Atomic Layer Deposition Derived Zirconia Coatings on Ni‐Rich Cathodes in Solid‐State Batteries: Correlation Between Surface Constitution and Cycling Performance

Protective coatings are required to address interfacial incompatibility issues in composite cathodes made from Ni-rich layered oxides and lithium thiophosphate solid electrolytes (SEs), one of the most promising combinations of materials for high energy and power density solid-state battery (SSB) applications. Herein, the preparation of conformal ZrO2 nanocoatings on a LiNi0.85Co0.10Mn0.05O2 (NCM85) cathode-active material (CAM) by atomic layer deposition (ALD) is reported and the structural and chemical evolution of the modified NCM85 upon heat treatment—a post-processing step often required to boost battery performance—is investigated. The coating properties are shown to have a strong effect on the cyclability of high-loading SSB cells. After mild annealing (≈400 °C), the CAM delivers high specific capacities (≈200 mAh g−1 at C/10) and exhibits improved rate capability (≈125 mAh g−1 at 1C) and stability (≈78% capacity retention after 200 cycles at 0.5C), enabled by effective surface passivation. In contrast, annealing temperatures above 500 °C lead to the formation of an insulating interphase that negatively affects the cycling performance. The results of this study demonstrate that the preparation conditions for a given SE/CAM combination need to be tailored carefully and ALD is a powerful surface-engineering technique toward this goal

Influence of NCM Particle Cracking on Kinetics of Lithium-Ion Batteries with Liquid or Solid Electrolyte

In liquid electrolyte-type lithium-ion batteries, Nickel-rich NCM (Li$_{1+x }$(Ni$_{1−y−z}$Co$_{ y}$Mnz)$_{1−x}$O$_{2}$) as cathode active material allows for high discharge capacities and good material utilization, while solid-state batteries perform worse despite the past efforts in improving solid electrolyte conductivity and stability. In this work, we identify major reasons for this discrepancy by investigating the lithium transport kinetics in NCM-811 as typical Ni-rich material. During the first charge of battery half-cells, cracks form and are filled by the liquid electrolyte distributing inside the secondary particles of NCM. This drastically improves both the lithium chemical diffusion and charge transfer kinetics by increasing the electrochemically active surface area and reducing the effective particle size. Solid-state batteries are not affected by these cracks because of the mechanical rigidity of solid electrolytes. Hence, secondary particle cracking improves the initial charge and discharge kinetics of NCM in liquid electrolytes, while it degrades the corresponding kinetics in solid electrolytes. Accounting for these kinetic limitations by combining galvanostatic and potentiostatic discharge, we show that Coulombic efficiencies of about 89% at discharge capacities of about 173 mAh g$_{1+x }$NCM$^{-1}$ can be reached in solid-state battery half-cells with LiNi$_{0.8}$Co$_{0.1}$Mn$_{0.1}$O$_{2}$ as cathode active material and Li$_{6}$PS$_{5}$Cl as solid electrolyte

Cathode electrolyte reaction in the spotlight: Study on degradation processes in lithium ion batteries using the example of Al2O3- and CeO2-coated NCM111 thin film model cathodes

Die Weiterentwicklung von Lithium-Ionen-Batterien (LIB) und deren Materialien ist ein entscheidender Faktor für die Nutzung mobiler Elektronik. Während des Lade- und Entladevorgangs einer LIB kommt es jedoch zu Nebenreaktionen an Anode und Kathode. Auf Anodenseite sind diese Nebenreaktionen inzwischen weitreichend untersucht und können gezielt genutzt werden, um die Grenzflächeneigenschaften zu beeinflussen. Für Kathodenmaterialien (engl. cathode active material, CAM) sind diese unerwünschten Nebenreaktionen noch nicht vollumfänglich untersucht. Ein Dünnschichtmodellsystem auf entsprechendem Kathodenmaterial (Lithium-Nickel-Cobalt-Mangan-Oxid, kurz: NCM) ist daher notwendig, um eine genaue Analyse der Grenzflächenreaktionen durchzuführen. So lassen sich auch Optimierungen der Oberfläche, wie beispielsweise Schutzbeschichtungen, und deren Einfluss auf die Reaktionen an der Grenzfläche untersuchen. In dieser Arbeit wurden Dünnschichtkathoden basierend auf dem Material LiNi0,33Co0,33Mn0,33O2 (kurz: NCM111) abgeschieden und mittels Atomlagenabscheidung (engl. atomic layer deposition, ALD) beschichtet. Ausgangspunkt der Abscheidung des Kathodenmaterials war eine Sol-Gel-basierte Lösung aus Metallnitraten in entsprechender Stöchiometrie, die mittels Rotationsbeschichtung (engl. spin coating) auf ein platinbeschichtetes Saphirsubstrat aufgebracht wurde. Die strukturelle Analyse der Dünnschichten nach der thermischen Behandlung bestätigte, dass es sich um NCM111 mit zufälliger kristalliner Orientierung handelt, vergleichbar zur kristallinen Orientierung in NCM111-Partikeln. Auch die elektrochemischen Untersuchungen zeigen, dass die hergestellten Dünnschichten in ihren elektrochemischen Daten qualitativ vergleichbar sind zu kommerziellen Kathodenmaterialien. Oberflächenuntersuchungen an unbeschichteten Dünnschichtkathoden bestätigten die Korrosion der Übergangsmetalle aus dem Kathodenmaterial und die Degradation der Elektrolytbestandteile. Bei Al2O3-beschichteten Dünnschichtkathoden konnte eine Fluorierung der Beschichtung nachgewiesen werden, welche die Oberfläche gegen weitere Korrosion passivierte, was vorherige thermodynamische Abschätzungen bestätigte. Zudem konnten Elektrolytzerfallsprodukte nachgewiesen werden, die die Leistung der Zelle verbessern. Ähnliche thermodynamische Abschätzungen wurden für CeO2-beschichtete Dünnschichtkathoden durchgeführt. Oberflächenuntersuchungen mittels Röntgenphotoelektronenspektroskopie (engl. X-ray photoelectron spectroscopy, XPS) zeigten, dass die Beschichtung mit CeO2 anfälliger ist gegenüber Korrosion durch HF und sich im Verlauf mehrerer Zyklen abbaut. Gemeinsam mit Daten, die aus der Impedanz-Analyse der Schichten gewonnen wurden, konnte zudem der Einfluss der Schutzschicht auf die ionische Leitfähigkeit des Gesamtsystems näher beleuchtet werden. So konnte eine Methodik entwickelt werden, mit der zukünftige Beschichtungsmaterialien systematisch untersucht werden können. Durch die Kombination aus struktureller Oberflächencharakterisierung und elektrochemischen Messmethoden ist eine sich gegenseitig ergänzende Analytik der Grenzflächenprozesse möglich. So können neuartige Beschichtungsmaterialien nach gleicher Methodik untersucht und auf ihre Einsatzfähigkeit in LIB getestet werden.Bundesministerium für Bildung und Forschung (BMBF); ROR-ID:04pz7b18

