JP4595352B2 - Aqueous electrolyte lithium secondary battery - Google Patents

Description

  The present invention relates to an aqueous electrolyte lithium secondary battery having an aqueous electrolyte obtained by dissolving a lithium salt in water as an electrolyte.

  Lithium rechargeable batteries that use the lithium absorption and desorption phenomenon are high voltage, high energy density, and can be reduced in size and weight. Practical use has progressed in the field of communication equipment, and it has become widely popular. In other fields, the use of lithium secondary batteries as a power source for electric vehicles is being studied while the development of electric vehicles is urgent due to environmental issues and resource issues.

  Currently, non-aqueous lithium secondary batteries containing a non-aqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent as an electrolyte solution are mainly used as lithium secondary batteries in practical use. As such a non-aqueous lithium secondary battery, in general, a positive electrode active material composed of a lithium transition metal composite oxide, a conductive agent composed of a conductive carbon material, and a positive electrode mixture containing a binder composed of a fluororesin, A negative electrode mixture containing a positive electrode applied to a current collector made of aluminum foil, a negative electrode active material made of a carbon material capable of inserting and extracting lithium, and a binder made of a fluororesin or a water-soluble resin, What has the negative electrode formed by apply | coating to the collector which consists of foil is used.

  However, since non-aqueous lithium secondary batteries contain non-aqueous electrolytes such as organic solvents with a low flash point as the electrolyte, there is a risk of ignition or explosion due to overcharge or short circuit. . Further, when the battery is overcharged or exposed to a high temperature environment, the electrolytic solution may be decomposed to generate a flammable gas. For this reason, non-aqueous lithium secondary batteries are generally equipped with devices such as PCT elements and safety valves for the purpose of ensuring safety. However, since non-aqueous lithium secondary batteries originally contain a flammable solvent, it is difficult to ensure sufficient safety. In particular, when using a non-aqueous lithium secondary battery as a power source for automobiles or the like, the battery becomes larger and the amount of the organic solvent used increases. Therefore, a lithium secondary battery with higher safety has been demanded.

  In addition, in a non-aqueous lithium secondary battery, if there is even a small amount of moisture in the battery, gas is generated due to electrolysis of water, water reacts with lithium and lithium is consumed, There is a risk of corrosion of the material constituting the battery. Therefore, in a nonaqueous lithium secondary battery, it is necessary to maintain a thorough dry environment in the manufacturing process. As a result, there is a problem that special equipment and a great amount of labor are required to completely remove moisture, resulting in an increase in manufacturing cost.

On the other hand, there is an aqueous electrolyte lithium secondary battery using an aqueous solution as an electrolyte (see Patent Document 1). This aqueous electrolyte lithium secondary battery is very advantageous for the above-described problems of the non-aqueous lithium secondary battery.
That is, since the aqueous electrolyte lithium secondary battery does not contain the organic solvent, there is almost no risk of ignition. Moreover, since a dry environment is not required at the time of manufacture, the manufacturing cost can be reduced.
In general, an aqueous electrolyte lithium secondary battery needs to be charged / discharged in a potential range where electrolysis of water does not occur. However, an aqueous solution has higher conductivity than a non-aqueous solution. Compared to the secondary battery, there is an advantage that the reaction resistance of the battery is low and the output characteristics and rate characteristics of the battery are improved.

  As in the case of the non-aqueous lithium secondary battery, the positive electrode and the negative electrode of such an aqueous electrolyte lithium secondary battery are made of an electrode mixture (positive electrode mixture or negative electrode mixture) composed of an active material, a conductive agent, and a binder. It is manufactured by applying to a current collector made of metal foil or the like and drying. The aqueous electrolyte lithium secondary battery has a short history of research, and there are few reports on binders used for positive and negative electrodes. Therefore, until now, as binders for aqueous electrolyte lithium secondary batteries, fluororesins such as polyvinylidene fluoride and tetrafluoroethylene used for the positive and negative electrodes of non-aqueous lithium secondary batteries, styrene butadiene rubber, etc. The hydrocarbon-based resin has been used (see Patent Document 1 and Patent Document 2).

