JP3130341B2 - Solid electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte secondary battery having a small capacity, a high capacity, a long charge / discharge cycle life, and excellent low-temperature charge / discharge properties.

[0002]

_2. Description of the Related Art Light metals such as lithium, sodium and aluminum are used as a negative electrode active material, chalcogen compounds of transition metals such as MoS ₂ and TiS ₂ are used as a positive electrode, and a solid electrolyte is used as an electrolyte. So-called solid electrolyte secondary batteries have a high energy density, have no liquid leakage accidents, and have the potential for long-term use that was impossible with conventional batteries. Efforts are being made.

By the way, as such a conventional solid electrolyte secondary battery, for example, a coin type solid electrolyte secondary battery as shown in FIG. 3 can be mentioned.

1) A positive electrode 1 is formed by pelletizing or sheeting a mixture of a powder of a metal chalcogen compound and a binder such as polytetrafluoroethylene. 2) A solid electrolyte 2 is formed of, for example, polyethylene oxide. And LiClO ₄ , LiAlO ₄ , LiBF ₄ , LiP
F _6, a mixture of alkali metal salts of LiAsF _6, etc., 3) a negative electrode, is composed of an alkali metal foil mainly comprising Li foil or Li, it is placed on the positive electrode 1 through the solid electrolyte 2 ing.

The positive electrode 1, the solid electrolyte 2 and the negative electrode 3
Constitutes a power generation part as a whole, and this power generation part is incorporated in a battery container composed of the positive electrode can 4 and the negative electrode can 5, and is insulated by the insulating packing 6. Further, a current collector 7 is interposed between the positive electrode 1 and the positive electrode can 4, and the current collector 7 is usually made of a metal mesh made of nickel, stainless steel, punched metal, or form metal. I have.

However, in such a conventional solid electrolyte secondary battery, the conductivity of the electrolyte is 10 ⁻⁶ S / cm or less, and the Lithium inside the positive electrode is lower than that of a liquid electrolyte.
There is a drawback that the charge / discharge characteristics at low temperatures are significantly reduced due to poor ion transfer efficiency.

When the solid electrolyte is formed into a film in order to reduce the weight and size of the battery, the mechanical strength of the film is reduced. In addition, when the battery is charged and discharged, dendrites are easily generated in the lithium negative electrode. There was a disadvantage that the number of cycles was reduced.

On the other hand, as a method for increasing the mechanical strength of the solid electrolyte film, a method of crosslinking by reacting a trifunctional polyethylene glycol with a diisocyanate derivative (see Japanese Patent Application Laid-Open No. 62-48716), polyethylene glycol diacrylate (See JP-A-62-285954), and the like.

However, when a thin film of a solid electrolyte is used for a battery by these methods, the balance of the strength, the ionic conductivity of the solid electrolyte and the adhesion to the positive and negative electrodes is poor, and further improvement is desired. I was

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide excellent charge / discharge characteristics even at a low temperature, a long charge / discharge cycle life,
An object of the present invention is to provide a solid electrolyte secondary electric field which has a high capacity and can be manufactured at low cost.

[0011]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that an ionic conductive polymer containing a specific component is used as a solid electrolyte in a network molecule composed of a polyethylene glycol diacrylate polymer. ,
That the ionic conductivity is 10 ^-5 S / cm or more at room temperature, and that a solid electrolyte film having excellent film strength even at a thickness of 100 μm or less and excellent adhesion to positive and negative electrodes can be obtained. By using a positive electrode having a layer of the ionic conductive polymer on the surface of the metal chalcogen compound powder, L
The present inventors have found that the transfer efficiency of i-ion can be improved, and have reached the present invention.

According to the present invention, the solid electrolyte comprises a network molecule comprising a polyethylene glycol diacrylate polymer,
The following positive electrode comprises a copolymer of (a), (b) a low molecular weight polyethylene glycol in which both terminals are methyl etherified, and (c) an ion conductive polymer film containing an alkali metal salt or an ammonium salt. A solid electrolyte secondary battery comprising a metal chalcogen compound-containing material and a negative electrode comprising a light metal or an alloy thereof. (a) The following formula (I):

[0013]

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(Wherein R ¹ is a hydrogen atom or a carbon number of 1 to 5)
R ² represents an alkyl group having 1 to 5 carbon atoms, m represents an integer of 2 ≦ m ≦ 30) and a compound represented by the following formula (II):

[0015]

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(Wherein R ³ is a hydrogen atom or a group having 1 to 3 carbon atoms)
And / or a compound represented by the following formula:
(III):

[0017]

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(Wherein R ⁴ represents a hydrogen atom or a carbon number of 1 to 3)
And a compound represented by the following formula:

Hereinafter, the present invention will be described in detail. The polyethylene glycol diacrylate polymer used for the solid electrolyte in the present invention has an acrylic group or a methacryl group capable of vinyl polymerization at both ends, and has four oxyethylene units.
Those having from 30 to 30 are preferable.

