Study On The Design And Preparation Of High Performance Biomass-based Activated Carbons For Supercapacitors

Supercapacitor,as an advanced energy storage device,has been applied in many fields of the national economy due to its long cycle stability,high power density and fast charge-discharge ability.However,supercapacitor also has many disadvantages in the actual application,such as fast capacitance fade,inferior rate performance,low energy density and so on.The electrode material is one of important factors affecting the performance of supercapacitor.Therefore,high performance electrode material has attracted much attention of this research area.Activated carbon（AC）was considered as a promising electrode material because of its low cost,high specific surface area and developed pore structure.In this paper,biomass raw materials were used as precursor to prepare 3D network pore structure activated carbon by physical-chemical activation.The coconut shell-based AC showed ideal properties as electrode material and also exhibited the long-term cycle stability,low capacitance fading rate and high specific capacitance in both aqueous and organic electrolytes.And the indica rice was used as precursor to prepare activated carbon with the high specific surface area,large total volume,excellent electrical conductivity,high content of surface oxygen functional groups.Dead pine needle-derived O,N co-doped activated carbon was prepared by an easy one-step carbonization.It was due to the unique structure of cells in dead pine needle,abundant contents of metal elements（K,Na,Ca,Mg）.The as-obtained PN-X samples had the high rate performance as electrodes for supercapacitors.The main research contents and results are summarized as follows:（1）The preparation of 3D network pore structure activated carbon as supercapacitor electrode with long-term cycle stabilityThe high performance bio-based activated carbon（BAC）has been prepared via the novel combination of chemical and physical activation process by using coconut shells as precursor.The as-obtained BAC exhibited the three-dimensional network pore structure,high specific surface area（3242.05 m²/g）,unobstructed and interconnected pores,and large pore volume（1.919 cm³/g）.The BAC exhibited the high specific capacitance of 337 F/g（202 F/cm³）and it kept at 331 F/g（190 F/cm³）after 10000 cycles（98% capacitance reservation）at the current density of 0.5 A/g in the 6 M KOH electrolyte.And the gravimetric capacitance values of AC-W was 240 F/g while the volumetric capacitance value was 120 F/cm³ in 1 M TEABF₄/AN electrolyte.The BAC showed ideal properties as the electrode material,such as the long-term cycle stability,low capacitance loss rate and high specific capacitance as electrode materials in both aqueous and organic electrolytes.The results are expected to develop the efficient environment friendly and low-cost supercapacitors,as well as to promote their applications for future electric vehicles,mobile phones and power electronics.（2）Manufacturing oxygen-enriched mesoporous carbon with excellent electrochemical performance for supercapacitor electrode material from indica riceAn indica rice-derived mesoporous carbon with excellent electrochemical performance was prepared via the novel thermoplastic carbonization and chemical activation process.The as-obtained mesoporous carbon showed hierarchical nanostructures with well interconnected pores and channels,which had the high specific surface area（2982.4 m²/g）,large total volume（2.21 cm³/g）,excellent electrical conductivity（10 S/cm）,high content of surface oxygen functional groups（14.12 at%）and optimal proportion of mesopores（2-5 nm）up to 86%.It exhibited the high specific capacitance at current densities of 0.5 and 50 A/g,i.e.,429 F/g（236 F/cm³）and 182 F/g（100 F/cm³）in H₂SO₄ electrolyte,respectively.Moreover,excellent electrochemical performances in Et₄NBF₆/AN electrolyte were also achieved,including the high specific capacitance of 211 F/g（116 F/cm³）at the current density of 0.5 A/g.The energy density of RAC-800 in ionic liquid electrolyte was calculated to be 64.4 W h/kg（35.4 W h/L）at the power density of 105 W/kg（57.8 W/L）,and about 26.3 W h/kg（14.4 W h/L）at the high power density of 10500 W/kg（5775 W/L）.In this research,a readily available and renewable source was provided as raw material and a novel method for preparing mesoporous carbon as electrodes for supercapacitor was found.What’s more,the results can promote the practical application of mesoporous activated carbon materials and supercapacitors.（3）From dead pine needles to O,N co-doped activated carbons by an one-step carbonization for high rate performance supercapacitorsDead pine needle-derived O,N co-doped activated carbons were prepared by an easy one-step carbonization without adding any chemical reagents.The as-obtained PN-X samples had a high rate performance as electrodes for supercapacitors.It was due to the unique structure of cells in dead pine needles,abundant contents of metal elements（K,Na,Ca,Mg）and a large number of heteroatom contents（O,N）.All chemical and physical properties of PN-X samples were provided in detail.Especially,the PN-1000 showed a high specific capacitance of 223 F/g（178 F/cm³）at the current density of 0.5 A/g while it still had 150 F/g（120 F/cm³）even at 100 A/g.The results suggested the unique and low cost PN-1000 to be a promising electrode material for supercapacitors in many practical applications.