JP2006339011A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable lithium ion secondary battery causing no expansion of the battery by overcharge, and adopting a lightweight aluminum laminate as a case material. <P>SOLUTION: In this lithium ion secondary battery, a battery element formed by laminating or winding a positive electrode, a separator having an electrolyte containing Li salt, and a negative electrode is sealed by an aluminum laminate sheet. The gel electrolyte contains a polymer of a compound expressed by the formula: B[O(C<SB>a</SB>H<SB>2a</SB>O)<SB>b</SB>]<SB>3</SB>Z<SB>3</SB>(1). In the formula, Z is a polymerizable functional group, (a) and (b) are integers of 1-6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery using an aluminum laminate sheet as an exterior material.

  Lithium ion secondary batteries are used as a drive power source for electronic devices such as mobile phones and mobile personal computers because they can achieve higher energy density than nickel metal hydride batteries.

  In lithium ion secondary batteries, materials capable of reversibly occluding / releasing lithium, such as compounds containing lithium and carbon-based materials, are used for the positive electrode active material and the negative electrode active material, respectively. These bipolar active materials are arranged so as to face each other through a separator that electrically insulates and holds the electrolytic solution, thereby constituting a battery element.

  In recent years, attempts have been made to adapt lithium ion secondary batteries to mobile power sources such as electric vehicles, and there is a demand for improvement in energy density per weight. In light of this requirement, weight reduction of battery materials has been studied. For example, it is attempted to change the exterior material for sealing battery elements from a metal can such as aluminum or stainless steel to a lightweight material such as an aluminum laminate material. It has been.

  By the way, it is common to use a plurality of lithium ion secondary batteries in series and in parallel as a power source for movement of electric vehicles and mobile electronic devices, but the voltage of each battery is inadequate. If it is uniform, some batteries may be overcharged during charging, and the Li salt may decompose to generate gas inside the battery. Moreover, the use under high temperature is also assumed. When an aluminum laminate material with low mechanical strength is used as an exterior material to reduce the weight of the battery, the battery may expand due to gas generated by overcharging, or the battery may be deformed due to high temperature. There was a problem that the contact resistance between the electrodes increased and the battery capacity decreased.

  As a technique for solving the above problems, for example, as described in Japanese Patent Application Laid-Open No. 2003-157908, voltage measurement is performed for each unit cell constituting the assembled battery to control the charge amount. There is a method including a mechanism for preventing charging. However, this method has problems such as a complicated control circuit.

JP 2003-157908 A

  As described above, when an aluminum laminate material, which has a lower mechanical strength than a metal can, is used as an exterior material of a lithium ion secondary battery, the battery expands due to gas generated at an overcharged state or high temperature. In some cases, performance was degraded.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable lithium ion secondary battery that employs a lightweight aluminum laminate as an exterior material and does not expand the battery due to overcharge or high temperature.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that it is effective to use a polymer gel electrolyte containing a polyalkylene oxide system containing boron to solve the problems.

