JP2014096238A - Process of manufacturing positive electrode for power storage device and positive electrode - Google Patents

Abstract

A positive electrode manufacturing method and a positive electrode for a lithium ion electricity storage device are provided that have low environmental burden and low manufacturing cost.
A mixing step of mixing a spinel type lithium nickel manganese composite oxide and an alginate binder, a film forming step of forming the mixture into a film, and a drying step of drying the film. A positive electrode comprising a method for producing a positive electrode for an electricity storage device, a spinel-type lithium nickel manganese composite oxide, and an alginate binder.
[Selection] Figure 1

Description

  The present invention relates to a positive electrode used for an electricity storage device, particularly a positive electrode used for a lithium ion secondary battery, and a method for producing the same.

  In recent years, power storage devices such as lithium ion secondary batteries have been used as power sources for electric devices and the like, and are also being used as power sources for electric vehicles (EV, HEV, etc.). Power storage devices such as lithium ion secondary batteries further improve their characteristics, such as energy density (high capacity), output density (high output), and cycle characteristics (cycle life). High safety is desired.

  In the production of an electrode of an electricity storage device, an electrode material slurry is obtained by adding and mixing a binder (binder) and a solvent mainly into a powdery positive electrode or negative electrode active material. Furthermore, an electrode is manufactured by shape | molding and drying this.

  As the binder used for manufacturing the electrode material, an organic material having excellent adhesiveness and flexibility is generally used, and an organic solvent that dissolves the organic material is used.

  In particular, since the positive electrode of a non-aqueous storage device generally uses a positive electrode active material containing lithium ions and the like that are highly reactive with water, an organic solvent that has been sufficiently dehydrated in the production of the positive electrode Is assumed to be used.

  Since the organic solvent is released from the electrode formed in this way in each step of forming and drying, there is a concern about the influence on the human body and the environment. For this reason, in manufacture of the electrode using an organic solvent, installation of a solvent recovery device is unavoidable, leading to an increase in cost.

  Thus, a method has been proposed for manufacturing electrodes at low cost, protecting the human body and the environment, and ensuring safety.

  For example, in Patent Document 1, a solid that has a functional powder (positive electrode active material, negative electrode active material) and a binder and does not contain a solvent, and manufactures an electrode or the like by preparing a low environmental load slurry. A method for manufacturing a lithium ion secondary battery is disclosed.

  Furthermore, Patent Document 2 discloses a slurry for forming a negative electrode coating film and a negative electrode of a non-aqueous electrolyte secondary battery in which a binder with an alginate or an alginate and an aqueous medium are applied to a carbon negative electrode active material such as graphite. A coating is disclosed. It is described that the slurry for forming a negative electrode coating film or the negative electrode coating film is excellent in safety in handling and excellent in adhesion between the synthetic carbon material or graphite material and the current collector.

  Non-Patent Document 1 discloses a negative electrode of a lithium ion secondary battery using sodium alginate as a binder and water as a solvent in a silicon alloy negative electrode active material.

JP 2009-252629 JP 2001-15114

Igor Kovalenko, et al., Science 334, 75 (2011); “A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries”

  However, in the method of Patent Document 1, the environmental load is reduced because no solvent is used in the production of the electrode. However, in the formation of an electrode from a mixture containing a molten binder and an active material, the above mixture is added even during molding. It is necessary to warm, there is room for improvement in workability, and the manufacturing cost increases.

  Further, in Patent Document 2 and Non-Patent Document 1, although water can be used as a solvent in the production of the negative electrode, it is possible to reduce the environmental load and reduce the production cost, No proposals have been made for lowering manufacturing costs.

  However, an object of the present invention is to provide a positive electrode manufacturing method and a positive electrode for a lithium ion power storage device, which are low in environmental load and manufacturing cost.

