First-principles Study Of Penta-Graphene/-BCN Based Heterostructures As Anode For Li Ion Batteries

The limitation of non-renewable energy sources and people’s increasing energy demand are driving the development of the energy storage industry.Among them,electrochemical energy storage involves all aspects of life,and lithium-ion batteries（LIBs）occupy a major position.LIBs have been extensively studied due to their long cycle life,environmental friendliness,and high energy conversion efficiency.As the main component of LIBs,the choice of anode electrode material greatly affects the working efficiency of LIBs.To improve the performance of LIBs,it is a major task that research the suitable high-performance anode materials.With the progress of science and technology,theoretical simulation provides a reliable basis for experiments,which is greatly reduces the cost,and lays a solid foundation for applications.In this work,based on density functional theory（DFT）,the first-principles methods are used to analyze the heterostructure PG/MoS₂ and CoS/pBCN composed of Penta-Graphene（PG）and MoS₂,Co S and Penta-BCN（p BCN）,respectively.The performance of the two composite material as anode materials for LIBs were calculated and analyzed.The results are as follows:Firstly,based on the first-principles method,the stability,electronic structure and Li-ion adsorption performance of the PG/MoS₂ van der Waals heterostructure were studied by the Atomistix Tool Kit（ATK）.The stability of the structure was demonstrated by formation energy（-5.998 e V）and molecular dynamics.After a Li ion intercalated,the heterostructure transforms from semiconductor to metal,demonstrating the system has good electrical conductivity.And the Li ion diffusion barrier between the PG/MoS₂ layers is as low as 0.13 e V,indicating that the composite system is suitable for efficient charge and discharge processes.In addition,we found that the PG/MoS₂ system can achieve a high lithium storage capacity with a maximum capacity of 751 m Ah/g when fully adsorbed Li ions on the structure.At the same time,the open circuit voltage（OCV）is as low as 0.37 V,and the overall average OCV is 0.592 V.The results show that the PG/MoS₂heterostructure can significantly improve the performance of LIBs as an anode material.Therefore,PG/MoS₂heterostructure is a promising anode material.Secondly,using the Vienna Ab-initio Simulation Package（VASP）package to study the performance of CoS/pBCN heterostructure as anode for LIBs.First of all,formation energy and molecular dynamics calculations show that the CoS/pBCN heterostructure has good thermodynamic stability.The van der Waals heterostructure constructed by two-dimensional materials of Co S and Penta-BCN exhibits metallic properties,demonstrating the high conductivity of the composite material.Taking the adsorption of Li ions as the main research content,we analyzed and compared the characteristics of Li adsorb on monolayer Co S,monolayer Penta-BCN and CoS/pBCN heterostructure,respectively.The Li ion adsorption strength of CoS/pBCN is stronger than that of the monolayer Co S and Penta-BCN,and the charge transfer is also corresponding increase,however,it also leads to a high barrier of interlayer Li ion migration.When Li ions diffuse on its outer surface,the original good migration characteristics are retained,and the energy barrier range is between0.2 e V and 0.26 e V.Then,the capacity and voltage（V）of multi-lithium adsorption of the CoS/pBCN system were calculated,the results show that the theoretical specific capacity of the CoS/pBCN reaches 1572.6m Ah/g,meanwhile the voltage is as low as 0.22 V,realizing the absolute advantages of high capacity and low voltage.In a word,CoS/pBCN is expected to be an ideal LIBs anode material.