JP2010113963A - Aqueous lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance charge and discharge efficiency that is a ratio of an initial discharge capacity to an initial charge capacity, or enhance a capacity maintenance rate after repeating charge and discharge cycles, in an aqueous lithium secondary battery. <P>SOLUTION: In the aqueous lithium ion secondary battery 10, a winding type electrode body A pinching a separator between a cathode sheet and an anode sheet and being wound is housed in a battery vessel 30 with aqueous electrolyte solution with lithium ion dissolved in water. The battery vessel 30 is manufactured by electrolysis-restraining material (such as polyacetal) hardly occurring electrolysis of water compared with iron-system metal, a cathode collector 14 electrically connected with the cathode sheet and an anode collector 18 electrically connected with an anode sheet are exposed outside from the battery vessel 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aqueous lithium ion secondary battery.

  Conventionally, an aqueous lithium ion secondary battery using an aqueous solution as an electrolytic solution is known (see, for example, Patent Document 1). This aqueous lithium ion secondary battery has the following advantages with respect to the problems of non-aqueous lithium ion secondary batteries. That is, the water-based lithium ion secondary battery does not basically burn because an organic solvent is not used for the electrolyte. In addition, since a dry environment is not required in the manufacturing process, manufacturing costs can be significantly reduced. Furthermore, since an aqueous electrolyte generally has higher conductivity than a non-aqueous electrolyte, an internal resistance of an aqueous lithium ion secondary battery is lower than that of a non-aqueous lithium ion secondary battery. On the other hand, the water-based lithium ion secondary battery is required to be used in a potential range where no water electrolysis reaction occurs, and therefore, the electromotive force is smaller than that of the non-aqueous lithium ion secondary battery. . Thus, in a water-based lithium ion secondary battery, high safety, low cost, and low internal resistance are ensured at the expense of high voltage and high energy density.

As for the water-system lithium ion secondary battery of patent document 1, CR2016 type coin cell is illustrated. The battery container of this coin cell is made of SUS. Specifically, in this coin cell, a positive electrode is formed inside a container body made of SUS, a gasket having a shape along the inner periphery of the container body is disposed, and a negative electrode is disposed on the positive electrode via a separator. In addition, after injecting the aqueous electrolyte, the opening of the container body is closed with a SUS lid and caulked.
JP2007-103298A

  However, in the above-described coin cell, even when charging is performed at a voltage of about 1.3 V, which is generally considered not to cause electrolysis of water, the electrolysis of water cannot be sufficiently suppressed, and the initial discharge capacity and the initial charge are reduced. There was a problem that the charge / discharge efficiency, which is the ratio to the capacity, was low, and the capacity retention rate after repeating the charge / discharge cycle was also low. In this way, the electrolysis of water cannot be sufficiently suppressed because the lid is at the same potential as the negative electrode and in contact with the aqueous electrolyte, and the container body is at the same potential as the positive electrode and in contact with the aqueous electrolyte. It is done.

  The present invention has been made to solve such problems, and in a water-based lithium ion secondary battery, charge / discharge efficiency and charge / discharge cycle, which are the ratio of the initial discharge capacity to the initial charge capacity, are repeated. The main purpose is to increase the capacity maintenance rate after the operation.

  In order to achieve the above-described object, the present inventors have studied various materials for battery containers. As a result, the inventors have found that the charge / discharge efficiency and capacity retention rate are increased, and have completed the present invention.

  That is, the water-based lithium ion secondary battery of the present invention has a positive electrode sheet that uses a material that releases lithium ions during charging and occludes lithium ions during discharging as a positive electrode active material, and occludes lithium ions during charging and releases lithium ions during discharging. An aqueous lithium ion secondary battery having a structure in which an electrode body having a separator sandwiched between a negative electrode sheet having a negative electrode active material as a material to be accommodated in a battery container together with an aqueous electrolyte solution in which lithium ions are dissolved in water, The battery container is made of an electrolysis-inhibiting material that is less susceptible to water electrolysis than ferrous metals, and is electrically connected to the positive electrode current collector and the negative electrode sheet that are electrically connected to the positive electrode sheet. The negative electrode current collector is exposed to the outside from the battery container.

