Nano-single-crystal-constructed submicron MnCO₃ hollow spindles enabled by solid precursor transition combined Ostwald ripening in situ on graphene toward exceptional interfacial and capacitive lithium storage

Hollow structuring has been identified as an effective strategy to enhance the cycling stability of electrodes for rechargeable batteries due to the outstanding volume expansion buffering efficiency, which motivates ardent pursuing on the synthetic approaches of hollow materials. Herein, an intriguing route, combining solid precursor transition and Ostwald ripening (SPTOR), is developed to craft nano single-crystal (SC)-constructed MnCO₃ submicron hollow spindles homogeneously encapsulated in a reduced graphene oxide matrix (MnCO₃ SMHSs/rGO). It is noteworthy that the H-bonding interaction between Mn₃O₄ nanoparticles (NPs) and oxygen-containing groups on GO promotes uniform anchoring of Mn₃O₄ NPs on GO, mild reductant ascorbic acid triggers the progressive solid-to-solid transition from Mn₃O₄ NPs to MnCO₃ submicron solid spindles (SMSSs) in situ on GO, and the Ostwald ripening process induces the gradual dissolution of interior polycrystals of MnCO₃ SMSSs and subsequent recrystallization on surface SCs of MnCO₃ SMHSs. Remarkably, MnCO₃ SMHSs/rGO delivers a 500th lithium storage capacity of 2023 mAh g⁻¹ at 1000 mA g⁻¹, which is 10 times higher than that of MnCO₃ microspheres/rGO fabricated from a conventional Mn²⁺ salt precursor (202 mAh g⁻¹). The ultrahigh capacity and ultralong lifespan of MnCO₃ SMHSs/rGO can be primarily attributed to the superior reaction kinetics and reversibility combined with exceptional interfacial and capacitive lithium storage capability, enabled by the fast ion/electron transfer, large specific surface area, and robust electrode pulverization inhibition efficacy. Moreover, fascinating in-depth lithium storage reactions of MnCO₃ are observed such as the oxidation of Mn²⁺ in MnCO₃ to Mn³⁺ in charge process after long-term cycles and the further lithiation of Li₂CO₃ in discharge process. As such, the SPTOR approach may represent a viable strategy for crafting various hollow functional materials with metastable nanomaterials as precursors.