Metal cyanometallate synthesis method

Abstract

A method is provided for synthesizing metal cyanometallate (MCM). The method provides a solution of A.sub.XM1.sub.Y(CN).sub.Z; where “A” is selected from a first group of metals and M1 is selected from a second group of metals. The method adds a material including M2 to the solution to form a liquid phase material that may be either a suspension or a solution. M2 is selected from the second group of metals. The method adds acid to the liquid phase material. The addition of acid to the liquid phase material decomposes the M2 material into M2-ions. Simultaneous with the addition of the acid, a precipitate of A.sub.NM1.sub.PM2.sub.Q(CN).sub.R.FH.sub.2O is formed, where N is in a range of 1 to 2. A variation of the above-described synthesis method is also provided.

Claims

1. A method for synthesizing metal cyanometallate (MCM), the method comprising: providing a solution of A.sub.XM1.sub.Y(CN).sub.Z; where “A” is selected from a first group of metals consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), silver (Ag), aluminum (Al), magnesium (Mg), and combinations thereof; where M1 is selected from a second group of metals consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), ruthenium (Ru), tin (Sn), indium (In), cadmium (Cd), Ca, Mg, strontium (Sr), and barium (Ba); where X is in a range of 0 to 10; where Y is in a range of 1 to 10; where Z is in a range of 1 to 10; adding a material including M2 to the solution to form a liquid phase material selected from a group consisting of a suspension and a solution; where M2 is selected from the second group of metals; adding an acid to the liquid phase material; simultaneously with the addition of the acid, forming a precipitate of A.sub.NM1.sub.PM2.sub.Q(CN).sub.R.FH.sub.2O; where N is in a range of 1 to 2; where P is less than or equal to 2; where F is in a range of 0 to 20; where Q is less than or equal to 2; and, where R is less than or equal to 6.

2. The method of claim 1 wherein adding the acid to the liquid phase material includes the acid decomposing the material including M2 into M2-ions.

3. The method of claim 1 wherein adding the acid to the liquid phase material includes adding an acid selected from a group consisting of hydrochloric acid (HCl), sulfuric acid (H.sub.2SO.sub.4), sulfurous acid (H.sub.2SO.sub.3), acetic acid (CH.sub.3COOH), formic acid (CHOOH), oxalic acid (C.sub.2H.sub.2O.sub.4), and ascorbic acid.

4. The method of claim 1 wherein adding the acid to the liquid phase material includes additionally adding a reducing agent to the liquid phase material.

5. The method of claim 4 wherein adding the reducing agent to the liquid phase material includes adding a reducing agent selected from a group consisting of sodium borohydride, sodium hyposulfite, sodium sulfite, and polyvinylpyrrolidon.

6. The method of claim 1 wherein adding the acid to the liquid phase material includes adding the acid to the liquid phase material in an inert atmosphere.

7. The method of claim 1 further comprising: drying the precipitate in a vacuum environment at a temperature in a range between 0 and 200 degrees Centigrade (C.).

8. The method of claim 1 wherein adding the material including M2 to the solution includes adding a material selected from a group consisting of pure M2 and compounds selected from a group consisting of oxides, sulfides, sulfites, carbonates, cyanides, and fluorides.

9. A method for synthesizing metal cyanometallate (MCM), the method comprising: providing a solution of A.sub.XM1.sub.Y(CN).sub.Z; where “A” is selected from a first group of metals consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), silver (Ag), aluminum (Al), magnesium (Mg), and combinations thereof; where M1 is selected from a second group of metals selected from a group consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), ruthenium (Ru), tin (Sn), indium (In), cadmium (Cd), Ca, Mg, strontium (Sr), and barium (Ba); where X is in a range of 0 to 10; where Y is in a range of 1 to 10; where Z is in a range of 1 to 10; adding an acid to the solution; simultaneously with the addition of the acid, forming a precipitate of A.sub.NM1.sub.D(CN).sub.E.GH.sub.2O; where N is in a range of 1 to 2; where G is in a range of 0 to 20; where D is less than or equal to 2; and, where E is less than or equal to 6.

10. The method of claim 9 wherein adding the acid to the solution includes: the acid decomposing the A.sub.XM1.sub.Y(CN).sub.Z; and, releasing M1-ions into the solution.

11. The method of claim 9 wherein adding the acid to the solution includes adding an acid selected from a group consisting of hydrochloric acid (HCl), sulfuric acid (H.sub.2SO.sub.4), sulfurous acid (H.sub.2SO.sub.3), acetic acid (CH.sub.3COOH), formic acid (CHOOH), oxalic acid (C.sub.2H.sub.2O.sub.4), and ascorbic acid.

12. The method of claim 9 wherein adding the acid to the solution includes additionally adding a reducing agent to the solution.

13. The method of claim 12 wherein adding the reducing agent to the solution includes adding a reducing agent selected from a group consisting of sodium borohydride, sodium hyposulfite, sodium sulfite, and polyvinylpyrrolidon.

14. The method of claim 9 wherein adding the acid to the solution includes adding the acid to the solution in an inert atmosphere.

