Solid Electrolyte Thin Films Research Articles

Advanced Impedance Spectroscopy Study of the Influence of the Crystalline Structure on the Ionic Conduction of Thin Solid-State Electrolytes

In this work, an experimental and modeling approach that considers the crystalline nature of the material is used to u the electrical behavior of thin film solid state electrolytes. In this research, the complex electrical properties at different temperatures of nanocrystal yttrium-doped ceria (YDC) are determined by electrochemical impedance spectroscopy (EIS). The impedance modeling provides a description of the electrical behavior of the material. The influence of the geometry of the electrodes in the electrical measurements is investigated by finite element simulations for different electrode spacing. The combined analysis represents a strong approach to elucidate the experimental evidence that is not explained by the available physical models.

Properties of aerosol deposited NASICON-type Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte thin films

NASICON-type Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte thin films were fabricated without any heat treatment by aerosol deposition (AD). Ball-milled LAGP powders with different particle sizes were used as raw material and deposited directly on a stainless steel substrate via room temperature impact consolidation. X-ray diffraction patterns revealed that as-deposited LAGP film has a same crystal structure with raw LAGP powder and no secondary phases are formed during deposition. SEM observation showed that film consists of fractured LAGP nanoparticles but the porosity is strongly influenced by an averaged particle size of raw LAGP powder. Maximum total (bulk+grain-boundary) ionic conductivity at room temperature in aerosol deposited (ADed) LAGP film was 0.5×10−5Scm−1, while the bulk conductivity of film was approximately 10−4Scm−1, which is comparable with the bulk property of LAGP as previously reported. Therefore, lower total conductivity of ADed LAGP film is mainly attributed to large grain-boundary resistance between the LAGP nanoparticles in the film. Improvement of film density and the connectivity among the LAGP nanoparticles in the film should be needed to enhance the total conductivity.

Cycle stability increase by insertion of Li–La–Ta–O thin-film electrolyte between cathode and solid electrolyte for all-solid-state battery

Recently, all‐solid-state batteries (ASSBs) with an inorganic solid electrolyte have attracted significant interest because of their high potential for unique applications in space, deep sea, and radioactive environments. The inorganic solid electrolyte is one of the most fundamental parts since it determines the C rate and self-discharge properties. We prepared a series of ASSBs based on lithium lanthanum tantalum oxide (LLTO) solid-electrolyte thin films with thicknesses of 0, 100, and 200nm by radio frequency (RF) magnetron sputtering. The microstructure and composition of the LLTO thin films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The results show that the LLTO thin films have a high ionic conductivity, and they reduce the contact resistance between the cathode and the solid electrolyte, and increase the ion path between the cathode and the bulk electrolyte. Thus, they can be applied to ASSBs as an interlayer between the cathode and the solid electrolyte.

In situ and nonvolatile photoluminescence tuning and nanodomain writing demonstrated by all-solid-state devices based on graphene oxide.

In situ and nonvolatile tuning of photoluminescence (PL) has been achieved based on graphene oxide (GO), the PL of which is receiving much attention because of various potential applications of the oxide (e.g., display, lighting, and nano-biosensor). The technique is based on in situ and nonvolatile tuning of the sp(2) domain fraction to the sp(3) domain fraction (sp(2)/sp(3) fraction) in GO through an electrochemical redox reaction achieved by solid electrolyte thin films. The all-solid-state variable PL device was fabricated by GO and proton-conducting mesoporous SiO2 thin films, which showed an extremely low PL background. The device successfully tuned the PL peak wavelength in a very wide range from 393 to 712 nm, covering that for chemically tuned GO, by adjusting the applied DC voltage within several hundred seconds. We also demonstrate the sp(2)/sp(3) fraction tuning using a conductive atomic force microscope. The device achieved not only writing, but also erasing of the sp(2)/sp(3)-fraction-tuned nanodomain (both directions operation). The combination of these techniques is applicable to a wide range of nano-optoelectronic devices including nonvolatile PL memory devices and on-demand rewritable biosensors that can be integrated into nano- and microtips which are transparent, ultrathin, flexible, and inexpensive.

