Evaluation of Aging Suppression of LiBr-coated Lithium-Air Batteries Using Time-of-Flight Secondary Ion Mass Spectrometry and Sparse Autoencoder

For understanding complex reactions in the electrodes of lithium-air batteries (LABs), time-of-flight secondary ion mass spectrometry (ToF-SIMS) is one of the most powerful methods because ToF-SIMS provides molecular information including organic and organic-inorganic complex materials. Although ToF-SIMS has been used to characterize various lithium-ion battery electrodes, low-mass peaks, less than 100 Da, were mainly focused for obtaining the distribution images and depth profiles. Nonetheless, high-mass peaks are important for identifying the products and reactions that cause battery aging. The selection of the mass peaks specific to a particular sample among similar samples, such as a particular electrode and control electrodes, is generally very difficult by manual analysis because the ToF-SIMS spectra contain more than hundreds of mass peaks. This renders the detailed evaluation by TOF-SIMS for improved LABs challenging. Herein, we demonstrate that by applying a sparse autoencoder to the ToF-SIMS data of air electrodes containing a redox mediator that suppressed aging, it was possible to distinguish specific mass peaks corresponding to the electrodes with the redox mediator, initial electrodes before aging, and aged electrodes. The results indicate that the intensity of the mass peaks originating directly from the electrolyte material increases when the residual products on the air electrode are removed by the redox mediator. The analysis presented herein can be utilized to monitor the aging and degradation of these next-generation batteries.