Researchers have found a way to make lithium ion batteries hold a charge ten times greater than they do at present, and charge ten times faster. To do this they have had to overcome some limitations of wonder-material graphene.
Consider the anode of a standard Lithium ion battery. It is made up of layers of graphene sheets which react with incoming lithium ions and trap them. Silicon would actually have a better charge density that graphene for this job, as it can hold four Lithium ions per silicon atom, compared to graphene’s one per six. But it is too fragile and brittle to withstand multiple charge cycles, and quickly fragments, losing the ability to charge at all.
The researchers discovered that introducing silicon in clusters between layers of graphene allows more charge to be held, while the graphene sheets stabilise the silicon as its volume changes during the charging process. The result is an increase in charge density without the degraded performance that comes using silicon alone.
Another problem is that the route a Lithium ion must take through the graphene sheet is long, and causes a build up of ions at the edges of the carbon material which the researchers refer to as "an ionic traffic jam". This limits the speed with which the battery can be re-charged.
The team dealth with this by introducing small holes – just 10-20 nanometers across - into the graphene lattice. These effectively provide a shortcut into the anode for the Lithium ions, hugely increasing the charge rate.
The paper "In-Plane Vacancy-Enabled High-Power Si-Graphene Composite Electrode for Lithium-Ion Batteries" is published in the journal Advanced Energy Materials.