JP2021051990A - Secondary battery, battery pack, vehicle, and stationary power supply - Google Patents

Abstract

To provide a secondary battery having excellent storage performance and cycle efficiency.SOLUTION: A secondary battery according to an embodiment includes a positive electrode, a first aqueous electrolyte held in the positive electrode, a negative electrode, a second aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode, and a difference between the osmotic pressure of a first aqueous electrolyte (N/m2) and the osmotic pressure of a second aqueous electrolyte (N/m2) is 90% or less (including 0%) for bigger one of the osmotic pressure of the first aqueous electrolyte or the osmotic pressure of the second aqueous electrolyte.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to secondary batteries, battery packs, vehicles, and stationary power supplies.

Non-aqueous electrolyte batteries using carbon materials and lithium titanium oxide as the negative electrode active material and layered oxides containing nickel, cobalt, manganese, etc. as the positive electrode active material, especially secondary batteries, have already been put into practical use as power sources in a wide range of fields. ing. On the other hand, most of the organic solvents are flammable substances, and the safety of the secondary battery tends to be inferior in principle as compared with the secondary battery using an aqueous solution. Although various measures have been taken to improve the safety of secondary batteries using organic solvent-based electrolytes, they are not always sufficient. Further, the non-aqueous secondary battery requires a dry environment in the manufacturing process, so that the manufacturing cost is inevitably high. In addition, since the organic solvent-based electrolyte is inferior in conductivity, the internal resistance of the non-aqueous secondary battery tends to increase. Such issues have become major issues in electric vehicles and hybrid electric vehicles in which battery safety and battery cost are important, and in large storage battery applications for power storage. In order to solve the problems of non-aqueous secondary batteries, secondary batteries using an aqueous electrolyte have been proposed. In the water-based electrolyte, it is necessary to limit the potential range for charging and discharging the battery to the potential range in which the electrolysis reaction of water contained as a solvent does not occur. For example, by using lithium manganese oxide as the positive electrode active material and lithium vanadium oxide as the negative electrode active material, electrolysis of the aqueous solvent can be avoided. With these combinations, an electromotive force of about 1 to 1.5 V can be obtained, but it is difficult to obtain a sufficient energy density as a battery.

Even if the combination of the positive electrode active material and the negative electrode active material is devised in order to obtain sufficient electromotive force, in the aqueous electrolyte, the potential of lithium insertion and desorption of lithium titanium oxide is about 1. Since it is 5 V (vs. Li ^/ Li +), electrolysis of the aqueous electrolyte is likely to occur, and the active material can be easily separated from the current collector due to the effect. Therefore, the operation of such a battery is not stable, and it is difficult to charge and discharge the battery satisfactorily.

In the prior art, it has been possible to provide a lithium secondary battery having sufficient energy density, excellent storage performance and cycle characteristics, and being inexpensive and highly safe by including zinc in the current collector. There was room for improvement in terms of storage performance and cycle characteristics.

Japanese Patent No. 6383038

An object to be solved by the present invention is to provide a secondary battery having excellent storage performance and cycle characteristics in a secondary battery using an aqueous electrolyte.

The secondary battery of the embodiment includes a positive electrode, a first aqueous electrolyte held by the positive electrode, a negative electrode, a second aqueous electrolyte held by the negative electrode, and a separator interposed between the positive electrode and the negative electrode. .. The difference between the osmotic pressure of the first aqueous electrolyte (N / m ²⁾ and osmotic pressure of the second aqueous electrolyte (N / m ²⁾ larger one of osmotic pressure and the osmotic pressure of the second aqueous electrolyte of the first aqueous electrolyte It is 90% or less (including 0%) with respect to the one.

FIG. 5 is a cross-sectional view schematically showing an example of a secondary battery according to the first embodiment. FIG. 5 is a cross-sectional view schematically showing another example of the secondary battery according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of part A in FIG. The perspective view which shows an example of the assembled battery which concerns on 2nd Embodiment. The perspective view which shows an example of the battery pack which concerns on 3rd Embodiment. An exploded perspective view of another example of the battery pack according to the third embodiment. The block diagram which shows the electric circuit of the battery pack of FIG. FIG. 5 is a cross-sectional view schematically showing an example vehicle according to a fourth embodiment. The figure which showed schematic the vehicle of another example which concerns on 4th Embodiment. The block diagram which shows an example of the system including the stationary power source which concerns on 5th Embodiment.

Hereinafter, embodiments will be described with reference to the drawings. In addition, the same reference numerals are given to common configurations throughout the embodiment, and duplicate description will be omitted. In addition, each figure is a schematic view for explaining the embodiment and promoting its understanding, and the shape, dimensions, ratio, etc. of the figure are different from those of the actual device. The design can be changed as appropriate by taking into consideration. Unless otherwise specified, the values are shown at 25 ° C. and 1 atm (atmosphere).

(First Embodiment)
The secondary battery according to the first embodiment includes a positive electrode, a first aqueous electrolyte held in the positive electrode, a negative electrode, a second aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode. the equipped, the difference between the osmotic pressure of the first aqueous electrolyte (N / m ²⁾ and osmotic pressure of the second aqueous electrolyte (N / m ²⁾ is the osmotic pressure and the osmotic pressure of the second aqueous electrolyte of the first aqueous electrolyte It is 90% or less with respect to whichever is larger. For example, if the water-based electrolyte with a lower osmotic pressure is the first water-based electrolyte and the water-based electrolyte with a higher osmotic pressure is the second water-based electrolyte, ((the osmotic pressure of the first water-based electrolyte and the penetration of the second water-based electrolyte) It can be expressed as (absolute value of pressure difference) ÷ (osmotic pressure of second aqueous electrolyte)) × 100%.

The secondary battery according to the present embodiment may further include a compound whose osmotic pressure can be adjusted. A compound whose osmotic pressure can be adjusted may be referred to as an osmotic pressure adjusting agent for convenience. Specific examples of compounds whose osmotic pressure can be adjusted will be described later. By using a compound whose osmotic pressure can be adjusted, the concentrations of the first aqueous electrolyte and the second aqueous electrolyte can be adjusted, and the difference in osmotic pressure between the first aqueous electrolyte and the second aqueous electrolyte can be reduced. It is possible to prevent the 1-water electrolyte and the 2nd water-based electrolyte from being mixed with each other. If it is possible to prevent the water-based electrolyte from being mixed in this way, the cycle characteristics of the secondary battery can be improved.

More specifically, when an aqueous electrolyte is used, electrolysis of water can occur as a side reaction of the aqueous electrolyte. In the electrolysis of water, the chemical reaction represented by the formula (1) occurs at the negative electrode, and the chemical reaction represented by the formula (2) occurs at the positive electrode.
2H ⁺ + 2e ⁻ ⇒ H ₂ (1)
_{^{2O 2- ⇒ O 2 + 2e -}} (2)

Further, in the redox reaction of an aqueous electrolyte such as electrolysis of water, there are a potential window in which decomposition due to the oxidation reaction does not occur and a potential window in which decomposition does not occur due to the reduction reaction. For example, in the electrolysis of water, if the relationship represented by the formula (3) is established with respect to the potential E1 of the negative electrode from the Nernst equation, hydrogen is likely to be generated at the negative electrode by the reduction reaction. Then, when the relationship represented by the formula (4) is established with respect to the potential E2 of the positive electrode, oxygen is likely to be generated at the positive electrode by the oxidation reaction. Here, in the formulas (3) and (4), the pH indicates the pH of the aqueous electrolyte.
E1 <−0.059 × pH (3)
E2> 1.23-0.059 x pH (4)

From the formulas (3) and (4), when the water-based electrolyte is not isolated between the negative electrode side and the positive electrode side, the voltage between the negative electrode and the positive electrode is 1.23 V or more regardless of the pH of the water-based electrolyte. As the size increases, the electrolysis of water tends to occur thermodynamically. Even if a separator having low air permeability is used, if the movement of the aqueous electrolyte is completely prevented, the movement of cations will also be hindered, and the performance of the secondary battery will be deteriorated.

Further, if the lithium salt concentration differs between the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte, the movement of water is more likely to occur, the reaction represented by the above formula occurs, and the performance of the secondary battery is likely to be deteriorated.

Therefore, at least one of the first aqueous electrolyte and the second aqueous electrolyte is provided with an osmotic pressure adjusting agent in order to suppress the movement of the aqueous electrolyte, and the difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is By setting 90% or less (including 0%) of the osmotic pressure of the first aqueous electrolyte or the osmotic pressure of the second aqueous electrolyte, whichever is greater, the movement of the aqueous electrolyte is suppressed and the electrolysis of water is suppressed. can do. If the osmotic pressure difference is larger than 90% on the side where the osmotic pressure is large, the mixing of the aqueous electrolytes on the positive electrode side and the negative electrode side due to the osmotic pressure becomes intense, which is not preferable.

Further, it is possible to suppress the precipitation of salt on the electrode by increasing the salt concentration of either the first aqueous electrolyte or the second aqueous electrolyte due to the movement of the aqueous electrolyte. With such a configuration of the secondary battery, it is possible to suppress an increase in resistance due to salt precipitation and capacity deterioration during a long-term cycle test, and it is possible to improve storage performance. By improving the storage performance, the Coulomb efficiency can also be improved. This is because the Coulomb efficiency represents the slope of self-discharge. Therefore, if the Coulomb efficiency is good, that is, if it is high, the storage performance is also good.

Further, the difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte should be 80% or less with respect to the larger of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. Therefore, it is more preferable because the mixing of positive and negative water-based electrolytes due to the difference in osmotic pressure can be sufficiently suppressed in terms of speed.

Even more preferably, it is 50% or less. Within this range, mixing of the aqueous electrolyte due to osmotic pressure can be suppressed for a long period of time, so that the storage performance can be improved and the Coulomb efficiency can also be improved. Further, this is because the cycle life can be greatly improved.

The difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is 90% or less with respect to the larger of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. As the positive electrode side aqueous electrolyte and the negative negative side aqueous electrolyte, aqueous electrolytes having different pH from each other and aqueous electrolytes of different types can be used. Here, by using an aqueous electrolyte having a pH lower than that of the negative electrode side aqueous electrolyte as the positive electrode side aqueous electrolyte, electrolysis of water is less likely to occur even if the voltage between the negative electrode and the positive electrode becomes larger than 1.23 V. .. For example, when an aqueous electrolyte having a pH of 1 is used as the positive electrode side aqueous electrolyte and an aqueous electrolyte having a pH of 14 is used as the negative electrode side aqueous electrolyte, unless the voltage between the negative electrode and the positive electrode rises to about 2 V, It is considered that electrolysis of water is unlikely to occur.

The material of each member that can be used in the secondary battery according to the first embodiment will be described in detail.

