Functionalization of Ca2MnO4–δ by controlled calcium extraction: Activation for electrochemical Li intercalation

Calcium manganate Ruddlesden–Popper phases Ca2MnO4–δ were prepared by soft chemistry and treated with acid to extract a part of the calcium ions. Combined structural, morphological and spectroscopic analyses by XRD, SEM/EDX, TEM and Raman revealed an amorphization of the treated surface with a preserved inner crystalline phase in the core of the particles. The inner part of the particles consists of Ca2MnO4–δ and the outer part of hydrated amorphous manganese oxide MnO2·xH2O. Although pristine Ca2MnO4–δ is not electrochemically active, electrochemical characterization of the acid-treated powders shows a significant change in capacity that correlates to the amount of extracted calcium. The cycling stability of the Ca2 + extracted compounds was improved by more than a factor of 10 in comparison to pure MnO2·xH2O. The acid-treated Ca2MnO4–δ showed enhanced capacity retention of up to 50% after 70 cycles compared to 4% for bare MnO2·xH2O due to its crystalline core.

New electrochemical functionality was created treating Ca2MnO4 − δ with H2SO4. Ca2 + extraction-dependent specific charge and improved capacity retention were obtained.Figure optionsDownload as PowerPoint slide