JPWO2016129677A1 - Aqueous sodium ion secondary battery - Google Patents

Abstract

[PROBLEMS] To solve the problem of safety anxiety associated with a battery using a conventionally proposed non-aqueous solvent, and to solve the problem of deterioration of battery characteristics and charge / discharge cycle, and does not become a gel. A novel aqueous sodium ion secondary battery provided with an electrolytic solution is provided. A water-based sodium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution, the electrolyte solution comprising: a) an electrolyte salt, b) water, and c) an aldobionic acid derivative, an aldonic acid derivative, or uronic acid. An aqueous sodium ion secondary battery comprising a derivative. [Selection figure] None

Description

  The present invention relates to a water-based sodium ion secondary battery, and more particularly, to a water-based sodium ion secondary battery including an ion-conductive electrolyte solution that does not become a gel, using a specific organic acid derivative.

  In recent years, non-aqueous electrolyte secondary batteries have the advantages of high voltage and high energy density and low self-discharge rate, so that non-aqueous electrolyte secondary batteries can be used as alternatives to aqueous secondary batteries such as lead batteries and nickel cadmium batteries. It has been ordered and some of them have already been commercialized. For example, more than half of notebook computers and mobile phones are driven by non-aqueous electrolyte secondary batteries.

  Also, in response to the recent demand for smaller and lighter electronic devices, laminate batteries that use laminate films instead of conventional metal cases are lighter, thinner, and more flexible in shape. Has been attracting attention. However, because of its structure, laminated batteries are weak in resistance to internal stimuli such as an increase in internal pressure and external stimuli such as tearing, and there is a high risk of rupture and ignition due to deformation or breakage. It is often used by being stored in a pack case, and the weight reduction has not been achieved. In addition, the laminate battery, like other non-aqueous electrolyte batteries, generally uses a flammable organic solvent such as an ester compound and an ether compound as an electrolyte, and the flammable organic solvent is used to rupture the battery. This is one of the major causes of problems such as ignition.

  As an example of solving such a problem, a polymer solid electrolyte having a form in which a solid electrolyte is uniformly dissolved in a polymer has been proposed. The polymer solid electrolyte has a higher ionic conductivity than a liquid electrolyte. Therefore, there is a problem in practical use because it is extremely low. Recently, a polymer gel electrolyte obtained by impregnating the above polymer with a liquid electrolyte conventionally used has been proposed as a technique for solving the problem of electrolyte ignition due to liquid leakage to the outside of the battery. However, the battery using the polymer gel electrolyte has the same problems as conventional batteries using non-aqueous electrolytes (for example, short circuit, overcharge, etc. when the battery is abnormal) in terms of ensuring safety against liquid leakage. ) And the battery itself is not fundamentally safe.

In recent years, as a new type of battery, a water-based lithium ion battery in which 1M Li ₂ SO ₄ is gelled with a water-soluble polymer polyvinyl acetamide to form a gel electrolyte has been reported (Patent Document 1). The above-described water-based lithium ion secondary battery does not use an organic solvent in the electrolyte, and therefore basically does not burn or ignite, and avoids the problem of ignition in the conventionally proposed secondary battery. It is expected that Furthermore, since manufacturing process does not require moisture management, the manufacturing cost can be greatly reduced. In addition, since the aqueous electrolyte generally has higher conductivity than the non-aqueous electrolyte, an advantage that the internal resistance can be lowered as compared with the non-aqueous lithium ion secondary battery is also expected.

  On the other hand, there is an increasing need for large-sized storage batteries in addition to the use of mobile devices for small terminals such as notebook computers and mobile phones. This is because the demand for larger storage batteries in households and commercial and industrial facilities is rapidly increasing in order to avoid the risk of power outages and power shortages in recent years. However, in the lithium ion secondary battery described above, the lithium metal used as a raw material is a rare metal, which is high in cost. In addition, it is necessary to spread a secondary battery that has been enlarged in terms of the balance of resource reserves and supply amount. Fundamental issues remain.