In order to achieve the above-mentioned object, the present inventors mixed a spinel type lithium nickel manganese composite oxide and an alginate binder, a film forming step of forming the mixture into a film, A method for producing a positive electrode for an electricity storage device, comprising a drying step of drying a film, and a positive electrode comprising a spinel type lithium nickel manganese composite oxide and an alginate binder.

  The positive electrode manufacturing method and the positive electrode of the present invention can minimize the environmental load and the manufacturing cost.

  Moreover, since an alginate binder is rich in flexibility, it can follow a relatively large volume change of the positive electrode during charge and discharge. That is, the positive electrode is configured in a state where it can sufficiently expand / contract.

  Furthermore, the positive electrode in the present invention includes an alginate binder, and thus has sufficient oxidation resistance to ensure the stability as the positive electrode.

  Since the organic solvent is not contained in the manufacturing method of a positive electrode of this invention thru | or a positive electrode, the load with respect to an environment is reduced. Furthermore, since it is not necessary to use an organic solvent recovery device, the manufacturing cost is also reduced.

  The positive electrode according to the present invention has excellent flexibility and oxidation resistance. Furthermore, the lithium ion secondary battery including the positive electrode of the present invention is excellent in energy density and cycle characteristics.

It is a schematic sectional drawing which shows an example of embodiment of the electrical storage device (lithium ion secondary battery) of this invention. It is a schematic sectional drawing which shows another example of embodiment of the electrical storage device (lithium ion secondary battery) of this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

The method for producing the positive electrode of the electricity storage device of the present invention is as follows.
A mixing step of producing a positive electrode slurry by mixing a spinel type lithium nickel manganese composite oxide and an alginate binder;
A film forming step of forming a positive electrode slurry into a film; and
A drying step of drying the film;
It is characterized by including.

The spinel type lithium nickel manganese composite oxide used as the positive electrode active material of the present invention has a spinel type crystal structure (octahedral crystal structure composed of AB2O4 composed of metal elements A and B and oxygen). Examples of the lithium nickel manganese composite oxide include Li Ni _0.5 Mn _1.5 O ₄ .

  The spinel type lithium nickel manganese composite oxide is a material obtained by mixing and firing an oxide raw material containing nickel and manganese and a lithium compound powder, and is capable of applying a high voltage of 4.5 V or higher. It is a high density positive electrode active material.

  In the present invention, an alginate binder, particularly sodium alginate is used for this positive electrode active material. By using an alginate binder, the solvent in the production of the positive electrode can be water. In general, since water has a lower boiling point than an organic solvent used for manufacturing a positive electrode, the drying temperature of the positive electrode is also reduced, and the manufacturing cost can be reduced.

  In addition, since spinel-type nickel manganese composite oxide is not an active material that is highly reactive with water, it does not require water management such as coating in a dry room. Is advantageously used.

  Alginates are excellent in adhesive strength as a binder and high in flexibility, and thus can hold an active material in a positive electrode having a larger basis weight than a negative electrode. For example, when SBR (Stadien / Butane / Rubber), one of the typical water-soluble binders used in the negative electrode, is used for the positive electrode, the binder has excellent adhesive strength, but it is not flexible, so it has a large weight. It cannot be held, cracks occur, and the active material slides down.

  Alginates are easy to handle because they are excellent in water dispersibility, and since they are moderately dispersible, they are blended uniformly in the positive electrode mixture, so that a positive electrode film with no bias in composition can be easily produced. The For example, when using SBR, which is a typical water-soluble binder used in negative electrodes, SBR has no viscosity and poor dispersibility, so a CMC (carboxymethylmethylcellulose) aqueous solution is added as a thickener to add dispersibility. Need to improve.

  In addition, in the present invention, in addition to one or more kinds of alginates such as sodium alginate, potassium alginate, and ammonium alginate, one or more kinds of alginate esters such as propylene glycol ester may be mixed and used.

