1 s
2 s is by far the largest "jump" you could possibly think of in the whole of the periodice table, both with respect to energy as as with respect to distance ,..., you name it.
becoming an element, Li has to "invest" all this energy, thereby along the way loosing all the advantages of a "small, noble-gas like configuration" (which is a huge "investment")
therefore, it sports this ultra huge negative electron affinity of - 0.76 eV
... and whenever there's the option to make someone else carry named burden of this mostly unwanted electron, it is eager to get rid of it.
that's why
regards
Ingo