From this point of view, there is an interest in water-based sodium ion secondary batteries using sodium that is cheaper and rich in reserves than metallic lithium. So far, several literatures and patents relating to electrode active materials constituting sodium ion secondary batteries have been reported. For example, those composed of crystalline NaFeO ₂ having a layered rock salt structure (Non-patent Document 1), NASICON, etc. There is one composed of crystalline Na ₃ V ₂ (PO ₄ ) ₃ having a type structure (Non-patent Document 2). On the other hand, there are few knowledge about a negative electrode, and there are some reports of the negative electrode active material in the optimal combination with a positive electrode active material (for example, patent document 2). However, a sufficient discharge voltage, discharge capacity, and charge / discharge cycle sufficient to withstand practical use have not yet been obtained.

Japanese Patent Laid-Open No. 2001-102086 JP 2013-89391 A

S. Okada, Y .; Takahashi, T .; Kiyabu, T .; Doi, J .; Yamakiand T. et al. Nishida, Abstract of 210th ECS Meeting, B2, # 201, (2006). Yoshinori Noguchi, Eiji Kobayashi, L. S. Pushnitsa, Takayuki Doi, Shigeto Okada, Junichi Yamaki, 49th Battery Symposium, 2E07 (2008).

  As described above, since non-aqueous solvents are used for electrolytes in general lithium ion batteries, there is a risk of ignition or explosion if a battery leaks due to damage to the battery. At the same time, it has a big safety problem. Lithium polymer gel batteries in which non-aqueous electrolytes are gelled avoid the risk of leakage, but basically use non-aqueous solvents so that ignition and explosion can be completely avoided. Yes, not.

  On the other hand, water-based lithium-ion batteries do not use non-aqueous solvents in the electrolyte, so the risk of ignition and explosion can be avoided, but when using aqueous solutions, leakage due to battery damage should be avoided. In addition, the aqueous lithium polymer gel battery proposed so far is due to the presence of the gelling agent and the increased viscosity of the solution compared to the battery of the aqueous electrolyte without using the gelling agent. Lithium ion migration is reduced, which leads to a decrease in electrical conductivity and deterioration of charge / discharge capacity, and there is a concern that another problem of deterioration of battery characteristics due to gelation of the electrolytic solution may occur. . Furthermore, a large-sized secondary battery using metallic lithium as a raw material still has a fundamental problem for widespread use in terms of cost, reserves and supply.

  The present invention has been made on the basis of the above circumstances, and the problem to be solved is to solve the problem of safety anxiety associated with a battery using a conventionally proposed non-aqueous solvent, And it is providing the novel water-system sodium ion secondary battery provided with the electrolyte solution which does not become a gel form which can also solve the problem of a fall of a battery characteristic and a charging / discharging cycle.

  As a result of diligent research to solve the above problems, the present inventors have conducted electrolysis that does not form a gel containing a specific organic acid derivative, an electrolyte salt, and water as an electrolyte of an aqueous sodium ion secondary battery. By adopting the solution, the solution of the problem of ensuring safety in the use of the organic solvent, which has been a problem in the conventional electrolyte solution, is solved, and it has good ionic conductivity and uses the conventional liquid electrolyte solution. The present inventors have found that charge / discharge characteristics superior to those of conventional batteries can be obtained.

