JP2004199939A - Nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution secondary battery with high reliability, improved cycle property, and improved safety by preventing short circuit from being caused by the preservation for long time at high temperature. <P>SOLUTION: The nonaqueous electrolytic solution secondary battery has a structure of winding a positive electrode, a negative electrode and a separator interposed between the electrodes, and stores the electrode group having the lead terminals 10 extending outward in the outer case, connected to a current collector of the positive electrode and the negative electrode respectively, together with the nonaqueous electrolytic solution. At least one electrode out of the positive electrode 4 and the negative electrode 6 is turned up in the vicinity of a connection part of the lead terminal 10, and wraps the the connection part of the lead terminal 10 by winding. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８７】
前記表１から明らかなように実施例１〜７のリチウムイオン二次電池は、ほぼ１００個の電池の漏液、発火破裂がなく、優れた高温貯蔵信頼性を有することがわかる。
【００８８】
一方、比較例１〜３のリチウムイオン二次電池は、実施例１〜７に比べて、電池の漏液、発火破裂に至らない個数が少ない。
【００８９】
特に、正極リード端子を電極群の捲き始め端部に位置させた実施例１〜３と比較例１とを対比すると、比較例１の二次電池において９５℃、１００時間貯蔵後の漏液、発火破裂に至らない個数が７７個であるのに対し、実施例１〜３の二次電池において同漏液、発火破裂に至らない個数が９９〜１００個と優れた高温貯蔵信頼性を有することがわかる。
【００９０】
また、表１から明らかなように実施例１〜７のリチウムイオン二次電池は、容量維持率が約８０％以上と高いことがわかる。
【００９１】
一方、比較例１〜３のリチウムイオン二次電池は、実施例１〜７に比べて、容量維持率が約６０％と低いことがわかる。
【００９２】
なお、前述した実施例においては正極リード端子に適用した例について説明したが、負極リード端子についても適用できる。
【００９３】
前述した実施例においては、円筒形非水電解液二次電池に適用した例を説明したが、有底矩形筒状の容器内に正極、負極、セパレータ及び非水電解液が収納された構造の角形非水電解液二次電池にも同様に適用することができる。また、外装材としてラミネートフィルムを使用する非水電解液二次電池、ゲル状非水電解質を用いる二次電池にも同様に適用することができる。
【００９４】
【発明の効果】
以上詳述したように、本発明によれば高温貯蔵時おける短絡を防止し、優れた信頼性を有し、かつ充放電サイクル特性に優れた非水電解液二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例および比較例で用いた円筒形非水電解液二次電池を示す切欠斜視図。
【図２】本発明の実施例１〜３および比較例１で用いた正極を示す斜視図。
【図３】本発明の実施例１〜５および比較例１、２で用いた負極を示す斜視図。
【図４】本発明の実施例１で用いた電極群を示す図。
【図５】本発明の実施例２で用いた電極群を示す図。
【図６】本発明の実施例３で用いた電極群を示す図。
【図７】本発明の実施例４，５および比較例２で用いた正極を示す斜視図。
【図８】本発明の実施例４で用いた電極群を示す図。
【図９】本発明の実施例５で用いた電極群を示す図。
【図１０】本発明の実施例６，７および比較例３で用いた正極を示す斜視図。
【図１１】本発明の実施例６，７および比較例３で用いた負極を示す斜視図。
【図１２】本発明の実施例６で用いた電極群を示す図。
【図１３】本発明の実施例７で用いた電極群を示す図。
【図１４】比較例１で用いた電極群を示す図。
【図１５】比較例２で用いた電極群を示す図。
【図１６】比較例３で用いた電極群を示す図。
【符号の説明】
１…容器、３…電極群、４…正極、５…セパレータ、６…負極、７…正極集電体、８ａ，８ｂ…正極活物質層未形成領域、９…正極活物質層、１０…正極リード端子、１１…負極集電体、１２ａ，１２ｂ…負極活物質層未形成領域、１３…負極活物質層、１４…負極リード端子、１５…折り返し部、１７…正極リード接続板、１８…遮断弁、１９…ＰＴＣ素子、２１…絶縁ガスケット。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to a non-aqueous electrolyte secondary battery in which at least one of a positive electrode and a negative electrode to which a lead terminal is connected has an improved structure near a lead terminal connection portion. Get involved.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as electronic devices such as mobile phones and VTRs have been reduced in size and demand has increased, there has been a demand for higher capacity secondary batteries serving as power supplies for these electronic devices. In addition, air pollution due to exhaust gas from automobiles has become a social problem, and it is expected that lightweight and high-performance secondary batteries will be used as power supplies for electric vehicles.
[0003]
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, and is expected as a power source for portable equipment. The demand for lithium ion secondary batteries is expanding because they can achieve high energy density. In such a lithium ion secondary battery, high capacity and high capacity can be achieved by improving the electrode materials such as the positive electrode active material and the negative electrode active material to higher capacity materials, reducing the thickness of the separator, and improving the battery structure. Energy density is being increased.