(Aqueous electrolyte)
Examples of the aqueous electrolyte include an aqueous electrolyte containing an aqueous solvent and a first electrolyte, and a gel-like aqueous electrolyte in which a polymer material is compounded with the aqueous electrolyte. For convenience, the electrolyte as a solute is referred to as a first electrolyte in order to distinguish between the aqueous electrolyte used to collectively refer to the aqueous electrolyte and the gelled aqueous electrolyte and the electrolyte as the solute. Examples of the above-mentioned polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO) and the like. The aqueous electrolyte contains at least one anion selected from the group consisting of _{NO 3} ⁻ , Cl ⁻ , LiSO ₄ ⁻ , SO ₄ ^2- , and OH ^−. These anions contained in the aqueous electrolyte may contain one kind or two or more kinds of anions.

As the aqueous solvent, a solution containing water can be used. Here, the solution containing water may be pure water, or may be a mixed solution or a mixed solvent of water and a substance other than water.

The water-based electrolyte preferably has an amount of water solvent (for example, the amount of water in the water-based solvent) of 1 mol or more with respect to 1 mol of the salt as a solute. A more preferable form is that the amount of the aqueous solvent with respect to 1 mol of the salt as a solute is 3.5 mol or more.

As the first electrolyte, one that dissociates when dissolved in an aqueous solvent to generate the anion can be used. In particular, a lithium salt that dissociates between the Li ion and the anion is preferable. Examples of such a lithium salt include LiNO ₃ , LiCl, Li ₂ SO ₄ , LiOH and the like.

In addition, the lithium salt that dissociates from the Li ion and the anion has a relatively high solubility in an aqueous solvent. Therefore, an aqueous electrolyte having a high anion concentration of 1-10M and good Li ion diffusivity can be obtained.

NO ^3- and / or Cl ^- electrolyte containing may be used in a wide range of anion concentration of about 0.1-10M. From the viewpoint of achieving both ionic conductivity and lithium equilibrium potential, the concentration of these anions is preferably as high as 3-12M. More preferably the anion concentration of the aqueous electrolyte containing a is 8-12M ^- NO ^3- and / or Cl.

LiSO ₄ ^- is and / or water based electrolyte including _SO ^{4 2-a,} can be used in the range of the anion concentration of about 0.05-2.5M. From the viewpoint of ionic conductivity, the concentration of these anions is preferably as high as 1.5-2.5M.

To be specific, the anion concentration of the positive side-aqueous electrolyte ^{is, NO 3-, Cl -, LiSO} 4 -, when the water-based electrolyte containing _SO ^{4 2-1} or more, about 0.5-3M is preferred. If the lithium salt concentration is higher than this, the lithium insertion / desorption potential shifts in a noble direction and the side reaction becomes violent, which is not preferable. Further, the anion concentration of the negative-aqueous ^{electrolyte, NO 3-, Cl -, LiSO} 4 -, when the water-based electrolyte containing _SO ^{4 2-1} or more, about 6-13M is preferred. If the lithium ion concentration is lower than this, the potential for lithium insertion and desorption shifts to the lower side, and the side reaction becomes violent, which is not preferable.

OH in the aqueous electrolyte ^- concentration ^is desirably 10 -10-0.1 M.

In addition, the aqueous electrolyte can contain both lithium ions and sodium ions.

As for the pH of the aqueous electrolyte, the pH of the positive electrode aqueous electrolyte is preferably 1 or more and 7 or less. When the pH of the aqueous electrolyte of the positive electrode is 8 or more, the oxygen evolution reaction caused by the electrolysis of water proceeds advantageously, and when the pH is less than 1, the decomposition of the active material proceeds, which is not preferable. The pH of the aqueous electrolyte of the negative electrode is preferably 7 or more and 14 or less, and if it is less than 7, the hydrogen generation reaction caused by the electrolysis of water proceeds advantageously, which is not preferable. The solute in the aqueous electrolyte, that is, the first electrolyte, can be qualitatively and quantified by, for example, ion chromatography. The ion chromatograph method is particularly preferable as an analytical method because of its high sensitivity.
An example of specific measurement conditions for qualitative quantitative analysis of solutes contained in electrolytes by ion chromatography is shown below:
System: Prominence HIC-SP
Analytical column: Sim-packIC-SA3
Guard column: Sim-packIC-SA3 (G)
Eluent: 3.6 mmol / L sodium carbonate aqueous solution Flow rate: 0.8 mL / min
Column temperature: 45 ° C
Injection volume: 50 μL
Detection: Electrical conductivity

Whether or not water is contained in the aqueous electrolyte can be confirmed by gas chromatography-mass spectrometry (GC-MS) measurement. Further, the calculation of the water content in the aqueous electrolyte can be measured by, for example, luminescence analysis of inductively coupled plasma (ICP: Inductively Coupled Plasma). By measuring the specific gravity of the aqueous electrolyte, the number of moles of the solvent can be calculated. The same aqueous electrolyte may be used on the positive electrode side and the negative electrode side, or different aqueous electrolytes may be used.

An inorganic compound or an organic compound can be used as the osmotic pressure adjusting agent for the aqueous electrolyte on the positive electrode side. Oxide as an inorganic compound or chloride ion (Cl ^-), fluoride ion (F ^-), iodide ion (I ^-), perchlorate ion (ClO 4 ^_-), formate ions (HCO 2 ^_-), acetic acid ion ^{_{(C 2 H 3 O 2 -}} ), hydrate ions (OH ^-), oxalate _{(C 2 O} 2 ^-), nitrate ion (NO ^3-), nitrite ion (NO ₂ ^-), sulfate ion (SO ₄ ^2- ), Thiosulfate Ion (S ₂ O ₃ ^2- ) _{Sulfate Ion (SO 3} ^2- ), Carbonate Ion (CO ₃ ^2- ), Bicarbonate Ion (HCO ₃ ^2- ), Thiosic Acid Ion (SO 3 2-) SCN ^-), ammonium ions (NH ₄ ^+), but a compound containing at least one herd consisting of phosphate ions (PO ₄ ^3-) and hydrogen phosphate ions (HPO ₄ ^2-) is dissolved in an aqueous electrolyte, It is preferable because it does not react or oxidize. Examples include sodium chloride, potassium chloride, zinc chloride, sodium fluoride, calcium fluoride, calcium perchlorate, ammonium formate, potassium formate, potassium acetate, sodium acetate, potassium hydroxide, sodium hydroxide, oxalic acid, shu. Potassium acid, ammonium oxalate, nitrate, potassium nitrate, sodium nitrate, sodium nitrite, ammonium sulfite, sodium sulfate, sulfuric acid, ammonium thiosulfate, potassium thiosulfate, ammonium carbonate, potassium carbonate, ammonium hydrogencarbonate, potassium hydrogencarbonate, ammonium thiosocyanate , Potassium thiocyanate, ammonium phosphate, potassium phosphate, ammonium hydrogen phosphate, potassium hydrogen phosphate.

As the organic compound, a compound that dissolves in an aqueous electrolyte like an inorganic compound but does not react or oxidize is preferable. Examples are methanol, ethanol, butanol, isobutanol, isopropyl alcohol, normal propyl alcohol, tertiary butanol, secondary butyl alcohol, 1,3-butanediol, 1,4-butanediol, 2-ethyl-1-hexanol, benzyl. Alcohols such as alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, diacetone alcohol and other ketones, ethyl acetate, methyl acetate, butyl acetate, sec-butyl acetate, methoxybutyl acetate, amyl acetate, normal acetate Esters such as propyl, isopropyl acetate, ethyl lactate, methyl lactate, butyl lactate, ethyl 3-ethoxypropionate, isopropyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, 1,4-dioxane, tetrahydrofuran, methyl tertiary butyl ether, etc. Glycos such as ethers, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, butyl carbitol acetate, ethyl carbitol acetate, methyl carbitol, ethyl carbitol, Glycols such as butyl carbitol, methyl triglycol, propylene glycol monomethyl ether, propylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, hexyl diglycol, propylene glycol monomethyl ether propionate, dipropylene glycol methyl ether Grimes such as ethers, monoglyme, jigglime, ethylglyme, ethyl diglime, triglime, butyl jigglime, tetraglime, dipropylene glycol dimethyl ether, dimethylformamide, dimethylacetamide, hexamethylphosphoric triamide, acetonitrile, propionitrile , Butyronitrile, Isobutyronitrile, Valeronitrile, Isovaleronitrile, Lauronitrile, 2-Methylbutyronitrile, trimethylnitrile, Hexanitrile, Cyclopentanecarbonitrile, Cyclohexanecarbonitrile, Acrylonitrile, Methaclonitrile, Crotononitrile, N-Methyl-2-pyrrolidone, N-ethyl-2-pyrroli Aprotonic polar solvents such as dong and γ-butylolactam, cyclic carboxylic acid esters such as gamma butyrolactone, gamma valerolactone, gamma caprolactone and epsilon caprolactone, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n -Chain carbonate compounds such as propylisopropylcarbonate, ethylmethylcarbonate, methyl-n-propylcarbonate, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, triethanolamine, N, N-diisopropylethylamine, etc. An organic compound that is compatible with water, such as an amine solvent, is used.

Further, as an osmotic pressure adjusting agent, a surfactant can be added to the aqueous electrolyte. Surfactants include, for example, polyoxyalkylene alkyl ether, polyethylene glycol, polyvinyl alcohol, thiourea, 3,3'-dithiobis (1-propanephosic acid) disodium, dimercaptothiaizole, boric acid, oxalic acid, malonic acid, saccharin. , Nonionic surfactants such as sodium naphthalene sulfonate, gelatin, potassium nitrate, aromatic aldehydes, heterocyclic aldehydes and the like. The surfactant may be used alone or in combination of two or more. These osmoregulators may be used alone or in combination of two or more with respect to the aqueous electrolyte, regardless of whether they are inorganic compounds, organic compounds or surfactants. By adding these, the osmotic pressure with the aqueous electrolyte on the negative electrode side can be adjusted. Further, as the osmotic pressure adjusting agent on the negative electrode side, the same osmotic pressure adjusting agent as the positive electrode can be used.

By adding the osmotic pressure adjusting agent in this way, the osmotic pressure difference between the two electrolytes can be adjusted to a range of 90% or less of the osmotic pressure on the side having the larger osmotic pressure.

