CN112615067A

CN112615067A - Secondary battery, battery pack, vehicle, and stationary power supply

Info

Publication number: CN112615067A
Application number: CN202010659895.5A
Authority: CN
Inventors: 关隼人; 海野航; 堀田康之; 松野真辅
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2019-09-19
Filing date: 2020-07-10
Publication date: 2021-04-06
Anticipated expiration: 2040-07-10
Also published as: JP7475942B2; CN112615067B; JP2021051990A

Abstract

The present invention provides a secondary battery having excellent storage performance and cycle efficiency. The secondary battery of the embodiment comprises a positive electrode, a 1 st aqueous electrolyte held in the positive electrode, a negative electrode, a 2 nd aqueous electrolyte held in the negative electrode, and a positive electrode and a negative electrode interposed therebetweenThe osmotic pressure (N/m) of the intermediate separator, 1 st aqueous electrolyte²) Osmotic pressure (N/m) with 2 nd aqueous electrolyte²) The difference in (b) is 90% or less (including 0%) with respect to the greater of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte.

Description

Secondary battery, battery pack, vehicle, and stationary power supply

Cross Reference to Related Applications

The present application is based on the claims of priority from japanese patent application No. 2019-170917, filed on 19.9.2019, and from japanese patent application No. 2020-072134, filed on 14.4.2020, which are hereby incorporated by reference in their entirety.

Technical Field

Embodiments of the present invention relate to a secondary battery, a battery pack, a vehicle, and a stationary power supply.

Background

Nonaqueous electrolyte batteries, particularly secondary batteries, using a carbon material and a lithium titanium oxide as a negative electrode active material and a layered oxide containing nickel, cobalt, manganese, and the like as a positive electrode active material have been put to practical use as power sources in a wide range of fields.

On the other hand, since most organic solvents are combustible substances, the safety of a secondary battery is liable to be inferior to that of a secondary battery using an aqueous solution in principle. Various measures have been taken to improve the safety of secondary batteries using organic solvent-based electrolytes, but these measures are not necessarily sufficient. In addition, since a nonaqueous secondary battery requires a dry environment in a manufacturing process, manufacturing costs inevitably increase. In addition, the organic solvent-based electrolyte has poor conductivity, and thus the internal resistance of the nonaqueous secondary battery is likely to be increased. Such a problem is a major problem in electric vehicles and hybrid electric vehicles in which battery safety and battery cost are important, and in large-sized storage batteries for power storage. In order to solve the problems of nonaqueous secondary batteries, secondary batteries using an aqueous electrolyte have been proposed. In the aqueous electrolyte, it is necessary to maintain the potential range in which the charge and discharge of the battery are performed within a potential range in which the electrolytic reaction of water contained as a solvent does not occur. For example, by using a lithium manganese oxide as the positive electrode active material and a lithium vanadium oxide as the negative electrode active material, electrolysis of the aqueous solvent can be avoided. In these combinations, although an electromotive force in the range of 1 to 1.5V can be obtained, it is difficult to obtain a sufficient energy density as a battery.

In order to obtain sufficient electromotive force, even if the combination of the positive electrode active material and the negative electrode active material is devised, electrolysis is performed in an aqueous systemIn the electrolyte, the potential for lithium intercalation and deintercalation due to lithium titanium oxide is about 1.5V (vs. Li/Li) based on the lithium potential⁺) However, electrolysis of the aqueous electrolyte is likely to occur, and the active material is likely to be separated from the current collector due to the influence thereof. Therefore, such a battery is unstable in operation and is difficult to be satisfactorily charged and discharged.

In the prior art, a lithium secondary battery having sufficient energy density, excellent storage performance and cycle characteristics, and low cost and high safety can be provided by including zinc in a current collector, but there is still room for improvement in storage performance and cycle characteristics.

Disclosure of Invention

An object of an embodiment is to provide a secondary battery using an aqueous electrolyte, which is excellent in storage performance and cycle characteristics.

The secondary battery of the embodiment includes a positive electrode, a 1 st aqueous electrolyte held in the positive electrode, a negative electrode, a 2 nd aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode. Osmotic pressure (N/m) of the 1 st aqueous electrolyte²) Osmotic pressure (N/m) with 2 nd aqueous electrolyte²) The difference in (b) is 90% or less (including 0%) with respect to the greater of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of a secondary battery according to embodiment 1.

Fig. 2 is a cross-sectional view schematically showing another example of the secondary battery according to embodiment 1.

Fig. 3 is an enlarged sectional view of a portion a of fig. 2.

Fig. 4 is a perspective view showing an example of the assembled battery according to embodiment 2.

Fig. 5 is a perspective view showing an example of the battery pack according to embodiment 3.

Fig. 6 is an exploded perspective view of another example of the battery pack according to embodiment 3.

Fig. 7 is a block diagram showing a circuit of the battery pack of fig. 6.

Fig. 8 is a sectional view schematically showing a vehicle according to an example of embodiment 4.

Fig. 9 is a view schematically showing a vehicle according to another example of embodiment 4.

Fig. 10 is a block diagram showing an example of a system including the stationary power supply according to embodiment 5.

Detailed Description

Hereinafter, embodiments will be described with reference to the drawings. In the through embodiments, the same reference numerals are given to the common components, and redundant description is omitted. The drawings are schematic views for facilitating description of the embodiments and understanding thereof, and the shapes, dimensions, proportions, and the like of the drawings are different from those of actual apparatuses, but they can be appropriately modified in design by referring to the following description and known techniques. Unless otherwise specified, the values at 25 ℃ and 1 atmosphere (atmospheric pressure) are indicated.

(embodiment 1)

The secondary battery according to embodiment 1 includes a positive electrode, a 1 st aqueous electrolyte held in the positive electrode, a negative electrode, a 2 nd aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the osmotic pressure (N/m) of the 1 st aqueous electrolyte²) Osmotic pressure (N/m) with 2 nd aqueous electrolyte²) The difference in (b) is 90% or less with respect to the greater of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte. For example, when a water system electrolyte having a small osmotic pressure is used as the 1 st water system electrolyte and a water system electrolyte having a large osmotic pressure is used as the 2 nd water system electrolyte, the osmotic pressure can be expressed as ((absolute value of difference between osmotic pressure of the 1 st water system electrolyte and osmotic pressure of the 2 nd water system electrolyte) ÷ (osmotic pressure of the 2 nd water system electrolyte)) × 100%.

The secondary battery according to the present embodiment may further include a compound capable of adjusting osmotic pressure. Compounds that can regulate osmotic pressure are also sometimes referred to as osmoregulators for convenience. Specific examples of the compound capable of adjusting osmotic pressure will be described later. By using the compound capable of adjusting the osmotic pressure, the concentrations of the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte can be adjusted, the osmotic pressure difference between the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte can be reduced, and the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte can be prevented from mixing. If the mixing of the aqueous electrolyte can be prevented in this manner, the cycle characteristics of the secondary battery can be improved.

In particular, when an aqueous electrolyte is used, water electrolysis may occur as a side reaction of the aqueous electrolyte. In the electrolysis of water, a chemical reaction represented by formula (1) occurs in the negative electrode, and a chemical reaction represented by formula (2) occurs in the positive electrode.

In addition, in an oxidation-reduction reaction of an aqueous electrolyte such as electrolysis of water, there are potential windows in which decomposition by an oxidation reaction does not occur and potential windows in which decomposition by a reduction reaction does not occur. For example, in the electrolysis of water, if the relationship expressed by the formula (3) is established with respect to the potential E1 of the negative electrode according to the nernst formula, hydrogen is easily generated in the negative electrode by the reduction reaction. Further, if the relationship expressed by the formula (4) is established with respect to the potential E2 of the positive electrode, oxygen is easily generated in the positive electrode by the oxidation reaction. Here, in the formulae (3) and (4), pH represents pH of the aqueous electrolyte.

E1＜－0.059×pH (3)

E2＞1.23－0.059×pH (4)

According to the formulas (3) and (4), when the aqueous electrolyte cannot be separated on the negative electrode side and the positive electrode side, electrolysis of water is thermodynamically easily generated if the voltage between the negative electrode and the positive electrode is greater than 1.23V regardless of the pH of the aqueous electrolyte. Even if a separator having low gas permeability is used as the separator, if the movement of the aqueous electrolyte is completely inhibited, the movement of cations is inhibited, and the performance of the secondary battery is degraded.

Further, if the lithium salt concentration is different between the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte, water is more likely to move, and the reaction represented by the above formula occurs, which tends to degrade the performance of the secondary battery.

Therefore, in order to suppress the movement of the aqueous electrolyte, at least one of the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte is provided with an osmotic pressure regulator, and by setting the difference between the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte to 90% or less (including 0%) with respect to the larger of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte, the movement of the aqueous electrolyte can be suppressed, and the electrolysis of water can be suppressed. If the osmotic pressure difference is greater than 90% of the side where the osmotic pressure is large, the mixing of the aqueous electrolyte on the positive electrode side and the aqueous electrolyte on the negative electrode side due to the osmotic pressure becomes severe, which is not preferable. The osmotic pressure regulator preferably contains at least 1 of an inorganic compound, an organic compound, and a surfactant.

In addition, since the salt concentration of both the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte is increased by the movement of the aqueous electrolyte, the deposition of salt on the electrode can be suppressed. With such a configuration, the increase in resistance associated with salt precipitation and the deterioration in capacity during a long-term cycle test can be suppressed, and the storage performance can be improved. By improving the storage performance, coulombic efficiency can also be improved. This is because the coulombic efficiency indicates the slope of the self-discharge. Therefore, as long as the coulombic efficiency is good, i.e., as long as it is high, the storage performance is also good.

Further, it is more preferable to set the difference between the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte to 80% or less of the greater one of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte, because mixing of the positive and negative aqueous electrolytes due to the difference in osmotic pressures can be sufficiently suppressed kinetically.

More preferably 50% or less. By setting the range, mixing of the aqueous electrolyte due to osmotic pressure can be suppressed for a long period of time, and therefore, storage performance can be improved and coulombic efficiency can also be improved. In addition, the cycle life can be greatly improved.

