A film maturation process for improving the cycle life of Si-based anodes for Li-ion batteries

• Storing Si–C–CMC electrode in humid air for a few days improves its cycling behavior.
• The ester bonds between Si and CMC are partially converted into hydrogen bonds.
• The covalent/hydrogen bond ratio impacts on the electrode cracking behavior.

This study shows that storage for a few days in humid air before cell assembling of Si-carboxymethyl cellulose (CMC) composite electrode prepared with a slurry buffered at pH 3 has a major positive impact on its cycle life and coulombic efficiency. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy analysis shows that water molecules in humid air partly convert the ester bonds between Si particles and CMC binder into less rigid hydrogen bonds. Complementary to cycling tests, scanning electron microscopy (SEM) observations suggest that the mechanical integrity of the film is better maintained for an optimal ratio of ester bonds to hydrogen bonds between Si particles and the CMC chains. Such a favorable impact of storage in humid air on the cycling behavior of a composite electrode for lithium battery was unexpected when compared to standard practices that show a detrimental aging of active electrode materials when exposed to water.

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