JP2019212449A - Power storage device including stainless steel current collector - Google Patents

Abstract

To provide a power storage device in which corrosion of a stainless steel current collector hardly occurs even in the presence of a salt of a sulfonic acid derivative.SOLUTION: A power storage device includes an electrolyte including a salt of a sulfonic acid derivative and a phosphate ester represented by O=P(OR)(R is independently an alkyl group), and a stainless steel current collector.SELECTED DRAWING: None

Description

  The present invention relates to a power storage device including a stainless steel current collector.

Power storage devices such as lithium ion secondary batteries are used as power sources for portable devices such as portable information terminals and vehicles. The power storage device includes a positive electrode, a negative electrode, and an electrolytic solution as main components. The electrolytic solution is obtained by dissolving an electrolyte in an organic solvent. For example, a lithium salt such as LiPF ₆ , (FSO ₂ ) ₂ NLi, or LiBF ₄ is generally dissolved in an electrolyte of a lithium ion secondary battery using lithium ions as a charge carrier as an electrolyte.

  The positive electrode is generally composed of a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. In general, the positive electrode current collector is made of aluminum. The reason is that the positive electrode current collector made of aluminum suppresses corrosion of the current collector that may occur during charging and discharging of the power storage device.

  The negative electrode is generally composed of a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. And as a negative electrode collector, the thing made from copper is generally employ | adopted. The reason for this is that when an aluminum current collector similar to the positive electrode is employed, the charge carrier and aluminum may be alloyed during charging / discharging of the power storage device, whereas with a copper current collector, This is because such a risk is small.

  On the other hand, aluminum current collectors and copper current collectors have problems in terms of strength. Stainless steel exists as a highly conductive material. However, in a power storage device employing a stainless steel current collector, it is known that stainless steel can be corroded during charging and discharging.

For example, Patent Literature 1 includes a test result in which a voltage is applied to a half cell (Example 12) that includes an electrolytic solution in which (FSO ₂ ) ₂ NLi is dissolved as an electrolyte and includes an aluminum foil, and the electrolyte. (FSO ₂₎ 2 with an electrolyte prepared by dissolving a _NLi, and test results of applying a voltage to the half cell comprises a foil made of stainless steel (Comparative example 7) have been described (evaluation example 10, FIG. 32 See).
In these test results, a large increase in current was not observed in the half cell with aluminum foil even under high potential conditions of 4 V or higher, but a large increase in current was observed in the half cell with stainless steel foil. You can see that That is, it can be said that the positive electrode current collector made of aluminum suppresses corrosion of the current collector that may occur during charging and discharging of the power storage device, but if the current collector for positive electrode made of stainless steel is used, the power storage device It can be said that the current collector corrodes during charging and discharging.

Patent Document 2 describes a bipolar lithium ion secondary battery including a bipolar electrode in which a positive electrode active material layer is formed on one surface of a stainless steel current collector foil and a negative electrode active material layer is formed on the other surface. ing. In this document, as a specific example of a bipolar lithium ion secondary battery, a positive electrode active material layer containing lithium manganate as a positive electrode active material is formed on one surface of a stainless steel current collector foil, and on the other surface, A bipolar lithium ion secondary battery comprising a bipolar electrode in which a negative electrode active material layer containing graphite as a negative electrode active material is formed, and an electrolyte containing LiPF ₆ as an electrolyte is described. It is also described that the ion secondary battery operated under repeated charge and discharge.

Japanese Patent Laying-Open No. 2015-133315 JP 2010-33769 A

Considering comprehensively from the descriptions in Patent Document 1 and Patent Document 2, corrosion of a stainless steel current collector is unlikely to occur in the presence of LiPF ₆ , but a salt of a sulfonic acid derivative such as (FSO ₂ ) ₂ NLi. It can be said that it is likely to occur in the presence of.

  A so-called bipolar power storage device in which a positive electrode active material layer is formed on one surface of the current collector foil and a bipolar electrode having a negative electrode active material layer formed on the other surface is stacked, and the cells are arranged in series in the device. Therefore, the current collector foil is required to have reduction resistance that can withstand the negative electrode potential and oxidation resistance that can withstand the positive electrode potential. The current collector foil is also required to have mechanical strength that can withstand the volume change of the active material accompanying charge / discharge and the increase in internal pressure due to the gas derived from the electrolyte.