15. The method of claim 9 further comprising: drying the precipitate in a vacuum environment at a temperature in a range between 0 and 200 degrees Centigrade (C.).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram representing a metal cyanometallate (MCM) open framework (prior art).

(2) FIG. 2 is a diagram generally depicting a process for synthesizing MCM with a high content of “A”-ions.

(3) FIG. 3 is the energy-dispersive X-ray spectroscopy (EDX) spectrum of a Na.sub.2FeFe(CN).sub.6 sample prepared by the above-described second precipitation method.

(4) FIGS. 4 and 5 are charge and discharge curves of Na.sub.2FeFe(CN).sub.6 prepared by Method 1 and Method 2, respectively.

(5) FIG. 6 is a flowchart illustrating a method for synthesizing metal cyanometallate (MCM).

(6) FIG. 7 is a flowchart illustrating another method for synthesizing MCM.

DETAILED DESCRIPTION

(7) Disclosed herein are methods for the synthesis of metal cyanometallates (MCMs) or A.sub.NM1.sub.PM2.sub.Q(CN).sub.R.FH.sub.2O as the electrode in rechargeable metal-ion batteries. The metal-ions can be from metal lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), calcium (Ca), and/or magnesium (Mg). Some examples of transition metal M1 and M2 include titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn) iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), ruthenium (Ru), tin (Sn), indium (In), and cadmium (Cd).

(8) In general, the precipitation method is used to synthesize MCM materials as electrodes. However, noteworthy is the fact that metal-ions with low valence are susceptible to being oxidized, resulting in low-“A” containing MCM. The “A” deficiency causes a low capacity when MCM is used as an electrode in a rechargeable “A”-ion battery with a counter electrode without “A”-ions. For example, Prussian white, Na.sub.2FeFe(CN).sub.6 is expected to be synthesized with ferrous ions and ferrocyanide. But, the fact is that only Prussian blue, Na.sub.xFeFe(CN).sub.6 (x<1), can conventionally be obtained because ferrous ions are easily oxidized.

(9) FIG. 2 is a diagram generally depicting a process for synthesizing MCM with a high content of “A”-ions. To obtain a MCM electrode with a high capacity for use as a battery electrode, new approaches must be adopted to reduce the possibility of metal oxidation during synthesis. Disclosed herein is a “simultaneous” synthesis process where M2-ions, from the decomposition of stable M2 materials, immediately react with an M1-cyanide with a minimum possibility of oxidization. A reductive environment is used to protect the M1-ions from oxidizing.

(10) To clarify the process, two examples are given here.

(11) Method 1:

(12) 0.7 grams (g) iron (Fe) powder was mixed with 100 milliliters (mL) 0.02 moles (mol) L.sup.−1 Na.sub.4Fe(CN).sub.4.10H.sub.2O solution to form a suspension. As used herein, a suspension is understood to be a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents. Generally, without agitation, the solid particles will eventually settle. A solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The solvent does the dissolving. The solution more or less takes on the characteristics of the solvent including its phase, and the solvent is commonly the major fraction of the mixture. The concentration of a solute in a solution is a measure of how much of that solute is dissolved in the solvent.

(13) Continuing the description of the method, 10 mL 0.1 mol L.sup.−1 hydrogen chloride (HCl) solution was added into the suspension and stirred at room temperature. The Fe was decomposed by the to form Fe.sup.2+, which reacted with ferrocynide immediately to form Na.sub.2FeFe(CN).sub.2. The obtained precipitate was collected by centrifuge or filtration, washed by water, and dried at 0-200° C. in a vacuum oven for 6-20 hours.

(14) Method 2:

(15) In a typical synthesis, 2 millimoles (mmol) Na.sub.4Fe(CN).sub.4.10H.sub.2O and 0.1 mL HCl (37%) was dissolved in 500 mL of distilled water to obtain a homogenous solution. The solution was maintained at 0-100° C. for 0.5-60 hours being vigorous stirred to obtain Na.sub.2FeFe(CN).sub.6. In the reaction, Fe.sup.2+-ions result from the decomposition of ferrocynide by HCl. The precipitate was collected by filtration in air, washed by water, and dried at 0-200° C. in a vacuum over for 0.5-60 hours.

(16) FIG. 3 is the energy-dispersive X-ray spectroscopy (EDX) spectrum of a Na.sub.2FeFe(CN).sub.6 sample prepared by the above-described second precipitation method. A high concentration of Na was observed in the as-prepared material. Silver (Ag) was coated on the material to increase conductivity for scanning electron microscope (SEM) characterization.

(17) FIGS. 4 and 5 are charge and discharge curves of Na.sub.2FeFe(CN).sub.6 prepared by Method 1 and Method 2, respectively. Two plateaus at 3.0 and 3.4 V during charge and discharge were observed with a very small polarization. Na.sub.2FeFe(CN).sub.6 prepared by precipitation in aqueous solution delivers a high capacity of 120-145 milliamp hours per gram (mAh/g).

