WO2014088452A1

WO2014088452A1 - Air cathode including delta-manganese dioxide catalyst

Info

Publication number: WO2014088452A1
Application number: PCT/RU2012/001030
Authority: WO
Inventors: Daniil Mikhailovich ITKIS; Dmitry Alexandrovich SEMENENKO; Alina Igorevna BELOVA
Original assignee: Obschestvo S Ogranichennoi Otvetstvennostyu "Fm Lab"
Priority date: 2012-12-07
Filing date: 2012-12-07
Publication date: 2014-06-12

Abstract

An air cathode for a metal-air battery (e.g., a Li-air battery) including delta-manganese dioxide, is provided. The delta-manganese dioxide is prepared by chemical reaction between potassium permanganate and potassium persulfate. Li-air battery including such cathode including the delta-manganese dioxide is also provided. In some embodiments, the Li-air battery includes an anode including lithium metal, and a solid-state electrolyte disposed between the anode and the cathode.

Description

AIR CATHODE INCLUDING DELTA-MANGANESE DIOXIDE CATALYST

TECHNICAL FIELD

The disclosed subject matter generally relates to electrochemical devices such as batteries. More specifically, the disclosed subject matter relates to cathodes for metal-oxygen batteries, such as lithium-air batteries.

BACKGROUND

Metal-air batteries are a class of electrochemical cells in which oxygen, which is typically obtained from the ambient environment, is reduced at a catalytic cathode surface as part of the electrochemical cell reaction. Reduction of the oxygen can form an oxide or peroxide ion which reacts with a cationic metal species. Metal-oxygen batteries have been developed based upon Fe, Zn, Al, Mg, Ca, and Li. For purposes of the present disclosure, the term "battery" will generally refer to electrochemical power generation and/or storage devices comprised of single cells as well as plural, interconnected cells.

Lithium-air (Li-air) batteries represent one type of metal-air battery. In devices of this type, an electro-active cathode and a lithium-containing anode are disposed in contact with an electrolyte which provides for ionic communication therebetween, but which is not electrically conductive. For example, for a Li-air battery that uses a non-aqueous electrolyte for the air cathode, during the discharge of the cell, oxygen can be reduced at the electro-active cathode (or air cathode) to produce 0^~2 and/or 0₂ ^-2 ions which react with the lithium to produce Li₂0₂ and/or Li₂0 which deposits on the cathode.

The cathode of a Li-air battery can include catalyst(s) to lower charge potential, accelerate the reaction kinetics, and enable rechargeability. The composition of the cathode catalyst and the construction of the cathode including the catalyst can influence the performance of the battery. For example, metal oxide nanoparticles, such as a- or β- manganese dioxide have been used as cathode catalysts. Results have been reported for -Μη0₂ nanowires having a tunnel structure. However, even in nanocrystalline form, this material does not have sufficiently high surface area. Moreover, the tunnel structure could not provide sufficient lithium-ion transport for battery operation at large currents.

Hence, there is a need to develop cathode catalysts for metal-air batteries, in particular Li- air batteries, with improved performance.

SUMMARY

The purpose and advantages of the disclosed subject matter will be set forth in and apparent from the description that follows, as well as will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes an air cathode for a metal-air battery, such as a Li-air battery. The air cathode includes delta- manganese dioxide (delta-Mn0₂, or δ-Μηθ2). The air cathode can also include conductive carbon powders admixed with delta- manganese dioxide, and the mixture can be coated onto a current collector. The delta- manganese dioxide can be prepared by chemical reaction between potassium permanganate and potassium persulfate.

In another aspect, the disclosed subject matter provides a method for preparing an air cathode for a metal-air battery. The method includes preparing delta- manganese dioxide by chemical reaction between potassium permanganate and potassium persulfate in aqueous solution. The delta- manganese dioxide can be admixed with conductive carbon powders, which can be applied as a slurry or suspension onto a current collector.

In a further aspect, the disclosed subject matter provides a metal-air battery, e.g., Li-air battery that includes a cathode including the delta- manganese dioxide as described above. The cathode can further include a nonaqueous liquid electrolyte for the cathode. In some embodiments, the Li-air battery includes an anode including lithium metal, and a solid-state electrolyte disposed between the anode and the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la is a schematic diagram of the crystal structure of delta-manganese dioxide as a cathode catalyst according to a representative embodiment of the disclosed subject matter.

Figure lb is X-ray diffraction patterns of delta-manganese dioxide before and after annealing according to a representative embodiment of the disclosed subject matter.

