Protected lithium electrode structure for lithium-air battery

Abstract

Protected lithium electrode structure (1) for a lithium-air battery, comprising: a negative electrode current collector (3); a negative electrode active material layer (5) made of a lithium metal, a mainly lithium-containing alloy or a mainly lithium-containing compound, and stacked on the negative electrode current collector (3); and a separator (7) which is stacked on the negative electrode active material layer (5), wherein the negative electrode active material layer (5) is sealed by connecting the separator (7) and the negative electrode current collector (3) around the negative electrode active material layer (5), the separator (7) being bonded to the negative electrode current collector (3) at a circumferential edge section of the separator (7), and the negative electrode active material layer (5) being stacked onto a surface of the negative electrode current collector (3) to cover an area smaller than the area of ​​the negative electrode current collector (3), and a trapping layer (11) for finely powdered lithium, which is arranged between the negative electrode active material layer (5) and the separator (7) and has electrical conductivity via a bond on one side of the trapping layer (11) for finely powdered lithium, wherein the trapping layer (11) for finely powdered lithium is a conductive foam or a structure made of metal fiber and traps finely powdered lithium metal that is generated during charging and discharging.

Description

[Technical field]

[0001] The present invention relates to a protected lithium electrode structure used for a lithium-air battery. [Technical background]

[0002] Metal-air batteries have recently been proposed as the next generation of batteries, potentially offering higher energy density than conventional lithium-ion batteries. A metal-air battery uses a metal as the negative electrode active material and atmospheric oxygen as the positive electrode active material. This type of metal-air battery, which uses lithium metal as the negative electrode active material, is of particular interest because it is theoretically capable of generating more energy per unit weight. Such a metal-air battery, which uses lithium metal as the metallic negative electrode active material, is referred to as a "lithium-air battery."

[0003] Lithium-air batteries are generally classified into two types: one that uses an aqueous electrolyte and another that uses a non-aqueous electrolyte. The lithium-air battery using an aqueous electrolyte is advantageous because it is less affected by atmospheric moisture than one using a non-aqueous electrolyte. It should be noted that the lithium metal used for the negative electrode active material must be protected from the atmosphere and aqueous solutions, as lithium metal reacts chemically with oxygen and water upon contact. For this purpose, a method has been proposed that, for example, uses a solid electrolyte conductive to lithium ions as an insulating layer.

[0004] For example, patent document 1 discloses as a lithium-air battery using an aqueous electrolyte a lithium-air battery with a protected lithium electrode in which a buffer layer of polymer electrolyte is formed on a surface of a plate-shaped lithium metal and is covered with a glass ceramic conductive for lithium ions. [State of the art][Patent document]

[0005] [Patent Document 1] JP 2010-192313 A [Summary of the invention][Problems to be solved by the invention]

[0006] When the lithium-air battery disclosed in patent document 1 is used in practice, the lithium metal used as the negative electrode active material is fixed as a metal (negative electrode current collector) that serves as the negative terminal. A situation can arise in which, during repeated charging and discharging of the lithium-air battery with such a structure, dendrites of lithium metal are deposited on a section (for example, the back surface) of the negative terminal during charging. Furthermore, a situation can arise in which, when the tip of a dendrite breaks off, fine lithium powder (dead lithium) is produced and dispersed in the electrolyte solution. This dispersed lithium powder does not contribute to charging and discharging because it moves away from the negative terminal. Consequently, the charging and discharging performance of the lithium-air battery gradually decreases, while the amount of dead lithium increases.

[0007] In view of the above circumstances, an object of the present invention is to provide a protected lithium electrode structure for use in a lithium-air battery, the charging and discharging performance of which is less prone to degradation. [Means of solving the problems]

[0008] To solve the above problem, a protected lithium electrode structure for a lithium-air battery has the features of claim 1. According to one aspect of the present invention, the structure comprises: a negative electrode current collector; a negative electrode active material layer made of a lithium metal, a mainly lithium-containing alloy, or a mainly lithium-containing compound, and stacked on the negative electrode current collector; a separator stacked on the negative electrode active material layer, wherein the negative electrode active material layer is sealed by the separator and the negative electrode current collector, the separator being bonded to the negative electrode current collector at a circumferential edge portion of the separator, and the negative electrode active material layer being stacked on a surface of the negative electrode current collector to cover an area.which is smaller than the area of ​​the negative electrode current collector, and a fine-powder lithium trapping layer that captures fine-powder lithium metal generated during charging and discharging, and which is arranged between the negative electrode active material layer and the separator and has electrical conductivity via a bond on one side of the fine-powder lithium trapping layer, wherein the fine-powder lithium trapping layer is a conductive foam or a metal fiber structure. It is noted that the separator may, for example, be a layer of porous resin or the like. [Advantageous effects of the invention]

