JPH0554913A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolytic secondary battery having a good charge/discharge cyclic life, high-output property, lithium charge/discharge efficiency, and storage performance by specifying active material and binding agent for a positive pole, and composition of nonaqueous electrolyte. CONSTITUTION:A negative pole 6 has active material of light metal or its alloy. A positive pole 4 includes active material mainly composed of spinal type lithium manganese oxide, conductive agent, and binding agent mainly comprising elastomer comprising copolymer mainly of ethylene-propylene. Nonaqueous electrolyte 11 comprises mixed solvent of ethylene carbonate and 2-methyl tetrahydrofuran or mixed solvent of ethylene carbonate, 2-methyl tetrahydrofuran, and tetrahydrofuran in which lithium hexafluorophosphate and/or lithium tetrafluoroborate is dissolved. A nonaqueous electrolytic secondary battery having a good charge/discharge cyclic life, high-output property, lithium charge/discharge efficiency, and storage performance can thus be provided.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an operating voltage, an output characteristic,
The present invention relates to a non-aqueous electrolyte secondary battery having improved charge / discharge efficiency, charge / discharge cycle life, storage characteristics and the like.

[0002]

2. Description of the Related Art In recent years, a non-aqueous electrolyte battery using a light metal such as lithium, sodium or aluminum as a negative electrode active material has been attracting attention as a high energy density battery, and manganese dioxide (MnO ₂ ) or fluorine is used as a positive electrode active material. Secondary batteries using carbonized carbon [(CF) _n ], thionyl chloride (SOCl ₂ ) and the like are already widely used as power sources for calculators, watches, and backup batteries for memories.

Furthermore, in recent years, with the miniaturization and weight reduction of various electronic devices such as VTRs and communication devices, the demand for high energy density secondary batteries as their power source has increased, and non-aqueous solutions using light metals as negative electrode active materials have been increasing. Electrolyte secondary batteries are being actively researched.

In these non-aqueous electrolyte secondary batteries, generally, a light metal such as lithium, sodium or aluminum is used as a negative electrode active material, and propylene carbonate (P) is used as an electrolyte.
C), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-BL), tetrahydrofuran (TH
F) in a non-aqueous solvent such as LiClO ₄ , LiBF ₄ , Li
A solution of an electrolyte such as AsF ₆ , LiPF ₆ or the like, which has a topochemical reaction with lithium as a positive electrode active material, is MnO ₂ , TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃
Etc. are used.

However, in these non-aqueous electrolyte secondary batteries, when lithium ions in the electrolyte are deposited as metallic lithium during charging, the solvent reacts with lithium and a part of the lithium surface becomes inactive. Turn into. Therefore, during repeated charging and discharging, there is a drawback that the deposited lithium is dendrite-like (dendritic) or is desorbed from the current collector, and the grown dendrite-like metallic lithium is the positive electrode. There is a defect that the separator that insulates the negative electrode penetrates or wraps around the separator to reach the positive electrode and short-circuits.

As an attempt to solve such a drawback, addition of an additive for preventing the generation of dendrite-like lithium in the electrolytic solution or the use of a lithium-aluminum alloy as a negative electrode material has been studied. None of them have produced satisfactory results.

As the non-aqueous electrolytic solution, a solution in which an electrolyte is dissolved in a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran, which hardly reacts with lithium, has been studied. For example, a solution using LiAsF ₆ as the electrolyte. in (Electrochim.Acta 30, 1715 (1985) ), although relatively improvement of charge and discharge efficiency is observed, there is a risk that LiAsF ₆ is toxic not preferred, also LiAsF ₆
In the case of using LiPF ₆ or LiBF ₄ instead, the charge / discharge efficiency is inferior and the stability of LiPF ₆ or LiBF ₄ itself is poor, so that sufficient charge / discharge cycle life and storage performance cannot be obtained. there were.

Further, in such a conventional non-aqueous electrolyte secondary battery, TiS ₂ , MoS _2, etc. have been used as the positive electrode active material, but when these active materials are used, the average operating voltage is In addition to having the drawback of being low (usually 2 V or less), the positive electrode molded using these active materials and a binder and a conductive material such as polytetrafluoroethylene (PTFE), etc. , The active material repeatedly expands and contracts, as a result, the contact between the conductive material and the active material deteriorates, or the active material falls off from the electrode to cause poor conductivity in the positive electrode, so sufficient charge / discharge cycle It had the drawback of not having a life.

