The structural behavior of electrochemically delithiated LixNi0.8Co0.15Al0.05O2 (x<1) battery cathodes

A full series of variously delithiated LixNi0.8Co0.15Al0.05O2 (NCA) (x < 1) battery cathodes is extracted from cylinder Li-ion batteries of 18650-type, and structural studies of electrode materials are performed ex situ applying high-resolution neutron powder diffraction. A set of structural and microstructural parameters at different state-of-charges (SOC) is gathered from full-profile Rietveld refinements. Accurate cell metrics of the NCA lattice are obtained and compared for both, ex situ and operando modes of data collection. A detailed analysis of lithium occupancies and interatomic distances in the NCA cathode is carried out, revealing a shrinking material response of the NCA structure during delithiation, while the experimental quantification of Li/Ni cation mixing showed an SOC independent behavior. The observed deintercalation driven anisotropic broadening of the Bragg reflections in real-life NCA cathodes were analyzed and assigned to an increasing internal anisotropic microstrain, which is linked to the non-uniform distribution of Li in the structure of NCA, resulting in an unstable and unpredictable performance of LIBs. © 2023 Elsevier B.V.

Keywords

Cathodes, Lithium ion batteries, Lithium alloys, Electrochemistry, Bragg reflection, Structural chemical analysis, Neutron diffraction, Bragg reflection

Citation

Hölderle, T., Monchak, M., Baran, V., Dolotko, O., Bette, S., Mikhailova, D., Voss, A., Avdeev, M., Ehrenberg, H., Müller-Buschbaum, P., & Senyshyn, A. (2023). The structural behavior of electrochemically delithiated LixNi0.8Co0.15Al0.05O2 (x<1) battery cathodes. Journal of Power Sources, 564, 232799. doi:10.1016/j.jpowsour.2023.232799