Figure 2 is a TEM image of delta-manganese dioxide as a cathode catalyst according to a representative embodiment of the disclosed subject matter.

Figure 3 is a schematic representation of a structure of a Li-air battery incorporating a cathode including delta-manganese dioxide according to a representative embodiment of the disclosed matter.

Figure 4 is a cyclic voltammogram for a Li-air battery incorporating an air cathode including delta-manganese dioxide as a cathode catalyst, according to a representative embodiment of the disclosed matter, as well as a cyclic voltammogram of Li-air battery including alpha-manganese dioxide for comparison.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the disclosed subject matter claimed.

The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the disclosed subject matter. Together with the description, the drawings serve to explain the principles of the disclosed subject matter.

DETAILED DESCRIPTION

Reference will now be made in detail to the various aspects of the disclosed subject matter, exemplary embodiments of which are illustrated in the accompanying drawings.

In one aspect, the disclosed subject matter provides an air cathode for metal-air batteries, e.g., Li-air batteries. Such air cathode includes delta-manganese dioxide as cathode catalyst. The disclosed subject matter also provides fabrication techniques for such air cathodes, as well as metal-air batteries including such air cathodes.

Delta-Manganese As Cathode Catalyst

In one aspect of the disclosed subject matter, an air cathode for a metal-air battery is provided. The air cathode includes delta-manganese dioxide. The delta-manganese dioxide can include certain amount of Mn³⁺ along with Mn⁴⁺. The ratio of Mn³⁺ to Mn⁴⁺ can be from about 0.2 to about 0.5. Other cations can compensate the positive charge deficiency. For example, the delta-manganese dioxide can include an amount of potassium ions, e.g., about 5 mol % of manganese or less, that can impede lithium ion migration inside the material. As illustrated in Figure la (schematic crystal structure of delta-manganese dioxide), delta-manganese dioxide has a generally layered birnessite structure, with [Mn0₆] octahedral layers interspaced with cations such as K⁺, Li⁺, and/or H⁺. In the preparation of the delta-manganese dioxide, although it is desirable to remove K⁺ to the maximum extent possible, the birnessite structure need be maintained, as the layered structure of the delta-manganese dioxide allows for enhanced ionic transport between manganese dioxide layers.

The delta-Mn0₂ of the disclosed subject matter can be prepared by chemical reaction between potassium permanganate and potassium persulfate, at e.g., about 95°C in aqueous solution, for about 1 hour. Polycrystalline product can be filtered, washed by ammonia buffer solution, and dried at about 60°C and then annealed at 300°C in vacuum to remove most of the potassium ions. Figure lb shows the X-ray diffraction patterns of delta-Mn0₂ particles as prepared. The structure was confirmed by comparison to a birnessite XRD card (PDF [43- 1456]). Figure 2 shows transmission electron microscopy (TEM) images (LE0912 AB OMEGA) of delta-Mn0₂ particles as prepared (porous nanospheres having a diameter about 50 nm, and surface area about 190 m²/g or greater). Furthermore, the layered structure of delta-Mn0₂ have larger specific surface area than the alpha- and beta- Mn0₂ structures (which can have representative specific surface area of less than 70 m /g, and less than 20 m /g, respectively).

Cathode Including Delta-Manganese Dioxide

The delta-Mn0₂ of the disclosed subject matter can be incorporated in any metal-air electrochemical system, including cathodes used in zinc-air, lithium-air, aluminum-air batteries. In particular, the delta-Mn0₂ can be incorporated in lithium-air batteries containing either aqueous or nonaqueous electrolytes. For example, an air cathode can include the delta-Mn0₂ and a current collector. To construct such a cathode, the delta-Mn0₂ can be applied onto metallic material such as metal sheet or foil, porous or perforated metal, or metal mesh. The metal can be aluminum, nickel, titanium, stainless steel, or noble metal. Additionally or alternatively, the delta-Mn0₂ can be admixed with conductive carbon materials such as carbon black, charcoal, activated carbon, acetylene carbon, Ketjen® black, Vulcan® XC-72, graphite, graphite foam, etc. Such mixture can further be applied on a current collector.

