Tracking lithium ions in an electrolyte

Over time, lithium-ion batteries need more frequent recharging. And on rare occasions, the batteries can catch fire when lithium builds up on the anode, forming sharp spikes that pierce the membrane that separates the anode from the cathode. A new way to directly image lithium ions could help researchers better understand why these problems happen (ACS Sens. 2017, DOI: 10.1021/acssensors.7b00087). Randall H. Goldsmith of the University of Wisconsin, Madison, and colleagues redesigned a fluo­rescent organic molecule that binds selectively to lithium ions so that the molecule fluo­resces when excited by blue light instead of ultraviolet light, which can reduce image quality. The researchers then created a simple test platform consisting of the molecule—2-(2-hydroxyphenyl)naphthoxazole (shown)—and an electrolyte within a microfluidic channel. They injected lithium chloride solutions into the channel and showed that the fluorescence intensity grew with increasing ion concentration. Then the group used the system to track the diffusion of lithium through the electrolyte. They now plan to design a test battery that’s transparent on one side to evaluate the fluo­rescence imaging method further.