Improvement of Electrochemical Performance of Bulk-Type All-Solid-State Lithium Secondary Batteries By Using Sulfide Solid Electrolyte Thin Films

All-solid-state batteries using inorganic solid electrolytes are widely studied as next generation batteries. Two types (bulk or thin-film) of batteries have been investigated. Especially, bulk-type batteries, which use composite electrodes of active material and electrolyte powders, are anticipated for power sources with high energy density. Solid electrolyte thin films are useful for bulk-type batteries with an ideal electrode-electrolyte interface. Furthermore, the solid electrolyte contents in composite electrodes can be reduced significantly. We previously fabricated amorphous Li2S-P2S5 and Li2S-GeS2 thin films with high lithium-ion concentrations by pulsed laser deposition (PLD) [1, 2], and this technique was used for coating solid electrolyte thin films on active material particles. Consequently, the energy density of all-solid-state batteries normalized by the total weight of the composite electrode increased [2, 3]. In order to further improve the battery performance, solid electrolyte thin films with higher lithium-ion conductivity are indispensable. We prepared the 33Li4GeS4·67Li3PS4 (mol%) thin film with an ionic conductivity of 1.1×10-4 S cm-1, and the conductivity was increased to 1.8×10-3 S cm-1 by a heat treatment at 200 oC. The all-solid-state cell using LiCoO2 particles coated with the 33Li4GeS4·67Li3PS4 (SE) thin film was charged and discharged with a larger capacity of 67 mAh g-1 than that using non SE-coated LiCoO2 particles. Moreover, the capacity of all-solid-state cell increased to 80 mAh g-1after enhancing the ionic conductivity of SE-coating layer after the heat treatment. The coating of highly-ion conductive solid electrolyte thin films on active material particles is considered to be effective in forming an ideal interface between electrode and electrolyte, resulting in the increase of energy density in bulk-type all-solid-state batteries.Acknowledgement: This study is financially supported by Toyota Motor Corporation.

Preparation and electrical properties of garnet-type Li6BaLa2Ta2O12 lithium solid electrolyte thin films prepared by pulsed laser deposition

Abstract The growth of Li-ion conducting Li6BaLa2Ta2O12 garnet-type thin films by pulsed laser deposition (PLD) is reported. Li6BaLa2Ta2O12 was synthesized as target material by a high temperature solid-state reaction. Thin films were grown on MgO(100) by ablation of the respective bulk target material consisting of Li6BaLa2Ta2O12 with 5 mol% excess of Li2O to compensate lithium loss during thin film growth. X-ray diffraction revealed a garnet-type structure of the prepared thin films. The bulk material showed electrical conductivity of up to σ = 5.0 ⋅ 10− 5 S cm− 1 at 25 °C, whereas the Li6BaLa2Ta2O12 garnet-type films exhibit a lower conductivity of σ = 2 ⋅ 10− 6 S cm− 1 at 25 °C, which is comparable to the ionic conductivity of LiPON being about σ = 2 ⋅ 10− 6 S cm− 1 at the same temperature. The activation energy Ea of bulk and thin film samples results in 0.44 eV and 0.42 eV, respectively, as determined by temperature-dependent conductivity measurements. Ohara glass-ceramic was successfully protected against reduction by deposition of a thin garnet-type film on top of the glass ceramic. The partial electronic conductivity of the bulk material was determined by the Wagner–Hebb-polarization technique. The electronic partial conductivity took values between σel = 2.87 ⋅ 10− 13 S cm− 1 and σel = 3.47 ⋅ 10− 10 S cm− 1 in the range of the polarization voltage U = 2.8 V to U = 4.3 V, resulting in low electronic transference numbers between tel = 5.74 ⋅ 10− 9 and tel = 6.76 ⋅ 10− 6.

Scalable Oxygen‐Ion Transport Kinetics in Metal‐Oxide Films: Impact of Thermally Induced Lattice Compaction in Acceptor Doped Ceria Films

In this paper, we focus on the effect of processing‐dependent lattice strain on oxygen ion conductivity in ceria based solid electrolyte thin films. This is of importance for technological applications, such as micro‐SOFCs, microbatteries, and resistive RAM memories. The oxygen ion conductivity can be significantly modified by control of lattice strain, to an extent comparable to the effect of doping bulk ceria with cations of different diameters. The interplay of dopant radii, lattice strain, microstrain, anion‐cation near order and oxygen ion transport is analyzed experimentally and interpreted with computational results. Key findings include that films annealed at 600 °C exhibit lattice parameters close to those of their bulk counterparts. With increasing anneal temperature, however, the films exhibited substantial compaction with lattice parameters decreasing by as much as nearly 2% (viz, Δd600–1100 °C: –1.7% (Sc+3) > –1.5% (Gd+3) > –1.2% (La+3)) for the annealing temperature range of 600–1100 °C. Remarkably 2/3rd of the lattice parameter change obtained in bulk ceria upon changing the acceptor diameter from the smaller Sc to larger La, can be reproduced by post annealing a film with fixed dopant diameter. While the impact of lattice compaction on defect association/ordering cannot be entirely excluded, DFT computation revealed that the main effect appears to result in an increase in migration energy and consequent drop in ionic conductivity. As a consequence, it is clear that annealing procedures should be held to a minimum to maintain the optimum level of oxygen ion conductivity for energy‐related applications. Results reveal also the importance to understand the role of electro‐chemo‐mechanical coupling that is active in thin film materials.

