Oxygen/Sulfur-Doped Porous Carbon:Design,Preparation And Electrochemical Energy Storage Research

As an energy storage device with environment friendly property,outstanding cycle sability,and the ability to charge-discharge rapidly,supercapacitors（SCs）have received widespread attention.However,most researchers focus on SCs operating at room temperature,and few reports involve the development and research of high-temperature SCs because of several challenges（such as:poor cycling stability of the electrode material at high temperature and low boiling point of the electrolyte）.In daily life,electron devices operating at high temperatures,such as electric vehicles and large communication stations switching 5G signal,are inevitable.Therefore,there is an urgent need to develop SCs that could operate stably at high temperatures to expand their application range.Furthermore,metal-ion（Li,Na,K）hybrid capacitors could offer energy density close to ion batteries in addition to power density and cycle life comparable to SCs,which enables them to meet the dual demands of a new generation of large energy-consuming devices for high energy/power density.Among them,the abundant resources and low cost of potassium endow potassium-ion hybrid capacitors（PIHCs）the bright prospect for large-scale application.Unfortunately,most PIHCs anode materials usually suffer from dramatic volume expansion and sluggish kinetics due to the large size of potassium ion（1.38?）,leading to a notorious rate performance and recyclability.In addition,the limited cathode capacity and mismatched kinetics between the two electrodes also severely limit the development and application of high-performance PIHCs.In this work,we prepared a series of heteroatom-doped porous carbons suitable for SCs and PIHCs based on the dual modification strategy of heteroatom doping and pore structure regulation.（1）Using commercial tetrasodium ethylenediaminetetraacetate （EDTA4Na）as the carbon source,we prepared an oxygen-doped hierarchical porous carbon nanosheet network with multiscale pores（combination of micropores,small-size mesopores and supermesopores）,ultra-high specific surface area(3400 m²g^-1)and extremely large active ion-accessible pore volume(V_{0.5-5 nm}=1.750 m³g^-1,V_{0.76-5 nm}=1.533 m³g^-1)by a simple self-templated pyrolysis supplemented by a KOH activation strategy.We explored the electrochemical properties of this carbon nanosheet network in 6M KOH and 1-ethyl-3-methylimidazolium tetrafluoroborate（EMIMBF₄）ionic liquid electrolytes and revealed the effect of heteroatoms and pore structure on its charge storage.Finally,a high-temperature SCs device based on EMIMBF₄electrolyte was successfully constructed,which exhibited superior charge storage capability(2 A g^-1,290 F g^-1),excellent rate capability(50 A g^-1,203 F g^-1)and considerable durability over 2500 cycles at 20 A g^-1.The ultimate energy density and power density are as high as 122.23 Wh kg^-1(corresponding power density of 1.74 k W kg^-1)and 40.6 k W kg^-1(corresponding energy density of 70.79 Wh kg^-1).（2）We prepared sulfur-doped hierarchical porous hollow carbon spheres with controllable sulfur content by carbonization of SiO₂in situ hard template-induced resorcinol/formaldehyde condensate,HF acid etching,and subsequent high-temperature sulfur doping strategy.We systematically studied the effect of sulfur content on the potassium storage performance of porous carbon anode materials,and revealed the mechanism of action of sulfur doping in potassium storage.Electrochemical tests in K half-cells showed that sulfur doping improved the reversible specific capacity and initial Coulombic efficiency,but excessive sulfur content would reduce cycling stability.Benefiting from suitable sulfur content,rational sulfur configuration and hollow hierarchical porous structure,the optimized sulfur-doped porous hollow carbon spheres（SHCS）exhibited ultra-high initial potassium storage capacity(0.1 A g^-1,520 m Ah g^-1),outstanding rate capability(5 A g^-1,137m Ah g^-1)and durable cycling stability(223 m Ah g^-1after 1000 cycles of galvanostatic charge/discharge under 2 A g^-1).Furthermore,cucurbit[6]uril-based activated carbon（ACBC）with narrow pore size distribution（0.5-4 nm）,high specific surface area(3549 m²g^-1),and large ion-accessible pore volume(V_{0.5-4 nm}=1.506 m³g^-1)was prepared by KOH activation strategy.When used as a cathode for PIHCs,ACBC exhibited a specific capacity(0.1 A g^-1,86 m Ah g^-1)far superior to that of commercial activated carbon.Finally,the assembled PIHCs device based on SHCS anode and ACBC cathode could deliver maximum energy/power density of 135.6Wh kg^-1/17.7 k W kg^-1and extraordinary durability over 26,000 cycles at 2 A g^-1.