JP6715209B2 - Lithium air secondary battery - Google Patents

Description

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

In a lithium-air battery that uses oxygen in the air as the positive electrode active material, oxygen is constantly supplied from the outside of the battery, and a large amount of metallic lithium that is the negative electrode active material can be filled in the battery. Therefore, it is known that the value of the discharge capacity per unit volume of the battery can be increased.

Meanwhile, Non-Patent Document 1 reports an example in which a transition metal oxide such as λ-MnO ₂ is used as an electrode catalyst for an air electrode. In addition, Non-Patent Document 2 reports an example in which a transition metal oxide such as iron oxide (Fe ₂ O ₃ ) or cobalt oxide (Co ₃ O ₄ ) is mainly used.

J. Read, “Characterization of the Lithium/Oxygen Organic ElectrolyteBattery”, Journal of The Electrochemical Society, Vol. 149, pp. A1190-A1195 (2002). Aurelie Debart et al. “An O2 cathode for rechargeable lithium batteries: The effect of a catalyst”, Journal of Power Sources, Vol. 174, pp. 1177 (2007).

In the secondary battery disclosed in Non-Patent Document 1, the discharge capacity after four cycles of charging and discharging is reduced to about 1/4, and the performance as a secondary battery is low. The charging voltage is about 4.0V, which is higher than the average discharging voltage of 2.7V, and the charging/discharging energy efficiency is low. That is, this secondary battery has a problem that the difference between the charging voltage and the discharging voltage is large and the charging/discharging cycle performance is poor.

Further, the secondary battery disclosed in Non-Patent Document 2 can obtain a large discharge capacity of 1000 to 3000 mAh/g based on the weight of carbon contained in the air electrode. However, the capacity retention rate drops to about 65% after 10 cycles of charging and discharging. Thus, the secondary battery disclosed in Non-Patent Document 2 also has a problem that the performance as a secondary battery is low, like the secondary battery in Non-Patent Document 1.

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 having a small difference between the charging voltage and the discharging voltage and excellent charge/discharge cycle performance.

A lithium-air secondary battery according to one aspect of the present embodiment is a positive electrode that uses oxygen in the air as a positive electrode active material, a negative electrode that uses metallic lithium or a lithium-containing material as a negative electrode active material, and an organic electrolyte solution that contains a lithium salt. In the lithium-air secondary battery including the above, the positive electrode is an air electrode mainly composed of carbon, and it is summarized that a material containing metal, phosphorus and oxygen is added as an electrode catalyst.

According to the present invention, it is possible to provide a lithium-air secondary battery having a small difference between the charging voltage and the discharging voltage and good charge/discharge cycle performance.

It is a figure which shows typically the structure of the lithium air secondary battery which concerns on embodiment of this invention. FIG. 3 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 figure which shows the discharge characteristic of the lithium air secondary battery which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.

[Outline of lithium-air secondary battery]
FIG. 1 is a basic conceptual diagram of the lithium-air secondary battery of this embodiment. As shown in the figure, a lithium-air secondary battery 100 includes an air electrode 101, a negative electrode 102 containing lithium, and an organic electrolyte solution 103 sandwiched 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 and a conductive material as constituent elements. The negative electrode 102 can be made of a material such as metallic lithium or a lithium-containing alloy that can release and absorb lithium ions.

Hereinafter, each component of the lithium-air secondary battery 100 of this embodiment will be described. Note that the electrolytic solution here means a case where the electrolyte is in a liquid form.

(I) Air Electrode The air electrode 101 of the present embodiment includes at least a catalyst and a conductive material, and optionally an additive such as a binder.

(I-1) Catalyst In the lithium-air secondary battery 100 of the present embodiment, the air electrode 101 contains a material containing metal, phosphorus, and oxygen as a catalyst.

In the air electrode 101 of the lithium secondary battery 100, the electrode reaction proceeds in the three-phase portion of electrolyte/electrode catalyst/gas (oxygen). That is, the organic electrolyte solution 103 permeates into the air electrode 101, oxygen gas in the atmosphere is supplied at the same time, and a three-phase portion where electrolyte solution-electrode catalyst-gas (oxygen) coexists is formed. If the electrode catalyst is highly active, oxygen reduction (discharge) and oxygen generation (charge) will proceed smoothly, and battery performance will be greatly improved.

