Battery electrode with metal particles and pyrolyzed coating

Abstract

A method is provided for forming a metal battery electrode with a pyrolyzed coating. The method provides a metallorganic compound of metal (Me) and materials such as carbon (C), sulfur (S), nitrogen (N), oxygen (O), and combinations of the above-listed materials, expressed as Me.sub.XC.sub.YN.sub.ZS.sub.XXO.sub.YY, where Me is a metal such as tin (Sn), antimony (Sb), or lead (Pb), or a metal alloy. The method heats the metallorganic compound, and as a result of the heating, decomposes materials in the metallorganic compound. In one aspect, decomposing the materials in the metallorganic compound includes forming a chemical reaction between the Me particles and the materials. An electrode is formed of Me particles coated by the materials. In another aspect, the Me particles coated with a material such as a carbide, a nitride, a sulfide, or combinations of the above-listed materials.

Claims

1. A battery electrode comprising: metal (Me) particles selected from a group consisting of metals and metal alloys; a pyrolyzed coating formed over the Me particles, formed from materials selected from the group consisting of carbon (C), sulfur (S), nitrogen (N), oxygen (O), and combinations of the above-listed materials, expressed as C.sub.YN.sub.ZS.sub.XXO.sub.YY; where Y is greater than 0; where Z is greater than or equal to 0; where XX is greater than or equal to 0; and, where YY is greater than or equal to 0.

2. The battery electrode of claim 1 wherein the materials are selected from the group consisting of a carbide, a nitride, a sulfide, and combinations of the above-listed materials.

3. The battery electrode of claim 1 wherein the Me particles are selected from the group consisting of tin (Sn), antimony (Sb), lead (Pb), and combinations of the above-listed metals.

4. The battery electrode of claim 1 wherein at least one variable selected from the group consisting of Z, XX, and YY is greater than zero.

5. A battery comprising: an electrolyte; an ion-permeable membrane; a cathode; an anode comprising: metal (Me) particles selected from a group consisting of metals and metal alloys; a pyrolyzed coating formed over the Me particles, formed from materials selected from the group consisting of carbon (C), sulfur (S), nitrogen (N), oxygen (O), and combinations of the above-listed materials, expressed as C.sub.YN.sub.ZS.sub.XXO.sub.YY; where Y is greater than 0; where Z is greater than or equal to 0; where XX is greater than or equal to 0; and, where YY is greater than or equal to 0.

6. The battery of claim 5 wherein the materials are selected from the group consisting of a carbide, a nitride, a sulfide, and combinations of the above-listed materials.

7. The battery of claim 5 wherein the Me particles are selected from the group consisting of tin (Sn), antimony (Sb), lead (Pb), and combinations of the above-listed metals.

8. The battery of claim 5 wherein at least one variable selected from the group consisting of Z, XX, and YY is greater than zero.

9. A battery electrode comprising: metal (Me) particles selected from a group consisting of metals and metal alloys; a pyrolyzed coating chemically bonded to the Me particles, formed from materials selected from the group consisting of carbon (C), sulfur (S), nitrogen (N), oxygen (O), and combinations of the above-listed materials, expressed as C.sub.YN.sub.ZS.sub.XXO.sub.YY; where Y is greater than 0; where X is greater than or equal to 0; where XX is greater than or equal to 0; and, where YY is greater than or equal to 0.

10. The battery electrode of claim 9 wherein the materials are selected from the group consisting of a carbide, a nitride, a sulfide, and combinations of the above-listed materials.

11. The battery electrode of claim 9 wherein the Me particles are selected from the group consisting of tin (Sn), antimony (Sb), lead (Pb), and combinations of the above-listed metals.

12. The battery electrode of claim 9 wherein at least one variable selected from the group consisting of Z, XX, and YY is greater than zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart illustrating a method for forming a metal battery electrode with a pyrolyzed coating.

(2) FIG. 2 is a flowchart illustrating a method for forming metal particles with a pyrolyzed coating.

(3) FIGS. 3A and 3B are schematic drawings depicting the pyrolysis process.

(4) FIG. 4 is a partial cross-sectional view of a battery.

DETAILED DESCRIPTION

(5) FIG. 1 is a flowchart illustrating a method for forming a metal battery electrode with a pyrolyzed coating. 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 100.

(6) Step 102 provides a metallorganic compound of metal (Me) and a material that may be carbon (C), sulfur (S), nitrogen (N), oxygen (O), or combinations of the above-listed materials, expressed as Me.sub.XC.sub.YN.sub.ZS.sub.XXO.sub.YY.

