Study On Electrochemical Performance Of Macadamia Nut Shell-based Porous Carbon Material As Cathode Material For Lithium-Sulfur Battery

The popularity of new energy vehicles requires higher battery life.Lithium-sulfur batteries have received widespread attention due to their super large theoretical specific capacity and energy density.However,the insulation and volume expansion effect of sulfur and the"shuttle effect"of polysulfides have always restricted the commercial application of lithium-sulfur batteries.At present,the most effective way to solve these problems is the development and improvement of cathode materials.The preparation process of biomass carbon materials is simple,the raw materials are cheap and easily available,the specific surface area is large and the chemical properties are stable.Therefore,the agricultural waste macadamia nut shell is used as the carbon source,and the prepared porous carbon material is used as the sulfur carrier,and the influence of different preparation conditions on its microstructure and electrochemical performance is systematically explored.In addition,the activated carbon nanotubes and macadamia nut shell porous carbon material are composited,and the electrochemical properties of the composite materials are explored.We use macadamia husk as the precursor and KOH as the activator,the porous carbon preparation conditions were optimized,and it is found that the porous carbon material OPC-4 prepared when the carbonization temperature is 500°C,the ratio of KOH and carbon is 4:1,and the activation temperature is 900°C has the largest specific surface area and pore volume,which are as high as 3553 m²·g^-1 and 2.231cm³·g^-1,respectively.It also has a rich lotus root-like pore structure.The sulfur/carbon composite cathode material S/OPC-4 prepared from the porous carbon material also has the best electrochemical performance,not only has a high specific capacity,but also has good cycle performance.The initial discharge specific capacity at 0.2 C is 942.4 mAh·g^-1,after 500 charge-discharge cycles,the specific capacity remains at 338.4 mAh·g^-1,the decay rate per cycle is 0.128%,and the initial discharge specific capacity can reach 740.3 mAh·g^-1 even at 1 C,The capacity retention rate is still 50.2%after 400 cycles.In order to further improve the electrochemical performance of the cathode material,CNT with excellent conductivity is selected to be composited with the porous carbon material of macadamia nut shell.The results show that activated carbon nanotubes have a higher capacity,and when the mass ratio of KOH to CNT is 1:1,the prepared material S/OCNT-1 has the highest specific capacity and excellent cycle stability.The composite materials S/OCNT@OPC-1:4,S/OCNT@OPC-1:1,S/OCNT@OPC-7:3 are obtained by compounding S/OCNT-1and S/OPC-4 through mechanical grinding.The specific capacity of the two materials at 0.2 C is higher than that of the two materials when they are not compounded,and the cycle performance and rate performance are also better,indicating that the combination of the two produces a synergistic effect.At the same time,the analysis found that when the two materials are compounded in a ratio of1:1,the synergistic effect is the most significant.The composite carbon material S/OCNT@OPC-1:1 has the largest specific capacity,the best cycle stability and rate performance,the specific capacity at 0.2 C is as high as 1252.6 mAh·g^-1;after 500cycles at 1 C,the specific capacity decreases from 984.3 mAh·g^-1 to 631.7 mAh·g^-1,and the capacity retention rate is as high as 64.7%;The specific capacity is still as high as 692.8 mAh·g^-1 at 2 C,and the specific capacity remains at a high level of419.0 mAh·g^-1 after 500 cycles.The macadamia nut shell porous carbon material prepared in this study has excellent electrochemical properties,which provides a new idea for the preparation and application of biomass-based lithium-sulfur battery cathode materials.