CURED PRODUCT FOR LITHIUM ION SECONDARY BATTERIES, NEGATIVE ELECTRODE FOR LITHIUM ION SECONDARY BATTERIES, AND LITHIUM ION SECONDARY BATTERY

A cured product for lithium ion secondary batteries includes water-soluble polymers, a crosslinking agent and cellulose nanofibers. The crosslinking agent crosslinks different water-soluble polymers or the water-soluble polymer and the cellulose nanofibers. When wide-angle X-ray scattering (WAXS) measurement is performed using CuKα rays, the diffraction angle 2θ has a peak in a range of 16° or more and 21° or less. The half-value width of the peak is 5.5° or less.