That is, the first aspect of the present invention is a water-based sodium ion secondary battery including a positive electrode, a negative electrode, and an electrolytic solution, and the electrolytic solution includes:
a) electrolyte salt,
The present invention relates to an aqueous sodium ion secondary battery comprising b) water and c) an aldobionic acid derivative, an aldonic acid derivative or a uronic acid derivative.
As a second aspect, the aldobionic acid derivative is represented by the following formula (1):




(Wherein, Z ₁ represents an alkali metal or an alkaline earth metal, and X _{1 to} X ₈ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). A compound,
The aldonic acid derivative is represented by the following formula (2):




(Wherein Z ₂ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{9 to} X ₁₃ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). A compound represented by
The uronic acid derivative is represented by the following formula (3):




(Wherein Z ₃ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{14 to} X ₁₇ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). It is related with the water-system sodium ion secondary battery as described in a 1st viewpoint which is a compound represented.
As a third aspect, in the first aspect or the second aspect, the positive electrode includes a positive electrode active material, a conductive auxiliary material and a binder, and the negative electrode includes a negative electrode active material, a conductive auxiliary material and a binder. The present invention relates to the aqueous sodium ion secondary battery described.
As a fourth aspect, the positive electrode active material and the negative electrode active material are both composed of a sodium-transition metal composite oxide capable of inserting and removing sodium ions, but the two active materials are different from each other. The present invention relates to the aqueous sodium ion secondary battery according to the third aspect.
As a fifth aspect, the positive electrode active material is composed of a sodium-transition metal composite oxide containing one or more transition metal elements selected from Co, Ni, Mn, Cr, V, Ti, and Fe. It is related with the water-system sodium ion secondary battery as described in a 4th viewpoint.
As a sixth aspect, the present invention relates to the aqueous sodium ion secondary battery according to the fifth aspect, wherein the positive electrode active material is olivine-type NaFePO ₄ or olivine-type NaMnPO ₄ .
As a seventh aspect, in the sixth aspect, the negative electrode active material is composed of a sodium-transition metal complex oxide containing one or more transition metal elements selected from V, Ti, and Fe. The present invention relates to an aqueous sodium ion secondary battery.
As an eighth aspect, the present invention relates to the aqueous sodium ion secondary battery according to the seventh aspect, wherein the negative electrode active material is NASICON type NaTi ₂ (PO ₄ ) ₃ .
As a ninth aspect, the conductive auxiliary material is carbon black, ketjen black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, carbon nanoparticle, carbon nanotube, titanium oxide, ruthenium oxide, aluminum, nickel and The aqueous sodium ion secondary battery according to the third aspect, which is selected from the group consisting of these mixtures.
As a tenth aspect, the present invention relates to the aqueous sodium ion secondary battery according to the ninth aspect, wherein the conductive auxiliary material is acetylene black.
As an eleventh aspect, the binder is 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-tetrafluoro Tylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer and ethylene -The aqueous sodium ion secondary battery according to the third aspect, which is selected from the group consisting of acrylic acid copolymers.
As a twelfth aspect, the aqueous sodium ion secondary battery according to the eleventh aspect is characterized in that the binder is polytetrafluoroethylene (PTFE).
As a thirteenth aspect, the electrolyte salt is NaNO ₃ , NaOH, NaF, NaCl, NaBr, NaI, NaClO ₄ , Na ₂ SO ₄ , Na (CH ₃ COO), NaBF ₄ , NaPF ₆ , NaN (CF ₃ SO ₂ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , Na ₂ O, Na ₂ CO ₃ and a mixture thereof, any one of the first to twelfth aspects The present invention relates to the aqueous sodium ion secondary battery described in item 1.
As a fourteenth aspect, the present invention relates to the aqueous sodium ion secondary battery according to the thirteenth aspect, wherein the electrolyte salt is NaClO ₄ or Na ₂ SO ₄ .
As a fifteenth aspect, the electrolytic solution relates to the aqueous sodium ion secondary battery according to any one of the first aspect to the fourteenth aspect, further including a water-soluble polymer.
As a sixteenth aspect, the water-soluble polymer is gelatin, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), starch, cellulose and derivatives thereof, polyethylene oxide, polysaccharide, polyvinylamine, chitosan, polylysine, polyacrylic acid, poly The aqueous sodium ion secondary battery according to the fifteenth aspect, which is selected from the group consisting of alginic acid, polyhyaluronic acid, carboxycellulose, and a mixture thereof.

