Suppression of electrode swelling of SiOx nanoflake anode using LiFSI/glyme localized high-concentration electrolytes

Charge and discharge characteristics and electrode swelling of SiO_x nanoflake anode (O/Si = 0.68) are investigated in various LiFSI/glyme-based high-concentration electrolytes (HCEs) and localized HCEs (LHCEs). The SiO_x anode shows a high capacity of ca. 1350 mAh g⁻¹ with good cycleability for 1000 cycles in LiFSI/DME, diglyme (G2), triglyme, and tetraglyme HCEs, and LiFSI/G2-based LHCEs using fluorinated diluents (1:1 by volume) without any film-forming additives. Raman spectra of these electrolytes show that FSI⁻ anions are predominantly in the form of aggregates (AGGs) in all the LHCEs. SiO_x anode shows good cycleability in LiFSI/G2+1H,1H,5H-perfluoropentyl l,1,2,2-tetrafluoroethyl ether (OTE) LHCEs of different fractions (1:1) to (1:6). However, remarkable differences in rate-capability are observed, and the LHCE (1:4) shows the best rate-capability. SEM observation of the anode cross-sections after cycling reveals that electrode swelling in LiFSI/G2 HCE and LiFSI/G2+OTE (1:4) are x 1.7 and x 1.8, respectively, after 300 cycles, which are much thinner than that after 100 cycles in a conventional electrolyte (x 3.7). These facts prove that increasing the stability of the electrolyte solution against reduction is effective for suppressing the electrode swelling of SiO_x anode, and that the LiFSI/G2+OTE (1:4) LHCE is promising for LIBs using Si-based anodes.