WO2013094689A1 - Aqueous lithium ion secondary battery - Google Patents

Abstract

[Problem] To provide a novel aqueous lithium ion secondary battery whereby it becomes possible to solve the problem of safety inherent in conventionally proposed batteries utilizing a non-aqueous solvent and also solve the problem of deterioration in battery properties caused by the gelatinization of an electrolytic solution. [Solution] An aqueous lithium ion secondary battery provided with a positive electrode, a negative electrode and a gel-like solid electrolyte, said secondary battery being characterized in that the gel-like solid electrolyte comprises a solid electrolyte salt, water and at least one lipid-peptide-type gelatinizing agent selected from a compound represented by formula (1) (wherein R¹ represents a C_9-23 aliphatic group; R² represents a hydrogen atom or a C_1-4 alkyl group having a C_1-2 branched chain; R³ represents a group -(CH₂)_n-X; n represents a numerical value of 1 to 4; X represents an amino group, a guanidino group, a group -CONH₂, or a 5-membered ring, a 6-membered ring or a fused heterocyclic ring composed of a 5-membered ring and a 6-membered ring each of which may have 1 to 3 nitrogen atoms) and analogous compounds and pharmaceutically usable salts thereof.

Description

Water-based lithium ion secondary battery

The present invention relates to an aqueous lithium ion secondary provided with a gel-like solid electrolyte, and more specifically, an aqueous lithium ion secondary provided with an ion conductive gel-like solid electrolyte using a low molecular lipid peptide type gelling agent. It relates to batteries.

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, as with other non-aqueous electrolyte batteries, the laminate battery generally uses a flammable organic solvent such as an ester compound and an ether compound as the electrolyte, and the flammable organic solvent causes the battery to burst, ignite, etc. This is one of the major causes of problems.

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, an aqueous lithium 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 aqueous lithium secondary battery as described above does not use an organic solvent in the electrolyte solution, and therefore basically does not burn or ignite, and avoids the problem of ignition in the conventionally proposed secondary battery. It is expected to be possible. Furthermore, since manufacturing process does not require moisture management, the manufacturing cost can be greatly reduced.
Moreover, 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 secondary battery is also expected.
In this way, in a battery using an aqueous electrolyte, the electrolyte is gelled with a gelling agent, so that safety is greatly improved in response to problems of ignition and liquid leakage, and manufacturing management is easy. In addition, it is expected to be a secondary battery having various advantages such as low internal resistance.

JP 2001-102086 A

As described above, since non-aqueous solvents are used for electrolytes in general lithium batteries, there is a risk of ignition or explosion if liquid leakage occurs due to battery damage. I have 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 batteries do not use non-aqueous solvents in the electrolyte, so the risk of ignition and explosion can be avoided, but when aqueous solutions are used, leakage due to battery damage can be avoided. Can not.
In addition, the aqueous lithium polymer gel batteries proposed so far are more effective in the migration of lithium ions due to the presence of the gelling agent and the higher viscosity of the solution compared to the battery of the aqueous electrolyte without the gelling agent. As a result, there is a concern that a decrease in electric conductivity and a decrease in charge / discharge capacity are observed, which causes another problem of deterioration in battery characteristics due to gelation of the electrolytic solution.

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, Another object of the present invention is to provide a novel aqueous lithium ion secondary battery that can also solve the problem of deterioration of battery characteristics due to gelation of the electrolyte.

As a result of intensive studies to solve the above problems, the present inventors have found that a lipid peptide gel comprising a low molecular weight lipid peptide or a pharmaceutically usable salt thereof as a solid electrolyte of an aqueous lithium ion secondary battery. By adopting a gel-like solid electrolyte containing an agent, a solid electrolyte salt and water, the problem of ensuring safety in the use of an organic solvent, which has been a problem in conventional electrolytes, is solved, and good The inventors have found that charge / discharge characteristics similar to those of a battery having ion conductivity and using a conventional liquid electrolyte can be obtained, and the present invention has been completed.

That is, the present invention, as a first aspect, is a water based lithium ion secondary battery comprising a positive electrode and a negative electrode, and a gel solid electrolyte, the gel solid electrolyte comprising a solid electrolyte salt, water, The following formulas (1) to (3):

(In the formula, R ¹ represents an aliphatic group having 9 to 23 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms which may have a branched chain having 1 or 2 carbon atoms. R ³ represents a — (CH ₂ ) _n —X group, n represents a number of 1 to 4, X represents an amino group, a guanidino group, a —CONH ₂ group, or 1 to 3 nitrogen atoms. And represents a condensed heterocyclic ring composed of a 5-membered ring or a 6-membered ring or a 5-membered ring and a 6-membered ring.)

(Wherein R ⁴ represents an aliphatic group having 9 to 23 carbon atoms, and R ^{5 to} R ⁷ each independently represents a hydrogen atom or a carbon atom having a branched chain having 1 or 2 carbon atoms. 1 to 4 alkyl groups or — (CH ₂ ) _n —X group, n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a nitrogen atom of 1 to 3 This represents a 5-membered ring or 6-membered ring which may have one or a fused heterocyclic ring composed of a 5-membered ring and a 6-membered ring

(In the formula, R ⁸ represents an aliphatic group having 9 to 23 carbon atoms, and R ^{9 to} R ¹² each independently represents a hydrogen atom, or a carbon atom number that can have a branched chain having 1 or 2 carbon atoms. 1 to 4 alkyl groups or — (CH ₂ ) _n —X group, n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a nitrogen atom of 1 to 3 A 5-membered ring or a 6-membered ring or a condensed heterocyclic ring composed of a 5-membered ring and a 6-membered ring.) Or a pharmaceutically usable salt thereof The present invention relates to an aqueous lithium ion secondary battery comprising a lipid peptide type gelling agent.
As a second aspect, the present invention relates to the aqueous lithium ion secondary battery according to the first aspect, characterized in that the gel-like solid electrolyte further contains a water-soluble polymer.
As a third aspect, the water-soluble polymer is gelatin, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), starch, cellulose and derivatives thereof, polyethylene oxide, polysaccharides, polyvinyl amine, chitosan, polylysine, polyacrylic acid, poly The aqueous lithium ion secondary battery according to the second aspect, which is selected from the group consisting of alginic acid, polyhyaluronic acid, carboxycellulose, and a mixture thereof.
As a 4th viewpoint, the said water-soluble polymer is polyvinyl alcohol (PVA), It is related with the water based lithium ion secondary battery as described in a 3rd viewpoint.
As a fifth aspect, the present invention relates to the aqueous lithium ion secondary battery according to any one of the first to fourth aspects, wherein the gel-like solid electrolyte further contains a non-aqueous solvent.
As a sixth aspect, the non-aqueous solvent is N, N-dimethylformamide, dimethyl sulfoxide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, tetrahydrofuran , Methanol, ethanol, n-propanol, isopropanol, 1,2-diethoxyethane (ethylene glycol diethyl ether), ethyl acetate, butyl acetate, methoxybutyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, diethyl A solvent selected from the group consisting of carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, acetonitrile and a mixture of two or more thereof. Relates to aqueous lithium ion secondary battery according to the fifth aspect.
A seventh aspect relates to the aqueous lithium ion secondary battery according to the sixth aspect, wherein the non-aqueous solvent is N-methyl-2-pyrrolidone.
As an eighth 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 lithium ion secondary battery according to any one of the above.
As a ninth aspect, the positive electrode active material and the negative electrode active material are both composed of a lithium-transition metal composite oxide capable of inserting and removing lithium ions, but the two active materials are different from each other. The present invention relates to an aqueous lithium ion secondary battery according to an eighth aspect.
As a tenth aspect, the positive electrode active material is composed of a lithium-transition metal composite oxide containing one or more transition metal elements selected from Co, Ni, Mn, Cr, V, Ti, and Fe. And an aqueous lithium ion secondary battery according to the ninth aspect.
As an eleventh aspect, the present invention relates to the water based lithium ion secondary battery according to the tenth aspect, wherein the positive electrode active material is LiFePO ₄ .
According to a twelfth aspect, in the ninth aspect, the negative electrode active material is composed of a lithium-transition metal composite oxide containing one or more transition metal elements selected from V, Ti, and Fe. The present invention relates to an aqueous lithium ion secondary battery.
As a thirteenth aspect, the present invention relates to the aqueous lithium ion secondary battery according to the twelfth aspect, wherein the negative electrode active material is LiTi ₂ (PO ₄ ) ₃ .
As a fourteenth 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 water-based lithium ion secondary battery according to the eighth aspect, which is selected from the group consisting of these mixtures.
As a fifteenth aspect, the present invention relates to the aqueous lithium ion secondary battery according to the fourteenth aspect, wherein the conductive auxiliary material is acetylene black.
In a sixteenth 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 water-based lithium ion secondary battery according to the eighth aspect, which is selected from the group consisting of acrylic acid copolymers.
As a seventeenth aspect, the present invention relates to the aqueous lithium ion secondary battery according to the sixteenth aspect, wherein the binder is polytetrafluoroethylene (PTFE).
As an eighteenth aspect, the solid electrolyte salt is LiNO ₃ , LiOH, LiF, LiCl, LiBr, LiI, LiClO ₄ , Li ₂ SO ₄ , Li (CH ₃ COO), LiBF ₄ , LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Li ₂ O, Li ₂ CO ₃ and a mixture thereof, any one of the first to seventeenth aspects The aqueous lithium ion secondary battery according to claim 1.
As a nineteenth aspect, the present invention relates to the aqueous lithium ion secondary battery according to the eighteenth aspect, wherein the solid electrolyte salt is LiClO ₄ or Li ₂ SO ₄ .

