| With the rapid growth of the world’s population and the rapid development of the global economy,the energy crisis caused by the excessive consumption of a large number of non-renewable fossil fuels and the environmental problems caused by the excessive emission of greenhouse gases caused by the burning of fossil fuels are causing huge impacts on human society.Therefore,the development of clean energy represented by solar energy,wind energy,hydropower,geothermal energy and tidal energy is an effective solution to the aforementioned environmental and energy crisis.However,it is necessary to develop stable and efficient secondary high-performance energy storage devices for full use of these energy resources because they do not have good continuity and uniformity.Among them,lithium-ion capacitors have higher energy density than traditional supercapacitors and higher power density than traditional lithium-ion batteries,so they have great development prospects in the field of electrochemical energy storage in the future.In this paper,the cheap petroleum pitch is used as the carbon source,and three different methods of hard template method,one-step carbonization-activation method,and soft template method are used to prepare porous carbon materials with unique morphology and rich pore structure to construct three different types of lithium-ion capacitors.The main research contents are as follows:1.Using petroleum asphalt as raw material and basic magnesium carbonate as template to prepare porous carbon nanosheets HCNs-4.Using magnesium oxide as a template with activation by potassium hydroxide,a three-dimensional hierarchically cross-linked porous carbon AMOPC was prepared.The prepared porous carbon materials were used as negative and positive materials to construct lithium-ion capacitor HCNs-4//AMOPC.Under the power density of 235 W kg-1,the energy density could deliver 165 Wh kg-1 and under the high power density of 23.5 k W kg-1,the energy density could also reach 89 Wh kg-1.When it was cycled 4000 times at the current density of 1 A g-1,the specific capacity decayed from 50 m Ah g-1 to 40 m Ah g-1,and the capacity retention was as high as 80%,showing good long-term cycling stability.2.Using petroleum asphalt as raw material and potassium bicarbonate as template and activator to prepare three-dimensional cross-linked hierarchically porous carbon nanosheet PCNs-800.The symmetrical dual-carbon lithium-ion capacitor PCNs-800//PCNs-800 was fabricated by using PCNs-800 as the negative and positive materials.When the mass ratio of positive and negative electrodes is 1:1,it showed the highest energy density and power density and the most excellent long-cycle stability.Under the power density of 260 W kg-1,the energy density could reach 112 Wh kg-1and under an ultrahigh power density of 52 k W kg-1,the energy density could also exhibit 48 Wh kg-1.When it was cycled 9000 times at the current density of 1 A g-1,the specific capacity decayed from 40 m Ah g-1 to 28 m Ah g-1,and the capacity retention was as high as 70%,showing good cycling lifespan.3.Using petroleum asphalt as raw material and the precursor obtained by mixing melamine and cyanuric acid as the soft template,the pleated N/O co-doped two-dimensional cross-linked carbon nanosheets NOCNS was prepared.Then,the three-dimensional hierarchically porous carbon NOACNS is prepared by KOH activation with the obtained anode material as the carbon source.The prepared porous carbon materials were used as negative and positive materials to assemble lithium-ion capacitor NOCNS//NOACNS.When the mass ratio of positive and negative electrodes is 2:1,it showed the highest energy density and power density and the most excellent long-cycle stability.Under the power density of 235 W kg-1,the energy density could deliver 159Wh kg-1 and under the high power density of 23.5 k W kg-1,the energy density could also reach 98 Wh kg-1.When it was cycled 10000 times at the current density of 1 A g-1,the capacity retention was as high as 72%,showing excellent cycling stability. |
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