Structure of lithium dendrite in polymer electrolytes

The structure of Li dendrites grown in solid polymer electrolytes (SPE) has been studied using a symmetric sandwich cell of Li / poly(ethyleneoxide) (PEO) : lithium bis(trifluoromethane) sulfonamide (LiTFSI) / Li as a model system. In situ neutron depth profiling (NDP) during directional Li pumping and plating shows that dendrites start to grow, and eventually short-circuit the battery. Li dendrite 3D mapping reveals rather heterogeneous lateral distribution of Li over wide length scales from below a millimeter to centimeters. While the lateral mobility of Li appears to be large, most dendrites grow from the plating electrode, with the overall composition decreases linearly from the electrode interface to the bulk of the electrolyte. It is observed that dendrites also grow from the bottom electrode, where presumably only Li oxidation reaction occurs. The revelation poses new design and engineering challenges in using Li metal electrode in future batteries.