Garnet-Type Li₇La₃Zr₂O₁₂Solid Electrolyte Thin Films Grown by CO₂-Laser Assisted CVD for All-Solid-State Batteries

Abstract

The detailed characterization of garnet-type Li-ion conducting Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolyte thin films grown by novel CO 2 -laser assisted chemical vapor deposition (LA-CVD) is reported. A deposition process parameter study reveals that an optimal combination of deposition temperature and oxygen partial pressure is essential to obtain high quality tetragonal LLZO thin films. The polycrystalline tetragonal LLZO films grown on platinum have a dense and homogeneous microstructure and are free of cracks. A total lithium ion conductivity of 4.2 · 10 −6 S · cm −1 at room temperature, with an activation energy of 0.50 eV, is achieved. This is the highest total lithium ion conductivity value reported for tetragonal LLZO thin films so far, being about one order of magnitude higher than previously reported values for tetragonal LLZO thin films prepared by sputtering and pulsed laser deposition. The results of this study suggest that the tetragonal LLZO thin films grown by LA-CVD are applicable for the use in all-solid-state thin film lithium ion batteries. Over the last decades a progressive miniaturization of electronic components took place. As a result there is an increasing demand for micro-sized power sources that drives the current research on thin film batteries. Possible applications range from sensors and radiofrequency identification tags to implantable medical devices. For these applications an all-solid-state thin film Li-ion battery is desirable due to considerable advantages such as excellent safety properties and easy integration in microelectronics. Furthermore, the energy density of such an all-solid-state cell can be increased compared to a cell with conventional liquid electrolyte, if the chosen solid electrolyte material is stable toward high voltage cathode materials as well as toward a lithium metal anode. The garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 (LLZO), first reported in 2007 by Murugan et al., 1 is a material that combines those properties with reasonably high lithium ion conductivity of up to 2.3 · 10 −5 S · cm −1 in its tetragonal 2 and up to 1.2 · 10 −3S · cm −1 in its cubic 3 modification. However, these high conductivity values have so far only been achieved for bulk ceramics, but not for thin films. Apparently, over the last years researchers have focused on the optimization of the lithium ion conductivity in bulk ceramics, e.g. by stabilization of the cubic LLZO phase via doping, 4,5 while only a few publications have addressed LLZO thin film deposition at all. 6-12The advantage of thin films is that their lithium ion conductivity for the use in an all-solid-state battery does not need to be as high as compared to bulk solid electrolytes, taking into account the electrolyte resistance R:where A is the contact area, l is the thickness and σ is the Li-ion conductivity of the solid electrolyte, respectively. For example, in their recent study Liu et al. 13 report on a functioning bulk all-solid-state battery using cubic LLZO as solid electrolyte with ∼ 1 mm thickn...

Surface analytical approaches to reliably characterize lithium ion battery electrodes

“…Moreover, we have recently shown this also for Zr as well as for Pt and Au containing samples. These findings accordingly were transferred to the even more complex Li‐Ni‐Mn‐Co‐O thin films. Here, the Mn 2p region shown in Figure a is strongly overlapped by AlKα X‐ray induced intense Ni LMM Auger peaks.…”

Dendrite nucleation in lithium-conductive ceramics

“…Impedance spectroscopy shows the dielectric constant to be 50. 19,20 3 Results and discussion Ceramic electrolytes exhibit substantial electrical polarizability, as well as being conductive. The range of possible electrical responses can be explored by comparing the portion of the voltage drop across the electrolyte owing to electrode surface charge (capacitive behavior) to that arising from faradaic current (resistive).…”

Tape‐Casting Li0.34La0.56TiO3 Ceramic Electrolyte Films Permit High Energy Density of Lithium‐Metal Batteries

“…Amorphous lithium phosphorus oxynitride (LiPON) thin‐film electrolytes have exhibited outstanding performance in the application of ASSLBs after they were reported by the Oak Ridge National Laboratory for the first time . Pulsed laser deposition, radio frequency (RF) magnetron sputtering, chemical vapor deposition, and atomic layer deposition can be used to produce oxide thin films with a thickness of 100 nm to 1 µm. Thin‐film batteries could realize a low interfacial resistance of 8.6 Ω cm 2 between LiPON electrolytes and LiCoO 2 cathodes by RF magnetron sputtering .…”