To add borders inside a cell and sub-divide it with a different border line type, you can follow these steps:

1. Select the cell or cells that you want to add borders to.
2. Click on the "Borders" dropdown menu in the "Home" tab of the ribbon.
3. Select "More Borders" at the bottom of the menu.
4. In the "Format Cells" dialog box, go to the "Border" tab.
5. Under "Presets", select the type of border you want to apply to the outside of the cell.
6. Under "Style", select the type of border you want to apply to the inside of the cell.
7. Under "Color", select the color you want for the border.
8. Under "Width", select the thickness of the border.
9. Use the preview pane to see how the border will look.
10. Click "OK" to apply the border to the selected cell(s).

You can also use the "Draw Borders" tool to draw custom borders inside the cell. To do this, follow these steps:

1. Select the cell or cells that you want to add borders to.
2. Click on the "Borders" dropdown menu in the "Home" tab of the ribbon.
3. Select "Draw Borders" at the bottom of the menu.
4. Use the pencil tool to draw the border inside the cell.
5. Use the eraser tool to remove any unwanted lines.
6. Use the preview pane to see how the border will look.
7. Click "OK" to apply the border to the selected cell(s).

By following these steps, you can easily add borders inside a cell and sub-divide it with a different border line type.