That is, the present invention includes the following inventions.
(1) A lithium ion secondary battery in which a battery element obtained by laminating or winding a positive electrode, a separator holding a gel electrolyte containing a Li salt, and a negative electrode is sealed with an aluminum laminate sheet, and the gel electrolyte includes: Formula I:
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
The lithium ion secondary battery characterized by including the polymer of the compound represented by these.
(2) The gel electrolyte has the formula II:
B [{O (C _c H _2c O) _d } R] ₃ (II)
[Wherein, c and d are integers of 1 to 6, and R is a C _1-6 alkyl group. ]
The lithium ion secondary battery according to (1), further comprising a compound represented by the formula:
(3) The lithium ion secondary battery according to (2), wherein the gel electrolyte contains a compound of formula I and a compound of formula II in a molar ratio of 1: 1 to 1: 3.
(4) The lithium according to any one of (1) to (3), wherein the gel electrolyte contains a polymer of a compound represented by the formula (I) at 5 wt% to 20 wt%. Ion secondary battery.
(5) The lithium ion secondary battery according to any one of (1) to (4), wherein the separator is made of polyethylene and has an air permeability of 100 to 600 seconds / 100 ml.
(6) The above (1) to (5), wherein the positive electrode contains LiMn _x Ni _1-xy Co _y O ₂ (where x and y are in the range of 0.001 ≦ x, y ≦ 0.5). The lithium ion secondary battery in any one of.
(7) The lithium ion secondary battery according to any one of (1) to (6), wherein the negative electrode contains amorphous carbon.
(8) A method for producing a lithium ion secondary battery in which a battery element obtained by laminating or winding a positive electrode, a separator holding a gel electrolyte containing a Li salt, and a negative electrode is sealed with an aluminum laminate sheet. :
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
A method for producing a lithium ion secondary battery, comprising injecting a solution of a compound represented by formula (1) into a void of a separator and then polymerizing the solution.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to prevent a battery from expanding due to a gas generated by overcharging, and to provide a long-life and highly reliable lithium ion secondary battery employing a lightweight aluminum laminate as an exterior material.

The lithium ion secondary battery of the present invention has the following configuration:
A lithium ion secondary battery in which a battery element in which a positive electrode, a separator holding a gel electrolyte containing a Li salt, and a negative electrode are laminated or wound is sealed with an aluminum laminate sheet, wherein the gel electrolyte has the formula I:
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
The lithium ion secondary battery characterized by including the polymer of the compound represented by these.

The positive electrode active material is not particularly limited as long as it is usually used in lithium ion secondary batteries. For example, amorphous-V ₂ O ₅ , LiMn ₂ O ₄ , MnO ₂ , LiV ₃ O ₈ , V ₆ O ₁₃ , LiCoO ₂ , LiNiO ₂ , MoS ₂ , TiS _{2 and the} like, LiCoO ₂ , LiNiO _2, LiMn _x Ni _1-xy Co _y O ₂ (where x and y are 0.001 ≦ x, y ≦ 0.5), LiMn ₂ O ₄ and LiMnO ₂ are preferred. In addition, an organic compound positive electrode active material, for example, a conductive polymer such as a polyaniline derivative, a polypyrrole derivative, or a polythiophene derivative may be used.

  The positive electrode current collector is not particularly limited as long as it is usually used for a lithium ion secondary battery, and for example, a thin film or mesh such as copper, nickel, or aluminum can be used.

  The negative electrode active material is not particularly limited as long as it is usually used for a lithium ion secondary battery, and examples thereof include those containing a carbon material such as graphite and amorphous carbon.

  The current collector for the negative electrode is not particularly limited as long as it is normally used for a lithium ion secondary battery, and for example, a copper thin film or a mesh can be used.

  For the positive electrode and the negative electrode, for example, the positive electrode active material or the negative electrode active material and a conductive auxiliary agent are dispersed in a suitable solvent together with a binder (binder), and this is coated on the positive electrode or the negative electrode current collector. It can be produced by evaporation.

  As the conductive auxiliary agent, carbon fine particles such as acetylene black, carbon black, and graphite are used.

  Moreover, as a binder used in order to adhere | attach a positive electrode active material or a negative electrode active material to a collector, Teflon, a polyfluoro vinylidene, polyethylene, a polypropylene polyvinylidene fluoride-6 fluoropropylene copolymer, an ethylene propylene copolymer Etc. The amount of the binder used is preferably about 3 to 10% by weight in terms of the solid content ratio of the active material and the conductive aid.

  The separator (porous membrane, porous sheet, etc.) used in the battery of the present invention holds a gel electrolyte containing a Li salt.

The Li salt is not particularly limited as long as it is a Li salt electrolyte usually used in a lithium ion secondary battery. For example, LiBR ₄ (R is a phenyl group, an alkyl group), LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiBF ₄ , LiClO ₄ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (CF ₃ CF ₂ SO ₂ ) ₂ NLi etc. can be exemplified, LiBF ₄ , (CF ₃ CF ₂ SO ₂ ) ₂ NLi is preferred.

