Knowledge of the breakthrough materials in your chosen topic of energy application. So defunct technologies or technologies that are 10 years old or in commercial applications is not of interest.
For example, the paper should not focus on the different types of fuel cells but rather new materials developed to enhance the performance of the current materials. For this you have to review journal papers newer than 2010.
So for example, if you wanted to do work on fuel cells, there are many options for you. One - you can report the new developments on fuel cells latest innovation materials. Any one of these topics will have enough literature review for a 7 page paper and more.