Research On Preparation And Performance Of Transition Metal Hydroxide Supercapacitor Electrode Materials Based On Biomass Activated Carbon

Supercapacitors have attracted much attention due to their high power density,fast charging and recharging capability,and long cycle life.However,the low energy density severely limits their practical applications,so the preparation of advanced electrode materials is the key to achieve high performance in supercapacitors.Although activated carbon is currently the most widely used electrode material commercially,its production is heavily dependent on fossil energy sources.Biomass activated carbon is prepared by using various animal,plant and household wastes as raw materials,and is highly preferred for its large specific surface area,rich pore structure,wide source of raw materials,low price and good chemical stability.The pore structure and the level of heteroatoms are the keys to prepare high performance biomass activated carbon materials.In this thesis,the preparation of high-performance biomass activated carbon is investigated,and the activated carbon/transition metal hydroxide composite electrode material is prepared for the problem of low energy density of carbon electrode.Firstly,both self-templating and self-doping methods were used with biomass waste turtle shell as raw material.The turtle shell is composed of laminated keratin and contains the natural salt template hydroxyapatite（HAP）,which provides a certain pore structure for the turtle shell activated carbon.Further combines with the chemical activation method,which makes the prepared tortoise shell activated carbon with excellent pore structure.In addition,the abundant protein content allows for self-doping,thus providing a high level of heteroatom doping.The role of HAP and KOH in the carbonization and activation stages is investigated.The prepared turtle shell activated carbon（TSHC-5）has high specific surface area(2828 m²·g^-1),pore volume(1.91 m³·g^-1)and heteroatom content（O 6.88%,N 5.64%）.The energy density of the symmetric supercapacitor assembled using TSHC-5 activated carbon in 1 M Na₂SO₄ aqueous solution is 45.1 Wh·kg^-1.Secondly,although Ni（OH）₂ has a high capacity,its drawbacks such as poor electrical conductivity and severe accumulation severely limit its practical application.A synergistic effect was produced by introducing turtle shell biomass activated carbon（TSHC-5）with a hierarchical porous structure as a substrate to grow Ni（OH）₂nanosheets through a simple solvothermal method.TSHC-5 provides abundant growth sites for Ni（OH）₂,improving interfacial contact and electrical conductivity.In addition,the three-dimensional porous structure of TSHC-5 allows faster transport of electrolyte ions and diminished stacking during Ni（OH）₂ growth,thus exposing more active sites and hence faster and more adequate redox reactions.The role of TSHC-5 and Ni（OH）₂in Ni（OH）₂/TSHC-5 is investigated.The asymmetric supercapacitor assembled with Ni（OH）₂/TSHC-5 achieve an energy density of 58.18 Wh·kg^-1 at a power density of 800W·kg^-1 in a 6 M KOH aqueous solution.Finally,since the doping of metal ions in a single metal hydroxide structure can broaden its interlayer space and reduce the mechanical stress during its charging and discharging,which leads to a significant increase in its electrochemical capacity and prevents electrode failure.Therefore,layered bimetallic hydroxides（NiCo-LDH）are prepared by introducing Co.Then NiCo-LDH was compounded with TSHC-5 to attenuate the stacking of NiCo-LDH and improve the poor electrical conductivity.The improvement effect of Co to Ni（OH）₂ and the role of TSHC-5 and NiCo-LDH in NiCo-LDH/TSHC-5 are investigated.The energy density of the asymmetric supercapacitor assembled with NiCo-LDH/TSHC-5 reach 61.8 Wh·kg^-1 at a power density of 800 W·kg^-1 in 6 M KOH aqueous solution.