Rate dependence of the reaction mechanism in olivine NaFePO4 Na‐ion cathode material. (10th May 2018)

• Record Type: Journal Article
• Authors: Saurel, Damien; Galceran, Montserrat; Reynaud, Marine; Anne, Henri; Casas‐Cabanas, Montse
• Is Part Of: International journal of energy research. Volume 42:Number 10(2018)
• Page Start: 3258
• Page End: 3265
• Publication Date: 2018-05-10
• Subjects: NaFePO4 -- Na‐ion batteries -- olivine -- operando XRD -- reaction mechanism; Power resources -- Periodicals; Power (Mechanics) -- Periodicals; Power resources -- Research -- Periodicals; 621.042
• DOI: 10.1002/er.4078
• Languages: English
• ISSNs: 0363-907X

Abstract

Summary: When electrode materials are driven away from equilibrium conditions, significant differences occur in their (dis)charge mechanism. In this paper, the changes in the phase transformations of the olivine NaFePO4 are examined as a function of the cycling rate from the thorough analyses of both the voltage‐composition profiles of galvanostatic cycling, and operando laboratory and synchrotron X‐ray diffraction experiments. While the charge mechanism remains unchanged at all C‐rates, high cycling rates enable to unveil 2 concomitant biphasic reactions appearing as a 3‐phase state at lower rates. This finding allows rationalising the asymmetries observed at low rates, which are rooted in different reaction kinetics. Abstract : The occurrence of a 3‐phase region has been found to be the result of 2 consecutive biphasic reactions. Due to a strong difference in volume mismatch between the separated phases for these 2 mechanisms, their reaction potentials are very close and overlap at low rates, inducing a 3‐phase state, while separate at high rates owing to different kinetics.