CN110537284B - Polymer electrolyte composition and polymer secondary battery - Google Patents

Polymer electrolyte composition and polymer secondary battery Download PDF

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Publication number
CN110537284B
CN110537284B CN201780089823.8A CN201780089823A CN110537284B CN 110537284 B CN110537284 B CN 110537284B CN 201780089823 A CN201780089823 A CN 201780089823A CN 110537284 B CN110537284 B CN 110537284B
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positive electrode
polymer
polymer electrolyte
mass
poly
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CN110537284A (en
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小川秀之
三国纮挥
濑良祐介
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LG Energy Solution Ltd
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LG Energy Solution Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/54—Electrolytes
    • H01G11/58—Liquid electrolytes
    • H01G11/62—Liquid electrolytes characterised by the solute, e.g. salts, anions or cations therein
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The present invention discloses a polymer electrolyte composition comprising: a polymer having a structural unit represented by the following general formula (1); and a complex of at least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts and calcium salts with a (poly) ethylene glycol dialkyl ether represented by the following general formula (2). [ in formula (1), X ‑ Represents a counter anion.]R 1 O‑(CH 2 CH 2 O) m ‑R 2 (2) [ in formula (2), R 1 And R is 2 Each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 1 to 6.]

Description

Polymer electrolyte composition and polymer secondary battery
Technical Field
The present invention relates to a polymer electrolyte composition and a polymer secondary battery.
Background
Lithium secondary batteries are energy devices having high energy density, and are widely used as power sources for portable electronic devices and electric vehicles. For example, in a 18650 type lithium secondary battery, a wound electrode body is accommodated inside a cylindrical battery case. The wound electrode body is formed by sandwiching a microporous separator between a positive electrode and a negative electrode, winding them in a spiral shape, and impregnating the separator with a flammable electrolyte. In such a lithium secondary battery, if the temperature of the battery suddenly increases during an abnormal situation, the electrolyte is vaporized, and the internal pressure may increase, resulting in a possibility of rupture. In addition, if the temperature of the battery suddenly rises, there is also a possibility that the electrolyte fires.
Preventing ignition or firing of the lithium secondary battery is important in the design of the lithium secondary battery. In order to further increase the energy density and the size of lithium secondary batteries in the future, further improvement in safety is required.
As a basic solution for improving the safety of lithium secondary batteries, development of all-solid batteries in which an electrolyte is replaced with a polymer electrolyte or an inorganic solid electrolyte and all of the constituent materials are solid has been underway. In particular, polymer electrolytes are actively studied because they can be easily formed into sheets by coating a polymer solution.
A widely studied material in polymer electrolytes is polyethylene oxide (PEO). PEO showed more than 1X 10 at 60℃ -4 The high ion conductivity of S/cm has been practically used in some vehicle-mounted applications (for example, refer to patent document 1 and non-patent document 1).
In addition, nonaqueous solvents combined with polymer electrolytes are also being actively studied in order to improve ion conductivity. As the nonaqueous solvent, an organic solvent such as dialkyl carbonate is widely used from the viewpoint of ion conductivity (for example, refer to patent document 2).
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 2006-294326
Patent document 2: japanese patent laid-open No. 2007-141467
Non-patent literature
Non-patent document 1: hovington et al, nano Lett.2015, 15, 2671-2678
Disclosure of Invention
Problems to be solved by the invention
However, the polymer electrolyte using PEO described in patent document 1 has not been widely put into practical use because of its low oxidation stability and its significantly reduced ionic conductivity at low temperatures below room temperature.
In addition, the polymer electrolyte described in patent document 2 in combination with an organic solvent exhibits high ionic conductivity, but safety is a concern. In addition, since the organic solvent is easily volatilized, it is difficult to handle the organic solvent when formed into a sheet shape, and it is difficult to remove moisture by drying, which is necessary for improving battery characteristics. In addition, depending on the kinds of the polymer electrolyte and the organic solvent, there is a fear that the polymer electrolyte is separated from the organic solvent, and the ionic conductivity and mechanical strength of the polymer electrolyte sheet are remarkably reduced.
The present invention has been made in view of the above circumstances, and a main object thereof is to provide a polymer electrolyte composition which can produce a sheet having excellent ionic conductivity at room temperature (for example, 25 ℃) and high self-supporting properties, even without using an organic solvent.
Means for solving the problems
The first aspect of the present invention is a polymer electrolyte composition comprising: a polymer having a structural unit represented by the following general formula (1); and a complex of at least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts and calcium salts with (poly) ethylene glycol dialkyl ether (Glyme) represented by the following general formula (2).
[ chemical 1]
[ in formula (1), X - Represents a counter anion.]
R 1 O-(CH 2 CH 2 O) m -R 2 (2)
[ in formula (2), R 1 And R is 2 Each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 1 to 6.]
In the present specification, a complex of at least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts, and calcium salts with a (poly) ethylene glycol dialkyl ether represented by the general formula (2) is sometimes referred to as a "(poly) ethylene glycol dialkyl ether complex).
According to the polymer electrolyte composition according to the first aspect of the present invention, a sheet having excellent ionic conductivity at room temperature and high self-supporting property can be produced without using an organic solvent. (Poly) ethylene glycol dialkyl ether complexes are produced by drying (e.g., at 60 ℃ C. Or less than or equal to 1.0X10) 4 The polymer electrolyte composition is substantially nonvolatile in drying under reduced pressure of 0.1 atm or less for 10 hours or more, and thus can be a material having high thermal stability.
The content of the (poly) ethylene glycol dialkyl ether complex may be 10 to 70 mass% based on the total amount of the composition.
The anions of the salt may be selected from PF 6 - 、BF 4 - 、N(FSO 2 ) 2 - 、N(CF 3 SO 2 ) 2 - 、B(C 2 O 4 ) 2 - And ClO 4 - At least one of the group consisting of. The salt may be a lithium salt.
M in formula (2) may be 3 or 4. The (poly) ethylene glycol dialkyl ether represented by the general formula (2) may be triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.
The polymer electrolyte composition may be formed into a sheet shape. The sheet formed using the polymer electrolyte composition may be a sheet capable of maintaining its shape even without a substrate or the like. In the present specification, the polymer electrolyte composition formed into a sheet shape is sometimes referred to as a "polymer electrolyte sheet".
A second aspect of the present invention is a polymer secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer provided between the positive electrode and the negative electrode and containing the polymer electrolyte composition.
Effects of the invention
According to the present invention, there can be provided a polymer electrolyte composition capable of producing a sheet having excellent ionic conductivity at room temperature and high self-supporting property even without using an organic solvent. In addition, according to the present invention, a polymer secondary battery using such a polymer electrolyte composition can be provided.
Drawings
Fig. 1 is a perspective view showing a polymer secondary battery according to a first embodiment.
Fig. 2 is an exploded perspective view illustrating one embodiment of an electrode group in the polymer secondary battery shown in fig. 1.
Fig. 3 is a schematic cross-sectional view illustrating one embodiment of an electrode group in the polymer secondary battery shown in fig. 1.
In fig. 4, (a) is a schematic cross-sectional view showing a polymer electrolyte sheet according to one embodiment, and (b) is a schematic cross-sectional view showing a polymer electrolyte sheet according to another embodiment.
