I have a class on empathy and these are the books my professor has on the bibliography:

• Edwards, D.C.(1999): Motivation and Emotion: evolutionary, physiological, cognitive and social influences. Thousand Oaks, CA,USA: Sage
• Frijda, N.H. (1986). The emotions. New York: Cambridge University Press,
• LeDoux, J. (1998). The Emotional Brain. The Mysterious Underpinnings of Emotional Life. New York: Simon & Schuster
• Lewis, M., Haviland Jones, J.M. & Barrett, L.F. (2010). Handbook of Emotions (3rd Edition). New York: The Guilford Press
• Panksepp, J.(1998/2004). Affective Neuroscience. The Foundations of Human and Animal Emotions (Series in Affective Science (paperback). Oxford: OUP
• Reeve, J. (2015). Understanding Motivation and Emotion, 6th Edition. NY: John Wiley & Sons
• Toates, F. (2011). Biological Psychology 3rd Edition. Essex, UK: Pearson.
• Weiner, B. (1992). Human Motivation: Metaphors, Theories and Research. London: Sage

I hope it helps!