JP6298415B2 - Lithium air secondary battery - Google Patents

Description

  The present invention relates to a lithium air secondary battery. The present invention relates to a lithium-air secondary battery that is smaller and lighter than a conventional secondary battery such as a lead storage battery or a lithium ion battery and that can realize a discharge capacity that is much larger.

  A lithium-air secondary battery that uses oxygen in the air as a positive electrode active material is always supplied with oxygen from the outside of the battery, and a large amount of metallic lithium, which is a negative electrode active material, can be filled in the battery. For this reason, it has been reported that the value of the discharge capacity per unit volume of the battery can be greatly increased.

  As reported in Non-Patent Document 1 and Non-Patent Document 2 so far, attempts have been made to improve battery performance such as discharge capacity and cycle characteristics by adding various catalysts to the air electrode as the positive electrode. ing.

Transition metal oxides have been studied as electrode catalysts for air electrodes. For example, in the above document, transition metal oxides such as λ-MnO ₂ are used in Non-Patent Document 1, and iron oxide (Fe ₂ O ₃ ), cobalt oxide (Co ₃ O ₄ ) and the like are mainly used in Non-Patent Document 2. Transition metal oxides have been investigated.

J. Read, Journal of The Electrochemical Society, Vol.149, pp.A1190-A1195 (2002). Aurelie Debart et al., Journal of Power Sources, Vol.174, pp.1177-1182 (2007).

  Non-Patent Document 1 and Non-Patent Document 2 show the results of the battery characteristic test of the lithium air secondary battery as follows.

  In the secondary battery disclosed in Non-Patent Document 1, a charge / discharge cycle was possible, but after 4 cycles, the discharge capacity was reduced to about 1/4, and the performance as a secondary battery was low. . Further, in the secondary battery disclosed in Non-Patent Document 1, the charging voltage is about 4.0V, which is very large compared to the average discharge voltage of 2.7V, and the charge / discharge energy efficiency is low. There is.

On the other hand, in Non-Patent Document 2, nine types of catalysts are examined, and a very large discharge capacity of 1000 to 3000 mAh / g is obtained per weight of carbon contained in the air electrode. However, when charging and discharging are repeated, the discharge capacity is remarkably reduced. For example, in the case of Co ₃ O ₄ , the capacity retention rate becomes about 65% after 10 cycles. As described above, the lithium-air secondary battery of Non-Patent Document 2 also shows a significant decrease in capacity, and sufficient characteristics as a secondary battery are not obtained. In most cases, the average discharge voltage is about 2.5 V, while the charging voltage is 4.0 to 4.5 V, and the lowest is about 3.9 V. For this reason, the charge / discharge energy efficiency of the lithium-air secondary battery of Non-Patent Document 2 is low.

  The present invention provides a lithium-air secondary battery in which a lithium-air secondary battery is operated as a high-capacity secondary battery, a voltage difference between charge and discharge is small, and a decrease in discharge capacity is small even after repeated charge and discharge cycles. With the goal.

An example of means for solving the problems of the present invention is a lithium-air secondary battery including an air electrode, a negative electrode containing lithium, and an electrolyte, and the electrolyte is disposed between the air electrode and the negative electrode. there are, said air electrode comprises YMn _1-x Fe x O ₃ a (1 ≧ x ≧ 0) as catalyst, a lithium-air battery.

  Here, x is preferably 0.4 or more and 0.6 or less.

  According to the lithium air secondary battery of the present invention, the battery performance can be improved. According to the lithium air secondary battery of the present invention, it is possible to realize cycle characteristics superior to those of the prior art, and further improve energy efficiency and the like. Specifically, it is possible to provide a lithium-air secondary battery that has a small charge / discharge voltage difference and that can suppress a decrease in discharge capacity even after repeated charge / discharge cycles.

1 is a basic conceptual diagram of a lithium air secondary battery according to the present invention. An example of a synthesis scheme of YMn _1-x Fe _x O ₃ used as a catalyst is shown. It is a schematic sectional drawing for showing the structure of the lithium air secondary battery cell used for the measurement in an Example. 2 is a graph showing an initial charge / discharge curve of the lithium-air secondary battery of Example 1. FIG.

  Hereinafter, an embodiment of the lithium-air secondary battery of the present invention will be described in detail with reference to the drawings.

[Configuration of lithium-air secondary battery]
As shown in FIG. 1, the lithium air secondary battery 100 of this embodiment includes at least an air electrode 101, a negative electrode 102, and an electrolyte (for example, an organic electrolyte) 103. The air electrode 101 functions as a positive electrode. An electrolyte 103 is disposed between the air electrode 101 and the negative electrode 102.

