Materials that could make batteries charge faster identified
Researchers from University of Cambridge have identified a group of materials that could be used to make batteries charge faster. In the study published in the journal Nature, the researchers used materials with a complex crystalline structure and found that lithium ions move through them at rates that far exceed those of typical electrode materials.
Although these materials, known as niobium tungsten oxides, do not result in higher energy densities when used under typical cycling rates, they come into their own for fast charging applications, the study said.
"Many battery materials are based on the same two or three crystal structures, but these niobium tungsten oxides are fundamentally different," said Kent Griffith, a postdoctoral researcher in Cambridge's Department of Chemistry and the paper's first author.
The oxides are held open by "pillars" of oxygen, which enables lithium ions to move through them in three dimensions.
"The oxygen pillars, or shear planes, make these materials more rigid than other battery compounds, so that, plus their open structures means that more lithium ions can move through them, and far more quickly," Griffith said.
In their simplest form, batteries are made of three components: a positive electrode, a negative electrode and an electrolyte.
When a battery is charging, lithium ions are extracted from the positive electrode and move through the crystal structure and electrolyte to the negative electrode, where they are stored.
The faster this process occurs, the faster the battery can be charged.
Using a technique called pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy, which is not readily applied to battery electrode materials, the researchers measured the movement of lithium ions through the oxides, and found that they moved at rates several orders of magnitude higher than typical electrode materials.
Most negative electrodes in current lithium-ion batteries are made of graphite, which has a high energy density, but when charged at high rates, tends to form spindly lithium metal fibres known as dendrites, which can create a short-circuit and cause the batteries to catch fire and possibly explode.
"In high-rate applications, safety is a bigger concern than under any other operating circumstances," said Professor Clare Grey who is the paper's senior author.
"These materials (niobium tungsten oxides), and potentially others like them, would definitely be worth looking at for fast-charging applications where you need a safer alternative to graphite," Grey said.
In addition to their high lithium transport rates, the niobium tungsten oxides are also simple to make, the study said.
Apart from a possibility of a smartphone which could be fully charged in minutes, better batteries can also lead to the widespread adoption of two major clean technologies: electric cars and grid-scale storage for solar power.
