Preparation And Properties Of Manganese-based Anode Materials For Hybrid Capacitor

As anode of the hybrid capacitors,manganese-based anode materials have attracted extensive attention because of the advantages such as abundant reserves,environmental friendliness,and high theoretical specific capacity.However,due to the‘valence state conversion’reaction mechanism of manganese compounds,there are problems such as obvious volume expansion and serious agglomeration in the cycle process of Mn-based materials,and the Mn-based materials themselves also have poor electrical conductivity and low coulomb efficiency in the first cycle.This paper aims to solve the problems such as poor rate performance,fast capacity decay,and low first-coulomb efficiency of Mn-based anode materials.The properties of cathode materials are improved by various means,including carbon coating,bimetallic synergy,three-dimensional structure construction,and the combination of crystalline and amorphous states.The alkali metal etching method is used to improve the specific surface area of the cathode,and the in-situ heteroatom doping method is used to improve the capacity and electrical conductivity to match the capacity of anode and cathode electrodes,thus improving the overall performance of the capacitor.The spherical Mn₃O₄composite graphene anode material was prepared by the hydrothermal method.The material can provide good rate performance(the capacity is still obtained 172.2 m Ah g^-1at current density of 10 A g^-1)and cycle stability(the capacity is still 394.7 m Ah g^-1after 200 cycles at 1 A g^-1current density).Polyaniline activated carbon cathode was synthesized by a two-step method.Based on the larger specific surface area(1641.9 m²g^-1),the material has higher capacity and conductivity than commercial activated carbon under large current.The two materials were assembled into a lithium ion hybrid capacitor with good capacity retention after a long cycle and the maximum energy density is 97.2Wh kg^-1and the power density is 6250 W kg^-1.For Mn-based material volume expansion,the loop stability problem,adopt the way of the vanadium-manganese double metal composite structure to de-insertion type combined with transformation type Mn₂V₂O₇anode materials,makes up for the de-insertion type material capacity is low,the worse performance of transformational material circulation problems,using low-temperature hydrothermal method for Mn₂V₂O₇material coating with graphene to improve the dispersion of Mn₂V₂O₇particles and the electrical conductivity of the material and the Mn₂V₂O₇-G has a capacity of 660 m Ah g^-1at 1 A g^-1for 500 cycles.Hydrothermal pretreatment and high-temperature sintering were used to prepare biomass-activated carbon that has larger specific surface area(2040.8 m²g^-1),which was assembled into a carbon-carbon symmetric capacitor and Mn₂V₂O₇@r GO asymmetric capacitor with higher power density(15 k W kg^-1)and energy density(148.1 Wh kg^-1).Two-dimensional graphene materials can effectively prevent the anode materials volume expansion,improve overall conductive materials,but in the cycling of graphene layers also collapsed,and cause irreversible capacity loss,aiming at this problem,introduced the polyaniline carbon nanotubes in graphene,building three-dimensional structure,the extension of the conductive network between graphene.The effective support of the post-cycle broken graphene structure provides effective space for the volume expansion of higher capacity Zn Mn₂O₄,which improves the electrochemical performance of the anode and the capacitor.Because of the shortage of lithium sources,the application of Mn Co₂O_4.5and amorphous Mn Co₂S₄materials was extended to a new type of potassium ion capacitor.The anode of potassium ion capacitor with good performance was obtained by combining crystalline Mn Co₂S₄and amorphous Mn Co₂S₄materials and composite graphene,with the capacity of 272.3 m Ah g^-1(1.0 A g^-1)and the highest energy density of the MCO@MCS@r GO//SAC KICs is 85.3 Wh kg^-1and the energy density is still 47.5 Wh kg^-1at the highest power density of 9000 W kg^-1.