Deep TEM Study of Ageing Mechanisms of Li-Ion Batteries Associated with Renewable Energies

The main objective of the ANR Vision project is to propose Li-ion batteries for energy storage application associated with renewable energy with a lifetime of 15-20 years. The scientific goal is to improve knowledge of long time aging mechanisms according to use conditions. This understanding would be helpful for improvement of prototypes that will be tested during the project. Batteries made of Li[Ni_1-x-yMn_xCo_y]O₂(NMC) and carbon a are investigated.

Electron microscopy techniques (Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution-High Angle Annular Dark Field (HR-HAADF), Focused Ion Beam (FIB), Electron Dispersive Spectroscopy (EDS) and Electron Energy Loss Spectroscopy (EELS)), were deeply used to determine the degradation of the aged active materials: stress, strain, fracture, phase transformations, dissolution resulting from intense cycling.

By comparison of pristine and cycled materials, SEM investigation on FIB electrode slices revealed detachments and cracks inside and between active material and the binder (Figure 1) as well as preferential dissolution [1] of transition metal (EDS). SAED patterns show the creation of defects and highlight a transition phase from lamellar to spinel phase (Figure 2-A). In order to nicely visualized spinel domains [2, 3], images were recorded on a FEI Cs-corrected Titan Ultimate microscope fitted with HR-HAADF camera (Figure 2-B).

 Afterwards, all these results, combined with information recorded by the other VISION partners, are used to make recommendations to create new generations of prototype cells.

[1] Nicholas P. W. Pieczonka et al., J. Phys. Chem. C 2013, 117, 15947−15957.

 [2] A. Boulineau et al.,Chem. Mater. 2012, 24, 3558−3566.

[3] D. Mohanty et al., Journal of Power Sources 229 (2013) 239-248.

Acknowledgement: This work was funded by ANR (Agence Nationale de la Recherche) and is part of the VISION project.