It is commonly accepted that Shields works very well with the Imperius. However, with the new "Power" update, the method of obtaining ships changed, and the battleship was added. With the new update, not only does this strategy require the shields and navigation techs, it also requires a strong economy.
The Imperius generally start out near large bodies of water, and the amount of resources they have is considerable. In order to use this strategy to full effect, you must first expand your economy alongside expanding your territory. If you only focus on one, then your economy will never achieve full power. Sometime along the way, you must research Shields in order to defend your cities. After you have increased your star production to ~20 stars per turn, you should begin researching the Sailing and Navigation techs, as they will allow you to build different warships and increase your economy. The last step is the simplest and easiest. If you have managed to miraculously expand your economy to size, the game is basically yours. All you need to do is spam defenders and build battleships with them. If you have managed to do this, Congratulations! You have managed to use a strategy that was almost rendered dead with the new "Flight" update. However, keep in mind one thing: this strategy used to be very easy to use, but it is now way harder. Perfect timing is the key to this strategy. You have to be able to expand your economy while not capturing so many cities that technology becomes too expensive. Good luck and best wishes!