JP2000348704A - Non-aqueous electrolyte electrochemical device - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte electrochemical device capable of sufficiently operating a safety function even when a large current flows due to an external short circuit, overcharge, etc., and the temperature inside the electrochemical device rises. I do. SOLUTION: In a non-aqueous electrolyte electrochemical device provided with a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator interposed between the positive electrode and the negative electrode, the temperature in the electrochemical device is increased by a certain amount. A material having a property that the content of the electrolytic solution increases when the temperature is exceeded is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte electrochemical device.

[0002]

2. Description of the Related Art A non-aqueous electrolyte electrochemical device using a light metal such as lithium or sodium as a negative electrode active material is used for various types of electric and
Used in a wide range of electronic devices. Non-aqueous electrolyte electrochemical devices include primary batteries, secondary batteries, capacitors for electric double layer, etc. In particular, non-aqueous electrolyte secondary batteries have a high energy density and can be reduced in size and weight. Therefore, active research and development are currently underway.

This non-aqueous electrolyte secondary battery comprises a non-aqueous electrolyte, a positive electrode made of a lithium-containing oxide or the like, a negative electrode made of a host material such as a carbon material, and a separator interposed between the positive electrode and the negative electrode. It is configured. For non-aqueous electrolyte, L
A separator prepared by dissolving an electrolyte salt such as iPF _{6 in} a non-aqueous solvent such as ethylene carbonate or dimethyl carbonate uses a polyolefin porous film such as polyethylene or polypropylene as a separator.

[0004] The polyolefin-based porous membrane has a feature that it dissolves when the temperature rises and closes the pores of the porous membrane.
With this function, in an actual battery, when the temperature rises abnormally, the pores of the porous film are blocked and the film becomes an insulating film. By this action, the battery circuit is cut off, thereby preventing a further rise in temperature and maintaining the safety.

[0005]

However, this function is effective when the battery is short-circuited due to malfunction or the like. However, the battery continues to be charged from the normal full charge due to malfunction of the machine such as overcharge. When the temperature rises abnormally, there is a problem that the safety function does not function sufficiently.

Although the cause is not well understood, when the battery is overcharged, the temperature rises more rapidly than the short circuit temperature before the pores of the porous membrane of the separator are closed and the above-mentioned effect is exhibited. It is thought that it is.

[0007] With regard to currently commercially available batteries, in order to maintain safety even in such an overcharged state, a current interrupting device is provided on the sealing plate of the battery. The current interrupting device has a function of interrupting the internal pressure by a current interrupting device in the sealing plate when the internal pressure becomes equal to or higher than a certain internal pressure, so that no more electricity flows.

That is, in general, when the battery is in an overcharged state, gas is generated with an increase in the temperature of the battery, and the internal pressure inside the battery is increased.

However, the use of a sealing plate having such a current interrupting function has problems in that the production is troublesome and costly.

[0010] The present invention solves the above-mentioned problems of the prior art, and a non-aqueous electrolyte electrochemical device capable of sufficiently operating a safety function without using a sealing plate having a current interrupting function. The purpose is to provide.

[0011]

In order to solve the above-mentioned problems, a non-aqueous electrolyte electrochemical device according to the present invention comprises a separator interposed between a positive electrode and a negative electrode. When the temperature exceeds a certain temperature, an electrolyte having a property of increasing the content of the electrolyte is used. As a result, even if the internal temperature of the electrochemical device rises during overcharging or the like, the separator absorbs the electrolyte, and as a result, the electrolyte becomes scarce inside the electrode and polarization increases. The ions cannot move between them, and the current in the electrochemical device can be reliably shut off.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be implemented by the embodiments described in the claims. That is, in a non-aqueous electrolyte electrochemical device including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator interposed between the positive electrode and the negative electrode, the separator increases the temperature in the electrochemical device and reduces the temperature to a certain level. This is a non-aqueous electrolyte electrochemical device having a property that the content of the electrolyte increases when the amount exceeds the limit.

[0013] By using a separator having such properties, even if the internal temperature of the battery rises due to an external short circuit or overcharging, the separator absorbs the electrolyte when the temperature exceeds a certain temperature. As a result, the electrolyte inside the electrode becomes scarce and the polarization increases, so that ions cannot be conducted between the positive and negative electrodes, and the current in the electrochemical device can be reliably shut off. Therefore, non-aqueous electrolyte electrochemical devices, such as lithium batteries and electric double layer capacitors, that can suppress overheating in the electrochemical device and sufficiently operate the safety function in the event of an external short circuit or overcharge, etc. Can be provided. That is, since the separator has the function of reliably interrupting the current, the current interrupting function can be omitted from the sealing plate, and safety devices related to other current interrupting functions can be omitted.

The principle that the temperature rises and, when the temperature exceeds a certain temperature, the amount of absorbing the electrolyte increases increases, although the details are not clear, it is considered as follows. In other words, a material that has the property of increasing the amount of electrolyte absorbed when it exceeds a certain temperature,
Although it originally has hydrophobicity at low temperatures and does not absorb polar solvents such as electrolytes, it becomes hydrophilic when it exceeds a certain temperature, so it is considered that it absorbs and swells the electrolytes.

As the separator of the present invention, when the temperature exceeds a certain temperature, that is, when the temperature exceeds the normal operating temperature range of the electrochemical device, the amount of absorbing the electrolyte increases, the polarization increases, and the current is cut off. It is not particularly limited as long as it is one. For example, those obtained by copolymerizing polyethylene oxide and polymethyl vinyl ether and those containing polyvinylidene fluoride and polymethyl vinyl ether as main components can be used. In such a polymer, the temperature at which the amount of absorbing the electrolyte component increases can be freely set by arbitrarily selecting the copolymer ratio.

The positive electrode of the present invention is not particularly limited, but in the case of a primary battery, for example, graphite fluoride, manganese dioxide (MnO ₂ ) and the like can be mentioned.

When a secondary battery is used, for example,
Lithium tomate (LiCoO_Two), Lithium nickelate (Li
NiO_Two), Lithium manganate (LiMn_TwoO_Four, LiM
nO _Two), Lithium ferrate (LiFeO_Two) And their transition gold
Part of the genus Co, Ni, Mn, Fe is replaced with another transition metal, tin,
Substituted with aluminum, etc., vanadium oxide (V _Two
O_Five), Manganese dioxide (MnO_Two), Molybdenum oxide
(MnO_Two, MnO_Three) And titanium sulfide
(TiS_Two), Molybdenum sulfide (MoS_Two, MoS_Three), Sulfuric acid
Iron fossil (FeS_Two) And other transition metal sulfides and polyanily
, Polypyrrole, polythiophene and other polymers
No. In addition, when making an electric double layer capacitor
Is, for example, activated carbon.

The negative electrode of the present invention is not particularly limited. However, in the case of a primary battery, for example, an alkali metal or an alkali metal and aluminum (Al), lead (Pb), tin (Sn), bismuth (Bi) , Silicon (Si) and the like. In the case of a secondary battery, for example, lithium ion or sodium ion is used as an active material that moves between the positive electrode and the negative electrode during charge and discharge, and an amorphous carbon material is used as a host material thereof, which is fired at a temperature of 2000 ° C. or more. Aluminum (Al), lead (Pb), tin (S) alloyed with carbon materials such as artificial graphite and natural graphite and alkali metals
n), cubic intermetallic compounds (AlSb, Mg ₂ Si, NiSi ₂ ) or lithium nitrogen compounds (Li ₍ Li), which occlude and release metals such as bismuth (Bi) and silicon (Si) and alkali metals between lattices. _3-x) M _x N (M: transition metal)). When an electric double layer capacitor is used, for example, activated carbon or the like can be used.

When the electrochemical device is a non-aqueous electrolyte battery, a non-aqueous electrolyte solution obtained by dissolving an alkali metal salt in an organic solvent is used.

Examples of the alkali metal salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium perchlorate (LiC ₄ ).
lO ₄ ), lithium trifluoromethanesulfonate (Li
CF ₃ SO _3), trifluoromethanesulfonic acid imide lithium _{(LiN (CF 3 SO 2)} 2) but like those used one or two or more of, but is not limited thereto.

Examples of the organic solvent include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone or a lactone derivative, tetrahydrofuran or a derivative thereof, dimethyl carbonate,
Diethyl carbonate, methyl ethyl carbonate,
1, 2-dimethoxyethane, dimethyl sulfoxide or the like, or a mixture of two or more thereof, or the like, for the purpose of improving discharge and charge / discharge characteristics, the purpose of making the electrolyte solution flame-retardant,
Examples thereof include those to which other compounds are added for the purpose of improving the storage characteristics at high temperatures, but are not limited thereto.

The non-aqueous electrolyte for use as an electric double layer capacitor includes, for example, propylene carbonate, ethylene carbonate, butylene carbonate, sulfolane, methylsulfolane, dioxane, dioxolan, γ-butyrolactone or a lactone derivative. , Tetrahydrofuran or a derivative thereof, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, dimethyl sulfoxide, or the like, or a mixture of two or more thereof can be used.

The electrolyte salts dissolved in the electrolyte include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium perchlorate (L
lithium salts such as iClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium imide trifluoromethanesulfonate (LiN (CF ₃ SO ₂ ) ₂ ), lithium iodide (LiI), and tetraethylammonium perchlorate [(C ₂ H ₅ ) ₄ NClO ₄ ], tetrabutylammonium perchlorate [(n-C ₄ H ₉ ) ₄ NClO ₄ ],
Alternatively, tetraethylammonium borofluoride [(C ₂
H _5), such as ₄ NBF _4] tetraalkylammonium salts, or the like can be used.

The structure of the non-aqueous electrolyte electrochemical device of the present invention can have various shapes such as a coin shape, a button shape, a sheet shape, a cylindrical shape, and a square shape.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments.

Example 1 FIG. 1 is a sectional view of a coin-type battery used in this example. 1 is a stainless steel case, 2
Is a stainless steel disc spring, 3 is a positive electrode, 4 is a negative electrode, 5 is a stainless steel sealing plate, 6 is a polypropylene insulating gasket, and 7 is a separator of the present invention. The dimensions of the battery for evaluation are 20 mm in diameter and 1.6 mm in total battery height.

As the positive electrode material, lithium cobalt oxide (LiCoO ₂ ) synthesized by firing a mixture of Li ₂ CO ₃ and Co ₃ O ₄ at 900 ° C. for 10 hours was used. This LiCoO ₂
Acetylene black 1 as a conductive agent in 100 parts by weight of powder
0 part by weight and 6 parts by weight of a fluororesin-based binder were dry-mixed, rolled and formed into a pellet to obtain a positive electrode 3.

As the negative electrode material, 28 mesophase spheres were used.
Graphitized at a high temperature of 00 ° C. (hereinafter referred to as mesophase graphite) was used. 100 parts by weight of mesophase graphite and 5 parts by weight of styrene butadiene rubber are mixed, and this mixture is suspended in an aqueous solution of carboxymethyl cellulose to form a paste, which is applied to one surface of a copper foil having a thickness of 0.02 mm,
After drying, the resultant was rolled to obtain a negative electrode 4.

The separator used was a copolymer of polymethyl vinyl ether and polyethylene oxide having a thickness of 0.025 mm, and the electrolyte contained 1 mol / mol of a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. Liter of lithium hexafluorophosphate (L
iPF ₆₎ was prepared by dissolving the. This was poured into a battery case containing the above-mentioned electrode group and then sealed. Thus, Battery A was prepared.

Example 2 A separator having a thickness of 0.02
A battery was formed in the same manner as in Example 1 except that a copolymer of 5 mm of polymethyl vinyl ether and polyvinylidene fluoride was used.

(Comparative Example) A separator having a thickness of 0.025
A battery was constructed in the same manner as in Example 1 except that polypropylene of mm was used.

The above batteries A, B, and C were prepared in ten units,
At an ambient temperature of 20 ° C., the current density is 0.5 mA / cm.
^The charge / discharge test was performed at a voltage of 4.1 V to 3.0 V. Batteries A and B exhibited the same charge / discharge characteristics as battery C of the comparative example.

An overcharge test was performed on the charged battery. This overcharge test was performed by attaching leads to both ends of the test battery and connecting both ends to an external power supply. Further, a thermocouple was attached to the negative electrode side, and the temperature was measured. The current density was set to ^2.5 mA / cm ^2, and the current continued to flow until the battery voltage reached 24 V unless an abnormality occurred in the battery. FIG. 2 shows the results of the overcharge test.

As a result, in the battery C of the comparative example, the temperature rose to near 90 ° C. after the battery surface temperature rose, whereas in the batteries A and B, the battery surface temperature reached 60 ° C.
After rising to the vicinity, the temperature dropped, and no rapid temperature rise as seen in Battery C was observed. A similar test was performed for 10 cells of each battery, and it was examined whether or not a rapid temperature rise occurred. Table 1 shows the results of these tests.

[0035]

[Table 1]

As shown in (Table 1), the battery C of the comparative example
In all the batteries, rapid temperature rise occurred in all 10 cells, but in batteries A and B, no rapid temperature rise occurred. After the measurement, the batteries A and B were disassembled, and the cross sections of the positive electrode and the negative electrode were observed. As a result, it was found that both the positive electrode plate and the negative electrode plate of A and B were significantly depleted of the electrolyte inside the electrode plates.

This is because when the separator of the battery of the present invention exceeds a certain temperature, the electrolyte absorbs the electrolyte, the electrolyte in the electrode is depleted, the polarization increases, and the movement of lithium ions between the electrode plates is increased. It is considered that this did not occur, and as a result, a rapid temperature increase did not occur. From the above, it can be seen that the safety of the battery of the present invention has been improved.

In the above embodiment, lithium cobalt oxide was used as the positive electrode material and carbon material was used as the negative electrode material. However, the present invention is not limited to these.

[0039]

As is apparent from the above description, as a separator for a non-aqueous electrolyte electrochemical device, the temperature rises and the electrolyte is absorbed when the temperature exceeds a certain temperature, that is, the operating temperature range of the electrochemical device. By using a device that interrupts the current, the separator absorbs the electrolyte even when the internal temperature of the battery rises during an abnormality such as overcharging, and as a result, the electrolyte inside the electrode is reduced. As a result of exhaustion, ions cannot move between the positive electrode and the negative electrode, and the current in the electrochemical device can be reliably shut off.

From this, it is possible to provide a non-aqueous electrolyte electrochemical device such as a lithium battery or an electric double layer capacitor in which overheating in the electrochemical device can be suppressed and the safety function operates sufficiently in the event of an abnormality. .

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a diagram showing a change in battery temperature due to an overcharge test.

[Explanation of symbols]

 3 Negative electrode 4 Positive electrode 7 Separator

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Claims (1)

[Claims] 1. A non-aqueous electrolyte electrochemical device comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator interposed between the positive electrode and the negative electrode, wherein the temperature of the separator increases when the temperature in the electrochemical device increases. A non-aqueous electrolyte electrochemical device having a property that the content of the electrolyte increases when the temperature exceeds the temperature.