  Since the aqueous sodium ion secondary battery of the present invention uses water, which is an aqueous solvent, as a solvent, it is possible to avoid the risk of ignition or explosion due to liquid leakage due to battery damage. For this reason, compared with the battery which gelatinizes and uses the electrolyte solution of a general sodium ion battery and a nonaqueous solvent, safety | security can be improved significantly.

In addition, the aqueous sodium ion secondary battery of the present invention suppresses the deterioration of battery performance seen in the conventionally proposed aqueous sodium ion battery, and obtains charge / discharge characteristics similar to those of a battery using a conventional liquid electrolyte. be able to.
Thus, the following two possibilities are assumed as the reason why the effect of improving the cycle characteristics was observed even with an additive that does not gel.
(1) Buffer effect: The NASICON negative electrode is weak against alkali, and the additive may relax the negative electrode surface during the charge / discharge cycle.
(2) Effect of counter electrode zinc: Possibility of preventing zinc corrosion.

1 is an X-ray diffraction pattern of an active material Na ₂ FeP ₂ O ₇ synthesized in an example of the present invention. 1 is an X-ray diffraction pattern of an active material NaTi ₂ (PO ₄ ) ₃ synthesized in an example of the present invention. Positive _Na 2 _FeP 2 _{O 7} was synthesized in Examples of the present invention, the negative electrode NaTi _{2 (PO 4)} is a schematic diagram of a ₃ rating beaker type full cell. Positive _Na 2 _FeP 2 _{O 7} was synthesized in Examples of the present invention, is a graph showing the cycle characteristics of the negative electrode NaTi _{2 (PO 4) 3} current density rating for a beaker-type full cell 2.0 mA / cm ^2.

The present invention relates to an aqueous sodium ion secondary battery comprising at least a positive electrode and a negative electrode made of a substance capable of inserting and removing sodium ions, respectively, and an electrolyte solution that does not become a gel containing an aqueous solution in which a sodium salt is dissolved. . This electrolytic solution is an electrolytic solution composed of an electrolyte salt (sodium salt), water, and a compound represented by the formula (1).
In particular, the present invention is characterized in that an electrolytic solution containing no aldobionic acid derivative, aldonic acid derivative or uronic acid derivative is used as the electrolytic solution of the aqueous sodium ion secondary battery.
Hereinafter, each component will be described.

[Positive electrode]
As a positive electrode used in the aqueous sodium ion secondary battery of the present invention, a positive electrode conventionally proposed as a positive electrode of a sodium ion secondary battery can be used, and among them, one having a flat discharge portion of 4 V or less with respect to sodium. Is preferred.
For example, the positive electrode is composed of a positive electrode active material, a conductive auxiliary material, and a binder, and specifically, a positive electrode material obtained by adding a binder to the positive electrode active material and the conductive auxiliary material is formed by pressure bonding to a current collector. Is done.

The positive electrode active material is composed of a sodium-transition metal composite oxide capable of inserting and desorbing sodium ions, specifically, as a transition metal element whose valence changes with the insertion or desorption of sodium ions. It consists of a sodium-transition metal complex oxide containing at least one selected from Co, Ni, Mn, Cr, V, Ti, and Fe. For example, olivine-type NaFePO ₄ , olivine-type NaMnPO ₄ , Na ₂ FePO ₄ F , O3 type NaFeO ₂ , O3 type NaCrO ₂ , O3 type NaFe _0.5 Co _0.5 O ₂ , P2 type Na _2/3 Fe _0.5 Mn _0.5 O ₂ , Na ₃ V ₂ (PO ₄ ) ₃ , Na ₃ V ₂ (PO ₄ ) ₂ F ₃ , Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O _{7, and the} like.
However, the positive electrode active material is preferably a composite oxide different from a sodium-transition metal composite oxide contained in the negative electrode described later.
Among the positive electrode active materials, it is more preferable to use NaFePO ₄ or NaMnPO ₄ .