[0009] The present invention comprises: a negative electrode current collector; a negative electrode active material layer, which is a lithium metal, a mainly lithium-containing alloy, or a mainly lithium-containing compound, and which is stacked on the negative electrode current collector; and a separator, which is stacked on the negative electrode active material layer, wherein the negative electrode active material layer is sealed by the separator and the negative electrode current collector; and a fine-powder lithium trap layer, which traps fine-powder lithium metal generated during charging and discharging, and which is provided between the negative electrode active material layer and the separator. This makes it possible to encapsulate the fine-powder lithium metal generated during charging and discharging in the fine-powder lithium trap layer.This allows for the recovery of additional lithium metal, which contributes to charging and discharging, and increases the lithium metal utilization rate, as dispersion of the finely powdered lithium metal in the electrolyte solution is prevented. Therefore, the charging and discharging performance does not decrease significantly, and multiple charging and discharging cycles are possible. Consequently, the charging and discharging characteristics can be improved. [Brief description of the drawings] [ Fig. 1] Fig. Figure 1 is a cross-sectional view showing a protected lithium electrode of a lithium-air battery according to a first embodiment. [ Fig. 2] Fig. Figure 2 is an enlarged view of a cross-section representing an enlarged protected lithium electrode of the lithium-air battery according to the first embodiment. [ Fig. 3] Fig. Figure 3 is an enlarged view of a cross-section representing a negative electrode of the lithium-air battery according to the first embodiment. [ Fig. 4] Fig. Figure 4 is a top view showing an example of the negative electrode of the lithium-air battery according to the first embodiment. [ Fig. 5] Fig. Figure 5 represents another example of the negative electrode of the lithium-air battery according to the first embodiment: Fig. 5A is a top view of the negative electrode; and Fig. Figure 5B is a top view showing a state in which a pouch-shaped separator is spread out to receive the negative electrode. [ Fig. 6] Fig. Figure 6 is a cross-sectional view showing a protected lithium electrode of a lithium-air battery according to a second embodiment. [ Fig. 7] Fig. Figure 7 is a top view showing a negative electrode of a lithium-air battery according to Example 1. [ Fig. 8] Fig. Figure 8 is a bottom view showing the negative electrode of the lithium-air battery according to Example 1. [ Fig. 9] Fig. Figure 9 is a top view showing a negative electrode, which is used for a performance comparison with the one in Fig. 7 and Fig. The negative electrode shown in diagram 8 is used. [ Fig. 10] Fig. Figure 10 is a bottom view showing the negative electrode, which is used for a performance comparison with the one in Fig. 7 and Fig. The negative electrode shown in diagram 8 is used. [ Fig. 11] Fig. Figure 11 is a diagram showing the relationship between time and a charge and discharge voltage of the lithium-air battery according to Example 1. [Modes of implementation of the invention]

[0010] With reference to the attached drawings, a detailed and specific description of embodiments of a protected lithium electrode structure for a lithium-air battery according to the present invention is now given. [First embodiment]

[0011] First, a protected lithium electrode structure for a lithium-air battery according to a first embodiment is described based on: Fig. 1. As in Fig. Figure 1 shows a protected lithium electrode 1 of the lithium-air battery according to the first embodiment having a stacked structure in which upper and lower metal foil laminate films 2 and 2 surround a negative electrode 30 and a solid electrolyte 8 in a sandwich-like manner to insulate the negative electrode, for example, against moisture. The metal foil laminate film 2 on the upper side of the figure is a layer in which, from the inside (bottom side of the figure) to the outside (top side of the figure), three layers are stacked in the following order: a resin layer 21, such as a heat-sealable PP resin layer, a metal foil layer 22, and a resin layer 23, such as a heat-resistant PET resin layer.Similarly, the metal foil laminate film 2 on the lower side of the figure is a layer in which, from the inside (upper side of the figure) to the outside (lower side of the figure), three layers are stacked in the order resin layer 21, metal foil layer 22 and resin layer 23.

[0012] The metal foil laminate film 2 on the upper side in Fig. The metal foil laminate film 2 has an opening section 4 located in the center or substantially in the center. Viewed from the top of the figure, this opening section 4 is a quadrilateral. Furthermore, a solid electrolyte 8 is provided on the underside of the opening section 4 of the metal foil laminate film 2 for insulating the negative electrode, formed, for example, from a glass ceramic, against, for example, moisture. The solid electrolyte 8 referred to here is a solid material that allows the permeation of ions (lithium ions) when a voltage is applied. In this embodiment, the solid electrolyte 8 has the form of a relatively thin plate. Moreover, the surface area of ​​the upper surface of this solid electrolyte 8 is somewhat larger than the opening section 4 of the metal foil laminate film 2.

[0013] A circumferential edge section of the opening section 4 of the upper metal foil laminate film 2 is welded directly to the upper surface of the solid electrolyte 8, or preferably with a heat-sealable material 10 in between (see Fig. 2) In this way, the solid electrolyte 8 seals this opening section 4. The closed opening section 4 allows for an improvement in safety by reducing the reactivity of the highly reactive lithium powder generated by charging and discharging, so that if water or the like enters the negative electrode in the event of damage to the lithium-air battery, the water or the like cannot quickly penetrate into the interior of the negative electrode.

