Here are some books from the Books wiki under the slavery section in Africa.

"Portuguese" Style and Luso-African Identity by Peter Mark. It's about 16th-19th century Senegambia and how long distance trade prior to colonialism influenced both Europe and Africa. Through the lens of architecture Mark is able to communicate the nature of ethnicity and identity in Africa prior to colonialism. It seems specific- but it's a great book to learn about the fluidity of identity and ethnicity in African societies before colonialism- which is a significant concept for all of precolonial Africa.

Africa and Africans in the Making of the Atlantic World; 1400-1800 by John K. Thornton. A scholarly account of the economic and social drivers of the Atlantic Slave Trade, but highlights the agency of African rulers in engaging in trade.

The African Slave Trade by Basil Davidson, revised ed., 1988. As he was an expert in Portuguese colonies, his research and knowledge are particularly strong in that area.

Transformations in Slavery by Paul E. Lovejoy, 2000 (2nd edition). Attempts to provide a comprehensive overview of the institution of Slavery in Africa, from the Islamic slave trade and the Atlantic Slave Trade to African domestic slavery. Notable for Lovejoy's critique that African domestic slavery was not as mild as previous generations of scholars had thought.

The Way of Death: Merchant Capitalism and the Angolan Slave Trade 1730-1830 by Joseph C. Miller. Dealing exclusively with the Congolese and Angolan Portuguese lead slave trades in the Atlantic this Miller goes into great detail into how slaves were procured in the interior and transported to the coasts and eventually to the Americas. Miller is particularly good at teasing out the intricicies of African slave trade based states and how the institution of slavery became a full blown enterprise for wealth creation in Central Africa.

From Slave Trade to 'Legitimate' Commerce edited by Robin Law, 1995. A collection of scholarly papers exploring the economic transformations that occurred in coastal West Africa following the outlawing of the slave trade in the early 19th century. These essays attempt to answer the central question "was there an economic crisis of adaptation among African polities following the outlawing of the Atlantic Slave Trade?"