Comparative study of solid-state redox reactions of LiCo 1/4Ni 3/4O 2 and LiAl 1/4Ni 3/4O 2 for lithium-ion batteries

Abstract

Comparative study of the solid-state redox reactions of LiCo 1/4Ni 3/4O 2 and LiAl 1/4Ni 3/4O 2 was carried out by XRD and electrochemical methods. XRD examinations indicated that the reactions proceeded in single phase for both samples. The change in interlayer distance between MeO 2-sheets for LiCo 1/4Ni 3/4O 2 or LiAl 1/4Ni 3/4O 2 was almost the same as that for LiNiO 2 in the region 0< x<3/4 in Li 1− x MeO 2 (Me=Ni, Co 1/4Ni 3/4, or Al 1/4Ni 3/4). Reversible potentials as a function of x were measured and the solid-state redox reactions involving in the lithium insertion reactions were characterized by using simple equations to describe the redox potentials. According to our results, substitution of aluminum for nickel in LiNiO 2 raised the levels of solid-state redox potentials primarily derived from nickel species by about 0.1 V, while the substitution of cobalt did not affect the solid-state redox potentials in that range. Differences and similarities between the solid-state electrochemical reactions of LiCo 1/4Ni 3/4O 2 and LiAl 1/4Ni 3/4O 2 were discussed therefrom.