Each of the above components will be described below.
(I) Air electrode (positive electrode)
The air electrode 101 includes at least a catalyst.

(I-1) catalytic cathode 101 comprises the catalytic YMn _1-x Fe x O ₃ as the (electrode catalyst) (1 ≧ x ≧ 0) . In the air electrode of the lithium secondary battery, an electrode reaction proceeds in a three-phase portion of electrolyte / electrode catalyst / gas (oxygen). Typically, the organic electrolyte as the electrolyte 103 permeates into the air electrode 101, and at the same time, oxygen gas in the atmosphere is supplied to form a three-phase site in which electrolyte-electrode catalyst-gas (oxygen) coexists. The If the electrode catalyst is highly active, oxygen reduction (discharge) and oxygen generation (charge) proceed smoothly, and battery performance is greatly improved.

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

2Li ⁺ + (1/2) O ₂ + 2e ⁻ → Li ₂ O (1)
2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (2)

Lithium ions (Li ⁺ ) in the above formula have been dissolved in the electrolyte (typically organic electrolyte) 103 from the negative electrode 102 by electrochemical oxidation, and have moved through the electrolyte 103 to the surface of the air electrode 101. Is. Oxygen (O ₂ ) is taken into the air electrode 101 from the atmosphere (air). The material (Li ⁺⁾ to dissolve from the anode 102, the material to be deposited at the cathode 101 (Li ₂ O _2), and showed air (O ₂₎ together with the components of FIG.

YMn _1-x Fe _x O ₃ is used as an air electrode (positive electrode) 101 of the electrode catalyst, is large (expressed in m ² / g) specific surface area, pore (the ability to incorporate oxygen into the oxide In the specification, it is also referred to as an oxygen vacancy).

  Such an oxide catalyst has a strong interaction with oxygen, which is a positive electrode active material, so that many oxygen species can be adsorbed on the oxide surface or oxygen species can be occluded in oxygen vacancies.

  Thus, the oxygen species adsorbed on the oxide surface or occluded in the oxygen vacancies is used as an oxygen source (active intermediate reactant) of the above formulas (1) and (2) for the oxygen reduction reaction. The above reaction can easily proceed. Moreover, said oxide has activity also with respect to the charging reaction which is a reverse reaction of Formula (1) and Formula (2). Therefore, battery charging, that is, oxygen generation reaction on the air electrode 101 also proceeds efficiently.

  In the lithium-air secondary battery, in order to increase the efficiency of the battery, it is desirable that there are more reaction sites (the three-phase portion of the above-described electrolyte / electrode catalyst / air (oxygen)) that cause an electrode reaction. From such a viewpoint, it is important that the above-mentioned three-phase sites are present in a large amount on the surface of the electrode catalyst, and the catalyst used preferably has a high specific surface area.

The YMn _1-x Fe _x O ₃ catalyst can be synthesized by various methods. For example, a known process such as a solid phase method or a liquid phase method can be used for the synthesis method. However, it is more preferable to use a wet method in which particles having a high specific surface area are obtained.

  The specific surface area can be measured using a commercially available apparatus. For example, the specific surface area can be measured by a procedure using liquid nitrogen as a cooling medium using a commercially available measuring device.

(I-2) Conductive Material The air electrode 101 can include a conductive material. An example of the conductive material is carbon. Specific examples include carbon blacks such as ketjen black and acetylene black, activated carbons, graphites, and carbon fibers. In order to secure sufficient reaction sites in the air electrode 101, carbon having a large specific surface area is suitable. Specifically, those having a BET specific surface area of 300 m ² / g or more are desirable. These carbons can be obtained, for example, as commercial products or by a known synthesis method.

  The specific surface area of the catalyst used for the air electrode 101 and preferable carbon desirably has a predetermined value. The specific surface area can be measured using a commercially available apparatus. For example, the specific surface area can be measured by a BET method using liquid nitrogen as a cooling medium using a commercially available measuring apparatus.

(I-3) Binder (binder)
The air electrode 101 can contain additives such as a binder (binder) for integrating the materials as necessary. Although this binder is not specifically limited, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polybutadiene rubber, etc. can be mentioned as an example. These binders can be used as a powder or as a dispersion.

(I-4) Preparation of air electrode The air electrode 101 can be prepared as follows. The air electrode 101 can be formed by mixing a catalyst powder such as oxide powder, carbon powder and polyvinylidene fluoride (PVDF), and pressing the mixture onto a support such as a titanium mesh. . Moreover, the air electrode 101 can be formed by dispersing the above-mentioned mixture in a solvent such as an organic solvent to form a slurry, and applying the mixture onto a metal mesh or carbon cloth or carbon sheet and drying.

