JPH10168194A - Polymer solid electrolyte - Google Patents

Abstract

(57) [Problem] To provide a solid polymer electrolyte having high ionic conductivity and not causing an increase in internal resistance. SOLUTION: An electron-withdrawing group is introduced into a molecular main chain of a solid polymer electrolyte to form an alkali metal salt. Preferably, the following formulas (1) to (5) Or a homopolymer or a copolymer composed of the respective monomer units.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a solid polymer electrolyte. More specifically, the present invention relates to a solid polymer electrolyte having high ion conductivity that can be used as an electrolyte of a lithium secondary battery.

[0002]

2. Description of the Related Art The use of a solid electrolyte as an electrolyte for a battery eliminates the need for a container for accommodating a liquid, thereby enabling the battery structure to be reduced in size and simplicity. There is an advantage that a battery having excellent long-term reliability can be formed.

[0003] As such a solid electrolyte, conventionally, polymer compounds such as polyethylene oxide (PEO) and polypropylene oxide (PPO) have been added to alkali metal salts (eg, lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate). (LiBF ₄ ) and the like are known as polymer solid electrolytes.

However, a secondary battery using such a PEO-based solid polymer electrolyte is not so remarkable as a battery using an electrolytic solution, and when a charge / discharge cycle is repeated, PEO reacts with the lithium of the negative electrode to form a film such as lithium oxide having low electron conductivity at the interface between the negative electrode and the electrolyte. Was not.

To solve such a problem, Japanese Patent Laid-Open No.
In Japanese Patent Application No. 320781, a solid polymer electrolyte that does not easily react with the negative electrode is proposed. This polymer solid electrolyte is obtained by compounding a conventionally used electrolyte salt such as LiClO ₄ with a vinyl copolymer such as a vinyl chloride-vinyl acetate copolymer or a vinyl chloride-acrylonitrile copolymer. . Since this polymer solid electrolyte does not easily react with the negative electrode formed of metallic lithium or the like, the internal resistance hardly increases even after repeated charge / discharge cycles, and a lithium secondary battery having excellent charge / discharge cycle characteristics is obtained. Have been.

[0006]

However, the disclosed vinyl copolymer-based solid electrolyte has a problem of low ionic conductivity at low temperatures. Furthermore, in this solid electrolyte, both anions and cations carry charges, but the anion has no acceptor on the electrode side, and at the end of charge / discharge, the anion without the acceptor becomes supersaturated and the internal resistance increases. There's a problem.

The present invention has been made to solve the above problems, and has as its object to provide a solid polymer electrolyte having high ionic conductivity and no increase in internal resistance.

[0008]

According to a first aspect of the present invention, there is provided a solid polymer electrolyte having an electron-withdrawing group in the molecular main chain and being an alkali metal salt. You. Since this polymer electrolyte has an electron-withdrawing group in its molecular main chain, depolarization of anionic charges is promoted, and as a result, cations are easily moved and ionic conductivity is improved. In addition, since the charge is carried only by the alkali metal cation, there is no problem of an increase in internal resistance caused by supersaturation of the anion as in the related art.

In the second invention, in order to solve the above problems, the polymer solid electrolyte according to the first invention has a polymerization degree of 10 to 1,000,000 and the following formula:

Embedded image (Where M is an alkali metal, Y ¹ , Y ² ,
Y ³ and Y ⁴ may be the same or different, and are each independently —SO ₂ —, —CO—, —SO ₃ —,
CO ₂ — or a direct bond, R ¹ and R ² may be the same or different and each independently has 1 to 5 carbon atoms
And X is -O-, -COO-, -CONH-,
—NH— or a direct bond, wherein R ³ and R ⁴ may be the same or different, and each independently has 1 to 1 carbon atoms.
5 represents an alkyl group or a halogenated alkyl group, or a direct bond, and may be cross-linked with another monomer unit; -Y ³ -R ³ and -Y ⁴ -R ⁴ are, in addition to the above,
(Representing —CHO, —NO ₂ , —CN, or —F), a homopolymer comprising the monomer units of (1) to (5) or a copolymer comprising two or more of these monomer units. Is done. The monomer unit has a group having a high electron-withdrawing property such as —SO ₂ —CF ₃ or —SO ₂ —CF ₂ — in the main chain, and a homopolymer or copolymer formed from this monomer unit has an anion. Depolarization of charges is promoted, cations are easily moved, and ionic conductivity is improved.

