JP5562204B2 - Positive electrode for lithium air secondary battery, method for producing the same, and lithium air secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a lithium air secondary battery, a positive electrode manufacturing method for a lithium air secondary battery, and a lithium air secondary battery, and is particularly suitable for a lithium air secondary battery having a low charge voltage and excellent charge / discharge cycle characteristics. The present invention relates to a positive electrode for a lithium-air secondary battery, a positive electrode manufacturing method for a lithium-air secondary battery, and the lithium-air secondary battery.

  Metal-air batteries have a theoretical energy density that far surpasses lithium-based batteries such as lithium ion batteries. Among these, zinc-air primary batteries have a large discharge capacity of about 300 mAh / g, and are mainly used for hearing aids and the like. However, since the zinc-air primary battery can only obtain a voltage of about 1 V as compared with a lithium battery using a non-aqueous electrolyte, it is considered difficult to use it widely.

  In recent years, as a positive electrode reaction system, as with a zinc-air battery, electrochemical reduction (discharge) and generation (charge) of oxygen are used, and metal lithium is combined in place of zinc as a negative electrode, and nonaqueous is used as an electrolyte. An attempt has been made to produce a lithium-air secondary battery exhibiting a high voltage of 2 to 3 V by using an electrolyte, and a prototype example in which a larger discharge capacity of 1000 mAh / g or more can be obtained at the first discharge is reported. Has been.

  However, in such a lithium-air secondary battery, the voltage at the time of charging is high, the electrolytic solution is decomposed, and the reversibility of deposition and decomposition of the discharge product (lithium oxide) is insufficient. For this reason, when the charge / discharge cycle is repeated, the discharge capacity is remarkably reduced.

  Therefore, attempts have been made to increase the activity of the electrode by adding a catalyst to the positive electrode for a lithium-air secondary battery. For example, in the following Non-Patent Document 1, a lithium-air secondary battery using a positive electrode to which platinum (Pt) or various metal oxides are added as a catalyst is manufactured, and a charge / discharge test is performed. As a result of the charge / discharge test, when nickel oxide (NiO) was added as the metal oxide catalyst, the discharge capacity at the first charge / discharge cycle was 1600 mAh / g, and even after the 10th charge / discharge cycle, The discharge capacity is 600 mAh / g.

When iron trioxide (Fe ₂ O ₃ ) is added, the discharge capacity at the first charge / discharge cycle is 2700 mAh / g, and after the 10th charge / discharge cycle, it is 75 mAh / g. When triiron tetroxide (Fe ₃ O ₄ ) is added, the discharge capacity at the first charge / discharge cycle is 1200 mAh / g, and the discharge capacity after the 10th charge / discharge cycle is 800 mAh / g. Yes.

  However, in the results of the charge / discharge test of Non-Patent Document 1, all of them have a high charge voltage and a significant decrease in discharge capacity due to the charge / discharge cycle. For practical use as a secondary battery, further charge / discharge is required. This indicates that the cycle characteristics need to be improved.

“An 02 cathode for rechargeable lithiumbatteries: The effect of a catalyst”, A. Debart, J.A. Bao, G. Armstrong, P.A. G. Bruce, Journal of Power Sources, Vol. 174, pp. 1177-1182 (2007).

  As described above, the conventional lithium-air secondary battery as described in Non-Patent Document 1 has a problem that it has a high charge voltage and it is difficult to obtain good charge / discharge cycle characteristics.

  The present invention has been made to solve the above-described problems, and can provide a positive electrode for a lithium-air secondary battery capable of reducing a charging voltage and having good charge / discharge cycle characteristics, a manufacturing method thereof, and a lithium-air secondary battery. The purpose is to provide.

  The present invention comprises the following technical means in order to solve the above-mentioned problems.

The first technical means is a positive electrode for a lithium-air secondary battery used for a lithium-air secondary battery, comprising carbon, a catalyst, and a binder, wherein the catalyst contains at least iron (Fe) ions and nickel (Ni) ions. When the number of moles of iron (Fe) ions and nickel (Ni) ions constituting the mixed oxide used as the catalyst is expressed as NFe and NNi, (NFe: NNi) = By making the molar ratio of 2: 1 or (NFe: NNi) = 1: 2, the mixed oxide is a spinel oxide .

A second technical means is a positive electrode manufacturing method for a lithium air secondary battery for manufacturing a positive electrode of a lithium air secondary battery, wherein a molar ratio of iron (Fe) ions to nickel (Ni) ions is predetermined. The iron nitrate nonahydrate (Fe (NO ₃ ) ₃ · 9H ₂ O) powder and the nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ · 6H ₂ O) powder in a weight ratio to be a ratio are ion-exchanged water A first step of adding a malic acid (C ₄ H ₆ O ₅ ) and an aqueous ammonia solution to a mixed aqueous solution of metal salt dissolved in a solution to prepare a mixed aqueous solution having a predetermined pH (potential hydrogen); A precursor obtained by evaporating to dryness by heating the mixed aqueous solution prepared at a predetermined pH at a predetermined temperature is heat-treated at a predetermined temperature and time as an oxide catalyst. Formation And a third step of mixing the formed oxide catalyst with carbon and a binder at a predetermined weight ratio, and further molding to produce a positive electrode for a lithium-air secondary battery. And the molar ratio of iron (Fe) ions to nickel (Ni) ions is 2: 1 or 1: 2, whereby the composition of Fe _x Ni _y O _z is used as the oxide catalyst. In the formula, a spinel oxide having a relationship of x: y = 2: 1 or x: y = 1: 2 is obtained .

The third technical means comprises a positive electrode made of carbon, a catalyst, and a binder, and a negative electrode made of metal lithium or a substance capable of occluding and releasing lithium ions, and one surface of the positive electrode is in contact with air, In the lithium-air battery in which the other surface of the positive electrode is in contact with a non-aqueous electrolyte and the non-aqueous electrolyte is disposed between the positive electrode and the negative electrode, the positive electrode is composed of carbon, a catalyst, and a binder. The catalyst is a mixed oxide containing at least iron (Fe) ions and nickel (Ni) ions, and each mole of iron (Fe) ions and nickel (Ni) ions constituting the mixed oxide serving as the catalyst. When the number is expressed as NFe, NNi, the mixed oxide is spinned by setting the molar ratio of (NFe: NNi) = 2: 1 or (NFe: NNi) = 1: 2. Characterized in that it is constituted by a type oxides.

  According to the positive electrode material for a lithium air secondary battery, the positive electrode material manufacturing method for a lithium air secondary battery, and the lithium air secondary battery of the present invention, the positive electrode considered to be important for reducing the charging voltage of the lithium air secondary battery In addition, since a highly active catalyst is added, the following effects can be obtained.

  That is, by adding a highly active catalyst to the positive electrode for a lithium-air secondary battery, decomposition of precipitates generated during discharge is accelerated, and good reversibility of the discharge products is obtained, so the charging voltage is reduced. Therefore, it is possible to produce a lithium-air secondary battery having very good charge / discharge cycle characteristics.

It is sectional drawing which shows an example of the cell structure of the lithium air secondary battery by this invention. It is a characteristic view which shows an example of the charging / discharging curve at the time of the first charge / discharge of the lithium air secondary battery by this invention. It is a characteristic diagram showing the XRD pattern of the perovskite type oxide used as a positive electrode of a catalyst of a lithium air secondary cell according to the present invention _{(La 0.6 Sr 0.4 Fe 0.8 Ni} 0.2 O 3).

  Hereinafter, preferred embodiments of a positive electrode for a lithium air secondary battery, a positive electrode manufacturing method for a lithium air secondary battery, and a lithium air secondary battery according to the present invention will be described in detail with reference to the drawings. .