By setting the difference between the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte to 90% or less with respect to the greater of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte, aqueous electrolytes having different pH values and different types of aqueous electrolytes can be used as the positive-side aqueous electrolyte and the negative-side aqueous electrolyte, and here, by using an aqueous electrolyte having a lower pH value than the negative-side aqueous electrolyte as the positive-side aqueous electrolyte, water electrolysis is less likely to occur even if the voltage between the negative electrode and the positive electrode is greater than 1.23V. 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, it is considered that water electrolysis is difficult to occur unless the voltage between the negative electrode and the positive electrode is increased to about 2V.

The materials of the respective members usable in the secondary battery according to example 1 will be described in detail.

(aqueous electrolyte)

Examples of the aqueous electrolyte include an aqueous electrolyte solution containing an aqueous solvent and the 1 st electrolyte, and a gel-like aqueous electrolyte in which a polymer material is compounded in the aqueous electrolyte solution. The aqueous electrolyte and the gel-like aqueous electrolyte are collectively referred to as an aqueous electrolyte, and the electrolyte as a solute is referred to as a 1 st electrolyte for the sake of distinguishing the electrolyte as a solute. Examples of the polymer material include polyvinylidene fluoride (PVdF), Polyacrylonitrile (PAN), and polyethylene oxide (PEO). The aqueous electrolyte contains NO₃ ^-、Cl^-、LiSO₄ ^-、SO₄ ^2-And OH^-At least 1 anion. These anions contained in the aqueous electrolyte may be 1 kind, or may contain 2 or more kinds of anions.

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

The amount of the aqueous electrolyte (for example, the amount of water in the aqueous solvent) is preferably 1mol or more based on 1mol of the salt to be a solute. More preferably, the amount of the water solvent is 3.5mol or more based on 1mol of the salt to be a solute.

As the 1 st electrolyte, an electrolyte that dissociates when dissolved in an aqueous solvent to generate the anion can be used. In particular, lithium salts that can be dissociated into Li ions and the above anions are preferable. Examples of such lithium salts include LiNO₃、LiCl、Li₂SO₄LiOH, etc.

In addition, the lithium salt dissociated into Li ions and the above anions has a relatively high solubility in an aqueous solvent. Therefore, an aqueous electrolyte having a high anion concentration of 1 to 10M, Li and excellent ion diffusibility can be obtained.

Containing NO₃ ^-And/or Cl^-The electrolyte of (3) can be used in a wide range of anion concentration ranging from 0.1 to 10M. From the viewpoint of satisfying both ion conductivity and lithium equilibrium potential, it is preferable that the concentration of these anions is as high as 3 to 12M. More preferably NO₃ ^-And/or Cl^-The aqueous electrolyte of (2) has an anion concentration of 8 to 12M.

Containing LiSO₄ ^-And/or SO₄ ^2-The aqueous electrolyte of (3) can be used in an anion concentration range of 0.05 to 2.5M. From the viewpoint of ionic conductivity, it is preferable that the concentration of these anions is as high as 1.5 to 2.5M.

In particular, in the presence of NO₃ ^-、Cl^-、LiSO₄ ^-、SO₄ ^2-In the case of 1 or more kinds of the aqueous electrolytes, the anion concentration of the positive electrode-side aqueous electrolyte is preferably in the range of 0.5 to 3M. If the concentration of the lithium salt is higher than this, the lithium intercalation/deintercalation potential shifts in the direction of the high potential, and the side reaction becomes severe, which is not preferable. In addition, in the presence of NO₃ ^-、Cl^-、LiSO₄ ^-、SO₄ ^2-In the case of 1 or more kinds of aqueous electrolytes, the negative electrode-side aqueous electrolyte preferably has an anion concentration in the range of 6 to 13M. If the lithium ion concentration is lower than this, lithium is intercalated and deintercalatedIs not preferable because the potential of (2) is shifted in the low potential direction and side reactions become severe.

OH in aqueous electrolytes^-The concentration is preferably 10^-10-0.1M。

The aqueous electrolyte may contain both lithium ions and sodium ions.

The pH of the aqueous electrolyte is preferably 1 or more and 7 or less. If the pH of the aqueous electrolyte of the positive electrode is 8 or more, the oxygen generation reaction due to the electrolysis of water favorably progresses, and if the pH is less than 1, the decomposition of the active material proceeds, which is not preferable. The aqueous electrolyte of the negative electrode is preferably pH7 or more and 14 or less, and if it is less than 7, the hydrogen generation reaction due to electrolysis of water favorably progresses, which is not preferable. The solute 1 in the aqueous electrolyte can be qualitatively and quantitatively determined by ion chromatography, for example. Ion chromatography is particularly preferred as an analysis method because of its high sensitivity. The following shows an example of specific measurement conditions for qualitative and quantitative analysis of a solute contained in an electrolyte by ion chromatography:

the system comprises the following steps: prominence HIC-SP

And (3) analyzing the column: shim-pack IC-SA3

Protection of the column: shim-pack IC-SA3(G)

Eluent: 3.6mmol/L aqueous sodium carbonate solution

Flow rate: 0.8mL/min

Column temperature: 45 deg.C

Injection amount: 50 μ L

And (3) detection: electrical conductivity of

Whether or not the aqueous electrolyte contains water can be confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). The water content in the aqueous electrolyte can be calculated by, for example, a luminescence analysis by Inductively Coupled Plasma (ICP). The number of moles of the solvent can be calculated by measuring the specific gravity of the aqueous electrolyte. The aqueous electrolyte may be used on the positive electrode side and the negative electrode side, and may be used on the negative electrode side.

On the positive sideIn the aqueous electrolyte, an inorganic compound, an organic compound, or a surfactant can be used as the osmotic pressure regulator. The inorganic compound is preferably an oxide or an inorganic compound containing a chloride ion (Cl) selected from the group consisting of^-) Fluoride ion (F)^-) Iodide ion (I)^-) Perchloric acid ion (ClO)₄ ^-) Formic acid ion (HCO)₂ ^-) Acetic acid ion (C)₂H₃O₂ ^-) Hydrate ion (OH)^-) Oxalic acid ion (C)₂O₂ ^-) Nitrate ion (NO)₃ ^-) Nitrite ion (NO)₂ ^-) Sulfuric acid ion (SO)₄ ^2-) Thiosulfuric acid ion (S)₂O₃ ^2-) Sulfite ion (SO)₃ ^2-) Carbonic acid ion (CO)₃ ^2-) Bicarbonate ion (HCO)₃ ^2-) Thiocyanate ion (SCN)^-) Ammonium ion (NH)₄ ⁺) Phosphate ion (PO)₄ ^3-) And hydrogen phosphate ion (HPO)₄ ^2-) At least 1 compound of (1). Examples thereof include sodium chloride, potassium chloride, zinc chloride, sodium fluoride, calcium perchlorate, ammonium formate, potassium acetate, sodium acetate, potassium hydroxide, sodium hydroxide, oxalic acid, potassium oxalate, ammonium oxalate, nitric acid, potassium nitrate, sodium nitrite, ammonium sulfite, sodium sulfate, sulfuric acid, ammonium thiosulfate, potassium thiosulfate, ammonium carbonate, potassium carbonate, ammonium bicarbonate, potassium bicarbonate, ammonium thiocyanate, potassium thiocyanate, ammonium phosphate, potassium phosphate, ammonium hydrogen phosphate, and potassium hydrogen phosphate.

As the organic compound, a compound which is dissolved in an aqueous electrolyte but does not undergo reaction or oxidation is preferable as in the case of the inorganic compound. Examples of the solvent include alcohols such as methanol, ethanol, butanol, isobutanol, isopropanol, n-propanol, t-butanol, sec-butanol, 1, 3-butanediol, 1, 4-butanediol, 2-ethyl-1-hexanol and benzyl alcohol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexyl ketone and diacetone alcohol, esters such as ethyl acetate, methyl acetate, butyl acetate, sec-butyl acetate, methoxybutyl acetate, pentyl acetate, n-propyl acetate, isopropyl acetate, ethyl lactate, methyl lactate, butyl lactate and ethyl 3-ethoxypropionate, ethers such as isopropyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, 1, 4-dioxane, tetrahydrofuran and methyl t-butyl ether, ethers such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, ethylene glycol monoethyl ether acetate, and the like, Glycols such as propylene glycol monomethyl ether acetate, butyl carbitol acetate, and ethyl carbitol acetate, glycol ethers such as methyl carbitol, ethyl carbitol, butyl carbitol, methyl triethylene glycol, propylene glycol monomethyl ether, propylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, hexyl diethylene glycol, propylene glycol monomethyl ether propionate, and dipropylene glycol methyl ether, glymes such as monoglyme, diglyme, ethyl glyme, ethyl diglyme, triglyme, butyl diglyme, tetraglyme, and dipropylene glycol dimethyl ether, glymes such as dimethylformamide, dimethylacetamide, hexamethylphosphoric triamide, acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, dodecanonitrile, 2-methylbutyronitrile, butyronitrile, and the like, Aprotic polar solvents such as trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, acrylonitrile, methacrylonitrile, butenenitrile, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and γ -butyrolactam, cyclic carboxylic acid esters such as γ -butyrolactone, γ -valerolactone, γ -caprolactone, and ∈ -caprolactone, chain carbonate compounds such as dimethyl carbonate, diethyl carbonate, di-N-propyl carbonate, diisopropyl carbonate, N-propyl isopropyl carbonate, methylethyl carbonate, and methyl-N-propyl carbonate, and amine solvents such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, triethanolamine, and N, N-diisopropylethylamine, and organic compounds having miscibility with water.

As the osmotic pressure regulator, a surfactant may be added to the aqueous electrolyte. Examples of the surfactant include nonionic surfactants such as polyoxyalkylene alkyl ethers, polyethylene glycols, polyvinyl alcohols, thiourea, 2 sodium 3, 3' -dithiobis (1-propanephosphonic acid), dimercaptothiadiazole, boric acid, oxalic acid, malonic acid, saccharin, sodium naphthalenesulfonate, gelatin, potassium nitrate, aromatic aldehydes, heterocyclic aldehydes, and the like. The surfactants may be used alone or in combination of 2 or more. These osmotic pressure regulators may be used alone or in combination of 2 or more types, regardless of the inorganic compound, organic compound, or surfactant, with respect to the aqueous electrolyte. By adding these substances, the osmotic pressure with the aqueous electrolyte on the negative electrode side can be adjusted. As the osmotic pressure regulator on the negative electrode side, the same osmotic pressure regulator as that on the positive electrode can be used.