According to a third aspect of the present invention, there is provided a polymer solid electrolyte which is swollen by an electrolyte solution containing an electrolyte salt and is in a gel state in order to solve the above problems. You. Since the gel-like solid electrolyte exhibits rubber-like elasticity, the adhesion between the positive electrode and the negative electrode is increased, and the contact resistance between the electrolyte and the electrode is reduced.

According to a fourth aspect of the present invention, there is provided a lithium secondary battery having a positive electrode, a negative electrode, and the above solid polymer electrolyte.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the solid polymer electrolyte of the present invention is characterized by having an electron-withdrawing group in the molecular main chain. The electron-withdrawing group is not particularly limited, and examples thereof include nitro, nitroso, carbonyl, carboxyl, cyano, trialkylammonium, and trifluoroalkyl, which can be introduced into the main chain of the molecule. The polymer solid electrolyte of the present invention can be synthesized by an ordinary organic synthesis method, and can have a desired structure by selecting a starting material. Further, this electron-withdrawing group may be included as a side chain.

Preferably, the solid polymer electrolyte of the present invention is a homopolymer comprising monomer units represented by the following formulas (1) to (5) or a copolymer comprising two or more of these monomer units.

Embedded image

In the above formula, M is an alkali metal, preferably lithium. Y ¹ , Y ² , Y ³ , and Y ⁴ may be the same or different, and each is independently a group having a high electron-withdrawing property, preferably —SO ₂ —, —CO—, —S
It represents O ₃ —, —CO ₂ — or a direct bond, more preferably all —SO ₂ —. R ¹ and R ² may be the same or different and are each independently an alkylene having 1 to 5 carbon atoms or a halogenated alkylene, or a direct bond, preferably a halogenated alkylene, more preferably All are alkylene fluorides. X is -O
-, -COO-, -CONH-, -NH- or a direct bond. R ³ and R ⁴ may be the same or different and each independently represents an alkyl group having 1 to 5 carbon atoms or a halogenated alkyl group, or a direct bond, and is further crosslinked with another monomer unit. And preferably a halogenated alkyl group, and more preferably an alkyl fluoride. —Y ³ —R ³ and —Y ⁴ —R ⁴ may be —CHO, —NO ₂ , —CN, or —F in addition to the above definition.

In the above, "direct bond" means R ¹ , R
² means that there is no group such as X and the groups or atoms before and after these groups are directly bonded. Therefore, for example, if the monomer unit of the above formula (2) is more clearly shown, it is represented by the following formula.

[0016]

Embedded image Various monomers can be derived from the other formulas (1) and (3) to (5) as in the above formula.

The degree of polymerization of the solid polymer electrolyte of the present invention is 10 to
If it is 1,000,000, and if it is less than 10, the electrolyte may become liquid, while if it exceeds 1,000,000, it may become hard and cause problems in mechanical strength and ionic conductivity.
Further, when the degree of polymerization is less than 100, the solid electrolyte is in a gel state and exhibits rubber-like elasticity, so that the adhesion between the positive electrode and the negative electrode is increased, and the contact resistance between the electrolyte and the electrode can be reduced. it can. Even if the degree of polymerization is 100 or more and the solid is completely solid, the solid electrolyte can be gelled by swelling the solid electrolyte using a conventionally used electrolyte and solvent.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), and lithium hexafluorophosphate (Li
PF _6), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF _6), lithium trifluoromethanesulfonate imide (LiN (CF ₃ SO ₂ ) ₂ ) etc. can be used alone or as a mixture.

As the solvent, an aprotic solvent such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (γ-BL), sulfolane (SL), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DE
E), ethoxymethoxyethane (EMC), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2
M-THF), 1,3-dioxolane (DOXL), 4-methyl-1,3-dioxolane (4M-DOXL) and the like can be used alone or as a mixture.

A lithium secondary battery using the solid polymer electrolyte of the present invention as an electrolyte is also included in the present invention.
This lithium secondary battery includes a positive electrode, a negative electrode, and the above-described solid polymer electrolyte. For the positive electrode and the negative electrode of this secondary battery, those used in a normal lithium secondary battery can be used.For example, as the negative electrode, metal lithium, or lithium-aluminum, lithium-carbon such as lithium-carbon is used. Oxides such as manganese, cobalt, nickel, vanadium, and niobium can be used as the positive electrode active material.

