There are many factors which account for the useful life of a battery. The charges left is one of them but there are also other concerns which include swelling and shrinking as they absorb the lithium ions.
Apparently the electrodes do swell which lead to the batteries eventually breaking down. But with a new conductive elastic polymer, batteries may eventually last longer with the new coating that reportedly heals its own cracks after each use.
The said polymer coating incorporates an elastic material which were already developed by a team from Stanford University led by on Dr. Zhenan Bao. Carbon nanoparticles were added for this application, to make the polymer electrically conductive.
When silicon electrodes were coated with the material, it held them together throughout their swelling and shrinking cycles a reported ten times longer than when they were left uncoated. The self-healing quality of the material was made possible by deliberately weakening some of the existing polymer’s chemical bonds.