Examples of the binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer. Polymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer Polymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer , Ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer or ethylene-acrylic acid Copolymers can be used.
Among them, in the present invention, it is preferable to use polytetrafluoroethylene (PTFE) as the binder to be used.

As the conductive auxiliary material, carbon black, ketjen black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, carbon nanoparticles, carbon nanotubes and other carbon materials, or titanium oxide, ruthenium oxide, aluminum, Metals such as nickel or metal oxides can be used. As the shape of these conductive auxiliary materials, a shape selected from powder, sphere, flake, filament, fiber, spike, needle and the like can be adopted.
In the present invention, the conductive auxiliary material used is preferably acetylene black.

  Furthermore, as the current collector, a stainless mesh, a nickel mesh, a gold mesh, or the like can be used.

[Negative electrode]
As the negative electrode used in the aqueous sodium ion secondary battery of the present invention, a negative electrode conventionally proposed as a negative electrode for sodium ion secondary batteries can be used.
For example, a negative electrode is composed of a negative electrode active material, a conductive auxiliary material, and a binder. Specifically, a negative electrode material obtained by adding a binder to the negative electrode active material, a conductive auxiliary material, and a current collector are formed on the current collector. Is done.
Here, as the conductive auxiliary material, the binder, and the current collector used for the negative electrode, those mentioned in the above [Positive electrode] can be preferably used.

The negative electrode active material is composed of a sodium-transition metal composite oxide capable of inserting and desorbing sodium ions, and specifically, V as a transition metal element whose valence changes with the insertion and desorption of sodium ions. It consists of a sodium-transition metal composite oxide containing at least one selected from Ti, Ti, and Fe, and examples thereof include composite oxides such as NaTi ₂ (PO ₄ ) ₃ and NaV ₂ (PO ₄ ) _3. .
However, the negative electrode active material is preferably a composite oxide different from the sodium-transition metal composite oxide contained in the positive electrode described above.
Among the negative electrode active materials, it is more preferable to use NaTi ₂ (PO ₄ ) ₃ .

[Electrolyte]
<Aldobionic acid derivative>
In the present invention, as the aldobionic acid derivative used for the electrolyte solution that does not become a gel, the following formula (1):




(Wherein, Z ₁ represents an alkali metal or an alkaline earth metal, and X _{1 to} X ₈ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). Compounds.

Examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include magnesium, calcium, and barium.
Alkaline earth metals are preferred, and calcium is preferred as the alkaline earth metal.
Preferred examples of Z ₁ include 1 / 2Ca.
Examples of the alkyl group having 1 to 23 carbon atoms include a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, an isobutyl group, a secondary butyl group, a tertiary butyl group, a normal pentyl group, and a normal decyl group. Etc.
Preferable X _{1 to} X ₈ include a hydrogen atom.
A preferred aldobionic acid derivative is calcium lactobionate.

<Aldonic acid derivative>
In the present invention, as an aldonic acid derivative used in an electrolyte solution that does not become a gel, the following formula (2):




(Wherein Z ₂ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{9 to} X ₁₃ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). And the compounds represented.

Examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include magnesium, calcium, and barium.
Alkaline earth metals are preferred, and calcium is preferred as the alkaline earth metal.
Preferred examples of Z ₂ include a hydrogen atom and 1 / 2Ca.
Examples of the alkyl group having 1 to 23 carbon atoms include a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, an isobutyl group, a secondary butyl group, a tertiary butyl group, a normal pentyl group, and a normal decyl group. Etc.
Preferable X _{9 to} X ₁₃ include a hydrogen atom.
Preferable aldonic acid derivatives include gluconic acid, calcium gluconate, galactonic acid, calcium galactonate, mannonic acid, calcium mannonic acid and the like.

