Excel export does not contain Sys ID field but in some cases it's required to provide it when importing data back to the system. Below is one of the methods how to include the Sys ID value associated with a record in the export.
Append the following parameter to a URL of a list view to get it to include Sys ID in the resulting file:
This parameter tells the web service to export all fields from the table including the Sys ID. Beware that this also brings every other field along with it. Example URL:
Alternatively, you can use XML export or JSON export (Jakarta and later versions) which contain Sys IDs.
More on exporting data with Sys IDs in this blog post on the Developer site: Exporting data with Sys IDs