[0014] The negative electrode 30 is in Fig. 1 below the solid electrolyte 8. This negative electrode 30 is attached by welding both ends of each of the four sides shown in the figure, which are sandwiched together by the upper and lower metal foil laminate films 2. In addition, the upper and lower metal foil laminate films 2 are welded to the heat-sealable materials 10, 10 between them at corresponding upper and lower positions of the negative electrode.

[0015] Fig. 2 represents the protected lithium electrode 1 Fig. 1 enlarged, and Fig. 3 places the negative electrode 30 in Fig. 1 enlarged. As in Fig. 1 to Fig. As shown in Figure 3, the negative electrode 30 has a structure in which, from bottom to top in the figure, five layers are stacked in the following order: a film 9, a copper foil negative electrode current collector 3, a lithium metal negative electrode active material layer 5, a fine-powder lithium trapping layer 11 that traps fine-powder lithium metal generated during charging and discharging, as will be described later, and a separator 7. The film 9 is, for example, a film of polypropylene resin and covers the lower surface of the negative electrode current collector 3 by means of a welded connection. It is noted that the negative electrode active material layer 5 is sealed by the negative electrode current collector 3 and the separator 7, although this is not shown in Figure 3. Fig. 1 and Fig. Figure 2 is not shown because it is a cross-sectional view. Details of this structure will be described later.

[0016] The trapping layer 11 for finely powdered lithium is, for example, a conductive foam or a structure made of metal fiber (metal wool such as conductive copper, or a felt-like structure or fabric). For the metal wool made of conductive material such as copper wool, a wool processed in the form of a layer with a fiber diameter of 0.02 mm or less and a thickness of 2 mm or less is advantageous.

[0017] If the fiber diameter of the metal fiber structure is greater than 0.02 mm, the surface area of ​​each fiber is considered a reaction field for the lithium deposition reaction. Therefore, as the fiber diameter decreases, the number of reaction fields increases, leading to insufficient effectiveness of the metal fiber structure. Conversely, if the fiber diameter increases, the weight and volume of the metal fiber structure increase, negatively impacting the reduction in battery size and weight (energy density).

[0018] If the thickness of the metal fiber structure exceeds 2 mm, the following problem arises. Since this structure is one in which the entire negative lithium metal electrode, including the metal fiber structure, is covered by the pouch-shaped separator 7, the size of the pouch-shaped separator 7 must be increased if the thickness of the structure exceeds 2 mm. Furthermore, if the metal fiber structure has the same fiber diameter and weight but a different thickness, the porosity within the metal fiber structure is high. In this case, with a large separator 7 (large volume within the pouch) and high porosity of the metal fiber structure, bubbles become trapped inside the protected lithium electrode, which must be filled with an organic electrolyte solution, causing an increase in internal resistance.

[0019] The trapping layer 11 for finely powdered lithium can be a felted layer that has undergone fiberization to wool followed by needle punching, instead of a layer of porous metal or a layer of wool-like metal interspersed with conductive fine metal fibers. Preferably, the same material as in the negative electrode current collector is used; however, the material can also be different as long as the battery functions properly within its operating range.

[0020] If conductive foam is used as the trapping layer 11 for finely powdered lithium, the advantage here is that the thickness of the foam layer is easily controllable, the foam is filled with lithium during charging, and, for example, suppression of the thickness increase is possible.

[0021] If a structure made of metal fiber (a wool-like or felt-like structure or fabric) is used as the trapping layer 11 for finely powdered lithium, which has flexibility due to its fiber structure, returns to its original state when bent (does not deform plastically) and consists of a fine fiber, there are also the advantages that, for example, the specific surface area is large, a conductive path can be easily constructed, the amount of fiber can be easily increased and decreased, the porosity can be easily adjusted and welding can be easily carried out by, for example, a resistance welding apparatus.

[0022] The separator 7 has the property of allowing the electrolyte to pass through, as will be described later, and conducts lithium ions. Furthermore, the left and right end faces of this separator 7 in the figures are both connected to the negative electrode current collector 3 (see Fig. 1 and Fig. 3) Furthermore, the separator 7 is bonded to the negative electrode current collector 3 at four bonded sections 73, including a front-side edge section and a rear-side edge section. Thus, the negative electrode active material layer 5 is sealed to an unbonded section 74 located on the surface of the negative electrode current collector 3, which is not bonded to the separator 7. It is noted that the size of the negative electrode active material layer 5 is the same as, or slightly smaller than, that of the unbonded section 74. As shown in Fig. As shown in Figure 1, this unbound section 74 is located at a position that is almost identical to that shown in Fig. 1 corresponds to the solid electrolyte 8 provided on the upper side. Due to this structure, the negative electrode active material layer 5 is insulated from the solid electrolyte 8 and is not in direct contact with it. It is noted that a small amount of electrolyte (for example, a non-aqueous electrolyte solution, an organic electrolyte solution, or a polymer electrolyte) is sealed in the space between the negative electrode current collector 3 and the metal foil laminate film 2.