  The separator has a low resistance to ion migration of the electrolyte and has excellent gel electrolyte retention, and is selected from, for example, glass, polyester, Teflon, polyethylene, polypropylene, or one or more materials thereof. Porous films, non-woven fabrics and woven fabrics. In the present invention, it is preferable to use a polyethylene separator. Further, the air permeability of the separator is preferably 100 to 600 seconds / 100 ml. The thickness of the separator is desirably about 0.01 to 0.04 mm. It has been found that by using such a separator, coulomb efficiency is increased and energy loss is suppressed.

The gel electrolyte retained in the separator is represented by the following formula I:
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
The polymer of the boron compound represented by these is included.

The polymerizable functional group Z means a polymerizable group such as an unsaturated bond or a group capable of condensation polymerization, such as a methacrylate group (—CO—C (CH ₃ ) ═CH ₂ ) or an acrylate group ( -CO-CH = CH ₂ ) and the like.

  In the present invention, diethylene glycol monomethacrylate is preferably used as the compound of formula I.

  The gel electrolyte used in the present invention contains a solvent. Examples of the solvent include carbonate solvents (propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.), amide solvents (N-methylformamide, N-ethylformamide, N, N- Dimethylformamide, N-methylacetamide, N-ethylacetamide, N-methylpyrrolidone, etc.), lactone solvents (γ-butyllactone, γ-valerolactone, δ-valerolactone, etc.), ether solvents (methylal, 1,2-dimethoxy) Ethane, 1,2-diethoxyethane, 1-ethoxy-2-dimethoxyethane, etc.), nitrile solvents (benzonitrile, acetonitrile, 3-methoxypropionitrile, etc.), furan solvents (tetrahydrofuran, 2-methylteto) Hydrofuran, etc.), dioxolane, dioxane, Jikurooetan and the like, can be used alone or in combination.

  The aluminum laminate sheet used in the present invention is not particularly limited as long as it is usually used for a lithium ion secondary battery. For example, a laminate having an aluminum foil having a thickness of about 0.02 to 0.04 mm as a core material. Sheets can be used. Place a thermoplastic resin (eg, polyethylene, polypropylene, etc.) on the surface (battery element side) where heat welding is performed, and place a resin such as nylon, polyethylene terephthalate on the surface (exterior part side) where heat welding is not performed The oxidation of aluminum can be prevented.

For gel electrolytes, as a plasticizer, the formula II:
B [{O (C _c H _2c O) _d } R] ₃ (II)
[Wherein, c and d are integers of 1 to 6, and R is a C _1-6 alkyl group. ]
You may add the compound represented by these.

Examples of the C _1-6 alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, and an isobutyl group.
As the plasticizer, triethylene glycol monomethyl ether is preferable.

  Next, the manufacturing method of the lithium ion secondary battery of this invention is demonstrated.

  A positive electrode and a negative electrode can be manufactured as follows, for example. A positive electrode active material or negative electrode active material, a conductive additive and a binder are added to and mixed with a suitable solvent (for example, 1-methyl-2-pyrrolidone) to form a paste, which is applied to both sides of the current collector and dried. . Subsequently, it is pressed and dried to obtain a positive electrode or a negative electrode.

  When manufacturing a laminated battery, first, each electrode and separator are cut into appropriate sizes, and are laminated in the order of separator / negative electrode / separator / positive electrode. This is laminated to obtain a desired number of layers, and current terminals are joined to the tab portions of the positive electrode and the negative electrode, respectively, to manufacture a battery element. As a joining method, it is desirable to perform spot welding or ultrasonic welding.

  Next, a precursor solution of gel electrolyte (ie, a solution of the compound of formula I) is injected / filled into the battery element, and the electronic element is sealed with an aluminum laminate sheet exterior material. As the aluminum laminate sheet exterior material, for example, an aluminum foil whose both surfaces are covered with polypropylene or the like can be used.