When an aluminum foil is employed as the current collector foil of the bipolar power storage device, aluminum is highly resistant to oxidation, and thus is suitable as a current collector foil for a positive electrode. However, regarding the negative electrode, for example, in the case of a lithium ion secondary battery, aluminum and lithium can cause an alloying reaction at a potential of about 0.6 V or less. Due to the alloying of aluminum and lithium, the capacity of the lithium ion secondary battery is reduced and the aluminum foil becomes brittle.
Therefore, when an aluminum foil is employed as the current collector foil of the bipolar power storage device, it has been required to employ a negative electrode active material that can perform a charge / discharge reaction at a relatively high potential. Further, as described above, the aluminum foil has a problem in terms of mechanical strength.

  A stainless steel current collector is known to have excellent mechanical strength, but as described above, it can be said that it is easily corroded in the presence of a salt of a sulfonic acid derivative.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a power storage device in which corrosion of a stainless steel current collector hardly occurs even in the presence of a salt of a sulfonic acid derivative.

The inventor has studied an electrolytic solution containing a salt of a sulfonic acid derivative and a phosphate ester, and a coin battery including the electrolytic solution. Since the present inventor has obtained knowledge that an electrolyte containing a salt of a sulfonic acid derivative can corrode stainless steel, when using an electrolyte containing a salt of a sulfonic acid derivative, as a battery container in a coin battery In general, the one made of aluminum or the one whose surface is coated with aluminum such as stainless steel has been adopted.
At some point, the inventor mistakenly tested using a stainless steel battery container not coated with aluminum. However, the present inventor has noticed that, contrary to the conventional knowledge, the result of the test using the battery container made of stainless steel is good, that is, the corrosion of the stainless steel is suppressed.

  The present invention has been completed based on these findings.

The power storage device of the present invention is
An electrolyte containing a salt of a sulfonic acid derivative and a phosphate ester represented by O = P (OR) ₃ (wherein each R is independently an alkyl group);
And a stainless steel current collector.

  In the power storage device of the present invention, corrosion of the stainless steel current collector is suppressed.

It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of Example 1. It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of the comparative example 1. It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of the comparative example 2. It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of the reference example 1. It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of the reference example 2. It is a graph which shows the relationship between an electric potential and a response current in the cyclic voltammetry evaluation with respect to the coin cell of the reference example 3. 3 is a schematic cross-sectional view of a bipolar lithium ion secondary battery of application example 1. FIG.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

The power storage device of the present invention is
An electrolyte solution containing a salt of a sulfonic acid derivative and a phosphate ester represented by O = P (OR) ₃ (wherein each R is independently an alkyl group) (hereinafter sometimes referred to as the electrolyte solution of the present invention). )When,
And a stainless steel current collector.

  As power storage devices, secondary batteries such as lithium ion secondary batteries, sodium secondary batteries and magnesium secondary batteries, primary batteries such as lithium ion primary batteries and sodium primary batteries, capacitors such as electric double layer capacitors and lithium ion capacitors Can be illustrated.

The salt of the sulfonic acid derivative is an electrolyte.
Examples of the sulfonic acid derivative include sulfonic acid, sulfonic acid amide, and sulfonic acid imide. As the sulfonic acid derivative, those containing fluorine are preferable.

Examples of the chemical structure of a preferable sulfonic acid derivative anion include RSO ₃ , RSO ₂ NH, and (RSO ₂ ) ₂ N. Each R is independently represented by C _n H _l F _m (n, l, m are integers of 0 or more. 2n + 1 = 1 + m is satisfied). When the chemical structure of the anion is sulfonic acid imide, R may be bonded to each other to form a ring, in which case C _n H _l F _m (n is an integer of 1 or more. _L and m are 0 or more) (2n = 1 + m is satisfied.)
Examples of n include 0, 1, 2, 3, and 4.

For example, as the chemical structure of a suitable sulfonic imide anion, (FSO ₂ ) ₂ N, (CF ₃ SO ₂ ) ₂ N, (C ₂ F ₅ SO ₂ ) ₂ N, FSO ₂ (CF ₃ SO ₂ ) N , (SO ₂ CF ₂ CF ₂ SO ₂ ) N, (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) N, FSO ₂ (CH ₃ SO ₂ ) N, FSO ₂ (C ₂ F ₅ SO ₂ ) N, FSO ₂ (C ₂ H ₅ SO ₂ ) N can be exemplified.

  As the cation of the salt, a metal cation that can be a charge carrier is preferable, and examples of the metal include lithium, sodium, potassium, and magnesium.

  From the viewpoint of ionic conductivity, the salt concentration of the sulfonic acid derivative is preferably 0.4 to 2.5 mol / L, more preferably 0.5 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L. More preferably, 0.5 to 1.25 mol / L is even more preferable, 0.6 to 1 mol / L is particularly preferable, and 0.7 to 0.9 mol / L is most preferable. When the concentration of the electrolyte is too high, the viscosity of the electrolytic solution increases, and the ionic conductivity of the electrolytic solution may decrease.

