Impact of Excess Li on the Structural and Electrochemical Properties of Li_1+x(Ni_zCo_1−2zMn_z)_1−xO₂ Materials for Lithium-Ion Batteries

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LiNi_zCo_1−2zMn_zO₂ materials have been investigated as promising positive electrode materials for lithium-ion secondary batteries, in which cobalt ions are simultaneously substituted with nickel and manganese ions while preserving the α-NaFeO₂ structure. The materials can be regarded as solid solutions of LiNiO₂, LiCoO₂, and LiMnO₂, in which the transition metals are trivalent in all three materials, whereas the transition metals found in LiNi_zCo_1−2zMn_zO₂ materials are Ni²⁺, Co³⁺, and Mn⁴⁺. The electrochemical lithium deintercalation-intercalation processes of these materials are mainly accompanied by the Ni^2+/4+ and Co^3+/4+ redox reactions, whereas Mn⁴⁺ ions do not participate in the electrochemical redox reaction. Recently, Li⁺ substitution for transition metals in Li_1+x(Ni_zCo_1−2zMn_z)_1−xO₂, so called overlithiation, has been introduced to improve their structural integrity and electrochemical performances.
In this paper, we introduce the overlithiation effects on the structural and electrochemical properties of the Li_1+x(Ni_zCo_1−2zMn_z)_1−xO₂ materials having diffrrent x- and z-values in the ranges from x=0.00 to x=0.17 and z=0.00 to z=0.50.