Academic style isn't the same as writing a journal or a piece of fiction. The best way to become familiar with this style and tone is to read more formal content - newspapers, academic-based magazines and newsletters etc. Many universities offer samples of good quality academic essays. Reading is a brilliant way to broaden your vocabulary and pick up useful style tips. You may dislike books, but they are invaluable for skills improvement.
Examine the style, language, and level of vocabulary and grammar in academic works. You won't spot any slang or smiley faces! When you write an academic essay, don't write as you speak. That is, you must follow certain norms in format and tone to make an effective argument. The reader isn't one of your friends. He or she is someone with an academic background, so write with your audience in mind.