However, in an aqueous electrolyte lithium secondary battery containing a binder for a non-aqueous lithium secondary battery in the positive electrode or the negative electrode, the adhesion between the electrode mixture and the current collector is insufficient, and there is no water between them. There was a possibility that swelling would occur in the electrode during charging / discharging of the battery.
Moreover, the binder used for the non-aqueous lithium secondary battery has almost no affinity with water and has a property of shrinking in an aqueous solution. Therefore, when the particles of the positive electrode active material and the negative electrode active material expand and contract with charge / discharge, the binder contracted in the aqueous electrolyte solution is easily detached from the surface of the active material particles. As a result, the bonding force between the particles of the positive electrode active material and the negative electrode active material is lost, and the particles of the positive electrode active material and the negative electrode active material may slide off from the current collector. For this reason, as charge / discharge is repeated, there is a problem in that the discharge capacity tends to decrease and charge / discharge cycle characteristics that can withstand practical use cannot be exhibited.

JP-T 9-508490 JP 2001-52747 A

  The present invention has been made in view of such conventional problems, and is an aqueous electrolyte lithium secondary battery excellent in adhesion between a positive electrode composite or negative electrode composite and a current collector and excellent in charge / discharge cycle characteristics. Is to provide.

The present invention relates to a positive electrode formed by binding a positive electrode mixture to a positive electrode current collector, a negative electrode formed by binding a negative electrode mixture to a negative electrode current collector, and an aqueous electrolyte solution obtained by dissolving a lithium salt in water In an aqueous electrolyte lithium secondary battery having
The positive electrode mixture contains a positive electrode active material made of a lithium-containing composite oxide capable of reversibly inserting and extracting lithium, a conductive agent made of a carbon-based material having conductivity, and a binder.
The negative electrode mixture is composed of a negative electrode active material composed of a composite oxide having a lower lithium storage and desorption potential than the lithium-containing composite oxide contained in the positive electrode active material, and a conductive carbon-based material. Containing a conductive agent and a binder,
Both of the positive electrode mixture and the negative electrode mixture contain a water-insoluble polymer composed of acrylonitrile or an acrylic resin as the binder, in an aqueous electrolyte lithium secondary battery (Claim 1).

The most notable point in the aqueous electrolyte lithium secondary battery of the present invention is that the binder in the positive electrode mixture and the negative electrode mixture is composed of a water-insoluble polymer made of acrylonitrile or acrylic resin. It is in.
Therefore, in the said aqueous electrolyte lithium secondary battery, the adhesiveness of the said positive electrode compound material and the said negative electrode compound material, and the positive electrode collector and negative electrode collector which consist of metal foil, for example is excellent.
That is, the positive electrode current collector and the negative electrode current collector made of, for example, a metal foil are usually oxidized, and the surface is covered with oxygen atoms. The binder may be an upper Symbol positive electrode composite and negative electrode mixture, respectively in close contact with good binding to the positive electrode collector and the negative electrode current collector. Therefore, in the aqueous electrolyte lithium secondary battery, water of the aqueous electrolyte enters between the positive electrode current collector and the positive electrode mixture or between the negative electrode current collector and the positive electrode mixture. It is difficult, and it is possible to prevent the positive electrode mixture and the negative electrode mixture from peeling from the current collector due to the occurrence of swelling on the positive electrode and the negative electrode.

Moreover, since the binder has an affinity for water, it hardly shrinks even in an aqueous electrolyte solution. Furthermore, since the binder is insoluble in water, it does not elute in the aqueous electrolyte solution.
Therefore, even if the particles of the positive electrode active material and the negative electrode active material expand and contract with the charge and discharge of the aqueous electrolyte lithium secondary battery, the binder can maintain the bond between the particles.