(Features of the present invention)
Prior to the description of the embodiments of the present invention, an outline of the features of the present invention will be described first. The present invention relates to a positive electrode for a lithium air secondary battery, a method for producing the same, and a lithium air secondary battery using the positive electrode.

  In the present invention, the positive electrode of the lithium-air secondary battery is made of carbon, a catalyst, and a binder, and the catalyst contains at least iron (Fe) ions and nickel (Ni) ions, and has a predetermined molar ratio (for example, 8 : 2, 2: 1, 6: 4, 4: 6, 1: 2, 2: 8), which is a mixed oxide composed of iron (Fe) ions and nickel (Ni) ions. .

  The manufacturing method of the lithium air secondary battery positive electrode containing this catalyst is as follows, for example. First, as a first step, iron (Fe) ions and nickel (Ni) having a predetermined molar ratio (for example, 8: 2, 2: 1, 6: 4, 4: 6, 1: 2, 2: 8) are used. ) After adding malic acid and an aqueous ammonia solution to a mixed aqueous solution of metal salt with ions to prepare an aqueous solution having a predetermined pH (potential hydrogen: hydrogen ion concentration index), for example, an aqueous solution having a pH of 2.5, As a process of the above, a precursor obtained by evaporating to dryness by heating at a predetermined temperature (for example, 170 ° C.) is heat-treated under conditions of a predetermined temperature and time (for example, heat treatment for 5 hours or more at 600 ° C.) ) To form a mixed oxide.

  Thereafter, as the third step, using the mixed oxide obtained in the second step as an oxide catalyst, a weight ratio (for example, oxide catalyst: carbon: binder = 5: 3: 2 weight ratio), and further molded (for example, formed into a sheet and then cut into a circle) to produce a positive electrode for a lithium-air secondary battery.

  By using a positive electrode for a lithium-air secondary battery containing a catalyst made of a mixed oxide such as this, it is possible to realize a lithium-air secondary battery having a low charge voltage and excellent charge / discharge cycle characteristics. It becomes possible.

Here, by setting the molar ratio of iron (Fe) ions to nickel (Ni) ions to 2: 1 or 1: 2, as the oxide catalyst, in the composition formula of Fe _x Ni _y O _z , x By using a spinel oxide having a relationship of: y = 2: 1 or x: y = 1: 2, a lithium-air secondary battery having even better characteristics can be realized.

In addition, in the first step, before adding the malic acid and the ammonia aqueous solution to the metal salt mixed aqueous solution, the metal salt mixed aqueous solution has a weight that includes a predetermined number of moles of lanthanum (La) ions. Lanthanum nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) powder, or lanthanum (La) ions and alkaline earth metal ions (for example, calcium (Ca) ions, strontium (Sr) ions, barium ( A step of further adding a lanthanum nitrate hexahydrate powder and a nitrate-based alkaline earth metal powder in a weight ratio at which the molar ratio with any one of Ba) ions becomes a predetermined molar ratio; Malic acid and the aqueous ammonia solution may be further added to prepare a mixed aqueous solution having a predetermined pH.

In the case where an oxide containing lanthanum (La) ions or a composite oxide containing both lanthanum (La) ions and alkaline earth metal ions is further added, the alkaline earth metal ions are expressed as M ions, and iron When the number of moles of (Fe) ion, nickel (Ni) ion, lanthanum (La) ion, and alkaline earth metal ion (M ion) is expressed as NFe, NNi, NLa, NM, nitric acid is added to the metal salt mixed aqueous solution. When lanthanum hexahydrate (Ni (NO ₃ ) ₂ · 6H ₂ O) powder is further added, (NFe + NNi): NLa = 1: 1, or lanthanum nitrate hexahydrate in a metal salt mixed aqueous solution When the powder and nitrate alkaline earth metal powder are further added, the molar ratio of (NFe + NNi) :( NLa + NM) = 1: 1 is established. As compound _catalyst, in the composition formula La _x Fe z _Ni u _{O v} or _{La x M y Fe z Ni u} O v, x = (z + u) or (x + y) = (z + u) perovskite type oxide consisting relation to By using it, a lithium air secondary battery having even better characteristics can be realized.

(Embodiment)
Next, an example of the outline of the lithium air secondary battery according to the present invention will be described.

  The positive electrode in which the electrochemical redox reaction of oxygen, which is the positive electrode active material, is made of carbon, catalyst, and binder, and is a mixture of carbon powder and catalyst powder with binder powder such as polytetrafluoroethylene (PTFE). Is applied to a metal mesh by applying pressure-molding on a support such as a breathable metal mesh or by dispersing the above mixture in a solvent such as an organic solvent to form a slurry (Slurry). It is produced using means such as drying.

  One surface of the produced positive electrode is exposed to the atmosphere, and the other surface of the positive electrode is disposed in contact with the non-aqueous electrolyte. Here, in order to increase the strength of the electrode and prevent leakage of the electrolytic solution, it is possible to produce a positive electrode with more stability by performing hot pressing as well as cold pressing. .

  The discharge reaction on the positive electrode can be expressed by the following formulas (1) and (2).

2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (1)
Or 2Li ⁺ + (1/2) O ₂ + 2e ⁻ → Li ₂ O (2)
The lithium ions (Li ⁺ ) in the formulas (1) and (2) have moved from the negative electrode to the positive electrode surface via the electrolytic solution. Further, oxygen is taken into the positive electrode from the atmosphere.

When Li ₂ O ₂ or Li ₂ O produced by the discharge reaction as described above is deposited on the positive electrode and covers all the reaction sites on the positive electrode, the discharge reaction is completed. At the time of charging, a reaction opposite to the discharge reaction occurs, and when all the discharge products generated at the time of decomposition are decomposed, the charging is completed.

  As the carbon used as the positive electrode material of the lithium air secondary battery according to the present invention, ketjen black, acetylene black, activated carbon, carbon fiber, etc. can be used. It is desirable to use a material with a small surface area and a high surface area in which many reaction sites exist.

  In addition, the present inventors have intensively studied the charge / discharge characteristics of a lithium-air secondary battery manufactured using a positive electrode to which a metal oxide is added as a catalyst as described above. As a result of the study, when a mixed oxide containing at least iron (Fe) ions and nickel (Ni) ions is added to the positive electrode as a catalyst, the charging voltage is lowered and the charge / discharge cycle characteristics are greatly improved. I found out.

In particular, when the number of moles of iron (Fe) ions and nickel (Ni) ions are expressed as NFe and NNi, respectively, the molar ratio of iron (Fe) ions and nickel (Ni) ions used as a catalyst is
(NFe: NNi) = 2: 1 or (NFe: NNi) = 1: 2.
As described above, when only a spinel type oxide (for example, NiFe ₂ O ₄ , FeNi ₂ O ₄ ) is obtained, a lithium air secondary battery having excellent charge / discharge characteristics can be realized.

  Further, by mixing iron (Fe) ions, nickel (Ni) ions, and lanthanum (La) ions, or iron (Fe) ions, nickel (Ni) ions, lanthanum (La) ions, and alkaline earth metals. It has been found that by mixing the ions, the resulting mixed oxide is added to the positive electrode as a catalyst, thereby showing even better characteristics. Here, as the alkaline earth metal ion, for example, any of calcium (Ca) ion, strontium (Sr) ion, and barium (Ba) ion is used.

