When I add library WebPart I lose the navigation bar (A=>B) th ebreadcrumb
I added webpart to get folder and subfolders: like this : https://anothersharepointblog.wordpress.com/2013/04/03/sharepoint-document-library-list-view-view-web-part-with-clickable-breadcrumbs/
There isn't an OOB way. You can inject a script that create a breadcrumb to enable you to navigate the folder structure.
You can find the code here: https://github.com/RiccardoGDev/sp-breadcrumb