JP2007335308A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of obtaining excellent quick charging characteristics and volume energy density in a short manufacturing time. <P>SOLUTION: In the nonaqueous electrolyte secondary battery equipped with an electrode group 1 with a cathode 2 and an anode 3 wound around through a separator 4 into a flat spiral, the cathode 2 and the anode 3 each contain a collector made of aluminum or an aluminum alloy, at least one lead part connected to a long-side end part of the collector, and an active material carried by the collector, satisfying the formula (1) (L/W)≤30 wherein, L is an effective length of a collector per lead part 1, and W is a width in a short-side direction of the collector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Nonaqueous electrolyte secondary batteries that charge and discharge via lithium ions have a high energy density and are widely used in small portable devices typified by mobile phones and the like. In recent years, the demand for rapid charging and discharging for the purpose of miniaturization and improvement of convenience of portable devices and the increasing concern about environmental problems have led to non-aqueous electrolytes for electric vehicles, hybrid vehicles, power storage, etc. With the aim of applying secondary batteries, there are increasing demands for improving energy density, input / output characteristics, and cycle characteristics.

  In the same type of battery, methods for improving the energy density, rapid charge / discharge characteristics, and input / output characteristics include increasing the specific surface area of the active material, thinning the electrode, and increasing the density. As the negative electrode active material, a carbon material capable of occluding and releasing lithium ions is generally used from the viewpoint of energy density. In the negative electrode using a carbon material, copper is used for the current collector. However, when copper is used for the current collector, the copper surface of the current collector dissolves due to an increase in the potential of the negative electrode in an overdischarged state, and this phenomenon becomes prominent particularly in a high temperature environment. There was a problem that the capacity deteriorated due to a decrease in efficiency.

On the other hand, as described in Patent Document 1, a negative electrode current collector made of aluminum or aluminum alloy foil having an average crystal grain size of 50 μm or less, and a negative electrode active material having a particle size distribution with a primary particle diameter of 1 μm or less, A non-aqueous electrolyte secondary battery using a battery has been proposed. By setting the average crystal grain size of the current collector to 50 μm or less, the strength of the current collector is improved. Therefore, even if a powder having a particle size distribution with a primary particle size of 1 μm or less is used as the negative electrode active material, the electrode density The energy density and input / output characteristics are improved.
JP-A-2005-123183

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery capable of obtaining excellent rapid charge characteristics and volume energy density in a short manufacturing time.

A nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery comprising an electrode group in which a positive electrode and a negative electrode are wound in a flat spiral shape through a separator,
Each of the positive electrode and the negative electrode is carried by the current collector, a current collector made of aluminum or an aluminum alloy, at least one lead portion connected to a long side end of the current collector, and An active material-containing layer, and satisfy the following formula (1).

(L / W) ≦ 30 (1)
Here, L is the effective current collector length per one lead portion, and W is the width in the short side direction of the current collector.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery which can obtain the quick charge characteristic and volume energy density which were excellent in the short manufacturing time can be provided.

  The volume resistivity of aluminum used for the current collector of the non-aqueous electrolyte secondary battery described in Patent Document 1 is 2.62 [μΩ · cm] and 1.69 [μΩ · cm] of copper. Since it is relatively high, it is disadvantageous in terms of the conductivity of the current collector. In addition, if the current collector thickness is reduced for the purpose of improving energy density and input / output characteristics, the resistance of the current collector increases, and electrons collected from the active material are sufficiently collected and quickly extracted. In some cases, the input / output density may decrease. Therefore, the electrode is strip-shaped and the current collector lead is taken out from each leaf to reduce the substantial length of the current collector, thereby suppressing the voltage loss due to the resistance of the current collector. Attempts have been made to ensure output characteristics. In this case, since a plurality of electrodes are required to increase the battery capacity and the facing area, there are problems such as low productivity and high cost when manufacturing the electrode group.