For purpose of illustration and not limitation, the cathode can be fabricated by applying a slurry of delta-Mn0₂ (which can also include the conductive carbon materials described above, in a suitable solvent, such as acetone, N-methylpyrrolidone, etc.) on the surface of a current collector made from a metal (Ni or stainless) mesh. The slurry can then be dried under air flow or in vacuum to evaporate the solvent. In some embodiments, the delta-Mn0₂ slurry can further include binders, such as a polymer binder including but not limited to: Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), copolymer of PVDF and PTFE, copolymer of PVDF and hexafluoropropylene (HFP). The catalyst slurry can further include plasticizers, such as diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether. The catalyst slurry can also further include lithium salts such as LiGC>4, LiTFSI, and LiPF₆.

Before assembling the cathode prepared above with other components of batteries, as further discussed below, the electrode can be moistened with cathode electrolyte. Exemplary cathode electrolyte include non-aqueous solvents such as alkyl carbonate, ester, ether, tetraglyme, N-methyl-N-proopylpiperidinium bis(trifluoro methanesulfonyl)imide (PP13 TFSI), or 1-ethyl- 3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI TFSI) ) that can also further include lithium salts such as LiC10₄, LiTFSI, and LiPF₆.

Li-air Batteries Including δ·Μηθ₂ Cathode Catalyst

The air cathode including the δ-Μη0₂ catalyst described above can be used to construct a metal-air battery. As disclosed herein the representative battery is a Li-air battery including an anode made of lithium metal or lithium intercalated into a porous substrate. The anode can be sealed gas-tight, and include either a nonaqueous anolyte, and lithium salts such as L1CIO4, LiTFSI and L1CF3SO3. A separator can be disposed between the anode and the cathode. The separator can include a solid-state lithium ion conductive electrolyte, ceramic or glass-ceramic, such as L13N, perovskite, LISICON, or NASICON type crystals. Such solid state electrolyte can include a matrix of polymer, such as PVDF, PVDF-co-PTFE, PVDF-co-HFP. For example, the solid-state electrolyte can include Lii_+x+y(Al, Ga)_x(Ti, Ge)₂__xSiyP3-_yOi₂ (where 0≤x < l, 0≤y < 1). Other examples of the lithium ion conductive glass-ceramic include lithium-aluminum- germanium-phosphate (LAGP), lithium-aluminum-titanium-phosphate (LATP), lithium- aluminum-titanium-silicon-phosphate (LATSP), and the like. The above-described cathode can be placed adjacent the solid electrolyte membrane.

An exemplary Li-air battery 100 according to the disclosed subject matter is shown in Figure 3. As shown, the Li-air battery includes an cathode chamber 8, an gas-tight anode chamber 7, and a solid state electrolyte 3 disposed therebetween. In the cathode chamber 8, the cathode 1 including the delta-manganese dioxide described above is applied on the cathode current collector 9, which contacts the solid state electrolyte 3. A spring 6 is attached to a perforated piston 4, which is in contact with cathode 1. In the anode chamber 7, the anode 2 including Li metal contacts a bottom piston 5 supported on another spring 6. The Li-air battery is assembled by pressing the two springs 6 against each other to hold all the components in place. The disclosed subject matter is further described with reference to the following examples, which are presented for illustration for some embodiments only and not intended to limit the purpose or scope of the appended claims.

Example 1

δ-Μη0₂ catalyst was prepared as follows. 2 mmol (540 mg) of potassium permanganate and 2 mmol (316 mg) of potassium persulfate were dissolved in 100 mL of distilled water. The solution was heated up to 95°C and stirred at this temperature during 1 hour. The brown precipitate was filtered, washed by ammonia buffer solution several times, dried at 60°C in air, and then annealed for 2 hours at 300°C in vacuum.

Example 2

An air cathode was prepared as follows. A stainless steel mesh of 2 cm diameter (150 micron thick, and a hole of dimension 0.2 x 0.2 mm ) was used as the current collector. 80 mass.% of carbon powder and 15 mass.% of the δ-Μη0₂ (or 20 mass.% if no binder is used) were suspended in organic solvent (acetone or N-methyl-2-pyrrolidone) with 5 mass.% of dissolved binder (PVDF or PVDF/PTFE copolymer) using ultrasonic treatment. This slurry was applied onto one side of the current collector and dried at 60-80°C in air to evaporate the solvent. Then the electrode was dried in vacuum at 100°C.

