def METHOD_NAME(self):
    if self.domain == "separator":
        return {}
    delta_phi_av = pybamm.Variable(
        f"X-averaged {self.domain} electrode surface potential difference [V]",
        domain="current collector",
        reference=self.domain_param.prim.U_init,
    )
    variables = self._get_standard_average_surface_potential_difference_variables(
        delta_phi_av
    )
    return variables