JP2019087374A - Lithium air secondary battery - Google Patents

Abstract

To provide a lithium air secondary battery that can realize practical discharge capacity by using an inexpensive carbon material.SOLUTION: A lithium air secondary battery 100 having an air electrode 101 which is a positive electrode using oxygen in air as a positive electrode active material, a negative electrode 102 using metal lithium or a lithium-containing material as a negative electrode active material, and an organic electrolyte containing a lithium salt. The air electrode 101 is obtained by filling a carbon-coated foam metal sheet with a sintered air electrode reaction layer by mixing carbon powder and binder powder, and drying the carbon-coated foam metal sheet.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium air secondary battery using oxygen as a positive electrode active material.

  In a lithium air battery using oxygen in air as a positive electrode active material, oxygen is always supplied from the outside of the battery, and a large amount of negative electrode active material metal lithium can be filled in the battery. For this reason, it is known that the value of the discharge capacity per unit volume of a battery can be enlarged. So far, it has been disclosed in Non-Patent Document 1 that 70 charge / discharge cycles are possible at a discharge capacity per weight of 1000 mAh / g using PtCo alloy / carbon nanotubes as an air electrode material.

  In addition, Non-Patent Document 2 discloses a lithium air secondary battery capable of performing 400 charge / discharge cycles with a discharge capacity of 1000 mAh / g using PdFe alloy / nitrogen-doped graphene oxide as an air electrode material. ing.

Byung Gon Kim, Hyung-Jin Kim, Seoin Back, Kwan Woo Nam, Yousung Jung, Young-Kyu Han, Jang Wook Choi, “Improved reversal in lithium-oxygen battery: Understanding elementary reactions and surface charge engineering of metal alloy catalyst”, Scientific Reports, 4: 4225, DOI: 10.1038 (2014). Limin Leng, Jing Li, Xiaoyuan Zeng, Huiyu Song, Ting Shu, Haishui Wang, Shijun Liao. ”Enhancing the cyclability of Li-O2 batteries using PdM alloy nanoparticles anchored on nitrogen-doped reduced spectra as the cathode catalyst Sources, Vol. 337, pp. 173-179 (2017).

However, the discharge capacity of the lithium-air secondary battery disclosed in Non-Patent Documents 1 and 2, respectively, 0.6mAh / cm ^2, a 0.2 mAh / cm ² or so, per positive electrode area of general lithium ion battery There is a problem that it is very small compared to the discharge capacity (2 to 5 mAh / cm ² ).

  The present invention has been made in view of this problem, and an object of the present invention is to provide a lithium air secondary battery that can realize a practical discharge capacity per electrode area using an inexpensive carbon material.

  The lithium-air secondary battery according to one aspect of the present embodiment includes an air electrode which is a positive electrode using oxygen in air as a positive electrode active material, a negative electrode using metal lithium or a lithium-containing material as a negative electrode active material, and a lithium salt. In the lithium-air secondary battery having an organic electrolyte containing, the air electrode is filled with a carbon-coated foam metal sheet, a carbon powder and a binder powder are mixed to form a slurry, and the air electrode reaction layer is filled and dried. The summary is that

  According to the present invention, it is possible to provide a lithium-air secondary battery that can realize a practical discharge capacity per electrode area using an inexpensive carbon material.

FIG. 1 is a view showing a basic configuration of a lithium air secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a more detailed configuration example of the lithium-air secondary battery according to the embodiment of the present invention. It is a schematic diagram which shows the structure of an air electrode simply. It is a figure which shows the first time discharge curve of Experimental example 1 and the comparative example 1 provided with the air electrode shown in FIG.

  Hereinafter, embodiments of the present invention will be described using the drawings.

[Outline of lithium air secondary battery]
FIG. 1 is a basic configuration diagram of a lithium air secondary battery according to the present embodiment. As shown in the figure, the lithium-air secondary battery 100 includes an air electrode 101, a negative electrode 102 configured to contain lithium, and an organic electrolyte solution 103 disposed between the air electrode 101 and the negative electrode 102. Prepare. The air electrode 101 functions as a positive electrode.

  The cathode 101 can include a catalyst, a conductive material, and a support as components. The negative electrode 102 can be made of a substance such as lithium-containing alloy capable of releasing and absorbing metallic lithium or lithium ions.

  Hereinafter, each component of the lithium air secondary battery 100 of the present embodiment will be described. In addition, an electrolyte solution means the case where an electrolyte is a liquid form here.

(I) Air electrode The air electrode 101 of this embodiment contains at least a catalyst, a conductive material, and a support, and optionally contains an additive such as a binder.

