JP4899043B2 - Lithium ion conductive composite - Google Patents

Description

The present invention relates to a polymer composite with lithium ion conductivity. More specifically, the present invention provides a lithium ion useful as a polymer solid electrolyte, which exhibits good ion conductivity and lithium ion transport number, and has good mechanical properties, molding processability and adhesion to electrodes. It relates to a conductive composite.
By using such a lithium ion conductive composite, a high-performance solid lithium secondary battery can be provided.

A lithium battery is a battery having a large electric capacity and a high voltage, and has been put to practical use. However, the reactivity of lithium metal is high, and there is a problem in safety when an electrolytic solution is used. In order to solve such a problem, a lithium polymer battery or the like is produced and used from a polymer electrolyte using a branched poly (ethylene oxide) having lithium ion conductivity instead of an electrolytic solution (for example, see Non-Patent Document 1). ).
Many solid polymer electrolytes in which lithium salts are added to poly (ethylene oxide) polymers have been reported. However, there is a problem that the lithium ion transport number is small (for example, see Non-Patent Document 2).
As a method for increasing the transport number of lithium ions, a method of adding an inorganic filler has been reported, but it is not easy to make an organic / inorganic composite by compositing inorganic filler particles with high polymer compatibility ( For example, see Non-Patent Documents 3 and 4).
The ionic liquid is expected to be an excellent electrolyte (see, for example, Non-Patent Document 5), but has a problem of liquid leakage because of the liquid.

  Patent Document 1 discloses a polymer composite electrolyte composed of lithium haloborosite particles and a polar polymer having an oxygen-containing polar group. However, there is a demand for a polymer solid electrolyte with further improved performance as an electrolyte. It has been.

Patent Document 2 discloses a lithium ion conductive organic-inorganic composite mainly composed of poly (ethylene oxide) and Li ₂ S—SiS ₂ -based amorphous, but Li ₂ S—SiS ₂ -based amorphous. Since it is unstable and deactivated in the atmosphere, it can be handled only in a special environment, and this composite cannot be said to be suitable for manufacturing an industrial solid-state secondary battery.
JP 2003-272438 A JP 2001-316583 A Yuko Ikeda: Lithium ion conductive amorphous matrix using branched polymer, Polymers, 57, No. 12, 761-769 (2000) A. Nishimoto, K. Agehara, N. Furuya, T. Watanabe, M.M. Watanabe, Macromolecules, 32, 1541-1548 (1999) F. Croce, L. Peri, B.B. Scrosati, F.A. Serraino-Fiory, E.M. Plichta, M.C. A. Hendrickson, Electrochimica Acta, 46, 2457-2461 (2001) F. Forsyth, D.C. R. MacFarlane, A. Best, J. Adebahr, J.A. Jacobsson, A.J. J. Hill, Solid State Ionics, 147, 203-211 (2002) H. Every, A. G. Bishop, M.M. Forsyth, D.C. R. MacFarlane, Electrochimica Acta, 45, 1279-1284 (2000)

  An object of the present invention is to provide a lithium electrolyte useful as a polymer electrolyte exhibiting good lithium ion conductivity and lithium ion transport number, good mechanical properties, and excellent molding processability and improved adhesion to electrodes. It is to provide an ion conductive solid composite.

According to the present invention, the above object is achieved, Ri Na contain organic silicon compound or a modified organic silicon compound having a lithium ion point having polymer, and lithium ion points including oxygen-containing segments in the main chain, 70 to 90 It can be solved by a lithium ion conductive composite annealed at a temperature of ° C.

The lithium ion conductive composite of the present invention has good electrical conductivity and good lithium ion transport number at the use temperature of the battery, as well as excellent mechanical properties, molding processability and good adhesion to electrodes. Have.
By using this lithium ion conductive solid composite as a solid electrolyte, particularly a solid electrolyte of a lithium ion solid electrolyte battery, it is possible to manufacture a highly safe battery in which risks such as ignition and liquid leakage are reduced or eliminated. it can.