[0004]
However, with the increase in capacity and energy density, there is a concern that the cyclability of the battery may decrease. For this reason, the cycle characteristics have been improved by improving the electrolytic solution and the electrodes.
[0005]
Also, with the increase in capacity and energy density, the risk of safety of lithium ion secondary batteries has also increased. For example, when a current is supplied to a lithium ion secondary battery for a long time to cause an overcharge state or a short-circuit state due to long-term storage at a high temperature, the electrolytic solution is decomposed to generate gas and the internal pressure of the battery is reduced. Rises. If the overcharge or short circuit continues, the battery temperature rises sharply due to decomposition of the electrolytic solution or the like, rupture is activated, and the liquid leaks. At this time, if the temperature rises extremely, the battery may rupture and ignite.
[0006]
Therefore, it is important to design a highly safe battery by preventing leakage and ignition and rupture due to a rise in internal pressure of the battery and heat generation. At present, in order to reduce the risk of safety, in lithium ion secondary batteries, a rupture that can release gas inside the battery to the outside when the pressure inside the battery reaches a predetermined pressure, current A current cutoff valve that shuts off the flow or a PTC element that increases the resistance of the battery when the battery temperature rises and makes it difficult for the current to flow is provided. Further, a separator having a function of closing its pores by a rise in temperature inside the battery and shutting down at a predetermined temperature is used as a separator. Such measures prevent a rise in temperature and a rise in battery internal pressure.
[0007]
On the other hand, in Patent Literature 1, a positive electrode-side current collector foil exposed portion on which no positive electrode active material is applied is disposed between the positive electrode-side current collector foil exposed portion, a negative electrode plate, and a battery can serving as a negative electrode. A non-aqueous battery provided with an electrode plate laminate having a separator formed of an insulating film thinner than a separator interposed between active materials of both electrodes is disclosed.
[0008]
Further, in Patent Document 2, a positive electrode equipotential exposed metal portion extending in the longitudinal direction over one or more turns is formed, and the positive electrode equipotential exposed metal portion is provided in association with the negative electrode. A non-aqueous battery including a wound laminated electrode assembly that is disposed so as to face the exposed metal portion over one or more turns is disclosed.
[0009]
[Patent Document 1]
JP-A-8-203541
[0010]
[Patent Document 2]
JP-A-8-153542
[0011]
[Problems to be solved by the invention]
In a lithium ion secondary battery, a positive electrode current collector and a negative electrode current collector, which are components of an electrode group, are connected to a lid and a lead terminal, which is an electrical connection path for electrical connection to an outer can. I have. When such a lithium-ion secondary battery is stored at high temperatures for a long period of time, the lead terminals connected and connected to the innermost electrodes of the electrode group apply local pressure to the separator on the outer side, causing the separator to creep at high temperatures. And the risk of the separator breaking and short-circuiting increases.
[0012]
The electrode group is twisted by the lead terminals connected to the current collectors of the positive and negative electrodes, or is partially stressed, so that the electrolyte impregnation inside the electrode group is uneven, the gap between the positive and negative electrodes is uneven, or the electrode is filled. Since discharge unevenness occurs, it becomes a cause of deterioration of cycle characteristics.
[0013]
An object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery in which short circuit due to high-temperature long-term storage is prevented, safety is improved, and cycle characteristics are improved.
[0014]
[Means for Solving the Problems]
The non-aqueous electrolyte secondary battery according to the present invention has a structure in which a positive electrode, a negative electrode and a separator interposed between these electrodes are wound, and is connected to a current collector of the positive electrode and the negative electrode, respectively. A non-aqueous electrolyte secondary battery containing an electrode group having lead terminals extended to a non-aqueous electrolyte in an outer can,
At least one of the positive electrode and the negative electrode is folded back near the connection part of the lead terminal, and wraps the connection part of the lead terminal by the winding.
[0015]
In the nonaqueous electrolyte secondary battery according to the present invention, the lead terminal is connected to the positive electrode or the negative electrode located at the winding start end of the electrode group, and the electrode to which the lead terminal is connected is connected to the lead terminal. It is preferable that the connection part of the lead terminal be wrapped around the connection part and wrapped by the winding.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0017]
The non-aqueous electrolyte secondary battery according to the present invention, for example, a lithium ion secondary battery has a structure in which a positive electrode, a negative electrode and a separator interposed between these electrodes are wound, and a current collector of the positive electrode and the negative electrode And an electrode group having lead terminals extended to the outside by being connected to the battery pack together with a non-aqueous electrolyte in an outer can. At least one of the positive electrode and the negative electrode is folded along the winding direction in the vicinity of the connection portion of the lead terminal, and the folded portion surrounds the connection portion of the lead terminal by the winding.
[0018]
The positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte have the following configurations.