Further, in the above aqueous electrolytic solution lithium secondary battery, the positive electrode active material and the negative active material, both Ri composite oxide der, has excellent affinity with the upper Symbol binder. Therefore, the binder has a strong adsorptive power to the positive electrode active material and the negative electrode active material particles. Therefore, the binder can firmly bond the particles of the positive electrode active material and the particles of the negative electrode active material.

  As described above, the binder can maintain the bond between the active material particles by the expansion and contraction of the active material particles accompanying the charge / discharge, and can firmly bond the particles of the active material. Therefore, even if charging / discharging is repeated, the particles of the positive electrode active material and the negative electrode active material are hardly detached. Therefore, the above-mentioned aqueous electrolyte lithium secondary battery is excellent in charge / discharge cycle characteristics because the battery capacity hardly decreases even when charge / discharge is repeated.

  As described above, according to the present invention, it is possible to provide a water-based electrolyte lithium secondary battery that is excellent in adhesion between a positive electrode mixture or a negative electrode mixture and a current collector and excellent in charge / discharge cycle characteristics.

  Next, embodiments of the aqueous electrolyte lithium secondary battery of the present invention will be described for each battery component. Here, as described above, the aqueous electrolyte lithium secondary battery includes a positive electrode formed by binding a positive electrode mixture to a positive electrode current collector, and a negative electrode formed by binding a negative electrode mixture to a negative electrode current collector. And an aqueous electrolyte solution obtained by dissolving a lithium salt in water. The positive electrode mixture contains a positive electrode active material, a conductive agent, and a binder, and the negative electrode mixture contains a negative electrode active material, a conductive agent, and a binder.

First, the binder contained in the positive electrode mixture and the negative electrode mixture will be described.
(binder)
The binder is preferably made of a water-insoluble polymer that is insoluble in water and contains one or more elements selected from oxygen, nitrogen, sulfur, and phosphorus. Such a water-insoluble polymer contains one or more elements selected from oxygen, nitrogen, sulfur, and phosphorus in addition to carbon and hydrogen, or carbon, hydrogen, and fluorine. As said binder, what mixed the said water-insoluble polymer 1 type (s) or 2 or more types can be used.

Specific examples include those containing oxygen in addition to carbon and hydrogen, such as an acrylic resin, an epoxy resin, or a carboxy-modified product or a hydroxy-modified product of a hydrocarbon resin such as polypropylene or polybutadiene. Examples of those containing oxygen and nitrogen in addition to carbon and hydrogen include polyacrylonitrile, urethane resins, melamine resins, or amine-modified products of hydrocarbon resins and nitro group addition products. Examples of sulfur-containing compounds include thiol-modified products and sulfonic acid adducts. In addition to carbon, hydrogen, and fluorine, those containing oxygen and the like include tetrafluoroethylene, modified fluororesins such as carboxy-modified products and hydroxy-modified products of fluororesins such as polyvinylidene fluoride, and the like. Further, there are a hydrocarbon resin, a copolymer of a fluororesin, and a resin including at least one selected from oxygen, nitrogen, sulfur, and phosphorus.
The binder for the positive electrode mixture and the binder for the negative electrode mixture may be the same as or different from each other.

(Positive electrode)
The positive electrode can be formed, for example, by applying the positive electrode mixture containing the positive electrode active material, the conductive agent, and the binder to the positive electrode current collector, drying, and pressing as necessary. .
The positive electrode active material is made of a lithium-containing composite oxide capable of reversibly inserting and extracting lithium. Specifically, for example, there are lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, lithium iron composite phosphorus oxide, and the like.
The conductive agent is for ensuring the electrical conductivity of the electrode. For example, one or more selected from carbon-based materials such as carbon black, acetylene black, ketjen black, and graphite can be used. .

