Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials. Characterizing the minute-variations in complementary aspects such as crystal structure, chemical bonds, and electron/ion conductivity will give an in-depth understanding on the reaction mechanism of electrode materials, as well as revealing pathways for optimization. Here, vanadium pentoxide (V₂O₅), a typical cathode material suffering from severe capacity decay during cycling, is characterized by in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy combined with electrochemical tests. The phase transitions of V₂O₅ within the 0–1 Li/V ratio are characterized in detail. The V–O and V–V distances became more extended and shrank compared to the original ones after charge/discharge process, respectively. Combined with electrochemical tests, these variations are vital to the crystal structure cracking, which is linked with capacity fading. This work demonstrates that chemical bond changes between the transition metal and oxygen upon cycling serve as the origin of the capacity fading.

Hybrid or composite heterostructured electrode materials have been widely studied for their potential application in electrochemical energy storage. Whereas their physical or chemical properties could be affected significantly by modulating the heterogeneous interface, the underlying mechanisms are not yet fully understood. In this work, we fabricated an electrochemical energy storage device with a MoS₂ nanosheet/MnO₂ nanowire heterostructure and designed two charge/discharge channels to study the effect of the heterogeneous interface on the energy storage performances. Electrochemical measurements show that a capacity improvement of over 50% is achieved when the metal current collector was in contact with the MnO₂ instead of the MoS₂ side. We propose that this enhancement is due to the unidirectional conductivity of the MoS₂/MnO₂ heterogeneous interface, resulting from the unimpeded electrical transport in the MnO₂-MoS₂ channel along with the blocking effect on the electron transport in the MoS₂-MnO₂ channel, which leads to reaction kinetics optimization. The present study thus provides important insights that will improve our understanding of heterostructured electrode materials for electrochemical energy storage.