JP3426903B2 - Non-aqueous electrolyte secondary battery - Google Patents

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 secondary battery provided with a PTC element having a function of interrupting a current path when an excessive current is applied. In particular, the PTC
The present invention relates to a non-aqueous electrolyte secondary battery having an improved element.

[0002]

2. Description of the Related Art In recent years, secondary batteries such as lithium secondary batteries and lithium ion secondary batteries using non-aqueous electrolytes have higher energy density than nickel-cadmium secondary batteries and nickel-hydrogen secondary batteries. Further, since it has a characteristic of showing a high voltage of 3 V or more, it has come to be widely used as a power source for portable electronic devices.

However, when such a secondary battery is charged by an excessive current and charged by an excessive voltage (hereinafter, these charges are collectively referred to as overcharge), the chemistry of the positive electrode and the negative electrode constituting the electrode group is The change or decomposition of the non-aqueous electrolyte may increase the internal pressure of the battery, which may lead to electrolyte leakage, battery rupture or ignition.

Therefore, conventionally, a safety valve mechanism for reducing the battery internal pressure to prevent the battery from bursting when the battery internal pressure rises, and a rise in the battery internal pressure are detected to cause the battery internal pressure. A current interruption mechanism for interrupting an excessive current and a PTC element for detecting an increase in battery temperature to interrupt an excessive current have been introduced.

For example, the nominal capacity is 650 mAh, 1250
In the mAh non-aqueous electrolyte secondary battery, PTC elements having direct current resistances of about 40 mΩ and 30 mΩ at 25 ° C. are used, respectively.

Although the objectives of these measures are all the same, the time, temperature, and current range until the operation is different because the operating principles of the respective mechanisms and elements are different, and these balances should be balanced. In many cases, a lot of trials and examinations are required to obtain the product, which has been a bottleneck in product development.
In addition, when the non-aqueous electrolyte secondary battery is charged with a large current of 3 C or more, the current interruption is generally performed by the PTC element. For this reason, optimization of the PTC element requires careful attention, and the shape of the PTC element is usually limited by the size of the battery, which is often extremely difficult.

On the other hand, Japanese Unexamined Patent Publication No. HEI 5-7449 of Japanese Unexamined Patent Publication No.
The claim of claim 3 is a secondary battery using a composite metal oxide containing Li and Co as main components as a positive electrode active material and a carbonaceous material as a negative electrode active material. The temperature is 140 ° C or lower, and the sensitive temperature coefficient is -10 to -13.
A secondary battery with a safety element is disclosed, which is equipped with a PTC element in the range of 0. Further, the publication describes that the use of the PTC element can prevent rupture when charged with a large current of about 2C.

[0008]

The object of the present invention is to provide a PT
By improving the C element, it is intended to provide a non-aqueous electrolyte secondary battery with improved safety against overcharging, particularly charging with an excessive current of 3 C or more.

[0009]

According to the present invention, a non-aqueous electrolytic solution comprising a positive electrode that absorbs and releases lithium ions, a negative electrode that absorbs and releases lithium ions, a non-aqueous electrolyte, and a PTC element. In the secondary battery, the PTC element has the following formula (1) when the DC resistance at 25 ° C. is R (mΩ) and the nominal capacity of the secondary battery is P (Ah).
And the operating temperature of the PTC element is 70 ° C. to 1
A non-aqueous electrolyte secondary battery is provided which is in the range of 50 ° C. 50 / P <R <167 / P (1)

According to the present invention, a bottomed cylindrical container having an opening, a positive electrode that stores and releases lithium ions stored in the container, and a lithium ion that stores and releases lithium ions stored in the container. A negative electrode, a separator arranged between the positive electrode and the negative electrode, a non-aqueous electrolyte contained in the container, and arranged in the opening of the container, PT
A non-aqueous electrolyte secondary battery comprising a sealing member having a C element, wherein the PTC element has a DC resistance at 25 ° C. of R (mΩ) and a nominal capacity of the secondary battery is P (A
h), the following expression (1) is satisfied, and the PTC
There is provided a non-aqueous electrolyte secondary battery, wherein the operating temperature of the device is in the range of 70 ° C to 150 ° C. 50 / P <R <167 / P (1)

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a cylindrical non-aqueous electrolyte secondary battery, which is an example of a non-aqueous electrolyte secondary battery according to the present invention, will be described in detail below with reference to FIG. For example, a bottomed cylindrical metal (eg, mild steel) container 1 also serving as a negative electrode terminal has a bent portion 2 formed by bending an upper end inward,
It has a step portion 3 formed below the bent portion 2 and having an inwardly projecting shape. The opening above the step 3 of the container 1 is an opening. In the container 1, an electrode group 7 made by stacking a positive electrode 4, a separator 5 and a negative electrode 6 and winding them in a spiral shape is housed. The non-aqueous electrolytic solution is contained in the container 1. Insulation plate 8
Is arranged at the bottom of the container 1 to prevent the positive electrode 4 of the electrode group 7 from electrically contacting the container 1 which also serves as the negative electrode terminal. The negative electrode 6 of the electrode group 7 and the bottom of the container 1 are connected by a negative electrode lead (not shown). The sealing member 9 which also functions as an explosion-proof mechanism and a positive electrode terminal,
For example, an insulating gasket 10 made of a synthetic resin such as polypropylene, a first lid 11 also serving as a positive electrode terminal,
A second lid 12 having an explosion-proof mechanism and a PTC element 13 are provided. The insulating gasket 10 has a bottomed cylindrical shape and has a circular hole 14 at the bottom. The PTC element 13
Is arranged between the first lid 11 and the second lid 12. The first lid body 11, the second lid body 12, and the PTC element 13 are arranged in the insulating gasket 10. Such an insulating gasket 10 is placed on the step portion 3 of the container 1, and is compressed by the bent portion 2, the opening and the step portion 3 of the container 1.
That is, the first lid 11, the second lid 12, and the PTC element 13 have the insulating gasket 10 in the space surrounded by the bent portion 2 and the step portion 3 in the container 1. It is fixed by crimping through.

