Researchers have developed a battery anode based on a new nanostructured alloy. The zinc- and manganese-based alloy further opens the door to replacing solvents commonly used in battery electrolytes with something much safer, less expensive, and abundant: seawater.
A battery stores power in the form of chemical energy and through reactions, converts it to the electrical energy needed to power vehicles, cellphones, laptops, and many other devices and machines. A battery consists of two terminals — the anode and cathode, typically made of different materials — as well as a separator and electrolyte, a chemical medium that allows for the flow of electrical charge.
In a lithium-ion battery, as its name suggests, a charge is carried via lithium ions as they move through the electrolyte from the anode to the cathode during discharge and back again during recharging. Electrolytes in lithium-ion batteries are commonly dissolved in organic solvents that are flammable and often decompose at high operation voltages. Thus, there are safety concerns with lithium dendrite growth at the electrode-electrolyte interface that can cause a short between the electrodes. Dendrites resemble tiny trees growing inside a lithium-ion battery and can pierce the separator like thistles growing through cracks in a driveway. The result is unwanted and sometimes unsafe chemical reactions.
Aqueous batteries are a promising alternative for safe and scalable energy storage. Aqueous electrolytes are cost-competitive, environmentally benign, capable of fast charging and high power densities, and highly tolerant of mishandling. Their large-scale use, however, has been hindered by a limited output voltage and low energy density (batteries with a higher energy density can store larger amounts of energy, while batteries with a higher power density can release large amounts of energy more quickly).
The new anode is made up of a three-dimensional “zinc-M alloy” as the battery anode (M refers to manganese and other metals). The use of the alloy with its special nanostructure not only suppresses dendrite formation by controlling the surface reaction thermodynamics and the reaction kinetics, but also demonstrates super-high stability over thousands of cycles under harsh electrochemical conditions. The use of zinc can transfer twice as many charges as lithium, thus improving the energy density of the battery.
The team used X-ray absorption spectroscopy and imaging to track the atomic and chemical changes of the anode in different operation stages, which confirmed how the 3D alloy was functioning in the battery. The concept could influence the design of high-performance alloy anodes for aqueous and non-aqueous batteries.