Bulk-type All-solid-state Lithium Secondary Batteries Using Highly Ion-conductive Sulfide Solid Electrolyte Thin Films

LiCoO2 particles were coated with 33Li4GeS4·67Li3PS4 (mol%) solid electrolyte (SE) thin films by pulsed laser deposition (PLD). The all-solid-state cells using positive electrodes, composed of only LiCoO2 particles coated with SE thin films, were fabricated and their electrochemical performances were investigated. The cell was charged and discharged with a higher capacity of 67 mAh g−1 than that using LiCoO2 particles without SE-coating. Moreover, the capacity of all-solid-state cell increased to 80 mAh g−1 after enhancing the ionic conductivity of SE thin films by heat treatment at 200°C. The use of highly lithium-ion conductive thin films was effective in the formation of sufficient lithium-ion conduction paths in positive electrodes for bulk-type all-solid-state batteries.

Relationship between Electrical Properties and Stress Field in Solid Electrolyte Thin Films

Stress in yttria stabilized zirconia (YSZ) thin films was controlled by using various substrates, which had different thermal expansion coefficient (TEC), and electrical properties of the films were measured to study the relationship between the stress filed and electrical properties. Thin films of YSZ were deposited by PLD method on Al2O3 and AlN substrates. Because TEC of YSZ is larger than that of the substrates, tensile stress field was introduced into the films at room temperature. Measured stress value by XRD was varied from 0.7 to 1.7 GPa at R.T. This value is significantly higher than literature value. However, the films also showed different lattice volume on the different substrates. Although electrical properties in the films showed different tendencies by the substrates, both stress field and lattice volume were different. Hence, stress dependence of electrical properties was not clearly observed.

Electrical Characterization of YSZ Thin Films Using a Calibrated Platinum Micro-Electrode

A bulk platinum microelectrode calibration method, aiming at providing reliable measurements of the electrical properties of thin solid electrolyte films, is described. The method consists in the determination of the electrically active surface of an electrode of microscopic dimensions based on the confident measurement of the conductivity of a well know reference sample. The method is demonstrated to be efficient, reliable and reproducible in the case of yttria-stabilized zirconia films prepared by different techniques for films thicknesses ranging from 1.5 µm to 10 µm.

Lithium borophosphate thin film electrolyte as an alternative to LiPON for solder-reflow processed lithium-ion microbatteries

Microbatteries are energy sources well adapted to power various microsystems. To be considered as a microelectronic component, the microbatteries must be compatible with the solder-reflow treatment. During this industrial process, the temperature reaches 260 °C during few seconds. Having noticed an increase of the activation energy of the most used solid electrolyte lithium phosphate thin film (LiPON) after this type of thermal treatment, from 0.57 eV to 0.80 eV, we have investigated the correlations between composition, local structure (by XPS) and the electrical properties of lithium borophosphate solid electrolyte thin films. The lithium borophosphate thin films were prepared by radio-frequency sputtering using five different targets having the following compositions x LiBO2: (1 − x) Li3PO4 (x = 5, 10, 15, 20 and 25) in a pure argon discharge gas. In the absence of a thermal treatment, the addition of a small amount of boron (B/P ratio equal to 0.1) leads to an increase of the ionic conductivity (1.1 × 10− 6 S·cm− 1) and a decrease of the activation energy (0.52 eV) compared to a pure lithium phosphate. However, for B/P ratio higher than 0.12, the ionic conductivity decreases. The study of the local structure by X-ray photoelectron spectroscopy (XPS) shows that the borate groups have less reacted with the phosphate groups leading to a phase separation reducing the connectivity between phosphate and borophosphate networks and so the ionic conductivity. The solder-reflow type thermal treatment leads to an increase of the ionic conductivity. The best ionic conductivity, 1.9 × 10− 6 S·cm− 1, is obtained for a B/P ratio equal to 0.24 with an activation energy of 0.57 eV instead of 0.80 eV for the LiPON thin film. For a use of Li-ion microbattery at low temperature after the solder-reflow type thermal treatment, the lithium borophosphate solid electrolyte would be a potential candidate to replace LiPON with several industrial advantages.

