Degradation Analysis of LiCoO₂Positive Electrode Material of a Li-Ion Battery Using the Li K-Edge Signal Obtained from STEM-EELS Measurements

Abstract

The Li distribution in positive electrode material (LiCoO2) was observed after a charge-discharge cycling test by analytical transmission electron microscopy (TEM). The electron energy-loss spectroscopy (EELS) imaging method revealed an inhomogeneous Li distribution in the LiCoO2 particles after the charge-discharge cycling test. Using the alternating least-squares (ALS) method for the data matrix of the EELS spectra, we obtained LiCoO2 and Li-poor LiCoO2 spectra from the LiCoO2 particles. Around the degraded LiCoO2 particles, Co3O4 and fluoride components were detected. It is suggested that inhomogeneous electrochemical reactions are one cause of LiCoO2 and electrolyte degradation.

Ex situ and operando study of LiCoO2 thin films by Raman spectroscopy: Thermal and electrochemical properties

“…This means that air is absolutely required to transform the LT‐LiCoO 2 structure to HT‐LiCoO 2 . Furthermore, lithium is known to be very reactive with air and probably reacts with O 2 or CO 2 , forming species such as Li 2 CO 3 or Li 2 O at the surface . However, practically no signal of Li 2 CO 3 is observed on Raman spectra, and Li 2 O is more easily formed than Li 2 CO 3 when lithium is exposed to the air .…”

“…Furthermore, lithium is known to be very reactive with air and probably reacts with O 2 or CO 2 , forming species such as Li 2 CO 3 or Li 2 O at the surface. [24,25] However, practically no signal of Li 2 CO 3 is observed on Raman spectra, and Li 2 O is more easily formed than Li 2 CO 3 when lithium is exposed to the air. [25,26] The most convincing hypothesis is then the formation of lithium oxides by a reaction with O 2 from the air.…”

Oxygen Release Degradation in Li‐Ion Battery Cathode Materials: Mechanisms and Mitigating Approaches

“…Additionally, high extent of delithiation (high cutoff voltage charging) can promote the glide of partial dislocations, and provides a path for transition metal migration to the Li octahedral sites that leads to formation of the spinel phase . Spinel phase formation and oxygen release have been observed primarily at the surface of the cycled particles (Figure B) . This is explained by the electrochemically induced Li deficiency at the surface and inhomogeneous Li distribution throughout the cathode particles .…”

“…Similarly, local heating of the overcharged cathodes can trigger the migration of transition metal cations by breaking TMO bonds. This leads to OO bond formation between the undercoordinated oxygen atoms and results in the parasitic oxygen release that is explained in length throughout the article with regards to specific cathode systems (Figure C) …”

Systematic analysis of electron energy-loss near-edge structures in Li-ion battery materials

“…While measurements with resolutions up to 0.3 eV (as determined by the full width half maximum (FWHM) of the zero-loss peak) can be obtained using cold-FE guns, 21 to obtain resolutions better than 0.1 eV requires use of monochromators. [22][23][24] The latter allows Li-K edge spectra to be used to measure Li concentrations and distributions quantitatively with nanoscale resolution, as reported for materials LiCoO 2 , 25,26 LiFePO 4 27,28 and Li 2 MnO 3 . 29 One drawback of this method, however, is that TM-M 2,3 (or TM-N 2,3 ) edges lie near to Li-K edges, making their peaks difficult to deconvolute.…”