Is there a material that conducts heat well and has a very high melting point, but is also an insulator?
Diamond, BeO and AlN are useful heat transfer materials with
negligible electrical conductivity.   There's nothing perfect, however,
and diamond is expensive, BeO is associated with toxic
dusts at manufacturing time, and AlN is a modern material few people
are familiar with.

Aluminum's thermal conductivity is a little over 200 watts per
meter x Kelvin (W/K-m), while diamond is 900-2320 W/K-m.
BeO is 330 W/K-m, and AlN is 285 W/K-m.