What Is the Solid Electrolyte Interface (SEI)

The Solid Electrolyte Interface (SEI) is the interface between the solid electrode material and the liquid electrolyte.

Interface refers to a location. Interphase refers to the processes that take part between the two phases of solid active material, and the liquid electrolyte phase (that is, interphase reaction).

SEIs are created between interfacing liquid-solid regions, where both the Li-Ion Concentration model, and the Li-Ion Electric Potential model are selected on both sides.

At the Solid Electrolyte Interface (SEI) and in the electrolyte, both physics models are coupled in the following manner:

  • The interface conditions for both electric fluxes and concentration depend on the same SEI normal component of electric current density. The SEI normal current is computed from the Butler-Volmer relationship, which is in turn a function of both solid/liquid electric potentials and solid/liquid concentrations.
  • The electric potential is solved using Eqn. (4101) which depends on the solution for the Lithium/Salt Concentration c .
  • Concentration transport depends on electric potential, see Eqn. (4097) and Eqn. (4103).

The model transport equations for the solid phase (Eqn. (4100) and Eqn. (4102)) do not contain terms which are directly coupling the electric potential with the Li-Ion concentration.