JP2010135144A - Lithium air secondary battery and method for manufacturing lithium air secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium air secondary battery having a structure capable of producing an anode electrode containing lithium ions with small deterioration by a process simpler than before, and a method for manufacturing the lithium air secondary battery having a structure capable of producing an anode electrode containing lithium ions with small deterioration by a process simpler than before. <P>SOLUTION: The lithium air secondary battery is provided with a gas diffusion type cathode electrode 8 having carbon as a component, and an anode electrode 7 having a lithium occlusion material capable of occluding or discharging lithium, and being in a state not containing lithium, as a component, wherein a nonaqueous electrolyte is arranged between the gas diffusion type cathode electrode 8 and the anode electrode 7. An auxiliary electrode 2 made of metallic lithium is arranged so as to contact with the nonaqueous electrolyte contacting with the anode electrode 7 in the lithium air secondary battery at a position farther than the anode electrode 7 when viewed from the gas diffusion type cathode electrode 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium air secondary battery and a method for manufacturing a lithium air secondary battery.

  Commercially available zinc-air batteries have a large discharge capacity per weight of about 300 mAh / g, and are therefore mainly used for hearing aids and the like. However, compared with a lithium battery using a non-aqueous electrolyte, only a voltage of about 1 V can be obtained, so it is considered difficult to use in a wide range.

In recent years, electrochemical reduction (discharge) / oxidation (charge) of oxygen is used as a positive electrode reaction system in the same manner as a zinc-air battery, and metal lithium is combined in place of zinc as a negative electrode, and it is not used as an electrolyte. Attempts have been made to produce a lithium / air secondary battery exhibiting a high voltage of 2 to 3 V by using a water electrolyte (see Patent Document 1 and Non-Patent Document 1 below), a large value of 1000 mAh / g or more, The discharge capacity per weight is obtained. However, since lithium is contained inside the battery, there is a problem in its safety.
Japanese Patent No. 4015899 “An O2 cathode for rechargeable lithium batteries: The effect of a catalyst”, A. Debart, J. Bao, G. Armstrong and PG Bruce, Journal of Power Sources, Vol. 174, pp. 1177-1182 (2007).

  As described above, the conventional lithium-air battery has a problem that safety is lowered because metallic lithium having high reactivity is contained therein.

In addition, as a solution, for example, when LiC ₆ is electrochemically synthesized using a lithium / carbon cell, and this LiC ₆ is taken out from the cell and used as a negative electrode of a lithium air battery, In the case of working in, the negative electrode is deteriorated, and when working in an inert gas atmosphere, an expensive glove box is required and an inert gas such as high-purity Ar gas is required, which complicates the process and reduces the cost. There is a problem that it takes.

  The present invention has been made in view of the above-described problems, and the problem to be solved by the present invention is to provide lithium air having a structure capable of producing a lithium ion-containing negative electrode with less deterioration by a simpler process. The present invention provides a secondary battery and a method for producing a lithium-air secondary battery that produces a lithium ion-containing negative electrode with less deterioration by a simpler process than before.

In the present invention, in order to solve the above problem, as described in claim 1,
A positive electrode comprising a gas diffusion type oxygen electrode comprising carbon as a constituent element, and a negative electrode comprising a lithium occluding substance capable of occluding and releasing lithium and not containing lithium as a constituent element, In a lithium-air secondary battery configured by disposing a non-aqueous electrolyte between a positive electrode and the negative electrode, the non-aqueous electrolyte in contact with the negative electrode is viewed from the positive electrode inside the lithium-air secondary battery. Thus, an auxiliary electrode made of metallic lithium, which is in contact with a position far from the negative electrode, is disposed.

In the present invention, as described in claim 2,
The amount of metallic lithium constituting the auxiliary electrode is an amount that allows all of the metallic lithium to be dissolved in the nonaqueous electrolyte by a charging reaction, transferred to the negative electrode, and occluded in the negative electrode. The lithium air secondary battery according to claim 1 is configured.

In the present invention, as described in claim 3,
3. The lithium air secondary battery according to claim 1, wherein the lithium storage material is carbon, silicon, or tin.

