Review comments
This review article comprehensively presents a wide range of in-situ and ex-situ characterization techniques used to study charge storage mechanisms in 2D and layered material-based electrochemical energy storage (EES) devices. The authors cover various methods, including optical spectroscopy, transmission electron microscopy, X-ray and neutron-based techniques, mechanical probing, and nuclear magnetic resonance spectroscopy. The article is well-structured, and the content is of high quality, providing valuable insights for researchers in the field of 2D materials and EES. However, there are some areas that need improvement before it can be considered for acceptance.

1. The introduction briefly mentions the advantages of 2D materials for electrochemical energy storage but fails to clearly highlight the significance of this review in the broader context of the field. It should emphasize how the comprehensive overview of characterization techniques fills a gap in the existing literature.
2. When discussing the limitations of characterization techniques, provide more in - depth analysis of their impact on understanding charge storage mechanisms in 2D materials and suggest more ways to overcome them.
3. The manuscript uses some terms inconsistently. For example, "charge storage mechanism" and "energy storage process" are used interchangeably in some places. It is recommended to standardize the terminology. Decide on a single term for the overall concept of how charge is stored in 2D materials for electrochemical energy storage and use it consistently throughout the manuscript to avoid confusion.
4. When presenting examples of how a characterization technique is applied (e.g., in - situ Raman spectroscopy examples), some important information is missing. It should include more analysis of how the experimental results contribute to the understanding of charge storage mechanisms.
5. When you emphasize the importance of probing charge storage mechanisms in 2D and thin-layered material-based systems, several literatures are suggested to be considered in order to enhance the research background of this work, such as: “PNAS 2021, 118 (40), e2110036118.; Adv. Energy Mater. 2025, 2405236.; PNAS 2023, 120 (26), e2303262120.; Nano Lett. 2020, 20 (10), 7662-7669.”
6. Integrate the discussion of different characterization techniques to show their complementary nature, for example, how combining XRD and NMR can comprehensively understand charge storage mechanisms.

accept