JP3699786B2 - Air lithium secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air lithium secondary battery that uses oxygen as a positive electrode active material, a solid electrolyte as an electrolyte, and a carbonaceous material that absorbs and releases lithium ions as a negative electrode.
[0002]
[Prior art]
In recent years, nonaqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries. For example, primary batteries using manganese dioxide (MnO ₂ ), fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl ₂ ), etc. as positive electrode active materials have already been used as backup batteries for calculators, watches, and memories. It is used a lot.
[0003]
Furthermore, in recent years, with the reduction in size and weight of various electronic devices such as VTRs and communication devices, there is an increasing demand for secondary batteries with high energy density as their power source. In response to such demands, research on lithium secondary batteries using lithium as a negative electrode active material has been actively conducted.
[0004]
As such a lithium secondary battery, J. Org. Electrochem. Soc. , Vol. 143, no. 1, January 1996 discloses an air lithium secondary battery having a configuration as described below.
[0005]
That is, the air lithium secondary battery is obtained by press-bonding an acetylene black layer containing a cobalt catalyst and a polymer electrolyte film made of polyacrylonitrile, ethylene carbonate, propylene carbonate and LiPF ₆ to a nickel net or an aluminum net. A positive electrode, a negative electrode made of lithium foil, a polymer electrolyte membrane interposed between the positive electrode and the negative electrode, and an oxygen permeable membrane laminated on the positive electrode. It has a structure enclosed in a plastic bag covered with. An air hole is opened on the positive electrode side surface of the plastic bag.
[0006]
However, in such an air lithium secondary battery, since the negative electrode is made of metallic lithium, the negative electrode is deteriorated by moisture taken into the bag through the air hole. In addition, when charging / discharging is repeated on the surface of the negative electrode, lithium is deposited in a dendritic (dendritic) or small spherical shape, penetrating the polymer electrolyte membrane and contacting the positive electrode to cause an internal short circuit. Therefore, the air lithium secondary battery has a problem that the charge / discharge cycle life is short.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide an air lithium secondary battery with greatly improved battery capacity and charge / discharge cycle life.
[0008]
[Means for Solving the Problems]
An air lithium secondary battery according to the present invention includes a container in which an air hole is opened,
A positive electrode that is housed in the container and includes a solid electrolyte and an activated carbon fiber having a specific surface area of 100 m ² / g or more by a BET method ;
A negative electrode containing a carbonaceous material stored in the container and occluding and releasing lithium ions;
A solid electrolyte layer interposed between the positive electrode and the negative electrode in the container;
An oxygen permeable membrane is provided between the surface of the container where the air holes are opened and the positive electrode.
[0009]
The positive electrode preferably contains a solid electrolyte and a carbonaceous material having a specific surface area of 100 m ² / g or more by the BET method.
The carbonaceous material of the positive electrode is preferably activated carbon fiber.
The carbonaceous material of the negative electrode is preferably mesophase pitch-based carbon fiber.
Another air lithium secondary battery according to the present invention includes a container having an air hole,
A positive electrode contained in the container and containing a solid electrolyte and a carbonaceous material having a specific surface area of 100 m ² / g or more by the BET method;
A negative electrode containing a carbonaceous material stored in the container and occluding and releasing lithium ions;
A solid electrolyte layer interposed between the positive electrode and the negative electrode in the container;
An oxygen permeable membrane is provided between the surface of the container where the air holes are opened and the positive electrode.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an air lithium secondary battery according to the present invention will be described with reference to FIG.
Two positive electrodes 1 and one negative electrode 2 are alternately stacked with a solid electrolyte layer 3 interposed therebetween. The positive electrode 1 is located outside the laminate composed of the positive electrode 1, the negative electrode 2, and the solid electrolyte layer 3. Two oxygen permeable membranes 4 are laminated on the positive electrode 1. Such a seven-layer laminate is housed in a plastic sheet-like container 5 having a plurality of air holes (not shown) on both sides. The positive electrode terminal 6 has one end connected to each positive electrode 1 and the other end protruding from the container 5. The negative electrode terminal 7 has one end connected to the negative electrode 2 and the other end protruding from the container 5.
[0011]
The solid electrolyte layer 3, the positive electrode 1, the negative electrode 2, and the oxygen permeable membrane 4 will be described.
1) Solid electrolyte layer 3
As the solid electrolyte layer 3, a film containing a polymer material in which a lithium salt is dissolved can be used.
[0012]
Examples of the polymer material include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and the like.
[0013]
Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and bistrifluoromethyl. Examples include sulfonylimidolithium {LiN (CF ₃ SO ₂ ) ₂ }.
