Ion batteries, such as lithium-ion batteries, undergo various degradation mechanisms that affect their structural integrity and performance over time. Degradation involves complex structural transformations within the anode, electrolyte, and cathode. Repeated lithium intercalation and deintercalation for the anode can cause significant volumetric changes, leading to mechanical stress, fracturing, and forming a solid-electrolyte interphase (SEI) layer. In the cathode, phase transitions and structural rearrangements can result in the loss of active material and reduced capacity. The electrolyte, meanwhile, may decompose and react with both the anode and cathode, further contributing to performance degradation and capacity fading.  

Researchers utilize in situ transmission electron microscopy (TEM) to understand these degradation mechanisms comprehensively. This advanced technique allows for real-time, atomic-scale observation of structural changes within the battery materials during operation. By constructing a miniaturized battery cell inside the TEM, scientists can directly observe how the anode, cathode, and electrolyte evolve during charge and discharge cycles. 

In this Methods Collection, we aim to include a wide range of characterization approaches to thoroughly investigate the different components of ion batteries during operation using TEM. Our objective is to compile a comprehensive set of methodologies that can address the specific needs and questions of each battery component. This approach will provide readers with the necessary tools to select appropriate techniques for their research, facilitating a deeper understanding of battery behavior and degradation mechanisms.