JP3536534B2 - 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 which is safe even in abnormal situations such as overcharge.

[0002]

2. Description of the Related Art Conventionally, a positive electrode capable of occluding and releasing lithium, a negative electrode made of lithium metal, a lithium alloy, and a substance or a conductive substance capable of occluding and releasing lithium, a separator, a nonaqueous electrolyte, and a battery container are conventionally used. Non-aqueous electrolyte secondary batteries are widely used. The non-aqueous electrolyte secondary battery has low self-discharge and is excellent in storage stability. Also,
The non-aqueous electrolyte secondary battery can be easily reduced in size and weight. For this reason, it is regarded as a promising power source for cordless phones, electric vehicles, and the like.

[0003]

However, in the above-mentioned non-aqueous electrolyte secondary battery, there is a case where a chemical reaction in the battery runs away in an abnormal situation such as overcharge and overdischarge or a short circuit and the temperature inside the battery becomes high. is there. Also, the pressure inside the battery may rise abnormally. When such an abnormal phenomenon occurs,
In the worst case, the battery may be broken.

The present invention has been made in view of the above problems,
No breakage occurs due to overdischarge or abnormal temperature rise.
An object of the present invention is to provide a safe non-aqueous electrolyte secondary battery.

[0005]

According to the first aspect of the present invention, a positive electrode capable of inserting and extracting lithium, a lithium metal, a lithium alloy,
In a non-aqueous electrolyte secondary battery including a negative electrode made of a substance capable of inserting and extracting lithium or a conductive substance, a separator, a non-aqueous electrolyte, and a battery container, the non-aqueous electrolyte is overcharged and overcharged. At least one of discharge and temperature rise
When the temperature inside the battery rises abnormally due to two abnormal phenomena
Positive electrode high by heat denaturation polymer, or overcharge, etc. hardens
And electrolytic polymerization monomer which is cured when it becomes a potential, and an organic solvent, Ri Na more and an electrolyte salt, and the electrolytic polymerizable
Monomers are naphthalene derivatives, anthracene derivatives,
Glue of polyfluorene and thiophene derivatives
A non-aqueous electrolyte secondary battery characterized in that it is at least one kind selected from batteries.

It is most remarkable in the present invention that the above-mentioned non-aqueous electrolyte is used when at least one abnormal phenomenon of overcharge, over-discharge and temperature rise occurs in the non-aqueous electrolyte secondary battery. The above-mentioned specific heat-denatured polymer or the above-mentioned specific electropolymerizable monomer, and an organic solvent,
And an electrolyte salt.

The heat-modified polymer is added to a non-aqueous electrolyte as a battery electrolyte so that when the temperature inside the battery rises abnormally due to the above-mentioned abnormal phenomenon, the heat-modified polymer becomes non-aqueous electrolyte. The non-aqueous electrolyte is cured while containing the solution. As a result, the ionic conductivity of the nonaqueous electrolyte rapidly decreases, and the nonaqueous electrolyte secondary battery loses its battery characteristics.

Therefore, the chemical reaction which caused the abnormal rise in temperature inside the non-aqueous electrolyte secondary battery also stops,
Therefore, breakage of the battery and the like can be prevented. The hardening of the non-aqueous electrolyte preferably occurs at 80 ° C. or higher.

Next, the above-mentioned electropolymerizable monomer can be polymerized by applying a potential difference of a certain value or more. Therefore, when the positive electrode of the non-aqueous electrolyte secondary battery has a high potential due to overcharging or the like, an oxidized polymer film formed by the polymerization of the above-mentioned electrolytic polymerizable monomer to polymerize the positive electrode is formed on the positive electrode. Precipitates.

For example, when an electropolymerizable monomer which polymerizes at a potential difference of 4.5 V or more is contained in the non-aqueous electrolyte, the positive electrode becomes a high potential of 4.5 V or more due to overcharging. Then, the oxidized polymer film formed by the polymerization of the above-mentioned electrolytic polymerizable monomer to polymerize is deposited.