According to the aqueous lithium ion secondary battery having a gel-like solid electrolyte of the present invention, by using water as a non-aqueous solvent as a solvent, there is a risk of ignition or explosion due to liquid leakage due to battery damage or the like. Risk can be avoided. For this reason, compared with the battery which gelatinizes and uses the electrolyte solution of a general lithium battery and a nonaqueous solvent, safety | security can be improved significantly.

In addition, the aqueous lithium ion secondary battery of the present invention can suppress the deterioration of battery performance seen in the conventionally proposed aqueous lithium battery, and can obtain the same charge / discharge characteristics as a battery using a conventional liquid electrolyte. it can.

FIG. 1 is a schematic view of water-based lithium ion secondary batteries of Examples and Comparative Examples. FIG. 2 is a diagram showing a bead mill used for producing a gel-like solid electrolyte precursor dispersion used in the aqueous lithium ion secondary battery of the present invention (in FIG. 2, (a) a bead mill, (b). Cross section of rotor part). FIG. 3 shows constant current charge / discharge of the aqueous lithium ion secondary battery (1) of Example 1, the aqueous lithium ion secondary battery (3) of Example 3, and the aqueous lithium ion secondary battery (4) of Comparative Example 1. It is a figure which shows the result (cycle characteristic) of a test. FIG. 4 is a diagram showing the results (cycle characteristics) of a constant current charge / discharge test of the water based lithium ion secondary battery (2) of Example 2 and the water based lithium ion secondary battery (5) of Comparative Example 2. FIG. 5 shows constant-current charge / discharge of the aqueous lithium ion secondary battery (1) of Example 1, the aqueous lithium ion secondary battery (3) of Example 3, and the aqueous lithium ion secondary battery (4) of Comparative Example 1. It is a figure which shows the result (rate characteristic) of a test. 6 is a graph showing the results (rate characteristics) of constant current charge / discharge tests of the aqueous lithium ion secondary battery (2) of Example 2 and the aqueous lithium ion secondary battery (5) of Comparative Example 2. FIG.

The present invention includes at least a positive electrode and a negative electrode made of a material capable of inserting and desorbing lithium ions, respectively, and a gel-like solid electrolyte (hereinafter also simply referred to as a gel electrolyte) containing an aqueous solution in which a lithium salt is dissolved. The present invention relates to an aqueous lithium ion secondary battery. The gel electrolyte is a lipid peptide comprising at least one of a solid electrolyte salt (lithium salt), water, a compound represented by the above formulas (1) to (3), or a pharmaceutically usable salt thereof. It is a gel-like solid electrolyte containing a mold gelling agent.
In particular, the present invention is characterized in that a gel-like solid electrolyte containing a lipid peptide type gelling agent is used as an electrolyte of an aqueous lithium ion secondary battery.
Hereinafter, each component will be described.

[Positive electrode]
As the positive electrode used in the aqueous lithium secondary battery of the present invention, a positive electrode conventionally proposed as a positive electrode for a lithium secondary battery can be used.
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 lithium-transition metal composite oxide capable of inserting and desorbing lithium ions, and specifically, as a transition metal element whose valence changes with the insertion or desorption of lithium ions. It consists of a lithium-transition metal composite oxide containing one or more selected from Co, Ni, Mn, Cr, V, Ti, and Fe. In addition, this lithium-transition metal composite oxide has a redox potential within the range of the potential window of water, and can perform insertion / extraction reaction of lithium ions without generation of oxygen due to oxidative decomposition of water, and charge / discharge As long as the two conditions of not dissolving in water over the entire composition range are satisfied, there is no particular limitation. For example, composite oxides such as LiFePO ₄ , LiMnPO ₄ , LiNiO ₂ , Li ₃ V ₂ (PO ₄ ) ₃ , and LiMn ₂ O ₄ can be given.
However, the positive electrode active material is preferably a composite oxide different from a lithium-transition metal composite oxide contained in the negative electrode described later.
Among the positive electrode active materials, it is more preferable to use LiFePO ₄ .

Examples of the binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, and 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, stainless steel mesh, nickel mesh, gold mesh or the like can be used as the current collector.

[Negative electrode]
As the negative electrode used in the aqueous lithium secondary battery of the present invention, a negative electrode conventionally proposed as a negative electrode for a lithium secondary battery 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 lithium-transition metal composite oxide capable of inserting and removing lithium ions, and specifically, V as a transition metal element whose valence changes with the insertion and removal of lithium ions. And a lithium-transition metal composite oxide containing at least one selected from Ti, Fe, and Fe. In addition, the redox potential is within the range of the potential window of the water, the lithium ion insertion / desorption reaction can be performed without hydrogen generation by reductive decomposition of water, and it does not dissolve in water over the entire charge / discharge composition range. As long as the two conditions are satisfied, there is no particular limitation. For example, complex oxides such as LiTi ₂ (PO ₄ ) ₃ , Li ₃ V ₂ (PO ₄ ) ₃ , LiMn ₂ O ₄ , VO ₂ , LiV ₃ O ₃ , Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ Can be mentioned.
However, the negative electrode active material is preferably a composite oxide different from the lithium-transition metal composite oxide contained in the positive electrode described above.
Among the negative electrode active materials, it is more preferable to use LiTi ₂ (PO ₄ ) ₃ .

