Hi Ljalem Hadush Abrha

FTIR is a tool that gives the idea of various bonds/functional groups present in a molecule. The appearance of new kind of peaks as compared to the previously synthesized molecule clearly states for happening of any chemical phenomenon e.g. chemisorption. For example, if a material is able to adsorb fluoride or any kind of anions, so there will be new kind of peak paper in the FTIR analysis of the adsorbed material emphasizing the chemisorption behavior. For your case, the slight shift position of the functional group or peak intensity after the introduction of a Li+ may cause some chemical change. That is why the change in intensity occurred. There may be a trapping of Li+ in the polymer. From my point of view, I can suggest to you the above.

Regards

Dear Ljalem Hadush Abrha this is a very good question which is of significant importance in lithium battery research. In addition to the expert answer provided by Arnab Mukherjee I would like to suggest to you a few relevant literature references about this topic. For example, in the following study FTIR spectroscopy has been successfully employed to characterize Li-salt – polymer interactions:

Lithium Salt Dissociation in Diblock Copolymer Electrolyte Using Fourier Transform Infrared Spectroscopy

https://www.frontiersin.org/articles/10.3389/fenrg.2020.569442/full

(see attached pdf file)

Please also have a look at the following interesting article:

Solvation and Dynamics of Lithium Ions in Carbonate-Based Electrolytes During Cycling Followed by Operando Infrared Spectroscopy: The Example of NiSb 2 , a Typical Negative Conversion-Type Electrode Material for Lithium Batteries

Article Solvation and Dynamics of Lithium Ions in Carbonate-Based El...

This paper has been posted by the authors as public full text on RG, so that you can freely download it as pdf file.

Yet another relevant article about this topic is the following:

The Effect of Solvation Shell Structure and Composition on Ion Pair Formation: The Case Study of LiTDI in Organic Carbonates

https://par.nsf.gov/servlets/purl/10158184

(see attachment)

I hope this helps. Good luck with your work and best wishes, Frank Edelmann