The positive electrode mixture contains 60 to 95 parts by weight of the positive electrode active material, 4 to 20 parts by weight of the conductive agent, and 1 to 20 parts by weight of the binder in 100 parts by weight of the positive electrode mixture. Is preferred.
When the content of the positive electrode active material is less than 60 parts by weight, the aqueous electrolyte lithium secondary battery may not exhibit a sufficient charge / discharge capacity to withstand practical use. On the other hand, when it exceeds 95 parts by weight, the content of the conductive agent or the binder is insufficient, and the aqueous electrolyte lithium secondary battery has a high electric resistance, which may cause a practical problem.

Moreover, when content of the said electrically conductive agent is less than 4 weight part, the electroconductivity of a positive electrode falls, the electrical resistance of the said aqueous electrolyte lithium secondary battery becomes high, and there exists a possibility that it may be a problem practically. On the other hand, when it exceeds 20 weight part, there exists a possibility that the battery capacity of the said aqueous electrolyte lithium secondary battery may fall.
Further, when the content of the binder is less than 1 part by weight, the effect of improving the adhesion between the positive electrode mixture and the positive electrode current collector, and the negative electrode mixture and the negative electrode current collector is sufficient. There is a risk that it will not be demonstrated. On the other hand, when it exceeds 20 weight part, there exists a possibility that the battery capacity of the said aqueous electrolyte lithium secondary battery may fall.

  When the positive electrode mixture is applied to the positive electrode current collector, for example, a binder solution is prepared using an organic solvent suitable for dissolving the binder, and the positive electrode active material and the conductive agent are sufficiently contained in the solution. And further adjusted to a viscosity suitable for coating with the organic solvent, and then coated on the current collector. As such an organic solvent, for example, N-methyl-2-pyrrolidone or the like can be used.

(Negative electrode)
The negative electrode can be formed, for example, by applying the negative electrode mixture containing the negative electrode active material, the conductive agent, and the binder to the negative electrode current collector, drying, and pressing as necessary. . In the said negative electrode, the thing similar to the said positive electrode can be used except containing the said negative electrode active material as an active material.
The negative electrode active material is composed of a composite oxide having a lithium occlusion potential and a desorption potential lower than those of the lithium-containing composite oxide contained in the positive electrode active material. Specifically, for example, there are lithium transition metal composite oxides such as lithium vanadium composite oxide and lithium titanium composite oxide, or iron hydroxide.

  In addition, the negative electrode mixture contains 60 to 95 parts by weight of the negative electrode active material, 4 to 20 parts by weight of the conductive agent, and 1 to 20 parts by weight of the binder in 100 parts by weight of the negative electrode mixture. Is preferred. About these critical significance, it is the same as that of the said positive electrode compound material.

(Electrolyte)
The aqueous electrolyte lithium secondary battery contains an aqueous electrolyte obtained by dissolving a lithium salt in water as an electrolyte. The lithium salt is dissociated by dissolving in water, and lithium ions are present in the electrolytic solution. Examples of such a lithium salt include lithium nitrate, lithium sulfate, lithium hydroxide, and lithium iodide. These lithium salts can be used alone or in combination of two or more.

The aqueous electrolyte solution preferably has a pH in a range of 6 ≦ pH ≦ 10.
In this case, the stability of the positive electrode active material and the negative electrode active material in the positive electrode and the negative electrode in an aqueous solution can be improved, and lithium ion occlusion and desorption in the positive electrode active material and the negative electrode active material can be improved. The reaction becomes smoother.

When the pH of the aqueous electrolyte is less than 6, the positive electrode active material and the negative electrode active material may be dissolved and cannot be stably present in the aqueous electrolyte. On the other hand, when the pH exceeds 10, a reaction occurs between the aqueous electrolyte and the positive electrode current collector or the negative electrode current collector made of, for example, a metal foil, and the electrode may not exist stably. There is.
In addition, the lithium salt concentration in the aqueous electrolyte solution should be a saturated concentration or a concentration close to it from the viewpoint of increasing the electrical conductivity of the electrolyte solution and reducing the internal resistance of the aqueous electrolyte lithium secondary battery. Is preferred.

