JPH11283664A - Solid-electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-electrolyte battery of high energy density, whose battery characteristics such as rate characteristic and preservability are enhanced, so that it is particularly excellent in charge and discharge cycle characteristic as a secondary battery. SOLUTION: This solid-electrolyte battery 1 is basically constructed of a pair of positive and negative electrodes 2, 3 with a solid electrolyte 4 intervening therebetween and at least one intermediate layer 5, 6 placed between the solid electrode 4 and at least either of the electrodes 2, 3, the intermediate layer having a composition of a solid electrolyte comprising 5-95 wt.% active materials and 5-95 wt.% solid electrolyte. In this case, at least either of the intermediate layer 5, 6 consists of three layers and is made up of 30 to 70 wt.% active materials and 30 to 70 wt.% solid electrolyte; the active materials forming the intermediate layer are preferably LiCoO2 for the positive electrode and one kind selected from TiO2 and V2 O5 for the negative electrode, and the solid electrolyte is preferably Li3 PO4 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery using a solid electrolyte as an electrolyte interposed between electrodes, and more particularly to a battery using an electrode active material capable of inserting and extracting lithium ions. The present invention relates to a solid electrolyte battery optimal as a secondary battery having excellent cycle characteristics.

[0002]

2. Description of the Related Art Conventionally, as an electrolyte for various batteries,
In general, aqueous or non-aqueous electrolytes have been used. In recent years, there has been a demand for thinner, lighter, and smaller electronic devices such as video photographing devices, notebook computers, and portable information terminals such as mobile phones. Accordingly, a solid electrolyte battery using a solid electrolyte composed of a polymer material between a pair of positive and negative electrodes instead of the liquid electrolyte as described above has been receiving attention.

[0003] Such a solid electrolyte battery has excellent characteristics that the electrolyte is not in a liquid state, so that there is no fear of liquid leakage, which is a major problem relating to the safety such as ignition of the battery, and the corrosiveness is small. there were.

However, when such a solid electrolyte made of a polymer material is used, for example, as an electrolyte for a secondary battery, the ionic conductivity of the polymer material is low, so that a large current cannot be taken out. There is a problem that the battery performance such as rate characteristics, cycle characteristics, and storage characteristics in charge and discharge is poor.

In order to solve the above-mentioned problems, a small amount of a metal oxide is added to a solid electrolyte composed of the polymer material to promote and stabilize the polymerization of the polymer material, or to improve the stability of the active material. The surface is modified, or as shown in FIG. 5, one of the pair of positive and negative electrodes 20, 21 is formed by laminating an active material 22 and a solid electrolyte 23, which are thinned by a vapor deposition technique or the like. And electrodes 20, 2
Various proposals have been made, such as reducing the polarization resistance of the solid electrolyte 1 and the solid electrolyte 24 (Japanese Patent Application Laid-Open No. 9-97616,
See JP-A-61-263060).

[0006]

However, in the above proposal, a small amount of a metal oxide is added to stabilize a polymer material, or the surface of an active material is modified to impart ionic conductivity. Also, the ionic conductivity is several steps lower than the conventional liquid electrolyte and insufficient, and further, when one of the pair of positive and negative electrodes is formed by laminating a thinned active material and a solid electrolyte. However, the internal resistance increases due to the presence of the interface caused by stacking, the obtained current density is not sufficient, and the capacity that can be charged and discharged from the ion trap at the macro interface by the history of the charge and discharge cycle. There were problems such as deterioration of cycle characteristics such as short-term deterioration.