[Gel-like solid electrolyte]
<Lipid peptide type gelling agent>
In the present invention, the lipid peptide-type gelling agent used for the gel solid electrolyte is a compound (lipid peptide) represented by the following formulas (1) to (3) or a pharmaceutically usable salt thereof (hydrophobic). A low molecular weight compound having a lipid part which is a sex part and a peptide part which is a hydrophilic part).

In the above formula (1), R ¹ represents an aliphatic group having 9 to 23 carbon atoms, and preferably R ¹ is a straight chain having 11 to 23 carbon atoms which may have 0 to 2 unsaturated bonds. An aliphatic group is desirable.
Specific examples of the lipid moiety (acyl group) composed of R ¹ and the adjacent carbonyl group include lauroyl group, dodecylcarbonyl group, myristoyl group, tetradecylcarbonyl group, palmitoyl group, margaroyl group, oleoyl group, and eridoyl. Group, linoleoyl group, stearoyl group, baccenoyl group, octadecylcarbonyl group, arachidyl group, eicosylcarbonyl group, behenoyl group, ercanoyl group, docosylcarbonyl group, lignoceyl group, nerbonoyl group, etc. , Lauroyl group, myristoyl group, palmitoyl group, margaroyl group, stearoyl group, oleoyl group, elidoyl group and behenoyl group.

In the above formula (1), R ² contained in the peptide part represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms which may have a branched chain having 1 or 2 carbon atoms.
The alkyl group having 1 to 4 carbon atoms that may have a branched chain having 1 or 2 carbon atoms is a branched chain having 1 to 4 carbon atoms in the main chain and 1 or 2 carbon atoms. Means an alkyl group which may have, and specific examples thereof include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group or tert-butyl group Etc.

R ² is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms which may have a branched chain having 1 carbon atom, and more preferably a hydrogen atom.
The alkyl group having 1 to 3 carbon atoms which can have a branched chain having 1 carbon atom is an alkyl group having 1 to 3 carbon atoms in the main chain and having a branched chain having 1 carbon atom. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an i-butyl group, or a sec-butyl group, preferably a methyl group, an i-propyl group, An i-butyl group or a sec-butyl group.

In the above formula (1), R ³ represents a — (CH ₂ ) n—X group. In the — (CH ₂ ) n—X group, n represents a number of 1 to 4, and X is an amino group, a guanidino group, a —CONH ₂ group, or a 5-membered cyclic group having 1 to 3 nitrogen atoms. Represents a group, a 6-membered cyclic group, or a condensed heterocyclic group composed of a 5-membered ring and a 6-membered ring.
In the — (CH ₂ ) n—X group representing R ³ , X is preferably an amino group, guanidino group, carbamoyl group (—CONH ₂ group), pyrrole group, imidazole group, pyrazole group or indole group, and more Preferably it is an imidazole group. In the — (CH ₂ ) n—X group, n is preferably 1 or 2, and more preferably 1.
Therefore, the — (CH ₂ ) n- group is preferably an aminomethyl group, 2-aminoethyl group, 3-aminopropyl group, 4-aminobutyl group, carbamoylmethyl group, 2-carbamoylethyl group, 3-carbamoyl group. Represents a butyl group, a 2-guanidinoethyl group, a 3-guanidinobutyl group, a pyrrolemethyl group, a 4-imidazolemethyl group, a pyrazolemethyl group, or a 3-indolemethyl group, more preferably a 4-aminobutyl group, a carbamoylmethyl group Represents a 2-carbamoylethyl group, a 3-guanidinobutyl group, a 4-imidazolemethyl group or a 3-indolemethyl group, more preferably a 4-imidazolemethyl group.

In the compound represented by the above formula (1), a lipid peptide particularly suitable as a lipid peptide-type gelling agent is a compound formed from the following lipid part and peptide part (amino acid assembly part). As abbreviations of amino acids, alanine (Ala), asparagine (Asn), glutamine (Gln), glycine (Gly), histidine (His), isorosine (Ile), leucine (Leu), lysine (Lys), tryptophan (Trp) ), Valine (Val). : Lauroyl-Gly-His, Lauroyl-Gly-Gln, Lauroyl-Gly-Asn, Lauroyl-Gly-Trp, Lauroyl-Gly-Lys, Lauroyl-Ala-His, Lauroyl-Ala-Gln, Lauroyl-Ala-Asn, Lauroyl -Ala-Trp, Lauroyl-Ala-Lys; Myristoyl-Gly-His, Myristoyl-Gly-Gln, Myristoyl-Gly-Asn, Myristoyl-Gly-Trp, Myristoyl-Gly-Lys, Myristoyl-Ala-His, Myristoyl-Ala -Gln, Myristoyl-Ala-Asn, Myristoyl-Ala-Trp, Myristoyl-Ala-Lys; Palmitoyl-Gly-His, Palmitoyl-Gly-Gln, Palmitoyl-Gly-A n, Palmitoyl-Gly-Trp, Palmitoyl-Gly-Lys, Palmitoyl-Ala-His, Palmitoyl-Ala-Gln, Palmitoyl-Ala-Asn, Palmitoyl-Ala-Trp, Palmitoyl-Ala-Lys; Stearoyl-Gly-His Stearoyl-Gly-Gln, stearoyl-Gly-Asn, stearoyl-Gly-Trp, stearoyl-Gly-Lys, stearoyl-Ala-His, stearoyl-Ala-Gln, stearoyl-Ala-Asn, stearoyl-Ala-Trp, stearoyl- Ala-Lys.

Most preferred are lauroyl-Gly-His, lauroyl-Ala-His-myristoyl-Gly-His, myristoyl-Ala-His; palmitoyl-Gly-His, palmitoyl-Ala-His; stearoyl-Gly-His, stearoyl-Ala -His.

In the above formula (2), R ⁴ represents an aliphatic group having 9 to 23 carbon atoms, and preferred specific examples include the same groups as defined for R ¹ above.
In the above formula (2), R ^{5 to} R ⁷ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a branched chain having 1 or 2 carbon atoms, or — ( CH ₂ ) nX group, and at least one of R ^{5 to} R ⁷ represents a — (CH ₂ ) nX group. n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a 5-membered cyclic group or a 6-membered cyclic group that may have 1 to 3 nitrogen atoms, or a 5-membered ring And a condensed heterocyclic group composed of a 6-membered ring. Here, preferred specific examples of R ^{5 to} R ⁷ include the same groups as defined for R ² and R ³ above.

In the compound represented by the above formula (2), a preferable lipid peptide is a compound formed from the following lipid part and peptide part (amino acid assembly part). Myristoyl-Gly-Gly-His, Myristoyl-Gly-Gly-Gln, Myristoyl-Gly-Gly-Asn, Myristoyl-Gly-Gly-Trp, Myristoyl-Gly-Gly-Lys, Myristoyl-Gly-Ala-His, Myristoyl-His Gly-Ala-Gln, Myristoyl-Gly-Ala-Asn, Myristoyl-Gly-Ala-Trp, Myristoyl-Gly-Ala-Lys, Myristoyl-Ala-Gly-His, Myristoyl-Ala-Gly-Gln, Myristoyl-Ala- Gly-Asn, Myristoyl-Ala-Gly-Trp, Myristoyl-Ala-Gly-Lys, Myristoyl-Gly-His-Gly, Myristoyl-His-Gly-Gly, Palmitoyl-Gly Gly-His, Palmitoyl-Gly-Gly-Gln, Palmitoyl-Gly-Gly-Asn, Palmitoyl-Gly-Gly-Trp, Palmitoyl-Gly-Lys, Palmitoyl-Gly-Ala-His, Palmitoyl-Gly-Gly Gln, Palmitoyl-Gly-Ala-Asn, Palmitoyl-Gly-Ala-Trp, Palmitoyl-Gly-Ala-Lys, Palmitoyl-Ala-Gly-His, Palmitoyl-Ala-Gly-Gln, Palmitoyl-Ala-Gly-As Palmitoyl-Ala-Gly-Trp, Palmitoyl-Ala-Gly-Lys, Palmitoyl-Gly-His-Gly, Palmitoyl-His-Gly-Gly.