In particular, moles of iron (Fe) ion, nickel (Ni) ion, lanthanum (La) ion, alkaline earth metal ion (for example, any of calcium (Ca), strontium (Sr), and barium (Ba) ions) When the numbers are expressed as NFe, NNi, NLa, and NM, respectively (however, when only iron (Fe) ions, nickel (Ni) ions, and lanthanum (La) ions are used as catalysts, NM = 0)) , The molar ratio of each metal ion of iron (Fe) ion, nickel (Ni) ion, lanthanum (La) ion and alkaline earth metal ion,
(NFe + NNi) :( NLa + NM) = 1: 1
It was found that when only a perovskite type oxide is obtained by mixing so as to satisfy the following conditions, the charge voltage is further lowered and the charge / discharge cycle characteristics are further improved. In particular, it has been found that when strontium (Sr) ions are used as alkaline earth metal ions, the most excellent characteristics are exhibited.

Here, the composition formula of the perovskite-type oxide using M as the alkaline earth metal of any one of calcium (Ca), strontium (Sr), and barium (Ba) is _defined as La _x M _y Fe _z. When expressed as Ni _u O _v , setting (x + y) = (z + u) is equivalent to setting the molar ratio to (NLa + NM) :( NFe + NNi) = 1: 1 as described above. When only lanthanum (La) ions are mixed with iron (Fe) ions and nickel (Ni) ions without containing alkaline earth metal ions (M ions), the composition formula of the perovskite oxide used as a catalyst Is expressed as La _x Fe _z Ni _u O _v , x = (z + u), and as described above, NM = 0, and the molar ratio is NLa: (NFe + NNi) = 1: 1 Are equivalent.

  As a catalyst synthesis method, a conventionally known method such as a solid phase method or a wet method can be used, but a wet method capable of synthesizing an oxide with a large surface area is more preferable.

  As the binder used as the positive electrode material of the lithium-air secondary battery, in addition to the PTFE powder as described above, a PTFE dispersion liquid, a polyvinylidene fluoride (PVdF) powder, or a dispersion liquid thereof is used. It is also possible.

As for the negative electrode of the lithium-air secondary battery, metallic lithium or a substance capable of occluding and releasing lithium ions (for example, carbon, silicon (Si), tin (Sn), Li _2.6 Ni _0.4 ). N) or the like can be used. However, in the case of using a compound such as carbon that does not contain lithium as the negative electrode material first, prior to the production of the lithium-air secondary battery, a lithiated carbon containing lithium (chemically or electrochemically in advance) It is necessary to chemically change to a compound such as C ₆ Li).

Moreover, as a non-aqueous electrolyte of a lithium air secondary battery, what is necessary is just a non-aqueous electrolyte which can move lithium ion, and an organic electrolyte or an ionic liquid can be used. Here, for the organic electrolyte, metal salts such as lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (LiPF ₆ ) are used as propylene carbonate (PC: Propylene Carbonate), ethylene carbonate (EC: Ethylene Carbonate). In addition, an organic solvent such as dimethyl carbonate (DMC) or a mixture thereof can be used.

  In addition, conventionally well-known various materials can be used also about battery constituent materials, such as a separator of a lithium air secondary battery, and a battery case, and there is no restriction | limiting in particular.

(Example)
Examples of a positive electrode for a lithium air secondary battery, a positive electrode manufacturing method for a lithium air secondary battery, and a lithium air secondary battery according to the present invention will be described in detail below. In addition, this invention is not limited only to the Example demonstrated below, In the range which does not change the summary, it cannot be overemphasized that it can change suitably and can implement.

Example 1
First, as Example 1, a case where a catalyst added to a positive electrode for a lithium-air secondary battery is formed by iron (Fe) ions and nickel (Ni) ions will be described.

(1) Manufacturing method of positive electrode for lithium air secondary battery First, the manufacturing method of the positive electrode for lithium air secondary battery is demonstrated.

In the first step, when the number of moles of iron (Fe) ions and nickel (Ni) ions is expressed as NFe and NNi, the molar ratio of iron (Fe) ions to nickel (Ni) ions is (NFe: NNi) = 8: 2
So that, in the ion exchanged water 400 ml, iron nitrate nonahydrate _{0.016mol (Fe (NO 3) 3} · 9H 2 O) powder (purity: 99.0%) and 0.004mol of nickel nitrate Hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) powder (purity: 99.0%) was dissolved to obtain a mixed metal nitrate aqueous solution.

Thereafter, 8.1 g of malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) was added to the obtained mixed aqueous solution of metal nitrate, and an aqueous ammonia solution was further added with stirring. potential Hydrogen) is set to a predetermined value, that is, 2.5 in the first embodiment.

  Furthermore, in the second step, the aqueous solution having a pH of 2.5 is evaporated to dryness while stirring at a predetermined temperature, that is, 170 ° C. in Example 1, and the obtained precursor is heated to a predetermined temperature and time. In other words, in Example 1, heat treatment was performed at 600 ° C. or higher for 5 hours to obtain an oxide catalyst as a mixed oxide.

Next, in the third step, carbon and binder (PTFE powder: polytetrafluoroethylene powder) are added to the obtained oxide catalyst in a predetermined weight ratio, that is, in Example 1,
Oxide catalyst: Carbon: PTFE = 5: 3: 2
The sheet electrode was mixed and roll-molded so as to have a weight ratio of 0.5 mm to produce a sheet-like electrode having a thickness of 0.5 mm and cut into a circle having a diameter of 23 mm to obtain a positive electrode for a lithium-air secondary battery.

  Further, not only when the molar ratio (NFe: NNi) of iron (Fe) ions to nickel (Ni) ions is (8: 2), but as shown in Table 1 described later, the molar ratio (NFe: NNi) A positive electrode in which five types of catalysts having (2: 1), (6: 4), (4: 6), (1: 2), and (2: 8) are added to carbon and a binder (PTFE powder) Was also prepared in the same procedure as the manufacturing method described above.

That is, iron nitrate nonahydrate (Fe (NO ₃ ) ₃ · 9H ₂ O) powder (purity: 99.0%) and nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ · 6H ₂ O powder (purity) : 99.0%) so that the molar ratios (NFe: NNi) of (2: 1), (6: 4), (4: 6), (1: 2), and (2: 8) are obtained. In addition, malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) was added to the resulting metal nitrate mixed aqueous solution dissolved in ion-exchanged water, and an aqueous ammonia solution was further added while stirring. The pH of the aqueous solution with a molar ratio (NFe: NNi) of 2.5 was adjusted to 2.5.

  Thereafter, the aqueous solution of each molar ratio (NFe: NNi) is also evaporated to dryness while stirring at 170 ° C., and the obtained precursor is heat-treated at 600 ° C. or more for 5 hours to obtain an oxide catalyst. It was.

Carbon and binder (PTFE powder) were added to each of the obtained oxide catalysts.
Oxide catalyst: Carbon: PTFE = 5: 3: 2
The resulting mixture was mixed and roll-molded to produce a sheet electrode having a thickness of 0.5 mm and cut into a circle having a diameter of 23 mm to obtain each positive electrode.

  For comparison, as shown in Table 1, a positive electrode composed of carbon (Ketjen Black EC600JD) and a binder (PTFE) without adding a catalyst was also subjected to the same manufacturing method as described above. Produced. In this case, the weight ratio of carbon to binder is 6: 4.

(2) Manufacturing method of lithium air secondary battery Next, the manufacturing method of the lithium air secondary battery using each positive electrode for lithium air secondary batteries manufactured by the manufacturing method demonstrated in the (1) term is demonstrated. FIG. 1 is a cross-sectional view showing an example of a cell structure of a lithium-air secondary battery according to the present invention, and shows an outline of the cell structure of the cylindrical lithium-air secondary battery manufactured in Example 1.

