Theoretical Simulation On The Electrode Materials Oflithium Ions Batteries And Photovoltaic Cells

Energy is the basis for human survival.With the depletion of fossil energy,the development and utilization of new energy materials is imminent.Novel batteries,such as lithium batteries and photovoltaic cells,can transform,store and utilize clean energy efficiently,which is an important way to make full use of clean energy.Electrode materials are the kernel components of batteries,which play a vital role in battery life,charge and discharge performance.The development of electrode materials for new generation lithium batteries and photovoltaic cells has practical research significance.In this paper,based on the calculation of Density Functional Theory,the electrode materials of lithium batteries and photovoltaic cells are designed and simulated.Three types of energy materials have been studied in detail,including the high-performance of prelithiation MS2 monolayers as the anode material of lithium ion batteries,the catalytic performance of y-PN for photocatalytic water splitting,and the photoelectric performance of DTPC-based molecules.Their underlying mechanisms have been analyzed and the feasibility of their practical application has been discussed.Our research is helpful to excavate the internal mechanism and develop new electrode materials,and also provides theoretical guidance for the experimental work.The main contents and conclusions are as follows:(1)Recent experimental study shows that the pre-lithiated MoS2 monolayer exhibits an enhanced electrochemical performance,coulombic efficiency of which is 26%higher than the pristine MoS2 based anode.The underlying mechanism of such significant enhancement,however,has not yet been addressed.By means of density functional theory calculations,we systematically investigated the adsorption and diffusion behavior of lithium(Li)atoms on the MS2(M=Mo,W,V)monolayers.On the pre-lithiated MS2 monolayers,the adsorption energy of extra Li ions are not significantly changed,implying the feasibility of multilayer adsorption.Of importance,the Li diffusion barriers on prelithiated MS2 are negligibly small because of the charge accumulation between the diffusing Li ions and the pre-lithiating Li layer.Correspondingly,we report that the prelithiation should be a general treatment which can be employed on many transition-metal di-chalcogenides to improve their storage capacities and charge-discharge performance in Li ion batteries.In addition,we propose that the pre-lithiated VS2 may serve as an outstanding anode material in LIBs.(2)The advanced technology of visible-light-driven water-splitting shows great potential as it could produce hydrogen sustainably and renewably,and the catalyst with suitable oxidizing and reducing potential is the kernel of this technology.In this paper,we perform the theoretical research on the 2D γ-phosphorus nitride(γ-PN)monolayer.With density functional theory and molecular dynamics,we explore the feasibility that the γ-PN would be employed as a photocatalyst for water splitting.The calculation results demonstrate that γ-PN is an indirect semiconductor.Importantly,its conduction and valence band edges locate around the chemical potential of H+/H2 and O2/H2O energetically.In addition,we apply the strain effect to tune the optical properties of theγ-PN,and the results show that the band gap will be decreased while the valence band edges will be upshifted if the tensile strain is applied.The γ-PN monolayer has the best catalytic performance when the 10%tensile strain is applied.In this case,its band gap is lowest and its absorbing ability is highest.Last but not least,the stability of the γ-PN in the aqueous solution have been verified after 100 ps molecular simulation.These results confirm that the γ-PN monolayer will have widespread application as water-splitting photocatalyst if be synthesized.(3)Dithienopicenocarbazole(DTPC)as the kernel module of low-energy-gap organic dyes in dye-sensitized solar cells have received widespread attention because of their high conversion efficiency.The ground-state geometries,electronic structures,spectra and photoelectric properties of three dyes(C279,C280 and C281)have been calculated by density functional theory and time-dependent density functional theory.To simulate the realistic environment,we perform the calculation under the condition of the solvent.To interpret the origin that caused the difference of photoelectric properties,we assess the energy levels,the frontier molecular orbitals,the electron density,absorption,the total static first hyperpolarizability and the driving force of electron injection.The relationship between structure and property should be implemented and the reason of the high conversion efficiency would be found.