(I-1) Catalyst In the lithium-air secondary battery 100 of this embodiment, an oxide containing at least one metal of Cr, Mn, Fe, Co, and Ni as a catalyst in the air electrode 101, or Pt, It is required that the material contains at least one metal of Ru and Ir, and more preferably, a material containing at least Pt and Ru.

  In the air electrode 101 of the lithium air secondary battery 100, an electrode reaction proceeds in the three-phase portion of the electrolyte solution / electrode catalyst / gas (oxygen). That is, the organic electrolyte solution 103 penetrates into the air electrode 101, and oxygen gas in the air is simultaneously supplied to form a three-phase portion in which the electrolyte solution-electrode catalyst-gas (oxygen) coexist. If the electrode catalyst has high activity, oxygen reduction (discharge) and oxygen generation (charge) proceed smoothly, and battery performance is greatly improved.

  The discharge reaction at the cathode 101 can be expressed as follows.

2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (1)
The lithium ion (Li ⁺ ) in the formula (1) is dissolved in the organic electrolyte solution 103 from the negative electrode 102 by electrochemical oxidation, and moves in the organic electrolyte solution 103 to the surface of the air electrode 101. Further, oxygen (O ₂ ) is taken into the air electrode 101 from the atmosphere (air). Note that a material (Li ⁺ ) dissolved from the negative electrode 102, a material (Li ₂ O ₂ ) deposited at the air electrode 101, and air (O ₂ ) are shown together with the components in FIG.

  Since the catalyst used in the present embodiment has a strong interaction with oxygen which is a positive electrode active material, many oxygen species can be adsorbed on the material surface, and the electrode reaction of the air electrode 101 can be activated.

  Thus, oxygen species adsorbed on the oxide surface or occluded in oxygen vacancies are used in the oxygen reduction reaction as an oxygen source (active intermediate reactant) of the formula (1), Will go forward easily. Moreover, the above-mentioned material has activity also to the charge reaction which is a reverse reaction of Formula (1). Therefore, the charge of the battery, that is, the oxygen generation reaction on the air electrode 101 also proceeds efficiently.

  In the lithium-air secondary battery 100 of the present embodiment, reaction sites (the above-mentioned electrolyte solution / electrode catalyst (or conductive material) / air (oxygen) three-phase portion) causing an electrode reaction to increase the efficiency of the battery It is desirable that there be more From this point of view, in the present embodiment, it is important that the above-described three-phase site be present in a large amount on the surface of the electrode catalyst, and the catalyst used preferably has a high specific surface area.

  The catalyst used in the present embodiment can be synthesized by various known methods. For example, although known processes such as a solid phase method and a liquid phase method can be used for the synthesis method, it is more preferable to use a wet method in which particles of high specific surface area can be obtained.

  In the lithium-air secondary battery according to the present embodiment, the catalyst content in the air electrode is desirably, for example, more than 5 and 60% by weight or less. The proportions of the other components are the same as in the conventional lithium air secondary battery.

(I-2) Carbon Material The conductive material contained in the air electrode 101 of the present embodiment is preferably carbon. In particular, examples of the conductive material of the present embodiment include, but are not limited to, carbon blacks such as ketjen black and acetylene black, activated carbons, graphites, and the like. Also, these carbons can be obtained, for example, as commercial products or by synthesis. Similar to the catalyst of (I-1), it is desirable that more reaction sites (the above-mentioned electrolyte solution / carbon material / air (oxygen) three-phase part) causing the electrode reaction be present. From such a point of view, it is preferable that the carbon material to be used has a high specific surface area, and the value of the BET specific surface area is preferably 1000 m ² / g or more. More desirably, inexpensive carbon blacks may be used.

(I-3) Binder (Binder)
The air electrode 101 can contain a binder. The binder is for adhering the electrode active material to the electrode.

  The binder is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and polybutadiene rubber. These binders can be used as powders or as dispersions.

(I-4) Support As an air electrode support, it is essential that it has conductivity, has a structure capable of holding carbon and a catalyst, and has air permeability. In addition, it is desirable that the air battery does not have corrosiveness in a working atmosphere (in an organic electrolyte) or a working condition (high voltage of about 2 V) of the air battery, and has shape stability.

  Specifically, a porous (approximately 80% or more porosity) foamed metal sheet having a large amount of pores inside the metal can be used. The metal material is preferably titanium or nickel having high stability under the above conditions, and the porosity of the foam metal sheet is in the range of 90 to 97% where the retention of the electrode material and the permeability of air are good. Is desirable.

