Adorno coined the term ‘identitarianism’ in Negative Dialectics (1966), prompted by critique of Kantian and Hegelian philosophies.
The argument, very briefly, goes something like this. Like Hegel, Adorno rejected the manner of Kant’s distinction between noumenal and phenomenal forms. Put simply, Adorno granted Hegel’s claim concerning the historically- and conceptually-generative qualities of non-correspondence, but wanted to press Marx’s critique of philosophical idealism further against Hegelian Marxism. Adorno remains a dialectician. But, unlike Hegel and more like Marx, he eschewed the affirmative, synthetic moves of consciousness (ie., philosophical idealism) and accorded epistemological-historical priority to the object (matter, materialism) rather than the subject (idealism) in explaining the course of this generative, non-correspondence (or non-identity). Identitarianism and the idealist philosophies of Kant and Hegel are thereby contrasted to a materialist philosophy of non-correspondence, or what Adorno calls “negative dialectics.”
How it happened that ‘identitarianism’ came to be plausibly used as a synonym for ‘identity politics’—or, more accurately, co-opted by arch-identitarian Hegelian Marxists against any emphasis on race, gender and/or sexuality, and in their defense of more or less explicit arguments that class is the a priori or primary categorical division of substance—is a mystery to me.
There are a lot of criticisms to be made of Adorno. But I’m not sure what or who it serves to pretend he didn’t launch a massive assault on the elementary logical reasoning of Hegelian Marxism and Leninism.
Angela Mitropoulos 
The term “identitarian” as it appears in Adorno is an artifact of translation, not something he explicitly coined. So, “identitarian philosophy” = Identitätsphilosophie, “identitarian thinking” = Identitätsdenken, “identitarian logic” = identitätslogisch.
Nevertheless, accepting the term’s novelty in English, the distinction you make is valid. About this difference I’ve written the following: “On the term ‘identitarian’.”
Still, I’m not where you’re getting this idea that Adorno was not a Hegelian Marxist, in the tradition of Lenin, Korsch, and Lukács. Even in 1956 he was still calling for a Leninist party.
I’m sure we all know the issue of translation is beside the point. Denis Redmond’s translation doesn’t render any of those terms as “identitarianism” whereas more widely-used translations have done.
None of that affects the issue at hand, which is that Adorno’s critique of Hegel and Kant simply does not lend philosophical weight to the reanimation of a Hegelian theory of class (the Spirit), often conducted through the denunciation of “identity politics,” as if the former is not an arch-idealist understanding of identity (it is definitively not marxist), and as if race or gender can only be understood (from within a Hegelian frame) as rivalrous categories, always characterised or perhaps simply felt as thwarting the manifestation of the Holy Spirit (‘class consciousness’).
If anything, Adorno’s criticisms of Kant and Hegel serve as a critique of the Hegelian dumpster-fire that is current “anti-identity politics” polemics.
On the related points: I did say that Adorno remained a dialectician. Not all dialectics is Hegelian. I also explained, however briefly, how Adorno’s dialectics differed in key respects from that of Hegel.
Also, of less relevance, Lukacs’ marxian history of ideas is not Hegel’s history of the spirit/concept, and Lukacs’ efforts to avoid censure in the 1950s are not always apparent on the page – but both he and Korsh are longer stories, though Adorno was not unaffected by the course of that history and sought to intervene in it by, at times, presenting his arguments as ‘more-Leninist-than-thou.’ I think the readings of Adorno on Lenin you point to conveniently downplay those dynamics, and how attached Adorno was to (a non-Hegelian) dialectics over much of his writing.
It may complicate, but I do not think it invalidates my point about the misuse of Adorno’s theory of non-identity in the context of current ‘debates’ over ‘identity-politics.’ Not least because Adorno published Negative Dialectics in 1966.
I am liking, in a certain sense, these comments. But it seems very obvious to me, even in the title “negative dialectics”, that what is not negative or by virtue of the fact that Adorno might even be able to see his way of what is needed, which is to say what had been lacking up to that point philosophically and dialectically, that which remains positive cannot but be that which has identity; and this is to say the negotiation or the arena in which such identities play is exactly the political as well as the ideological.
I think it is well to see that when a person gets caught up in names and ideas and comparing this person to that person they are playing identity politics for any term. The whole point that out Dino is making is the same point that all these other authors are making in their own way in their own time; Adorno just saw that none of those ways before him worked and so what was required once someone understood this motion, this Hegalian historical motion, that the next move what is exactly to remove the topic from its usual understood recourse: this recourse is exactly identity, what is positive once the negative precipitates out from the saturation of thought that even Adorno talks about.
All these names and comparing various authors with their various thoughts and the differences between them and whether or not the term was translated right – all these things really missed the point of what all these authors are talking about that Adorno felt compelled to bring about this negative dialectics.