  The type and topology of the polymer containing an oxygen-containing segment in the main chain used in the present invention is not limited as long as it contains an oxygen-containing segment in the main chain, but a polyether polymer or polyether is one component. A polymer, particularly a polymer comprising a linear polyether polymer or a linear ether polymer as one component is preferred. Typical examples of polyether polymers are poly (tetramethylene oxide) [also called poly (tetrahydrofuran) or poly (oxytetramethylene)], poly (propylene oxide), poly (ethylene oxide), and their blocks There are copolymers and random copolymers, and two or more of them may be used in combination. Among them, poly (tetramethylene oxide) ionene, particularly poly (tetramethylene oxide) ionene is preferable, and aliphatic poly (tetramethylene oxide) ionene is particularly preferable. Poly (tetramethylene oxide) and (aliphatic) poly (tetramethylene oxide) ionene may be linear or branched.

（式中、ｍおよびｎはそれぞれ１以上の数であり、ｍは好ましくは２〜５００、より好ましくは５〜２００の数であり、ｎは好ましくは２〜７００、より好ましくは１０〜３００の数である。Ｘ⁻は対アニオンであり、好ましくは、トリフルオロメタンスルホニルアニオン、トリフルオロメタンスルホニルイミドアニオン、ハロゲンアニオンなどである。）
で示されるアイオネンであり、好ましい脂肪族系ポリ（テトラメチレンオキシド）アイオネンの一例は、式：

（式中、ｍおよびｎは前記と同意義である。）
で示されるアイオネン（以下、「ＤＰＩ」と略称する。）である。 Aliphatic poly (tetramethylene oxide) ionene is represented, for example, by the formula:

(In the formula, m and n are each a number of 1 or more, m is preferably a number of 2 to 500, more preferably 5 to 200, and n is preferably 2 to 700, more preferably 10 to 300. a number .X ^- is a counter anion, preferably, trifluoromethanesulfonyl anion, trifluoromethanesulfonyl imide anion, a halogen anion).
An example of a preferred aliphatic poly (tetramethylene oxide) ionene is represented by the formula:

(In the formula, m and n are as defined above.)
Ionene (hereinafter abbreviated as “DPI”).

（式中、ｍおよびｎはそれぞれ１以上の数であり、ｍは好ましくは２〜５００、より好ましくは５〜２００の数であり、ｎは好ましくは２〜７００、より好ましくは１０〜３００の数である。Ｘ⁻は対アニオンであり、好ましくはトリフルオロメタンスルホニルアニオン、トリフルオロメタンスルホニルイミドアニオン、ハロゲンアニオンなどである。）
で示されるアイオネンである。
これら脂肪族系および複素環系ポリ（テトラメチレンオキシド）アイオネンのほか、芳香族系ポリ（テトラメチレンオキシド）アイオネンも好ましい。 Heterocyclic poly (tetramethylene oxide) ionene is represented, for example, by the formula:

(In the formula, m and n are each a number of 1 or more, m is preferably a number of 2 to 500, more preferably 5 to 200, and n is preferably 2 to 700, more preferably 10 to 300. a number .X ^- is a counter anion, preferably trifluoromethanesulfonyl anion, trifluoromethanesulfonyl imide anion, a halogen anion).
It is the ionene indicated by.
In addition to these aliphatic and heterocyclic poly (tetramethylene oxide) ionenes, aromatic poly (tetramethylene oxide) ionenes are also preferred.

The molecular weight of the overall poly (tetramethylene oxide) ionene is usually 1000 to 3000000, preferably 5000 to 100000, more preferably 10,000 to 50000.
The molecular weight between ion points of poly (tetramethylene oxide) ionene is preferably 144 to 20000, more preferably 500 to 10,000, more preferably 2000 to 6000, especially about 3000. As a result, the crystallinity of the polymer chain between ionic points, for example, poly (tetramethylene oxide) can be reduced and further amorphized, and mixed with an organosilicon compound having an ionic group or its modified organosilicon compound. Thus, it is possible to obtain a lithium ion conductive composite having excellent processability and excellent mechanical properties with little change in electrical conductivity at room temperature with time.
A method for producing the poly (tetramethylene oxide) ionene is described in Patent Document 1.

  The molecular weight of the polymer containing an oxygen-containing segment in the main chain may be approximately the same as the molecular weight of the poly (tetramethylene oxide) ionene.

