Structural Design And Interfacial Modulation Of Micrometer-scale Silicon-based Anode Materials For Lithium-ion Batteries

Nowadays,with the increasing demand for portable electronic devices and electric vehicles,the development of high energy density lithium-ion batteries and fast charging technologies has become a key area of research.As crucial components within batteries,electrode materials play a vital role in determining battery performance.Silicon,as an anode material,has garnered significant attention from both academia and industry due to its ultra-high theoretical capacity(3579 m Ah g^-1)and natural abundance.However,during battery operation,silicon’s volume expansion（>300%）and poor interface stability lead to rapid capacity decay and continuous electrolyte consumption,hindering commercialization efforts.Nano-engineering of silicon has proven to be an effective solution to address these issues,yet high cost,low Coulombic efficiency,and low tap density serve as impediments to widespread adoption.Micrometer-scale silicon presents a low-cost alternative;however,the repeated volumetric changes inevitably lead to the fracture,exposure,and pulverization of large-sized particles,exacerbating battery degradation.To tackle these challenges,this research work starts from microscale silicon（1～3μm）,focusing on structural design and interface modulation.A series of silicon-based composite materials have been designed and developed for application in lithium-ion battery anodes.Through rational structural design,silicon/carbon composite materials have been prepared,enhancing cycling stability and reaction kinetics.Tailored silicon surface coatings have effectively mitigated damage to electrode structure and interfaces during cycling.Additionally,through the design of porous structure and the regulation of the solid electrolyte interface（SEI）,the fast-charging capability of silicon-based materials has been improved.The specific work content and summary are as follows:（1）High-density silicon/carbon composite particles(～0.7 g cm^-3)were prepared from micron-scale silicon and phenolic resin-based carbon spheres（CS）by the bonding effect of pitch solution.The micron-scale silicon is embedded in the cavities formed by stacking carbon spheres,effectively alleviating stress concentration and maintaining good electrical contact.The carbonization of pitch tightly connects the components,maintaining the integrity of the composite particles and stabilizing the electrode/electrolyte interphase.The effects of the silicon/carbon precursor ratio on the particle size,structure and electrochemical properties of the composite particles were investigated.The optimized composite material（CSSi45-75）exhibits impressive electrochemical performance:a reversible specific capacity of1099.2 m Ah g^-1after 200 cycles at 0.5 A g^-1,and a capacity of 750.3 m Ah g^-1after 400 cycles at 1 A g^-1.Furthermore,CSSi45-75 also exhibits a considerable initial Coulombic efficiency（84.1%）and rate capability(capacity retention of 29.6%at a high current density of 5 A g^-1).The structural design and manufacturing process of this study provide an effective solution for the industrial development of silicon-based anode materials.Furthermore,a stable three-dimensional porous carbon integrated silicon/carbon composite particle was prepared through in-situ foaming and carbonization of phenolic resin.The carbon foam framework possesses excellent conductivity and mechanical flexibility,effectively suppressing the volume change and dispersing internal stress to prevent overall particle fracture.Moreover,the porous structure of the carbon matrix provides ion transport pathways and enhances the ion diffusion rate.Optimized,the integrated electrode exhibits excellent comprehensive electrochemical performance in a half-cell,including superior rate capability(762.8 m Ah g^-1at5 A g^-1),outstanding cycling performance(reversible specific capacity of1043.3 and 804.4 m Ah g^-1after 200 cycles at 0.5 and 1 A g^-1,respectively),and good structural stability（volume expansion rate of 23.9%after 50 cycles）.It was matched with commercial Li Fe PO₄（LFP）cathode to assemble a full battery,showing 84.3%capacity retention after 100 cycles.This research presents a simple preparation method with low raw material costs and provides an effective structural design solution as an alternative to traditional complex silicon/carbon composite materials.（2）Through efficient"click chemistry"polymerization reactions,an organic/inorganic hybrid structural coating—polyhedral oligomeric silsesquioxane-lithium bis（allylmalonato）borate（PSLB）—was constructed on the surface of micron-scale silicon particles.PSLB features a unique structure with the"rigid core"of oligomeric silsesquioxane（POSS）and the"flexible chains"formed by polymer cross-linking,contributing to enhanced interfacial mechanical strength of the particles and serving as a passivation layer to improve electrochemical stability.Furthermore,the results demonstrate that PSLB coating tends to preferentially adsorb Li PF₆over organic solvent molecules,inducing the formation of inorganic-rich SEIs,which can effectively homogenise the lithium-ion flux.Importantly,the interfacial modulus dominated by inorganics is significantly improved,thus weakening the performance degradation induced by the volume change.The prepared Si@PSLB anode obtains significantly improved cycle life and reduced volume expansion.In half-cell tests,a reversible capacity of 1083m Ah g^-1is still provided after 300 cycles at a current density of 1 A g^-1.Matching with the high specific energy ternary cathode Li Ni_0.9Co_0.05Mn_0.05O₂（NCM90）,the capacity retention of the full cell is 80.8%after 150 cycles.This study serves as a beneficial reference for surface functionalization of silicon anodes as a complement to conventional inorganic and carbon coatings.（3）Three-dimensional porous micro-particles composed of pitch-derived carbon-coated compacted silicon nano-flakes（c Si PC）were prepared,and their fast-charging performance was investigated.These micro-particles are designed to provide smoother ion transport pathways,enhance the material’s intrinsic rate capability,and maintain a high tap density.Additionally,the compatibility between the silicon anode and the designed localized high-concentration electrolyte（LHCE）was investigated.LHCE exhibits a lower Li⁺desolvation energy barrier and can generate a Li F-rich solid electrolyte interphase（SEI）,forming uniform and rapid Li⁺diffusion channels;it effectively improves the Young’s modulus of the electrode interface and suppresses volume expansion and irregular lithium plating during fast charging.Based on this,the lithium plating process of c Si PC electrodes with LHCE electrolyte is significantly delayed under the same capacity conditions.Even during lithium plating,the SEI composition and structure on the electrode surface remained stable,reducing the risk of lithium dendrite and dead lithium formation.The reversibility of the lithium plating process reaches99.45%after 100 cycles（1 C）.In addition,thin-film battery matched with LFP demonstrates stable cycling performance.And even under high-speed charging at 6 C,it can reach a state of charge（SOC）of 94.5%within 10 min.This study focuses on both structural design and interface modulation,providing new development strategies for fast-charging high-energy lithium-ion batteries integrated with silicon-based anode.