Collagen-derived Porous Carbons:design,Synthesis And Applications On Electrochemical Energy Storage

As efficient electric energy storage(EES)devices,supercapacitors(SCs)and Li-ion/Na-ion batteries(LIBs/NIBs)have been widely studied in the past decades.However,due to the energy storage mechanisms,the low energy density of SCs and the low power density and short lifetime of LIBs/NIBs impede the large-scale applications of these two kinds of EES devices.Recently,Li-ion/Na-ion capacitors(LICs/NICs)have gained great attentions as newborn EES devices.In the LICs/NICs,high energy density can be contributed from battery-type anodes,while high power density and long cycling performance can be provided by capacitor-type cathodes.Although LICs/NICs inherit the merits of SCs and LIBs/NIBs,the improvement of device performance still depends on the design and synthesis of high-performance electrode materials.Thanks to the good electrical conductivities,large specific surface areas,high chemical stabilities,tunable morphologies and resourceful precursors,porous carbons have been successfully used as electrodes for SCs and anodes for LIBs/NIBs.The hybrid battery-capacitive storage features enable porous carbons to be promising electrode materials for LICs/NICs.Previously reported works primarily focus on enhancing the performance of porous carbon electrodes by nanostructure engineering and chemical composition regulating.Unfortunately,most of them ignore the cost,safety and sustainability of material synthesis,restricting the practical applications of high-performance porous carbon electrodes.In this paper,low-cost and collagen-based precursors(cattle bone,sheep bone and gelatin)are used to prepare porous carbons with open structures and heteroatom doping.Several efficient and environmental-friendly methods are proposed based on the structures and compositions of the precursors,and the formation mechanisms of the resultant porous carbons are detailly explored.In addition,all the prepared porous carbons are used as electrodes for EES devices(including SCs,LIBs,NMBs,LICs and NICs)to further determine their electrochemical performance.The effects of material morphologies,nanostructures and chemical compositions on electrochemical energy-storage behavior and performance for porous carbon electrodes are detailly analyzed and summarized.LICs and NICs with integrated high energy and power densities as well as long cycling performance are successfully assembled.Based on the above works,the design principles of high-performance porous carbon electrodes for LICs and NICs were proposed as well.The specific works and results are as follows:(1)An efficient,tunable and eco-friendly method is proposed to prepare N,O-doped porous carbon bulks.Without any additional activators and templates,N,O-doped porous carbon bulks are prepared through direct carbonization of cattle bone.The porosity for the porous carbon bulks can be simply adjusted by changing pyrolysis temperature.The mechanism of pore formation is identified to be the self-activation induced by hydroxyapatite(HA)within cattle bone.The porous carbon bulk obtained at 1100? possesses rich defects,high specific surface area(2096 m2 g-1),large mesopore volume(1.829 cm3 g-1),narrow mesopore size distribution(?4.0 nm)and good electrical conductivity(5141 S m-1).Due to the synergistic effect of defects and pores,the resultant porous carbon bulk electrode exhibites battery-capacitive storage feature,which can be simultaneously used as the anode for LIB and electrode for SC.In half-cell device(using metallic Li as counter electrode),the porous carbon anode exhibits high reversible capacity of 1488 mAh g-1 after 250 cycles at 1 A g-1 and 661 mAh g-1 after 1500 cycles at 10 A g-1.Even at 30 A g-1,the porous carbon anode can still deliver a high reversible capacity of 281 mAh g-1,showing superior Li storage capability.Moreover,the symmetric SC based on the porous carbon electrodes(in neat EMIM-BF4 electrolyte)exhibits 258 and 176 F g-1 at the current density of 5 and 100 A g-1,respectively.Correspondingly,the symmetric SC shows high energy density of 109.9 Wh kg-1 and ultrahigh power density of 81.5 kW kg-1 as well as superior cycling performance(96.4%of the initial capacitance after 5000 cycles).