  The catalyst content in the air electrode 101 is preferably, for example, more than 30% by weight and 60% by weight or less. The ratio of other components is the same as that of the conventional lithium air secondary battery.

  Moreover, in order to increase the strength as an electrode and prevent leakage of the electrolytic solution, the air electrode 101 with higher stability can be produced by applying not only a cold press but also a hot press. One side of the air electrode 101 is exposed to the atmosphere, and the other side is in contact with the electrolyte.

(II) Negative electrode The negative electrode 102 contains lithium as a negative electrode active material. The negative electrode active material is not particularly limited as long as it is a lithium-containing material that can be used as a negative electrode material for a lithium secondary battery. Examples of the negative electrode active material include metallic lithium. Alternatively, examples of the lithium-containing material include lithium and silicon or tin alloy, or lithium nitride such as Li _2.6 Co _0.4 N, which is a material capable of releasing and occluding lithium ions.

  Note that when the above-described silicon or tin alloy is used as the negative electrode 102, silicon or tin that does not contain lithium may be used when the negative electrode 102 is synthesized. However, in this case, prior to the production of the air battery, a chemical method or an electrochemical method (for example, a method in which an electrochemical cell is assembled and lithium and silicon or tin are alloyed) is used to form silicon or silicon. It is necessary to treat so that tin is in a state containing lithium. Specifically, it is preferable that the working electrode contains silicon or tin, the counter electrode is lithium, and a treatment such as alloying is performed by flowing a reducing current in the organic electrolyte.

  The negative electrode 102 can be formed by a known method. For example, in the case where lithium metal is used as the negative electrode 102, the negative electrode 102 may be manufactured by stacking a plurality of metal lithium foils into a predetermined shape.

  Here, the reaction of the negative electrode (metallic lithium) 102 during discharge can be expressed as follows.

(Discharge reaction)
Li → Li ⁺ + e ⁻ (3)
In addition, in the negative electrode 102 at the time of charge, the lithium precipitation reaction which is the reverse reaction of Formula (3) occurs.

(III) Electrolyte The lithium-air secondary battery of the present invention includes an electrolyte 103. Note that in this specification, the electrolytic solution refers to a case where the electrolyte 103 is in a liquid form. The electrolyte 103 may be any substance that can move lithium ions between the air electrode (positive electrode) 101 and the negative electrode 102. For example, a nonaqueous solvent in which a metal salt containing lithium ions is dissolved can be used. Specifically, as a metal salt containing lithium ions, a metal salt containing lithium ions such as lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), etc. Can be mentioned. Nonaqueous solvents include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), diethyl carbonate (DEC), and ethyl propyl carbonate. (EPC), ethyl isopropyl carbonate (EIPC), ethyl butyl carbonate (EBC), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), carbonic acid 1, Carbonate ester solvents such as 2-butylene (1,2-BC), ether solvents such as 1,2-dimethoxyethane (DME) and tetraethylene glycol dimethyl ether (TEGDME), and lactone systems such as γ-butyrotactone (GBL) Solvent or dimethylsulfoxy A sulfoxide solvent such as (DMSO), and a solvent in which two or more of these are mixed [for example, a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1), EC and carbonic acid Mixed solvent such as diethyl (DEC) and the like.

Other electrolytes 103 include solid electrolytes that pass lithium ions (for example, sulfide-based solid electrolytes including Li ₂ S and P ₂ S ₅ ), polymer electrolytes that pass lithium ions (for example, polyethylene oxides, specifically, For example, a material obtained by compositing the organic electrolyte and polyethylene oxide may be used. However, this invention is not limited to these, It can use suitably if it is a solid electrolyte which lets the known lithium ion used for a lithium air secondary battery, or a polymer electrolyte which lets lithium ion pass.

(IV) Other elements The lithium air secondary battery includes structural elements such as a separator, a battery case, a metal mesh (for example, titanium mesh), and other elements required for the lithium air secondary battery, in addition to the above components. be able to. Conventionally known ones can be used.

  Hereinafter, embodiments and comparative examples of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited to what was shown to the following Example, In the range which does not change the summary, it can change suitably and can implement.

(Example 1-6)
The YMn _1-x Fe _x O ₃ powder used as an electrode catalyst of the air electrode 101 described above, was synthesized by the following procedure shown in FIG.

