New sodium metal anode for rechargeable batteries could replace lithium

“We’re essentially solving two problems at once. Typically, the faster you charge, the more of these dendrites you grow. So if you suppress dendrite growth, you can charge and discharge faster, because all of a sudden it's safe.”David Mitlin

Scientists at the University of Texas at Austin have developed a new sodium-based battery material that offers useful stability and can recharge as fast as a standard lithium-ion battery. As the new material overcomes a major problem with sodium batteries, it could lead to delivering more energy than existing battery technologies.

With demand growing for household energy storage systems and to smooth out variations in renewable energy on electric grids, an alternative to lithium-ion batteries, which contain expensive and non-environmentally friendly lithium and cobalt, has been much sought after. Although sodium has been seen as a replacement, the anode in earlier sodium batteries often grew needle-like filaments called dendrites, which can result in the battery electrically shorting, or even catching fire or exploding.

As reported in Advanced Materials [Wang et al. Adv. Mater. (2021) DOI: 10.1002/adma.202106005], here the researchers produced a material that overcomes the difficulty of dendrites and recharges just as quickly as a lithium-ion battery. As the designer of the new material, David Mitlin, said “We’re essentially solving two problems at once. Typically, the faster you charge, the more of these dendrites you grow. So if you suppress dendrite growth, you can charge and discharge faster, because all of a sudden it's safe.”

On charging a rechargeable battery, ions such as lithium or sodium move from the cathode to the anode, and when the battery is being used to generate electricity, the ions move in the reverse direction. Here, the new material, sodium antimony telluride intermetallic - Na metal composite (NST-Na), was produced by rolling a thin sheet of sodium metal onto an antimony telluride powder, folding it over on itself, and then repeating the process many times.

The process allows for a very uniform distribution of sodium atoms, making it less likely to form dendrites or surface corrosion than current sodium metal anodes, and also means the battery is more stable and has charges faster than lithium-ion batteries. The battery also has a higher energy capacity than existing sodium-ion batteries. The breakthrough offers a robust approach based on in situ reacted metallurgical composite foil, and is effective in tuning sodium anode's plating behavior without adding much weight to the electrode, as well as providing useful insight on the metal microstructures and the associated energetics.

In separate research, the team demonstrated that even electrolyte wetting is not favored on planar copper foils, and that dendrites are an intrinsic feature of the plating process. This means that, when transitioning to metal batteries, it could be necessary to incorporate a further feature into the anode architecture beyond the planar copper foils.