  The lithium air secondary battery shown in FIG. 1 includes a positive electrode connector 1, an electrode case 2, a positive electrode 3, a separator 4, a metal lithium negative electrode 5, a negative electrode connector 6, a negative electrode support 7, an O-ring 8, and a negative electrode terminal 9. The positive electrode connector 1, the negative electrode connector 6, and the negative electrode support 7 are all made of SUS (Special Use Stainless steel). The diameter of the circular air hole for taking air into the positive electrode 3 is 16 mm.

  The steps for manufacturing the lithium-air secondary battery shown in FIG. 1 are as follows. First, a positive electrode 3 made of carbon, a catalyst, and a binder is arranged on one side of an electrode case 2 whose surface is coated with Teflon (but no contact with the positive electrode 3). The positive electrode 3 was fixed by fitting 1. Here, the positive electrode 3 is a positive electrode for a lithium-air secondary battery described in the section (1), and was prepared for comparison with the case of a positive electrode to which six types of molar ratio (NFe: NNi) catalysts were added. A lithium-air secondary battery having a total of seven types of positive electrodes 3 in the case of a positive electrode composed of carbon without a catalyst and a binder alone is manufactured.

  Next, a non-aqueous electrolyte was injected on the side opposite to the positive electrode 3 of the electrode case 2 to which the positive electrode 3 was fixed. Further, after the separator 4 was inserted, the electrode case 2 was cut out into a circular shape and pressure-bonded to the negative electrode connector 6. The metallic lithium negative electrode 5 is fitted together with the negative electrode support 7 so that the separator 4 is sandwiched between the electrode cases 2. As a result, the positive electrode 3 is in a state where one surface is in contact with air and the other surface is in contact with the non-aqueous electrolyte.

  Further, after attaching the O-ring 8 to the electrode case 2, the negative electrode terminal 9 was fitted into a lithium air secondary battery.

As the non-aqueous electrolyte, an organic electrolyte was used, and a solution in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a propylene carbonate (PC) solvent at a concentration of 1 mol / l was used. Further, as described above, the metal lithium negative electrode 5 may be configured using a substance capable of inserting and extracting lithium ions instead of metal lithium.

(3) Characteristic Evaluation Test of Lithium Air Secondary Battery Next, results of conducting a charge / discharge cycle test as a characteristic evaluation test on a total of seven types of lithium air secondary batteries manufactured by the manufacturing method described in (2). Will be described.

For each of the seven types of lithium-air secondary batteries, the discharge end voltage was 2.0 V and the charge end voltage was 4. mA at a current density of 0.1 mA / cm ² (current density normalized by the area of the positive electrode 3 exposed to the atmosphere). A charge / discharge cycle test was performed under the condition of 5V. In addition, about the capacity | capacitance which shows a measurement result, it describes using the capacity | capacitance (mAh / g) per carbon weight contained in the positive electrode 3 for subsequent comparison.

  Table 1 is a table showing the measurement results of the discharge capacity in each cycle (first time, 20th time, 50th time) of a total of seven types of lithium-air secondary batteries produced in Example 1.

表１に示すように、本実施例１において作製したモル比（ＮＦｅ：ＮＮｉ）が（８：２）、（２：１）、（６：４）、（４：６）、（１：２）、（２：８）のそれぞれの酸化物触媒添加の正極３を用いる６種類すべての電池において、リチウム空気二次電池としての良好な作動を確認したが、正極３に触媒として添加した鉄（Ｆｅ）イオンとニッケル（Ｎｉイオン）との金属硝酸塩の混合比率すなわちモル比（ＮＦｅ：ＮＮｉ）の違いによって、放電特性に差異があることが分かった。

As shown in Table 1, the molar ratios (NFe: NNi) produced in Example 1 were (8: 2), (2: 1), (6: 4), (4: 6), (1: 2). ), (2: 8) In all six types of batteries using the positive electrode 3 to which the oxide catalyst was added, good operation as a lithium-air secondary battery was confirmed. It has been found that there is a difference in discharge characteristics depending on the mixing ratio of metal nitrate of Fe) ions and nickel (Ni ions), that is, the molar ratio (NFe: NNi).

  Particularly, when the molar ratio (NFe: NNi) of iron (Fe) ions and nickel (Ni ions) added to the positive electrode 3 as a catalyst is (2: 1) or (1: 2), extremely good discharge The characteristics are shown.

That is, when the molar ratio (NFe: NNi) of iron (Fe) ions to nickel (Ni ions) from which only FeNi ₂ O ₄ spinel type oxide is obtained is (2: 1), the initial discharge capacity is 1720 mAh / g. The 20th discharge capacity was 1593 mAh / g, and the 50th discharge capacity was 1233 mAh / g, showing the largest discharge capacity among the seven types of lithium air secondary batteries.

Further, when the molar ratio (NFe: NNi) of iron (Fe) ions to nickel (Ni ions) from which only NiFe ₂ O ₄ spinel type oxide is obtained is (1: 2), the initial discharge capacity is 1663 mAh. Among the seven types of lithium air secondary batteries, the 20th discharge capacity was 1501 mAh / g and the 50th discharge capacity was 1212 mAh / g, showing the second largest discharge capacity.

  In addition, in the case of the positive electrode 3 made of carbon alone (that is, only carbon and binder) without adding a catalyst, the initial discharge capacity is as large as 2031 mAh / g, but the 20th discharge capacity is 7 mAh / g. g, It was found that when the 50th discharge capacity was 0 mAh / g and the charge / discharge cycle was repeated, the discharge capacity drastically decreased.

  A lithium-air secondary battery using a positive electrode 3 to which a catalyst having a molar ratio (NFe: NNi) of Example 1 of (2: 1) and (1: 2) was added, and a positive electrode made of carbon alone without a catalyst For the lithium air secondary battery using No. 3, the charge / discharge curves at the first charge / discharge are shown as curves (a), (b), and (c) in FIG. FIG. 2 is a characteristic diagram showing an example of a charge / discharge curve at the time of initial charge / discharge of the lithium-air secondary battery according to the present invention. Not only this Example 1, but also Example 2 and Comparative Example 1 described later are shown. And 2 are also shown. In FIG. 2, the horizontal axis represents charge / discharge capacity (Capacity), and the vertical axis represents battery voltage (Voltage).

  In FIG. 2, when using a positive electrode to which a catalyst having a molar ratio (NFe: NNi) of Example 1 of (2: 1) is used, the average voltage is approximately about during discharge, as shown by curve (a). The discharge capacity was 1720 mAh / g. During charging, the average voltage was 4.10 V and the charging capacity was 1593 mAh / g.

  In addition, when a positive electrode to which a catalyst having a molar ratio (NFe: NNi) of Example 1 of (1: 2) was used was used, as shown in the curve (b), the average voltage was about 2. The discharge capacity was 1663 mAh / g. During charging, the average voltage was 4.10 V, and the charging capacity was 1751 mAh / g.

  On the other hand, when a positive electrode made of carbon alone without a catalyst was used, as shown in the curve (c), the average voltage during discharge was about 2.70 V, and the discharge capacity was 2031 mAh / g. Further, during charging, the average voltage was a high voltage value of 4.30 V, and the charging capacity was a remarkably low value of 451 mAh / g.

In Example 1, as shown in Table 1 and FIG. 2, the molar ratio (NFe: NNi) of iron (Fe) ions to nickel (Ni) ions is (8: 2), (2: 1), In all cases where the catalysts (6: 4), (4: 6), (1: 2), and (2: 8) were added, good charge / discharge cycle characteristics were shown, but the molar ratio (NFe: NNi) is (2: 1) compared to the case where a plurality of oxide catalysts are obtained as in (8: 2), (6: 4), (4: 6), and (2: 8). When the catalyst of only the spinel type oxide (NiFe ₂ O ₄ , FeNi ₂ O ₄ ) in the case of (1: 2) is obtained, the charging voltage is low and the charge / discharge capacity is also large and the best. The charge / discharge cycle characteristics were shown.

