DFT Calculation Study On Ti₂CS₂-Based Heterostructures Anode Materials Of Alkali Metal Ion Batteries

With the development of portable electronic devices,electric vehicles and grid energy storage,there are increasing demands for Li-ion batteries（LIBs）.But LIBs can not meet the demands of markets due to scarcity of lithium resource,low specific capacity（372 m Ah/g）of Graphite anode and so on.The large abundance of sodium and potassium in the crust is beneficial for Na-ion batteries（NIBs）and K-ion batteries（KIBs）to supplement extra demands of markets.However,the traditional anode materials of LIBs show poor performance in NIBs and KIBs.Therefore,it is necessary to develop new anode materials of alkali metal ion batteries with excellent performance.Constructing van der Waals heterostructures is an effective strategy to obtain the anode materials for alkali metal ion batteries with superior performance,because heterostructures can integrate the advantages of monomer materials.In this work,three heterostructures of G-Zn O/Ti₂CS₂,Ti S₂/Ti₂CS₂ and Nb S₂/Ti₂CS₂ have been designed,and their stabilities,conductivities and electrochemical performance have been investigated by the density functional theory（DFT）calculations,so as to evaluate the possibility of these heterostructures as anode materials for alkali metal ion batteries.Three heterostructures exhibited excellent stabilities and conductivities.The results of electrochemical performance are as follows:（1）G-Zn O/Ti₂CS₂ heterostructure:the diffusion barriers of alkali metal ion in G-Zn O/Ti₂CS₂ interlayer are all lower than 0.5 e V（Li/Na/K-ion:0.468/0.305/0.113 e V）,which indicates G-Zn O/Ti₂CS₂ has excellent rate performance.The average open circuit voltages（OCVs）of G-Zn O/Ti₂CS₂ are in the range of 0～1 V（LIBs/NIBs/KIBs:0.571/0.749/0.292 V）,and the corresponding specific capacities（529/317/317 m Ah/g）all are higher than that of Graphite（372/35/279 m Ah/g）.These results indicate G-Zn O/Ti₂CS₂ is a promising anode material of LIBs,NIBs and KIBs.（2）Ti S₂/Ti₂CS₂ heterostructure:the diffusion barriers of alkali metal ion in interlayer are all below 0.35 e V（Li/Na/K-ion:0.333/0.146/0.055 e V）,implying the superior rate performance of Ti S₂/Ti₂CS₂.For NIBs and KIBs,the average OCVs of Ti S₂/Ti₂CS₂ are in the range of 0～1 V（NIBs/KIBs:0.626/0.995 V）,but its average OCV for LIBs is 1.663 V（higher than 1 V）.Ti S₂/Ti₂CS₂ exhibits higher specific capacities（NIBs/KIBs:566/283 m Ah/g）than that of other anode materials（e.g.Graphite）.Overall,Ti S₂/Ti₂CS₂ is a potential anode material for NIBs and KIBs.（3）Nb S₂/Ti₂CS₂ heterostructure:the diffusion barriers of alkali metal ion in interlayer are all below 0.5 e V（Li/Na/K-ion:0.455/0.247/0.204 e V）,suggesting the good rate capability of Nb S₂/Ti₂CS₂.For NIBs and KIBs,the average OCVs of Nb S₂/Ti₂CS₂ are in the range of 0～1 V（NIBs/KIBs:0.617/0.929 V）,but the average OCV for LIBs is 1.190 V（higher than 1 V）.In addtion,the specific capacity of Nb S₂/Ti₂CS₂ is 489 m Ah/g as an anode material for NIBs,which is higher than that of other anode materials（e.g.Graphite）.In a word,Nb S₂/Ti₂CS₂ is a promising anode material of NIBs.