Unfortunately for us all, the secondary sources in Western academia on Chinese identity are few and far between. Identity is quite often mentioned in passing in a lot of research dealing with other things. Actually, there may be more written about China's "new" identity in the modern 21st century. I think maybe because China post-Mao has become such a fundamental part of the global economy, and there are plenty of American politicians who are worried about a more belligerent China in the future and how that can displace and/or disrupt the current order. But onto your question...

One of the more definitive works in the field is Lowell Dittmer's China's Quest for National Identity (Cornell University Press, 1993). This is a great start for you.

Jonathan Spence's The Search for Modern China (W. W. Norton & Company, 1991) also delves into identity, but goes as far back as the 17th century, so maybe not exactly what you want but perhaps worth a look.

I haven't read it, but Mark Elliot's The Manchu Way (Stanford University Press, 2001) does a lot to tie in how Manchu identity developed alongside Han identity throughout the Late Imperial Period.

From there, if you decide to buy or get a hold of some of these, you can check into the bibliography and see what citations they're using.

Also, if you have access to JSTOR, you should check out certain articles like this that cover the subject.

But back to the warning in my first paragraph. You'll notice that the dates of these works are all 1990s/early 2000s. Recent research has shifted towards the new Chinese identity forming in a post-Mao world, which is very unlike Republican/Mao China. Indeed a current argument among academics centers around Xi Jinping himself and the adoption of new governing policies which reek of Confucian influence rather than any sort of Western-leftist influence (see: Social Credit System for example).

Perhaps a silver lining? If you're Chinese and can read Hanzi, then there are plenty of documents out there that address this subject in Chinese. On the other hand, it is increasingly hard for academics to do research inside China. The whole things a pretty prickly situation right now. I hope those sources help you, and if you have any additional questions, feel free to reply.

A late addition to what /u/Drdickles has already written, but Edward J. M. Rhoads' Manchus and Han (University of Washington Press, 2000) and Pamela Crossley's Orphan Warriors (Princeton University Press, 1990) both go into the transformation of Manchu identity in the 19th-20th centuries, the former somewhat more in-depth than the latter, as Rhoads covers 1862-1928 in full, whereas Crossley takes three case studies from ~1750 to 1962. Crossley's very specifically Manchu-focussed whereas Rhoads also devotes space to the creation of Han discourses of nationhood in parallel with developments in Manchu identity. Mark Elliott's discussion in The Manchu Way is a bit thin after 1850, so these post-Taiping perspectives are probably a bit more directly relevant to your specific inquiry – though Elliott's book would be really useful background reading regardless, and is highly recommended in general.