Porous carbon encapsulated Mn3O4 for stable lithium storage and its ex-situ XPS study

Highlights: • Mn₃O₄@C composite is prepared via a MOF-derived strategy. • Mn₃O₄@C shows attractive electrochemical performance in both half cells and full cells. • Ex-situ XPS unveils the conversion mechanism between metallic Mn⁰ and MnO. -- Abstract: The low electrical conductivity and poor cycling stability at high current density of hausmannite (Mn₃O₄) have greatly limited its practical application in commercial lithium ion batteries (LIBs). In order to tackle these above issues, porous carbon encapsulated Mn₃O₄ has been designed and prepared. Carbon-encapsulated Mn₃O₄ (Mn₃O₄@C) prepared via a MOF-derived strategy shows attractive cycling stability and rate performance in both half-cells and full cells. It could stably deliver a capacity of 730.20 mAh g⁻¹ after 200 cycles at 250 mA g⁻¹. An average capacity of 421 mAh g⁻¹ is obtained at a current density of 4000 mA g⁻¹. After a 400-cycle test at 2000 mA g⁻¹, the Mn₃O₄@C anode can maintain 70.90% of its initial capacity. Full cells using Mn₃O₄@C as anode and NCM-523 as cathode could stably cycle for 100 times at 200 mA g⁻¹, with a 73.30% capacity retention. Conversion mechanism of the Mn₃O₄@C anode has been investigated by ex-situ XPS. Upon the first discharge, Mn₃O₄ is initially reduced into MnO and further reduced into metallic Mn⁰. The metallic Mn⁰ is then converted into MnO during the following charge. Subsequent lithiation/de-lithiation are governed by reversible conversion between MnO and metallic Mn⁰. Improved electrochemical performance of the Mn₃O₄@C anode is attributed to introduction of porous carbon, which could not only limit loss of active species but also enhance overall electrical conductivity. The Mn₃O₄@C composite can be a promising anode material for LIBs.