### A New Method for Visualizing Binders in Lithium-Ion Batteries

A study using energy-selective backscattered electron (EsB) imaging has enabled the detection of nanoscale layers of carboxymethyl cellulose (CMC) and agglomerates of styrene-butadiene rubber (SBR) on graphite particles in a lab-made lithium-ion battery anode after bromine treatment. Differences in the stability of brominated SBR and CMC during electron imaging allow for the individual identification of both binders in EsB images. To further distinguish the binder phases, the images were additionally colorized.

#### Method Development and Its Significance

An advanced technique was developed that allows for clear visualization of key components within lithium-ion battery electrodes, which were previously difficult to track. The results, published on February 17 in Nature Communications, could improve battery manufacturing efficiency and help enhance charging speed and battery lifespan.

#### The Role of Binders in Batteries

The research focused on polymer binders used in the negative electrodes (anodes) of lithium-ion batteries. These binders act as glue, holding the electrode materials together. Although they make up less than 5% of the electrode’s total mass, they significantly affect mechanical strength, electrical and ionic conductivity, and the battery’s durability over many charge cycles. Due to their small quantities and lack of clear visual markers, pinpointing their location within the electrode has been challenging, limiting the ability to optimize battery characteristics, since binder distribution directly impacts conductivity, structural stability, and lifespan.

#### Patented Marking Method

To address this, a patented staining method was developed, in which traceable silver and bromine markers are attached to widely used cellulose and latex binders in graphite and silicon anodes. After marking, the binders become detectable through characteristic X-ray signals (measured by energy-dispersive X-ray spectroscopy) or by the reflection of high-energy electrons from the sample surface (measured by energy-selective backscattered electron imaging). When observed under an electron microscope, these signals allow for detailed mapping of element distribution and electrode surface structure, providing a much more accurate analysis of binder distribution.

The method is applicable to both standard graphite electrodes and modern materials such as silicon and SiOx, making it relevant for current and next-generation batteries.

#### Impact of Binder Distribution on Battery Performance

Using this new visualization tool revealed that even minor changes in binder distribution can significantly affect charging efficiency and battery life. During testing, adjusting the mixing and drying stages of the slurry reduced the internal ionic resistance of experimental electrodes by up to 40%, a crucial factor for fast charging.

Detailed images were obtained of extremely thin CMC layers coating graphite particles. The method enabled detection of CMC layers as thin as 10 nm and visualization of structures spanning four orders of magnitude in a single image. It was found that initially uniform CMC coatings can fragment during electrode processing, potentially reducing battery performance and stability.

#### Application Prospects

This interdisciplinary work, combining chemistry, electron microscopy, electrochemical testing, and modeling, has led to an innovative approach to visualization that advances understanding of key surface processes affecting battery longevity and performance. This opens up opportunities for progress across a wide range of battery technology applications.

The research was supported by the Nextrode Faraday Institution project and has already attracted significant interest from industry, including major battery and electric vehicle manufacturers.