Preparation of Li2S–GeS2 solid electrolyte thin films using pulsed laser deposition

Amorphous Li2S–GeS2 solid electrolyte thin films were prepared using pulsed laser deposition (PLD) at the compositions of 67–83mol% Li2S. The ionic conductivities at room temperature increased with increasing Li2S contents and attained a maximum value of 1.8×10−4Scm−1 at the composition of 78mol% Li2S. The obtained solid electrolyte thin film was applied to form an ideal electrode–electrolyte interface in all-solid-state batteries. The all-solid-state lithium cell using LiCoO2 coated with the solid electrolyte thin film operated as a lithium secondary battery at room temperature.

Retraction: “Lithium-ion conducting La2/3–xLi3xTiO3 solid electrolyte thin films with stepped and terraced surfaces” [Appl. Phys. Lett. 100, 173107 (2012)

Retraction: “Lithium-ion conducting La2/3–<i>x</i>Li3<i>x</i>TiO3 solid electrolyte thin films with stepped and terraced surfaces” [Appl. Phys. Lett. 100, 173107 (2012)

Synthesis and Electrical Properties of Garnet-type Solid Oxide Electrolyte Thin Films from Solution Route

ABSTRACTDevelopment of Al-stabilized Li7La3Zr2O12 (LLZO) fast Li ion conducting thin films was attempted by chemical solution deposition (CSD) method with the nominal composition of Li5.95Al0.35La3Zr2O12. The films were crystallized at 600°C on Pt-coated Si substrates in almost single phase without a preferred orientation to any crystallographic axis. Subsequent thermal annealing at 760°C improved packing of LLZO grains with the film thickness of 1.1μm. AC impedance measurements were conducted both with Li reversible and Au blocking microelectrodes deposited on the films annealed at 760°C. Total Li ion conductivity σtotal comprised of bulk and grain boundary contribution was studied. The temperature dependence of σtotal was described with single thermal activation process and σtotal∼2x10-5 S/cm and activation energy of Ea=0.58eV were estimated. These values may be attributed to tetragonal modification of LLZO crystal.

Radical Assisted Sputtering 法によるTa&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; 固体電解質薄膜の作製

During fabrication of Ta2O5 solid-electrolyte thin films by radical-assisted sputtering, it was found that a radical-source (RS) treatment involving oxygen-radical irradiation of the Ta2O5 thin-film surface for different times enhanced its ECD response characteristics. The Ta2O5 films remained amorphous, regardless of the RS treatment time, even though changes were observed in their surface structure and relative density. The ionic conductivity of the films improved substantially due to the RS treatment, and tended to increase with treatment time. FT-IR identified no peak attributable to O-H stretching vibrations with or without the RS treatment, but the intensity of the peak associated with Ta-O stretching vibrations was found to increase with RS treatment time. This indicates that the increase in ionic conductivity was not related to the water content, but was instead the result of effective termination of oxygen defects in the thin film by the highly reactive oxygen radicals, thus enabling unimpeded H+ movement.

Synthesis and orientation control of Li-ion conducting epitaxial Li0.33La0.56TiO3 solid electrolyte thin films by pulsed laser deposition

Epitaxial thin films of the Li-ion conducting solid electrolyte Li0.33La0.56TiO3 were grown by pulsed laser deposition. The growth temperature and oxygen partial pressure required for crystallization were higher than 900°C and 5Pa, respectively. Further optimization of growth conditions led to the formation and orientation control of Li-ion conducting epitaxial Li0.33La0.56TiO3 thin films.

