You need the TEXT() Function along with the Vlookup to display the result in % Format.
I have had the same issues while I was using the Vlookup Function and Importjson.gs
Below is a sample Formula, will help you.
NB: For more details on this issue you can also refer this link.
Now let me clear one crucial issue. The above written Formula will convert the looked up value into percentage, simply multiply it by 100. Like 1 will 100%, and Excel therefore mean it. So be careful.
If your simple intention is display the % sign along with the Number then use this,