Here, the osmotic pressure Π (N / m ² ) is calculated as follows. That is, the volume of the solvent in the electrolyte (electrolyte solution) is V (m ³ ), the amount of substance of the solute in the electrolyte (total number of moles) is n (mol), and the gas constant is R (m ² · kg / (s ² ·). K · mol)), where the absolute temperature of the electrolyte is T (K), the osmotic pressure Π is calculated by the following equation (5).
Π = (n ・ R ・ T) / V (5)

Here, when the aqueous electrolyte is an aqueous electrolyte, the solute (first electrolyte) of the aqueous electrolyte is an inorganic salt, an organic compound, or the like. The structure of inorganic salts is identified by ICP emission analysis, and the structure of organic compounds is identified by Fourier transform infrared spectroscopy (FTIR). Then, by fractionating the electrolyte (water-based electrolyte), the concentration of the water-based electrolyte is calculated, and the amount of substances such as inorganic salts and organic compounds in the water-based electrolyte is calculated. The amount of substance n is the total number of moles of the solute, and the ionization of the solute is also taken into consideration. In fact, when the solutes are inorganic salts, organic compounds, etc., it is considered that all of these solutes are ionized in the aqueous electrolytic solution. For example, when the solute is an alkali metal salt, an alkaline earth metal salt, or the like, it is considered that the alkali metal ion and the alkaline earth ion are all ionized with respect to the anion, and the amount of substance n is calculated. For example, when LiCl is dissolved as a solute at 12 mol / L, the concentration is considered to be 24 mol / L because it is ionized into ^{Li +} and Cl ^{− in the aqueous electrolytic solution.}

The osmotic pressure adjusting agent may be added to either one of the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte, and may be contained in both. The molar concentration of the osmotic pressure adjusting agent contained in the aqueous electrolyte is, for example, 2 mol / L or more and 8 mol / L or less when the osmotic pressure adjusting agent is added to the positive electrode side aqueous electrolyte. When the mol concentration of the osmotic pressure adjusting agent of the positive electrode side aqueous electrolyte is in this range, it is possible to provide an osmotic pressure difference without interfering with the operation of the secondary battery. More preferably, it is 2.5 mol / L or more and 7 mol / L or less.

When an osmotic pressure adjusting agent is added to the negative electrode side aqueous electrolyte, the mol concentration of the osmotic pressure adjusting agent is, for example, 0.1 mol / L or more and 5 mol / L or less. Within this range, the osmotic pressure difference can be reduced without increasing the resistance of the aqueous electrolyte. The range is preferably 0.5 mol / L or more and 4 mol / L or less, and more preferably 0.7 mol / L or more and 3 mol / L or less.

Whether or not the surfactant is contained in the aqueous electrolyte can be examined by using the above-mentioned GC-MS. For example, the aqueous electrolyte is extracted with hexane to separate the organic solvent in the aqueous electrolyte. It can be identified by performing nuclear magnetic resonance measurement (NMR) with GC-MS on the separated organic solvent.

The molecular weight of the surfactant can be measured by MALDI-TOF-MS (Matrix Assisted Laser Deposition / Ionization Time-of-Flight Mass Spectrometry) analysis. As the apparatus, for example, a JMS-S3000 Spiral TOF manufactured by JEOL Ltd. can be used. For data analysis, for example, MS Tornado Analysis manufactured by JEOL Ltd. can be used. Polymethylmethacrylate (molecular weight standard for size exclusion chromatography) is used as the external standard for mass composition.

The value of the peak top position in the MALDI-MS spectrum obtained by the measurement is recorded as the molecular weight.

The interfacial tension of the aqueous electrolyte is preferably 80 mN / m or less, for example, less than 55 mN / m. Within this range, it can penetrate into the inside of the separator. Since the aqueous electrolyte can penetrate well into the separator, the resistance of the separator can be lowered, the Coulomb efficiency at the time of initial charge / discharge can be increased, and the capacity ratio of the positive electrode and the negative electrode at the time of battery design can be brought close to 1. be able to. Therefore, it is possible to design a battery with little capacity loss. It is more preferably 50 mN / m or less, and even more preferably 40 mN / m or less. The surfactant may be used alone or in combination of two or more with respect to the aqueous electrolyte.

The method for measuring the interfacial tension is as follows.

<Measurement method of interfacial tension of aqueous electrolyte>
The interfacial tension of the aqueous electrolyte can be determined, for example, by using the suspension method. As the measuring device, for example, an automatic contact angle meter Dme-201 manufactured by Kyowa Interface Science Co., Ltd. can be used. As the measurement conditions, for example, the conditions shown in Table 1 below are used.

The suspension method is used to calculate the interfacial tension, and the interfacial tension of the aqueous electrolyte is calculated from the following formula (6).
Interfacial tension (mN / M) = Δρgde ² (1 / H) ... (6)
Each symbol in equation (6) is as follows:
Δρ: Density difference, g: Gravity acceleration, de: Maximum diameter of suspended droplet, 1 / H: Correction coefficient.
For example, the measurement is performed 5 times, and the average value is regarded as the interfacial tension.

<Measurement method of contact angle of water-based electrolyte>
The contact angle of the aqueous electrolyte can be determined by, for example, the sessile drop method. As the measuring device, for example, an automatic contact angle meter Dme-201 manufactured by Kyowa Interface Science Co., Ltd. can be used. As the measurement conditions, for example, the conditions shown in Table 2 below are used.

(Separator)
A separator can be arranged between the positive electrode and the negative electrode. By forming the separator with an insulating material, it is possible to prevent the positive electrode and the negative electrode from electrically contacting each other. Further, it is desirable to use a shape in which the electrolyte can move between the positive electrode and the negative electrode. In the example below, the separator is air permeable. Examples of separators include non-woven fabrics, films, paper and the like. Examples of the constituent materials of the separator include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferable separators include non-woven fabrics containing cellulose fibers and porous films containing polyolefin fibers.

The air permeability coefficient of the separator ^{is preferably 1 × 10-14} m ² or less. 1 × and 10 is greater than ^-14 m ^2, will be mixed positive side-aqueous electrolyte and the negative-aqueous electrolyte is not preferable because the aqueous electrolyte of the smaller of osmotic pressure is prone to wither liquid. The air permeability coefficient is ^{more preferably 1 × 10 -15} m ² or less, and even more preferably 1 × 10 ^-16 m ² or less. A separator having such an air permeability coefficient is preferable because the mixing of the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte can be sufficiently suppressed in terms of kinetics, and the Coulomb efficiency is improved. This is because the water-based electrolyte is sufficiently impregnated into the separator, the resistance of the separator is low, and the ionic conductivity is high, so that the rate characteristics are improved. The water-based electrolyte soaks into the separator well, but the water-based electrolyte does not mix well on the positive electrode side and the negative electrode side.

The air permeability coefficient KT (m ² ) of the separator is measured as follows.
In the calculation of the air permeability coefficient KT, for example, when a separator having a thickness of L (m) is to be measured, a gas having a viscosity coefficient σ (Pa · s) is allowed to permeate within the range of the ^{measurement area A (m 2).} At this time, the gas is permeated under a plurality of conditions in which the pressure p (Pa) of the injected gas is different from each other, and the amount of gas Q (m ³ / s) permeated through the separator is measured under each of the plurality of conditions. To do. Then, from the measurement result, the gas amount Q with respect to the pressure p is plotted to obtain the slope dQ / dp. Then, the air permeability coefficient KT is calculated from the thickness L, the measurement area A, the viscosity coefficient σ, and the slope dQ / dp as in the equation (7).
KT = ((σ ・ l) / A) × (dQ / dp) (7)

In one example in which the air permeability coefficient KT is calculated, the separator is sandwiched between a pair of stainless steel plates each having a hole having a diameter of 10 mm. Then, air is sent at a pressure p from the hole of one of the stainless steel plates. Then, the gas amount Q of the air leaking from the hole of the other stainless steel plate is measured. Therefore, the area of the hole (25π mm ² ) is used as the measurement area A, and 0.000018 Pa · s is used as the viscosity coefficient σ. ^{The gas amount Q is calculated by measuring the amount δ (m 3} ) leaking from the hole in 100 seconds and dividing the measured amount δ by 100.

Then, the amount of gas Q with respect to the pressure p is measured as described above at four points where the pressures p are separated from each other by at least 1000 Pa. For example, the gas amount Q with respect to the pressure p is measured at each of the four points where the pressure p is 1000 Pa, 2500 Pa, 4000 Pa, and 6000 Pa. Then, the gas amount Q with respect to the pressure p is plotted at the four measured points, and the slope (dQ / dp) of the gas amount Q with respect to the pressure p is calculated by linear fitting (least squares method). Then, the air permeability coefficient KT is calculated by multiplying the calculated slope (dQ / dp) by (σ · L) / A.

In the measurement of the air permeability coefficient of the separator, the battery is disassembled and the separator is separated from other parts of the battery. After rinsing both sides of the separator with pure water, it is immersed in pure water and left for 48 hours or more. Then, both sides are further rinsed with pure water, dried in a vacuum drying oven at 100 ° C. for 48 hours or more, and then the air permeability coefficient is measured. In addition, the air permeability coefficient is measured at an arbitrary plurality of points on the separator. Then, the value at the position where the air permeability coefficient is the lowest value among any plurality of points is defined as the air permeability coefficient of the separator.

The porosity of the separator is preferably 60% or more. The fiber diameter is preferably 10 μm or less. By setting the fiber diameter to 10 μm or less, the affinity of the separator with respect to the electrolyte is improved, so that the battery resistance can be reduced. A more preferable range of the fiber diameter is 3 μm or less. A cellulose fiber-containing non-woven fabric having a porosity of 60% or more has good electrolyte impregnation properties and can exhibit high output performance from low temperature to high temperature. In addition, it does not react with the negative electrode even during long-term charge storage, float charging, and overcharging, and a short circuit between the negative electrode and the positive electrode does not occur due to dendrite precipitation of lithium metal. A more preferable range is 62% to 80%.

Moreover, a solid electrolyte can also be used as a separator. As the solid electrolyte, LATP (Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ ; 0.1 ≤ x ≤ 0.4) _{having a NASICON type skeleton and amorphous LIPON (Li 2.9} PO _{3.). Oxides such as 3} N _0.46 ) and garnet-type LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) are preferred.

Further, β-alumina, Na _{1 + x} Zr ₂ Si _x P _3-x O ₁₂ (0 ≦ x ≦ 3), NaAlSi ₃ O _{8 and the} like can also be mentioned.

As the separator, a separator having a solid electrolyte layer on at least one of the main surfaces of the porous self-supporting membrane can also be used. As the solid electrolyte provided in the solid electrolyte layer, the above-mentioned LATP or the like can be used.

The separator preferably has a thickness of 20 μm or more and 100 μm or less and a density of 0.2 g / cm ³ or more and 0.9 g / cm ³ or less. Within this range, a balance between mechanical strength and reduction of battery resistance can be achieved, and a secondary battery having high output and suppressed internal short circuit can be provided. Moreover, the heat shrinkage of the separator in a high temperature environment is small, and good high temperature storage performance can be obtained.

(Negative electrode)
The negative electrode includes a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector. The negative electrode active material layer is arranged on at least one surface of the negative electrode current collector. For example, the negative electrode active material layer may be arranged on one surface on the negative electrode current collector, or the negative electrode active material layer may be arranged on one surface on the negative electrode current collector and its back surface. ..

The negative electrode active material layer contains a negative electrode active material containing at least one compound selected from the group consisting of titanium oxide, lithium titanium oxide, and lithium titanium composite oxide. These oxides may be used alone or in combination of two or more. With these oxides, the Li insertion / desorption reaction occurs within the range of 1 V or more and 2 V or less (vs. ^{Li / Li +) based on the lithium potential.} Therefore, when these oxides are used as the negative electrode active material of the secondary battery, a long life can be realized because the change in volume expansion / contraction due to charging / discharging is small.

