TW201822396A - Solid electrolyte and battery - Google Patents

Abstract

A solid electrolyte which is characterized by containing a polymer, cellulose nanofibers, and a metal salt.

Description

   Solid electrolyte and battery   

The present invention relates to a solid electrolyte and a battery.

Unlike liquid electrolytes, solid electrolytes have no concerns about leakage and are lightweight and flexible electrolyte membranes. Therefore, the application of a solid electrolyte to a secondary battery using lithium ion or the like is expected.

For example, Non-Document 1 (F. Croce et al., Electrochimica Acta, 46, 2457 (2001)) describes that a metal oxide such as alumina is added to a polyethylene oxide electrolyte.

In addition, for example, Document 1 (Japanese Patent Application Laid-Open No. 2006-252878) describes a method for producing an ion conductor composition containing a polyether polymer and a metal oxide filler. Document 1 describes a method of kneading by coexisting a boron-containing compound and the like when kneading an ion conductive polymer and a metal oxide filler.

Although the strength of the solid electrolyte membrane can be improved by adding a metal oxide filler, the self-supporting property of the solid electrolyte membrane is not sufficient.

An object of the present invention is to provide a solid electrolyte having improved self-supporting properties of a membrane, and a battery using the solid electrolyte.

A solid electrolyte according to one aspect of the present invention includes a polymer, cellulose nanofiber, and a metal salt.

In one aspect of the present invention, when the molar number of the repeating unit of the polymer is x (mol) and the molar number of the metal in the metal salt is z (mol), it is preferably satisfied Conditions represented by the following formula (F1).

0.7 ≦ (z / x). ． ． (F1)

In the solid electrolyte according to one aspect of the present invention, the content of the cellulose nanofiber is preferably 4.5% by mass or less.

In one aspect of the present invention, the metal salt is preferably an alkali metal salt.

In the solid electrolyte according to one aspect of the present invention, the metal salt is preferably a lithium salt.

In one aspect of the solid electrolyte according to the present invention, the lithium salt preferably contains at least one of lithium bis (trifluoromethanesulfonyl) fluorenimide and lithium bis (fluorosulfonyl) fluorenimide.

In one aspect of the present invention, the polymer is preferably an aliphatic polycarbonate.

A battery according to one aspect of the present invention includes the solid electrolyte according to one aspect of the present invention.

According to the present invention, a solid electrolyte having improved self-supporting properties of a membrane, and a battery using the solid electrolyte can be provided.

FIG. 1 is a graph showing the relationship between the salt concentration and the common logarithm of ion conductivity in Example 1 and Comparative Example 1. FIG.

FIG. 2 is a graph showing the relationship between the salt concentration and the common logarithm of ion conductivity in Examples 1 and 2. FIG.

    [Solid electrolyte]    

Hereinafter, the present invention will be described by way of example. The present invention is not limited to the contents of the embodiments.

The solid electrolyte of this embodiment contains a polymer described below, cellulose nanofiber described below, and a metal salt described below.

    (Polymer)    

Examples of the polymer in this embodiment include aliphatic polycarbonate, polyalkylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polymethacrylate. These polymers may be used individually by 1 type, and may use 2 or more types together. Further, these polymers may be copolymers having a plurality of repeating units. In the case of a copolymer, it may be a random copolymer or a block copolymer.

Among these polymers, from the viewpoint of performance as a solid electrolyte, aliphatic polycarbonate or polyalkylene oxide is particularly preferable; and aliphatic polycarbonate is more preferable.

Examples of the aliphatic polycarbonate include an aliphatic polycarbonate having a repeating unit represented by the following general formula (1).

In the aforementioned general formula (1), m is 2 or 3, and R ¹ is independently a hydrogen atom, an alkyl group (such as a methyl group and an ethyl group), or an alkoxy group. Here, the alkyl group and the alkoxy group may have a substituent. Moreover, a plurality of R ¹ may be the same as or different from each other.

In this embodiment, m is preferably 2 from the viewpoint of improving the ion conductivity. From the viewpoint of improving the ion conductivity, R ^{1 is} preferably a hydrogen atom.

Examples of the polyalkylene oxide include a polyalkylene oxide having a repeating unit represented by the following general formula (2).

In the aforementioned general formula (2), n is 2 or 3, and R ² is independently a hydrogen atom, an alkyl group (such as a methyl group and an ethyl group), or an alkoxy group. Here, the alkyl group and the alkoxy group may have a substituent. Moreover, a plurality of R ² may be the same as or different from each other.

