Electrochemistry Coupled to Mass Transport, Battery, and Tertiary Current Distribution Models
If the model involves electrochemistry coupled to mass transport, here are a few things to try to help improve model convergence.
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Review the Initial Values for the concentration values. Zero initial concentration values can cause issues in tertiary current distributions and battery simulations since that could imply that no charge carriers or no reacting material is present initially.
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If steep concentration gradients are expected close to electrode surfaces, use boundary layer meshing or finer size settings at these boundaries.
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When setting up user-defined kinetics expressions, avoid evaluating negative concentrations by using expressions such as max(c, eps^2), where eps is the machine epsilon; that is, it is a very small floating-point number.
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Try to solve for low currents or low overpotentials first, then increase the cell load (for stationary problems this can be done using an Auxiliary Sweep with Continuation enabled).
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If a problem involving mass transport is hard to solve for high currents, but solves for low currents, it might be due to mass transport limitations. In this case, review the transport parameter values and check that the current magnitudes are reasonable. If the current densities are unreasonably high, review the electrode reaction settings.
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Electrochemistry Interfaces
In the COMSOL Multiphysics Reference Manual:
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2D and 3D Boundary Layer Meshes
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Stationary and Parametric Sweep