<Uronic acid derivative>
In the present invention, the uronic acid derivative used in the electrolyte solution that does not become a gel is represented by the following formula (3):




(Wherein Z ₃ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{14 to} X ₁₇ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). And the compounds represented.

Examples of the alkali metal include lithium, sodium, and potassium, and examples of the alkaline earth metal include magnesium, calcium, and barium.
Alkaline earth metals are preferred, and calcium is preferred as the alkaline earth metal.
Preferred examples of Z ₃ include a hydrogen atom and 1 / 2Ca.
Examples of the alkyl group having 1 to 23 carbon atoms include a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, an isobutyl group, a secondary butyl group, a tertiary butyl group, a normal pentyl group, and a normal decyl group. Etc.
Preferable X _{14 to} X ₁₇ include a hydrogen atom.
Preferable uronic acid derivatives include glucuronic acid, calcium glucuronic acid, galacturonic acid, calcium galacturonic acid, mannuronic acid, calcium mannuronic acid and the like.

  In the electrolytic solution used for the aqueous sodium ion secondary battery in the present invention, the ratio of the aldobionic acid derivative, aldonic acid derivative or uronic acid derivative is 0.1 to 30% by mass of the total mass of the obtained electrolytic solution, preferably 0.5 to 20% by mass, more preferably 1 to 5% by mass.

<Electrolyte salt>
As the electrolyte salt used in the electrolytic solution in the present invention, an electrolyte salt that has been proposed as being usable for a sodium ion secondary battery can be used. Specific examples include, for example, NaNO ₃ , NaOH, NaF, NaCl, NaBr, NaI, NaClO ₄ , Na ₂ SO ₄ , Na (CH ₃ COO), NaBF ₄ , NaPF ₆ , NaN (CF ₃ SO ₂ ) ₂ , Examples thereof include sodium salts such as NaN (C ₂ F ₅ SO ₂ ) ₂ , Na ₂ O, Na ₂ CO ₃ and mixtures thereof.

As the electrolyte salt used in the electrolytic solution in the present invention (sodium salt), particularly preferably NaClO ₄ or _Na 2 SO _4.

  In the electrolytic solution of the present invention, the electrolyte salt is used in the obtained electrolytic solution at a concentration of 0.01 to 5 mol / kg, preferably 1 to 3 mol / kg.

<Water-soluble polymer>
The electrolyte solution may contain a water-soluble polymer as long as it is not gelled. By using a water-soluble polymer, the mechanical strength of the gel electrolyte can be increased, and the gel can also serve as a water separation inhibitor.
Examples of the water-soluble polymer include gelatin, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), starch and other polysaccharides, cellulose and derivatives thereof, polyethylene oxide, polysaccharides, polyvinylamine, chitosan, polylysine, polyacrylic acid, Examples include polyalginic acid, polyhyaluronic acid, carboxycellulose, and the like.

  Among the water-soluble polymers, polyvinyl alcohol (PVA) and polyvinyl pyrrolidone are preferable, and polyvinyl alcohol (PVA) is particularly preferable.

  In the electrolytic solution used in the aqueous sodium ion secondary battery according to the present invention, the proportion when the water-soluble polymer is used is 0.1 to 30% by mass, preferably 0. 5 to 20% by mass, more preferably 1 to 5% by mass.

EXAMPLES Hereinafter, although an Example is given and this invention is described more concretely, this invention is not limited by the following description.
The abbreviations used in the examples are as follows.
LA: lactobionic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
Chemical structural formula:




CaLA: calcium lactobionate (manufactured by Tokyo Chemical Industry Co., Ltd.)
Chemical structural formula:

