Provided is a lithium ion secondary cell having high energy density and exceptional cycle characteristics. The present invention pertains to a lithium ion secondary cell comprising: a negative-electrode active material that includes a material including silicon as a constituent element; and an electrolyte. The electrolyte contains: a non-aqueous solvent including a fluorinated ether compound, an acyclic sulfone compound, and a cyclic carbonate compound; and a supporting electrolyte that includes LiPF6, lithium bis(fluorosulfonyl) imide, and lithium bis(oxalate) borate (LiBOB), the LiBOB content in the electrolyte being 0.2% by mass or greater.