In-situ X-ray absorption spectroscopy analysis of capacity fade in nanoscale-LiCoO2

• Published in: Journal of solid state chemistry 2013-07, Vol.203, p.134-144
• Main Authors: Patridge, Christopher J., Love, Corey T., Swider-Lyons, Karen E., Twigg, Mark E., Ramaker, David E.
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Cathode; Complement; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Cycles; Delta mu; Exact sciences and technology; EXAFS; Fine structure; Materials science; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Other topics in nanoscale materials and structures; Physics; Reduction; SEI; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Surface; Surface chemistry; X-rays; XANES
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2013.04.008

The local structure of nanoscale (∼10–40nm) LiCoO2 is monitored during electrochemical cycling utilizing in-situ X-ray absorption spectroscopy (XAS). The high surface area of the LiCoO2 nanoparticles not only enhances capacity fade, but also provides a large signal from the particle surface relative to the bulk. Changes in the nanoscale LiCoO2 metal-oxide bond lengths, structural disorder, and chemical state are tracked during cycling by adapting the delta mu (Δμ) technique in complement with comprehensive extended X-ray absorption fine structure (EXAFS) modeling. For the first time, we use a Δμ EXAFS method, and by comparison of the difference EXAFS spectra, extrapolate significant coordination changes and reduction of cobalt species with cycling. This combined approach suggests Li–Co site exchange at the surface of the nanoscale LiCoO2 as a likely factor in the capacity fade and irreversible losses in practical, microscale LiCoO2. Electrochemical cycling of Li-ion batteries has strong impact on the structure and integrity of the cathode active material particularly near the surface/electrolyte interface. In developing a new method, we have used in-situ X-ray absorption spectroscopy during electrochemical cycling of nanoscale LiCoO2 to track changes during charge and discharge and between subsequent cycles. Using difference spectra, several small changes in Co-O bond length, Co-O and Co-Co coordination, and site exchange between Co and Li sites can be tracked. These methods show promise as a new technique to better understand processes which lead to capacity fade and loss in Li-ion batteries. [Display omitted] •A new method is developed to understand capacity fade in Li-ion battery cathodes.•Structural changes are tracked during Li intercalation/deintercalation of LiCoO2.•Surface structural changes are emphasized using nanoscale-LiCoO2 and difference spectra.•Full multiple scattering calculations are used to support Δμ analysis.