By adding the osmotic pressure adjusting agent in this manner, 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 where the osmotic pressure is higher.

Here, the osmotic pressure pi (N/m)²) This can be calculated as follows. That is, if the volume of the solvent in the electrolyte (electrolytic solution) is set to V (m)³) The amount of substance (total number of moles) of solute in the electrolyte is n (mol), and the gas constant is R (m)²·kg/(s²K · mol)), and the absolute temperature of the electrolyte is set to t (K), the osmotic pressure Π can be calculated according to the following formula (5).

Π＝(n·R·T)/V (5)

Here, when the aqueous electrolyte is an aqueous electrolyte solution, the solute (1 st electrolyte) of the aqueous electrolyte solution is an inorganic salt, an organic compound, or the like. Inorganic salts can be used for structural identification by ICP emission analysis, and organic compounds can be used for structural identification by Fourier transform Infrared Spectroscopy (FTIR). Then, the concentration of the aqueous electrolytic solution is calculated by fractionating the electrolyte (aqueous electrolytic solution), and the amount of substances such as inorganic salts and organic compounds in the aqueous electrolytic solution is calculated. The amount of substance n is the total number of moles of solute, and the ionization of the solute is also considered. In fact, when the solute is an inorganic salt, an organic compound, or the like, it is considered that all of the solute is ionized in the aqueous electrolytic solution. For example, when the solute is an alkali metal salt or an alkaline earth metal salt, the alkali metal ion and the alkaline earth ion are considered to be ionized together with the anion, and the substance amount n is calculated. For example, in the form of a solute having dissolved therein 12mol/LLiCl is ionized into Li in an aqueous electrolyte⁺And Cl^-Therefore, the concentration was considered to be 24 mol/L.

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, or may be contained in both of them. The molar concentration of the osmotic pressure regulator contained in the aqueous electrolyte is, for example, 2mol/L to 8mol/L when the osmotic pressure regulator is added to the positive electrode-side aqueous electrolyte. When the molar concentration of the osmotic pressure regulator in the positive electrode-side aqueous electrolyte is within this range, the osmotic pressure difference can be obtained without hindering the operation of the secondary battery. More preferably 2.5mol/L or more and 7mol/L or less.

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

Whether or not the surfactant is contained in the aqueous electrolyte can be examined by the above-mentioned GC-MS. For example, an aqueous electrolyte is extracted with n-hexane, and an organic solvent in the aqueous electrolyte is separated. The identification can be performed by GC-MS and Nuclear Magnetic Resonance (NMR) measurement of the separated organic solvent.

In addition, the molecular weight of the surfactant can be determined by MALDI-TOF-MS (Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) analysis. As the apparatus, for example, JMS-S3000Spiral TOF manufactured by JEOL (JEOL) can be used. For the data analysis, for example, MS tornado analysis manufactured by japan electronics corporation may be used. As an external standard for mass constitution, polymethyl methacrylate (molecular weight standard for volume exclusion chromatography) can be used.

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

The interfacial tension of the aqueous electrolyte is preferably 80mN/m or less, for example, less than 55 mN/m. By being in this range, the membrane can be immersed inside the membrane. The aqueous electrolyte can be satisfactorily impregnated into the separator, so that the separator resistance can be reduced, the coulombic efficiency at the time of initial charge and discharge can be improved, and the capacity ratio of the positive electrode and the negative electrode at the time of battery design can be made close to 1. Therefore, a battery design with less capacity loss can be performed. More preferably 50mN/m or less, and still more preferably 40mN/m or less. The surfactant may be used in 1 kind or in combination of 2 or more kinds with respect to the aqueous electrolyte.

The interfacial tension was measured as follows.

< method for measuring interfacial tension of aqueous electrolyte >

The interfacial tension of the aqueous electrolyte can be determined by, for example, the pendant drop method. As the measuring apparatus, for example, an automatic contact angle measuring apparatus Dme-201 manufactured by Kyowa interface science was used. As the measurement conditions, for example, the conditions shown in table 1 below were used.

TABLE 1

The interfacial tension of the aqueous electrolyte was calculated from the following formula (6) by the pendant drop method. Interfacial tension (mN/M) ═ Δ ρ gde²(1/H) (6). Each symbol in the formula (6) is as follows, Δ ρ: density difference, g: acceleration of gravity, de: maximum diameter of hanging drop, 1/H: and (5) correcting the coefficient. For example, 5 measurements are made, and the average value is regarded as the interfacial tension.

< method for measuring contact Angle of aqueous electrolyte >

The contact angle of the aqueous electrolyte can be determined by, for example, a droplet method. As the measuring apparatus, for example, an automatic contact angle measuring apparatus Dme-201 manufactured by Kyowa interface science was used. As the measurement conditions, for example, the conditions shown in table 2 below were used.

TABLE 2

(diaphragm)

A separator may be disposed between the positive electrode and the negative electrode. By forming the separator with an insulating material, electrical contact between the positive electrode and the negative electrode can be prevented. Further, it is preferable to use a separator having a shape in which an electrolyte can move between the positive electrode and the negative electrode. In the following examples, the separator has air permeability. Examples of the separator include nonwoven fabric, film, and paper. Examples of the material constituting the separator include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferable separators include nonwoven fabrics containing cellulose fibers and porous films containing polyolefin fibers.

The permeability coefficient of the separator is preferably 1X 10^-14m²The following. If it is larger than 1X 10^-14m²When the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte are mixed, the aqueous electrolyte having a low osmotic pressure is liable to be depleted, which is not preferable. The permeability coefficient is more preferably 1X 10^-15m²Hereinafter, more preferably 1 × 10^-16m²The following. The separator having such a gas permeability coefficient is preferable because mixing of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte can be sufficiently suppressed kinetically, and coulombic efficiency is improved. This is because the rate characteristics are improved because the electrical resistance of the separator is reduced and the ionic conductivity is increased by sufficiently penetrating the separator with the aqueous electrolyte. Although the aqueous electrolyte is favorably impregnated into the separator, the aqueous electrolyte is not mixed on the positive electrode side and the negative electrode side.

Air permeability coefficient KT (m) of separator²) The measurement was carried out as follows. In the calculation of the air permeability coefficient KT, for example, when a membrane having a thickness l (m) is to be measured, the area a (m) is measured²) In the range of (a) and (b), a gas having a viscosity coefficient σ (Pa · s) is allowed to permeate therethrough. At this time, the gas is permeated under a plurality of conditions where the pressures p (Pa) of the introduced gas are different from each other, and the amount Q (m) of the gas permeated through the membrane is measured under each of the plurality of conditions³In s). Then, from the measurement results, the gas quantity Q is plotted against the pressure p,the slope, dQ/dp, is determined. 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 in accordance with the formula (7).

KT＝((σ·l)/A)×(dQ/dp) (7)

In one example of the method for calculating the permeability coefficient KT, a separator is sandwiched between a pair of stainless steel plates each having a hole with a diameter of 10 mm. Then, air was fed from the hole of one stainless steel plate by pressure p. Then, the amount Q of air leaking from the hole of the other stainless steel plate was measured. Therefore, the area of the hole (25 π mm)²) For the measurement area A, 0.000018 pas was used as the viscosity coefficient σ. Further, the gas quantity Q can be measured by measuring the quantity delta (m) of gas leaking out of the hole in 100 seconds³) The measured quantity δ is divided by 100 to calculate.

Then, at 4 points where the pressures p differ from each other by at least 1000Pa, the gas amount Q with respect to the pressure p is measured as described above. For example, the gas amount Q with respect to the pressure p is measured at 4 points where the pressure p is 1000Pa, 2500Pa, 4000Pa and 6000Pa, respectively. Then, the gas quantity Q with respect to the pressure p is plotted for the measured 4 points, and the slope (dQ/dp) of the gas quantity Q with respect to the pressure p is calculated by straight line fitting (least square 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 gas permeability coefficient of the separator, the battery is disassembled, and the separator is separated from other members of the battery. The separator was washed on both sides with pure water, immersed in pure water, and left to stand for 48 hours or more. Then, both surfaces were rinsed with pure water, dried in a vacuum oven at 100 ℃ for 48 hours or more, and then the air permeability was measured. Further, the permeability coefficient was measured at arbitrary plural places on the separator. Then, the value of the place where the air permeability coefficient is the lowest value among the arbitrary plural places is taken 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. When the fiber diameter is 10 μm or less, the affinity of the separator with respect to the electrolyte improves, and therefore the battery resistance can be reduced. A more preferable range of the fiber diameter is 3 μm or less. A nonwoven fabric containing cellulose fibers having a porosity of 60% or more is excellent in impregnation with an electrolyte, and shows high output performance from low temperature to high temperature. Further, the lithium ion secondary battery does not react with the negative electrode even during long-term charge storage, float charge, and overcharge, and short-circuiting between the negative electrode and the positive electrode due to dendrite precipitation of lithium metal does not occur. A more preferable range is 62% to 80%.

Further, as the separator, a solid electrolyte may also be used. As the solid electrolyte, LATP (Li) having a NASICON type skeleton is preferable_1+xAl_xTi_2-x(PO₄)₃X is 0.1. ltoreq. x.ltoreq.0.4) and amorphous LIPON (Li)_2.9PO_3.3N_0.46) Garnet-type LLZ (Li)₇La₃Zr₂O₁₂) And the like.

In addition, beta alumina and Na are also included_1+xZr₂Si_xP_3-xO₁₂(0≤x≤3)、NaAlSi₃O₈And the like.

As the separator, a separator further including a solid electrolyte layer on at least one of the main surfaces of the porous self-supporting film may be used. The solid electrolyte provided in the solid electrolyte layer may be LATP or the like as described above.

The separator preferably has a thickness of 20 to 100 μm and a density of 0.2g/cm³Above and 0.9g/cm³The following. Within this range, a balance between mechanical strength and reduction in battery resistance can be achieved, and a secondary battery having high output and suppressed internal short circuits can be provided. In addition, the thermal shrinkage of the separator in a high-temperature environment is small, and excellent high-temperature storage performance can be exhibited.

(cathode)

The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer is disposed on at least 1 surface of the negative electrode current collector. For example, the negative electrode active material layer may be disposed on the 1-side of the negative electrode current collector, or the negative electrode active material layer may be disposed on the 1-side and the back-side of the negative electrode current collector.