In the present invention, as described in claim 4,
A positive electrode comprising a gas diffusion type oxygen electrode comprising carbon as a constituent element, and a negative electrode comprising a lithium occluding substance capable of occluding and releasing lithium and not containing lithium as a constituent element, Lithium-air secondary battery manufacturing method for manufacturing a lithium-air secondary battery comprising a non-aqueous electrolyte disposed between a positive electrode and the negative electrode is capable of occluding and releasing lithium and does not contain lithium After assembling the lithium air secondary battery according to claim 1, 2 or 3, using the lithium storage material in a state, a charging current is passed between the auxiliary electrode made of metallic lithium and the negative electrode, A method for producing a lithium-air secondary battery comprising the steps of dissolving metallic lithium in a non-aqueous electrolyte, moving to the negative electrode, and occluding in the negative electrode is provided. .

  By using the auxiliary electrode according to the present invention, it is possible to produce a lithium-air secondary battery having high energy density while having little safety during cell production and having high safety performance.

  The present invention relates to a lithium air secondary battery that is superior in safety to other lithium air secondary batteries and has a higher energy density than lithium ion secondary batteries currently used for various applications.

  In the present invention, a positive electrode comprising a gas diffusion type oxygen electrode having carbon as a constituent element, and a negative electrode having a lithium occluding substance capable of occluding and releasing lithium and not containing lithium as constituent elements. A lithium-air secondary battery comprising a non-aqueous electrolyte between a positive electrode and a negative electrode is characterized in that an auxiliary electrode made of metallic lithium is further arranged in the non-aqueous electrolyte inside the battery.

  In order to achieve the above-described object, a negative electrode is formed using the lithium storage material that does not contain lithium, and charging is performed between the negative electrode and the auxiliary electrode so that lithium ions are stored in the negative electrode. A charging reaction is caused by passing an electric current, and the metallic lithium constituting the auxiliary electrode is converted into lithium ions in the non-aqueous electrolyte, moved in the electrolyte, and occluded in the negative electrode to produce a negative electrode containing lithium. . All the metallic lithium as the auxiliary electrode is dissolved and occluded in the negative electrode to prevent deterioration in the atmosphere and dendrite formation of metallic lithium at the time of cell preparation, suppress short circuit inside the battery, and prevent metallic lithium in the battery. Therefore, a lithium air secondary battery having excellent safety and high energy density can be manufactured at low cost.

  The outline of the lithium-air secondary battery according to the present invention will be described below.

  By passing a charging current for inserting lithium ions into the negative electrode between the negative electrode using the lithium storage material and an auxiliary electrode made of metallic lithium, a lithium-containing negative electrode is synthesized, As a result, all the metallic lithium as the auxiliary electrode is dissolved, and lithium is occluded in the negative electrode.

  In order to form a gas diffusion electrode in which an electrochemical reduction reaction of oxygen, which is a positive electrode active material, proceeds, a mixture of carbon powder and a binder powder such as polytetrafluoroethylene (PTFE) is air permeable. A method such as pressure forming (pressing) on a support such as a metal mesh or a method of dispersing the above-mentioned mixture in a solvent such as an organic solvent to form a slurry and applying the slurry onto a metal mesh and drying is used.

  One side of the gas diffusion electrode produced by such a method is exposed to the atmosphere, and the other side is in contact with a non-aqueous electrolyte that is an electrolytic solution.

  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 discharge reaction on the gas diffusion type electrode (positive electrode) can be expressed as follows.

2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (1)
Or 2Li ⁺ +1/2 O ₂ + 2e ⁻ → Li ₂ O (2)
The lithium ion Li ⁺ in the above formula has moved from the negative electrode to the positive electrode surface via the electrolyte. Oxygen O ₂ is taken into the gas diffusion electrode from the atmosphere. Li ₂ O ₂ or Li ₂ O produced by this discharge reaction is deposited on the positive electrode, and the discharge reaction ends when all the reaction sites on the positive electrode are covered.

  In addition, the electrode reaction during charging is the reverse reaction of reactions (1) and (2), the generated oxygen is discharged out of the battery, and lithium ions are inserted again into the negative electrode through the electrolyte.

Ketjen black, acetylene black, activated carbon, carbon fiber, etc. can be used as the positive electrode material in the gas diffusion electrode. To increase the reaction sites at the positive electrode and increase the degree of dispersion of the catalyst. It is desirable to use carbon having a particle size of 40 nm or less and a surface area of 1000 m ² / g or more. As a method for adding the electrode catalyst to the positive electrode, a solid phase method in which carbon or a binder is mechanically mixed with a ball mill or the like, or a wet method such as stirring and mixing in an alcohol or the like can be used. The latter is desirable for improving the degree of dispersion of the catalyst and allowing the electrode reaction to proceed efficiently. Moreover, about the addition amount of the said catalyst to a positive electrode, since the production | generation of a reaction site is inadequate if it is a small amount addition, and the electrical resistance of an electrode will increase in a large amount addition, in the range of 20 to 60 weight%. It is preferable to add.

