The only thing wrong with this, in terms of normal author-year citations, is that by. It should be in. In author-year citations, the citation "Name (NNNN)" acts as a noun meaning the paper itself. It can also act as a noun meaning the author(s). In this case it means the paper. Now, if it were about something that Li and others had found in their paper, you might phrase it with by:
These new species were discovered by Li et al. (2013).
In that case, you are using "Li et al. (2013)" as a reference to the authors, rather than the paper. As such, you can, if you wish, say:
More information on those functions can be found in the paper by Li et al. (2013).
This would be unnecessary words and seem strange to an academic English-using audience. The most appropriate way to refer to the paper, in author-year citations, is:
More information on those functions can be found in Li et al. (2013).
I see in the comments someone suggesting the title should be there. That is incorrect. "Li et al. (2013)" is a citation, a reference, and the full information will then appear in the reference list at the end of the paper. One of the entries in the list with be something like:
Li, X, Zhang, Q and Huang, C (2013), "Title of paper", Title of journal, etc. etc.
The title appears in the reference list. The citation names the author, or both authors if there are two, or the first named author if there are more than two, and gives the year. That's enough to find it in the reference list. If it would be ambiguous to do that, so you couldn't find the specific reference in the list, you would add letters to the years. One reference would be 2013a, and another 2013b.