Preparation, characterization, and an electrochemical study of Mg.sub.0.1V.sub.2O.sub.5 prepared by a novel sol-gel method with no high-temperature post-processing are disclosed. Cyclic voltammetry showed the material to be quasi-reversible, with improved kinetics in an acetonitrile-, relative to a carbonate-, based electrolyte. Galvanostatic test data under a C/10 discharge showed a delivered capacity >250 mAh/g over several cycles. Based on these results, a magnesium anode battery, as disclosed, would yield an average operating voltage ˜3.2 Volts with an energy density ˜800 mWh/g for the cathode material, making the newly synthesized material a viable cathode material for secondary magnesium batteries.

An electrode active material for lithium-ion secondary batteries that has a sufficiently high initial capacity, improved charge-and-discharge cycle characteristics, and improved coulombic efficiency in the mid-term charge-and-discharge cycles can be obtained by a phosphorus-containing low-crystalline vanadium sulfide comprising vanadium, phosphorus, and sulfur as constituent elements, the composition ratio of the phosphorus to the vanadium (P/V) being 0.1 to 1.0 in terms of the molar ratio, the composition ratio of the sulfur to the vanadium (S/V) being 4.00 to 10.00 in terms of the molar ratio.

An electrode active material for lithium-ion secondary batteries that has a sufficiently high initial capacity, improved charge-and-discharge cycle characteristics, and improved coulombic efficiency in the mid-term charge-and-discharge cycles can be obtained by a phosphorus-containing low-crystalline vanadium sulfide comprising vanadium, phosphorus, and sulfur as constituent elements, the composition ratio of the phosphorus to the vanadium (P/V) being 0.1 to 1.0 in terms of the molar ratio, the composition ratio of the sulfur to the vanadium (S/V) being 4.00 to 10.00 in terms of the molar ratio.

In general, the present disclosure is directed to methods for synthesizing vanadium oxide nanobelts, as well as the corresponding chemical composition of the vanadium oxide nanobelts. Also described are materials which can incorporate the vanadium oxide nanobelts, such as including the vanadium oxide nanobelts as a cathode material for use in energy storage applications (e.g., batteries). The vanadium oxide nanobelts described herein display structural characteristics that may provide improved diffusion and/or charge transfer between ions. Thus, batteries incorporating implementations of the current disclosure may demonstrate improved properties such as higher capacity retention over charge discharge cycling.

A production method includes: an alkali extraction step of adding an alkali and water, or an alkali solution, to raw material ash containing an ammonium sulfate component, sulfuric acid, vanadium, and at least one other metal selected from nickel, iron, and magnesium, wherein a pH of 13 or higher is achieved, to obtain an alkali leachate; a solid-liquid separation step on the alkali leachate to obtain a leach filtrate containing vanadium; an evaporation concentration step of evaporating and concentrating the leach filtrate to obtain a concentrated liquid; and a crystallization/solid-liquid separation step of cooling and crystalizing the concentrated liquid and recovering a precipitate containing a vanadium compound. Another production method includes an alkali extraction step, a solid-liquid separation step, an evaporation concentration step, an alkali concentration adjustment step of further adding an alkali or alkali solution to a concentrated liquid to obtain a concentration-adjusted liquid, and a crystallization/solid-liquid separation step.

A layered double hydroxide is represented by the following formula (I): Ni.sup.2+.sub.1−(x+y+z)Fe.sup.3+.sub.xV.sup.3+.sub.yCo.sup.3+.sub.z(OH).sub.2A.sup.n−.sub.(x+y+z)/n.Math.mH.sub.2O . . . (I). In one embodiment, in the formula (I), (x+y+z) is from 0.2 to 0.5, “x” represents more than 0 and 0.3 or less, “y” represents from 0.04 to 0.49, and “z” represents more than 0 and 0.2 or less.

A lithium vanadium oxide crystal and usage thereof that can achieve further excellent electrochemical characteristics are provided. New lithium vanadium oxide crystal is a lithium vanadium oxide crystal which is Li.sub.3VO.sub.4 to which tetravalent metal species M is doped, in which the lithium vanadium oxide crystal is represented by a chemical formula of Li.sub.3+1V.sub.1−xM.sub.xO.sub.4 and includes only a single crystal structure with γ-phase as Li.sub.3VO.sub.4 under a temperature environment including normal temperature, and the tetravalent metal species M is included in a ratio of x≥0.2.

A preparation method of a tetragonal NaV.sub.2O.sub.5.H.sub.2O nanosheet-like powder includes steps of: (Step 1) simultaneously adding NaVO.sub.3 and Na.sub.2S.9H.sub.2O into deionized water, and then magnetically stirring, and obtaining a black turbid solution; (Step 2) sealing after putting the black turbid solution into an inner lining of a reaction kettle, fixing the sealed inner lining in an outer lining of the reaction kettle, placing the reaction kettle into a homogeneous reactor, and then performing a hydrothermal reaction; and (Step 3) after completing the hydrothermal reaction, naturally cooling the reaction kettle to the room temperature, and then alternately cleaning through water and alcohol, and then collecting a product, drying the product, and finally obtaining the tetragonal NaV.sub.2O.sub.5.H.sub.2O nanosheet-like powder with a thickness in a range of 30-60 nm and a single crystal structure grown along a (002) crystal orientation.

A preparation method of a tetragonal NaV.sub.2O.sub.5.H.sub.2O nanosheet-like powder includes steps of: (Step 1) simultaneously adding NaVO.sub.3 and Na.sub.2S.9H.sub.2O into deionized water, and then magnetically stirring, and obtaining a black turbid solution; (Step 2) sealing after putting the black turbid solution into an inner lining of a reaction kettle, fixing the sealed inner lining in an outer lining of the reaction kettle, placing the reaction kettle into a homogeneous reactor, and then performing a hydrothermal reaction; and (Step 3) after completing the hydrothermal reaction, naturally cooling the reaction kettle to the room temperature, and then alternately cleaning through water and alcohol, and then collecting a product, drying the product, and finally obtaining the tetragonal NaV.sub.2O.sub.5.H.sub.2O nanosheet-like powder with a thickness in a range of 30-60 nm and a single crystal structure grown along a (002) crystal orientation.

A CoVO.sub.x composite electrode and method of making is described. The composite electrode comprises a substrate with an average 0.5-5 μm thick layer of CoVO.sub.x having pores with average diameters of 2-200 nm. The method of making the composite electrode involves contacting the substrate with an aerosol comprising a solvent, a cobalt complex, and a vanadium complex. The CoVO.sub.x composite electrode is capable of being used in an electrochemical cell for water oxidation.