Aqueous zinc-ion batteries (ZIBs) have attracted significant interest as safe, low-cost, and environmentally friendly energy storage systems. However, their performance and stability are limited by complex interfacial phenomena such as zinc dendrite growth, parasitic side reactions, and the evolution of the solid electrolyte interphase. These processes are inherently dynamic and span multiple spatial and temporal scales, posing challenges to traditional ex situ characterization techniques. To address this, advanced in situ and operando techniques have been developed, broadly categorized into imaging, spectroscopic, synchrotron scattering/diffraction, and coupled mass spectrometry approaches. These methods enable real-time visualization and chemical analysis of the electrode/electrolyte interface, providing insights into nucleation and dissolution dynamics, interfacial chemical transformations, and the mechanisms driving dendrite formation and parasitic reactions. Through the integration of these complementary techniques, structural evolution can be correlated with electrochemical behavior, elucidating the underlying physicochemical mechanisms. This review systematically summarizes recent advances in in situ and operando characterization methods and highlights their contributions to understanding interfacial stability in aqueous ZIBs. Future directions emphasizing multi-modal strategies and data integration to guide the rational design of high-performance ZIBs are discussed. These insights are expected to accelerate the development of next-generation aqueous energy storage systems.

The formation of by-products significantly hinders ion transport in aqueous zinc-ion batteries (AZIBs), adversely affecting the stability of Zn metal anodes. Inspired by the scale-inhibition effect in oilfield chemistry, we introduced a hydrolysis-resistant 2-acrylamide-2-methylpropanesulfonic acid (AMPS) monomer additive with strong anionic groups into the electrolyte to form a high-quality solid electrolyte interphase. This interphase ensures the inhibition of hydrogen evolution reaction (HER), resulting in stabilizing the local pH through reduced H⁺ consumption and minimizing the formation of by-products. Leveraging the strong polarity of the –SO₃H in AMPS, the solvation structure of Zn²⁺ and the surface energy of the zinc substrate during deposition are effectively modulated. This behavior mitigates uneven nucleation at grain boundaries and defects, which facilitates the ordered deposition of Zn along the (002) plane, contributing to improved Zn electrode stability. Therefore, the Zn//Zn cell demonstrates cycling stability for over 4500 h at 1 mA·cm⁻²/1 mAh·cm⁻², while the Zn//MnO₂ full cell retains 84% of its capacity after 4500 cycles. We believe our design concept offers a new pathway for developing by-product-free high-stability AZIBs.

With the increased demand from the storage of renewable energy sources, some safe and inexpensive energy storage technologies instead of Li-ion batteries become urgently needed. Therefore, K-ion batteries (KIBs) have attracted much attention and evolved significant development because of the low price, safety, and similar property compared with Li-ion batteries. Due to the high reversibility, stability, and low potential plateau, graphite becomes a current research focus and is regarded as one of the most promising KIB’s anode materials. In this review, we mainly discuss the electrochemical reaction mechanism of graphite during potassiation-depotassiation process and analyze the effects of electrode/electrolyte interface on graphite for K-ion storage. Besides, we summarize several kinds of methods to improve the performance of graphite for KIBs, including the design of graphite structure, selection of appropriate binder, solvent chemistry, and salt chemistry. Meanwhile, a concept of “relative energy density” is raised, which can be more accurate to evaluate the genuine electrochemical performance of graphite anode involving the specific capacity and potential. In addition, we also summarize the considerable challenges to current graphite anode in KIBs and we believe our work will offer alterative solutions to further explore high-performance graphite anode of K-ion storage.