Surface Modification And Electrochemical Properties Of Porous Silicon Composite Coated With Titanium Dioxide

Lithium-ion battery has the characteristics of high specific capacity,high output voltage,long cycle life,low self-discharge rate,no memory effect and environmental friendliness.It has rapidly developed into an important power system and is widely used in energy storage,electric vehicles and various electronics.In order to further meet the demand for high energy density in the lithium-ion battery market,it is urgent to explore new electrode materials.Due to its ultra-high theoretical specific capacity(4200 m Ah/g),abundant reserves and good safety performance,silicon anode materials are expected to become the first choice for the next generation of anode materials.However,two obvious shortcomings severely limit its commercial application:one is the poor conductivity of the silicon material itself,which is not conducive to the conduction of electrons;the other is that serious volume expansion occurs in the process of intercalation/deintercalation of lithium ions,which causes the pulverization of the material and the battery capacity to decrease rapidly.In response to these two problems,this paper uses micron-sized aluminum-silicon alloy powder as the silicon source,and modifies it by designing coral-like porous structure,surface coating modification,and compounding with a second phase with good conductivity.Finally,the electrochemical performance of the material is effectively improved.The main research contents of this paper are as follows:1.Coral-like porous silicon material with appropriate pore structure was obtained by dealloying process,using micron-sized Al-Si alloy balls as raw materials.Then the sol-gel process was used to prepare the composite material with amorphous Ti O₂ coated porous silicon structure.The amount of tetrabutyl titanate(TBOT)was controlled to adjust the amount of amorphous Ti O₂.With the increase of the amount of TBOT,the thickness of the coating also gradually increased.The thicknesses of the coating layers prepared in this paper were 4,10 and 20 nm.Analyzed and revealed the preparation mechanism of Ti O₂ layer and the influence of coating thickness on the electrochemical performance of composite materials.When the coating layer was 10 nm,the modification effect of the material was the best.The electrode potential difference of the P-Si@a-Ti O₂ composite material was only 0.321 V.The first discharge specific capacity was 3190.0 m Ah/g and the first coulomb efficiency was76.8%.After 80 cycles at a current density of 1.0 A/g,it still had a specific discharge capacity of 769.3 m Ah/g,the diffusion coefficient was 2.1×10^-13 cm²/s and there was no obvious pulverization on the surface,showing superior electrochemical performance.The results showed that the coral-like porous Si structure and the coating layer of appropriate thickness can effectively buffer the volume expansion of the material and improve the cycle stability of the electrode.2.The porous silicon and artificial graphite sheets were composite in the ratios of 1:6,1:3,1:1 and 6:1.The study found that when the ratio of was 1:1,the electrochemical performance of the composite material was the best.The initial discharge capacity was 1857.7m Ah/g,the first coulomb efficiency was 87.1%,and the specific capacity was 819.1 m Ah/g after 40 cycles at 0.1 A/g.Based on the above mentioned research foundation,the P-Si@a-Ti O₂ material and artificial graphite were compounded at the optimal ratio to prepare the P-Si@a-Ti O₂/C composite material.Compared with the P-Si@a-Ti O₂ sample,The initial discharge specific capacity was 2063.5 m Ah/g,and the discharge specific capacity was 537.4m Ah/g after 80 cycles at the current density of 1.0 A/g.Compared with P-Si@a-Ti O₂ material,the coulomb efficiency was improved to 88.2%for the first time,and the EIS test showed that,The diffusion and migration rate of Li⁺inside the electrode material was faster,and the diffusion coefficient was 2.3×10^-12 cm²/s.As a stable matrix,artificial graphite reduced the contact between particles,restricted its volume expansion effect,and improved the conductivity of the electrode material.