  As the phosphate ester, those having 1 to 6 carbon atoms in the alkyl group of R are preferable, those having 1 to 3 carbon atoms are more preferable, and those in which R is a methyl group or an ethyl group are more preferable.

  Examples of the preferred molar ratio of the phosphate ester to the salt of the sulfonic acid derivative in the electrolytic solution of the present invention include 3 to 20, 4 to 16, 5 to 14, 6 to 12, and 7 to 10.

  Since phosphate esters are known to exhibit self-extinguishing properties or nonflammability, it can be said that the electrolyte solution of the present invention containing phosphate esters is excellent in heat resistance.

  The electrolytic solution of the present invention may contain an organic solvent other than the phosphate ester without departing from the spirit of the present invention.

  In the electrolytic solution of the present invention, the ratio of the phosphoric acid ester to the total organic solvent contained is preferably 50% by mass or more, 50% by volume or more, or 40% by mol or more, and is 70 to 98% by mass or 70 to 98% by volume. % Or 60 to 95 mol%, more preferably 80 to 95 mass%, 80 to 95 vol%, or 70 to 90 mol%.

  As the organic solvent other than the phosphate ester, a cyclic carbonate having a halogen or a cyclic carbonate having a carbon-carbon double bond is preferable. In particular, in a power storage device that employs a negative electrode active material that has a relatively low potential during charge and discharge, an electrolytic solution containing a cyclic carbonate having halogen or a cyclic carbonate having a carbon-carbon double bond is suitable.

  A cyclic carbonate having a halogen or a cyclic carbonate having a carbon-carbon double bond has a relatively high reductive decomposition potential and can be decomposed during charging. For example, the reductive decomposition potential of fluoroethylene carbonate is about 1.15 V on the basis of lithium, and the reductive decomposition potential of vinylene carbonate is about 1.35 V on the basis of lithium. In the power storage device of the present invention comprising an electrolytic solution containing a cyclic carbonate having a halogen or a cyclic carbonate having a carbon-carbon double bond because a coating film is formed on the negative electrode surface due to the decomposition product derived from the cyclic carbonate. It is speculated that an inconvenient reaction can be suppressed.

  As the cyclic carbonate having halogen or the cyclic carbonate having a carbon-carbon double bond, a 5-membered carbonate is preferable. As the halogen, fluorine or chlorine is preferable, and fluorine is more preferable. Since the fluorine-containing film advantageous for battery characteristics is formed on the negative electrode surface by the decomposition of the cyclic carbonate having fluorine, it is preferable to employ the cyclic carbonate having fluorine.

  Specific examples of the cyclic carbonate having fluorine include fluoroethylene carbonate, 4- (trifluoromethyl) -1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, 4-fluoro-4-methyl-1,3-dioxolan-2-one, 4- (fluoromethyl) -1,3-dioxolan-2-one, 4,5-difluoro-1,3-dioxolan-2-one 4-fluoro-5-methyl-1,3-dioxolan-2-one and 4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one, among which fluoroethylene carbonate Is preferred.

  Specific examples of the cyclic carbonate having a carbon-carbon double bond include vinylene carbonate, fluorovinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl Examples thereof include vinylene carbonate, dipropyl vinylene carbonate, trifluoromethyl vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate. Among these, vinylene carbonate is preferable.

  In the electrolytic solution of the present invention, the molar ratio of the cyclic carbonate having halogen or the cyclic carbonate having a carbon-carbon double bond to the electrolyte is preferably in the range of 0.1 to 6, and in the range of 0.3 to 3 The inside is more preferable, the inside of the range of 0.5 to 2 is further preferable, and the inside of the range of 0.7 to 1.5 is particularly preferable.

  In the electrolytic solution of the present invention, the ratio of the cyclic carbonate having halogen or the cyclic carbonate having carbon-carbon double bond to the total organic solvent contained is 1 to 55% by mass, 1 to 55% by volume, or 1 to 60 mol. %, More preferably 2 to 40% by weight, 2 to 40% by volume or 5 to 40% by mole, and 3 to 20% by weight, 3 to 20% by volume or 7 to 20% by mole. More preferably, it is 5-10 mass%, 5-10 volume%, or 10-15 mol% is especially preferable.