  The positive electrode active material is prepared, for example, by dissolving an alginate or an alginate in a solvent and then adding the mixture to a spinel type lithium nickel manganese composite oxide to produce a slurry, or a spinel type lithium nickel manganese composite oxide Then, alginate or alginate and a solvent can be mixed simultaneously to form a positive electrode slurry.

  As the solvent for the binder, water, particularly distilled water can be used, and it is preferable to use only water as the solvent for preparing the positive electrode. However, as long as the properties and environment of the binder and the positive electrode active material are not adversely affected, a water-miscible solvent such as a lower alcohol such as ethanol can be added at a ratio of 0 to 30 with respect to water. Is done.

  The mixing ratio of the spinel type lithium nickel manganese composite oxide, the alginate binder, and the solvent is 60 to 90: 1 to 20:80 to 150, preferably 70 to 90: 5 to 10:95 to 120 (mass basis). It is.

  As a mixer for producing the positive electrode slurry, a planetary disper, particularly a rotation / revolution mixer can be used (mixing step).

  The positive electrode slurry thus obtained is applied to a positive electrode current collector to form a film (slurry film) (film formation step), and this is performed at a temperature of 60 ° C. or higher and 100 ° C. or lower for 10 minutes to 60 minutes. By drying (drying step), the positive electrode of the present invention is manufactured.

Further, after the film forming step and before the drying step, when the film is pressed by a roll press or the like until the volume density of the film becomes 2.0 to 4.0 g / cm ³ , the positive electrode is maintained while maintaining the charge / discharge capacity. It can be downsized. Further, if the pressing is performed after the film forming process and before the drying process, the adhesiveness of the film is improved and the processing becomes easy.

  It is preferable to perform a drying process normally at 100 to 120 degreeC and a vacuum state for 1 hour-24 hours.

  Thus, in the present invention, a positive electrode containing a spinel-type lithium nickel manganese composite oxide and an alginate binder can be obtained by the above-described method, for example.

  The content (dry mass) of the alginate binder with respect to the total mass of the positive electrode is preferably in the range of 1 to 20 mass%, particularly 3 to 10 mass%. By setting it as the mass of this range, the adhesive force of a binder is fully acquired and a positive electrode comes to have a required softness | flexibility.

  If the dry mass of the binder is less than 1% by mass with respect to the total mass of the positive electrode, film formation becomes difficult. If the dry mass exceeds 20% by mass, the proportion of the positive electrode active material in the entire positive electrode decreases, so the energy density decreases. In addition to this, a large amount of binder may act as a resistance to inhibit lithium ion migration.

  The positive electrode of the present invention thus obtained can constitute a lithium ion secondary battery excellent in energy density and cycle characteristics.

  Hereinafter, an example of a lithium ion secondary battery will be described as an example of an embodiment of a lithium ion electricity storage device of the present invention with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a lithium ion secondary battery according to the present invention. As shown in the figure, in the lithium ion secondary battery 20, a positive electrode 21 and a negative electrode 22 are disposed to face each other with a separator 23 interposed therebetween.

  The positive electrode 21 includes a positive electrode mixture layer 21a including the positive electrode of the present invention and a positive electrode current collector 21b. The positive electrode mixture layer 21a is formed on the separator 23 side surface of the positive electrode current collector 21b. The negative electrode 22 includes a negative electrode mixture layer 22a and a negative electrode current collector 22b.

  The negative electrode mixture layer 22a is formed on the separator 23 side surface of the negative electrode current collector 22b. The positive electrode 21, the negative electrode 22, and the separator 23 are sealed in an outer container (not shown), and the outer container is filled with a non-aqueous electrolyte. Examples of the exterior material include a battery can and a laminate film. Further, leads (not shown) for connecting external terminals are respectively connected to the positive electrode current collector 21b and the negative electrode current collector 22b as necessary.

