Provided are a binder aqueous solution for a lithium ion battery, a negative electrode slurry for a lithium ion battery, a negative electrode for a lithium ion battery, and a lithium ion battery. The binder aqueous solution for a lithium ion battery has a pH of 5 or higher and contains: a water-soluble polymer (A) that is a polymer of a monomer group containing, with respect to 100 mol % of the monomer group, 15 mol % to 99.9 mol % of an unsaturated carboxylic acid or an inorganic salt thereof, and that has a glass transition temperature of 110° C. or lower; and a hydrolyzed partial condensate (B) of an amino group-containing trialkoxysilane.