  In the electrolytic solution of the present invention, the cyclic carbonate having a halogen or the cyclic carbonate having a carbon-carbon double bond with respect to the total amount of the phosphate ester, the cyclic carbonate having a halogen and the cyclic carbonate having a carbon-carbon double bond. The proportion is preferably 1 to 55% by mass, 1 to 55% by volume or 1 to 60% by mol, more preferably 2 to 40% by mass, 2 to 40% by volume or 5 to 40% by mol, More preferably, it is 3-20 mass%, 3-20 volume%, or 7-20 mol%, and it is especially preferable that it is 5-10 mass%, 5-10 volume%, or 10-15 mol%.

  The electrolytic solution of the present invention may contain an organic solvent other than a phosphate ester, a cyclic carbonate having a halogen, and a cyclic carbonate having a carbon-carbon double bond (hereinafter sometimes referred to as another organic solvent). .

  Other organic solvents include 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane, 2,2-dimethyl-1, Ethers such as 3-dioxolane, 2-methyltetrahydropyran, 2-methyltetrahydrofuran and crown ether, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, cyclic carbonates such as ethylene carbonate and propylene carbonate, benzene , Aromatics such as toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, 1-methylnaphthalene, saturated hydrocarbons such as hexane, heptane, octanecyclohexane, cycloheptane, methyl acetate, ethyl acetate, acetic acid The Pills, methyl propionate, methyl formate, ethyl esters such as vinyl acetate, dimethyl sulfite, sulfite esters such as dipropyl sulfite, dimethyl sulfide, may be mentioned sulfides such as diethyl sulfide. As another organic solvent, 1 type may be employ | adopted and 2 or more types may be employ | adopted.

A stainless steel current collector will be described.
Stainless steel is an alloy steel containing 50% by mass or more of iron and 10.5% by mass or more of chromium. As the stainless steel, those described in JIS G 4304, JIS G 4305, etc. may be adopted. As the stainless steel current collector, stainless clad steel whose base material is coated with stainless steel may be adopted.

  Examples of the stainless steel include austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, austenitic / ferritic stainless steel, and precipitation hardening stainless steel. Examples of the austenitic stainless steel include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS310, SUS316, SUS317, SUS321, and SUS347. Examples of martensitic stainless steel include SUS403, SUS410, SUS420, and SUS431. Examples of the ferritic stainless steel include SUS405, SUS430, and SUS430LX. An example of the austenitic / ferritic stainless steel is SUS329J1. Examples of the precipitation hardening stainless steel include SUS630. Austenitic stainless steels such as SUS304 and SUS316 are preferred.

The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. When the current collector is in the form of a foil, sheet, or film, the thickness is preferably in the range of 1 μm to 1000 μm, and more preferably in the range of 10 μm to 700 μm.
A stainless steel current collector may also serve as a part of the battery container.

  The stainless steel current collector may be a positive electrode current collector or a negative electrode current collector. Alternatively, a bipolar electrode current collector in which a positive electrode active material layer is formed on one surface of a stainless steel current collector foil and a negative electrode active material layer is formed on the other surface thereof may be used.

  Hereinafter, the power storage device of the present invention will be described using a lithium ion secondary battery, which is a typical example of the power storage device, as an example.

The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode current collector and / or the negative electrode current collector are made of stainless steel. For example, the positive electrode current collector may be made of stainless steel, and the negative electrode current collector may be a material other than stainless steel, or the negative electrode current collector may be made of stainless steel, and the positive electrode current collector The body may be a material other than stainless steel. Furthermore, both the positive electrode current collector and the negative electrode current collector may be made of stainless steel.
The lithium ion secondary battery of the present invention is preferably a bipolar lithium ion secondary battery in which a positive electrode active material layer is formed on one surface of a stainless steel current collector foil and a negative electrode active material layer is formed on the other surface. .

  The positive electrode includes a current collector and a positive electrode active material layer containing a positive electrode active material that is bound to the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and, if necessary, a conductive additive and / or a binder.

As the positive electrode active material, a layered rock salt structure Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu , Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, at least one element, 1.7 ≦ f ≦ 3), Li _a Ni _b Co _c Al _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, At least one element selected from S, Si, Na, K, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, and La, 1.7 ≦ f ≦ 3), and Li ₂ MnO ₃ . be able to. In addition, as a positive electrode active material, a solid solution composed of a spinel structure compound such as LiMn ₂ O ₄ and a mixture of a spinel structure compound and a layered rock salt structure compound, LiMPO ₄ , LiMVO _4, or Li ₂ MSiO ₄ (formula M in the middle is selected from at least one of Co, Ni, Mn, and Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above-described composition formula as a basic composition, and those obtained by substituting the metal elements contained in the basic composition with other metal elements can also be used as the positive electrode active material. . Further, as a positive electrode active material, a positive electrode active material that does not contain lithium ions contributing to charge / discharge, for example, sulfur alone, a compound in which sulfur and carbon are combined, metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO ₂ and other oxides, polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetate-based organic materials, and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material.

