Theoretical Investigation Of Novel Anode Materials For Alkali Metal Ion Batteries

Batteries play an important role in our daily life.In particular,sodium/potassium-ion batteries have received extensive attention in energy storage and conversion due to their high safety,low cost,and wide operating temperature range.Therefore,exploring new anode materials for sodium/potassium ion batteries is an effective way to promote their faster development.Now,screening suitable electrode materials through experiments often consumes a lot of resources.First-principles calculations can theoretically explore fundamental properties and possible applications of materials.Therefore,in this paper,a series of novel anode materials for alkaline metal ion batteries were designed and screened by using first-principles calculations.The main contents are as follows:1.Transition metal carbides（MXenes） show great potential for energy applications due to their excellent electrical conductivity.Therefore,we designed a series of novel XYZC₂ and further investigated their stability and electronic properties by first-principles calculations.First,by considering the energetic properties,we screened out 48 energetically favorable structures from 147 initial structures.Then,we obtained five kinetically stable XYZC₂ by phonon spectral calculations.ab initio molecular dynamics（AIMD）simulations indicate that XYZC₂ have excellent thermodynamic stability at room temperature.Moreover,XYZC₂ exhibit different electronic properties from single-metal MXenes due to their special asymmetric "sandwich"structure and tunable metal layers.2.By using first-principles calculations,we evaluated the possibility of XYZC₂ as anode materials for Na/K-ion batteries from several perspectives,such as adsorption energy,diffusion barrier,and average open circuit voltage.Both Na and K ions exhibit strong adsorption energies（-1.08～-1.63 eV）and low diffusion barriers（0.01～0.03 eV）on the XYZC₂ surfaces.In addition,as the anode materials for Na-ion batteries,VHfMoC₂ and VHfWC₂ show good structural stability and electrochemical performance,so their reversible capacities can reach 123 mAhg^-1 and 153 mAhg^-1,and the average open circuit voltage are 0.59 V and 0.58 V,respectively.Overall,XYZC₂ exhibit strong adsorption energy,low diffusion barrier,and suitable average open circuit voltage,so we can predict that XYZC₂ are a sea of promising anode materials for Na/K-ion batteries from a theoretical point of view.3.Based on first-principles calculations,we explored the stability and electronic properties of two-dimensional SiS₂ and SiSe₂,and predicted their performance as anode materials for Na-ion batteries.Phonon spectra and AIMD calculations show that SiS₂ and SiSe₂ are kinetically and thermodynamically stable.The adsorption energies of Na ion on SiS₂ and SiSe₂ surfaces are as high as-1.01 eV and-1.24 eV,respectively.AIMD calculations show that Na ions have large diffusion coefficients in SiS₂ and SiSe₂（6.72× 10-5～1.06× 10-3 cm²/s）,which are beneficial to the migration of Na ions.In addition,the average open circuit voltages of SiS₂ and SiSe₂ are 0.19 V and 0.25 V,and the reversible capacities of SiS₂ and SiSe₂ are 517 mAh g^-1 and 864 mAh g^-1,indicating that SiS₂ and SiSe₂ may exhibit high energy density.In conclusion,our calculations suggest that SiS₂ and SiSe₂ are two high-performance anode materials for Naion batteries.