The negative electrode active material layer contains a negative electrode active material containingAt least 1 compound selected from titanium oxide, lithium titanium oxide and lithium titanium composite oxide. These oxides may be used in 1 kind or in plural kinds. Among these oxides, the lithium potential is 1V or more and 2V or less (vs. Li/Li)⁺) In the range of (1) to produce Li insertion and extraction reaction. Therefore, when these oxides are used as a negative electrode active material of a secondary battery, the change in volume expansion and contraction accompanying charge and discharge is small, and a long life can be achieved.

The negative electrode current collector preferably contains at least 1 element selected from Zn, Ga, In, Bi, Tl, Sn, Pb, Ti, and Al. These elements will also be referred to hereinafter as element a. These elements may be used in 1 kind or in plural kinds, and may be contained as a metal or a metal alloy. These metals and metal alloys may be contained alone or in combination of 2 or more. When these elements are contained in the current collector, the mechanical strength of the current collector is improved, and the workability is improved. In addition, electrolysis of the aqueous solvent is suppressed, and the effect of suppressing hydrogen generation is improved. Among the above elements, Zn, Pb, Ti and Al are more preferable.

The current collector is, for example, a metal foil formed of these metals. The current collector is, for example, a foil formed of an alloy containing these metals. Such foils may contain other elements in addition to element a, such as Cu. Examples of the shape of the metal body include a mesh and a porous body, in addition to a foil. In order to increase the energy density and output, the foil is preferably small in size and large in surface area.

In addition, the negative electrode current collector may further 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 in at least a part of the surface of the substrate. The compound containing the element a present on the surface is preferably disposed so as to contact the negative electrode active material layer. For example, by plating the substrate with the element a, a compound containing the element a can be made to exist on the surface of the substrate. Alternatively, the substrate surface may be subjected to plating treatment using an alloy containing the element a.

The current collector may also contain a member selected fromAt least 1 compound of the group consisting of a. Preferably, the oxide of the element a, and/or the hydroxide of the element a, and/or the basic carbonate compound of the element a, and/or the sulfate compound of the element a is contained in a depth region of 5nm or more and 1 μm or less from the surface to the depth direction in at least a part of the surface region of the current collector. Further, ZnO is exemplified as the oxide of the element A, and Zn (OH) is exemplified as the hydroxide of the element A₂Examples of the basic carbonate compound of element A include 2ZnCO₃·3Zn(OH)₂Examples of the sulfate compound of the element A include ZnSO₄·7H₂O, and the like.

If at least 1 of an oxide of the element a, a hydroxide of the element a, a basic carbonate compound of the element a, and a sulfuric acid compound of the element a is present in the surface layer portion of the current collector, hydrogen generation can be suppressed. Further, if these compounds are present in the surface layer portion of the current collector, the adhesion to each of the current collector, the active material, the conductive assistant and the binder is improved, and the electron conduction path can be increased, so that the cycle characteristics can be improved and the resistance can be reduced.

Preferably, the substrate contains at least 1 metal selected from the group consisting of Al, Fe, Cu, Ni, and Ti. These metals can also be contained in the form of alloys. The substrate may contain such a metal or metal alloy alone, or may contain 2 or more kinds in combination. From the viewpoint of weight reduction, the substrate preferably contains Al, Ti, or an alloy thereof.

Whether or not the current collector contains at least 1 compound selected from the group consisting of the elements a can be examined by decomposing the battery as described above and then performing inductively coupled plasma ICP emission analysis.

The negative electrode active material contains 1 or 2 or more compounds selected from titanium oxide, lithium titanium oxide, and lithium titanium composite oxide. Examples of the lithium titanium composite oxide include niobium titanium oxide and sodium niobium titanium oxide. The Li-insertion potential of these compounds is preferably 1V (vs. Li/Li)⁺) Li/Li of 3V (vs. Li/Li) above⁺) The following ranges.

Examples of titanium oxides include monoclinicCrystalline titanium oxide, rutile titanium oxide, and anatase titanium oxide. For each crystal structure of titanium oxide, the composition before charging may be TiO₂Meaning that the composition after charging can be represented by Li_xTiO₂(x is 0. ltoreq. x). Further, the pre-charge structure of monoclinic titanium oxide can be represented as TiO₂(B)。

Examples of the lithium titanium oxide include spinel-structured lithium titanium oxide (for example, of the general formula Li)_4+xTi₅O₁₂(x is-1. ltoreq. x. ltoreq.3)), a lithium titanium oxide of a ramsdellite structure (e.g., Li)_2+xTi₃O₇(-1≤x≤3))、Li_1+xTi₂O₄(0≤x≤1)、Li_1.1+xTi_1.8O₄(0≤x≤1)、Li_1.07+xTi_1.86O₄(0≤x≤1)、Li_xTiO₂(0<x) and the like.

Examples of niobium titanium oxides include Li_aTiM_bNb_2±βO_7±σ(a is not less than 0 and not more than 5, b is not less than 0 and not more than 0.3, beta is not less than 0 and not more than 0.3, sigma is not less than 0 and not more than 0.3, and M is at least 1 element selected from the group consisting of Fe, V, Mo and Ta).

Examples of sodium niobium titanium oxides include those of the formula Li_2+vNa_2-wM1_xTi_6-y-zNb_yM2_zO_14+δ(V is 0. ltoreq. v.ltoreq.4, W is 0. ltoreq. w.ltoreq.2, x is 0. ltoreq. x.ltoreq.2, y is 0. ltoreq. y.ltoreq.6, z is 0. ltoreq. z.ltoreq.3, y + z is < 6, -0.5. ltoreq. delta.ltoreq.0.5, M1 contains at least 1 selected from Cs, K, Sr, Ba, Ca, M2 contains at least 1 selected from Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, Al).

Preferred compounds for 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. The Li insertion potential of each compound was 1.4V (vs. Li/Li)⁺) Li/Li of 2V (vs. Li/Li) above⁺) The following ranges allow, for example, a high electromotive force to be obtained by combining with a lithium manganese oxide as a positive electrode active material. Wherein the lithium titanium oxide having a spinel structure undergoes a volume change due to a charge-discharge reactionVery small and is therefore more preferred.

The negative electrode active material may be contained in the form of particles in the negative electrode active material layer. The negative electrode active material particles may be primary particles alone, secondary particles that are aggregates of the primary particles, or a mixture of primary particles and secondary particles alone. The particle shape is not particularly limited, and may be, for example, a spherical shape, an elliptical shape, a flat shape, a fibrous shape, or the like.

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

The negative electrode active material having an average particle diameter of the secondary particles of 3 μm or more can be obtained, for example, by the following method. First, an active material precursor having an average particle diameter of 1 μm or less is prepared by reacting and synthesizing active material raw materials. Then, the active material precursor is fired and pulverized by a pulverizer such as a ball mill or a jet mill. Next, in the firing treatment, the active material precursor is agglomerated and grown into secondary particles having a large particle size.

The average particle diameter of the primary particles of the negative electrode active material is preferably set to 1 μm or less. This shortens the diffusion distance of Li ions in the active material, and increases the specific surface area. Therefore, excellent high input performance (quick charging performance) can be obtained. On the other hand, if the average particle diameter is small, the particles are likely to aggregate, the electrolyte distribution may be biased to the negative electrode, and the electrolyte may be depleted in the positive electrode, and therefore the lower limit is preferably set to 0.001 μm. More preferably, the average particle diameter is 0.1 μm or more and 0.8 μm or less.

Negative electrode active material particles based on N₂The specific surface area in the BET method of the precipitate is preferably 3m²More than 200 m/g²(ii) a range of,/g or less. This can further improve the affinity between the negative electrode and the electrolyte.

The specific surface area of the negative electrode active material layer (excluding the current collector) is preferably 3m²More than 50 m/g²(ii) a range of,/g or less. Of specific surface areaMore preferably in the range of 5m²More than 50 m/g²The ratio of the carbon atoms to the carbon atoms is less than g. The negative electrode active material layer may be a porous layer containing a negative electrode active material, a conductive agent, and a binder, which is supported on a current collector.

The porosity (excluding the current collector) of the negative electrode is preferably in the range of 20 to 50%. This makes it possible to obtain a high-density negative electrode having excellent affinity for an electrolyte. A more preferable range of the porosity is 25 to 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 kinds of the conductive agent may be specified to be 1 kind or 2 or more kinds. The carbon material generates hydrogen from itself, and thus metal powder is preferably used as the conductive agent.

Examples of the binder include Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, ethylene-butadiene rubber, polypropylene (PP), Polyethylene (PE), carboxymethyl cellulose (CMC), Polyimide (PI), and polyamide-imide (PAI). The kinds of the binder may be specified to be 1 kind or 2 or more kinds.

Regarding the mixing 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 preferably in a range of 70 wt% to 95 wt%, the conductive agent is preferably in a range of 3 wt% to 20 wt%, and the binder is preferably in a range of 2 wt% to 10 wt%. The negative electrode can have good conductivity if the mixing ratio of the conductive agent is 3 wt% or more, and the decomposition of the electrolyte on the surface of the conductive agent can be reduced if the mixing ratio is 20 wt% or less. When the mixing ratio of the binder is 2 wt% or more, sufficient electrode strength can be obtained, and when the mixing ratio is 10 wt% or less, the insulating portion of the electrode can be reduced.

The negative electrode can be produced, for example, as follows. First, a negative electrode active material, a conductive agent, and a binder are dispersed in an appropriate solvent to prepare a slurry. The slurry is applied to a current collector, and the coating film is dried, thereby forming a negative electrode active material layer on the current collector. Here, for example, the slurry may be applied to the current collector on the 1-side surface, or the slurry may be applied to the current collector on the 1-side surface and the back surface thereof. Next, the current collector and the negative electrode active material layer are subjected to pressure such as hot pressing, whereby a negative electrode can be produced.

(Positive electrode)

The positive electrode may have a positive electrode current collector and a positive electrode layer which is supported on 1 or both surfaces of the positive electrode current collector and contains an active material, a conductive agent, and a binder.

As the positive electrode current collector, a foil, a porous body, or a mesh made of metal such as stainless steel, Al, or Ti is preferably used. In order to prevent corrosion of the current collector caused by the reaction of the current collector with the electrolyte, the surface of the current collector may be coated with a different element.