In this embodiment, from the viewpoint of improving the ion conductivity, n is preferably 2. From the viewpoint of improving the ion conductivity, R ^{2 is} preferably a hydrogen atom.

When the molecular weight of the polymer according to this embodiment is expressed as a weight average molecular weight (Mw), it is measured by a gel permeation chromatography (GPC) method, and in terms of standard polystyrene, it is preferably 5,000 to 5,000,000, and more preferably Above 10,000 and below 1,000,000.

When expressed as a number average molecular weight (Mn), it is preferably 3,000 or more and 3,000,000 or less, and more preferably 5,000 or more and 500,000 or less.

The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1 or more and 10 or less, and more preferably 1.1 or more and 5 or less.

    (Cellulose nanofiber)    

The cellulose nanofibers of this embodiment are obtained by defibrating cellulose fibers. Cellulose fibers include fiber separated from plant fibers (pulp derived from plants, wood, cotton, hemp, bamboo, cotton, kenaf, hemp, jute, banana, coconut, seagrass, tea, etc.), animal fiber Isolated fibers (fibers separated from animal fibers produced by sea squirts of marine animals), bacterial cellulose (bacterial cellulose produced by acetic acid bacteria, etc.). Among these, natural cellulose fibers separated from plant fibers are preferred; natural cellulose fibers separated from pulp or cotton are more preferred.

As the cellulose nanofiber of this embodiment, a commercially available cellulose nanofiber can be appropriately used. Commercially available cellulose nanofibers include, for example, a cellulose nanofiber aqueous solution "BiNFi-s" manufactured by Sugino Machine.

The average fiber diameter (short diameter) of the cellulose nanofibers of this embodiment is preferably 10 nm to 100 nm, more preferably 10 nm to 40 nm, and particularly preferably 15 nm to 25 nm.

The fiber length of the cellulose nanofiber in this embodiment is preferably 5 μm or more.

In this embodiment, the content of cellulose nanofibers in the solid electrolyte is not particularly limited. However, from the viewpoint of improving the ion conductivity, the content of cellulose nanofibers is preferably more than 0% by mass and 4.5% by mass or less, more preferably 0.1% by mass or more with respect to the total amount of the solid electrolyte. 4 It is preferably 1% by mass or more and 3.5% by mass or less, and particularly preferably 2% by mass or more and 3% by mass or less. Furthermore, if the content is above the aforementioned lower limit, the self-supporting property of the film can be sufficiently improved. On the other hand, if the content is below the aforementioned upper limit, the self-supporting property of the film can be sufficiently improved, and the ion conductivity can be improved.

    (Metal salt)    

The metal salt of this embodiment is not particularly limited, and for example, at least one of the alkali metal salts can be used. Examples of the alkali metal salt include a lithium salt, a sodium salt, and a potassium salt. These may be used individually by 1 type, and may use 2 or more types together.

In this embodiment, the metal salt is more preferably a lithium salt. In a solid electrolyte, a metal salt may exist as a cation of an alkali metal or the like and a counter ion of the cation. When the metal salt is a lithium salt, the energy density is further increased.

Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiI, LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ COO, LiNO ₃ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) N, Li (FSO ₂ ) ₂ N, and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, from the viewpoint of ion conductivity, Li (CF ₃ SO ₂ ) ₂ N (lithium bis (trifluoromethanesulfonyl) fluorenimide: LiTFSI) and Li (FSO ₂ ) _{2 are particularly included.} At least one kind of N (lithium bis (fluorosulfonyl) fluorenimide: LiFSI) is more preferable. The solid electrolyte may contain plural kinds of metal salts.

In this embodiment, the content of the metal salt in the solid electrolyte is not particularly limited. However, from the viewpoint of improving the ion conductivity, it is preferable that the molar number of the repeating unit in the polymer is x (mol) and the molar number of the metal in the metal salt is z (mol). In order to satisfy the condition represented by the following formula (F1).

0.7 ≦ (z / x). ． ． (F1)

From the viewpoint of improving ion conductivity, the value of (z / x) is more preferably 0.8 or more and 2 or less, still more preferably 1 or more and 1.6 or less, and particularly preferably 1.1 or more and 1.3 or less. In addition, if the value of (z / x) is at least the aforementioned lower limit, the ion conductivity can be sufficiently exhibited. On the other hand, if the value of (z / x) is less than the aforementioned upper limit, the salt can be sufficiently dissolved, so salt precipitation can be suppressed, which can reduce the decrease in ion conductivity, and the proportion of the polymer will not be excessively reduced. Keeps solid shape.

