Abstract
Lithium-ion batteries featuring electrodes of silicon nanoparticles, conductive carbon, and polymer binders were constructed with electrolyte containing 1.2 M LiPF6 in 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.
Highlights
Silicon electrodes containing carboxymethyl cellulose (CMC) binder performed only slightly less well, showing capacity fade equal to about 250 mA h/g in excess of those containing polyacrylic acid (PAA) and CMCPAA, which were very similar after 20 cycles
Coin cell LIBs using PAA, CMCPAA, CMC, and Polyvinylidene difluoride (PVdF) as the binder material in electrodes composed of silicon nanoparticles, carbon black, and binder in the ratio of 2:1:1 by weight with identical electrolyte formulations have been investigated
Electrodes from the batteries have been characterized by hard X-ray photoelectron spectroscopy (HAXPES), which provides a number of conclusions about the solid electrolyte interphase (SEI) formation and maturation during cycling
Summary
Novel electrode construction and electrolyte materials are two widely researched avenues to accommodate the silicon volume fluctuation, either by mitigating the stresses within the electrode or generating more effective SEI layers.[4,5,6] The silicon SEI is reportedly similar to the. High photon energies available from synchrotron radiation gives access to more tightly bound core electrons and impart more energy to less tightly bound ones than traditional XPS studies. This enables characterization of the SEI layer at shallower, but primarily deeper levels in the film than have previously been studied
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