Abstract:
The development of next-generation rechargeable batteries requires not only advanced electrode materials with high energy density and long-term stability but also a fundamental understanding of their dynamic structural evolution and charge-storage mechanisms. In this work, operando synchrotron X-ray techniques, complemented by advanced microscopy and density functional theory (DFT) calculations, were employed to elucidate the structure–property relationships of emerging electrode materials for sodium-ion, lithium-ion, and aqueous zinc-ion batteries.
For sodium-ion batteries, a high-entropy O3-type layered oxide, NaCu0.1Ni0.3Fe0.2Mn0.2Ti0.2O2 (NCNFMT), was developed as a structurally stable cathode. Operando synchrotron X-ray diffraction (XRD) revealed that the high-entropy effect delayed the phase transition until the extraction of approximately 0.32 Na⁺, thereby stabilizing the O3 framework and enabling excellent long-term cycling performance. Furthermore, a high-energy P2-type oxygen-redox cathode, Ca-doped Na0.67[Mg2/9Cu1/9Mn2/3]O2, was designed through Cu substitution and Ca doping. Operando X-ray absorption spectroscopy (XAS) and XRD demonstrated that Cu stabilized lattice oxygen during oxygen redox, whereas Ca acted as structural pillars to suppress irreversible phase transitions, leading to a high capacity of 205 mAh g⁻¹ and a full-cell energy density of 250.7 Wh kg⁻¹.
For alloying- and conversion-type electrodes, amorphous MoSnSe1.5S1.5 (MSSS) nanoflowers exhibited high capacities and exceptional rate capability in both lithium- and sodium-ion batteries. In situ/operando XAS and transmission X-ray microscopy provided direct insights into their multistep reaction pathways and demonstrated that structural amorphization effectively accommodated volume variation while promoting pseudocapacitive charge storage.
Operando synchrotron characterization was further applied to hydrated vanadium oxide cathodes for aqueous zinc-ion batteries. Combined operando XRD, XANES, EXAFS, and DFT analyses revealed that high-valence Mo ions predominantly substituted V sites within the vanadium–oxygen layers, enhancing electronic conductivity, accelerating Zn2+ transport, and stabilizing the host lattice. In addition, synergistic Ni2+/Al3+ co-preintercalation enlarged the interlayer spacing and enabled highly reversible Zn2+ storage, resulting in high capacity, ultrafast rate capability, and prolonged cycling stability.
These studies highlight the unique capability of operando synchrotron X-ray techniques to correlate electronic-state evolution, local coordination, phase transitions, and ion-storage behavior under realistic electrochemical conditions. The mechanistic insights provide rational design principles for developing high-energy, fast-charging, and durable electrode materials for next-generation rechargeable batteries.
Keywords – sodium-ion batteries, zinc-ion batteries, operando X-ary absorption spectroscopy, operando XRD