Fig. 5 is a schematic cross-sectional view showing an embodiment of an electrode group of a polymer secondary battery according to a second embodiment.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including steps) are not necessarily required unless otherwise specifically indicated. The sizes of the constituent elements in the drawings are conceptual, and the relative relationship of the sizes of the constituent elements is not limited to the case shown in the drawings.
The numerical values and ranges thereof in the present specification are also not limiting to the present invention. In the present specification, the numerical range indicated by the term "to" means a range including numerical values described before and after the term "to" as a minimum value and a maximum value, respectively. In the numerical ranges described in stages in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stage. In the numerical ranges described in the present specification, the upper limit or the lower limit of the numerical range may be replaced with the values shown in the examples.
In the present specification, the following marks may be used as abbreviations.
[EMI] + : 1-ethyl-3-methylimidazoleCations (cationic)
[DEME] + : n, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation
[Py12] + : N-ethyl-N-methylpyrrolidineCations (cationic)
[Py13] + : N-methyl-N-propylpyrrolidineCations (cationic)
[PP13] + : N-methyl-N-propylpiperidineCations (cationic)
[LiG4] + : tetraethylene glycol dimethyl ether lithium cation
[FSI] - : bis (fluorosulfonyl) imide anions
[TFSI] - : bis (trifluoromethanesulfonyl) imide anions
[f3C] - : tri (fluorosulfonyl) anion
[BOB] - : biethyl diacid borate anions
[ P (DADMA) ] [ Cl ]: polydiallyl dimethyl ammonium chloride
[ P (DADMA) ] [ TFSI ]: poly (diallyldimethylammonium) bis (trifluoromethanesulfonyl) imide
First embodiment
Fig. 1 is a perspective view showing a polymer secondary battery according to a first embodiment. As shown in fig. 1, a polymer secondary battery 1 includes an electrode group 2 including a positive electrode, a negative electrode, and an electrolyte layer, and a pouch-shaped battery case 3 accommodating the electrode group 2. Positive and negative electrode collector tabs 4 and 5 are provided on the positive and negative electrodes, respectively. Positive electrode collector tab 4 and negative electrode collector tab 5 protrude from the inside of battery case 3 to the outside, respectively, so that the positive electrode and the negative electrode can be electrically connected to the outside of polymer secondary battery 1, respectively.
The battery case 3 may be formed of, for example, a laminate film. The laminate film may be, for example, a laminate film in which a resin film such as a polyethylene terephthalate (PET) film, a metal foil such as aluminum, copper, stainless steel, and a sealant layer such as polypropylene are laminated in this order.
Fig. 2 is an exploded perspective view showing one embodiment of the electrode group 2 in the polymer secondary battery 1 shown in fig. 1. Fig. 3 is a schematic cross-sectional view showing one embodiment of the electrode group 2 in the polymer secondary battery 1 shown in fig. 1. As shown in fig. 2 and 3, the electrode group 2A according to the present embodiment includes a positive electrode 6, an electrolyte layer 7, and a negative electrode 8 in this order. The positive electrode 6 includes a positive electrode current collector 9 and a positive electrode mixture layer 10 provided on the positive electrode current collector 9. The positive electrode collector 9 is provided with a positive electrode collector tab 4. The negative electrode 8 includes a negative electrode current collector 11 and a negative electrode mixture layer 12 provided on the negative electrode current collector 11. Negative electrode collector tab 5 is provided on negative electrode collector 11.
The positive electrode current collector 9 may be formed of aluminum, stainless steel, titanium, or the like. Specifically, the positive electrode current collector 9 may be an aluminum perforated foil, expanded metal, foam metal sheet, or the like having holes with a pore diameter of 0.1 to 10 mm. In addition to the above, the positive electrode current collector 9 may be formed of any material as long as it does not undergo any change such as dissolution or oxidation during use of the battery, and the shape, manufacturing method, and the like thereof are not limited.
The thickness of the positive electrode current collector 9 may be 1 μm or more, 5 μm or more, or 10 μm or more. The thickness of the positive electrode current collector 9 may be less than or equal to 100 μm, less than or equal to 50 μm, or less than or equal to 20 μm.
In one embodiment, the positive electrode mixture layer 10 contains a positive electrode active material, a conductive agent, and a binder.
The positive electrode active material may be LiCoO 2 、Li 0.3 MnO 2 、Li 4 Mn 5 O 12 、V 2 O 5 、LiMn 2 O 4 、LiNiO 2 、LiFePO 4 、LiCo 1/3 Ni 1/3 Mn 1/3 O 2 、Li 1.2 (Fe 0.5 Mn 0.5 ) 0.8 O 2 、Li 1.2 (Fe 0.4 Mn 0.4 Ti 0.2 ) 0.8 O 2 、Li 1+x (Ni 0.5 Mn 0.5 ) 1-x O 2 (wherein, x=0 to 1.), liNi 0.5 Mn 1.5 O 4 、Li 2 MnO 3 、Li 0.76 Mn 0.51 Ti 0.49 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、Fe 2 O 3 、LiCoPO 4 、LiMnPO 4 、Li 2 MPO 4 F(M＝Fe、Mn)、LiMn 0.875 Fe 0.125 PO 4 、Li 2 FeSiO 4 、Li 2-x MSi 1-x P x O 4 (m=fe, mn) (where x=0 to 1), liMBO 3 (M＝Fe、Mn)、FeF 3 、Li 3 FeF 6 、Li 2 TiF 6 、Li 2 FeS 2 、TiS 2 、MoS 2 FeS, etc.
The positive electrode active material may be primary particles that have not been granulated, or may be secondary particles that have been granulated.
The particle diameter of the positive electrode active material is adjusted to be less than or equal to the thickness of the positive electrode mixture layer 10. When coarse particles having a particle diameter equal to or larger than the thickness of the positive electrode mixture layer 10 are present in the positive electrode active material, the coarse particles are removed in advance by screening classification, air classification, or the like, and the positive electrode active material having a particle diameter equal to or smaller than the thickness of the positive electrode mixture layer 10 is selected.
The average particle diameter of the positive electrode active material is preferably 1 μm or more, more preferably 3 μm or more, further preferably 5 μm or more, and further preferably 30 μm or less, more preferably 25 μm or less, further preferably 20 μm or less, from the viewpoint of suppressing deterioration of the filling property of the positive electrode active material accompanying the particle diameter reduction and improving the holding ability of the electrolyte. The average particle diameter of the positive electrode active material means the particle diameter (D) at which the ratio (volume fraction) of the volume to the total volume of the positive electrode active material is 50% 50 ). Average particle diameter of positive electrode active material (D 50 ) The preparation method comprises the following steps of: the positive electrode active material was suspended in water by laser light scattering measurement using a laser light scattering particle size measuring device (e.g., microtrac)And a suspension obtained by the method.
The content of the positive electrode active material may be 80 mass% or more, 85 mass% or more, or 90 mass% or more based on the total amount of the positive electrode active material, the conductive agent, and the binder. The content of the positive electrode active material may be, for example, 99 mass% or less based on the total amount of the positive electrode active material, the conductive agent, and the binder.
The conductive agent can be carbon black, graphite, carbon fiber, carbon nanotube, acetylene black, etc.
