JPH0922734A - Polymer electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte secondary battery equipped with a high cyclic characteristics in charging and discharging, self-discharge characteristics, and high capacity density. SOLUTION: A polymer electrolyte secondary battery includes an active material, a positive electrode 2 containing non-aqueous electrolytic solution and polymer for retaining it, and a negative electrode 4 containing a lithium type spinel oxide to occlude and release lithium ions and retaining non-aqueous electrolytic solution. The arrangement further includes a solid polymer electrolyte layer 5 interposed between the two electrodes 2, 4 and containing non- aqueous electrolytic solution and a polymer for retaining it.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer electrolyte secondary battery, and more particularly to a polymer electrolyte secondary battery having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As such a secondary battery, a lithium secondary battery including a negative electrode using lithium or a lithium alloy as an active material and a positive electrode using an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as an active material is used. Secondary batteries are known. However, a secondary battery provided with a negative electrode using lithium or a lithium alloy as an active material has a problem that the charge / discharge cycle life is short because lithium dendrites are generated in the negative electrode when charge / discharge cycles are repeated.

[0003] For this reason, the negative electrode, for example coke, graphite, carbon fiber, resin fired body, a lithium ion, such as pyrolytic vapor carbon using a carbonaceous material for absorbing and releasing, electrolytes such as LiPF ₆ A non-aqueous solvent secondary battery using an electrolytic solution comprising a non-aqueous solvent such as ethylene carbonate and propylene carbonate has been proposed.
The non-aqueous solvent secondary battery can improve the negative electrode characteristics due to the precipitation of dendrite, and thus can improve the battery life and safety.

On the other hand, US Pat. No. 5,296,318 discloses a rechargeable lithium intercalation having a hybrid polymer electrolyte which has been made flexible by adding polymers to the cathode, anode and electrolyte layers. A battery, that is, a polymer electrolyte secondary battery is disclosed. Such a polymer electrolyte secondary battery has, for example, A
a positive electrode in which a positive electrode layer containing an active material, a non-aqueous electrolytic solution and a polymer holding the electrolytic solution is laminated on a current collector made of a foil, and a material which absorbs and releases lithium ions in a current collector made of Cu foil, A negative electrode in which a negative electrode layer containing a non-aqueous electrolytic solution and a polymer holding the electrolytic solution is laminated, a non-aqueous electrolytic solution interposed between the positive electrode layer and the negative electrode layer, and a polymer holding the electrolytic solution And a solid polymer electrolyte layer.

The negative electrode layer comprises a carbonaceous material such as artificial graphite that absorbs and releases lithium ions, an electrolyte such as lithium hexafluorophosphate and a non-aqueous solvent such as ethylene carbonate and propylene carbonate. A composition having a composition comprising a non-aqueous electrolytic solution and a polymer holding the electrolytic solution such as a copolymer of vinylidene fluoride-hexafluoropropylene (VDF-HFP) is used. A negative electrode having such a negative electrode layer has a lithium-based potential of 0 V when charging and discharging.
Therefore, the voltage of the secondary battery obtained by the lithium reference potential of the positive electrode incorporated together with the negative electrode is determined.

[0006]

The present invention is intended to provide a polymer electrolyte secondary battery having high charge / discharge cycle characteristics, self-discharge characteristics, and high capacity density.

[0007]

A polymer electrolyte secondary battery according to the present invention comprises a positive electrode containing an active material, a non-aqueous electrolytic solution and a polymer holding the electrolytic solution, and a lithium-based spinel oxide which absorbs and releases lithium ions. And a solid polymer electrolyte layer containing a non-aqueous electrolyte solution and a polymer holding the non-aqueous electrolyte solution and the electrolyte solution interposed between the positive electrode and the negative electrode. It is a feature.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A polymer electrolyte secondary battery according to the present invention will be described below with reference to FIG. The positive electrode is a current collector 1 made of an aluminum foil or an aluminum net.
Has a structure in which the positive electrode layer 2 is laminated. The negative electrode has a structure in which a negative electrode layer 4 is laminated on a collector 3 made of, for example, a nickel foil, a copper foil, a net made of nickel or a net made of copper, and the negative electrode layer 4 faces the positive electrode layer 2 of the positive electrode. Are arranged.
The solid polymer electrolyte layer 5 is interposed between the positive electrode layer 2 and the negative electrode layer 4.

