Coupling effects of thermodynamics in multiple ion co-precipitation for precursors towards a layered oxide cathode

Abstract

The co-precipitation process is the most frequently employed method to realize the simultaneous stoichiometric crystallization of multiple ions. The precipitation of different elements under a driving force can directly and primarily determine the degree of homogeneity of the co-precipitation product. Unlike individual element crystallization, the multiple ion coexistence co-precipitation process is complicated and a coupling effect is involved, as the thermodynamic behaviour of certain elements is much superior to that of others. This coupling effect can dramatically influence the whole thermodynamic behaviour in the liquid solution. Therefore, in order to achieve a high-quality product or precursor with various elements in a homogeneous distribution, the co-precipitation process can be efficiently controlled and balanced by the coupling effect resulting from the addition of certain elements. In an environment where Co²⁺, Ni²⁺, and Mn²⁺ ions coexist, owing to the thermodynamic coupling effect, the superior high supersaturation of Al³⁺ and the more negative change in the Gibbs free energy (ΔG) can efficiently balance the whole crystallization reaction by realizing a consistent precipitation driving force among the various ions, accelerating the precipitation of Ni²⁺ and Mn²⁺ ions and inhibiting the precipitation of Co²⁺ ions. Meanwhile, based on the initial formation of the Al(OH)₃ seed crystals in the solution, multiple ions in the solution can be adsorbed and thus grow on the surface of Al(OH)₃ to completely precipitate. The obtained Li-rich cathode material has demonstrated excellent electrochemical performance which can be attributed to the high quality precursor (0.54MnCO₃·0.13NiCO₃·0.125CoCO₃·0.005Al(OH)₃) with a homogeneous distribution of elements.