JP2002025623A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a decrease in discharge capacity by suppressing an increase in internal pressure of a battery and a reaction of a nonaqueous electrolytic solution with a positive electrode in cases where the lithium battery is exposed to a high-temperature environment condition such as in a reflow furnace in which the lithium battery is placed for automatic soldering. SOLUTION: This lithium battery is equipped with the positive electrode 1, a negative electrode 2, a separator 3 for separating the positive electrode from the negative electrode, and the nonaqueous electrolytic solution, housed in a battery container 4. An endoergic agent made of a material different from the separator, with a melting point ranging from 100 to 210 deg.C and heat of melting being 16 cal/g or more, is put as an additive into the battery container.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a battery container,
The present invention relates to a lithium battery including a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte. In the case where the lithium battery is put into a reflow furnace and automatic soldering is performed, the lithium battery is used. It is characterized in that the discharge capacity is prevented from lowering even when exposed to high-temperature environmental conditions.

[0002]

2. Description of the Related Art In recent years, as one of new batteries having a high output and a high energy density, a high electromotive force lithium battery utilizing oxidation and reduction of lithium by using a non-aqueous electrolyte has been used. In addition, since such a lithium battery uses a non-aqueous electrolyte as described above, it is assumed that the positive electrode and the negative electrode rarely react during storage to generate hydrogen or oxygen, and are used for emergency purposes such as memory backup. Has come to be used as a power source.

Here, as such a lithium battery, a battery provided with a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte in a battery container is generally used. .

When such a lithium battery is used as an emergency power supply for memory backup or the like, the lithium battery is put into a reflow furnace, and lead terminals of the lithium battery are automatically soldered to a printed circuit board. Have been tried to.

Here, when the lithium battery is placed in a reflow furnace and the lead terminals of the lithium battery are automatically soldered to a printed circuit board as described above, the lithium battery is exposed to a high temperature in the reflow furnace.
It is left for about 10 seconds under the high temperature condition.

However, as described above, a lithium battery has a capacity of 250
When left at high temperature of about 10 ° C. for about 10 seconds, the non-aqueous electrolyte in the battery container of this lithium battery evaporates and the internal pressure of the battery increases, or the non-aqueous electrolyte and the positive electrode mainly in the battery container. And thereby caused a problem that the discharge capacity of the lithium battery was significantly reduced.

For this reason, in recent years, Japanese Patent Application Laid-Open
As shown in JP-A-40525, when using a sulfolane having a high boiling point as a solvent for a non-aqueous electrolyte and placing it in a reflow furnace for automatic soldering, the non-aqueous electrolyte vaporizes and the internal pressure of the battery rises. It has been proposed to prevent this from happening.

However, even when sulfolane having a high boiling point is used as the solvent of the non-aqueous electrolyte, the reaction between the non-aqueous electrolyte and the positive electrode or the like cannot be suppressed at a high temperature. There is a problem that the discharge capacity of the P.I.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a lithium battery including a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte in a battery container. When the lithium battery is exposed to high-temperature environmental conditions, such as when a lithium battery is placed in a reflow furnace and automatically soldered, the internal pressure of the battery rises or becomes non- It is an object of the present invention to suppress a reaction between a water electrolyte and a positive electrode, thereby preventing a discharge capacity from decreasing.

[0010]

According to the present invention, in order to solve the above-mentioned problems, a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, a non-aqueous electrolyte, In the lithium battery provided with the above, a heat absorbing agent made of a material different from that of the separator having a melting point in the range of 100 to 210 ° C. and a heat of fusion of 16 cal / g or more is added to the battery container.

As in the lithium battery according to the present invention, when a heat absorbing agent made of a material different from the separator having a melting point in the range of 100 to 210 ° C. and a heat of fusion of 16 cal / g or more is added to the battery container. Just like putting a lithium battery in a reflow oven for automatic soldering,
When exposed to high-temperature environmental conditions, the above-described heat absorbing agent in the battery container takes away heat and melts, suppressing the rise in the temperature of the lithium battery, evaporating the non-aqueous electrolyte, and reducing the internal pressure of the battery. The battery is prevented from rising and reacting between the non-aqueous electrolyte and the positive electrode in the battery container, so that the discharge capacity of the lithium battery is prevented from lowering.