The compound represented by the formula (I) of the copolymer (a) is a polyether macromonomer having an oxyethylene unit m of 2 ≦ m ≦ 30.

Examples of the compound represented by the formula (II) include acrylotrile, methacrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile and the like, among which acrylonitrile and methacrylonitrile are preferable.

Examples of the compound represented by the formula (III), there may be mentioned methyl acrylate, methyl methacrylate, methyl α- ethyl acrylate, main Ji Le α- propyl acrylate, and methyl alpha-n-butyl acrylate, among others Methyl acrylate and methyl methacrylate are preferred.

The copolymer can be obtained by radical copolymerization using a known radical initiator such as azobisisobutyronitrile. The above formula in the copolymer
The content of the compound (I) is 20 to 80 mol%, preferably 40 to 60 mol%. When the content is less than 20 mol%, the ionic conductivity of the film may decrease, and when it exceeds 80 mol%, the strength of the film may decrease.

The molecular weight of the copolymer is 5,000 to 200,
000, preferably 10,000 to 100,000.

The low molecular weight polyethylene glycol (b) is
Both ends are methyl etherified, and the molecular weight is 200 to 3,000, preferably 300 to 2,
000.

As the alkali metal salt (c), lithium perchlorate, sodium perchlorate, potassium perchlorate, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, lithium hexafluorophosphate , Potassium hexafluorophosphate, lithium trifluoroacetate, lithium trifluoromethanesulfonate and the like.

Examples of the ammonium salt (c) include tetraisopropylammonium perchlorate, n-butylammonium terola perchlorate, tetra-n-butylammonium tetrafluoroborate, tetra-n-butylammonium hexafluorophosphate, trifluoromethane Tetra sulfonic acid n-
Butyl ammonium and the like can be mentioned.

The weight ratio of the low molecular weight polyethylene glycol (b) to the copolymer (a) is from 1: 0.1 to 1:10. The blending amount of polyethylene glycol diacrylate is 10 to 200 parts by weight, preferably 30 to 100 parts by weight, based on 100 parts by weight of the total of the copolymer and the low molecular weight polyethylene glycol.

The amount of the alkali metal salt or ammonium salt is 1 to 30 parts by weight, preferably 3 to 20 parts by weight, based on 100 parts by weight of the total amount of the copolymer, low molecular weight polyethylene glycol and polyethylene glycol diacrylate. It is.

The presence of the copolymer is indispensable for the ion-conductive polymer, and a polymer containing no copolymer cannot provide a strong film because of poor film-forming properties.

The ionic conductive polymer used in the present invention is:
As described above, the film forming property of the solid electrolyte is remarkably improved, and the ionic conductivity is also improved. In addition, the electrical conductivity is excellent at room temperature in the range of 10 ^-5 to 10 ^-3 S / cm with the electrode,
And a film excellent in strength can be obtained.

The method for producing the ion-conductive polymer film is not particularly limited, and a predetermined amount of a copolymer, a low-molecular-weight polyethylene glycol and an alkali metal salt or an ammonium salt, and further a polyethylene glycol diacrylate, A photopolymerization initiator (1-2% by weight) such as hydroxy-2-methylpropiophenone or a radical polymerization initiator such as azobisisobutyronitrile is uniformly dissolved in a solvent such as acetone, ethanol, or terahydrofuran. Then, a method of casting the obtained solution on a substrate, removing the solvent, and irradiating with ultraviolet light or heating to cure the solution can be used.

The solid electrolyte secondary battery of the present invention uses the above-mentioned ionic conductive polymer film as a solid electrolyte.
For the positive electrode, a metal chalcogen compound-containing material can be used as an active material.When a powder of a metal chalcogen compound is used by molding, a powder having a thin layer of the ionic conductive polymer on the surface of the powder is used. Preferably, the transfer efficiency of Li ions inside the positive electrode can be improved.