The content of the conductive agent may be 1 mass% or more, 3 mass% or more, or 5 mass% or more based on the total amount of the positive electrode active material, the conductive agent, and the binder. From the viewpoint of suppressing an increase in the volume of the positive electrode 6 and a concomitant decrease in the energy density of the polymer secondary battery 1, the content of the conductive agent is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 9% by mass or less, based on the total amount of the positive electrode active material, the conductive agent, and the binder.
The binder is not limited as long as it does not decompose on the surface of the positive electrode 6, and is, for example, a polymer. The binder can be polyvinylidene fluoride, polyacrylonitrile, styrene-butadiene rubber, carboxyl-methyl cellulose, fluororubber, ethylene-propylene rubber, polyacrylic acid, polyimide, polyamide and other resins; resins having copolymers having these resins as a main skeleton (for example, polyvinylidene fluoride-hexafluoropropylene copolymers and the like), and the like.
The content of the binder may be 1 mass% or more, 3 mass% or more, or 5 mass% or more based on the total amount of the positive electrode active material, the conductive agent, and the binder. The content of the binder may be 15 mass% or less, 12 mass% or less, or 9 mass% or less based on the total amount of the positive electrode active material, the conductive agent, and the binder.
The positive electrode mixture layer 10 may further contain a soft viscous crystal, a molten salt such as an ionic liquid, and the like, if necessary. The content of the molten salt may be 0.01 to 20% by mass based on the total amount of the positive electrode mixture layer.
From the viewpoint of further improving the conductivity, the thickness of the positive electrode mixture layer 10 is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 30 μm or more, of the average particle diameter of the positive electrode active material. The thickness of the positive electrode mixture layer 10 is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 60 μm or less. By setting the thickness of the positive electrode mixture layer to 100 μm or less, it is possible to suppress the unevenness of charge and discharge caused by the variation in the charge level of the positive electrode active material in the vicinity of the surface of the positive electrode mixture layer 10 and the vicinity of the surface of the positive electrode current collector 9.
From the viewpoint of bringing the conductive agent and the positive electrode active material into close contact with each other and reducing the electron resistance of the positive electrode mixture layer 10, the mixture density of the positive electrode mixture layer 10 is preferably 1g/cm or more 3 。
The negative electrode current collector 11 may be formed of copper, stainless steel, titanium, nickel, or the like. Specifically, the negative electrode current collector 11 may be a rolled copper foil (for example, a perforated foil made of copper having holes with a diameter of 0.1 to 10 mm), an expanded metal mesh, a foamed metal plate, or the like. The negative electrode current collector 11 may be formed of any material other than the above, and the shape, manufacturing method, and the like thereof are not limited.
The thickness of the anode current collector 11 may be 1 μm or more, 5 μm or more, or 10 μm or more. The thickness of the anode current collector 11 may be less than or equal to 100 μm, less than or equal to 50 μm, or less than or equal to 20 μm.
In one embodiment, the anode mixture layer 12 contains an anode active material and a binder.
As the negative electrode active material, a material used as a negative electrode active material in a general energy device field such as a secondary battery can be used. Examples of the negative electrode active material include lithium metal, lithium alloy, metal compound, carbon material, metal complex, and organic polymer compound. These may be used alone or in combination of two or more. Among these, the anode active material is preferably a carbon material. Examples of the carbon material include graphite such as natural graphite (e.g., flake graphite) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; amorphous carbon, carbon fiber, and the like.
From the viewpoint of obtaining a balanced anode 8 in which the electrolyte retention capacity is improved while suppressing an increase in irreversible capacity with a decrease in particle size, the average particle size (D 50 ) Preferably 1 μm or more, more preferably 3 μm or more, further preferably 5 μm or more, and further preferably 20 μm or less, more preferably 18 μm or less, further preferably 16 μm or less. Average particle diameter of negative electrode active material (D 50 ) By the average particle diameter (D) 50 ) The same method was used for measurement.
The content of the negative electrode active material may be the same as that of the positive electrode active material in the positive electrode mixture layer 10 described above.
The binder and the content thereof may be the same as those in the positive electrode mixture layer 10 described above.
The negative electrode mixture layer 12 may further contain a conductive agent from the viewpoint of further reducing the resistance of the negative electrode 8. The conductive agent and the content thereof may be the same as those in the positive electrode mixture layer 10 described above.
The negative electrode mixture layer 12 may further contain a soft viscous crystal, a molten salt such as an ionic liquid, and the like, if necessary. The molten salt may be exemplified by the same molten salt as described later. The content of the molten salt may be 0.01 to 20% by mass based on the total amount of the negative electrode mixture layer.
From the viewpoint of further improving the conductivity, the thickness of the anode mixture layer 12 is greater than or equal to the average particle diameter of the anode active material, preferably greater than or equal to 10 μm, more preferably greater than or equal to 15 μm, and still more preferably greater than or equal to 20 μm. The thickness of the anode mixture layer 12 is preferably 50 μm or less, more preferably 45 μm or less, and further preferably 40 μm or less. By setting the thickness of the negative electrode mixture layer 12 to 50 μm or less, it is possible to suppress the unevenness of charge and discharge caused by the variation in the charge level of the positive electrode active material in the vicinity of the surface of the negative electrode mixture layer 12 and the vicinity of the surface of the negative electrode collector 11.
From the viewpoint of bringing the conductive agent and the anode active material into close contact with each other and reducing the electron resistance of the anode mixture layer 12, the mixture density of the anode mixture layer 12 is preferably 1g/cm or more 3 。
The electrolyte layer 7 may be formed of a polymer electrolyte composition. The polymer electrolyte composition contains a polymer having a specific structural unit, and a specific complex, i.e., a (poly) ethylene glycol dialkyl ether complex.
[ Polymer ]
The polymer electrolyte composition contains a polymer having a structural unit represented by the following general formula (1).
[ chemical 2]
In the general formula (1), X - Represents a counter anion. Here, as X - For example, BF can be mentioned 4 - (tetrafluoroborate anion), PF 6 - (hexafluorophosphate anion), N (FSO) 2 ) 2 - (bis (fluorosulfonyl) imide anion, [ FSI ]] - )、N(CF 3 SO 2 ) 2 - (bis (trifluoromethanesulfonyl) imide anion, [ TFSI ]] - )、C(SO 2 F) 3 - (tris (fluorosulfonyl) anion, [ f 3C)] - )、B(C 2 O 4 ) 2 - (bis (oxalato) borate anion, [ BOB ]] - )、BF 3 (CF 3 ) - 、BF 3 (C 2 F 5 ) - 、BF 3 (C 3 F 7 ) - 、BF 3 (C 4 F 9 ) - 、C(SO 2 CF 3 ) 3 - 、CF 3 SO 2 O - 、CF 3 COO - 、RCOO - (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). They areWherein X is - Preferably selected from BF 4 - 、PF 6 - 、[FSI] - 、[TFSI] - And [ f3C] - At least one of the group consisting of [ TFSI ]] - Or [ FSI ]] - 。
The polymer having the structural unit represented by the general formula (1) has a viscosity average molecular weight Mv (g.mol) -1 ) There are no particular restrictions, and it is preferably 1.0X10 or more 5 More preferably 3.0X10 or more 5 . In addition, the viscosity average molecular weight of the polymer is preferably less than or equal to 5.0X10 6 More preferably 1.0X10 6 . If the viscosity average molecular weight is greater than or equal to 1.0X10 5 The polymer electrolyte sheet tends to have more excellent self-supporting properties. In addition, if the viscosity average molecular weight is less than or equal to 5.0X10 6 The coating processability tends to be further improved.
