![]() However, their high-voltage instability (e.g., > 4.3 V vsLi) limited their usable capacities corresponding to about 60 – 70 % of theoretical capacities. Ni-rich LiNi 1-xCo x/2Mn x/2O 2 layered materials have been widely adopted as cathodes for current electric vehicles (EVs) due to their high gravimetric and volumetric energy densities. Our findings suggest that limiting the bonding temperature and avoiding CO 2 in the sintering environment can help to remedy the interfacial degradation. The interfacial resistance for Li transfer, measured by electrochemical impedance spectroscopy, increases significantly upon the onset and evolution of the detected interface chemistry. By analyzing spectroscopy results along with X-ray diffraction, we identified Li 2CO 3, La 2Zr 2O 7, and La(Ni,Co)O 3 as the secondary phases that formed at 700 ☌. We found that the Ni and Co chemical environments change already at moderate temperatures, on-setting from 500 ☌ and becoming especially prominent at 700 ☌. The thin-film cathode approach enabled us to use interface-sensitive techniques such as X-ray absorption spectroscopy in the near-edge as well as the extended regimes and identify the onset of detrimental reactions. We prepared model systems by depositing thin-film NMC622 cathode layers on LLZO pellets. Herein, we assessed the interfacial more » reactions between LiNi 0.6Mn 0.2Co 0.2O 2 (NMC622) and Li 7La 3Zr 2O 12 (LLZO) as a function of temperature in air. It is necessary to find out which phases arise as a result of interface sintering and evaluate their effect on electrochemical properties. Many solid electrolyte and cathode materials react to form secondary phases. Sintering at elevated temperature is needed in order to get good contact between the ceramic solid electrolyte and oxide cathodes and thus to reduce contact resistances. A challenge to implement them is the high resistances, especially at the solid electrolyte interface with the cathode. Solid-state batteries offer higher energy density and enhanced safety compared to the present lithium-ion batteries using liquid electrolytes. Furthermore, this work highlights the importance of understanding the process-structure-property relationships and may guide the synthesis of other SC Ni-rich cathode = , SC-LiNi 0.6Mn 0.2Co 0.2O 2 materials prepared via TSS exhibit large grain size (~4 μm), a low degree of cation mixing (~0.9%), and outperform the control samples prepared by the conventional sintering method. A high-temperature sintering is first used for a short period of time to increase grain size and then the reaction temperature is lowered and kept constant for a longer period of time to improve structural ordering and complete the lithiation process. Here we report a temperature-swing sintering (TSS) strategy with two isothermal stages that fulfils the needs for grain growth and structural ordering sequentially. High temperature promotes grain growth but induces cation mixing that negatively impacts the electrochemical performance. However, the preparation of large-size yet high performance SC-NMC particles faces a challenge in choosing a suitable temperature for sintering. It is favorable to further increase the grain size of SC-NMC particles to achieve a higher volumetric energy density and minimize surface-related degradations. Single-crystal lithium-nickel-manganese-cobalt-oxide (SC-NMC) has recently emerged as a promising battery cathode material due to its outstanding cycle performance and mechanical stability over the tradional polycrystalline NMC.
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