"Think of the cathode in a lithium-ion battery (LIB) as a building," said Vyacheslav Volkov of the Kurnakov Institute of General and Inorganic Chemistry in Moscow, and leader of the research project. "Whenever the supports inside the building are removed, the walls and ceiling might be damaged and collapse."

In Volkov’s analogy, the supports are the lithium ions that cycle back and forth as the battery is used and replenished. In work presented at the International Conference on Advanced Energy Materials held last week at the University of Surrey in the UK, Volkov described how the walls and ceiling can be reinforced, and the structure of the electrode maintained.

Volkov and colleagues started with a standard LNMC battery, in which the cathode is composed of nickel, manganese and cobalt. The group then used an inexpensive, wet-chemistry technique to coat the cathode with a thin film of α-Al2O3. Known more commonly as corundum, α-Al2O3 is second in hardness only to diamond, and served here to stabilize the electrode’s grain structure. Electron diffraction measurements showed that the metal oxide film was deposited epitaxially on the electrode material, and this strong coupling of materials is the key factor that enables the improvement in durability.

Although the Al2O3 coating helped prolong the electrode’s lifespan as expected, its insulating effect compromised the performance of the battery. To compensate for this, Volkov’s team incorporated a film of carbon within the electrode. This addition provided a conducting interface between the grains and allowed current to flow despite the insulating coating of Al2O3.

The researchers found that their Al2O3- and carbon-treated battery was much more resilient than the pristine equivalent, suffering half as much capacity degradation after 100 cycles.