[0014]
It is preferable to add an organic solvent to the solid electrolyte layer 3 in order to improve ionic conductivity. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butyrolactone (BL), fluorine-containing carbonates, chain carbonates, and the like. These organic solvents may be used alone or in combination of two or more. In particular, it is preferable to use a solid electrolyte layer made of a film containing polyvinylidene fluoride (PVDF) in which LiPF ₆ , EC and PC are dissolved. Such a solid electrolyte layer can increase the ionic conductivity of lithium ions, and can prevent diffusion of oxygen and moisture into the negative electrode. A secondary battery can be provided.
[0015]
2) Positive electrode 1
The positive electrode 1 is used for oxidizing and reducing oxygen. The positive electrode 1 preferably includes a solid electrolyte and a carbonaceous material having a specific surface area of 100 m ² / g or more by the BET method. The BET method is based on nitrogen gas adsorption.
[0016]
The positive electrode 1 is made, for example, by preparing a film containing a solid electrolyte, a carbonaceous material having a specific surface area of 100 m ² / g or more by BET method, lithium peroxide (Li ₂ O ₂ ), and a binder. It can be manufactured by rolling and drying.
[0017]
Examples of the solid electrolyte include a polymer material in which a lithium salt is dissolved. As the lithium salt and the polymer material, the same materials as those described for the solid electrolyte layer can be used.
[0018]
Examples of the carbonaceous material include activated carbon fiber, activated carbon, carbon black, acetylene black, furnace black, and charcoal.
The reason why the specific surface area of the carbonaceous material by the BET method is limited to the above range is as follows. If the specific surface area is less than 100 m ² / g, the reaction area of the positive electrode may be insufficient, and the discharge capacity and cycle life of the secondary battery may be reduced. The upper limit of the specific surface area is preferably 5000 m ² / g. If the specific surface area exceeds 5000 m ² / g, the positive electrode volume may increase and the thickness of the positive electrode may increase significantly. A more preferable specific surface area is in the range of 1000 to 3000 m ² / g.
[0019]
Among the carbonaceous materials, activated carbon fibers are preferable. Since this activated carbon fiber has a high specific surface area, high conductivity, and high filling properties, it is possible to dramatically improve the discharge capacity and cycle characteristics of the secondary battery. More preferable activated carbon fibers are those having a specific surface area of 1000 to 3000 m ² / g by BET method and a pore volume of 0.1 to ³ cm ³ / g. This activated carbon fiber can be synthesized by, for example, insolubilizing and activating a spun polyacrylonitrile fiber or pitch-based carbon fiber, and then firing at 600 ° C. or higher.
[0020]
A catalyst is preferably added to a carbonaceous material having a specific surface area of 100 m ² / g or more by the BET method in order to efficiently perform redox decomposition of oxygen or oxygen ions.
The charge / discharge efficiency of the positive electrode can be improved by adding a catalyst. As such a catalyst, for example, a platinum-based, cobalt-based, nickel-based, iron-based, tungsten-based catalyst having a function of reducing oxygen generation overvoltage can be used.
[0021]
As the current collector, it is preferable to use a porous (mesh, mesh) metal plate in order to allow oxygen to diffuse quickly. Examples of the metal include stainless steel, nickel, aluminum, and iron. The current collector may be coated with an oxidation-resistant metal or alloy on the surface in order to suppress oxidation.
[0022]
Examples of the binder include polyvinylidene fluoride (PVDF).
In the positive electrode, lithium oxide (Li ₂ O) can be added to the film instead of the lithium peroxide (Li ₂ O ₂ ).
[0023]
3) Negative electrode 2
The negative electrode 2 includes a carbonaceous material that occludes and releases lithium ions.
The negative electrode 2 can be manufactured, for example, by dispersing the carbonaceous material, solid electrolyte, and binder in a solvent, preparing a slurry, applying the slurry to a current collector, drying, and pressing. it can.
[0024]
Examples of the carbonaceous material include graphite, coke, mesophase pitch carbon fiber, spherical carbon, and resin-fired carbon. Among them, it is preferable to use mesophase pitch-based carbon fibers. Since this mesophase pitch-based carbon fiber has a radial orientation of the graphite crystallites in the cross section of the fiber, it can quickly occlude lithium ions from the solid electrolyte layer, which can greatly improve cycle life. it can.
[0025]
The carbonaceous material may preferably be in the range of 0.3354nm~0.344nm surface spacing d ₀₀₂ of (002) plane.
The specific surface area of the carbonaceous material is preferably in the range of 0.5 to ⁵ m ² / g in terms of the specific surface area of the BET method using nitrogen gas.
