The title basically says it all. [amazon asin=1585189421&text=Mental Toughness Training for Volleyball] by Mike Voight looks at how the game is played between a player’s ears. Small sections consider and discuss physical factors. Broadly, though, the focal points are things like motivation, intention, concentration, and confidence. As such, this book could be quite handy to help surface and address any number of issues for coaches seeking ways to go beyond technical and tactical training.
The text comprises four sections. The first two mainly focus on defining mental toughness, and they point out issues contributory to performance problems. The third section is where the author addresses mental toughness. For most readers this is the meat of the book. The last section wraps things up. It looks at the responsibilities of players and coaches in the process. The chapters tend toward being short, making for a book which is pretty easy to read.
Throughout the book the author provides a number of questionnaires and other tools. You can use these tools to help assess where players are at in terms of their motivation and mental toughness. Further, they can help identify potential issues, both with individuals and the team overall. Additionally, there is a good-sized reference section at the back of the book for further reading. All together, this makes a pretty good long-term reference for volleyball coaches.
You may also want to look at The Brain Always Wins.