Fabrication Of Silicon Anode And In-situ Optical Characterization Of Lithium Metal Anode For Lithium-based Batteries

With the ever increasing demand of electronic devices and electric vehicles,the research and development of new electrode materials are particularly critical.In the case of anode material,the main anode material is graphite for current commercial lithium ion batteries.The theoretical capacity of graphite anode is 372 mAh g-1.The graphite anode based lithium ion battery is approaching its energy density limit.In order to further increase energy density,it is necessary to develop new anode materials.High energy density anode materials,including silicon,tin and lithium metal,have attracted a lot of interest.The silicon and tin anodes are alloy anode materials with theoretical specific capacities of 4200 mAh g-1 and 994mAh g-1,respectively.The main problem is that during lithium ion insertion and extraction,there is a 400%volume expansion,resulting in material fracture and unstable solid electrolyte interphase(SEI).To solve these problems,many research groups have designed various nanostructures,including nanowires,nanoparticles,and porous structures.Even though these structures increase the cycling performance,complex fabrication processes and expensive raw materials limit the large-scale commercial applications of silicon and tin anodes.Therefore,it is truely important to develop new methods to reduce the fabrication cost of high-capacity alloy anodes.Lithium metal is the lightest element with theoretical capacity of 3600 mAh g-1.The problem of lithium metal is lithium dendrites formation during repeated cycling.leading to limited cycling performance,low coulombic efficiency and battery safety problem.Although there are many studies that inhibit the growth of lithium dendrites.including electrolyte additives and lithium deposition host,more in-depth research is needed to further promote the practical application of lithium metal.On one hand,we need more fundamental understandings of the dynamic lithiun metal deposition process,and therefore require high-resolution and non-destructive in-situ observation platforms.On the other hand,we need to develop a dendrite detection platform and improve the safety performance for the pratical application of the battery.To solve the above problems,we have achieved the following results1.Low cost and scalable fabrication of high performance silicon anodes from low grade silicon.We focus on two different kinds of low grade industrial silicon(including 99 wt%metallurgical silicon and 83 wt%ferrosilicon).Through a combined process of ball milling and metal-assisted chemical etching,the morphology and porosity of the porous silicon can be controlled.Silicon purity can be increased from 83.40%to 99.40%.The purified porous silicon particles exhibite reversible capacity of 1287 mAh g-1 after 100 cycles at a current density of 2 A g-1.2.Preparation of high performance porous silicon and porous tin anode by a one-step method with ball milling and selective chemical etching.The outer graphite layer can stabilize the surface SEI layer and maintain electrical contact.The inner porous structure can alleviate volume change and improve cycling performance.Porous silicon maintains reversible specific capacity of 910 mAh g-1 after 600 cycles at 0.5 C and the porous tin anode remains reversible specific capacity of 750 mAh g-1 after 300 cycles at 0.2 C.3.In-situ plasmonic monitoring of electrochemical evolution of lithium metal.The platform can be used to detect lithium dendrite formation and improve batter)safety effectively.Relashionship between lithium deposition morphologies and reflection spectra is developed.One is hybridization of size-dependent surface plasmon resonance and period-dependent Wood's anomaly,leading to a dip at 800 nm and 1200 nm in the reflectance spectra as lithium particle growth.However,the broadband optical absorption of lithium dendrites results in low reflectance spectra(<10%).With the correlations between reflectance spectra and lithium metal morphologies,the fast and non-destructive platform can serve as a useful tool to determine different factors on the lithium metal morphology,including current density and electrolyte additive.This optical characterization platform can also be used for electrolyte study.The above research has significant impacts on both fundamental and application levels.On one hand,low grade silicon usage reduces the fabrication cost of silicon and tin alloy anodes,and can also serve as a promising candidate for large scale applications.On the other hand,in-situ optical observation technique based on plasmonic can be used not only for fundamental understanding of the lithium metal but also provide a new platform to improve battery safety practically.