Currently, the Expansion Panel provides a single property that allows developers to use custom icons and built-in Kendo icons. In order to use a built-in icon the developer should use the whole class name rather than just the name of the icon. In contrast, the Drawer provides icon and iconClass properties that allow developers to specify whether they want to use built-in icons or custom icons: 

https://www.telerik.com/kendo-angular-ui/components/layout/api/DrawerItem/#toc-icon

https://www.telerik.com/kendo-angular-ui/components/layout/api/DrawerItem/#toc-iconclass