[0021]

【Example】

Example 1 Synthesis of-[SO ₂ N (Li) SO ₂ (CF ₂ ) ₃ ] _n-To 600 ml of liquid NH ₃ (−78 ° C.) in a 1000 ml three-necked flask on a cooling bath equipped with a mechanical stirrer. 200 g of FSO ₂ (CF ₂ ) ₃ SO ₂ F
Was added, the cooling bath was removed, and NH ₃ was evaporated off by heating. Then 600 ml of dioxane was added and dry HCl was blown through the dioxane solution until the pH was 2-3. The solution was filtered, the filtrate was concentrated to 75 ml by an evaporator, 200 ml of benzene was added, and H ₂ NSO ₂ (C
F ₂ ) ₃ SO ₂ NH ₂ was obtained. This was filtered, and the filtrate was further concentrated and recrystallized to obtain purified H ₂ NSO ₂ (CF ₂ ) ₃ SO ₂ NH ₂ .

150 g of this H ₂ NSO ₂ (CF ₂ ) ₃ SO ₂ NH ₂ was dissolved in 100 ml of methanol, and a methanol solution of CH ₃ ONa obtained from 25 g of Na and 300 ml of CH ₃ OH was added. After evaporating methanol with an evaporator, the obtained solid was washed with benzene. NaNHSO ₂ (CF ₂ ) ₃ SO ₂ NH thus obtained
Put Na (170 g) in a 1000 ml three-necked flask, mechanical stirrer,
A reflux tube and a drying tube were attached, 600 ml of [(CH ₃ ) ₃ Si] NH and 100 ml of dioxane were added, and the mixture was refluxed at 145 ° C. for 12 hours. The dioxane was then evaporated off and the remaining salt was vacuum dried in the same flask.

The obtained (CH ₃ ) ₃ SiN (Na) SO ₂ (CF ₂ ) ₃ SO ₂ N (Na)
Si (CH ₃ ) ₃ was placed in a 500 ml stainless steel pressure vessel, several steel balls were put therein, and a pressure of 1000 psi was applied. Subsequently, 150 ml of dioxane was added, and the mixture was cooled to -192 ° C and evacuated. FSO ₂ (CF ₂ ) ₃ SO ₂ F (0.5 mol) was distilled under vacuum to obtain 110
Heat for 3 hours at 0 ° C with occasional shaking. When the pressure stopped increasing, the mixture was cooled and the obtained-[SO ₂ N (Na) SO ₂ (CF ₂ ) ₃ ] _n
-Was washed with dioxane, filtered off and dried in air. This was purified by recrystallization, placed in a 500 ml round bottom flask and treated with 100 ml of concentrated sulfuric acid. Thus obtained
_{- [SO 2 NHSO 2 (CF} 2) 3] n - to give a _{- [SO 2 N (Li)} SO 2 (CF 2) 3] n - of the present invention is treated with lithium methoxide.

The above reaction is shown by the following formula.

Embedded image

Example 2:-[SO_Two(CF_ThreeSO_Two) C (Li) SO_Two(CF_Two)_Three]
_n-Synthesis of 15 g (0.1 m
ol) CF_ThreeSO_TwoF is cooled to a solution of 150 ml of THF.
100ml (0.1mol) of CH_ThreeSlowly add the THF solution of Li
I got it. Obtained CF_ThreeSO_TwoCH_Three(14g) 0.9mol CH_ThreeLi THF
The solution was added dropwise while cooling. CF_ThreeSO_TwoCH_Two ^-Li⁺Precipitation
The material was transferred to a pressure vessel, sealed and cooled to -40 ° C. Next
33g (0.09mol) FSO_Two(CF_Two)_FourSO_TwoF through the valve
Well, it was sealed. Heat the vessel to 70 ° C. and allow
For 48 hours, then cooled to room temperature and the container was opened. solvent
And volatile components were removed under reduced pressure and the residual solid was treated with acid.
Purified by recrystallization and dried under vacuum to obtain-[SO_Two(CF
_ThreeSO_Two) CHSO_Two(CF_Two)_Three]_n-Got it. This is lithium metoki
By treating with sid,-[SO_Two(CF_ThreeSO_Two) C (Li) SO _Two(CF
_Two)_Three]_n-Got it.

The above reaction is shown by the following formula.