Of these, lauroyl-Gly-Gly-His, myristoyl-Gly-Gly-His, palmitoyl-Gly-Gly-His, palmitoyl-Gly-His-Gly, palmitoyl-His-Gly-Gly, stearoyl -Gly-Gly-His.

In the above formula (3), R ⁸ represents an aliphatic group having 9 to 23 carbon atoms, and preferred specific examples include the same groups as defined for R ¹ above.
In the above formula (3), R ^{9 to} R ¹² are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a branched chain having 1 or 2 carbon atoms, or — ( CH ₂ ) nX group, and at least one of R ^{9 to} R ¹² represents a — (CH ₂ ) n—X group. n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a 5-membered cyclic group or a 6-membered cyclic group that may have 1 to 3 nitrogen atoms, or a 5-membered ring And a condensed heterocyclic group composed of a 6-membered ring. Here, preferred specific examples of R ^{9 to} R ¹² include the same groups as defined for R ² and R ³ above.

Therefore, in the compound represented by the above formula (3), as a suitable lipid peptide type gelling agent, particularly preferred lipid peptides include lauroyl-Gly-Gly-Gly-His, myristoyl-Gly-Gly-Gly-His. Palmitoyl-Gly-Gly-Gly-His, Palmitoyl-Gly-Gly-His-Gly, Palmitoyl-Gly-His-Gly-Gly, Palmitoyl-His-Gly-Gly-Gly, Stearoyl-Gly-Gly-Gly-Gly-Gly Etc.

The lipid peptide gelling agent used in the present invention comprises at least one of the compounds represented by the above formulas (1) to (3) (lipid peptide) or a pharmaceutically usable salt thereof, and is a gel. These compounds can be used alone or in combination of two or more as the agent.

In the gel-like solid electrolyte used in the aqueous lithium ion secondary battery in the present invention, the ratio of the lipid peptide type gelling agent is 0.1 to 30% by mass of the total mass of the gel-like solid electrolyte to be obtained, preferably 0.5 to 20% by mass, more preferably 1 to 5% by mass.

<Water-soluble polymer>
The gel-like solid electrolyte may contain a water-soluble polymer. Use of the water-soluble polymer is useful because it can increase the mechanical strength of the gel-like solid electrolyte and can also serve as a water separation inhibitor for the gel.
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 gel-like solid electrolyte used in the aqueous lithium ion secondary battery in the present invention, the proportion when the water-soluble polymer is used is 0.1 to 30% by mass of the total mass of the gel-like solid electrolyte obtained. The content is preferably 0.5 to 20% by mass, more preferably 1 to 5% by mass.

<Non-aqueous solvent>
The gel-like solid electrolyte may contain a non-aqueous solvent. The lipid peptide type gelling agent of the present invention includes a hydrophilic site and a hydrophobic site. For this reason, it is possible to dissolve (and disperse) more uniformly by mixing a small amount of non-aqueous solvent as compared with the case of dissolving (and dispersing) with water alone. The gel solid electrolyte precursor solution described later (a solution obtained by heating a dispersion obtained by dispersing a lipid peptide type gelling agent in an aqueous solution in which a solid electrolyte and, if necessary, a water-soluble polymer or the like are dissolved) is not available. If the solution is uniform, it may lead to non-uniform gelation (insufficient gelation), and the gel strength of the resulting gel may be partially reduced. And water separation, collapse, etc. occur from a portion where gelation is insufficient, which may be a factor of reducing the mechanical strength of the entire gel electrolyte. On the other hand, when a gel is prepared from a uniform precursor solution, the entire gel is gelled uniformly, so that it is possible to prevent a decrease in mechanical strength caused by water separation or collapse of the gel as described above. Become.
Examples of the non-aqueous solvent include N, N-dimethylformamide, dimethyl sulfoxide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, and tetrahydrofuran. Aprotic polar solvent; lower aliphatic alcohol solvent such as methanol, ethanol, n-propanol, isopropanol; ether solvent such as 1,2-diethoxyethane (ethylene glycol diethyl ether); ethyl acetate, butyl acetate, methoxy Aliphatic esters or aliphatic ester ether solvents such as butyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate and propylene glycol monomethyl ether acetate; chain carbonate esters such as diethyl carbonate and diethyl carbonate System solvent; ethylene carbonate, cyclic carbonate-based solvent such as propylene carbonate; and acetonitrile.

Among the non-aqueous solvents, N-methyl-pyrrolidone is particularly preferable.

In the gel-like solid electrolyte used for the aqueous lithium ion secondary battery in the present invention, the proportion when a non-aqueous solvent is used is 0.1 to 30% by mass of the total mass of the obtained gel-like solid electrolyte, Preferably, it is 0.5 to 20% by mass, more preferably 1 to 10% by mass.

<Solid electrolyte salt>
As the solid electrolyte salt used for the gel-like solid electrolyte in the present invention, a solid electrolyte salt that has been conventionally proposed as being usable for a lithium ion secondary battery can be used. As specific examples, for example, LiNO ₃ , LiOH, LiF, LiCl, LiBr, LiI, LiClO ₄ , Li ₂ SO ₄ , Li (CH ₃ COO), LiBF ₄ , LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , Examples thereof include lithium salts such as LiN (C ₂ F ₅ SO ₂ ) ₂ , Li ₂ O, Li ₂ CO ₃ and mixtures thereof.

The solid electrolyte salt (lithium salt) used for the gel solid electrolyte in the present invention is particularly preferably LiClO ₄ or Li ₂ SO ₄ .

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

<Solvent>
In the present invention, the solvent used for the gel solid electrolyte is water.
That is, the gel-like solid electrolyte of the present invention contains the solid electrolyte salt that is the above-described lithium salt.

<Method for producing gel-like solid electrolyte>
The gel-like solid electrolyte used in the aqueous lithium ion secondary battery of the present invention can be obtained by various methods. For example, first, the lipid peptide type gelling agent is dispersed in an aqueous solution in which the solid electrolyte salt and, if necessary, the water-soluble polymer and the non-aqueous solvent are dissolved, respectively, to obtain a gel-like solid electrolyte precursor. A dispersion is obtained. And this precursor dispersion liquid is heated and a precursor solution (casting liquid) is obtained. The temperature at the time of heating should just be 100 degrees C or less which is the boiling point of the water which is a solvent.
Next, if necessary, for example, an appropriate amount of this precursor solution is dropped on a smooth surface or poured into an appropriate mold, and then cooled to room temperature or lower and allowed to stand, whereby a gel-like solid electrolyte is obtained. Can be obtained.

In the present invention, the method for obtaining the gel-like solid electrolyte precursor dispersion is, for example, by applying a wet pulverization method to a mixture comprising a lipid peptide type gelling agent and an aqueous solution of a solid electrolyte salt to obtain a lipid. A method of dispersing a peptide-type gelling agent in water or the like can be mentioned.
Examples of the wet pulverization method applied during the production of the gel solid electrolyte precursor dispersion described above include, for example, a homodisper, a homomixer, a homogenizer, an ultrasonic homogenizer, a pipe mixer, a counter collision method, a bead mill, an annular mill, and a medium. An apparatus suitable for wet grinding such as a stirring mill can be used. Among these, from the viewpoint of simplicity and dispersion stability, a bead mill or an annular mill, a homomixer and a homomixer are preferable.

