JP6048937B2 - Lithium air battery - Google Patents

Description

  The present invention relates to a lithium air battery excellent in long-term stability.

  Lithium-air batteries use oxygen in the air as the positive electrode active material, oxygen is always supplied from the outside of the battery, and a large amount of lithium metal, which is a negative electrode active material, can be filled in the battery. It has been reported to show.

For example, in Non-Patent Document 1, using 1 mol / l lithium hexafluorophosphate (LiPF ₆ ) as a solute and a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) as an organic solvent, An electrolytic solution is prepared and a lithium air (oxygen) battery is evaluated.

In Non-Patent Document 2, as an electrolytic solution, 1 mol / l Li (CF ₃ SO ₂ ) ₂ N (hereinafter referred to as LiTFSI) is used as a solute, and ethylene carbonate (EC) and diethyl carbonate (DEC) are used as organic solvents. A lithium-air battery is produced and evaluated using the above mixed solvent.

  In any literature, it reports that it operates as an air battery and a large discharge capacity is obtained.

  However, since the organic solvent used in these documents has volatility, it is considered that a lithium-air battery having a structure for taking in air into the battery has a problem in stability during long-term operation. That is, when the battery is operated for a long time, it is expected that the battery resistance increases due to volatilization of the electrolytic solution from the positive electrode side, and the battery performance is significantly reduced. Moreover, since these organic electrolytes are volatile and flammable, there is a concern about safety such as fire accidents.

J. et al. Read et al. , Journal of The Electrochemical Society, Vol. 150, pp. A1351-A1356 (2003). A. K. Thapa, Kazuki Nishimi, Hiroshige Matsumoto, Tatsumi Ishihara, Abstracts of the 76th Annual Meeting of the Electrochemical Society, 3P23, pp. 383 (2009).

  It is an object of the present invention to provide a safe lithium-air battery in which a decrease in electrolyte is suppressed and a long-term stable operation of the battery is possible.

An example of means for solving the above-described problems and achieving the object is a positive electrode configured as an air electrode, a negative electrode containing metallic lithium or a lithium-containing substance, and an electrolyte disposed between the positive electrode and the negative electrode. A lithium-air battery. Here, the electrolyte is a lithium ion conductive solid substance, and for example, a volatilization phenomenon such as an organic electrolyte cannot occur. Therefore, the electrolyte greatly contributes to stable operation of the battery. The electrolyte includes any one of lithium borohydride (LiBH ₄ ), lithium iodide (LiI), and lithium amide (LiNH ₂ ), or the electrolyte includes lithium borohydride (LiBH _4). ), Lithium iodide (LiI), or lithium amide (LiNH ₂ ).

  Here, the electrolyte is preferably an electrolyte that is melted on the positive electrode and then re-solidified.

Also, the positive electrode, lithium borohydride (LiBH _4), lithium iodide (LiI), and more preferably contains any one of the lithium amide (LiNH _2).

Alternatively, the positive electrode preferably further includes a mixture of at least two of lithium borohydride (LiBH ₄ ), lithium iodide (LiI), and lithium amide (LiNH ₂ ).

Another example of means for solving the above-described problems and achieving the object is a method for producing a lithium-air battery, in which the lithium-air battery includes a positive electrode configured as an air electrode and metallic lithium or a lithium-containing substance. And an electrolyte disposed between the positive electrode and the negative electrode, wherein the electrolyte is a lithium ion conductive solid electrolyte, and lithium borohydride (LiBH ₄ ), lithium iodide (LiI) ), And lithium amide (LiNH ₂ ), or the electrolyte is a lithium ion conductive solid electrolyte, and lithium borohydride (LiBH ₄ ), lithium iodide (LiI), and wherein a mixture of at least two lithium amide (LiNH _2), a step of melting the electrolyte in the positive electrode And a step of re-solidifying the molten said electrolyte is a method of manufacturing a lithium-air battery.

According to the present invention, it is possible to provide a lithium-ion battery that has excellent long-term stability, high safety, and high performance. In particular, by using a solid electrolyte, since there is no flammability or the like compared to the case of using a volatile organic electrolytic solution, an effect of greatly improving the safety of the battery can be obtained. Further, the ion conductivity is improved, and the battery can obtain the highest performance particularly in the case of LiBH ₄ + LiNH ₂ .