  The amount of the positive electrode active material in the positive electrode active material layer is preferably in the range of 70 to 97% by mass, more preferably in the range of 75 to 96% by mass, still more preferably in the range of 80 to 95% by mass, A range of 95% by mass is particularly preferable.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber) and various metal particles. These conductive assistants can be added to the active material layer alone or in combination of two or more.

  The compounding amount of the conductive additive in the positive electrode active material layer is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 5% by mass, and still more preferably in the range of 1 to 3% by mass. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the formability of the positive electrode active material layer is deteriorated and the energy density of the electrode is lowered.

  The binder plays a role of securing an active material or a conductive auxiliary agent to the surface of the current collector and maintaining a conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Poly (meth) acrylic resins including meth) acrylic acid and its derivatives, styrene-butadiene rubber (SBR), carboxymethylcellulose, sodium alginate, alginates such as ammonium alginate, water-soluble cellulose ester crosslinked product, starch-acrylic acid A graft polymer can be illustrated. These binders may be used singly or in plural.

  A cross-linked polymer obtained by cross-linking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid with a polyamine such as diamine disclosed in International Publication No. 2016/063882 may be used as a binder. The crosslinked polymer is an embodiment of a poly (meth) acrylic resin.

  Examples of the diamine used in the crosslinked polymer include alkylene diamines such as ethylene diamine, propylene diamine, and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylenediamine, 2,6-tolylenediamine, xylylenediamine, and naphthalenediamine are exemplified.

  The amount of the binder in the positive electrode active material layer is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 7% by mass, and still more preferably in the range of 2 to 5% by mass. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a conductive additive and / or a binder.

As the negative electrode active material, a material that can occlude and release charge carriers can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release charge carriers such as lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. Specific examples of the alloy or compound include tin-based materials such as an Ag—Sn alloy, Cu—Sn alloy, and Co—Sn alloy, carbon-based materials such as various graphites, Si, SiO _x (0.2 ≦ x ≦ 1. Examples thereof include Si-containing materials such as 6) and composites obtained by combining Si-containing materials and carbon-based materials. Further, the anode active _material, oxides such as _{Nb 2 O 5, TiO 2,} Li 4 Ti 5 O 12, WO 2, MoO 2, Fe 2 O 3, _{or, Li 3-x M x N} (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

  In view of the possibility of increasing the capacity, preferred negative electrode active materials include graphite and Si-containing materials. Moreover, lithium titanate can be mentioned as a preferable negative electrode active material from points, such as a rate characteristic.

  When the electrolytic solution of the present invention contains a cyclic carbonate having a halogen or a cyclic carbonate having a carbon-carbon double bond, in view of the action that it can support a good charge / discharge reaction for graphite, as the negative electrode active material, It is preferred to select graphite.

  The compounding amount of the negative electrode active material in the negative electrode active material layer is preferably within the range of 70 to 99% by mass, more preferably within the range of 80 to 98% by mass, and even more preferably within the range of 90 to 97% by mass.

  What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about the conductive support agent used for a negative electrode. The amount of the conductive additive in the negative electrode active material layer is preferably in the range of 0.1 to 5% by mass, more preferably in the range of 0.3 to 4% by mass, and in the range of 0.5 to 3% by mass. Is more preferable.

  What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about the binder used for a negative electrode. The amount of the binder in the negative electrode active material layer is preferably in the range of 0.5 to 10% by mass, more preferably in the range of 1 to 5% by mass, and still more preferably in the range of 2 to 3% by mass.

  In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a solvent, and, if necessary, a binder and / or a conductive aid are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The slurry is applied to the surface of the current collector and then dried. In order to increase the electrode density, the dried product may be compressed.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  Next, the manufacturing method of a lithium ion secondary battery is demonstrated.

The separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a lead for current collection, etc., an electrolyte is added to the electrode body and a lithium ion secondary Use batteries.
In the case of a bipolar lithium ion secondary battery, the bipolar electrode and the separator are laminated in order so that the single cells composed of the positive electrode active material layer, the separator, and the negative electrode active material layer are arranged in series. .

  The lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode. The lithium ion secondary battery of the present invention is suitable for charging and discharging under high potential conditions because corrosion of a stainless steel current collector is suppressed. Examples of the high potential condition include 4 to 5.5 V, 4.2 to 5 V, 4.4 to 4.8 V, and 4.5 to 4.7 V based on lithium.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

(Example 1)
The electrolyte solution of Example 1 was manufactured by mixing (FSO ₂ ) ₂ NLi and trimethyl phosphate at a molar ratio of 1:10.