The second lid 12 has a metal (for example, aluminum) plate-shaped sealing plate 15, a valve membrane 16 formed of a flexible thin film, and a metal (for example, stainless steel) reinforcing plate 17. . The dish-shaped sealing plate 15 is used for the electrode group 7
It is arranged opposite to. The valve membrane 16 is arranged on the sealing plate 15. The reinforcing plate 17 is arranged on the valve membrane 16 and is sandwiched by an annular portion 18 formed by bending the periphery of the sealing plate 15 inward. The PTC element 13 is arranged on the annular portion 18 of the sealing plate 15. The PTC element 13 is a ring-shaped PT.
Ring-shaped current collectors 20a and 20b on both sides of the C element part 19
Has a laminated structure. The first lid 11 has a hat shape and is made of metal such as stainless steel. The first lid 11 has a current collector 20 of the PTC element 13.
It is arranged so that the peripheral edge portion abuts on a. The sealing plate 1
5, the reinforcing plate 17, the PTC element 13, and the first lid body 11 have gas vent holes 21, 22, 2 respectively.
3, 24 are opened. One end of the positive electrode lead 25 is connected to the positive electrode 4 of the electrode group 7, and the other end is connected to the lower surface of the sealing plate 15 of the sealing member 11.

The positive electrode 4, negative electrode 6, separator 5, non-aqueous electrolyte and PTC element 13 will be described. 1) Positive electrode 3 As the positive electrode 3, for example, a positive electrode material that absorbs and releases lithium ions as an active material, a conductive agent and a binder are suspended in an appropriate solvent, and the suspension is applied to a positive electrode current collector. ,
It is produced by drying and pressing.

The positive electrode material is Li _x MO ₂ , provided that M
Is one or more transition metals, M is Co and / or N
It is preferable that i is satisfied, and x is 0.05 <x <1.10.
Li _x M ₂ O, a lithium composite oxide represented by
₄ , provided that M is at least one transition metal, M is preferably Mn, and x is 0.05 <x <1.10. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O
₄ , Li _x Ni _y Co _(1-y) O ₂ , where x and y are
0.05 <x <1.10 and 0 <y <1 respectively,
The complex oxide represented by

The composite oxide is, for example, lithium,
Cobalt and nickel carbonates are used as starting materials, and these carbonates are mixed according to the composition, and 600
It can be produced by firing at a temperature of from 1000 to 1000 ° C. Further, the starting material is not limited to carbonate, and hydroxide or oxide can be similarly synthesized.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
E), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and the like can be used.

As the current collector, it is preferable to use, for example, aluminum foil, stainless steel foil, or the like. 2) Structure of Negative Electrode 5 The negative electrode 5 is specifically manufactured by the following method. That is, in the negative electrode 5, a negative electrode material which absorbs and releases lithium ions as an active material and a binder are suspended in an appropriate solvent, the suspension is applied to a negative electrode current collector, dried and then pressed. It is produced by

Examples of the negative electrode material include carbonaceous materials, metallic lithium, lithium alloys, intermetallic compounds, polyacetylene, polypyrrole and the like. Examples of the carbonaceous material include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.),
Graphites (natural graphite, artificial graphite, fibrous graphite, spherical graphite, etc.), glassy carbons, organic polymer compounds (phenolic resin,
Those obtained by firing a furan resin or the like at an appropriate temperature), particularly mesophase pitch-based carbon are preferable. Among the mesophase pitch-based carbons, mesophase pitch-based carbon fibers graphitized at 2500 ° C. or higher and mesophase spherical carbon graphitized at 2500 ° C. or higher are preferable. Such a carbon fiber or a negative electrode containing spherical carbon is preferable because it has a high capacity.

The carbonaceous material has an exothermic peak at 700 ° C. or higher, more preferably at 800 ° C. or higher by differential thermal analysis, and has a (101) diffraction peak (P ₁₀₁ ) of a graphite structure (P ₁₀₁ ) determined by X-ray diffraction. The intensity ratio P ₁₀₁ / P _{100 of the} 100) diffraction peak (P ₁₀₀ ) is preferably in the range of 0.7 to 2.2. Since the negative electrode containing such a carbonaceous material can rapidly store and release lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

As the current collector, it is preferable to use, for example, copper foil, stainless steel foil, nickel foil, or the like. 3) Separator 4 The separator 4 can be formed of, for example, a synthetic resin non-woven fabric, a polyethylene porous film, a polypropylene porous film, or the like.

4) Non-Aqueous Electrolyte Solution As this non-aqueous electrolyte solution, a solution in which an electrolyte (lithium salt) is dissolved in a non-aqueous solvent is used.