First, yttrium nitrate, manganese nitrate, and iron nitrate were mixed and dissolved in distilled water so as to obtain a desired Y: Mn: Fe ratio. For example, when synthesizing YMn _0.6 Fe _0.4 O ₃ , it was prepared so that the molar concentrations were Y: 1 mol / l, Mn: 0.6 mol / l, and Fe: 0.4 mol / l. Subsequently, 0.1 mol / l malic acid was mixed into the metal nitrate aqueous solution so as to be three times the number of moles of dissolved metal ions. Thereafter, as shown in FIG. 2, pH adjustment with ammonia water and evaporation to dryness were performed to obtain an amorphous precursor containing Y, Mn and Fe. By firing the precursor powder further in air, to obtain the desired _{YMn 1-x Fe x O 3} . Specifically, x = 0 (Example 1), 0.2 (Example 2), 0.4 (Example 3), 0.6 (Example 4), 0.8 (Example 5), A Y-Mn-Fe oxide of 1.0 (Example 6) was synthesized. This powder was evaluated by X-ray diffraction (XRD) measurement and BET specific surface area measurement.

The powder after firing was subjected to XRD measurement and identified with reference to ICDD patterns (YMnO ₃ : 01-081-1945, YMn _0.7 Fe _0.3 O ₃ : 01-077-4046, YFeO ₃ : 01-073-1345), It was confirmed that a single phase of YMn _1-x Fe _x O ₃ was obtained without containing single oxides of Y, Mn, and Fe. Here, the ICDD pattern is an abbreviation for International Center for Diffraction Data, and refers to powder diffraction data used for identification of crystalline substances and materials.

(Preparation of air electrode)
Then, making such _{YMn 1-x Fe x O 3} (1 ≧ x ≧ 0) lithium-air battery cell 200 using the air electrode 1 and the air electrode 1 using powder as follows did.

_{YMn 1-x Fe x O 3} (1 ≧ x ≧ 0) powder, sufficiently pulverized using a kneader Ketjen black EC600JD powder and polytetrafluoroethylene (PTFE) powder in a weight ratio of 50:30:20 It mixed and roll-formed and produced the sheet-like electrode (thickness: 0.5 mm). The sheet-like electrode was cut into a circle having a diameter of 23 mm and pressed onto a titanium mesh to obtain a gas diffusion type air electrode 1.

(Production of lithium secondary battery cells)
A cylindrical lithium-air secondary battery cell 200 having the cross-sectional structure shown in FIG. 3 was produced. FIG. 3 is a schematic longitudinal sectional view of the lithium air secondary battery cell 200. The lithium air secondary battery cell 200 was produced in the following procedure in dry air having a dew point of −60 ° C. or less.

The air electrode (positive electrode) 1 prepared by the above method was placed in the recess of the PTFE-coated air electrode support 10 and fixed with the air electrode fixing PTFE ring 8. The portion where the air electrode 1 and the air electrode support 10 are in contact with each other was not covered with PTFE in order to make electrical contact. The effective area of the electrode in contact with the air electrode 1 and air was 2 cm ² .

Next, a separator 5 for a lithium secondary battery was disposed on the bottom surface of the recess on the surface opposite to the surface where the air electrode 1 and the atmosphere contacted. Subsequently, four metal lithium foils (effective area: 2 cm ² ) having a thickness of 150 μm as the negative electrode 2 were stacked on the concentric circle and pressure bonded to the negative electrode fixing washer 7 as shown in the figure. Next, the negative electrode fixing PTFE ring 6 was disposed in a concave portion opposite to the concave portion in which the air electrode 1 was installed, and a negative electrode fixing washer 7 having metal lithium bonded thereto was further disposed in the central portion. Subsequently, the O-ring 9 was disposed at the bottom of the air electrode support 10 as shown in the figure.

  Next, the inside of the cell (between the air electrode (positive electrode) 1 and the negative electrode 2) is filled with an organic electrolytic solution as the electrolyte 3, and the negative electrode support 11 is covered, and the entire cell is fixed with the cell fixing screw 12. Fixed. As the organic electrolyte 3, a 1 mol / l lithium trifluoromethanesulfonylamide / triethylene glycol dimethyl ether (LiTFSA / TEGDME) solution was used.

  Subsequently, the air electrode (positive electrode) terminal 4 was installed on the air electrode support 10, and the negative electrode terminal 13 was installed on the negative electrode support 11.

(Battery performance)
The battery performance of the lithium air secondary battery cell 200 prepared by the above procedure was measured. In addition, the air electrode (positive electrode) terminal 4 and the negative electrode terminal 13 shown in FIG. 3 were used for the battery performance measurement test.