In the present specification, the "viscosity average molecular weight" can be evaluated by a viscosity method which is a usual measurement method, and can be calculated from the limiting viscosity [ η ] measured in accordance with JIS K7367-3:1999, for example.
From the viewpoint of ion conductivity, the polymer having the structural unit represented by the general formula (1) is preferably a polymer composed of only the structural unit represented by the general formula (1), that is, a homopolymer.
The polymer having a structural unit represented by the general formula (1) may be a polymer represented by the following general formula (1 a).
[ chemical 3]
In the general formula (1 a), n is 300 to 4000 and Y - Represents a counter anion. Y is Y - Can be used and at X - Counter anions illustrated herein are the same counter anions.
n is greater than or equal to 300, preferably greater than or equal to 400, and more preferably greater than or equal to 500. In addition, 4000 or less, preferably 3500 or less, more preferably 3000 or less. N is 300 to 4000, preferably 400 to 3500, more preferably 500 to 3000. If n is 300 or more, the self-supporting property of the polymer electrolyte sheet tends to be more excellent. If n is 4000 or less, the ionic conductivity of the polymer electrolyte sheet tends to be further improved.
The method for producing the polymer having the structural unit represented by the general formula (1) is not particularly limited, and for example, the production method described in Journal of Power Sources 2009, 188, 558-563 can be used.
A polymer (X) having a structural unit represented by the general formula (1) - ＝[TFSI] - ) For example, the composition can be obtained by the following production method.
Firstly, polydiallyl dimethyl ammonium chloride ([ P (DADMA) ] [ Cl) is dissolved in deionized water, and an aqueous [ P (DADMA) ] [ Cl ] solution is prepared by stirring. For example, commercially available products can be used as such as [ P (DADMA) ] [ Cl ]. Next, li [ TFSI ] was additionally dissolved in deionized water to prepare an aqueous solution containing Li [ TFSI ].
Then, the two aqueous solutions were mixed and stirred for 2 to 8 hours so that the molar ratio of Li [ TFSI ] to [ P (DADMA) ] [ Cl ] (molar amount of Li [ TFSI ]/[ P (DADMA) ] [ Cl ]) became 1.2 to 2.0, and the solid was precipitated, and the obtained solid was collected by filtration. The solid was washed with deionized water and vacuum-dried for 12 to 48 hours, whereby a polymer ([ P (DADMA) ] [ TFSI ]) having a structural unit represented by the general formula (1) was obtained.
The content of the polymer having the structural unit represented by the general formula (1) is not particularly limited, but is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, based on the total amount of the composition. The content of the polymer is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less, based on the total amount of the composition. If the content of the polymer is 10 mass% or more, the strength of the polymer electrolyte sheet tends to be further improved. In addition, by setting the content of the polymer to 80 mass% or less and increasing the amount of other components ((poly) ethylene glycol dialkyl ether complex, etc.), the ion conductivity of the polymer electrolyte sheet can be further improved.
[ (Poly) ethylene glycol dialkyl ether Complex ]
The polymer electrolyte composition contains a complex of at least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts, and calcium salts with a (poly) ethylene glycol dialkyl ether represented by the general formula (2) ((poly) ethylene glycol dialkyl ether complex).
The (poly) ethylene glycol dialkyl ether complex is preferably liquid at room temperature (e.g., 25 ℃). The (poly) ethylene glycol dialkyl ether complex has superior oxidation resistance compared to the (poly) ethylene glycol dialkyl ether that does not form the complex. In addition, the (poly) ethylene glycol dialkyl ether complex has flame retardancy and difficult volatility, and can have a wide potential window.
The anion of the salt may be a halide (I) - 、Cl - 、Br - Etc.), SCN - 、BF 4 - 、BF 3 (CF 3 ) - 、BF 3 (C 2 F 5 ) - 、BF 3 (C 3 F 7 ) - 、BF 3 (C 4 F 9 ) - 、PF 6 - 、ClO 4 - 、SbF 6 - 、[FSI] - 、[TFSI] - 、N(C 2 F 5 SO 2 ) 2 - 、BPh 4 - 、B(C 2 H 4 O 2 ) 2 - 、[f3C] - 、C(CF 3 SO 2 ) 3 - 、CF 3 COO - 、CF 3 SO 2 O - 、C 6 F 5 SO 2 O - 、[BOB] - 、RCOO - (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group or a naphthyl group). Among them, the anions of the electrolyte salt are preferably selected from the group consisting of PF 6 - 、BF 4 - 、[FSI] - 、[TFSI] - 、[BOB] - And ClO 4 - At least one of the group consisting of [ TFSI ]] - Or [ FSI ]] - 。
The lithium salt as the salt may be LiPF 6 、LiBF 4 、Li[FSI]、Li[TFSI]、Li[f3C]、Li[BOB]、LiClO 4 、LiBF 3 (CF 3 )、LiBF 3 (C 2 F 5 )、LiBF 3 (C 3 F 7 )、LiBF 3 (C 4 F 9 )、LiC(SO 2 CF 3 ) 3 、LiCF 3 SO 2 O、LiCF 3 COO, liRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group), and the like. These may be used alone or in combination of two or more.
The sodium salt as a salt may be NaPF 6 、NaBF 4 、Na[FSI]、Na[TFSI]、Na[f3C]、Na[BOB]、NaClO 4 、NaBF 3 (CF 3 )、NaBF 3 (C 2 F 5 )、NaBF 3 (C 3 F 7 )、NaBF 3 (C 4 F 9 )、NaC(SO 2 CF 3 ) 3 、NaCF 3 SO 2 O、NaCF 3 COO, naRCOO (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group), and the like. These may be used alone or in combination of two or more.
The magnesium salt may be Mg (PF 6 ) 2 、Mg(BF 4 ) 2 、Mg[FSI] 2 、Mg[TFSI] 2 、Mg[f3C] 2 、Mg[BOB] 2 、Mg(ClO 4 ) 2 、Mg[BF 3 (CF 3 ) 3 ] 2 、Mg[BF 3 (C 2 F 5 )] 2 、Mg[BF 3 (C 3 F 7 )] 2 、Mg[BF 3 (C 4 F 9 )] 2 、Mg[C(SO 2 CF 3 ) 3 ] 2 、Mg(CF 3 SO 2 O) 2 、Mg(CF 3 COO) 2 、Mg(RCOO) 2 (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used alone or in combination of two or more.
As the calcium salt of the salt, ca (PF 6 ) 2 、Ca(BF 4 ) 2 、Ca[FSI] 2 、Ca[TFSI] 2 、Ca[f3C] 2 、Ca[BOB] 2 、Ca(ClO 4 ) 2 、Ca[BF 3 (CF 3 ) 3 ] 2 、Ca[BF 3 (C 2 F 5 )] 2 、Ca[BF 3 (C 3 F 7 )] 2 、Ca[BF 3 (C 4 F 9 )] 2 、Ca[C(SO 2 CF 3 ) 3 ] 2 、Ca(CF 3 SO 2 O) 2 、Ca(CF 3 COO) 2 、Ca(RCOO) 2 (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used alone or in combination of two or more.
