In situ electron microscopy analysis of electrochemical Zn deposition onto an electrode

Aqueous zinc-based batteries are expected to be realized as low-cost and high energy density batteries; however, dendrite formation during the charging process of zinc-air batteries remains a major problem. Dendrite growth from the zinc anode is known to cause short-circuiting in zinc-based batteries because of their fast growth toward the cathode and it seems to be the main cause of cycle degradation for these batteries. Therefore, to realize long-life rechargeable zinc-based batteries, characterization of electrochemical zinc deposition is required. In situ transmission electron microscopy (TEM) observation was utilized to visualize the initial state of electrodeposition of a zinc anode with high spatial resolution. A platinum counter electrode was covered with metallic zinc by vacuum deposition, so that observation of the electrodeposition process of pure zinc was successfully achieved while preventing elution of the counter electrode. Analysis using in situ TEM observations of the zinc deposition and dissolution indicated that dissolution after dendrite growth proceeds from the parts near the root to the tips of the dendrites. It is concluded that this phenomenon is evidence that there are concentration gradients between the electrode surface and the surrounding environment during the initial process of dendrite formation.