[0009]

The object of the present invention is to provide a non-aqueous electrolyte solution with low toxicity, high energy density at high voltage, output characteristics, charge / discharge efficiency, charge / discharge cycle life and storage characteristics. Another object is to provide an excellent non-aqueous electrolyte secondary battery.

[0010]

The non-aqueous electrolyte secondary battery of the present invention is characterized by comprising the following negative electrode, positive electrode and non-aqueous electrolyte.

A. A negative electrode whose active material is a light metal or its alloy. B. A positive electrode comprising an active material mainly composed of spinel type lithium manganese oxide, a conductive material and a binder mainly composed of an elastomer composed of a copolymer mainly composed of ethylene-propylene. C. A non-aqueous electrolytic solution in which lithium hexafluorophosphate and / or lithium tetrafluoroborate are dissolved in a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran or a mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran and tetrahydrofuran.

The present invention will be described in detail below. The non-aqueous electrolyte secondary battery of the present invention includes the following negative electrode, positive electrode and non-aqueous electrolyte.

A. Negative Electrode Examples of the light metal or its alloy constituting the negative electrode include lithium, aluminum, and lithium-aluminum alloy.

B. Positive electrode The positive electrode is a spinel type lithium manganese oxide (LiMn
₂ O ₄ ) as an active material, a conductive material, and a binder having an elastomer composed of an ethylene-propylene copolymer as a main component.

Examples of the conductive material include metal powder such as acetylene black, carbon black and nickel. The compounding ratio of the active material mainly composed of spinel type lithium manganese oxide to the conductive material is 80 to 98% by weight. The content of the binder in the positive electrode is 3 to 1
5% by weight is preferred.

C. Non-Aqueous Electrolyte Solution A non-aqueous electrolyte solution was prepared by adding lithium hexafluorophosphate (Li) to a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran or a mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran and tetrahydrofuran.
PF ₆ ) and / or lithium tetrafluoroborate (L
It is a solution of iBF ₄ ).

The mixing ratio of ethylene carbonate in the mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran is 40 to 80% by volume, preferably 45 to 60% by volume. When the mixing ratio is less than 40% by volume,
The polarization of the negative electrode lithium electrode may be enhanced or the charge / discharge efficiency may be decreased, which is not preferable.

The mixing ratio of ethylene carbonate, 2-methyltetrahydrofuran, and tetrahydrofuran in the mixed solvent is 30 to 70 for ethylene carbonate.
%, 2-methyltetrahydrofuran 10 to 60% by volume, and tetrahydrofuran 10 to 40% by volume. The mixing ratio of tetrahydrofuran is 40% by volume
When it exceeds, the reactivity between lithium and the mixed solvent may increase.

Lithium hexafluorophosphate (LiPF
₆ ) and / or lithium tetrafluoroborate (LiB
The content of F ₄ ) in the mixed solvent is 0.1 mol / l or more and less than 1 mol / l, preferably 0.2 to 0.8 mol / l.
l.

By controlling the content ratio to the mixed solvent within the above range, the stability of lithium hexafluorophosphate and lithium tetrafluoroborate can be enhanced, and at the time of discharging at high output, the surface of the lithium electrode is Since lithium hexafluorophosphate and / or lithium tetrafluoroborate do not become supersaturated, their deposition on the surface of the lithium electrode can be suppressed, and high output characteristics and storage performance of the battery can be improved. it can. When the content ratio to the mixed solvent is 1 mol / l or more, the stability of the non-aqueous electrolyte may be deteriorated and the lithium charge / discharge efficiency may decrease. The polarization of the negative electrode may be rapidly increased, which is not preferable.

The non-aqueous electrolyte secondary battery of the present invention can be prepared by accommodating each of the negative electrode, the positive electrode and the non-aqueous electrolyte in a known battery container by a conventional method.

The non-aqueous electrolyte may be treated by contacting it with an inert adsorbent such as alumina, energization treatment, or a combination of these treatments before being sealed in the battery container. preferable.

By treating the non-aqueous electrolytic solution in this way, impurities in the non-aqueous electrolytic solution can be removed, so that the reaction between the negative electrode lithium and the non-aqueous electrolytic solution can be suppressed, and the lithium Prevent deterioration.

[0024]

[Operation] (1) Since the positive electrode contains a binder containing an elastomer composed of a copolymer mainly composed of ethylene-propylene as a main component together with the active material and the conductive material, the adhesion between the active material and the conductive material is improved. This prevents the active material from falling out of the positive electrode due to expansion or contraction of the active material due to charge / discharge, and deterioration of contact between the active material and the conductive material.

(2) Since the spinel type lithium manganese oxide, which has a large expansion and contraction rate due to charge and discharge, is used as the active material of the positive electrode, the positive electrode expands gradually while repeating this expansion and contraction, Since the negative electrode facing this is pressed, lithium is prevented from being deposited in a dendrite form.

(3) The reaction with lithium is suppressed by using a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran as the solvent of the non-aqueous electrolyte. (4) By using a mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran, and tetrahydrofuran as the solvent of the non-aqueous electrolyte, the conductivity of the non-aqueous electrolyte is increased and the polarization of the negative electrode lithium is suppressed.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below more specifically with reference to the drawings. Example 1 In the non-aqueous electrolyte secondary battery of this example, as shown in FIG. 1, a bottomed cylindrical stainless steel container 1 also serving as a negative electrode terminal, in which an insulator 2 was disposed, was used.

In this container 1, a negative electrode 6 and a separator 5 are provided.
An electrode group 3 was housed in which a band-shaped material in which the positive electrode 4 was laminated in this order was formed into a spiral shape so that the negative electrode 6 was located outside.

A strip-shaped lithium foil is used as the negative electrode 6, a polypropylene porous film is used as the separator 5, 80% by weight of spinel type lithium manganese oxide (LiMn ₂ O ₄ ) powder is used as the positive electrode 4, and a conductive material is used. 15% by weight of acetylene black and 5% by weight of a binder (EPT) containing an elastomer composed of a copolymer mainly composed of ethylene-propylene as a main component are mixed together, and further formed into a sheet and pressure-bonded to an expanded metal current collector. What was done was used.

An insulating paper 7 having a central opening is arranged near the upper end of the electrode group 3 in the container 1, and an insulating sealing plate 8 having a central opening is provided on the insulating paper 7. The upper part was crimped and placed airtight.

The positive electrode terminal 9 was fitted in the central opening of the insulating sealing plate 8. The positive electrode terminal 9 was connected to the positive electrode 4 of the electrode group 3 via a positive electrode lead 10. The negative electrode 6 of the electrode group 3 was connected to the container 1 serving as a negative electrode terminal via a negative electrode lead (not shown).

In this embodiment, lithium hexafluorophosphate (LiPF ₆ ) having a concentration of 0.5 mol / l was mixed with ethylene carbonate and 2-methyltetrahydrofuran in a container 1 containing such an electrode group 3 and the like. Non-aqueous electrolyte solution 11 having a composition dissolved in a mixed solvent (mixing volume ratio 50:50)
Then, a non-aqueous electrolyte secondary battery was produced.

Example 2 As a non-aqueous electrolytic solution, lithium hexafluorophosphate (LiPF ₆ ) having a concentration of 0.5 mol / l was mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran and tetrahydrofuran (mixing volume ratio 50:25). No. 25) was used to prepare a non-aqueous electrolyte secondary battery having the same configuration as in Example 1.

Example 3 As a non-aqueous electrolytic solution, lithium tetrafluoroborate (LiBF ₄ ) at a concentration of 0.5 mol / l was added to a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran (mixing volume ratio 50:50). Other than using the dissolved one,
A non-aqueous electrolyte secondary battery having the same structure as in Example 1 was produced.

Example 4 As a non-aqueous electrolytic solution, lithium tetrafluoroborate (LiBF ₄ ) at a concentration of 0.5 mol / l was mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran and tetrahydrofuran (mixing volume ratio 50:25). No. 25) was used to prepare a non-aqueous electrolyte secondary battery having the same configuration as in Example 1.

Comparative Example 1 Example 1 was repeated except that Teflon powder was used as the binder.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in.

Comparative Example 2 As a non-aqueous electrolyte, lithium perchlorate (LiClO ₄ ) at a concentration of 1.0 mol / l and propylene carbonate and 1,
Mixed solvent with 2-dimethoxyethane (mixed volume ratio 5
A non-aqueous electrolyte secondary battery having the same structure as in Example 1 was prepared except that the one dissolved in 0:50) was used.

(Evaluation) Example 1 thus obtained
4 and Comparative Examples 1 and 2, the discharge capacities and cycle lives of the respective non-aqueous electrolyte secondary batteries were measured. Discharge capacity and cycle life are measured by charging current 10
Charging and discharging were repeated under the conditions of 0 mA and discharge current of 100 mA. The results are shown in Figure 2.

As is apparent from FIG. 2, the non-aqueous electrolyte secondary batteries produced in Examples 1 to 4 showed equivalent initial discharge capacities as compared with those produced in Comparative Examples 1 and 2. However, the cycle life was remarkably excellent. Especially Example 2
In the non-aqueous electrolyte secondary battery prepared in step 2, the difference was remarkable.

Next, the discharge current of each of the non-aqueous electrolyte secondary batteries prepared in Examples 1 to 4 was set to 100 to 10.
The change in discharge capacity when increasing to 00 mA was measured.
Results are shown in FIG. As is clear from the ABCD curve in FIG. 3, the non-aqueous electrolyte secondary batteries produced in Examples 1 to 4 showed a gradual decrease in discharge capacity, and particularly in the electrolyte secondary batteries produced in Example 2, It was possible to perform high current density discharge.

Furthermore, as an evaluation of storage performance, Example 1 was used.
4 and the non-aqueous electrolyte secondary battery prepared in Comparative Example 2
The sample was left at 5 ° C. for 6 months, and the cycle life of the non-aqueous electrolyte secondary battery was measured in the same manner as above.

As a result, the cycle life of the non-aqueous electrolyte secondary batteries produced in Comparative Example 2 was reduced by 35%, but the non-aqueous electrolyte secondary batteries produced in Examples 1 to 4 were all produced. It was less than 10% and the storage performance was excellent.

[0043]

According to the present invention, the charge / discharge cycle life,
It is possible to provide a non-aqueous electrolyte secondary battery having high output characteristics, lithium charge / discharge efficiency, and excellent storage performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cylindrical non-aqueous electrolyte secondary battery of an example.

FIG. 2 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity of the non-aqueous electrolyte secondary batteries produced in Examples 1-4 and Comparative Examples 1-2.

FIG. 3 is a characteristic diagram showing the relationship between the discharge capacity and the discharge current of the non-aqueous electrolyte secondary batteries produced in Examples 1-4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Stainless steel container 3 ... Electrode group 4 ... Positive electrode 5 ... Separator 6 ... Negative electrode 8 ... Sealing plate 9 ... Positive electrode terminal 11 ... Nonaqueous electrolytic solution A ... Nonaqueous electrolytic solution secondary battery B of Example 1 ... Nonaqueous Electrolyte Secondary Battery C ... Nonaqueous Electrolyte Secondary Battery of Example 3 D ... Nonaqueous Electrolyte Secondary Battery of Example 4 a ... Nonaqueous Electrolyte Secondary Battery of Comparative Example 1 b ... Comparative Example 2 non-aqueous electrolyte secondary battery

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroyoshi Nose, 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo, Toshiba Battery Co., Ltd. (72) Norio Takami, Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture 1 Incorporated company Toshiba Research Institute (72) Inventor Takahisa Osaki 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research Institute (72) Inventor Shuji Yamada Komukai-Toshiba, Kawasaki-shi, Kanagawa No. 1 Incorporated company Toshiba Research Institute

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising the following negative electrode, positive electrode and non-aqueous electrolyte. A. A negative electrode whose active material is a light metal or its alloy. B. A positive electrode comprising an active material mainly composed of spinel type lithium manganese oxide, a conductive material and a binder mainly composed of an elastomer composed of a copolymer mainly composed of ethylene-propylene. C. A non-aqueous electrolytic solution in which lithium hexafluorophosphate and / or lithium tetrafluoroborate are dissolved in a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran or a mixed solvent of ethylene carbonate, 2-methyltetrahydrofuran and tetrahydrofuran.