  Next, FIG. 2 is a schematic sectional view showing another example of the embodiment of the lithium ion secondary battery according to the present invention. As shown in the figure, the lithium ion secondary battery 30 includes an electrode unit 34 in which a plurality of positive electrodes 31 and negative electrodes 32 are alternately stacked via separators 33. The positive electrode 31 is configured by providing a positive electrode mixture layer 31a on both surfaces of a positive electrode current collector 31b. The negative electrode 32 is configured such that the negative electrode mixture layer 32a is provided on both surfaces of the negative electrode current collector 32b (however, for the uppermost and lowermost negative electrodes 32, the negative electrode mixture layer 32a is only on one side).

  Further, although not shown, the positive electrode current collector 31b has a protruding portion, the protruding portions of the plurality of positive electrode current collectors 31b are overlapped, and the lead 36 is welded to the overlapped portion. Similarly, the negative electrode current collector 32b has a protruding portion, and a lead 37 is welded to a portion where the protruding portions of the plurality of negative electrode current collectors 32b are overlapped. The lithium ion secondary battery 30 is configured by enclosing an electrode unit 34 and a non-aqueous electrolyte in an exterior container such as a laminate film (not shown). The leads 36 and 37 are exposed to the outside of the outer container for connection with an external device.

  In addition, the lithium ion secondary battery 30 has the negative electrode disposed at the uppermost part and the lowermost part. However, the present invention is not limited thereto, and the positive electrode may be disposed at the uppermost part and the lowermost part.

[Production of positive electrode]
In the present invention, a spinel type lithium nickel manganese composite oxide is used as the positive electrode active material, and as a specific example, Li Ni _0.5 Mn _1.5 O ₄ is particularly preferably used.

  In addition to the above materials, a binder (binder), a conductive additive, and a solvent are used for forming the positive electrode mixture layer.

  In the formation of the positive electrode mixture layer of the present invention, one or more alginate binders, preferably sodium alginate, potassium alginate, and ammonium alginate, particularly preferably sodium alginate, is used as a binder. Further, a water-soluble binder other than the alginate binder may be further mixed as long as it does not inhibit the activity of the spinel type lithium nickel manganese composite oxide. Examples of binders that can be added include one or more alginate esters, such as propylene glycol esters.

  It is preferable that the compounding quantity of a binder is 1-20 mass% (dry mass) with respect to the said positive electrode compound material amount, especially 3-10 mass%.

  Examples of the conductive assistant used for forming the positive electrode mixture layer include conductive carbon such as ketjen black, metals such as copper, iron, silver, nickel, palladium, gold, platinum, indium and tungsten, indium oxide and tin oxide. Conductive metal oxides such as can be used. As for the compounding quantity of an electrically conductive material, 1-30 mass% is preferable with respect to the said positive electrode active material.

  A positive electrode mixture layer in which a positive electrode slurry in which a mixture containing the high-voltage positive electrode active material, a binder, and a conductive additive is dispersed in a solvent is coated on a positive electrode current collector to form a film and dried. Form. You may press-press etc. after a drying process. As a result, the positive electrode mixture layer is uniformly and firmly pressed onto the current collector.

  The thickness of the positive electrode mixture layer is 10 to 200 μm, preferably 20 to 100 μm.

  The positive electrode current collector need only be a conductive substrate whose surface in contact with the positive electrode mixture layer exhibits conductivity. For example, a conductive substrate formed of a conductive material such as metal, conductive metal oxide, or conductive carbon. In addition, a conductive foil or a non-conductive base body covered with the conductive material can be used. As the conductive material, copper, gold, aluminum, an alloy thereof, or conductive carbon is preferable.

  As the positive electrode current collector, an expanded metal, a punching metal, a foil, a net, a foam, or the like of the above materials can be used. The shape and number of through holes in the case of a porous body are not particularly limited, and can be appropriately set within a range that does not inhibit the movement of lithium ions.