  As a result of extensive research, the present inventors have found that even when aluminum or an aluminum alloy is used for the current collector in order to suppress elution of the current collector in a high-temperature overdischarge environment, By restricting the dimensions of the long and short sides of the shank electrode as shown in the following formula (1), it is possible to add a current collecting lead to each leaf of the small electrode and to make an electrode structure in which a plurality of sheets are stacked. The inventors have found that the input / output characteristics and energy density at a large current can be improved by using an electrode group having a wound structure, and the present invention has been achieved.

(L / W) ≦ 30 (1)
Here, L is the effective current collector length per one lead portion, and W is the width in the short side direction of the current collector.

In addition, with the above configuration, voltage loss due to the resistance of the current collector is greatly reduced, so that the positive electrode and negative electrode lead portions are drawn out only from one end surface, and the wound electrode group having a small lead cross-sectional area Even if is used, excellent input / output characteristics can be obtained. This wound electrode group is advantageous in terms of volumetric energy density because the dead space in the container can be reduced as compared with the case where the positive and negative electrode lead portions are drawn out from both end faces. If only one end face elicit lead portion of the positive electrode and the negative electrode, the sectional area of the lead portion of the positive electrode in the range of 0.1 to 10 mm ^2, the cross-sectional area of the lead portion of the negative electrode in the range of 0.1 to 10 mm ² can do. In addition, when a positive electrode has multiple lead parts, the total value of the cross-sectional areas of each lead part is used. The same applies to the negative electrode.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the electrode group 1 has a structure in which a positive electrode 2 and a negative electrode 3 are wound into a flat shape with a separator 4 interposed therebetween. The strip-like positive electrode lead portion 5 is electrically connected to the positive electrode 2. On the other hand, the strip-shaped negative electrode lead portion 6 is electrically connected to the negative electrode 3. The electrode group 1 is housed in a laminate film container 7 in which a sealing portion 8 is formed on both long sides and one short side. As shown in FIGS. 1 and 2, the tips of the positive electrode lead portion 5 and the negative electrode lead portion 6 are drawn out from the sealing portion 8 on the short side of the container 7.

  As shown in FIG. 3, the positive electrode 2 includes a positive electrode current collector 2a and a positive electrode active material-containing layer 2b supported on one or both surfaces of the positive electrode current collector 2a. The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on one or both surfaces of the negative electrode current collector 3a. The separator 4 is interposed between the positive electrode active material-containing layer 2b and the negative electrode active material-containing layer 3b.

  The lead part attachment positions of the positive electrode 2 and the negative electrode 3 will be described with reference to FIG. FIG. 4 shows the case of the negative electrode 3. Both the positive electrode 2 and the negative electrode 3 have a strip shape. A negative electrode lead portion 6 is welded to one end portion of the long side of the negative electrode current collector 3a. The tip of the negative electrode lead portion 6 is drawn out in the short side direction of the negative electrode 3. The negative electrode active material-containing layer 3 b is formed on both surfaces of the negative electrode current collector 3 a except for the welded portion of the negative electrode lead portion 6. The positive electrode 2 has the same configuration as that of the negative electrode 3. The positive electrode lead portion 5 is welded to one end portion of the long side of the positive electrode current collector 2a. The tip of the positive electrode lead portion 5 is drawn out in the short side direction of the positive electrode 2. The positive electrode active material-containing layer 2 b is formed on both surfaces of the positive electrode current collector 2 a except for the welded portion of the positive electrode lead portion 5. Each of the positive electrode 2 and the negative electrode 3 satisfies the following formula (1).

(L / W) ≦ 30 (1)
However, L is the effective current collector length per lead portion, and W is the width of the current collector in the short side direction.

  When the negative electrode lead part 6 is welded to one end portion of the long side of the negative electrode current collector 3 a as shown in FIG. 4, L is a short located on the opposite side of the negative electrode lead part 6 and the negative electrode lead part 6. The distance from the side (the width of the negative electrode lead portion 6 is not included). Also in the case of the positive electrode 2, when the positive electrode lead portion 5 is welded to one end portion of the long side of the positive electrode current collector 2 a, L is positioned on the opposite side of the positive electrode lead portion 5 and the positive electrode lead portion 5. The distance from the short side (the width of the positive electrode lead portion 5 is not included).

