  Over the past decade, capacitive deionization (CDI) has realized a surge in
attention in the field of water desalination and can now be considered as an
important technology class, along with reverse osmosis and electrodialysis.
While many of the recently developed technologies no longer use a mechanism
that follows the strict definition of the term "capacitive", these methods
nevertheless share many common elements that encourage treating them with
similar metrics and analyses. Specifically, they all involve electrically
driven removal of ions from a feed stream, storage in an electrode (i.e., ion
electrosorption) and release, in charge/discharge cycles. Grouping all these
methods in the technology class of CDI makes it possible to treat evolving new
technologies in standardized terms and compare them to other technologies in
the same class.
