Tracing structural changes in energy materials: A novel multi sample capillary setup for in house powder X‐ray diffraction

Lithium ion batteries (LIBs) are currently a major subject of applied electrochemical research as there is a fast growing demand of electrochemical energy storage, driven by the transformation of the automotive sector and the expansion of renewable energies. One of the key strategies to improve LIBs is the optimization of the cathode active materials (CAMs). Therefore, in order to find structure property relations, both crystallographic and electrochemical properties need to be investigated and well understood. However, standard laboratory powder X-ray diffraction (PXRD) possibly comes to its limit when minor structural variations such as atomic defects, cation order, or minor impurity phases are addressed. In order to focus on such minor structural changes and to find decisive differences in crystalline properties of battery materials, a multi-sample capillary setup for a multipurpose in-house PXRD setup was developed. The latter is made up from a six-circle diffractometer, a microfocus molybdenum rotating anode, and a 2D area detector. The capillary spinner itself is made from commercial components and simple custom-made adapters. A goniometer head is installed on a rotary module and sample spinning is enabled by a 12 V gear motor. Mounted on a xyz-stage of the diffractometer, the position of the rotating capillary exposed to the primary beam can be varied while remaining perfectly aligned in the center of the diffractometer. Hence, by packing up to 10 different powder samples separated from each other into a single glass capillary, subsequent measurements of all samples can be carried out without remounting or readjustment. Within a series of samples, the setup is extremely reliable, precise, and accurate, while errors originating from sample displacement, misalignment, or calibration are minimized

Enhancing the Stability of LiNio.5_{o.5}0Mn1.5_{1.5}O4_{4} by Coating with LiNbO3_{3} Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method

LiNbO$_{3}$-coated LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role

On the Composition of LiNi0.5_{0.5}Mn1.5_{1.5}O4_4 Cathode Active Materials

LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO) cathode active materials for lithium-ion batteries have been investigated for over 20 years. Despite all this effort, it has not been possible to transfer their favorable properties into applicable, stable battery cells. To make further progress, the research perspective on these spinel type materials needs to be updated and a number of persisting misconceptions on LNMO have to be overcome. Therefore, the current knowledge on LNMO is summarized and controversial points are addressed by detailed considerations on the composition and crystallography of LNMO. The findings are supported by an in-situ high temperature X-ray diffraction study and the investigation of four different types of LNMO materials, including Mn(III) rich ordered LNMO, and disordered LNMO with low Mn(III) content. It is shown that the importance of cation order is limited to a small composition range. Furthermore, new evidence contradicting the idea of oxygen defects in LNMO is presented and an enhanced classification of LNMO based on the Ni content of the spinel phase is proposed. Moreover, a balanced chemical equation for the formation of LNMO is presented, allowing for comprehensive calculations of key properties of LNMO materials. Finally, suitable target compositions and calcination programs are suggested to obtain better LNMO materials

Instantaneous Surface Li3_{3}PO4_{4} Coating and Al–Ti Doping and Their Effect on the Performance of LiNi0.5_{0.5}Mn1.5_{1.5}O4_{4} Cathode Materials

Using hydrogen peroxide (H2O2), a novel approach was applied for the synthesis of LiNi0.5Mn1.5O4 (LNMO) coated with Li3PO4 and doped with Al3+ and Ti4+ ions. The reaction between LNMO and H2O2 resulted in particles with a partially damaged surface. If the same reaction is done in the presence of lithium, aluminum, titanium, and phosphate ingredients, then all particle facets are intact and show no sign of destruction. It appears that the H2O2 decomposition activates the LNMO surface, generating perfect conditions for the homogeneous deposition of the Li, Al, Ti, and phosphate ions. Electrochemical investigations show a very slow fading process during the cycling, and even after more than 500 cycles, the obtained cathode material shows a high specific capacity of 127 mAh g–1 (at 1 C) (∼98% capacity retention) and an excellent Coulombic efficiency (99.5%)

A multipurpose laboratory diffractometer for operando powder X-ray diffraction investigations of energy materials