  In addition, compared with the positive electrode of carbon alone without a catalyst, the discharge capacity is slightly lower at the time of the first discharge, but by adding a catalyst, the charging voltage is lowered and the charge / discharge cycle characteristics are also improved. Greatly improved. This is because the addition of a catalyst to the positive electrode changed the gas diffusivity, conductivity, wettability, etc. of the positive electrode, so the initial discharge capacity decreased, but mixed oxidation of iron (Fe) and nickel (Ni). It can be considered that the product has a high activity for oxygen generation and can promote the decomposition of the discharge product at the time of charging, so that the charging voltage is lowered and the charge / discharge cycle characteristics are improved. it can.

(Example 2)
Next, as Example 2, the catalyst to be added to the positive electrode for the lithium-air secondary battery was changed to iron (Fe) ions and nickel (Ni) ions in the case of Example 1, and further lanthanum (La) ions and strontium. A case of forming with a mixed oxide added with (Sr) ions will be described.

(1) Manufacturing method of positive electrode for lithium air secondary battery First, the manufacturing method of the positive electrode for lithium air secondary battery in the present Example 2 is demonstrated.

First, in the first step, as in Example 1, when the number of moles of iron (Fe) ions and nickel (Ni) ions is expressed as NFe and NNi, iron (Fe) ions and nickel (Ni) The molar ratio with ions is (NFe: NNi) = 8: 2.
So that, in the ion exchanged water 400 ml, iron nitrate nonahydrate _{0.016mol (Fe (NO 3) 3} · 9H 2 O) powder (purity: 99.0%) and 0.004mol of nickel nitrate Hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) powder (purity: 99.0%) was dissolved to obtain a mixed metal nitrate aqueous solution.

Furthermore, in Example 2, when the number of moles of lanthanum (La) ions and strontium (Sr) ions is expressed as NLa and NSr, the molar ratio of lanthanum (La) ions to strontium (Sr) ions is (NLa : NSr) = 6: 4
So that, in the metal nitrate mixed aqueous solution, lanthanum nitrate hexahydrate _{0.03mol (La (NO 3) 3} · 6H 2 O) powder (purity: 99.99%) and strontium nitrate 0.02mol (Sr (NO ₃ ) ₂ ) powder (purity: 99.0%) is further dissolved, and finally, iron (Fe) ions, nickel (Ni) ions, lanthanum (La) ions, and strontium (Sr) ions (NFe + NNi) :( NLa + NSr) = 1: 1
A metal nitrate mixed aqueous solution was obtained.

Thereafter, 8.1 g of malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) was added to the finally obtained metal nitrate mixed aqueous solution as in Example 1, and the mixture was stirred. Then, an aqueous ammonia solution was further added so that the pH (potential Hydrogen) of the aqueous solution was 2.5 as in the case of Example 1.

  Furthermore, in the second step, as in Example 1, the aqueous solution having a pH of 2.5 was evaporated to dryness while stirring at 170 ° C., and the obtained precursor was heat-treated at 600 ° C. or more for 5 hours. As a result, an oxide catalyst was obtained as a mixed oxide.

Next, in the third step, carbon and a binder (PTFE powder) are added to the obtained oxide catalyst in the same manner as in Example 1.
Oxide catalyst: Carbon: PTFE = 5: 3: 2
The sheet electrode was mixed and roll-molded so as to have a weight ratio of 0.5 mm to produce a sheet-like electrode having a thickness of 0.5 mm and cut into a circle having a diameter of 23 mm to obtain a positive electrode for a lithium-air secondary battery.

Further, in the first step in Example 2, not only the molar ratio (NLa: NSr) of lanthanum (La) ions to strontium (Sr) ions is (6: 4), but also Table 2 described later. As shown in Fig. 4, the four kinds of molar ratios (NLa: NSr) of (10: 0), (8: 2), (4: 6), and (2: 8) were also prepared, and the molar ratio (NLa: In each of the five cases in total where NSr) is (10: 0), (8: 2), (6: 4), (4: 6), (2: 8), the molar ratio is (NFe: NNi). ) = (8: 2) The ratio of the molar ratio of lanthanum (La) ion to strontium (Sr) ion with respect to iron (Fe) ion and nickel (Ni) ion,
(NFe + NNi) :( NLa + NSr) = 1: 2, 1: 1, 2: 1
The respective metal nitrate mixed aqueous solutions having the three types of relationships were prepared.

Thereafter, malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) was added to each of the 15 mixed metal nitrate mixed aqueous solutions, and an aqueous ammonia solution was further added while stirring. The pH of the aqueous solution of {(NLa: NSr) and (NFe + NNi) :( NLa: NSr)} was set to 2.5, the same as in Example 1.

  Furthermore, in the second step, the aqueous solutions of the respective molar ratios {(NLa: NSr) and (NFe + NNi) :( NLa: NSr)} were also evaporated to dryness while stirring at 170 ° C. as in Example 1. The oxide precursor was obtained by solidifying and heat-treating the obtained precursor at 600 ° C. or more for 5 hours.

Next, in the third step, as in Example 1, carbon and a binder (PTFE powder) were added to each of the obtained oxide catalysts.
Oxide catalyst: Carbon: PTFE = 5: 3: 2
Are mixed, roll-molded to produce a sheet-like electrode having a thickness of 0.5 mm, and each positive electrode (positive electrode for a lithium-air secondary battery) is cut out into a circle having a diameter of 23 mm. Obtained.

  Thereafter, the lithium-air secondary battery having the cross-sectional structure shown in FIG. 1 was produced by the same manufacturing method as in Example 1, using the respective positive electrodes for the lithium-air secondary battery.

(2) Lithium-air secondary battery characteristic evaluation test Next, a result of conducting a charge / discharge cycle test as a characteristic evaluation test on a total of 15 types of lithium-air secondary batteries manufactured by the manufacturing method described in (1). Will be described.

For each of the 15 types of lithium-air secondary batteries, the same measurement method as in Example 1 was used, that is, a current density of 0.1 mA / cm ² (normalized by the area of the positive electrode 3 exposed to the atmosphere). Current density), a charge / discharge cycle test was performed under the conditions of a discharge end voltage of 2.0 V and a charge end voltage of 4.5 V. The capacity indicating the measurement result of Example 2 is also described using the capacity per unit weight of carbon (mAh / g) contained in the positive electrode 3 as in Example 1.

  For the oxide catalyst, the relationship of the molar ratio of lanthanum (La) ion to strontium (Sr) ion with respect to iron (Fe) ion and nickel (Ni) ion is {(NFe + NNi) :( When NLa + NSr)} is in a (1: 1) relationship, only perovskite type oxides are obtained.

For example, the molar ratio of iron (Fe) ions to nickel (Ni) ions (NFe: NNi) is (8: 2), and the molar ratio of lanthanum (La) ions to strontium (Sr) ions (NLa: NSr) is In the case of (6: 4), the relationship {(NFe + NNi) :( NLa + NSr)} of the molar ratio of lanthanum (La) ions and strontium (Sr) ions to iron (Fe) ions and nickel (Ni) ions is ( 1: 1) Malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) is added to a metal nitrate mixed aqueous solution that has a relationship of 1: 1), and an aqueous ammonia solution is further added with stirring. The pH of the aqueous solution was adjusted to 2.5, and then the precursor obtained by evaporating and drying the aqueous solution having a pH of 2.5 while stirring at 170 ° C. was subjected to heat treatment at 600 ° C. or more for 5 hours. Thus, a perovskite oxide catalyst having a composition of (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) can be obtained.