[0023] Furthermore, the embodiment features a configuration in which the trapping layer 11 for finely powdered lithium is arranged on the negative electrode active material layer 5 and the negative electrode current collector 3 is located on the inner side of the separator 7, one of the edge sections is bonded in such a way that it has electrical conductivity, and the negative electrode active material layer 5 is completely covered from above by the separator 7. Thus, the lithium powder, which is formed into a fine powder by charging and discharging, can be enclosed between the separator 7 and the negative electrode current collector 3.This prevents direct contact between the solid electrolyte 8 and the negative electrode 30 and simultaneously suppresses the dispersion and passage of fine-powdered lithium generated during the charge and discharge cycle within the protected lithium electrode 1. This reduces the amount of fine-powdered lithium that does not contribute to charging and discharging, thus delaying degradation of the solid electrolyte 8, resulting in a longer cell lifespan and improved safety. Furthermore, if the trapping layer 11 for fine-powdered lithium is bound within the separator 7 pouch to achieve electrical conductivity, the utilization rate of the fine-powdered lithium metal generated during charging and discharging can be increased, additional lithium can be recovered to contribute to charging and discharging, and, thanks to these effects, the charging and discharging characteristics can be improved.

[0024] The following is a description of the case in which the protected lithium electrode 1 in Fig. 1 is used for a lithium-air battery. In this case, an air electrode (not shown) is used, which is installed above the solid electrolyte 8 in the figure. When the lithium-air battery with this protected lithium electrode 1 is discharged, the negative electrode active material layer 5 (lithium metal) used for the negative electrode 30 splits into lithium ions (Li + ) and electrons (e - ), as shown in Formula 1. The lithium ions (Li + ) then dissolve into the electrolyte solution, and the electrons (e - The electrons are supplied to a connection section 32 via an electron collection section 31 of the negative electrode current collector 3. Therefore, the design value of the battery capacity can be controlled by changing the thickness and area of ​​the negative electrode active material layer 5. Li → Li+ + e - [Formula 1]

[0025] Furthermore, the positive electrode (not shown) is supplied with electrons, where ambient oxygen and water react with each other to form hydroxide ions (OH⁻). - ) generate (Formula 2). Furthermore, these hydroxide ions (OH) react - ) with lithium ions (Li + ) at the positive electrode, so that lithium hydroxide (LiOH) is produced. [Formula 2] O2 + 2H2O + 4e - → 4OH -

[0026] When this lithium-air battery is charged, lithium ions supplied from the positive electrode pass through the solid electrolyte 8 and the separator 7 to reach the surface of the electron collection part 31 of the negative electrode current collector 3 in the negative electrode 30, and as a result, the deposition reaction of the lithium metal takes place (formula 3). [Formula 3] Li+ + e- → Li

[0027] The separator is 7, as in Fig. Figure 3 shows that the bound sections 73 are bound to the electron collector area 31. Therefore, the surface of the electron collector area 31 is not exposed at the bound sections 73, and the deposition reaction of the lithium metal does not occur. Thus, the deposition reaction of the lithium metal only takes place in the unbound section 74. Fig. 4.

[0028] As in Fig. As shown in Figure 4, the back surface of the electron collector 31 is covered with the film 9. For this reason, the electrolyte solution does not reach the back surface of the electron collector 31, and consequently the deposition reaction of the lithium metal does not occur.

[0029] If, unlike the above, the back surface of the electron storage region 31 is not covered with film 9, dendrites are deposited on this back surface. Fine lithium, which is generated when tips of these dendrites break off, is dispersed in the electrolyte solution. Since this dispersed fine lithium does not contribute to charging and discharging, this reduces the charging and discharging performance of the lithium-air battery.

[0030] In contrast, with the protected lithium electrode structure according to the embodiment, a high-performance lithium-air battery can be provided by suppressing the generation of such dead lithium.

[0031] Meanwhile, an oxygen-generating reaction takes place at the positive electrode, as indicated by formula 4. [Formula 4] 4OH- → O2 + 2H2O + 4e-

[0032] The materials used for the first embodiment are described below.

[0033] Resins based on polyolefins, such as polypropylene resins and polyethylene resins, can be used as the resin layer 21 in the metal foil laminate film 2. These resins have low melting points, are easily heat-processable, and are suitable for heat sealing (thermal bonding), which facilitates the production of the protected lithium electrode 1.

[0034] Furthermore, the metal foil laminate film 2 is provided with the metal foil layer 22 to improve its gas barrier properties and strength. Metal foils such as aluminum foil, stainless steel foil, and copper foil can be used for the metal foil layer 22.

[0035] Finally, nylon-based and polyester-based resins, such as polyethylene terephthalate resins, can be used as resin layer 23. These resin materials have very good heat resistance and strength. Thus, the service life, heat resistance, strength, etc., of the protected lithium electrode 1 can be improved.

[0036] Although the metal foil laminate film 2 in the first embodiment has a three-layer structure, it can also have a structure with four or more layers, in which one or more resin films, such as a nylon film, are stacked between the layers.