[0026]
Examples of the solid electrolyte include a polymer material in which a lithium salt is dissolved. As the lithium salt and the polymer material, the same materials as those described for the solid electrolyte layer can be used.
[0027]
Examples of the solvent include organic solvents such as n-methyl-2-pyrrolidone.
Examples of the binder include polyvinylidene fluoride (PVDF).
[0028]
Examples of the current collector include copper foil.
4) Oxygen permeable membrane 4
As the oxygen permeable membrane 4, a water-repellent porous membrane having a function of allowing oxygen in the air to permeate and preventing water from entering can be used.
[0029]
The air lithium secondary battery having such a configuration uses a carbonaceous material that uses oxygen gas in the air as a positive electrode active material and occludes and releases lithium ions in the negative electrode. In this secondary battery, during discharge, lithium ions are occluded in the positive electrode, and oxygen gas in the air is taken into the positive electrode through the oxygen permeable membrane, and the oxygen gas is reduced by the carbonaceous material of the positive electrode. As a result, a lithium peroxide (Li ₂ O ₂ ) or lithium oxide (Li ₂ O) discharge product is generated on the surface of the carbonaceous material. On the other hand, at the time of charging, the discharge product is oxidized on the surface of the carbonaceous material, oxygen gas is released from the positive electrode through the oxygen permeable film, and lithium ions are released.
[0030]
When the secondary battery is used from the discharge reaction after assembling, the secondary battery is not manufactured by the method described above as the positive electrode and the negative electrode, but uses the positive electrode and the negative electrode manufactured by the method described below.
[0031]
That is, as the positive electrode, one produced by the same method as described above is used except that lithium peroxide or lithium oxide is not added to the film. On the other hand, as the negative electrode, a slurry prepared, applied to a current collector, dried and pressed in the same manner as described above, and then subjected to a treatment for occluding lithium ions is used. In addition, you may perform the process which occludes lithium ion after a secondary battery assembly.
[0032]
The air lithium secondary battery according to the present invention described above includes a positive electrode that oxidizes and reduces oxygen, a negative electrode that includes a carbonaceous material that absorbs and releases lithium ions, and a solid electrolyte layer that is interposed between the positive electrode and the negative electrode. And an oxygen permeable membrane. Since such a secondary battery includes a negative electrode containing a carbonaceous material that occludes and releases lithium ions, it is possible to suppress or avoid deterioration of the negative electrode due to moisture mixed in the container, and charge and discharge cycles. It is possible to prevent metallic lithium from being deposited on the negative electrode surface as it progresses. As a result, an air lithium secondary battery with improved discharge capacity and cycle life can be provided.
[0033]
Furthermore, since the positive electrode of the secondary battery includes a solid electrolyte and a carbonaceous material having a specific surface area of 100 m ² / g or more according to the BET method, the reaction area of the positive electrode can be increased. The discharge capacity and cycle life of the battery can be further improved. By making the carbonaceous material into activated carbon fiber, the positive electrode can improve the ionic conductivity of lithium ions and can increase the specific surface area, so that the resistance when occluding and releasing lithium ions is reduced. Can be reduced. Moreover, since the said positive electrode can reduce a bulk density, it can improve a volume specific capacity. Therefore, the secondary battery including the positive electrode can dramatically improve the discharge capacity and the cycle life.
[0034]
Further, by making the carbonaceous material of the negative electrode of the secondary battery into mesophase pitch-based carbon fiber, the carbon fiber has a radial orientation of the graphite crystallites in its cross section, so the lithium ion occlusion / release rate of the negative electrode is increased. The cycle life of the secondary battery can be greatly improved.
[0035]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Example 1)
<Production of negative electrode>
Graphitized mesophase pitch-based carbon fiber fired at 3000 ° C., slurry containing 5% by weight of PVDF, LiN (CF ₃ SO ₂ ) ₂ and n-methyl-2-pyrrolidone mixed with the carbon fiber Then, the slurry was applied to a copper foil, dried, and pressed to prepare a negative electrode having a density of 1.3 g / cm ³ .
[0036]
<Preparation of positive electrode>
The activated carbon fiber having a specific surface area of 2000 m ² / g by nitrogen gas and a cobalt catalyst added thereto, Li ₂ O ₂ , PVDF and LiN (CF ₃ SO ₂ ) ₂ are mixed with the activated carbon fiber and the Li ₂ O. _After mixing at a blending ratio of ₂ to 20%: 40% and forming into a film shape, this was rolled into a stainless mesh and dried to produce a positive electrode.
