X-ray Photoelectron Spectroscopy and AC Impedance Spectroscopy Studies of Li-La-Zr-O Solid Electrolyte Thin Film/LiCoO₂Cathode Interface for All-Solid-State Li Batteries

Abstract

Li ion half-cell electrode-based configuration was prepared by spin-coating using precursor of Li-stuffed garnet with intended composition of Li 7 La 3 Zr 2 O 12 on LiCoO 2 . The main goal of this study was lowering the heat-treatment to 400 • C, which is well below the chemical reaction temperature of these phases. Liquid precursor of the nominal compound was prepared and spin-coated on the top surface of MgO(100) and LiCoO 2 pellets until the appropriate thickness was obtained. Electrochemical impedance spectroscopy (EIS) was used to understand the resistance and capacitance behavior of the electrolyte and electrolyte-electrode interface. The ac impedance of half-cell shows semicircles, corresponding to the response from bulk electrolyte, second phase and interface. The interfacial region between LiCoO 2 and Li-La-Zr-O film was deeply studied with X-ray photoelectron spectroscopy (XPS) depth profile analysis. XPS results show that Co diffuses from the substrate toward the solid electrolyte; Li depletes in the interface region, and moves to the top surface, which changes the electronic structure of Co to a multiplicity of reduced forms. The present study shows that even at 400 • C, the Li-stuffed garnet precursor and LiCoO 2 cathode seem to form reaction products, suggesting that is critical for applications to develop protecting layers between the cathodes and Li-stuffed garnet electrolytes. Switching from an organic polymer-based Li ion electrolyte to a ceramic Li ion electrolyte in conventional Li ion batteries is expected to allow for higher energy density, improve safety and prolong lifetime. These, all-solid-state Li batteries can also be miniaturized, which will streamline the packing design and save cargo space. A solid electrolyte has to have several criteria to be able to use in the Li ion batteries such as high ionic conductivity at room temperature, high Li + ion transference number, chemical stability versus the Li cathodes and the Li anodes during preparation and battery operation, sustainability and economic feasibility.1-3 Although all-solid-state batteries offer lots of advantages over conventional liquid and polymer based batteries, the widespread applications of currently developed solid-state (ceramic) Li ion electrolytes have been postponed by low conductivity and or high reactivity with the electrodes which impede reaching high power density required for electric vehicles. 4,5 Li-stuffed garnet is a promising type of solid electrolyte offering an advantage of very high electrochemical stability window (∼6 V versus Li/Li + for Zr and Ta-based garnets), which opens up the possibility of using alternative cathodes and anodes for high voltage applications. It solely allows Li ions to move, and reduces the chance of capacity fading by unwanted reactions and or self-discharging. It is benign and resistant to Li dendrite electroplating.6-8 Interfacial resistance of Li stuffed garnet with Li metal and LiCoO 2 has been the scope of some recent studies targeting developing high performance battery f...

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Powder aerosol deposition method — novel applications in the field of sensing and energy technology

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