[0037] For example, a glass-ceramic that is non-combustible and has very good lithium-ion conductivity can be used as the solid electrolyte 8. In particular, if an aqueous electrolyte solution is used, a LATP-based glass-ceramic electrolyte with high water resistance can be employed. LATP is an oxide with a NASICON-like crystal structure, containing, for example, Li, Ti, Al, P, Si, and O.

[0038] For example, film 9 can be a resin layer such as polypropylene or polyethylene, which is resistant to an electrolyte solution (organic electrolyte solution). It is noted that film 9 is bonded to the entire back surface of the electron collection portion 31 of the negative electrode current collector 3. However, it is also possible that only the circumferential edge sections are bonded. Furthermore, not only the back surface but also the side surfaces (edge ​​sections) of the negative electrode current collector 3 can be covered.

[0039] Separator 7 can, for example, be a layer of cellulose or a polyolefin-based resin such as porous polyethylene or polypropylene, used as a separator for a lithium-ion battery. Other materials include aramid and polytetrafluoroethylene with a porous structure. The aforementioned separator can be used, for example, impregnated with an electrolyte solution (non-aqueous electrolyte solution, organic electrolyte solution) or a polymer electrolyte.

[0040] Additionally, separator 7 can be used with a porosity of approximately 40% to 90% and a thickness of approximately 10 to 300 µm, more preferably approximately 15 to 100 µm. The size of each pore can be approximately 20 nm to 500 nm, more preferably approximately 20 to 70 nm. Furthermore, separator 7 itself preferably has a certain degree of stiffness and strength.

[0041] Regarding the electrolyte solution, for example as a non-aqueous electrolyte solution, it is possible to use a mixed solvent consisting of an organic solvent based on carbonic acid esters, containing PC (propylene carbonate), EC (ethylene carbonate), DMC (dimethyl carbonate) or EMC (ethyl methyl carbonate), or an ether-based solvent such as ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and triethylene glycol dimethyl ether, to which an electrolyte such as LiPF6 (lithium hexafluorophosphate), LiClO4 (lithium perchlorate), LiBF4 (lithium tetrafluoroborate), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide). With reference to an aqueous electrolyte solution, for example as a lithium salt soluble in water, the use of LiCl (lithium chloride), LiOH (lithium hydroxide), LiNO3 (lithium nitrate) and CH3COOLi (lithium acetate) or a mixture thereof is possible.

[0042] It is noted that the positive electrode (not shown) can be, for example, a catalytically active noble metal such as platinum, gold, iridium, or ruthenium, or an oxide thereof, or a catalytically active metal oxide such as catalytically active manganese dioxide with a large specific surface area, mixed with an electrically conductive material such as highly conductive carbon and, as a binder, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, etc., and can be mounted on an air electrode current collector with conductivity and gas dispersion properties. For example, it is possible to use carbon paper, carbon cloth, a carbon fleece, titanium braid, nickel braid, copper braid, stainless steel braid, porous nickel (metal foam made of nickel), and metal braid using a highly corrosion-resistant metal such as nickel, titanium, or stainless steel as this air electrode current collector.It is noted that the carbon cloth mentioned here refers to a cloth-like layer woven with, for example, carbon fibers, while the carbon fleece refers to layered carbon fibers that are randomly twisted together. It is further noted that if an aqueous electrolyte solution is used, the air electrode current collector must also be corrosion-resistant to the electrolyte solution. Therefore, it is possible to preferably use, for example, carbon fibers that exhibit high conductivity, are corrosion-resistant to both acidic and alkaline solutions, and are lightweight.

[0043] Fig. Figure 4 represents an example of the negative electrode 30 in the first embodiment and is a diagram of the negative electrode from Fig. 2, viewed from above. The negative electrode current collector 3 has the electron collection section 31, arranged on the left in the figure, and the connection section 32, arranged on the right in the figure. The electron collection section 31 has the shape of a quadrilateral with a larger area than that of the connection section 32. The negative electrode active material layer 5 and the separator 7 are stacked within the electron collection section 31. In the negative electrode 30, a film of the negative electrode active material layer 5, which consists of a lithium metal and is smaller than the area of ​​the negative electrode current collector 3, is bonded to the negative electrode current collector 3, which has a structure in which the electron collection section 31 and the connection section 32, formed, for example, from copper foil, are integrated.Furthermore, on the negative electrode active material layer 5, an edge section of the trapping layer 11 for fine-powdered lithium is bonded to a side of the negative electrode current collector by a resistance welding apparatus at a bonded section 12. On this section, the separator 7, which consists of a thermoplastic resin such as porous polyethylene or polypropylene commonly used in lithium-ion batteries to cover these elements, is placed. The separator 7 is bonded by welding to the bonded sections 73, which are the four sides of the circumferential edge section where the negative electrode active material layer 5 and the trapping layer 11 for fine-powdered lithium, located on the surface of the negative electrode current collector 3, are not located. Furthermore, the rear surface of the electron collection part 31 of the negative electrode current collector 3 is completely covered with the film 9 (see ). Fig. 1) This film 9 is also preferably a resin layer that is impermeable to an electrolyte solution and resistant to degradation by an electrolyte solution, for example, a resin layer resistant to an organic electrolyte solution such as polypropylene or polyethylene. In this example, the trapping layer 11 for finely powdered lithium is bonded to the copper foil of the negative electrode current collector 3, for example, by a spot welding device. This bonded section is designated by reference numeral 12 and is a section where an edge section of the trapping layer 11 for finely powdered lithium and the copper foil of the negative electrode current collector 3 are stacked on top of each other. It is noted that in Fig. 4 the reference numeral 13 indicates a thermal bonding layer which is used to heat-seal the separator 7 and the copper foil of the negative electrode current collector 3 together.