The discharge reaction at the air electrode 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 electrolytic solution 103 from the negative electrode 102 by electrochemical oxidation, and moves in the organic electrolytic 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). In addition, the material (Li ⁺ ) that dissolves from the negative electrode 102, the material (Li ₂ O ₂ ) that precipitates at the air electrode 101, and the air (O ₂ ) are shown together with the constituent elements in FIG. 1.

Since the catalyst containing metal, phosphorus, and oxygen has a strong interaction with oxygen that is the positive electrode active material, many oxygen species can be adsorbed on the surface of the material, and the electrode reaction of the air electrode 101 can be activated.

Thus, the oxygen species adsorbed on the oxide surface or occluded in the oxygen vacancies are used in the oxygen reduction reaction as the oxygen source (active intermediate reactant) of the formula (1), Will be easier to proceed. Further, the above-mentioned materials have activity also in the charging reaction which is the reverse reaction of the formula (1). Therefore, the charging 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, in order to increase the efficiency of the battery, there are more reaction sites (three-phase portion of the above-mentioned electrolytic solution/electrode catalyst/air (oxygen)) that cause an electrode reaction. Is desirable. From this point of view, in the present embodiment, it is important that the above three-phase sites are present on the surface of the electrode catalyst in a large amount, and the catalyst used preferably has a high specific surface area.

The catalyst containing metal, phosphorus and oxygen used in this embodiment 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.

Further, a material containing metal, phosphorus, and oxygen, even if crystalline or amorphous, has catalytic activity and can accelerate the electrode reaction.

On the other hand, the surface of the catalyst particles is coated with carbon by mixing the catalyst containing the metal, phosphorus, oxygen and carbon with a ball mill or by evaporating to dryness in a suspension in which the catalyst and organic matter are dissolved. The electric conductivity is improved, and the catalytic activity can be further improved. As the carbon, various carbons such as carbon black, graphite and carbon fiber can be used. As the carbon source, organic acids such as citric acid and malic acid and sugars such as glucose, fructose, maltose, sucrose, ascorbic acid and erythorbic acid can be used.

As a material for the positive electrode 101, at least one phosphoric acid raw material selected from P ₂ O ₅ , H ₃ PO ₄ , and NH ₄ H ₂ PO ₄ is used. Further, in the present embodiment, at least one transition metal compound from the chromium source material, the manganese source material, the iron source material, the cobalt source material, the nickel source material and the ruthenium source material, and the phosphoric acid source described above. By heat-treating the raw material mixture obtained by mixing the above, the material of the air electrode 101 containing metal, phosphorus, and oxygen is synthesized.

Specifically, as the chromium source, for example, a chromium raw material of chromium oxide (Cr ₂ O ₃ or the like) may be used. In addition, as the manganese source, for example, a raw material of manganese oxide (at least one selected from MnO 2, MN ₃ O ₄ , and MnO) may be used. As the iron source, for example, iron oxide (FeO, _Fe 3 _{O 4,} and at least one selected from _Fe 2 _{O 3),} iron phosphate _{(II) (Fe 3 (PO} 4) 2 · 5H 2 O), ferrous chloride (FeCl ₂ , FeCl ₂ .4H ₂ O), iron nitrate Fe(NO ₃ ) ₃ or the like may be used.

As the cobalt source, for example, a raw material of cobalt oxide (at least one selected from Co ₃ O ₄ , CoO, and Co ₂ O ₃ ) may be used. As the nickel source, for example, a raw material of nickel oxide (at least one selected from NiO and Ni ₂ O ₃ ) may be used. Further, as the ruthenium source, for example, a raw material of ruthenium oxide (at least one selected from RuO ₂ and Ru ₂ O ₃ ) and ruthenium chloride (at least one selected from RuCl ₃ and RuCl ₄ ) may be used. Good.

The raw materials corresponding to the respective constituent elements are selected and mixed so that the desired composition ratio is obtained, and the materials are synthesized by performing heat treatment at about 500° C. in argon using a gold boat.

The generation phase of the sample after the heat treatment was identified by XRD measurement, and it was confirmed to be an amorphous phase in which no diffraction peak was observed except for FePO ₄ and MnPO ₄ . No peak of the metal oxide mixed as the raw material was observed, and it was found that the generated phase was a single phase and uniform. Furthermore, it was also confirmed from the analysis of the chemical composition using ICP emission analysis that the molar ratio of M:P:O was in agreement with the desired composition ratio.

(I-3) Binder
The air electrode 101 can include a binder. The binder is not particularly limited, but examples thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polybutadiene rubber. These binders can be used as a powder or as a dispersion liquid.

