Synthesis And Electrochemical Performance Of Silicon-metal Composite Anode Materials

Silicon（Si）is regarded as a promising candidate to replace the traditional commercial graphite anode for lithium-ion batteries（LIBs）owing to its advantages,including high theoretical specific capacity,low working potential,bundant natural reserves,and environmental compatibility.However,the practical application of Si anodes is hindered due to their large volume expansion,low conductivity,quickly fading capacity,and poor rate capability.Nanostructuring has been demonstrated to be successful in alleviating these issues and improving the cycle and rate performance of nanostructured Si anodes.However,it is very difficult to incorporate nanostructured electrodes into traditional industrial electrode technology because of their low initial coulombic efficiency,poor volumetric performance,and high volumetric resistance.To address these issues,based on the review of the research development of Si-based,this work focuses on micron-sized Si,mainly from the perspective of electrode and active material buffer and conductive network construction.The structural characteristics and electrochemical performances of the prepared composite electrodes and materials by introducing different condutive agents and condutive phases were studied systematically,and mechanisms related to the improved performances were elucidated.The structure and characteristics of the electrodes are essential for the performance of microscale silicon-based anodes for lithium-ion batteries.In this study,various carbon sources with different degrees of graphitization,morphologies,and dispersities were utilized as conductive agents for a microstructured silicon electrode.The findings indicate that micron-sized silicon electrodes can benefit from the addition of flake-conductive graphite,particularly SFG-6,which possesses a high degree of graphitization and dispersion,as well as a particle size similar to that of silicon.This combination results in a well-distributed,uniform conductive and buffering network,leading to improved electrochemical performance overall.After 450 cycles,the Si-SFG-6 composite anode exhibited exceptional long-term stability,delivering a specific capacity of 1102 m A·h g^-1 at a current density of 200 m A g^-1.Furthermore,even at a higher current density of 2000 m A g^-1,the reversible capacity remained impressive at 964 m A·h g^-1.Based on the above studies,the conductivity of the micron Si bulk has been further improved by compositing with the conductive metallic elements.The Si O_x amorphous matrix-protected micron Si-Fe composites were prepared by heating a mixture of 7Si-2Li H-x Fe₂O₃ and then ball milling under O₂ atmosphere using cheap ferric oxide as the iron source.The outer Si O_xamorphous matrix of Si-Fe composites contained dispersed Fe Si₂ and Fe nanocrystals.The Si-Fe composite electrode（x=0.5）protected by the special buffer matrix exhibited improved cycling stability and rate capability.The Si-Fe composite electrode（x=0.5）delivered charge/discharge specific capacities of 1354/1809 m A·h g^-1 at a current density of 100 m A g^-1and the reversible capacity remained at 1069 m A·h g^-1after 200 cycles（capacity retention of 78.0%）.At a higher current density of 2 A g^-1,the discharge specific capacity was measured to be 650 m A·h g^-1.To further improve the electrochemical properties of micron Si-based anode,in-situ composition of conductive Cu in micron Si bulk have been performed by Cu O as the Cu source.7Si-2Li H-x Cu O mixtures were heated and ball-milled in an O₂ atmosphere to obtain amorphous matrix-protected Si-Cu composites consisting of polycrystalline Si,amorphous Si O_x,nanocrystalline Cu₃Si and Cu.The presence of Cu₃Si nanocrystallines significantly enhanced the mechanical properties of the Si O_x matrix with elastic modulus and hardness values of 55.48 and2.55 GPa,respectively,effectively suppressing the pulverization of the micron-sized Si composite during lithiation/delithiation.More importantly,the band gap of the Si-Cu composite with Cu₃Si and Cu nanocrystallines dispersed was reduced from 1.23 e V to 0.75 e V of pristine Si.The resistivity of micron-sized Si-Cu composite was reduced by five orders of magnitude and its electron transport capability was substantially enhancedof.As a result,a high specific capacity(1608/2133 m A·h g^-1 of charge/discharge specific capacities at 100 m A g^-1),a long-term cyclability(1096 m A·h g^-1 after 500 cycles),and a good rate performance(1013 m A·h g^-1 at a current density of 2 A g^-1)are achieved in the micron Si-Cu composite anodes.