  In general, in an all-solid battery, the contact resistance between the electrode and the solid electrolyte is large, which significantly reduces the battery performance. In the present invention, when the solid electrolyte is heated above the melting point on the positive electrode and melted and then re-solidified, the contact resistance between the positive electrode and the solid electrolyte is reduced, the overvoltage is reduced, the discharge voltage is increased and the charge voltage is increased. Reduction is possible.

  Furthermore, the battery performance can be remarkably improved by mixing the solid electrolyte material into the air electrode. The solid electrolyte is desirably 1 to 20% by weight, more desirably 1 to 10% by weight, based on the whole positive electrode. Alternatively, in order to efficiently reduce the contact resistance, the additional amount of the solid electrolyte to the positive electrode is 1 to 10 wt%, 1 to 20 wt%, 1 to 25 wt%, 5 to 10 wt%, It is good also as 5-20 weight%, 5-25 weight%, 10-20 weight%, and 10-25 weight%.

It is a schematic sectional drawing which shows the structural example of the lithium air battery of this invention. It is a discharge curve of the lithium air battery of Examples 7, 10, and 12. It is a graph which shows the discharge time after leaving for a comparative example and Example 10 for a long time.

  The lithium-air battery according to the present invention is a lithium-air battery including a positive electrode configured as an air electrode, a negative electrode containing metallic lithium or a lithium-containing substance, and an electrolyte disposed between the positive electrode and the negative electrode. .

The positive electrode (hereinafter also referred to as air electrode) is preferably configured as an air electrode containing carbon, a catalyst, and a binder. As carbon, carbon blacks such as ketjen black and acetylene black, activated carbons, graphites, carbon fibers, etc. can be used, but those having a large surface area to ensure sufficient reaction sites in the air electrode. Specifically, a BET specific surface area of 300 m ² / g or more is desirable.

Further, a highly active catalyst for oxygen reduction / oxygen generation reaction is preferably added to the air electrode. As the catalyst, an oxide containing at least one of transition metals such as Mn, Fe, Co, Ni, V, and W in the structure is suitable. Specifically, MnO ₂ , Mn ₃ O ₄ , MnO , FeO ₂ , Fe ₃ O ₄ , FeO, CoO, Co ₃ O ₄ , NiO, NiO ₂ , V ₂ O ₅ , WO ₃ and other single oxides, La _0.6 Sr _0.4 MnO ₃ , La _{0 .6} Sr _0.4 FeO ₃ , La _0.6 Sr _0.4 CoO, La _0.6 Ca _0.4 CoO ₃ , Pr _0.6 Ca _0.4 MnO ₃ , LaNiO ₃ , La _0.6 Sr ₀ A composite oxide having a perovskite structure such as _.4 Mn _0.4 Fe _0.6 O ₃ can be used.

As a method for synthesizing these catalysts, known processes such as a solid phase method and a liquid phase method can be used. However, it is important to generate a large amount of three-phase interface sites on the surface of the electrode catalyst. The catalyst to be used preferably has a high surface area, and the specific surface area after calcination is preferably 10 m ² / g or more. Therefore, it is desirable to use a liquid phase method typified by a technique of obtaining an amorphous precursor by evaporating and drying a mixed aqueous solution of metal acetate or metal nitrate or hydrolysis of metal alkoxide.

  As the catalyst, a macrocyclic metal complex such as porphyrin or phthalocyanine containing at least one of transition metals such as Mn, Fe, Co, Ni, V, and W as a central metal can be used. The activity of these metal complexes is increased by performing heat treatment in an inert gas atmosphere after mixing with carbon.

  As the catalyst, not only the above-mentioned compound system, but also noble metals such as Pt, Au, and Pd, oxides thereof, and transition metals such as Co, Ni, and Mn can be used. High activity can be expressed by carrying these metals in high dispersion on carbon. Specifically, high dispersibility can be achieved by adsorbing and supporting metal particles on carbon by dispersing carbon in a colloidal solution in which these metals are dispersed, and knowing that the sales are vigorously expanded.

  The positive electrode preferably contains a binder. The binder is not limited to a specific one, and polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polyvinylidene fluoride (PVDF), styrene butadiene rubber and the like are used.

  In order to form a gas diffusion electrode (positive electrode), the catalyst powder, a mixture of the carbon powder and the binder powder is pressure-molded on a support such as a titanium mesh, or the above mixture is made of an organic solvent or the like. It can be formed by dispersing in a solvent to form a slurry, coating on a metal mesh or carbon cloth, and drying. One side of the electrode is exposed to the atmosphere, and the other side is in contact with the nonaqueous electrolyte. Further, in order to increase the strength of the electrode and prevent leakage of the electrolytic solution, it is possible to produce an electrode having higher stability by performing not only cold pressing but also hot pressing.

