Probing the Reaction between PVDF and LiPAA vs Li7Si3: Investigation of Binder Stability for Si Anodes

Abstract

The chemical interaction of the highly reactive lithiated Si anode with other cell components, such as binders and electrolytes, is one of the most critical issues in batteries using Si electrodes. In this work, crystalline lithium silicide (LS) with Li7Si3 composition is synthesized to study the direct chemical reactions between the lithiated Si anodes and two typical binders, polyvinylidenefluoride (PVDF) and lithiated polyacrylic acid (LiPAA). The solid-state nuclear magnetic resonance (NMR) and Raman characterization experiments show that LiPAA binder is chemically stable against LS. On the contrary, PVDF binder reacts more readily with the LS, resulting in significant loss of Li from the bulk. 13C NMR shows the C-H bonds and C-C PVDF backbone were affected, whereas 19F MAS NMR shows the C-F bonds are relatively more stable. No LiF is detected, however HF release is confirmed by gas chromatography/mass spectrometry. The characterization results are consistent with electrochemical tests, which show the Si electrode using LiPAA as the binder has a much higher cyclability than when compared with PVDF. This work demonstrates the using of LS as an effective approach to evaluate and investigate the reactions between lithiated Si and different cell components, in order to stabilize Si anodes.