[0019]
1) Positive electrode
For this positive electrode, for example, a positive electrode material paste obtained by dispersing a positive electrode active material, a conductive agent and a binder in an appropriate solvent is applied to a current collector, leaving an exposed portion of a desired area on one or both sides, and dried. After that, it is manufactured by cutting into a desired size. The positive electrode lead terminal is connected to the exposed current collector by welding or the like without forming the positive electrode material layer.
[0020]
As the positive electrode active material, a lithium composite metal oxide can be used. Specifically, LiCoO _Two , LiNiO _Two , LiMnO _Two , LiMn _Two O _Four Are used. Examples of the binder include polyvinylidene fluoride, vinylidene fluoride-6-propylene fluoride copolymer, polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride terpolymer, vinylidene fluoride-pentafluoropropylene , A copolymer of vinylidene fluoride-chlorotrifluoroethylene, or a copolymer of another fluorine-based monomer and vinylidene fluoride. Other copolymers of a fluorine-based monomer and vinylidene fluoride include a copolymer of tetrafluoroethylene-vinylidene fluoride and a terpolymer of tetrafluoroethylene-perfluoroalkylvinyl ether (PFA) -vinylidene fluoride. Copolymer, 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.
[0021]
As the organic solvent for dispersing the binder, for example, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethyl acetate and the like can be used.
[0022]
Examples of the conductive agent include acetylene black, Ketjen black, graphite and the like.
[0023]
The compounding amount of the binder is 2% by weight to 8% by weight based on 100 parts by weight of the active material and the binder in total (or 100 parts by weight of the conductive agent when the conductive agent is included). % Is preferable.
[0024]
As a dispersing device for preparing the positive electrode material paste, for example, a ball mill, a bead mill, a dissolver, a sand grinder, a roll mill, or the like can be used.
[0025]
As the current collector, for example, an aluminum foil, a stainless steel foil, a titanium foil, or the like having a thickness of 10 to 40 μm can be used.
[0026]
2) Negative electrode
The negative electrode is prepared by dispersing a negative electrode material paste obtained by dispersing a negative electrode material selected from, for example, a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions, a conductive agent and a binder in a suitable solvent, onto one side or both sides of a current collector. It is prepared by applying the coating composition with leaving an exposed portion of a desired area, drying, and then cutting it to a desired size. The negative electrode lead terminal is not formed with the negative electrode material layer and is connected to the exposed current collector by welding or the like.
[0027]
Examples of the carbonaceous material that occludes and releases lithium ions include, for example, coke, carbon fiber, pyrolytic gas-phase carbonaceous material, graphite, fired resin, fired mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. . Among them, the use of mesophase pitch-based carbon fibers graphitized at 2500 ° C. or higher is preferable because the electrode capacity increases.
[0028]
Examples of the chalcogen compound that stores and releases lithium ions include titanium disulfide (TiS). _Two ), Molybdenum disulfide (MoS _Two ), Niobium selenide (NbSe) _Two ). 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 can be improved. Furthermore, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery can be improved.
[0029]
The negative electrode (for example, a negative electrode composed of a carbon material) is prepared by dispersing the carbon material, a conductive agent and a binder in an appropriate solvent, and forming a negative electrode material paste on one side or both sides of a current collector. It is produced by applying a continuous or desired length and an uncoated portion alternately to an area larger than the size to be dried, and cutting the dried and thin plate into a desired size.
[0030]
The mixing ratio of the negative electrode material and the binder is preferably 80 to 98% by weight of the negative electrode material and 2 to 20% by weight of the binder.
[0031]
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 consideration of electrochemical stability, flexibility at the time of winding, and the like. The thickness of this foil is preferably 8 to 20 μm.
[0032]
The negative electrode is allowed to be formed from a light metal. Examples of the light metal include aluminum, an aluminum alloy, a magnesium alloy, a lithium metal, and a lithium alloy.
[0033]
3) Separator
This separator is formed from a porous sheet.
[0034]
As the porous sheet, for example, a porous film or a nonwoven fabric can be used. In particular, the porous sheet is preferably made of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.
[0035]
It is desirable that the thickness of the porous sheet is 30 μm or less, more preferably 25 μm or less. The lower limit of the thickness of the porous sheet is 5 μm, more preferably 8 μm.
[0036]
The porous sheet preferably has a heat shrinkage at 120 ° C. for one hour of 20% or less, more preferably 15% or less.
[0037]
It is desirable that the porous sheet has a porosity of 30 to 60%, more preferably 35 to 50%.
[0038]
The porous sheet has an air permeability of 600 seconds / 100 cm. ^Three The following is preferred. Air permeability is 100cm ^Three Means the time (seconds) required for the air to pass through the porous sheet. Air permeability is 500 seconds / 100cm ^Three It is more preferable to set the following. The lower limit of the air permeability is 50 seconds / 100 cm. ^Three , More preferably 80 seconds / 100 cm ^Three It is desirable that
[0039]
An electrode having a structure in which such a positive electrode, a negative electrode and a separator interposed between these electrodes are wound, and having lead terminals extended to the outside connected to the current collectors of the positive electrode and the negative electrode, respectively. In the group, at least one of the positive electrode and the negative electrode is folded along the winding direction near the connection portion of the lead terminal, and the connection portion of the lead terminal is wrapped around the folded portion by the winding.