Among them, from the viewpoint of ion conductivity, the salt is preferably a lithium salt, more preferably selected from the group consisting of LiPF 6 、LiBF 4 、Li[FSI]、Li[TFSI]、Li[f3C]、Li[BOB]And LiClO 4 At least one of the group consisting of Li [ TFSI ], further preferably]Or Li [ FSI ]]。
The (poly) ethylene glycol dialkyl ether is a compound represented by the following general formula (2).
R 1 O-(CH 2 CH 2 O) m -R 2 (2)
In the formula (2), R 1 And R is 2 Each independently represents an alkyl group having 1 to 4 carbon atoms, and m represents an integer of 1 to 6.
As R 1 And R is 2 Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl. Among them, the alkyl group is preferably methyl or ethyl.
M in the formula (2) is 1 to 6, preferably 3 or 4, preferably 4. If a (poly) ethylene glycol dialkyl ether having m in such a range is used, there is a tendency that a (poly) ethylene glycol dialkyl ether complex is easily formed with a salt.
The (poly) ethylene glycol dialkyl ether may be ethylene glycol dimethyl ether (referred to as "Monoglyme" or "G1"), diethylene glycol dimethyl ether (referred to as "Diglyme" or "G2"), triethylene glycol dimethyl ether (referred to as "Triglyme" or "G3"), tetraethylene glycol dimethyl ether (referred to as "Tetraglyme" or "G4"), pentaethylene glycol dimethyl ether (referred to as "Pentaglyme" or "G5"), hexaethylene glycol dimethyl ether (referred to as "Hexaglyme" or "G6"), or the like. Among them, the (poly) ethylene glycol dialkyl ether is preferably triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether, more preferably tetraethylene glycol dimethyl ether.
The (poly) ethylene glycol dialkyl ether complex is preferably a complex of a lithium salt and tetraethylene glycol dimethyl ether. Specifically, a complex of Li [ TFSI ] and tetraethyleneglycol dimethyl ether [ LiG ] [ TFSI ], a complex of Li [ TFSI ] and tetraethyleneglycol dimethyl ether [ LiG ] [ FSI ], and the like can be mentioned.
The (poly) ethylene glycol dialkyl ether complex can be obtained, for example, by mixing the above-mentioned salt with the above-mentioned (poly) ethylene glycol dialkyl ether.
The mixed molar ratio of the number of moles of the (poly) ethylene glycol dialkyl ether to the number of moles of the salt ((mole of the (poly) ethylene glycol dialkyl ether)/mole of the salt) is preferably 0.5 to 2.0, more preferably 0.7 to 1.4, still more preferably 0.9 to 1.0. If the mixing molar ratio is 0.5 or more, the viscosity of the (poly) ethylene glycol dialkyl ether complex tends to be in an appropriate range. If the mixing molar ratio is 2.0 or less, the proportion of the (poly) ethylene glycol dialkyl ether that does not form a complex tends to become small.
The method for producing the (poly) ethylene glycol dialkyl ether complex is not particularly limited. The (poly) ethylene glycol dialkyl ether complex can be obtained, for example, by mixing a salt and a (poly) ethylene glycol dialkyl ether at a temperature less than or equal to the boiling point of the (poly) ethylene glycol dialkyl ether. The mixing time and temperature can be appropriately set.
The content of the (poly) ethylene glycol dialkyl ether complex is not particularly limited, and is 10 to 70% by mass based on the total amount of the composition. The content of the (poly) ethylene glycol dialkyl ether complex is preferably 20% by mass or more, more preferably 30% by mass or more, based on the total amount of the composition. The content of the (poly) ethylene glycol dialkyl ether complex is preferably 65 mass% or less, more preferably 55 mass% or less, based on the total amount of the composition. If the content of the (poly) ethylene glycol dialkyl ether complex is 10 mass% or more, the ionic conductivity of the polymer electrolyte sheet tends to be further improved. If the content of the (poly) ethylene glycol dialkyl ether complex is 70 mass% or less, the self-supporting property of the polymer electrolyte sheet tends to be more excellent.
The polymer electrolyte composition may further contain at least one selected from the group consisting of lithium salts, sodium salts, magnesium salts, and calcium salts, which do not form a complex with the (poly) ethylene glycol dialkyl ether. These salts can function as electrolyte salts. The salts may be the same as those exemplified above.
The salt that does not form a complex with the (poly) ethylene glycol dialkyl ether may be a lithium salt. The lithium salt is preferably selected from LiPF 6 、LiBF 4 、Li[FSI]、Li[TFSI]、Li[f3C]、Li[BOB]And LiClO 4 At least one of the group consisting of Li [ TFSI ], more preferably]Or Li [ FSI ]]。
The content of the salt which does not form a complex with the (poly) ethylene glycol dialkyl ether is not particularly limited, but is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, based on the total amount of the composition. The content of the salt is preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less, based on the total amount of the composition. If the salt content is 3 mass% or more, the ionic conductivity tends to be further improved. If the salt content is 30 mass% or less, the flexibility of the polymer electrolyte sheet tends to be further improved.
The polymer electrolyte composition may further contain a (poly) ethylene glycol dialkyl ether represented by the general formula (2) which does not form a complex with at least one selected from the group consisting of lithium salts, sodium salts, magnesium salts, and calcium salts. The content of the (poly) ethylene glycol dialkyl ether that does not form a complex with the salt may be less than or equal to 10 mass%, less than or equal to 5 mass%, or less than or equal to 1 mass%, based on the total amount of the composition.
[ other Components ]
The polymer electrolyte composition may also beParticles or fibers containing oxides such as silica and alumina as needed, and Li 7 La 3 Zr 2 O 12 And (LLZ) and other inorganic solid electrolytes, boric acid esters, aluminate esters and other additives having lithium salt dissociating ability. They may be used singly or in combination of two or more. In the case where these components are further contained in the polymer electrolyte composition, the content of these components may be 0.01 to 20% by mass based on the total amount of the composition.
The polymer electrolyte composition may be formed into a sheet shape.
The thickness of the polymer electrolyte sheet may be adjusted to a desired thickness according to the constitution of the battery. The thickness of the polymer electrolyte sheet is preferably 1 μm or more, more preferably 3 μm or more, and further preferably 5 μm or more. In addition, the thickness of the polymer electrolyte sheet is preferably 200 μm or less, more preferably 100 μm or less, and further preferably 70 μm or less. If the thickness is 1 μm or more, short-circuiting between the electrodes tends to be more suppressed. If the thickness is 200 μm or less, there is a tendency that the energy density can be further improved.
Next, a method for manufacturing the polymer secondary battery 1 will be described. The method for manufacturing a polymer secondary battery 1 according to the present embodiment includes: a first step of forming a positive electrode mixture layer 10 on a positive electrode current collector 9 to obtain a positive electrode 6; a second step of forming a negative electrode mixture layer 12 on a negative electrode current collector 11 to obtain a negative electrode 8; and a third step of providing an electrolyte layer 7 between the positive electrode 6 and the negative electrode 8.
In the first step, the positive electrode 6 can be obtained, for example, as follows: the material for the positive electrode mixture layer is dispersed in a dispersion medium using a kneader, a disperser, or the like to obtain a slurry-like positive electrode mixture, and the positive electrode mixture is applied to the positive electrode current collector 9 by a doctor blade method, a dipping method, a spraying method, or the like, and then the dispersion medium is volatilized. After volatilizing the dispersion medium, a compression molding process using a roll squeezer may be provided as needed. The positive electrode mixture layer 10 may be formed into a multilayer structure by performing the steps from the application of the positive electrode mixture to the volatilization of the dispersion medium a plurality of times.
