strongly dependent on the fuels (namely, methane or hydrogen) used, and possible mechanisms leading to the observations are discussed. Results presented here project insights to enable direct use of hydrocarbons with high performance, and are of potential relevance to advancing low temperature micro-fuel cell technology for portable power.

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Controllable fabrication of compositionally graded Gd0.1Ce0.9O2‐δ and Y0.16Zr0.84O2‐δ electrolytes using co‐sputtering is demonstrated. Self‐supported membranes were lithographically fabricated to employ the new electrolytes into thin film solid oxide fuel cells. Devices integrating such electrolytes demonstrate performance of over 1175 mW cm−2 and 665 mW cm−2 at 520 °C using hydrogen and methane as fuel, respectively. The results present a general strategy to fabricate nanoscale functionally graded materials with selective interfacial functionality for energy conversion.

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