For the catalyst, the positive electrode is made of noble metals such as Pt, Au, Ag, Ru, Ir, Rh, transition metal oxides such as CuO, MnO ₂ , TiO ₂ , CrO ₂ , V ₂ O ₅ , MnO ₃ , cobalt phthalocyanine, etc. Transition metal organic complexes and the like can be used.

  As the binder, in addition to the PTFE powder, a PTFE dispersion or a polyvinylidene fluoride (PVdF) powder or dispersion may be used.

  For the negative electrode, a carbon material capable of occluding and releasing lithium ions, silicon, and tin can be used.

  The non-aqueous electrolyte may be any non-aqueous electrolyte that can move lithium ions, and organic electrolytes, solid electrolytes such as polymers, and ionic liquids may also be used.

As the organic electrolyte, a solution obtained by dissolving a metal salt such as LiClO ₄ or LiPF _{6 in} an organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), or dimethyl carbonate (DMC) can be used. Can be obtained by adding a metal salt such as LiPF ₆ or Li (CF ₃ SO ₂ ) ₂ N to a polymer material such as polyethylene oxide (PEO) or polyacrylonitrile (PAN). , PF ₆ 1-ethyl-3-methylimidazolium cation such as ions ^- may be used a combination of anions, and the like.

  Various conventionally known materials can be used for battery constituent materials such as separators and battery cases, and there is no particular limitation.

[Example 1]
The gas diffusion electrode of the positive electrode is prepared by mixing a highly conductive carbon black powder and a polytetrafluoroethylene (PTFE) powder in a weight ratio of 1: 1, roll-molding to form a sheet-like electrode, and cutting it into a circle Obtained.

  The negative electrode was obtained by mixing natural graphite powder, which is a lithium occluding material, and polytetrafluoroethylene (PTFE) powder in a weight ratio of 1: 1, roll-forming to form a sheet-like electrode, and cutting it into a circle. .

  After assembling the lithium-air secondary battery according to the present invention using the positive electrode and the negative electrode, between the negative electrode and the auxiliary electrode using a carbon material (natural graphite) capable of occluding and releasing lithium ions, A negative electrode containing lithium is synthesized by supplying a charging current for inserting lithium into the negative electrode, and all the metallic lithium as the auxiliary electrode is dissolved and stored in the negative electrode. As a result, a lithium air secondary battery having a negative electrode for storing lithium is completed.

  In this example, in the stage before the charging current is passed, since the lithium is not occluded in the negative electrode, the performance of the negative electrode does not deteriorate due to oxygen in the air, and the battery assembly work is compared with the conventional method. It will be much easier.

  FIG. 1 is a schematic diagram of a cell structure of a lithium-air secondary battery according to the present invention, in which the left part of the figure is a diagram showing the components of the cell structure spaced apart, and the right part is after assembly. It is sectional drawing of a cell structure.

  In the figure, 1 is an auxiliary electrode case, 2 is a metallic lithium auxiliary electrode, 3 is a connector for each case, 4 is an electrolyte case, 5 is an electrolyte injection and venting port, 6 is a negative electrode case, 7 is a negative electrode, Reference numeral 8 denotes a gas diffusion type positive electrode, and 9 denotes a positive electrode case. A circular air hole (diameter 16 mm) for taking oxygen into the gas diffusion type positive electrode 8 is formed on the bottom surface (upper surface in the drawing) of the positive electrode case 9.

An auxiliary electrode 2 made of lithium in an amount capable of being occluded by a carbon negative electrode material capable of occluding and releasing lithium ions was placed in the PVdF auxiliary electrode case 1 and fixed by fitting a fastener 3. On top of that, the PVdF electrolyte case 4 and the auxiliary electrode case 1 are joined, the negative electrode case 6 and the case 4 are joined through the fasteners 3, respectively, the negative electrode 7 is arranged in the negative electrode case 6, and another fastener 3 is fitted. . Further, the gas diffusion type positive electrode 8 is disposed in the positive electrode case 9 made of PVdF, and the fastener 3 is fixed by being fitted in the positive electrode layer case, and is joined to the above-described cell, and each electrolyte is injected and degassed therein. The electrolyte was injected from the mouth 5 and all the mouths were plugged. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a propylene carbonate (PC) solvent at a concentration of 1 mol / liter was used.