As a result, the ionic conductivity of the non-aqueous electrolyte rapidly decreases, and the non-aqueous electrolyte secondary battery loses its battery characteristics.
Therefore, excessive heat generation in the non-aqueous electrolyte secondary battery is also stopped, so that breakage of the battery and the like can be prevented.

[0012] As described above, in the non-aqueous electrolyte secondary battery of the present invention, non-aqueous electrolyte, on which cure overcharge, overdischarge, by at least one of the abnormal phenomenon of temperature increase
It comprises the specific heat-modified polymer or the specific electrolytic polymerizable monomer, an organic solvent, and an electrolyte salt.

As a result, in the event of the above-described abnormal situation, a chemical reaction occurs inside the battery due to the heat-modified polymer or the electrolytic polymerizable monomer. By the above chemical reaction,
The internal resistance of the non-aqueous electrolyte increases. As a result, the non-aqueous electrolytic secondary battery loses its battery characteristics, stops the chemical reaction that caused the battery characteristics, and does not raise the temperature or the internal pressure more than the current level. Therefore, breakage of the non-aqueous electrolyte secondary battery can be prevented.

As described above, according to the present invention, overcharging,
No breakage occurs due to overdischarge or abnormal temperature rise.
A safe, non-aqueous electrolyte secondary battery can be provided.

Next, as in the second aspect of the present invention, it is preferable that the heat-modified polymer or the electrolytic polymerizable monomer is encapsulated in a microcapsule. As a result, when the non-aqueous electrolyte secondary battery reaches an abnormal temperature, the microcapsules collapse or melt, and the heat-modified polymer or the electropolymerizable monomer contained in the microcapsules becomes non-aqueous. Released into the electrolyte. As a result, the abnormal rise in temperature can be suppressed as described above, and breakage of the battery can be prevented. When the battery is at a normal temperature, the heat-modified polymer or the electropolymerizable monomer is stably stored in the microcapsule. Therefore, even after long-term use, the heat-modified polymer or the electropolymerizable monomer can effectively exhibit the above-mentioned effects.

The above-mentioned microcapsule is made of a material capable of disintegrating or melting the microcapsule when the battery reaches an abnormal temperature and releasing the thermally denatured polymer or the electropolymerizable monomer contained in the microcapsule. Is used. Also, the melting point of the wall film material of the microcapsules is preferably a temperature slightly lower than the temperature at which the content of the thermally modified polymer or the electropolymerizable monomer starts to cure. As a result, the microcapsules collapse or melt before the heat-modified polymer or the electropolymerizable monomer is cured,
The heat-modified polymer or the electropolymerizable monomer is released into the non-aqueous electrolyte. Therefore, the heat-modified polymer or the electropolymerizable monomer is cured in the non-aqueous electrolytic solution, and the above-mentioned effect can be effectively exhibited.

More specifically, the melting point of the wall material of the microcapsules is more preferably in the range of 90 ° C. to 120 ° C. If the temperature is lower than 90 ° C., the microcapsules may be broken or melted in a normal use state of the battery. Conversely, if the temperature exceeds 120 ° C, when the battery reaches an abnormally high temperature, the microcapsules do not collapse or melt and release the heat-modified polymer or electropolymerizable monomer into the non-aqueous electrolyte. May not be possible.

A general method of encapsulating a heat-denatured polymer or an electropolymerizable monomer in a microcapsule is to first prepare a heat-denatured polymer or an electropolymerizable monomer in the form of fine particles dispersed therein, An agent, that is, a substance that becomes a wall film, is added, cured, and fixed, thereby enclosing the heat-modified polymer or the electropolymerizable monomer and encapsulating.

As the wall material of the microcapsules, for example, a polymer material is used. That is, the polymer material is deposited around the heat-modified polymer or the electrolytic polymerizable monomer. In the deposition method, a non-solvent in which the polymer is not dissolved is added to a solution of the polymer to be a wall film, or the solvent is dried.

As the encapsulating agent, for example, polyethylene is used. Furthermore, in order to improve the safety of the battery, the microcapsule can be prevented from firing when the battery is abnormally heated by adding a flame retardant to the microcapsules in addition to the heat-modified polymer or the electrolytic polymerizable monomer.