Moreover, in this invention, the outstanding cycling characteristics can be acquired by making the fabric weight of a positive electrode compound-material layer into 4 mg / cm < ² > or more and 25 mg / cm < ² > or less. When the basis weight is less than 4 mg / cm ² or more than 25 mg / cm ² , cycle deterioration occurs. Note that the larger the basis weight, the higher the capacity. The basis weight of the positive electrode mixture layer is more preferably 10 mg / cm ² or more and 20 mg / cm ² or less. Note that the basis weight here means the basis weight of the positive electrode mixture layer on one surface side of the positive electrode current collector. In the case where the positive electrode mixture layer is formed on both surfaces of the positive electrode current collector, the positive electrode mixture layer on one surface and the other surface is formed so as to be included in the above ranges.

[Manufacture of negative electrode]
In the present invention, the negative electrode is not particularly limited, and can be produced using a known material.

  Any material can be used as the negative electrode active material as long as it is a material capable of removing and inserting lithium ions, and examples thereof include a carbon-based material, a silicon-based material, a tin-based material, and a polyacene-based material.

More specifically, as the carbon-based material, for example, lithium intercalation carbon material (substance capable of reversibly removing and inserting lithium ions) such as graphite, non-graphitizable carbon, and graphitizable carbon,
Examples of silicon-based materials include silicon and silicon alloys.
Examples of tin-based materials include tin and tin alloys.
Examples of lithium metal materials include lithium alloys (Li-Al alloys and the like) and lithium compounds (lithium nitride and the like)
Examples of the polyacene organic semiconductor include insoluble and infusible PAS having a polyacene skeleton.

  Of these, carbon-based materials, silicon-based materials, and tin-based materials are preferably used in the present invention.

  These negative electrode active materials are excellent in the ability to occlude lithium ions, and can constitute a lithium ion electricity storage device having a large charge / discharge capacity.

  The negative electrode active material may be composed of one type of material or a mixture of two or more types of materials.

  In the production of the negative electrode in the present invention, a negative electrode mixture layer is formed by applying a negative electrode slurry in which a mixture containing the negative electrode active material and the binder described above is dispersed in a solvent and drying the mixture on a negative electrode current collector. Note that the same binder (binder), solvent, and current collector as those for the positive electrode described above can be used.

  The thickness of the negative electrode mixture layer is generally 10 to 200 μm, preferably 20 to 100 μm.

  In the present invention, the basis weight of the negative electrode mixture layer is appropriately designed in accordance with the basis weight of the positive electrode mixture layer. Usually, a lithium ion secondary battery is designed so that the capacity (mAh) of the positive electrode and the negative electrode is approximately the same from the viewpoint of capacity balance and energy density of the positive and negative electrodes. Therefore, the basis weight of the negative electrode mixture layer is set based on the type of the negative electrode active material, the capacity of the positive electrode, and the like.

[Non-aqueous electrolyte]
There is no restriction | limiting in particular in the non-aqueous electrolyte in this invention, A well-known material can be used. For example, an electrolytic solution in which a general lithium salt is used as an electrolyte and is dissolved in an organic solvent can be used from the viewpoint that electrolysis does not occur even at a high voltage and that lithium ions can exist stably.

Examples of the electrolyte include CF ₃ SO ₃ Li, C ₄ F ₉ SO ₈ Li, (CF ₃ SO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, LiBF ₄ , LiPF ₆ , LiClO _4, etc. The mixture of 2 or more types is mentioned.

As an organic solvent, for example,
C ₁ -C ₁₀ alkylene carbonate, preferably C ₁ -C ₆ alkylene carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate,
C ₁ -C ₁₀ alkyl carbonate, preferably C ₁ -C ₆ alkyl carbonates, such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate, vinyl carbonate, trifluoromethyl propylene carbonate, 1,2-dimethoxyethane, Examples include 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, and propiotolyl.

  In the present invention, any one of these or a mixed solvent of two or more thereof is used.