As the positive electrode active material, a positive electrode active material capable of intercalating and deintercalating lithium and sodium can be used. The positive electrode may contain 1 kind of positive electrode active material, or may contain 2 or more kinds of positive electrode active materials. Examples of the positive electrode active material 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, lithium manganese cobalt composite oxide, lithium iron fluoride sulfate, and phosphate compound having an olivine crystal structure (for example, Li_xFePO₄(0≤x≤1)、Li_xMnPO₄(x is 0. ltoreq. x.ltoreq.1)), and the like. The phosphate 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. Examples thereof include spinel-structured Li_xMn₂O₄(0＜x≤1)、Li_xMnO₂(0 < x.ltoreq.1) lithium manganese complex oxides such as Li_xNi_1-yAl_yO₂(0 < x.ltoreq.1, 0 < y.ltoreq.1) or the like, for example, Li_xCoO₂(0 < x.ltoreq.1) or the like lithium cobalt composite oxides, e.g. Li_xNi_1-y- _zCo_yMn_zO₂(0 < x.ltoreq.1, 0 < y.ltoreq.1, 0. ltoreq.z.ltoreq.1) or the like, for example, Li_xMn_yCo_1-yO₂(0 < x.ltoreq.1, 0 < y.ltoreq.1) or the like, for example, Li_xMn_2-yNi_yO₄Spinel-type lithium manganese nickel composite oxides such as (0 < x.ltoreq.1, 0 < y.ltoreq.2), e.g. Li_xFePO₄(0＜x≤1)、Li_xFe_1-yMn_yPO₄(0＜x≤1、0≤y≤1)、Li_xCoPO₄(0 < x.ltoreq.1), and the like, lithium phosphorus oxides having an olivine structure, and fluorinated iron sulfates (e.g., Li)_xFeSO₄F(0＜x≤1))。

In addition, sodium manganese composite oxide, sodium nickel composite oxide, sodium cobalt composite oxide, sodium nickel cobalt manganese composite oxide, sodium iron composite oxide, sodium phosphate (for example, sodium iron phosphate, sodium vanadium phosphate), sodium iron manganese composite oxide, sodium nickel titanium composite oxide, sodium nickel iron composite oxide, sodium nickel manganese composite oxide, and the like are also included.

In a preferred example of the positive electrode active material, an iron composite oxide (e.g., Na) is contained_yFeO₂0. ltoreq. y. ltoreq.1), iron manganese composite oxide (e.g., Na)_yFe_1-xMn_xO₂0 < x < 1, 0 < y < 1), nickel titanium composite oxide (for example, Na)_yNi_1-xTi_xO₂0 < x < 1, 0 < y < 1), nickel-iron composite oxide (for example, Na)_yNi_1-xFe_xO₂0 < x < 1, 0 < y < 1), nickel manganese complex oxide (e.g., Na)_yNi_1-xMn_xO₂0 < x < 1, 0 < y < 1), nickel-manganese-iron composite oxide (for example, Na)_yNi_1-x-zMn_xFe_zO₂0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < 1-x-z < 1), iron phosphate (e.g., Na)_yFePO₄，0≤y≤1)。

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

It is preferable to coat at least a part of the particle surface of the positive electrode active material with a carbon material. The carbon material may take the form of a layer structure, a particle structure, or an aggregate of particles.

Examples of the conductive agent for improving the electron conductivity of the positive electrode layer and suppressing the contact resistance with the current collector include acetylene black, carbon black, graphite, and carbon fibers having an average fiber diameter of 1 μm or less. The kinds of the conductive agent may be specified to be 1 kind or 2 or more kinds.

The binder for binding the active material and the conductive agent includes, for example, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, ethylene-butadiene rubber (SBR), polypropylene (PP), Polyethylene (PE), carboxymethyl cellulose (CMC), Polyimide (PI), polyamide-imide (PAI). The kinds of the binder may be specified to be 1 kind or 2 or more kinds.

The mixing ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode layer is preferably in a range of 70 wt% to 95 wt%, a range of 3 wt% to 20 wt% of the conductive agent, and a range of 2 wt% to 10 wt% of the binder. The positive electrode can have good conductivity if the mixing ratio of the conductive agent is 3 wt% or more, and the decomposition of the electrolyte on the surface of the conductive agent can be reduced if the mixing ratio is 20 wt% or less. When the mixing ratio of the binder is 2 wt% or more, sufficient electrode strength can be obtained, and when the mixing ratio is 10 wt% 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. The slurry is applied to a current collector, and the coating film is dried, thereby forming a positive electrode layer on the current collector. Here, for example, the slurry may be applied to the 1 surface of the current collector, or the slurry may be applied to the 1 surface of the current collector and the back surface thereof. Next, the current collector and the positive electrode layer are subjected to pressure such as hot pressing, whereby a positive electrode can be produced.

(Container)

As the container for housing the positive electrode, the negative electrode, and the electrolyte, a metal container, a laminate film container, and a resin container such as polyethylene and polypropylene can be used.

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

The plate thickness of each of the resin container and the metal container is preferably 1mm or less, more preferably 0.5mm or less, and still more preferably 0.3mm or less. The lower limit of the thickness of the sheet is preferably 0.05 mm.

Examples of the laminate film include a multilayer film in which a metal layer is coated with a resin layer. Examples of the metal layer include stainless steel foil, aluminum foil, and aluminum alloy foil. As the resin layer, polymers such as polypropylene (PP), Polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used. The thickness of the laminated film is preferably in a range of 0.5mm or less, and more preferably in a range of 0.2mm or less. The lower limit of the thickness of the laminate film is preferably set to 0.01 mm.

The secondary battery according to the embodiment can be applied to secondary batteries having various shapes such as a rectangular shape, a cylindrical shape, a flat shape, a thin shape, and a coin shape. More preferably, the secondary battery has a bipolar structure. This has the advantage that a plurality of series-connected cells can be produced with 1 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 includes a negative electrode 3 including a negative electrode current collector 3a and a negative electrode active material layer 3b, a positive electrode 5 including a positive electrode current collector 5a and a positive electrode active material layer 5b, a 1 st aqueous electrolyte 11 in contact with the positive electrode, a 2 nd aqueous electrolyte 12 in contact with the negative electrode, and an exterior member 2. The negative electrode active material layer 3b is provided on a part of both surfaces of the negative electrode current collector 3 a. The positive electrode active material layer 5b is provided on a part of both surfaces of the positive electrode current collector 5 a. The negative electrode collector 3a is not provided with the negative electrode active material layer 3b and functions as a negative electrode tab 3 c. The positive electrode current collector 5a at a position where the positive electrode active material layer 5b is not provided functions as a positive electrode tab 5 c. A separator 4 is present between the negative electrode 3 and the positive electrode 5.

The positive electrode 5 is housed in the exterior member 2 in a state where the positive electrode tab 5c protrudes outward. The negative electrode 3 is housed in the exterior member 2 in a state where the negative electrode tab 3c protrudes outward. The 1 st aqueous electrolyte 11 and the 2 nd aqueous electrolyte 12 are contained in the exterior member 2.

The 1 st aqueous electrolyte 11 contained in the secondary battery 10 shown in fig. 1 is a gel-like aqueous electrolyte. The 2 nd aqueous electrolyte 12 is a liquid aqueous electrolyte. Although not shown, the 1 st aqueous electrolyte 11 may be a liquid aqueous electrolyte, the 2 nd aqueous electrolyte 12 may be a gel-like aqueous electrolyte, and both the 1 st aqueous electrolyte 11 and the 2 nd aqueous electrolyte 12 may be liquid aqueous electrolytes or both may be gel-like aqueous electrolytes.

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

Fig. 2 is a cross-sectional view schematically showing another example of the secondary battery according to the embodiment.

Fig. 3 is an enlarged sectional view of a portion a of fig. 2.

The secondary battery 10 shown in fig. 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 1 st aqueous electrolyte 11. The 1 st aqueous electrolyte 11 is provided on both surfaces of the positive electrode 5. The separator 4 is interposed between the 1 st aqueous electrolyte 11 and the negative electrode 3. The wound electrode group 1 can be formed by laminating a negative electrode 3, a separator 4, and a positive electrode 5 provided with a 1 st aqueous electrolyte 11 on both surfaces to form a laminate, winding the laminate in a spiral shape with the negative electrode 3 on the outside as shown in fig. 3, and then press molding.

The anode 3 includes an anode current collector 3a and an anode active material layer 3 b. As shown in fig. 3, the outermost negative electrode 3 has a structure in which a negative electrode active material layer 3b is formed only on one surface of the negative electrode current collector 3a on the inner surface side. The other negative electrode 3 has a negative electrode active material layer 3b formed on both surfaces of a negative electrode current collector 3 a.

The positive electrode 5 has a positive electrode active material layer 5b formed on both surfaces of a positive electrode current collector 5 a. The 1 st aqueous electrolyte 11 is stacked on the positive electrode active material layer 5b formed on both surfaces of the positive electrode 5 a.

As shown in fig. 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 connected to the positive electrode current collector 5a of the inside positive electrode 5.

The wound electrode assembly 1 is housed in an outer package member (pouch container) 2, and the outer package member 2 is formed of a laminate film in which a metal layer is sandwiched between 2 resin layers.

The negative electrode terminal 6 and the positive electrode terminal 7 extend outward from the opening of the pouch container 2. For example, a liquid 2 nd aqueous electrolyte (not shown) is injected from an opening of the baglike container 2 and stored in the baglike container 2.

The opening of the pouch container 2 is heat-sealed with the negative electrode terminal 6 and the positive electrode terminal 7 interposed therebetween, whereby the wound electrode group 1 and the 2 nd aqueous electrolyte are completely sealed. In the secondary battery 10 shown in fig. 2 and 3, the positive electrode 5 is in contact with the 1 st aqueous electrolyte, and the negative electrode 3 is in contact with the 2 nd aqueous electrolyte.

According to the embodiment described above, the secondary battery according to embodiment 1 includes the positive electrode, the 1 st aqueous electrolyte held in the positive electrode, the negative electrode, the 2 nd aqueous electrolyte held in the negative electrode, and the separator interposed between the positive electrode and the negative electrode, and the difference between the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte is 90% or less with respect to the larger of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte. With such a configuration, the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte can be prevented from mixing, the aqueous electrolytes can be maintained at appropriate pH, and electrolysis of water contained in the aqueous electrolytes can be prevented. Therefore, a secondary battery having excellent storage performance and cycle characteristics can be provided.