The particle size of the metal chalcogen compound powder is 1
１００100 μm, preferably 3-25 μm.

As the metal chalcogen compound, for example,
_{W O 3, V 2 O 5} , MoO 3, Cr 3 O 8 metal oxides such _{as, V 6 O 13; MoS 2} , TiS 2, V 2 S 2, MoS 3, Cu
Metal sulfides such as S, Cr _0.5 V _0.5 S ₂ ; VSe ₂ , NbS
metallic selenium compounds such as e _3; ones of these metallic chalcogen compound _{amorphized; Li-V 2 O 5,} Li-Mn 2
A composite compound of lithium and a metal chalcogen compound such as O ₄ can be given.

The method for forming a thin layer of an ion conductive polymer on the surface of the powder of the metal chalcogen compound is not particularly limited. For example, the above-mentioned copolymer, low molecular weight polyethylene glycol, alkali metal salt or ammonium salt may be used. After adding a metal chalcogen compound powder to a solution of acetone or the like in which is dissolved and removing the solvent,
A method of curing by air drying or irradiation with ultraviolet rays can be employed.

The thickness of the layer of the ion conductive polymer on the surface of the powder cannot be determined unconditionally depending on the particle size of the metal chalcogen compound, but it is 0.5 to several μm.

The positive electrode has a thin layer of an ion conductive polymer on the surface of the metal chalcogen compound or the powder thereof, and a binder such as polytetrafluoroethylene, polyethylene, or polyethylene-polypropylene copolymer; A mixture of conductive materials such as carbon black and acetylene black may be formed into a pellet or a thin layer.

The negative electrode is preferably made of lithium or an alloy of lithium and aluminum, manganese, indium or the like.

In the solid electrolyte secondary battery of the present invention, such a positive electrode, a negative electrode, and a solid electrolyte are formed in a positive electrode container which also serves as a terminal without changing the positive electrode, as in a coin-type secondary battery as shown in FIG. Or attached to a metal such as stainless steel or nickel, and then provided integrally with the positive electrode container, the solid electrolyte film is mounted thereon, and the negative electrode is further mounted thereon. Can be manufactured.

The solid electrolyte secondary battery of the present invention is not limited to a coin-type secondary battery. For example, a solid electrolyte secondary battery such as a cylindrical, flat, or rectangular solid electrolyte battery is similarly used. Applicable.

[0042]

According to the present invention, the following effects can be obtained. (1) As a solid electrolyte, a unique ionic conductive polymer that has high conductivity and can be thinned on the surface of the active material is used, so that the ability to move Li ions in the positive electrode and the solid electrolyte is improved. And the charge / discharge characteristics at low temperatures can be greatly improved.

(2) Since the solid electrolyte has excellent film strength, and the adhesion between the solid electrolyte and the positive and negative electrodes is uniform and good, lithium dendrite is not generated on the negative electrode. The charge / discharge characteristics that determine pass / fail can be greatly improved.

(3) In the case where a material having the above-mentioned ion conductive polymer layer on the surface of the powder of the metal chalcogen compound is used as the positive electrode active material, the ability of Li ions to move inside the positive electrode is further improved. Thus, the utilization rate of the active material is improved, and the battery capacity can be increased.

[0045]

【Example】

Example 1 (1) Production of ion-conductive polymer film Polyethylene glycol monomethacrylate (the number of CCO units is 9) and acrylonitrile were radically copolymerized in a toluene solvent using azobisisobutyronitrile as an initiator.

The composition ratio of the copolymer can be appropriately adjusted depending on the charge ratio at the time of polymerization. The composition ratio of the copolymer in this example is 48.3 mol % of polyethylene glycol monomethacrylate and acrylonitrile. Was 51.7 mol%, and the molecular weight was 47,000.

1 g of the above copolymer and 1 g of polyethylene glycol dimethacrylate (the number of CCO units is 23)
And 1 g of polyethylene glycol dimethyl ether (the number of CCO units is 8) and 158 mg of lithium perchlorate
(8% by weight) was dissolved in 10 ml of acetone. After a small amount of azobisisobutyronitrile was added thereto and sufficiently stirred, the mixture was polymerized on a Teflon petri dish under nitrogen at 60 ° C. while evaporating acetone, and the thickness was 0.1 m / m. An ionic conductive polymer film which was transparent and had high mechanical strength was obtained. This ion-conductive polymer film was used as a solid electrolyte in the battery of this example.

