Study On Preparation Of Carbonized Wood Electrode And Its Supercapacitor Performance

Supercapacitor（SC）is an essential green energy storage device with advantages of high-power density,fast charging and discharging,and long cycle life,which is a great alternative to batteries in high power applications and an attractive development direction for future electrochemical energy storage technology.As a renewable and biodegradable natural polymer material,wood has a unique hierarchical cell structure,excellent mechanical flexibility and adjustable versatility,which makes it ideal for preparing self-supporting carbonized wood（CW）electrodes for electrochemical energy storage.CW electrodes inherit the advantages of light weight,high specific surface area and good electrical conductivity of carbon materials,and retain a low-tortuosity hierarchical porous pipe structure,which can effectively reduce the ion diffusion resistance,increase the active material loading and the overall device energy density.In this study,the effect of different species of wood on the performance of CW electrodes was investigated,and a high-performance SC cathode and anode were prepared by a self-activation method and in situ growth of nickel-cobalt phosphate（Ni Co-P）,respectively,and an asymmetric supercapacitor（ASC）with high energy density and high-rate performance was successfully constructed.The main research results are as follows.（1）Eight different species of wood carbon electrodes were prepared by the same carbonization method,and their microstructure,physical properties and electrochemical properties were analyzed and compared.The results show that the density of wood is the primary factor affecting the various properties of CW electrodes,and the microstructure and chemical composition of wood also affect them.With decreasing wood density,the density,wall thickness,electrical conductivity,and compressive strength of CW electrodes decrease.The unimpeded pipe structure and low lignin content favor the self-activation of wood during carbonization to produce more pores,which makes CW electrodes exhibit high specific surface area,low electrochemical impedance and high specific capacitance,but leads to a decrease in conductivity and compressive strength.（2）The SCW electrode was prepared by carbonization method with low inert gas flow rate.The results show that more CO₂ can be released during pyrolysis of wood chips pre-oxidized at 220°C.Increasing the carbonization temperature can effectively improve the self-activation strength and electrical conductivity.The inert gas flow rate can significantly modulate the self-activation intensity.The prepared SCW-1000-10 electrodes have specific surface area,conductivity,area specific capacitance and mass specific capacitance up to 1145 m² g^-1,20.3 S cm^-1,6.63 F cm^-2 and 143.6 F g^-1,respectively.The assembled SSC has a specific capacitance of 13.15 F cm^-3 and 28.9 F g^-1,an energy density of up to 1.35 m Wh cm^-3(3.97 Wh kg^-1),and a capacitance retention rate of 103.6%after 10,000cycles.（3）Ni Co-P/CNT/CW electrodes were prepared by carbonization,chemical vapor deposition,and electrochemical deposition.The results show that increasing the electrodeposited solution concentration can increase the loading of Ni Co-P,and the electrode will exhibit higher area specific capacitance,but the rate performance will decrease.The growth of CNT can effectively increase the active site and conductivity of the material,which makes the Ni Co-P capacitive performance fully utilized.The Ni Co-P/CNT/CW electrode has a high specific capacitance of 11.2 F cm^-2 and 230.0 F g^-1.The assembled ASC device has an ultra-high specific capacitance of 18.4 F cm^-3 and 38.6 F g^-1 and an initial capacitance retention of 89.1%(30 m A cm^-2).ASC shows an ultra-high energy density of 5.74 m Wh cm^-3(12.1 Wh kg^-1)and a capacitance retention of 92.5%after 10,000 cycles.