A coin cell using the electrolytic solution of Example 1 was manufactured as follows.
A stainless steel foil (corresponding to SUS316) having a diameter of 15.5 mm and a thickness of 0.5 mm was used as a working electrode, and the counter electrode was metallic lithium. As the separator, a 0.44 mm thick glass filter nonwoven fabric was used.
The working electrode, the counter electrode, the separator, and the electrolytic solution of Example 1 were accommodated in an aluminum battery case (CR2032-type coin cell case manufactured by Hosen Co., Ltd.) to produce a half cell. This was designated as a coin cell of Example 1.

(Comparative Example 1)
The electrolyte solution of Comparative Example 1 was produced by mixing (FSO ₂ ) ₂ NLi and dimethyl carbonate at a molar ratio of 1:10.
A coin cell of Comparative Example 1 was manufactured in the same manner as in Example 1 except that the electrolytic solution of Comparative Example 1 was used.

(Comparative Example 2)
The electrolyte solution of Comparative Example 2 was produced by mixing (FSO ₂ ) ₂ NLi and tris (2,2,2-trifluoroethyl phosphate) at a molar ratio of 1:10.
A coin cell of Comparative Example 2 was manufactured in the same manner as in Example 1 except that the electrolytic solution of Comparative Example 2 was used.

(Reference Example 1)
A coin cell of Reference Example 1 was manufactured in the same manner as in Example 1 except that aluminum foil (JIS A1000 series) was used instead of stainless steel foil.

(Reference Example 2)
A coin cell of Reference Example 2 was manufactured in the same manner as in Comparative Example 1 except that aluminum foil (JIS A1000 series) was used instead of stainless steel foil.

(Reference Example 3)
A coin cell of Reference Example 3 was manufactured in the same manner as in Comparative Example 2 except that aluminum foil (JIS A1000 series) was used instead of stainless steel foil.

(Evaluation example 1)
For the coin cells of Example 1, Comparative Example 1, Comparative Example 2, and Reference Examples 1 to 3, 12 cycles of cyclic voltammetry evaluation was performed under the conditions of 3.5 V to 4.6 V and 1 mV / s.
The graph which shows the relationship between the electric potential with respect to each coin cell and the response current in 1 cycle, 6 cycles and 12 cycles is shown in FIGS.

The coin cells of Example 1, Comparative Example 1 and Comparative Example 2 are all made of stainless steel foil as a working electrode. 2 and 3, it can be seen that in the coin cells of Comparative Example 1 and Comparative Example 2, an excessive current is generated as the voltage is increased, and that the amount of current is remarkably increased as the number of cycles is increased. The excess current is presumed to be due to corrosion of the stainless steel foil.
On the other hand, it can be seen from FIG. 1 that in the coin cell of Example 1, almost no current is generated even when the voltage rises to 4.6V. It can be said that the power storage device of the present invention including a stainless steel current collector can suppress the corrosion of stainless steel even under high potential conditions. Moreover, since it can be said from the results of Comparative Example 2 that the electrolytic solution containing the fluorine-containing phosphate ester causes corrosion of the stainless steel, the corrosion inhibition effect of the stainless steel observed in Example 1 is the electrolysis of the present invention. It can be said that it is peculiar to the phosphate ester represented by O = P (OR) ₃ (R is each independently an alkyl group) defined by the liquid.

Each of the coin cells of Reference Examples 1 to 3 has an aluminum foil as a working electrode. 4 and 6, in the coin cells of Reference Example 1 and Reference Example 3, a slight current was generated in the first cycle, but almost no current was generated in the sixth and twelfth cycles. .
Further, it can be seen from FIG. 5 that in the coin cell of Reference Example 2, an excessive current was generated in the first cycle. It can be said that the electrolytic solution of Comparative Example 1 containing (FSO ₂ ) ₂ NLi and dimethyl carbonate in a molar ratio of 1:10 corrodes aluminum under a high potential condition of 4 V or higher.

(Production Example 1)
The electrolytic solution of Production Example 1 was produced by mixing (FSO ₂ ) ₂ NLi, trimethyl phosphate, and fluoroethylene carbonate in a molar ratio of 0.5: 9: 1. In the electrolytic solution of Production Example 1, the molar ratio of the phosphate ester to the electrolyte is 18. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Production Example 1 is 0.40 mol / L.

(Production Example 2)
The electrolytic solution of Production Example 2 was produced by mixing (FSO ₂ ) ₂ NLi, trimethyl phosphate and fluoroethylene carbonate in a molar ratio of 1: 9: 1. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Production Example 2 is 0.76 mol / L.

