Influence of temperature on the aging behavior of 18650-type lithium ion cells: A comprehensive approach combining electrochemical characterization and post-mortem analysis

The understanding of the aging behavior of lithium ion batteries in automotive and energy storage applications is essential for the acceptance of the technology. Therefore, aging experiments were conducted on commercial 18650-type state-of-the-art cells to determine the influence of the temperature during electrochemical cycling on the aging behavior of the different cell components. The cells, based on Li(Ni0.5Co0.2Mn0.3)O2 (NCM532)/graphite, were aged at 20 °C and 45 °C to different states of health. The electrochemical performance of the investigated cells shows remarkable differences depending on the cycling temperature. At contrast to the expected behavior, the cells cycled at 45 °C show a better electrochemical performance over lifetime than the cells cycled at 20 °C. Comprehensive post-mortem analyses revealed the main aging mechanisms, showing a complex interaction between electrodes and electrolyte. The main aging mechanisms of the cells cycled at 45 °C differ strongly at contrast to cells cycled at 20 °C. A strong correlation between the formed SEI, the electrolyte composition and the electrochemical performance over lifetime was observed

Facile and General Synthesis of Thermally Stable Ordered Mesoporous Rare-Earth Oxide Ceramic Thin Films with Uniform Mid-Size to Large-Size Pores and Strong Crystalline Texture

We describe the general synthesis of submicrometer-thick rare-earth/lanthanide sesquioxide (RE₂O₃) films with tailorable pore and grain sizes via polymer templating of hydrated chloride salt precursors. Mesostructured RE₂O₃ (RE = Sm, Tb–Lu) ceramics with cubic pore symmetry and high surface area (<i>S</i>_BET ≥ 50 m² g^–1) were prepared using different diblock copolymer structure-directing agents and were characterized by a combination of electron microscopy, in situ and ex situ grazing incidence small-angle X-ray scattering, N₂ physisorption, X-ray photoelectron spectroscopy, X-ray diffraction including Rietveld refinement, and ultraviolet–visible spectroscopy. In the present work, we specifically focus on Dy₂O₃ and Yb₂O₃ and use both of these materials as model systems to study, among other things, the film formation and microstructure. Our research data collectively demonstrate that (1) record pore sizes of up to 42 nm in diameter can be achieved without the need for swelling agents, (2) the nanostructure can be preserved up to 1000 °C for the heavier oxides, (3) the sizes of the optical band gaps (4.9–5.6 eV) are comparable to those reported for single crystals, (4) the sol–gel-derived materials are single phase and adopt the <i>C</i>-type crystal structure, and (5) the grain growth is virtually linear, with domain sizes in the range of 3–16 nm. We also show that, except for Yb₂O₃, all of the samples have a fiber texture and the preferred orientation is significant in Sm₂O₃ and Lu₂O₃ films (March parameter <i>G</i>₂ < 0.1). Overall, the synthesis parameters described in this work provide a blueprint for the preparation of thermally stable rare-earth oxide ceramics with both a mesoporous morphology and iso-oriented nanocrystalline walls