  In the present embodiment, a large discharge capacity of the battery can be realized particularly by using a foam metal sheet mainly composed of nickel. Furthermore, higher battery performance can be realized when the foam metal sheet is coated with carbon and the carbon coating amount is 0.1 to 2 wt% with respect to the weight of the foam metal sheet.

  As a carbon coating method, a foam metal sheet is impregnated with a solution in which alcohol such as methanol or organic substance such as sucrose is dissolved, the solvent is removed by drying or evaporation to dryness, and heat treatment is performed in an inert gas atmosphere. Can be used.

(I-5) Method of Producing Air Electrode The air electrode 101 can be prepared as follows.

  First, an air electrode reaction layer powder mixed with a catalyst powder, a carbon powder and a binder powder such as polyvinylidene fluoride (PVDF) is mixed with an N-methyl-2-pyrrolidone solvent at a predetermined ratio to prepare a slurry (a slurry). . The slurryed air electrode reaction layer is dropped in the form of a metal foam sheet, and the metal spatula is kneaded while applying a certain amount of force so that the slurry penetrates into the sheet. Thereafter, drying and weight measurement are performed to measure the filling amount. The carbon loading is adjusted by repeating this procedure as necessary.

(II) Negative Electrode In the lithium air secondary battery 100 of the present embodiment, the negative electrode 102 contains a negative electrode active material. The negative electrode active material is not particularly limited as long as it is a material that can be used as a negative electrode material of a lithium secondary battery. For example, metallic lithium can be mentioned. Alternatively, as the lithium-containing substance, lithium and an alloy of silicon or tin, which is a substance capable of releasing and occluding lithium ions, or lithium nitride such as Li _2.6 Co _0.4 N are exemplified. be able to.

  In the case of using the above-described alloy of silicon or tin as the negative electrode, silicon or tin containing no lithium can be used at the time of synthesizing the negative electrode. However, in this case, silicon or silicon may be chemically or electrochemically (e.g., a method of alloying lithium and silicon or tin in an electrochemical cell) prior to fabrication of the air battery. The tin needs to be treated to be in a state of containing lithium. Specifically, it is preferable to use silicon or tin as a working electrode, use lithium as a counter electrode, and perform processing such as performing alloying by supplying a reduction current in an organic electrolytic solution.

  For example, in the case of using lithium metal as the negative electrode, the negative electrode 102 of the lithium-air secondary battery 100 may be manufactured by stacking a plurality of metal lithium foils and forming the same into a predetermined shape.

  Here, the reaction of the negative electrode (metallic lithium) at the time of discharge can be expressed as follows.

(Discharge reaction) Li → Li ⁺ + e ⁻ (2)
In addition, in the negative electrode at the time of charge, the precipitation reaction of lithium which is a reverse reaction of Formula (2) occurs.

(III) Electrolyte As the organic electrolyte 103, any non-aqueous solvent in which a metal salt containing lithium ion (lithium salt) is dissolved may be used as long as it is a substance capable of lithium ion transfer between the positive and negative electrodes, As a solute, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethanesulfonylimide [(CF ₃ SO ₂ ) ₂ N Li] (LiTFSI), etc. can be used, and as a solvent Are, for example, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), diethyl carbonate (DEC), ethyl propyl carbonate (EPC), Ethyl isopropyl carbonate (EIPC), Ethyl butyl carbonate (EBC), Dicarbonate Carbonic ester solvents such as pill (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), and 1,2-butylene carbonate (1,2-BC), 1 Ether solvents such as 2-dimethoxyethane (DME), lactone solvents such as γ-butyrolactone (GBL), glyme solvents such as tetraethylene glycol dimethyl ether (TEGDME), sulfoxide solvents such as dimethyl sulfoxide (DMSO) or the like The solvent which mixed two or more types among them can be mentioned, The mixing ratio in the case of using a mixed solvent is not particularly limited.

  In addition to the above-mentioned organic electrolytic solution, it is also possible to use a solid electrolyte having lithium ion conductivity, a polymer electrolyte, an ionic liquid in which a lithium metal salt is dissolved, and the like.

(IV) Other Elements In addition to the above components, the lithium air secondary battery 100 of the present embodiment includes a separator, a structural member such as a battery case, and other elements required for the lithium air secondary battery. As these elements, conventional ones can be used.

[Configuration of lithium air secondary battery]
Next, the configuration of the lithium air secondary battery 100 of the present embodiment will be described.

  FIG. 2 is a cross-sectional view showing a more detailed configuration example of the lithium air secondary battery 100 of the present embodiment.

