Study On The Application Of Novel Silicon-based Two-dimensional Materials As Anode Materials For Lithium Ion Batteries

Recently rapid development of self-powering smart portable electronics,electric vehicles and energy storage power stations has kept pushing the demand for high-performance energy storage systems with high energy density,stable cyclability and inexpensive cost.Currently,rechargeable lithium ion batteries(LIBs),one of the most competitive energy storage media for the next generation energy technology,have become the research focus of scientific community and industry since their first commercialization in 1991 due to their high energy density,stable recyclability,light weight and intrinsic safety.With the rapid development of computational materials science,simulation calculation has become an important means to study lithium ion batteries simultaneously.First-principles calculations based on density functional theory(DFT)play an increasingly important role in studying high-performance electrode materials.The electrode materials play a decisive role in the electrochemical performance of lithium ion batteries,but subject to the specific capacity of conventional anode materials,it is difficult for commercial lithium ion batteries to meet the demand of higher energy density.Finding excellent electrode materials has become the key to improve the energy density of batteries.Silicon,as the most promising candidate electrode material to replace graphite,is the inevitable choice of new high-capacity lithium ion battery anode materials in the future because of its high theoretical specific capacity,low voltage platform and rich resources.Nevertheless,the drawbacks of the colossal volume expansion/shrinkage and poor conductivity of silicon during initial(de)lithiation cycles make the cycle performance and rate performance of the battery poor,severely limiting its further application in high-power electronic devices.Recently,the emergence and development of two-dimensional(2D)materials has offered new prospective options to design electrode materials on the nanoscale due to its planar structures,large surface-to-volume ratio,and the loose packing.Therefore,reducing the silicon-based materials dimensions,to some extent,can alleviate issue.In this thesis,we study the silicon-based two-dimensional materials based on the first-principles calculations.The research contents and conclusions are as follows:Chapter 1:Introduction to the operating principle of lithium ion batteries and the development of silicon-based anode materials.Chapter 2:Introduction of the first-principles calculations and the package covered in this article.Chapter 3:In combination of the merits of Si-and C-based anode materials for lithium ion batteries,we propose and evaluate the potential of novel Si3C as an anode material,which consists of light silicon and carbon atom.Our results reveal that the energy barrier for Li diffusion on Si3C is low,indicative of a fast charge/discharge rate.In addition,Si3C exhibits a semimetallic nature with a great advantage in electrical conductivity.Remarkably,the fully lithiumed phase of(Li6Si3C)2 possesses a high theoretical capacity of 1675 mAh/g and a low open-circuit voltage of 0.2 V.These intriguing superiorities endow the Si3C a promising anode material for lithium ion batteries.Chapter 4:We systematically investigate the adsorption and diffusion of Li on the SiB2 by combining the first-principles simulations.SiB2 is shown to be a promising anode material for its intrinsically metallic,fast Li diffusion,and moderate average open-circuit voltage.Moreover,multilayer adsorption is beneficial to increase the theoretical capacities.More intriguingly,the low voltage window is fairly stable,which can guarantee a stable output voltage.We thoroughly confirm that SiB2 well satisfies the demands of the anode material of lithium ion batteries.This novel 2D silicon-based material provides an excellent alternative to advanced metal-free anode of lithium ion batteries.Chapter 5:We propose a unique material that consists of one-dimensional(1D)molecular chain as its basic building block and explore the electronic properties of its nanostructure.It has been shown that the exfoliation of P-AuBr monolayer from bulk is highly feasible.We performed first-principles computations to investigate the structures,stability,interlayer quantum effects,strain effects,mechanical and electronic properties of P-AuBr nanostructures in detail.AuBr exhibits pronounced interlayer interactions.The layer-dependent direct-to-indirect gap transition and semiconductor-metal transition can be observed in AuBr systems.Also,the band gap of AuBr monolayer can be modulated by strain.AuBr chains are direct gap semiconductors,which can be modulated by the number of chains.Our results provide new promising choice for the future molecular devices due to the diversity of the structural and electronic properties of P-AuBr of different dimensions.Chapter 6:The summary of main content and innovation points of this thesis,and the prospect for high-performance silicon-based anode materials for mental ion batteries.