(7) Me is a metal, such as tin (Sn), antimony (Sb), lead (Pb), combinations of the above-listed metals, or a metal alloy. A metal alloy is defined as Sn, Sb, or Pb (or a combination of these metals) combined with another, unmentioned metal.

(8) The variables listed above are defined as follows: X is greater than 0; Y is greater than 0; Z is greater than or equal to 0; xx is greater than or equal to 0; and, YY is greater than or equal to 0;

(9) In one aspect, Step 102 provides a plurality of metallorganic compounds with independent definitions of Me, X, Y, Z, XX, and YY.

(10) Step 104 heats the metallorganic compound, using for example, a furnace, a laser, microwave, or plasma (sputtering) energy source. The metallorganic compound is typically heated at a temperature in the range of 200 to 2500 degrees C.

(11) As a result of the heating in Step 104, Step 106 decomposes materials in the metallorganic compound. Step 108 forms an electrode comprising Me particles coated by the materials. Typically, the particles have a diameter in the range of 1 nanometer and 500 microns. In one aspect, forming the electrode in Step 108 includes forming the Me particles coated by the materials on a metal current collector. The electrode may be used, for example, as the anode in a sodium or potassium ion battery.

(12) In another aspect subsequent to forming the electrode in Step 108, Step 110 treats the Me particles coated by the material with trace elements of oxidants or nitrogen. Then, Step 112 forms an end product, respectfully, of metal oxides or metal nitrides (in addition to the materials formed in Step 110).

(13) In one aspect, heating the metallorganic compound in Step 104 includes heating the metallorganic compound in an atmosphere of inert gases or an atmosphere including a reducing agent, for example, hydrogen-containing nitrogen, ammonia-containing nitrogen, hydrogen-containing argon, or ammonia-containing argon.

(14) In one aspect, decomposing materials in the metallorganic compound in Step 106 includes forming a chemical reaction between the Me particles and the materials. As a result, in Step 108 the Me particles may be coated with a material such as a carbide, a nitride, a sulfide, or combinations of the above-listed materials.

(15) In another aspect, heating the metallorganic compound in Step 104 includes reducing the heating time from a first duration to a second duration. Then, forming the electrode comprising Me particles coated by the materials in Step 108 includes reducing the size of the Me particles coated by the materials from a first size, to a second size in response to the second duration of time.

(16) In one explicit example, Step 102 provides a metallorganic compound where Me is a tin (Sn), comprising one of the following exemplary precursors:

(17) tin 2-ethylhexanoate, tin bis(acetylacetonate) dichloride, tin bis(acetylacetonate) dibromide, tin oxalate, tin tert-butoxide, tin acetylacetonate, tin stearate, tetrakis (dimethylamido) tin, tin phthalocyanine oxide, tin phthocyanine, tin ionophore, tin 2,3-naphthalocyanine, tin 2,3-naphthalocyanine dichloride/dibromide, tributyl(vinyl) tin, trimethyl(pheny) tin, tributyl (phenylethynyl) tin, tributyl (1-ethoxyvinyl) tin, bis[bis(trimethylsilyl)amino] tin, tributyl (1-propynyl) tin, tributyl (3-methyl-2-butenyl) tin, tetrakis (diethylamido) tin, trimethyl (phenylethynyl) tin, butyl (1-propenyl) tin, dioctyl (maleate) tin, tetramethyl tin, tetrabutyl tin, tetraphenyl tin, (trimethyl stannyl) acetylene, stannane, (nitrophenyl) tin oxide, ethylhexanoyloxy-thrimethylhexyl-tin, tetrakis (hydroxyphenyl) tin, tetrakis(chlorophenyl) tin, tetrakis (tolyl) tin, tetrakis (pentafluorophenyl) tin, tetrakis (triphenylsilyl) tin, tetrakis (triphenyl stannyl) tin, triphenyl tin, triphenyl (triphenyl methyl) tin, tributyl tin bhloride, trimethyltin chloride, tributyl tin, dimethyltin dichloride, dibutyltin dichloride, cyhexatin, diphenyltin dichloride, tetraethyl tin, (tributyl tin) oxide, tributyl tin methoxide, butyltin trichloride, dibutytin oxide, triphenyltin hydroxide, fentin, dibutyl dimethoxytin, butyltin oxide, tributyltin fluoride and its polymer, tricyclohexyltin chloride, and dibutyl chlorotin oxide. Note: this is not an exhaustive list of possible tin precursors, as other precursors exist including at least the elements of tin, with carbon, sulfur, or nitride elements.