The negative electrode current collector preferably contains at least one element selected from Zn, Ga, In, Bi, Tl, Sn, Pb, Ti, and Al in the current collector. Hereinafter, these elements will also be referred to as element A. These elements may be used in one of these elements, or a plurality of types of elements may be used, and may be included as a metal or a metal alloy. Such metals and metal alloys may be contained alone or in combination of two or more. When these elements are contained in the current collector, the mechanical strength of the current collector is increased and the processing performance is improved. Further, the effect of suppressing the electrolysis of the aqueous solvent and suppressing the generation of hydrogen is increased. Among the above elements, Zn, Pb, Ti and Al are more preferable.

The current collector is, for example, a metal leaf made of these metals. The current collector is, for example, a foil made of an alloy containing these metals. Such a foil may contain other elements other than the element A, for example Cu. Examples of the shape of the metal body include a mesh and a porous body in addition to the foil. In order to improve energy density and output, a foil shape with a small volume and a large surface area is desirable.

Further, the negative electrode current collector can include a substrate containing a metal different from the element A. In such a case, hydrogen generation can be suppressed by the presence of the compound containing the element A on at least a part of the surface of the substrate. It is desirable that the compound containing the element A existing on the surface is arranged so as to be in contact with the negative electrode active material layer. For example, the substrate can be plated with element A so that a compound containing element A can be present on the surface of the substrate. Alternatively, the surface of the substrate can be plated with an alloy containing the element A.

The current collector may contain at least one compound selected from the group consisting of element A. These oxides of element A and / or hydroxides of element A and / or basic carbon dioxide compounds of element A and / or sulfuric acid compounds of element A are present in at least a portion of the surface region of the current collector. It is preferably contained in a depth region of 5 nm or more and 1 μm or less in the depth direction from the surface. _{Incidentally, 2ZnCO 3 · 3Zn (OH)} 2 Examples of example as basic carbonate compound of ZnO, examples of the hydroxide of an element A Zn (OH) _2, element A oxide of the element A, the element examples of sulfuric acid compounds of a, and the like ZnSO ₄ · 7H ₂ O.

When at least one of an oxide of element A, a hydroxide of element A, a basic carbonic acid compound of element A, and a sulfuric acid compound of element A is present on the surface layer of the current collector, hydrogen generation is suppressed. Can be done. Further, when these compounds are present on the surface layer of the current collector, the adhesion to each of the current collector, the active material, the conductive auxiliary agent, and the binder is improved, and the path of electron conduction can be increased. It is possible to improve and reduce the resistance.

The substrate preferably contains at least one metal selected from Al, Fe, Cu, Ni and Ti. These metals can also be included as alloys. Further, the substrate may contain such a metal and a metal alloy alone, or may contain a mixture of two or more kinds. From the viewpoint of weight reduction, it is preferable that the substrate contains Al, Ti, or an alloy thereof.

Whether or not the current collector contains at least one compound selected from the group consisting of element A can be investigated by disassembling the battery as described above and then performing inductively coupled plasma ICP emission analysis. it can.

The negative electrode active material contains one or more compounds selected from the group consisting of titanium oxides, lithium titanium oxides, and lithium titanium composite oxides. Examples of lithium-titanium composite oxides include niobium-titanium oxide and sodium niobium-titanium oxide. Li insertion potential of these compounds is preferably a 1V (vs.Li/Li ⁺⁾ or 3V (vs.Li/Li ⁺⁾ or less.

Examples of titanium oxides include monoclinic titanium oxides, rutile titanium oxides, and anatase titanium oxides. The titanium oxide having each crystal structure can be represented by a composition of TiO ₂ before charging and a composition of Li _x TiO ₂ (x is 0 ≦ x) after charging. Further, the pre-charging structure of titanium oxide having a monoclinic structure _{can be represented as TiO 2} (B).

Examples of lithium titanium oxides include spinel-structured lithium titanium oxides (eg, general formula Li _{4 + x} Ti ₅ O ₁₂ (x is -1≤x≤3)) and rams delite-structured lithium titanium oxides (eg, Li). _{2 + x} Ti ₃ O ₇ (-1 ≤ x ≤ 3)), Li _{1 + x} Ti ₂ O ₄ (0 ≤ x ≤ 1), Li _{1.1 + x} Ti _1.8 O ₄ (0 ≤ x ≤ 1) 1), Li _{1.07 + x} Ti _1.86 O ₄ (0 ≦ x ≦ 1), Li _x TiO ₂ (0 <x), and the like are included.

Examples of niobium titanium oxides include Li _a TiM _b Nb _{2 ± β} O _{7 ± σ} (0 ≦ a ≦ 5, 0 ≦ b ≦ 0.3, 0 ≦ β ≦ 0.3, 0 ≦ σ ≦ 0.3, M includes those represented by at least one element selected from the group consisting of Fe, V, Mo and Ta).

Examples of sodium niobium titanium oxide, the general formula _{Li 2 + v Na 2-w} M1 x Ti 6-yz Nb y M2 z O 14 + δ (0 ≦ v ≦ 4,0 <w <2,0 ≦ x < 2, 0 <y <6, 0 ≦ z <3, y + z <6, −0.5 ≦ δ ≦ 0.5, M1 contains at least one selected from Cs, K, Sr, Ba, Ca. M2 comprises an orthodox Na-containing niobium-titanium composite oxide represented by (including at least one selected from Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, Al).

Preferred compounds as the negative electrode active material include titanium oxide having an anatase structure, titanium oxide having a monoclinic structure, and lithium titanium oxide having a spinel structure. Each compound, since Li insertion potential is in a range 1.4V (vs.Li/Li ⁺⁾ or 2V (vs.Li/Li ⁺⁾ following, for example, by combining the lithium-manganese oxide as the positive electrode active material , High electromotive force can be obtained. Among these, lithium titanium oxide having a spinel structure is more preferable because the volume change due to the charge / discharge reaction is extremely small.

The negative electrode active material can be contained in the negative electrode active material layer in the form of particles. The negative electrode active material particles can be a single primary particle, a secondary particle which is an aggregate of the primary particles, or a mixture of a single primary particle and a secondary particle. The shape of the particles is not particularly limited, and can be, for example, spherical, elliptical, flat, fibrous, or the like.

The average particle size (diameter) of the secondary particles of the negative electrode active material is preferably 3 μm or more. More preferably, it is 5 μm or more and 20 μm or less. Within this range, since the surface area of the active material is small, the effect of suppressing hydrogen generation can be enhanced.

A negative electrode active material having an average particle size of secondary particles of 3 μm or more can be obtained, for example, by the following method. First, an active material raw material is reacted and synthesized to prepare an active material precursor having an average particle size of 1 μm or less. After that, the active material precursor is fired and crushed using a crusher such as a ball mill or a jet mill. Then, in the firing process, the active material precursor is aggregated and grown into secondary particles having a large particle size.

It is desirable that the average particle size of the primary particles of the negative electrode active material is 1 μm or less. As a result, the diffusion distance of Li ions inside the active material is shortened, and the specific surface area is increased. Therefore, excellent high input performance (quick charging performance) can be obtained. On the other hand, if the average particle size is small, agglutination of particles is likely to occur, and the distribution of the electrolyte is biased toward the negative electrode, which may lead to the depletion of the electrolyte at the positive electrode. Therefore, it is desirable to set the lower limit value to 0.001 μm. .. A more preferable average particle size is 0.1 μm or more and 0.8 μm or less.

It is desirable that the negative electrode active material particles have a specific surface area of 3 m ² / g or more and 200 m ² / g or less in the _{BET method by N 2 precipitation.} As a result, the affinity between the negative electrode and the electrolyte can be further increased.

The specific surface area of the negative electrode active material layer (excluding the current collector) is preferably in the range of ^{3 m 2} / g or more and 50 m ^{2 / g or less.} A more preferable range of the specific surface area is 5 m ² / g or more and 50 m ² / g or less. The negative electrode active material layer can be a porous layer containing a negative electrode active material, a conductive agent, and a binder supported on the current collector.

The porosity of the negative electrode (excluding the current collector) is preferably in the range of 20 to 50%. As a result, it is possible to obtain a negative electrode having excellent affinity between the negative electrode and the electrolyte and having a high density. A more preferred range of porosity is 25-40%.

Examples of the conductive agent include carbon materials such as acetylene black, carbon black, coke, carbon fiber and graphite, and metal powders such as nickel and zinc. The type of the conductive agent can be one type or two or more types. Since hydrogen is generated from the carbon material itself, it is desirable to use a metal powder as the conductive agent.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, ethylene-butadiene rubber, polypropylene (PP), polyethylene (PE), carboxymethyl cellulose (CMC), and polyimide ( PI), polyacrylicimide (PAI) and the like. The type of binder can be one or more.

Regarding the compounding ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer, the negative electrode active material is 70% by weight or more and 95% by weight or less, the conductive agent is 3% by weight or more and 20% by weight or less, and the binder is It is preferably in the range of 2% by weight or more and 10% by weight or less. When the compounding ratio of the conductive agent is 3% by weight or more, the conductivity of the negative electrode can be improved, and when it is 20% by weight or less, the decomposition of the electrolyte on the surface of the conductive agent can be reduced. When the compounding ratio of the binder is 2% by weight or more, sufficient electrode strength can be obtained, and when it is 10% by weight or less, the insulating portion of the electrode can be reduced.

The negative electrode can be produced, for example, as follows. First, the negative electrode active material, the conductive agent and the binder are dispersed in an appropriate solvent to prepare a slurry. This slurry is applied to the current collector and the coating film is dried to form a negative electrode active material layer on the current collector. Here, for example, the slurry may be applied to one surface on the current collector, or the slurry may be applied to one surface on the current collector and its back surface. Next, the negative electrode can be produced by applying a press such as a heating press to the current collector and the negative electrode active material layer.

(Positive electrode)
This positive electrode can have a positive electrode current collector and a positive electrode layer supported on one or both sides of the positive electrode current collector and containing an active material, a conductive agent, and a binder.

As the positive electrode current collector, it is preferable to use a foil, a porous body, or a mesh made of a metal such as stainless steel, Al, or Ti. In order to prevent corrosion of the current collector due to the reaction between the current collector and the electrolyte, the surface of the current collector may be coated with a different element.

As the positive electrode active material, a material capable of occluding and releasing lithium and sodium can be used. The positive electrode may contain one kind of positive electrode active material, or may contain two or more kinds of positive electrode active materials. Examples of positive electrode active materials include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, spinel type lithium manganese nickel composite oxide, and lithium manganese cobalt composite oxide. , Lithium iron oxide, lithium fluorinated sulfate, phosphoric acid compounds having an olivine crystal structure (for example, Li _x FePO ₄ (0 ≦ x ≦ 1), Li _x MnPO ₄ (0 ≦ x ≦ 1)) and the like. .. The phosphoric acid compound having an olivine crystal structure is excellent in thermal stability.