In general, in the case of a secondary battery, the charge / discharge reaction on the electrode is determined by the micro-interface between the active material for the electrode and the solid electrolyte, and the rate of the charge / discharge reaction is controlled. In a battery, it is thought that the larger the micro interface itself between the electrode active material and the solid electrolyte is, the more it contributes to the improvement of the charge / discharge performance.However, in the above proposal, the ion conduction at the interface is not performed promptly. Therefore, despite the fact that the electrode lamination in the manufacturing process is complicated such as a vapor deposition method, the obtained current density is small, and as a secondary battery having a high energy density, there is a problem of lack of practicality. there were.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve various characteristics such as a rate characteristic and a storage property of a battery, and particularly to provide a secondary battery with excellent charge-discharge cycle characteristics. Another object of the present invention is to provide a solid electrolyte battery having a high energy density.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, when a solid electrolyte is used as an electrolyte of a secondary battery, the reason why a large current cannot be taken out is that the electrodes and In the polarization resistance at the interface of the solid electrolyte, as a result of various attempts to reduce the polarization resistance that affects ionic conductivity, an intermediate layer comprising an active material and the solid electrolyte is provided between the electrode and the solid electrolyte. It has been found that the polarization resistance can be reduced by increasing the microscopic interface of the particle size of the active material and the solid electrolyte, that is, by electrochemically and physically assisting the ion conduction of lithium ions between the electrodes at the particle level. Thus, the present invention has been achieved.

That is, in the solid electrolyte battery of the present invention, a solid electrolyte is interposed between a pair of positive and negative electrodes, and between the solid electrolyte and at least one electrode, 5 to 95% by weight of an active material and 5 to 95% by weight. At least one intermediate layer composed of a solid electrolyte of about 10% by weight is provided.

In particular, the intermediate layer is composed of three layers, and further comprises 30 to 70% by weight of the active material and 30 to 70% by weight.
The active material forming the intermediate layer is made of LiCoO ₂ on the positive electrode side, and one made of TiO ₂ or V ₂ O ₅ on the negative electrode side. The solid electrolyte is more preferably Li ₃ PO ₄ which is a Li ion conductor.

[0012]

According to the solid electrolyte battery of the present invention, since the intermediate layer composed of the specific ratio of the active material and the solid electrolyte is provided between the electrode and the solid electrolyte, the particle size of the active material and the solid electrolyte is reduced. The microscopic interface increases and the polarization resistance at the interface between the electrode and the solid electrolyte decreases, and since a thin insulating layer consisting of only the solid electrolyte is provided between the electrodes, short-circuiting of the electrodes can be prevented and the distance between the electrodes can be reduced. It is possible to make it extremely narrow.

As a result, the amount of the solid electrolyte that does not directly participate in the charging and discharging of the secondary battery can be suppressed to a minimum, and the amount of the electrode active material that determines the capacity of the battery can be increased. Since the contact area with the electrolyte increases and the polarization resistance at the interface decreases, the internal resistance of the battery decreases,
Ion conduction at the interface is performed quickly, and a large current can be obtained from the battery.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a solid electrolyte battery according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an example in which the solid electrolyte battery of the present invention is applied to a coin-type battery.

In FIG. 1, reference numeral 1 denotes a solid electrolyte battery having a pair of electrodes 2 and 3, a solid electrolyte 4 and intermediate layers 5 and 6 as a basic structure. Each of the intermediate layers 5 and 6 is sandwiched therebetween, and a current collector 7 made of aluminum foil is provided on the outer surfaces of the electrodes 2 and 3 to constitute a main part. A sealed battery is formed.

In the solid electrolyte battery of the present invention, the active material forming the intermediate layer is manganese (Mn) on the intermediate layer provided between the positive electrode and the solid electrolyte, ie, on the positive electrode side.
n), a metal oxide containing at least one of cobalt (Co), nickel (Ni), vanadium (V), and niobium (Nb). In particular, lithium ions can be supplied and moved. , LiCoO ₂ and Li
NiO ₂ , LiNi _1/2 Co _1/2 O ₂ , LiMn ₂ O ₄
Etc. are preferred.

On the other side of the negative electrode, metallic lithium (Li) or lithium (Li) and aluminum (Al), indium (metal) capable of inserting and extracting lithium ions by an electrochemical redox reaction. I
n), tin (Sn), lead (Pb), silicon (Si),
Zinc (Zn), Cadmium (Cd), Calcium (C
a) an alloy with at least one of barium (Ba),
Metal oxides such as e ₂ O ₃ , TiO ₂ , Nb ₂ O ₃ , V ₂ O ₅ , and WO ₃ , and carbon materials such as natural graphite, artificial graphite, and amorphous carbon can be used. A metal oxide containing at least one of titanium (Ti), vanadium (V), and niobium (Nb) is preferable.

