Elucidation of the Transport Properties of Calcium-Doped High Entropy Rare Earth Aluminates for Solid Oxide Fuel Cell Applications.

Solid oxide fuel cells (SOFCs) are paving the way to clean energy conversion, relying on efficient oxygen-ion conductors with high ionic conductivity coupled with a negligible electronic contribution. Doped rare earth aluminates are promising candidates for SOFC electrolytes due to their high ionic conductivity. However, they often suffer from p-type electronic conductivity at operating temperatures above 500 °C under oxidizing conditions caused by the incorporation of oxygen into the lattice. High entropy materials are a new class of materials conceptualized to be stable at higher temperatures due to their high configurational entropy. Introducing this concept to rare earth aluminates can be a promising approach to stabilize the lattice by shifting the stoichiometric point of the oxides to higher oxygen activities, and thereby, reducing the p-type electronic conductivity in the relevant oxygen partial pressure range. In this study, the high entropy oxide (Gd,La,Nd,Pr,Sm)AlO3 is synthesized and doped with Ca. The Ca-doped (Gd,La,Nd,Pr,Sm)AlO3 compounds exhibit a higher ionic conductivity than most of the corresponding Ca-doped rare earth aluminates accompanied by a reduction of the p-type electronic conductivity contribution typically observed under oxidizing conditions. In light of these findings, this study introduces high entropy aluminates as a promising candidate for SOFC electrolytes.

Embracing disorder in solid-state batteries.

Enhanced ion transport is achieved by chemically induced structural distortion.

Microstrain and electrochemical performance of garnet solid electrolyte integrated in a hybrid battery cell.

Garnet type solid electrolytes are promising candidates for replacing the flammable liquid electrolytes conventionally used in Li-ion batteries. Al-doped Li7La3Zr2O12 (LLZO) is synthesized using nebulized spray pyrolysis and field assisted sintering technology (FAST), a novel synthesis route ensuring the preparation of samples with a homogeneous elemental distribution and dense ceramic electrolytes. Ceramic preparation utilizing field assisted sintering, in particular the applied pressure, has significant influence on the material structure, i.e. microstrain, and thereby its electrochemical performance. The phenomenon of microstrain enhancement of electrochemical performance might open a new route towards improved garnet solid electrolytes. A detailed mechanism is proposed for the lattice distortion and resulting microstrain during sintering. The charge transfer resistance of Li-ions at the interface between LLZO and Li is characterized using AC impedance spectroscopy and is amongst the best reported values to date. Additionally, the solid electrolyte is integrated in a full hybrid cell, a practical approach combining all the advantages of the solid electrolyte, while maintaining good contact with the cathode material.