The negative electrode includes metallic lithium or a lithium-containing material. As the negative electrode active material, metallic lithium or lithium nitride, such as lithium-containing silicon or tin alloy, or lithium nitride such as Li _2.6 Co _0.4 N, which can release lithium ions, is also used. can do. Any other compound can be used as long as it can be used as a negative electrode material for a lithium secondary battery. However, when silicon, tin, or the like that does not contain lithium is used during synthesis, it is necessary to perform treatment in advance so that these materials contain lithium by a chemical method or an electrochemical method.

The electrolyte is a material that is configured as a conductive solid electrolyte disposed between the positive electrode and the negative electrode and has lithium ion conductivity. Specifically, any one of LiBH ₄ , LiI, and LiNH ₂ is used as the electrolyte. Alternatively, a solid electrolyte in which at least two of these materials are mixed is used. In particular, a material of LiBH ₄ + LiNH ₂ is preferable because it exhibits the highest performance due to its conductivity.

  By further mixing an electrolyte material into the air electrode, battery performance can be significantly improved. In order to efficiently reduce the contact resistance, the solid electrolyte is desirably added in an amount of 1 to 20% by weight, more preferably 1 to 10% by weight, based on the whole positive electrode. Alternatively, the additional amount of the solid electrolyte to the positive electrode is 1 to 10 wt%, 1 to 20 wt%, 1 to 25 wt%, 5 to 10 wt%, 5 to 20 wt%, 5 to 25 wt%, The desired effect is achieved even when the content is 10 to 20% by weight or 10 to 25% by weight.

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

[Examples 1 to 9]
The lithium air battery was produced by the following procedure.

For the positive electrode, La _0.6 Sr _0.4 Fe _0.6 Mn _0.4 O ₃ (LSFM) powder, ketjen black powder and polytetrafluoroethylene (PTFE) powder, which are electrode catalysts, are 50:30:20. In a weight ratio, it was sufficiently pulverized and mixed using a rough machine, and roll-formed to produce a sheet-like electrode (thickness: 0.5 mm). The sheet electrode was cut into a circle having a diameter of 15 mm and pressed onto a titanium mesh to obtain a gas diffusion electrode. The La _0.6 Sr _0.4 Fe _0.6 Mn _0.4 O ₃ powder was synthesized by a known method using metal nitrate as a starting material.

The following materials were used for the solid electrolyte (the coefficient in the mixture indicates the molar ratio). Specifically, Example 1 is LiBH ₄ , Example 2 is LiI, Example 3 is LiNH ₂ , Example 4 is 3LiBH ₄ + LiI, Example 5 is 2LiBH ₄ + LiI, Example 6 is 3LiBH ₄ + LiNH ₂ , Example 7 used LiBH ₄ + LiNH ₂ , Example 8 used LiI + 6LiNH ₂ , and Example 9 used LiI + 3LiNH ₂ .

LiBH ₄ , LiI, and LiNH ₂ were powders manufactured by Aldrich. The solid electrolytes of Examples 4 to 9 were prepared by mixing various powder samples at a predetermined ratio and ball milling in Ar. Each powder was used by molding into a disk shape (diameter 16 mm, thickness 0.2 mm) by pressing at 1 ton / cm ² .

  FIG. 1 shows a schematic cross-sectional view of the lithium-air battery of the present invention. In this lithium-air battery, lithium-air battery cells are formed in a cylindrical shape. The positive electrode 1 was disposed in a concave portion of the positive electrode support 2 coated with PTFE, and fixed with a positive electrode fixing PTFE ring 3. Note that the portion where the positive electrode 1 and the positive electrode support 2 are in contact with each other is not covered with PTFE in order to make electrical contact. The negative electrode fixing washer 6 was concentrically overlapped with four metallic lithium foils (diameter: 15 mm) having a thickness of 150 μm as the negative electrode 7. The negative electrode fixing ring 5 was disposed in a concave portion opposite to the concave portion in which the positive electrode 1 is disposed, and a negative electrode fixing washer 6 having metallic lithium bonded thereto was further disposed in the center. The O-ring 8 was set as shown in the figure. The disc of solid electrolyte 9 was filled so as to be sandwiched between the positive electrode 1 and the negative electrode 7 inside the cell, covered with the negative electrode support 10, and the entire cell was fixed with a cell fixing screw 11. For the battery performance measurement test, positive and negative terminals 4 and 12 were used.