Examples of the non-aqueous solvent include ethylene carbonate (EC) and propylene carbonate (PC).
Such as cyclic carbonates, for example, chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC) and diethyl carbonate (DEC), chain chains such as dimethoxyethane (DME), diethoxyethane (DEE) and ethoxymethoxyethane Ethers, cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), crown ethers, fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), sulfolane (SL). And sulfur compounds such as dimethyl sulfoxide (DMSO).
The non-aqueous solvent may be used alone or in combination of two or more. Among them, EC, DMC, DEC and M
At least one selected from EC may be used as the non-aqueous solvent. The non-aqueous electrolyte secondary battery provided with the non-aqueous electrolyte containing such a non-aqueous solvent can further improve safety during overcharge.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (Li
PF ₆ ), lithium borofluoride (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃
SO ₂ ) ₂ ] and the like.
Above all, it is preferable to use it as an electrolyte composed of LiPF ₆ and / or LiBF ₄ . The non-aqueous electrolyte secondary battery including the non-aqueous electrolyte containing such an electrolyte can further improve the safety during overcharge.

The amount of the electrolyte dissolved in the non-aqueous solvent is
It is preferably in the range of 0.1 mol / l to 3.0 mol / l. 5) PTC element 13 The PTC element 13 satisfies the following expression (1).

50 / P <R (1) where R (mΩ) is the DC resistance of the PTC element at 25 ° C. and P (Ah) is the non-aqueous electrolyte secondary battery having the PTC element. Indicates the nominal capacity of. The nominal capacity P (Ah) means the theoretical capacity of the secondary battery.

The DC resistance R (mΩ) is a resistance to a DC current. The DC resistance R (mΩ) can be measured by a 4-wire resistance measuring device. This measurement is performed by holding the PTC element in an upright state in the measuring instrument. Further, in the case of the ring-shaped PTC element 13, as shown in FIG. 2, the measurement point is set to the lower half portion on both sides of the PTC element, that is, the shaded area in FIG. A four-wire resistance measuring device manufactured by Hewlett Packard is available.
It is recommended to use the product name HP3456A or an equivalent device.

The PTC element is a Positive T
It has a thermal coefficient characteristic (PTC characteristic). An example of the relationship between the temperature and the logarithm of the DC resistance value in such a PTC element is shown in FIG. As shown in FIG. 3, the PTC element having the PTC characteristic has a low resistance value ( _RL ) until it rises to a certain constant temperature (T ₀ ).
When the temperature exceeds this temperature (T ₀ ), the resistance value rapidly increases, and when the temperature is higher than the temperature T ₁ , high resistance ( _RH ) is exhibited, and when the temperature is lowered to the previous temperature (T ₀ ), low resistance ( R _L ) means a PTC element. The temperature at which the resistance value of the PTC element reaches a resistance value (Rt) intermediate between the low resistance value ( _RL ) and the high resistance value ( _RH ) is called the operating temperature T (° C).

The operating temperature T (° C.) is preferably in the range of 70 to 150. This is due to the following reasons. When the operating temperature T is lower than 70 ° C., although the secondary battery does not generate abnormal heat, the P
There is a risk that the TC element will operate and the battery function will stop.
On the other hand, when the operating temperature T exceeds 150 ° C., it may be difficult to suppress the temperature rise and the internal pressure rise at the time of overcharging, and there is a risk of explosion or ignition. Further, even if the secondary battery is not ruptured or ignited, the secondary battery is repeatedly exposed to a high temperature each time it is overcharged, so that the positive electrode and the negative electrode are likely to be deteriorated by heat. The more preferable operating temperature T (° C) is in the range of 80 to 130.

The PTC element portion of the PTC element can be formed of, for example, ceramics or a conductive polymer having PTC characteristics. In particular, the conductive polymer is preferable from the viewpoint of avoiding damage such as cracks in the PTC element during caulking and fixing.

The PTC element portion containing such a conductive polymer is prepared, for example, by mixing an appropriate amount of conductive carbon and a polymer such as polyolefin or fluororesin that repeatedly expands and contracts due to temperature change, and cross-link them by radiation. Can be made. In such a PTC element, carbon dispersed in the polymer exhibits a low resistance by forming a conductive path in a normal state, and when the temperature becomes higher than the melting point of the polymer, the volume expansion of the polymer occurs. The conductive path due to carbon is cut off to have a high resistance, and when the temperature is lowered again, the polymer is solidified to form a conductive path due to the carbon, which has a property of showing a low resistance. PT having such a PTC element part
Examples of the C element include a PTC element manufactured by Raychem under the trade name of LTP series. The rate of change in resistance of this PTC element is in the range of 10 ⁴ to 10 ⁶ times.

The current collector of the PTC element is, for example,
It can be formed from nickel. We have 3
By analyzing the operation mechanism of the PTC element at the time of charging with a large current of C or more, P satisfying the above expression (1) is obtained.
It has been found that a non-aqueous electrolyte secondary battery equipped with a TC element can improve safety when overcharged, particularly when charged with a large current of 3 C or more.

That is, the operation mechanism of the PTC element at the time of charging with a large current of 3 C or more is as follows (a)-
It was found to have the characteristics of (d). (A) When the charging is performed, the battery temperature gradually rises at the beginning, and suddenly rises when a certain amount of charge is exceeded.

(B) The PTC element is heated by the self-heating of the energized current as well as the heat generation of the electrode group in the battery container, which causes the resistance to rise sharply.