Here, as the heat absorbing agent, one having a melting point in the range of 100 to 210 ° C. as described above is used. When dissolved in a non-aqueous electrolyte and exposed to high-temperature environmental conditions, the increase in the temperature of the lithium battery cannot be sufficiently suppressed. When placed in a reflow oven for automatic soldering, this heat absorbing agent is difficult to melt,
This is because the increase in the temperature of the lithium battery cannot be sufficiently suppressed.

The heat absorbing agent having a heat of fusion of 16 cal / g or more is used as described above.
If the heat of fusion is low, the amount of heat taken when the heat absorbing agent is melted is small, and it is not possible to sufficiently suppress the temperature of the lithium battery from rising.

Examples of such a heat absorbing agent include 2,3-dimethylnaphthalene, 2,6-dimethylnaphthalene, p-diiodobenzene, α-α′-dichloro-p-xylene, bicyclooctane, -Methylheptane, fluorene, pyrene, fluoranthene, 1,2-benzanthracene, 3,4-benzopyrene, o-phenylenepyrene, hexamethylbenzene, polyvinyl fluoride, silver nitrate, potassium thiocyanate, lithium and the like can be used. Preferably, 2,3-dimethylnaphthalene, 2,6-dimethylnaphthalene, fluorene, hexamethylbenzene, polyvinyl fluoride, silver nitrate is used, and more preferably, 2,3-dimethylnaphthalene, 2,6-dimethylnaphthalene, Dimethyl naphthalene, polyvinyl fluoride,
Use silver nitrate.

In addition, when such a heat absorbing agent is added to the battery container, if the amount is small, it is possible to sufficiently prevent the temperature of the lithium battery from rising when the lithium battery is exposed to high-temperature environmental conditions. On the other hand, if the amount is too large, the amount of the electrode material and the like in the battery container decreases, so that the amount of the electrode material is 0.1% with respect to the entire lithium battery.
It is preferable to add in the range of 02 to 3% by weight.

In addition, when the heat absorbing agent is added to the battery container, the heat absorbing agent is used to suppress the reaction between the nonaqueous electrolyte and the positive electrode when the lithium battery is exposed to high-temperature environmental conditions. It is preferable to add it between the positive electrode and the separator.

The lithium secondary battery according to the present invention is characterized in that the heat absorbing agent is added to the battery container as described above, and the type of solvent and solute used for the non-aqueous electrolyte, The materials used for the positive electrode and the negative electrode are not particularly limited, and those generally used in conventional lithium batteries can be used.

The solvent used in the non-aqueous electrolyte is, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, vinylene carbonate, γ-butyrolactone, sulfolane, 1,2-
Dimethoxyethane, 1,2-diethoxyethane, 1,2
Ethoxymethoxyethane, tetrahydrofuran, 1,
Solvents such as 3-dioxolan, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used alone or in combination of two or more.

The solute used for the non-aqueous electrolyte is as follows:
For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li
_{SbF 6, LiBiF 4, LiAlF 4} , LiGa
F ₄ , LiInF ₄ , LiClO ₄ , LiCF ₃ S
O ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ S
A lithium compound such as O ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ can be used. In order to further improve the cycle characteristics of the lithium secondary battery, LiPF ₆ ,
LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ S
O ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF
₃ SO ₂ ) ₃ , more preferably Li
CF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C
₂ F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ are used.

Further, in the lithium battery according to the present invention,
As the positive electrode material constituting the positive electrode, for example, manganese dioxide, vanadium pentoxide, niobium oxide, lithium cobaltate, lithium nickelate, spinel manganese, and the like can be used.In particular, boron or a boron compound is dissolved. When the boron-containing lithium-manganese composite oxide is used, a lithium battery exhibiting excellent charge / discharge cycle characteristics can be obtained.

