Thin film batteries based on solid electrolytes having a garnet-structure like Li 7 La 3 Zr 2 O 12 (LLZ) are considered as one option for safer batteries with increased power density. In this work we show the deposition of Ta-and Al-substituted LLZ thin films on stainless steel substrates by r.f. magnetron sputtering. The thin films were characterized by XRD, SEM and time-of-flight-secondary ion mass spectrometry (ToF-SIMS) to determine crystal structure, morphology and element distribution. The substrate temperature was identified to be one important parameter for the formation of cubic garnet-structured LLZ thin films. LLZ formation starts at around 650°C. Single phase cubic thin films were obtained at substrate temperatures of 700°C and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF-SIMS and XRD indicated that this layer consists of γ-LiAlO 2. The combined total ionic conductivity of the γ-LiAlO 2 interlayer and the LLZ thin film (perpendicular to the plane) was determined to be 2.0x10-9 S cm-1 for the sample deposited at 700°C. In-plane measurements showed a room temperature conductivity of 1.2x10-4 S cm-1 with an activation energy of 0.47 eV for the LLZ thin film.
Solid-state lithium batteries comprising a ceramic electrolyte instead of a liquid one enable safer highenergy batteries. Their manufacturing usually requires a high temperature heat treatment to interconnect electrolyte, electrodes, and if applicable, further components like current collectors. Tantalum-substituted Li 7 La 3 Zr 2 O 12 as electrolyte and LiCoO 2 as active material on the cathode side were chosen because of their high ionic conductivity and energy density, respectively. However, both materials react severely with each other at temperatures around 1085 °C thus leading to detrimental secondary phases. Thin-film technologies open a pathway for manufacturing compounds of electrolyte and active material at lower processing temperatures. Two of them are addressed in this work to manufacture thin electrolyte layers of the aforementioned materials at low temperatures: physical vapor deposition and coating technologies with liquid precursors. They are especially applicable for electrolyte layers since electrolytes require a high density while at the same time their thickness can be as thin as possible, provided that the separation of the electrodes is still guaranteed.
The time evolution of the resistance of amorphous thin films of the phase change materials Ge 2 Sb 2 Te 5 , GeTe and AgIn-Sb 2 Te is measured during annealing at T = 80 • C. The annealing process is interrupted by several fast temperature dips to determine the changing temperature dependence of the resistance. This procedure enables us to identify to what extent the resistance increase over time can be traced back to an increase in activation energy E A or to a rise of the prefactor R * . We observe that, depending on the material, the dominating contribution to the increase in resistance during annealing can be either a change in activation energy (Ge 2 Sb 2 Te 5 ) or a change in prefactor (AgIn-Sb 2 Te). In the case of GeTe, both contribute about equally. We conclude that any phenomenological model for the resistance drift in amorphous phase change materials that is based on the increase of one parameter alone (e.g., the activation energy) cannot claim general validity.
Garnet Li 6.4 La 3 Zr 1.6 Ta 0.4 O 12 thin films prepared by magnetron sputtering were analysed by secondary ion mass spectrometry, nuclear reaction analysis and Rutherford backscattering to identify, localize and quantify the reactions associated with the presence of low amounts of water and carbon dioxide. Samples in a pristine state and after storage in an Argon-filled glove box for months were compared. Both, lithium hydroxide and lithium carbonate were detected, with carbon-containing species and hydrogen-containing having surprisingly different depth profiles.
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