(Current collector)
In the aqueous electrolyte lithium secondary battery, the positive electrode has the positive electrode current collector, and the negative electrode has the negative electrode current collector. As such a current collector, a metal foil or the like that is excellent in conductivity and stable in an aqueous electrolyte can be used. Specifically, for example, there is a metal foil made of nickel, aluminum, platinum, or an alloy thereof.

Moreover, it is preferable that both of the positive electrode current collector and the negative electrode current collector are made of aluminum.
In this case, the positive electrode current collector and the negative electrode current collector react in the aqueous electrolyte solution even when the pH of the aqueous electrolyte solution is in the preferred range of 6 ≦ pH ≦ 10 as described above. Can be prevented and stability can be improved. In this case, the manufacturing cost of the aqueous electrolyte lithium secondary battery can be reduced, and the weight can be reduced.

(Other)
In the aqueous electrolyte lithium secondary battery, a separator can be sandwiched between the positive electrode and the negative electrode.
The said separator isolate | separates a positive electrode and a negative electrode, and hold | maintains the said aqueous electrolyte solution, A stable thing can be used in the said aqueous electrolyte solution. Specifically, what consists of thin microporous films, such as a cellulose, polyethylene, and a polypropylene, can be used, for example.

Examples of the shape of the aqueous electrolyte lithium secondary battery include a coin shape, a cylindrical shape, and a square shape. As the battery case that accommodates the positive electrode, the negative electrode, the aqueous electrolyte, and the like, those corresponding to these shapes can be used.
The aqueous electrolyte lithium secondary battery includes, for example, an electrode body in which the separator is sandwiched between the positive electrode and the negative electrode in a battery case having a predetermined shape, and the positive electrode current collector and the negative electrode The current collector is electrically connected to the positive electrode external terminal and the negative electrode external terminal provided outside the battery via lead wires, and the electrode body is impregnated with the aqueous electrolyte solution, and the battery case is sealed. can do.

Example 1
Next, examples of the aqueous electrolyte lithium secondary battery of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the aqueous electrolyte lithium secondary battery 1 of this example includes a positive electrode 2 formed by binding a positive electrode mixture 25 to a positive electrode current collector 21, and a negative electrode current collector 31. It has the negative electrode 3 formed by binding the material 35 and an aqueous electrolyte solution obtained by dissolving lithium salt in water.

As shown in FIG. 2, the positive electrode mixture 25 includes a positive electrode active material 251 made of a lithium-containing composite oxide capable of reversibly inserting and extracting lithium, a conductive agent 253 made of a carbon-based material having conductivity, and a binder. 255.
Further, the negative electrode mixture 35 is composed of a negative electrode active material 35 made of a composite oxide having a lower lithium storage and desorption potential than the lithium-containing composite oxide contained in the positive electrode active material 25, and a carbon-based conductive material. A conductive agent 353 made of a material and a binder 355 are contained.
The binders 255 and 355 in the positive electrode mixture 25 and the negative electrode mixture 35 are made of a water-insoluble polymer containing one or more elements selected from oxygen, nitrogen, sulfur and phosphorus.

  As shown in FIG. 1, the aqueous electrolyte lithium secondary battery 1 of this example is of a cylindrical type and includes a positive electrode 2, a negative electrode 3, a separator 4, a gasket 5, a battery case 6, and the like. The battery case 6 is an 18650 type cylindrical battery case, and includes a cap 61 and an outer can 62. In the battery case 6, a sheet-like positive electrode 2 and a negative electrode 3 are arranged in a wound state together with a separator 4 sandwiched between them, and have a wound electrode.