In the battery cycle test, a charge / discharge measurement system (VMP3: manufactured by Bio Logic) was used to conduct 0.1 mA / cm ² at a current density per effective area of the air electrode. The discharge voltage was measured until it decreased to 2.0V. Further, the battery charge test was performed until the battery voltage increased to 4.2 V at the same current density as during discharge. The battery discharge test was performed in a normal living environment. Discharge capacity was expressed as the air electrode (carbon _{+ YMn 1-x Fe x O} 3 + PTFE) 1 per weight values (mAh / g).

The initial discharge and charge curves are shown in FIG. From the figure, it was confirmed that when YMn _0.6 Fe _0.4 O ₃ (Example 3) was used for the air electrode catalyst, the average discharge voltage was 2.68 V and the discharge capacity was as large as 1420 mAh / g. Here, the average charge / discharge voltage is defined as a discharge voltage and a charge voltage at an intermediate value of the total discharge capacity in the figure. In addition, the initial charge capacity is 1430 mAh / g which is almost the same as the discharge capacity, and it can be seen that the reversibility is excellent.

Battery performance was also measured for other examples. The transition of the discharge voltage and the discharge capacity in the case of repeated 100 charge-discharge cycles, are shown in Table 1 together with the BET specific surface area of _{YMn 1-x Fe x O 3} .

From Table 1, YMn _0.6 Fe _0.4 O ₃ of x = 0.4 (Example 3) is the most average discharge voltage is high, it was found that the discharge capacity is large. In addition, the discharge capacity retention rate after 100 cycles was as high as 95%, and it was confirmed that after 100 cycles, a higher discharge voltage and a larger discharge capacity were exhibited than any composition of YMn _1-x Fe _x O ₃ . Following x = 0.4, the sample that showed high cycle performance was x = 0.6, and the discharge capacity retention after 100 cycles was about 84%. Table 1 suggests that such dependency on the amount of substitution of Fe (x) has an influence on the BET specific surface area of the obtained sample. Therefore, it turns out that a preferable substitution amount is the range of 0.4-0.6 in which a high specific surface area sample is obtained.

_{Thus, YMn 1-x Fe x O} 3 (1 ≧ x ≧ 0) was found to have very good activity as a catalyst for the air electrode of a lithium air battery.

(Comparative Example 1)
Using manganese oxide (MnO ₂ ), which is known as an electrode catalyst for the air electrode, a lithium air secondary battery cell was produced in the same manner as in the example. As the manganese oxide (MnO ₂ ), a commercially available reagent (manufactured by Kishida Chemical Co., Ltd.) was used. The conditions of the battery cycle test are the same as those in the example.

  The cycle performance regarding the discharge capacity of the lithium air secondary battery according to this comparative example is shown in Table 1 together with the results of Examples 1 to 6.

  As shown in Table 1, in this comparative example, the initial discharge capacity showed a moderate value of about 850 mAh / g, but the discharge capacity after 100 cycles was almost zero and the cycle stability was poor.

These results lithium-air secondary battery comprising the electrode including YMn _1-x Fe _x O ₃ with (1 ≧ x ≧ 0) as an electrode catalyst as an air electrode as in the present invention, when using the known material than has excellent cycle characteristics with respect to capacity and _{voltage, YMn 1-x Fe x O} 3 (1 ≧ x ≧ 0) , it is confirmed to be effective as a catalyst for the air electrode for a lithium air battery It was.

By using _{YMn 1-x Fe x O 3} (1 ≧ x ≧ 0) as an electrode catalyst for the cathode of lithium-air battery, is possible to produce a superior lithium-air secondary cell charge-discharge cycle performance It can be used effectively as a drive source for various electronic devices.

1, 101 Air electrode (positive electrode)
2, 102 Negative electrode 3, 103 Electrolyte 4 Air electrode (positive electrode) terminal 5 Separator 6 Negative electrode fixing PTFE ring 7 Negative electrode fixing washer 8 Air electrode (positive electrode) fixing PTFE ring 9 O-ring 10 Air electrode (positive electrode) support ( PTFE coating)
11 Negative electrode support 12 Cell fixing screw (PTFE coating)
13 Negative terminal 100 Lithium air secondary battery 200 Lithium air secondary battery cell

Claims (2)

An air electrode, a negative electrode containing lithium, and an electrolyte, wherein the electrolyte is disposed between the air electrode and the negative electrode,
It said air electrode _comprises YMn _1-x Fe _{x O} 3 a (1 ≧ x> 0) as catalyst, lithium-air battery. An air electrode, a negative electrode containing lithium, and an electrolyte, wherein the electrolyte is disposed between the air electrode and the negative electrode,
The air electrode includes YMn _1-x Fe _x O ₃ (1 ≧ x ≧ 0) as a catalyst;
x is 0.4 to 0.6, Lithium air secondary battery.