(II) Negative Electrode In the lithium-air secondary battery 100 of this 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, an alloy of lithium and silicon or tin, which is a substance capable of releasing and storing lithium ions, or a lithium nitride such as Li _2.6 Co _0.4 N is given as an example. be able to.

When the above alloy of silicon or tin is used as the negative electrode, silicon or tin that does not contain lithium can be used when the negative electrode is synthesized. However, in this case, prior to the production of the air battery, the silicon or the silicon is formed by a chemical method or an electrochemical method (for example, a method of forming an electrochemical cell to alloy lithium with silicon or tin). The tin must be treated so that it contains lithium. Specifically, it is preferable that the working electrode contains silicon or tin, lithium is used as the counter electrode, and a treatment such as alloying is performed by flowing a reducing current in the organic electrolytic solution.

For the negative electrode 102 of the lithium-air secondary battery 100, for example, when lithium metal is used as the negative electrode, the negative electrode 102 may be formed by stacking a plurality of metallic lithium foils and molding them into a predetermined shape.

Here, the reaction of the negative electrode (metal lithium) during discharging can be expressed as follows.
(Discharge reaction) Li→Li ⁺ +e ⁻ (2)
In the negative electrode during charging, a lithium precipitation reaction, which is a reverse reaction of the formula (2), occurs.

(III) Organic Electrolyte Solution As the organic electrolyte solution 103, any substance capable of transferring lithium ions between the positive and negative electrodes may be used, and a non-aqueous solvent in which a metal salt (lithium salt) containing lithium ions is dissolved is used. As a solute, lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethanesulfonylimide [(CF ₃ SO ₂ )2NLi] (LiTFSI), or the like can be used, Examples of the solvent include 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), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), carbonate 1,2-carbonate. Carbonic ester solvents such as butylene (1,2-BC), ether solvents such as 1,2-dimethoxyethane (DME), lactone solvents such as γ-butyrolactone (GBL), tetraethylene glycol dimethyl ether (TEGDME, etc. Examples thereof include a glyme-based solvent, a sulfoxide-based solvent such as dimethylsulfoxide (DMSO), or a solvent in which two or more of these are mixed, and the mixing ratio of the mixed solvent is not particularly limited.

Further, not only the above-mentioned organic electrolytic solution but also a solid electrolyte having lithium ion conductivity, a polymer electrolyte, an ionic liquid in which a lithium metal salt is dissolved can be used.

(IV) Other Elements The lithium-air secondary battery 100 of the present embodiment is required to have a separator, a battery case, a structural member such as a metal mesh (for example, titanium mesh), and other lithium-air secondary batteries in addition to the above-described constituent elements. Can be included. As these, conventionally known ones can be used.

[Configuration of lithium-air secondary battery]
Next, the configuration of the lithium-air secondary battery 100 of this 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 this 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 housed in a cylindrical air electrode support 115. The air electrode support 115 is made of metal and makes electrical contact with the air electrode 101. However, the portion where the air electrode support 115 is in contact with the organic electrolyte solution 103 and the separator 105 is covered with polytetrafluoroethylene (PTFE) for insulation separation.

The air electrode support 115 has a partition 151 in the center of the cylinder. The partition 151 divides the inside of the cylinder of the air electrode support 115 into a region in which the air electrode 101 is arranged and a region in which the negative electrode 102 and the separator 105 are arranged. The partition 151 has an opening at the center and both regions communicate with each other.

The organic electrolytic solution 103 is arranged in the opening of the partition 151 and is sandwiched between the air electrode 101 and the separator 105 serving as a salt bridge. The organic electrolyte solution 103 is impregnated in the separator 105 and also exists around the separator 105.

The air electrode 101 is fixed by being sandwiched between a cylindrical air electrode fixing ring 104 made of PTFE and a partition 151.

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

The negative electrode 1042 and the negative electrode fixing washer 108 are stacked, and are 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 with a fixing screw 110. An O-ring 111 is arranged between the air electrode support 115 and the negative electrode support 109. The fixing screw 110 is covered 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 against the air electrode support 115 side by the fixing screw 110. The negative electrode 104 is pressed through the negative electrode fixing washer 108 and is brought into pressure contact with the separator 105.

The air electrode 101 is arranged in conduction with the air electrode support 115, and the negative electrode terminal 122 is arranged in conduction with the negative electrode support 109.