When the content of the active material in the intermediate layer is less than 5% by weight, that is, when the content of the solid electrolyte exceeds 95% by weight, the characteristics of the solid electrolyte become the same, and mixing is performed. When the content of the active material exceeds 95% by weight, that is, when the content of the solid electrolyte is less than 5% by weight, the characteristics of the active material dominate in the intermediate layer. All of them are unsuitable for lowering the polarization resistance at the interface.

In particular, when attention is paid to the point of effectively improving the cycle characteristics among the battery characteristics, the content of the active material is 30 to 70% by weight, and the content of the solid electrolyte is 30 to 70%. It is more desirable that the content be% by weight.

On the other hand, the solid electrolyte forming the intermediate layer is not particularly limited as long as it has ion conductivity of lithium ions, and includes, for example, lithium sulfide (LiS) and lithium sulfide (LiS). Ion conductive glass, Li ₃ N—LiI compound, Li ₃ PO ₄ , or a lithium oxide containing a transition metal such as Ti, V, Cr, Mn, Fe, Co, Ni, and the like. Li ₃ PO ₄ is most desirable from the viewpoint that mixing with the active material is uniform and good ion conductivity is ensured.

Next, as shown in FIG. 2 showing an example of the basic structure of the solid electrolyte battery of the present invention, the intermediate layer composed of the active material and the solid electrolyte is provided with the pair of electrodes 2 and 3 having the current collector 7. Among them, even if the intermediate layer 5 is provided between one of the electrodes 2 and the solid electrolyte 4, as shown in FIG. 3 showing another example of the basic configuration of the solid electrolyte battery of the present invention, the current collector 7 is provided. Intermediate layers 5, 6 between the electrodes 2, 3 and the solid electrolyte 4, respectively.
The intermediate layer may be formed as a single layer, or may be formed as two or more layers.

In particular, considering the configuration of the interface where the ionic conductivity is fast, the intermediate layers 5 and 6 are provided with a current collector 7 as shown in FIG. 4 showing another example of the basic configuration of the solid electrolyte battery of the present invention.
From the electrodes 2 and 3 having the first intermediate layer 5a and the second intermediate layer 5b to the solid electrolyte 4 side, respectively.
6b and the third intermediate layers 5c and 6c are optimally formed.

Further, each layer constituting the intermediate layer may be formed of a single composition or a different composition as long as the composition of the active material and the solid electrolyte satisfies the above-mentioned contents. In consideration of the properties, it is desirable that the composition of the intermediate layer is such that the mixing ratio of the solid electrolyte is changed in the order of the first intermediate layer 5a, 6a <second intermediate layer 5b, 6b <third intermediate layer 5c, 6c.

Therefore, the intermediate layer is formed from the electrode side to the solid electrolyte side in one layer or in two or more layers so that the content of the electrode active material is gradually reduced, that is, the solid electrolyte is gradually increased. It goes without saying that it may be formed in any of the multilayer structures.

In the solid electrolyte battery of the present invention, the type of ions to be transferred is not particularly limited, but is particularly effective for lithium ions, and lithium (L
The ion conduction in the solid electrolyte containing i) is promptly performed because the supply of ions from the electrode active material is balanced.

Therefore, it is necessary to increase as much as possible the reaction area where the electrochemical oxidation-reduction reaction of lithium (Li) supplied from or to the electrode active material takes place. By disposing an intermediate layer having a uniform mixed form between the electrode and the solid electrolyte, or by disposing an intermediate layer having a form in which the mixing ratio of the active material and the solid electrolyte is arranged to be inclined, the active material and the solid electrolyte can be disposed. A remarkable reaction area can be obtained as compared with the case where the interface of the solid electrolyte is clearly separated.

As a material constituting a pair of electrodes in the solid electrolyte battery of the present invention, various metal oxides and natural graphite have been described as the active materials of the intermediate layer as described in detail for the positive electrode side and the negative electrode side, respectively. And carbon materials such as artificial graphite and amorphous carbon.

However, the configuration of the active material forming the positive and negative electrode materials depends on where the battery operating voltage determined by the difference between the charging and discharging potentials of the selected materials is taken. Instead of being fixed, the operating voltage of the solid electrolyte battery changes depending on which combination of active materials is selected.

