JPH1197071A - High polymer solid electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve charge and discharge cycle characteristics as well as to improve capacity by forming a layer made of a complex of poyalkylene oxide-group high polymer having the specified number average molecular weight and electrolyte salt on the surface to be joined to a high polymer solid electrolyte film of a negative electrode. SOLUTION: The number average molecular weight of a polyalkylene oxide- group high polymer is in the range of 80000 to 800000. Preferably, polyethylene oxide, polypropylene oxide, and a copolymer of polyethylene oxide and polypropylene oxide are given. As electrolyte salt for forming a complex together with the high polymer, alkaline metallic salt such as LiClO4 is given. Since a composite layer of a polyalkylene oxide-base high polymer having the small molecular weight in comparison with a high polymer for forming a base material of the high polymer solid electrolyte film and electrolyte salt is formed, the contact area of the negative electrode and the high polymer solid electrolyte is large, in particular, the discharge amount in high efficient discharge is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer solid electrolyte secondary battery using a carbon material as a cation storage material for a negative electrode, and more particularly, to a polymer solid electrolyte having a high capacity and good charge / discharge cycle characteristics. The present invention relates to an improvement in a surface of a negative electrode to be joined to a solid polymer electrolyte membrane for the purpose of providing a secondary battery.

[0002]

2. Description of the Related Art
As an electrolyte for a secondary battery using a carbon material for the negative electrode,
Liquid electrolyte with excellent ionic conductivity is used,
Liquid electrolytes have problems such as liquid leakage and elution of electrode materials.

[0003] For this reason, a solid electrolyte membrane which does not have such a problem, particularly a polymer solid electrolyte membrane which can be easily formed into a thin film and is inexpensive, has recently attracted attention.

However, even if a polymer solid electrolyte membrane is used for a secondary battery using a carbon material for the negative electrode, only a battery having a small discharge capacity, particularly a discharge capacity at a large current discharge (high-rate discharge), can be obtained. . This is because the electric resistance (interface resistance) at the interface between the negative electrode and the solid polymer electrolyte membrane is large because the contact area between the negative electrode and the solid polymer electrolyte membrane is small.

As a method for increasing the contact area between the electrode and the polymer solid electrolyte membrane, a polymer electrolyte solution obtained by dissolving an electrolyte salt in a polymer solution is dispersed together with a surfactant in a nonpolar organic solvent. There has been proposed a method in which a low-viscosity dispersion solution is applied, the dispersion solution is applied on a porous electrode, dried, and a polymer solid electrolyte membrane is integrally formed on the porous electrode (Japanese Patent Laid-Open No. Hei 5 (1993) -105). -144315).
According to the publication, the polymer electrolyte solution solidifies in a state in which a part thereof enters the fine voids of the porous electrode, so that the contact area between the porous electrode and the polymer solid electrolyte membrane is large,
It is said that a high-capacity polymer solid electrolyte battery can be manufactured.

[0006] However, in the above method, the surfactant contained therein may be gradually deteriorated with the progress of the charge / discharge cycle, and may hinder the charge / discharge.

Accordingly, an object of the present invention is to provide a polymer solid electrolyte secondary battery having a high capacity and good charge / discharge cycle characteristics without using a surfactant.

[0008]

A polymer solid electrolyte secondary battery (battery of the present invention) according to the present invention comprises a positive electrode, a polymer solid electrolyte membrane also serving as a separator, and a negative electrode using a carbon material as a cation storage material. A layer comprising a composite of a polyalkylene oxide polymer having a number average molecular weight of 80,000 to 800,000 and an electrolyte salt is formed on a surface of the negative electrode, which is to be bonded to the polymer solid electrolyte membrane. is there.

As the positive electrode active material, compounds of Group I elements of the periodic table (CuO, Cu ₂ O, Ag ₂ O, CuS, CuS
O ₄ ), compounds of Group IV elements of the periodic table (TiS ₂ , S
iO ₂ , SnO, etc.), compounds of Group V elements of the periodic table (V
₂ O ₅ , V ₆ O ₁₂ , Nb ₂ O ₅ , Bi ₂ O ₃ , Sb ₂ O
₃ ), compounds of Group VI elements of the periodic table (CrO ₃ , Cr
₂ O ₃ , MoO ₃ , WO ₃ , SeO ₃ etc.), periodic table
Group VII compounds (MnO ₂ , MnO _3, etc.) and Periodic Table VIII group compounds (Fe ₂ O ₃ , FeO, Fe ₃
O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, etc.),
Lithium-containing vanadium oxides (such as LiV ₂ O ₅ ),
Lithium-containing cobalt oxide (such as LiCoO ₂ ), lithium-containing nickel oxide (such as LiNiO ₂ ), lithium-containing manganese oxide (such as LiMn ₂ O ₄ ), lithium-containing titanium oxide (such as LiTiO ₂ ), and lithium-containing chromium oxide (LiCrO ₂ etc.).