Further, in the lithium battery of the present invention,
As the negative electrode material constituting the negative electrode, for example, metallic lithium, Li-Al, Li-In, Li-Sn, Li-
Pb, Li-Bi, Li-Ga, Li-Sr, Li-S
i, Li-Zn, Li-Cd, Li-Ca, Li-Ba
And carbon materials such as graphite, coke, and organic fired bodies capable of occluding and releasing lithium ions. Particularly, when a Li-Al alloy is used, excellent ion conduction on the negative electrode can be achieved. Thus, a lithium battery exhibiting excellent discharge characteristics can be obtained.

[0022]

EXAMPLES Hereinafter, the lithium battery according to the present invention will be described in detail with reference to examples, and the discharge capacity of the lithium battery in this example will decrease even when exposed to high-temperature environmental conditions. The fact that this is prevented will be described with reference to comparative examples. It should be noted that the lithium battery according to the present invention is not limited to those shown in the following examples, but can be implemented by appropriately changing the scope of the invention without changing its gist.

(Examples 1 to 19) In Examples 1 to 19, a positive electrode and a negative electrode were prepared as described below, and a non-aqueous electrolyte was prepared as described below. A flat coin-shaped lithium secondary battery was manufactured.

[Preparation of Positive Electrode] In preparing the positive electrode, lithium hydroxide LiOH, boron oxide B ₂ O _3, and manganese dioxide MnO ₂ were mixed at an atomic ratio of Li: B: Mn of 0.53: 0.06. : 1.00, and heat-treat this mixture in air at 375 ° C. for 20 hours, and then pulverize the powder to obtain a boron-containing lithium-manganese composite oxide powder used as a positive electrode active material. Obtained.

Then, the boron-containing lithium-manganese composite oxide powder, the carbon black powder as the conductive agent, and the fluororesin powder as the binder are mixed in a weight ratio of 85: 10: 5. A positive electrode mixture was obtained.

Next, the positive electrode mixture was molded into a disk-shaped mold, and dried in a vacuum at 250 ° C. for 2 hours to obtain a positive electrode.

[Preparation of Negative Electrode] In preparing the negative electrode, a lithium-aluminum (Li-Al) alloy was punched into a disk to obtain a negative electrode.

[Preparation of Non-Aqueous Electrolyte] A mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) in a volume ratio of 1: 1 was mixed with lithium trifluoromethanesulfonimide as a solute. LiN
(CF ₃ SO ₂ ) ₂ was dissolved at a concentration of 1 mol / liter to prepare a non-aqueous electrolyte.

[Preparation of Battery] In preparing a battery, as shown in FIG. 1, the positive electrode 1 was attached to a positive electrode current collector 5 made of a stainless steel plate (SUS316), while the negative electrode 2 was attached to a stainless steel plate. Attached to the negative electrode current collector 6 made of (SUS304), the separator 3 made of a microporous film made of polypropylene is impregnated with the above nonaqueous electrolytic solution, and the separator 3 is interposed between the above positive electrode 1 and the above negative electrode 2. In addition, in Examples 1 to 19,
Different types of heat absorbing agents were added between the separator 3 and the positive electrode 1.

Then, these are mixed with a positive electrode can 4a and a negative electrode can 4b.
And a positive electrode current collector 5
The positive electrode 1 is connected to the positive electrode can 4a via the negative electrode current collector 6, while the negative electrode 2 is connected to the negative electrode can 4b via the negative electrode current collector 6, and the positive electrode can 4a and the negative electrode can 4b are electrically insulated by the insulating packing 7. Thus, a lithium secondary battery having an outer diameter of 24 mm, a thickness of 3 mm, and a total weight of 4.0 g was produced. The internal resistance before charging and discharging of this lithium secondary battery was about 10Ω.