When the polymer is an aliphatic polycarbonate, if the value of (z / x) is 0.7 or more, the self-supporting property of the film tends to be insufficient. However, when the aliphatic polycarbonate and cellulose nanofiber are combined, the self-supporting property of the film can be secured.

In addition, (z / x) indicates that the metal of the solid electrolyte (a metal derived from a metal salt, not only the metal ion dissociated by the metal salt, but also the concept of the metal not dissociated by the metal salt) is relative to the polymer. Mole ratio of repeating units. In addition, (z / x) × 100 (unit: mol%) is referred to as Salt Concentration of the solid electrolyte according to circumstances.

The solid electrolyte of this embodiment may contain components other than the polymer, cellulose nanofiber, and metal salt of this embodiment as long as the object of the present invention is not impaired.

For example, the solid electrolyte of this embodiment may be a solid state containing no solvent (the solvent does not contain a solid electrolyte), or a solid state containing a solvent (a polymer gel electrolyte). When the solid electrolyte is a polymer gel electrolyte, the content of the solvent in the polymer gel electrolyte is usually 30% to 99% by mass of the entire solid electrolyte.

Moreover, for example, the solid electrolyte of this embodiment may contain a filler or other additives. When a filler or other additives are used, the blending amount thereof is preferably 5% by mass or less with respect to the total amount of the solid electrolyte. Examples of the filler include talc, kaolin, clay, calcium silicate, alumina, zirconia, zinc oxide, antimony oxide, indium oxide, tin oxide, titanium oxide, iron oxide, magnesium oxide, aluminum hydroxide, and magnesium hydroxide. , Silicon dioxide, calcium carbonate, potassium titanate, barium titanate, mica, montmorillonite and glass fiber. These may be used individually by 1 type, and may use 2 or more types together. Among these, it is preferable to contain at least one of alumina, zirconia, magnesium oxide, and barium titanate.

When these fillers are used, the blending amount is preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.1% by mass or less with respect to the total amount of the solid electrolyte. Moreover, compared with these fillers, cellulose nanofibers have a higher effect of improving the self-supporting property of the film. Therefore, in this embodiment, it is preferable not to contain such fillers.

When other additives are used, the blending amount thereof is preferably 5% by mass or less with respect to the total amount of the solid electrolyte.

The method for manufacturing the solid electrolyte of this embodiment is not particularly limited, and examples include (i) polymerizing monomers to obtain a polymer, forming a composite of a polymer and cellulose nanofiber, and containing a metal salt Method, or (ii) a method in which monomers are polymerized in the presence of a metal salt to form a polymer, and cellulose nanofibers are contained therein. In the case of the method (i), a solid electrolyte can be obtained by adding a metal salt and a solvent to the polymer and the cellulose nanofiber complex of this embodiment to dissolve it, and removing the solvent.

The form and structure of the solid electrolyte in this embodiment are not particularly limited. According to the solid electrolyte of this embodiment, since the self-supporting property of the membrane can be improved, a solid electrolyte membrane having a self-supporting property can be formed. Self-supporting solid electrolyte membrane with excellent operability. A self-supporting film refers to a film that can be peeled off from a support while maintaining the shape of the solid electrolyte film, and can be handled.

A solid electrolyte membrane can be manufactured as follows. For example, a mixed solution containing the polymer of this embodiment, cellulose nanofibers, a metal salt, and a solvent can be applied to the surface of a support to form a coating film, and the solvent in the coating film can be removed to obtain a film-like shape. Solid electrolyte membrane. In this case, when it is necessary to peel the solid electrolyte membrane from the support, it is preferable to perform a peeling treatment on the surface of the support.

The solid electrolyte according to this embodiment can be suitably used in, for example, batteries. The battery containing the solid electrolyte of this embodiment includes a primary battery and a secondary battery.

    [Battery]    

The battery of this embodiment contains the solid electrolyte of this embodiment. In this embodiment, the constituent material of the electrolyte layer of the battery preferably contains the solid electrolyte of this embodiment. The battery is composed of an anode, a cathode, and an electrolyte layer disposed between the anode and the cathode. With such a configuration, a battery having excellent characteristics can be obtained. The battery is preferably a secondary battery, and more preferably a lithium ion secondary battery.