(embodiment 2)

According to embodiment 2, an assembled battery in which a secondary battery is a single battery can be provided. As the secondary battery, the secondary battery of embodiment 1 may be used.

Examples of the assembled battery include an assembled battery including a plurality of unit cells electrically connected in series or in parallel as a constituent unit, an assembled battery including a unit constituted by a plurality of unit cells electrically connected in series or a unit constituted by a plurality of unit cells electrically connected in parallel, and the like.

The battery pack may be housed in the case. The housing may be a metal can or a plastic container made of aluminum alloy, iron, stainless steel, or the like. The thickness of the container is preferably 0.5mm or more.

Examples of the form of electrically connecting the plurality of secondary batteries in series or in parallel include a form of electrically connecting the plurality of secondary batteries each having a container in series or in parallel, and a form of electrically connecting the plurality of electrode groups housed in a common housing in series or in parallel. A specific example of the former is a case where positive and negative terminals of a plurality of secondary batteries are connected by a bus bar made of metal (for example, aluminum, nickel, or copper). A specific example of the latter is to store a plurality of electrode groups in 1 enclosure in an electrochemically insulated state by partition walls, and to electrically connect the electrode groups in series. The number of batteries electrically connected in series is set to be in the range of 5 to 7, whereby voltage compatibility with a lead storage battery can be improved. To further improve voltage compatibility with the lead-acid battery, it is preferable to connect 5 or 6 cells in series.

An example of the assembled battery will be described with reference to fig. 4. An assembled battery 31 shown in fig. 4 includes a plurality of prismatic secondary batteries (e.g., fig. 1 and 2)32 according to embodiment 1 as unit cells₁～32₅. Battery 32₁And the battery 32 adjacent thereto and the positive electrode conductive tab 8₂The negative electrode conductive tab 9 is electrically connected by a lead 33. In addition, the battery 32₂And the battery 32 adjacent thereto and the positive electrode conductive tab 8₃The negative electrode conductive tab 9 is electrically connected by a lead 33. The batteries 32 are thus connected in series₁～32₅And (3) removing the solvent.

According to the assembled battery of embodiment 2, since the assembled battery includes the secondary battery of embodiment 1, an assembled battery excellent in storage performance and cycle characteristics can be provided.

(embodiment 3)

According to embodiment 3, a battery pack may be provided. The battery pack includes the secondary battery according to embodiment 1.

The battery pack according to embodiment 3 may include 1 or more secondary batteries (cells) according to embodiment 1 described above. The plurality of secondary batteries that can be included in the battery pack according to embodiment 3 can be electrically connected in series, in parallel, or in a combination of series and parallel. Further, a plurality of secondary batteries can also constitute an electrically connected assembled battery. When a battery is constituted by a plurality of secondary batteries, the battery pack of embodiment 2 may be used.

The battery pack according to embodiment 3 may further include a protection circuit. The protection circuit controls charging and discharging of the secondary battery. Alternatively, as the protection circuit of the battery pack, a circuit included in a device (for example, an electronic device, an automobile, or the like) using the battery pack as a power source may be used.

The battery pack according to embodiment 3 may further include an external terminal for conducting electricity. The external terminals for energization are used for outputting a current from the secondary battery to the outside and/or inputting a current to the battery cell 51. In other words, when the battery pack is used as a power source, a current is supplied to the outside through the external terminal for energization. When the battery pack is charged, a charging current (including regenerative energy of power of an automobile or the like) is supplied to the battery pack through the external terminal 59 for energization.

An example of the battery pack according to embodiment 3 will be described with reference to fig. 5. Fig. 5 is a schematic perspective view showing an example of a battery pack.

The battery pack 40 includes a battery pack including the secondary batteries shown in fig. 3 and 5. The battery pack 40 includes a housing 41 and a battery pack 42 housed in the housing 41. The assembled battery 42 electrically connects a plurality of (e.g., 5) secondary batteries 43 in series₁～43₅. Secondary battery 43₁～43₅Are stacked in the thickness direction. The housing 41 has openings 44 in the upper part and 4 side surfaces, respectively. Secondary battery 43₁～43₅The side surfaces of the housing 41 from which the positive and negative terminals 12 and 13 protrude are exposed through the opening 44. The positive electrode terminal 45 for output of the battery pack 42 is formed in a band shape, and one end thereof is connected to the secondary battery 43₁～43₅One of the positive electrode terminals 13 is electrically connected, and the other end protrudes from the opening 44 of the housing 41 and protrudes from the upper portion of the housing 41. On the other hand, the output negative electrode terminal 46 of the battery pack 42 is formed in a band shape, and one end thereof is connected to the secondary battery 43₁～43₅One of the negative electrode terminals 12 is electrically connected, and the other end protrudes from the opening 44 of the housing 41 and protrudes from the upper portion of the housing 41.

Another example of the battery pack according to embodiment 3 will be described in detail with reference to fig. 6 and 7. Fig. 6 is an exploded perspective view of a battery pack according to another example of embodiment 3. Fig. 7 is a block diagram showing a circuit of the battery pack of fig. 6.

A plurality of unit cells 51, each of which is a flat secondary battery, are stacked such that a negative electrode terminal 52 and a positive electrode terminal 53 extending outward are aligned in the same direction, and are bound with an adhesive tape 54 to form a battery pack 55. These cells 51 are electrically connected in series with each other as shown in fig. 7.

The printed circuit board 56 is disposed to face the side surfaces of the cells 51 from which the negative electrode terminal 52 and the positive electrode terminal 53 extend. As shown in fig. 7, a thermistor 57, a protection circuit 58, and an external terminal 59 for energizing are mounted on the printed circuit board 56. An insulating plate (not shown) is attached to the surface of the printed circuit board 56 facing the battery pack 55 in order to avoid unnecessary connection with the wiring of the battery pack 55.

The positive electrode lead 60 is connected to the positive electrode terminal 53 positioned at the lowermost layer of the battery pack 55, and the tip thereof is inserted into and electrically connected to the positive electrode connector 61 of the printed circuit board 56. The negative electrode lead 62 is connected to the negative electrode terminal 52 located at the uppermost layer of the battery pack 55, and the tip thereof is inserted into and electrically connected to the negative electrode connector 63 of the printed circuit board 56. These

connectors

61 and 63 are connected to the protection circuit 58 through

wirings

64 and 65 formed on the printed wiring board 56.

The thermistor 57 detects the temperature of the single cell 51 and sends its detection signal to the protection circuit 58. The protection circuit 58 can block the positive-side wiring 66a and the negative-side 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 temperature detected by the thermistor 57 becomes equal to or higher than a predetermined temperature. The predetermined condition is detection of overcharge, overdischarge, overcurrent, or the like of the battery cell 51. The detection of the overcharge and the like is performed for each of the single cells 51 or the assembled battery 55. When each single cell 51 is detected, the cell voltage may be detected, and 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 cell 51. In the case of fig. 6 and 7, the wires 67 for voltage detection are connected to the cells 51, respectively, and the detection signal is transmitted to the protection circuit 58 through these wires 67.

On three side surfaces of the assembled battery 55 except for the side surfaces from which the positive electrode terminal 53 and the negative electrode terminal 52 protrude, protective sheets 68 made of rubber or resin are disposed, respectively.

The battery pack 55 is housed in a housing container 69 together with the protective sheets 68 and the printed circuit board 56. That is, the protective sheets 68 are disposed on both inner surfaces in the longitudinal direction and the inner surface in the short direction of the storage container 69, and the printed wiring board 56 is disposed on the inner surface on the opposite side in the short direction. The battery pack 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.

In addition, a heat shrinkable tape may be used instead of the adhesive tape 54 for fixing the battery pack 55. In this case, protective sheets are disposed on both side surfaces of the assembled battery, and after the assembled battery is wound with a heat-shrinkable tape, the heat-shrinkable tape is heat-shrunk to bind the assembled battery.

Fig. 6 and 7 show a configuration in which the cells 51 are connected in series, but may be connected in parallel in order to increase the battery capacity. Or a combination of series and parallel connections may be used. Furthermore, the assembled battery packs can be connected in series and/or in parallel.

The form of the battery pack may be appropriately changed depending on the application. The battery pack is preferably used in applications where charge and discharge under a large current are expected. Specifically, the battery may be used for a power source of a digital camera, a two-to four-wheeled hybrid electric vehicle, a two-to four-wheeled electric vehicle, a power-assisted bicycle, a vehicle such as a railway vehicle, and the like, and for a stationary battery. Is particularly suitable for vehicle-mounted use.

In a vehicle such as an automobile on which the battery pack according to embodiment 3 is mounted, the battery pack can recover regenerative energy of power of the vehicle, for example.

According to the battery pack of embodiment 3 described above, since the secondary battery of embodiment 1 is included, a battery pack excellent in storage performance and cycle characteristics can be provided.

(embodiment 4)

According to embodiment 4. A vehicle may be provided. The vehicle is mounted with the battery pack according to embodiment 3.

In the vehicle according to embodiment 4, the battery pack can recover regenerative energy of the power of the vehicle, for example.

Examples of the vehicle according to embodiment 4 include a two-to-four-wheeled hybrid electric vehicle, a two-to-four-wheeled electric vehicle, a power-assisted bicycle, and a railway vehicle.

The position where the battery pack is mounted in the vehicle according to embodiment 4 is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack may be mounted in an engine room, a rear part of a vehicle body, or under a seat of the vehicle.

Next, an example of a vehicle according to embodiment 4 will be described with reference to the drawings.

Fig. 8 is a sectional view schematically showing an example of the vehicle according to embodiment 4.

The vehicle 200 shown in fig. 8 includes a vehicle main body 201 and a battery pack 202. The battery pack 202 may be the battery pack according to embodiment 3.

The vehicle 200 shown in fig. 8 is a four-wheeled automobile. As the vehicle 200, for example, a two-to-four-wheeled hybrid electric vehicle, a two-to-four-wheeled electric vehicle, a power-assisted bicycle, and a railway vehicle can be used.

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

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 a seat. The battery pack 202 can be used as a power source of the vehicle 200. Further, the battery pack 202 can recover regenerative energy of the power of the vehicle 200.