The dispersion medium used in the first step may be water, 1-methyl-2-pyrrolidone (hereinafter referred to as nmp), or the like.
In the second step, the negative electrode mixture layer 12 may be formed on the negative electrode current collector 11 by the same method as in the first step.
In the third step, in one embodiment, the electrolyte layer 7 is formed, for example, by producing a polymer electrolyte sheet containing the polymer electrolyte composition described above on a substrate. Fig. 4 (a) is a schematic cross-sectional view showing a polymer electrolyte sheet according to an embodiment. As shown in fig. 4 (a), the polymer electrolyte sheet 13A has a base material 14 and an electrolyte layer 7 provided on the base material 14.
The polymer electrolyte sheet 13A is produced, for example, as follows: after a slurry is obtained by dispersing the polymer electrolyte composition for the electrolyte layer 7 in a dispersion medium, it is coated on the substrate 14, and then the dispersion medium is volatilized. The dispersion medium for dispersing the polymer electrolyte composition for the electrolyte layer 7 may be, for example, acetone, methyl ethyl ketone, γ -butyrolactone, or the like.
The base material 14 is not limited as long as it has heat resistance capable of withstanding heating when volatilizing the dispersion medium, does not react with the polymer electrolyte composition, and does not swell due to the polymer electrolyte composition, and is, for example, a metal foil, a film made of a resin, or the like. Specifically, the base material 14 may be a metal foil such as an aluminum foil, a copper foil, or a nickel foil; films made of resins (general engineering plastics) such as polyethylene terephthalate, polytetrafluoroethylene, polyimide, polyethersulfone, and polyetherketone.
In the case of using a film composed of a resin as the base material 14, the heat-resistant temperature of the base material 14 is preferably 50 ℃ or higher, more preferably 100 ℃ or higher, still more preferably 150 ℃ or higher, and may be, for example, 400 ℃ or lower from the viewpoint of suitability for the dispersion medium for the electrolyte layer 7. If a base material having the above heat resistant temperature is used, the above-described dispersion medium can be suitably used. When a film made of a resin is used, the heat-resistant temperature of the base material 14 indicates the melting point or decomposition temperature of the resin.
The thickness of the base material 14 is preferably as thin as possible while maintaining strength capable of withstanding the tensile force of the coating apparatus. From the viewpoint of securing strength when the polymer electrolyte composition is applied to the substrate 14 while reducing the volume of the entire polymer electrolyte sheet 13, the thickness of the substrate 14 is preferably 5 μm or more, more preferably 10 μm or more, further preferably 25 μm or more, and further preferably 100 μm or less, more preferably 50 μm or less, further preferably 40 μm or less.
The polymer electrolyte sheet may be continuously produced while being wound into a roll. In this case, the electrolyte layer 7 may be damaged because a part of the electrolyte layer 7 is stuck to the base material 14 by the contact between the surface of the electrolyte layer 7 and the back surface of the base material 14. In order to prevent this, as another embodiment, the polymer electrolyte sheet may be provided with a protective material on the side of the electrolyte layer 7 opposite to the base material 14. Fig. 4 (b) is a schematic cross-sectional view showing a polymer electrolyte sheet according to another embodiment. As shown in fig. 4 (B), the polymer electrolyte sheet 13B further includes a protective material 15 on the side of the electrolyte layer 7 opposite to the base material 14.
The protective material 15 may be easily peeled off from the electrolyte layer 7, and is preferably a nonpolar resin film such as polyethylene, polypropylene, polytetrafluoroethylene, or the like. If a nonpolar resin film is used, the electrolyte layer 7 and the protective material 15 are not adhered to each other, and the protective material 15 can be easily peeled off.
The thickness of the protective material 15 is preferably 5 μm or more, more preferably 10 μm or less, and further preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less, from the viewpoint of securing strength while reducing the volume of the entire polymer electrolyte sheet 13B.
From the viewpoint of suppressing deterioration in a low-temperature environment and softening in a high-temperature environment, the heat-resistant temperature of the protective material 15 is preferably-30 ℃ or higher, more preferably 0 ℃ or higher, and further preferably 100 ℃ or lower, more preferably 50 ℃ or lower. In the case of providing the protective material 15, the above-described step of volatilizing the dispersion medium is not necessary, and therefore, it is not necessary to raise the heat-resistant temperature.
In the method of providing the electrolyte layer 7 between the positive electrode 6 and the negative electrode 8 using the polymer electrolyte sheet 13A, for example, the base material 14 is peeled off from the polymer electrolyte sheet 13A, and the positive electrode 6, the electrolyte layer 7, and the negative electrode 8 are laminated by lamination, to obtain the polymer secondary battery 1. At this time, the electrolyte layer 7 is laminated so as to be positioned on the positive electrode mixture layer 10 side of the positive electrode 6 and on the negative electrode mixture layer 12 side of the negative electrode 8, that is, so as to be arranged in this order, namely, the positive electrode current collector 9, the positive electrode mixture layer 10, the electrolyte layer 7, the negative electrode mixture layer 12, and the negative electrode current collector 11.
In the third step, in other embodiments, the electrolyte layer 7 is formed by coating on at least one of the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the negative electrode 8, preferably on both the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the negative electrode 8. In this case, for example, the positive electrode 6 provided with the electrolyte layer 7 and the negative electrode 8 provided with the electrolyte layer 7 are laminated, for example, by lamination, so that the electrolyte layers 7 are in contact with each other, whereby the polymer secondary battery 1 can be obtained.
The method of forming the electrolyte layer 7 by coating on the positive electrode mixture layer 10 is, for example, the following method: the polymer electrolyte composition used for the electrolyte layer 7 was dispersed in a dispersion medium to obtain a slurry, and then the polymer electrolyte composition was applied to the positive electrode mixture layer 10 using an applicator. The dispersion medium for dispersing the polymer electrolyte composition used for the electrolyte layer 7 may be, for example, acetone, methyl ethyl ketone, γ -butyrolactone, or the like.
The method of forming the electrolyte layer 7 by coating on the negative electrode mixture layer 12 may be the same method as the method of forming the electrolyte layer 7 by coating on the positive electrode mixture layer 10.
Second embodiment
Next, a polymer secondary battery according to a second embodiment will be described. Fig. 5 is a schematic cross-sectional view showing an embodiment of an electrode group in a polymer secondary battery according to a second embodiment. As shown in fig. 5, the polymer secondary battery of the second embodiment is different from the polymer secondary battery of the first embodiment in that the electrode group 2B is provided with a bipolar electrode 16. That is, the electrode group 2B includes the positive electrode 6, the first electrolyte layer 7, the bipolar electrode 16, the second electrolyte layer 7, and the negative electrode 8 in this order.
The bipolar electrode 16 includes a bipolar electrode collector 17, a positive electrode mixture layer 10 provided on the surface of the bipolar electrode collector 17 on the negative electrode 8 side, and a negative electrode mixture layer 12 provided on the surface of the bipolar electrode collector 17 on the positive electrode 6 side.
