Direct Observation of Active Material Concentration Gradients and Crystallinity Breakdown in LiFePO

DOI: 10.1021/jp411152s
PMID: 24790684

Authors: Matthew Roberts (University of Southampton) , Alex Madsen (University of Southampton) , Chris Nicklin (Diamond Light Source) , Jonathan Rawle (Diamond Light Source) , Michael Palmer (University of Southampton) , John R Owen (University of Southampton) , Andrew Hector (University of Southampton)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C , VOL 118 (13)

State: Published (Approved)
Published: February 2014
Diamond Proposal Number(s): 6799 , 7698

Abstract: The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate.

Journal Keywords: Phase Change; Battery; Energy

Subject Areas: Chemistry, Energy, Materials


Instruments: I07-Surface & interface diffraction