Next, an embodiment of the vehicle according to embodiment 4 will be described with reference to fig. 9.

Fig. 9 is a diagram schematically showing another example of the vehicle according to embodiment 4. 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 (ECU: Electric Control Unit) 380 as a higher-order Control means of the vehicle power supply 302, an external terminal (terminal for connection to an external power supply) 370, a converter 340, and a drive motor 345.

In the vehicle 300, the vehicle power supply 302 is mounted in an engine room, a rear part of a vehicle body, or under a seat, for example. In a vehicle 300 shown in fig. 9, a mounting position of a vehicle power supply 302 is schematically shown.

The vehicle power supply 302 includes a plurality of (e.g., 3)

Battery packs

312a, 312b, and 312c, a Battery Management Unit (BMU) 311, and a communication bus 310.

The 3

battery packs

312a, 312b, and 312c are electrically connected in series. The battery pack 312a includes a battery pack 314a and a battery pack Monitoring device (VTM) 313 a. The battery pack 312b includes a battery pack 314b and a battery pack monitoring device 313 b. The battery pack 312c includes a battery pack 314c and a battery pack monitoring device 313 c. The battery packs 312a, 312b, and 312c are independently detachable and exchangeable with other battery packs 312.

Each of the assembled batteries 314a to 314c includes a plurality of cells connected in series. At least 1 of the plurality of cells is the secondary battery according to embodiment 1. The assembled batteries 314a to 314c are charged and discharged through a positive electrode terminal 316 and a negative electrode terminal 317, respectively.

In order to collect information on maintenance of the vehicle power supply 302, the battery management device 311 communicates between the assembled battery monitoring devices 313a to 313c and collects information on the voltage, temperature, and the like of the unit cells included in the assembled batteries 314a to 314c included in the vehicle power supply 302.

A communication bus 310 is connected between the battery management device 311 and the battery pack monitoring devices 313a to 313 c. The communication bus 310 is configured such that a plurality of nodes (the battery management apparatus and 1 or more battery pack monitoring apparatuses) share 1 communication line. The communication bus 310 is, for example, a communication bus configured based on CAN (Control Area Network) standard.

The assembled battery monitoring devices 313a to 313c measure the voltage and temperature of each of the unit cells constituting the assembled batteries 314a to 314c based on a communication command from the battery management device 311. However, the temperature may be measured at only several places for 1 battery cell, or may not be measured for all the unit cells.

The vehicle power supply 302 may further have an electromagnetic contactor (e.g., the switching device 333 shown in fig. 9) for switching the connection of the positive terminal 316 and the negative terminal 317. The switching device 333 includes a precharge switch (not shown) that is turned on when the battery packs 314a to 314c are charged and a main switch (not shown) that is turned on when the battery output is supplied to the load. The precharge switch and the main switch include a relay circuit (not shown) that is turned on or off based on a signal supplied to a coil disposed near the switching element.

The converter 340 converts an 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 converter 340 are connected to the three-phase input terminals of the drive motor 345. The converter 340 controls the output voltage based on a control signal from the battery management device 311 or the vehicle ECU380 for controlling the operation of the entire vehicle.

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

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

One terminal of the connection line L1 is connected to the negative 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 input terminal of the converter 340.

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

The external terminal 370 is connected to the battery management device 311. The external terminal 370 is connectable to an external power supply, for example.

In response to an operation input from a driver or the like, the vehicle ECU380 controls the battery management device 311 in cooperation with other devices to manage the entire vehicle. Between battery management device 311 and vehicle ECU380, data transmission related to maintenance of vehicle power supply 302, such as the remaining capacity of vehicle power supply 302, is performed through the communication line.

The vehicle according to embodiment 4 includes the battery pack according to embodiment 3. That is, since the vehicle according to embodiment 4 has the battery pack excellent in storage performance and cycle performance, the vehicle according to embodiment 4 has excellent storage performance and cycle performance, and also has excellent battery pack life performance, and therefore, a vehicle with high reliability can be provided.

(embodiment 5)

According to embodiment 5, a stationary power supply can be provided. The stationary power supply is mounted with the battery pack according to embodiment 3. Instead of the battery pack according to embodiment 3, the stationary power supply may be equipped with the assembled battery according to embodiment 2 or the secondary battery according to embodiment 1.

The stationary power supply according to embodiment 5 is mounted with the battery pack according to embodiment 3. Therefore, the stationary power supply according to embodiment 5 can have a long life.

Fig. 10 is a block diagram showing an example of a system including the stationary power supply according to embodiment 5. Fig. 10 is a diagram showing an application example of the

stationary power supplies

112 and 123 as a use example of the battery packs 40A and 40B according to embodiment 3. In one example shown in fig. 10, a system 110 is shown that can employ

stationary power supplies

112, 123. The system 110 includes a power plant 111, a stationary power source 112, a consumer-side power system 113, and an Energy Management System (EMS) 115. Further, a power grid 116 and a communication network 117 are formed in the system 110, and the power plant 111, the stationary power source 112, the customer-side electric power system 113, and the EMS115 are connected via the power grid 116 and the communication network 117. The EMS115 performs control for stabilizing the entire system 110 using the power grid 116 and the communication network 117.

The power plant 111 generates a large amount of electric power from a fuel source such as thermal power or nuclear power. Electric power is supplied from the power plant 111 through the grid 116 and the like. The stationary power supply 112 may be equipped with a battery pack 40A. The battery pack 40A can store electric power and the like supplied from the power station 111. Further, the stationary power source 112 can supply the electric power stored in the battery pack 40A through the grid 116 or the like. The system 110 is provided with a power conversion device 118. The power conversion device 118 includes a converter, an inverter, a transformer, and the like. Therefore, the power converter 118 can perform conversion between dc and ac, conversion between ac having different frequencies, transformation (voltage boosting and voltage dropping), and the like. Therefore, the power conversion device 118 can convert the electric power from the power plant 111 into the electric power that can be stored in the battery pack 40A.

The customer-side power system 113 includes a plant power system, a building power system, a home power system, and the like. The customer-side power system 113 includes a customer-side EMS121, a power conversion device 122, and a stationary power supply 123. The stationary power source 123 can be mounted with a battery pack 40B. The customer-side EMS121 performs control to stabilize the customer-side power system 113.

The customer-side power system 113 is supplied with power from the power plant 111 and power from the battery pack 40A through the grid 116. The battery pack 40B can store electric power supplied to the consumer-side power system 113. The power conversion device 122 includes a converter, an inverter, a transformer, and the like, as in 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, transformation (voltage boosting and voltage dropping), and the like. Therefore, the power conversion device 122 can convert the electric power supplied to the consumer-side electric power system 113 into electric power that can be stored in the battery pack 40B.

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

The following examples are described, but the embodiments are not limited to the examples shown below.

In a secondary battery using an aqueous electrolyte, the generated voltage cannot be increased by using only 1 kind of electrolyte. In the following examples, experiments were performed while changing the concentrations of the positive-side aqueous electrolyte and the negative-side aqueous electrolyte.

(example 1)

The secondary battery was fabricated as follows.

< preparation of Positive electrode >

The positive electrode was produced as follows. LiMn as a positive electrode active material was kneaded using a kneader₂O₄(5g) Acetylene black (0.25g) as a conductive agent and a PVDF dispersion (NMP solution with a solid fraction of 8%, 6.25g) as a binder (binder resin) were mixed for 3 minutes to obtain a viscous slurry. The slurry was coated on one side of a Ti foil. Then, the solvent was distilled off at 120 ℃ to obtain a laminate. Next, the laminate was rolled by roll pressing. Then, the laminate was dried and then punched out into a circular shape having a diameter of 10 mm. The weight per unit area of the obtained positive electrode was 116g/m²。

< preparation of negative electrode >

Mixing Li as a negative electrode active material with a kneader₄Ti₅O₁₂(10g) Graphite (1g) as a conductive agent, a PTFE dispersion (40 wt% in solid content, 1g) as a binder (binder resin), and NMP (N-methyl-2-pyrrolidone) (8 g) were mixed for 3 minutes to obtain a slurry. The slurry was coated on one side of the Zn foil. Then, the solvent was distilled off at 120 ℃ to obtain a laminate. Next, the laminate was rolled by roll pressing. Then, the laminate was dried and then punched out into a circular shape having a diameter of 10 mm. The weight per unit area of the obtained negative electrode was 35g/m²。

< adjustment of aqueous electrolyte >

The positive-side aqueous electrolyte and the negative-side aqueous electrolyte were adjusted using the lithium salt concentrations, osmotic pressure regulators, and surfactants of the positive-side aqueous electrolyte and the negative-side aqueous electrolyte described in table 1.

< surfactant >

Specific examples of the nonionic surfactant include, for example, polyoxyethylene alkyl ethers (e.g., C)₁₂H₂₅O(CH₂CH₂O) nH, 0.9 < n.ltoreq.2.1) and polyoxyalkylene alkyl ethers (e.g. C)₁₂H₂₅O[(CH₂CH(CH₃)O)m·(CH₂CH₂O)n]N is more than 0 and less than or equal to 35, m is more than 0 and less than or equal to 40, or C₄H₉O(CH₂CH₂O)n[(CH₂CH(CH₃)O)m]H, n is more than 0 and less than or equal to 35, m is more than 0 and less than or equal to 28). Furthermore, the formula C relates to polyoxyethylene alkyl ethers₁₂H₂₅O(CH₂CH₂The above-mentioned numerical ranges for the subscript n in O) nH include 0.89 < n.ltoreq.2.1. Furthermore, as the following formula C₁₂H₂₅O[(CH₂CH(CH₃)O)m·(CH₂CH₂O)n]Specific examples of the polyoxyalkylene alkyl ether represented by H include compounds having subscripts n and m of 1.4. ltoreq. n.ltoreq.35 and 8.4. ltoreq. m.ltoreq.40, respectively. Polyoxyalkylene alkyl ether (C) was used in the examples₁₂H₂₅O[(CH₂CH(CH₃)O)m·(CH₂CH₂O)n]H, 0 < n.ltoreq.35, 0 < m.ltoreq.40), the surfactants are used by assuming that a surfactant having a molecular weight of 2000, n.10, m.ltoreq.40, B surfactant having a molecular weight of 500, n.1.4, m.ltoreq.8.4, C surfactant having a molecular weight of 3238, n.ltoreq.35, m.ltoreq.28, and D surfactant having a molecular weight of 2000, n.ltoreq.10, m.ltoreq.30. In example 1, surfactant a was used.