  The lithium air secondary battery 100 shown in FIG. 2 is a cylindrical lithium air battery, and includes an air electrode 101, a negative electrode 102, an organic electrolyte solution 103, a separator 105, an air electrode support 115, an air electrode fixing ring 104, and a negative electrode. The fixing ring 107, the negative electrode fixing washer 108, the negative electrode support 109, the fixing screw 110, the O-ring 111, the air electrode terminal 121, and the negative electrode terminal 122 are provided.

  The air electrode 101, the negative electrode 102, the organic electrolyte solution 103, and the separator 105 are accommodated in a cylindrical air electrode support 115. The air electrode support 115 has a partition 151 at the center in the cylinder, and is divided by the partition 151 into a first region 105 a where the air electrode 101 is disposed, and a second region 105 b where the anode 102 and the separator 105 are disposed. ing. Further, the partition 151 is open at the central portion, and the first region 105a and the second region 105b are in communication with each other by the opening.

  The organic electrolyte solution 103 is disposed at the opening of the partition 151, and is sandwiched between the air electrode 101 and the separator 105. The organic electrolytic solution 103 is impregnated in the separator 105. The organic electrolytic solution 103 is also present around the separator 105.

  The air electrode 101 is sandwiched and fixed between an air electrode fixing ring 104 made of polytetrafluoroethylene (PTFE) and a partition 151.

  The separator 105 is sandwiched and fixed between a cylindrical negative electrode fixing ring 107 and a partition 151 made of PTFE.

  A negative electrode fixing washer 108 is stacked on the negative electrode 102 and is in contact with the separator 105 inside the cylinder of the negative electrode fixing ring 107.

  The negative electrode fixing washer 108 is covered with a negative electrode support 109 made of metal. The negative electrode support 109 is fixed to the air electrode support 115 by a fixing screw 110. An O-ring 111 is disposed between the air electrode support 115 and the negative electrode support 109. The fixing screw 110 is coated with PTFE so that the air electrode support 115 and the negative electrode support 109 are electrically separated.

  The negative electrode support 109 is pressed to the air electrode support 115 by the fixing screw 110. The negative electrode 102 is pressed through the negative electrode fixing washer 108 and pressed against the separator 105.

  The air electrode 101 is disposed to be conductive to the air electrode support 115, and the negative electrode terminal 122 is disposed to be conductive to the negative electrode support 109.

[Production procedure of lithium air secondary battery]
Then, the preparation procedure of the lithium air secondary battery 100 shown in FIG. 2 is demonstrated.

  The lithium-air battery cell is fabricated in dry air having a dew point of -55 ° C. or less according to the following procedure.

(Air electrode preparation method)
The air electrode 101 is manufactured by the procedure described in the method of manufacturing the (I-5) air electrode. The manufacturing method of the air electrode 101 of a specific experiment example is shown next.

[Experimental Example 1]
FIG. 3 is a schematic view showing the structure of the air electrode 101 of Experimental Example 1 in a simplified manner.

  First, impregnate foamed nickel (for example, 0.6 mm in thickness, 1 cm in diameter, manufactured by Magx Co., Ltd., with a porosity of 96%) 10 into 300 ml of a sucrose aqueous solution (for example, concentration: 50 wt%) Was completely removed. Thereafter, heat treatment was performed at 800 ° C. for 5 hours in argon.

  The carbon coating amount was calculated by TG-DTA measurement in air of a piece of the obtained carbon-coated foamed nickel 10 (hereinafter referred to as a foamed metal sheet 10). As a result, it was found that the amount of carbon coating was 1.0 wt% with respect to the weight of the foam metal sheet 10.

Next, the catalyst Pt ₁₀ Ru ₉₀ was supported on ketjen black EC 600 JD powder (BET specific surface area: 1270 m 2 / g, hereinafter abbreviated as KB). Specifically, referring to a known method (reference “Y. Yui et al., Journal of Power Sources, Vol. 340, pp. 121-125, 2017”), Pt ₁₀ Ru ₉₀ by weight ratio: KB The cathode reaction layer 20 was prepared so that PVdF = 10: 80: 10.

  The air electrode reaction layer 20 is foamed by pressing the viscous slurry prepared (slurryed) so that the weight ratio by weight of the air electrode reaction layer 20 and the NMP solvent is 5: 9.5 on the metal foam sheet 10 described above. The metal sheet 10 was filled. Thereafter, pre-drying was performed at 80 ° C. for 12 hours, and vacuum drying was further performed at 100 ° C. for 12 hours.

Comparative Example 1
In the same manner as in Experimental Example 1, an air electrode 101 having a thickness of, for example, 0.6 mm was produced using a foamed nickel sheet without carbon coating. The air electrode 101 in the comparative example 1 is the same as the experimental example 1 except that the foamed nickel sheet is not coated with carbon, and the composition of the air electrode reaction layer 20 is the same.