In the battery discharge test, a charge / discharge measurement system was used, and 1.25 · A / cm ² was applied at a current density per effective area of the positive electrode until the battery voltage dropped from the open circuit voltage to 1.0V. Measurements were made. The battery was produced in dry air having a dew point of −60 ° C. or lower, and the battery discharge test was performed at 25 ° C. in an atmosphere where the temperature was not controlled.

  The discharge curve of the battery produced in Example 7 is shown in FIG. 2. From FIG. 2, it was confirmed that the lithium air battery according to Example 7 exhibited about 2.6 V as an open circuit voltage, was capable of discharging for about 220 hours, and operated as an air battery.

  Table 1 shows the battery performance for the voltage and discharge time of the lithium-air batteries in Examples 1 to 9.

  In any of the examples, the operation as an air battery was confirmed, and it was found that the air battery in Example 7 can discharge at the highest voltage for the longest time.

[Example 10]
In Example 10, LiBH ₄ + LiNH ₂ that showed high performance in Example 7 was melted at 95 ° C. on the positive electrode and re-solidified to increase the battery interface performance by increasing the contact interface site of the positive electrode / solid electrolyte. Tried to improve.

  The positive electrode, negative electrode, and solid electrolyte were produced in the same manner as described above.

  Specifically, a metal ring having a cavity with the same inner diameter as that of the positive electrode 1 and the solid electrolyte 9 shown in FIG. 1 is placed on a hot plate, and the positive electrode 1 and the solid electrolyte 9 are sequentially placed in the cavity from the bottom. Then, the solid electrolyte was melted by heating at 95 ° C. for 1 hour, air-cooled for 2 hours, and re-solidified on the air electrode. As shown in the figure, the positive electrode 1 and the solid electrolyte 9 are integrated so that the solid electrolyte 9 and the negative electrode 7 are in contact with the concave portion of the positive electrode support 2 coated with PTFE, as shown in FIG. 3 fixed. Note that the portion where the positive electrode 1 and the positive electrode support 2 are in contact with each other is not covered with PTFE in order to make electrical contact. The negative electrode fixing washer 6 was concentrically overlapped with four metallic lithium foils (diameter: 15 mm) having a thickness of 150 μm as the negative electrode 7. The negative electrode fixing ring 5 was disposed in a concave portion opposite to the concave portion in which the positive electrode 1 is disposed, and a negative electrode fixing washer 6 having metallic lithium bonded thereto was further disposed in the center. The O-ring 8 was set as shown in the figure. The negative electrode support 10 was covered so that the solid electrolyte 9 was sandwiched between the positive electrode 1 and the negative electrode 7 inside the cell, and the entire cell was fixed with a cell fixing screw 11. For the battery performance measurement test, positive and negative terminals 4 and 12 were used.

  FIG. 2 shows the discharge curves of the batteries according to Examples 7 and 10. Table 2 shows the results of the average discharge voltage and discharge time of the batteries according to Examples 7 and 10. From FIG. 2 and Table 2, it was confirmed that the battery performance was improved with respect to the average discharge voltage and discharge time. This indicates that the technique of melting and re-solidifying the solid electrolyte is effective.

[Examples 11 to 13]
In Examples 11 to 13, an attempt was made to improve battery performance by increasing the contact interface sites of the positive electrode / solid electrolyte by mixing LiBH ₄ + LiNH ₂ that showed high performance in Example 7 into the air electrode.

The method for producing the positive electrode, the negative electrode, etc. was performed in the same manner as described above. The addition of LiBH ₄ + LiNH _{2 to} the air electrode was sufficiently pulverized and mixed with a catalyst, carbon, and PTFE using a rough machine so that LiBH ₄ + LiNH ₂ was highly dispersed in the positive electrode.

  Table 3 shows the composition of the air electrode and battery performance, and particularly shows battery performance such as voltage and discharge time when the amount of solid electrolyte added is changed. For comparison, the results of Example 10 in which no solid electrolyte was added to the air electrode are also shown in Table 3.

