1：Experimental Design and Method Selection:

The study involves designing and manufacturing optical sensors (core Bragg gratings and surface cladding waveguide Bragg gratings) using femtosecond laser inscription methods. These sensors are integrated into lithium ion battery cells to monitor internal parameters such as strain, temperature, and refractive index. The experiments include cell cyclization, abuse testing, and post-mortem analysis to evaluate sensor performance and cell behavior.

2：Sample Selection and Data Sources:

Lithium ion pouch cells with a capacity of 5 Ah are manufactured using specific electrode materials (graphite anode, NMC cathode) and electrolytes (EC:DEC with LiPF6). Optical sensors are integrated into the anode or separator layers. Data is collected during charging/discharging cycles and abuse tests using optical spectrum analyzers and electrical cyclization units.

3：6). Optical sensors are integrated into the anode or separator layers. Data is collected during charging/discharging cycles and abuse tests using optical spectrum analyzers and electrical cyclization units. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes femtosecond pulsed lasers (Spectra-Physics Ti:Sapphire Tsunami/Spitfire pro), translation stages (PI N-565.260), optical spectrum analyzers (Yokogawa AQ6370B), cyclization units (BaSyTec HPS), temperature chambers (V?tsch VT 4021), and various chemicals for etching and electrolyte preparation. Materials include standard telecommunication glass fibers (Leoni SMF810-E5/125PI), electrode materials (e.g., Imerys TIMREX SLP-30 graphite), and electrolytes.

4：260), optical spectrum analyzers (Yokogawa AQ6370B), cyclization units (BaSyTec HPS), temperature chambers (V?tsch VT 4021), and various chemicals for etching and electrolyte preparation. Materials include standard telecommunication glass fibers (Leoni SMF810-E5/125PI), electrode materials (e.g., Imerys TIMREX SLP-30 graphite), and electrolytes. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Sensors are inscribed into fibers using laser methods, integrated into battery cells during manufacturing, and subjected to formation cycles and abuse tests. Optical signals are monitored during cyclization, and data is analyzed for correlations with electrical performance. Post-mortem analyses are conducted to inspect cell components.

5：Data Analysis Methods:

Optical signals are analyzed using Gaussian curve fitting and averaging. Wavelength shifts are correlated with strain, temperature, and refractive index changes. Statistical methods are used to establish relationships between optical signals and cell states, such as state of charge and health.