  A metallic lithium auxiliary electrode 2 having a weight of about 0.03 g and a graphite negative electrode 7 having a weight of about 0.4 g are loaded between the auxiliary electrode case 1 and the negative electrode case 6, and a charging current of 120 mAh is applied. Lithium ions are electrochemically inserted into the substrate. At this time, all metallic lithium is dissolved. The charging reaction at this time is represented by the following formula.

Auxiliary electrode: Li → Li ⁺ + e ⁻ (3)
Negative electrode: C ₆ + Li ⁺ + e ⁻ → LiC ₆ (4)
The battery was measured between a positive electrode and a negative electrode at a current density of 0.1 mA / cm ² (standardized by the area of the gas diffusion positive electrode exposed to the atmosphere) at a discharge end voltage of 2.0 V and a charge end voltage of 4.5 V. A charge / discharge test was conducted. The discharge capacity is indicated by the capacity per unit weight of the positive electrode carbon (mAh / g) for the following comparison.

  A discharge curve and a charge curve of the lithium-air secondary battery produced in this example are shown in FIG. In the first discharge, the average discharge voltage was a high voltage of about 2.4 V, and the discharge capacity was a very large value of 2035 mAh / g. In addition, it was confirmed that the charging is almost stable, the charging can be performed at the same level as the discharge capacity, and the secondary battery can be reversibly cycled. The initial characteristics of the battery and the transition when the charge / discharge cycle is repeated are shown in the column of “Natural graphite (Example 1)” in Table 1.

サイクルを繰り返しても、平均放電電圧にほとんど変化は見られず、また、放電容量については、表１より、１０回の充放電を繰り返しても、１０％程度の容量減少しか見られず、安定にサイクルできることが分かった。また、同様の電池を１５個作製し、同様の条件で充放電試験を行ったところ、すべての電池において８０％以上の容量を維持しており、２０サイクル後で、それぞれの負極表面を確認したところ、デンドライトの形成は確認されなかった。

Even when the cycle is repeated, there is almost no change in the average discharge voltage, and with regard to the discharge capacity, even if the charge / discharge is repeated 10 times, only a capacity decrease of about 10% is observed and stable. It turned out that it can cycle. Further, 15 similar batteries were produced and subjected to charge / discharge tests under the same conditions. As a result, the capacity of 80% or more was maintained in all batteries, and the surface of each negative electrode was confirmed after 20 cycles. However, formation of dendrite was not confirmed.

[Example 2]
A lithium air battery was produced using silicon as the negative electrode, and a charge / discharge test of the battery was performed. The negative electrode is prepared by mixing a commercially available silicon powder and carbon powder in a mass ratio of 1: 1 and a binder with an isopropyl alcohol solvent, and using a stirrer, a mixer, etc., in a slurry state. A mixture paste was prepared, applied to a metal plate, dried, and then press molded with a press. The amount of silicon added to the negative electrode was such that all the metallic lithium of the auxiliary electrode was dissolved and occluded in the negative electrode. Other electrolyte solutions and auxiliary electrodes were prepared in the same manner as in Example 1.

The battery was measured between a positive electrode and a negative electrode at a current density of 0.1 mA / cm ² (standardized by the area of the gas diffusion positive electrode exposed to the atmosphere) at a discharge end voltage of 2.0 V and a charge end voltage of 4.5 V. A charge / discharge test was conducted. The results are shown in the column “Silicon (Example 2)” in Table 1.

[Example 3]
A lithium air battery was produced using tin as the negative electrode, and the battery was charged and discharged. The negative electrode was prepared in the same manner as in Example 2 except that commercially available tin powder and carbon powder were mixed at a mass ratio of 1: 1.

The battery was measured between a positive electrode and a negative electrode at a current density of 0.1 mA / cm ² (standardized by the area of the gas diffusion positive electrode exposed to the atmosphere) at a discharge end voltage of 2.0 V and a charge end voltage of 4.5 V. A charge / discharge test was conducted. The results are shown in the column “Tin (Example 3)” in Table 1.

  In Examples 2 to 3, it was found that all the batteries showed a large discharge capacity, but both silicon and tin were polarized and the discharge voltage was reduced compared to natural graphite.