[0048] The obtained using a vacuum drier ion conductive polymer film, after thoroughly dried at 70 ° C., was measured conductivity by the complex impedance method at 25 ° C. As shown in FIG. 1 8.0 × 10 ^- It was ⁵ S / cm.

(2) Production of Positive and Negative Electrodes For the positive electrode, a spinel-type manganese oxide (Li--Mn ₂ O
₄ ) A mixture obtained by mixing 80 g of powder with 15% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder was formed into a sheet, and then punched to a predetermined size. For the negative electrode, a metal lithium sheet punched into a certain size was used.

(3) Battery assembly The positive electrode was mounted on a stainless steel positive electrode can, and the ionic conductive polymer film was mounted thereon.
The negative electrode was placed thereon to form a power generation part, and a coin-type secondary battery having the same structure as that shown in FIG. 3 except for the power generation part was produced.

(4) Characteristics of Battery The battery fabricated in this manner was regulated at a constant current of 50 μA to an upper limit of 3.3 V and a lower limit of 2.0 V, and repeated five cycles of preliminary charging and discharging. The discharge capacity at the third cycle was 6.8 mAh. This capacity was used as the initial capacity.

Thereafter, the upper limit is 3.3 V and the lower limit is 2.0.
The potential was regulated to V and charge / discharge was repeated at the same constant current, and the capacity retention ratio of the discharge capacity to the initial capacity in each cycle was measured to evaluate the charge / discharge cycle. The results are shown in FIG.

Further, with respect to the manufactured battery, a temperature of 20 ° C.
A charge / discharge test was performed at 0 ° C. to measure a capacity retention ratio with respect to a capacity of 20 ° C. The charge / discharge test was performed under the same conditions as described above. The results are shown in FIG.

Comparative Example 1 (1) Production of Ion-Conducting Polymer Film No copolymer was added, and lithium perchlorate was added to 17
An ion conductive polymer film was prepared in the same manner as in Example 1 except that 4 mg (8 wt%) was used. This film was a very brittle film even at a thickness of 0.1 m / m. The ionic conductivity was 2.1 × 10 ⁻⁵ S / cm.

(2) Production of Positive and Negative Electrodes and Assembly of Battery A positive and negative electrode was produced in the same manner as in Example 1. The battery was assembled in the same manner as in Example 1 except that the ion-conductive polymer film of (1) was used.

(3) Battery Characteristics Battery characteristics were measured in the same manner as in Example 1. Figure 1 shows the results
And FIG.

Example 2 (1) Production of ion-conductive polymer film 2 g of polyethylene glycol dimethyl ether (CCO unit number: 8) and 210 mg of lithium perchlorate (8
An ionic conductive polymer film was prepared in the same manner as in Example 1 except that the ionic conductive polymer film was used. When the conductivity was measured in the same manner as in Example 1, as shown in FIG.
Was 9.2 × 10 ⁻⁵ S / cm.

(2) Production of Positive and Negative Electrodes and Assembly of Battery A positive and negative electrode was produced in the same manner as in Example 1. The battery was assembled in the same manner as in Example 1 except that the ion-conductive polymer film of (1) was used.

(3) Battery Characteristics Battery characteristics were measured in the same manner as in Example 1. Figure 1 shows the results
And FIG.

COMPARATIVE EXAMPLE 2 Lithium perchlorate was added without adding a copolymer.
An ionic conductive polymer was produced in the same manner as in Example 2 except that 1 mg (8% by weight) was used. The resulting electrolyte is
The liquid did not solidify and had a high viscosity.

Example 3 (1) Production of ion conductive polymer film A copolymer was synthesized in the same manner as in Example 1 except that methyl methacrylate was used instead of acrylonitrile.
The composition of the obtained copolymer was 51.6 mol% of polyethylene glycol monomethacrylate and 48.4% of methyl methacrylate, and the molecular weight was 58,000.