Fabrication and Characterization of Li7La3Zr2O12 Thin Films for Lithium Ion Battery

The last few decades have seen a drastic miniaturization of electronic devices following the famous Moore’s law predicted by Gordan Moore in 1971. These developments in the electronic industry have resulted in ultra-low-weight electronic devices such as palm-top computers, smart phones, tablet PCs etc. Batteries constitute one of the most important and essential components of these devices. At present, lithium ion batteries (LIBs) are considered the most suitable candidateforuseinportableelectronicdevices.However,thesebatteriesare available only in the bulk form and comprise a significant percentage of the overall weight of the device. As the miniaturization of electronic devices continues, we need more advanced batteries which are light weight, safe, and environment friendly. One possible solution is the development of thin film batteries (TFBs) which can be integrated onto the microprocessor chips themselves. For these applications, we would require solid-state (SS) electrolyte. Currently, a major obstacle in this field is the low ionic conductivity of SS electrolytes and high temperature needed to fabricate thin films of these materials. As far as the research in SS electrolyte materials is concerned, many different kinds of inorganic systems have been explored to date. These include Nasicon-type electrolytes, 1‐4 perovskite-type lithium lanthanum tantantes, 5,6 and garnet-type Li ion conductors. 7,8 Among all of them, garnet type Li7La3Zr2O12 (LLZO), synthesized lately by Weppner’s group 9 has been reported to possess very high ionic conductivity. What’s more, LLZO is electrochemically stable with a potential window wider than 0‐7 V, is environment friendly, and is relatively inexpensive. 9‐11 However, to our knowledge, LLZO has so far been synthesized in bulk form only; no work has been reported on the preparation of LLZO thin films. For realizing thin film batteries, it is essential to be able to grow thin films of solid electrolytes and preferably at low temperatures. In this paper, we are reporting the fabrication of LLZO thin films on SrTiO3 (100) and Sapphire (0001) substrates by pulsed laser deposition at room temperature. The effect of annealing was investigated by detailed characterization of thin film structures and properties. Studies were also performed to understand the influence of lithium loss during the deposition process.

Electrical Characterization of Ultrathin Film Electrolytes for Micro-SOFCs

The reliability of solid oxide fuel cells (SOFCs) particularly depends on the high quality of solid oxide electrolytes. The application of thinner electrolytes and multi electrolyte layers requires a more reliable characterization method. Most of the investigations on thin film solid electrolytes have been made for the parallel transport along the interface, which is not however directly related to the fuel cell performance of those electrolytes. In this work an array of ion-blocking metallic Ti/Au microelectrodes with about a 160 μm diameter was applied on top of an ultrathin (1 μm) yttria-stabilized-zirconia/gadolinium-doped-ceria (YSZ/GDC) heterolayer solid electrolyte in a micro-SOFC prepared by PLD as well as an 8-μm thick YSZ layer by screen printing, to study the transport characteristics in the perpendicular direction relevant for fuel cell operation. While the capacitance variation in the electrode area supported the working principle of the measurement technique, other local variations could be related to the quality of the electrolyte layers and deposited electrode points. While the small electrode size and low temperature measurements increaseed the electrolyte resistances enough for the reliable estimation, the impedance spectra appeared to consist of only a large electrode polarization. Modulus representation distinguished two high frequency responses with resistance magnitude differing by orders of magnitude, which can be ascribed to the gadolinium-doped ceria buffer electrolyte layer with a 200 nm thickness and yttria-stabilized zirconia layer of about 1 μm. The major impedance response was attributed to the resistance due to electron hole conduction in GDC due to the ion-blocking top electrodes with activation energy of 0.7 eV. The respective conductivity values were obtained by model analysis using empirical Havriliak-Negami elements and by temperature adjustments with respect to the conductivity of the YSZ layers.

Relationship between Electrical Properties and Stress Field in Solid Electrolyte Thin Films

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Metal supported tubular solid oxide fuel cells fabricated by suspension plasma spray and suspension high velocity oxy-fuel spray

Low temperature (LT) metal supported solid oxide fuel cells (SOFCs) have many advantages in comparison to conventional electrode or electrolyte supported type SOFCs. NRC has demonstrated high performance LT metal supported planar SOFCs fabricated by either wet colloidal spray/sintering or suspension thermal spray. The combination of tubular configuration and metal supported SOFCs may produce more unique and very attractive advantages such as easy and inexpensive sealing method and materials, high specific and volumetric power density, cost-effective fabrication, enhanced robustness, rapid start up, red-ox cycle tolerance and potential use for a pressurized integrated system.In this paper, thin film solid electrolyte of Sm0.2Ce0.8O1.90 (SDC) and NiO-SDC composite anode on sintered porous tubular metal supports were deposited by suspension HVOF spray and suspension plasma spray, respectively on sintered porous tubular metal support. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathode on the SDC electrolyte was formed by wet colloidal spray and subsequent sintering process as the final fabrication step. The detailed investigation of suspension and process-related parameters for suspension thermal spray was performed in order to produce thin and crack-free SDC thin film coatings. The electrochemical performance of single cells was demonstrated.