  The air electrode 101 according to Experimental Example 1 and Comparative Example 1 molded as described above is disposed in the recess of the air electrode support 115 coated with PTFE, and is fixed by the air electrode fixing ring 104. In addition, in the part which the air electrode 101 and the air electrode support body 115 contact, in order to take an electrical contact, PTFE coating shall not be given.

  For example, when lithium metal is used, a plurality of metal lithium foils are stacked and formed into a predetermined shape. The negative electrode 102 fixes four metal lithium foils of 150 μm in thickness by pressure bonding to the negative electrode fixing washer 108.

  The separator 105 is disposed inside the cylinder of the air electrode support 115 in contact with the partition 151 from the side opposite to the air electrode 101, and the negative electrode fixing ring 107 is the cylinder of the air electrode support 115 from the same side as the separator 105. The negative electrode fixing washer 108 is disposed inside and the negative electrode 102 is crimped and disposed inside the cylinder of the negative electrode fixing ring 107.

  The organic electrolyte solution 103 is filled in the inside of the cell (between the air electrode 101 and the negative electrode 102), the negative electrode support 109 is covered, and the air electrode support 115 and the negative electrode support 109 are fixed by the fixing screw 110. As the organic electrolytic solution 103, a 1 mol / l solution of lithium trifluoromethanesulfonylamide / triethylene glycol dimethyl ether (LiTFSI / TEGDM solution, Toyama Pharmaceutical Co., Ltd.) was used.

  Finally, the air electrode terminal 121 is connected and fixed to the air electrode support 115, and the negative electrode terminal 122 is connected and fixed to the negative electrode support 109.

[Battery cycle test]
Next, a battery cycle test will be described. In the cycle test of the battery, 0.2 mA / cm ² of current density per area of the air electrode 101 is supplied using a charge / discharge measurement system (VMP3, manufactured by Bio Logic), and the battery voltage is 2.0 from the open circuit voltage. The measurement of the discharge voltage was carried out until it fell to V. The battery charging test was conducted at the same current density as the time of discharge until the battery voltage reached 4.2V. The charge and discharge test of the battery was performed under a normal living environment. The charge and discharge capacity was represented by the value per area of the air electrode (mAh / cm ² ).

<Evaluation Results of Experimental Example 1>
FIG. 4 is an initial discharge curve of a battery using the air electrode 101 of Experimental Example 1 and Comparative Example 1. The horizontal axis in FIG. 4 is the discharge capacity (mAh / cm ² ), and the vertical axis is the discharge voltage (V). The discharge curve of Experimental Example 1 is shown by a solid line, and the discharge curve of Comparative Example 1 is shown by a broken line.

As shown in FIG. 4, Experimental Example 1 in which the foam metal sheet 10 provided with the carbon coating was used has a discharge capacity of 31 mAh / cm ² larger than that of Comparative Example 1 where the carbon coating is not provided. Table 1 shows the results of charge and discharge cycle tests of Experimental Example 1 and Comparative Example 1.

  As shown in Table 1, the experimental example 1 has a large discharge capacity, a high discharge voltage, and a low charge voltage. From this result, it can be understood that the carbon coating treatment to the foam metal is an effective means for improving the battery performance.

<Battery performance when changing carbon coating amount>
The air electrodes 101 of Experimental Examples 2 and 3 and Comparative Examples 2 and 3 were manufactured for the purpose of confirming the influence of the carbon coating amount on the battery performance, and the charge and discharge cycle test was performed.

[Experimental Example 2]
In the process of Experimental Example 1, a foamed metal sheet 10 having a 0.1 wt% carbon coating was prepared using a 20 wt% sucrose solution.

[Experimental Example 3]
The process of Example 1 was repeated twice to prepare a foamed metal sheet 10 having a 2 wt% carbon coating.

Comparative Example 2
In the process of Experimental Example 1, a foamed metal sheet 10 coated with a 0.08 wt% carbon coating was prepared using a 15 wt% sucrose solution.

Comparative Example 3
The process of Example 1 was repeated twice, and the process of Example 2 was further performed to prepare a foamed metal sheet 10 to which a 2.05 wt% carbon coating was applied.

<Evaluation Results of Experimental Examples 2 and 3 and Comparative Examples 2 and 3>
Table 2 shows the results of the charge and discharge cycle test including the result of Experimental Example 1 for comparison.

  It can be seen from Table 2 that excellent battery performance is exhibited when the carbon coating amount is 0.1 to 2 wt%. In particular, the best battery performance is shown when the carbon coating amount in Experimental Example 1 is 1 wt%.