[Synthesis of Active Material Na ₂ FeP ₂ O ₇ ]
Na ₂ FeP ₂ O ₇ to be a positive electrode was synthesized by a solid phase method. NaH ₂ PO ₄ and Fe (COO) ₂ .2H ₂ O were mixed at a stoichiometric ratio, and Na ₂ FeP ₂ O ₇ was obtained by firing at 600 ° C. for 6 hours in an Ar atmosphere (FIG. 1). From the XRD pattern of the figure, the main phase was identified as Na ₂ FeP ₂ O ₇ . The synthesized active material and acetylene black (AB) were mixed at a weight ratio of 70:25 and subjected to carbon coating treatment at 300 rpm for 10 hours using a planetary ball mill. The obtained powder (active material and AB) was heat-treated in an Ar atmosphere at 600 ° C. for 10 hours. The obtained powder and PTFE were mixed at a weight ratio of 95: 5 and molded into pellets to make a positive electrode.

[Synthesis of Active Material NaTi ₂ (PO ₄ ) ₃ ]
NaTi ₂ (PO ₄ ) ₃ serving as the negative electrode was synthesized by the Pechini method. To 40 mL of a solution of Ti (OCH ₂ CH ₂ CH ₂ CH ₃ ) ₄ dissolved in a 30% hydrogen peroxide solution, 15 mL of 28% aqueous ammonia and 2-fold molar amount of citric acid of Ti were added, and Na ₂ CO _{3 was} further added. 10 mL of an aqueous solution prepared by dissolving 0.25 mol / L, 10 mL of an aqueous solution prepared by dissolving NH ₄ H ₂ PO ₄ and adjusting to 1.5 mol / L, and 0.02 mol of ethylene glycol were added and evaporated to dryness at 80 ° C. for 1-2 hours. After solidification, it is heated at 140 ° C. for an additional 2-4 hours to obtain an orange gel. This was fired in air at 350 ° C. and 800 ° C. to obtain NaTi ₂ (PO ₄ ) ₃ (FIG. 2). From the XRD pattern of the figure, the main phase coincided with ICDD # 33-1296, and it was identified as a NASICON type NaTi ₂ (PO ₄ ) ₃ single phase. The synthesized active material and acetylene black (AB) were mixed at a weight ratio of 70:25, and subjected to carbon coating treatment at 400 rpm for 1 hour using a planetary ball mill. The obtained powder (active material and AB) was heat-treated at 800 ° C. for 1 hour in a nitrogen atmosphere. The obtained powder and PTFE were mixed at a weight ratio of 95: 5 and molded into pellets to make a negative electrode.

[Production of aqueous sodium full cell]
Pellets were prepared for the annealed products of Na ₂ FeP ₂ O ₇ and NaTi ₂ (PO ₄ ) ₃ obtained in the examples, and used as a positive electrode and a negative electrode, respectively, and electrolyte Na ₂ SO ₄ was used as ultrapure water as an electrolyte. A beaker-type full cell was prepared using a melted 2M Na ₂ SO ₄ aqueous electrolyte and a solution prepared by adding 3 wt% of CaLA and LA to the prepared electrolyte (FIG. 3).

FIG. 4 shows the sodium full cell cycle characteristics obtained above at a current density of 2.0 mA / cm ² . When CaLA is added, the cycle characteristics are improved compared to the electrolyte solution with no additive and other additives. This is because the alkalinity of the electrolyte caused by the hydrogen generation reaction due to the occurrence of an irreversible reaction between the positive and negative electrodes, which is considered to be the cause of cycle deterioration when no additive is added, is mitigated by the additive becoming a buffer. This is probably because of this. In addition, the reason why the cycle characteristics were not improved when LA was added is considered to be because the positive electrode weak against acid was deteriorated by the electrolytic solution that became an acidic environment by LA. Among the additives, CaLA showed excellent characteristics.