Among these, in the present invention, in particular, it is preferable to include one or more of C ₁ -C ₁₀ alkyl carbonate and C ₁ -C ₁₀ alkylene carbonate, and by using these carbonates in the electrolyte, lithium ion conductive A good SEI film can be produced.

  The electrolyte concentration in the non-aqueous electrolyte is preferably 0.1 to 5.0 mol / L, and more preferably 0.5 to 3.0 mol / L.

  The non-aqueous electrolyte may be liquid, or may be a solid electrolyte or polymer gel electrolyte mixed with a plasticizer or a polymer.

[Separator]
The separator used in the present invention is not particularly limited, and a known separator can be used. For example, a porous body having durability against an electrolytic solution, a positive electrode active material, and a negative electrode active material and having continuous air holes and having no electronic conductivity can be preferably used. Examples of such a porous body include woven fabric, non-woven fabric, synthetic resin microporous membrane, and glass fiber. A synthetic resin microporous membrane is preferably used, and a polyolefin microporous membrane such as polyethylene or polypropylene is particularly preferable in terms of thickness, membrane strength, and membrane resistance.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to this embodiment.

I. Manufacture of coin cell [Example 1]
[Positive electrode]
A positive electrode mixture was prepared from the following materials.

Spinel type lithium nickel manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) 85 parts by mass Sodium alginate 5 parts by mass Carbon black 10 parts by mass Distilled water 100 parts by mass

After sodium alginate was dissolved in water, this was added to the positive electrode active material (LiNi _0.5 Mn _1.5 O ₄ ), and the remaining materials were mixed to obtain a positive electrode mixture slurry.

The positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil (thickness 10 μm) at a thickness of 400 μm by a doctor blade method and pre-dried to form a positive electrode mixture layer on the positive electrode current collector. The basis weight of the positive electrode mixture layer was 20 mg / cm ² (per one side).

The pre-dried electrode was pressed by a roll press and subjected to main drying at 120 ° C. in a vacuum state for 12 hours using a vacuum dryer. A positive electrode according to the invention having a volume density of 2.7 g / cm ³ was obtained.

[Negative electrode]
As the negative electrode, a 38 μm thick Li metal foil was used as the negative electrode.

[Electrolyte]
An electrolyte solution in which 1.2 M LiPF6 was dissolved in EC / DMC / MEC / FEC (mixing ratio = (5: 5: 5: 1)) was used.

[Production of coin cell]
A lithium ion secondary battery as shown in FIG. 1 was produced using two positive electrodes produced as described above and one negative electrode. Specifically, it is laminated between a positive electrode and a negative electrode via a polyethylene separator, and the non-aqueous electrolyte is injected, and the electrolyte is infiltrated into the electrode by vacuum impregnation. An ion secondary battery) was produced.

[Example 2]
A lithium ion secondary battery of the present invention was produced in the same manner as in Example 1 except that the composition of the positive electrode mixture was changed as follows.

Spinel type lithium nickel manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) 80 parts by mass Sodium alginate 10 parts by mass Carbon black 10 parts by mass Distilled water 100 parts by mass

[Comparative Example 1]
A comparative lithium ion secondary battery was produced in the same manner as in Example 1 except that the composition of the positive electrode mixture was changed as follows.

Spinel type lithium nickel manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) 85 parts by mass Styrene butadiene rubber (SBR) 3 parts by mass Carboxymethylcellulose (CMC) 2 parts by mass Carbon black 10 parts by mass Distilled water 100 parts by mass

[Comparative Example 2]
A comparative lithium ion secondary battery was prepared in the same manner as in Example 1 except that the composition of the positive electrode mixture was changed as follows, and the main drying was changed to 125 ° C. and 12 hours in a vacuum state. .

Spinel type lithium nickel manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) 85 parts by mass Polyvinylidene fluoride (PVDF) 5 parts by mass Carbon black 10 parts by mass N-methyl 2-pyrrolidone (NMP: boiling point 202 ° C.) 100 parts by mass

  In each Example and Comparative Example, no electrode peeling was observed, and it was found that the minimum amount of binder that did not cause electrode peeling was 5 parts by mass (dry mass 5% by mass) or less.

