This study presents an electrochemical repair strategy for porous graphene membranes to achieve precise ion-ion separation. The method involves depositing a 10-nm-thick conjugated microporous polymer (CMP) layer on graphene through electropolymerization, which effectively masks larger non-selective pores and reduces the contribution of the tail-end of the pore size distribution (PSD). This results in a large Li⁺/Mg²⁺ selectivity of 300 with a high Li⁺ ion permeation rate, surpassing the performance of reported materials. The strategy enables the fabrication of monolayer graphene membranes with customizable pore sizes, limiting the contribution of nonselective pores and offering a versatile platform for various separations. The research highlights the potential of porous graphene membranes for high selectivity and high flux in ion and small molecule separation, which could revolutionize energy, water, and chemical sectors. The development of these membranes relies on new materials and fabrication methods, with chemical vapor deposition (CVD) graphene being a promising candidate due to its atomic-thin lattice and potential for uniform Å-scale pores. However, avoiding non-selective pores in monolayer graphene remains a challenge. The electrochemical repair strategy effectively masks non-selective pores and cracks, enhancing selectivity. The CMP layer, with a strong interaction with graphene, masks pores and reduces the role of larger pores in the PSD, enabling precise ion-ion separation. The study demonstrates that the CMP-masked graphene membranes exhibit high ion selectivity and permeation rates, with Li⁺/Mg²⁺ selectivity reaching 300. The membranes also show stability under high pressure and pH conditions, and they perform well in various ion separation tests. The CMP layer provides mechanical reinforcement, preventing graphene from cracking and tearing. The results show that the CMP-masked graphene membranes outperform many state-of-the-art ion-sieving membranes, including COFs, polymers with intrinsic microporosity (PIM), graphene oxide (GO), and MXene. The study underscores the significant potential of graphene membranes for precise ion separations and highlights the effectiveness of the electrochemical repair strategy in enhancing ion-ion selectivity and permeation.This study presents an electrochemical repair strategy for porous graphene membranes to achieve precise ion-ion separation. The method involves depositing a 10-nm-thick conjugated microporous polymer (CMP) layer on graphene through electropolymerization, which effectively masks larger non-selective pores and reduces the contribution of the tail-end of the pore size distribution (PSD). This results in a large Li⁺/Mg²⁺ selectivity of 300 with a high Li⁺ ion permeation rate, surpassing the performance of reported materials. The strategy enables the fabrication of monolayer graphene membranes with customizable pore sizes, limiting the contribution of nonselective pores and offering a versatile platform for various separations. The research highlights the potential of porous graphene membranes for high selectivity and high flux in ion and small molecule separation, which could revolutionize energy, water, and chemical sectors. The development of these membranes relies on new materials and fabrication methods, with chemical vapor deposition (CVD) graphene being a promising candidate due to its atomic-thin lattice and potential for uniform Å-scale pores. However, avoiding non-selective pores in monolayer graphene remains a challenge. The electrochemical repair strategy effectively masks non-selective pores and cracks, enhancing selectivity. The CMP layer, with a strong interaction with graphene, masks pores and reduces the role of larger pores in the PSD, enabling precise ion-ion separation. The study demonstrates that the CMP-masked graphene membranes exhibit high ion selectivity and permeation rates, with Li⁺/Mg²⁺ selectivity reaching 300. The membranes also show stability under high pressure and pH conditions, and they perform well in various ion separation tests. The CMP layer provides mechanical reinforcement, preventing graphene from cracking and tearing. The results show that the CMP-masked graphene membranes outperform many state-of-the-art ion-sieving membranes, including COFs, polymers with intrinsic microporosity (PIM), graphene oxide (GO), and MXene. The study underscores the significant potential of graphene membranes for precise ion separations and highlights the effectiveness of the electrochemical repair strategy in enhancing ion-ion selectivity and permeation.