The polymer solid electrolyte membrane also serving as a separator is a composite of a polymer and an electrolyte salt. As the polymer, polyethylene oxide, polypropylene oxide,
Examples thereof include a copolymer of polyethylene oxide and polypropylene oxide, polyetherimide, polyethersulfone, polysiloxane, and polysulfone. Since the polymer solid electrolyte membrane is a member also serving as a separator, a polymer having a high mechanical strength and a high molecular weight is used as a polymer forming a base of the membrane. For example, in the case of polyethylene oxide, the number average molecular weight Mn is usually 2,000,000 to 800.
About ten thousand are used. Examples of the electrolyte salt that forms a complex with a polymer include LiClO ₄ and LiCF ₃ S.
O ₃ , LiPF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Li
_{BF 4, LiSbF 6, LiAsF 6} ( above, a lithium battery), NaI, NaSCN, NaBr, NaClO
₄ (above, for sodium batteries), KClO ₄ , KSCN
(Above, for a potassium battery) and the like.

As the carbon material of the negative electrode, graphite, petroleum coke, cresol resin fired carbon, furan resin fired carbon,
Examples thereof include polyacrylonitrile fired carbon, carbon produced by a vapor phase growth method, and mesophase pitch fired carbon.

Examples of the polyalkylene oxide polymer include polyethylene oxide, polypropylene oxide,
Copolymers of polyethylene oxide and polypropylene oxide are exemplified. Examples of the electrolyte salt that forms a complex with the polyalkylene oxide-based polymer include those exemplified above. The reason why the number average molecular weight Mn of the polyalkylene oxide polymer is limited to 80,000 to 800,000 is that if the number average molecular weight is out of this range, the battery capacity becomes small and the charge / discharge cycle characteristics deteriorate. is there. As the polyalkylene oxide-based polymer, those having a number average molecular weight Mn of 100,000 to 600,000 are particularly preferable.

As the polymer solid electrolyte secondary battery to which the present invention is applied, a lithium secondary battery, a sodium secondary battery,
An example is a potassium secondary battery.

In the battery of the present invention, the surface of the negative electrode, which is to be bonded to the solid polymer electrolyte membrane, comprises a polyalkylene oxide-based polymer having a smaller molecular weight than the polymer forming the matrix of the solid polymer electrolyte membrane and an electrolyte salt. Since the composite layer is formed, the contact area between the negative electrode and the solid polymer electrolyte is larger than that of a conventional battery in which the negative electrode and the solid polymer electrolyte membrane are directly joined, and the capacity is high. . In particular, the discharge capacity in high-rate discharge is large. In addition, the battery of the present invention has good charge / discharge cycle characteristics because the degradation product does not contain a surfactant that inhibits charge / discharge in the solid polymer electrolyte.

[0015]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples and can be carried out by appropriately changing the scope of the invention without changing its gist. It is something.

[Preparation of positive electrode] LiC as positive electrode active material
A mixture of 85 parts by weight of oO _2, 10 parts by weight of carbon powder as a conductive agent, and 5 parts by weight of polyvinylidene fluoride powder as a binder in an NMP (N-methyl-2-pyrrolidone) solution was mixed. About 80μ by doctor blade method
m, and heat-treated at 130 ° C to a diameter of 10 mm.
Was produced.

[Preparation of Negative Electrode] A mixture of 95 parts by weight of graphite powder having an average particle diameter of 10 μm as a lithium ion storage material and an NMP solution of 5 parts by weight of polyvinylidene fluoride as a binder was mixed with a doctor. About 7 thickness by blade method
0 μm and heat-treated at 130 ° C.
mm was prepared as a disk-shaped negative electrode.

A solution prepared by dissolving 0.5 mol / liter of LiClO ₄ in acetonitrile and a number average molecular weight of 50,000,
80,000, 100,000, 200,000, 400,000, 600,000, 800,000
Nine kinds of polyethylene oxides different from 100,000 or 1.2 million are mixed so that the molar ratio of the ethylene oxide units to LiClO ₄ is 6: 1, and the mixture is applied on the previously prepared negative electrode to evaporate acetonitrile. Heat treatment at 100 ° C. in a vacuum so that polyethylene oxide and LiClO 4 are formed on the surface of the negative electrode to be joined to the solid polymer electrolyte membrane.
_A layer composed of the composite with No. ₄ was formed. The cross section of the negative electrode was observed with a scanning electron microscope (SEM), and the thickness of the formed layer was examined.
m. In addition, since the negative electrode was a porous electrode, it was visually confirmed that a part of the polymer solid electrolyte also entered the inside of the negative electrode.