  On the other hand, the discharge capacity retention rates after 20 cycles of Comparative Example 2 in which the carbon coating amount is small and Comparative Example 3 in which the carbon coating amount is large are 54% and 50%, respectively, and are significantly lower than Experimental Examples 1 to 3. Indicates

  Thus, it has been confirmed that the carbon coating amount in the present embodiment has an appropriate range, and is an important parameter for achieving good battery performance.

  As described above, the battery performance can be improved by filling the foam metal sheet 10 with an appropriate amount of KB (Ketjen black EC 600 JD powder) as a carbon component.

  The air electrode 101 may contain two or more carbon components. Next, an experimental example will be described in which KB is the first component carbon and the other second component carbon is also contained.

<Battery performance when containing second component carbon>
The experiment was conducted on carbon nanotubes and graphene as the second component carbon.

<In the case of carbon nanotubes>
The carbon nanotube which is 2nd component carbon used the Meijo nano carbon-made single-walled carbon nanotube MEIJ0eDIPS (EC 2.0). The cathode reaction layer 20 having the composition shown in Experimental Examples 4 to 6 and Comparative Examples 4 to 5 was prepared, and filled into the foam metal sheet 10 in the same manner as described above. The mixing of the first component carbon (KB) and the second component carbon (carbon nanotube) was carried out with a modifier (High-Flex Homogenizer manufactured by As One).

[Experimental Example 4]
Second component carbon content: 0.1 wt%
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: PVdF = 10: 79.92: 0.08: 10
[Experimental Example 5]
Second component carbon loading: 2.5 wt%
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: PVdF = 10: 78: 2: 10
[Experimental Example 6]
Second component carbon additive amount: 5.0 wt%
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: PVdF = 10: 76: 4: 10
Comparative Example 4
Second component carbon additive amount: 0.09 wt%
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: PVdF = 10: 79. 928: 0.072: 10
Comparative Example 5
Second component carbon loading: 5.1 wt%
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: PVdF = 10: 75.92: 4.08: 10
Table 3 shows the results of the charge and discharge cycle test including the result of Experimental Example 1 for comparison.

  From Table 3, it can be seen that excellent battery performance is exhibited when the range of carbon nanotube addition is 0.1 to 5 wt%. In particular, in the case of the addition amount of 2.5 wt% of Experimental Example 5, a larger discharge capacity is obtained than in the case of other addition amounts.

  In the case of Comparative Example 4 in which the addition amount was 0.1 wt% or less and Comparative Example 5 in which the addition amount was more than 5.0 wt%, a slight decrease in battery performance was observed compared to Experimental Example 1 in which no carbon nanotube was added. Seen. It is considered that this is because the addition of carbon nanotubes having a surface area smaller than that of KB reduces the reaction site and thus reduces the discharge capacity.

  On the other hand, when the addition amount is more than 0.1 wt%, the discharge voltage becomes high and the battery performance is improved. It is considered that this is because the carbon nanotube improves the conductivity.

  However, when the addition amount exceeds 5.0 wt%, the battery performance is degraded. This is considered to be due to the fact that the surface area of the reaction site is reduced by the increase of carbon nanotubes whose surface area is smaller than KB.

  Thus, it is understood that the carbon nanotubes are preferably contained in a proportion of 0.1 to 5 wt% with respect to the total weight of carbon loaded in the air electrode 101.

<In the case of graphene>
As graphene as the second component carbon, graphene powder (boron 2-4%) substitution type, BET surface area: 500 m 2 / g, manufactured by Aldrich Co., was used. The cathode reaction layer 20 having the composition shown in Experimental Examples 7 to 9 and Comparative Examples 6 to 7 was prepared, and filled into the foam metal sheet 10 in the same manner as described above.

[Experimental Example 7]
Second component carbon content: 0.1 wt%
Pt ₁₀ Ru ₉₀ : KB: Graphene: PVdF = 10: 79.92: 0.08: 10
[Experimental Example 8]
Second component carbon content: 3.5 wt%
Pt ₁₀ Ru ₉₀ : KB: Graphene: PVdF = 10: 77.2: 2.8: 10
[Experimental Example 9]
Second component carbon additive amount: 5.0 wt%
Pt ₁₀ Ru ₉₀ : KB: Graphene: PVdF = 10: 76: 4: 10
Comparative Example 6
Second component carbon additive amount: 0.09 wt%
Pt ₁₀ Ru ₉₀ : KB: Graphene: PVdF = 10: 79. 928: 0.072: 10
Comparative Example 7
Second component carbon loading: 5.1 wt%
Pt ₁₀ Ru ₉₀ : KB: Graphene: PVdF = 10: 75.92: 4.08: 10
Table 4 shows the results of the charge and discharge cycle test including the result of Experimental Example 1 for comparison.