The bipolar electrode collector 17 may be formed of aluminum, stainless steel, titanium, or the like. Specifically, the bipolar electrode current collector 17 may be an aluminum perforated foil, expanded metal, foamed metal plate, or the like having holes with a pore diameter of 0.1 to 10 mm. In addition to the above, the bipolar electrode collector 17 may be formed of any material as long as no change such as dissolution or oxidation occurs during use of the battery, and the shape, manufacturing method, and the like thereof are not limited.
The thickness of the bipolar electrode current collector 17 may be greater than or equal to 10 μm, greater than or equal to 15 μm, or greater than or equal to 20 μm. The thickness of the bipolar electrode current collector 17 may be less than or equal to 100 μm, less than or equal to 80 μm, or less than or equal to 60 μm.
Next, a method for manufacturing a secondary battery according to a second embodiment will be described. The method for manufacturing a secondary battery according to the present embodiment includes the steps of: a first step of forming a positive electrode mixture layer 10 on a positive electrode current collector 9 to obtain a positive electrode 6; a second step of forming a negative electrode mixture layer 12 on a negative electrode current collector 11 to obtain a negative electrode 8; a third step of forming a positive electrode mixture layer 10 on one surface of a bipolar electrode collector 17 and forming a negative electrode mixture layer 12 on the other surface to obtain a bipolar electrode 16; and a fourth step of providing an electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16 and between the negative electrode 8 and the bipolar electrode 16.
The first and second steps may be the same as those in the first embodiment.
In the third step, the positive electrode mixture layer 10 may be formed on one surface of the bipolar electrode collector 17 by the same method as in the first step of the first embodiment. The method of forming the negative electrode mixture layer 12 on the other surface of the bipolar electrode collector 17 may be the same as the second step in the first embodiment.
In the fourth step, as a method of disposing the electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16, in one embodiment, the electrolyte layer 7 is formed by, for example, manufacturing a polymer electrolyte sheet containing a polymer electrolyte composition on a substrate. The method for producing the polymer electrolyte sheet may be the same as the method for producing the polymer electrolyte sheets 13A and 13B of the first embodiment.
In the fourth step, the electrolyte layer 7 may be provided between the negative electrode 8 and the bipolar electrode 16 in the same manner as the above-described method of providing the electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16.
The method of forming the electrolyte layer 7 by coating on the positive electrode mixture layer 10 of the positive electrode 6 and the negative electrode mixture layer 12 of the bipolar electrode 16 may be the same method as the method of forming the electrolyte layer 7 by coating on the positive electrode mixture layer 10 and the method of forming the electrolyte layer 7 by coating on the negative electrode mixture layer 12 in the third step in the first embodiment.
As a method of disposing the electrolyte layer 7 between the positive electrode 6 and the bipolar electrode 16 in the fourth step, in other embodiments, the electrolyte layer 7 is formed by coating on at least one of the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the bipolar electrode 16, preferably on both the positive electrode mixture layer 10 side of the positive electrode 6 and the negative electrode mixture layer 12 side of the bipolar electrode 16. In this case, for example, the positive electrode 6 provided with the electrolyte layer 7 and the bipolar electrode 16 provided with the electrolyte layer 7 are laminated by lamination in such a manner that the electrolyte layers 7 are in contact with each other.
Examples
The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[ Synthesis of Polymer ]
By adding to the counter anion Cl of polydiallyl dimethyl ammonium chloride - Change to [ TFSI ]] - To synthesize a polymer having a structural unit represented by the general formula (1).
First, 100 parts by mass of [ P (DADMA)][Cl]The aqueous solution (20% by mass aqueous solution, manufactured by Aldrich) was diluted with 500 parts by mass of distilled water to prepare an aqueous solution of the diluted polymer. Next, 43 parts by mass of Li [ TFSI ]](manufactured by Shore chemical Co., ltd.) was dissolved in 100 parts by mass of water to prepare Li [ TFSI ]]An aqueous solution. By adding it dropwise to the diluted aqueous polymer solution and stirring for 2 hours, a white precipitate was obtained. The precipitate was separated by filtration, washed with 400 parts by mass of distilled water, and then filtered again. Washing and filtration were repeated 5 times. Then, the water was evaporated by vacuum drying at 105℃to give [ P (DADMA)][TFSI]。[P(DADMA)][TFSI]Has a viscosity average molecular weight of 2.11X10 6 g·mol -1 。
Regarding the viscosity average molecular weight Mv, after measuring the viscosity [ η ] of the polymer at 25 ℃ using a black-bone viscometer using polymethyl methacrylate (PMMA) as a standard substance, it is calculated based on [ η ] = KMv (here, K represents the expansion coefficient, which depends on temperature, polymer and solvent properties).
Example 1
[ preparation of Polymer electrolyte sheet ]
As shown in Table 1, 10 parts by mass of [ LiG4 ] as a (poly) ethylene glycol dialkyl ether complex was added to 8 parts by mass of the obtained polymer][TFSI](content of (Poly) glycol dialkyl ether Complex in composition: 50% by mass), 2 parts by mass of Li [ TFSI ] as a salt which does not form a complex with (Poly) glycol dialkyl ether]And 16 parts by mass of acetone as a dispersion medium were stirred to prepare a slurry. Note that [ LiG4][TFSI]Tetraethylene glycol dimethyl ether (Sigma-Aldrich Co.) and Li [ TFSI ] were used in advance](manufactured by Shore chemical Co., ltd.) in a molar ratio of 1:1. The slurry was coated on an aluminum foil with a gap of 100 μm using a doctor blade method, and dried at 40℃for 2 hoursThe acetone was volatilized. Then, at 60 ℃ less than or equal to 1.0X10 4 Drying under reduced pressure of Pa (0.1 atm or less) for 10 hours, to obtain a polymer electrolyte sheet having a thickness of 28. Mu.m.
[ measurement of Mass residual Rate ]
Drying under reduced pressure at 60℃was measured (at 1.0X10 or less) 4 The mass change of the polymer electrolyte sheet before and after drying under reduced pressure of Pa (0.1 atm or less) for 10 hours was calculated as the mass residual ratio of the polymer electrolyte sheet. The mass residual ratio was calculated based on the following equation. The results are shown in table 2.
Mass residual ratio [ mass% ] = [ mass of polymer electrolyte composition after drying [ g ]/(mass of polymer electrolyte composition before drying [ g ] ] ×100 of volatile component (mass of dispersion medium) contained in polymer electrolyte composition before drying [ g ]) ]
Since volatile components such as acetone and water may remain in the polymer electrolyte composition before drying, the mass residual ratio is calculated based on a value obtained by subtracting the mass of volatile components such as acetone and water remaining in the polymer from the mass of the polymer electrolyte composition before drying in the above measurement. The "mass of volatile components (dispersion medium) contained in the polymer electrolyte composition before drying" was determined by subjecting the polymer electrolyte composition produced in the same manner as in example 1 to drying under reduced pressure at 60℃with the exception that the (poly) ethylene glycol dialkyl ether complex was not used, and by changing the mass before and after drying.
[ evaluation of self-supporting sheet Forming Property ]
The polymer electrolyte sheet formed on the aluminum foil obtained in example 1 was peeled off from the aluminum foil, and the self-supporting property of the polymer electrolyte sheet was verified. For evaluation, a polymer electrolyte sheet formed on an aluminum foil of 20cm square was used. The case where the polymer electrolyte sheet could be peeled off in a size of more than 10cm square was evaluated as a, the case where the polymer electrolyte sheet could be peeled off in a size of 5cm square to 10cm square was evaluated as B, and the case where the polymer electrolyte sheet could be peeled off in a size of less than 5cm square was evaluated as C. The results are shown in table 2.
