Electrolytes, secondary batteries, and composite materials

Abstract

To provide an electrolyte with elasticity and flexibility that can prevent a decrease in the durability of the electrolyte. [Solution] An electrolyte containing a polymer obtained by polymerizing monomers represented by formula (1), a glyme represented by formula (2), and a lithium salt, etc. JPEG2026063114000011.jpg25118 (R1 and R2 are linear, branched, or cyclic alkyl groups with 1 to 20 hydrogen atoms or carbon atoms. X1 and X2 are oxygen or NH groups. When X2 is oxygen, n is between 0 and 30; when X2 is NH, n is between 1 and 30.) JPEG2026063114000012.jpg21141 (R3 and R4 are alkyl groups with 1 to 4 carbon atoms, and m is 1 to 4.)

Description

Technical Field

[0001] The disclosure in the present application relates to an electrolyte, a secondary battery, and a composite material.

Background Art

[0002] Lithium-ion batteries have a high energy density. Therefore, they are used as power sources for portable electronic devices such as notebook computers and mobile phones, as well as for automobiles. Furthermore, the use of lithium-ion batteries is expected to expand in the future, and their development for new applications is also anticipated.

[0003] Conventionally, liquid electrolytes have been used for the electrolytes of lithium-ion batteries. However, when the temperature of a lithium-ion battery using a liquid electrolyte rises due to some abnormality, the electrolyte solution may catch fire. In addition, the electrolyte may vaporize, increasing the pressure inside the battery and causing the battery to rupture.

[0004] There is a demand to prevent the ignition and rupture of lithium-ion batteries and further enhance their safety. Therefore, in order to improve safety, it has been proposed to use solid electrolytes for the electrolytes of lithium-ion batteries, and research and development have been carried out.

[0005] Examples of solid electrolytes include electrolytes using polymers and inorganic solid electrolytes. In particular, electrolytes using polymers can be easily manufactured by applying and polymerizing an electrolyte composition containing monomers. In addition, electrolytes using polymers are superior to inorganic solid electrolytes in terms of formability and processability, and can be used especially in applications where flexibility is required. Furthermore, they have a high degree of freedom in shape and are easy to laminate, so an improvement in output density and energy density can be expected.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] Patent documents 1 and 2 describe electrolytes using polymers. While polymer electrolytes can be used in various shapes due to their elasticity and flexibility, maintaining that shape during use places significant stress on the electrolyte. As a result, there is a risk of reduced electrolyte durability due to breakage, thinning, etc. Therefore, there is a need for electrolytes with greater elasticity and flexibility than conventional electrolytes.

[0008] Therefore, the disclosure in this application aims to provide an electrolyte, secondary battery, and composite material having elasticity and flexibility that can prevent a decrease in the durability of the electrolyte. Other optional additional effects of the disclosure in this application will be revealed in the embodiments for carrying out the invention. [Means for solving the problem]

[0009] (1) A polymer obtained by polymerizing monomers represented by the following formula (1), [ka] (In formula (1), R1 and R2 each independently represent H or a linear, branched, or cyclic alkyl group having 1 to 20 carbon atoms. X1 and X2 each independently represent O or NH. When X2 is O, n represents an integer on average between 0 and 30, and when X2 is NH, n represents an integer on average between 1 and 30.) The grime represented by the following formula (2) and [ka] (In formula (2), R3 and R4 each independently represent an alkyl group having 1 to 4 carbon atoms, and m represents an integer from 1 to 4.) At least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts, potassium salts, and calcium salts, Electrolytes it contains. (2) The salt anion is PF6 - BF4 - ClO4 - B(C2O4)2 - , N(FSO2)2 - and N(CF3SO2)2 - It is at least one species selected from the group consisting of, The electrolytes listed in (1) above. (3) The salt anion is N(FSO2)2 - Or N(CF3SO2)2 - That is, The electrolytes listed in (2) above. (4) The salt is a lithium salt. The electrolyte listed in any one of the above (1) to (3). (5) In equation (1), when X2 is O, n is on average between 3 and 14, and when X2 is NH, n is on average between 4 and 15. The electrolyte listed in any one of the above (1) to (4). (6) In equation (2), m is 4. The electrolyte listed in any one of the above (1) to (5). (7) Anode and, Cathode and, An electrolyte layer between the anode and the cathode It includes at least, The electrolyte layer is an electrolyte described in any one of (1) to (6) above. Secondary battery. (8) an electrolyte as described in any one of (1) to (6) above, Porous carrier and A composite material that possesses [the following characteristics]. (9) The porous carrier has through holes that penetrate in the thickness direction, The composite material described in (8) above. (10) The porous carrier is a honeycomb membrane. The composite material described in (8) or (9) above. (11) Anode and, Cathode and, An electrolyte layer is placed between the anode and the cathode, It includes at least, The electrolyte layer is a composite material described in any one of (8) to (10) above. Secondary battery. [Effects of the Invention]

[0010] It can provide electrolytes that are elastic and flexible. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view of a battery. [Figure 2] A diagram showing the temperature dependence of the ionic conductivity of electrolytes 1-4. [Figure 3] Figure 3A shows the mechanical properties of electrolyte 1 manufactured in Example 1. Figure 3B is a photograph used as a substitute for a drawing, showing electrolyte 4 manufactured in Example 4 after deformation. [Figure 4] A diagram showing the charge and discharge characteristics of electrolyte 1. [Figure 5] Figure showing the results of linear sweep voltammetry of electrolyte 1. [Figure 6] Figure 6A shows the results of chronoamperometry of electrolyte 1. Figure 6B shows the results of AC impedance measurement of electrolyte 1. [Figure 7] A photograph used as a substitute for a drawing of a honeycomb film viewed from the thickness direction. [Figure 8] A figure showing the temperature dependence of the ionic conductivity of composite material 1. [Figure 9] Figure 7A shows the charge-discharge characteristics of composite material 1. Figure 7B shows the charge-discharge characteristics over a measurement period of 0 to 100 hours. [Figure 10] This figure shows the results of linear sweep voltammetry on composite material 1. [Figure 11] Figure 11A shows the results of chronoamperometry of composite material 1. Figure 11B shows the results of AC impedance measurement of composite material 1. [Figure 12] Figure 12A is a photograph showing electrolyte 5, used as a substitute for a drawing. Figure 12B is a photograph showing electrolyte 9, used as a substitute for a drawing. Figure 12C is a photograph showing electrolyte 13, used as a substitute for a drawing. [Figure 13] Figure 13A shows the temperature dependence of the ionic conductivity of electrolytes 5-8. Figure 13B shows the temperature dependence of the ionic conductivity of electrolytes 9-12. Figure 13C shows the temperature dependence of the ionic conductivity of electrolyte 13. [Modes for carrying out the invention]

[0012] The following provides a more detailed explanation of electrolytes.

