  Construction of binary black hole initial data is a prerequisite for
numerical evolutions of binary black holes. This paper reports improvements to
the binary black hole initial data solver in the Spectral Einstein Code, to
allow robust construction of initial data for mass-ratio above 10:1, and for
dimensionless black hole spins above 0.9, while improving efficiency for lower
mass-ratios and spins. We implement a more flexible domain decomposition,
adaptive mesh refinement and an updated method for choosing free parameters. We
also introduce a new method to control and eliminate residual linear momentum
in initial data for precessing systems, and demonstrate that it eliminates
gravitational mode mixing during the evolution. Finally, the new code is
applied to construct initial data for hyperbolic scattering and for binaries
with very small separation.
