Single‐Phase Mixed Transition Metal Carbonate Encapsulated by Graphene: Facile Synthesis and Improved Lithium Storage Properties

Abstract Transition metal carbonates (TMCs) with complex composition and robust hybrid structure hold great potential as high‐performance electrode materials for lithium‐ion batteries (LIBs). However, poor ionic/electronic conductivities and large volume changes of TMCs during lithiation/delithiation processes have hindered their applications. Herein, single‐phase MnCo mixed carbonate composites encapsulated by reduced graphene oxide (Mn_xCo_1−xCO₃/RGO), in which Mn and Co species are distributed randomly in one crystal structure, are successfully synthesized through a facial liquid‐state method. When evaluated as LIB anodes, the Mn_xCo_1−xCO₃/RGO composites exhibit enhanced electrochemical performance compared with the reference CoCO₃/RGO and MnCO₃/RGO. Specifically, the Mn_0.7Co_0.3CO₃/RGO delivers an ultrahigh capacity of 1454 mA h g⁻¹ after 130 cycles at 100 mA g⁻¹ and exhibits an ultralong cycling stability (901 mA h g⁻¹ after 1500 cycles at 2000 mA g⁻¹). This is the best lithium storage performance among carbonate‐based anodes reported up to date. Such superb performance is attributed to the hybrid structure and enhanced electroconductivity due to the integration of Co and Mn into one crystal structure, which is complemented by electrochemical impedance spectroscopy and density functional theory calculations. The facile synthesis, promising electrochemical results, and scientific understanding of the Mn_xCo_1−xCO₃/RGO provides a design principle and encourages more research on TMCs‐based electrodes.