[0040]
The width of the folded portion is wider than the width of the lead terminal, and is preferably 2 to 10 mm wider than the width of the lead terminal.
[0041]
As the material of the lead terminal, aluminum, titanium, or the like is used for the positive terminal, and nickel, copper, or the like is used for the negative terminal.
[0042]
The lead terminal is connected to a current collector of any one of a positive electrode and a negative electrode located between the winding start end, the winding end end, or the winding start and the winding end of the electrode group. . In particular, in a mode in which a lead terminal is connected to the current collector of the electrode located at the winding start end of the electrode group, the electrode is folded near the connection portion of the lead terminal (near the winding start end), and the electrode group is folded. It is more preferable to wrap the connection part of the lead terminal by the folded part by the winding from the viewpoint of short-circuit prevention and cycle characteristics.
[0043]
4) Electrolyte
This electrolytic solution has a composition in which an electrolyte is dissolved in a non-aqueous solvent.
[0044]
Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), and chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC) and diethyl carbonate (DEC); , 2-dimethoxyethane (DME), diethoxyethane (DEE), etc., chain ethers, such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), cyclic ethers and crown ethers, γ-butyrolactone (γ-BL) ), Nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO).
[0045]
Among them, at least one selected from EC, PC, and γ-BL, and 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. Further, when a negative electrode containing a carbonaceous material that occludes and releases lithium ions is used, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, and EC and PC It is preferable to use a mixed solvent composed of EC and DEC, 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.
[0046]
Examples of the additives include vinylene carbonate (VC), trioxyl phosphate and the like.
[0047]
As the electrolyte, for example, lithium perchlorate (LiClO _Four ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium borofluoride (LiBF _Four ), Lithium arsenic hexafluoride (LiAsF) ₆ ), Lithium trifluorometasulfonate (LiCF _Three SO _Three ), Lithium aluminum tetrachloride (LiAlCl _Four ), Lithium bistrifluoromethylsulfonylimide [LiN (CF _Three SO _Two ) _Two ] And the like. Among them, LiPF6, LiBF _Four , LiN (CF _Three SO _Two ) _Two The use of is preferred because conductivity and safety are improved.
[0048]
The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.5 mol / L.
[0049]
As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte mainly containing a non-aqueous solvent and a lithium salt, a gel non-aqueous electrolyte containing a non-aqueous solvent, a lithium salt and a polymer can be used.
[0050]
The electrode group holding the gelled non-aqueous electrolyte can be manufactured by the following method.
[0051]
(1) The separator is impregnated with a slurry containing a non-aqueous solvent, a lithium salt and a gelling agent, and the separator is interposed between the positive electrode and the negative electrode. Can be prepared by applying a slurry containing the following to a positive electrode or a negative electrode, and interposing a separator between the positive and negative electrodes.
[0052]
(2) It can be produced by applying a slurry containing a non-aqueous solvent, a lithium salt and a gelling agent to a positive electrode and a negative electrode, bonding them together, and not interposing a separator.
[0053]
(3) The separator, the positive electrode, and the negative electrode group were impregnated with a mixed solution (electrolyte raw material) of a monomer, an electrolytic solution, and a polymerizing agent. Then, heat is applied and the electrolyte is gelled by thermal polymerization.
[0054]
The non-aqueous electrolyte secondary battery according to the present invention allows a safety valve, a mechanism such as a PTC, or a current cutoff valve mechanism, a mechanism such as a PTC to be incorporated as a safety mechanism.
[0055]
As described above, the present invention has a structure in which a positive electrode, a negative electrode, and a separator interposed between these electrodes are wound, and is connected to the positive electrode and negative electrode current collectors and extended to the outside. The electrode group having the output lead terminal is housed together with the nonaqueous electrolyte in the outer can, and at least one of the positive electrode and the negative electrode is folded along the winding direction in the vicinity of the connection portion of the lead terminal, By wrapping the connection portion of the lead terminal with the folded portion by winding, a short circuit due to high-temperature long-term storage can be prevented, and a nonaqueous electrolyte secondary battery with improved cycle characteristics can be obtained.
[0056]
That is, in high-temperature long-term storage, the corners of the lead terminals connected to the electrodes of the electrode group apply local pressure to the separator facing the outside of this electrode (for example, the positive electrode), and the separator undergoes creep deformation at high temperatures, The possibility that the separator is broken increases. For this reason, there is a high risk that the lead terminal will break through the separator and come into contact with the opposite electrode (negative electrode) of the opposite polarity to cause a short circuit.