FIG. 3 is a characteristic diagram showing an XRD pattern of a perovskite oxide (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) used as a catalyst for a positive electrode of a lithium-air secondary battery according to the present invention. It is. As shown in the XRD pattern of FIG. 3, the lithium-air secondary battery to which the oxide obtained by the above-described manufacturing method is added as a positive electrode catalyst is expressed as (La _0.6 Sr _0.4 Fe _0.8). It shows that the positive electrode contains only a perovskite oxide having a composition of Ni _0.2 O ₃ ).

  Table 2 is a table showing the measurement results of the discharge capacity in each cycle (first time, 20th time, 50th time) of a total of 15 types of lithium-air secondary batteries produced in Example 2.

表２に示すように、本実施例２において作製した、鉄（Ｆｅ）イオンとニッケル（Ｎｉ）イオンとのモル比（ＮＦｅ：ＮＮｉ）が（８：２）であり、かつ、ランタン（Ｌａ）イオンとストロンチウム（Ｓｒ）イオンとのモル比（ＮＬａ：ＮＳｒ）が（１０：０）、（８：２）、（６：４）、（４：６）、（２：８）のそれぞれにおいて、鉄（Ｆｅ）イオン、ニッケル（Ｎｉ）イオンに対するランタン（Ｌａ）イオン、ストロンチウム（Ｓｒ）イオンのモル比の関係｛（ＮＦｅ+ＮＮｉ）：（ＮＬａ+ＮＳｒ）｝が、（１：２）、（１：１）、（２：１）のそれぞれの酸化物触媒添加の正極を用いた１５種類すべての電池において、酸化物触媒がペロブスカイト型酸化物であるか否かによらず、リチウム空気二次電池としての良好な作動を確認することができた。

As shown in Table 2, the molar ratio (NFe: NNi) of iron (Fe) ions to nickel (Ni) ions produced in Example 2 is (8: 2), and lanthanum (La) In each of the molar ratio of ions to strontium (Sr) ions (NLa: NSr) (10: 0), (8: 2), (6: 4), (4: 6), (2: 8), The relationship of the molar ratio of lanthanum (La) ion and strontium (Sr) ion to iron (Fe) ion and nickel (Ni) ion {(NFe + NNi) :( NLa + NSr)} is (1: 2), ( In all 15 types of batteries using the positive electrode with the addition of the oxide catalyst (1: 1) and (2: 1), the lithium-air secondary battery is used regardless of whether the oxide catalyst is a perovskite oxide. Confirm good operation as a battery It could be.

However, among them, the molar ratio of iron (Fe) ions to nickel (Ni) ions (NFe: NNi) is (8: 2), and the molar ratio of lanthanum (La) ions to strontium (Sr) ions. (NLa: NSr) is (6: 4), and the relationship of the molar ratio of lanthanum (La) ion and strontium (Sr) ion to iron (Fe) ion and nickel (Ni) ion {(NFe + NNi) :( NLa + NSr)} has a relationship of (1: 1), that is, only a perovskite oxide catalyst having a composition of (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) Is obtained, the best discharge characteristics are shown.

A charge / discharge curve at the time of the first charge / discharge of a lithium air secondary battery using a positive electrode from which only a perovskite type oxide (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) catalyst is obtained This is shown as the curve (d) in FIG.

As shown in the curve (d) of FIG. 2, when only the perovskite oxide (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) is contained as a positive electrode catalyst, The average voltage was about 2.75 V, and the discharge capacity was 2295 mAh / g. During charging, the average voltage was 3.85 V and the charging capacity was 2647 mAh / g.

  That is, in Example 2, as shown in Table 2 and FIG. 2, the molar ratio (NFe: NNi) of iron (Fe) ions and nickel (Ni) ions, which showed good characteristics in Example 1, is The catalyst obtained by mixing the metal nitrate mixed aqueous solution of (8: 2) with a metal nitrate of lanthanum (La) ion and strontium (Sr) ion is further used for the positive electrode of the lithium air secondary battery. It was confirmed that the charge voltage can be lowered and the charge / discharge cycle characteristics can be improved.

In particular, the molar ratio (NLa: NSr) of lanthanum (La) ions to strontium (Sr) ions in the metal nitrate mixed aqueous solution is (6: 4), and lanthanum with respect to iron (Fe) ions and nickel (Ni) ions ( La) ions, the relationship of the molar ratio of strontium (Sr) ions {(NFe + NNi) :( NLa + nSr)} is (1: in the case of _{1), (La 0.6 Sr 0.4 Fe 0} . Only an oxide catalyst with a composition of ₈ Ni _0.2 O ₃ ) is obtained. By using a positive electrode containing only an oxide catalyst having such a composition, the average charging voltage is 3.85 V, which is the lowest, and even after the 50th charge / discharge cycle test, as shown in Table 2, It has very good characteristics, such as having a discharge capacity of 1798 mAh / g, far exceeding 1000 mAh / g.

This is because the mixed metal valence of the transition metal is obtained when the oxide catalyst having the composition of (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) added to the positive electrode forms a perovskite structure. It can be considered that the state and oxygen defects are introduced into the lattice, the activation of the catalyst is improved, and the characteristics of the positive electrode are improved.

  Therefore, from the above characteristic evaluation results, it is preferable to use a mixture of iron (Fe) and nickel (Ni) as a catalyst to be mixed with the positive electrode, and further, by mixing lanthanum (La) and strontium (Sr), Charge / discharge cycle characteristics can be further improved. Among them, it is preferable to use a perovskite oxide having a molar ratio of mixed metal ions {(NFe + NNi) :( NLa + NSr)} of (1: 1) as a catalyst for the positive electrode.

(Example 3)
Next, as Example 3, the best characteristics as a catalyst to be added to the positive electrode for a lithium-air secondary battery of Example 2 were shown. (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) In the perovskite type oxide having a composition of ₃ ), when the alkaline earth metal to which strontium (Sr) belongs is expressed as M, calcium (Ca) and barium belonging to the same alkaline earth metal (M) other than strontium (Sr) A case where strontium (Sr) ions are replaced by respective ions (M ions = calcium (Ca) ions, barium (Ba) ions) with (Ba) will be described.

(1) Manufacturing method of positive electrode for lithium air secondary battery First, the manufacturing method of the positive electrode for lithium air secondary battery in the present Example 3 is demonstrated.

  First, in the first step, using the same method as in Example 2, iron (Fe) ions, nickel (Ni) ions, lanthanum (La) ions, calcium (Ca) ions, barium (Ba) ions Are expressed as NFe, NNi, NLa, NSr, and NBa, the following two types of metal nitrate mixed aqueous solutions were prepared.

That is, first, the molar ratio of iron (Fe) ions to nickel (Ni) ions is (NFe: NNi) = 8: 2.
And the molar ratio of lanthanum (La) ion to calcium (Ca) ion is (NLa: NCa) = 6: 4
And the relationship of the molar ratio of iron (Fe) ion, nickel (Ni) ion, lanthanum (La) ion and calcium (Ca) ion is (NFe + NNi) :( NLa + NCa) = 1: 1
A metal nitrate mixed aqueous solution was prepared.

Similarly, the molar ratio of iron (Fe) ions to nickel (Ni) ions is (NFe: NNi) = 8: 2.
And the molar ratio of lanthanum (La) ions to barium (Ba) ions is (NLa: NBa) = 6: 4
And the relationship of the molar ratio of iron (Fe) ion, nickel (Ni) ion, lanthanum (La) ion and barium (Ba) ion is (NFe + NNi) :( NLa + NBa) = 1: 1
A metal nitrate mixed aqueous solution was prepared.

