Search

Solid-state batteries (SSBs) using a garnet-based oxide electrolyte, Li7La3Zr2O12 (LLZ), are attracting considerable attention as a future power storage solution with a promising higher safety level than that of the conventional lithium-ion batteries (LIBs) using liquid organic electrolytes due to the non-flammability of LLZ. However, the major obstacle in realizing oxide-based SSBs is their high-temperature fabrication process (e.g., above 600 °C), resulting in the formation of insulating impurities by the reaction between the cathode and electrolyte materials. Herein, we have demonstrated the fabrication of a solid-state Li/LLZ/Li(Ni1/3Co1/3Mn1/3)O2 battery at a remarkably low temperature (400 °C) using our invented "low temperature sintering triggered by an ion-exchange reaction (LTI)". The LTI promotes element diffusion via limited ion exchange within a range that maintains the crystal structure, enabling a lower sintering temperature and shorter sintering time. The high capacity of the fabricated SSB was confirmed to be 127 mA h g−1 for the electrode and the operation temperature was increased up to 100 °C, where conventional LIBs with liquid electrolytes do not work due to the vaporization of the solvent. [ABSTRACT FROM AUTHOR]

We have earned out a basic study on the charge transfer across the interface between LiNi0.5Mn1.5O4 (LNMO) thin-film cathodes and different solid electrolyte coatings, namely LiNbO3, ZrO2 and Li4Ti5O12. In contact to LNMO, the spinel material Li4Ti5O12 should act as a solid electrolyte, since it exhibits a very low electronic conductivity in the fully oxidized state. The thin films were prepared by means of sol-gel chemistry and spin-coating. The electrochemical and interfacial properties were studied by combining electrochemical impedance spectroscopy (EIS), time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and cross-sectional SEM imaging. The results show that the LNMO / LiNbO3 interface combines a low charge transfer resistance with a high stability. [ABSTRACT FROM AUTHOR]

Abstract: We report on the structure and lithium ion transport properties of Li1.5Al0.5Ge1.5(PO4)3 (LAGP). This material is commercially available and is prepared as amorphous powders via a flame spray technique called Flash Creation Method (FCM). We crystallize and sinter the amorphous powders at different temperatures in order to alter grain size and grain boundary properties. The structure is then characterized by means of powder X-ray diffraction, atomic force microscopy, scanning electron microscopy and transmission electron microscopy with energy dispersive X-ray spectroscopy. AC impedance spectroscopy is used to study lithium ion transport. A maximum total conductivity of 2×10−4 Scm−1 at room temperature is found for a sample sintered at 750°C for 2h. In order to distinguish between grain and grain boundary contributions to the impedance spectra, equivalent circuit fits are carried out. The results are analysed in the framework of the classical brick layer model and of a finite-element approach taking into account non-ideal grain contacts. Our experimental results for the grain and grain boundary resistances are in good agreement with the predications of the finite-element approach. [Copyright &y& Elsevier]

Abstract: Lithium iron phosphate (LiFePO4) thin film electrodes were prepared by pulsed laser deposition (PLD). The thin films were annealed at various temperatures under argon gas flow and the influence of annealing temperature on their electrochemical performance was studied. The thin films annealed at 773 and 873K exhibited a couple of redox peaks at 3.4V (versus Li/Li+) that are characteristics of the electrochemical lithium insertion/extraction of LiFePO4. Atomic force microscopy (AFM) observation revealed that the film annealed at 773K (773K-film) consisted of small grains with 50nm in thickness, and the grain size increased with an increase of annealing temperature. Because of its small-sized grains, the 773K-film showed high rate capability and the discharge capacity at 10μA maintained 65% of that at 25nA. However, the discharge capacity of the 773K-film was ca. 10% smaller than that of the film annealed at 873K, indicating that annealing at 773K is slightly insufficient to obtain well-crystallized LiFePO4. From these results, it was concluded that a point of optimization between high rate capability and capacity would be found between 773 and 873K. [Copyright &y& Elsevier]

An electrochemically stable and cobalt-free cathode material is prepared by impregnating Li 2 MnO 3 with nickel nitrate and subsequent calcination at 650 °C. X-ray diffraction and scanning electron microscopy reveal a phase pure material with a homogenous distribution of nickel over the particle surface. Structural changes related to the treatment before and after cycling as well as electrochemical performance are investigated. The surface modified samples exhibit improved cycling stability and rate capability. In particular, the material with a nickel content of 5.7 wt% shows 173 mAh g −1 at rate C/10 and 104 mAh g −1 at rate 3C. Furthermore, a constant capacity of 155 mAh g −1 is obtained at rate C/5. Derivative plots of galvanostatic curves in combination with Raman spectroscopy depict a reduced transition from a layered to spinel-like structure compared with pristine Li 2 MnO 3 , while ICP measurements reveal a drastically decreased dissolution of manganese. [ABSTRACT FROM AUTHOR]

Abstract: The structure and ionic conductivity of a lithium-ion conductive Li–Al–Ti–P–O-type glass ceramic (LATP) was studied by means of powder X-ray diffraction, transmission electron microscopy, and broadband impedance spectroscopy. The results were compared to a Li1.5Al0.5Ge1.5P3O12 (LAGP) ceramic. While the grain conductivity of LATP is higher than that of LAGP, the total conductivity of LATP is lower due to a large grain boundary resistance. The grain boundary resistance of LATP is characterized by a slightly higher activation energy and a slightly higher pre-exponential factor than the grain resistance. Our results indicate that the origin of the grain boundary resistance in these fast lithium ion conductors is clearly distinct from oxide ion conductors. [Copyright &y& Elsevier]

Abstract: Thin films of LiNi0.5Mn1.5O4 (LNMO) were prepared on gold-coated stainless steel substrates via a poly(vinylpyrrolidone)-based sol-gel process. Films with a thickness in the range of 1μm were found to exhibit a capacity close to the theoretical one. The formation of interlayers (i) between the LNMO films and the LP30 electrolyte (mixture of dimethyl carbonate (DMC) and ethylene carbonate (EC) (1:1 v/v) containing 1 mol·l−1LiPF6) and (ii) between the LNMO films and the gold-coated substrate was studied by means of electrochemical impedance spectroscopy (EIS), time-of-flight secondary-ion mass-spectrometry (ToF-SIMS), and scanning transmission electron microscopy together with energy dispersive X-ray spectroscopy (STEM/EDX). The combination of these methods turns out to be very powerful for understanding the chemical composition and properties of interlayers and for identifying the origin of semicircles in Nyquist impedance plots. At the LNMO/LP30 interface, we observe an interlayer (solid electrolyte interface, SEI) with a thickness of about 50 nm, while at the LNMO/gold interface, a mixed oxide layer with a thickness in the range of 250nm is found. The mixed oxide layer is caused by diffusion of Cr and Ni from the stainless steel through the gold layer. While the LNMO/LP30 interlayer contributes significantly to the interfacial impedance, the impedance of the LNMO/gold interlayer seems to be negligible, despite its larger thickness. [Copyright &y& Elsevier]