  As a sealing method, three sides of the sheet exterior material are preliminarily heat-welded to prepare a bag-like material, a battery element is accommodated in this, and a gel electrolyte precursor solution is injected (sheet exterior material). A method may be mentioned in which the inside of the opening is sealed at the end. Alternatively, an aluminum laminate sheet is processed in advance into a concave shape that can accommodate the battery element by a hydraulic press or the like, and the battery element is fitted into the concave part, and an unprocessed aluminum laminate sheet material is placed on the lid as a lid and sealed. There is a technique to do. It is desirable to use the latter method for the convenience of manufacturing.

  The precursor solution of the gel electrolyte is, for example, a compound of formula I (monomer) and a polymerization initiator (for example, an organic peroxide such as peroxydicarbonate or peroxyester) in a suitable solvent (for example, a carbonate-based solvent). ) And a Li salt, and optionally a compound of formula II (plasticizer).

  Next, the edge portion of the aluminum laminate sheet exterior material containing the battery element in which the gel electrolyte precursor solution is injected into the gap of the separator is thermally welded and sealed with a heat welding apparatus. The conditions for sealing by thermal welding are preferably carried out under such temperature conditions that the peel strength according to JIS K7125 (JIS standard value) is 40 N / 15 mm or more.

After sealing, the gel electrolyte precursor solution is cured (polymerized) to form a gel. This curing reaction can be performed, for example, by placing it in a thermostatic bath at 40 to 100 ° C., preferably 50 to 90 ° C. for 0.5 to 5 hours, preferably 1 to 3 hours.
As described above, the lithium ion secondary battery of the present invention can be manufactured.

Next, specific examples of the lithium ion secondary battery of the present invention will be described with reference to the drawings.
FIG. 1 is a projected view of a lithium ion secondary battery placed horizontally and viewed from above. FIG. 2 is a perspective view of a lithium ion secondary battery. 3 and 4 are schematic views when the cross-sectional direction is viewed perpendicular to the battery element. FIG. 3 shows a battery in which electrodes are stacked, and FIG. 4 shows a flat wound battery. FIG. 5 is an enlarged view of the encircled portion of FIG.

  In FIG. 5, the lithium ion secondary battery includes a positive electrode 1 in which a positive electrode active material is applied to a positive electrode current collector, and a negative electrode 2 in which a negative electrode active material is applied to a negative electrode current collector. A separator 3 is interposed between the positive electrode 1 and the negative electrode 2. The tab portions 4 and 5 of the positive electrode current collector and the negative electrode current collector are not coated with the positive electrode active material and the negative electrode active material. The tab portions 4 and 5 are connected to the current collecting terminals 6 and 7 to the outside in FIG. In FIG. 1, an aluminum laminate sheet is welded to the outer peripheral portion 10 of the battery element 8 by heat welding, thereby sealing the battery element.

  In FIG. 2, a battery element 8 is placed on a flat aluminum laminate sheet, an aluminum laminate sheet exterior material 9 having a box-shaped part (concave part) and an adhesive part is placed thereon, and the battery element 8 is fitted in the concave part. It is an example of a battery that is formed by covering and bonding the adhesive part. At that time, the current collecting terminals 6 and 7 are arranged so as to extend from the exterior material 9. In addition, you may arrange | position the position of a current collection terminal extended from the opposing position 180 degree | times.

  EXAMPLES The present invention will be described below by way of examples, but the present invention is not limited to these examples.

Example 1 Method for Producing Gel Electrolyte Precursor As a solvent, a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1: 1: 1 by volume) was used. A boron compound of diethylene glycol monomethacrylate was used as the compound of formula I (monomer). Further, a boron compound of triethylene glycol monomethyl ether was used as the compound of formula II (plasticizer). T-Hexyl peroxypivalate was used as the polymerization initiator. As the Li salt, lithium bispentafluoroethane sulfonate imide was used.