Examples of positive electrode active materials that can obtain a high positive electrode potential are described below. For example a spinel structure _{Li x Mn 2 O 4 (0} <x ≦ 1), Li x MnO 2 (0 <x ≦ 1) lithium manganese composite oxide such as, for example, _{Li x Ni 1-y Al y} O 2 (0 Lithium nickel-aluminum composite oxides such as <x ≦ 1, 0 <y ≦ 1), such as lithium cobalt composite oxides such as _{Li x} CoO _{2 (0 <x ≦ 1), such as Li x} Ni _1-y−z Co. _{Lithium nickel-cobalt composite oxides such as y} Mn _z O ₂ (0 <x ≦ 1, 0 <y ≦ 1, 0 ≦ z ≦ 1), such as Li _x Mn _y Co _1-y O ₂ (0 <x ≦ 1). , 0 <y ≦ 1) and other lithium manganese cobalt composite oxides, for example _{spinel type lithium manganese nickel composite oxides such as Li x} Mn _2-y N _y O ₄ (0 <x ≦ 1, 0 <y <2). For example, Li _x FePO ₄ (0 <x ≦ 1), Li _x Fe _1-y Mn _y PO ₄ (0 <x ≦ 1, 0 ≦ y ≦ 1), Li _x CoPO ₄ (0 <x ≦ 1), etc. Examples thereof include a lithium phosphorus oxide having an olivine structure and iron fluorinated sulfate (for example, Li _x FeSO ₄ F (0 <x ≦ 1)).

In addition, sodium manganese composite oxide, sodium nickel composite oxide, Natrim cobalt composite oxide, Natrim nickel cobalt manganese composite oxide, sodium iron composite oxide, sodium phosphorus oxide (for example, iron sodium phosphate, vanadium sodium phosphate). ), Sodium iron-manganese composite oxide, sodium nickel titanium composite oxide, sodium nickel iron composite oxide, sodium nickel manganese composite oxide and the like.

Examples of preferred positive electrode active material, iron composite oxide (e.g., _{Na y FeO 2, 0 ≦ y} ≦ 1), iron-manganese composite oxide (e.g., _{Na y Fe 1-x Mn x} O 2, 0 <x <1, 0 ≦ y ≦ 1), nickel-titanium composite oxide (eg Na _y Ni _1-x Ti _x O ₂ , 0 <x <1, 0 ≦ y ≦ 1), nickel iron composite oxide (eg Na _y Ni _{1-) x Fe x O 2, 0 <} x <1,0 ≦ y ≦ 1), nickel-manganese composite oxide (e.g., _{Na y Ni 1-x Mn x} O 2, 0 <x <1,0 ≦ y ≦ 1), nickel manganese iron composite oxide (e.g., _{Na y Ni 1-x-z} Mn x Fe z O 2, 0 <x <1,0 ≦ y ≦ 1,0 <z <1,0 <1-x-z <1 ) include iron phosphate (e.g. _{Na y FePO 4, 0 ≦ y} ≦ 1).

The particles of the positive electrode active material can include single primary particles, secondary particles that are aggregates of primary particles, or both single primary particles and secondary particles. The average particle size (diameter) of the primary particles of the positive electrode active material is preferably 10 μm or less, more preferably 0.1 μm to 5 μm. The average particle size (diameter) of the secondary particles of the positive electrode active material is preferably 100 μm or less, more preferably 10 μm to 50 μm.

It is preferable that at least a part of the particle surface of the positive electrode active material is coated with a carbon material. The carbon material can take the form of a layered structure, a particle structure, or an aggregate of particles.

Examples of the conductive agent for increasing the electron conductivity of the positive electrode layer and suppressing the contact resistance with the current collector include acetylene black, carbon black, graphite, carbon fibers having an average fiber diameter of 1 μm or less, and the like. The type of the conductive agent can be one type or two or more types.

The binder for binding the active material and the conductive agent is, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, ethylene-butadiene rubber (SBR), polypropylene (PP). , Polyethylene (PE), Carboxymethyl Cellulose (CMC), Polyimide (PI), Polyacrylicimide (PAI). The type of binder may be one type or two or more types.

Regarding the compounding ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode layer, the positive electrode active material is 70% by weight or more and 95% by weight or less, the conductive agent is 3% by weight or more and 20% by weight or less, and the binder is 2% by weight. It is preferably in the range of% or more and 10% by weight or less. When the compounding ratio of the conductive agent is 3% by weight or more, the conductivity of the positive electrode can be improved, and when it is 20% by weight or less, the decomposition of the electrolyte on the surface of the conductive agent can be reduced. When the compounding ratio of the binder is 2% by weight or more, sufficient electrode strength can be obtained, and when it is 10% by weight or less, the insulating portion of the electrode can be reduced.

The positive electrode can be produced, for example, as follows. First, a positive electrode active material, a conductive agent and a binder are dispersed in an appropriate solvent to prepare a slurry. This slurry is applied to a current collector and the coating film is dried to form a positive electrode layer on the current collector. Here, for example, the slurry may be applied to one surface on the current collector, or the slurry may be applied to one surface on the current collector and its back surface. Next, the positive electrode can be produced by applying a press such as a heating press to the current collector and the positive electrode layer.

(container)
As the container in which the positive electrode, the negative electrode and the electrolyte are housed, a metal container, a laminated film container, and a resin container such as polyethylene or polypropylene can be used.

As the metal container, a metal can made of nickel, iron, stainless steel, element A or the like and having a square or cylindrical shape can be used.

The plate thickness of each of the resin container and the metal container is preferably 1 mm or less, and a more preferable range is 0.5 mm or less. A more preferable range is 0.3 mm or less. Further, it is desirable that the lower limit of the plate thickness is 0.05 mm.

Examples of the laminated film include a multilayer film in which a metal layer is coated with a resin layer. Examples of metal layers include stainless steel foils, aluminum foils, and aluminum alloy foils. As the resin layer, a polymer such as polypropylene (PP), polyethylene (PE), nylon, or polyethylene terephthalate (PET) can be used. The preferable range of the thickness of the laminated film is 0.5 mm or less. A more preferable range is 0.2 mm or less. Further, it is desirable that the lower limit of the thickness of the laminated film is 0.01 mm.

The secondary battery according to the embodiment can be applied to various types of secondary batteries such as a square type, a cylindrical type, a flat type, a thin type, and a coin type. Further, it is preferable that the secondary battery has a bipolar structure. This has the advantage that a plurality of series of cells can be produced by one cell.

FIG. 1 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment.
The secondary battery 10 shown in FIG. 1 is in contact with the negative electrode 3 including the negative electrode current collector 3a and the negative electrode active material layer 3b, the positive electrode 5 including the positive electrode current collector 5a and the positive electrode active material layer 5b, and the positive electrode. It includes a 1-water-based electrolyte 11, a second water-based electrolyte 12 in contact with a negative electrode, and an exterior member 2. The negative electrode active material layer 3b is provided on a part of both sides of the negative electrode current collector 3a. The positive electrode active material layer 5b is provided on a part of both sides of the positive electrode current collector 5a. The portion of the negative electrode current collector 3a where the negative electrode active material layer 3b is not provided functions as a negative electrode tab 3c. Of the positive electrode current collector 5a, the portion where the positive electrode active material layer 5b is not provided functions as the positive electrode tab 5c. A separator 4 exists between the negative electrode 3 and the positive electrode 5.

The positive electrode 5 is housed in the exterior member 2 with the positive electrode tab 5c protruding outward. The negative electrode 3 is housed in the exterior member 2 with the negative electrode tab 3c protruding outward. The first aqueous electrolyte 11 and the second aqueous electrolyte 12 are housed in the exterior member 2.

The first water-based electrolyte 11 contained in the secondary battery 10 shown in FIG. 1 is a gel-like water-based electrolyte. The second aqueous electrolyte 12 is a liquid aqueous electrolyte. Although not shown, the first aqueous electrolyte 11 may be a liquid aqueous electrolyte, the second aqueous electrolyte 12 may be a gel-like aqueous electrolyte, and both the first aqueous electrolyte 11 and the second aqueous electrolyte 12 are liquid. It may be an aqueous electrolyte or both may be gelled aqueous electrolytes.

Another example of the secondary battery according to the present embodiment will be described with reference to FIGS. 2 and 3.

FIG. 2 is a schematic cross-sectional view showing another example of the secondary battery according to the embodiment. FIG. 3 is an enlarged cross-sectional view of part A in FIG.

The secondary battery 10 shown in FIGS. 2 and 3 includes a flat wound electrode group 1.
As shown in FIG. 3, the wound electrode group 1 includes a negative electrode 3, a separator 4, a positive electrode 5, and a first aqueous electrolyte 11. The first aqueous electrolyte 11 is provided on both sides of the positive electrode 5. The separator 4 is interposed between the first aqueous electrolyte 11 and the negative electrode 3. The wound electrode group 1 is formed by laminating a negative electrode 3, a separator 4, and a positive electrode 5 provided with a first aqueous electrolyte 11 on both sides thereof, with the negative electrode 3 on the outside as shown in FIG. It can be formed by winding it in a spiral shape and press-molding it.

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material layer 3b. As shown in FIG. 3, the outermost negative electrode 3 has a structure in which the negative electrode active material layer 3b is formed only on one surface on the inner surface side of the negative electrode current collector 3a. In the other negative electrode 3, negative electrode active material layers 3b are formed on both sides of the negative electrode current collector 3a.

In the positive electrode 5, positive electrode active material layers 5b are formed on both sides of the positive electrode current collector 5a. The first aqueous electrolyte 11 is laminated on the positive electrode active material layer 5b formed on both sides of the positive electrode 5a.

As shown in FIGS. 2 and 3, in the vicinity of the outer peripheral end of the wound electrode group 1, the negative electrode terminal 6 is connected to the negative electrode current collector 3a of the outermost negative electrode 3, and the positive electrode terminal 7 is the inner positive electrode 5. It is connected to the positive electrode current collector 5a.

The wound electrode group 1 is housed in an exterior member (bag-shaped container) 2 made of a laminated film in which a metal layer is interposed between two resin layers.

The negative electrode terminal 6 and the positive electrode terminal 7 extend outward from the opening of the bag-shaped container 2. For example, a liquid second aqueous electrolyte (not shown) is injected through the opening of the bag-shaped container 2 and stored in the bag-shaped container 2.

By heat-sealing the opening of the bag-shaped container 2 with the negative electrode terminal 6 and the positive electrode terminal 7 interposed therebetween, the wound electrode group 1 and the second aqueous electrolyte are completely sealed. In the secondary batteries 10 shown in FIGS. 2 and 3, the positive electrode 5 is in contact with the first aqueous electrolyte, and the negative electrode 3 is in contact with the second aqueous electrolyte.

According to the embodiment described above, the secondary battery according to the first embodiment includes a positive electrode, a first aqueous electrolyte held by the positive electrode, a negative electrode, and a second aqueous electrolyte held by the negative electrode. A separator is provided between the positive electrode and the negative electrode, and the difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is either the osmotic pressure of the first aqueous electrolyte or the osmotic pressure of the second aqueous electrolyte. It is 90% or less with respect to the larger one. With such a configuration, it is possible to prevent the first water-based electrolyte and the second water-based electrolyte from being mixed, and it is possible to maintain the respective water-based electrolytes at an appropriate pH, and the electrolysis of water contained in the water-based electrolyte is possible. Can be prevented. Therefore, it is possible to provide a secondary battery having excellent storage performance and cycle characteristics.

(Second embodiment)
According to the second embodiment, it is possible to provide an assembled battery having a secondary battery as a unit cell. As the secondary battery, the secondary battery of the first embodiment can be used.

Examples of assembled batteries include a plurality of unit cells electrically connected in series or in parallel as a constituent unit, a unit composed of a plurality of electrically connected unit cells in series, or electrically connected in parallel. Examples thereof include those including a unit composed of a plurality of unit cells.

The assembled battery may be housed in a housing. As the housing, a metal can made of aluminum alloy, iron, stainless steel, etc., a plastic container, or the like can be used. Further, it is desirable that the plate thickness of the container is 0.5 mm or more.

Examples of the form in which a plurality of secondary batteries are electrically connected in series or in parallel include those in which a plurality of secondary batteries each having a container are electrically connected in series or in parallel, and are housed in a common housing. This includes those in which a plurality of electrode groups are electrically connected in series or in parallel. A specific example of the former is to connect the positive electrode terminal and the negative electrode terminal of a plurality of secondary batteries with a metal bus bar (for example, aluminum, nickel, copper). A specific example of the latter is that a plurality of electrode groups are accommodated in one housing in a state of being electrochemically insulated by a partition wall, and these electrode groups are electrically connected in series. By setting the number of batteries electrically connected in series in the range of 5 to 7, the voltage compatibility with the lead storage battery is improved. In order to improve the voltage compatibility with the lead storage battery, a configuration in which 5 or 6 unit cells are connected in series is preferable.

An example of the assembled battery will be described with reference to FIG. FIG assembled battery 31 shown in 4 includes a plurality prismatic secondary battery according to the first embodiment (e.g. FIG. 1, FIG. ₂₎ 32 1-32 ₅ as a unit cell. Positive electrode conductive tab 8 of the battery 32 _1, a negative electrode conductive tab 9 of the battery 32 ₂ located next to it, are electrically connected by a lead 33. Furthermore, a positive electrode conductive tab 8 of the battery 32 ₂ and the negative electrode conductive tab 9 of the battery 32 ₃ positioned next to it, are electrically connected by a lead 33. Thus between the battery ₃₂₁ to 323 ₅ are connected in series.

According to the assembled battery of the second embodiment, since the secondary battery according to the first embodiment is included, it is possible to provide an assembled battery having excellent storage performance and cycle characteristics.

(Third Embodiment)
According to the third embodiment, a battery pack is provided. This battery pack includes a secondary battery according to the first embodiment.

The battery pack according to the third embodiment may include one or more secondary batteries (unit cells) according to the first embodiment described above. The plurality of secondary batteries that can be included in the battery pack according to the third embodiment can be electrically connected in series, in parallel, or in combination of series and parallel. Further, the plurality of secondary batteries can also form an electrically connected assembled battery. When the assembled battery is composed of a plurality of secondary batteries, the assembled battery of the second embodiment can be used.

The battery pack according to the third embodiment may further include a protection circuit. The protection circuit controls the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (for example, an electronic device, an automobile, etc.) can be used as a protection circuit of the battery pack.

Further, the battery pack according to the third embodiment may further include an external terminal for energization. The external terminal for energization is for outputting the current from the secondary battery to the outside and / or for inputting the current to the unit cell 51. In other words, when the battery pack is used as a power source, current is supplied to the outside through an external terminal for energization. Further, when charging the battery pack, a charging current (including regenerative energy of power of an automobile or the like) is supplied to the battery pack through an external terminal 59 for energization.

An example of the battery pack according to the third embodiment will be described with reference to FIG. FIG. 5 is a schematic perspective view showing an example of a battery pack.

The battery pack 40 includes an assembled battery composed of the secondary batteries shown in FIGS. 3 and 5. The battery pack 40 includes a housing 41 and an assembled battery 42 housed in the housing 41. Battery pack 42 has a plurality (e.g. five) of the rechargeable battery ₄₃ 1-43 ₅ are electrically connected in series. The secondary battery ₄₃ 1-43 ₅ is laminated in the thickness direction. The housing 41 has openings 44 on each of the upper part and the four side surfaces. Side positive and negative terminals 12, 13 of the secondary battery ₄₃ 1-43 ₅ is protruded is exposed to the opening 44 of the housing 41. Output positive terminal 45 of the assembled battery 42, without a band, one end connected secondary battery 43 _{1-43 5} either positive terminal 13 electrically in, and opening 44 of the other end housing 41 It protrudes from the upper part of the housing 41. On the other hand, the output negative terminal 46 of the assembled battery 42, without a band, one end connected secondary battery 43 _1-43 either the negative terminal of the ₅ 12 electrically, and the other end of the housing 41 opening It protrudes from the portion 44 and protrudes from the upper part of the housing 41.

Another example of the battery pack according to the third embodiment will be described in detail with reference to FIGS. 6 and 7. FIG. 6 is an exploded perspective view of a battery pack of another example according to the third embodiment. FIG. 7 is a block diagram showing an electric circuit of the battery pack of FIG.

A plurality of unit cells 51 composed of a flat secondary battery are laminated so that the negative electrode terminals 52 and the positive electrode terminals 53 extending to the outside are aligned in the same direction, and are fastened with an adhesive tape 54 to form an assembled battery. It constitutes 55. These unit cells 51 are electrically connected in series with each other as shown in FIG.

The printed wiring board 56 is arranged so as to face the side surface of the unit cell 51 in which the negative electrode terminal 52 and the positive electrode terminal 53 extend. As shown in FIG. 7, the printed wiring board 56 is equipped with a thermistor 57, a protection circuit 58, and an external terminal 59 for energization. An insulating plate (not shown) is attached to the surface of the printed wiring board 56 facing the assembled battery 55 in order to avoid unnecessary connection with the wiring of the assembled battery 55.

The positive electrode lead 60 is connected to a positive electrode terminal 53 located at the bottom layer of the assembled battery 55, and its tip is inserted into a positive electrode connector 61 of a printed wiring board 56 and electrically connected. The negative electrode lead 62 is connected to the negative electrode terminal 52 located on the uppermost layer of the assembled battery 55, and the tip thereof is inserted into the negative electrode side connector 63 of the printed wiring board 56 and electrically connected. These connectors 61 and 63 are connected to the protection circuit 58 through the wirings 64 and 65 formed on the printed wiring board 56.

The thermistor 57 detects the temperature of the unit cell 51, and the detection signal is transmitted to the protection circuit 58. The protection circuit 58 can cut off the positive wiring 66a and the negative wiring 66b between the protection circuit 58 and the external terminal 59 for energization under predetermined conditions. The predetermined condition is, for example, when the detection temperature of the thermistor 57 becomes equal to or higher than the predetermined temperature. Further, the predetermined condition is when overcharge, overdischarge, overcurrent, etc. of the unit cell 51 are detected. The detection of overcharging or the like is performed on each unit cell 51 or the assembled battery 55. When detecting the individual unit cells 51, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each unit cell 51. In the case of FIGS. 6 and 7, a wiring 67 for voltage detection is connected to each of the unit cells 51, and a detection signal is transmitted to the protection circuit 58 through these wirings 67.

Protective sheets 68 made of rubber or resin are arranged on the three side surfaces of the assembled battery 55 except for the side surfaces on which the positive electrode terminal 53 and the negative electrode terminal 52 project.

The assembled battery 55 is housed in the storage container 69 together with the protective sheet 68 and the printed wiring board 56. That is, the protective sheet 68 is arranged on both inner side surfaces in the long side direction and the inner side surface in the short side direction of the storage container 69, and the printed wiring board 56 is arranged on the inner side surface on the opposite side in the short side direction. The assembled battery 55 is located in a space surrounded by the protective sheet 68 and the printed wiring board 56. The lid 70 is attached to the upper surface of the storage container 69.

A heat-shrinkable tape may be used instead of the adhesive tape 54 to fix the assembled battery 55. In this case, protective sheets are arranged on both side surfaces of the assembled battery, the heat-shrinkable tape is circulated, and then the heat-shrinkable tape is heat-shrinked to bind the assembled battery.

Although the unit cells 51 are connected in series in FIGS. 6 and 7, they may be connected in parallel in order to increase the battery capacity. Alternatively, a series connection and a parallel connection may be combined. In addition, the assembled battery packs can be connected in series and / or in parallel.

In addition, the mode of the battery pack is appropriately changed depending on the application. The battery pack is preferably used for charging and discharging with a large current. Specifically, it is used as a power source for digital cameras, in-vehicle vehicles such as two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, assisted bicycles, and railroad vehicles, and as stationary batteries. Can be mentioned. In particular, it is suitable for in-vehicle use.

In a vehicle such as an automobile equipped with the battery pack according to the third embodiment, the battery pack recovers, for example, the regenerative energy of the power of the vehicle.

According to the battery pack of the third embodiment described above, since the secondary battery of the first embodiment is included, it is possible to provide a battery pack having excellent storage performance and cycle characteristics.

(Fourth Embodiment)
According to a fourth embodiment, a vehicle is provided. This vehicle is equipped with the battery pack according to the third embodiment.

In the vehicle according to the fourth embodiment, the battery pack recovers, for example, the regenerative energy of the power of the vehicle.

Examples of vehicles according to the fourth embodiment include two-wheel to four-wheel hybrid electric vehicles, two-wheel to four-wheel electric vehicles, assisted bicycles, and railway vehicles.

The mounting position of the battery pack in the vehicle according to the fourth embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine room of the vehicle, behind the vehicle body, or under the seat.

Next, an example of the vehicle according to the fourth embodiment will be described with reference to the drawings.

FIG. 8 is a cross-sectional view schematically showing an example of the vehicle according to the fourth embodiment.

The vehicle 200 shown in FIG. 8 includes a vehicle body 201 and a battery pack 202. The battery pack 202 can be the battery pack according to the third embodiment.

The vehicle 200 shown in FIG. 8 is a four-wheeled vehicle. As the vehicle 200, for example, a two-wheel to four-wheel hybrid electric vehicle, a two-wheel to four-wheel electric vehicle, an assisted bicycle, and a railroad vehicle can be used.

The vehicle 200 may be equipped with a plurality of battery packs 202. In this case, the battery pack 202 may be connected in series, in parallel, or in combination of series connection and parallel connection.

The battery pack 202 is mounted in an engine room located in front of the vehicle body 201. The mounting position of the battery pack 202 is not particularly limited. The battery pack 202 may be mounted behind the vehicle body 201 or under the seat. The battery pack 202 can be used as a power source for the vehicle 200. In addition, the battery pack 202 can recover the regenerative energy of the power of the vehicle 200.

Next, an embodiment of the vehicle according to the fourth embodiment will be described with reference to FIG. 9.

FIG. 9 is a diagram schematically showing another example of the vehicle according to the fourth embodiment. The vehicle 300 shown in FIG. 9 is an electric vehicle.

