Role of binders in solid electrolyte interphase formation in lithium ion batteries studied with hard X-ray photoelectron spectroscopy

Lithium-ion batteries featuring electrodes of silicon nanoparticles, conductive carbon, and polymer binders were constructed with electrolyte containing 1.2 M LiPF6in ethylene carbonate and diethyl carbonate (1:1, w/w). Material binders used include polyvinylidene difluoride (PVdF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and a mixture of equal masses of CMC and PAA (CMCPAA). Hard X-ray photoelectron spectroscopy (HAXPES) was performed on the electrodes when fresh, cycled at reduced potential, and cycled one full time to study how substrate material binders affect the early formation of the solid electrolyte interphase (SEI) layer. Electrodes cycled 5, 10, and 20 times were also analyzed to discern what changes to the SEI occur after initial formation. We also present estimates of the SEI thickness by cycle count, indicating that PAA develops the thinnest SEI, followed by CMCPAA, CMC, and PVdF in order of increasing layer thickness.