Excel chart show year intervals on axis
Solution 1:
Not sure how your data is laid out, but you can do this by putting the year in its own column.
Then select the month and year as the axis labels.
Source: Show Months & Years in Charts without Cluttering
Solution 2:
Format years as dates in source. For horizontal axis use Years for Major unit and Months for Minor unit. Format Axis Number as something like " | "yyyy may be about as close as Excel will get you, without say overlaying a text box with the desired layout:
