Performance Enhancement of Nickel Manganese Cobalt Oxide Cathodic Material for Solid-State Battery Technology by Surface Engineering
Authors: Melgari Paolo , Bridgewater Grace , Copley Mark , Dogaru Daniela 
Published: February 2024

Batteries as any other electronic devices are affected by parasitic phenomena including physical processes and chemical reactions occurring within the battery materials as well as their interfaces. The phenomena lead to degradation in performance, impose operation restrictions and potentially make devices unsafe.
Solid-state, lithium-metal-based, batteries show promise to meet electric vehicle market requirements, but technical challenges to overcome rapid degradation and cost-effective processing remains. Cathode/electrolyte interfacial side reactions can lead to passivating layer formation, thus increasing cell resistance, unwanted additional overvoltage, and ultimately capacity loss. These phenomena are exacerbated in solid-to-solid contact between solid state electrolytes, active materials, and electronic conductive agents. Therefore, electrode manufacturing design is required to mitigate these issues.
Within this work we have evaluated Spray Drying (SD) and Atomic Layer Deposition (ALD) coating processes to engineer the cathode/ electrolyte interface of SSBs, thus improving performance and overall cell cycle life. Cathode materials coating is utilised as an effective strategy to mitigate the degradation of the interface. SD is classically utilised in the food and pharma industries, and it has recently been expanded to include the synthesis/shaping of battery electrode materials as a versatile and robust methodology that can be easily scaled up. ALD is a widely exploited technique in the semiconductor (SC) industry based on self-limiting chemical reactions to deposit stoichiometrically-fixed, defect-free and nanometric-thick materials on surfaces. As such, the application of ALD to coat powders in the battery community is innovative and currently under development.
Cathodic materials such as NMC (Nickel Manganese Cobalt Oxides) have been investigated, as the need for improving the capacity retention is strong for high-content (>80%) nickel cathodes. Indeed, ALD utilised to coat NMC powder provides a nanometric thick layer of a dielectric but ionic conductive metal oxide. Optimisation of aluminium oxide shell on a core of polycrystalline high nickel material has been investigated with surface engineering. In parallel, we have been exploring the benefit of SD to create an NMC811 powder showing a decorated structure using two different approaches. Indeed, we have either used preformed metal oxide nanoparticles dispersed in an NMC suspension or synthesised a metal oxide layer on top of the NMC in-situ by a chemical reaction during the spray process.
Morphological and chemical characterisation of the products have been crucial to develop the coating processes. Electrochemical Impedance Spectroscopy (EIS) probed the engineered cathode/ electrolyte interface within half- and full-coin cell configuration. Rate performance and long-term cycling evaluation has driven the design of an oxide-based lithium metal solid state battery.
Alumina coated powder NMC showed longer capacity retention than raw materials when tested in coin cell batteries. The cells were assembled using thin lithium metal anode, Lithium-Lanthanum Zirconium Oxide (LLZO) electrolyte, and surface-engineered NMC811 supported by aluminium current collector.

Key words:
Surface Engineering, Coatings, Solid-State Batteries (SSB), Spray Dry, Atomic Layer Deposition (ALD), Preformed Nanoparticles, Nickel Manganese Cobalt Oxide (NMC), NMC811, Lithium Lanthanum Zirconium Oxide (LLZO), Interfaces.

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