The growing demand of numerous industries for clean energy sources necessitates the development of high performance lithium-ion batteries. This in turn requires a deeper understanding of the corresponding electrode degradation phenomena. The formation of the solid electrolyte interphase, formed by chemical reactions of active materials with the electrolyte, is a major factor governing the cycling-induced degradation of lithium-ion battery anode materials. Therefore, the visualization of solid electrolyte interphase layers and the characterization of their chemical and electrical properties are tasks of high practical importance. Herein, we visualize the solid electrolyte interphase layers formed inside lithium-ion battery anodes comprising a mixture of Si-C composites and graphite particles as active materials by scanning spreading resistance microscopy. Quantitative and comparative scanning spreading resistance microscopy of pristine and 100-fold cycled anodes reveal that the latter sample features solid electrolyte interphase layers exhibiting a prominently higher electrical resistance than the active materials and demonstrate that thick solid electrolyte interphase layers start to form in the voids between active materials in the cycled anodes with the capacity decreased by similar to 17%. This study confirms that scanning spreading resistance microscopy is useful for characterizing solid electrolyte interphase layers and active materials in various lithium-ion battery electrodes.