Thereafter, 8.1 g of malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) was added to each of the obtained two mixed aqueous metal nitrate solutions as in Example 1, and the mixture was stirred. While further adding an aqueous ammonia solution, the pH (potential Hydrogen) of the aqueous solution was adjusted to 2.5, the same as in Example 1.

  Furthermore, in the second step, as in Example 1, each of these two aqueous solutions having a pH of 2.5 was evaporated to dryness while stirring at 170 ° C., and the resulting precursor was 600 ° C. or higher. By performing heat treatment for 5 hours, respective oxide catalysts were obtained as two types of mixed oxides.

Next, in the third step, as in Example 1, carbon and a binder (PTFE powder) were added to each of the two types of oxide catalysts obtained.
Oxide catalyst: Carbon: PTFE = 5: 3: 2
Two types of positive electrodes (positive electrodes for lithium-air secondary batteries) are prepared by mixing, roll-molding to produce a sheet-like electrode having a thickness of 0.5 mm, and cutting out into a circle having a diameter of 23 mm. Got.

  Thereafter, the lithium-air secondary battery having the cross-sectional structure shown in FIG. 1 was produced by the same manufacturing method as in Example 1, using the respective positive electrodes for the lithium-air secondary battery.

(2) Lithium-air secondary battery characteristic evaluation test First, two kinds of the above-described two types of catalysts used as the positive electrode catalyst for the lithium-air secondary battery manufactured by the manufacturing method described in the section (1) are used. Crystal structure of mixed oxides (La _0.6 Ca _0.4 Fe _0.8 Ni _0.2 O ₃ , La _0.6 Ba _0.4 Fe _0.8 Ni _0.2 O ₃ ) by XRD pattern measurement Measurements were made. The measured XRD patterns are two kinds of mixed oxides (La _0.6 Ca _0.4 Fe _0.8 Ni _0.2 O ₃ , La _0.6 Ba _0.4 Fe _0.8 Ni _0.2 O _3. ) Show similar patterns to the XRD pattern of the mixed oxide (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) shown in FIG. 3, and only perovskite oxide is obtained. It was confirmed to have a crystal structure.

  Next, the results of conducting a charge / discharge cycle test as a characteristic evaluation test using the same measurement method as in Example 1 for two types of lithium-air secondary batteries will be described. The capacity indicating the measurement result of Example 3 is also described using the capacity per unit weight of carbon (mAh / g) contained in the positive electrode 3, as in Example 1.

Table 3 shows the measurement results of the discharge capacity in each cycle (first time, 20th time, 50th time) of the two types of lithium-air secondary batteries produced in Example 3, and shows the best characteristics in Example 2. The measurement results of the discharge capacity of a lithium air secondary battery using a perovskite oxide having a composition of (La _0.6 Sr _0.4 Fe _0.8 Ni _0.2 O ₃ ) as a positive electrode catalyst (transcribed from Table 2) It is a table shown together.

表３に示すように、実施例２のストロンチウム（Ｓｒ）イオンというアルカリ土類金属イオン（Ｍイオン）を用いる場合と同様、該ストロンチウム（Ｓｒ）イオンを、同じアルカリ土類金属イオン（Ｍイオン）であるカルシウム（Ｃａ）イオンやバリウム(Ｂａ）イオンに置換した本実施例３の場合においても、ペロブスカイト型酸化物（Ｌａ_０.６Ｃａ_０.４Ｆｅ_０.８Ｎｉ_０.２Ｏ_３、Ｌａ_０.６Ｂａ_０.４Ｆｅ_０.８Ｎｉ_０.２Ｏ_３）の結晶構造が得られるので、遷移金属の混合原子価状態や酸素欠陥が格子内に導入されて、触媒の活性化が向上し、而して、正極の特性が改善されることが確認された。

As shown in Table 3, the same strontium (Sr) ion is used as the alkaline earth metal ion (M ion) as in the case of using the alkaline earth metal ion (M ion) called strontium (Sr) ion in Example 2. In the case of this Example 3 substituted with calcium (Ca) ions and barium (Ba) ions, the perovskite oxides (La _0.6 Ca _0.4 Fe _0.8 Ni _0.2 O ₃ , La _0.6 Ba _0.4 Fe _0.8 Ni _0.2 O ₃ ) crystal structure is obtained, so that mixed metal valence states and oxygen vacancies are introduced into the lattice to improve catalyst activation. Thus, it was confirmed that the characteristics of the positive electrode were improved.

  However, as shown in Table 3, among the substituted alkaline earth metal species such as calcium (Ca), strontium (Sr), and barium (Ba), the best characteristics are obtained when strontium (Sr) is used. It was found that

  Therefore, it is most preferable to use strontium (Sr) as the alkaline earth metal substitution species in the oxide having a perovskite structure as a positive electrode catalyst of a lithium-air secondary battery.

  Although not shown in Table 3, lanthanum (La) ions, calcium (Ca) ions, barium (Ba) ions, etc. with respect to iron (Fe) ions and nickel (Ni) ions are used as the positive electrode oxide catalyst. When the molar ratio of the alkaline earth metal ion (M ion) is not (1: 1) but (2: 1) or (1: 2), the perovskite oxide is Even in the case where it is not obtained, the perovskite type oxide having a molar ratio of (1: 1) as in the case of Example 2 using strontium (Sr) ions as alkaline earth metal ions (M ions). However, it has good battery characteristics as a lithium air secondary battery, and is effective as an oxide catalyst added to the positive electrode for a lithium air secondary battery. It was.

  As ions to be further mixed with a mixed oxide containing iron (Fe) ions and nickel (Ni) ions, lanthanum (La) ions and alkaline earth metal ions (calcium (Ca), strontium (Sr), barium ( It is also possible to mix only oxides containing lanthanum (La) ions instead of complex oxides containing any one of Ba).

That is, in the first step, lanthanum (La) is added to a metal nitrate mixed aqueous solution containing iron (Fe) ions and nickel (Ni) ions without adding nitrate hydrate powder containing alkaline earth metal ions. ) the weight of lanthanum nitrate hexahydrate containing only mole number of a predetermined ion _{(La (NO 3) 3 ·} 6H 2 O) powder (purity: 99.99%) was further added, ammonia while stirring The aqueous solution and malic acid (C ₄ H ₆ O ₅ ) powder (purity: 99.0%) are added so that the pH of the aqueous solution is 2.5, which is the same as in the case of Example 1. After that, even if a lithium air secondary battery is produced using the positive electrode for a lithium air secondary battery that has undergone the second and third steps as described above, Good battery characteristics can be obtained. Can.

Here, when only adding lanthanum (La) ions, when the number of moles of each of iron (Fe) ions, nickel (Ni) ions, lanthanum (La) ions is expressed as NFe, NNi, NLa, (NFe + NNi): NLa = 1: with 1 relationship, as an oxide _catalyst, in the composition formula _{La x Fe z Ni u O v} , to perovskite type oxide consisting relation x = z + u is obtained Thus, even better battery characteristics can be obtained.

(Comparative example)
Next, for a lithium air secondary battery using a positive electrode to which an oxide catalyst of a positive electrode for a lithium air secondary battery according to the present invention is added, known catalysts such as iron trioxide (Fe ₂ O ₃ ) and nickel oxide ( The result of comparing charge / discharge characteristics with the battery when NiO) is added will be described.