Next, as in the third aspect of the present invention, the microcapsules are preferably contained in one or both of the separator and the non-aqueous electrolyte. As a result, when the microcapsules collapse or melt, the heat-modified polymer or the electropolymerizable monomer in the microcapsules is released into the non-aqueous electrolyte.

Next, as in the invention of claim 4, claim 1
It is preferable that a chain carbonate is used in place of the heat-modified polymer or the electrolytic polymerizable monomer described above, and the chain carbonate is encapsulated in microcapsules. By adding the above-mentioned chain carbonate to the non-aqueous electrolyte, when the temperature inside the battery rises abnormally, a lithium alkyl carbonate compound is generated by the reaction with lithium, and this is a trace amount contained in the electrolyte. Reacts with water to form a stable passive film, lithium carbonate, at the electrolyte / electrode interface. Therefore, the chemical reaction inside the non-aqueous electrolyte secondary battery that caused the abnormal temperature rise also stopped,
Therefore, breakage of the battery and the like can be prevented.

Further, since the chain carbonate is encapsulated in the microcapsules, similar to the case where the above-mentioned heat-modified polymer or electrolytic polymerizable monomer is encapsulated in the microcapsules, after the battery has been used for a long time, Also, the chain carbonate in the microcapsule can effectively exhibit the above-mentioned effects.

Next, as in the invention of claim 5, it is preferable that the heat-denatured polymer is a protein. The above proteins are excellent because they are non-catalytic, single component systems that do not require a curing agent, and have a short curing time. And, as in the invention of claim 6, the protein is preferably one or more selected from the group of albumin, casein, actin, myosin, keratin, and collagen.

Next, as in the invention of claim 7, the chain carbonate is represented by the general formula: R1-O- (C = O) -O-
Compounds represented by R2 (where R1 and R2 are alkyl groups) are preferred. The compound represented by the above general formula is excellent because it has high reactivity with lithium at a high temperature and easily forms a passive film.

Also, as in the invention of claim 8, the chain carbonate is preferably one or more substances selected from the group consisting of dimethyl carbonate, diethyl carbonate, diisopropyl carbonate, and ethyl methyl carbonate. . They are particularly excellent in reactivity with lithium at high temperatures.

Further, the upper Symbol electropolymerization monomer, naphthalene derivatives, anthracene derivatives, polyfluorene derivatives, and be one or more substances selected from the group of Chi thiophene-induced body preferably. The above materials are excellent because they produce polymer films with low ionic conductivity.

The above-mentioned heat-modified polymer or chain carbonate may be used alone or in combination of two or more.

According to the ninth aspect of the present invention, the content of the heat-modified polymer, the electropolymerizable monomer or the chain carbonate in the non-aqueous electrolyte is 1% by weight to 50% by weight.
It is preferable that When the weight mixing ratio is less than 1% by weight, the inherent curing reaction of the heat-modified polymer, the electropolymerizable monomer or the chain carbonate is unlikely to occur during overcharge, overdischarge, and temperature rise. The internal resistance of the non-aqueous electrolyte does not increase. Therefore, it is difficult to obtain the effect of reducing the current flowing inside the battery and suppressing the temperature rise. On the other hand, when the weight mixing ratio exceeds 50% by weight, normal battery characteristics may be reduced, and the performance of the nonaqueous electrolyte secondary battery may be reduced.

Next, as in the invention of claim 10, the microcapsules preferably has at least a flame retardant. Thereby, ignition at the time of abnormal heat generation of the battery can be prevented. Next, as in the eleventh aspect of the present invention, the flame retardant is preferably one or more selected from the group consisting of a phosphorus compound, a halogen compound, and a compound containing phosphorus and a halogen element. Thus, ignition of the battery can be reliably prevented.

