JP2005302382A - Nonaqueous electrolyte secondary battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery pack for absorbing shock and vibration properties applied to a battery pack from the outside. <P>SOLUTION: The nonaqueous electrolyte secondary battery pack comprises: the battery pack in which a plurality of nonaqueous electrolyte secondary batteries are electrically connected one another; an insulating case for accommodating and closing the battery pack; and a gel agent filled into the insulating case so that the gap of the battery pack and that between the battery pack and the inner surface of the case are buried. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery pack in which a non-aqueous electrolyte secondary battery is housed in an insulating case.

  In recent years, with the downsizing and increasing demand of electronic devices such as mobile phones and VTRs, it is required to increase the capacity of secondary batteries that are power sources of these electronic devices. In addition, air pollution due to exhaust gas from automobiles has become a social problem, and it is expected to use a lightweight and high-performance secondary battery as a power source for electric vehicles.

  In particular, since a lithium ion secondary battery has a high battery voltage and a high energy density, the battery can be reduced in size and weight. Therefore, it is expected to be used as a power source for portable devices in the future.

  Recently, the application of nonaqueous electrolyte secondary batteries as power sources for electric vehicles, power tools, cordless cleaners, and the like has been studied. In such applications, conventionally, a plurality of secondary batteries are connected in series, connected in parallel, and further connected in series to form an assembled battery, and the assembled battery is made of a resin such as plastic. Used as a battery pack housed in an insulating case.

  However, since the conventional battery pack has a gap between the insulating case and the assembled battery, when the battery pack is used as a power source for an electric vehicle, a power tool, a cordless cleaner, or the like, a plurality of two batteries that constitute the assembled battery by impact or vibration are used. There is a possibility that the connection between the secondary batteries is disconnected and the battery does not function as an assembled battery.

For this reason, Patent Document 1 discloses a resin container, an assembled battery in which a plurality of nickel-hydrogen secondary batteries housed in the container are connected to each other, and a gap between the container inner surface and the secondary battery. Ni-MH rechargeable battery module, which has a heat conductivity member such as silicone grease filled only with air and has a heat conductivity larger than that of air, and can quickly release heat generated by charging and discharging of the rechargeable battery Is disclosed.
However, in this secondary battery module, since the heat transfer member is filled only in the gap between the inner surface of the container and the secondary battery, the connection between the plurality of secondary batteries constituting the assembled battery may be disconnected due to impact or vibration. was there.
JP-A-5-36392

  The present invention provides a non-aqueous electrolyte secondary battery pack capable of absorbing shock and vibration applied to the assembled battery from the outside.

According to the present invention, a battery pack in which a plurality of nonaqueous electrolyte secondary batteries are electrically connected to each other;
An insulating case for storing and sealing the assembled battery;
Provided is a non-aqueous electrolyte secondary battery pack comprising a gel agent filled in the insulating case so as to fill a gap between the assembled battery and a gap between the assembled battery and the inner surface of the case.

  The present invention can provide a highly reliable non-aqueous electrolyte secondary battery pack having excellent impact resistance and vibration resistance.

  Hereinafter, an example of a non-aqueous electrolyte secondary battery pack according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

The insulating case 1 has a base plate 2 made of a synthetic resin such as ABS resin, and an upper end sealed rectangular cylindrical shape made of a synthetic resin such as an ABS resin that is ultrasonically fused to the base plate 2 and has an injection port 3. The case body 4 is constituted. The assembled battery 5 is stood on the base plate 2 inside the insulating case 1 and stored and sealed. The assembled battery 5 is configured by connecting, for example, 12 non-aqueous electrolyte secondary batteries (cylindrical lithium ion secondary batteries) 6 in parallel 6 in series with a connection plate 7. Gel agent 8 is injected into the insulating case 1 from the injection port 3 and filled so as to fill the gap between the batteries 4 and the gap between the inner surface of the insulating case 1 and the assembled battery 4. The injection port 3 is sealed with a plug (not shown) after the gel agent is injected.
As the gel agent, for example, silicone gel or polyurethane gel is used. Examples of the silicone gel include polyorganosiloxane and alpha gel.

The gel is allowed to further contain an insulating powder having good heat conductivity such as aluminum nitride powder.
The cylindrical lithium ion secondary battery has the following structure, for example. In a bottomed cylindrical container made of stainless steel also serving as a negative electrode terminal, an electrode group is housed via an insulator disposed on the bottom. This electrode group has a structure in which a strip in which a positive electrode, a separator, and a negative electrode are laminated in this order is wound on a spiral so that the negative electrode is located outside. A non-aqueous electrolyte is accommodated in the container. A cap-shaped positive electrode terminal having a PTC element having a hole in the center, a safety valve disposed on the PTC element, and a vent hole disposed in the safety valve is provided through an insulating gasket in the upper opening of the container. It is fixed by caulking. The positive electrode lead has one end connected to the positive electrode and the other end connected to the PTC element. One end of the negative electrode lead is connected to the negative electrode, and the other end is connected to a container having the negative electrode terminal.

  In addition, you may arrange | position a PTC element in the insulation case outside an assembled battery, without arrange | positioning in the container of a secondary battery.

  Next, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolytic solution will be specifically described.

1) Positive electrode This positive electrode is a continuous positive electrode material paste obtained by dispersing a positive electrode active material, a conductive agent and a binder in an appropriate solvent, for example, on a current collector on one side or both sides in a larger area than desired. Alternatively, it is produced by alternately applying a desired length and an unapplied portion, and cutting a dried sheet into a desired size.

A lithium composite metal oxide can be used as the positive electrode active material. Specifically such _{LiCoO 2, LiNiO 2, LiMnO 2} , LiMn 2 O 4 is used. Examples of the binder include polyvinylidene fluoride, a copolymer of vinylidene fluoride-6-propylene fluoride, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride, and vinylidene fluoride-pentafluoropropylene. And a copolymer of vinylidene fluoride-chlorotrifluoroethylene, or a copolymer of other fluorine-based monomer and vinylidene fluoride. Examples of such a copolymer of another fluorine-based monomer and vinylidene fluoride include a copolymer of tetrafluoroethylene-vinylidene fluoride and a terpolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) -vinylidene fluoride. Polymer, Tetrafluoroethylene-hexafluoropropylene (FEP) -vinylidene fluoride terpolymer, Tetrafluoroethylene-ethylene-vinylidene fluoride copolymer, Chlorotrifluoroethylene-vinylidene fluoride copolymer And a terpolymer of chlorotrifluoroethylene-ethylene-vinylidene fluoride and a copolymer of vinyl fluoride-vinylidene fluoride. These binders may be used alone.

  As the organic solvent for dispersing the binder, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethyl acetate and the like are used.

  Examples of the conductive agent include acetylene black, ketjen black, and graphite.

  The amount of the binder is 2% to 8% by weight based on 100 parts by weight of the active material and the binder (100 parts by weight of the conductive agent when the conductive agent is included). % Is preferable.

  The blending amount of the conductive agent is preferably in the range of 1% by weight to 15% by weight with respect to 100 parts by weight of the active material.

  The organic solvent is blended in an amount of 65% to 150% by weight based on 100 parts by weight of the active material and the binder (100 parts by weight of the conductive agent when the conductive agent is included). It is preferable to be in the range.

  As a dispersion apparatus used when preparing the paste, a ball mill, a bead mill, a dissolver, a sand grinder, a roll mill, or the like can be used.

  Examples of the current collector include aluminum foil, stainless steel foil, and titanium foil having a thickness of 10 to 40 μm.

2) Negative electrode The negative electrode is made of, for example, a carbonaceous material that occludes / releases lithium ions or a chalcogen compound, or a light metal. Among these, a negative electrode containing a carbonaceous material or a chalcogen compound that occludes / releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

  Examples of the carbonaceous material that occludes / releases lithium ions include coke, carbon fiber, pyrolytic vapor phase carbon material, graphite, resin fired body, mesophase pitch-based carbon fiber, or mesophase spherical carbon fired body. . Among them, it is preferable to use mesophase pitch carbon fiber graphitized at 2500 ° C. or higher because the electrode capacity is increased.

Examples of the chalcogen compound that absorbs and releases lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe ₂ ). When such a chalcogen compound is used for the negative electrode, although the voltage of the secondary battery drops, the capacity of the negative electrode increases, so that the capacity of the secondary battery is improved. Furthermore, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

  Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, and lithium alloy.

  Examples of the binder include polyvinylidene fluoride, a copolymer of vinylidene fluoride-6-propylene fluoride, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride, and vinylidene fluoride-pentafluoropropylene. And a copolymer of vinylidene fluoride-chlorotrifluoroethylene, or a copolymer of other fluorine-based monomer and vinylidene fluoride. Examples of such a copolymer of another fluorine-based monomer and vinylidene fluoride include a copolymer of tetrafluoroethylene-vinylidene fluoride and a terpolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) -vinylidene fluoride. Polymer, Tetrafluoroethylene-hexafluoropropylene (FEP) -vinylidene fluoride terpolymer, Tetrafluoroethylene-ethylene-vinylidene fluoride copolymer, Chlorotrifluoroethylene-vinylidene fluoride copolymer , Chlorotrifluoroethylene-ethylene-vinylidene fluoride terpolymer, vinyl fluoride-vinylidene fluoride copolymer, styrene butadiene copolymer, nitrile butadiene copolymer, acrylic copolymer, polyacrylic Acid, carboxymethylcellulose, Mention may be made of Le cellulose.

  As an organic solvent for dispersing the binder, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethyl acetate, water and the like are used.

  The negative electrode (for example, a negative electrode made of a carbon material) is specifically desired on one side or both sides of a negative electrode material paste obtained by dispersing the carbon material, a conductive agent, and a binder in an appropriate solvent. A continuous or desired length and an unapplied portion are alternately applied to an area larger than the size to be formed, and dried and cut into a desired plate size.

The mixing ratio of the negative electrode material and the binder is preferably in the range of 80 to 98% by weight of the negative electrode material and 2 to 20% by weight of the binder. In particular, the carbon material is preferably in the range of 50 to 200 g / m ² as the coating amount per side in the state in which the negative electrode 6 is produced.

  As the current collector, for example, a copper foil, a nickel foil, or the like can be used, but a copper foil is most preferable in view of electrochemical stability and flexibility during winding. In this case, the thickness of the foil is preferably 8 μm or more and 20 μm or less.

3) Separator As this separator, for example, a porous film or a nonwoven fabric can be used. The separator is preferably made of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

4) Nonaqueous electrolyte This nonaqueous electrolyte has a composition in which an electrolyte is dissolved in a nonaqueous solvent.

  Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC). , 2-dimethoxyethane (DME), chain ethers such as diethoxyethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), crown ethers, γ-butyrolactone (γ-BL) ), Nitrogen compounds such as acetonitrile (AN), sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO), and the like.

Among these, at least one selected from EC, PC, and γ-BL, at least one selected from EC, PC, and γ-BL and DMC, MEC, DEC, DME, DEE, THF, 2-MeTHF, It is desirable to use a mixed solvent composed of at least one selected from AN. Moreover, when using what contains the carbonaceous material which occludes / releases the said lithium ion for a negative electrode, from a viewpoint of improving the cycle life of the secondary battery provided with the said negative electrode, EC and PC, (gamma) -BL, EC and PC It is desirable to use a mixed solvent consisting of EC and MEC, EC and PC and DEC, EC and PC and DEE, EC and AN, EC and MEC, PC and DMC, PC and DEC, or EC and DEC.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and lithium trifluorometasulfonate. Examples thereof include lithium salts such as (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), and bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ]. Of these, LiPF ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ are preferable because conductivity and safety are improved.

  The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L.

  The non-aqueous electrolyte is generally used in the form of a solution, but may be in a solid form, for example, a sol form, a gel form, or a mixed form of a solid form and a solution form.

