Anomalous interfacial stress generation during sodium intercalation/extraction in MoS₂ thin-film anodes

Although the generation of mechanical stress in the anode material is suggested as a possible reason for electrode degradation and fading of storage capacity in batteries, only limited knowledge of the electrode stress and its evolution is available at present. Here, we show real-time monitoring of the interfacial stress of a few-layer MoS₂ system under the sodiation/desodiation process using microcantilever electrodes. During the first sodiation with a voltage plateau of 1.0 to 0.85 V, the MoS₂ exhibits a compressive stress (2.1 Nm^-1), which is substantially smaller than that measured (9.8 Nm^-1) during subsequent plateaus at 0.85 to 0.4 V due to the differential volume expansion of the MoS₂ film. The conversion reaction to Mo below 0.1 V generates an anomalous compressive stress of 43 Nm^-1 with detrimental effects. These results also suggest the existence of a separate discharge stage between 0.6 and 0.1 V, where the generated stress is only approximately one-third of that observed below 0.1 V. This approach can be adapted to help resolve the localized stress in a wide range of electrode materials, to gain additional insights into mechanical effects of charge storage, and for long-lifetime battery design.