In order to add the heat absorbing agent between the separator 3 and the positive electrode 1 as described above, as shown in Table 1 below, in Example 1, the melting point was 104 ° C. and the heat of fusion was 3
In Example 2, 8 cal / g of 2,3-dimethylnaphthalene was used, and in Example 2, a melting point of 110 ° C. and a heat of fusion of 38 cal / g of 2,6-dimethylnaphthalene were used.
Dimethylnaphthalene, p-diiodobenzene having a melting point of 129 ° C. and a heat of fusion of 16 cal / g in Example 3, and α-α ′ having a melting point of 100 ° C. and a heat of fusion of 32 cal / g in Example 4.
-Dichloro-p-xylene, melting point 174 in Example 5
C., bicyclooctane having a heat of fusion of 18 cal / g, 4-methylheptane having a melting point of 121 ° C. and a heat of fusion of 22 cal / g in Example 6, and 114 ° C. and a heat of fusion of 2 in Example 7.
8 cal / g fluorene, melting point 151 in Example 8
C., pyrene with a heat of fusion of 20 cal / g, Example 9 used fluoranthene with a melting point of 107 ° C. and heat of fusion of 22 cal / g, and Example 10 used fluoranthene with a melting point of 161 ° C. and heat of fusion of 22 cal / g.
g of 1,2-benzanthracene, a melting point of 181 ° C. and a heat of fusion of 16 cal / g 3,4-benzopyrene in Example 11, and a melting point of 162 ° C. and a heat of fusion of 18 ca in Example 12.
1 / g of o-phenylenepyrene, Example 13 with hexamethylbenzene having a melting point of 164 ° C. and a heat of fusion of 30 cal / g, and Example 14 having a melting point of 197 ° C. and a heat of fusion of 39 cal.
/ G of polyvinyl fluoride in Example 15 with a melting point of 210
C., silver nitrate having a heat of fusion of 16 cal / g, a melting point of 179 ° C., potassium thiocyanate having a heat of fusion of 23 cal / g in Example 16, and a melting point of 180 ° C., heat of fusion of 101 in Example 17.
Cal / g of lithium was added in an amount of 0.04 g corresponding to 1% by weight of the total weight of the lithium secondary battery of 4.0 g.

(Comparative Example 1) In Comparative Example 1, the heat absorbing agent was not added in the production of the batteries in Examples 1 to 19, and otherwise,
In the same manner as in the case of No. 19, a lithium secondary battery was produced. The internal resistance of the lithium secondary battery before charging and discharging was about 10Ω.

Comparative Example 2 In Comparative Example 2, sulfolane (SL) was used as the solvent in the preparation of the non-aqueous electrolyte in Examples 1 to 19, and no heat absorbing agent was added in the production of the battery. Otherwise,
A lithium secondary battery was manufactured in the same manner as in Examples 1 to 19 described above. The internal resistance of the lithium secondary battery before charging and discharging was about 10Ω.

(Comparative Examples 3 to 10) In Comparative Examples 3 to 10, in the production of the batteries in Examples 1 to 19, the melting point of the heat absorbing agent added between the separator 3 and the positive electrode 1 was 100 to 100. In the range of 210 ° C and heat of fusion of 1
A material that does not satisfy the condition of 6 cal / g or more is used.
As shown in Table 1 below, Comparative Example 3 had a melting point of 181 ° C.
In Comparative Example 4, 1,2-benzopyrene having a heat of fusion of 15 cal / g was used.
2,3,3-tetramethylbutane, iodoform having a melting point of 125 ° C. and a heat of fusion of 9 cal / g in Comparative Example 5, polyisoprene having a melting point of 74 ° C. and a heat of fusion of 45 cal / g in Comparative Example 6, and Comparative Example 7 Melting point 239 ° C, heat of fusion 19 ca
1 / g of polystyrene, Comparative Example 8 was a polyethylene oxide having a melting point of 66 ° C. and a heat of fusion of 45 cal / g, Comparative Example 9 was polyacrylonitrile having a melting point of 317 ° C. and a heat of fusion of 23 cal / g, and Comparative Example 10 was a melting point of 156 ° C. And 0.04 g of indium having a heat of fusion of 6 cal / g, which is 1% by weight of the total weight of the lithium secondary battery of 4.0 g.

Other than that, the above Examples 1 to 1
In the same manner as in the case of No. 9, each lithium secondary battery of Comparative Examples 3 to 10 was produced. The internal resistance of each of the lithium secondary batteries before charging and discharging was about 10Ω.

