Cations differentiation-induced core–shell heterostructure and mutual doping for achieving high-performance transitional metal carbonates electrode

Transition metal carbonates (TMCs) hold great potential as high-performance electrodes for alkali metal-ion batteries, owing to multiple-ion storage mechanisms involving conversion process and electrocatalytic reaction. However, they still suffer from inferior electronic conductivity and volume variation during delithiation/lithiation. Heterostructure and heteroatoms doping offer immense promise in enhancing reaction kinetics and structural integrity, which unfortunately have not been achieved in TMCs. Herein, a unique TMCs heterostructure with Ni-doped MnCO₃ as “core” and Mn-doped NiCO₃ as “shell”, which is wrapped by graphene (NM@MN/RGO), is achieved by cations differentiation strategy. The formation process for core–shell NM@MN consists of epitaxial growth of NiCO₃ from MnCO₃ and synchronously mutual doping, owing to the similar crystal structures but different solubility product constant/formation energy of MnCO₃ and NiCO₃. In-situ electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, differential capacity versus voltage plots, theoretical calculation and kinetic analysis reveal the superior electrochemical activity of the NM@MN/RGO to MnCO₃/RGO. The NM@MN/RGO shows excellent lithium storage properties (1013.4 mAh·g⁻¹ at 0.1 A·g⁻¹ and 760 mAh·g⁻¹ after 1000 cycles at 2 A·g⁻¹) and potassium storage properties (capacity decay rate of 0.114 mAh·g⁻¹ per cycle). This work proposes an efficient cation differentiation strategy for constructing advanced TMC electrodes.