Study On The Structure Design And Performance Of Silicon-carbon Anode Layered Electrode

With the rapid popularization and promotion of electric power,increasing energy density is an inevitable direction for the development of lithium-ion batteries.Silicon-based materials with high specific capacity and high-load electrode structure design are effective ways to increase the energy density of lithium-ion batteries.In high-load silicon-based electrodes,the length of the electron transmission path limits the electron transfer.Simultaneously,as lithium is inserted and released,the active material with a large volume effect is easy to peel off from the current collector,which ultimately leads to the instability of the electrode structure.The silicon-based negative electrode designed with a single-layer structure has poor stability of surface structure,uneven utilization of the internal components of the electrode,and uneven internal polarization.The above-mentioned problems will hinder the cycle performance and rate performance of the lithium-ion battery,and is not conducive to meet the high-energy density and the cycle stability needs of the battery.Through the simulation and calculation of the electrode structure,a reasonable pore distribution and the gradient distribution of the material inside the electrode,to a certain extent,can make the potential distribution inside the electrode more uniform,which is beneficial to improve the cycle stability of the electrode.Therefore,the multi-layer composite electrode structure design is expected to break through the performance bottleneck of single-layer electrodes.The paper applies the composite electrode structure design to the high specific capacity silicon-carbon anode,through respectively preparing three types of silicon-carbon layered composite structure electrodes,including conductive coating composite structure electrode,silicon content layered composite structure electrode,and conductive agent layered composite structure electrode;and studies its cycle performance,rate performance and other electrochemical behaviors.In the composite electrode structure,the upper structure with enhanced stability can promote the stability of the overall structure of the electrode,and the lower structure with strong conductivity can reduce the overall charge transfer resistance of electrode structure and improve rate performance of silicon carbon anode.This paper provides guidance for the design of high specific capacity silicon-based anode electrodes and the application of high specific capacity silicon-based anode materials in high specific capacity lithium-ion batteries.In the design of the conductive coating composite electrode structure,single-walled carbon nanotubes were selected as the conductive coating,and three composite structure electrodes with the thickness of the coating of 0.09 mg/cm2(AM/SWCNTO.09),0.18 mg/cm2(AM/SWCNT0.18),and 0.22 mg/cm2(AM/SWCNT0.22)were prepared.Compared with the single-layer electrode without the conductive coating structure(AM),the thickness expansion rate of the AM/SWCNT0.22 structure electrode after 50 cycles is reduced by 27%,and the capacity retention rate after 100 cycles is increased by 18.4%.The addition of conductive coating on the upper surface of the electrode can improve the structural stability of the electrode during cycling.The over-thick conductive coating causes the electrode energy density to be relatively reduced.The silicon-carbon anode material with a specific capacity of 480 mAh/g and stable cycle performance is selected as the upper active material of the electrode,and high-specific-capacity silicon-carbon anode material of 850 mAh/g is selected as the lower layer,which increases the overall specific capacity of the electrode to 650 mAh/g,recorded as Cu84.Compared with the Cu650 with the same areal density of the single-layer silicon-carbon negative electrode structure,the specific capacity of the Cu84 structure electrode increased by 79.4 mAh/g,and the capacity retention rate increased by 9.03%after 70 cycles.In addition,when the Cu48 structure and the carbon-coated current collector are applied to the design of the full-battery soft pack,the stress and thickness changes in the battery cycle of the carbon-coated current collector are minimal.The improved stability of the upper structure contributes to the overall stability of the electrode structure,and the lower buffer structure can alleviate the stress in the battery cycle.Keeping the overall structure of the electrode unchanged and adjusting the content of the upper and lower conductive agents in the electrode composite structure,the paper prepares six kinds of conductive agent content layered composite structure electrodes,which SP content of the upper and lower conductive agents is 10:0(S0-10),9:1(S1-9),7:3(S3-7),3:7(S7-3),1:9(S9-1)and 0:10(S10-0).Compared with the S5 single-layer structure electrode with the same surface density,the capacity retention rate of the SO-10,S1-9,S3-7,S7-3,S9-1 and S10-0 structures under 1C charging rate has been improved respectively by 2.02%,17.42%,22.4%,21.77%,and 8.63%.Appling layered composite structure of conductive agent to the soft pack battery,as the lower layer contains more SP,under the magnification of 2.5C and 3C the capacity retention rate is increased by 12.79%and 28.92%respectively,compared with the single-layer structure soft pack battery.The capacity retention rate of the structure with more CNT content on lower layer is increased by 12.05%and 30.1%at the rate of 2.5C and 3C,respectively.The layered composite structure design of conductive agent can improve the rate performance of the electrode.In summary,the composite electrode structure design can improve the physical and chemical properties of the silicon-carbon anode,and has a good application prospect.