[0057]
For this reason, as in the present invention, at least one of the positive electrode and the negative electrode is folded along the winding direction in the vicinity of the connection portion of the lead terminal, and the lead terminal is connected at the folded portion by the winding. By wrapping the portion, the corners of the lead terminals connected to the electrodes of the electrode group apply local pressure to the separator facing the outside of the electrodes at the folded portions of the electrodes wrapping the connection portions of the lead terminals. Since this can be alleviated, it is possible to prevent breakage of the separator and reduce the risk of short circuit.
[0058]
Particularly, since the curvature of the wound positive electrode and negative electrode becomes large at the winding start end of the electrode group, when a positive electrode lead terminal is connected to the electrode (for example, the positive electrode) at this location, the lead terminal breaks through the separator and faces the negative electrode. The probability that a short circuit will occur due to contact with the wire will increase. For this reason, in the form in which the lead terminal is connected to the current collector of the electrode located at the winding start end of the electrode group, the electrode is folded near the connection portion of the lead terminal (near the winding start end), Wrapping the connection portion of the lead terminal with the folded portion by winding the group can effectively prevent a short circuit.
[0059]
In addition, when the electrodes of the electrode group expand and contract with an increase in the cycle, distortion occurs. This distortion causes the electrode group to be twisted by the lead terminals, causes partial stress on the electrode group, and causes uneven electrolyte impregnation inside the electrode group and uneven charging / discharging due to variation in the interval between the positive electrode and the negative electrode. It causes deterioration.
[0060]
Therefore, as in the present invention, at least one of the positive electrode and the negative electrode is folded along the winding direction in the vicinity of the connection portion of the lead terminal, and the connection portion of the lead terminal is wrapped around the folded portion by the winding. Accordingly, the pressure applied to the electrode group from the lead terminals is reduced, and the torsion of the electrode group and partial stress of the electrode group can be prevented. As a result, unevenness of impregnation of the electrolytic solution inside the electrode group and unevenness of charge / discharge due to variation in the interval between the positive electrode and the negative electrode can be suppressed, and cycle characteristics can be improved.
[0061]
In particular, at the beginning of the winding of the electrode group, the electrodes of the electrode group expand and shrink due to an increase in the cycle, causing a large distortion.Therefore, when the positive electrode lead terminal is connected to the electrode at this point, the electrode group is twisted by the lead terminal, The partial stress of the electrode group increases. In such an embodiment in which a lead terminal is connected to the current collector of the electrode located at the winding start end of the electrode group, the electrode is folded near the connection portion of the lead terminal (near the winding start end), and the electrode is folded. By wrapping the connection portion of the lead terminal with the folded portion by winding the group, it is possible to effectively prevent torsion of the electrode group and partial stress of the electrode group and improve cycle characteristics.
[0062]
【Example】
Hereinafter, embodiments of the present invention will be described in detail.
[0063]
(Example 1)
<Preparation of positive electrode>
LiCoO _Two 100 parts by weight of 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 are mixed with a mixer, and polyvinylidene fluoride 5 as a binder is further mixed. A positive electrode paste was prepared by adding parts by weight to the mixture and adding and dispersing N-methylpyrrolidone. Subsequently, this paste was applied to both surfaces of a current collector made of an aluminum foil so that the vicinity of both ends was exposed as an active material non-applied region, and dried and rolled to produce a positive electrode. Thereafter, a positive electrode lead terminal made of aluminum was ultrasonically welded to an active material non-applied region on one end side of the positive electrode so that the upper end thereof extended upward.
[0064]
<Preparation of negative electrode>
The mesophase pitch carbon fiber made from mesophase pitch is graphitized to produce mesophase pitch carbon fiber, 90 parts by weight of the mesophase pitch carbon fiber is added with 10 parts by weight of natural graphite, and 100 parts by weight of this mixture is polyfluorinated. 7 parts by weight of vinylidene chloride was added, and N-methylpyrrolidone was added and dispersed to prepare a paste. Subsequently, this paste is applied to both sides of a current collector made of copper foil so that the vicinity of both ends is exposed as an active material non-applied area, dried, and then roll-pressed to obtain a packing density of 1.4 g / cm. ^Three Was produced. Thereafter, a negative electrode lead terminal made of nickel was ultrasonically welded to an active material non-applied region on one end side of the negative electrode such that the lower end of the negative electrode lead terminal extends downward.
[0065]
<Non-aqueous electrolyte>
A non-aqueous electrolyte was prepared by dissolving 1 M of lithium hexafluorophosphate (LiPF6) in a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2).
[0066]
Using the above-described positive electrode, negative electrode, and electrolyte, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1900 mAh and having a built-in current cutoff valve mechanism shown in FIG. 1 was assembled.
[0067]
That is, in FIG. 1, a stainless steel bottomed cylindrical container 1 has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1, and the electrolyte 6 g prepared by the above method is housed in the container 1. The electrode group 3 includes a positive electrode 4 prepared by the above method, a separator 5 made of a porous film made of polyethylene and having a thickness of 20 μm, and a negative electrode 6 prepared by the above method. It has a structure wound spirally so as to be located.
[0068]
As shown in FIG. 2, the positive electrode 4 has positive electrode active material layers 9 formed on both surfaces of a current collector 7 made of aluminum foil so that the vicinity of both ends is exposed as active material layer non-formed regions 8a and 8b. In addition, the positive electrode lead terminal 10 made of aluminum is, for example, ultrasonically welded to the active material layer non-formed region 8a on one end side (for example, the left end side) so that the upper end extends upward.
[0069]
As shown in FIG. 3, the negative electrode 6 is formed with a negative electrode active material layer 13 on both surfaces of a current collector 11 made of copper foil such that the vicinity of both ends is exposed as active material layer non-formed regions 12a and 12b, In addition, the negative electrode lead terminal 14 made of nickel is, for example, ultrasonically welded to the active material layer non-formation region 12b on one end side (for example, the right end side) so that the lower end extends downward.
[0070]
As shown in FIG. 4 (A) and FIG. 4 (B), which is an enlarged view of the main part of FIG. 4 (A), the electrode group 3 has the positive electrode lead terminal 10 at the winding start end thereof. The active material layer non-formed region 8a is welded to the active material layer non-formed region 8a, and the active material layer unformed region 8a is folded in the middle. Is wrapped around.
[0071]
The holding plate 16 is arranged above the electrode group 3. A shut-off valve 18 having a positive electrode lead connection plate 17 on the lower surface, a PTC element 19 having a hole opened in the center, and a hat-shaped positive electrode terminal 20 are laminated in this order. It is caulked and fixed to the upper opening via an insulating gasket 21. The current cutoff valve 22 is constituted by the shutoff valve 18 having the positive electrode lead connection plate 16 and the PTC element 19. The positive electrode terminal 20 has a gas vent hole (not shown).
[0072]
The pipe 23 is inserted in the center of the electrode group 3. The upper end of the positive electrode lead terminal 10 connected to the positive electrode 4 is connected to the positive electrode lead connection plate 17. The lower end of the negative electrode lead terminal 14 connected to the negative electrode 6 is connected to the bottom of the container 1 also serving as the negative electrode terminal.
[0073]
(Example 2)
The above-described positive electrode lead terminal 10 shown in FIG. 2 uses the positive electrode 4 in which the positive electrode 4 is ultrasonically welded to the active material layer non-formed region 8a of the current collector 7, and the main part of FIG. 5A and FIG. As shown in the enlarged view (B) of the drawing, the positive electrode lead terminal 10 is located at the winding start end, and the front end of the active material layer non-formed region 8a is folded outward, so that the positive electrode 4 is wound. A lithium ion secondary battery similar to that of Example 1 was assembled except that the electrode group 3 having a structure in which the connection portion of the positive electrode lead terminal 10 was wrapped around the folded portion 15 was used.
[0074]
(Example 3)
The above-described positive electrode lead terminal 10 shown in FIG. 2 uses the positive electrode 4 which is ultrasonically welded to the active material layer-unformed region 8a of the current collector 7, and is a main part of FIGS. 6 (A) and 6 (A). As shown in the enlarged view (B) of the drawing, the positive electrode lead terminal 10 is located at the winding start end, and the tip of the active material layer non-formed region 8a is folded inward, so that the positive electrode 4 is wound. A lithium ion secondary battery similar to that of Example 1 was assembled except that the electrode group 3 having a structure in which the connection portion of the positive electrode lead terminal 10 was wrapped around the folded portion 15 was used.
[0075]
(Example 4)
The positive electrode 4 shown in FIG. 8A and FIG. 7A is used by using the positive electrode 4 in which the positive electrode lead terminal 10 shown in FIG. 7 is ultrasonically welded to the active material layer non-formed region 8 formed near the center of the current collector 7. As shown in FIG. 2B, which is an enlarged view of a main part, the positive electrode lead terminal 10 is located between the winding start end and the winding end end, and the active material layer-free area 8 is folded inward. Then, a lithium ion secondary battery similar to that of Example 1 was assembled except that the electrode group 3 having a structure in which the connection portion of the positive electrode lead terminal 10 was wrapped around the folded portion 15 by winding the positive electrode 4 was used.
[0076]
(Example 5)
9 (A) and (A) of FIG. 9 using the positive electrode 4 in which the positive electrode lead terminal 10 shown in FIG. 7 described above is ultrasonically welded to the active material layer non-formed region 8 formed near the center of the current collector 7. As shown in FIG. 3B, which is an enlarged view of a main part of FIG. 3, the positive electrode lead terminal 10 is located between the winding start end and the winding end end, and the active material layer non-formed region 8 is located outside. A lithium-ion secondary battery similar to that of Example 1 was assembled, except that the electrode group 3 was folded and wound around the positive electrode 4 so as to enclose the connection part of the positive electrode lead terminal 10 at the folded part 15. Was.
[0077]
(Example 6)
A positive electrode active material layer 9 is formed on both surfaces of the current collector 7 made of aluminum foil shown in FIG. 10 so that the vicinity of both ends is exposed as active material layer non-formed regions 8a and 8b, and one end (right end) The positive electrode 4 is ultrasonically welded so that the positive electrode lead terminal 10 made of aluminum extends upward in the active material layer non-formation region 8b, and the current collector 11 made of copper foil as shown in FIG. Negative electrode active material layers 13 are respectively formed on both surfaces such that the vicinity of both ends thereof are exposed as active material layer non-formed regions 12a and 12b, and nickel is formed in one end (left end) active material layer non-formed region 12a. FIG. 13A is a main part enlarged view of FIG. 12A and FIG. 12A, using the negative electrode 6 in which the negative electrode lead terminal 14 is ultrasonically welded so that the lower end extends downward. End of winding as shown in B) The positive electrode lead terminal 10 is located in the portion, and the middle of the active material layer unformed region 8b is folded inward, and the connection portion of the positive electrode lead terminal 10 is folded at the folded portion 15 by winding the positive electrode 4. A lithium ion secondary battery was assembled in the same manner as in Example 1 except that the electrode group 3 having a wrapped structure was used.
[0078]
(Example 7)
The positive electrode 4 in which the positive electrode lead terminal 10 shown in FIG. 10 described above is ultrasonically welded to the active material layer-free region 8b of the current collector 7 and the negative electrode lead terminal 14 shown in FIG. As shown in FIG. 13 (A) and FIG. 13 (B) which is an enlarged view of a main part of FIG. The positive electrode lead terminal 10 is located at a position, and the middle of the active material layer non-formed region 8a is folded outward, and the connection of the positive electrode lead terminal 10 is wrapped around the folded portion 15 by the winding of the positive electrode 4. A lithium ion secondary battery was assembled in the same manner as in Example 1 except that the electrode group 3 having an elliptical structure was used.
[0079]
(Comparative Example 1)
The above-described positive electrode lead terminal 10 shown in FIG. 2 uses the positive electrode 4 ultrasonically welded to the active material layer non-formed region 8a of the current collector 7, and as shown in FIG. A lithium ion secondary battery similar to that of Example 1 was assembled, except that the electrode group 3 having the structure indicated by was used.
[0080]
(Comparative Example 2)
Using the above-described positive electrode 4 in which the positive electrode lead terminal 10 shown in FIG. 7 was ultrasonically welded to the active material layer non-formed region 8 formed near the center of the current collector 7, as shown in FIG. A lithium ion secondary battery similar to that of Example 1 was assembled, except that the electrode group 3 having a structure in which the positive electrode lead terminal 10 was located in the middle of the end end was used.
[0081]
(Comparative Example 3)
The positive electrode lead terminal 10 shown in FIG. 10 described above is ultrasonically welded to the active material layer-unformed region 8b of the current collector 7 and the negative electrode lead terminal 14 shown in FIG. Example 1 was the same as Example 1 except that the negative electrode 6 ultrasonically welded to the layer non-formed area 8a and the electrode group 3 having the structure in which the positive electrode lead terminal 10 was located at the end of winding as shown in FIG. A similar lithium ion secondary battery was assembled.
[0082]
The obtained secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to the following high-temperature storage test and charge / discharge cycle test.
[0083]
(High temperature storage test)
The secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to two cycles of charge and discharge. The charging at this time was performed at a charging current of 1900 mA (1 C) and a constant voltage of 4.2 V at 20 ° C. for a total of 3 hours. The discharge was performed at a constant current of 1900 mA (1 C), and the discharge end voltage was set to 3.0 V. The rest time after charging and discharging was 10 minutes, respectively. After such charge / discharge, the battery was held at 1900 mA (1 C) and a constant voltage of 4.2 V at 20 ° C. for a total of 3 hours. Thereafter, a storage test was started for each of the secondary batteries. The storage conditions were 85 ° C., 100 hours and 95 ° C., 100 hours, and the number of tests for each secondary battery was 100.
[0084]
In such a high-temperature storage test, the number of batteries that did not lead to liquid leakage, battery rupture, or ignition was examined. Table 1 shows the results.
[0085]
(Charge / discharge cycle test)
Charge / discharge cycle tests were performed on the secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3. The charging was performed at a charging current of 1900 mA (1 C) and a constant voltage of 4.2 V at 20 ° C. for a total of 3 hours. The discharge was performed at a constant current of 1900 mA (1 C), and the discharge end voltage was set to 3.0 V. The rest time after charging and discharging was 10 minutes, respectively. Such charge / discharge was performed for two cycles, and the capacity was confirmed. Thereafter, the battery was charged at 20 ° C. and maintained at a constant voltage of 1900 mA (1 C) and 4.2 V, performed for a total of 3 hours, discharged at a constant current of 1900 mA (1 C), and the discharge end voltage was 3.0 V. The rest time after charging and discharging was 10 minutes, respectively. This cycle was performed 500 times, and the capacity retention ratio after the 500th cycle with respect to the capacity in the first cycle was examined. The test number of each secondary battery was five, and the average results of the capacity retention ratios are shown in Table 1 below.