  According to the water-based lithium ion secondary battery of the present invention, the charge / discharge efficiency is higher than when a battery container made of an iron-based metal (for example, nickel-plated iron or SUS) is used, and the charge / discharge cycle is repeated. The capacity maintenance rate is also increased. The reason why such an effect is obtained is not clear, but when the battery container composed of the container body and the lid is made of iron-based metal, the entire container body has the same potential as one electrode, and the entire lid is the other. When the battery container is made of an electrolysis-suppressing material, only the current collector of each electrode has the same potential as that of each electrode. It is presumed that the area of the conductive material such as a metal is overwhelmingly smaller than that in the former case.

  The water-based lithium ion secondary battery of the present invention includes a positive electrode current collector in which a battery container is made of an electrolysis-suppressing material that is less susceptible to water electrolysis than iron-based metals, and is electrically connected to a positive electrode sheet; The negative electrode current collector electrically connected to the negative electrode sheet is exposed from the battery container to the outside.

In the water based lithium ion secondary battery of the present invention, the positive electrode is not particularly limited as long as the positive electrode active material is a material that releases lithium ions during charging and occludes lithium ions during discharging. For example, a lithium having a spinel structure Manganese composite oxide, lithium manganese composite oxide with olivine structure, lithium manganese composite oxide with layered structure, lithium manganese composite oxide with defective layered structure, lithium phosphate compound with olivine structure, etc. may be used as the positive electrode active material preferable. It is preferable that the positive electrode active material can reversibly store and release as much lithium ions as possible in a potential range where oxygen is not generated by electrolysis of water. From this point of view, the positive electrode active material is preferably an olivine-structure lithium phosphate compound, more preferably an olivine-structure lithium phosphate compound containing Li and Fe as main components of a metal element, and more preferably LiFePO ₄ .

In the aqueous lithium ion secondary battery of the present invention, the negative electrode is not particularly limited as long as the negative electrode active material is a material that occludes lithium ions during charge and releases lithium ions during discharge. For example, vanadium, iron, An oxide or hydroxide containing a metal such as titanium or manganese, or a composite oxide of these metal and lithium is preferably used as the negative electrode active material. Examples of such a negative electrode active material include LiV ₂ O ₄ , LiV ₃ O ₈ , VO ₂ , and FeOOH. It is preferable that the negative electrode active material can reversibly store and release as much lithium ions as possible in a potential range where hydrogen is not generated by electrolysis of water. From this point of view, the negative electrode active material is preferably a spinel-structure lithium composite oxide, more preferably a spinel-structure lithium composite oxide containing Li and V as main components of a metal element, and more preferably LiV ₂ O ₄ .

  In the water based lithium ion secondary battery of the present invention, the positive electrode and the negative electrode may contain a conductive material. The conductive material is not particularly limited as long as it is a conductive material. For example, carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black and thermal black may be used, and natural graphite such as flake graphite, graphite such as artificial graphite and expanded graphite may be used. Further, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper, silver, nickel, and aluminum, or organic conductive materials such as polyphenylene derivatives may be used. These may be used alone or in combination.

  In the aqueous lithium ion secondary battery of the present invention, the positive electrode and the negative electrode may contain a binder or a thickener. Although it does not specifically limit as a binder, A thermoplastic resin, a thermosetting resin, etc. are mentioned. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer ( FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer ( ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene- Rollotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, etc. Is mentioned. These materials may be used alone or in combination. Although it does not specifically limit as a thickener, Carboxymethylcellulose (CMC) etc. are mentioned.

In the aqueous lithium ion secondary battery of the present invention, the aqueous electrolyte solution is not particularly limited as long as it has a lithium salt as a main electrolyte. Examples of the lithium salt include LiNO ₃ , LiOH, LiCl, and Li ₂ S. These lithium salts can be used alone or in combination of two or more. The pH of the aqueous electrolyte is preferably 4-11. When the pH of the aqueous electrolyte is less than 4, generally, the positive electrode active material and the negative electrode active material are likely to become unstable, and the battery capacity and charge / discharge cycle characteristics may be deteriorated. On the other hand, when the pH exceeds 11, the electrolysis potential of water, that is, the hydrogen generation potential and the oxygen generation potential are lowered, so that oxygen and hydrogen may be easily generated at the positive electrode and the negative electrode.

