Mitigating volume expansion of silicon-based anode through interfacial engineering based on intermittent discharge strategy

Silicon is considered to be one of the most promising anode materials for lithium-ion batteries(LIBs),but its application is limited by the large volume expansion during alloying and dealloying.The constructing of a high-performance solid electrolyte interface(SEI) film on the surface of the anode material is considered to be one of the effective strategies to mitigate volume expansion of silicon-based anode.In this study,an intermittent discharge strategy which helps to improve the utilization efficiency of electrolyte additive of lithium difluorobisoxalate phosphate(LiDFBOP) is proposed to construct a highly conductive and dense SEI film.The results of electrochemical and physical characterization and theoretical calculations show that the intermittent discharge in the voltage range from open circuit voltage(OCV) to 1.8 V facilitates the diffusion of the soluble products,creates the conditions for the repeated direct contact between Si@C anode and LiDFBOP additive,increases the decomposition of LiDFBOP additive,and thus produces a uniform,dense and inorganics-rich(Li_(2)C_(2)O_(4),LiF and Li_(x)PO_yF_z) SEI film.Subsequently,this SEI film helps to ensure the even intercalation/de-intercalation of Li^(+) in the SEI film and the homogeneous diffusion of Li^(+) inside the Si particles,decreasing the internal stresses and anisotropic phase transitions,maintaining the integrity of Si particles,inhibiting the volume expansion and thu s improving the electrochemical performance of cells.This study not only improves the utilization efficiency of expensive additives through a simply and low-cost method,but also enriches the strategy to improve the electrochemical performance of Si@C anode through interfacial engineering.

Design and performance improvement of SiNPs@graphene@C composite with a popcorn structure

Silicon anodes are considered to be the most promising alternatives owing to their theoretical specific capacity,which is almost 10 times higher than that of graphite anodes.However,huge volume changes during charging and discharging affect their interface stability,which strongly limits their application in commercial batteries.Herein,a popcorn-structured silicon-carbon composite(SiNPs@graphene@C),composed of silicon nanoparticles(SiNPs),graphene spheres and pitch-based carbon,is prepared by spraydrying followed by a wet process.The resulting SiNPs@graphene@C composite has good flexibility and elastic-strain capacity due to the graphene substrate,and it possesses macrostructural integrity and mechanical stability during cycling due to the rigid carbon–carbon chemical bonds.As a result,it shows a discharge-specific capacity of 481.3 mAh g^(-1)and a capacity retention of 82.9%after 500 cycles at 1 A g^(-1).Besides,the initial coulomb efficiency is increased from 65.7%to 86.5%by pre-lithiation,which improves the feasibility of commercialising the SiNPs@graphene@C composite.