Example 3

A Li-air battery whose configuration has been shown in Figure 3 was constructed as follows. The gas-tight anode chamber includes a round Li foil (diameter 2 cm, 20 micron thick) and nonaqueous liquid electrolyte (1 M LiC10₄ in propylene carbonate: 1,2-

The cathode chamber includes an air cathode having δ-Μη0₂ catalyst as fabricated according to the procedure of Example 2. The cathode chamber also contains nonaqueous liquid electrolyte (1 M LiTFSI in tetraglyme or EMI TFSI). The two chambers are separated from each other by a solid state Li-ion conductive membrane (glass- ceramic round plate composed of main phase Lii._xAl_xTi_2-x(P0₄)3 with x = 0.3 - 0.7 and additional phase LiB0₂ up to 50 wt.%, 450 micron thick, diameter 2 cm). The battery was assembled in a glove box under argon atmosphere. Electrodes were soaked with appropriate liquid electrolytes and pressed to the solid electrolyte membrane by springs and pistons as shown in Figure 3 and described above. The cell was saturated by oxygen before measurements. Example 4

The performance of Li-air batteries constructed according to the procedure of Example 3 was evaluated, and the results are shown in Fig. 4, which are cyclic voltammograms of 2 Li-air cells with delta- and alpha-Mn0₂ catalysts respectively (sweep rate 200 μν/s). The cathodes include the respective catalysts and carbon black (Vulcan XC-72) at a ratio of 80:20 and no binder. Total mass of cathode materials is 1 mg (not including the current collector). It can be seen that the Li-air battery having delta-Mn0₂ as the cathode catalyst has much lower charge potential (about 3.5 V versus about 3.9 V). Moreover, delta-Mn0₂ helps the Li-air battery achieve higher discharge capacity and performance.

While the disclosed subject matter is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements can be made to the disclosed subject matter without departing from the scope thereof. Moreover, although individual features of one embodiment of the disclosed subject matter can be discussed herein or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment can be combined with one or more features of another embodiment or features from a plurality of embodiments.

In addition to the specific embodiments claimed below, the disclosed subject matter is also directed to other embodiments having any other possible combination of the dependent features claimed below and those disclosed above. As such, the particular features presented in the dependent claims and disclosed above can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter should be recognized as also specifically directed to other embodiments having any other possible combinations. Thus, the foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

It will be apparent to those skilled in the art that various modifications and variations can be made in the method and system of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1. An air cathode for a metal-air battery, comprising a catalyst made from delta- manganese dioxide.

2. The air cathode of claim 1, wherein the delta- manganese dioxide comprises Mn³⁺ and Mn⁴⁺, wherein the ratio of Mn³⁺ to Mn⁴⁺ is from about 0.2 to about 0.5.

3. The air cathode of claim 1, wherein the delta- manganese dioxide has a specific surface area of at least about 190 m²/g.

4. The air cathode of claim 1, wherein the delta- manganese dioxide includes about 5% mole fraction of potassium ions relative to manganese of the delta- manganese dioxide.

5. The air cathode of claim 1, further comprising conductive carbon powders admixed with the delta-manganese dioxide.

6. The air cathode of claim 1, wherein the metal-air battery is a Li- Air battery.

7. The air cathode of claim 1, wherein the delta-manganese dioxide is prepared by reacting potassium permanganate and potassium persulfate in aqueous solution.

8. The air cathode of claim 7, wherein the reaction is performed at about 95°C.

9. A metal-air battery, comprising:

a cathode including a cathode catalyst,

wherein the cathode catalyst comprises delta- manganese dioxide.

10. The metal-air battery of claim 9, further comprising a nonaqueous liquid electrolyte for the cathode.

11. The metal-air battery of claim 9, further comprising an anode including lithium metal.'

12. The metal-air battery of claim 11, wherein the specific capacity of the battery is greater than 3000 mAh/g.

13. The metal-air battery of claim 11, wherein the charge potential of the battery is about 3.5 to about 3.7 V.

14. The metal-air battery of claim 9, further comprising a solid-state electrolyte disposed between the anode and the cathode.

15. A method for fabricating an air cathode for a metal-air battery, comprising:

preparing a catalyst including delta-manganese dioxide by reacting potassium permanganate and potassium persulfate in aqueous solution.

16. The method of claim 15, wherein reacting potassium permanganate and potassium persulfate is performed at about 95°C.

17. The method of claim 15, further comprising:

preparing a suspension of the delta-manganese dioxide in an organic solvent; and applying the suspension onto a current collector.

18. The method of claim 17, wherein preparing the suspension comprises admixing the delta-manganese dioxide with conductive carbon powders.

19. A method of making a metal-air battery, comprising:

preparing a cathode including a catalyst of delta-manganese dioxide;

providing an anode comprising a lithium metal; and

disposing a solid state electrolyte between the cathode and the anode.