| Aqueous ammonium ion batteries have become a new direction in the field of energy storage due to fast ion diffusion rate,low manufacturing cost,abundant resources,high safety and good environmental compatibility.At present,the exploration of electrode materials with good electrical conductivity,high electrochemical activity,strong ion transport capacity and stable structure is an urgent demand for the development of aqueous ammonium ion batteries.Transition metal tungsten/vanadium oxides have been widely used in electrochemical energy storage owing to the diversity of elemental valence and microstructure,controllability of synthesis techniques and multiplicity of energy storage mechanisms.However,the disadvantages of tungsten/vanadium oxides such as narrow electrochemical window,low energy density,poor electrochemical stability and conductivity have seriously hindered their application in aqueous ammonium ion batteries.The transition metal tungsten/vanadium oxides have been prepared by the corresponding synthetic methods with tungsten（W）and vanadium（V）elements as the core.The physicochemical properties,macro electrochemical properties,electrochemical kinetic parameters,electrochemical ammonium storage mechanism and practical applications of transition metal oxides have been systematically investigated.The main research contents and results are as follows:（1）The monoclinic WO3nanospheres with high purity,good crystallinity and dispersibility were successfully prepared by the hydrothermal method followed calcination,and used as anodes for aqueous ammonium-ion batteries.The formation and phase transformation mechanisms of WO3 were systematically discussed by analyzing the surface morphology and microstructure of monoclinic WO3.The results suggestted that the homogeneity and dispersion of monoclinic WO3 nanospheres depended on the formations and decompositions for the oxalic peroxytungstatic acid complex.The novel three-dimensional equilibrium diffusion behavior along the（200）,（020）and（002）crystal planes in monoclinic WO3 lattices for NH4+ions during electrochemical process were innovatively proposed according to the comprehensive results of ex-situ XRD analyses and electrochemical performance.The geometric evolution laws of reversible building/breaking between trifurcated hydrogen bonds and traditional hydrogen bonds during the NH4+diffusion in monoclinic WO3 lattices were acquired by first-principles calculations and ex-situ measurements.Therefore,monoclinic WO3delivered an outstanding specific capacity of 150.6 m Ah g-1 at the current density of 0.1 A g-1 and retained a reversible capacity of 86.6%after 500 cycles.Furthermore,the aqueous ammonium-ion full batteries based onγ-Mn O2 cathode and WO3 anode submitted an energy density of 64.9 Wh/kg and a power density of 2339W/kg,and exhibited excellent long-cycle stability with 95.4%capacity retention after5000 cycles at the current density of 3.0 A·g-1.（2）The dual transition metal oxide for Zn3V3O8 and Mn V2O4 were fabricated by a facile evaporative crystallization followed calcination method under the condition of regulating the species of coupled metal atoms,and firstly used as anodes for aqueous ammonium-ion batteries.Zn3V3O8 presented a well-dispersed nanorod-like structure with a higher content of adsorbed/crystalline water and a more stable structure than the agglomerated Mn V2O4 nanoparticles,which facilitated the shortening of the diffusion distance of NH4+ions,increasing the ion-conductive channels for NH4+ion diffusion and relieving the inevitable volume expansion after long-term cycling.Zn3V3O8revealed a high specific capacity of 101.7 m Ah g-1 at the current density of 0.1 A g-1and maintained a reversible capacity of 84.5%after 500 cycles.The ex-situ measurement results illustrated that the irreversible phase transformation from Zn3V3O8to Zn3（OH）2V2O7·2H2O occurred during the first charge process;Transition metal V and Zn undergone simultaneously redox reactions during the electrochemical reaction process,and their synergistic effects were beneficial to improving the specific capacity;Meanwhile,the pseudocapacitance characteristic of the Zn3V3O8 characterized by the reversible NH4+ion insertion/extraction behavior within the Zn3V3O8 lattice,and the NH4+diffusion processes were consistently accompanied by the continuous and alternate hydrogen bonds breaking/rebuilding behaviors.When coupled withβ-Mn O2cathode,β-Mn O2//Zn3V3O8aqueous ammonium-ion full batteries delivered superb initial charge/discharge specific capacities of 227.7/224.2 m Ah g-1 at current density of0.1 A g-1 with superior coulombic efficiency of 98.4%,and a reversible capacity retention of 92.8%after 5000 cycles.The full batteries revealed maximum energy density of 86 Wh kg-1 and maximum power density of 677 W kg-1,demonstrating the possibility of practical application of Zn3V3O8 in the aqueous ammonium-ions batteries.（3）Mn V2O4-1 and Mn V2O4-2 materials were prepared by evaporative crystallization and ultrasonic spraying methodes,respectively,and firstly used as anodes for aqueous ammonium-ion batteries.The systematic analyses of the physicochemical properties illustrated that Mn V2O4 nanospheres with more stable structure,smaller particle size and better dispersion could be obtained by ultrasonic spray method.The electrochemical performance of Mn V2O4-2 was much better than that of Mn V2O4-1 due to the superior physicochemical properties.Specifically,the first discharge specific capacity of Mn V2O4-2 electrodes at a current density of 0.1 A g-1 was115.5 m Ah g-1 and the capacity retention after 500 cycles was 71.4%,while the first discharge specific capacity of Mn V2O4-1 electrodes was only 39.4 m Ah/g and the capacity retention was only 40.8%.The ex-situ measurement results illustrated that the transition metal V and Mn elements coordinated in the electrochemical ammonium storage processes of spinel Mn V2O4;The highly reversible insertion/extraction behaviors of NH4+ions in the Mn V2O4 lattice were always accompanied by the continuous hydrogen bond formation/fracture processes between NH4+ions and lattice oxygen from Mn V2O4;The particle size and lattice spacing of the electrode material exhibited regular expansion/contraction changes with the insertion/extraction of NH4+ions.The aqueous ammonium-ion full batteries constructed by spinel Mn V2O4 anode and cubic Mn2O3 cathode provided a maximum energy density of 104 Wh·kg-1 and a power density of 1313.5 W kg-1,and delivered a high first discharge capacity of 120.5m Ah g-1 at a current density of 0.1 A g-1 with corresponding coulombic efficiency of97.6%,and 77.3%reversible capacity retention after 1000 cycles. |