  In the mixed solvent, 3 to 25% by weight of the monomer and a plasticizer were dissolved. The molar ratio of the monomer to the plasticizer was 1: 2. Li salt was added to this so that a density | concentration might be set to 1M. Next, a gel electrolyte precursor was prepared by adding 0.4 wt% of a polymerization initiator.

(Example 2) Curing of gel electrolyte precursor (gelation by polymerization)
The gel electrolyte precursor prepared in Example 1 was cured under various conditions.
A gel electrolyte precursor containing a predetermined amount of monomer was placed in a Teflon container with a screw lid and left in a constant temperature bath at 60 ° C. or 80 ° C. for 1.5 hours. The container was taken out of the thermostat and the inside of the container was confirmed. If the supernatant liquid did not remain, it was determined that the curing was satisfactory, and if the unreacted supernatant liquid remained, it was determined that the curing was insufficient. The results are shown in Table 1.

  When the monomer concentration (polymer concentration) in the gel electrolyte is 3% by weight, gelation is insufficient and the supernatant liquid remains, and the battery may expand at a high temperature. In this case, the supernatant liquid did not remain and gelation was good.

(Example 3) Production of lithium ion secondary battery 87% by weight of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as a positive electrode active material, 8.7% by weight of artificial graphite as a conductive auxiliary agent, polyfluoride 4.3% by weight of vinylidene chloride was added to 1-methyl-2-pyrrolidone and mixed to obtain a paste. This paste was applied on both sides of an aluminum foil and dried in the air at 80 ° C. for 3 hours. Subsequently, it was pressed to a density of about 2.7 g / cm ³ and dried in vacuum at 120 ° C. for 3 hours to obtain a positive electrode.

As a negative electrode active material, 90% by weight of amorphous carbon and 10% by weight of polyvinylidene fluoride were added to 1-methyl-2-pyrrolidone, and the solid content was adjusted to 45% by weight. The obtained slurry was coated on both sides of a copper foil and dried in the air at 80 ° C. for 3 hours. Subsequently, it was pressed to a density of about 1.0 g / cm ³ and dried in vacuum at 120 ° C. for 3 hours to obtain a negative electrode.

As the separator, a polyethylene porous membrane (thickness: 0.02 to 0.03 mm) was used.
As the gel electrolyte precursor, the one prepared in Example 1 was used.

  The positive electrode and the negative electrode were cut into a width of 83 mm and a height of 115 mm. At that time, a tab (current collector portion on which the positive electrode or the negative electrode active material was not coated) to be joined to the current terminal was left about 15 mm in width and about 5 mm in height. An aluminum current terminal was joined to the positive tab portion, and a nickel current terminal was joined to the negative tab portion. The separator was cut about several mm larger than the electrode in both width and height in order to prevent short circuit.

  A battery element was constructed using the above positive electrode, negative electrode and separator. Next, the aluminum laminate sheet outer packaging material in which both sides of the battery element and the aluminum foil are covered with polypropylene or the like is previously dried in a vacuum at 60 ° C. for 12 hours, and the battery element is impregnated with a gel electrolyte precursor solution to obtain an aluminum laminate sheet. It heat-sealed with the exterior material and sealed. This was placed in a constant temperature bath at 80 ° C. for 1.5 hours to gel the gel electrolyte precursor solution to produce a lithium ion secondary battery.

(Example 4) Battery capacity test A battery capacity test was conducted using the battery manufactured in Example 3 (designed battery capacity 4.0 Ah).
The lithium ion secondary battery was left at 25 ° C. for 8 hours, and then charged with 4.3 V at 0.1 CA (0.4 A) for 20 hours with a constant current / constant voltage control. Subsequently, it preserve | saved for 14 days at 25 degreeC, Then, the constant current discharge was performed to 3V at 0.1 CA, and the battery capacity was measured. The results are shown in Table 2.

