[en] Highlights: • Brain-like MnO microspheres were synthesized and porous structure was achieved due to the release of CO₂ during thermal decomposition of MnCO₃. • PAN was introduced as a binder and subsequent heat-treated of the working electrode was conducted. Perfect electrochemical performance was achieved due to the cross-linked PAN after thermal treatment. • Excess specific capacity is detected because of the porous brain-like structure. Brain-like manganese monoxide (MnO) microspheres were synthesized by simple precipitation method with subsequent heat treatment. MnO with polyacrylonitrile (PAN) as a binder delivers an initial reversible specific capacity of 976.1 mAh g⁻¹ and it remains at 912.3 mAh g⁻¹ after 30 cycles. The excellent cyclic performance is attributed to the effective conductive network of cross-linked PAN that formed during the thermal treatment. FTIR, ex situ XRD and XAS were performed to investigate the excess reversible capacity of MnO. The results show that the excess capacity is partially ascribed to the interfacial lithium storage between nanosized Li₂O and Mn which is formed during the conversion reaction. The porous microspheres with large surface area also provide some active sites for lithium storage.