A gasket 5 is arranged inside the cap 61 of the battery case 6, and an aqueous electrolyte is injected into the battery case 6.
The positive electrode 2 and the negative electrode 3 are respectively provided with a positive electrode current collecting lead 28 and a negative electrode current collecting lead 38 by welding. The positive electrode current collector lead 28 is connected by welding to a positive electrode current collector tab 285 disposed on the cap 61 side. Further, the negative electrode current collecting lead 38 is connected by welding to a negative electrode current collecting tab 385 arranged at the bottom of the outer can 62.
Further, a saturated concentration of lithium nitrate aqueous solution (pH = 7) is used as the aqueous electrolyte, and the aqueous electrolyte is injected into the battery case 6.

Next, the manufacturing method of the aqueous electrolyte lithium secondary battery of this example will be described.
First, an olivine-structured lithium iron composite phosphorus oxide represented by the composition formula LiFePO ₄ was prepared as a positive electrode active material, acetylene black as a conductive agent, and acrylonitrile containing nitrogen atoms as a binder.
Further, N-methyl-2-pyrrolidone as an organic solvent was prepared, and the binder prepared above was dissolved therein to prepare a 5 wt% binder solution. In this binder solution, the positive electrode active material and the conductive agent were dispersed and mixed to obtain a positive electrode mixture. This positive electrode mixture contains 80 parts by weight of the positive electrode active material, 10 parts by weight of the conductive agent, and 10 parts by weight of the binder.
Next, an aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector, and a positive electrode mixture was applied to both surfaces of the positive electrode current collector and dried to evaporate the organic solvent. Furthermore, it pressed with the pressure of about 1 ton / cm < ² >, and produced the sheet-like positive electrode.

Next, a lithium vanadium composite oxide represented by a composition formula LiV ₂ O ₄ was prepared as a negative electrode active material, acetylene black as a conductive agent, and acrylonitrile containing nitrogen atoms as a binder were prepared as described above. A sheet-like negative electrode was produced in the same manner as the positive electrode.

Next, as shown in FIG. 1, a positive electrode current collecting lead 28 and a negative electrode current collecting lead 38 were welded to the sheet-like positive electrode 2 and negative electrode 3 obtained as described above, respectively. Next, the positive electrode 2 and the negative electrode 3 were wound with a cellulose-based separator 4 sandwiched between them to produce a spiral wound electrode.
Subsequently, the wound electrode was inserted into an 18650 type cylindrical battery case 6 including an outer can 62 and a cap 61. At this time, the positive electrode current collector lead 28 is connected to the positive electrode current collector tab 285 disposed on the cap 61 side of the battery case 6 by welding, and the negative electrode current collector lead 385 is disposed on the negative electrode current collector tab 385 disposed on the bottom of the outer can 6. 38 were connected by welding.

  Next, the battery case 6 was impregnated with a saturated lithium nitrate aqueous solution (pH = 7) as an aqueous electrolyte solution. The gasket 5 was disposed inside the cap 61, and the cap 61 was disposed in the opening of the outer can 62. Subsequently, the battery case 6 was sealed by caulking the cap 61 to produce the aqueous electrolyte lithium secondary battery 1. This is designated as Sample E1.

In the aqueous electrolyte lithium secondary battery of this example, as shown in FIG. 2, the binders 255 and 355 contained in the positive electrode mixture 25 and the negative electrode mixture 35 are made of acrylonitrile, which is a water-insoluble polymer containing nitrogen atoms. Become. Therefore, the adhesion between the positive electrode mixture 25 and the negative electrode mixture 35 and the positive electrode current collector 21 and the negative electrode current collector 31 made of aluminum foil is excellent.
That is, the positive electrode current collector 21 and the negative electrode current collector 31 are usually oxidized, and the surfaces are covered with oxygen atoms. Since the binders 255 and 355 contain nitrogen atoms having high affinity with oxygen atoms, the positive electrode mixture 25 and the negative electrode mixture 35 are bonded to the positive electrode current collector 21 and the negative electrode current collector 31 with good adhesion, respectively. Can be made.