An ion-conductive polymer film was prepared in the same manner as in Example 2, except that 1 g of the copolymer obtained in this example and 348 mg (8% by weight) of lithium perchlorate were used. When the conductivity was measured in the same manner as in Example 1,
As shown in FIG. 1, it was 1.4 × 10 ⁻⁴ S / cm at 25 ° C.

(2) Production of Positive and Negative Electrodes and Assembly of Battery A positive and negative electrode was produced in the same manner as in Example 1. The battery was assembled in the same manner as in Example 1 except that the ion-conductive polymer film of (1) was used.

(3) Battery Characteristics Battery characteristics were measured in the same manner as in Example 1. Figure 1 shows the results
And FIG.

Example 4 (1) Production of ion-conductive polymer film An ion-conductive polymer film was produced in the same manner as in Example 3.

(2) Production of positive and negative electrodes and assembly of battery 1 g of a copolymer similar to the copolymer used in Example 1, 1 g of polyethylene glycol dimethacrylate (the number of CCO units is 23), and 1 g of polyethylene glycol dimethyl ether (The number of CCO units is 8) 1 g of lithium perchlorate and 158 mg (8 wt%) of lithium perchlorate are added to acetone, and then a spinel-type manganese oxide is added to 1 liter of a solid electrolyte solution containing a small amount of azobisisobutyronitrile. Object (Li-Mn ₂ O
₄₎ After mixing by adding powder 80 g, acetone was evaporated in a predetermined manner to obtain a Li-Mn ₂ O ₄ active material on the surface of the manganese oxide powder having a thin layer of the ion conductive polymer.

A mixture of this active material, together with 15% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder, was formed into a sheet and then punched into a predetermined size to obtain a positive electrode. A battery was assembled in the same manner as in Example 1 except that this positive electrode was used.

(3) Battery Characteristics Battery characteristics were measured in the same manner as in Example 1. Figure 1 shows the results
And FIG.

(Evaluation) As is apparent from FIGS. 1 and 2, the solid electrolyte secondary batteries of Examples 1 to 3 are the same as those of Comparative Example 1.
The discharge capacity deterioration rate was reduced as compared with the same battery, and the charge / discharge cycle life was significantly improved. In addition, the discharge characteristics at low temperatures could be significantly improved. Further, the solid electrolyte secondary battery using the positive electrode having the thin layer of the ion conductive polymer on the surface of the metal chalcogen compound powder of Example 4 was able to further improve the cycle life and the low-temperature discharge characteristics.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of charge / discharge cycles and the capacity retention ratio of batteries in Examples 1 to 4 and Comparative Example 1.

FIG. 2 is a graph showing the capacity retention ratio of the discharge capacity at 0 ° C. discharge to the 20 ° C. capacity in Examples 1 to 4 and Comparative Example 1.

FIG. 3 is a cross-sectional view illustrating a coin-shaped solid electrolyte secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode 2 ... Solid electrolyte 3 ... Negative electrode a ... Example 1 b ... Example 2 c ... Example 3 d ... Comparative example 1 e ... Example 4

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nobuyuki Kuroda 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Japan Japan Petroleum Corporation Central Research Laboratory (72) Inventor Seiichi Akita 8 Chidori-cho, Naka-ku, Yokohama, Kanagawa Japan Petroleum Co., Ltd. Central Research Laboratory (72) Inventor Masanobu Suga 8 Chidoricho, Naka-ku, Yokohama-shi, Kanagawa Japan Japan Petroleum Co., Ltd. Central Research Laboratory (56) References JP-A-2-40867 (JP, A) Hei 1-107472 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40

Claims (1)

(57) [Claims] 1. A solid electrolyte comprising, in a network molecule composed of a polyethylene glycol diacrylate polymer, a copolymer of the following (a): (b) a low molecular weight polyethylene glycol in which both ends are methyl-etherified; c) a solid electrolyte secondary battery comprising an ion conductive polymer film containing an alkali metal salt or an ammonium salt, the positive electrode comprising a metal chalcogen compound-containing material, and the negative electrode comprising a light metal or an alloy thereof. A solid electrolyte secondary battery, wherein the positive electrode has a thin layer of the ionic conductive polymer on the surface of the metal chalcogen compound powder. (A) The following formula (I): (Wherein, R ¹ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms,
m represents an integer of 2 ≦ m ≦ 30) and a compound represented by the following formula (II): (Wherein R ³ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms) and / or the following formula (III): (Wherein R ⁴ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms).