Abstract
To obtain full advantage of state-of-the-art solid-state lithium-based batteries, produced by sequential deposition of high voltage cathodes and promising oxide-based electrolytes, the current collector must withstand high temperatures (>600 °C) in oxygen atmosphere. This imposes severe restrictions on the choice of materials for the first layer, usually the cathode current collector. It not only must be electrochemically stable at high voltage, but also remain conductive upon deposition and annealing of the subsequent layers without presenting a strong diffusion of its constituent elements into the cathode. A novel cathode current collector based on a Ni–Al–Cr superalloy with target composition Ni0.72Al0.18Cr0.10 is presented here. The suitability of this superalloy as a high voltage current collector was verified by determining its electrochemical stability at high voltage by crystallizing and cycling of LiCoO2 directly onto it.
Highlights
IntroductionTemperature for cathode materials such as LMNO18 and LiCoO2 (LCO),[19,20] and fast solid-state electrolytes such as the garnettype Li7La3Zr2O12 (LLZO) and perovskite-type Li0.17La0.61TiO3 (LLTO) are at least 700–750 C in order to get the desired phases and attain high ionic conductivity.[21,22,23,24] The commonly used CCs such as Al cannot withstand such high temperatures in an oxidizing atmosphere without melting or becoming highly insulating
All-solid-state lithium-based batteries (SSBs) are regarded as the next-generation energy storage solution to surpass the physicochemical limit on volumetric/gravimetric energy density and eliminate the risks from the liquid electrolyte.[1]
Stainless steels (SSs), on the other hand, are a tempting choice due to their oxidation resistance at high temperature, but it has been shown for LiMn2O4 that both Fe and Cr diffuse into the cathode degrading its performance.[25]
Summary
Temperature for cathode materials such as LMNO18 and LiCoO2 (LCO),[19,20] and fast solid-state electrolytes such as the garnettype Li7La3Zr2O12 (LLZO) and perovskite-type Li0.17La0.61TiO3 (LLTO) are at least 700–750 C in order to get the desired phases and attain high ionic conductivity.[21,22,23,24] The commonly used CCs such as Al cannot withstand such high temperatures in an oxidizing atmosphere without melting or becoming highly insulating. Stainless steels (SSs), on the other hand, are a tempting choice due to their oxidation resistance at high temperature, but it has been shown for LiMn2O4 that both Fe and Cr diffuse into the cathode degrading its performance.[25] Similar shortcomings are observed for LCO on SS and are reported in this work. Incorporation of Al into LCO begins already at 400 C, a er long annealing periods of 8 hours, while in Mn-based cathode materials Al does not diffuse in but results in the formation of the electrical insulator LiAlO2 at 600 C.29. The simultaneous incorporation of Cr and Al in a Ni superalloy has a synergetic effect on the oxidation resistance, decreasing the minimum amount of these alloying elements required to prevent bulk oxidation compared to Ni–Cr and Ni–Al binary alloys.[31] The tunable composition can enlarge the electrochemical window together with a reduced diffusion of Cr and Al into the cathode at 700 C. We demonstrate a thermally stable Ni–Al–Cr current collector on which LCO can readily crystallize, achieving 80% of the theoretical capacity even without major optimization of the LCO deposition conditions
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