< production of test Battery >

An aluminum plate subjected to anodic acidification treatment was fixed to a plastic plate, and a negative electrode was fixed thereto. The Ti plate was fixed to another plastic plate, and the positive electrode was fixed thereto. The negative electrode-side aqueous electrolyte prepared was dropped onto the negative electrode, and a separator was placed on the aqueous electrolyte to adhere the separator to the negative electrode. On the opposite side of the separator, a positive electrode side aqueous electrolyte was dropped, and a positive electrode was placed thereon, and was tightly adhered, and then fixed with bolts.

The secondary battery thus produced was measured as follows.

< osmotic pressure measurement >

The osmotic pressure of the battery having finished the constant current charge-discharge test was measured. The volume of the solvent of the electrolyte was set to V (m)³) The amount of substance (total number of moles) of solute in the electrolyte is set to n (mol), and the gas constant is set to R (m)²·kg/(s²K · mol)), the absolute temperature of the electrolyte was set to t (K), and the osmotic pressure was calculated. The results are shown in tables 5 and 6.

< measurement of air permeability >

The battery is disassembled and the separator is separated from the other components of the battery. The separator was immersed in pure water after both sides were washed with pure water and left for 48 hours or longer. Then, both surfaces were rinsed with pure water, dried in a vacuum oven at 100 ℃ for 48 hours or more, and then the air permeability was measured. The thickness (m) of the separator was measured at 4 places of the separator thus taken out. In each of the 4 measurement sites, a diaphragm was sandwiched between a pair of stainless steel plates having holes of 10mm in diameter, and air was blown through the holes of one stainless steel plate by a pressure p. The pressure p is 1000Pa, 2500Pa, 4000Pa and 6000 Pa. Then, the hole was measured from the other stainless steel plateThe amount Q of air leaking out. The area of the hole (25 pi mm)²) As the measurement area A, 0.000018 pas was used as the viscosity coefficient σ. By measuring the amount delta (m) of leakage from the hole in 100 seconds³) The measured quantity δ is divided by 100 to calculate the gas quantity Q.

The gas quantity Q with respect to the pressure p was plotted at 4 points of measurement, and the slope (dQ/dp) of the gas quantity Q with respect to the pressure p was calculated by straight line fitting (least square method). Then, the calculated slope (dQ/dp) is multiplied by (σ · L)/A to calculate the air permeability coefficient KT. The values of the portions of 4 where the air permeability was the lowest were set as the air permeability of the separator, and are shown in tables 5 and 6.

Tables 3 and 4 show the kind and concentration of lithium salts of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte, the kind and concentration of osmotic pressure regulators (inorganic compounds and organic compounds), and the kind and concentration of surfactants, and tables 5 and 6 show the interfacial tension (mN/m) and osmotic pressure (N/m) of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte²) Permeability coefficient of the membrane (m)²) Osmotic pressure difference (%), cycle characteristics (next), coulombic efficiency (%). The measurements of examples 2 to 44 and comparative examples 1 to 2 described later were also performed in the same manner as in example 1.

< constant Current Charge/discharge test >

In each of examples and comparative examples, after the test cell was produced, the test was started quickly without waiting time. Both charging and discharging were performed at a 0.5C rate. In addition, at the time of charging, one of the earlier until the current value reaches 0.25C, until the charging time reaches 130 minutes, and until the charging capacity reaches 170mAh/g is set as the termination condition. The discharge was terminated after 130 minutes.

The cycle characteristics were determined by repeating the cycle in which the discharge capacity reached 80% with respect to the 50 th cycle, with the discharge capacity of the 50 th cycle set to 100% for 1 cycle of charge and discharge in which the charge and the discharge were performed once. Further, from the charge capacity and discharge capacity of the 50 th cycle, coulombic efficiency was calculated by the following method. Since it is good as long as the coulombic efficiency is good as the storage performance, the storage performance was measured using the coulombic efficiency. Since the coulomb efficiency is stable at the 50 th cycle, the 50 th cycle is adopted. Coulombic efficiency (%) < 100 × (discharge capacity/charge capacity)

Examples 2 to 20 secondary batteries were produced in the same manner as in example 1, with the lithium salt concentrations of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte, the osmotic pressure adjusting agent (compound capable of adjusting osmotic pressure), and the surfactant adjusted as described in table 3, and interfacial tension measurement, osmotic pressure difference measurement, cycle characteristics, and coulombic efficiency were evaluated. The evaluation results are set forth in table 5. Secondary batteries were produced in the same manner as in example 1 by adjusting the lithium salt concentrations of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte, the osmotic pressure regulators, and the surfactants as described in table 4 for examples 21 to 44 and comparative examples 1 and 2, respectively, and the interfacial tension measurement, the osmotic pressure difference measurement, the cycle characteristics, and the coulombic efficiency were evaluated. The evaluation results of examples 21 to 44 and comparative examples 1 and 2 are shown in Table 6. The "-" in the table means not added.

TABLE 3

TABLE 4

TABLE 5

TABLE 6

When examples 1 to 44 and comparative examples 1 and 2 are compared, it is found that if the difference in osmotic pressure is greater than 90%, the cycle characteristics and the coulombic efficiency are lowered. This is considered to be because the mixing of the positive-electrode-side aqueous electrolyte and the negative-electrode-side aqueous electrolyte causes the aqueous electrolyte to fall short of an appropriate pH range, and electrolysis of water is generated.

In examples 37 and 38, the osmotic pressure difference was 90% or less, but the cycle characteristics and the coulombic efficiency were inferior to those of the other examples. This is considered to be because in example 37, the interface tension was higher than 50mN/m, and the membrane was difficult to be immersed. In example 38, it is considered that the permeability coefficient of the separator was more than 1X 10^-14m²Therefore, the aqueous electrolyte was mixed with the other examples.

It is known from the examples that a difference in osmotic pressure of 50% or less can realize high cycle characteristics and coulombic efficiency. According to at least 1 embodiment and example described above, a secondary battery can be provided. The secondary battery comprises a positive electrode, a 1 st aqueous electrolyte held in the positive electrode, a negative electrode, a 2 nd aqueous electrolyte held in the negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the difference between the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte is 90% or less with respect to the larger of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte. Therefore, a secondary battery having excellent storage performance and cycle characteristics can be provided.

While several 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 other various forms, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Description of the symbols

1-electrode group, 2-container (outer packaging member), 3-positive electrode, 3 a-positive electrode collector, 3 b-positive electrode layer, 4-negative electrode, 4 a-negative electrode collector, 4 b-negative electrode layer, 5-separator, 6-positive electrode lead, 7-negative electrode lead, 8-positive electrode conductive tab, 9-negative electrode conductive electrodeEar, 10-sealing plate, 11-insulating member, 12-negative terminal, 13-positive terminal, 31-battery, 32₁～32₅、43₁～43₅Secondary batteries, 33-lead wires, 40A, 40B-battery packs, 41-housings, 42-battery packs, 44-openings, 45-positive terminals for output, 46-negative terminals for output, 51-cells, 55-battery packs, 56-printed circuit boards, 57-thermistors, 58-protection circuits, 59-external terminals for energization, 110-systems, 111-power stations, 112-stationary power sources, 113-consumer-side power systems, 116-grids, 117-communication networks, 118-power conversion devices, 121-power conversion devices, 122-power conversion devices, 123-stationary power sources, 200-vehicles, 201-vehicle bodies, 202-battery packs, 300-vehicles, 301-vehicle bodies, 302-vehicle power sources, 310-communication buses, 311-battery management devices, 312 a-312 c-battery packs, 313 a-313 c-battery pack monitoring devices, 314 a-314 c-battery pack, 316-positive terminal, 317-negative terminal, 333-switching device, 340-converter, 345-drive motor, 370-external terminal, 380-vehicle ECU, L1, L2-connecting line, W-drive wheel.

Claims

1. A secondary battery is provided with:

a positive electrode,

A 1 st aqueous electrolyte held in the positive electrode,

A negative electrode,

A 2 nd aqueous electrolyte held in the negative electrode, and

a separator interposed between the positive electrode and the negative electrode;

osmotic pressure (N/m) of the 1 st aqueous electrolyte²) Osmotic pressure (N/m) with the 2 nd aqueous electrolyte²) The difference in (b) is 90% or less (including 0%) with respect to the greater of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte.

2. The secondary battery according to claim 1, wherein a difference between an osmotic pressure of the 1 st aqueous electrolyte and an osmotic pressure of the 2 nd aqueous electrolyte is 80% or less with respect to a larger one of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte.

3. The secondary battery according to claim 1 or 2, wherein a difference between an osmotic pressure of the 1 st aqueous electrolyte and an osmotic pressure of the 2 nd aqueous electrolyte is 50% or less with respect to a larger one of the osmotic pressure of the 1 st aqueous electrolyte and the osmotic pressure of the 2 nd aqueous electrolyte.

4. The secondary battery according to any one of claims 1 to 3, wherein a compound capable of adjusting osmotic pressure is contained in at least one of the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte.

5. The secondary battery according to claim 4, wherein the compound capable of adjusting osmotic pressure contains at least 1 of an inorganic compound, an organic compound, and a surfactant.

6. The secondary battery according to any one of claims 1 to 5, wherein the separator has an air permeability coefficient of 1 x 10^- ¹⁴m²The following.

7. The secondary battery according to any one of claims 1 to 6, wherein the interface tension of the larger one of the interface tensions of the 1 st aqueous electrolyte and the 2 nd aqueous electrolyte is 50mN/m or less.

8. The secondary battery according to any one of claims 1 to 7, wherein the negative electrode active material of the negative electrode is at least 1 selected from titanium oxide, lithium titanium oxide, and lithium titanium composite oxide.

9. A battery pack comprising the secondary battery according to any one of claims 1 to 8.

10. The battery pack according to claim 9, further comprising an external terminal for energization and a protection circuit.

11. The battery pack according to claim 9 or 10, wherein a plurality of the secondary batteries are provided, and the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

12. A vehicle equipped with the battery pack according to any one of claims 9 to 11.

13. A stationary power supply comprising the battery pack according to any one of claims 9 to 11.