(1) Method for Producing Lithium-Air Secondary Battery for Comparison First, a lithium-air battery comprising a positive electrode to which iron trioxide (Fe ₂ O ₃ ), which is a known catalyst, was added was produced by a production method similar to Example 1. did.

In other words, regarding a method for producing a lithium air battery using a positive electrode of an iron trioxide (Fe ₂ O ₃ ) catalyst to be compared, iron trioxide (Fe ₂ O ₃ ) powder to be used as a catalyst, carbon (Ketjen Black EC600JD) ), Binder (PTFE),
Iron trioxide catalyst: Carbon: Binder = 5: 3: 2
The sheet electrode having a thickness of 0.5 mm was prepared and cut into a circle having a diameter of 23 mm to obtain a positive electrode.

  Thereafter, a lithium air secondary battery having the cross-sectional structure shown in FIG. 1 was produced by the same production method as in Example 1 using the obtained positive electrode.

Next, similarly to the case of iron trioxide (Fe ₂ O ₃ ), a lithium air battery including a positive electrode to which nickel oxide (NiO) as a known catalyst was added was produced.

That is, the manufacturing method of the lithium air battery using the positive electrode of the nickel oxide (NiO) catalyst to be compared is similarly the iron trioxide (Fe ₂ O ₃ ) powder, carbon (Ketjen Black EC600JD) to be the catalyst. , Binder (PTFE),
Nickel oxide catalyst: Carbon: Binder = 5: 3: 2
The sheet electrode having a thickness of 0.5 mm was prepared and cut into a circle having a diameter of 23 mm to obtain a positive electrode.

  Thereafter, a lithium air secondary battery having the cross-sectional structure shown in FIG. 1 was produced by the same production method as in Example 1 using the obtained positive electrode.

(2) Characteristic evaluation test of lithium-air secondary battery for comparison Two types of lithium-air secondary batteries prepared using positive electrodes to which a known iron trioxide (Fe ₂ O ₃ ) catalyst and nickel oxide (NiO) catalyst were added, respectively. The secondary battery was subjected to a charge / discharge cycle test as a characteristic evaluation test using the same measurement method as in Example 1.

The charging / discharging curve at the time of the first charge / discharge of the lithium air secondary battery using the positive electrode to which the iron trioxide (Fe ₂ O ₃ ) catalyst is added is shown as the curve (e) of FIG. .

  In addition, a charge / discharge curve at the time of initial charge / discharge of a lithium-air secondary battery using a positive electrode to which a nickel oxide (NiO) catalyst is added is also shown as the curve (f) in FIG.

A lithium-air secondary battery using a positive electrode to which an iron trioxide (Fe ₂ O ₃ ) catalyst showing charge / discharge characteristics as a curve (e) in FIG. 2 is added is shown in curves (a), (b), ( d) The charging voltage is higher than any of the lithium-air secondary batteries in Examples 1 to 3 shown in Tables 1 to 3 above. Moreover, the lithium air secondary battery using the positive electrode to which the nickel oxide (NiO) catalyst which shows a charge / discharge characteristic as the curve (f) of FIG. 2 was added is the curve (a), (b), (d) of FIG. In addition, the deterioration of the charge / discharge cycle characteristics is remarkable as compared with any of the lithium-air secondary batteries in Examples 1 to 3 shown in Tables 1 to 3 above.

Such deterioration of the characteristics of two types of lithium-air secondary batteries prepared using positive electrodes to which a known iron trioxide (Fe ₂ O ₃ ) catalyst and nickel oxide (NiO) catalyst were added, respectively. The activated state is lower than that of the positive electrode of the lithium-air secondary battery in the case of Example 3, the discharge product is not sufficiently decomposed during charging, and the number of reaction sites is reduced. It can be considered that the discharge cycle characteristics have deteriorated.

Thus, as compared with the conventional known positive electrode catalyst, by mixing an oxide containing iron (Fe) ions and nickel (Ni) ions which are highly active against oxygen generation, further, lanthanum (La) By further mixing an oxide containing ions or a composite oxide containing both lanthanum (La) ions and alkaline earth metal ions, particularly strontium (Sr) ions, the resulting mixed oxide catalyst can be used as a positive electrode. If used, a highly active catalyst will be added to the positive electrode, which will accelerate the decomposition of precipitates generated during discharge and provide good reversibility of the discharge products, thus reducing the charging voltage. It was confirmed that charge / discharge cycle characteristics could be improved. In particular, the molar ratio of metal ions in the mixed oxide is (NFe + NNi) :( NLa + NSr) = 1: 1.
By adding such a perovskite oxide as a catalyst to the positive electrode, it is possible to produce a lithium-air secondary battery having extremely higher charge / discharge cycle characteristics than a battery using a conventionally known positive electrode catalyst. .

  As described above, according to the present invention, since a high-performance lithium-air secondary battery can be manufactured, it can be used as a driving source for various electronic devices such as mobile phones and digital cameras. Can do.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode connector, 2 ... Electrode case, 3 ... Carbon positive electrode, 4 ... Separator, 5 ... Metal lithium negative electrode, 6 ... Negative electrode connector, 7 ... Negative electrode support body, 8 ... O-ring, 9 ... Negative electrode terminal.

Claims (3)

A positive electrode for a lithium air secondary battery used for a lithium air secondary battery,
Carbon consists catalyst and binder, Ri mixed oxide der said catalyst containing at least iron (Fe) ions and nickel (Ni) ions,
When the moles of iron (Fe) ions and nickel (Ni) ions constituting the mixed oxide used as the catalyst are expressed as NFe and NNi, (NFe: NNi) = 2: 1 or (NFe: NNi) = 1: 2 molar ratio, whereby the mixed oxide is a spinel oxide, and a positive electrode for a lithium air secondary battery. A positive electrode manufacturing method for a lithium air secondary battery for manufacturing a positive electrode of a lithium air secondary battery,
Iron (Fe) ions and nickel (Ni) iron nitrate nonahydrate in a weight ratio of the molar ratio of the ions becomes predetermined molar ratio _{(Fe (NO 3) 3 ·} 9H 2 O) powder and nickel nitrate Further, malic acid (C ₄ H ₆ O ₅ ) and an aqueous ammonia solution are added to a metal salt mixed aqueous solution in which a Japanese (Ni (NO ₃ ) ₂ · 6H ₂ O) powder is dissolved in ion-exchanged water. A first step of preparing a mixed aqueous solution having a predetermined pH (potential hydrogen), and a precursor obtained by evaporating to dryness by heating the mixed aqueous solution prepared to a predetermined pH at a predetermined temperature. The second step of forming an oxide catalyst by performing a heat treatment under conditions of a predetermined temperature and time, and the formed oxide catalyst are mixed with carbon and a binder in a predetermined weight ratio. And, further, by molding, and a third step of preparing a positive electrode for lithium-air secondary battery, at least viewed contains a
The molar ratio of iron (Fe) ions and nickel (Ni) ions, 2: 1 or 1: With 2, as the oxide _catalyst, in the composition formula _{Fe x Ni y O z, x} : y = A method for producing a positive electrode for a lithium-air secondary battery , wherein a spinel oxide having a relationship of 2: 1 or x: y = 1: 2 is obtained . A positive electrode made of carbon, a catalyst and a binder, and a negative electrode made of metal lithium or a substance capable of occluding and releasing lithium ions, wherein one surface of the positive electrode is in contact with air, and the other surface of the positive electrode is In the lithium air battery which contacts a nonaqueous electrolyte and arrange | positions the said nonaqueous electrolyte between the said positive electrode and the said negative electrode, the said positive electrode is comprised by the positive electrode for lithium air secondary batteries of Claim 1. Lithium-air secondary battery, characterized in that

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