[ measurement of ion conductivity ]
Sandwiching the polymer electrolyte sheet obtained in example 1 with aluminum foil, and punchingA sample for measuring ion conductivity was prepared. The sample was placed in a bipolar sealed battery Cell (HS Cell, manufactured by baoquan corporation) and measured using an ac impedance measuring device (1260, manufactured by Solartron corporation). The AC impedance was measured in a constant temperature bath at 15℃intervals between-5℃and 70℃and in the range of 10mV and 1Hz to 2 MHz. The resistance value is calculated from the intersection with the real axis of the nyquist curve, and the ion conductivity is calculated from the resistance value. The results of ionic conductivity at 25℃are shown in Table 2. The operation of disposing the sample in the sealed battery cell was performed in a glove box in an argon atmosphere.
[ production of Battery ]
90 parts by mass of LiFePO 4 (cathode active material), 5 parts by mass of acetylene black (conductive agent, trade name: HS-100, average particle diameter 48nm (manufacturing original catalog value), electric chemical industry Co., ltd.), 100 parts by mass of polyvinylidene fluoride solution (binder, trade name: KUREHA KF Polymer #7305, solid content 5% by mass, KUREHA, co., ltd.), and 28 parts by mass of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a cathode mixture paste. The positive electrode mixture paste was applied to both surfaces of a positive electrode current collector (aluminum foil having a thickness of 20 μm), dried at 120℃and then rolled to give a coating having a thickness of 91 μm on one surface and a coating weight of 50g/m on one surface 2 Density of mixture 1.8g/cm 3 The positive electrode is produced by the positive electrode active material layer. For manufacturing a button cell for test, the positive electrode was prepared by punchingIs a positive electrode of (a).
As a negative electrode, a lithium foil was die-cutIs a negative electrode of (a). The positive electrode, the polymer electrolyte sheet, and the lithium foil were stacked in this order and disposed in a CR2032 type coin cell container. In this case, the lithium foil functions as a negative electrode active material, and the stainless steel of the coin cell case functions as a negative electrode current collector. The upper part of the battery container was fastened and sealed with an insulating gasket interposed therebetween, thereby obtaining a lithium polymer secondary battery.
[ evaluation of Battery Performance ]
The lithium polymer secondary battery manufactured by the above method was used to evaluate battery performance. The charge/discharge measurement was carried out at 25℃and 0.05C using a charge/discharge apparatus (TOSCAT-3200, trade name, toyo System Co., ltd.) to calculate the designed capacity ratio based on the following formula for the discharge capacity at the 3 rd cycle. The results are shown in table 2. The "current value [ a ]/design theoretical capacity [ Ah ]" is denoted by C, and 1C is denoted by a current value required for fully charging or fully discharging the battery within 1 hour.
Design capacity ratio [% ] = (discharge capacity [ mAh ]/cell design capacity [ mAh ]) x 100
Example 2
A polymer electrolyte sheet was produced in the same manner as in example 1, except that the content of the (poly) ethylene glycol dialkyl ether complex in the composition was changed from 10 parts by mass to 4.3 parts by mass (content of the (poly) ethylene glycol dialkyl ether complex in the composition: 30% by mass), and the polymer electrolyte sheet was evaluated in the same manner as in example 1. The results are shown in table 2.
Example 3
A polymer electrolyte sheet was produced in the same manner as in example 1, except that the content of the (poly) ethylene glycol dialkyl ether complex in the composition was changed from 10 parts by mass to 1.1 parts by mass (content of the (poly) ethylene glycol dialkyl ether complex in the composition: 10% by mass), and the polymer electrolyte sheet was evaluated in the same manner as in example 1. The results are shown in table 2.
Comparative example 1
A polymer electrolyte sheet was produced in the same manner as in example 1, except that [ LiG4] [ TFSI ] as a (poly) ethylene glycol dialkyl ether complex was changed to dimethyl carbonate (DMC) as an organic solvent, and the polymer electrolyte sheet was evaluated in the same manner as in example 1. The results are shown in table 2.
TABLE 1
TABLE 2
Polymer having structural unit represented by general formula (1) and (poly) ethylene glycol dialkyl ether complex [ LiG4]][TFSI]The polymer electrolyte compositions of examples 1 to 3 have excellent high ion conductivity even at room temperature, and can maintain their shape by the sheet itself even without a base material or the like. It was also found that the polymer electrolyte compositions of examples 1 to 3 were 1.0X10 or less even at 60 ℃ 4 Drying under reduced pressure of Pa (0.1 atm or less) for 10 hours also does not substantially reduce the mass, which is a material with high thermal stability. In contrast, the polymer electrolyte composition of comparative example 1 using DMC was 1.0X10 or less at 60 ℃ 4 Drying under reduced pressure of Pa (0.1 atm or less) for 10 hours volatilizes most of DMC and greatly reduces ionic conductivity. From these results, it was confirmed that: the polymer electrolyte composition of the present invention can produce a sheet having excellent high ion conductivity even at room temperature and high self-supporting properties.
Industrial applicability
According to the present invention, there can be provided a polymer electrolyte composition which can produce a sheet having excellent ionic conductivity at room temperature and high self-supporting properties, which can maintain the shape of the sheet itself without using a base material or the like, even without using an organic solvent. In addition, according to the present invention, a polymer secondary battery using such a polymer electrolyte composition can be provided.
Symbol description
1: polymer secondary battery, 2a,2b: electrode group, 3: battery exterior body, 4: positive collector tab, 5: negative collector tab, 6: positive electrode, 7: electrolyte layer, 8: negative electrode, 9: positive electrode current collector, 10: positive electrode mixture layer, 11: negative electrode current collector, 12: negative electrode mixture layer, 13a,13b: polymer electrolyte sheet, 14: base material, 15: protection material, 16: bipolar electrode, 17: a bipolar electrode current collector.

Claims (3)

1. A polymer electrolyte composition formed in a sheet shape and containing:
a polymer having a structural unit represented by the following general formula (1); and
a complex of a lithium salt and a (poly) ethylene glycol dialkyl ether represented by the following general formula (2), and,
wherein the content of the complex is 10 to 70 mass% based on the total amount of the composition,
wherein the polymer electrolyte composition further comprises a lithium salt that does not form a complex with the (poly) ethylene glycol dialkyl ether, and the content of the lithium salt that does not form a complex with the (poly) ethylene glycol dialkyl ether is 3 to 30 mass% based on the total amount of the composition,
[ chemical 1]
In the formula (1), X - Represents a counter-anion of the formula,
R 1 O-(CH 2 CH 2 O) m -R 2 (2)
in the formula (2), R 1 And R is 2 Each independently represents an alkyl group having 1 to 4 carbon atoms, and m is 4.
2. The polymer electrolyte composition according to claim 1, wherein the anion of the salt is selected from the group consisting of PF 6 - 、BF 4 - 、N(FSO 2 ) 2 - 、N(CF 3 SO 2 ) 2 - 、B(C 2 O 4 ) 2 - And ClO 4 - At least one of the group consisting of.
3. A polymer secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer,
the electrolyte layer is provided between the positive electrode and the negative electrode, and contains the polymer electrolyte composition according to claim 1 or 2.
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