Insights into Lithium Ion Battery Charging Mechanisms: Ex Situ Studies on NMC Materials
Authors: Glaszczka Alicja , Buchberger Dominika , Manippady Sai Rashmi , Winkowska-Struzik Magdalena , Struzik Michal , Czerwinski Andrzej 
Published: December 2024

Lithium-ion batteries are crucial in modern energy storage systems, and their performance is heavily influenced by the properties of the positive electrode materials they employ. Nickel-rich layered oxide cathodes, such as NMC811 (LiNi0.8Mn0.1Co0.1O2) and NMC622 (LiNi0.6Mn0.2Co0.2O2), have received significant attention due to their high energy density and potential for enhancing battery performance[1]. Understanding the structural and chemical changes occurring within these cathodes during charging is essential for optimizing LIB performance and longevity. Raman mapping and X-ray diffraction (XRD) can be employed as powerful analytical techniques to probe the structural and chemical changes occurring within the cathode materials. Raman spectroscopy provides insights into the evolution of the cathode's local structure, phase transitions, and chemical composition, while XRD enables the determination of crystallographic changes and phase transitions. Thus far, Raman spectroscopy mapping has been employed to differentiate between charged and discharged regions, but transient states have not been indicated[2,3]. Regarding X-ray diffraction, the research primarily concentrated on in situ investigations, conducting measurements while the cell was in operation[4].

In this study, we present ex situ investigations employing Raman mapping and X-ray diffraction (XRD) techniques to clarify the charging mechanisms of NMC811 and NMC622 cathodes. Since lithium ion batteries mainly use a charging method based on a constant current followed by a constant voltage[5], we applied a similar sample preparation technique based on this typical charging procedure (CCCV). The combination of ex situ studies based on Raman spectroscopy and XRD gives insight into the phenomena occurring in NMC materials during cell charging and consequences for its structure stability. By analyzing samples at different SOC, we aim to clarify the impact of cycling on the structural integrity, phase evolution, and chemical composition of NMC811 and NMC622 cathodes. Specifically, we investigate how the cathode materials evolve in response to lithium-ion insertion and extraction processes during charge and discharge cycles. Additionally, we focus on the charging strategies employed, emphasizing the influence of charging protocols on the structural stability and electrochemical performance of the cathode materials. Understanding the relationship between charging protocols and cathode degradation is crucial for optimizing battery cycling protocols to enhance performance and prolong battery lifespan. Our findings provide valuable insights into the structural changes of NMC811 and NMC622 cathodes under selected cycling conditions, guiding the development of strategies to mitigate possible degradation and improve the overall performance and durability of nickel-rich NMC-based lithium-ion batteries. This work was funded by the National Center for Science in Poland through the Sonata BIS 11 programme (No. UMO-2021/42/E/ST5/00390).

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