Next, Example 1 manufactured as described above was used.
And each of the lithium secondary batteries of Comparative Examples 1 to 10 before heating in a reflow furnace,
After heating at 250 ° C. for 10 seconds in a reflow furnace, a discharge capacity of 10 V was discharged at a discharge current of 10 mA to a discharge end voltage of 2.0 V, and the discharge capacity Qo before heating in the reflow furnace was measured at 250 ° C. The discharge capacity Qa after heating for 10 seconds was measured, and the ratio of the discharge capacity Qa after heating to the discharge capacity Qo before heating in the reflow furnace (capacity remaining rate) (Qa / Qo) × 100 (%) was calculated. And the results are shown in Table 1 below.

[0037]

[Table 1]

As is apparent from the results, the melting point between the separator 3 and the positive electrode 1 is in the range of 100 to 210 ° C.
Each of the lithium secondary batteries of Examples 1 to 19 in which a heat absorbing agent having a heat of fusion of 16 cal / g or more was added at 1% by weight based on the total weight of the lithium secondary battery of 4.0 g, the heat absorbing agent was added. Each of the lithium secondary batteries of Comparative Examples 1 and 2 and the heat absorbing agent whose melting point is in the range of 100 to 210 ° C. and whose heat of fusion does not satisfy 16 cal / g or more were added to the total weight of the lithium secondary batteries 4.0 g. Comparative Examples 3 to 10 in which 1% by weight was added
The residual capacity ratio was improved as compared with each of the lithium secondary batteries.

When the lithium secondary batteries of Examples 1 to 19 were compared, the lithium secondary battery of Example 1 using 2,3-dimethylnaphthalene as the heat absorbing agent, and 2,6-dimethylnaphthalene were used. The lithium secondary battery of Example 2,
The lithium secondary battery of Example 7 using fluorene, the lithium secondary battery of Example 13 using hexamethylbenzene, the lithium secondary battery of Example 14 using polyvinyl fluoride, and Example 15 using silver nitrate. In the lithium secondary batteries of the above, the remaining capacity ratio is a high value of 70% or more. In particular, in each of the lithium secondary batteries of Examples 1, 2, 14, and 15, the remaining capacity ratio is 75%. % Or higher.

(Examples A1 to A6) In Examples A1 to A6, in the production of the batteries in the above Examples 1 to 19, as in the case of the above Example 1, the separator 3 was used.
2,3-dimethylnaphthalene is added as a heat absorbing agent between the positive electrode 1 and the positive electrode 1, and the amount of 2,3-dimethylnaphthalene added is 4.0, based on the total weight of the lithium secondary battery.
As shown in Table 2 below, 0.02% by weight in Example A1, 0.1% by weight in Example A2, 0.5% by weight in Example A3, and 2% by weight in Example A4 with respect to g. %, 3% by weight in Example A5, and 5% by weight in Example A6.

Other than the above, Examples 1 to 1
In the same manner as in the case of No. 9, the lithium secondary batteries of Examples A1 to A6 were produced. The internal resistance of each of the lithium secondary batteries before charging and discharging was about 10Ω.

Next, the embodiment A1 manufactured in this manner was used.
Similarly, the discharge capacity Qo before heating in the reflow furnace and the discharge capacity Qo at 250 ° C. The discharge capacity Qa after heating for 2 seconds was measured, and the remaining capacity rate (Qa / Qo) × 100 was measured.
(%) Was determined, and the results are shown in Table 2 below together with the results of Example 1 described above.

[0043]

[Table 2]

As is apparent from the results, when the amount of the heat-absorbing agent 2,3-dimethylnaphthalene to be added is 0.02% by weight or more based on the total weight of the lithium secondary battery, the residual capacity ratio becomes 70%. %, And when the addition amount was 0.5% by weight or more, the residual capacity ratio showed a very high value of 90% or more. In Examples A5 and A6 in which the addition amount was 3% by weight and 5% by weight, the residual capacity ratio was 98%, and the addition amount was 3%.
Even when the amount was more than the weight%, the residual capacity ratio hardly changed. In this case, if a large amount of the heat absorbing agent is added, the amount of the electrode material and the like in the battery container is relatively reduced. Therefore, it is preferable to set the amount of the heat absorbing agent to 3% by weight or less.