Next, the above-mentioned negative electrode layer 4, positive electrode layer 2 and solid polymer electrolyte layer 5 will be described in detail. 1) Negative Electrode Layer 4 This negative electrode layer 4 contains a lithium-based spinel oxide that absorbs and releases lithium ions, a non-aqueous electrolytic solution, and a polymer that holds this electrolytic solution.

As the lithium-based spinel oxide,
For example, Li _{4 + z} Ti ₅ O ₁₂ (where z is an atomic ratio of 0 ≦
z <3) or Li _{1 + z} V ₂ O ₄ (where z is 0 ≦ z ≦ 1 in terms of atomic ratio) or the like can be used.

The lithium spinel oxide is preferably blended in an amount of 70 to 90% by weight based on the total solid content in the negative electrode layer. The electrolytic solution is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane and diethyl ether. , Tetrahydrofuran, 2-
Methyltetrahydrofuran, γ-butyrolactone and the like can be mentioned. The non-aqueous solvent may be used alone or in combination of two or more.

As the electrolyte contained in the non-aqueous electrolyte, for example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenide hexafluoride ( LiAsF
₆ ), lithium trifluorometasulfonate (LiCF
₃ SO ₃ ) and lithium bis (trifluoromethylsulfonylimide) [LiN (CF ₃ SO ₂ ) ₂ ]. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / l.

Examples of the polymer include vinylidene fluoride-hexafluoropropylene (VDF-HF).
The copolymer of P) can be used. In such a copolymer, VDF contributes to the improvement of the mechanical strength in the skeleton of the copolymer, and HFP is incorporated into the copolymer in an amorphous state, so that the electrolyte is retained and the lithium ion is retained. Function as a transparent part of the. The copolymerization ratio of the HFP depends on the method of synthesizing the copolymer, but is usually at most about 20% by weight.

In the negative electrode layer, it is preferable that artificial graphite, carbon black such as acetylene black, or a conductive ceramic such as titanium carbide is mixed as a conductive material.

2) Positive Electrode Layer 2 This positive electrode layer 2 contains an active material, a conductive material, a non-aqueous electrolytic solution and a polymer which holds this electrolytic solution.

Examples of the active material include lithium manganese oxide such as lithium manganese oxide, manganese dioxide, and Li _y NiO ₂ (where y is 0.05 <y ≦ 1.0 in atomic ratio). A lithium-containing cobalt oxide such as Li _y CoO ₂ (where y is an atomic ratio of 0.05 <y ≦ 1.0), Li _y Co _z Ni
_1-z O ₂ (where y and z are each 0.05 in atomic ratio)
<Y ≦ 1.0, 0 <z <1.0), various oxides such as amorphous vanadium pentoxide containing lithium, titanium disulfide, and disulfide. Chalcogen compounds such as molybdenum can be used. In particular, a lithium manganese composite oxide is preferable. Among such lithium manganese composite oxides, it is preferable to use one having a composition formula represented by Li _x Mn ₂ O ₄ (where x is an atomic ratio of 0.05 <x ≦ 2.0). A polymer electrolyte secondary battery provided with a positive electrode containing a lithium manganese composite oxide having such a composition has improved discharge capacity.

As the conductive material, for example, artificial graphite, acetylene black, carbon black such as coke-like carbon, or the like can be used. The same non-aqueous electrolyte solution and polymer as those described in the negative electrode layer are used.

3) Polymer Electrolyte Layer 5 This polymer electrolyte layer 5 contains a non-aqueous electrolytic solution and a polymer that holds this electrolytic solution.

