Research On Energy Storge Of Novel Two-dimensional Carbide MXene

The design, preparation, properties and application research for new high-performance energy storage material are considered as an important issue to solve energy and environmental problems in today. MXene, a new class of two-dimensional transition metal carbides, has exhibited promising application in new energy storage field for only four-year development and attracted widespread attention.Firstly, electronic structure and formation enery for 24 MXene were studied by using first-principles calculation in this paper. The results show that MXene with bare surfaces are conductive; the more active of A element in MAX phases are, the easyer to obtain their corresponding MXene by etching.Secondly, the hydrogen storage properties of Ti2 C were studied by using first-principles calculation. The results showed that hydrogens are bound on Ti2 C by three modes: chemisorption(1.7 wt. %), Kubas-type(3.4 wt. %) and physisorption(3.4 wt. %). Molecular dynamics simulations indicate that Kubas-type hydrogen can be reversibly adsorbed and released at 300- 400 K. In addition, theoretical hydrogen storage capacity of Sc2 C is about 9.0 wt.% under physisorption, Kubas interaction and chemisorption.Thirdly, lithium storage performances of V2CO2 under high lithium concentration were studied by first-principles calculation. The results showed that:(1) for first layer of Li adsorption, H1H2- V2CO2 Lix converts to H1T- V2 COLix as x increases to change, accompanied by a series of changes in volume. The essence of this structural transition is a rearrangement of oxygen atoms on V2 C surface induced by High concentration of lithium ion.(2) For second layer of Li adsorption, as the concentration of lithium increases, oxygen atoms migrate between the two layers of lithium atoms, forming a sandwich structure which is similar to the structure of Li2 O. Thus, this process may generate V2 C and Li2 O by the transition reaction. Under intercalation and transition mechanism, theoretical capacities of V2CO2 are up to 1470 mAh g-1.(3) Depend on whether structural transition occurs, lithium storage behavior of OMX(MXene functioned by O groups) can be divided into three categories, namely V- type, Nb- type and Ti- type. The change rate of layer thickness φ can be used as parameter to determine the types of lithium storage of OMX.Finally, we prepared ex- Ti3C2 and in- Ti3C2 and measured their electrochemical performance. The results show that at 1 C, in-Ti3C2 have a reversible specific capacity of 123.6 mAh g-1, more than that of ex- Ti3C2, indicating that to increase lattice parameter c is an effective way to improve the capacity of MXene.