Preparation And Modification Of Electrode Materials For High Energy Density Lithium-ion Batteries

Silicon（Si）material due to its high theoretical specific capacity(4200 m Ah g^-1)and low discharge plateau,and Si element reserves are considered as one of the most promising anode materials.But Si has a huge volume expansion during the process of lithium de-embedding and has low electronic conductivity,which makes the capacity decay serious and limits the application of silicon anode in practice.Herein,we prepared organic small molecule-coated silicon anode materials based on a simple process using a large amount of sawdust silicon generated by the photovoltaic industry as the active material,which has the advantages of low cost and environmental friendliness.The specific research is as follows:（1）Si@PPA materials were prepared by surface engineering strategy using phenyl propargylic acid（PPA）grafting to form a cladding layer on the silicon surface.The presence of the cladding layer was verified using FTIR,XPS,and TEM tests.Excellent performance was demonstrated by electrochemical performance tests,with initial coulomb efficiency of 78.2%from 59.6%before modification,and a specific capacity of 1797.7 m Ah g^-1 after 100 cycles at a current density of 400 m A g^-1 with a capacity retention of 81.2%,69.1%capacity retention even at a high current density of 1000 m A g^-1 for 250 cycles.In general,the PPA coating layer effectively buffered the huge volume expansion of silicon,isolated the direct contact between electrolyte and silicon thus inhibiting the occurrence of side reactions,formed a stable solid electrolyte interphase（SEI）on the silicon surface,and improved the electrochemical performance of the material.（2）Through the strategy of surface engineering and binder modification,a small amount of pyromellitic acid（PA）was used as an additive to passivate the silicon surface,and it formed a 3-dimensional cross-linked network structure with CMC and played a key role in anchoring the electrode to the collector copper foil.Thus,the side-reactions between Si-electrolyte and volume expansion during charge-discharge process were effectively suppressed.Moreover,the addition of PA also increased the porosity of the electrode by altering the compositions distribution,and the introduction of Ni²⁺as the complexant can further enhance these effects.The results show that the initial coulomb efficiency of the obtained Si@2%PA-Ni electrode is increased from 50%to 80.9%.After 500 cycles at a current density of 1000 m A g^-1,the initial specific capacity was2325.0 m Ah g^-1 and a charge capacity retention of 1268.8 m Ah g^-1,which corresponds to an average decay rate of 0.091%per cycle.Additionally,a capacity of 1079.7 m Ah g^-1 can be still achieved at high current densities up to 10 A g^-1,and an SBR-free Si@5%PPA-5%CMC electrode was prepared to maintain a stable specific capacity of1460.7 m Ah g^-1 after 500 cycles at a current density of 2000 m Ah g^-1.The mechanism of performance enhancement was investigated by XPS,FTIR,and BET characterization.the PA-modified electrodes outperformed those reported in the literature using similar silicon wafers and had the advantage of simple and low-cost process.Overall,our work enabled a simple and cost-effective way for the practical application of Si materials.