(C) In the non-aqueous electrolyte secondary battery,
Usually, when charging with a large current, the amount of heat generated by the electrode group inside the container is overwhelmingly larger than the amount of heat generated by the PTC element. However, the heat generated by the electrode group is transmitted to the PTC element after being transmitted to various battery components such as the container.
The effect on the temperature rise of the PTC element should be smaller than self-heating.

(D) The larger the battery size, the PT
Safety should be ensured even if the C element operates slowly. From these findings, in order to quickly operate the PTC element under abnormal conditions such as overcharging, a structure is used that efficiently transmits heat generated by the electrode group in the battery container, which has been widely said in the past, to the PTC element. It has been found that it is more effective to set the structure and conditions for efficiently causing heat generation of the PTC element itself.

Since the self-heating of the PTC element is Joule heating due to ohmic loss due to the applied current,
It is considered that the element impedance has a great influence. Here, the DC resistance of the PTC element at 25 ° C. is R
Letting (mΩ) and the energizing current be I (A), the self-heating of the PTC element is expressed by the equation (I).

I ² · R (I) Further, the heat generation of the electrode group in the overcharge region is as follows, considering that the battery voltage during overcharge and the chemical reaction amount generated inside the battery due to overcharge are almost constant. ), It is proportional to the energizing current I (A).

I · K ₀ (II) Here, K ₀ is a constant for converting the energizing current into the amount of heat generation. It is considered that, of the calorific values obtained from the equations (I) and (II), the portion that is transmitted to the PTC element and causes the temperature rise of the PTC element causes the operation of the PTC element. This amount can be represented by the following formula (III).

I ² · R · K ₁ + I · K ₂ (III) where K ₁ is substantially P out of the heat generated by the above formula (I).
It is a constant for obtaining the amount of heat accumulated in the TC element.
Further, K ₂ is obtained by multiplying the constant K ₀ in the formula (II) by the heat transfer coefficient between the electrode group in the container and the PTC element.

The second term (I · K) in the equation (III)
The contribution of ₂ ) is considered to be small as described in the above feature (c). It is considered that the PTC element operates when the calorific value obtained from the equation (III) reaches a certain value, and this certain value is set as K _3, and the empirical rule described in the characteristic (d), that is, the battery is used. PTC as capacity increases
Considering that the safety can be secured even if the operation of the element is slow, this constant value K ₃ is proportional to the nominal capacity P (Ah) of the battery, and therefore the following equation (IV) is established.

I ² · R · K ₁ + I · K ₂ > K ₃ · P (IV) Further, when the charge / discharge current is displayed as a C rate, the difference in battery capacity when examining the charge / discharge characteristics of the battery Since it is not necessary to consider it, it becomes easy to study charge / discharge characteristics. From this, the C rate display is also introduced to the equation (IV).
Since 1C is a current value capable of charging and discharging the battery nominal capacity in 1 hour, 1C becomes the same value as 1P. Therefore, the above formula (IV) becomes P ² · R · K ₁ + P · K ₂ > K ₃ · P (V). In the above formula (V), the following formula (VI) can be obtained by transposing and combining the constants.

R> K / P (VI) where K is a set of constants K _{1 to} K ₃ {K =
It is a _{(K 3 -K 2) / K} 1}.

By using the PTC element satisfying the formula (VI) thus obtained, that is, the DC resistance R (mΩ) at 25 ° C. is a constant K and the battery nominal capacity P (A
The present inventors have found that by using a PTC element larger than the value obtained by dividing h), safety can be improved during overcharge, particularly during charge of 3C or more.

Further, the values of K _{1 to} K ₃ mentioned above are examined,
Moreover, by investigating the phenomenon at the time of overcharge of the secondary battery provided with the PTC element whose DC resistance R (mΩ) is K / P or less, it was found that the constant K is optimally 50. That is, when the direct current resistance R (mΩ) at 25 ° C. is set to 50 / P or less, the self-heating amount of the PTC element due to the conduction current decreases during overcharging, particularly when charging with a large current of 3 C or more, so that the PTC The time required to cut off the current by the element becomes long. For this reason, a chemical reaction due to the overcharge inside the battery progresses, the internal pressure of the battery rises as the battery temperature rises, and there is a possibility that liquid leakage or ignition from the sealing portion may occur. By making the DC resistance R (mΩ) larger than 50 / P, it is possible to promote self-heating of the PTC element during overcharging, particularly when charging at 3 C or more, so that the PTC element can be quickly operated, The current path of the secondary battery can be cut off, and excessive temperature rise and internal pressure rise can be prevented. From the viewpoint of further improving safety, the DC resistance R (mΩ) is preferably larger than 70 / P. However, the DC resistance R (mΩ)
Is 167 / P or more, there is a possibility that the voltage drop at the time of discharge due to the provision of the high resistance PTC element becomes remarkable. Such a voltage drop causes problems as described below, for example.

That is, when a non-aqueous electrolyte secondary battery equipped with a PTC element having a large direct current resistance as described above is incorporated in a portable electronic device such as a cellular phone or a personal computer and discharged with a large current (for example, 3C). The discharge voltage drops remarkably due to the PTC element. For example, when a PTC element having a resistance of 167 / P is used, the magnitude of the voltage drop is about 0.5V. When this secondary battery was discharged at 3C, the average terminal voltage was 3.
It becomes a value obtained by subtracting the above 0.5V from 5V, that is, 3V. As a result, the terminal voltage of the battery falls below the operating voltage (for example, 3 V) of the over-discharge inhibiting circuit of the portable electronic device even though the capacity of the battery still remains, so that the circuit operates. Therefore, the battery cannot be discharged despite its remaining capacity, resulting in a problem that the discharge capacity is reduced. In the portable electronic device, which is a main application of a small-sized consumer non-aqueous electrolyte secondary battery,
98% is used below C, and 80% or more is used below 1C. In addition, the operating voltage of the over-discharge inhibiting circuit incorporated in the portable electronic device is 3V.
Many are set in the vicinity. Therefore, by setting the upper limit of the DC resistance of the PTC element to 167 / P, the safety is improved while avoiding the interruption of the discharge due to being mistakenly recognized as over-discharge when discharged with a large current. be able to. In particular, the operating voltage of the overdischarge inhibition circuit is 3
It is possible to prevent the discharge capacity from decreasing due to discharge with a large current such as 3C in the portable electronic device set near V. From the viewpoint of further improving this large current discharge characteristic, it is preferable that the DC resistance R (mΩ) is smaller than 120 / P. Particularly, from the viewpoint of further improving safety while maintaining excellent large current discharge characteristics, it is preferable to use a PTC element that satisfies the following expression (2).

70 / P <R <120 / P (2) In the equation (VI), the self-heating of the PTC element contributes to the element operation at a desired ratio, as described in the step of deriving the equation. It is derived based on the assumption of. In a large non-aqueous electrolyte secondary battery for an electric vehicle having a nominal capacity of 40 Ah or more, the surface area with respect to the battery capacity is small, and when the electrode group in the container generates heat during overcharging, the heat near the center of the electrode group is released to the outside. The PTC element is not released but accumulated as it is, and the PTC element is heated by this heat. Therefore, the PTC
It is considered that the element is heated to a temperature exhibiting a high resistance before the self-heating occurs or shortly after the self-heating occurs. That is, in the large non-aqueous electrolyte secondary battery, it is considered that the contribution of the heat generation of the electrode group to the element operation is sufficiently larger than the contribution of the self-heat generation of the PTC element. In some cases, even a PTC element having a resistance lower than that of the PTC element satisfying the above-described formula (1) can ensure the safety during overcharge.

Therefore, the nominal capacity P (A
h) is preferably in the range of 0.5 to 5 Ah.
In a non-aqueous electrolyte secondary battery having a nominal capacity in such a range, the heat generation of the electrode group inside the container during overcharge is appropriately released to the outside, and the self-heat generation of the PTC element is high in the operation of the PTC element. P that satisfies the above formula (1)
High safety can be secured by using the TC element. A more preferable nominal capacity P (Ah) is 0.
It is in the range of 5 to 3 Ah.

When a laminate in which a positive electrode and a negative electrode are alternately laminated with a separator interposed therebetween is used as the electrode group, the thickness thereof is used, and as the electrode group, the positive electrode and the negative electrode are separated by a separator. In the case of using a product manufactured by spirally winding with the interposition of, a diameter of 0.
It is preferably in the range of 5 to 4 cm. Since the non-aqueous electrolyte secondary battery including the electrode group having such a thickness or diameter can appropriately release the heat generation of the electrode group at the time of overcharging, the above formula (1) is used. PT to meet
High safety can be secured by using the C element.

As described above, the non-aqueous electrolyte secondary battery according to the present invention includes the PTC element whose direct current resistance R (mΩ) at 25 ° C. satisfies the following expression (1). 50 / P <R (1) In the formula (1), P (Ah) represents the nominal capacity of the non-aqueous electrolyte secondary battery having the PTC element.

Such a secondary battery is overcharged, especially 3C.
At the time of charging as described above, the amount of self-heating of the PTC element due to this charging current can be increased.
The temperature of the device can be raised to the operating temperature in a short period of time. As a result, since the current path of the secondary battery can be interrupted by the PTC element while the temperature of the secondary battery is relatively low, it is possible to prevent excessive temperature rise and internal pressure rise. The safety can be improved.

When the PTC element satisfies the following equation (2) 50 / P <R <167 / P (2), while maintaining excellent discharge characteristics,
In particular, it is possible to improve the safety during overcharge while preventing the discharge from being interrupted due to being erroneously recognized as overdischarge when discharged with a large current.

Although the example applied to the cylindrical non-aqueous electrolyte secondary battery has been described with reference to FIG. 1 described above, the non-aqueous electrolyte secondary battery according to the present invention is also applied to a prismatic structure. be able to. An example of this is shown in FIG. For example, an electrode group 32 is housed in a bottomed rectangular tubular container 31 that also serves as a negative electrode terminal and is made of mild steel. The electrode group 32 includes the positive electrode 3
3, a laminate of the separator 34 and the negative electrode 35 is spirally wound. The electrode group 32 is housed in a basket-shaped electrode cover 36. The non-aqueous electrolytic solution is contained in the container 31. The positive electrode 33 has a structure in which the positive electrode mixture 33a, 33b is formed on both surfaces of the positive electrode current collector described above. Such a positive electrode 33 can be produced, for example, by applying a suspension containing the above-described positive electrode material on both surfaces of the current collector, drying and then pressing. On the other hand, the negative electrode 35 has a structure in which negative electrode mixtures 35a and 35b are formed on both surfaces of a negative electrode current collector. Such a negative electrode 35 can be produced, for example, by applying a suspension containing the above-described negative electrode material on both surfaces of the current collector, drying and then pressing.

A sealing body 39 made of, for example, mild steel having a circular hole 37 in the center and a rectangular pressure releasing hole 38 at a position adjacent to the hole 37 is formed by laser welding on the upper end opening of the container 31. It is attached airtightly. For example, the positive terminal pin 40 made of high chromium steel is inserted into the hole 37 of the sealing body 39 such that the upper and lower ends thereof project from the upper and lower surfaces of the sealing body 39, and is filled in the hole 37. Hermetically sealed by a glass insulating material 41. The positive terminal pin 40
Is connected to the positive electrode 33 of the electrode group 32 by a lead 42.

A rectangular thin plate 4 made of, for example, stainless steel
3 is airtightly attached to the upper surface of the sealing body 39 by laser welding so as to close the pressure release hole 38. A cut portion 44 having a straight portion and V-shaped ends thereof is formed in the thin plate 43. P
The TC element 45 is fixed to the bottom surface of the container 1 via a nickel strip connection tab 46. The PTC element 45 has a structure in which rectangular plate-shaped current collectors 48a and 48b are laminated on both surfaces of a rectangular plate-shaped PTC element part 47. For example, the rectangular plate-shaped negative electrode terminal plate 49 made of stainless steel is
The PTC element 45 is attached to the lower surface of the current collector 48b. The outer tube 50 made of a heat-shrinkable resin covers the outer peripheral surface of the container 31, the bottom edge of the container 31, and the top edge of the sealing body 39. Although the PTC element is arranged on the bottom of the container in FIG. 4 described above, it may be arranged on the side surface of the container.

[0056]

Embodiments of the present invention will now be described in detail with reference to FIG. Example 1 <Preparation of Negative Electrode> 87% by weight of MCF (mesophase carbon fiber) which is fibrous graphite, 10% by weight of conductive graphite as a conductive auxiliary agent, and a binder (1.7% by weight of styrene-butadiene rubber). Carboxymethyl cellulose (1.3% by weight) was kneaded with water as a solvent, a paste was applied to a copper foil, dried and pressed to prepare a negative electrode. <Production of Positive Electrode> On the other hand, lithium cobalt oxide (LiC
oO ₂ ) powder 97.6% by weight, acetylene black 1.
2% by weight, graphite 1.2% by weight and fluororubber 2
A positive electrode was prepared by adding a mixed solution of ethyl acetate and ethyl cellosolve to the weight% and mixing them, coating the mixture on an aluminum foil, drying and pressing.

A polyethylene porous separator was interposed between the positive electrode and the negative electrode thus obtained and spirally wound to prepare an electrode group having a diameter of 16 mm. <Production of Sealing Member> The sealing member has a ring shape as shown in FIGS. 1 and 2 described above, an outer diameter of 14.5 mm and an inner diameter of 6
A PTC element (manufactured by Raychem Co .; trade name LTP series) having a DC resistance R of 78 mΩ at 25 ° C. and an operating temperature T of 110 ° C. was prepared. In addition, 25 of PTC element
DC resistance R at ℃ is Hewlett Packard (H
Made by EWLET PACK), and the product name is HP
It was measured by a 4-wire resistance measuring instrument of 3456A. The measurement was performed with the PTC element standing upright in the measuring instrument. The measurement points were set in the lower half of both sides of the PTC element. FIG. 1 described above using the PTC element.
The sealing member having the explosion-proof mechanism and the positive electrode terminal having the structure shown in FIG. <Battery assembly> It has a cylindrical shape with a bottom and a diameter of 17 mm.
Then, the electrode group is housed in a nickel-plated mild steel container having a height of 50 mm, and a LiPF 3 solution is added to a mixed solvent of ethylene carbonate and methyl ethyl carbonate.
_A solution obtained by dissolving 1 mol / l of ₆ was stored in the container as a non-aqueous electrolytic solution. It has the structure shown in FIG. 1 described above by caulking and fixing the first lid, the PTC element, and the second lid to the opening of the container through the insulating gasket, and the nominal capacity is 650 mAh. Of 175
A 00 type cylindrical lithium ion secondary battery was manufactured. Example 2 A cylindrical lithium ion secondary battery similar to that of Example 1 was manufactured except that the DC resistance R of the PTC element was set to 100 mΩ. Comparative Example 1 A cylindrical lithium ion secondary battery similar to that of Example 1 was manufactured except that the DC resistance R of the PTC element was set to 23 mΩ. Comparative Example 2 A cylindrical lithium ion secondary battery similar to that of Example 1 was manufactured except that the DC resistance R of the PTC element was set to 41 mΩ. Comparative Example 3 A cylindrical lithium ion secondary battery similar to that of Example 1 was manufactured except that the DC resistance R of the PTC element was set to 64 mΩ.

The obtained secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were assembled and allowed to stand for 2 days, and then at a constant current of 1 C until the battery voltage reached 4.2 V. .2
After reaching V, initial charging was performed by charging at a constant voltage of 4.2 V for a total of 5 hours.

Regarding the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 which were initially charged, 3C (1.95A), 4C
When the overcharge test is carried out by performing constant current charging with each current of (2.6A) and 5C (3.25A), and the battery function is safely stopped without the appearance change due to the PTC element being activated. Is evaluated as ◯, liquid leakage from the sealing portion before the PTC element operates is evaluated as Δ, and ignition occurs before the PTC element operates as x, and the results are shown in Table 1 below. Example 3 <Preparation of Negative Electrode> 87% by weight of MCF (mesophase carbon fiber) which is a fibrous graphite, 10% by weight of conductive graphite as a conductive auxiliary agent, and a binder (1.7% by weight of styrene-butadiene rubber). Carboxymethyl cellulose (1.3% by weight) was kneaded with water as a solvent, a paste was applied to a copper foil, dried and pressed to prepare a negative electrode. <Production of Positive Electrode> On the other hand, lithium cobalt oxide (LiC
oO ₂ ) powder 97.6% by weight, acetylene black 1.
2% by weight, graphite 1.2% by weight and fluororubber 2
A positive electrode was prepared by adding a mixed solution of ethyl acetate and ethyl cellosolve to the weight% and mixing them, coating the mixture on an aluminum foil, drying and pressing.

A polyethylene porous separator was interposed between the positive electrode and the negative electrode thus obtained and spirally wound to form an electrode group having a diameter of 17 mm. <Production of Sealing Member> The sealing member has a ring shape as shown in FIGS. 1 and 2 described above, an outer diameter of 15.5 mm, an inner diameter of 7.5 mm, and a DC resistance R at 25 ° C. of 42 mΩ.
Then, a PTC element (manufactured by Raychem; trade name LTP series) having an operating temperature T of 100 ° C. was prepared. In addition, PTC
The DC resistance R at 25 ° C. of the device was measured in the same manner as described above. The PTC element was used to assemble a sealing member having an explosion-proof mechanism having the structure shown in FIG. 1 and a positive electrode terminal. <Battery assembly> Cylindrical shape with a bottom and diameter of 18 mm
Then, the electrode group and the non-aqueous electrolytic solution having the same composition as in Example 1 were housed in a nickel-plated mild steel container having a height of 65 mm. It has the structure shown in FIG. 1 described above by caulking and fixing the first lid, the PTC element, and the second lid in the opening of the container, and the nominal capacity is 1250 mAh. Of 1
An 8650 type cylindrical lithium ion secondary battery was manufactured. Example 4 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 57 mΩ. Example 5 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 78 mΩ. Example 6 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 90 mΩ. Comparative Example 4 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 12 mΩ. Comparative Example 5 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 31 mΩ.

The secondary batteries of Examples 3 to 6 and Comparative Examples 4 to 5 thus obtained were assembled and left to stand for 2 days, and then initially charged in the same manner as described above. Regarding the secondary batteries of Examples 3 to 6 and Comparative Examples 4 to 5 that were initially charged,
3C (3.75A), 4C (5A), 5C (6.25)
When the overcharge test is performed by performing constant current charging with each current of A), and the battery function is safely stopped without the appearance change due to the PTC element operating, ◯, before the PTC element operating. △, PTC when leakage occurs from the sealing part
The case where the element was ignited before operating was evaluated as x, and the results are shown in Table 2 below.

[0062]

[Table 1]

[0063]

[Table 2]

Here, the DC resistance R (mΩ) at 25 ° C. of the PTC elements of the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 described above will be examined. The nominal capacity P of these secondary batteries is 0.65 Ah. Therefore, in the secondary battery, the DC resistance R at 25 ° C. of the PTC element is 50 /
If it is larger than 0.65, that is, 76.9 mΩ, the safety at the time of overcharge can be improved. As is apparent from Table 1, the secondary batteries of Examples 1 and 2 having a PTC element having a DC resistance R of greater than 76.9 mΩ, that is, the above-described formula (1), R> 50 / P, were 3C. It can be seen that safety can be secured during charging with the above-mentioned excessive current. On the other hand, the secondary batteries of Comparative Examples 1 to 3 provided with the PTC element having the DC resistance R of 76.9 mΩ or less, that is, the DC resistance R of 50 / P (mΩ) or less, are
It can be seen that liquid leakage from the sealing part and ignition occur before the element operates.

The DC resistance R (mΩ) at 25 ° C. of the PTC elements of the secondary batteries of Examples 3 to 6 and Comparative Examples 4 to 5 described above will be examined. The nominal capacity P of these secondary batteries is 1.25 Ah. Therefore, in the secondary battery, the DC resistance R at 25 ° C. of the PTC element is 50 /
If it is larger than 1.25, that is, 40 mΩ, the safety during overcharge can be improved. As is clear from Table 2, the secondary batteries of Examples 3 to 6 provided with the PTC element having the DC resistance R larger than 40 mΩ, that is, the expression (1), R> 50 / P, were 3C or more. It can be seen that safety can be secured when overcharging with an excessive current. On the other hand, Comparative Examples 4 to 4 provided with a PTC element having a DC resistance R of 40 mΩ or less, that is, the DC resistance of 50 / P (mΩ) or less.
It can be seen that the secondary battery of No. 5 causes liquid leakage from the sealing portion and ignition before the PTC element operates during the overcharge.

Therefore, from Tables 1 and 2, if the non-aqueous electrolyte secondary battery is equipped with the PTC element satisfying the above-mentioned formula (1), it can be charged with an excessive current of 3 C or more in any battery size. You can see that it is possible to avoid rupture and ignition. Example 7 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 130 mΩ. Example 8 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 152 mΩ. Example 9 A cylindrical lithium ion secondary battery similar to that of Example 3 was manufactured except that the DC resistance R of the PTC element was set to 185 mΩ.