(18) FIG. 6 is a flowchart illustrating a method for synthesizing metal cyanometallate (MCM). Although the method is depicted as a sequence of numbered steps for clarity, the numbering does not necessarily dictate the order of the steps. It should be understood that some of these steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of sequence. Generally however, the method follows the numeric order of the depicted steps. The method starts at Step 600.

(19) Step 602 provides a solution of A.sub.XM1.sub.Y(CN).sub.Z;

(20) where “A” is selected from a first group of metals;

(21) where M1 is selected from a second group of metals;

(22) where X is in the range of 0 to 10;

(23) where Y is in the range of 1 to 10; and,

(24) where Z is in the range of 1 to 10.

(25) Some examples from the first group of metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), strontium (Sr), barium (Ba), silver (Ag), aluminum (Al), magnesium (Mg), and combinations thereof.

(26) Step 604 adds a material including M2 to the solution to form a liquid phase material that is either a suspension or a solution. M2 is selected from the second group of metals. The M2 material may be pure M2 or a compound of oxides, sulfides, sulfites, carbonates, cyanides, fluorides, or a combination of these compounds. M1 and M2 are each independently selected from the second group of metals, some examples of which include titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), ruthenium (Ru), tin (Sn), indium (In), cadmium (Cd), Ca, Mg, strontium (Sr), and barium (Ba). Note: the materials listed above are examples used to illustrate the invention and do not necessarily represent an exhaustive list of all possible materials.

(27) Step 606 adds an acid to the liquid phase material. Some examples of acids include hydrochloric acid (HCl), sulfuric acid (H.sub.2SO.sub.4), sulfurous acid (H.sub.2SO.sub.3), acetic acid (CH.sub.3COOH), formic acid (CHOOH), oxalic acid (C.sub.2H.sub.2O.sub.4), and ascorbic acid. In one aspect, adding the acid to the liquid phase material in Step 606 includes the acid decomposing the M2 material into M2-ions.

(28) Optionally, adding the acid to the liquid phase material in Step 606 may additionally include adding a reducing agent to the liquid phase material. Some examples of reducing agents include sodium borohydride, sodium hyposulfite, sodium sulfite, and polyvinylpyrrolidon. In one aspect, adding the acid to the liquid phase material includes adding the acid to the liquid phase material in an inert atmosphere. For example, the process may be performed in an atmosphere of argon or nitrogen.

(29) Simultaneously with the addition of the acid in Step 606, Step 608 forms a precipitate of A.sub.NM1.sub.PM2.sub.Q(CN).sub.R.FH.sub.2O;

(30) where N is in the range of 1 to 2;

(31) where P is less than or equal to 2;

(32) where F is in the range of 0 to 20;

(33) where Q is less than or equal to 2; and,

(34) where R is less than or equal to 6.

(35) In one aspect, Step 610 dries the precipitate in a vacuum environment at a temperature in the range between 0 and 200 degrees C.

(36) FIG. 7 is a flowchart illustrating another method for synthesizing MCM. The method begins at Step 700. Step 702 provides a solution of A.sub.XM1.sub.Y(CN).sub.Z;

(37) where “A” is selected from a first group of metals;

(38) where M1 is selected from a second group of metals;

(39) where X is in the range of 0 to 10;

(40) where Y is in the range of 1 to 10; and,

(41) where Z is in the range of 1 to 10.

(42) As mentioned above in the description of FIG. 6, examples from the first group of metals include Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ag, Al, Mg, and combinations thereof. Examples from the second group of metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Ru, Sn, In, Cd, Ca, Mg, Sr, and Ba.

(43) Step 704 adds an acid to the solution. In one aspect, Step 704 includes the following substeps. In step 704a the acid decomposes the A.sub.XM1.sub.Y(CN).sub.Z. Step 704b releases M1-ions into the solution. Some examples of acids include HCl, H.sub.2SO.sub.4, H.sub.2SO.sub.3, CH.sub.3COOH, CHOOH, C.sub.2H.sub.2O.sub.4, and ascorbic acid. In one aspect, Step 704 optionally includes adding a reducing agent to the solution, in addition to the acid. Some examples of reducing agents include sodium borohydride, sodium hyposulfite, sodium sulfite, and polyvinylpyrrolidon. In another aspect, the acid is added to the solution in an inert atmosphere. Note: the materials listed above are examples used to illustrate the invention and do not necessarily represent an exhaustive list of all possible materials.

(44) Simultaneously with the addition of the acid in Step 704, Step 706 forms a precipitate of A.sub.NM1.sub.D(CN).sub.E.GH.sub.2O;

(45) where N is in the range of 1 to 2;

(46) where C is in the range of 0 to 20;

(47) where D is less than or equal to 2; and,

(48) where E is less than or equal to 6.

(49) In one aspect, Step 708 dries the precipitate in a vacuum environment at a temperature in the range between 0 and 200 degrees C.

(50) Processes for the synthesis of MCM have been provided. Examples of particular materials and process details have been presented to illustrate the invention. However, the invention is not limited to merely these examples. Other variations and embodiments of the invention will occur to those skilled in the art.