Embedded image

Example 3:-[SO_TwoN (Li) SO_TwoOCH_Two(CF_Two)_ThreeCH_TwoO]
_n-Synthesis of 21 g of HOCH in 300 ml of dichloromethane_Two(CF_Two)_ThreeCH_TwoOH and 12
g of triethylamine was added and cooled to 0 ° C. this
While stirring, 21 g of HN (SO_TwoC
l)_TwoWas slowly added dropwise. After the reaction, raw
The filtered salt is removed by filtration, and the filtrate is poured into a large amount of methanol.
And the precipitate was filtered off. Purified by several reprecipitations
Thereafter, the product is treated with lithium methoxide to give-[SO_TwoN (Li)
SO_TwoOCH_Two(CF _Two)_ThreeCH_TwoO]_n-Got it.

The above reaction is shown by the following formula.

Embedded image

Example 4:-[SO ₂ Si (Li) (SO ₂ (CF ₂ ) ₄ ) SO ₂ (CF
₂ ) Synthesis of ₄ ] _n- 6 g of SiLi ₄ and 100 ml of THF were placed in a pressure vessel, sealed, and cooled to -40 ° C. To this, 60 g of FSO ₂ (CF ₂ ) ₄ SO ₂ F was charged through a valve, and the container was sealed. Warm the vessel to 70 ° C., hold at 120-140 psi for 48 hours, then lower to room temperature,
The container was opened. After the solvent and volatile components were removed under reduced pressure, the product was purified by recrystallization, dried in vacuo, and then subjected to-[SO ₂ Si (Li) (SO
₂ (CF ₂ ) ₄ ) SO ₂ (CF ₂ ) ₄ ] _n − was obtained.

The above reaction is shown by the following formula.

Embedded image

Example 5: Synthesis of-[SO ₂ P (Li) SO ₂ (CF ₂ ) ₄ ] _n- 5 g of PLi ₃ and 100 ml of THF were placed in a pressure vessel, sealed, and cooled to -40 ° C. . To this, 40 g of FSO ₂ (CF ₂ ) ₄ SO ₂ F was charged through a valve and the vessel was sealed. The vessel was warmed to 70 ° C., kept at 120-140 psi for 48 hours, then cooled to room temperature and the vessel was opened. After removing the solvent and volatile components under reduced pressure, the product was purified by recrystallization, dried under vacuum, and subjected to-[SO ₂ P (Li) SO ₂ (CF
₂ ) ₄ ] _n -was obtained.

The above reaction is shown by the following formula.

Embedded image

[0033]

As described above, the solid polymer electrolyte of the present invention has an electron-withdrawing group in its main chain, which promotes the depolarization of anionic charges, facilitates the transfer of cations, and improves ionic conductivity. improves. Further, since the charge is carried only by the alkali metal cation, it is possible to prevent the internal resistance from increasing due to the movement of the anion.

[Procedure amendment]

[Submission date] June 6, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction contents]

[0033]

[Effect of the Invention] The polymer solid electrolyte of the present invention has an electron attractive group in its backbone, is promoted non-polar localization of anionic charge, cation movement is facilitated, ion conductivity improves. Further, since the charge is carried only by the alkali metal cation, it is possible to prevent the internal resistance from increasing due to the movement of the anion.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C08G 79/02 C08G 79/02 H01M 10/40 H01M 10/40 B

Claims (4)

[Claims] 1. A solid polymer electrolyte having an electron-withdrawing group in the molecular main chain and being an alkali metal salt. 2. A polymer having a degree of polymerization of 10 to 1,000,000 and the following formula: ## STR1 ## (In the above formula, M is an alkali metal, and Y ¹ , Y ² , Y ³ , and Y ⁴ may be the same or different, and each independently represents —SO ₂ —, —CO—, — S
O ₃ —, —CO ₂ — or a direct bond, wherein R ¹ and R ² may be the same or different,
Each independently of 1 to 5 carbon atoms alkylene or halogenated alkylene or a direct bond, X is -O -, - COO -, - CONH -, - NH-, or a direct bond, R ³ and R ⁴ May be the same or different,
Each independently represents an alkyl group having 1 to 5 carbon atoms or a halogenated alkyl group, or a direct bond, and may be further crosslinked with another monomer unit; -Y ³ -R ³ and -Y ⁴ -R ⁴ In addition to the above rules, -CH
O, -NO _2, -CN, or -F represented by the representative) (1) to (5) that is a copolymer of two or more homopolymers or their respective monomer units consisting of each monomer units The polymer solid electrolyte according to claim 1, wherein: 3. The polymer solid electrolyte according to claim 1, wherein the polymer solid electrolyte is swollen by an electrolyte solution containing an electrolyte salt to form a gel. 4. A lithium secondary battery comprising a positive electrode, a negative electrode, and the polymer solid electrolyte according to claim 1.