The organic solvent is used as a non-aqueous solvent for the electrolyte salt. The electrolyte salt is used as an electrolyte of a non-aqueous electrolyte secondary battery.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment A non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, a nonaqueous electrolyte secondary battery 1 of the present embodiment has a positive electrode 11 capable of absorbing and releasing lithium and a negative electrode 1 composed of lithium metal, a lithium alloy, a material capable of absorbing and releasing lithium or a conductive material.
2, a separator 13, a non-aqueous electrolyte 14, and a battery container 15. The non-aqueous electrolyte 14 includes a heat-modified polymer that cures due to an abnormal temperature rise, an organic solvent, and an electrolyte salt.

The non-aqueous electrolyte 14 is prepared by adding LiPF ₆ as an electrolyte salt to a 1 M (mol) mixture in an equal volume mixed solvent of propylene carbonate and dimethoxyethane as organic solvents.
Per liter) and 10% by weight of egg white protein as a heat-denatured polymer.

The positive electrode 11 is made of LiM which is a positive electrode active material.
A mixture of 90% by weight of n ₂ O ₄ , 6% by weight of Ketjen black as a conductive agent, and 4% by weight of polytetrafluoroethylene was pressure-formed on a stainless steel mesh as a positive electrode current collector 110. Then, a heat treatment at 200 ° C. is performed.

The negative electrode 12 is formed by press-bonding a lithium metal foil to a nickel expanded metal mesh as a negative electrode current collector 120 in a dry argon gas atmosphere.

The separator 13 is made of a polypropylene non-woven fabric. The above positive electrode 11 and negative electrode 1
2. Assemble the separator 13 and the non-aqueous electrolyte 14 into a battery case 15 composed of a positive electrode case 151, a negative electrode case 152 and a gasket 16 for fixing both, to obtain a coin-type non-aqueous electrolyte secondary battery 1. Incidentally, the nonaqueous electrolyte solution 14
Is impregnated in the separator 13 in advance.

Next, the operation and effect of this embodiment will be described. Non-aqueous electrolyte 1 in non-aqueous electrolyte secondary battery 1 of this example
No. 4 is composed of egg white protein which is hardened by an abnormal temperature rise, an organic solvent, and an electrolyte salt.

The above-mentioned egg white protein has such a property that when the temperature of the non-aqueous electrolyte solution exceeds 70 ° C., it hardens while containing propylene carbonate and dimethoxyethane as organic solvents. As a result, the ionic conductivity of the non-aqueous electrolyte rapidly decreases, so that the non-aqueous electrolyte secondary battery 1 loses battery characteristics. For this reason, the chemical reaction that caused the abnormal rise in temperature is also reduced, and the breakage of the nonaqueous electrolyte secondary battery 1 can be prevented.

Therefore, according to this embodiment, overcharging, overdischarging,
When the temperature rises abnormally, it will not break,
A non-aqueous electrolyte secondary battery can be provided.

In this example, an equal volume mixed solvent of propylene carbonate and dimethoxyethane was used as the organic solvent, and LiPF ₆ was used as the electrolyte salt. In addition, for example, ethylene carbonate, propylene carbonate as the organic solvent was used. , Dimethyl sulfoxide,
γ-butyrolactone, sulfolane dimethylformamide, 1,2-dimethoxyethane, tetrahydrofuran,
2-Methyltetrahydrofuran or the like, and a mixture thereof, for example, as an electrolyte salt, LiBF ₄ or LBF
Even when iAsF ₆ is used, a safe non-aqueous electrolyte secondary battery can be obtained as in the case of this example.

Embodiment 2 In this embodiment, several tests were performed on the samples 1 to 3 and the comparative sample according to the present invention, and their safety was examined. First, the samples 1 to 3 and the comparative sample are coin-type nonaqueous electrolyte secondary batteries having the configuration shown in the first embodiment.

The non-aqueous electrolyte in Sample 1 was prepared by mixing 90% by weight of a solution obtained by dissolving an electrolyte salt in an organic solvent and 10% by weight of egg white protein as a heat-denatured polymer, as shown in Embodiment 1. is there.