  As described above, according to the battery pack of the present embodiment, as shown in FIGS. 1 and 2, the gel agent 8 is filled between the insulating case 1 and the assembled battery 5 and between the plurality of secondary batteries of the assembled battery without any gaps. Therefore, for example, it is possible to prevent the connection plate 7 connecting the plurality of secondary batteries 6 constituting the assembled battery 5 from being detached due to shock and vibration when used as a power source for an electric vehicle, a power tool, a cordless cleaner, and the like. Can do.

  Further, when liquid leakage from a plurality of secondary batteries 6 constituting the assembled battery 5, rupture, or gas ejection occurs, a gel agent 8 is sealed as a buffer between the insulating case 1 and the assembled battery 5. Therefore, leakage from the insulating case 1, rupture, etc. can be suppressed.

Furthermore, the heat generated in the assembled battery can be released to the outside without causing a short circuit of a plurality of secondary batteries by further including a good heat conductive insulating powder such as aluminum nitride powder in the gel agent. .
That is, in a battery pack having a structure in which an assembled battery is housed in an insulating case, when the assembled battery is charged / discharged, the assembled battery generates heat, and the temperature of the assembled battery rises due to the heat insulating action of the insulating case made of synthetic resin or the like. To do. As a result, the assembled battery is charged and discharged at a high temperature, so that the cycle life is shortened.
For this reason, charging the assembled battery by filling the gel agent further containing the insulating powder having good heat conductivity between the insulating case and the assembled battery and between the secondary batteries of the assembled battery without any gaps. Heat generated at the time of discharge can be transmitted to the insulating case through the insulating powder with good thermal conductivity dispersed in the gel, and released to the outside. In addition, since the heat conductive powder dispersed in the gel is made of an insulating material, even if it is interposed between a plurality of secondary batteries of an assembled battery, a short circuit such as when using conductive powder such as metal is used. Occurrence can be avoided.
Therefore, it is possible to suppress the deterioration of the cycle characteristics of the assembled battery due to the heat trapping inside the insulating case by using the gel agent further containing the heat conductive insulating powder, and there is no occurrence of a short circuit. A safe non-aqueous electrolyte secondary battery pack can be provided.
In the nonaqueous electrolyte secondary battery pack of the present invention, a rupture valve may be provided on the upper part of the case body of the insulating case.
Hereinafter, embodiments of the present invention will be described in detail.

(Example 1)
As shown in FIGS. 1 and 2, the assembled battery 5 is housed in the insulating case 1, and the silicone gel 8 is filled in the insulating case 1 between the assembled batteries 5 and between the inner surface and the assembled battery 5. Thus, a non-aqueous electrolyte secondary battery pack was assembled. The cylindrical non-aqueous electrolyte secondary battery (single cell) constituting the assembled battery 5 has the following structure.
<Positive electrode>
A binder obtained by mixing 100 parts by weight of LiCoO ₂ powder, ₂ parts by weight of acetylene black having an average particle diameter of 50 nm and 3 parts by weight of flake graphite (artificial graphite) having an average particle diameter of 1 μm with a mixer A mixture of 5 parts by weight of polyvinylidene fluoride was dispersed in N-methylpyrrolidone to prepare a positive electrode paste. This positive electrode paste was applied to both surfaces of an aluminum foil as a current collector, dried and rolled to produce a positive electrode.

<Negative electrode>
Mesophase pitch carbon fibers were graphitized by graphitizing mesophase pitch carbon fibers made from mesophase pitch. Subsequently, a mixture of 10 parts by weight of natural graphite and 90 parts by weight of carbon material powder with respect to 90 parts by weight of this mesophase pitch-based carbon fiber is dispersed in N-methylpyrrolidone to form a paste. Then, it was applied to both surfaces of a copper foil as a current collector substrate, dried, and then roll-pressed to produce a negative electrode having a packing density of 1.4 g / cm ³ .