[0037]
<Preparation of solid electrolyte layer>
A solid electrolyte layer having a thickness of 30 μm was prepared by dissolving 80% by weight of PVDF in 20% by weight of LiN (CF ₃ SO ₂ ) ₂ and forming it into a film.
[0038]
Two pieces of the positive electrode and one piece of the negative electrode are alternately stacked so that the solid electrolyte layer is interposed therebetween and the positive electrode is positioned on the outer side, and two sheets of oxygen are formed on the outer surface of the obtained five-layer laminate. Each of the permeable membranes is placed, heated and rolled, and then sealed in a plastic sealing material having a plurality of air holes on both sides, thereby having a thickness of 200 μm and a size of 2 cm × 2 cm as described above. The film-like air lithium secondary battery shown in 1 was produced.
(Example 2)
An air lithium secondary battery similar to Example 1 was assembled except that carbon black having a BET specific surface area of 2000 m ² / g was used as the carbonaceous material for the positive electrode.
(Example 3)
A solid electrolyte layer having a thickness of 30 μm is prepared by dissolving 20% by weight of LiN (CF ₃ SO ₂ ) ₂ and 20% by weight of a mixed organic solvent composed of EC and PC in 60% by weight of PVDF and forming into a film shape. Except for this, an air lithium secondary battery similar to that of Example 1 was assembled.
(Example 4)
An air lithium secondary battery similar to that in Example 3 was assembled except that natural graphite was used as the carbonaceous material for the negative electrode.
(Example 5)
An air lithium secondary battery similar to that of Example 3 was assembled except that a non-graphitizable carbonaceous material obtained by firing a phenol resin at 1100 ° C. was used as the carbonaceous material of the negative electrode.
(Comparative Example 1)
Lithium metal foil is used as the negative electrode, and a cobalt black is added to carbon black having a specific surface area of 50 m ² / g by nitrogen gas, Li ₂ O ₂ , PVDF and LiN (CF ₃ SO ₂ ) ₂ The carbon black and the Li ₂ O ₂ are mixed at a blending ratio of 20%: 40%, formed into a film, rolled into a stainless mesh, and dried to produce a positive electrode. Except for this, an air lithium secondary battery similar to that of Example 3 was assembled.
(Comparative Example 2)
Lithium metal foil is used as the negative electrode, and a cobalt catalyst is added to activated carbon having a specific surface area of 50 m ² / g in a BET method using nitrogen gas, Li ₂ O ₂ , PVDF, and LiN (CF ₃ SO ₂ ) ₂ Except for preparing the positive electrode by mixing the activated carbon and the Li ₂ O _{2 at} a blending ratio of 20%: 40%, forming into a film, rolling it into a stainless mesh, and drying it. Assembled the same air lithium secondary battery as in Example 3.
[0039]
About the obtained air lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2, after charging to 4.1 V at a current density of 0.5 mA / cm ² , charging and discharging to 2 V were repeated, The discharge capacity was measured for each cycle, and the results are shown in FIG.
[0040]
As is clear from FIG. 2, the secondary batteries of Examples 1 to 5 including the negative electrode including the carbonaceous material that occludes and releases lithium ions are the secondary batteries of Comparative Examples 1 and 2 including the negative electrode made of lithium metal foil. It can be seen that the charge / discharge cycle life is longer than that shown in FIG.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, an air lithium secondary battery with improved discharge capacity and cycle life can be provided.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing an air lithium secondary battery according to the present invention.
FIG. 2 is a characteristic diagram showing the relationship between the number of cycles and discharge capacity in the air lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Solid electrolyte layer, 4 ... Oxygen permeable film, 5 ... Container, 6 ... Positive electrode terminal, 7 ... Negative electrode terminal.

Claims (4)

A container with an open air hole;
A positive electrode that is housed in the container and includes a solid electrolyte and an activated carbon fiber having a specific surface area of 100 m ² / g or more by a BET method ;
A negative electrode containing a carbonaceous material stored in the container and occluding and releasing lithium ions;
A solid electrolyte layer interposed between the positive electrode and the negative electrode in the container;
An air lithium secondary battery comprising: an oxygen permeable membrane disposed between a surface of the container in which the air holes are opened and the positive electrode. The air lithium secondary battery according to claim 1, wherein the carbonaceous material of the negative electrode is mesophase pitch-based carbon fiber . 3. The air lithium secondary battery according to claim 1, wherein a specific surface area of the activated carbon fiber by a BET method is 100 m ² / g or more and 5000 m ² / g or less . The air lithium secondary battery according to claim 1, wherein the positive electrode contains lithium peroxide or lithium oxide .

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