The non-aqueous electrolyte in Sample 2 is a mixture of the egg white protein of Sample 1 contained in microcapsules. The microcapsules were prepared as follows. Polyethylene was used as a capsule wall covering agent. After dissolving polyethylene in xylene, egg white protein was added to this solvent and dispersed well. Stirring was continued during this time. Ethanol was added to this to cause phase separation. The microcapsules were separated from this solution by filtration and then dried under reduced pressure.

The non-aqueous electrolyte in Sample 3 is a mixture of 20% by weight of 2-naphthylamine, which is an electropolymerizable monomer, and 80% by weight of the above solution. The non-aqueous electrolyte solution in Sample 4 is a mixture of Sample 3 in which microcapsules contain 2-naphthylamine. The microcapsules were produced in the same manner as in Sample 2 described above.

The non-aqueous electrolyte in Sample 5 contains 30% by weight of microcapsules containing dimethyl carbonate, which is a chain carbonate, and 70% by weight of the above solution.
Is mixed. Microcapsule is the above sample 2
It was produced in the same manner as described above. The comparative sample is a coin-type non-aqueous electrolyte secondary battery having the same configuration as Samples 1 to 5. However, the non-aqueous electrolyte does not contain a substance that acts as a curable organic substance.

Next, each test will be described. The first is a high-temperature storage test. In the above test, each sample is left in a thermostat kept at a temperature of 80 ° C. for 24 hours. The second is an overcharge test. In the above test,
Each sample is charged for 24 hours at an overvoltage of 4.5V.

The third is a short-circuit test. In the above test, the positive electrode and the negative electrode of each sample are connected by a conducting wire and left. After the completion of these tests, if no phenomena such as breakage occur, it can be concluded that the sample is a non-aqueous electrolyte secondary battery with excellent safety.

The results of the above test will be described. Samples 1 to 5 according to the present invention do not exceed a self-heating temperature of 120 ° C. in a high-temperature storage test. No rupture has occurred after the test.

In each of the samples 1 to 5, the battery temperature rises to some extent in the overcharge test and the short-circuit test. However, no break occurs. On the other hand, in the comparative sample, in the high temperature storage test and the overcharge test, expansion deformation and rupture of the battery container were confirmed, and in the short circuit test, an abnormal temperature rise inside the battery was observed. From the above, it can be seen that Samples 1 to 5 according to the present invention are non-aqueous electrolyte secondary batteries with higher safety than the comparative samples.

Further, the ionic conductivity of the non-aqueous electrolyte of each of the samples 1 to 5 was measured before and after performing the high-temperature storage test. The ionic conductivity was measured by the AC impedance method when the non-aqueous electrolytes of the samples 1 to 5 were at a temperature of 25 ° C. As a result, the non-aqueous electrolyte ionic conductivity of Samples 1 to 5 before the high-temperature storage test was 15
mS / cm. On the other hand, after the above high-temperature storage test,
The ionic conductivity of each sample was 1 mS / cm.

From these facts, it was found that Samples 1 to 5 according to the present invention
When the temperature of the battery rises,
It can be seen that the ionic conductivity of the non-aqueous electrolyte decreases at high temperatures due to the electropolymerizable monomer or the chain carbonate, and as a result, battery characteristics are lost and the battery does not break. Therefore, it can be said that the non-aqueous electrolyte secondary batteries of Samples 1 to 5 have high safety.

Embodiment 3 In this embodiment, charge / discharge cycle characteristics of a nonaqueous electrolyte secondary battery were evaluated. The charge-discharge cycle characteristics evaluation was 20
The charge / discharge cycle was performed 20 times at ℃, and the charge / discharge efficiency of the nonaqueous electrolyte secondary battery at that time was measured. As the non-aqueous electrolyte secondary batteries, the coin-type non-aqueous electrolyte secondary batteries of Samples 1 and 2 of Embodiment 2 were used. As a result, in the case of the sample 1 using no microcapsules, it was 82%, whereas in the case of the sample 2 using microcapsules, it was 95%.

Sample 1 without microcapsules and Sample 2 with microcapsules are described in Embodiment 2
As shown in the figure, the improvement in safety was recognized in each case. This suggests that, in Sample 2, in addition to the improvement in safety, a decrease in battery performance could be suppressed by microencapsulation of egg white protein.

