Research On The Yolk-shell Structured Si-Based Anode Materials For Lithium-ion Battery

As the energy storage devices,lithium-ion battery have been widely used in electric vehicles?EVs?,mobile phones and portable electronic devices.The commercial graphite anode?theoretical capacity of 370mAh/g?can hardly meet the demand of social economic development,so it prompt to the research on increasing the energy density of lithium-ion batteries.Silicon?Si?has been regarded as the promising anode due to its'high gravimetric capacity?⁴200mAh/g?,low working potential?⁰.5 V vs.Li/Li⁺?and abundant resources.However,Si has poor conductive properties and there is huge volume change?³00%?during alloying and dealloying.Considering of these problems,we aim to developing the microstructure,we have successfully prepared and developed the yolk-shell structured Si-based anode materials.The main results are as follows:In order to suppress the volume change of Si anode material,we had designed and prepared the yolk-shell structured Si@V@C1.Through improved St?ber method and sacrifice template method,we had successfully prepared Si@V@C1.We made the morphology and structure characterized by SEM,TEM,XRD,the result show the yolk-shell structured Si@V@C1.Electrochemical performance test showed that the specific capacity is 1221 mAh/g after 100 cycles at 0.2 A/g with 94.99%capacity retention.After 500 cycles,the electrode surface structure is still stable.It's found that specific capacity is 425 mAh/g at 4 A/g and 108 mAh/g at 8A/g,showing low rate capability.In order to improve the connection of Si NPs and carbon film,the yolk-shell structural Si@V@C2 anode had been prepared by taking advantage of the soft properties of phenolic resins.It was found that the volume of sample Si@V@C2,which obtained after removal of SiO₂ sacrifice layer,was significantly reduced by contrasting optical photos.Compared to Si@V@C1,the tap density of Si@V@C2,which obtained after carbonization,was significantly improved.Si@V@C2 was characterized by SEM,TEM,XRD,and the results show that the carbon film covers on the surface of Si NPs in the form of folds,indicating that the connection of silicon particles and carbon film is improved.At the meantime,the volume of microstructure is reduced,which was consistent with the phenomenon of the increasing tap density of the sample.The Si@V@C2 was used as the LIBs anode,and its electrochemical properties were tested and compared with the sample Si@V@C1.It exhibits that the electric conductivity and ionic conductivity of Si@V@C2,which obtained by improving the synthesis method,was significantly improved.Meanwhile,the rate capacity of Si@V@C2 was improved,which can be attributed to the excellent connection between the carbon film and the Si NPs in the sample of Si@V@C2.After 500 cycles,the specific capacity of sample Si@V@C2 is 703 mAh/g at the current density of 1 A/g,which is 26.2%higher than sample Si@V@C1.Through SEM characterization,it was found that the electrode surface structure of the sample Si@V@C2 was stable,which was attribute to the structural stability of the Si@V@C2.Therefore,the battery showed a good cycling performance.In order to improve the rate capacity of Si@V@C1,we had designed and prepared the yolk-shell structured Si@V@TiO₂-C by replacing Carbon?C?with Titanium dioxide-carbon complex?TiO₂-C?.Through improved St?ber method and sacrifice template method,we successfully prepared Si@V@TiO₂-C.We made the morphology and structure characterized by SEM,TEM,XRD,the result show the yolk-shell structured Si@V@TiO₂-C.Electrochemical performance test showed that the specific capacity is 1581 mAh/g,1530 mAh/g,1459 mAh/g,1361 mAh/g,1220 mAh/g,980mAh/g at the current density of 0.2 A/g,0.5 A/g,1 A/g,2 A/g,4 A/g,8 A/g,showing high rate capability.