The organosilicon compound having a lithium ion point or the modified organosilicon compound having a lithium ion point means a silicon atom-containing compound having a lithium ion group itself or a segment containing lithium ions. For example, the silicon atom containing compound containing the segment containing a lithium cation and an anion is mentioned. Here, the segment containing an anion means R ₁ SO ₃ ⁻ , R ₁ SO ₂ N ⁻ , R ₁ CO ₂ ⁻ , R ₁ SO ₂ C ⁻ , R ₁ SO ₂ YN ⁻ and R ₁ SO ₂ CN ^{_{-, R 1 B -, R}} 1 YB -, R 1 S -, R 1 YS - a silicon atom containing compound having a segment and lithium ion having an anionic group such as. In the formula, R ₁ may be an aliphatic, alicyclic or aromatic hydrocarbon group, or an organic group containing an element such as C, H, O, N, S or F. Preferably, it is a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms. Y is an electron-withdrawing group, preferably a nitro group, a nitroso group, a carbonyl group, a carboxyl group or a cyano group. The organosilicon compound or a modified organic silicon compound having lithium ion points, may contain segments of two or more same or different. Specifically, lithium sulfonyl (SO ₃ Li) group, lithium carboxyl (COOLi) group, lithium trifluoromethanesulfonyl imide (NLiSO ₂ CF ₃ ) group, lithium methane sulfonyl imide (NLiSO ₂ CH ₃ ) group, lithium phenyl sulfonyl imide (NLiSO ₂ C ₆ H ₅ ) group, lithium p-phenylenesulfonyl (C ₆ H ₄ SO ₃ Li) group, lithium sulfonyl p-benzyl (CH ₂ C ₆ H ₄ SO ₃ Li) group, lithium sulfonyl p-benzyloxy (OCH ₂ C ₆ H ₄ SO ₃ Li) group, lithium sulfonyl p-benzoyloxy (OCOC ₆ H ₄ SO ₃ Li) group, lithium sulfonyl p-benzyloxycarbonyl (COOC ₆ H ₄ SO ₃ Li) group, lithium sulfonyl phenoxy _{(OC 6 H 4 SO 3 Li} ) group, a lithium borate (BLi) group, a lithium sulfide (SLi) group, a lithium piperazinyl (LiNC ₅ H ₄₎ group, a lithium sulfonyl piperid Jiniru _{(C 5 H 4 NSO 3 Li} ) group such as a silicon atom-containing compound having the like. Silanol groups of the organic silicon compound may be a silicon atom containing compound having these ions points modified organic silicon compound undergoing chemical modification. However, it is not limited to these. A spacer such as an alkyl group, an oxyalkyl group, or a liquid crystal segment may be interposed between the organosilicon compound and the lithium ion group, and there are two or more of the same or different ionic points. You may do it.

で示される化合物である（以下、「Ｓｉ−Ｌｉ」と略称する。）。 A preferred example of an organosilicon compound having a lithium ion point has the formula:

(Hereinafter abbreviated as “Si-Li”).

The low molecular lithium salt used in the present invention may be any of the lithium salts conventionally used in lithium ion secondary batteries, and includes a compound comprising a lithium cation and an anion. Examples of anions include chlorine ion, bromine ion, iodine ion, perchlorate ion, thiocyanate ion, tetrafluoroborate ion, nitrate ion, AsF ₆ ⁻ , PF ₆ ⁻ , stearyl sulfonate ion, octyl sulfonate Ion, dodecyl sulfonate ion, 7,7,8,8-tetracyano-p-quinodimethane ion, R ₁ SO ₃ ⁻ , (R ₁ SO ₂ ) (R ₂ SO ₂ ) N ⁻ , (R ₁ SO ₂ ) (R ₂ SO ₂ ) (R ₃ SO ₂ ) C ⁻ , and (R ₁ SO ₂ ) (R ₂ SO ₂ ) YC ⁻ . In the formula, R ₁ , R ₂ , R ₃ , and Y are electron-withdrawing groups. Preferably, R ₁ , R ₂ , and R ₃ are each independently a perfluoroalkyl group or a perfluoroaryl group having 1 to 6 carbon atoms, and Y is a nitro group, a nitroso group, or a carbonyl group. , A carboxyl group, or a cyano group. R ₁ , R ₂ , and R ₃ may be the same or different. Two or more kinds of compounds having various anions as described above may be used in combination as the low molecular lithium salt. Of these, lithium perchlorate, lithium bis (trifluoromethanesulfonyl) imide, lithium trifluoromethanesulfonate, and the like are preferable.