Therefore, depending on the combination of the negative electrode materials, it is possible to form a battery by selecting the candidate materials listed as the positive electrode material as the negative electrode material.

[0031]

Next, the solid electrolyte battery of the present invention was evaluated as described in detail below.

Example 1 First, 11% by weight of acetylene black for imparting conductivity and 9% by weight of a known organic binder were mixed with 80% by weight of LiCoO ₂ as an active material for a positive electrode. Then, a known organic solvent was added to the mixture at the same weight ratio to prepare a positive electrode forming paste.

On the other hand, as a negative electrode active material, 90% by weight of TiO ₂ or V ₂ O _{5 was} mixed with 10% by weight of a known organic binder, and the negative electrode forming paste was mixed in the same manner as the positive electrode forming paste. Prepared.

Next, an aluminum foil having a thickness of 20 μm is used as a current collector, and a paste for forming a positive electrode and a paste for forming a negative electrode are applied on the aluminum foil, and then roll-rolled to a thickness of 80 μm for the positive electrode. After adjusting the thickness for the negative electrode to 60 μm, the organic solvent was volatilized by drying treatment to produce positive and negative electrodes having a current collector.

On the other hand, LiCo, which is the active material for the positive electrode, is used.
O ₂ and either of TiO ₂ or V ₂ O ₅ as an active material for the negative electrode and Li ₃ PO ₄ as a solid electrolyte were changed at the mixing ratio shown in Table 1, respectively, and the same as in the preparation of each electrode forming paste. Thus, pastes for forming an intermediate layer on the positive electrode side and the negative electrode side were respectively produced.

[0036]

[Table 1]

The pastes for forming the intermediate layers on the positive electrode side and the negative electrode side thus obtained are respectively applied on the positive and negative electrodes.
After coating with a thickness of μm, a drying treatment was performed to evaporate the organic solvent, and an intermediate layer was formed on each of the positive and negative electrodes.

On the other hand, a paste for forming a solid electrolyte was prepared by adding 10% by weight of an organic binder to 90% by weight of the Li ₃ PO ₄ and adding a known organic solvent in the same weight ratio as the mixture.

Next, the prepared solid electrolyte forming paste is applied to a thickness of 20 μm on the intermediate layer adhered to each of the positive and negative electrodes having the current collector plate, and then dried to evaporate the organic solvent. Rolled and rolled 120
A vacuum drying at a temperature of 2 ° C. for 2 hours, followed by bonding and integration by a roll press to produce a basic structure of a solid electrolyte battery, cutting out to a predetermined size, and using a resin for insulation sealing. Assembled into batteries.

Incidentally, a solid electrolyte forming paste was directly applied to each of the positive and negative electrodes having the current collector plate to form a basic structure, and a coin-type battery produced in the same manner as a comparative example.

Using the coin cell battery for evaluation thus obtained, first, the voltage of 0.1 to 4 V was applied in a voltage range of 1 to 4 V.
When the oxidation-reduction reaction was confirmed by cyclic voltammetry at a voltage sweep speed of 1 mV, the coin-type battery for evaluation according to the solid electrolyte battery of the present invention exhibited a peak current value, and thus constituted a battery. However, it was confirmed that the coin-type battery of the comparative example did not show a peak current value and did not constitute a battery.

Next, a charge / discharge device was applied to the coin-type battery for evaluation at a current of 500 μA as a charging condition.
After the voltage reaches 2.5 V, the charging is stopped and held for 5 minutes.
The battery was discharged with a discharge current of 00 μA, then charged again to 2.0 V, and after reaching the voltage, a charge / discharge cycle test was performed in which charging was stopped and held for 5 minutes, and the amount of discharged electricity was determined every fixed cycle. To evaluate the battery performance as a secondary battery.

[0043]

[Table 2]

As a result, in the sample No. 16 of the comparative example,
In Sample Nos. 1, 9, 10, and 15, which show no charge / discharge and fall outside the scope of the present invention, the amount of discharge electricity dropped to 3 mAh or less in 20 charge / discharge cycles, and the cycle characteristics were significantly deteriorated. On the other hand, in the present invention, the discharge electric quantity is 50% of the initial value in the same charge and discharge cycle.
It can be seen that the above is maintained and the cycle characteristics are excellent.

