Crucial Role of Volumetric\nVariation Tolerable Single-Walled\nCarbon Nanotube/Polymer Binder Network for Stabilizing Bulk Silicon\nAnode

Water-soluble polymer binders have shown better affinity\nto silicon-based\nanodes of lithium-ion batteries than the traditionally used polymer\nbinder poly(vinylidene difluoride), but their performance is still\nfar from desired while their ultimate capacity to improve the stability\nof a silicon-based anode is unclear. In this work, the composition\nof anodes with 80% weight fraction of pristine silicon nanoparticles,\nwhich can sufficiently embody giant volumetric variation of silicon\nand growth of the surface solid electrolyte interface (SEI), is set\nfor investigation of the role of binders. Carboxymethyl cellulose\n(CMC) and the single-walled carbon nanotube (SWCNT) are hybridized,\nforming easily processed dispersions of SWCNT–CMC that make\nthe industrial manufacturing process favorable. The ex-situ impedance\nunder different working potentials, lithium-ion diffusion coefficient,\nand polarization potential of anodes with CMC only and SWCNT–CMC\nare systematically studied. Furthermore, the role of SWCNT in CMC\nbinder bulk film along with binder sponge, the latter of which simulates\nthe binder network in the anode, has been studied via multiple mechanical\ntests. It is found that the SWCNT–CMC hybrid binder in the\n anode provides a dense network that a normal conducting agent cannot\nform, which highly effective delivers electrons to the anode, reducing\npolar potential, depressing overgrowth of SEI, and improving rate\nperformance of the anode. More importantly, the dense network of\nSWCNT–CMC is mechanically more stable than CMC. Even though\nan anode with SWCNT–CMC cracks after 100 cyclic charge/discharge\ntests, SWCNT–CMC still can bridge Si nanoparticles in the \nanode, preserving the bulk anode electrical conductance.