  When (L / W) of the positive electrode 2 or the negative electrode 3 exceeds 30, voltage loss due to the resistance of the positive electrode current collector 2a or the negative electrode current collector 3a becomes large, so that input / output characteristics at a large current are deteriorated. By setting (L / W) of the positive electrode 2 and the negative electrode 3 to 30 or more, a secondary battery excellent in input / output characteristics and volume energy density at a large current can be provided with high productivity. In addition, when the (L / W) of the positive electrode 2 or the negative electrode 3 is less than 7.5, the volume energy density of the secondary battery may be lowered. Therefore, the lower limit value of the (L / W) of the positive electrode 2 and the negative electrode 3 Is preferably 7.5.

  In the positive electrode 2 and the negative electrode 3, the thickness of the current collector is 20 μm or less, and the ratio (t / T) value between the thickness t of the active material containing layer and the thickness T of the current collector is 3 or less. Is desirable. Thereby, the input / output characteristics and volume energy density at a large current can be further improved. The lower limit value of the thickness of the current collector can be 3 μm, and the lower limit value of the thickness ratio (t / T) value can be 1.2 (more preferably 1.5). FIG. 5 shows the thickness T of the negative electrode current collector 3a of the negative electrode 3 and the thickness t of the negative electrode active material-containing layer 3b.

  The thickness t of the active material-containing layer and the thickness T of the current collector are measured by the method described below.

  The battery is disassembled and the positive and negative electrodes are removed and flattened. The thickness of the flat surface of the electrode is measured with a dial gauge (measuring pressure of 1.4 N or less) having a tip φ10 plane measuring terminal to obtain an electrode thickness T1. Further, the current collector thickness of the active material uncoated part (active material containing layer non-formed part) is measured in the same manner, and is defined as T. The value obtained by subtracting T from T1 is defined as the thickness t of the active material-containing layer. However, when the thickness of the electrode in which the active material-containing layer is formed on both surfaces of the current collector is T1, the value of 1/2 of (T1-T) is the thickness t of the active material-containing layer.

The number of the lead portions 5 of the positive electrode 2 or the lead portions 6 of the negative electrode 3 can be two or more. The case of the negative electrode 3 will be described as an example with reference to FIG. Negative electrode leads 6 ₁ and 6 ₂ are welded to both ends of the long side of the negative electrode current collector 3a. The tips of the negative electrode lead portions 6 ₁ and 6 ₂ are drawn out in the short side direction of the negative electrode 3. The negative electrode active material-containing layer 3b is formed on both surfaces of the negative electrode current collector 3a except for the welded portions of the negative electrode lead portions 6 ₁ and 6 ₂ . In this case, L is a length corresponding to half the distance (width of the negative electrode lead 6 is not included) of the negative electrode lead portion ₆₁ and the anode lead portion 6 _2. Also in the positive electrode 2, when the positive electrode lead part is welded to both ends of the long side of the positive electrode current collector 2a, L is the distance between the two positive electrode lead parts (not including the width of the positive electrode lead part). The length corresponds to half.

When two lead portions are used as illustrated in FIG. 6, two positive electrode lead portions and two negative electrode lead portions may be drawn out from one electrode group, but as illustrated in FIG. It is also possible to produce a plurality of electrodes and to draw out one positive electrode lead portion and one negative electrode lead portion from each electrode group. This will be specifically described. Each of the positive electrode and the negative electrode is cut in half with a length L, and two positive electrodes and two negative electrodes are prepared. Electrode groups are prepared from each of them, and two sets of electrode groups 1 ₁ and 1 ₂ are obtained as shown in FIG. By welding or the like and a negative electrode terminal 6 ₂ of the electrode group 1 negative terminal ₆₁ of the ₁ and the electrode group 1 ₂ as well as electrically connected, the electrode group 1 ₁ of the positive electrode terminal 5 ₁ and the positive terminal of the electrode group 1 ₂ 5 ₂ Are electrically connected to each other by welding or the like. According to such a method, since the lengths of the positive electrode and the negative electrode necessary for producing one electrode group can be shortened, it is easier to produce an electrode group having a plurality of lead portions. .