The pulverizers such as the above bead mill and annular mill are conventionally used for pulverizing inorganic substances such as ceramics. In these devices, the grinding media (beads) contained in the apparatus (container) are forcibly stirred by the rotor blades (rotor) and move intensely, and the object is ground by the grinding action of the grinding media. Since the inorganic substance is hard and poor in toughness, a fine phenomenon is achieved by causing a cracking phenomenon due to the grinding action between the medium and the medium when the medium collides with the inorganic substance. On the other hand, the cracking phenomenon hardly occurs in the organic substance, but the bead mill, the annular mill, etc. can make the lipid peptide type gelling agent used in the present invention extremely remarkably fine.

Also, a high shearing breaker such as a homodisper and a homomixer is preferable because it can prevent aggregation, and among them, a homomixer that can flow the treatment liquid more strongly is particularly preferable. In order to sufficiently disperse the lipid peptide type gelling agent, the rotational speed of the homomixer is preferably 3,000 rpm or more, more preferably 6,000 rpm or more.

Here, the manufacturing method of the gel-like solid electrolyte precursor dispersion will be described in detail by taking as an example the case where a bead mill (FIG. 2) is used as the pulverizing apparatus to be used. The bead mill 1 shown in FIG. 2A is miniaturized by rotating a rotor blade (rotor) 3 at a high speed. FIG. 2B shows a cross-sectional view in the vicinity of the rotary blade 3.
Specifically, the beads as a grinding medium in the bead mill container 2 shown in FIG. 2A, water in which the lipid peptide type gelling agent and the solid electrolyte salt are dissolved, and if necessary, a water-soluble polymer and a non-aqueous solvent And the built-in rotor 3 is rotated at high speed. The agitation by the high-speed rotation of the rotor blade 3 gives a forcible motion to the grinding medium, the dispersion medium collides with the lipid peptide type gelling agent to make it fine, and the gelling agent dissolves the solid electrolyte salt. Enables dispersion in water.

The grinding medium is preferably ceramic or metal beads having a diameter of 0.3 to 6.0 mm. Since it is considered that the dispersibility of the lipid peptide type gelling agent is improved by making the diameter of the beads finer and finer, the diameter of the grinding medium is more preferably 0.3 to 1.0 mm. Further, the material of the grinding medium is preferably a ceramic or metal having a high hardness, such as alumina beads, silicon carbide beads, silicon nitride beads, zircon beads, zirconia beads, carbide stainless beads, etc., but glass beads can also be used. .
The rotor blade 3 may have various shapes such as a pin type and a disk type. The rotor blades rotate at a high speed, and the peripheral speed is more preferably in the range of 5 to 9 m / sec.

In such a bead mill container 2, 10 to 40% of the volume of beads as a grinding medium, a lipid peptide type gelling agent, water in which a solid electrolyte salt is dissolved, and other water-soluble polymers are combined. % Of the volume to fill the voids to a volume of about 10 to 40%. By rotating the rotor 3, the grinding media move intensely, and the lipid peptide type gelling agent is refined by this grinding action.

The lipid peptide type gelling agent is refined by receiving a strong grinding effect in the container, but at the same time, heat of stirring is generated and the temperature rises. Therefore, when it is preferable not to increase the temperature by absorbing this heat generation, a cooling water inlet 5 and outlet 6 are attached to the outside of the container, and a cooling water jacket is attached to the inside of the bead mill container inner wall 4. In the case of continuous operation, if miniaturization is insufficient with a single pass, repeated processing may be performed.

After pulverization, the gel refined together with the pulverization medium is discharged from the container, and the pulverization medium is separated by a screen outside the container to obtain only the target and gel-like solid electrolyte precursor dispersion.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these Examples.
The meanings of the abbreviations used in the examples and the bead mill conditions are as follows.
-Gly: Glycine-His: Histidine [Bead mill conditions]
・ Equipment used: Batch-type ready mill (manufactured by Imex Corporation)
・ Used vessel: 950cc (08-type zirconia vessel) (inside volume: 800cc)
・ Crushing condition Rotational speed: 2760 rpm
Beads: Zirconia beads (φ500 μm) (Zirconia ground ball YTZ [registered trademark]: manufactured by Tosoh Corporation)
Bead usage: 320cc

[Synthesis of lipid peptides]
In this example, a lipid peptide used as a gelling agent was synthesized by the following method.
<Synthesis Example 1: Synthesis of N-palmitoyl-Gly-His>
A 500 mL four-necked flask was charged with 14.2 g (91.6 mmol) of histidine, 30.0 g (91.6 mmol) of N-palmitoyl-Gly-methyl and 300 g of toluene, and a sodium methoxide 28% methanol solution as a base. 35.3 g (183.2 mmol) was added, and the mixture was heated in a hot water bath at 60 ° C. and stirred for 1 hour. Thereafter, the hot water bath was removed and the mixture was allowed to cool to 25 ° C. This solution was reprecipitated with 600 g of acetone and collected by filtration. The solid obtained here was dissolved in a mixed solution of 600 g of water and 750 g of methanol, and 30.5 mL (183.2 mmol) of 6N hydrochloric acid was added thereto for neutralization to precipitate a solid, followed by filtration. Next, the obtained solid was dissolved in a mixed solution of 120 g of tetrahydrofuran and 30 g of water at 60 ° C., 150 g of ethyl acetate was added, and the mixture was cooled from 60 ° C. to 30 ° C. Thereafter, the precipitated solid was filtered. Further, the obtained solid was dissolved in a solvent of 120 g of tetrahydrofuran and 60 g of acetonitrile, heated to 60 ° C., stirred for 1 hour, cooled, and filtered. The solid obtained here was washed with 120 g of water, filtered and dried under reduced pressure to give white crystals of N-palmitoyl-Gly-His free form (hereinafter also simply referred to as N-palmitoyl-Gly-His), 26.9 g (Yield 65%) was obtained.

The following examples were carried out using N-palmitoyl-Gly-His, a lipid peptide obtained by the above synthesis, as a lipid peptide type gelling agent (hereinafter also referred to as a low molecular gelling agent).

[Preparation of precursor dispersion of gelled solid electrolyte]
<Production Example 1: Production of Precursor Dispersion A of Gel-Shaped Solid Electrolyte>
To a 500 mL volumetric flask, 159.2 g of LiClO ₄ (manufactured by Sigma Aldrich) and distilled water were added to prepare a 3 mol / L LiClO ₄ aqueous solution.
3.2 g of a low molecular weight gelling agent and 320.4 g of a 3 mol / L LiClO ₄ aqueous solution prepared by the above method were put into a container dedicated to a bead mill. Further, after adding 320 cc of zirconia beads (φ500 μm) to this mixture, the mixture was stirred at 2760 rpm for 30 minutes. After stirring, the zirconia beads and the content were separated, and a gel-like solid electrolyte precursor dispersion A (recovered amount 280.8 g, recovery rate 86.8%) was taken out.