  Therefore, in the aqueous electrolyte lithium secondary battery of this example, the water of the aqueous electrolyte is between the positive electrode current collector 21 and the positive electrode mixture 25 and between the negative electrode current collector 31 and the negative electrode mixture 35. Can prevent the positive electrode mixture 25 and the negative electrode mixture 35 from being detached from the positive electrode current collector 21 and the negative electrode current collector 31, respectively.

Moreover, since the binders 255 and 355 have affinity with water, they hardly shrink even in the aqueous electrolyte solution. Furthermore, since the binders 255 and 355 are insoluble in water, they are not eluted in the aqueous electrolyte solution.
Therefore, even when the particles of the positive electrode active material 251 and the negative electrode active material 351 expand and contract with the charge / discharge of the aqueous electrolyte lithium secondary battery, the binders 255 and 355 sufficiently maintain the bond between these particles. can do.

  Furthermore, in the aqueous electrolyte lithium secondary battery of this example, since the positive electrode active material 251 and the negative electrode active material 351 are both complex oxides, one or more elements selected from oxygen, nitrogen, sulfur and phosphorus are used. Excellent affinity with the binders 255 and 355 to be contained. Therefore, the binders 255 and 355 have a strong adsorptive power to the positive electrode active material 251 and the negative electrode active material 351 particles. Therefore, the binders 255 and 355 can firmly bond the particles of the positive electrode active material 251 and the particles of the negative electrode active material 351 together.

  Thus, as shown in FIG. 2, even when the active material particles 251 and 351 expand and contract with charge / discharge, the binder 255 and 355 can maintain the bond between the active material particles 251 and 351. In addition, the active material particles 251 and 351 can be firmly bonded. Therefore, even when charging and discharging are repeated, the particles of the positive electrode active material 251 and the negative electrode active material 351 are hardly detached. Therefore, the aqueous electrolyte lithium secondary battery of this example is excellent in charge / discharge cycle characteristics because the battery capacity does not easily decrease even when charge / discharge is repeated.

(Example 2)
Next, this example is an example of producing a four-type aqueous electrolyte lithium secondary battery in which the kind of binder in the positive electrode mixture and the negative electrode mixture is different from that in Example 1.
First, an aqueous electrolyte lithium secondary battery different from the aqueous electrolyte lithium secondary battery of Sample E1 of Example 1 only in the types of binder and organic solvent was produced. This is designated as Sample E2. Sample E2 was prepared in the same manner as Sample E1 except that an acrylic resin containing oxygen atoms was used as the binder and xylene was used as the organic solvent.

  In addition, polyvinylidene fluoride containing none of oxygen, nitrogen, sulfur, and phosphorus was used as a positive electrode binder, and a water-based electrolyte lithium secondary battery was prepared in the same manner as in the above sample E1. This is designated as Sample C1. Sample C1 was prepared using polyvinylidene fluoride as the positive electrode binder and acrylonitrile similar to that of sample E1 as the negative electrode binder. Others are the same as those of the sample E1.

  In addition, polyvinylidene fluoride containing none of oxygen, nitrogen, sulfur, and phosphorus was used as the negative electrode binder, and a water-based electrolyte lithium secondary battery was fabricated in the same manner as in the above sample E1. This is designated as Sample C2. Sample C2 was prepared using polyvinylidene fluoride as a negative electrode binder and acrylonitrile similar to that of sample E1 as a positive electrode binder. Others are the same as those of the sample E1.

  Further, as the binder for the positive electrode and the negative electrode, polyvinylidene fluoride containing none of oxygen, nitrogen, sulfur and phosphorus was used, and a water-based electrolyte lithium secondary battery was produced in the same manner as in the above sample E1. This is designated as Sample C3. Sample C3 was prepared using polyvinylidene fluoride as the binder for the positive and negative electrodes. Others are the same as those of the sample E1.