  When the monomer concentration (polymer concentration) in the gel electrolyte was 20% or less, it was confirmed that the battery capacity was as designed.

(Example 5) Influence of separator air permeability The influence of separator air permeability on battery performance was evaluated.
A polyethylene film having an air permeability of 70, 100, 220, 310, 580, 600, 700 (sec / 100 ml) was used as a separator, the monomer concentration (polymer concentration) was 10% by weight, and the mole of polymer and plasticizer was 1 : A lithium ion secondary battery was produced in the same manner as in Example 1 and Example 3 except that it was changed to 3.

Evaluation was performed as follows.
The battery was allowed to stand at 25 ° C. for 8 hours, and then charged at 0.1 CA (0.4 A) to 4.1 V under a constant current / constant voltage control for a total charging time of 20 hours. Subsequently, the voltage of the 5th second when it discharged by 0.1CA, 0.2CA, 0.5CA, and 1.0CA was measured. The DC resistance was calculated from the slope of the current-voltage plot. The results are shown in Table 3.

  When the separator air permeability was 600 (sec / 100 ml) or less, it was confirmed that the DC resistance was low (less than 4.00 mΩ). However, in a battery using a separator having a separator air permeability of 70 (sec / 100 ml), a short circuit occurs at a ratio of 2 out of 5 batteries, and the air permeability of the separator is 100 (sec / 100 ml) or more from the viewpoint of reliability. It is desirable that

(Example 6) Overcharge test It was evaluated whether the battery performance was maintained even when the battery was overcharged.
Example 1 and Example 1 except that a polyethylene film having an air permeability of 310 (sec / 100 ml) was used as a separator, the monomer concentration (polymer concentration) was 10% by weight, and the molar ratio between the polymer and the plasticizer was 1: 1. A lithium ion secondary battery was produced in the same manner as in Example 3. The design capacity of the battery used is 2.0 Ah. As a comparative example, an electrolyte type battery containing no gel electrolyte produced in the same manner as in Examples 1 and 3 except that no monomer was added was used.

The overcharge test was conducted as follows.
The battery was allowed to stand at 25 ° C. for 8 hours, and then charged at 0.1 CA (0.2 A) to 4.1 V under a constant current / constant voltage control for a total charging time of 20 hours. When the battery capacity when discharged to 3.0 V at 0.1 CA was measured, it was confirmed that it showed an initial capacity of 2 Ah. Next, charging was performed at 0.1 CA (0.2 A) to 4.5 V under constant current / constant voltage control for a total charging time of 20 hours to simulate an overcharged state, and discharging was performed at 0.1 CA to 2.7 V. Thereafter, charging was performed at 0.1 CA (0.2 A) to 4.1 V under constant current / constant voltage control for a total charging time of 20 hours. Finally, discharge to 3.0 V was performed at 0.1 CA. This was performed for 5 cycles, and the charge / discharge capacity retention rate was evaluated by relative comparison with the initial battery capacity. The case where the capacity maintenance rate was 90% or more of the initial battery capacity was judged as ◯, and the case where it was less than that was judged as x. The results are shown in Table 4.

  The battery of the present invention using the gel electrolyte has a charge / discharge capacity of 90% or more even after charging that simulates overcharging, and a highly reliable assembled battery can be configured by using the battery of the present invention.

(Example 7) High temperature tolerance test Moreover, it manufactured according to the lithium ion secondary battery and Examples 1 and 3 which changed the monomer concentration (polymer concentration) in the gel electrolyte by 0 to 20 weight%.

  The change in battery thickness was measured by leaving it in a constant temperature bath at 60 ° C. for 24 hours. The results are shown in Table 5. A battery thickness change of less than 5% when left in a constant temperature bath at 60 ° C. for 24 hours was judged as ◯, and a battery thickness change of 5% or more was judged as x.

  As a result, when the gel electrolyte of this invention was used, it turned out that the deformation | transformation by gas generation and high temperature is suppressed.