In the lithium ion conductive composite of the present invention, the proportion of the oxygen atom-containing segment in the main chain, the organosilicon compound having a lithium ion point, and the low molecular lithium salt that is an optional component is as long as the object of the present invention is achieved. There are no particular restrictions. The amount of the organosilicon compound having a lithium ion point is usually 10 to 500 parts by weight, preferably 10 to 300 parts by weight, more preferably 30 to 200 parts by weight with respect to 100 parts by weight of the oxygen atom-containing segment in the main chain. The amount of the low-molecular lithium salt is usually 700 parts by weight or less, preferably 300 parts by weight or less, more preferably 100 parts by weight or less, especially 80 parts by weight or less based on 100 parts by weight of the oxygen atom-containing segment in the main chain. It is. When a low molecular lithium salt is used, the lower limit amount is preferably 1 part by weight.

  In addition to the above-mentioned components, the lithium ion conductive composite of the present invention contains ordinary additives such as reagents for electrode production, materials such as powders, stabilizers, anti-aging agents, binders, and the like. Can be blended.

  The lithium ion conductive composite of the present invention can be produced by simply mixing the components. In order to facilitate mixing, an inert solvent (for example, tetrahydrofuran, acetonitrile, etc.) or a solvent mixture may be used for each component. In addition, the lithium ion conductive composite of the present invention may be cross-linked as necessary, and an appropriate cross-linking agent may be used as the cross-linking agent depending on the polymer to be used, such as diisocyanate and peroxide.

  The lithium ion conductive composite of the present invention may be able to improve conductivity by annealing at a high temperature, for example, 40 ° C. or higher, for example, 70 to 90 ° C. Moreover, the same effect can also be acquired by performing mixing at high temperature instead of annealing.

[Reference example]
The organosilicon compound (Si-Li) having lithium ions was produced as follows.
First, 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.), NaHSO ₃ , Na ₂ SO ₃ , and water are reacted on a 75 ° C. hot water bath, allowed to cool, and then stirred with acetone. Was added dropwise to obtain a sodium salt type precipitate. This was purified by reprecipitation three times, and the deposited precipitate was collected by suction filtration and decantation, dried at 50 ° C. under reduced pressure by heating, and pulverized into powder in an agate bowl. Thereafter, the cation exchange reaction of the powdery substance was performed several times with LiBr in 2- (2-ethoxyethoxy) ethanol, thoroughly washed with dehydrated ethanol and dehydrated methanol, dried and pulverized, Si- Li was obtained. In use, after drying at 100 ° C. under high vacuum, the product was stored in a glove box and used.

[Example]
The sample was prepared in a glove box under high-purity argon gas having a moisture concentration of 1 ppm or less, and aliphatic poly (tetramethylene oxide) ionene (molecular weight between ion points 3150) (hereinafter referred to as “KA1”), LiN (SO ₂ CF ₃ ) ₂ (lithium bistrifluoromethanesulfonimide; hereinafter referred to as “TFSI”), and Si—Li prepared in a quantity as shown in Table 1 by mixing with a spatula in a crucible heated to 40 ° C. did.
In addition, the meaning of the symbol of each sample is as follows. For example, in the case of Si-Li0.41-TFSI0.20, "Si-Li0.41" has [Li in Si-Li] / [-O- in KA1] (molar ratio) of 0.41. "TFSI0.20" indicates that [Li in TFSI] / [-O- in KA1] (molar ratio) is 0.20.

As an example, the production process of Si-Li0.41-TFSI0.20 was as follows.
KA1 (0.0740 g) transferred to a crucible in the glove box was heated to 40 ° C., and Si-Li (0.1110 g) and TFSI (0.0545 g) weighed out were added thereto and mixed.
Then, a cell having a structure in which the sample was packed in a spacer having an inner diameter of 10 mm and a thickness of 0.4 mm and sandwiched between SUS electrodes was prepared for conductivity measurement. The cell was subjected to heat treatment at 40 ° C. for about 12 hours, 25 ° C. for about 24 hours, or at 80 ° C. for about 12 hours and at 25 ° C. for about 24 hours, and then subjected to conductivity measurement by the complex impedance method. did.