(Examples B1 to B5)
In the above, the non-aqueous electrolyte solution in the above Examples 1 to 19
In preparation, the type of solute used for the non-aqueous electrolyte was changed.
As shown in Table 3 below, in Example B1,
Lithium xafluorophosphate LiPF₆In Example B2
In the case of lithium tetrafluoroborate LiBF
_FourIn Example B3, trifluoromethanesulfo
Lithium phosphate LiCF_ThreeSO_ThreeIn Example B4
Is lithium pentafluoroethanesulfonimide Li
N (C_TwoF_FiveSO _Two)_TwoIn Example B5,
Trifluoromethanesulfonic acid methide LiC (CF
_ThreeSO_Two)_ThreeWas used.

Then, the above solute was treated with propylene carbonate (PC) and 1,2-dimethoxyethane (DME).
And 1 at a volume ratio of 1: 1.
Each non-aqueous electrolyte was dissolved by dissolving to a concentration of mol / liter.

Then, as in Example 1, except that each non-aqueous electrolyte prepared as described above was used, 2,3-dimethylnaphthalene was placed between the separator 3 and the positive electrode 1 as a heat absorbing agent. To the total weight of the lithium secondary battery
By weight percent, the respective lithium secondary batteries of Examples B1 to B5 were produced. The internal resistance of each of the lithium secondary batteries before charging and discharging was about 10Ω.

Next, the embodiment B1 produced in this manner was used.
-B5, the discharge capacity Qo before heating in the reflow furnace and the discharge capacity Qo before heating at 250 ° C. in the reflow furnace in the same manner as in Examples 1-19 and Comparative Examples 1-10. The discharge capacity Qa after heating for 2 seconds was measured, and the remaining capacity rate (Qa / Qo) × 100 was measured.
(%) Was determined, and the results are shown in Table 3 below together with the results of Example 1 described above.

[0049]

[Table 3]

As is apparent from the results, LiPF ₆ , LiBF ₄ and LiCF ₃ S are used as solutes in the non-aqueous electrolyte.
O ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ S
In both cases of using O ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ , the residual capacity ratio shows a high value of 80% or more, and in particular, LiCF ₃ SO ₃ and LiN (CF ₃ SO 2)
₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃
In the lithium secondary batteries of Examples 1 and B3 to B5 using SO ₂ ) ₃ , the residual capacity ratio showed a very high value of 90% or more.

(Examples C1 to C12) Examples C1 to C1
In Example 2, in the preparation of the non-aqueous electrolyte in Examples 1 to 19, the type of the solvent used for the non-aqueous electrolyte was changed, and as shown in Table 4 below, in Example C1, ethylene carbonate ( EC) and 1,2-dimethoxyethane (DME) were mixed at a volume ratio of 1: 1. In Example C2, 1,2-butylene carbonate (BC) and 1,2-dimethoxyethane (DME) were mixed. DME)
Was mixed in a 1: 1 volume ratio with Example C.
In No. 3, vinylene carbonate (VC) and 1,2-
In Example C4, a mixed solvent in which dimethoxyethane (DME) was mixed at a volume ratio of 1: 1 was mixed with γ-butyrolactone (γ-BL) and 1,2-dimethoxyethane (DM
E) in a 1: 1 volume ratio, and in Example C5 a mixture of sulfolane (SL) and 1,2-dimethoxyethane (DME) in a 1: 1 volume ratio. In Example C6, a solvent obtained by mixing propylene carbonate (PC) and 1,2-diethoxyethane (DEE) in a volume ratio of 1: 1 was used as a solvent in Example C6.
In the above, propylene carbonate (PC) and 1,2-
In Example C8, a mixed solvent in which ethoxymethoxyethane (EME) was mixed at a volume ratio of 1: 1 was mixed with propylene carbonate (PC) and tetrahydrofuran (TH
F) and a mixed solvent obtained by mixing propylene carbonate (PC) and 1,3-dioxolane (DOXL) in a volume ratio of 1: 1 in Example C9. In Example C10, a mixed solvent obtained by mixing propylene carbonate (PC) and dimethyl carbonate (DMC) at a volume ratio of 1: 1 was used. In Example C11, propylene carbonate (PC) and diethyl carbonate (DEC) were used. ) And 1: 1
In Example C12, a mixed solvent obtained by mixing propylene carbonate (PC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 1 was used.