[Procedure for manufacturing lithium-air secondary battery]
Subsequently, a procedure for manufacturing the lithium-air secondary battery 100 of FIG. 2 will be described.

A lithium-air battery cell is manufactured by the following procedure in dry air with a dew point of -55°C or lower.

The air electrode 101 is formed by mixing a catalyst such as MPO powder, carbon powder, and binder powder such as polyvinylidene fluoride (PVDF), and pressing the mixture on a support such as a titanium mesh. To do. Alternatively, the air electrode 101 may be formed by dispersing the above mixture in a solvent such as an organic solvent to form a slurry, applying the mixture on a metal mesh, carbon cloth, or a carbon sheet and drying the mixture.

In the lithium-air secondary battery 100, the content of the catalyst in the air electrode 101 is preferably more than 10 and 60% by weight or less. The ratio of the components is the same as that of the conventional lithium-air secondary battery.

As a specific example, for example, M-P-O powder, Ketjenblack EC600JD powder and polytetrafluoroethylene (PTFE) powder are sufficiently pulverized and mixed at a weight ratio of 30:49:21 by using a raider machine, Roll forming was carried out to produce a sheet-like electrode (thickness: 0.5 mm). The sheet electrode is cut out into a circle having a diameter of 23 mm and pressed on a titanium mesh to form the air electrode 101.

For the air electrode 101, for the purpose of increasing the strength of the electrode and preventing the leakage of the electrolytic solution, not only cold pressing but hot pressing is applied to manufacture the air electrode 101 with more excellent stability. You can In the air electrode 101, one surface of its electrode is exposed to the atmosphere and the other surface is in contact with the electrolytic solution.

The air electrode 101 formed as described above is placed in the recess of the air electrode support 115 covered with PTFE, and is fixed by the air electrode fixing ring 104. The portion where the air electrode 101 and the air electrode support 115 are in contact with each other is not covered with PTFE in order to make electrical contact.

For example, when lithium metal is used, the negative electrode 104 is manufactured by stacking a plurality of metallic lithium foils and molding them into a predetermined shape. For the negative electrode 104, four metal lithium foils having a thickness of 150 μm are pressed and fixed to the negative electrode fixing washer 108.

The separator 105 is arranged inside the cylinder of the air electrode support 115 so as to be in contact with the partition 151 from the side opposite to the air electrode 101, and the negative electrode fixing ring 107 is arranged from the same side as the separator 105 to the cylinder of the air electrode support 115. A negative electrode fixing washer 108 to which the negative electrode 102 is pressure-bonded is arranged inside the cylinder of the negative electrode fixing ring 107.

The inside of the cell (between the air electrode 101 and the negative electrode 102) is filled with the organic electrolyte solution 103, covered with the negative electrode support 109, and the air electrode support 115 and the negative electrode support 109 are fixed with a fixing screw 110. As the organic electrolyte solution 103, a 1 mol/l lithium trifluoromethanesulfonylamide/triethylene glycol dimethyl ether (LiTFSI/TEGDME solution) solution 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, the cycle test of the battery will be described. For the battery cycle test, a charge/discharge measurement system (VMP3, manufactured by Bio Logic) was used, and the current density per unit area of the air electrode 101 was 0.1 mA/cm ² , and the battery voltage was 2.0 from the open circuit voltage. The discharge voltage was measured until the voltage dropped to V. The battery charge test was performed at the same current density as during discharge until the battery voltage reached 4.2V. The battery charge/discharge test was performed under a normal living environment. The charge/discharge capacity was expressed as a value (mAh/g) per weight of the air electrode (carbon+MPO+PTFE).

An experimental example in which the catalyst of the air electrode 101 of the lithium-air secondary battery 100 according to the present embodiment is changed and the battery performance is evaluated will be described. Experimental Example 1 is an air electrode 101 containing CrPO ₄ as a catalyst. Experimental Example 2 MnPO _4, Experiment 3 FePO _4, Example 4 is CoPO _4, Experiment 5 NIPO _4, Example 6 is Rupo _4.

FIG. 3 shows an example of initial discharge and charge curves of the lithium-air secondary battery 100 of Experimental Example 6. From FIG. 3, it was confirmed that when RuPO ₄ (Experimental Example 6) was used for the catalyst of the air electrode 101, the average discharge voltage was 2.83 V and the discharge capacity was 2790 mAh/g, which were large values.