The vehicle 300 shown in FIG. 9 includes a vehicle body 301, a vehicle power supply 302, a vehicle ECU (Electric Control Unit) 380 which is a higher control means of the vehicle power supply 302, and an external terminal (for an external power supply). It is provided with a terminal for connection) 370, an inverter 340, and a drive motor 345.

The vehicle 300 mounts the vehicle power supply 302, for example, in the engine room, behind the vehicle body of the vehicle, or under the seat. In the vehicle 300 shown in FIG. 9, the mounting location of the vehicle power supply 302 is schematically shown.

The vehicle power supply 302 includes a plurality of (for example, three) battery packs 312a, 312b and 312c, a battery management device (BMU: Battery Management Unit) 311 and a communication bus 310.

The three battery packs 312a, 312b and 312c are electrically connected in series. The battery pack 312a includes an assembled battery 314a and an assembled battery monitoring device (VTM: Voltage Temperature Monitoring) 313a. The battery pack 312b includes an assembled battery 314b and an assembled battery monitoring device 313b. The battery pack 312c includes an assembled battery 314c and an assembled battery monitoring device 313c. The battery packs 312a, 312b, and 312c can be removed independently and replaced with another battery pack 312.

Each of the assembled batteries 314a to 314c includes a plurality of cells connected in series. At least one of the plurality of cell cells is the secondary battery according to the first embodiment. The assembled batteries 314a to 314c are charged and discharged through the positive electrode terminal 316 and the negative electrode terminal 317, respectively.

The battery management device 311 communicates with the assembled battery monitoring devices 313a to 313c in order to collect information on the maintenance of the vehicle power supply 302, and is included in the assembled batteries 314a to 314c included in the vehicle power supply 302. Collect information about battery voltage, temperature, etc.

A communication bus 310 is connected between the battery management device 311 and the assembled battery monitoring devices 313a to 313c. The communication bus 310 is configured to share a set of communication lines among a plurality of nodes (battery management device and one or more set battery monitoring devices). The communication bus 310 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

The assembled battery monitoring devices 313a to 313c measure the voltage and temperature of the individual cells constituting the assembled batteries 314a to 314c based on a command by communication from the battery management device 311. However, the temperature can be measured at only a few points per set battery, and it is not necessary to measure the temperature of all the cells.

The vehicle power supply 302 may also have an electromagnetic contactor (for example, the switch device 333 shown in FIG. 9) for switching the connection between the positive electrode terminal 316 and the negative electrode terminal 317. The switch device 333 has a precharge switch (not shown) that turns on when the assembled batteries 314a to 314c are charged, and a main switch (not shown) that turns on when the battery output is supplied to the load. Includes. The precharge switch and the main switch include a relay circuit (not shown) that is turned on or off by a signal supplied to a coil arranged in the vicinity of the switch element.

The inverter 340 converts the input direct current voltage into a high voltage of three-phase alternating current (AC) for driving the motor. The three-phase output terminals of the inverter 340 are connected to the input terminals of each of the three phases of the drive motor 345. The inverter 340 controls the output voltage based on the control signal from the battery management device 311 or the vehicle ECU 380 for controlling the operation of the entire vehicle.

The drive motor 345 is rotated by the electric power supplied from the inverter 340. This rotation is transmitted to the axle and drive wheels W, for example, via a differential gear unit.

Although not shown, the vehicle 300 is provided with a regenerative braking mechanism. The regenerative braking mechanism rotates the drive motor 345 when the vehicle 300 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 340 and converted into a direct current. The direct current is input to the vehicle power supply 302.

One terminal of the connection line L1 is connected to the negative electrode terminal 317 of the vehicle power supply 302 via a current detection unit (not shown) in the battery management device 311. The other terminal of the connection line L1 is connected to the negative electrode input terminal of the inverter 340.

One terminal of the connection line L2 is connected to the positive electrode terminal 316 of the vehicle power supply 302 via the switch device 333. The other terminal of the connection line L2 is connected to the positive electrode input terminal of the inverter 340.

The external terminal 370 is connected to the battery management device 311. The external terminal 370 can be connected to, for example, an external power source.

The vehicle ECU 380 manages the entire vehicle by coordinating and controlling the battery management device 311 together with other devices in response to an operation input by the driver or the like. Data related to the maintenance of the vehicle power supply 302, such as the remaining capacity of the vehicle power supply 302, is transferred between the battery management device 311 and the vehicle ECU 380 via a communication line.

The vehicle according to the fourth embodiment includes the battery pack according to the third embodiment. That is, since the vehicle is provided with a battery pack having excellent storage performance and cycle characteristics, the vehicle according to the fourth embodiment is excellent in storage performance and cycle characteristics, and the battery pack is excellent in life performance, so that it is reliable. It is possible to provide a highly reliable vehicle.

(Fifth Embodiment)
According to a fifth embodiment, a stationary power supply is provided. This stationary power supply is equipped with the battery pack according to the third embodiment. The stationary power supply may be equipped with the assembled battery according to the second embodiment or the secondary battery according to the first embodiment instead of the battery pack according to the third embodiment.

The stationary power supply according to the fifth embodiment is equipped with the battery pack according to the third embodiment. Therefore, the stationary power supply according to the fifth embodiment can realize a long life.

FIG. 10 is a block diagram showing an example of a system including a stationary power supply according to a fifth embodiment. FIG. 10 is a diagram showing an example of application to the stationary power supplies 112 and 123 as an example of use of the battery packs 40A and 40B according to the third embodiment. In the example shown in FIG. 10, the system 110 in which the stationary power supplies 112 and 123 are used is shown. The system 110 includes a power plant 111, a stationary power supply 112, a consumer-side power system 113, and an energy management system (EMS) 115. Further, a power network 116 and a communication network 117 are formed in the system 110, and the power plant 111, the stationary power supply 112, the consumer side power system 113 and the EMS 115 are connected via the power network 116 and the communication network 117. The EMS 115 utilizes the power grid 116 and the communication network 117 to control the entire system 110 to be stabilized.

The power plant 111 produces a large amount of electric power from fuel sources such as thermal power and nuclear power. Power is supplied from the power plant 111 through the power grid 116 and the like. A battery pack 40A is mounted on the stationary power supply 112. The battery pack 40A can store electric power and the like supplied from the power plant 111. Further, the stationary power supply 112 can supply the electric power stored in the battery pack 40A through the power grid 116 or the like. The system 110 is provided with a power converter 118. The power converter 118 includes a converter, an inverter, a transformer, and the like. Therefore, the power converter 118 can perform conversion between direct current and alternating current, conversion between alternating currents having different frequencies with respect to each other, transformation (step-up and step-down), and the like. Therefore, the power conversion device 118 can convert the power from the power plant 111 into the power that can be stored in the battery pack 40A.

The consumer-side power system 113 includes a factory power system, a building power system, a household power system, and the like. The consumer-side power system 113 includes a consumer-side EMS 121, a power conversion device 122, and a stationary power supply 123. The battery pack 40B is mounted on the stationary power supply 123. The consumer-side EMS 121 controls to stabilize the consumer-side power system 113.

The electric power from the power plant 111 and the electric power from the battery pack 40A are supplied to the electric power system 113 on the consumer side through the electric power network 116. The battery pack 40B can store the electric power supplied to the consumer side electric power system 113. Further, the power conversion device 122 includes a converter, an inverter, a transformer, and the like, similarly to the power conversion device 118. Therefore, the power converter 122 can perform conversion between direct current and alternating current, conversion between alternating currents having different frequencies with respect to each other, transformation (step-up and step-down), and the like. Therefore, the power conversion device 122 can convert the power supplied to the consumer side power system 113 into the power that can be stored in the battery pack 40B.

The electric power stored in the battery pack 40B can be used, for example, for charging a vehicle such as an electric vehicle. Further, the system 110 may be provided with a natural energy source. In this case, the renewable energy source generates electric power by natural energy such as wind power and solar power. Then, power is supplied from the natural energy source in addition to the power plant 111 through the power grid 116.

Examples will be described below, but the embodiments are not limited to the examples described below.

In a secondary battery using an aqueous electrolyte, the voltage generated cannot be increased by using only one type of electrolyte. In the following examples, the experiment was conducted while changing the concentrations of the water-based electrolyte on the positive electrode side and the water-based electrolyte on the negative electrode side.

(Example 1)
A secondary battery was manufactured by the following procedure.

<Cathode preparation>
A positive electrode was prepared as follows.
_{LiMn 2} O ₄ (5 g) as the positive electrode active material, acetylene black (0.25 g) as the conductive agent, and PVDF dispersion liquid (NMP solution with a solid content of 8%, 6.25 g) as the binder (binder resin). Was mixed for 3 minutes using a kneader to obtain a viscous slurry. This slurry was applied on one side of the Ti foil. Then, the solvent was distilled off at 120 ° C. to obtain a laminate. The laminate was then rolled using a roll press. Then, after the laminated body was dried, it was punched into a circle having a diameter of 10 mm. The basis weight of the obtained positive electrode was 116 g / m ² .

<Manufacturing of negative electrode>
_{Li 4} Ti ₅ O ₁₂ (10 g) as the negative electrode active material, graphite (1 g) as the conductive agent, PTFE dispersion (solid content 40% by weight, 1 g) as the binder (binder resin), and NMP (N-methyl). 8 g of -2-pyrrolidone) was mixed for 3 minutes using a kneader to obtain a slurry. This slurry was applied on one side of the Zn foil. Then, the solvent was distilled off at 120 ° C. to obtain a laminate. The laminate was then rolled using a roll press. Then, after the laminated body was dried, it was punched into a circle having a diameter of 10 mm. The basis weight of the obtained negative electrode was 35 g / m ² .

<Adjustment of water-based electrolyte>
The positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte were adjusted using the lithium salt concentration, osmoregulation agent, and surfactant of the positive electrode side and negative electrode side aqueous electrolytes shown in Table 1.

<Surfactant>
Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers _{(e.g., C 12 H 25 O (CH} 2 CH 2 O) nH; 0.9 <n ≦ 2.1) and polyoxyalkylene alkyl Ether (for example, C ₁₂ H ₂₅ O [(CH ₂ CH (CH ₃ ) O) m · (CH ₂ CH ₂ O) n] H; 0 <n ≦ 35, 0 <m ≦ 40, or C ₄ H ₉ O (CH ₂ CH ₂ O) n [(CH ₂ CH (CH ₃ ) O) m] H; it can. The above numerical range for the subscript n in the chemical formula C ₁₂ H ₂₅ O (CH ₂ CH _{2 O) nH of the polyoxyethylene alkyl ether includes 0.89 <n ≦ 2.1.} Further, as a specific example of the polyoxyalkylene alkyl ether represented by the chemical formula C ₁₂ H ₂₅ O [(CH ₂ CH (CH ₃ ) O) m · (CH ₂ CH ₂ O) n] H, the subscripts n and m are 1 respectively. Examples thereof include compounds having .4 ≦ n ≦ 35 and 8.4 ≦ m ≦ 40. In the examples, polyoxyalkylene alkyl ether (C ₁₂ H ₂₅ O [(CH ₂ CH (CH ₃ ) O) m · (CH ₂ CH ₂ O) n] H; 0 <n ≦ 35, 0 <m ≦ 40) A surfactant with a molecular weight of 2000, n = 10, m = 40, a surfactant with a molecular weight of 500, n = 1.4, m = 8.4, B, a molecular weight of 3238, n = 35, m = The surfactant of 28 was C, the surfactant having a molecular weight of 2000, n = 10, and m = 30 was D, and the surfactant was used. In Example 1, surfactant A was used.