[0044] Fig. 5A and Fig. Figure 5B shows another example of the negative electrode 30 in the first embodiment. In this example, the separator 7 has bonded sections 75 at both ends, on which sections of the thermal bonding layers 14, 14 are placed and bonded, as shown in Fig. 5B is shown. Fig. The negative electrode 30 shown in 5A is formed by: bending a Fig. 5B separator 7 along a fold 7a near its center to form a mountain fold; heat sealing is performed on the thermal bonding sections 76, which are two circumferential edge sections, to form the separator into a pouch; a single unit of the negative electrode active material layer 5 and the negative electrode current collector 3 is inserted into the pouch, and then the thermal bonding sections 76 are thermally welded together to close the pouch, the separator 7 is thermally welded to the copper foil of the negative electrode current collector 3, and the thermal bonding layers 14, 15 are bonded to the bonded section 77 next to the bonded section 75 to seal the pouch more tightly. With the negative electrode 30 in such a configuration, the same effects as with the negative electrode 30 in Fig. 4. It is noted that the thermal bonding layer inserted between the separator 7 and the copper foil of the negative electrode current collector 3, and used to bond these elements, is preferably a thermal bonding layer based on acid-modified polypropylene. [Second embodiment]

[0045] Based on Fig. Section 6 now describes a protected lithium electrode structure for a lithium-air battery according to a second embodiment. It is noted that, since the second embodiment is a modification of the one described in Fig. 1 to Fig. As the first embodiment shown in section 4 is, a repetition of the explanation is omitted and only the differences are explained.

[0046] One in Fig. The protected lithium electrode 1 shown in Figure 6 has a configuration in which an opening section 4 of a solid electrolyte 8 of the protected lithium electrode is provided on both sides of the battery. In this second embodiment, the protected lithium electrode 1 has a structure in which a negative electrode active material layer 5, a trapping layer 11 for finely powdered lithium, a separator 7, a solid electrolyte, and a metal foil laminate film 2 are provided on both sides, the upper and the lower, with a negative electrode current collector 3 as a boundary.

[0047] Such a structure enables the elimination of a film 9 covering the back surface of the negative electrode current collector 3 and the metal foil laminate film 2 covering the back surface of the protected lithium electrode 1, as well as a reduction in the volumes and weights of the protected lithium electrode 1 and a lithium-air battery with the same compared to a structure in which the battery is sealed in a container, with a surface of an air electrode facing a surface of a protected lithium electrode 1.

[0048] Furthermore, in contrast to the upper cover material of the opening section 4 of the solid electrolyte 8 of the protected lithium electrode 1 (corresponding to the upper metal foil laminate film 2), the opposite side (corresponding to the lower metal foil laminate film 2) can have a structure in which the negative electrode active material layer 5 is bonded to a copper foil section of a copper foil / PET resin laminate film with a two-layer structure, and the negative electrode 30 is covered with the separator 7, which is the layer of porous resin according to this proposal. This design makes it possible to use the copper foil of the metal foil laminate film 2, which is a cover material, as the negative electrode current collector 3 and to reduce the number of parts as well as the thickness and weight of the battery. [Other embodiments]

[0049] The above descriptions of the embodiments are examples to illustrate the protected lithium electrode structure for the lithium-air battery according to the present invention and are not intended to limit the invention according to the claims. Furthermore, the design of each component of the present invention is not limited to the embodiments described above and can be modified in various ways within the technical scope described in the claims.

[0050] For example, in the embodiments described above, the trapping layer 11 for finely powdered lithium, the negative electrode active material layer 5, the negative electrode current collector 3, the solid electrolyte 8, etc., do not need to be rectangular or square. Depending on the intended use, the shape can be replaced by a round or polygonal one. Furthermore, a protected lithium electrode does not necessarily have to be provided with only one negative electrode active material layer 5, but can also be provided with more than one negative electrode active material layer 5. In addition, the protected lithium electrode does not have to be flat, but can be modified depending on the intended use. For example, the protected lithium electrode can have a three-dimensional shape.