  In the aqueous lithium ion secondary battery of the present invention, the separator is not particularly limited, but for example, a porous polyolefin film or a polyolefin nonwoven fabric subjected to hydrophilic treatment is preferable. Such a separator physically separates the positive electrode and the negative electrode, has electrical insulation to prevent a short circuit, is easily wetted with an aqueous electrolyte, has excellent liquid retention, and does not impair lithium ion conductivity. In addition, it satisfies the characteristics required for separators, such as being resistant to electrolytes and being physically and chemically stable, and not generating harmful substances that inhibit battery reactions. Such a separator can be obtained by subjecting a water-repellent (hydrophobic) polyolefin to a hydrophilic treatment such as sulfonation treatment, acrylic acid graft polymerization treatment, plasma treatment, or fluorine gas treatment. Of these, sulfonation is preferred because of its excellent chemical stability such as heat resistance and oxidation resistance. Although it does not specifically limit as polyolefin, Polyethylene and polypropylene are preferable at the point of availability.

  In the water-based lithium ion secondary battery of the present invention, the battery container is made of an electrolysis-inhibiting material that is less susceptible to water electrolysis than iron-based metals. Examples of the electrolysis suppressing material include a polymer material and aluminum. Among these, a polymer material is preferable. Polymer materials include polyolefin resins such as polyethylene, polypropylene, and polybutylene; aromatics such as polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), and polyether ether ketone ketone (PEEKK) Group polyetherketone resin; polyoxymethylene resin such as polyacetal; and fluorine-based resin such as polytetrafluoroethylene. Further, a positive electrode current collector is electrically connected to the positive electrode sheet, and a negative electrode current collector is electrically connected to the negative electrode sheet, but each current collector is exposed to the outside from the battery container. Such a current collector is preferably made of aluminum. In such a battery container, first and second caps are respectively joined to one end and the other end of a cylindrical container body, and the positive electrode current collector is disposed between one end of the container body and the first cap. It is preferable that the negative electrode current collector is disposed in a liquid-tight manner, and the negative electrode current collector is disposed in a liquid-tight manner between the other end of the container body and the cap. As for joining of each cap and the container body, in addition to screwing, heat fusion or the like can be mentioned.

  The water-based lithium ion secondary battery of the present invention may be used as a single unit, or a plurality of the water-based lithium ion secondary batteries may be connected in series. Moreover, as a use, it is good also as a power supply for electric vehicles other than the power supply for various electric devices. Examples of the electric vehicle include a battery electric vehicle driven only by a battery, a hybrid electric vehicle combining an internal combustion engine and a motor drive, a fuel cell vehicle generating power by a fuel cell, and the like.

  Hereinafter, specific examples of the present invention will be described using examples.

[Example 1]
A positive electrode active material was prepared as follows. That is, iron oxalate having a valence of iron, lithium carbonate, and ammonium dihydrogen phosphate as a starting material are mixed so that a molar ratio of Li: Fe: P is 1: 1: 2, and pelletized And then calcined in an argon gas atmosphere at 650 ° C. for 24 hours to obtain LiFePO ₄ having an olivine structure. This was used as a positive electrode active material.

A negative electrode active material was prepared as follows. That is, lithium carbonate (Li ₂ CO ₃ ) and vanadium pentoxide (V ₂ O ₅ ) were weighed according to the stoichiometric ratio and mixed for 120 minutes in an automatic mortar. Subsequently, this mixture was press-molded and fired at 700 ° C. for 3 hours in a hydrogen stream. The obtained mixture was sufficiently crushed in a mortar and then calcined at 650 ° C. for 48 hours in an oxygen-containing gas composed of carbon dioxide and oxygen. Furthermore, it was sufficiently pulverized in a mortar and fired again at 650 ° C. for 48 hours to obtain a spinel-structured LiV ₂ O ₄ . This was made into the negative electrode active material.

Next, a wound electrode body A shown in FIG. 1 was produced. Specifically, LiFePO ₄ , carbon black, carboxymethyl cellulose (thickener), styrene butadiene rubber (binder) are mixed at a weight ratio of 85: 10: 3: 2, and water is added to form a slurry. The positive electrode sheet 12 was obtained by coating the both sides of an aluminum foil having a thickness of 25 μm and then drying and cutting it into a rectangular shape having a width of 56 mm and a length of 500 mm. An aluminum tab having a width of 4 mm, a length of 70 mm, and a thickness of 100 μm was ultrasonically welded to the positive electrode sheet 12 to obtain a positive electrode tab 12a.

