"After The Prophet: The Epic Story Of The Shia Sunni Split In Islam" by Lesley Hazelton is one of the best books written on this topic. It is largely based on a neutral narrative and both the shia and sunni views about the incidents though more towards shia side view by the author in describing the incidents that took place after the death of Prophet Muhammad. Most narrative regarding the split comes from Shia side that is why it is understandable why we see mostly shia point of view given more importance. For example discussing events based on narrations that have been proven fake. The book can be downloaded in PDF format from here.