Next, the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery of Sample 5 were evaluated. For the non-aqueous electrolyte secondary battery of Sample 5, dimethyl carbonate encapsulated in microcapsules was used as described above. The charge and discharge cycle characteristics were evaluated by conducting 20 charge and discharge cycles at 60 ° C.
The measurement was performed by measuring the charge / discharge efficiency of the nonaqueous electrolyte secondary battery at that time.

For comparison, instead of dimethyl carbonate encapsulated in microcapsules,
Dimethyl carbonate not encapsulated in the microcapsules was added to the non-aqueous electrolyte to produce a non-aqueous electrolyte secondary battery. With respect to Comparative Example 1, the same charge / discharge cycle characteristics evaluation as that of Sample 5 was performed.

As a result, in the case of sample 5 using microcapsules, it was 95%, while in the case of comparative example 1 not using microcapsules, it was 20%, indicating a significant decrease in battery performance. Was. From this, it can be said that the chain carbonate is usually better encapsulated in microcapsules.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to a first embodiment.

[Explanation of symbols]

1. . . Non-aqueous electrolyte secondary battery, 11. . . Positive electrode, 12. . . Negative electrode, 13. . . Separator, 14． . . Non-aqueous electrolyte, 15. . . Battery case,

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-138735 (JP, A) JP-A-7-320778 (JP, A) JP-A-63-86355 (JP, A) 283206 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (11)

(57) [Claims] 1. A positive electrode capable of storing and releasing lithium, a negative electrode composed of a lithium metal, a lithium alloy, a substance capable of storing and releasing lithium or a conductive material, a separator, a non-aqueous electrolyte, and a battery container. In the non-aqueous electrolyte secondary battery, the temperature of the non-aqueous electrolyte may be reduced due to at least one abnormal phenomenon of overcharge, overdischarge, and temperature rise.
Thermally modified polymer that cures when it rises abnormally , or overcharge
The positive electrode and the electrolytic polymerization monomer which cures when it becomes a high potential, and an organic solvent, Ri Na more and an electrolyte salt, and the electrolytic polymerizable monomer, naphthalene derivatives,
Anthracene derivatives, polyfluorene derivatives, and thio
One or more selected from the group of phen derivatives
Non-aqueous electrolyte secondary battery characterized by the above . 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-modified polymer or the electropolymerizable monomer is encapsulated in a microcapsule. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the microcapsules are contained in one or both of a separator and a non-aqueous electrolyte. 4. A non-aqueous solution, wherein a chain carbonate is used in place of the heat-modified polymer or the electropolymerizable monomer according to claim 1, and the chain carbonate is encapsulated in microcapsules. Electrolyte secondary battery. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-denatured polymer is a protein. 6. The non-aqueous electrolyte secondary solution according to claim 5, wherein the protein is one or more selected from the group consisting of albumin, casein, actin, myosin, keratin, and collagen. battery. 7. The method according to claim 4, wherein the chain carbonate is represented by the general formula: R1-O- (C = O)-
A non-aqueous electrolyte secondary battery, which is a compound represented by O-R2 (where R1 and R2 are alkyl groups). 8. The method according to claim 7, wherein the chain carbonate is dimethyl carbonate, diethyl carbonate,
A non-aqueous electrolyte secondary battery comprising at least one member selected from the group consisting of diisopropyl carbonate and ethyl methyl carbonate. 9. The non-aqueous electrolyte according to claim 1, wherein the content of the heat-modified polymer, the electropolymerizable monomer or the chain carbonate in the non-aqueous electrolyte is 1 to 50% by weight. Water electrolyte secondary battery. 10. The non-aqueous electrolyte secondary battery according to claim 2, wherein the microcapsules have at least a flame retardant. 11. The method according to claim 11, wherein the flame retardant comprises:
One or two selected from the group consisting of a phosphorus compound, a halogen compound, and a compound containing phosphorus and a halogen element;
A non-aqueous electrolyte secondary battery characterized by at least one kind.