Merge and unmerge cells
You can't split an individual cell, but you can make it appear as if a cell has been split by merging the cells above it.
Merge cells
1. Select the cells to merge.
2. Select Merge & Center, then Merge Cells.
Merge Cells
Unmerge cells
1. Select the Merge & Center down arrow.
2. Select Unmerge Cells.
Unmerge Cells