Ultralow-field nuclear magnetic resonance for direct nondestructive observation of electrolyte composition in batteries

Rechargeable batteries represent a key transformative technology for electric vehicles, portable electronics, and renewable energy. Despite enormous developments in battery research, there are few nondestructive diagnostic techniques compatible with realistic commercial cell enclosures. Many battery failures result from the loss or chemical degradation of electrolyte. Here we show measurements through battery enclosures that allow quantification of electrolyte amount, composition, and potentially degradation. This study employs instrumentation and techniques developed in the context of zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR), with optical atomic magnetometers as the detection elements. In contrast to conventional NMR methodology, the reduced background magnetic fields employed here make even potentially thick stacks of battery housing and electrodes transparent to the lower-frequency electromagnetic fields involved. Both the solvent and lithium-salt components of the electrolyte signature can be quantified, as the results described herein demonstrate.