  From the above, by using a gel electrolyte lithium ion secondary battery containing 5 to 20% by weight of a polymer gel electrolyte containing a boron-containing polyalkylene oxide system, the battery swells even under high temperature storage or in an overcharged state. The battery performance is stable and battery reliability is improved. Since there is no generation of gas or swelling due to heat, an aluminum laminate sheet having low strength can be used as an exterior material, and a lightweight and highly reliable lithium ion secondary battery can be provided.

  In addition, the battery of the present invention does not decrease the battery capacity even when the charge protection circuit or the like breaks down and falls into an overcharged state, and is an assembled battery configured by connecting the batteries of the present invention in series or in parallel. Provides a battery pack that is safe even in an overcharged state, maintains its performance, and has high reliability. For this reason, it can be applied to a mobile power source that requires a life and safety exceeding 10 years.

  Furthermore, by using a polyethylene material having an air permeability of 600 (sec / 100 ml) or less as a separator, the direct current resistance is lowered, and energy loss is suppressed.

  Since the lithium ion secondary battery of the present invention does not swell or deform the electrolyte due to gas generation or high temperature, a low-strength aluminum laminate can be used for the exterior material, and since there is no such swell / deformation, Reliability can be greatly improved.

  A lithium ion secondary battery employing an aluminum laminate can be reduced in weight, and is useful as a driving power source or a moving power source for a mobile phone, a mobile personal computer, or the like.

An example of the lithium ion secondary battery which concerns on this invention is shown. It is a projection view at the time of putting an example of the lithium ion secondary battery which concerns on this invention horizontally, and seeing from the upper part. It is a cross-sectional schematic diagram of a laminated type lithium ion battery. It is a cross-sectional schematic diagram of a flat wound type lithium ion battery. FIG. 4 is an enlarged schematic diagram of an encircled portion in FIG. 3.

Explanation of symbols

1: Positive electrode 2: Negative electrode 3: Separator 4: Positive electrode tab 5: Negative electrode tab 6: Positive electrode current collector terminal 7: Negative electrode current collector terminal 8: Battery element 9: Exterior material 10: Sealing portion

Claims (8)

A lithium ion secondary battery in which a battery element in which a positive electrode, a separator holding a gel electrolyte containing a Li salt, and a negative electrode are laminated or wound is sealed with an aluminum laminate sheet, wherein the gel electrolyte has the formula I:
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
The lithium ion secondary battery characterized by including the polymer of the compound represented by these. The gel electrolyte has the formula II:
B [{O (C _c H _2c O) _d } R] ₃ (II)
[Wherein, c and d are integers of 1 to 6, and R is a C _1-6 alkyl group. ]
The lithium ion secondary battery according to claim 1, further comprising:   The lithium ion secondary battery according to claim 2, wherein the gel electrolyte contains a compound of formula I and a compound of formula II in a molar ratio of 1: 1 to 1: 3.   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the gel electrolyte contains a polymer of a compound represented by the formula (I) at 5 wt% to 20 wt%.   5. The lithium ion secondary battery according to claim 1, wherein the separator is made of polyethylene and has an air permeability of 100 to 600 seconds / 100 ml. The positive _{electrode, LiMn x Ni 1-x-} y Co y O 2 ( where x and y are 0.001 ≦ x, the range of y ≦ 0.5) according to any one of claims 1 to 5, characterized in that it comprises Lithium ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein the negative electrode contains amorphous carbon. A method for producing a lithium ion secondary battery in which a battery element obtained by laminating or winding a positive electrode, a separator holding a gel electrolyte containing a Li salt, and a negative electrode is sealed with an aluminum laminate sheet.
B [O (C _a H _2a O) _b ] ₃ Z ₃ (I)
[Wherein, Z is a polymerizable functional group, and a and b are integers of 1 to 6. ]
A method for producing a lithium ion secondary battery, comprising injecting a solution of a compound represented by formula (1) into a void of a separator and then polymerizing the solution.

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