Example 2 LiCoO ₂ as the active material on the positive electrode side, TiO ₂ as the active material on the negative electrode side, and Li ₃ PO ₄ as the solid electrolyte were applied to the positive and negative electrodes having a current collector plate.
, And a basic structure was formed in the same manner as in Example 1, except that two or more intermediate layers were formed by lamination as shown in Table 3 to form an intermediate layer.

[0046]

[Table 3]

The coin battery for evaluation thus obtained was evaluated in the same manner as in Example 1. The comparative example is the same as the first embodiment.

[0048]

[Table 4]

As a result, Sample Nos. 1, 6, 7, 12, 13, and 19, which are out of the scope of the present invention, were all 2
In 0 charge / discharge cycles, the amount of discharge electricity dropped to 2 mAh regardless of the number of intermediate layers, and the cycle characteristics were significantly deteriorated.
In Sample Nos. 8 to 11 of the present invention having a layer structure, the amount of discharge electricity in 20 charge / discharge cycles was 50% of the initial value.
%, Which indicates that the cycle characteristics are excellent.

The present invention is not limited to the above embodiment, but can be variously modified without departing from the gist of the present invention.

[0051]

As described above, the solid electrolyte battery of the present invention has a conventional secondary battery because an intermediate layer comprising a specific ratio of an active material and a solid electrolyte is disposed between an electrode and a solid electrolyte. It has superiority in terms of safety and performance as a secondary battery, such as no electrolyte leakage as described above, eliminating unsafety due to battery runaway reaction, and having a high degree of freedom in shape processing. Of course, the polarization resistance at the interface between the electrode and the solid electrolyte is reduced, and furthermore, the short circuit between the electrodes can be prevented, and the distance between the electrodes can be extremely reduced, so that the weight and size can be reduced.
Furthermore, the amount of the solid electrolyte that is not directly involved in the charging and discharging of such a secondary battery can be suppressed to a minimum, the amount of the electrode active material that determines the capacity of the battery is increased, and the polarization resistance at the interface is reduced. Therefore, the internal resistance of the battery is reduced, the ionic conduction at the interface is rapidly performed, the current that can be taken out of the battery is much larger, the charge / discharge characteristics are excellent, and the deterioration in cycle performance is extremely small. A secondary battery is obtained, and its industrial utility value is extremely high.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment in which a solid electrolyte battery of the present invention is applied to a coin-type battery.

FIG. 2 is a cross-sectional view illustrating an example of a basic configuration of a solid electrolyte battery of the present invention.

FIG. 3 is a sectional view showing another example of the basic configuration of the solid electrolyte battery of the present invention.

FIG. 4 is a sectional view showing another example of the basic configuration of the solid electrolyte battery of the present invention.

FIG. 5 is a cross-sectional view showing a basic configuration of a conventional solid electrolyte battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte battery 2, 3 electrode 4 Solid electrolyte 5, 6 Intermediate layer 5a, 6a First intermediate layer 5b, 6b Second intermediate layer 5c, 6c Third intermediate layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 4/58 H01M 4/58 4/62 4/62 Z 6/18 6/18

Claims (5)

[Claims] 1. A solid electrolyte battery having a solid electrolyte interposed between a pair of electrodes, wherein between at least one electrode and the solid electrolyte, 5 to 95% by weight of an active material and 5 to 95% by weight A solid electrolyte battery comprising at least one intermediate layer comprising: a solid electrolyte; 2. The solid electrolyte battery according to claim 1, wherein said intermediate layer comprises three layers. 3. The solid electrolyte according to claim 1, wherein the intermediate layer comprises 30 to 70% by weight of the active material and 30 to 70% by weight of the solid electrolyte. battery. 4. The active material forming the intermediate layer is made of LiCoO ₂ on the positive electrode side, and TiO ₂ , V ₂ O on the negative electrode side.
The solid electrolyte battery according to any one of claims 1 to 3, characterized in that it consists of any one of the _5. 5. The solid electrolyte battery according to claim 1, wherein said solid electrolyte is made of Li ₃ PO ₄ .