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Anatase TiO2 represents an attractive electrode material for application in sodium-ion batteries due to its relatively low cost, high environmental compatibility, high intrinsic safety, conferred by the relatively high operating voltage, and satisfactory theoretical capacity. Nonetheless, a comprehensive understanding of the Na uptake and release mechanism is still missing, which is crucial for a further insight-driven optimization of the electrode material. This work presents for the first time an extensive operando X-ray absorption near-edge structure spectroscopy (XANES) study at the Ti K-edge of a TiO2 anatase nanoparticle-based electrode, aiming at unraveling the structural evolution and consequent Ti oxidation state and coordination changes upon sodiation and following de-sodiation. By using two approaches, i.e. an analytical fit and principal component analysis (PCA) with a linear combination analysis (LCA) to the evaluation of the operando data, this study reveals the amount of irreversible and reversible Na + inserted upon cycling. In addition, a change of the Ti coordination during the first cycle is monitored, observing a decrease of the original 6-coordinated symmetry. Simultaneously, the irreversible loss of the nanoparticle structural ordering due to the effect of initial Na insertion in the anatase lattice is detected. These results support some of the (ex situ) findings reported previously and give a more comprehensive picture of the highly discussed sodiation mechanism of TiO2-based anodes under more realistic operating conditions.

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The development of freestanding and binder‐free electrode is an effective approach to perform the inherent capacity of active materials and promote the mechanism study by minimizing the interference from additives. Herein, we construct a freestanding cathode composed of MoS3/PPy nanowires (NWs) deposited on porous nickel foam (NF) (MoS3/PPy/NF) through electrochemical methods, which can work efficiently as sulfur‐equivalent cathode material for Li‐S batteries. The structural stability of the MoS3/PPy/NF cathode is greatly enhanced due to its significant tolerance to the volume expansion of MoS3 during the lithiation process, which we ascribe to the flexible 3D framework of PPy NWs, leading to superior cycling performance compared to the bulk‐MoS3/NF reference. Eliminating the interference of binder and carbon additives, the evolution of the chemical and electronic structure of Mo and S species during the discharge/charge was studied by X‐ray absorption near‐edge spectroscopy (XANES). The formation of lithium polysulfides was excluded as the driving cathode reaction mechanism, suggesting the great potential of MoS3 as a promising sulfur‐equivalent cathode material to evade the shuttle effect for Li‐S batteries. The present study successfully demonstrates the importance of structural design of freestanding electrode enhancing the cycling performances and revealing the corresponding mechanisms.