Hermann Tempel

Influence of microstructure and AlPO4 secondary-phase on the ionic conductivity of Li1.3Al0.3Ti1.7(PO4))3 solid-state electrolyte

A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li1.3Al0.3Ti1.7(PO4)3 (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77g⋅cm−3) with an ionic conductivity of 1.88×10−4 S⋅cm−1 (at 30∘C) was reached at a sintering temperature of 1100∘C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO4 secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO4 increased. For sintering temperatures above 1000∘C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructur...

Observing different modes of mobility in lithium titanate spinel by nuclear magnetic resonance

Lithium titanate (LTO) is a spinel material that is able to reversibly intercalate Li ions with minimal changes of the unit cell dimensions (“zero-strain”), making it an attractive choice as anode material for Li ion batteries. However, the nature of the Li transport in this material is still not fully understood. Here, the Li mobility in Li4+xTi5O12 with x = 0 and x ≈ 1.6 is investigated. By regularized inversion of nuclear magnetic resonance (NMR) relaxation and spin alignment echo (SAE) data and supported by DFT simulations, solid-state NMR spectra were analyzed as a function of the respective relaxation times and correlation time constants. A clear correlation between mobility and NMR spectral features was observed, suggesting the presence of local domains with high Li ion mobility. The long-range mobility is limited by the much slower hopping between such domains and appears to be faster for either larger or less ordered local domains. For x ≈ 1.6, spectral features indicate the formation of separate stoichiometric and overlithiated phases rather than a solid solution, yet no segregation into a fast and a slow component was observed in the relaxation and in the SAE dimension, which points towards an entangling of the two phases on a microscopic scale.

Monolithic All-Phosphate Solid-State Lithium-Ion Battery with Improved Interfacial Compatibility

High interfacial resistance between solid electrolyte and electrode of ceramic all-solid-state batteries is a major reason for the reduced performance of these batteries. A solid-state battery using a monolithic all-phosphate concept based on screen printed thick LiTi2(PO4)3 anode and Li3V2(PO4)3 cathode composite layers on a densely sintered Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte has been realized with competitive cycling performance. The choice of materials was primarily based on the (electro-)chemical and mechanical matching of the components instead of solely focusing on high-performance of individual components. Thus, the battery utilized a phosphate backbone in combination with tailored morphology of the electrode materials to ensure good interfacial matching for a durable mechanical stability. Moreover, the operating voltage range of the active materials matches with the intrinsic electrochemical window of the electrolyte which resulted in high electrochemical stability. A highly competitive discharge capacity of 63.5 mAh g-1 at 0.39 C after 500 cycles, corresponding to 84% of the initial discharge capacity, was achieved. The analysis of interfacial charge transfer kinetics confirmed the structural and electrical properties of the electrodes and their interfaces with the electrolyte, as evidenced by the excellent cycling performance of the all-phosphate solid-state battery. These interfaces have been studied via impedance analysis with subsequent distribution of relaxation times analysis. Moreover, the prepared solid-state battery could be processed and operated in air atmosphere owing to the low oxygen sensitivity of the phosphate materials. The analysis of electrolyte/electrode interfaces after cycling demonstrates that the interfaces remained stable during cycling.

Influence of microstructure and AlPO4 secondary-phase on the ionic conductivity of Li1.3

A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li1.3Al0.3Ti1.7(PO4)3 (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77g⋅cm−3) with an ionic conductivity of 1.88×10−4 S⋅cm−1 (at 30∘C) was reached at a sintering temperature of 1100∘C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO4 secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO4 increased. For sintering temperatures above 1000∘C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructur...

Transformation of Carbon-Supported Pt-Ni Octahedral Electrocatalysts into Cubes: Toward Stable Electrocatalysis

Octahedral Pt-Ni catalyst nanoparticles (NPs) are predicted to exhibit high activity for the oxygen reduction reaction. However, until now this class of catalysts has been limited by its long-term performance, as a result of compositional and morphological instabilities of the NPs. In situ transmission electron microscopy (TEM) is a powerful technique for understanding morphological and compositional evolution under controlled conditions. It is of great importance to study the evolution of the morphology and elemental distribution in bimetallic NPs and their interaction with the support in reducing and oxidizing treatments at the atomic scale for the rational design of catalysts. Here, we use in situ TEM to follow dynamic changes in the NP morphology, faceting and elemental segregation under working conditions in previously unreported Pt-Ni core-shell octahedral structures. We follow changes in the Pt-Ni catalyst from a segregated structure to an alloyed shell configuration and then a more spherical structure as a function of temperature under reducing conditions. Exposure to an oxidizing environment then leads to oxidation of the C support, while the spherical NPs undergo a cycle of transformations into cubic NPs followed by the reaction to spherical NPs. The formation of the cubic NPs results from CO formation during C oxidation, before it is finally oxidized to CO2. Our observations may pave the way towards the design of optimized structure-stability electrocatalysts and highlight the importance of TEM visualization of degradation and transformation pathways in bimetallic Pt-Ni NPs under reducing and oxidizing conditions.

Self-standing NASICON-type electrodes with high mass loading for fast-cycling all-phosphate sodium-ion batteries

A scalable strategy has been realized to produce anodic NaTi2(PO4)3 and cathodic Na3V2(PO4)3 supported on carbon nanotube fabrics (CNFs) as binder-free, metal current collector-free, carbon additive-free, bendable and self-standing electrodes for sodium-ion batteries. The NaTi2(PO4)3 and Na3V2(PO4)3 particles are not only anchored on the surface of the CNFs but also uniformly embedded in the framework of the CNFs via a two-step coating process followed by annealing treatment. In the relevant voltage range, the high electrochemical stability of the 3D electron conduction network of carbon nanotubes in the self-standing electrodes was confirmed by in situ Raman spectroscopy. Both electrodes possessed a thickness of around 130 μm and a high mass loading of greater than 7.5 mg cm−2 and exhibited a high specific capacity, high rate capability and long lifespan in both half cells and all-phosphate full cells. The all-phosphate full cells delivered more than half of their theoretical capacity even at a high current rate of 100C. Besides, a capacity retention of 75.6% over 4000 cycles at a rate of 20C was achieved. The reason for the capacity fade in the full cell during long-term cycling was the formation of a solid electrolyte interphase layer, as was indicated by XRD, TEM and in operando NMR measurements. Furthermore, the promising practical possibilities of the electrodes and all-phosphate sodium-ion battery were demonstrated by a prototype flexible pouch cell and by stacking multiple electrodes in a laboratory-scale battery.

Influence of microstructure and AlPO 4 secondary-phase on the ionic conductivity of Li

A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li1.3Al0.3Ti1.7(PO4)3 (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77g⋅cm−3) with an ionic conductivity of 1.88×10−4 S⋅cm−1 (at 30∘C) was reached at a sintering temperature of 1100∘C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO4 secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO4 increased. For sintering temperatures above 1000∘C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructur...