JP2000277152A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having battery characteristics that do not decrease and being excellent in safety such that explosion and firing are prevented even in the event of breakdown due to an internal short circuit or overcharging. SOLUTION: This lithium secondary battery, including positive and negative electrodes which reversibly store and release lithium and an electrolyte containing lithium ions, contains an oxygen absorber. The oxygen absorber is preferably heat polymerizable and is preferably a polysiloxane compound or phenylene oxide compound which absorbs and polymerizes oxygen desorbed from the electrodes. The lithium ion secondary battery having enhanced safety for battery breaking tests can thus be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly safe lithium secondary battery suitable for use in portable equipment such as portable telephones and notebook personal computers, as a drive power supply for electric vehicles and a power storage power supply.

[0002]

2. Description of the Related Art In recent years, secondary batteries have become one of the essential components that are indispensable as power sources for personal computers and mobile phones, or as power sources for electric vehicles and power storage.

A portable computer (including a pen computer) and a personal digital assistant (Personal Digita)
l Assistant or Personal Intelligent Communic
Requirements for mobile communication (mobile computing) such as ator or handheld communicator include miniaturization and weight reduction. However, it is difficult to make the system compact and lightweight because of the high power consumed by the backlight and drawing control of the liquid crystal display panel, and the fact that the capacity of the secondary battery is still insufficient at present. It is in.

[0004] Further, with the increase of global environmental problems, electric vehicles that do not emit exhaust gas and noise have attracted attention.
However, current batteries have problems such as short running distance, poor acceleration, small space in the vehicle, and poor stability of the vehicle body due to low energy density and low output density. Among secondary batteries, lithium secondary batteries capable of realizing a particularly high energy density have been actively researched and developed recently as alternative batteries to conventional lead-acid batteries or nickel-cadmium batteries.

However, such a lithium secondary battery has many problems with respect to safety such as overcharging, heating, and short circuit. Lithium secondary batteries use a non-aqueous electrolyte mainly composed of flammable organic solvents, so the cathode active material decomposes exothermically during internal short-circuit breakdown such as nailing or crushing of the battery or during overcharge. When the non-aqueous electrolyte is ignited, an exothermic runaway reaction occurs, causing the battery to burst and ignite.

For this reason, various measures have conventionally been proposed as a method of avoiding such a risk. For example, as a technique for improving the safety of an electrolyte by adding an additive to the electrolyte, a technique for containing a self-digestible phosphate ester (Japanese Patent Laid-Open No. 4-184870), (Japanese Unexamined Patent Publication No. Hei 8-88023), a technique for containing microcapsules containing a flame retardant or a chemical substance that causes an electrolytic solution curing reaction (Japanese Unexamined Patent Publication No. Hei 6-283206) Japanese Patent Application Laid-Open No. 10-155453), or a technique of containing a radical scavenger (Japanese Patent Application Laid-Open No. H10-155451). In addition, a technique for increasing the flash point and securing safety by using a fluorine-substituted compound (Japanese Patent Laid-Open No. 7-312227) or a chlorine-substituted compound (Japanese Patent Laid-Open No. 8-45544) in the electrolytic solution itself has been developed. Proposed.

[0007]

However, if the above-mentioned substance having self-extinguishing properties or a substance having a high flash point is contained in the electrolyte, the ionic conductivity of the electrolyte is reduced.
The high-rate discharge characteristics and low-temperature characteristics of the battery deteriorate. In addition, even if using technology to contain microcapsules containing flame retardants or chemicals that cause electrolyte curing reaction,
Oxygen released from the electrode at the time of internal short-circuit destruction or overcharge accelerates the combustion of the electrolytic solution, leading to rupture and ignition, which is not a sufficient characteristic in terms of safety. In addition, even when the technology for containing a radical scavenger is used, oxygen taken into the battery during battery production consumes the radical scavenger, and the radical scavenger itself reacts with the electrode, thereby deteriorating battery characteristics. There is.

An object of the present invention is to provide a highly safe secondary battery which does not lower battery characteristics and does not cause bursting and ignition even when an internal short circuit is broken or overcharged. It is in.

[0009]

The battery of the present invention contains an oxygen absorbent that absorbs oxygen generated at the time of internal short circuit breakdown or overcharge and accelerates the polymerization or crosslinking reaction with the generated Joule heat. It is characterized by the following. The present inventors include an oxygen absorbent that causes a curing reaction such as a polymerization reaction or a cross-linking reaction while absorbing oxygen when the temperature rises in the battery. It has been found that the desorbed oxygen and the solidification of the electrolyte can increase the internal resistance of the battery, thereby preventing ignition and rupture.

The oxygen absorbent used in the present invention is not particularly limited as long as it is a compound which absorbs oxygen and polymerizes or crosslinks. Examples thereof include polysiloxanes (preferably having a degree of polymerization of 3 to 9) and phenylene. Oxides and the like are used.

An example is shown in FIGS. In FIG. 1, R1 and R2 represent hydrogen or an organic functional group having 1 to 50 carbon atoms.

Among the above polysiloxanes, R1 and R2 are preferably functional groups having high polarity in terms of solubility in an electrolytic solution. When added to the positive electrode or the negative electrode, R is added so as to be easily dissolved or dispersed in accordance with a binder or a solvent at the time of preparing the electrode.
It is preferable to select 1.

In FIG. 2, R1 and R2 represent hydrogen or an organic functional group having 1 to 50 carbon atoms.

Among the above phenylene oxides, R1
And R2 is preferably a highly polar functional group from the viewpoint of solubility in an electrolytic solution. When added to the positive electrode or the negative electrode, it is preferable to select R1 so as to be easily dissolved or dispersed in accordance with a binder or a solvent at the time of manufacturing the electrode.

The amount of the oxygen absorbent added according to the present invention varies depending on the site inside the battery to be added. However, the weight ratio of the oxygen absorber to the electrode, electrolyte or separator is from 0.1 to 20%.
% Is preferred.

The positive electrode active material that can be used in the lithium secondary battery of the present invention is a layered compound such as lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ).
Alternatively, one obtained by substituting one or more transition metals or lithium manganate (Li _{1 + x} Mn _2-x O ₄ (where x = 0)
0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO
_2), copper - lithium oxide (Li ₂ CuO _2), or _{LiV 3 O 8, LiFe 3 O} 4, V 2 O 5, vanadium oxides such as Cu ₂ V ₂ O _7, or Formula LiNi _1-x M _x O
₂ (where M = Co, Mn, Al, Cu, Fe, M
g, B, Ga, where x = 0.01 to 0.3) Ni-substituted lithium nickelate or chemical formula LiMn _2-x M _x O ₂ (where M = Co, Ni, F
e, Cr, Zn, Ta, x = 0.01 to 0.1) or the chemical formula Li ₂ Mn ₃ MO ₈ (where M = Fe, Co,
Examples thereof include lithium manganese complex oxide represented by Ni, Cu, Zn) or LiMn ₂ O ₄ in which a part of the chemical formula Li is substituted with an alkaline earth metal ion, a disulfide compound, or Fe ₂ (MoO ₄ ) ₃ .

On the other hand, a metal which can be alloyed with lithium, for example, Al, Sn, Si, In, Ga, M
g or an alloy thereof. As these metals or alloys, materials alloyed with lithium can be used. In addition, natural graphite, artificial graphite, carbon fiber,
Carbonaceous materials such as vapor grown carbon fiber, pitch-based carbonaceous material, needle coke, polyacrylonitrile-based carbon fiber, carbon black, or 5- or 6-membered cyclic hydrocarbon or cyclic oxygen-containing organic compound Amorphous carbon material synthesized by pyrolysis or polyacene,
Conductive polymer material composed of polyparaphenylene, polyaniline, polyacetylene, or SnO, GeO ₂ , S
nSiO ₃ , SnSi _0.5 O _1.5 , SnSi _0.7 Al _0.1 B _0.3
An oxide of a Group 14 element or a Group 15 element including P _0.2 O _3.5 , SnSi _0.5 Al _0.3 B _0.3 P _0.5 O _4.15 , or the like, indium oxide, zinc oxide, or Li ₃ F
eN ₂ , or Fe ₂ Si ₃ , FeSi, FeSi ₂ , M
Silicides such as g ₂ Si can also be used as the negative electrode active material. Further, the present invention is applicable to other than the above-mentioned battery active material, and a lithium metal sheet may be used for the negative electrode.

The usable electrolyte of the lithium secondary battery is as follows:
Its chemical formula is LiPF ₆ , LiBF ₄ , LiClO ₄ , L
iCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiS
An electrolyte represented by bF ₆ , lithium lower aliphatic carboxylate, or a mixture thereof can be used.

As the non-aqueous electrolyte for the lithium secondary battery, a solution in which the above-mentioned lithium salt is dissolved in a solvent for the non-aqueous electrolyte is used. Examples of the solvent for the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2-methyltetrahydrofuran and dimethyl sulfonate. Foxide, 1,
3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane Or a derivative obtained by substituting a part of hydrogen in an organic solvent molecule with a halogen, or an alkyl group, an alkene group, an alkyne group or an aromatic compound And derivatives substituted with a group. Also, mixtures thereof can be used.

When a solid electrolyte is used, the above-mentioned lithium salt is used by being held in a polymer of ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate, and hexafluoropropylene.

When a gel electrolyte is used, the non-aqueous electrolyte listed above is held in a polymer of ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate, and hexafluoropropylene.

The use of the highly safe secondary battery of the present invention is as follows.
Although not particularly limited, for example, a personal computer,
Large electronic computer, notebook computer, pen input personal computer, notebook word processor, mobile phone, mobile card, wristwatch, camera, electric shaver, cordless phone, fax, video, video camera, electronic notebook, calculator, electronic notebook with communication function, Portable copiers, LCD TVs, power tools,
Vacuum cleaners, game machines with virtual reality functions, toys, electric bicycles, walking aids for medical care, wheelchairs for medical care, mobile beds for medical care, escalators, elevators, forklifts, golf carts, emergency power supplies , Load conditioners, power storage systems, etc. In addition to civilian use, it can also be used for military use and space use.

By using the non-aqueous electrolyte of the present invention,
A lithium secondary battery with improved safety against internal short circuit and overcharge of the battery can be obtained.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail based on embodiments. However, it should be noted that the present invention is not limited at all by the following examples, and can be appropriately changed without changing the gist of the present invention.

Example 1 LiCoO ₂ was used as a positive electrode active material, graphite powder was used as a conductive additive, and polyvinylidene fluoride (PVDF) was used as a binder. The weight ratio was 88%, 7%, and 5%, respectively. , N-methyl-2-pyrrolidone (NM
P) was added and mixed well to prepare a positive electrode mixture. This positive electrode mixture is applied to one side of a 20 μm thick Al foil,
After drying the NMP, it was molded by a roll press to produce a positive electrode sheet. As in the preparation of the positive electrode, graphite powder was used as the negative electrode active material, and polyvinylidene fluoride (PVDF) was used as the binder.
%, 5%, and N-methyl-2 as a solvent.
-Pyrrolidone (NMP) was added and mixed well to prepare a negative electrode mixture. This negative electrode mixture was applied to one surface of a Cu foil having a thickness of 20 μm, NMP was dried, and then formed by a roll press to prepare a negative electrode sheet.

The separator has a thickness of 25 μm and a diameter of 18
A microporous membrane made of mm mm polyethylene was used.

The electrolyte was mixed with 1 mol of a 1: 1 mixture of ethylene carbonate and diethyl carbonate by volume.
/ LLiPF ₆ was dissolved and adjusted, and polydimethylsiloxane having a degree of polymerization of 3 was added as an oxygen absorbent at a ratio of 5% by weight.

A positive electrode, a separator, and a negative electrode were stacked in this order, wound in a cylindrical shape, and a terminal was attached. After storing in a battery can,
Impregnated with electrolyte and caulked the battery lid to a diameter of 18m
An 18650 cylindrical battery with a height of 65 mm and a height of 65 mm was produced.

Using this lithium secondary battery, the charge / discharge current was 3 mA, the charge end voltage was 4.2 V, and the discharge end voltage was 1.
The charge and discharge were performed 5 times at 5 V. Battery is 1400
The battery was charged at a constant current of 4.2 V at mA and then charged at 4.2 V at a constant voltage for 3 hours, and then discharged and discharged to 2.7 V at 1400 mAh five times.

In the nail penetration test, the battery was charged at a constant current of 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. The battery with a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

Comparative Example 1 A secondary battery was prepared and evaluated in the same manner as in Example 1 except that no oxygen absorbent was added to the non-aqueous electrolyte. In the nail penetration test and the overcharge test, a burst explosion occurred. Example 2 Example 1 was repeated except that polydimethylsiloxane having a degree of polymerization of 3 was not added to the electrolytic solution but was added to the positive electrode at a weight ratio of 5%.
A battery was prepared in the same manner as described above, and a nail penetration test and an overcharge test were performed.

In the nail penetration test, the battery was charged at a constant current up to 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. A battery having a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

Example 3 Example 1 was repeated except that polydimethylsiloxane having a degree of polymerization of 3 was not added to the electrolyte but was added to the negative electrode at a weight ratio of 5%.
A battery was prepared in the same manner as described above, and a nail penetration test and an overcharge test were performed.

In the nail penetration test, the battery was charged at a constant current of 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. The battery with a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

Example 4 A battery was prepared in the same manner as in Example 1 except that polyphenylene oxide was added to the positive electrode at a weight ratio of 5% instead of polydimethylsiloxane, and a nail penetration test and an overcharge test were performed. Was.

In the nail penetration test, the battery was charged at a constant current of 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. The battery with a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

Example 5 A battery was prepared in the same manner as in Example 1 except that polyphenylene oxide was added to the electrolyte at a weight ratio of 5% instead of polydimethylsiloxane, and a nail penetration test and an overcharge test were performed. went.

In the nail penetration test, the battery was charged at a constant current of 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. The battery with a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

Example 6 A battery was prepared in the same manner as in Example 1 except that polyphenylene oxide was added to the negative electrode at a weight ratio of 5% instead of polydimethylsiloxane, and a nail penetration test and an overcharge test were performed. Was.

In the nail penetration test, the battery was charged at a constant current of 4.2 V at 1400 mA and then charged at a constant voltage of 4.2 V for 3 hours. The battery with a charge capacity of 1400 mAh was passed through the battery at a speed of 5 mm / sec. In the overcharge test, 2800 mA
The battery was charged at a constant current of. No rupture or ignition could be confirmed in either case.

[0041]

According to the present invention, it is possible to obtain a lithium ion secondary battery having improved safety against a battery destruction test.

[Brief description of the drawings]

FIG. 1 is a view showing a structural formula of polysiloxane which is an example of an oxygen absorbent contained in a battery of the present invention.

FIG. 2 is a view showing a structural formula of phenylene oxide which is another example of the oxygen absorbent contained in the battery of the present invention.

[Explanation of symbols]

R1, R2: hydrogen or an organic functional group having 1 to 50 carbon atoms.

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Claims (6)

[Claims] 1. A lithium secondary battery comprising a positive electrode which reversibly stores and releases lithium, a negative electrode, and an electrolyte containing lithium ions, wherein the secondary battery comprises an oxygen absorbent. 2. The lithium secondary battery according to claim 1, wherein said oxygen absorbent is thermally polymerized. 3. The lithium secondary battery according to claim 1, wherein said oxygen absorbing agent uses oxygen released from said electrode as a polymerization initiator. 4. The lithium secondary battery according to claim 1, wherein said oxygen absorbent absorbs oxygen and polymerizes it. 5. The method according to claim 1, wherein the oxygen absorbent is a polysiloxane compound having the structural formula shown in FIG.
The lithium secondary battery according to claim 1, wherein However, in FIG. 1, R1 and R2 represent hydrogen or an organic functional group having 1 to 50 carbon atoms. 6. The lithium secondary battery according to claim 1, wherein said oxygen absorbent is a phenylene oxide compound having a structural formula shown in FIG. However, in FIG. 2, R1 and R2 represent hydrogen or an organic functional group having 1 to 50 carbon atoms.