Here, the average charge/discharge voltage is defined as the discharge voltage and the charge voltage at the intermediate value of the total discharge capacity in the figure. Also, the initial charging voltage is 3.66 V, and the charging capacity is 2818 mAh/g, which is almost the same as the discharging capacity, which shows that the reversibility is excellent.

The battery performance was also measured for other experimental examples. Table 1 shows the changes in discharge voltage and discharge capacity when the charge/discharge cycle was repeated the first time, 20 times, and 50 times.

From Table 1, it can be seen that RuPO ₄ (Experimental Example 6) has the highest average discharge voltage and the largest discharge capacity. It was also confirmed that the discharge capacity retention rate after 50 cycles was as high as 95%, and that after 50 cycles, the discharge voltage and the discharge capacity were higher than those of the experimental examples of any composition. On the other hand, NIPO ₄ (Experimental Example 5) showed the lowest discharge capacity at the 50th time as compared with the other material systems. However, it shows a large discharge capacity of 1000 mAh/g or more even after 50 cycles, and is considered to have high catalytic activity and stability as compared with conventional electrode catalysts. The overall order of battery performance is RuPO ₄ (Experimental Example 6)>MnPO ₄ (Experimental Example 2)>CoPO ₄ (Experimental Example 4)>FePO ₄ (Experimental Example 3)>CrPO ₄ (Experimental Example 1)> This is NIPO ₄ (Experimental Example 5). Thus, it was confirmed that a material containing a metal M (M is at least one metal selected from Cr, Mn, Fe, Co, Ni, Ru) and a PO ₄ group as an electrode catalyst exhibits excellent activity. did it.

Next, Experimental Examples 7 to 12 in which the performance of the battery of the air electrode 101 containing a P ₂ O ₇ group as a catalyst was evaluated will be described. Experimental Example 7 is CrP ₂ O ₇ , Experimental Example 8 is MnP ₂ O ₇ , Experimental Example 9 is FeP ₂ O ₇ , Experimental Example 10 is CoP ₂ O ₇ , Experimental Example 11 is NiP ₂ O ₇ , and Experimental Example 12 is RuP. ₂ O ₇ .

Table 2 shows the conversion of the discharge voltage and the discharge capacity when the charge, discharge cycle was repeated 20 times and 50 times for each of Experimental Examples 7 to 12.

From Table 2, it can be seen that RuP ₂ O ₇ (Experimental Example 12) has the highest average discharge voltage and the largest discharge capacity. Also, the discharge capacity retention rate after 50 cycles was as high as 92%, and it was confirmed that after 50 cycles, the discharge voltage and the discharge capacity were higher than those of the experimental examples of any composition.

On the other hand, CrP ₂ O ₇ (Experimental Example 7) shows the lowest discharge capacity at the 50th time as compared with other material systems. However, it shows a large discharge capacity of 1000 mAh/g or more even after 50 cycles, and is considered to have high catalytic activity and stability as compared with conventional electrode catalysts. The overall order of battery performance is RuP ₂ O ₇ (Experimental Example 12)>MnP ₂ O ₇ (Experimental Example 8)>CoP ₂ O ₇ (Experimental Example 10)>FeP ₂ O ₇ (Experimental Example 9)> NiP ₂ O ₇ (Experimental Example 11)>CrP ₂ O ₇ (Experimental Example 7). As a general tendency, a decrease in charging voltage was confirmed as compared with the PO ₄ system, and it can be seen that it is effective in improving charge/discharge energy efficiency.

Thus, a material containing a metal M (M is at least one metal selected from Cr, Mn, Fe, Co, Ni and Ru) and a P ₂ O ₇ group as an electrode catalyst exhibits excellent activity. I was able to confirm that.

Next, Experimental Examples 13 to 18 in which the performance of the battery of the air electrode 101 containing P ₃ O ₉ group as a catalyst was evaluated will be described. Experimental Example 13 _CrP 3 _{O 9,} Experimental Examples 14 _MnP 3 _{O 9,} Experimental Examples 15 _FeP 3 _{O 9,} Experimental Examples 16 _CoP 3 _{O 9,} Experimental Examples 17 _NiP 3 _{O 9,} Experimental Examples 18 RuP ₃ O ₉ .

Table 3 shows the conversion of the discharge voltage and the discharge capacity when each of the Experimental Examples 13 to 18 was repeatedly charged and discharged for the first time, 20 times, and 50 times.

From Table 3, it was found that RuP ₃ O ₉ (Experimental Example 18) had the highest average discharge voltage and the largest discharge capacity. Further, the discharge capacity retention rate after 50 cycles was as high as 94%, and it was confirmed that after 50 cycles, the discharge voltage and the discharge capacity were higher than those of the experimental examples of any composition.