Further, LiV ₂ O ₄ , carbon black, carboxymethyl cellulose (thickening agent), styrene butadiene rubber (binder) are mixed at a weight ratio of 85: 10: 3: 2, and water is added to form a slurry. The negative electrode sheet 16 was obtained by coating the aluminum foil having a thickness of 25 μm on both sides and then drying, cutting into a rectangular shape having a width of 54 mm and a length of 450 mm. An aluminum tab having a width of 4 mm, a length of 70 mm, and a thickness of 100 μm was ultrasonically welded to the negative electrode sheet 16 to obtain a negative electrode tab 16a.

  The separator 13 is a hydrophilic sheet-like member having a width of 58 mm and a length of about 1100 mm, and was prepared as follows. In other words, 85-μm thick sheet-like non-woven fabric made of polyethylene and polypropylene is sulfonated in sulfuric acid atmosphere diluted with nitrogen gas, washed with deionized water and dried to sulfonate. A treated separator 13 was obtained. About the obtained separator 13, the hydrophilicity confirmation test was done. That is, one drop of deionized water was dropped on the upper surface of the separator 13 having a thickness of 25 μm, and it was examined whether the deionized water permeated the rear surface of the separator 13 after 1 minute. As a result, this sulfonated separator 13 was judged to have hydrophilicity because deionized water was permeated.

  And what laminated | stacked the positive electrode sheet 12, the separator 13, and the negative electrode sheet 16 was wound by the cylindrical shape, and it was set as the wound electrode body A. As shown in FIG.

On the other hand, as shown in FIG. 2, as a battery container 30, a polyacetal cylindrical container main body 32, a polyacetal first cap 34 that can be screwed into the upper end of the container main body 32, and a lower end of the container main body 22. A second cap 36 made of polyacetal that can be screwed in was prepared. The caps 34 and 36 are provided with openings 34a and 36a for exposing the current collectors 14 and 18, respectively. Then, the wound electrode body A is inserted into the container body 32 with the positive electrode tab 12a on the upper side and the negative electrode tab 16a on the lower side, and the positive electrode current collector 14 made of aluminum is connected to the positive electrode tab 12a. Similarly, the negative electrode current collector 18 made of aluminum was connected to the negative electrode tab 16a. At this time, between the upper opening of the container main body 32 and the positive electrode current collector 14 and between the lower opening of the container main body 32 and the negative electrode current collector 18, each is made of a fluororesin (Viton (registered trademark)). O-rings 20 and 22 were interposed. Subsequently, after the second cap 36 was closed, about 5 mL of 6M LiNO ₃ aqueous solution (pH 4.9) was injected as an aqueous electrolyte, and the first cap 34 was closed. The battery container 30 is liquid-tight by the O-rings 20 and 22. In this way, the 18650 type water-based lithium ion secondary battery 10 shown in FIG. 2 was produced.

[Example 2]
A water based lithium ion secondary battery 10 was produced in the same manner as in Example 1 except that the material of the battery container 30 was polyetheretherketone (PEEK).

[Example 3]
A water based lithium ion secondary battery 10 was produced in the same manner as in Example 1 except that the material of the battery container 30 was polypropylene.

[Comparative Example 1]
As shown in FIG. 3, a nickel-plated iron battery container 130 was prepared. Here, a wound electrode body A was produced in the same manner as in Example 1. Then, the wound electrode body A is inserted into the battery container 130, the negative electrode tab 16a is connected to the bottom surface of the battery container 130, the positive electrode tab 12a is connected to the positive electrode current collector 14, and the same aqueous electrolysis as in Example 1 is performed. After injecting the liquid, the battery container 130 was sealed with the gasket 136 interposed between the battery container 130 and the positive electrode current collector 14. Actually, the battery container 130 is divided into a cup-shaped container main body and a lid, which are sealed by caulking both. Thus, the water based lithium ion secondary battery 110 shown in FIG. 3 was produced.

[Comparative Example 2]
A water based lithium ion secondary battery 110 was produced in the same manner as in Comparative Example 1 except that the material of the battery container 130 was SUS304.

