Real-time detection of lithium plating under extreme conditions is critical for battery safety. Here, we use embedded fiber Bragg grating (FBG) sensors to achieve real-time monitoring of mechanical strain evolution in operating graphite pouch cells. At ultralow temperatures (−20 and −30 °C), we observe an anomalous suppression in differential strain (dε/dQ) during late-stage charging. Specifically, the strain generation rate is severely constrained, dropping to approximately 0.1 με·mAh⁻¹ (με = 10⁻⁶ strain) at high state-of-charge (SOC)—a stark contrast to the normal intercalation baseline of ~ 0.3 με·mAh⁻¹ observed under milder, non-plating conditions. Through synchronized electrochemical analysis and post-mortem characterization, we show that this mechanical anomaly reflects a fundamental shift in plating behavior: At cryogenic temperatures, internal mechanical constraints imposed by prior plating and solid electrolyte interphase (SEI) densification suppress further expansion, altering the progression of lithium deposition. The real-time strain signals also reveal a dynamic competition between SEI fracture–repair cycles and lithium re-plating, providing insight into coupled degradation mechanisms governing battery failure. This work establishes an in-situ diagnostic tool for battery failure and offers new mechanistic understanding of lithium plating under extreme conditions.

Aqueous zinc-ion batteries (AZIBs) are considered as one of the most promising next-generation electrochemical energy storage systems owing to their high-power density, environmental benign, intrinsic safety, and the low cost of the abundant zinc resources. However, their further development is still plagued by the inferior electrochemical performance of cathode materials. Though extensive research has been conducted to investigate various cathode materials (including manganese oxides, vanadium oxides, Prussian blues analogy, and organic materials), design of high-performance cathodes with satisfying capacity and long-term cycling stability still faces great challenges. Oxygen-free vanadium-based compounds, owing to their better conductivity, larger interlayer spacing, lower ion diffusion barrier and higher theoretical specific capacity than those of vanadium oxides, have gained increasing attention recently. In this review, we summarize the recent development about the emerging oxygen-free vanadium-based compounds in AZIBs, emphasizing the methods to design electrode materials with desired structures, effective strategies to improve their electrochemical performance, and the fundamental electrochemical mechanisms. Finally, the current challenges and outlooks of oxygen-free vanadium-based compounds are proposed, providing a novel perspective and useful guidance for the design of high-performance vanadium-based cathode materials for AZIBs.