[0051] It is noted that the trapping layer 11 for finely powdered lithium can be a layer made of the same material as that of the negative electrode current collector 3, for example, copper, stainless steel, and nickel, in a wool-like form. There is a phenomenon where, when different metals are in contact with each other, the corrosion of one of the metals (the metal with the higher ionization tendency) is generally promoted due to their differing ionization tendencies (galvanic corrosion). If, on the other hand, both are made of the same material, this has the advantage that the deterioration of the battery's quality can be delayed, since no galvanic corrosion occurs.Although bonding the trapping layer 11 for finely powdered lithium and the negative electrode current collector 3 by resistance welding, for example with a spot welding machine, is necessary to establish electrical conductivity, different metals are difficult to bond together even with such a welding device. However, if the trapping layer 11 for finely powdered lithium and the negative electrode current collector 3 are made of the same material, they are easy to bond, as the aforementioned problem is eliminated. This results in the advantage of improved productivity. [Example 1]

[0052] An example of a charging and discharging test for the lithium-air battery with a protected lithium electrode structure 1 according to the first embodiment is shown below.

[0053] First, a protected lithium electrode 1 is described (see Fig. 1 and Fig. 7), which is used in Example 1, a positive electrode and a method for producing a lithium-air battery using the same.

[0054] In this example, the metal foil laminate film 2 was used, comprising the resin layer 21 made of PP (polypropylene) resin, the metal foil layer 22 made of Al (aluminum) foil, and the resin layer 23 made of PET (polyethylene terephthalate) resin. An opening section 4 was created by punching a 2-square-centimeter hole in the central section of this metal foil laminate film 2. Next, a die-cut acid-modified polypropylene film (outer perimeter section: 3 square centimeters; inner perimeter: 2 square centimeters), a 2.5-square-centimeter solid electrolyte 8 (LATP), and another die-cut acid-modified polypropylene film (outer perimeter section: 3 square centimeters; inner perimeter: 2 square centimeters) were stacked, in that order, beneath the metal foil laminate film 2.The four sides of the solid electrolyte 8 were then heat-sealed and bound using a heat-sealing device to close the opening section 4. An adhesive bonding layer (die-cut film of acid-modified polypropylene (outer circumference: 3 square centimeters; inner circumference: 2 square centimeters)) was then inserted between each pair of layers, and the four sides of the solid electrolyte 8 were heat-sealed and bound to the metal foil laminate film 2 using a heat-sealing device.

[0055] Meanwhile, the negative electrode 30 was manufactured in a glove box under an argon atmosphere (see Fig. 3) First, a negative electrode current collector 3 (copper foil thickness: 10 µm; current collector size: 3 cm × 7 cm) was prepared, in which a film of acid-modified polypropylene was bonded to the back surface. Then, a copper wool trapping layer 11 for fine powdered lithium (processed into a layer shape with dimensions of 1.45 cm × 2 cm; fiber diameter: 0.02 mm or less and thickness: 2 mm or less) was stacked onto a surface mid-section of a 3-square-centimeter section of the tip section. The edge section on the terminal side of the negative electrode current collector 3 and one side of the fine powdered lithium trapping layer 11 were bonded with a micro-spot welder and then covered with a polypropylene resin separator 7 for a lithium-ion battery.The four sides of the edge sections were heat-sealed and bonded to a section to which polypropylene of the back surface of the negative electrode current collector 3 was bonded, and in this way the negative electrode 30 was integrally formed (. Fig. 7 and Fig. 8) It is noted that in Fig. 1 to Fig. 3 and Fig. 6 the reference numeral 12 indicates a bonded section where the trapping layer 11 for finely powdered lithium and the copper foil of the negative electrode current collector 3 are welded together, for example, with a spot welding device.

[0056] The upper metal foil laminate film 2, the negative electrode 30, and the lower metal foil laminate film 2 (without the solid electrolyte opening section 4) were stacked such that the solid electrolyte 8 and the negative electrode active material layer 5 on the negative electrode current collector 3 were positioned accordingly. Three sides of the circumferential section were then heat-sealed and bound using a heat sealer. Next, 1 ml of non-aqueous electrolyte solution (4 M (mol / l) LiFSI / EGDME) was injected into the protected lithium electrode through the remaining unbound side. Finally, after the gas was released from the interior, the remaining side of the circumferential section (connection section 32 of the negative electrode current collector 3) was bound and sealed using a heat sealer. In this way, the protected lithium electrode 1 was sealed. Fig. 3 made.

[0057] It is noted that LATP (LICGC, manufactured by OHARA INC.) was used as the solid electrolyte. Furthermore, the separator used for the lithium-ion battery was made of a polypropylene resin and had a thickness of 25 µm, a mean pore diameter of 0.03 µm or less, a porosity of 44%, and a permeability of 450 s / 100 cc.

[0058] Next, a positive electrode (not shown) was prepared. First, 0.8 g of MnO2 (specific surface area approximately 300 m²) was used. 2 / g) as a positive electrode catalyst, 0.1 g Ketjenblack (specific surface area approximately 800 m²) 2 / g) as an electrically conductive medium and 0.1 g polytetrafluoroethylene (PTFE) as a binder. These, with the addition of 5 ml ethanol as a dispersant, were mixed in an agate mortar to form a positive electrode material.

