Doesn't necessarily have to be books,
I'm trying to gather research material about cryptography relating to the blockchain
Especially the cutting edge research like DAG, zk-snarks, alternative consensus algorithms, alternative blockchain protocols
To know about bitcoin and blockchain, I'd recommend this book Mastering Bitcoin: Programming the Open Blockchain 2nd Edition
by Andreas M. Antonopoulos. Its 5 star on amazon. Its a little long, but you can skim through finding the main ideas for you research.
About the cryptography part, you may want to look at this one called "Cryptography and Network Security” Seventh Edition by William Stallings. A very good read. Again you can skim through and get the crucial points.