II. Charge / Discharge Test The lithium ion secondary batteries obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were charged to a voltage of 4.9 V at a current of 0.1 C and a constant current constant voltage for 24 hours using a charge / discharge device. The battery was discharged to a voltage of 3 V at a current of 0.2 C (first charge / discharge). Thereafter, the battery was charged at a constant current and a constant voltage for 7.5 hours at a current of 0.2 C to a voltage of 4.9 V, and discharged to a voltage of 3 V at a current of 0.2 C (second charge / discharge). Further, the third charge / discharge was performed under the same conditions as the second charge / discharge.

  Thereafter, a cycle of constant current and constant voltage charging at a current of 0.7 C to a voltage of 4.9 V for 3 hours and discharging to a voltage of 3 V at a current of 0.5 C was further repeated for 1 to 100 cycles. In addition, about Example 2, it has tested only to 40 cycles.

  The discharge capacity at the first cycle was measured, and the ratio of the discharge capacity obtained at the 40th or 100th cycle was calculated. The results are listed in Table 1.

  From the above table, the lithium ion secondary battery of the present invention shows no change in discharge capacity even after 40 cycles, and has cycle characteristics equivalent to those of the lithium ion secondary battery of Comparative Example 2 even after 100 cycles. You can see that

  In addition, a positive electrode using a mixture of styrene butadiene rubber and carboxymethyl cellulose as a water-soluble binder could be formed into a film, but constituted a lithium ion secondary battery (Comparative Example 1) containing this. However, charging / discharging could not be performed.

  As described above, it is understood that the lithium ion secondary battery using sodium alginate which is a water-soluble binder does not need to use an organic solvent and thus has a small environmental load and is excellent in cycle characteristics.

  In addition, since the organic solvent has a higher boiling point than water, the positive electrode according to Comparative Example 2 has a high drying temperature required for the main drying. On the other hand, in Examples 1 and 2, the drying temperature of the positive electrode is low, which is considered to lead to power saving.

  The present invention is not limited to the configurations and examples of the above-described embodiment, and various modifications are possible within the scope of the gist of the invention.

20, 30 Lithium ion secondary battery 21, 31 Positive electrode 21a, 31a Positive electrode mixture layer 21b, 31b Positive electrode collector 22, 32 Negative electrode 22a, 32a Negative electrode mixture layer 22b, 32b Negative electrode collector 23, 33 Separator 34 Electrode Unit 36, 37 lead

Claims (8)

A mixing step of mixing a spinel type lithium nickel manganese composite oxide and an alginate binder;
A film forming step of forming the mixture into a film;
A drying step of drying the film;
The manufacturing method of the positive electrode of the electrical storage device characterized by the above-mentioned. The process according to claim 1, spinel type lithium-nickel-manganese composite oxide is characterized by a Li Ni _0.5 Mn _1.5 O _4.   The production method according to claim 1 or 2, wherein the alginate is one or more materials selected from sodium alginate, potassium alginate, and ammonium alginate.   The method according to any one of claims 1 to 3, wherein the film is dried in the drying step at a temperature of 60C or higher and 120C or lower. The method further comprises a pressurizing step of pressurizing the film until the volume density of the film becomes 2.0 to 4.0 g / cm ³ after the film forming step and before the drying step. 5. The production method according to any one of 4 above.   A positive electrode comprising a spinel type lithium nickel manganese composite oxide and an alginate binder.   The positive electrode according to claim 6, wherein the alginate is one or more materials selected from sodium alginate, potassium alginate, and ammonium alginate.   The positive electrode according to claim 6 or 7, wherein the content (dry mass) of the alginate binder with respect to the total mass of the positive electrode is in the range of 1 to 20% by mass.

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