the propagation of a peace lily (spathiphyllum wallisii) is not difficult and can be made by division. it can be done any time of the year, for example when the plant needs to be re-potted.
use a sharp and clean knife to cut away a crown from the parent plant. this crown should be good rooted with a minimum of three leaves.
now you can pot the peace lily propagation by using a regular potting mix. for a better humidity put a freezing bag over the pot. to avoid mould ist should be aired once a day. remove it when spathiphyllum wallisii is showing new leaves.
the care is the same as for the parent plant. for the first two to three months there is no need for fertilizing.