(18) As another example, Step 102 provides a metallorganic compound where Me is antimony (Sb), comprising one of the following exemplary precursors:

(19) antimony acetate, potassium antimony tartrate, antimony ethoxide, antimony methoxide, antimony isopropoxide, antimony propoxide, (dimethylamido)antimony, triphenylantimony, dichlorotris(4-bromophenyl)antimony, (naphthyl)antimony, ((trifluoromethyl)phenyl)-antimony, ((diethylamino)phenyl)antimony, bromophenyl antimony, dibenzofuryl antimony, tolyl antimony, triphenylantimony dichloride, and antimony phtealocyanine. Note: this is not an exhaustive list of possible antimony precursors, as other precursors exist including at least the elements of antimony, with carbon, sulfur, or nitride elements.

(20) As a third example, Step 102 may provide a metallorganic compound where Me is lead (Pb), comprising one of the following exemplary precursors:

(21) lead acetate, lead subacetate, lead citrate, lead phthalocyanine, lead methanesulfonate, lead acetylacetonate, lead tetrakis (4-cumylphenoxy)phthalocyanine, lead ionophore, Bis(2,2,6,6-tetramethyl-3,5-heptanedionato)lead, triphenyl(phenylethynyl)lead, lead 2-hydroxy-2-methylpropionate, benzyl tri(p-tolyl)lead, bis-(ethyl thio)lead, hexadecyl thio lead, (methyl thio) lead, chlorodiphenyl (4-pentenyl) lead, chloro tris (4-chlorophenyl) lead, choro tris(4-methoxyphenyl) lead, di(2-furyl) bis(4-methoxyphenyl) lead, diphenyldi (1-pyrrolyl) lead, diphenyldi (p-tolyl) lead, iodo tris (mesityl) lead, and terakis (2-methoxyphenyl) lead). Note: this is not an exhaustive list of possible lead precursors, as other precursors exist including at least the elements of lead, with carbon, sulfur, or nitride elements.

(22) FIG. 2 is a flowchart illustrating a method for forming metal particles with a pyrolyzed coating. The method begins at Step 200. Step 202 provides a metallorganic compound of Me and materials such as carbon, sulfur, nitrogen, oxygen, and combinations of the above-listed materials, expressed as Me.sub.XC.sub.YN.sub.ZS.sub.XXO.sub.YY; where Me is selected from a group consisting of metals and metal alloys: where X is greater than 0; where Y is greater than 0; where Z is greater than or equal to 0; where XX is greater than or equal to 0; and, where YY is greater than or equal to 0.

(23) Examples of particular metals, metal precursors, and the use of a plurality of metallorganic compounds have been presented above in the explanation of Step 102, and they are not repeated here in the interest of brevity.

(24) Step 204 heats the metallorganic compound. Again, temperature, atmosphere, and energy source details of heating process have been presented above in the explanation of Step 104, and are therefore not repeated. As a result of the heating in Step 204, Step 206 decomposes materials in the metallorganic compound. Step 208 forms Me particles coated by the materials.

(25) In one aspect, decomposing materials in the metallorganic compound in Step 206 includes forming a chemical reaction between the Me particles and the materials. As a result, Step 208 may form Me particles coated with a material such as a carbide, a nitride, a sulfide, or combinations of the above-listed materials.

(26) As noted in Wikipedia, pyrolysis is a thermochemical decomposition of organic material at elevated temperatures, typically in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. Pyrolysis is a type of thermolysis, and is most commonly observed in organic materials exposed to high temperatures. In general, the pyrolysis of organic substances produces gas and liquid products, and leaves a solid residue richer in carbon content. In the case of the above-described methods, pyrolysis may leave a residue including sulfur and nitrogen. Pyrolysis differs from other high-temperature processes like combustion and hydrolysis in that it does not always involve reactions with oxygen, water, or any other reagents.