Regarding the obtained secondary batteries of Examples 7 to 9 and the secondary batteries of Examples 4 and 6, the overdischarge inhibiting circuit was 3
Built in a portable electronic device set to V, 3C (375
The discharge capacity when discharged at 0 mA) was measured, and the results are shown in Table 3 below.

[0068]

[Table 3]

As is clear from Table 3, the DC resistance R at 25 ° C. is smaller than 167 / P (mΩ), that is, 133.6 calculated by substituting P = 1.25 Ah into this formula.
It can be seen that the secondary batteries of Examples 4, 6 and 7 including the PTC element having a size smaller than mΩ have high average discharge voltage and discharge capacity at 3C discharge. On the other hand, the DC resistance is 167 / P
In the secondary batteries of Examples 8 to 9 equipped with PTC elements of (mΩ) or more, the average discharge voltage during 3C discharge is below 3V which is the operating voltage of the overdischarge prohibition circuit, and the overdischarge prohibition circuit is in the final stage of discharge. It can be seen that the discharge capacity is reduced as compared with Examples 4, 6 and 7 because it operates in the above manner. Therefore, from Tables 2 and 3, the secondary batteries of Examples 3 to 7 equipped with the PTC element satisfying 50 / P <R <167 / P were mistakenly recognized as over-discharge when discharged with a large current, It can be seen that the safety at the time of overcharging can be improved while preventing the discharge capacity from decreasing.

[0070]

As described in detail above, according to the non-aqueous electrolyte secondary battery of the present invention, the direct current resistance R (mΩ) at 25 ° C.
By including the PTC element satisfying the expression 50 / P <R, a remarkable effect such as rupture and ignition at the time of overcharging, particularly charging with an excessive current of 3 C or more, can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a plan view for explaining a method for measuring DC resistance at 25 ° C. of a PTC element incorporated in the non-aqueous electrolyte secondary battery according to the present invention.

FIG. 3 is a characteristic diagram showing an example of the relationship between temperature and DC resistance (logarithm) in a PTC element incorporated in the non-aqueous electrolyte secondary battery according to the present invention.

FIG. 4 is a sectional view showing an example of a non-aqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

1 ... Container, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 9 ...
Sealing member, 13 ... PTC element.

Claims (10)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode that absorbs and releases lithium ions, a negative electrode that absorbs and releases lithium ions, a non-aqueous electrolyte solution, and a PTC element. The element has a DC resistance of R (m
Ω) and the nominal capacity of the secondary battery is P (Ah), the following expression (1) is satisfied and the PTC element operates.
The temperature is within a range of 70 ° C. to 150 ° C. A non-aqueous electrolyte secondary battery. 50 / P <R <167 / P (1) 2. A bottomed cylindrical container having an opening, a positive electrode that stores and releases lithium ions stored in the container, and a negative electrode that stores and releases lithium ions stored in the container. Non-aqueous electrolysis including a separator disposed between the positive electrode and the negative electrode, a non-aqueous electrolytic solution housed in the container, and a sealing member having a PTC element, which is disposed in the opening of the container. A liquid secondary battery, wherein the PTC element has a DC resistance of R (m
Ω) and the nominal capacity of the secondary battery is P (Ah), the following expression (1) is satisfied and the PTC element operates.
The temperature is within a range of 70 ° C. to 150 ° C. A non-aqueous electrolyte secondary battery. 50 / P <R <167 / P (1) 3. The sealing member has a first lid that also serves as a terminal, and a second lid, and the PTC element is the first lid.
The non-aqueous electrolyte secondary battery according to claim 2, wherein the non-aqueous electrolyte secondary battery is arranged between the lid and the second lid. Wherein said PTC element is a non-aqueous electrolyte of the following formula (3) 70 / P <R <120 / P (3) satisfies that claim 1-3 or 1, wherein said two Next battery. 5. The operating temperature is in the range of 80 ° C. to 130 ° C.
Claim 1-4 nonaqueous electrolyte secondary battery according to any one of which is a囲内. 6. The nominal capacity P is 0.5 Ah to 5 Ah.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 , wherein the non-aqueous electrolyte secondary battery is within the range . 7. The positive electrode comprises Li _x MO ₂ (where M is 1
More than one kind of transition metal, x is 0.05 <x <1.1
Li _x M ₂ O ₄ and a lithium composite oxide represented by
(However, M is one or more transition metals, and x is 0.05
<X <1.1) and a lithium composite oxide
The non-aqueous electrolyte secondary battery according to claim 1 , comprising at least one oxide selected from the group consisting of : 8. The negative electrode is mesophase pitch carbon.
Claim 1-6 nonaqueous electrolyte secondary battery according to any one of which comprises a pledge. 9. The non-aqueous electrolytic solution comprises a non-aqueous solvent and the non-aqueous solvent.
An electrolyte dissolved in a water solvent, the non-aqueous solvent,
Ethylene carbonate, propylene carbonate, dime
Chill carbonate, methyl ethyl carbonate, diet
Carbonate, dimethoxyethane, diethoxyethane
Amine, tetrahydrofuran, 2-methyltetrahydrofuran
, Γ-butyrolactone, acetonitrile, sulfolane
And at least one selected from dimethyl sulfoxide
Claim 1-6 nonaqueous electrolyte secondary battery according to any one of which comprises a solvent like. 10. The electrolyte is LiClO ₄ , LiP
F ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ and
At least 1 selected from [LiN (CF ₃ SO ₂ ) ₂ ]
The non-aqueous electrolyte secondary battery according to claim 9, comprising a compound of a kind .