Design And Modification Of Hard Carbon Sodium Ion Anode Materials Based On Ball Milling Technolog

The development of new and environmentally friendly anode materials for secondary batteries is an important core to realize the path of green and low-carbon development proposed by the general secretary,in order to improve the energy structure and ensure the development of energy security and clean energy.Hard carbon（HC）is considered as an ideal carbon based anode material for sodium ion batteries（SIBs）due to its high theoretical capacity and relatively low charge discharge voltage.Hard carbon has a larger interlayer spacing than graphite,which is more conducive to the intercalation/stripping of sodium ions during the charge discharge process.However,there are problems with low initial coulombic efficiency and poor rate capability in charge discharge process,leading to the specific capacity degradation.Although a large number of hard carbons have been reported to be composite modified with other materials to improve their sodium storage properties,their capacities still hardly meet the applications in practical scenarios.The novel two-dimensional transition metal carbide and nitride MXene（Ti₃C₂T_x）exhibits excellent metallic conductivity and abundant functional groups（-OH,-F,-O）on the surface.Based on the above background,this topic innovatively designed a solvent mechanochemical scheme to enable the simultaneous in situ oxidation of MXene with abundant oxygen-containing functional groups to form MXene/Ti O₂ heterojunction structures by functionalizing hard carbon during ball milling,thereby improving the capacity and rate capability of the overall electrode structure.Combined with the current state of research,further exploration of ⁶⁰CoγPerformance impact of ray irradiation technique in terms of hard carbon modification.The main research content of this paper is as follows:（1）HC and MXene are ground in air with water as solvent.The thermodynamic metastable Ti atoms at the edge of MXene surface were oxidized in situ to form a Ti O₂nanorod under the action of the enormous energy generated by the ball mill beads to form a MXene/Ti O₂ heterojunction structure.In addition,the rich functional groups on the surface of MXene react with HC at the HC/MXene heterogeneous interface to form a stable Ti-O-C covalent bond.Due to the synergistic structure,HC-MXene/Ti O₂composites have a capacity of 690 m Ah g^-1 at current density of 30 m A g^-1 and a reversible capacity of 640 m Ah g^-1 after 100 cycles at current density of 1 A g^-1.It is advantageous to prove that the excellent design of HC and MXene can improve the electrochemical performance of SIBs.（2）The milled HC was modified by ⁶⁰Co gamma ray irradiation to increase its active sites and further enhance the negative sodium storage capacity.With high energy and high transmission characteristics gamma ray irradiation can effectively construct defects in hard carbon structure,thus exposing a large number of coordination unsaturated sites,which further accelerates the reaction kinetics on its surface.The capacity of hard carbon based on irradiation technology can reach a good reversible capacity of about 300 m Ah g^-1 at a current density of 30 m A g^-1.Moreover,the capacity retention reaches 87%after 500 charge discharge cycles at a current density of 1 A g^-1with excellent cycling stability.