(Production Example 3)
The electrolytic solution of Production Example 3 was produced by mixing (FSO ₂ ) ₂ NLi, trimethyl phosphate, and fluoroethylene carbonate in a molar ratio of 2: 9: 1. In the electrolytic solution of Production Example 3, the molar ratio of the phosphate ester to the electrolyte is 4.5. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Production Example 3 is 1.44 mol / L.

(Production Example 4)
The electrolytic solution of Production Example 4 was produced by mixing (FSO ₂ ) ₂ NLi, trimethyl phosphate, and fluoroethylene carbonate in a molar ratio of 3: 9: 1. In the electrolytic solution of Production Example 4, the molar ratio of the phosphate ester to the electrolyte is 3. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Production Example 4 is 2.09 mol / L.

(Evaluation example 2)
About the electrolyte solution of manufacture example 1-manufacture example 4, the ion conductivity was measured with the following method. The results are shown in Table 1.

Ion conductivity measurement method An electrolyte was sealed in a Pt / Pt symmetrical cell, and the AC impedance was measured at 25 ° C. The cell constant of the Pt / Pt symmetric cell has been calculated by measurement using a standard KCl aqueous solution. The ionic conductivity of each electrolyte was calculated from the intercept calculated from the impedance measurement result and the cell constant.

  From the results of Table 1, it is considered that particularly excellent ionic conductivity is exhibited in the electrolytic solution having a sulfonic acid derivative salt concentration of about 0.8 mol / L.

(Production Example 5)
The electrolytic solution of Production Example 5 was produced by mixing (FSO ₂ ) ₂ NLi, trimethyl phosphate, and fluoroethylene carbonate in a molar ratio of 1: 9.9: 0.1.

(Production Example 6)
_{(FSO 2)} 2 NLi and trimethyl phosphate and fluoroethylene carbonate in a molar ratio of 1: 4.3: By mixing 5.7 was prepared an electrolytic solution of Preparation 6.

(Evaluation example 3)
A heat resistance test was performed on the electrolytic solutions of Production Example 2, Production Example 5 and Production Example 6 by the following method. As a result, none of the electrolyte solutions burned. It can be said that the electrolytic solution of the present invention is excellent in heat resistance.

<Heat resistance test>
1) A glass filter having a diameter of 10 mm is impregnated with 100 μL of an electrolytic solution.
2) Bring the flame close to the glass filter impregnated with the electrolyte for several seconds.

(Application 1)
FIG. 7 shows a schematic cross-sectional view of the bipolar lithium ion secondary battery of Application Example 1 observed from the thickness side of the electrode.

The bipolar lithium ion secondary battery 1 of Application Example 1 is
A positive electrode 2 having a positive electrode active material layer 21 formed on one surface of a stainless steel current collector foil 20, and
A negative electrode 3 having a negative electrode active material layer 31 formed on one surface of a stainless steel current collector foil 30;
A bipolar electrode 4 having a positive electrode active material layer 41 formed on one surface of a stainless steel current collector foil 40 and a negative electrode active material layer 42 formed on the other surface;
Separator 5;
An electrolyte solution 10 containing a salt of a sulfonic acid derivative and a phosphate ester represented by O = P (OR) ₃ (wherein each R is independently an alkyl group) is provided.

  The electrolytic solution 10 includes a positive electrode active material layer 41, a space where the separator 5 and the negative electrode active material layer 42 exist, a positive electrode active material layer 21, a space where the separator 5 and the negative electrode active material layer 42 exist, and the positive electrode active material layer 41. The space where the separator 5 and the negative electrode active material layer 31 are present is sufficiently filled.

  The current collector foil 20 in the positive electrode 2 is made of stainless steel and is a rectangular foil having a thickness of 20 μm. A positive electrode active material layer 21 including a positive electrode active material, a conductive additive, and a binder is formed on the upper surface of the current collector foil 20. The peripheral edge of the current collector foil 20 is fixed with an outer frame 7 made of synthetic resin, and a resin seal portion 6 is disposed inside the outer frame 7. The seal portion 6 is bound to the upper surface and the lower surface of the current collector foil 20.

  A separator 5 is disposed on the upper surface of the positive electrode active material layer 21 of the positive electrode 2. The separator 5 is a polyolefin porous film. The surface of the separator 5 has a larger area than the surface of the positive electrode active material layer 21 in contact therewith.

  On the upper surface of the separator 5 disposed on the upper surface of the positive electrode active material layer 21 of the positive electrode 2, the bipolar electrode 4 is disposed in the direction in which the negative electrode active material layer 42 faces.