[0059] The positive electrode material was then divided into two equal sections, which were integrally bonded to both surfaces of a compression bond section made of Ti braid, with a compression bond section measuring 2.5 × 2.5 cm. 2 and a connection section of 1 × 5.5 cm 2The components were arranged and then compression-bound with a force of 20 kN. The resulting product was naturally dried for 24 hours to form a positive electrode structure. Subsequently, a lithium-air battery was constructed in which the protected lithium electrode 1 and the positive electrode were positioned opposite each other. The aqueous electrolyte solution used on the positive electrode side was a mixture of LiOH and LiCl. An aqueous electrolyte solution was prepared in which 1.5 M (mol / l) aqueous LiOH solution and 10 M (mol / l) aqueous LiCl solution were mixed in a 1:1 ratio, resulting in a pH of 10 or less. It is noted that, to retain the aqueous electrolyte solution, 1.5 mL of the solution was placed on the 3 cm² polyacrylamide layer and positioned between the protected lithium electrode 1 and the positive electrode.

[0060] Fig. 9 and Fig. 10 represent a negative electrode 30, which is used for performance comparisons with the one in Fig. 7 and Fig. The negative electrode 30 shown in Figure 8 was used. Fig. 9 is a top view, and Fig. Figure 10 is a bottom view of the negative electrode 30. With reference to the in Fig. 9 and Fig. The negative electrodes shown in Figure 10 and Figure 30 are the elements with the same functions as in Figure 30. Fig. 7 and Fig. 8 are marked with the same reference symbols, and a repeated explanation is omitted. The in Fig. 9 and Fig. The negative electrode 30 shown in Figure 10 differs from the negative electrode 30 in Fig. 7 and Fig. 8 only in that it does not have the capture layer 11 for finely powdered lithium.

[0061] Next, a charging and discharging test is described in Example 1.

[0062] First, the lithium-air battery, constructed as described above, was charged for five hours at 4 mA (corresponding to a current density of 2 mA / cm²). 2 (with reference to the area of ​​the copper wool), in order to achieve an adaptation to a capacity of the negative electrode corresponding to 20 mAh. Fig. Figure 11 represents a result of the voltage change at a temperature of 25°C when charging and discharging were repeated for one hour at 4 mA (corresponding to a current density of 2 mA / cm²). 2 (with reference to the area of ​​the copper wool), the same value as above, which was measured with an HJ1001SD8 manufactured by Hokuto Denko Corporation. Accordingly, in the Fig. 9 and Fig. In the comparative example 10, the unloading was stopped at the fifteenth cycle, whereas the charging and unloading continued at the point shown in Fig. 7 and Fig.Example 1, as shown in Figure 8, continued for 56 cycles, which means that the charging and discharging cycle characteristics were improved. [List of reference symbols] 1 protected lithium electrode 2 Metal foil laminate film 3 negative electrode current collector 4 Opening section 5 negative electrode active material layer 7 Separator 8 Solid electrolyte 9 Film 10 Heat sealing material (thermal bonding layer) 11. Capture layer for finely powdered lithium 12 bound section 13 Heat sealing material (thermal bonding layer) 14 Heat sealing material (thermal bonding layer) 21 Resin layer 22 Metal foil layer 23 Resin layer 24 resin layers 30 negative electrode 31 Electron collection section 32 Connection section 73 bound section 74 unbound section 75 bound section 76 Thermal bonding section 77 bound section

Claims

[1] Protected lithium electrode structure (1) for a lithium-air battery, comprising: a negative electrode current collector (3); a negative electrode active material layer (5) made of a lithium metal, a mainly lithium-containing alloy or a mainly lithium-containing compound, and stacked on the negative electrode current collector (3); and a separator (7) which is stacked on the negative electrode active material layer (5), wherein the negative electrode active material layer (5) is sealed by connecting the separator (7) and the negative electrode current collector (3) around the negative electrode active material layer (5), the separator (7) being bonded to the negative electrode current collector (3) at a circumferential edge section of the separator (7), and the negative electrode active material layer (5) being stacked onto a surface of the negative electrode current collector (3) to cover an area smaller than the area of ​​the negative electrode current collector (3), and a trapping layer (11) for finely powdered lithium, which is arranged between the negative electrode active material layer (5) and the separator (7) and has electrical conductivity via a bond on one side of the trapping layer (11) for finely powdered lithium, wherein the trapping layer (11) for finely powdered lithium is a conductive foam or a structure made of metal fiber and traps finely powdered lithium metal that is generated during charging and discharging. [2] Protected lithium electrode structure (1) for a lithium-air battery according to claim 1, wherein the trapping layer (11) for finely powdered lithium is made of the same material as that of the negative electrode current collector (3). [3] Protected lithium electrode structure (1) for a lithium-air battery according to claim 1, wherein the metal fiber structure is a wool-like or felt-like structure or fabric. [4] Protected lithium electrode structure (1) for a lithium-air battery according to any one of claims 1 to 3, wherein the negative electrode current collector (3) is foil- or plate-shaped, the negative electrode active material layer (5) is arranged on a surface of the negative electrode current collector (3) and another surface of the negative electrode current collector (3) is covered with a substance that is non-conducting to lithium ions.

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