[0013] In this specification, a numerical range indicated by "~" means a range that includes the numbers before and after "~" as the lower and upper limits. Furthermore, in this specification, numerical values, numerical ranges, and qualitative expressions (for example, expressions such as "identical" and "same") shall be interpreted as indicating numerical values, numerical ranges, and properties that include errors generally accepted in the relevant technical field.

[0014] (Electrolyte embodiment) The electrolyte according to this embodiment is a polymer obtained by polymerizing monomers represented by the following formula (1), [ka] (In formula (1), R1 and R2 each independently represent H or a linear, branched, or cyclic alkyl group having 1 to 20 carbon atoms. X1 and X2 each independently represent O or NH. When X2 is O, n represents an integer on average between 0 and 30, and when X2 is NH, n represents an integer on average between 1 and 30.) The grime represented by the following formula (2) and [ka] (In formula (2), R3 and R4 each independently represent an alkyl group having 1 to 4 carbon atoms, and m represents an integer from 1 to 4.) It contains at least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts, potassium salts, and calcium salts.

[0015] Electrolytes are produced by polymerizing a composition containing a monomer represented by formula (1), a glyme, and a salt. The materials required for the production of electrolytes are described below.

[0016] [Monomer represented by formula (1)] The electrolyte is a polymer obtained by polymerizing the monomer represented by formula (1). Since the monomer represented by formula (1) has polymerization groups at both ends, the resulting polymer forms a crosslinked network. Glyme is a plasticizer. Therefore, the polymer is a plasticized crosslinked network polymer containing oxyethylene.

[0017] In formula (1), R1 and R2 each independently represent H or an alkyl group having 1 to 20 carbon atoms. R1 and R2 may be the same or different. The alkyl group having 1 to 20 carbon atoms may be linear, branched, or cyclic. R1 and R2 are preferably H or an alkyl group having 1 to 5 carbon atoms, more preferably H or a linear alkyl group having 3 or fewer carbon atoms, and even more preferably H or CH3.

[0018] X1 and X2 each independently represent either O or NH. Furthermore, X1 and X2 may be the same or different.

[0019] When X2 is O, n is in the range of 0 to 30 on average, preferably in the range of 1 to 20 on average, and more preferably in the range of 3 to 14 on average. When X2 is NH, n is in the range of 1 to 30 on average, preferably in the range of 2 to 20 on average, and more preferably in the range of 4 to 15 on average.

[0020] More specifically, when X2 is O, the minimum value of n may be 0 or greater on average, 1 or greater, 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 11 or greater, 12 or greater, 13 or greater, 14 or greater, 15 or greater, 16 or greater, 17 or greater, 18 or greater, 19 or greater, or 20 or greater, and the maximum value of n may be 30 or less on average, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, or 10 or less. Furthermore, when X2 is NH, the minimum value of n may be 1 or greater on average, 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 11 or greater, 12 or greater, 13 or greater, 14 or greater, 15 or greater, 16 or greater, 17 or greater, 18 or greater, 19 or greater, or 20 or greater. The maximum value of n may be 30 or less on average, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, or 10 or less. Note that the range of n can be arbitrarily selected so that the minimum and maximum values ​​of n described above do not overlap.

[0021] Furthermore, the monomer represented by formula (1) is preferably a liquid at room temperature. If it is a liquid, the glyme or salt can be dissolved in the monomer without the need for a solvent when producing the electrolyte.

[0022] The monomer represented by formula (1) contains oxyethylene units, which improves the elasticity and flexibility of the polymerized polymer. Furthermore, the oxyethylene units of the polymerized polymer form a solvation structure with the salt's cations. Therefore, the polymer can contain many cations, and the electrolyte has high ionic conductivity.

[0023] The following problems arise when there are too few oxyethylene units in the monomer. 1) The number of oxyethylene units decreases, resulting in reduced elasticity and flexibility of the polymer. 2) The amount of cations that can be contained in the polymer decreases. 3) The solubility of the glyme and salts included in the manufacture of electrolytes decreases.

[0024] Conversely, if there are many oxyethylene units in the monomer, the polymer's elasticity, flexibility, and solubility with grime and salts will increase, but the crosslinking density will decrease, making it difficult to maintain the polymer's mechanical properties.

[0025] Specific examples of monomers represented by formula (1) include poly(ethylene glycol) di(meth)acrylate and poly(ethylene glycol) di(meth)acrylamide. The average molecular weight of monomers represented by formula (1) is in the range of 200 to 1500, preferably in the range of 240 to 1100, and more preferably in the range of 320 to 800.

[0026] In this specification, "(meth)acrylate" is a concept that encompasses both "acrylate" and "methacrylate." The same applies to terms similar to (meth)acrylate; for example, "(meth)acrylic acid" is a concept that encompasses both "acrylic acid" and "methacrylic acid," "(meth)acryloyl group" is a concept that encompasses both "acryloyl group" and "methacryloyl group," and "(meth)acrylamide" is a concept that encompasses both "acrylamide" and "methacrylamide."