(27) As noted above, the precursors are pyrolyzed at a temperature in the range of 200 to 2500 C. under inner or reductive atmospheres. The inert atmospheres can be nitrogen or argon. The reductive atmosphere can be hydrogen or ammonia-containing nitrogen or argon. The pyrolysis can be carried out by thermal (furnace), laser, microwave, or plasma treatment. As a result of pyrolysis, chemical interaction may exist between the metal particles and carbon, sulfur, or oxide layers. Depending on the precursor composition and treatment conditions, carbides, nitrides, or sulfides may form during the process. These products can prevent metal electrodes from pulverization during battery charge/discharge. The metal electrode materials can be post-treated by trace oxidants or nitrogen-containing material to form metal oxides or nitrides.

(28) In general, the metallorganic compounds mainly consist of metal ions, carbon, nitrogen, oxygen and sulfur, as expressed as Me.sub.XC.sub.YN.sub.ZS.sub.XXO.sub.YY. Aside from these elements, the metallorganic compounds may also include silicon, phosphorus, halogens, boron, and germanium, etc. Heated at a certain temperature, these compounds decompose to metals, carbon, carbides, nitrides, sulfides, and so on under an inert or reductive agent-including atmosphere. For example, cobalt phthalocyanine decomposes above to 780 C. under nitrogen flow.

(29) In battery applications, metals and alloys of tin, antimony, and lead are conventionally used as anode materials. For instance, as an anode material in sodium-ion batteries, tin can alloy with sodium to form Na.sub.3.75Sn. Its theoretical capacity is 846 mAh/g, much higher than that of hard carbon. The sodiation process can be expressed as:
Sn.fwdarw.NaSn.sub.5.fwdarw.NaSn.fwdarw.Na.sub.9Sn.sub.4.fwdarw.Na.sub.15Sn.sub.4 (Ref. V. L. Chevrier, G. Ceder, Challenges for Na-ion Negative Electrodes, J. Electrochem. Soc., 158 (2011) A1011-A1014)

(30) However, the alloying process causes volume changes of about 400% in the metal anode materials. After several cycles of sodiation/desodiation, the metal anode materials pulverize and lose their capability to host sodium. As a result, carbon coated SnSb was developed for a sodium-ion battery (Ref. L. Xiao, et at High capacity, reversible alloying reactions in SnSb/C nanocomposites for Na-ion battery applications, Chem. Commun., 48 (2012) 3321-3323). The occurrence of Sb with a carbon coating mitigated against the volume change of Sn, which demonstrated a better cyclability. Conventionally, metal-carbon composites are obtained with a ball-milling process. Carbon and metal particles are put into a container and to form carbon coated metal particles using high-energy mechanical milling equipment. However, the interaction between carbon layers and metal particles is weak.

(31) Electrode materials pyrolyzed from metallorganic compounds (MC) have two advantages over the ball-milling method.

(32) (1) With pyrolysis, the Me particles are surrounded by elements of C/N/S. As soon as the MC decomposes at a high temperature, Me is immediately coated by C/N/S. As a result, the Me particle size is smaller than that obtained from the ball-milling method.

(33) (2) The ball-milling process requires two steps to obtain N/C/S coated Me particles. The first step is to form small metal/alloy particles. The second step is to coat these particles with carbon or other elements. In contrast, the N/C/S coated Me particles obtained by pyrolysis are formed in a single step of heating the MC.

(34) In addition, it is very possible that a strong interaction between Me and C/N/S exists, even though the MC is heat-treated. It is believed by some researchers that pyrolysis forms a chemical bond between the Me and C/N/S. However, with the ball-milling, carbon is merely mechanically coated on Me, which causes a weak Me/C interaction.

(35) In order to obtain pyrolysis derived coating composites, a facile or readily occurring method is used. The metallorganic compounds are put into the chamber of a furnace, or exposed to laser, microwave, or plasma energy. Using an inert or reductive atmosphere, the metallorganic compounds decompose to carbon coated metals, carbides, nitrides, and so on at a certain temperature. Controlling the temperature and process time, the particle sizes of the composites can be controlled from 1 nanometer (nm) to several microns. Under some circumstances, chemical interaction between metals and carbon occurs, forming a strong adhesion of carbon, sulfur, or nitrogen layers on the metal particles to effectively retard the metals' expansion during battery charge/discharge.