<Production Example 2: Production of Precursor Dispersion B of Gelled Solid Electrolyte>
125.0 g of Li ₂ SO ₄ .H ₂ O (manufactured by Kanto Chemical Co., Ltd.) and distilled water were added to a 500 mL volumetric flask to prepare a ₂ mol / L Li ₂ SO ₄ aqueous solution.
6.5 g of the low-molecular gelling agent and 320.4 g of the 2 mol / L Li ₂ SO ₄ aqueous solution prepared by the above method were put into a container dedicated to the bead mill. The following was carried out in the same manner as in <Production Example 1>, and a gel-like solid electrolyte precursor dispersion B (recovered amount 170.0 g, recovery rate 52.0%) was taken out.

<Production Example 3: Production of precursor dispersion C of gel-like solid electrolyte>
To the flask, 26.3 g of polyvinyl alcohol (JC-25 (saponification degree: 99.0 mol% or more), hereinafter referred to as PVA) manufactured by Nihon Vitamin Poval Co., Ltd., hereinafter referred to as PVA) and 500.2 g of distilled water are added, and 100 minutes is added. A PVA aqueous solution was prepared by heating and stirring at ° C.
To a 500 mL volumetric flask, 159.6 g of LiClO ₄ (manufactured by Sigma Aldrich) and the PVA aqueous solution prepared by the above method were added to prepare a PVA aqueous solution containing 3 mol / L LiClO ₄ .
A bead mill dedicated container was charged with 15.2 g of a low molecular weight gelling agent, 288.0 g of a PVA aqueous solution containing 3 mol / L LiClO ₄ prepared by the above method, and 32.1 g of N-methyl-2-pyrrolidone. The following was carried out in the same manner as in <Production Example 1>, and a gel-like solid electrolyte precursor dispersion C (recovered amount 283.4 g, recovery rate 84.5%) was taken out.

<Production Example 4: Production of Positive Electrode Active Material LiFePO ₄ >
Weigh 0.933 g of lithium carbonate (Wako Pure Chemical Industries, Ltd.), iron oxalate dihydrate (Wako Pure Chemical Industries, Ltd.) 5.00 g, and ammonium hydrogen phosphate (Wako Pure Chemical Industries, Ltd.) 3.33 g. And mixed in a mortar. These were calcined at 400 ° C. for 3 hours (increase / decrease rate of 200 ° C./hour) in an argon atmosphere using an alumina crucible and an atmosphere-controlled horizontal tubular furnace (manufactured by Chino Corporation), and crushed in the atmosphere ( (Raikai: mixing). Thereafter, the crushed powder was further baked at 670 ° C. for 5 hours (increase / decrease rate of 200 ° C./hour) in an argon atmosphere using an atmosphere-controlled horizontal tubular furnace. After firing, LiFePO ₄ powder having a space group Pnma was obtained.

<Production Example 5: Production of negative electrode active material LiTi ₂ (PO ₄ ) ₃ >
Titanium tetrabutoxide (Titanium (IV) butoxide) (Aldrich) 3.50 g was weighed using an alumina crucible, 30% hydrogen peroxide solution (Kishida Chemical Co., Ltd.) 40 mL, 28% ammonia water (sum) (Kogaku Pharmaceutical Co., Ltd.) A 15 mL mixed solution was prepared, and anhydrous citric acid (Nacalai Tesque) (3.88 g) was added to this solution. This mixture was stirred at room temperature and 400 rpm for 30 minutes using a hot stirrer (REMIX, RSH-4DR, ASONE Corporation) and a magnetic stirrer chip to obtain a yellow solution 1.
Next, 0.187 g of lithium carbonate (Wako Pure Chemical Industries, Ltd.) was dissolved in 10 ml of 60% nitric acid (Nacalai Tesque) to obtain Solution 2.
Furthermore, 1.74 g of ammonium dihydrogen phosphate (Nacalai Tesque Co., Ltd.) was dissolved in 10 mL of ion-exchanged water to obtain a solution 3.
The stirring of the solution 1 prepared by the above method is started, and while stirring, the solution 2, the solution 3 prepared by the above method, and 1.25 g of ethylene glycol (Nacalai Tesque) are added to obtain an orange solution 4 It was. This solution 4 was stirred at 60 ° C. and 400 rpm for 2 hours.
Thereafter, the temperature of the solution 4 was increased to 140 ° C. at a temperature increase rate of 10 ° C./10 min on the same hot stirrer. After raising the temperature, the gel was dried at 140 ° C. and 400 rpm for about 5 hours until a gel was obtained. This gel was baked in the atmosphere using a desktop muffle furnace (manufactured by Denken Co., Ltd.) at 350 ° C. for 3 hours (increase / decrease rate of 200 ° C./hour) to obtain a powder.
After firing, the obtained powder was sufficiently pulverized in a menor mortar and compressed into a pellet at 300 kgf / cm ² using a hydraulic press. This pellet-shaped compressed powder is transferred into an alumina crucible, and LiTi ₂ (PO ₄ ) ₃ is calcined in the air at 800 ° C. for 12 hours (increase / decrease rate of 200 ° C./hour) in a desktop muffle furnace. Obtained.

[Example 1: Production of water-based lithium ion secondary battery using precursor dispersion A of gelled solid electrolyte]
<Positive electrode: LiFePO ₄ / acetylene black / PTFE = 75/25/5 (mass ratio)>
LiFePO ₄ (280 mg) and acetylene black (Electrochemical Industry Co., Ltd., 100 mg) produced in Production Example 4 were weighed, and zirconia mill pots and balls (φ20 mm-2 pieces, φ15 mm-4 pieces, φ10 mm-15 pieces, φ3 mm) -30 g) was used, and dry mixing was performed using a planetary ball mill (manufactured by Ito Manufacturing Co., Ltd., experimental planetary pot LP-4 / 2). The rotation speed was 200 rpm, and the treatment time was 1 hour.
PTFE (polytetrafluoroethylene, Daikin Industries, Ltd., 10 mg) was added to the obtained mixed powder (90 mg), and further mixed in a mortar. After mixing, the resulting pellet (30 mg) was pressure-bonded to a circularly shaped current collector (nickel expanded metal, Sank Metal Co., Ltd., diameter 15 mm) to produce a positive electrode. Thereafter, the current collector and the lead wire were welded.
<Negative electrode: LiTi ₂ (PO ₄ ) ₃ / acetylene black / PTFE = 75/25/5 (mass ratio)>
Using LiTi ₂ (PO ₄ ) ₃ (280 mg) produced in Production Example 5, acetylene black (Electrochemical Co., Ltd., 100 mg) was weighed in the same manner as the above positive electrode, and a zirconia mill pot and ball ( Dry mixing was performed using a planetary ball mill (manufactured by Ito Seisakusho, experimental planetary pot LP-4 / 2) using φ20 mm-2 pieces, φ15 mm-4 pieces, φ10 mm-15 pieces, φ3 mm-30 g). The rotation speed was 200 rpm, and the treatment time was 1 hour.
The obtained mixed powder was transferred to an alumina crucible and annealed at 800 ° C. for 1 hour (increase / decrease rate of 200 ° C./hour) in a N ₂ atmosphere using a small tube furnace (Koyo Thermo System Co., Ltd.). PTFE (polytetrafluoroethylene, Daikin Industries, Ltd., 10 mg) was added to the obtained mixed powder (90 mg), and further mixed in a mortar. After mixing, the obtained pellet (45 mg) was pressure-bonded to a circularly shaped current collector (nickel expanded metal, Sank Metal Co., Ltd., diameter 15 mm) to produce a negative electrode. Thereafter, the current collector and the lead wire were welded.
<Water-based lithium ion secondary battery (1)>
Using a beaker cell whose upper part was opened to the atmosphere, an aqueous lithium ion secondary battery 10 to be used in a charge / discharge test described later was created (see FIG. 1).
First, it installed in the cell 17 so that the positive electrode 11 and the negative electrode 13 which pressure-bonded the pellets 12 and 14 produced by said method may mutually oppose.
Next, 35 g of the gel-like solid electrolyte precursor dispersion A prepared in Production Example 1 is heated and dissolved at 80 ° C. to prepare a gel precursor solution. This gel precursor solution is the cell 17 in which positive and negative electrodes are installed. Added inside. This gel precursor solution gelled by cooling to room temperature, and became a gel-like solid electrolyte 15. Thereafter, liquid paraffin (Wako Pure Chemical Industries, Ltd., 5 g) 16 for preventing evaporation of the solvent (water) is added to the upper part of the gel-like solid electrolyte 15, and aqueous lithium ion two provided with the gel-like solid electrolyte. A secondary battery (1) was obtained.

