I have a couple of ways to do this...but they're not "FUN" ways
If you send your emails through a program builder - you can set it up to deploy through 2 different steps - then you can see the batch overview by the program step. This is a pretty easy modification and allows you to leverage the built in reports in E9
If you want to show historical data, you can export the "All Email Activity" Scheduled Export report. Then, you can create the batch overview from this data for subsets of contacts. You can export the contacts in the contact group to create your first subset - and then use the balance of the contacts to create your second subset. You will have to run sql scripts or database queries to recreate your report - it's a bit more time consuming but a nice way to be able to slice and dice the data without being limited to to the canned reports in E9.
Would love to hear if there is an easier way to do this Good Luck!