[Evaluation]
For each secondary battery, (1) initial discharge capacity and charge / discharge efficiency and (2) cycle test (capacity maintenance ratio) were evaluated as follows. The definition of “C” as a unit of current is as follows. That is, 1C means a current value that can be completely discharged in one hour when the battery is fully charged and then discharged at a constant current. In this specification, since all the battery capacities are adjusted to be 150 mAh, 1C is 150 mA.

(1) Initial discharge capacity and charge / discharge efficiency For Examples 1 to 3 and Comparative Examples 1 and 2, the initial discharge capacity and charge / discharge efficiency were evaluated. That is, each water based lithium ion secondary battery was charged to 1.3 V at a current of 15 mA (equivalent to 0.1 C) and then discharged to 0.7 V at a current of 0.15 mA. The initial discharge current capacity was defined as “initial discharge capacity” (unit: mAh). The value obtained by dividing the initial discharge capacity by the initial charge capacity and multiplying by 100 was defined as “charge / discharge efficiency” (unit%). The results are shown in Table 1.

  In Comparative Examples 1 and 2, since a battery container made of an iron-based metal was used, it was confirmed that a current considered to be a side reaction (probably hydrogen generation or oxygen generation) was flowing during the initial charge. Therefore, the charge / discharge efficiency was a low value. On the other hand, when the battery container made of the polymer material of Examples 1 to 3 was used, such side reaction was not observed, charging / discharging was performed relatively well, and the charging / discharging efficiency was about 87%. High value.

(2) Cycle test (capacity maintenance rate)
The cycle test of charging the battery that had been charged and discharged for the first time to 1.3 V at a current of 300 mA (corresponding to 2C) and discharging to 0.7 V at 300 mA was performed at 20 ° C. for 50 cycles. A value obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle and multiplying by 100 was defined as the “capacity maintenance ratio” (unit%). The results are shown in Table 1.

  In Comparative Examples 1 and 2, the capacity retention rate was greatly reduced because it was considered that side reactions occurred during the cycle test. However, in Examples 1 to 3, since such side reactions were not observed, the capacity was maintained. The rate was very high.

3 is a perspective view of a wound electrode body A. FIG. It is sectional drawing of the water-system lithium ion secondary battery 10 of an Example. It is sectional drawing of the water-system lithium ion secondary battery 110 of a comparative example.

Explanation of symbols

  10 water based lithium ion secondary battery, 12 positive electrode sheet, 12a positive electrode tab, 13 separator, 14 positive electrode current collector, 16 negative electrode sheet, 16a negative electrode tab, 18 negative electrode current collector, 20, 22 O-ring, 30 battery container, 32 Container body, 34 1st cap, 36 2nd cap, 34a, 36a Opening, 110 Water based lithium ion secondary battery, 130 Battery container, 136 Gasket.

Claims (6)

Between a positive electrode sheet that uses a material that releases lithium ions during charging and occludes lithium ions during discharge as a positive electrode active material, and a negative electrode sheet that uses a material that occludes lithium ions and discharges lithium ions during discharging as a negative electrode active material An aqueous lithium ion secondary battery having a structure in which an electrode body sandwiched between separators is housed in a battery container together with an aqueous electrolyte obtained by dissolving lithium ions in water,
The battery container is made of an electrolysis-inhibiting material that is less susceptible to electrolysis of water than ferrous metals,
The positive electrode current collector electrically connected to the positive electrode sheet and the negative electrode current collector electrically connected to the negative electrode sheet are exposed to the outside from the battery container,
Water-based lithium ion secondary battery. The electrode body is a wound electrode body wound by sandwiching the separator between the positive electrode sheet and the negative electrode sheet.
The water based lithium ion secondary battery according to claim 1. The electrolysis suppression material is made of a polymer material,
The water based lithium ion secondary battery according to claim 1 or 2. The electrolysis inhibiting material is a material selected from the group consisting of polyolefin resin, aromatic polyether ketone resin, polyoxymethylene resin and fluorine resin,
The water based lithium ion secondary battery according to claim 3. The positive electrode current collector and the negative electrode current collector are both made of aluminum.
The water based lithium ion secondary battery according to any one of claims 1 to 4. The battery container is formed by joining first and second caps to one end and the other end of a container body formed in a cylindrical shape, and the positive electrode current collector includes one end of the container body and the first cap. The negative electrode current collector is disposed in a liquid-tight manner between the other end of the container body and the cap.
The water based lithium ion secondary battery according to claim 5.

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