On the other hand, CrP ₃ O ₉ (Experimental Example 13) showed the lowest discharge capacity at the 50th time as compared with other material systems. However, it shows a large discharge capacity of 1000 mAh/g or more even after 50 cycles, and is considered to have high catalytic activity and stability as compared with conventional electrode catalysts.

The overall order of battery performance is RuP ₃ O ₉ (Experimental Example 18)>MnP ₃ O ₉ (Experimental Example 14)>FeP ₃ O ₉ (Experimental Example 15)>CoP ₃ O ₉ (Experimental Example 16)> NiP ₃ O ₉ (Experimental Example 17)>CrP ₃ O ₉ (Experimental Example 13). In Experimental Example 18, the largest discharge capacity was confirmed in the present embodiment, and it was found that the combination of Ru and P ₃ O ₉ had a great effect on increasing the discharge capacity.

As described above, a material containing a metal M (M is at least one metal selected from Cr, Mn, Fe, Co, Ni and Ru) and a P ₃ O ₉ group as an electrode catalyst exhibits excellent activity. Was confirmed.

Here, the result of comparison between the lithium-air secondary battery 100 of the present embodiment and a conventional lithium-air secondary battery will be described.

In Comparative Example 1, a well-known manganese oxide (MnO ₂ ) was used as an electrode catalyst for the air electrode, and the other conditions were the same as those of the above-described experimental example. A commercially available reagent (manufactured by Kanto Chemical Co., Inc.) was used as the manganese oxide (MnO ₂ ).

Table 4 shows the results of comparison between Comparative Example 1 and Experimental Example 18 described above.

As shown in Table 4, Comparative Example 1 showed a moderate initial discharge capacity of about 850 mAh/g, but the discharge capacity retention rate after 50 cycles was almost 27%, and the cycle stability was poor. Compared with Experimental Example 18 of the present embodiment, the battery performance is remarkably low.

As described above, the lithium-air secondary battery of the present embodiment in which the electrode including the material M-P-O containing metal, phosphorus, and oxygen as the electrode catalyst is the air electrode has a capacity higher than that in the case of using a known material. And excellent cycle characteristics with respect to voltage. It was confirmed that the material M-P-O containing metal, phosphorus, and oxygen is effective as a catalyst for an air electrode for a lithium-air secondary battery.

As described above, the lithium-air secondary battery of the present invention including the air electrode that uses the material M-P-O containing metal, phosphorus, and oxygen as a catalyst has a small difference between the charging voltage and the discharging voltage, and is charged and discharged. A secondary battery with good cycle performance can be provided. It should be noted that the present invention is not limited to the above-described embodiment, and can be modified within the scope of the gist thereof.

By using the material M-P-O containing metal, phosphorus, and oxygen as the electrode catalyst for the air electrode of the lithium-air secondary battery, a lithium-air secondary battery having excellent charge-discharge cycle performance can be produced. It can be effectively used as a drive source for various electronic devices.

100: Lithium-air secondary battery 101: Positive electrode (air electrode)
102: Negative electrode 103: Organic electrolyte 104: Air electrode fixing ring 105: Separator 107: Negative electrode fixing ring 108: Negative electrode fixing washer 109: Negative electrode support 110: Fixing screw 111: O ring 115: Air electrode support 121 : Air electrode terminal 122: Negative electrode terminal 151: Partition

Claims (2)

In a lithium-air secondary battery having a positive electrode using oxygen in the air as a positive electrode active material, a negative electrode using metallic lithium or a lithium-containing material as a negative electrode active material, and an organic electrolytic solution containing a lithium salt,
The positive electrode is an air electrode mainly composed of carbon, and at least one metal selected from Cr, Mn, Fe, Co, Ni and Ru and a material containing a P ₂ O ₇ group were added as an electrode catalyst . A lithium-air secondary battery characterized in that In a lithium-air secondary battery having a positive electrode using oxygen in the air as a positive electrode active material, a negative electrode using metallic lithium or a lithium-containing material as a negative electrode active material, and an organic electrolytic solution containing a lithium salt,
The positive electrode is an air electrode mainly composed of carbon, as an electrode catalyst, Cr, Mn, Fe, Co, Ni, and at least one metal in the Ru, was added a material containing P ₃ O ₉ group It features and to Brighter lithium air secondary battery that.

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