For conductivity measurement, Solatron Impedance Analyzer 1260 and Electrochemical Interface 1287 made by Solatron were used, and the temperature was increased from 25 ° C to 80 ° C and from 80 to -20 ° C at a temperature rising / falling rate of 20 ° C / hr and a hold time of 30 minutes. A temperature rise / fall process, an alternating current with a frequency range of 1 MHz to 0.1 Hz and a voltage of 10 to 1000 mV was used. The electrical conductivity (σ) was calculated by the following equation using the complex impedance method to obtain the bulk resistance R _b and using the sample thickness d and the sample area A:

The lithium cation transport number has a structure in which a sample is packed in a ring-shaped polypropylene spacer having an inner diameter of 10 mm, an outer diameter of 14 mm, and a thickness of 0.2 to 0.5 mm, sandwiched between 0.3 mm thick lithium foils, and further sandwiched between SUS electrodes. A cell was prepared, and this cell was subjected to heat treatment at 80 ° C. for about 12 hours or 40 ° C. for 12 hours and at 25 ° C. for 24 hours according to the heat treatment conditions for conductivity measurement, and then measured.
Lithium cation transport number is obtained by substituting the value obtained by performing potentiostat measurement at 60 ° C and applied voltage of 10mV and impedance measurement before and after using the same equipment as the conductivity measurement in the Evans equation below. Asked:

The dynamic viscoelasticity measurement was performed in a solid shear mode and frequency dispersion at a temperature of about 19 ° C. using a Leospectra DVE-V4 manufactured by UBM Co., Ltd., and a shear storage modulus was obtained. The measurement frequency was 1 to 100 Hz, and the sample size was 5 × 4 × about 1 mm.
The temperature in parentheses after the sample name in Table 2 is the temperature in the first heat treatment step in the heat treatment.

In the conductivity measurement, an Arrhenius plot of values obtained in the temperature lowering process of 80 ° C. to −20 ° C. is shown in FIG.
From FIG. 1, in the lithium ion conductive composite of the present invention, when the heat treatment is increased to 80 ° C., the conductivity increases remarkably, and in the sample of KA1-Si—Li0.41-TFSI0.20 (80 ° C.), 25 The conductivity was 6.1 × 10 ⁻⁵ S / cm at ℃ and 9.8 × 10 ⁻⁷ S / cm even at −20 ° C.

Table 3 shows the results of lithium cation transport number measurement at 60 ° C.
The lithium cation transport number at 60 ° C of KA1-Si-Li0.41-TFSI0.20 (80 ° C) was almost the same as that of KA1-Si-Li0.10-TFSI0.22.

It is an Arrhenius plot of the electrical conductivity of the sample manufactured in the Example.

Claims (8)

Ri Na contain organic silicon compound or a modified organic silicon compound having a lithium ion point having a polymer containing oxygen-containing segments in the main chain, and lithium ions point, lithium ion conductivity, which is annealed at a temperature of 70 to 90 ° C. Sex complex. Lithium ion conductive composite of claim 1 wherein the modified organic silicon compound having an organic silicon compound or lithium sulfonyl group organosilicon compound or a modified organic silicon compound having a lithium ion point has a lithium sulfonyl group having lithium ion point body.   Furthermore, the lithium ion conductive composite of Claim 1 or 2 containing a low molecular lithium salt.   The lithium ion conductive composite according to any one of claims 1 to 3, wherein the oxygen-containing segment is a polyether segment.   The lithium ion conductive composite according to claim 4, wherein the polymer containing the polyether segment is poly (tetramethylene oxide).   The lithium ion conductive composite according to claim 4, wherein the polymer containing the polyether segment is poly (tetramethylene oxide) ionene.   The lithium ion conductive composite according to claim 6, wherein the poly (tetramethylene oxide) ionene is an aliphatic poly (tetramethylene oxide) ionene.   A solid electrolyte secondary battery comprising the lithium ion conductive composite according to claim 1 as a solid electrolyte.

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