Preparation And Electrochemical Properties Of Carbon Aerogels And Their Composite Materials

Currently,lithium-ion batteries and supercapacitors have become the most promising new energy sources as alternatives to disposable non-renewable energy sources,and have been widely researched and applied in multiple fields.Green and sustainable electrodes is the future trend,which requires lithium-ion batteries and supercapacitor electrodes to not only provide excellent electrochemical properties,but also to be green.So a wide range of sources of green carbon materials have become the focus of researchers' attention.With its large porosity and rich mesoporous structure,carbon aerogels,in particular,can achieve controlled design and doping at nanoscale through sol-gel process,which can meet the structural and performance requirements of materials for different energy storage devices.Therefore,the preparation of carbon aerogels using environmentally friendly carbon sources as electrode materials for energy storage devices and the improvement of their electrochemical properties by doping methods has become an important work in research.In this study,nitrogen and silicon doped carbon aerogel composite electrode materials for high-performance energy storage devices were designed and synthesized.They took chitosan and aniline as precursors,respectively.Firstly,natural biomass chitosan was used as the nitrogen source,phytic acid and graphene oxide were used as additives,chitosan and graphene oxide were combined by phytic acid chelation,and a nitrogen-phosphorus co-doped carbon aerogel with a unique three-dimensional layered hierarchical porous structure was prepared by hydrothermal,freeze drying and carbonization activation.The effects of different phytic acid concentrations,different carbonization temperatures and activation processes on the structure and performance of nitrogen-phosphorus co-doped carbon aerogels were investigated,and electrochemically superior nitrogen-phosphorus co-doped carbon aerogel supercapacitor electrode materials were designed and synthesized.Secondly,in this study,the carbon aerogel-coated silicon nanocomposites were prepared by in situ polymerization and freeze-drying of silicon nanocomposites in polyaniline aerogels using aniline as precursor and phytic acid and ammonium per-sulfate as additive,and further by high temperature carbonization.The morphological structure and electrochemical properties of carbon aerogel-coated silicon nanomaterials were investigated using different testing methods,which laid the foundation for further research on high-capacity and high-performance anode materials for lithium-ion batteries in the future.The main findings of the study indicate that.(1)At 2.0 mL of phytic acid addition,the charred aerogel composites exhibited the best electrochemical properties when used as supercapacitor electrodes.The specific capacitance was 178 F·g-1 at a current density of 0.5 A·g-1;when the current density increased to 10 A·g-1,the specific capacitance was 99 F·g-1 and the capacitance retention rate was 55.6%.For the activated material,the aerogel composite exhibited the best electrochemical performance when used as a supercapacitor electrode with a specific capacitance of 119 F·g-1 at a current density of 0.5 A·g-1 when phytic acid was added at 1.5 mL,and a specific capacitance of 112 F·g-1 with a capacitance retention rate of 94.1%when the current density was increased to 10 A·g-1.(2)Taking the nitrogen-phosphorus co-doped carbon aerogel with a phytic acid addition of 1.0 mL as an example,the capacitance reached its maximum at a carbonization temperature of 1000?.The specific capacitance of the sample is 148 F·g-1 when the current density is 0.5 A·g-1 and 100 F·g-1 when the current density increased to 10 A·g-1.The capacitance retention rate is 67.6%,which provides relatively good multiplicity performance.(3)The carbon aerogel-coated nano-silicon materials prepared in this study were used as an anode for lithium-ion batteries.The first charge and the first discharge specific capacities are 1506 mAh·g-1 and 1239 mAh·g-1,respectively,at 50 mA·g-1 with the first Cullen efficiency of 82.3%.After 50 cycles,the reversible capacity was 1215 mAh·g-1,and when the current density increased to 3.0 A·g-1,the reversible capacity was maintained at 231 mAh·g-1.When the current density was restored to 50 mA·g-1,the reversible capacity returned to 1113 mAh·g-1,indicating that the carbon aerogel-coated nano-silicon has excellent electrochemical properties.