(2)The self-activation induced by HA is further confirmed using sheep bone as precursor.For the first time,the prepared porous carbon is simultaneously used as anode material and cathode material to assemble high-performance LIC.After pyrolysis at 1100?,the sheep bone-derived porous carbon bulk possesses similar material structure with the cattle bone-derived porous carbon bulk.The high defect density and unique porosity endow the porous carbon electrode with battery-capacitive storage feature,which show high reversible capacity,good rate capability and long cycling performance as anode and cathode in half-cells(using metallic Li as counter electrode).Moreover,for the first time,the porous carbon is used both as anode material and cathode material to assemble LIC.The assembled LIC can show integrated high energy density(106.4 Wh kg-1)and power density(88.8 kW kg-1)as well as superior cycling performance(with a capacitance retention of 88.3%after 8000 cycles).(3)A low-temperature and facile method is proposed to prepare N,O-doped hierarchically porous carbon nanosheet,which is further used as anode material for high-performance NIC.Due to the synergetic effect of HA and KOH,hierarchically porous carbon nanosheet with a carbon interlayer distance of 0.41 nm and specific surface area of 890.4 m2 g-1 is simply prepared via pyrolyzing cattle bone with KOH at relatively low temperature(550?).The resultant porous carbon nanosheet possesses high surface heteroatom content(17.1 at.%for oxygen and 6.4 at.%for nitrogen)due to the low-temperature thermal treatment.The rich heteroatoms and unique two-dimensional hierarchical structure endow the porous carbon nanosheet electrode with battery-capacitive storage feature when it is used as anode for Na-ion storage.The porous carbon nanosheet that is tested in half cell against metallic Na can deliver a high reversible capacity of 198.5 mAh g-1 after 1000 cycles at the current density of 0.7 A g-1,and maintains a capacity of 150.8 mAh g-1 even after 10000 cycles at the current density of 7 A g-1.Consequently,the NIC based on the porous carbon nanosheet anode possesses integrated high energy and power densities(105.2 Wh kg-1 and 60.4 kW kg-1)as well as good long-term cycling stability(85.8%of the initial capacitance after 4000 cycles).(4)Two efficient and sustainable methods are proposed to prepare P,N,O-doped interconnected carbon nanosheets with hierarchical porosity and N,O-doped carbon nanosheets with micropore-dominant porosity,which are further used as anode and cathode materials to assemble high-performance NICs,respectively.The former carbon is prepared using gelatin/phytic acid as precursors and KCl/ice as dual-templates.The latter carbon is prepared using gelatin as precursor and KOH/KOH-derived compounds as templates/activators.All the reagents in these two methods are resourceful,low-cost and low-toxicity.The good water solubility enables them to be mixed at molecular level in deionized water.After pyrolysis,the potassium compounds(high purity KCl and K2CO3)in the resultant carbons can be easily removed by deionized water and collected for further use.The unique synthetic methods result in the porous nanosheet structures and rich heteroatoms,which endow these two porous carbon nanosheet electrodes with hybrid energy-storage features and good electrochemical performance in half cells(using metallic Na as counter electrode).The assembled NIC based on these two porous carbon nanosheet electrodes shows high energy density of 135.3 Wh kg'1 and ultrahigh power density of 16.1 kW kg-1 as well as superior long cycling performance(with a capacity retention of 88.6%even after 8000 cycles).(5)Based on the above explorations,the design principles of porous carbon electrodes for LICs and NICs are also proposed:(?)The open structures and heteroatom doping can endow porous carbon electrodes with hybrid energy-storage features,which simultaneously improve the capacitive and diffusion-controlled capacities,leading to the high capacities,good rate capabilities and superior cycling performance of cathodes and anodes;(?)For the structure design of anode materials,the specific surface area should not be too high or it will cause low initial coulombic efficiency of anodes;(?)For the composition regulation of anode materials,heteroatoms that can reversibly store Li ions and Na ions at low potential are preferred to ensure high working voltage and power desntiy of LICs and NICs;(iv)For the structure design of cathode materials,the efficient specific surface area for ion storage should be paid more attention than the total specific surface area of materials.The former plays important role in enhancing the electrochemical performance of cathode and can be increased by introducing open structures and rich micropores.