Original press release was issued by Drexel University.
Building materials for energy storing is a lot like baking. It requires the right ingredients in right amounts, and assembly in the correct order and under ideal conditions. And just like an overly sweet cake can benefit from a pinch of salt, the same appears to be true for batteries.
The secret to making the best storage materials is to grow them with as much surface area as possible. The desired outcome is a thin sheet of material with the perfect chemical consistency to be useful for storing energy. A team of researchers from Drexel University, Huazhong University of Science and Technology, and Tsingua University recently discovered that using salt crystals as a template to grow thin sheets of conductive metal oxides make the materials turn out larger and more chemically pure — which makes them better suited for gathering ions and storing energy.
Energy storage device operate by a chemical transfer of ions from an electrolyte solution to thin layers of conductive materials. In theory, the best materials for the job should be thin sheets of metal oxides because their chemical structure and high surface area makes it easy for ions to attach – which is how energy storage occurs. However, metal oxides have thus far failed to live up to their theoretical performance.
“The challenge of producing a metal oxide that reaches theoretical performance values is that the methods for making it inherently limit its size and often foul its chemical purity, which makes it fall short of predicted energy storage performance,” said Jun Zhou, a professor at HUST’s Wuhan National Laboratory for Optoelectronics and an author of the research.
According to Zhou, Tang and the team from HUST, the problem lies in the process of making the nanosheets — which involves either a deposition from gas or a chemical etching — often leaves trace chemical residues that contaminate the material and prevent ions from bonding to it. In addition, the materials made in this way are often just a few square micrometers in size.
As it turns out, the structure of ordinary salt solves this issue. Using salt crystals as a substrate for growing the crystals lets them spread out evenly and form a larger uniform sheet of oxide material.
“Lateral growth of the 2D oxides was guided by salt crystal geometry and promoted by lattice matching and the thickness was restrained by the raw material supply. The dimensions of the salt crystals are tens of micrometers and guide the growth of the 2D oxide to a similar size,” the researchers write in the paper.
As predicted, the larger size of the oxide sheets also equated to a greater ability to collect and disburse ions from an electrolyte solution — the ultimate test for its potential to be used in energy storage devices. Results reported in the paper suggest that use of these materials may help in creating an aluminum-ion battery that could store more charge than the best lithium-ion batteries found in laptops and mobile devices today.
“The most significant result of this work thus far is that we’ve demonstrated the ability to generate high-quality 2D oxides with various compositions,” said Yury Gogotsi, an author of the paper. “I can certainly see expanding this approach to other oxides that may offer attractive properties for electrical energy storage, water desalination membranes, photocatalysis and other applications.”