Interrelationship Between the Open Circuit Potential Curves in a Class of Ni-Rich Cathode Materials

Abstract

Ni-rich cathodes, such as nickel cobalt aluminum oxides (NCAs, LixNi0.80+0.15ε Co0.15(1−ε)Al0.05O2, 0 ≤ ε ≤ 1), are a class of cathode materials for lithium-ion batteries (LIBs), which are among the leading candidates for battery electric vehicle (BEV) applications. In this study we focus on an important, fundamental electrochemical property, the open-circuit potential function (OCP, U vs x), and investigate its relationship with the Ni stoichiometry. First, we demonstrate that published differential capacity curves (dQ/dU vs U) for Ni-rich NCA materials can be derived as a stoichiometric linear combination of differential capacities of the two end members, LixNi0.8Co0.15Al0.05O2 and LixNi0.95Al0.05O2. Subsequently, the OCP curves are obtained by taking the inverse of the integrated dQ/dU vs U curves, which match literature OCP curves. Then, we apply the same method to determine the composition of an unknown cathode extracted from a commercially available LIB. Lastly, we show that the identified relationship also holds true for the LixNi0.60+0.20ε Co0.20(1−ε)Mn0.20O2 family by demonstrating that the OCP curve of LixNi0.70Co0.10Mn0.20O2 can be predicted from a fractional combination of LixNi0.60Co0.20Mn0.20O2 and LixNi0.80Mn0.20O2. We anticipate that this methodology can be adapted to predict OCP curves for additional cathode families and used to validate the chemical composition of newly synthesized materials.