Battery electrode transforms during use for faster charging
Scientists have demonstrated a new electrode material that could facilitate much faster charging for lithium batteries, and one that forms in a rather unusual way. The material actually adopts the optimal configuration of atoms through the charging process itself, in doing so taking on the form of a new material that allows for smoother transport of lithium ions.
The work was carried out by researchers at the Boise State University and the University of California San Diego, who set out to address an Achilles' heel in current lithium battery designs. As these devices are cycled, lithium ions travel from the positive electrode, called the cathode, to the negative electrode, the anode, but can only do so up to a certain speed.
At faster charging speeds, lithium metal builds up on the surface of the graphite anode, which compromises the battery’s performance and can cause it to short circuit, overheat or even catch fire. Known as lithium plating, the team sought to remove this roadblock on the route to faster charging with the help of a compound called niobium pentoxide.
The atoms within niobium pentoxide can be easily arranged into many stable configurations, and the scientists happened upon a rather convenient way of doing this. Put to use as an anode in a coin cell, the niobium pentoxide had a messy, disordered arrangement of atoms to begin with. But the scientists found that when the cell was charged and discharged several times, those atoms arranged themselves into an ordered crystalline structure.
This nanostructure is not one scientists have seen before. Described as a cubic rock-salt framework, it enables much easier transport of the lithium ions into the anode as the battery is charged. This resulted in a “superb” cycling stability at high charging speeds, with the battery exhibiting a capacity of 225 mAh g−1 at 200 mA g−1 across 400 cycles, with a Coulombic efficiency of 99.93%.
The scientists hope to adapt this approach to develop other innovative battery materials, and even materials for entirely separate fields such as semiconductors.
The research was published in the journal Nature Materials.
Source: Argonne National Laboratory