Furthermore, the solid electrolyte membrane may be directly formed on the electrode by coating the electrode and removing the solvent with the mixed solution containing the polymer, cellulose nanofiber, metal salt, and solvent. Various members included in the lithium ion secondary battery of this embodiment are not particularly limited, and for example, materials commonly used in batteries can be used.

In addition, the solid electrolyte of this embodiment has ion conductivity even if it does not contain a solvent. Therefore, if the battery of this embodiment is used as a battery that contains the solid electrolyte of this embodiment and contains no solvent, it can be safely used without leakage.

In addition, the present invention is not limited to the foregoing embodiments, and changes, improvements, and the like within a range that can achieve the object of the present invention are included in the present invention.

    [Example]    

The following examples are given to illustrate the present invention in more detail, but the present invention is not limited by these examples. The measurements in the following examples and comparative examples were performed by the methods shown below.

    [Measurement of ion conductivity]    

The obtained solid electrolyte membrane was cut into a circle having a diameter of 6 mm, and two stainless steel plates were sandwiched as electrodes to measure the impedance between the stainless steel plates. The measurement is an AC impedance method in which an alternating current (applied voltage of 10 mV) is applied between electrodes to measure a resistance component, and an ion conductivity is calculated from a real impedance slice of the obtained call-call plot. The measurement system used a potentiostat / galvanostat (product name "SP-150", manufactured by Biologic).

The ion conductivity (σ) is obtained from the following formula (F2).

σ = L / (R × S). ． ． (F2)

In the formula (F2), σ represents the ion conductivity (unit: S · cm ^-1 ), R represents the resistance (unit: Ω), S represents the cross-sectional area (unit: cm ² ) when measuring the solid electrolyte membrane, and L represents Distance between electrodes (unit: cm).

The measurement temperature was 60 ° C. The ion conductivity (σ) was calculated from the measurement result of the complex impedance.

    [Film shape observation]    

The solid electrolyte solution was cast on a fluororesin mold, and the dried 100um thick solid electrolyte was peeled off from the fluororesin mold. Those who remained self-supporting after peeling were judged to be "A", those who were unable to maintain self-supporting or unable to peel in the shape of a film were judged to be "B".

    [Example 1 (Examples 1-1 to 1-8)]         (Modulation of cellulose nanofiber / polycarbonate)    

Acetonitrile was added to a commercially available polyethylene carbonate (trade name "QPAC-25", manufactured by EMPOWER MATERIALS), and adjusted to 2% by mass of polyethylene carbonate to obtain a polyethylene carbonate solution. A cellulose nanofiber aqueous solution (trade name "BiNFi-s BMa-10002", manufactured by Sugino Machine) was added to the polyethylene carbonate solution to adjust the solution ratio (polyethylene carbonate solution: cellulose nanofiber aqueous solution). ) To 90% by mass: 10% by mass, and stirred. Thereafter, it was dried at 60 ° C. for 48 hours, and then dried under reduced pressure at 60 ° C. for 72 hours to prepare a cellulose nanofiber / polyethylene carbonate composite containing 10% by mass of cellulose nanofibers.

    (Manufacture of solid electrolyte membrane)    

Next, the cellulose nanofiber / polyethylene carbonate composite and LiFSI were weighed so that the ratio of the mole number z of the lithium salt to the mole number x of the repeating unit of polyethylene carbonate (unit: mol%, (z / x) × 100) were respectively 10 mol%, 20 mol%, 40 mol%, 60 mol%, 80 mol%, 100 mol%, 120 mol%, and 160 mol%, and after mixing, acetonitrile was added and stirred to obtain a solid electrolyte solution. Thereafter, the solid electrolyte solution was cast on a fluororesin mold, dried under a dry nitrogen environment at 60 ° C for 6 hours, and then dried under reduced pressure at 60 ° C for 24 hours to obtain the salt concentration (unit: mol) in the solid electrolyte. %, (Z / x) × 100) and the content of cellulose nanofibers (unit: mass%, content relative to the total solid electrolyte) are shown in Table 1 below.

The obtained solid electrolyte membrane was measured for ion conductivity (σ), and the shape of the membrane was observed. The results obtained are shown in Table 1.