Then, lithium trifluoromethanesulfonimide Li
N (CF ₃ SO ₂ ) ₂ was dissolved to a concentration of 1 mol / liter to prepare each non-aqueous electrolyte.

Then, in the same manner as in Example 1 except that each non-aqueous electrolyte prepared as described above was used, 2,3-dimethylnaphthalene was placed between the separator 3 and the positive electrode 1 as a heat absorbing agent. To the total weight of the lithium secondary battery
By weight percent, each of the lithium secondary batteries of Examples C1 to C11 was produced. The internal resistance of each of the lithium secondary batteries before charging and discharging was about 10Ω.

Next, the example C1 produced in this manner was used.
-C12, the discharge capacity Qo before heating in the reflow furnace and the discharge capacity Qo before heating at 250 ° C. in the reflow furnace in the same manner as in Examples 1 to 19 and Comparative Examples 1 to 10 above. The discharge capacity Qa after heating for 2 seconds was measured, and the remaining capacity rate (Qa / Qo) × 10
0 (%) was determined, and the results are shown in Table 4 below together with the results of Example 1 described above.

[0055]

[Table 4]

As is apparent from the results, even when each of the above-mentioned mixed solvents was used as the solvent of the non-aqueous electrolyte, the residual capacity ratio was as high as 73% or more.

PC and DM are used as the solvent of the non-aqueous electrolyte.
E, EC and DME, BC and DME, VC and DME, γ-
BL and DME, SL and DME, PC and DEE, PC and E
In the lithium secondary batteries of Examples 1 and C1 to C9 using each of the mixed solvents of ME, PC and THF, and PC and DOXL, the residual capacity ratio showed a high value of 80% or more.
C and DME, EC and DME, BC and DME, PC and DE
Example 1, C using each mixed solvent of E, PC and EME
In the lithium secondary batteries of 1, C2, C6 and C7,
The residual capacity ratio showed a very high value of 90% or more.

[0058]

As described in detail above, in the lithium battery according to the present invention, the melting point is 100
To 210 ° C., and a heat absorbing agent made of a material different from that of the separator having a heat of fusion of 16 cal / g or more was added. For example, when this lithium battery is put in a reflow furnace and automatically soldered, When exposed to high-temperature environmental conditions, the endothermic agent in the battery container takes away heat and melts, thereby preventing the temperature of the lithium battery from rising.

As a result, in the lithium battery of the present invention, even when the battery is placed in a reflow furnace and automatically soldered, the internal pressure of the battery increases due to the vaporization of the non-aqueous electrolyte and the non-aqueous electrolyte in the battery container. The reaction between the liquid and the positive electrode was suppressed, and the discharge capacity of the lithium battery was prevented from lowering.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing an internal structure of a lithium secondary battery produced in an example of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery container

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shin Fujitani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5H029 AJ12 AK02 AK03 AK05 AL06 AL07 AL08 AL12 AM03 AM04 AM05 AM07 BJ03 BJ12 DJ04 DJ08 EJ12 HJ00 HJ01 HJ14

Claims (5)

[Claims] 1. A lithium battery comprising a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte in a battery container, wherein the battery container has a melting point of 1%.
A lithium battery, wherein a heat absorbing agent made of a material different from that of the separator and having a heat of fusion in the range of 00 to 210 ° C. and 16 cal / g or more is added. 2. The lithium battery according to claim 1, wherein the heat absorbing agent is 2,3-dimethylnaphthalene,
A lithium battery, which is at least one selected from the group consisting of 2,6-dimethylnaphthalene, fluorene, hexamethylbenzene, polyvinyl fluoride, and silver nitrate. 3. The lithium battery according to claim 1, wherein the heat absorbing agent is 2,3-dimethylnaphthalene,
A lithium battery, which is at least one selected from the group consisting of 2,6-dimethylnaphthalene, polyvinyl fluoride, and silver nitrate. 4. The lithium battery according to claim 1, wherein a ratio of the heat absorbing agent to the whole lithium battery is in a range of 0.02 to 3% by weight. battery. 5. The lithium battery according to claim 1, wherein the heat absorbing agent is present between the positive electrode and the separator.