Claims (16)

A water-based sodium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is
a) electrolyte salt,
An aqueous sodium ion secondary battery comprising b) water and c) an aldobionic acid derivative, aldonic acid derivative or uronic acid derivative. The aldobionic acid derivative is represented by the following formula (1):




(Wherein, Z ₁ represents an alkali metal or an alkaline earth metal, and X _{1 to} X ₈ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). A compound,
The aldonic acid derivative is represented by the following formula (2):




(Wherein Z ₂ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{9 to} X ₁₃ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). A compound represented by
The uronic acid derivative is represented by the following formula (3):




(Wherein Z ₃ represents a hydrogen atom, an alkali metal or an alkaline earth metal, and X _{14 to} X ₁₇ each independently represents a hydrogen atom or an alkyl group having 1 to 23 carbon atoms). The aqueous sodium ion secondary battery according to claim 1, which is a compound represented. The aqueous sodium ion secondary battery according to claim 1 or 2, wherein the positive electrode includes a positive electrode active material, a conductive auxiliary material and a binder, and the negative electrode includes a negative electrode active material, a conductive auxiliary material and a binder. . The positive electrode active material and the negative electrode active material are both composed of a sodium-transition metal composite oxide capable of inserting and removing sodium ions, but the two active materials are different from each other. The aqueous sodium ion secondary battery described. The positive electrode active material comprises a sodium-transition metal composite oxide containing one or more transition metal elements selected from Co, Ni, Mn, Cr, V, Ti, and Fe. 4. The aqueous sodium ion secondary battery according to 4. The aqueous sodium ion secondary battery according to claim 5, wherein the positive electrode active material is olivine type NaFePO ₄ or olivine type NaMnPO ₄ . The aqueous sodium ion secondary according to claim 6, wherein the negative electrode active material comprises a sodium-transition metal composite oxide containing one or more transition metal elements selected from V, Ti, and Fe. battery. The aqueous sodium ion secondary battery according to claim 7, wherein the negative electrode active material is NASICON type NaTi ₂ (PO ₄ ) ₃ . The conductive auxiliary material is made of carbon black, ketjen black, acetylene black, carbon whisker, carbon fiber, natural graphite, artificial graphite, carbon nanoparticles, carbon nanotube, titanium oxide, ruthenium oxide, aluminum, nickel, and a mixture thereof. The aqueous sodium ion secondary battery according to claim 3, wherein the aqueous sodium ion secondary battery is selected from the group. The aqueous sodium ion secondary battery according to claim 9, wherein the conductive auxiliary material is acetylene black. The binder is polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer Copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer Coalescence (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, Tylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer and ethylene-acrylic acid copolymer The aqueous sodium ion secondary battery according to claim 3, wherein the aqueous sodium ion secondary battery is selected from the group consisting of a coalescence. The aqueous sodium ion secondary battery according to claim 11, wherein the binder is polytetrafluoroethylene (PTFE). The electrolyte salt is NaNO ₃ , NaOH, NaF, NaCl, NaBr, NaI, NaClO ₄ , Na ₂ SO ₄ , Na (CH ₃ COO), NaBF ₄ , NaPF ₆ , NaN (CF ₃ SO ₂ ) ₂ , NaN ( _{C 2 F 5 SO 2) 2} , Na 2 O, characterized in that it is selected from the group consisting of _Na 2 CO ₃ and mixtures thereof, according to any one of claims 1 to claim 12 Water-based sodium ion secondary battery. The aqueous sodium ion secondary battery according to claim 13, wherein the electrolyte salt is NaClO ₄ or Na ₂ SO ₄ . The aqueous sodium ion secondary battery according to any one of claims 1 to 14, wherein the electrolytic solution further contains a water-soluble polymer. The water-soluble polymer is gelatin, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), starch, cellulose and derivatives thereof, polyethylene oxide, polysaccharides, polyvinylamine, chitosan, polylysine, polyacrylic acid, polyalginic acid, polyhyaluronic acid. The aqueous sodium ion secondary battery according to claim 15, wherein the aqueous sodium ion secondary battery is selected from the group consisting of carboxycellulose and a mixture thereof.