Laboratory X-ray diffractometers are among the most widespread instruments in research laboratories around the world and are commercially available in different configurations and setups from various manufacturers. Advances in detector technology and X-ray sources push the data quality of in-house diffractometers and enable the collection of time-resolved scattering data during operando experiments. Here, the design and installation of a custom-built multipurpose laboratory diffractometer for the crystallographic characterization of battery materials are reported. The instrument is based on a Huber six-circle diffractometer equipped with a molybdenum microfocus rotating anode with 2D collimated parallel-beam X-ray optics and an optional two-bounce crystal monochromator. Scattered X-rays are detected with a hybrid single-photon-counting area detector (PILATUS 300K-W). An overview of the different diffraction setups together with the main features of the beam characteristics is given. Example case studies illustrate the flexibility of the research instrument for time-resolved operando powder X-ray diffraction experiments as well as the possibility to collect higher-resolution data suitable for diffraction line-profile analysis

Coating versus Doping: Understanding the Enhanced Performance of High‐Voltage Batteries by the Coating of Spinel LiNi0.5_{0.5}Mn1.5_{1.5}O4_4 with Li0.35_{0.35}La0.55_{0.55}TiO3_3

Li$_{0.35}$La$_{0.55}$TiO$_3$ (LLTO) coated spinel LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO) as cathode material is fabricated by a new method using hydrogen-peroxide as activating agent. The structure of the obtained active materials is investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes are probed by the charge–discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles is investigated by the SEM, which shows a fully dense and homogeneous coating (thickness ≈ 7 nm, determined by TEM) on the surface of active material. XRD studies of the coated active materials treated at different temperatures (between 300 °C and 1000 °C) reveal expansion or contraction of the unit cell in dependence of the coating concentration and degree of Ti diffusion. It is concluded, that for the LNMO particles calcined at low temperatures, the LLTO coating layer is still intact and protects the active material from the interaction with the electrolyte. However, for the coated particles treated at high temperatures, Ti ions migrate into the structure of LNMO during the modification process between 500 °C and 800 °C, resulting in “naked” and unprotected particles

Enabling Long‐term Cycling Stability of Na₃V₂(PO₄)₃ /C vs . Hard Carbon Full‐cells

Sodium-ion batteries are becoming an increasingly important complement to lithium-ion batteries. However, while extensive knowledge on the preparation of Li-ion batteries with excellent cycling behavior exists, studies on applicable long-lasting sodium-ion batteries are still limited. Therefore, this study focuses on the cycling stability of batteries composed of Na3V2(PO4)3/C based cathodes and hard carbon anodes. It is shown that full-cells with a decent stability are obtained for ethylene carbonate/propylene carbonate electrolyte and the conducting salt NaPF6. With cathode loadings of 1.2 mAh/cm2, after cell formation discharge capacities up to 92.6 mAh/g are obtained, and capacity retentions >90 % over 1000 charge/discharge cycles at 0.5 C/0.5 C are observed. It is shown that both, the additive fluoroethylene carbonate and impurities in the electrolyte, negatively affect the overall discharge capacity and cycling stability and should therefore be avoided. Remarkably, the internal resistances of well-balanced and well-built cells did not increase over 1500 cycles and 5 months of testing, which is a very promising result regarding the possible lifespan of the cells. The initial loss of active sodium ions in hard carbon remains a major problem, which can only be partially reduced by proper balancing

Enabling Long-term Cycling Stability of Na3V2(PO4)3/C vs. Hard Carbon Full-cells

<p>Battery cycling data to research paper: </p><p>https://doi.org/10.26434/chemrxiv-2023-jf6mq </p><p>for questions on the data files, please contact pirmin[dot]stueble[at]kit.edu or anna[dot]smith[at]kit.edu</p&gt

Enhancing the Stability of LiNi_0.5Mn_1.5O₄ by Coating with LiNbO₃ Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method

LiNbO3-coated LiNi0.5Mn1.5O4 spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi0.5Mn1.5O4 particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role