[Preparation of Polymer Solid Electrolyte Membrane] Polyethylene glycol ethyl ether acrylate (CH ₂ ＣＨCH—COO— (CH ₂ —CH ₂ — having a number average molecular weight of 360)
O) n-CH ₂ —CH ₃ ) and LiClO ₄ are mixed at a weight ratio of 94: 6, and a thickness of 50 μm is formed on the layer formed of the composite of polyethylene oxide and LiClO ₄ previously formed on the negative electrode. It is applied and irradiated with an electron beam at a moving speed of an object to be irradiated of 1 m / min by an electro-curtain type electron beam irradiation device (output: 200 kV, irradiation dose: 2 Mrad) to polymerize polyethylene glycol ethyl ether acrylate, A solid electrolyte membrane was formed.

[Preparation of Polymer Solid Electrolyte Secondary Battery] A flat polymer solid electrolyte is prepared by using the above positive electrode, polymer solid electrolyte membrane and negative electrode (three members are integrated). Secondary battery (lithium secondary battery) B1 (comparative battery; using polyethylene oxide having a number average molecular weight of 50,000), A1
(Battery of the invention; use of polyethylene oxide having a number average molecular weight of 80,000), A2 (battery of the invention; use of polyethylene oxide having a number average molecular weight of 100,000), A3 (battery of the invention; polyethylene oxide of 200,000 number average molecular weight) Use), A
4 (Battery of the present invention; polyethylene oxide having a number average molecular weight of 400,000), A5 (Battery of the present invention;
A6 (use of polyethylene oxide having a number average molecular weight of 800,000), B2 (use of polyethylene oxide having a number average molecular weight of 1,000,000), B3 (polyethylene having a number average molecular weight of 1.2 million) (Using ethylene oxide). Further, a flat polymer solid electrolyte was formed in the same manner as above except that a polymer solid electrolyte membrane was formed directly on the negative electrode without forming a layer composed of a composite of polyethylene oxide and LiClO ₄ on the negative electrode. An electrolyte secondary battery (lithium secondary battery) B4 (comparative battery) was produced. In each battery, the capacity ratio between the positive electrode and the negative electrode was 1: 1.1, and the battery capacity was regulated by the capacity of the positive electrode.

<Discharge capacity of first and 100th cycles of each battery> Each battery was charged at 25 ° C. at a current density of 100 μA / cm ² to 4.2 V, and then charged at a current density of 100 μA / cm ² . performed 100 cycles of charge and discharge for discharging to 2.75 V, the discharge capacity of the cathode 1 cm ² per 1 cycle and 100th cycle of each battery (m
Ah / cm ² ). Table 1 shows the results.

[0022]

[Table 1]

As shown in Table 1, the number average molecular weight is 80,000 to 8
Inventive battery A1 using 100,000 polyethylene oxide
To A6 are the first cycle and the first cycle compared to the comparative battery B4.
The discharge capacity at the 00th cycle is large. A comparative battery B1 using polyethylene oxide having a number average molecular weight of 50,000, a comparative battery B2 using polyethylene oxide having a number average molecular weight of 1,000,000, and a comparative battery B3 using polyethylene oxide having a number average molecular weight of 1,000,000 were in the first cycle. Although the discharge capacity is large, the discharge capacity at the 100th cycle is extremely small. From these facts, it can be seen that in order to obtain a battery having high capacity and good charge / discharge cycle characteristics, it is necessary to use polyethylene oxide having a number average molecular weight of 80,000 to 800,000. In addition, one of the batteries A2 to A5 of the present invention
Since the discharge capacity at the 00th cycle is particularly large, the polyethylene oxide has a number average molecular weight of 100,000 to 60
It turns out that ten thousand are preferable.

[0024]

According to the present invention, a polymer solid electrolyte secondary battery having a high capacity and good charge / discharge cycle characteristics is provided.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5-5 in Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A polymer solid electrolyte secondary battery comprising a positive electrode, a polymer solid electrolyte membrane also serving as a separator, and a negative electrode using a carbon material as a cation storage material.
A polymer solid having a layer formed of a complex of a polyalkylene oxide polymer having a number average molecular weight of 80,000 to 800,000 and an electrolyte salt formed on a surface to be joined to the polymer solid electrolyte membrane. Electrolyte secondary battery. 2. The polyalkylene oxide polymer according to claim 2,
2. The solid polymer electrolyte secondary battery according to claim 1, wherein the secondary battery is polyethylene oxide, polypropylene oxide, or a copolymer of polyethylene oxide and polypropylene oxide.