[0027] In the composition used to manufacture the electrolyte, there are no particular restrictions on the content of the monomer represented by formula (1), but it should be 10% by weight or more, more preferably 20% by weight or more, and even more preferably 30% by weight or more, based on the total amount of the composition. Furthermore, the monomer content should be 90% by weight or less, and preferably 80% by weight or less, based on the total amount of the composition.

[0028] [Grime] The glyme represented by formula (2) is used as a plasticizer to plasticize polymers formed by the polymerization of monomers represented by formula (1).

[0029] In formula (2), R3 and R4 each independently represent an alkyl group having 1 to 4 carbon atoms. m represents an integer of 1 to 4.

[0030] Examples of the alkyl groups of R3 and R4 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, etc. In particular, a methyl group or an ethyl group is preferable.

[0031] In formula (2), m is 1 to 4, preferably 3 or 4, and more preferably 4. Specific examples of the glyme represented by formula (2) include, for example, monoglyme (also referred to as ethylene glycol dimethyl ether), diglyme (also referred to as diethylene glycol dimethyl ether), triglyme (also referred to as triethylene glycol dimethyl ether), and tetraglyme (also referred to as tetraethylene glycol dimethyl ether). Among these, triglyme or tetraglyme is preferable, and tetraglyme is more preferable.

[0032] In the composition for producing the electrolyte, the content of glyme is not particularly limited, but it is 5% by weight or more to 50% by weight based on the total amount of the composition, and preferably 10% to 20% by weight.

[0033] [Salt] The salt contained in the electrolyte is an electrolyte salt. The salt may be a lithium salt, a sodium salt, a magnesium salt, a potassium salt, or a calcium salt.

[0034] Examples of the anion of the salt include, for example, halide ions (I - , Cl - , Br - , etc.), SCN - , BF4 - , BF3(CF3) - , BF3(C2F5) - , BF3(C3F7) - , BF3(C4F9) - , PF6 - , ClO4 - , SbF6 -, N(FSO2)2 - ([FIS] - It is sometimes written as: ), N(CF3SO2)2 - ([TFSI] - It is sometimes written as follows: ), N(C2F5SO2)2 - , BPh4 - B(C2H4O2) - , C(SO2F)3 - ([f3C] - It is sometimes written as follows: ), C(SO2CF3)3 - CF3COO - CF3SO2O - , C6F5SO2O - B(C2O4)2 - ([BOB] - It is sometimes written as follows: ), RCOO - (R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group.) Among these, PF6 - BF4 - [FSI] - [TFSI] - [BOB] - ClO4 - [FSI] is preferred. - [TFSI] - This is preferable.

[0035] Examples of lithium salts include LiPF6, LiBF4, Li[FSI], Li[TFSI], Li[f3C], Li[BOB], LiClO4, LiBF3(CF3), LiBF3(C2F5), LiBF3(C3F7), LiBF3(C4F9), LiC(SO2CF3)3, LiCF3SO2O, LiCF3COO, and LiRCOO (where R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used individually or in combination of two or more.

[0036] Examples of sodium salts include NaPF6, NaBF4, Na[FSI], Na[TFSI], Na[f3C], Na[BOB], NaClO4, NaBF3(CF3), NaBF3(C2F5), NaBF3(C3F7), NaBF3(C4F9), NaC(SO2CF3)3, NaCF3SO2O, NaCF3COO, and NaRCOO (where R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used individually or in combination of two or more.

[0037] Examples of magnesium salts include Mg(PF6)2, Mg(BF4)2, Mg[FSI]2, Mg[TFSI]2, Mg[f3C]2, Mg[BOB]2, Mg(ClO4)2, Mg[BF3(CF3)]2, Mg[BF3(C2F5)]2, Mg[BF3(C3F7)]2, Mg[BF3(C4F9)]2, Mg[C(SO2CF3)3]2, Mg(CF3SO2O)2, Mg(CF3COO)2, and Mg(RCOO)2 (where R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used individually or in combination of two or more.

[0038] Examples of potassium salts include KPF6, KBF4, K[FSI], K[TFSI], K[f3C], K[BOB], KClO4, KBF3(CF3), KBF3(C2F5), KBF3(C3F7), KBF3(C4F9), KC(SO2CF3)3, KCF3SO2O, KCF3COO, and KRCOO (where R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used individually or in combination of two or more.

[0039] Examples of calcium salts include Ca(PF6)2, Ca(BF4)2, Ca[FSI]2, Ca[TFSI]2, Ca[f3C]2, Ca[BOB]2, Ca(ClO4)2, Ca[BF3(CF3)]2, Ca[BF3(C2F5)]2, Ca[BF3(C3F7)]2, Ca[BF3(C4F9)]2, Ca[C(SO2CF3)3]2, Ca(CF3SO2O)2, Ca(CF3COO)2, and Ca(RCOO)2 (where R represents an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These may be used individually or in combination of two or more.

[0040] Among these, from the viewpoint of ionic conductivity, lithium salts are preferred, with LiPF6, LiBF4, Li[FSI], Li[TFSI], Li[f3C], Li[BOB], and LiClO4 being more preferred, and Li[FSI] and Li[TFSI] being even more preferred.

[0041] The oxygen of the polymer's ethylene oxide and the cation of the salt form a solvation structure. Therefore, the maximum salt content depends on the number of ethylene oxide units in the polymer. Consequently, there are no particular restrictions on the salt content in the composition used to produce the electrolyte, as long as the number of moles is less than the number of ethylene oxide units in the polymer.

[0042] [Polymerization initiator] The electrolyte according to the embodiment is produced by polymerizing a monomer represented by formula (1). A polymerization initiator is used in this process. The polymerization initiator is not particularly limited as long as it can polymerize the monomer represented by formula (1). Polymerization initiators include photopolymerization initiators and thermal polymerization initiators, with photopolymerization initiators curing faster than thermal polymerization initiators. Photopolymerization initiators include photoradical polymerization initiators, photoanionic polymerization initiators, and photocationic polymerization initiators. Photoradical polymerization initiators rapidly carry out addition reactions to double bonds and therefore do not generate impurities from the reaction. When producing electrolytes, if the polymerization reaction is slow, there is a risk that molecules will align within the resulting polymer and crystallize easily. Therefore, it is important to carry out the polymerization reaction quickly when producing electrolytes. Furthermore, if no impurities are generated, there is no need to remove impurities after the polymerization reaction, and the electrolyte production process can be simplified.

[0043] Therefore, it is preferable to use a photoradical polymerization initiator in the polymerization reaction of the monomer represented by formula (1). Since the crosslinked network polymer formed by the photoradical polymerization initiator undergoes a rapid polymerization reaction, polymerization occurs before the molecules within the polymer can align. In other words, the crosslinked network polymer is formed in an amorphous state.

[0044] The photoradical polymerization initiator is not particularly limited as long as the monomer polymerizes, but examples include acetophenone-based photoradical polymerization initiators, benzophenone-based photoradical polymerization initiators, thioxanthone-based photoradical polymerization initiators, and acylphosphine-based photoradical polymerization initiators. Specifically, 2,2-dimethoxy-2-phenylacetophenone, benzophenone, benzoylbenzoic acid, 2,2-diethoxyacetophenone, 2,4-diethyl-9H-thioxanthene-9-one, 4,4'-dimethoxybenzyl, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 2-ethoxy-2-phenylacetone, 2-ethylanthraquinone, 1-hydroxycyclohexylphenyl ketone, 2-(hydroxyimino)propiophenone, 2-hydroxy-2-phenylacetophenone, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, and p,p'-tetramethyldiaminobenzophenone are preferred, and 2,2-dimethoxy-2-phenylacetophenone is more preferred.

[0045] The amount of polymerization initiator used is not particularly limited, but for example, it is 0.001 to 0.1 parts by weight per 100 parts by weight of monomer, and preferably 0.005 to 0.01 parts by weight.

[0046] Electrolytes can be produced by mixing a monomer represented by formula (1), a grime represented by formula (2), a salt, and a polymerization initiator, and then polymerizing them. As mentioned above, the monomer represented by formula (1) is liquid at room temperature, so it can dissolve the grime, salt, and polymerization initiator. Therefore, electrolytes do not require a solvent. Furthermore, simply irradiating the composition of the above materials with light such as ultraviolet light or electron beams eliminates the need for heat treatment or other methods to stabilize the structure after polymerization. Thus, electrolytes can be easily produced.

[0047] The electrolyte according to this embodiment provides the following effects. (1) The electrolyte according to this embodiment is a plasticized crosslinked network polymer, and therefore has elasticity and flexibility, as well as sufficient mechanical strength. Thus, it is possible to suppress the effects of stress that occur when the electrolyte is bent, stretched, or its shape is changed. Consequently, it is possible to prevent damage to the electrolyte, thinning of the electrolyte, and a decrease in the durability of the electrolyte.

[0048] (2) The electrolyte according to the embodiment is a plasticized crosslinked network polymer having a sufficient number of oxyethylene units. Since the oxyethylene units form a solvation structure with the salt cations, the electrolyte can contain many cations. Therefore, the electrolyte has high ionic conductivity.

[0049] (3) The electrolyte according to the embodiment exhibits increased elasticity and flexibility due to the increased number of oxyethylene units. In addition, the cation content of the salt also increases. Therefore, by increasing the n of the monomer represented by formula (1), the effects of (1) and (2) above can be obtained synergistically.

[0050] (4) Generally, it is known that in electrolytes using polymers, the ionic conductivity decreases when the polymer has a crystalline structure. When a photoradical polymerization initiator with a fast reaction rate is used to produce the electrolyte according to the embodiment, polymerization occurs before the polymer crystallizes. As a result, the electrolyte becomes amorphous, and a decrease in ionic conductivity can be prevented.

[0051] (5) The electrolyte according to the embodiment can be manufactured without using a solvent. For example, when an organic solvent is used, it is difficult to handle when manufacturing the electrolyte because the organic solvent is highly volatile. Also, depending on the type of polymer and organic solvent of the electrolyte, the polymer and solvent may separate, causing a significant decrease in the ionic conductivity and mechanical strength of the electrolyte. However, since the electrolyte according to the embodiment does not use a solvent, the above problems do not occur.

[0052] (Embodiment of composite material) The electrolyte according to the above embodiment can also be used in a composite material. The composite material comprises the electrolyte and a porous carrier.

[0053] Porous carriers have voids that support electrolytes. Therefore, when composite materials are used in secondary batteries, the porous carrier isolates the positive and negative electrodes while ensuring ion conductivity. Furthermore, the support of the electrolyte in the porous carrier suppresses ion diffusion. Thus, porous carriers function as separators.

[0054] The structure of the porous carrier is not particularly limited, as long as it supports an electrolyte and has voids that ensure ion conductivity between the positive and negative electrodes in a secondary battery. The structure of the porous carrier may have regularly arranged voids or random voids. When the voids are regularly arranged, the porous carrier may be, for example, a honeycomb membrane with honeycomb-shaped voids. The honeycomb structure may consist of three-dimensional shapes such as polygonal prisms, cylinders, pyramidal shapes, cones, spheres, or ellipsoids arranged without gaps in any plane. The honeycomb membrane may consist of a single layer of layers with no gaps between the three-dimensional shapes, or it may be constructed by stacking multiple layers perpendicular to any plane. Examples of porous carriers with random voids include nonwoven fabrics, uniaxially oriented porous membranes, biaxially oriented porous membranes, and particle-template porous membranes.

[0055] The voids in the porous carrier are in the range of 0.1 μm to 60 μm in size. More specifically, the voids may be 0.1 μm or larger, 0.2 μm or larger, 0.3 μm or larger, 0.4 μm or larger, 0.5 μm or larger, 0.6 μm or larger, 0.7 μm or larger, 0.8 μm or larger, 0.9 μm or larger, 1 μm or larger, 2 μm or larger, 3 μm or larger, 4 μm or larger, 5 μm or larger, 6 μm or larger, 7 μm or larger, 8 μm or larger, 9 μm or larger, 10 μm or larger, 11 μm or larger, 12 μm or larger, 13 μm or larger, 14 μm or larger, 15 μm or larger, 16 μm or larger, 17 μm or larger, 18 μm or larger, 19 μm or larger, or 20 μm or larger. Furthermore, the void may be 60 μm or less, 59 μm or less, 58 μm or less, 57 μm or less, 56 μm or less, 55 μm or less, 54 μm or less, 53 μm or less, 52 μm or less, 51 μm or less, 50 μm or less, 49 μm or less, 48 ​​μm or less, 47 μm or less, 46 μm or less, 45 μm or less, 44 μm or less, 43 μm or less, 42 μm or less, 41 μm or less, 40 μm or less, 39 μm or less, 38 μm or less, 37 μm or less, 36 μm or less, 35 μm or less, 33 μm or less, 32 μm or less, 31 μm or less, 30 μm or less, 29 μm or less, 28 μm or less, 27 μm or less, 26 μm or less, 25 μm or less, 24 μm or less, 23 μm or less, 22 μm or less, 21 μm or less, or 20 μm or less. The range of the void can be arbitrarily selected so that the above values ​​do not overlap. In this specification, if the void is the above-mentioned solid in the honeycomb membrane, the size of the void is the diameter of the sphere inscribed in the above-mentioned solid.

[0056] As mentioned above, the porous carrier functions as a separator. The separator ensures ion conductivity between the positive and negative electrodes, and by making the distribution of ions between the positive and negative electrodes, i.e., the current distribution, uniform, the formation of dendrites can be suppressed. Therefore, in order to regulate the flow of ions between the positive and negative electrodes and make the current distribution uniform, it is preferable that the porous carrier has through holes in its thickness direction. The through holes in the porous carrier refer to holes that communicate with the first and second surfaces facing each other in the thickness direction of the porous carrier. The through holes only need to communicate with the first and second surfaces; for example, multiple voids in the porous carrier may connect to communicate with the first and second surfaces, or a single void may connect the first and second surfaces.

[0057] The porous support material is not particularly limited as long as it can form voids and is insoluble in electrolytes. Examples include polymers such as polybutadiene, polyisoprene, polystyrene, polycarbonate, polylactic acid, polycaprolactone, polyimide, polyamide, and polyolefin, as well as inorganic oxides such as silica, titania, and alumina. Furthermore, the porous support material is not particularly limited as long as it can be manufactured by a method that can form voids. For example, when manufacturing a honeycomb film as a porous support material, the honeycomb film can be manufactured by the breath-figure method or the like (SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 2018, VOL.19, NO.1, 802-822).

[0058] The electrolyte according to the above embodiment is a plasticized crosslinked network polymer. Therefore, any method of supporting the polymer on a porous carrier is sufficient for producing the composite material, and known methods can be used. For example, a composition containing the monomer represented by formula (1) above, glyme, and salt can be impregnated, coated, or otherwise held in the voids of a porous carrier, and the composition can be polymerized to produce the composite material.

[0059] The composite material according to this embodiment synergistically exhibits the following effects in addition to the effects of the electrolyte according to this embodiment. (1) In composite materials, the electrolyte is supported on a porous carrier, which improves mechanical properties such as mechanical strength and thermal stability. (2) When through-holes are provided in the thickness direction of the porous carrier, the flow of ions can be standardized. As a result, the composite material has high ionic conductivity. In addition, the current distribution can be made uniform and the formation of dendrites can be suppressed. (3) When the porous carrier is a honeycomb membrane, the voids are arranged regularly and without gaps, resulting in a uniform structure for the composite material and making it easier to control the flow of ions. (4) The composite material can prevent dendrites from penetrating even if they are formed.

[0060] (An embodiment of a secondary battery) The secondary battery will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view of the secondary battery. The secondary battery 1 comprises a positive electrode 2, an electrolyte layer 3, and a negative electrode 4 in that order. The positive electrode 2 comprises a positive electrode current collector 5 and a positive electrode active material layer 6. The negative electrode 4 comprises a negative electrode current collector 7 and a negative electrode active material layer 8.

[0061] The positive electrode current collector 5 can be made of any material as long as it does not undergo changes such as dissolution or oxidation during battery use. Examples include aluminum, stainless steel, titanium, and carbon materials. There are also no restrictions on its shape, and examples include perforated foil, expanded metal, and foamed metal plate.

[0062] The thickness of the positive electrode current collector 5 may be 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 20 μm.

[0063] The positive electrode active material used in the positive electrode active material layer 6 is, for example, LiCoO2, Li 0.3 MnO2, Li4Mn5O 12 , V2O5, LiMn2O4, LiNiO2, LiFePO4, LiCo 1 / 3 N 1 / 3 Mn 1 / 3 O2, Li 1.2 (Fe 0.5 Mn 0.5 ), Li 1.2 (Fe 0.4 Mn 0.4 Ti 0.2 ) 0.8 O2, Li 1+x (Ni 0.5 Mn 0.5 ) 1-x O2 (where x = 0 to 1), LiNi 0.5 Mn 1.5 O4, Li2MnO3, Li 0.76 Mn 0.51 Ti 0.49 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2, Fe2O3, LiCoPO4, LiMnPO4, Li2MPO4F(M=Fe,Mn), LiMn 0.875 Fe0.125 PO4, Li2FESiO4, Li 2-x MSi 1-x P x Examples include O4 (M=Fe,Mn) (where x=0 to 1), LiMBO3 (M=Fe,Mn), FeF3, Li3FeF6, Li2FeS2, TiS2, MoS2, and FeS.

[0064] The thickness of the positive electrode active material layer 6 may be 10 μm to 100 μm, preferably 20 μm to 80 μm, and more preferably 30 μm to 60 μm.

[0065] The electrolyte layer 3 can be made of an electrolyte or composite material according to the embodiment. The thickness of the electrolyte layer 3 may be 1 μm to 200 μm, preferably 3 μm to 100 μm, and more preferably 5 μm to 70 μm. A thickness of 1 μm or more can prevent short circuits between electrodes. Furthermore, a thickness of 200 μm or less can increase the energy density.

[0066] The material of the negative electrode current collector 7 can be, for example, copper, stainless steel, titanium, nickel, or carbon material. Its shape is also not limited; for example, it can be perforated foil, expanded metal, or foamed metal sheet.

[0067] The thickness of the negative electrode current collector 7 may be 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 20 μm.

[0068] Examples of negative electrode active materials used in the negative electrode active material layer 8 include metallic lithium, lithium alloys, metal compounds, carbon materials, metal complexes, and organic polymer compounds. Among these, carbon materials are preferred. Examples of carbon materials include graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and other carbon blacks, amorphous carbon, and carbon fibers.

[0069] A secondary battery using the electrolyte or composite material according to this embodiment in the electrolyte layer 3 can have a longer lifespan due to improved mechanical durability provided by the electrolyte or composite material and the ability to contain a large amount of cations in the electrolyte.

[0070] The embodiments disclosed in this application are described below in detail by illustrating the embodiments, but these embodiments are for illustrative purposes only and are not intended to limit or restrict the scope of the invention disclosed in this application. [Examples]

[0071] <Example 1> [Manufacturing of Electrolyte 1] The electrolyte was prepared using the procedure described below.

[0072] 〔material〕 • Poly(ethylene glycol) diacrylate (PEGDA; average molecular weight 700 (n~13), manufactured by Sigma-Aldrich) 0.2 ml (0.36 mol) • Tetraglyme (manufactured by Sigma-Aldrich) 0.17 ml (0.77 mol) • Li[TFSI] (manufactured by Kanto Chemical Co., Ltd.) 0.22g (0.77mol) [Manufacturing method] The above materials were mixed in a glass vial and stirred overnight. DMPA (7.32 mg) was added to this solution and stirred for a further 2 hours. Next, this solution was transferred to glass and photopolymerized by exposure (365 nm, 20 W) to both sides five times at 5-minute intervals. After that, the cured material was peeled off the glass and dried in a 60°C vacuum oven for 24 hours to produce electrolyte 1.

[0073] The resulting electrolyte 1 has a ratio of the number of moles of ethylene oxide units to the number of moles of lithium ions in the electrolyte ([EO] / [Li + ]) is 6.

[0074] <Example 2> [Manufacturing of Electrolyte 2] Electrolyte 2 was prepared using the same procedure as in Example 1, except that 0.4 ml (0.71 mol) of PEGDA was used. The obtained electrolyte [EO] / [Li + ] is 12.

[0075] <Example 3> [Manufacturing of Electrolyte 3] Electrolyte 3 was prepared using the same procedure as in Example 1, except that 0.7 ml (1.07 mol) of PEGDA was used. The obtained electrolyte [EO] / [Li + ] is 18.

[0076] <Example 4> [Manufacturing of Electrolyte 4] Electrolyte 4 was prepared using the same procedure as in Example 1, except that 0.9 ml (1.43 mol) of PEGDA was used. The obtained electrolyte [EO] / [Li + ] is 24.

[0077] <Example 5> [Temperature dependence of ionic conductivity of electrolytes 1-4] The ionic conductivity of electrolytes 1-4, manufactured in Examples 1-4, was measured at multiple temperatures. A sample consisting of an electrolyte (8mm diameter circular) sandwiched between two stainless steel (SUS304, Nilaco) electrodes was placed in a cell assembly (Hosen Co., Ltd.), and ionic conductivity was measured using an AC impedance measuring device (Hioki 3532-80 LCR HiTester). Measurements were performed in a temperature range of 25°C to 90°C, with 5°C intervals. Sufficient time was allowed at each temperature to ensure thermal equilibrium and data reproducibility.

[0078] Figure 2 shows the ionic conductivity of electrolytes 1-4, prepared in Examples 1-4, measured at each temperature. Electrolytes 1-4 showed linearity within the measurement range. This indicates that electrolytes 1-4 possess sufficient ionic conductivity. Furthermore, it was shown that higher lithium ion content in the electrolyte resulted in higher ionic conductivity.

[0079] <Example 6> [Mechanical properties of electrolytes] Tensile / force-displacement measurements were performed on electrolyte 1, which was prepared in Example 1. Electrolyte 1, a roughly rectangular sample measuring 30 mm x 10 mm with a thickness of approximately 0.4 mm, was used as the sample. The measurement was performed using a measuring stand (manufactured by IMADA Co., Ltd.), pulling the sample vertically away from the stand at room temperature at an elongation rate of 1.0 mm / min.

[0080] The results are shown in Figure 3A. Figure 3A shows that electrolyte 1 has an elongation rate of about 30%, indicating that it has good mechanical properties that allow it to stretch well. Therefore, it is possible to prevent the effects of stress on the electrolyte. Also, Figure 3A shows that electrolyte 1 stretched by about 10% with a small force. In other words, electrolyte 1 is easily deformed even with a small force. When an electrolyte is used in a secondary battery, the electrolyte expands and contracts due to temperature changes and charging / discharging during use, putting a load on the electrolyte. However, since electrolyte 1 can be deformed even with a small force, it is expected that the effects of temperature changes and charging / discharging will be suppressed and the load on the electrolyte will be reduced. Furthermore, because it deforms flexibly with a small force, it is also expected that short circuits between electrodes will be avoided and the risk of ignition will be reduced.

[0081] Figure 3B shows the results of experiments in which the prepared electrolyte 4 was stretched and bent using tweezers. Similar to Figure 3A, it was observed that the electrolyte stretched well.

[0082] <Example 7> [Charge and discharge characteristics of electrolyte 1] A polarization test was performed using electrolyte 1 prepared in Example 1. For the polarization test, a symmetric cell consisting of Li / electrolyte 1 / Li was used, and the test was conducted at 60°C for 30 minutes at a rate of 0.1 mA / cm². 2 The charging and discharging processes were repeatedly performed at the given current density.

[0083] The results of the polarization test are shown in Figure 4. From Figure 4, it was confirmed that the Li / electrolyte 1 / Li cell remained stable even after 100 hours of charging and discharging. Furthermore, from Figure 4, the voltage decay was very gradual even as time passed, suggesting that it maintains stable charging and discharging characteristics even after 100 hours. Therefore, it is expected that using electrolyte 1 in a secondary battery will result in a long-life secondary battery.

[0084] <Example 8> [Linear sweep voltammetry of electrolyte 1] Linear sweep voltammetry (LSV) was performed using electrolyte 1 prepared in Example 1.

[0085] The measurement was performed using a cell made of stainless steel (SUS304, manufactured by Nilaco) / electrolyte 1 / Li, with a scan range of 1.0~7.0V (vs.Li). + The scan was performed at a speed of 1 mV / s as the (Li) value. The measurement temperature was 60°C. The measuring instrument used was a 1470E potentiostat / galvanostat (Solartron Analytical).

[0086] The results are shown in Figure 5. Figure 5 shows that electrolyte 1 is stable up to around 4.5V. This indicates that electrolyte 1 has a wide potential window.

[0087] <Example 9> [Calculation of lithium ion transport fraction of electrolyte 1] Chronoamperometry and AC impedance measurements were performed using electrolyte 1, and the lithium ion transport fraction (t) of electrolyte 1 was determined. Li+ ) was calculated.

[0088] Lithium ion transport rate (t Li+The current was calculated by performing chronoamperometry and AC impedance measurements using a Li / electrolyte 1 / Li cell assembled in a glove box filled with argon (O2 and H2O < 0.1 ppm). For chronoamperometry, the initial current (I0) was measured by applying a potential of 10 mV to a cell that had been stabilized overnight at 60°C. Subsequently, the steady-state current (I0) was measured when the current value reached a steady state after continuously applying a potential of 10 mV to the cell. s The following measurements were taken: ) and the AC impedance was measured. Additionally, the initial interface resistance (R0) of a cell stabilized overnight at 60°C and the steady-state interface resistance (R0) of a cell that had reached a steady state after applying a potential of 10mV were measured. s The following was measured: ) was measured using a frequency response analyzer (1470E, manufactured by Solartron Analytical). Li+ This was calculated using the Bruce-Vincent-Evans equation shown below.

[0089]

number

[0090] The results of chronoamperometry are shown in Figure 6A. The results of AC impedance measurement are shown in Figure 6B. From the results shown in Figures 6A and 6B, the t of electrolyte 1 can be seen. Li+ When calculated, the t of electrolyte 1 was Li+ The value was 0.30.

[0091] <Example 10> [Manufacturing of Composite Material 1] 〔material〕 • 1,2-Polybutadiene (RB820, manufactured by JSR Corporation) • Surfactants represented by the following formula (3) (wherein X is approximately 0.8, manufactured by Tokyo Chemical Industry Co., Ltd.) • Poly(ethylene glycol) diacrylate (PEGDA; average molecular weight 700 (n~13), manufactured by Sigma-Aldrich) 0.9 ml (1.43 mmol) • Tetraglyme (manufactured by Sigma-Aldrich) 0.6819 ml (3.0 mmol) • Li[TFSI] (manufactured by Kanto Chemical Co., Ltd.) 0.8886g (3.0 mmol)

[0092] [ka]

[0093] [Preparation of honeycomb membrane] [1] A 5.0 mg / ml solution was prepared by mixing 1,2-polybutadiene with a surfactant represented by formula (3) in a weight ratio of 10:1. [2] The prepared solutions were cast onto a 10cm x 30cm glass substrate in volumes of 20ml, 25ml, and 45ml, respectively. [3] Honeycomb films with pore sizes of 3 μm, 8 μm, and 14 μm were obtained by blowing humidified air (relative humidity > 90%, flow rate 130 l / min) onto the film. Figure 7 shows a scanning electron microscope image of the 3 μm pore honeycomb film viewed from the thickness direction. Figure 7 shows that the honeycomb film has through-pores in the thickness direction.

[0094] [Preparation of Composite Material 1] [1] The honeycomb film with a pore size of 3 μm prepared as described above was scooped onto a PET film frame cut to a size of 50 mm square, and dried in ethanol or water. [2] A mixed solution of PEGDA, tetraglyme, LiTFSI, and DMPA (7.32 mg) was spread onto a petri dish, a honeycomb film was placed on top of it, and the mixed solution was then spread onto the honeycomb film. Note that the [EO] / [Li + ] is 6. [3] The honeycomb film coated with the mixed solution was subjected to reduced pressure to remove bubbles and other debris from the mixed solution, and composite material 1 was obtained by photocrosslinking with UV light (wavelength 365 nm, 20 W) in the same manner as with the electrolyte alone. The obtained composite material 1 was annealed at 60°C for 24 hours to complete the crosslinking. Furthermore, it was confirmed that the electrolyte had been introduced into the interior of the through-holes by observation with a scanning electron microscope.

[0095] <Example 11> [Temperature dependence of ionic conductivity of composite material 1] The ionic conductivity of composite material 1, manufactured in Example 10, was measured at multiple temperatures. The measurement procedure was the same as in Example 5, except that composite material 1 was used as the sample.

[0096] The results are shown in Figure 8. Composite material 1 showed linearity within the measurement range. Furthermore, composite material 1 also showed linearity at room temperature. -4 It exhibited high ionic conductivity of S / cm or higher. This is thought to be because the electrolyte was supported on the honeycomb membrane, suppressing ion diffusion and regulating the flow of ionic conduction, thus improving the ionic conductivity of composite material 1.

[0097] <Example 12> [Charge and discharge characteristics of composite material 1] A polarization test was performed using composite material 1 manufactured in Example 10. For the polarization test, a capacitor consisting of Li foil / composite material 1 / LiFePO4 (LFP) electrode was used, and a charge-discharge test was performed at 60°C using a 580 Battery Test System, Scribner Associates.

[0098] The results are shown in Figure 9. Stable charging and discharging were confirmed even after 100 hours from Figure 9A and 700 hours from Figure 9B. Furthermore, comparing Figure 9A and Figure 9B, the voltage decayed more in Figure 9B. However, the voltage decay was very gradual. Therefore, it is expected that using composite material 1 in a secondary battery will result in a long-life secondary battery.

[0099] <Example 13> [LSV measurement of composite material 1] LSV was performed using composite material 1 manufactured in Example 10. The measurement was the same as in Example 8, except that composite material 1 was used as the sample.

[0100] The results are shown in Fig. 10. From Fig. 10, it was shown that the composite material 1 was stable up to around 4.7 V. From this, it was shown that the composite material 1 has a wide potential window. Also, it was shown that the composite material has a wider potential window than only the electrolyte (Example 8).

[0101] <Example 14> [Calculation of Li + transport rate of composite material 1] Using the composite material 1 produced in Example 10, chronoamperometry and AC impedance measurement were performed to calculate the Li + transport rate of the composite material. The calculation of the Li + transport rate was the same as in Example 9 except that the sample was the composite material 1.

[0102] The results of chronoamperometry are shown in Fig. 11A. Also, the results of AC impedance measurement are shown in Fig. 11B. From the results shown in Fig. 11A and Fig. 11B, when calculating t Li+ of the composite material 1, t Li+ was 0.416.

[0103] <Examples 15> to <Example 23> [Production of electrolytes 5 to 13] When producing the electrolytes, electrolytes 5 to 13 were produced in the same procedure as in Example 1 except that each material with the addition amounts shown in Table 1 below was used. The [EO] / [Li + of the obtained electrolytes 5 to 13 is also shown in Table 1.

[0104]

Table 1

[0105] The produced electrolytes 5, 9, and 13 are shown in Fig. 12. The electrolytes 5, 9, and 13 with different average molecular weights of the used PEGDA were all transparent and maintained their shapes even when grasped with tweezers. Since electrolytes 5, 9, and 13 maintained their shapes even when grasped with tweezers, it is considered that electrolytes 5 to 13 have sufficient mechanical strength.

[0106] <Example 24> [Temperature dependence of ionic conductivity of electrolytes 5-13] The ionic conductivity of electrolytes 5-13, prepared in Examples 15-23, was measured at multiple temperatures. The measurement procedure was the same as in Example 5, except that electrolytes 5-13 were used as the samples.

[0107] Figure 13 shows the ionic conductivity of electrolytes 5 to 13, prepared in Examples 15 to 23, measured at each temperature. Figure 13A shows the results for electrolytes 5 to 8 using PEGDA with an average molecular weight of 250 (n~3). Figure 13B shows the results for electrolytes 9 to 12 using PEGDA with an average molecular weight of 575 (n~10). Figure 13C shows the results for electrolyte 13 using PEGDA with an average molecular weight of 1000 (n~20). Electrolytes 5 to 13 showed linearity within the measurement range. This indicates that electrolytes 5 to 13 possess sufficient ionic conductivity. Furthermore, it was shown that the ionic conductivity of the electrolyte tended to increase as the average molecular weight of the PEGDA used increased.

[0108] The results above demonstrate that the electrolyte disclosed in this application exhibits sufficient flexibility without breaking even when bent. Furthermore, the composite material using the electrolyte was shown to be more stable and have a higher transport rate than the electrolyte alone. [Industrial applicability]

[0109] The electrolyte disclosed in this application can provide an electrolyte that is stretchable and flexible. Furthermore, since the electrolyte can be used in batteries, it is useful in the field of battery technology. [Explanation of symbols]

[0110] 1... Secondary battery, 2... Anode, 3... Electrolyte layer, 4... Negative electrode, 5... Positive electrode current collector, 6... Positive electrode active material layer, 7... Negative electrode current collector, 8... Negative electrode active material layer

Claims

1. A polymer obtained by polymerizing monomers represented by the following formula (1), 【Chemistry 1】 (In formula (1), R １ and R ２ Each of these independently represents H or a linear, branched, or cyclic alkyl group having 1 to 20 carbon atoms. １ and X ２ Each of these independently represents either O or NH. ２ When is O, n represents an integer between 0 and 30 on average, and X ２ When n is NH, n represents an integer between 1 and 30 on average. Grime represented by the following formula (2), 【Chemistry 2】 (In formula (2), R ３ and R ４ Each of these independently represents an alkyl group with 1 to 4 carbon atoms, and m represents an integer from 1 to 4. At least one salt selected from the group consisting of lithium salts, sodium salts, magnesium salts, potassium salts, and calcium salts, Electrolytes it contains.

2. The anion of the salt is PF ６ － , BF ４ － , ClO ４ － , B(C ２ O ４ ), ２ － , N(FSO ２ ), ２ － and N(CF ３ SO ２ ), ２ － and is at least one selected from the group consisting of The electrolyte according to claim 1.

3. The salt anion is N(FSO) ２ ) ２ － or N(CF ３ SO ２ ) ２ － That is, The electrolyte according to claim 2.

4. The salt is a lithium salt. The electrolyte according to any one of claims 1 to 3.

5. In formula (1), X ２ When is O, n is on average 3 to 14, and X ２ When is NH, n is on average between 4 and 15. The electrolyte according to any one of claims 1 to 4.

6. In equation (2), m is 4. The electrolyte according to any one of claims 1 to 5.

7. Anode and, Cathode and, An electrolyte layer between the anode and the cathode It includes at least, The electrolyte layer is the electrolyte according to any one of claims 1 to 6. Secondary battery.

8. An electrolyte according to any one of claims 1 to 6, Porous carrier and A composite material that possesses [the following characteristics].

9. The porous carrier has through holes that penetrate in the thickness direction. The composite material according to claim 8.

10. The porous carrier is a honeycomb membrane. The composite material according to claim 8 or 9.

11. Anode and, Cathode and, An electrolyte layer is placed between the anode and the cathode, It includes at least, The electrolyte layer is the composite material according to any one of claims 8 to 10. Secondary battery.

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