  The discharge curve of the battery according to Example 12 is shown in FIG. 2 together with the curve of Example 10. From FIG. 2, it was confirmed that the battery performance was improved with respect to the average discharge voltage and the discharge time. This indicates that the method of adding a solid electrolyte to the positive electrode is effective.

  From Table 3, it was found that the battery performance is greatly affected by the amount of solid electrolyte added. For example, in Example 11 with a small amount of addition, no particular improvement effect from Example 10 was found. Conversely, when the addition amount was increased, the performance of Example 13 was lower than that of Example 12, and in Example 14 where the addition amount was further higher, the battery performance was further significantly reduced. This is considered to be because when the addition amount is small, the contact resistance is not sufficiently reduced, but when the addition amount is large, the increase in the resistance of the positive electrode itself and the diffusion of air in the positive electrode are hindered. . As a result, it is confirmed that the appropriate amount of the solid electrolyte added to the positive electrode is 10% by weight and 20% by weight with respect to the whole positive electrode, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight. It can be said. Alternatively, the additional amount of the solid electrolyte to the positive electrode is 1 to 10 wt%, 1 to 20 wt%, 1 to 25 wt%, 5 to 10 wt%, 5 to 20 wt%, 5 to 25 wt%, The desired effect is achieved even when the content is 10 to 20% by weight or 10 to 25% by weight.

[Comparative example]
As a comparative example, a battery using an organic electrolyte was produced. In the cell configuration described in Examples 1 to 10, a battery was fabricated by filling the cell with 1 mol / l LiPF ₆ / propylene carbonate (PC), which is an organic electrolyte, instead of the solid electrolyte, together with the separator. Five cells of the same configuration were produced.

  Also, five cells of the battery of Example 10 were produced.

  These cells were set in a constant temperature bath at 35 ° C., allowed to stand for 24, 72, 168, 240, and 480 hours, then measured, and compared with data measured at room temperature (0 hours). FIG. 3 shows the dependency of the discharge time and the standing time.

  From FIG. 3, it can be seen that the discharge capacity of the battery of the comparative example rapidly decreases as the standby time elapses. This is considered to be caused by a decrease due to volatilization of the organic electrolyte. On the other hand, the battery according to Example 10 using the solid electrolyte showed almost no decrease in discharge capacity within the measured time. This result shows that the use of the solid electrolyte according to the present invention is very effective for long-term stable operation of the battery.

  According to the present invention, a lithium-air battery that is excellent in long-term stability and safe can be manufactured, and can be used as a drive source for various electronic devices.

1 Positive electrode 2 Positive electrode support (PTFE coating)
3 Positive electrode fixing PTFE ring 4 Positive electrode terminal 5 Negative electrode fixing PTFE ring 6 Negative electrode fixing washer 7 Negative electrode 8 O-ring 9 Solid electrolyte 10 Negative electrode support 11 Cell fixing screw (PTFE coating)
12 Negative terminal

Claims (5)

A lithium-air battery comprising a positive electrode configured as an air electrode, a negative electrode containing metallic lithium or a lithium-containing substance, and an electrolyte disposed between the positive electrode and the negative electrode,
Wherein the electrolyte is a lithium ion conductive solid electrolyte, and lithium borohydride (LiBH _4), viewed contains a mixture of at least two lithium iodide (LiI), and lithium amide (LiNH _2),
A mixed material of lithium borohydride (LiBH ₄ ) and lithium amide (LiNH ₂ ) is further added in the positive electrode ,
The positive electrode is a lithium-air battery, characterized in including Mukoto a mixed material with 1-25% by weight of the total cathode weight of the lithium borohydride (LiBH ₄₎ and lithium amide (LiNH _2).   The positive electrode is made of the lithium borohydride (LiBH). _Four ) And lithium amide (LiNH ₂ The lithium-air battery according to claim 1, comprising 5 to 25% by weight of the total weight of the positive electrode.   The positive electrode is made of the lithium borohydride (LiBH). _Four ) And lithium amide (LiNH ₂ The lithium-air battery according to claim 1, comprising 5 to 20% by weight of the total weight of the positive electrode.   The positive electrode is made of the lithium borohydride (LiBH). _Four ) And lithium amide (LiNH ₂ The lithium-air battery according to claim 1, comprising 1 to 20% by weight of the total weight of the positive electrode.   The positive electrode is made of the lithium borohydride (LiBH). _Four ) And lithium amide (LiNH ₂ The lithium-air battery according to claim 1, comprising 1 to 10% by weight of the total weight of the positive electrode.

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