Preparation And Application Of Porous Carbon/Nickel Composite For Heavy Sulfur-loading Electrode In Li-S Battery

The limited energy density of traditional lithium-ion battery leads to the difficulty for increasing range of electric vehicles.Lithium-sulfur battery(Li-S battery)has attracted wide attention due to its high energy density,abundant active material reserves,low cost,and pollution-free.However,the shortcomings of Li-S batteries restricts its application.The poor electric conductivity of sulfur and lithium sulfide leads to the decrease in active material utilization.The huge volume expansion during sulfur litiation destabilizes electrode structure.Porous carbon as a sulfur carrier yields larger specific surface area for electroreactions but limited pore volume for sulpher loading,leading to the difficulty to decrease in the energy density of the sulfur electrode.On the other hand,nickel foam has high porosity and strength for sulfur loading but very small specific surface area for the reactions.Taking advantages of porous carbon and nickel foam to overcome their shortcomings,a high-performance porous carbon/nickel composite is developed as a sulfur carrier material.On the basis of study on deterioration of sulpher electrode and materials characterization,the achievements and conclusion are presented as follows:1.The poor electric conductivity of sulfur and its lithiated Li2S causes the decrease in active material utilization.In order to improve the conductivity of active material,macroporous carbon(MPC)is fabricated,using starch as the carbon source and nano-calcium carbonate as the template.For improvement of the conductivity of sulpher electrode,the nickel foam is used as the current collector connecting MPC particles without increase in mass transfer resistence.It is found that the MPC-based sulpher electrode reachs an initial capacity of 1056.6 mAh.g-1 at 0.1 C,much higher than that of the pure sulfur electrode(530.9 mAh·g-1).Furthermore,the MPC/Ni composite-based sulfur electrode presents excellent performance stability with a capacity degradation less than 0.347%per cycle within 100 cycles.2.MPC/Ni composite significantly enhances sulfur loading up to 13.1 mg·cm-2 with less decrease in actual specific capacity of sulfur and perforemance stability.Such a heavy S-loading electrode presents an initial capacity as high as 6.1 mAh.cm-2,and remains a capacity of 5.7 mAh·cm-2 after 100 cycles.The integrated structure of MPC/Ni composite ensures the cycling performance of the electrode.The capacity degradation rate is decreased as low as 0.064%per cycle within 300 cycles.It is found that MPC modified by Sn shows excellent affinity to nickel,improving the contact between MPC and Ni foam struts.The SnO2 on pore surfaces in MPC supresses the polysulfide shuttle.The pore structure and performance of MPC/Ni composite are dependent on calcination temperature.The MPC/Ni composite synthesized at 900℃ presents the best electrochemical performance.3.Nickel chloride is introduced in the precursor of MPC for fabrication of modified MPC/Ni composite with abundent pore structure and higher specific surface area which improve the utilization of S42-species for capacity promotion.The modified MPC/Ni composite after sulfur loading presents an initiak specific capacity of 1090 mAh·g-1,and 776 mAh.g-1 is reserved after 100 cycles.The MPC/Ni composite performance is determinded not only by the calcination temperature but also by the composition of MPC precursor.A sulfur electrode with sulfur loading of 20 mg·cm-2 demonstrates a stable capacity is 13.1 tAh·cm-2.