  The positive electrode lead portion and the negative electrode lead portion can be formed from aluminum or an aluminum alloy. The average crystal grain size of the aluminum foil and the aluminum alloy foil is desirably 50 μm or less.

  Hereinafter, the negative electrode, the positive electrode, the nonaqueous electrolyte, the separator, and the container will be described.

1) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer that is supported on one or both surfaces of the negative electrode current collector and includes a negative electrode active material, a conductive agent, and a binder.

  An aluminum foil or an aluminum alloy foil can be used for the negative electrode current collector. The average crystal grain size of the aluminum foil and the aluminum alloy foil is desirably 50 μm or less. When the average crystal grain size is 50 μm or less, dissolution of the current collector during an overdischarge cycle in a high-temperature environment is suppressed, and a thin and high-density negative electrode is formed without breaking the negative electrode current collector. Thus, the input / output characteristics at a large current can be further improved. A more preferable average crystal grain size is 3 μm or less. Further, it is desirable that the lower limit value of the average crystal grain size is 0.01 μm.

The average crystal grain size of aluminum and aluminum alloy is measured by the method described below. The structure of the current collector surface is observed with a metal microscope, the number n of crystal grains existing in a 1 mm × 1 mm visual field is measured, and the average crystal grain area S (μm ² ) is calculated from the following formula (A).

S = (1 × 10 ⁶ ) / n (A)
Here, the value represented by (1 × 10 ⁶ ) is a visual field area (μm ² ) of 1 mm × 1 mm, and n is the number of crystal grains.

  The average crystal grain size d (μm) is calculated from the following formula (B) using the obtained average crystal grain area S. Such calculation of the average crystal grain size d is performed for five locations (five fields of view), and the average value is defined as the average crystal grain size. Note that the assumed error is about 5%.

d = 2 (S / π) ^1/2 (B)
The thickness of the negative electrode current collector is preferably 20 μm or less in order to increase the capacity. A more preferable range is 12 μm or less. Further, the lower limit value of the thickness of the negative electrode current collector is desirably 3 μm.

  The purity of aluminum used for the negative electrode current collector is preferably 99.99% or more for improving corrosion resistance and increasing strength. The aluminum alloy is preferably an alloy containing one or more elements selected from the group consisting of iron, magnesium, zinc, manganese and silicon in addition to aluminum. For example, an Al-Fe alloy, an Al-Mn alloy, and an Al-Mg alloy can obtain higher strength than aluminum. On the other hand, the content of transition metals such as nickel and chromium in aluminum and aluminum alloys is preferably 100 ppm or less (including 0 ppm). For example, an Al—Cu-based alloy increases strength but deteriorates corrosion resistance, and is not suitable as a current collector. The aluminum content in the aluminum alloy is desirably 95% by weight or more and 99.5% by weight or less. If it is out of this range, sufficient strength may not be obtained even if the average crystal grain size is 50 μm or less. A more preferable aluminum content is 98% by weight or more and 99.5% by weight or less.

  The average particle size of the negative electrode active material is desirably 1 μm or less. By setting the average particle size of the negative electrode active material to 1 μm or less, the lithium ion diffusibility of the negative electrode active material is improved, so that the input / output characteristics at a large current can be further improved. A more preferable average particle diameter is 0.3 μm or less. Moreover, it is desirable that the lower limit value of the average particle diameter is 0.001 μm.

  For the measurement of the particle size of the negative electrode active material, a laser diffraction particle size distribution measuring device (Shimadzu Corporation, model number SALD-300) or a measuring device having an equivalent function is used. First, after putting about 0.1 g of a sample in a beaker or the like, a surfactant and 1 to 2 mL of distilled water are added, sufficiently stirred, and poured into a stirred water tank. The light intensity distribution is measured 64 times at intervals of 2 seconds, the particle size distribution data is analyzed, and the particle size (D50) having a cumulative frequency distribution of 50% is defined as the average particle size.

  As the negative electrode active material, a material that absorbs and releases lithium can be used. The lithium occlusion potential (open circuit) of the negative electrode active material is preferably 0.4 V or more with respect to the lithium metal potential. