In-situ/Operando characterization techniques for next-generation energy storage batteries: From fundamental mechanisms to advanced applications

Advanced battery systems hold great promise for next-generation energy storage owing to their high energy densities and low-cost potential. However, their commercialization is severely hindered by rapid capacity degradation, poor Coulombic efficiency, and unstable cycling performance, challenges that originate largely from an incomplete understanding of the dynamic physicochemical processes occurring during operation. Conventional ex situ characterization methods are limited to capturing static endpoints and frequently introduce artifacts during sample preparation, rendering them inadequate for revealing these transient reaction mechanisms. In-situ / operando characterization techniques offer a compelling solution by enabling real-time monitoring under controlled electrochemical operating conditions, thereby providing direct mechanistic insights essential for rational materials design and performance optimization. This review provides a comprehensive and systematic overview of recent progress in in-situ characterization techniques applied across the main battery chemistries. For each technique, we discuss its fundamental principles, characterization advantages, and key breakthroughs. We also discuss future directions toward multi-modal correlative imaging, advanced in-situ cell platforms compatible with extreme conditions, and machine-learning-assisted data analysis for automated phase identification and quantitative kinetic extraction. This review aims to guide the development of robust, multi-scale characterization strategies that can accelerate the commercialization of next-generation high-performance and safe batteries.