As the non-aqueous electrolyte and the polymer, the same ones as described for the positive electrode layer described above are used. The polymer electrolyte secondary battery according to the present invention described above includes a negative electrode containing a lithium-based spinel oxide that absorbs and releases lithium ions, and holds a non-aqueous electrolyte. A negative electrode containing such a lithium-based spinel oxide has excellent charge-discharge cycle characteristics because it is stable in insertion and extraction of lithium ions due to repeated charge and discharge of a polymer electrolyte secondary battery including this negative electrode. . Further, the polymer electrolyte secondary battery including the negative electrode containing the lithium-based spinel oxide has excellent self-discharge characteristics. further,
Since the lithium-based spinel oxide can increase the packing density in the negative electrode (in the negative electrode layer) as compared with the carbonaceous material,
A polymer electrolyte secondary battery with improved capacity density (mAh / l, mAh / g) can be realized.

Further, the negative electrode containing the lithium-based spinel oxide has a potential higher than the lithium-based potential of a normal negative electrode using a carbonaceous material as a material for inserting and extracting lithium ions. The voltage of the secondary battery is determined by the potential difference between the positive electrode and the negative electrode. Therefore, by using a negative electrode containing a lithium-based spinel oxide as a material that absorbs and releases lithium ions, a secondary battery with a low voltage can be realized.

For example, a negative electrode containing Li _{4 + z} Ti ₅ O ₁₂ which is a lithium-based spinel oxide is about 1.
Since the positive electrode having a potential of 5V and containing the positive electrode active material, lithium cobalt composite oxide, has a potential of about 4V, a low voltage polymer electrolyte secondary battery of about 2.5V can be obtained by using these positive and negative electrodes. Can be realized. Further, by using a lithium manganese composite oxide having a potential of about 3V as the positive electrode active material, a low voltage polymer electrolyte secondary battery of about 1.5V can be realized. Such a low-voltage polymer electrolyte secondary battery can be used in response to the recent decrease in drive backup voltage of electronic devices, and can also be used as a compatible battery for manganese dry batteries.

[0023]

Embodiments of the present invention will be described below in detail. Example 1 First, lithium carbonate (Li ₂ CO ₃ ) and manganese dioxide (MnO ₂ ) were mixed at a molar ratio of Li and Mn of 1 :.
The mixture was mixed so as to be 2, and this mixture was heated at a temperature of 800 ° C. for 24 hours to prepare a particulate lithium manganese composite oxide having a composition formula represented by LiMn ₂ O ₄ . Subsequently, 11% by weight of a vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer (copolymerization ratio of HFP; 12% by weight) was dissolved in acetone to prepare an acetone solution. Lithium-manganese composite oxide and acetylene black were added and mixed so that the solid content of the copolymer was 20% by weight, the lithium-manganese composite oxide was 72% by weight, and the acetylene black was 8% by weight. This suspension was formed into a film by casting, left to stand at room temperature and naturally dried to form a sheet-like positive electrode layer having a thickness of 100 μm.

Further, acetase type titanium dioxide was mixed with a saturated LiOH aqueous solution so that the molar ratio of Li: Ti was 4: 5, dried at 110 ° C. for 12 hours, and then pulverized at a temperature of 800 ° C. By heating for 6 hours, a lithium-based spinel oxide having a composition formula of Li4 Ti5 O12 was produced. Subsequently, a vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer (HFP copolymerization ratio; 12% by weight) was added to acetone with 11 parts.
After preparing an acetone solution by dissolving it in an amount of 1 wt%, the solid solution of the copolymer is added to the acetone solution in an amount of 20 wt% of the lithium spinel oxide powder consisting of Li ₄ Ti ₅ O ₁₂ and acetylene black. 72% by weight of powder and 8% by weight of acetylene black were added and mixed. The suspension is cast to form a film, which is left at room temperature and naturally dried to obtain a thickness of 100.
A sheet-shaped negative electrode layer having a thickness of μm was prepared.

Further, vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer (HF
Copolymerization ratio of P; 12 wt%) in acetone to 11 wt%
An acetone solution was prepared by dissolving, and the acetone solution was cast to form a film, which was left at room temperature and naturally dried to form a sheet-like solid polymer electrolyte layer having a thickness of 30 μm.

