Electrochemical engineering for phase-controlled exfoliation of transition metal dichalcogenides

Crystallographic phase engineering is crucial for the precise manipulation of the physical and electronic properties of materials. However, exfoliation of high-phase-purity atomic-layer transition-metal dichalcogenide (TMD) nanosheets remains a challenge. Conventional methods based on alkali metal-ion intercalation (Li ⁺ , Na ⁺ , K ⁺ ) yield MoS ₂ or WS ₂ flakes with uncontrolled phase mixing (2H/1T hybridization), severely limiting their functional reproducibility. Here, we demonstrate that phase-selective exfoliation for fabricating phase-pure 2H and 1T' TMD atomically thin nanosheets is both scalable and reliable. This process involves the electrochemical co-intercalation of Li-solvent (e.g., Li ⁺ -diethylene glycol dimethyl ether) and solvent-free Li-ion intercalation (e.g., propylene carbonate-based electrolyte) into 2H phase TMD crystal powders, followed by mild sonication and exfoliation. Quantitative modulation of the intercalation depth allows deterministic phase targeting, achieving monolayer yields exceeding 90% for 1T'-MoS ₂ , WS ₂ , and MoSe ₂ , and bilayer/trilayer 2H-MoS ₂ , WS ₂ , and MoSe ₂ with yields above 75%. Phase hybridization is further engineered at atomic precision, generating heterophase MoS ₂ nanosheets with 1T' ratios tunable from 13% to 92% via electrosynthesis parameters. Further, our approach enables the mass production of high-phase-purity MoS ₂ nanosheets on a hundred-gram scale via controlled charging of a LiFePO ₄ ||MoS ₂ pouch-cell configuration. This universal and selective synthesis of ultrathin TMD nanosheets presents opportunities to accelerate the exploration of electronic and photonic properties.