In order to submit a PyFerret job in batch mode, you need to create a .jnl script and execute it in batch mode. You can for instance submit a script example.jnl with the following command:
sbatch [Slurm options] --wrap="pyferret [pyferret options] -batch -script example.jnl"
Here you need to replace [pyferret options] with pyferret command line options (please run pyferret -h for getting a list of all command line options) and [Slurm options] with Slurm parameters for the resource requirements of the job. Please find a documentation about the parameters of sbatch on the wiki page about the batch system.