First-Principles Study Of Magnesium Storage On Defective Graphene/MoS₂ Heterostructures

The demand for high-performance energy storage systems for rechargeable batteries is increasing.Lithium-ion batteries（LIBs）,which currently dominate the market,are limited by price,resource availability,and theoretical capacity.Therefore,the development of alternative battery technologies has become an essential task.Magnesium-ion batteries（MIBs）are a promising multi-valent battery with abundant magnesium resources,high safety,high volumetric energy density,and low cost.However,the development of high-performance MIBs anode materials is hindered by issues such as dendrite growth and passivation layer on the pure magnesium anode,which requires further exploration and improvement of alternative anode materials.Graphene/Mo S₂ heterostructure（Gr/Mo S₂）material is a potential candidate for negative electrode materials in MIBs.Due to the fact that defects in the Gr/Mo S₂structure can greatly affect its physicochemical properties,defect engineering is considered one of the key factors for achieving high energy density in electrode materials.This article addresses the key challenges faced in the development of MIBs and employs a first-principles calculation method based on density functional theory to systematically investigate the adsorption difficulty,construction strategy and structure-activity relationship of magnesium in the defect reaction center of Gr/Mo S₂heterojunctions.This atomic-level research provides theoretical guidance for the rational design of two-dimensional materials.This article mainly investigates the following aspects:（1）This study explores the effects of the most stable adsorption sites,charge transfer,bonding nature,electronic properties,and diffusion barriers of magnesium atom in the pristine and vacancy-defected Gr/Mo S₂ system.A defect-free Gr/Mo S₂model with a lattice mismatch of 3.4%was established using MS software,and three intrinsic defect models were successfully constructed based on this model.The calculation of the formation energy shows that there is a difficulty gradient in the formation of intrinsic defects.The calculation of charge density difference shows the presence of electrostatic attraction between magnesium and the substrate.The electronic properties of different defects have been elucidated,and the presence of defects can adjust the electronic structure of materials and enhance the ability of materials to accept electrons.The calculation of diffusion barriers shows that the presence of vacancies significantly promotes the adsorption of magnesium while inhibiting its transport.（2）The study established four nitrogen doping models and found that the doping atoms affect the adsorption capability of magnesium on the Gr/Mo S₂ heterostructure by influencing its geometric shape,charge distribution,and electronic properties.Graphitic nitrogen doping leads to an increase in the electronegativity of the substrate,which weakens its ability to adsorb magnesium atoms.In contrast,pyridinic and pyrrolic nitrogen doping can enhance the adsorption performance of the Gr/Mo S₂heterojunction and suppress the growth of magnesium dendrites.Through analysis of the density of states and charge density difference,it was found that pyridinic and pyrrolic nitrogen doping induced p-type conductivity of the material and promoted charge transfer between the substrate and the adsorbate.The nitrogen doping defects studied in this thesis have a significant trapping effect,affecting the separation performance.（3）The influence of boron-doped defects on the magnesium storage performance of Gr/Mo S₂ heterojunctions was studied.The results show that as the number of boron atoms increases,the formation energy significantly increases and the adsorption capacity gradually strengthens.Due to the lower electronegativity of boron atoms compared to carbon atoms,electrons transfer from boron atoms to adjacent carbon atoms after doping,resulting in positively charged boron atoms.Boron doping is p-type doping,which increases the number of holes in the substrate and raises the carrier concentration.The density of states at the Fermi level also increases with the increase of boron doping concentration,reflecting its excellent performance potential in electron conduction.It was also found that the diffusion barrier of magnesium gradually decreases,leading to faster diffusion rates and effective improvement of theoretical magnesium storage capacity.This thesis contains 46 figures,11 tables,and 122 references.