Study On The Synthesis And Performance Of Novel Carbon-Based Electrode Materials For Sodium-ion Capacitors

Sodium ion capacitors are new energy storage devices,which have a combination of high energy density of sodium ion battery and high power density of supercapacitor.Sodium ion capacitors absorb and desorb the anions by the capacitor-type cathodes and conduct the redox reactions with sodium ions by battery-type anodes?such as,insertion/extraction,phase inversion,alloying,etc.?.Therefore,electrode materials are the major factors to affect the electrochemical performance of a device.At present,sodium ion capacitors are mostly composed of a metal-based anode of the sodium ion battery and a porous carbon cathode.However,metal-based anodes have low capacities,which are prone to volume expansion during cycling,causing problems in the safety and shortening the cycle life.Generally,carbon-based materials have a high specific surface area and a developed pore structure,which facilitate the adsorption-desorption process of anions?i.e.a capacitor-type charge mechanism?.In addition,carbon-based materials have adjustable sheet structure that facilitates the sodiation and desodiation process?i.e.the battery-type storage charge mechanism?.Therefore,the research and development of new carbon-based materials with high energy density,high power density and long cycle life have become the hot spot and difficulty in current research.Based on the different storage mechanisms of the cathode and anode,this work rationally designs and optimizes two different carbon materials,and conducts detailed structural characterization and electrochemical performance tests to explore the relation of microstructure and macroscopic properties.The specific research contents of this work are as follows:?1?Pine-cone shell carbon sheets?PSCSs?anode of sodium ion capacitors was prepared using waste biomass pine cone shells as carbon sources by controlling the activation temperature?300,600 and 800°C?.The effect of activation temperature on the interlayer spacing and pore structure of PSCSs were mainly investigated,and the electrochemical performance was also tested.It was found that PSCS-600 exhibited the best electrochemical performance,with a specific surface area of 63.3 m² g^-1,a nitrogen content of 1.14 wt%,and an interlayer spacing of 0.41 nm,which was favorable for intercalation/deintercalation of sodium ions.In a half cell,PSCSs showed significant redox peaks in the cyclic voltammetry curves.In 1 M NaClO₄?EC:DEC=1:1 Vol%,2.0 Vol%FEC?,at the current density of 0.1 A g^-1,the capacity of PSCS-600 was 134 mAh g^-11 after 1,000 cycles,and the specific capacity retention was 86%.In 1 M NaCF₃SO₃?TETRAGLYME?,at the current density of 0.1 A g^-1,the capacity of PSCS-600 was 174 mAh g^-11 after 100 cycles,and the specific capacity retention was 89.2%.?2?On the basis of the molecular design,we designed and prepared a new monomer OPDN,containing N and O heteroatoms,which was further polymerized and activated under specific conditions to obtain a covalent triazine-based framework,i.e.,OPDN-CTF-A.OPDN-CTF-A was used as the cathode of sodium ion capacitor,and its structural characterization and electrochemical performance tests were carried out.The results showed that OPDN-CTF-A has a high specific surface area(687.4 m² g^-1)and nitrogen content?5.86 wt%?,showing hierarchical 3D network structure?the pore size distribution is concentrated in 0.5⁴ nm?,which is favorable for adsorption/desorption of anions.In a half cell,the cyclic voltammetry curve of OPDN-CTF-A appears as a rectangular shape similar to the electric double layer capacitor,which indicates that the material has better rate performance.In 1 M NaClO₄?EC:DEC=1:1 Vol%,2.0 Vol%FEC?,at the current density of 0.1 A g^-1,the specific capacitance of OPDN-CTF-A was 140 F g^-1 and the specific capacitance retention was 85%after 10,000cycles.A sodium ion capacitor was assembled on the basis of the capacitor-type cathode OPDN-CTF-A and the battery-type anode PSCS-600 in 1 M NaClO4?EC:DEC=1:1 Vol%,2.0 Vol%FEC?.We tested the electrochemical performance of PSCS-600//OPDN-CTF-A sodium ion capacitor at the voltage window of 1.5⁴.2 V.The results indicate that our device delivered a high energy density of 83.4 Wh kg^-11 at 280 W kg^-11 and the outstanding capacitance retention of 91%after 10,000 cycles.