Next, a charge / discharge cycle test was performed on the sample E1, the sample E2, and the samples C1 to C3, and the maintenance rates of the discharge capacity at the 100th cycle were compared.
In the charge / discharge cycle test, each sample was charged to a battery voltage of 1.4 V at a constant current of 0.5 mA / cm ² under a temperature of 60 ° C., and then the current density of 0.5 mA / cm ^2. Charging / discharging to a battery voltage of 0.1 V at a constant current of 1 cycle was performed as one cycle, and this cycle was repeated 100 cycles. In each charging / discharging cycle, after charging to 1.4V and discharging to 0.1V, a charging suspension time and a discharging suspension time were provided for 1 minute each. And about each sample, the discharge capacity of 1st cycle (first time) and 100th cycle was measured.

The discharge capacity is determined by measuring the discharge current value (mA) at the first cycle or the 100th cycle, and multiplying this discharge current value by the time (hr) required for discharge to obtain the positive electrode active capacity in the battery. Calculated by dividing by weight (g) of material.
The results are shown in Table 1.
Further, the capacity retention rate was calculated from the following equation from the discharge capacity at the first time and the 100th cycle.
Capacity maintenance ratio (%) = (discharge capacity at 100th cycle / initial discharge capacity) × 100

As is known from Table 1, there was almost no difference in the initial discharge capacity in any of the aqueous electrolyte lithium secondary batteries of Samples E1, E2 and Samples C1-C3.
However, the sample E1 and the sample E2 have a higher discharge capacity at the 100th cycle and an excellent discharge capacity maintenance rate than the samples C1 to C3. Further, in sample E1 and sample E2, no swelling or the like occurred in the positive electrode or the negative electrode, and the electrode did not peel off.
Therefore, samples E1 and E2 using a water-insoluble polymer containing one or more elements selected from oxygen, nitrogen, sulfur and phosphorus as binders, such as acrylonitrile and acrylic resins, are positive electrode composites. It turns out that it is excellent in the adhesiveness of a material or negative electrode compound material, and a collector, and is excellent in charging / discharging cycle characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the aqueous electrolyte lithium secondary battery concerning Example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the positive electrode (negative electrode) concerning Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water-system electrolyte lithium secondary battery 2 Positive electrode 21 Positive electrode collector 25 Positive electrode compound 251 Positive electrode active material 253 (353) Conductive agent 255 (355) Binder 3 Negative electrode 31 Negative electrode collector 35 Negative electrode compound 351 Negative electrode active material

Claims (3)

An aqueous system having a positive electrode formed by binding a positive electrode mixture to a positive electrode current collector, a negative electrode formed by binding a negative electrode mixture to a negative electrode current collector, and an aqueous electrolyte solution obtained by dissolving a lithium salt in water In the electrolyte lithium secondary battery,
The positive electrode mixture contains a positive electrode active material made of a lithium-containing composite oxide capable of reversibly inserting and extracting lithium, a conductive agent made of a carbon-based material having conductivity, and a binder.
The negative electrode mixture is composed of a negative electrode active material composed of a composite oxide having a lower lithium storage and desorption potential than the lithium-containing composite oxide contained in the positive electrode active material, and a conductive carbon-based material. Containing a conductive agent and a binder,
An aqueous electrolyte lithium secondary battery, wherein both the positive electrode mixture and the negative electrode mixture contain a water-insoluble polymer made of acrylonitrile or an acrylic resin as the binder.   The aqueous lithium secondary battery according to claim 1, wherein the aqueous electrolyte has a pH in a range of 6 ≦ pH ≦ 10.   3. The aqueous electrolyte lithium secondary battery according to claim 1, wherein both of the positive electrode current collector and the negative electrode current collector are made of aluminum.

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