Google Summer of Code project 2016 (Importing and exporting simulator-independent model-descriptions with the Brian simulator)
The use of exporter to LEMS/NeuroML2 is very straightforward. Just set new device neuroml2 and specify the name of the output XML file.
from brian2 import *
import brian2lems
set_device('neuroml2', filename="nml2model.xml")
################
# Brian2 code #
################More details you may find in user or developer documentation.