The Effect of Water Contamination on the Transition Metal Dissolution in Water-enriched Electrolyte a Mechanistic Insight into a new Type of Dissolution

Transition metal (TM) dissolution from cathode active materials is a major factor in accelerating Li-ion battery aging. Residual moisture in the battery is suspected to enhance this degradation mechanism by reacting with the electrolyte, generating acidic species and other decomposition products. In previous studies, we presented a method to track the dissolution in real-time. In the present study, we demonstrate with this method the effect of water on the dissolution of TMs from LiNi0.33Co0.33Mn0.33O2 (NCM111) and LiCoO2 (LCO) used as thin-film model cathodes. We show highly increased dissolution rates in electrolytes with 100 and 1000 ppm of water added and a concomitant decline in electrode performance. More interestingly, we observe a novel hitherto undisclosed dissolution phenomenon during the cathodic back scan and with that give insight into a new dissolution mechanism. This study further reveals that the impact of moisture on TM dissolution may be mitigated by replacing the standard conductive salt, LiPF6, with hydrolysis-stable LiC2NO4F6S2 (LiTFSI)

Correlation between Surface Reactions and Electrochemical Performance of Al2O3- and CeO2-Coated NCM Thin Film Cathodes

Depositing ultrathin oxide coatings has been proven a successful approach to stabilize the surface of LiNixCoyMnzO2 active cathode material in lithium-ion batteries (LIB). The beneficial effect of Al2O3 coatings arises at least partly from spontaneous reactions between coating and liquid electrolyte. However, it remains unclear if comparable surface reactions occur for other oxide coatings. One difficulty is the characterization of reaction products at the cathode–electrolyte interface due to the multi-phase properties of composite cathodes. Here, thin films are utilized as model systems to correlate surface reactions with the performance of Al2O3- and CeO2-coated nickel cobalt manganese oxides (NCM). Electrochemical characterization confirms that an Al2O3 coating improves long-term cycling stability, while CeO2-coated thin films perform even worse than uncoated counterparts. The analysis of the surface reaction products using X-ray photoelectron spectroscopy shows that both coatings are fluorinated upon contact with liquid electrolyte in agreement with thermodynamic considerations. The fluorinated Al2O3 coating is stable during cycling, resulting in the improved cell performance. In contrast, the fluorinated CeO2 coating changes chemical composition, facilitating corrosion of the NCM surface. The results demonstrate the importance of a detailed analysis of surface reactions to evaluate the suitability of ultrathin oxide layers as protective coatings for LIBs.Deutsche Forschungsgemeinschaft (DFG); ROR-ID:018mejw6

Correlation between Surface Reactions and Electrochemical Performance of Al2O3‐ and CeO2‐Coated NCM Thin Film Cathodes

Abstract Depositing ultrathin oxide coatings has been proven a successful approach to stabilize the surface of LiNixCoyMnzO2 active cathode material in lithium‐ion batteries (LIB). The beneficial effect of Al2O3 coatings arises at least partly from spontaneous reactions between coating and liquid electrolyte. However, it remains unclear if comparable surface reactions occur for other oxide coatings. One difficulty is the characterization of reaction products at the cathode–electrolyte interface due to the multi‐phase properties of composite cathodes. Here, thin films are utilized as model systems to correlate surface reactions with the performance of Al2O3‐ and CeO2‐coated nickel cobalt manganese oxides (NCM). Electrochemical characterization confirms that an Al2O3 coating improves long‐term cycling stability, while CeO2‐coated thin films perform even worse than uncoated counterparts. The analysis of the surface reaction products using X‐ray photoelectron spectroscopy shows that both coatings are fluorinated upon contact with liquid electrolyte in agreement with thermodynamic considerations. The fluorinated Al2O3 coating is stable during cycling, resulting in the improved cell performance. In contrast, the fluorinated CeO2 coating changes chemical composition, facilitating corrosion of the NCM surface. The results demonstrate the importance of a detailed analysis of surface reactions to evaluate the suitability of ultrathin oxide layers as protective coatings for LIBs