The company then turned its attention to the opposite electrode,
which is usually made of graphite. Researchers decided to use
silicon, which can store far more energy but typically works for
only a short number of charges, since it swells and cracks.
Envia addressed these issues by using a porous form of silicon,
which is better able to tolerate expansion and contraction, and
by mixing the silicon with various forms of carbon, including
carbon fiber and graphite. The carbon is meant to provide a path
for electrons to take through the material, bridging gaps that
form as the silicon cracks. The researchers also had to modify
the electrolyte to keep it from breaking down at the high
voltage levels seen in the battery cell. To develop the
materials, Envia took the unusual approach of testing new
electrode materials in complete batteries, with both electrodes
and an electrolyte. Usually researchers test electrode materials
in isolation to identify those with promising properties, such
as high energy capacity. Bu