  It can be seen from Table 4 that excellent battery performance is exhibited when the graphene addition amount range is 0.1 to 5 wt%. In particular, in the case of the addition amount of 3.5 wt% of Experimental Example 8, a larger discharge capacity is obtained than in the case of other addition amounts.

  In the case of Comparative Example 6 in which the addition amount was 0.1 wt% or less, and Comparative Example 7 in which the addition amount was more than 5.0 wt%, a slight decrease in battery performance was observed compared to Experimental Example 1 in which no graphene was added. Be It is considered that this is because the reaction site is reduced by the addition of graphene having a surface area smaller than KB, and the discharge capacity is reduced.

  On the other hand, when the addition amount is more than 0.1 wt%, the discharge voltage becomes high and the battery performance is improved. It is considered that this is because the conductivity is improved by graphene.

  However, when the addition amount exceeds 5.0 wt%, the battery performance is degraded. It is considered that this is because the surface area of the reaction site is reduced by the increase of graphene whose surface area is smaller than KB.

  Thus, it is understood that the graphene is preferably contained at a ratio of 0.1 to 5 wt% with respect to the total weight of carbon loaded in the air electrode 101.

  In addition, in comparison with the carbon nanotube results (Table 3), the addition of carbon nanotubes as the second component carbon is more effective in improving the discharge capacity and the like in the improvement of the discharge capacity than the case of adding graphene. It is considered that this is because the carbon nanotubes have a fibrous structure while the graphene has a sheet-like structure. That is, it is considered that the carbon nanotube having a fibrous structure has an improved contact with the foamed nickel.

<Battery performance when containing the third component carbon>
As the third component carbon, carbon nanotubes may be contained with respect to the air electrode configurations of Experimental Examples 4 to 6 of KB + carbon nanotubes, or with respect to the air electrode configurations of Experimental Examples 7 to 9 of KB + Graphene .

  Using the above materials, carbon nanotubes and graphene were used to prepare an air electrode reaction layer 20 having the composition shown in Experimental Examples 10 to 12 and Comparative Examples 8 to 9, and filling into the foamed metal sheet 10 was performed in the same manner as above. .

  The mixture of carbon nanotubes and graphene (carbon nanotubes: graphene) can be performed at any ratio, and is not particularly limited. In Experimental Examples 10 to 12, the mixing ratio is, for example, 1: 1.

[Experimental Example 10]
Second and third component carbon loadings: 0.1 wt%, carbon nanotubes: graphene = 1: 1
Pt ₁₀ Ru ₉₀ : KB: Carbon nanotube: Graphene: PVdF = 10: 79.92: 0.04: 0.04: 10
Experimental Example 11
Second and third component carbon loading: 2.5 wt%, carbon nanotube: graphene = 1: 1
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: graphene: PVdF = 10: 78: 1: 1: 10
Experimental Example 12
Second and third component carbon loading: 5.0 wt%, carbon nanotube: graphene = 1: 1
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: graphene: PVdF = 10: 76: 2: 2: 10
Comparative Example 8
Second and third component carbon loadings: 0.09 wt%, carbon nanotubes: graphene = 1: 1
Pt ₁₀ Ru ₉₀ : KB: carbon nanotube: graphene: PVdF = 10: 79.928: 0.036: 0.036: 10
Comparative Example 9
Second and third component carbon loadings: 5.1 wt%, carbon nanotubes: graphene = 1: 1
Pt ₁₀ Ru ₉₀ : KB: Carbon nanotube: Graphene: PVdF = 10: 75.92: 2.04: 2.04: 10
Table 5 shows the results of the charge / discharge cycle test including the results of Experimental Example 1 for comparison.

  It can be seen from Table 5 that excellent battery performance is exhibited when the range of addition amount of carbon nanotubes and graphene is 0.1 to 5 wt%. In particular, in the case of the addition amount of 2.5 wt% of Experimental Example 11, a larger discharge capacity is obtained than in the case of other addition amounts. As described above, the cathode reaction layer 20 may contain two or more carbons.

  In the case of Comparative Example 8 in which the addition amount was 0.1 wt% or less, and Comparative Example 9 in which the addition amount was more than 5.0 wt%, the battery performance was slightly smaller than that of Experimental Example 1 in which carbon nanotubes and graphene were not added. A decline is seen. It is considered that this is because the addition of carbon nanotubes and graphene having a surface area smaller than that of KB reduces the reaction site and thereby reduces the discharge capacity.

