The structural and electrochemical properties of a quaternary layered compound with elemental composition Mn2Sb3O6Cl have been investigated upon reaction with lithium in Li half cells. Operando XRD was used to investigate the potential impact of this particular layered structure on the lithiation process. Although the results suggest that the material is primarily reacted through a conventional conversion mechanism, they also provide some hints that the space between the slabs may act as preferential entry points for lithium ions but not for the larger sodium ions. Cyclic voltammetry, galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed to unravel the details of the reaction mechanism with the lithium ions. It is found that two pairs of reactions are mainly responsible for the reversible electrochemical cycling of this compound, namely, the alloying of Li-Sb and the conversion of MnxOy to metallic Mn with concomitant formation of Li2O upon lithium uptake. A moderate cycling stability is achieved with a gravimetric capacity of 467 mAh g(-1) after 100 cycles between 0.05 and 2.2 V vs Li+/Li despite the large particle sizes of the active material and its nonoptimal inclusion into composite coatings. The electrochemical activity of the title compound was also tested in Na half cells between 0.05 and 2 V vs Ne/Na. It was found that a prolonged period of electrochemical milling is required to fully gain access to the active material, after which the cell delivers a capacity of 350 mAh CI. These factors are demonstrated to clearly limit the ultimate performances for these electrodes.