<Non-aqueous electrolyte>
1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) to prepare a non-aqueous electrolyte.
The positive electrode, a separator made of a polyethylene porous film (shutdown temperature of 135 ° C.), and the negative electrode were laminated in this order, and then wound in a spiral shape so that the negative electrode was located on the outer side to produce an electrode group. The electrode group and the non-aqueous electrolyte were respectively housed in a stainless steel bottomed cylindrical container to assemble a cylindrical lithium ion secondary battery (18650 size) having a design rated capacity of 1600 mAh.

(Example 2)
A non-aqueous electrolyte secondary battery pack similar to Example 1 was assembled except that polyurethane gel was used as the gel agent.
(Comparative Example 1)
A non-aqueous electrolyte secondary battery pack was assembled by simply housing an assembled battery in which twelve secondary batteries having the same configuration as in Example 1 were connected to each other by a connection plate in an insulating case.
100 battery packs of the obtained Examples 1 and 2 and Comparative Example 1 were prepared, and a drop test and a vibration test were performed.

(Drop test)
After dropping the battery pack from a height of 2 m, the voltage and impedance of the battery pack were measured. The good voltage rate per 100 pieces was determined by assuming that the obtained voltage and impedance were within a predetermined range, and that the voltage and impedance outside the range were defective. The results are shown in Table 1.
(Vibration test)
A vibration test was performed on the battery pack at a frequency of 200 Hz from three directions, and the vibration test was performed by increasing the frequency from the frequency to 500 Hz at a rate of 10 Hz / min, and then decreasing to 200 Hz at a rate of 10 Hz / min. . The good voltage rate per 100 pieces was determined by assuming that the obtained voltage and impedance were within a predetermined range, and that the voltage and impedance outside the range were defective. The results are shown in Table 1.

  As can be seen from Table 1, the secondary battery packs of Examples 1 and 2 have superior impact resistance as compared to the secondary battery pack of Comparative Example 1.

(Example 3)
A non-aqueous electrolyte secondary battery pack similar to that in Example 1 was assembled, except that a silicone gel in which 70% by weight of aluminum nitride (AlN) powder having an average particle diameter of 3 μm was dispersed was used as the gel agent.
The obtained 10 battery packs of Example 3 and Comparative Example 1 were charged at a constant current of 4.2 V and a constant voltage at a 1 C rate for 3 hours under an environment of 20 ° C. The discharge capacity at the time of discharging to 0 V was measured, and the average capacity of 10 pieces was obtained. Thereafter, charge / discharge under similar conditions was repeated 500 times, and the discharge capacity after 500 cycles (average capacity of 10 pieces) was measured. The average capacity retention rate was calculated from the average reference capacity and the average capacity after 500 cycles based on the following formula.
Average capacity retention rate (%) = (Average capacity after 500 cycles / Average reference capacity) × 100
As a result, the average capacity retention rate of the battery pack of Comparative Example 1 was 60%, whereas the average capacity retention rate of the battery pack of Example 3 was as high as 80%, indicating an excellent heat dissipation effect. .

  According to the present invention, it is possible to provide a highly reliable nonaqueous electrolyte secondary battery pack that is excellent in impact resistance and vibration resistance and is useful as a power source for an electric vehicle, a power tool, a cordless cleaner, and the like.

The perspective view which shows the nonaqueous electrolyte secondary battery pack concerning embodiment of this invention. The disassembled perspective view of the nonaqueous electrolyte secondary battery pack of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Insulation case, 2 ... Base plate, 4 ... Case main body, 5 ... Assembly battery, 6 ... Nonaqueous electrolyte secondary battery, 7 ... Connection board, 8 ... Gel agent.

Claims (2)

An assembled battery in which a plurality of nonaqueous electrolyte secondary batteries are electrically connected to each other;
An insulating case for storing and sealing the assembled battery;
A non-aqueous electrolyte secondary battery pack comprising a gel agent filled in the insulating case so as to fill a gap between the assembled battery and a gap between the assembled battery and the inner surface of the case.   The non-aqueous electrolyte secondary battery pack according to claim 1, wherein the gel agent further contains an insulating powder having good heat conductivity.

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