  In the bipolar electrode 4, a positive electrode active material layer 41 is formed on the upper surface of the current collector foil 40, and a negative electrode active material layer 42 is formed on the lower surface. The current collector foil 40 is the same as the current collector foil 20 of the positive electrode 2, and the positive electrode active material layer 41 is the same as the positive electrode active material layer 21 of the positive electrode 2. The negative electrode active material layer 42 of the bipolar electrode 4 contains a negative electrode active material, a conductive additive and a binder.

  The peripheral edge of the current collector foil 40 is fixed with an outer frame 7 made of synthetic resin, and a resin seal portion 6 is disposed inside the outer frame 7. The seal portion 6 is bound to the upper and lower surfaces of the current collector foil 40, and the seal portion 6 on the upper surface of the current collector foil 40 is also bound to the lower surface of the current collector foil 40 of the other bipolar electrode 4. In addition, the seal portion 6 on the lower surface of the current collector foil 40 is also bound to the upper surface of the current collector foil 20 of the positive electrode 2. That is, the positive electrode active material layer 21, the separator 5, the electrolytic solution 10, and the negative electrode active material layer 42 are in a sealed state by the seal portion 6.

A plurality of bipolar electrodes 4 are laminated on the upper surface of the bipolar electrode 4 laminated on the positive electrode 2 via the separator 5 via the separator 5.
The separator 5 is disposed on the upper surface of the positive electrode active material layer 41 of the uppermost bipolar electrode 4, and the negative electrode 3 is disposed on the upper surface of the separator 5 in the direction in which the negative electrode active material layer 31 faces.

  In the negative electrode 3, a negative electrode active material layer 31 is formed on the lower surface of the current collector foil 30. The current collector foil 30 is the same as the current collector foil 20 of the positive electrode 2 and the current collector foil 40 of the bipolar electrode 4, and the negative electrode active material layer 31 is the same as the negative electrode active material layer 42 of the bipolar electrode 4. is there. The peripheral edge of the current collector foil 30 is fixed by an outer frame 7 made of synthetic resin, and a resin seal portion 6 is disposed inside the outer frame 7. The seal portion 6 is bound to the upper and lower surfaces of the current collector foil 30, and the seal portion 6 on the lower surface of the current collector foil 30 is also bound to the upper surface of the current collector foil 40 of the bipolar electrode 4.

  Cooling units 8 are respectively arranged above and below in the thickness direction of the battery module including the positive electrode 2, the bipolar electrode 4, the negative electrode 3, and the separator 5. The cooling unit 8 is an aluminum rectangular plate, and is provided with a plurality of air-cooling through holes 80.

A module positive electrode 22 and a module negative electrode 32 that conduct electricity to the outside are disposed outside the cooling unit 8. The module positive electrode 22 and the module negative electrode 32 are metal rectangular plates.
And the restraining tool 9 is arrange | positioned on the outer side of the module positive electrode 22 and the module negative electrode 32, respectively. The restraining tool 9 is a rectangular plate made of synthetic resin. The two restraining tools 9 are fastened by a plurality of bolts and nuts (not shown), and pressurize and restrain the battery module in the thickness direction of the electrodes.

DESCRIPTION OF SYMBOLS 1 Bipolar lithium ion secondary battery 2 Positive electrode 3 Negative electrode 4 Bipolar electrode 5 Separator 6 Seal part 7 Outer frame 8 Cooling part 9 Restraint 10 Electrolyte 20 Stainless steel current collector foil (positive electrode current collector foil)
21 Positive electrode active material layer 22 Module positive electrode 30 Stainless steel current collector foil (negative electrode current collector foil)
31 Negative electrode active material layer 32 Module negative electrode 40 Stainless steel current collector foil (bipolar electrode current collector foil)
41 Positive electrode active material layer 42 Negative electrode active material layer 80 Through hole

Claims (4)

An electrolyte containing a salt of a sulfonic acid derivative and a phosphate ester represented by O = P (OR) ₃ (wherein each R is independently an alkyl group);
A stainless steel current collector,
A power storage device comprising: The power storage device is a bipolar power storage device including a bipolar electrode in which a positive electrode active material layer is formed on one surface of a current collector foil and a negative electrode active material layer is formed on the other surface,
The power storage device according to claim 1, wherein the current collector foil is made of stainless steel.   The power storage device according to claim 1, wherein the salt of the sulfonic acid derivative is a sulfonic acid imide salt.   The power storage device according to any one of claims 1 to 3, wherein a ratio of the phosphate ester to a total organic solvent contained in the electrolytic solution is 50 mass% or more, 50 volume% or more, or 40 mol% or more.