[Comparative Example 1]
The performance of the lithium-air secondary battery obtained in the present invention was compared with that of a metal lithium secondary battery without using an auxiliary electrode. About the preparation method of a metal lithium secondary battery, it carried out by the method similar to Example 1, removed the negative electrode part, and produced only with the carbon positive electrode and the metal lithium negative electrode.

The lithium secondary battery of this comparative example was subjected to a charge / discharge test at a current density of 0.1 mA / cm ² , which is a value normalized by the positive electrode area, at a charge end voltage of 4.5 V and a discharge end voltage of 2.0 V. The discharge capacity was expressed as a value (mAh / g) normalized by the weight of the positive electrode. The results of the cycle tests and the results of the cycle tests for the 15 batteries shown in Example 1 are shown in Table 2.

両リチウム空気二次電池とも、約２０００ｍＡｈ/ｇの大きな放電容量を示しているが、同様の電池を１５個作製したところ、比較例１において、４個はサイクル特性が悪くなった。これら４個の１０サイクル後に金属リチウム負極表面を観察したところ、デンドライトの形成を確認した。このことから、デンドライト形成による電圧降下がサイクル特性の悪化の原因と考えられ、デンドライトによる電極間の短絡の危険性もあり、安全性にも問題が生じると考えられる。すなわち、これは、本発明に係る二次電池が、安全性に優れた高エネルギー密度二次電池として、非常に有益であることを示唆するものである。

Both lithium-air secondary batteries showed a large discharge capacity of about 2000 mAh / g, but when 15 similar batteries were produced, 4 in Comparative Example 1 had poor cycle characteristics. When the surface of the metal lithium negative electrode was observed after these four 10 cycles, formation of dendrites was confirmed. From this, voltage drop due to dendrite formation is considered to be a cause of deterioration of cycle characteristics, there is a risk of short circuit between electrodes due to dendrite, and it is considered that there is a problem in safety. That is, this suggests that the secondary battery according to the present invention is very useful as a high energy density secondary battery excellent in safety.

[Industrial applicability]
As described above, according to the present invention, it is possible to produce a lithium-air secondary battery having the characteristics of being excellent in high safety and having a high energy density. It can be effectively used as a drive source for various electronic devices.

It is a figure of the cylindrical lithium air secondary battery cell which concerns on this invention. It is a charging / discharging curve of the lithium air secondary battery which used the graphite for the negative electrode based on this invention.

Explanation of symbols

  1: Auxiliary electrode case, 2: Metallic lithium auxiliary electrode, 3: Joiner, 4: Electrolytic solution case, 5: Electrolyte injection and venting port, 6: Negative electrode case, 7: Negative electrode, 8: Gas diffusion type positive electrode Electrode, 9: positive electrode case.

Claims (4)

A positive electrode comprising a gas diffusion type oxygen electrode comprising carbon as a constituent element, and a negative electrode comprising a lithium occluding substance capable of occluding and releasing lithium and not containing lithium as a constituent element, In a lithium air secondary battery configured by disposing a non-aqueous electrolyte between a positive electrode and the negative electrode,
Inside the lithium-air secondary battery, an auxiliary electrode made of metallic lithium that is in contact with the nonaqueous electrolyte that is in contact with the negative electrode at a position farther from the negative electrode when viewed from the positive electrode is disposed. Lithium air secondary battery.   The amount of metallic lithium constituting the auxiliary electrode is an amount that allows all of the metallic lithium to be dissolved in the nonaqueous electrolyte by a charging reaction, transferred to the negative electrode, and occluded in the negative electrode. The lithium air secondary battery according to claim 1.   The lithium air secondary battery according to claim 1, wherein the lithium storage material is carbon, silicon, or tin. A positive electrode comprising a gas diffusion type oxygen electrode comprising carbon as a constituent element, and a negative electrode comprising a lithium occluding substance capable of occluding and releasing lithium and not containing lithium as a constituent element, In the method for producing a lithium air secondary battery for producing a lithium air secondary battery constituted by disposing a nonaqueous electrolyte between a positive electrode and the negative electrode,
An auxiliary electrode made of metallic lithium after assembling the lithium air secondary battery according to claim 1, 2 or 3, using a lithium occluding material capable of occluding and releasing lithium and not containing lithium. A lithium-air secondary battery comprising a step of dissolving a lithium metal in a nonaqueous electrolyte by flowing a charging current between the negative electrode and the negative electrode, transferring the lithium to the negative electrode, and inserting the lithium into the negative electrode Production method.

Images