| At present,supercapacitors and lithium-ion batteries are the fastest growing and the most widely used electrochemical energy storage devices,because supercapacitors have the advantages of high power density,long life time and short charge-discharge time,and lithium-ion batteries have the advantages of high energy density,high average output voltage and no memory effect.As the key components of these two energy storage devices,electrode materials are the most important factors affecting their performance.Therefore,how to design and prepare new types of electrode materials with higher electrochemical performance and lower production cost is a hot issue in recent years.Expandable microspheres,kind of commercial polymer microspheres,have been widely used in many fields such as printing ink,sole and curing agent for paper products,and they have the unique core-shell structure and the special property of thermal expansion.In this paper,we prepared the porous activated carbon and silicon/carbon?Si/C?composite materials with hollow structures by means of simple and efficient treatment of the core materials-expandable microspheres.Also,the electrochemical properties of these two materials as the electrode materials of supercapacitors and lithium-ion batteries were studied and optimized,respectively.The main contents and conclusions are as follows:1.The porous activated carbon with a certain pore structure and large specific surface area was prepared by direct carbonization and activation of expandable microspheres.The effects of different activator proportion and different activation temperature on the electrochemical performance of products were investigated.The results show that the microstructures of the prepared activated carbon are irregular hollow structures,which have lots of microporous and mesoporous.The optimized sample,which was carbonized at 800 °C and activated at 700 °C,has the specific surface area of 1387 m2 g-1 and the pore volume of 0.686 cm3 g-1.The microporous are concentrated in 0.7 1 nm and the mesoporous between 2.3 5 nm are distributed uniformly in the sample.The electrochemical tests indicate that this sample has the best performance with a specific capacitance of 236 F g-1 at 1 A g-1,and the electrode maintains 95 % of its initial capacitance after 10000 cycles.As the current density increasing to 20 A g-1,the specific capacitance still maintains at 172 F g-1 with the capacity retention rate of 73 %.2.The Si/C composite materials with Si nanoparticles-loaded carbon hollow structures were fabricated via one-step pyrolysis of the mixture of Si nanoparticles and expandable microspheres,and the electrochemical properties of the composites were investigated.It is found by material characterization that the main phases of the Si/C composites are crystalline Si and amorphous C.The carbon shells have irregular hollow structures covered by wrinkles on their outer surface.Si nanoparticles fall into the voids or load on the rough surfaces of the hollow carbon shells.Electrochemical tests show that the best sample was carbonized at 800 °C and the ratio of expandable microspheres and Si nanoparticles in the sample was 7.5:1.The Si/C composites show a highly reversible lithium storage performance with the initial discharge/charge capacity of 1267.9/854.4 mAh g-1 at current density of 0.3 A g-1.After 50 cycles,the capacity retention rate is 80 %,and the rate performance is excellent. |
PDF Full Text Request