Anode-free metal batteries have the potential to maximize energy density by eliminating prefabricated anodes. For example, in magnesium metal batteries, instead of starting with an Mg anode, a bare metal current collector, usually copper or zinc, is used as the anode side. When the batteries are first charged, Mg from the cathode is deposited directly onto this collector, forming a thin Mg layer that acts as the anode. The elimination of excess anode materials can make batteries lighter, more compact and cheaper.
Unfortunately, these batteries suffer from dendrite formation, which significantly affects battery capacity and stability, and poses the risk of short-circuiting.
Now, a research team led by Associate Professor Hee-Dae Lim at Hanyang University in South Korea has developed a novel facet-guided metal plating strategy to address this issue. “We proposed a crystallographic strategy to achieve controlled Mg deposition by employing a facet-oriented Zn host, with a physicochemically polished surface,” explains Dr. Lim.
The team describes their work in “Facet-Guided in-Plane Metal Plating via Accelerated Surface Diffusion in Mg Metal Batteries,” published in Advanced Energy Materials.
Normally, current collector materials are used in their polycrystalline forms, which have randomly oriented grains and a high density of grain boundaries. Grain boundaries create an uneven surface and “hot spots” where Mg atoms pile up during plating, resulting in vertical Mg growth and eventually dendrites.
The researchers employed three key design approaches to solve this.
First, they chose Zn, which is structurally similar to Mg, as the host metal.
Second, they engineered the Zn host to selectively expose the thermodynamically stable facet, which gives Mg a smooth path to spread quickly and evenly across the surface.
Third, to minimize the impact of grain boundaries, the resulting zinc substrate was subjected to reactive ion etching, creating a physicochemically polished surface. In electrochemical tests, this effectively suppressed dendrite formation and improved battery stability, thanks to uniform, horizontal Mg growth. A full anode-free Mg cell retained 87.58% of its initial capacity over more than 900 cycles at a high current density of 200 mA g-1, well above typical operating conditions.
“Our facet-guided Mg-metal platform can lead to the development of next-generation Mg-metal batteries with high energy densities that will be valuable for upcoming renewable energy-based smart grid infrastructure,” says Dr. Lim.
Source: Hanyang University
