Significant
progress has been made in recent years in theoretical
modeling of the electric double layer (EDL), a key concept in electrochemistry
important for energy storage, electrocatalysis, and multitudes of
other technological applications. However, major challenges remain
in understanding the microscopic details of the electrochemical interface
and charging mechanisms under realistic conditions. This review delves
into theoretical methods to describe the equilibrium and dynamic responses
of the EDL structure and capacitance for electrochemical systems commonly
deployed for capacitive energy storage. Special emphasis is given
to recent advances that intend to capture the nonclassical EDL behavior
such as oscillatory ion distributions, polarization of nonmetallic
electrodes, charge transfer, and various forms of phase transitions
in the micropores of electrodes interfacing with an organic electrolyte
or ionic liquid. This comprehensive analysis highlights theoretical
insights into predictable relationships between materials characteristics
and electrochemical performance and offers a perspective on opportunities
for further development toward rational design and optimization of
electrochemical systems.