Electric Potential Distribution on Lithium Ion Battery Cathodes Measured Using Terahertz Chemical Microscopy

A terahertz chemical microscope has been developed to visualize electric potential distribution on lithium ion battery cathodes during battery operation. A sensing plate comprising a Si film grown epitaxially on a sapphire substrate was used as a terahertz emitter. The amplitude of terahertz radiation from the sensing plate could be related to the electric potential at the exact point where a femtosecond laser illuminated. Here, the sensing plate was integrated into a conventional can-type lithium ion battery and terahertz radiation from the sensing plate was observed during battery operation between 2.7 and 4.2 V. By scanning the laser, the distribution of terahertz amplitude radiated from the sensing plate was observed, which could be related to the electric potential distribution on the electrodes of the batteries. Localized electric potential could be visualized as the amplitude of terahertz radiation generated in the sensing plate, which was integrated beneath the battery electrode.