A method for producing active material particles for a lithium ion secondary battery, which comprises contacting active material particles (X) for a lithium ion secondary battery capable of oxidation/reduction reaction, with a composition containing a compound (a) having at least one metal element (M) selected from the following metal element group (A) and a composition containing the following fluoropolymer (b), and heating them:
- metal element group (A):
- a group consisting of Li, Mg, Ca, Sr, Ba, Pb, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Al, In, Sn, Sb, Bi, La, Ce, Pr, Nd, Gd, Dy, Er and Yb;
- fluoropolymer (b):
- a polymer having repeating units represented by the following formula (1):
- —[CF2—CR1R2]— (1)
- wherein each of R1 and R2 is a hydrogen atom, a fluorine atom or a trifluoromethyl group.