  On the other hand, when the addition amount is more than 0.1 wt%, the discharge voltage becomes high and the battery performance is improved. It is considered that this is because the conductivity is improved by carbon nanotubes and graphene.

  However, when the addition amount exceeds 5.0 wt%, the battery performance is degraded. This is considered to be because the surface area of the reaction site is reduced by the increase of carbon nanotubes and graphene whose surface area is smaller than KB.

  In addition, the battery characteristic at the time of making the air electrode reaction layer 20 contain three types of carbon has a characteristic improvement effect larger than the case of one type and two types. It is considered that this is because the fibrous carbon nanotubes form a conductive bridge to the graphene by contacting the graphene having a sheet-like structure with a low conductivity improving effect, thereby improving the conductivity.

<Battery performance when various foam metal sheets are used>
An experiment was conducted on the case where the foam metal sheet 10 (nickel) was replaced with another foam metal sheet. It experimented about the material shown to Experimental example 13-17. The configuration of the air electrode was the same as that of the above-mentioned Experimental Example 5.

  In addition, the porosity of the metal foam sheet 10 is 90% or more in all, even if materials differ, and there is no big difference.

Experimental Example 13
Aluminum (made by ERG Materials and Aerospace)
Experimental Example 14
Made of SUS430 (Magnex Co., Ltd.)
Experimental Example 15
Made of titanium (made by Nagamine Co., Ltd.)
[Experimental Example 16]
Copper (made by ERG Materials and Aerospace)
Experimental Example 17
Silver (Magnex Co., Ltd.)
Table 6 shows the results of the charge and discharge cycle test including the result of Experimental Example 5 for comparison.

As shown in Table 6, even when any of the foamed metal supports was used, the initial discharge capacity exhibited a value exceeding 30 mAh / cm ^2, and it was confirmed that stable operation as a secondary battery was possible. In particular, it can be seen that a large discharge capacity can be obtained when using nickel and titanium.

  As described above, the lithium-air secondary battery 100 according to the present embodiment includes the air electrode 101 which is a positive electrode using oxygen in air as a positive electrode active material, and the negative electrode using metal lithium or a lithium-containing material as a negative electrode active material. In a lithium-air secondary battery having an organic electrolyte 102 containing lithium salt 102 and a lithium salt, an air electrode 101 mixes a carbon powder and a binder powder with a carbon-coated foam metal sheet to produce an air electrode reaction. Layer 20 is filled and dried.

  Further, the cathode reaction layer 20 contains two or more types of carbon including one of carbon nanotubes and graphene. Further, the amount of carbon coating coated on the foam metal sheet 10 is 0.1 to 2 wt% with respect to the weight of the foam metal sheet 10. In addition, the content of carbon nanotubes or graphene relative to the weight of the cathode reactive layer 20 is 0.1 to 5 wt%.

  As a result, it is possible to provide a lithium-air secondary battery capable of realizing a practical discharge capacity per electrode area using an inexpensive carbon material.

  In addition, this invention is not limited to said embodiment, A deformation | transformation is possible within the range of the summary.

  The present embodiment can be applied to a lithium air secondary battery with a large discharge capacity, and can be used as a power supply for various electronic devices, automobiles, and the like.

10: Foamed nickel (foamed metal sheet)
20: catalyst + carbon + PVdF (air electrode reaction layer)
100: lithium air secondary battery 101: positive electrode (air electrode)
102: Negative electrode 103: Organic electrolyte 104: Ring for fixing air electrode 105: Separator 107: Ring for fixing negative electrode 108: Washer for fixing negative electrode 109: Negative electrode support 110: Fixing screw 111: O ring 121: Air electrode terminal 122: Negative terminal 151: partition

Claims (4)

In a lithium air secondary battery having an air electrode which is a positive electrode using oxygen in air as a positive electrode active material, a negative electrode using metal lithium or a lithium-containing material as a negative electrode active material, and an organic electrolyte containing a lithium salt
The air electrode is formed by filling a carbon-coated foam metal sheet with an air electrode reaction layer obtained by mixing a carbon powder and a binder powder, and then drying it. battery. The lithium air secondary battery according to claim 1, wherein the cathode reaction layer contains two or more types of carbon including one of carbon nanotubes and graphene. The lithium air secondary battery according to claim 1 or 2, wherein the amount of carbon coating coated on the foam metal sheet is 0.1 to 2 wt% with respect to the weight of the foam metal sheet. The lithium air secondary battery according to any one of claims 1 to 3, wherein the content of carbon nanotubes or graphene is 0.1 to 5 wt% with respect to the weight of the cathode reaction layer.