[Test Example 1: Charge / Discharge Test (1)]
Using the water based lithium secondary battery (1) produced in Example 1, the charge / discharge test was performed at a constant current, and the charge and discharge current density was 0.5 A / cm ² and the voltage range was 0.6 V to 1.2 V. A charge / discharge test was conducted at 25 ° C.
FIG. 3 shows the results of a constant current charge / discharge test (50 cycles) of the water based lithium ion secondary battery (1).

[Example 2: Production of aqueous lithium ion secondary battery using precursor dispersion B of gelled solid electrolyte]
The same procedure as in Example 1 was followed except that the gel-like solid electrolyte precursor dispersion A produced in Production Example 1 was changed to the gel-like solid electrolyte precursor dispersion B produced in Production Example 2. An aqueous lithium ion secondary battery (2) was produced.

[Test Example 2: Charge / Discharge Test (2)]
Using the aqueous lithium secondary battery (2) produced in Example 2, a charge / discharge test was performed in the same procedure as in Example 2.
FIG. 4 shows the results of a constant current charge / discharge test (50 cycles) of the water based lithium ion secondary battery (2).

[Example 3: Production of aqueous lithium ion secondary battery using precursor dispersion C of gel-like solid electrolyte]
The same procedure as in Example 1 was followed except that the gel-like solid electrolyte precursor dispersion A produced in Production Example 1 was changed to the gel-like solid electrolyte precursor dispersion C produced in Production Example 3. An aqueous lithium ion secondary battery (3) was produced.

[Test Example 3: Charge / Discharge Test (3)]
Using the water based lithium secondary battery (3) produced in Example 3, a charge / discharge test was carried out in the same procedure as in Example 2.
FIG. 3 shows the results of a constant current charge / discharge test (50 cycles) of the water based lithium ion secondary battery (3).

[Comparative Example 1: Production of water-based lithium ion secondary battery using 3 mol / L LiClO ₄ aqueous solution]
A water system was prepared in the same manner as in Example 1, except that the gel-like solid electrolyte precursor dispersion A produced in Production Example 1 was changed to the 3 mol / L LiClO ₄ aqueous solution produced by the method described in Production Example 1. A lithium ion secondary battery (4) was produced.

[Comparative Test Example 1: Comparative Charge / Discharge Test (1)]
Using the water based lithium secondary battery (4) prepared in Comparative Example 1, a charge / discharge test was performed in the same procedure as in Example 2.
FIG. 3 shows the results of a constant current charge / discharge test (50 cycles) of the water based lithium ion secondary battery (4).

[Comparative Example 2: Production of aqueous lithium ion secondary battery using ₂ mol / L Li ₂ SO ₄ aqueous solution]
The procedure was the same as in Example 1 except that the gel-like solid electrolyte precursor dispersion A produced in Production Example 1 was changed to a ₂ mol / L Li ₂ SO ₄ aqueous solution produced by the method described in Production Example 2. An aqueous lithium ion secondary battery (5) was manufactured.

[Comparative Test Example 2: Comparative Charge / Discharge Test (2)]
Using the water based lithium secondary battery (5) prepared in Comparative Example 2, a charge / discharge test was performed in the same procedure as in Example 2.
FIG. 4 shows the results of a constant current charge / discharge test (50 cycles) of the water based lithium ion secondary battery (5).

[Test Example 4: Charge / Discharge Test (Rate Characteristics)]
Charge / discharge tests (rate characteristics) of the aqueous lithium ion secondary battery (1) of Example 1, the aqueous lithium ion secondary battery (2) of Example 2, and the aqueous lithium ion secondary battery (3) of Example 3 are as follows. Carried out. The charge and discharge current density ^{0.5mA / cm 2, 0.1mA / cm} 2, 0.2mA / cm 2, 5mA / cm 2, 10mA / cm 2 except for changing the charge in the same manner as in Example 1 A discharge test was performed.
FIG. 5 shows the results of a constant current charge / discharge test of the aqueous lithium ion secondary battery (1) and (3), and FIG. 6 shows the aqueous lithium ion secondary battery (2).

[Comparative Test Example 3: Comparative Charge / Discharge Test (Rate Characteristics)]
The charge / discharge test (rate characteristic) of the aqueous lithium ion secondary battery (4) of Comparative Example 1 and the aqueous lithium ion secondary battery (5) of Comparative Example 2 was carried out. The charge and discharge current densities were performed under the same conditions as in Example 7.
FIG. 5 shows the results of a constant current charge / discharge test of the aqueous lithium ion secondary battery (4), and FIG. 6 shows the aqueous lithium ion secondary battery (5).

[Consideration of Test Results: Example 1 to Example 3, Comparative Example 1 and Comparative Example 2: Cycle Characteristic Evaluation]
As shown in FIG. 3, the aqueous lithium ion secondary battery (1) of Example 1 and the aqueous lithium ion secondary battery (3) of Example 3 using a 3 mol / L LiClO ₄ aqueous solution (both are low molecular gels). In addition, and in the aqueous lithium ion secondary battery (4) of Comparative Example 1 (no low molecular gelling agent added), the aqueous lithium ion secondary battery (1) added with the gelling agent over 50 cycles. And the discharge capacity of (3) exceeds the discharge capacity of the water-based lithium ion secondary battery (4) to which no gelling agent is added, and the surprising result is that the cycle characteristics are improved by the addition of the low molecular weight gelling agent. Obtained.
Moreover, as shown in FIG. 4, the aqueous lithium ion secondary battery (2) of Example 2 using a ₂ mol / L Li ₂ SO ₄ aqueous solution (addition of a gelling agent) and the aqueous lithium ion secondary battery of Comparative Example 2 ( 5) When comparing (with no gelling agent added), the cycle characteristics of the two show almost the same tendency, and the deterioration of battery performance due to gelation observed when using the conventional polymer gelling agent is recognized. No results were obtained.

