| Fossil fuels release a large amount of carbon dioxide during their use,causing serious environmental pollution.Therefore,comprehensively optimizing the distribution of energy structure,promoting green and low-carbon development is the important direction of our energy development.Among them,lithium-ion batteries are widely used in the field of power vehicles and energy storage because of their advantages of high specific capacity and long cycle life.Currently,graphite is widely used as the anode electrode for commercial lithium-ion batteries,but its theoretical capacity is low,which cannot meet further market demand.Transition metal sulfides are one of the potential negative electrodes for the next generation of lithium-ion batteries due to their high theoretical capacity,environmental friendliness,and abundant resources.However,they usually exhibit poor cycling stability due to large volume changes during the battery operation.In addition,their inferior electrical conductivity seriously affects the reaction kinetics.Therefore,this paper takes transition metal sulfide as the research subject.To improve the electrochemical performance of transition metal sulfide,it is modified by nonintrinsic doping to form bimetallic solid solution and composite material.The main research contents are as follows:(1)In this paper,the electronic structure of MnS was modulated by introducing nonintrinsic heterogeneous atom Fe,the components were designed and optimized.Firstly,rational composition and process design were carried out using phase diagram.Secondly,Mn1-xFexS solid solutions were prepared by pyrolysis and vulcanization.The effects of Fe doping on particle size,electronic structure,and ion diffusion kinetics were discussed in detail.As a result,the optimized Mn0.70Fe0.30S electrode exhibits a superior reversible lithium storage of 1085 mAh g-1 at 1 A g-1 after 500 cycles.The first cycle coulombic efficiency is as high as 80.29%.Even the reversible capacity remained 682 mAh g-1 at 2 A g-1 after 1200 cycles.The excellent electrochemical performance of the Mn0.70Fe0.30S solid solution is mainly attributed to the doped Fe atoms providing more nucleation sites,the particle size becoming smaller,and the reaction active site increasing.Meanwhile,density functional theory calculations reveal that the doped heterogeneous atoms Fe modulated the electronic structure of MnS,especially the electron concentration near the Fermi level increases significantly,improving the conductivity,accelerating the ion/electron transport,and improving the ion reaction kinetics.(2)To improve the low conductivity and slow reaction kinetics of FeS2,FeS2/NiS1.19 bimetallic sulfide composite was designed in this paper.FeS2/NiS1.19 bimetallic sulfide composite was synthesized by a simple solvothermal method.The effects of different composite ratios on the microstructure and electrochemical performance were investigated.The formation of multiphase provides abundant heterogeneous interfaces and more active sites.In addition,the synergistic effect of bimetal and Ni doped nucleation sites increased,particle size decreased,alleviated the volume change in the reaction process,shortened the Li+diffusion path,enhanced the ion reaction kinetics,and improved the electrochemical performance of the composite.The rate performance and long cycle results showed that the performance of FeS2/NiS1.19 bimetallic sulfide composite material is better than FeS2.The FeS2/NiS1.19 composite with a composite ratio of Fe:Ni=9:1 exhibits an outstanding reversible capacity of 1428 mAh g-1 at 0.5 A g-1 after 500 cycles and even 677 mAh g-1 at 2 A g-1 after 1000 cycles. |
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