(36) FIGS. 3A and 3B are schematic drawings depicting the pyrolysis process. Tin phthalocyanine is a macrocycle complex. Its structure is shown in FIG. 3A. Tin is located at the molecule center and is surrounded by nitrogen. Outside the nitrogen, there are carbon and hydrogen atoms. In a nitrogen atmosphere, the compound is heated in a furnace in a temperature range of 300-1200 C., and carbon coated tin is obtained, as shown in FIG. 3B. To obtain a smaller particle of carbon coated Sn, a shorter heating time is used. Using similar processes, carbon, sulfur, or nitrogen coated metal alloys can also be obtained. The precursors of metallorganic compounds containing different metals, for example, Sn and Sb, may be mixed together, and then heat-treated at high temperature, to obtain coated SnSb particles. The coated metals or alloys can be used as the anode materials in sodium or potassium ion batteries.

(37) FIG. 4 is a partial cross-sectional view of a battery. The battery 400 comprises an electrolyte 402, an ion-permeable membrane 404, and a cathode 406. The cathode 406 may be an oxide, sulfide, phosphate material. Some examples of oxides include LiCoO.sub.2, LiFePO.sub.4, LiNiO.sub.2, and LiMn.sub.2O.sub.4. One example of a sulfide includes TiS.sub.2. Some examples of phosphates include Na.sub.2PO.sub.4F, NaVPO.sub.4F, and Na.sub.1.5VOPO4F.sub.0.5. In one aspect, the cathode 406 is a cyanometallate comprising an active material A.sub.BM1.sub.CM2.sub.D(CN).sub.E.FH.sub.2O; where A is selected from a first group of metals; where M1 and M2 are transition metals; where B is less than or equal to 6; where C is less than or equal to 4; where D is less than or equal to 4; where E is less than or equal to 10; and, where F is less than or equal to 20.

(38) The battery 400 also comprises an anode 408, which in turn comprises metal (Me) particles 410 formed from metals or metal alloys, with a coating 412 formed over the Me particles 410. The coating 412 is formed from materials such as carbon (C), sulfur (S), nitrogen (N), oxygen (O), or combinations of the above-listed materials, expressed as C.sub.YN.sub.ZS.sub.XXO.sub.YY; where Y is greater than 0; where Z is greater than or equal to 0; where XX is greater than or equal to 0; and, where YY is greater than or equal to 0.

(39) The Me particle 410 with coating 412 is shown formed on a conductive current collector 414. A polymeric binder such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PVDF) may be used to provide adhesion between the Me particles 410 with coating 412 and the current collector 414 to improve the overall physical stability.

(40) In one aspect, the materials of the coating 412 are a carbide, a nitride, a sulfide, or combinations of the above-listed materials. Typically, the Me particles 410 are tin (Sn), antimony (Sb), lead (Pb), or combinations of the above-listed metals. In the case of the cyanometallate cathode, A is typically an alkali metal, alkaline metal, or combinations of the above-listed metals. More explicitly, the first group of metals may be comprised of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), calcium (Ca), magnesium (Mg), or combinations thereof. M1 and M2 are each independently derivedthey can be the same or a different transition metal, and are typically one of the following: titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), Ca, and Mg. In another aspect, at least one the variables Z, XX, and YY is greater than zero, when Y is greater than zero. That is, when the materials of the coating 412 include carbon, they additionally include S, N, O, or combinations of S, N, and O.

(41) The battery electrolyte 402 may be non-aqueous, such as an organic liquid electrolyte, or alternatively, gel electrolyte, polymer electrolyte, solid (inorganic) electrolyte, etc. Common examples of non-aqueous (liquid) electrolytes include organic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), etc., although many other organic carbonates and alternatives to organic carbonates exist. Typically, gel electrolytes consist of polymeric materials which have been swelled in the presence of liquid electrolytes. Examples of polymers employed as gel electrolytes include, but are not limited to, poly(ethylene)oxide (PEO) and fluorinated polymers such as poly(vinylidene) fluoride (PVDF)-based polymers and copolymers, etc. In contrast, (solid) polymer electrolytes may be prepared using the same classes of polymers for forming gel electrolytes although swelling of the polymer in liquid electrolytes is excluded. Finally, solid inorganic (or ceramic) materials may be considered as electrolytes, which may be employed in combination with liquid electrolytes. Overall, the appropriate electrolyte system may consist of combinations (hybrid) of the above classes of materials in a variety of configurations. Typically, the battery includes an ion-permeable membrane 404 separating the cathode 406 from the anode 408. In some instances, the ion-permeable membrane and the electrolyte can be the same material, as may be the case for polymer gel, polymer, and solid electrolytes.

(42) A pyrolysis process has been presented for fabricating coated metal particles for use as an anode in a battery. Examples of particular materials and process steps 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.