[0086]
[Table 1]

[0087]
As is clear from Table 1, the lithium ion secondary batteries of Examples 1 to 7 do not have liquid leakage and ignition burst of almost 100 batteries, and have excellent high-temperature storage reliability.
[0088]
On the other hand, in the lithium ion secondary batteries of Comparative Examples 1 to 3, the number of batteries that does not lead to liquid leakage or ignition and rupture is smaller than in Examples 1 to 7.
[0089]
In particular, comparing Examples 1 to 3 in which the positive electrode lead terminal is located at the winding start end of the electrode group and Comparative Example 1, the secondary battery of Comparative Example 1 has a liquid leakage after storage at 95 ° C. for 100 hours, While the number that does not lead to ignition and rupture is 77, the leakage in the secondary batteries of Examples 1 to 3 and the number that does not lead to ignition and rupture have an excellent high-temperature storage reliability of 99 to 100. I understand.
[0090]
Further, as is clear from Table 1, the lithium ion secondary batteries of Examples 1 to 7 have a high capacity retention of about 80% or more.
[0091]
On the other hand, it can be seen that the lithium ion secondary batteries of Comparative Examples 1 to 3 had a lower capacity retention ratio of about 60% than Examples 1 to 7.
[0092]
In the above-described embodiment, an example in which the present invention is applied to a positive electrode lead terminal has been described.
[0093]
In the above-described embodiment, an example in which the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery has been described, but a structure in which a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are accommodated in a bottomed rectangular cylindrical container. The same can be applied to a prismatic nonaqueous electrolyte secondary battery. Further, the present invention can be similarly applied to a non-aqueous electrolyte secondary battery using a laminate film as an exterior material and a secondary battery using a gelled non-aqueous electrolyte.
[0094]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that prevents short circuits during high-temperature storage, has excellent reliability, and has excellent charge / discharge cycle characteristics. .
[Brief description of the drawings]
FIG. 1 is a cutaway perspective view showing a cylindrical nonaqueous electrolyte secondary battery used in Examples and Comparative Examples of the present invention.
FIG. 2 is a perspective view showing a positive electrode used in Examples 1 to 3 and Comparative Example 1 of the present invention.
FIG. 3 is a perspective view showing a negative electrode used in Examples 1 to 5 and Comparative Examples 1 and 2 of the present invention.
FIG. 4 is a diagram showing an electrode group used in Example 1 of the present invention.
FIG. 5 is a diagram showing an electrode group used in Example 2 of the present invention.
FIG. 6 is a diagram showing an electrode group used in Example 3 of the present invention.
FIG. 7 is a perspective view showing a positive electrode used in Examples 4 and 5 and Comparative Example 2 of the present invention.
FIG. 8 is a diagram showing an electrode group used in Example 4 of the present invention.
FIG. 9 is a diagram showing an electrode group used in Example 5 of the present invention.
FIG. 10 is a perspective view showing a positive electrode used in Examples 6, 7 and Comparative Example 3 of the present invention.
FIG. 11 is a perspective view showing a negative electrode used in Examples 6 and 7 and Comparative Example 3 of the present invention.
FIG. 12 is a diagram showing an electrode group used in Example 6 of the present invention.
FIG. 13 is a diagram showing an electrode group used in Example 7 of the present invention.
FIG. 14 is a diagram showing an electrode group used in Comparative Example 1.
FIG. 15 is a diagram showing an electrode group used in Comparative Example 2.
FIG. 16 is a diagram showing an electrode group used in Comparative Example 3.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Container, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 7 ... Positive electrode current collector, 8a, 8b ... Positive electrode active material layer-free area, 9 ... Positive electrode active material layer, 10 ... Positive electrode Lead terminal, 11: Negative electrode current collector, 12a, 12b: Negative electrode active material layer unformed region, 13: Negative electrode active material layer, 14: Negative electrode lead terminal, 15: Folded portion, 17: Positive electrode lead connection plate, 18: Interruption Valve, 19: PTC element, 21: insulating gasket.

Claims (2)

An electrode group having a structure in which a positive electrode, a negative electrode, and a separator interposed between these electrodes are wound, and having a lead terminal extending to the outside connected to the current collector of the positive electrode and the negative electrode, respectively. A non-aqueous electrolyte secondary battery housed in a can with a non-aqueous electrolyte,
At least one electrode of the positive electrode and the negative electrode is folded near a connection part of the lead terminal, and wraps the connection part of the lead terminal by the winding, wherein the nonaqueous electrolyte secondary battery is characterized in that: . The lead terminal is connected to the positive electrode or the negative electrode located at the winding start end of the electrode group, and the electrode to which the lead terminal is connected is folded near a connection portion of the lead terminal, and the lead is wound by the winding. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery encloses a connection portion of the terminal.

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