    [Comparative Example 1 (Comparative Example 1-1 to Comparative Example 1-4)]    

Weigh commercially available polyethylene carbonate (trade name "QPAC-25", manufactured by EMPOWER MATERIALS) and LiFSI so that the mole number z of the lithium salt is relative to the mole number x of the repeating unit of polyethylene carbonate The ratios (units: mol%, (z / x) × 100) were 80 mol%, 100 mol%, 120 mol%, and 160 mol%, respectively. After mixing, acetonitrile was added and stirred sufficiently to obtain a solid electrolyte solution. Thereafter, the solid electrolyte solution was cast on a fluororesin mold, dried under a dry nitrogen environment at 60 ° C for 6 hours, and then dried under reduced pressure at 60 ° C for 24 hours to obtain the salt concentration (unit: mol) in the solid electrolyte. %, (Z / x) × 100) and the content of the cellulose nanofibers (unit: mass%, content relative to the total solid electrolyte) are shown in Table 2 below.

The obtained solid electrolyte membrane was measured for ion conductivity (σ), and the shape of the membrane was observed. The results obtained are shown in Table 2.

As shown in Tables 1 and 2, it was confirmed that the solid electrolyte containing cellulose nanofibers (Example 1) has a higher membrane strength than the solid electrolyte containing cellulose nanofibers (Comparative Example 1). Improved self-sustainability.

1 shows the relationship between the salt concentration and the common logarithm of ion conductivity in Examples 1-5 to 1-8 and Comparative Examples 1-1 to 1-4. It is also clear from the results shown in FIG. 1 that the solid electrolyte containing cellulose nanofibers (Example 1) was confirmed as compared with the solid electrolyte containing no cellulose nanofibers (Comparative Example 1). , The ion conductivity at the same salt concentration has improved.

    [Example 2 (Examples 2-1 to 2-4)]    

Weigh cellulose nanofiber / polyethylene carbonate composite, commercially available poly (ethylene carbonate) (trade name "QPAC-25", manufactured by EMPOWER MATERIALS), and LiFSI to make cellulose nano in the solid electrolyte The content of the fiber was 2.5% by mass, and the ratio of the molar number z of the lithium salt to the molar number x of the repeating unit of polyethylene carbonate (units: mol%, (z / x) × 100) was 10 mol, respectively. %, 20 mol%, 40 mol%, and 60 mol%. After mixing, add acetonitrile and stir well to obtain a solid electrolyte solution. Thereafter, the solid electrolyte solution was cast on a fluororesin mold, dried under a dry nitrogen environment at 60 ° C for 6 hours, and then dried under reduced pressure at 60 ° C for 24 hours to obtain the salt concentration (unit: mol) in the solid electrolyte. %, (Z / x) × 100) and the content of the cellulose nanofibers (unit: mass%, content relative to the total amount of solid electrolyte) are shown in the solid electrolyte membrane shown in Table 3 below.

The obtained solid electrolyte membrane was measured for ion conductivity (σ), and the shape of the membrane was observed. The results obtained are shown in Table 3.

As shown in Table 3, it was confirmed that the solid electrolyte containing cellulose nanofibers (Example 2) improved the self-supporting property of the membrane.

Fig. 2 shows the relationship between the salt concentration and the common logarithm of ion conductivity in Examples 1-1 to 1-4 and Examples 2-1 to 2-4. It is also clear from the results shown in FIG. 2 that a solid electrolyte having a lower content of cellulose nanofibers than that of Example 1 (Example 2) can be confirmed. Ionic conductivity has improved.

Claims (8)

    A solid electrolyte characterized by containing a polymer, cellulose nanofibers, and a metal salt.         For example, in the solid electrolyte of claim 1, wherein the molar number of the repeating unit of the aforementioned polymer is x (mol), and the molar number of the metal in the aforementioned metal salt is z (mol), the following formula ( F1), 0.7 ≦ (z / x). ． ． (F1).         The solid electrolyte according to claim 1, wherein the content of the aforementioned cellulose nanofibers is 4.5% by mass or less.         The solid electrolyte according to claim 1, wherein the aforementioned metal salt is an alkali metal salt.         The solid electrolyte according to claim 1, wherein the aforementioned metal salt is a lithium salt.         The solid electrolyte according to claim 5, wherein the lithium salt includes at least one of lithium bis (trifluoromethanesulfonyl) fluorenimide and lithium bis (fluorosulfonyl) fluorenimide.         The solid electrolyte according to any one of claim 1 to claim 6, wherein the aforementioned polymer is an aliphatic polycarbonate.         A battery characterized by containing the solid electrolyte according to any one of claim 1 to claim 7.