<Making test batteries>
An anodized aluminum plate was fixed on a plastic plate, and a negative electrode was fixed on the anodized aluminum plate. A Ti plate was fixed on another plastic plate, and a positive electrode was fixed on the Ti plate. The prepared negative electrode side aqueous electrolyte was dropped onto the negative electrode, and a separator was placed on the negative electrode to bring them into close contact with each other. An aqueous electrolyte on the positive electrode side was dropped on the opposite side of the separator, and the positive electrode was placed on the positive electrode to bring them into close contact with each other, and further fixed with screws.

The following measurements were performed on the prepared secondary battery.

<Osmotic pressure measurement>
The osmotic pressure of the battery after the constant current charge / discharge test was measured. The volume V (m ³ ) of the electrolyte solvent, the amount of substance of the solute in the electrolyte (total number of moles) is n (mol), the gas constant is R (m ² · kg / (s ² · K · mol)), and the electrolyte The absolute temperature of was T (K), and the osmotic pressure was calculated. The results are shown in Table 1.

<Measurement of air permeability coefficient>
It was disassembled from the battery and the separator was separated from the other parts of the battery. After rinsing both sides of the separator with pure water, the separator was immersed in pure water and left for 48 hours or more. Then, both sides were further rinsed with pure water, dried in a vacuum drying oven at 100 ° C. for 48 hours or more, and then the air permeability coefficient was measured. The thickness (m) of the separator was measured at four points of the separator taken out in this way. A separator is sandwiched between a pair of stainless steel plates having holes with a diameter of 10 mm at each of the four measurement points, and air is sent at pressure p from the holes in one of the stainless steel plates. The pressure p used was 1000 Pa, 2500 Pa, 4000 Pa and 6000 Pa. Then, the gas amount Q of the air leaking from the hole of the other stainless steel plate was measured. The area of the hole (25π mm ² ) was taken as the measurement area A, and 0.000018Pa · s was used as the viscosity coefficient σ. ^{The gas amount Q was calculated by measuring the amount δ (m 3} ) leaking from the hole in 100 seconds and dividing the measured amount δ by 100.

The gas amount Q with respect to the pressure p was plotted at the four measured points, and the slope (dQ / dp) of the gas amount Q with respect to the pressure p was calculated by linear fitting (least squares method). Then, the calculated slope (dQ / dp) was multiplied by (σ · L) / A to calculate the air permeability coefficient KT. Then, the value at the place where the air permeability coefficient is the lowest value among the four places is set as the air permeability coefficient of the separator and is shown in Table 1.

Table 3 shows the types and concentrations of lithium salts of the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte, the types and concentrations of the osmotic pressure adjusting agent, and the types and concentrations of the surfactant. Table 5 shows the positive electrode side aqueous electrolytes. Describes the interfacial tension (mN / m) and osmotic pressure (N / m ² ) separator air permeability coefficient (m ² ), osmotic pressure difference (%), cycle characteristics (times), and Coulomb efficiency (%) of the negative electrode side aqueous electrolyte. did. The measurements of Examples 2-38 and Comparative Example 1-2, which will be described later, were also carried out in the same manner as in Example 1.

<Constant current charge / discharge test>
For each Example and each Comparative Example, the test was started promptly without waiting time after the test battery was prepared. Both charging and discharging were performed at a 0.5 C rate. Further, at the time of charging, the termination condition was set to the earlier of the current value of 0.25 C, the charging time of 130 minutes, and the charging capacity of 170 mAh / g. At the time of discharge, the termination condition was 130 minutes later.

Performing the above charging once and performing the above discharging once is regarded as one cycle of charging and discharging, the discharging capacity of the 50th cycle is set to 100%, and the cycle is repeated so that the discharging capacity becomes 80% with respect to 50 cycles. The number was used as the cycle characteristic. Further, the coulombic efficiency was calculated by the following method from the charge capacity and the discharge capacity at the 50th cycle. If the Coulomb efficiency is good, the storage performance is also good, so the storage performance was measured using the Coulomb efficiency. Since the Coulomb efficiency became stable at the 50th cycle, the 50th cycle was used.
Coulomb efficiency (%) = 100 x (discharge capacity / charge capacity)

Examples 2-20 are adjusted by using the lithium salt concentration of the positive electrode side and the negative electrode side aqueous electrolyte, an osmotic pressure adjusting agent (a compound whose osmotic pressure can be adjusted), and a surfactant, respectively, as shown in Table 3. A secondary battery was produced in the same manner as in Example 1, and the interfacial tension measurement, osmotic pressure measurement, osmotic pressure difference measurement, cycle characteristics, and Coulomb efficiency were evaluated. The evaluation results are shown in Table 5. Examples 21-44 and Comparative Examples 1 and 2 were adjusted by using the lithium salt concentration, the osmometer, and the surfactant of the positive electrode side and the negative electrode side aqueous electrolytes, respectively, as shown in Table 4, respectively, and Example 1 A secondary battery was prepared in the same manner as in the above, and the interfacial tension measurement, osmometer measurement, osmometer difference measurement, cycle characteristics, and Coulomb efficiency were evaluated. The evaluation results of Examples 21-44 and Comparative Examples 1 and 2 are shown in Table 6. "-" In the table indicates that it is not added.

Comparing Examples 1-44 and Comparative Examples 1 and 2, it can be seen that the cycle characteristics and the Coulomb efficiency decreased when the osmotic pressure difference became larger than 90%. It is considered that this is because the positive electrode side water-based electrolyte and the negative electrode side water-based electrolyte are mixed, so that the water-based electrolyte does not reach an appropriate pH range and water electrolysis occurs.

Further, in Examples 37 and 38, although the osmotic pressure difference was 90% or less, the cycle characteristics and the Coulomb efficiency were poor as compared with the other Examples. It is considered that this is because in Example 37, the interfacial tension was larger than 50 mN / m, so that it was difficult to soak into the separator. In Example 38, the air permeability coefficient of the separator ^{was larger than 1 × 10 -14} m ^2, and it is considered that the aqueous electrolyte was mixed as compared with other Examples.

Even in the examples, it can be seen that higher cycle characteristics and Coulomb efficiency can be realized when the osmotic pressure difference is 50% or less. According to at least one embodiment and embodiment described above, a secondary battery is provided. This secondary battery includes a positive electrode, a first aqueous electrolyte held in the positive electrode, a negative electrode, a second aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode. The difference between the osmotic pressure of the aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is 90% or less with respect to the larger of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. Therefore, it is possible to provide a secondary battery having excellent storage performance and cycle characteristics.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Electrode group, 2 ... Container (exterior member), 3 ... Positive electrode, 3a ... Positive electrode current collector, 3b ... Positive electrode layer, 4 ... Negative electrode, 4a ... Negative electrode current collector, 4b ... Negative electrode layer, 5 ... Separator, 6 ... Positive electrode lead, 7 ... Negative electrode lead, 8 ... Positive electrode conductive tab, 9 ... Negative electrode conductive tab, 10 ... Seal plate, 11 ... Insulation member, 12 ... Negative electrode terminal, 13 ... Positive electrode terminal, 31 ... Assembly battery, 32 _{1-3 5, 43} 1 to 43 5 _... secondary battery, 33 ... lead, 40, 40A, 40B ... battery pack, 41 ... housing, 42 ... battery pack, 44 ... opening, 45 ... positive terminal for output, 46 ... output Negative electrode terminal, 51 ... unit cell, 55 ... assembled battery, 56 ... printed wiring board, 57 ... thermista, 58 ... protection circuit, 59 ... external terminal for energization, 110 ... system, 111 ... power plant, 112 ... for stationary Power supply, 113 ... Consumer side power system, 116 ... Power network, 117 ... Communication network, 118 ... Power conversion device, 121 ... Power conversion device, 122 ... Power conversion device, 123 ... Stationary power supply, 200 ... Vehicle, 201 ... Vehicle Main body, 202 ... Battery pack, 300 ... Vehicle, 301 ... Vehicle main body, 302 ... Vehicle power supply, 310 ... Communication bus, 311 ... Battery management device, 312a to 312c ... Battery pack, 313a to 313c ... Assembly battery monitoring device, 314a ~ 314c ... assembled battery, 316 ... positive electrode terminal, 317 ... negative electrode terminal, 333 ... switch device, 340 ... inverter, 345 ... drive motor, 370 ... external terminal, 380 ... vehicle ECU, L1, L2 ... connection line, W ... drive ring.

Claims (13)

With the positive electrode
The first aqueous electrolyte held on the positive electrode and
With the negative electrode
The second aqueous electrolyte held in the negative electrode and
A separator interposed between the positive electrode and the negative electrode,
With
The difference between the osmotic pressure of the first aqueous electrolyte (N / m ² ) and the osmotic pressure of the second aqueous electrolyte (N / m ² ) is the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. A secondary battery having a osmotic pressure of 90% or less (including 0%) with respect to the larger one. The difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is 80% with respect to the larger of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. The secondary battery according to claim 1, which is as follows. The difference between the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte is 50% with respect to the larger of the osmotic pressure of the first aqueous electrolyte and the osmotic pressure of the second aqueous electrolyte. The secondary battery according to claim 1 or 2, which is as follows. The secondary battery according to any one of claims 1 to 3, wherein at least one of the first aqueous electrolyte and the second aqueous electrolyte contains a compound whose osmotic pressure can be adjusted. The secondary battery according to claim 4, wherein the compound whose osmotic pressure can be adjusted includes at least one of an inorganic compound, an organic compound and a surfactant. The secondary battery according to any one of claims 1 to 5, wherein the separator has an air permeability coefficient of 1 × 10 ^-14 m ^{2 or less.} The secondary battery according to any one of claims 1 to 6, wherein the interfacial tension of the first aqueous electrolyte and the second aqueous electrolyte, whichever is greater, is 50 mN / m or less. The second item according to any one of claims 1 to 7, wherein the negative electrode active material included in the negative electrode is at least one selected from the group consisting of titanium oxide, lithium titanium oxide, and lithium titanium composite oxide. Next battery. A battery pack comprising the secondary battery according to any one of claims 1 to 8. With an external terminal for energizing
The battery pack according to claim 9, further comprising a protection circuit. The battery pack according to any one of claims 9 to 10, further comprising the plurality of the secondary batteries, wherein the secondary batteries are electrically connected in series, in parallel, or in series and in parallel. A vehicle equipped with the battery pack according to any one of claims 9 to 11. A stationary power supply comprising the battery pack according to any one of claims 9 to 11.

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