Amorphous Molybdenum Oxide Electrode For Aqueous Muti-ions Batteries

Lithium ion batteries have received widespread attention due to their high energy density.However,the safety issues and limited lithium storage caused by the use of flammable organic electrolytes limit the large-scale development of lithium ion batteries.The use of non-toxic water as a solvent for multi ion aqueous batteries significantly improves safety performance,while replacing lithium ions with other abundant cations such as Na⁺,K⁺,Ca²⁺and Mg²⁺shows great potential in the field of energy storage.However,only a few layered materials（e.g.,MXene,MoS₂,and LDHs）have been successfully explored for reversible multi-ions intercalation.This is mainly due to the fact that different cations can only be stored at specific active sites in the crystal structure,and the optimal crystal plane for achieving certain cation embedding may not be able to achieve other cation embedding,resulting in a limited variety of ions stored in materials.The limited ion diffusion channels and electrostatic repulsion in the rigid crystal structure further hinder the intercalation/deintercalation of ions.In addition,the storage process of cations in aqueous systems involves the migration of hydrated ions from the solution bulk to the electrode surface,the desolvation at the electrode surface,the charge transfer of ions at the electrode/electrolyte interface,and the diffusion in the electrode bulk phase.The rating determinantion steps for different ion embedding processes vary,and slow rating determinantion steps can lead to poor capacity and rate capability when storing ions.In response to the above problems,this paper proposes to improve the storage capacity of materials for multiple ions by reducing the degree of crystallization of materials and providing abundant transport channels and a large number of active sites（defects/vacancies）for ions through long-range disordered distribution networks.The specific research content is as follows:（1）Amorphous MoO_xanode for aqueous multi-ions batteries.Amorphous MoO_x（A-MoO_x）nanopores were grown in situ on Mo substrate by anodic oxidation method.The relationship between the crystallinity of A-MoO_xand different ion storage properties was explored by adjusting its crystallinity through heat treatment at different temperatures.The results show that the electrode capacity decreases with increasing crystallinity,and the capacity of A-MoO_xin Li⁺,Na⁺,K⁺,Mg²⁺,Ca²⁺,Zn²⁺,Al³⁺and H⁺electrolytes is more than four times that of crystalline MoO_x（C-MoO_x）.At a current density of 10 A g^-1,94.6%of the capacity can still be maintained after 20000 cycles.Experimental research and theoretical calculations prove that A-MoO_xprovides more active sites and ion transport channels for ion storage,accelerates charge transfer and ion diffusion,and improves energy storage performance.A-MoO_xanode was assembled with CoNi-LDHs cathode and CuFe-TBA cathode respectively to obtain Li⁺,Na⁺,K⁺,Mg²⁺,Ca²⁺,Zn²⁺,Al³⁺and H⁺full batteries with high energy density,high power density,and long cycle life.（2）Amorphous MoO_x/MoP anode for high rate performance aqueous multi-ions batteries.This work further improves the magnification performance of A-MoO_xby introducing P atoms into MoO_xto obtain MoP and changing the electronic structure of the electrode surface.By adjusting the content and distribution of MoP interface layer,the influence of MoP on the ion storage performance of MoO_xwas investigated.Experiments have shown that the introduction of MoP can change the ion desolvent process,accelerate the reaction rate of ions in the storage process,and thereby enhance the rate performance.For ions（such as H⁺）whose desolvent process is a rate determination step,the introduction of small amount of MoP can significantly improve the rate performance of MoO_x,at a high current density of 160 A g^-1,the capacity can be increased by 5 times.The differences in ion insertion/removal processes were characterized by in situ Raman spectroscopy:In the MoO_x/MoP structure,H₃O⁺is reversibly embedded/removed;In the MoO_xstructure,H⁺is reversibly embedded/removed.The full battery consisting of MoO_x/MoP anode and MnO₂@GF cathode has an energy density of 76 Wh Kg^-1at a power density of 120 W Kg^-1.This work provides a new strategy for the construction of anode for high rate performance aqueous multi-ions batteries.