“…One of the key challenges of SIBs is to develop sustainable, low-cost, high-capacity, and stable cathodes. Recently, layered P2-type transition metal oxides Na x TMO 2 (with TM = Ti, V, Cr, Mn, Fe, Co, Ni, or a combination of them) have gathered great interest because of their high theoretical capacity and energy density, attractive price, and environmental friendliness. − They are constituted by sheets of TMO 6 octahedra, providing 2D transport channels with a low barrier for Na + ion diffusion between them. − Especially Na x MnO 2 has been the subject of extensive studies. − However, despite expectations, the electrochemical performance for Na x MnO 2 is often unsatisfactory. Upon Na + intercalation, part of Mn 4+ cations reduce to Mn 3+ and MnO 6 octahedra experience an anisotropic distortion with shortening/lengthening of two/four Mn–O bonds .…”