# Chemical staining for fundamental studies and optimization of binders in Li-ion battery negative electrodes

## TL;DR

Researchers developed a staining method to visualize and optimize Li-ion battery binders, improving electrode performance and stability.

## Contribution

A novel staining technique using silver and bromine enables detailed imaging and optimization of Li-ion battery binders.

## Key findings

- Staining methods reduced electrode electronic resistivity by 14% and ionic resistance by 40%.
- Binder films on graphitic surfaces shatter into inhomogeneous fragments after calendering.
- Staining reveals nanoscale binder structures and agglomerates affecting battery performance.

## Abstract

The spatial distribution of binders in Li-ion battery electrodes is critical to electrode performance, yet remains challenging to visualise, limiting binder optimisation efforts to chemical modifications rather than spatial control. Here, we show an accessible approach to staining carboxymethyl cellulose and styrene butadiene rubber binders in graphitic and Si-based Li-ion electrodes with silver and bromine, enabling detailed electron imaging and precise spectroscopic quantification of the binder domain. Leveraging these methods, we perform binder-informed optimisation of electrode manufacturing, achieving a 14% reduction in electronic resistivity, suppression of binder migration during high-temperature electrode drying, and a 40% decrease in electrode ionic resistance. Furthermore, staining enables electrode-scale, high-resolution backscattered electron imaging of complex binder hierarchies, revealing multiple types of agglomerates and elusive nanoscale binder films. These films completely coat graphitic surfaces in pristine electrodes but shatter into highly inhomogeneous fragments after calendering in both research-grade and commercial electrodes, presenting new perspectives on interpreting common cycling stability and electrode performance issues. We show how binder staining can advance fundamental understanding, quality control and manufacturing optimisation of Li-ion electrodes, particularly those based on widely used water-processable binders.

Battery electrode binders are hard to image but strongly affect battery performance. Here, authors use silver and bromine staining to reveal common cellulose- and rubber-based binders in graphite and Si negative electrodes and identify processing that reduces electrode resistance.