The regulation of the ion selectivity by electric field and ion association on the Li+ selectivity of carboxyl functionalized graphene nanopores are investigated by molecular dynamics simulation. Carboxylate graphene nanopores of sub‐2 nm exhibit excellent Li+ selectivity under the electric field of 1.0 V nm−1. The results show that ion association inspired by electric field may be a key factor affecting ion selectivity of sub‐2 nm nanopores. The ion association of Mg2+ and Cl− can be promoted obviously near the nanopores under the electric field of 1.0 V nm−1. The migrating of Mg2+ can be retarded by stable clusters of Mg2+ and Cl− formed near nanopores. The degree of association of Li+ with Cl− is relatively low and the disassociation of the Li+ cluster is easier so that Li+ can more easily pass through the nanopores. These results gain insight into the effect of ion association inspired by electric field and nanoconfinement of graphene nanopore on Mg2+/Li+ separation, and provide helpful information for the application of nanoporous materials in extraction of Li+ ion from salt‐lake brine.

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