[Consideration of Test Results: Examples 1 to 3, Comparative Example 1 and Comparative Example 2: Rate Characteristic Evaluation]
As shown in FIG. 5, the aqueous lithium ion secondary battery (1) of Example 1 and the aqueous lithium ion secondary battery (3) of Example 3 using a 3 mol / L LiClO ₄ aqueous solution (both are low molecular gels). In addition to the water-based lithium ion secondary battery (4) of Comparative Example 1 (without addition of a low-molecular gelling agent), over the entire current density of 0.1 to 10 mA / cm ² in which the test was performed, As a result, the discharge capacity of the water-based lithium ion secondary batteries (1) and (3) to which the gelling agent is added exceeds the discharge capacity of the water-based lithium ion secondary battery (4) to which the gelling agent is not added. The surprising result was obtained that the discharge characteristics at a wide rate were improved by the addition of the molecular gelling agent.
Moreover, as shown in FIG. 6, the aqueous lithium ion secondary battery (2) of Example 2 using a ₂ mol / L Li ₂ SO ₄ aqueous solution (addition of a gelling agent) and the aqueous lithium ion secondary battery of Comparative Example 2 were used. (5) Comparing (no gelling agent added), the discharge capacity at a current density of 10 mA / cm ² is higher in the aqueous lithium ion secondary battery (2) to which the gelling agent is added. The water-based lithium ion secondary battery (5) was slightly exceeded, and the result was that the discharge characteristics at a high rate were improved by the addition of the low molecular gelling agent.

Thus, the results shown in the examples and comparative examples are the decrease in lithium ion movement due to the presence of the gelling agent and the increase in the viscosity of the solution, the decrease in electrical conductivity and the decrease in charge / discharge capacity due to this. This completely overturned the predictions derived from the knowledge obtained with secondary batteries using conventional gel electrolytes.
In this way, in the aqueous lithium ion secondary battery of the present invention, the factor that resulted in the discharge capacity being equivalent to or exceeding that of a secondary battery using a liquid electrolyte with no gelling agent added is Although it is not certain, as one of them, it leads to increasing the abundance ratio of lithium ions from the lithium salt by the action of carboxyl group and imidazole group present in the lipid peptide type low molecular gelling agent used in the present invention. It is conceivable that the electric conduction was improved without lowering the charge / discharge, and the battery performance in the aqueous lithium ion secondary battery was improved.

1 Bead mill 2 Bead mill container 3 Rotor blade
4 Bead mill container inner wall 5 Cooling water inlet 6 Cooling water outlet 10 Water based lithium ion secondary battery 11 Positive electrode 12 Pellet 13 Negative electrode 14 Pellet 15 Gel-like solid electrolyte 16 Liquid paraffin 17 Cell

Claims (19)

1. An aqueous lithium ion secondary battery comprising a positive electrode and a negative electrode, and a gelled solid electrolyte,
   The gel-like solid electrolyte includes a solid electrolyte salt, water, and the following formulas (1) to (3):
   

   

   (In the formula, R ¹ represents an aliphatic group having 9 to 23 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms which may have a branched chain having 1 or 2 carbon atoms. R ³ represents a — (CH ₂ ) _n —X group, n represents a number of 1 to 4, X represents an amino group, a guanidino group, a —CONH ₂ group, or 1 to 3 nitrogen atoms. And represents a condensed heterocyclic ring composed of a 5-membered ring or a 6-membered ring or a 5-membered ring and a 6-membered ring.)
   

   

   (Wherein R ⁴ represents an aliphatic group having 9 to 23 carbon atoms, and R ^{5 to} R ⁷ each independently represents a hydrogen atom or a carbon atom having a branched chain having 1 or 2 carbon atoms. 1 to 4 alkyl groups or — (CH ₂ ) _n —X group, n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a nitrogen atom of 1 to 3 This represents a 5-membered ring or 6-membered ring which may have one or a condensed heterocyclic ring composed of a 5-membered ring and a 6-membered ring.)
   

   

   (In the formula, R ⁸ represents an aliphatic group having 9 to 23 carbon atoms, and R ^{9 to} R ¹² each independently represents a hydrogen atom, or a carbon atom number that can have a branched chain having 1 or 2 carbon atoms. 1 to 4 alkyl groups or — (CH ₂ ) _n —X group, n represents a number of 1 to 4, and X represents an amino group, a guanidino group, a —CONH ₂ group, or a nitrogen atom of 1 to 3 A 5-membered ring or a 6-membered ring or a condensed heterocyclic ring composed of a 5-membered ring and a 6-membered ring.) Or a pharmaceutically usable salt thereof An aqueous lithium ion secondary battery comprising a lipid peptide type gelling agent.
2. The aqueous lithium ion secondary battery according to claim 1, wherein the gel-like solid electrolyte further contains a water-soluble polymer.
3. 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 lithium ion secondary battery according to claim 2, wherein the aqueous lithium ion secondary battery is selected from the group consisting of carboxycellulose and a mixture thereof.
4. The water-based lithium ion secondary battery according to claim 3, wherein the water-soluble polymer is polyvinyl alcohol (PVA).
5. The aqueous lithium ion secondary battery according to any one of claims 1 to 4, wherein the gel-like solid electrolyte further contains a non-aqueous solvent.
6. The non-aqueous solvent is N, N-dimethylformamide, dimethyl sulfoxide, N, N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, tetrahydrofuran, methanol, ethanol, n-propanol, isopropanol, 1,2-diethoxyethane (ethylene glycol diethyl ether), ethyl acetate, butyl acetate, methoxybutyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, diethyl carbonate, diethyl carbonate, 6. A solvent selected from the group consisting of ethylene carbonate, propylene carbonate, acetonitrile, and a mixture of two or more thereof. Aqueous lithium ion secondary battery.
7. 7. The aqueous lithium ion secondary battery according to claim 6, wherein the non-aqueous solvent is N-methyl-2-pyrrolidone.
8. The said positive electrode contains a positive electrode active material, a conductive support material, and a binder, The said negative electrode contains a negative electrode active material, a conductive support material, and a binder, It is any one of Claim 1 thru | or 7 characterized by the above-mentioned. A water-based lithium ion secondary battery according to 1.
9. 9. The positive electrode active material and the negative electrode active material are both composed of a lithium-transition metal composite oxide capable of inserting and removing lithium ions, but the two active materials are different from each other. The water based lithium ion secondary battery described.
10. The positive electrode active material is composed of a lithium-transition metal composite oxide containing one or more transition metal elements selected from Co, Ni, Mn, Cr, V, Ti, and Fe. The water based lithium ion secondary battery according to 9.
11. The water based lithium ion secondary battery according to claim 10, wherein the positive electrode active material is LiFePO ₄ .
12. 10. The aqueous lithium ion secondary according to claim 9, wherein the negative electrode active material comprises a lithium-transition metal composite oxide containing one or more transition metal elements selected from V, Ti, and Fe. battery.
13. The aqueous lithium ion secondary battery according to claim 12, wherein the negative electrode active material is LiTi ₂ (PO ₄ ) ₃ .
14. 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 water based lithium ion secondary battery according to claim 8, wherein the water based lithium ion secondary battery is selected from the group.
15. The aqueous lithium ion secondary battery according to claim 14, wherein the conductive auxiliary material is acetylene black.
16. The binder is polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluororubber, 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 Polymer (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 water based lithium ion secondary battery according to claim 8, wherein the water based lithium ion secondary battery is selected from the group consisting of coalescence.
17. The aqueous lithium ion secondary battery according to claim 16, wherein the binder is polytetrafluoroethylene (PTFE).
18. The solid electrolyte salt is LiNO ₃ , LiOH, LiF, LiCl, LiBr, LiI, LiClO ₄ , Li ₂ SO ₄ , Li (CH ₃ COO), LiBF ₄ , LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN. 18. The method according to claim 1, wherein the material is selected from the group consisting of (C ₂ F ₅ SO ₂ ) ₂ , Li ₂ O, Li ₂ CO ₃ and mixtures thereof. Water based lithium ion secondary battery.
19. The aqueous lithium ion secondary battery according to claim 18, wherein the solid electrolyte salt is LiClO ₄ or Li ₂ SO ₄ .

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