Next, the sheet-shaped positive electrode layer and the aluminum foil (positive electrode current collector) are laminated using a double roll laminator to form a sheet-shaped positive electrode, and at the same time, the sheet-shaped negative electrode layer and nickel foil (negative electrode current collector). And a) were laminated using a double roll laminator to form a sheet-shaped negative electrode, and the sheet-shaped solid polymer electrolyte layer was interposed between the positive electrode and the negative electrode, and laminated using a double roll laminator. This five-layer laminate is treated with lithium hexafluorophosphate (LiP
F ₆ ) is immersed in a mixed solvent of ethylene carbonate (EC) -dimethyl carbonate (DMC) (mixing ratio 2: 1) in an amount of 1 mol / l, and the sheet-shaped product is immersed for 10 minutes in the electrolytic solution. The polymer electrolyte secondary battery having the structure shown in FIG. 1 was manufactured by impregnating the layer, the sheet-shaped negative electrode layer and the sheet-shaped solid polymer electrolyte layer with the electrolytic solution.

Example 2 As a positive electrode active material, LiOH and MnO ₂ were mixed at a molar ratio of 1: 3 and mixed at 380 ° C. for 24 hours.
Li _0.33 MnO ₂ synthesized by heating for a period of time was used, and Li ₇ T doped with Li was used as a material for inserting and extracting lithium.
A polymer electrolyte secondary battery having the structure shown in FIG. 1 was produced in the same manner as in Example 1 except that i ₅ O ₁₂ was used.

Regarding the obtained secondary battery of Example 1, the charging current was 40 mA, 2.7 V, and the discharging current was 40 mA, 1.9.
The average operating voltage was measured when the V discharge test was performed. As a result, it was 2.3V. Further, the secondary battery of Example 2 was measured for an average operating voltage when a 0.9 V discharge test was performed at a discharge current of 40 mA. As a result, 1.2V
Met.

The secondary batteries obtained in Examples 1 and 2 were repeatedly charged and discharged with a charging current of 40 mA and a discharging current of 40 mA, and the discharge capacities of the respective batteries at the first cycle and the 200th cycle were measured. As a result, Example 1,
In all the secondary batteries of No. 2, the maintenance ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle was 95%. Therefore, the polymer electrolyte secondary batteries of Examples 1 and 2 have excellent charge / discharge cycle life.

Further, the secondary batteries of Examples 1 and 2 obtained were stored in a charged state at a high temperature of 60 ° C. for 20 days at a high temperature, and the capacity retention rate was measured. As a result, it was confirmed that each of the secondary batteries of Examples 1 and 2 had an excellent self-discharge characteristic with a capacity retention rate of 90%.

[0031]

As described above in detail, according to the present invention, there is provided a polymer electrolyte secondary battery having high charge / discharge cycle characteristics, self-discharge characteristics, high capacity density, and a low voltage of 3.0 V or less. Can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing a polymer electrolyte secondary battery according to the present invention.

[Explanation of symbols]

1, 3: current collector, 2: positive electrode layer, 4: negative electrode layer, 5: polymer electrolyte layer.

Claims (3)

[Claims] 1. A positive electrode containing an active material, a non-aqueous electrolytic solution, and a polymer holding the electrolytic solution; a negative electrode containing a lithium-based spinel oxide that absorbs and releases lithium ions and holding the non-aqueous electrolytic solution; A polymer electrolyte secondary battery comprising: a non-aqueous electrolyte solution interposed between the positive electrode and the negative electrode; and a solid polymer electrolyte layer containing a polymer holding the electrolyte solution. 2. The lithium-based spinel oxide is Li
The polymer electrolyte secondary battery according to claim 1, wherein _{4 + z} Ti ₅ O ₁₂ (where z is 0 ≦ z ≦ 3 in atomic ratio). 3. The active material of the positive electrode is Li _x Mn ₂ O ₄
(However, x has an atomic ratio of 0.05 <x ≦ 2.0), Li _y CoO ₂ and Li _y NiO ₂ (provided that y has an atomic ratio of 0.05 <y ≦ 1.0). And Li _y C
O _z Ni ₁ -z O ₂ (where y and z are 0.05 <y ≦ 1.0 and 0 <z <1.0, respectively, in atomic ratio), and at least one selected from the group consisting of The polymer electrolyte secondary battery according to claim 1.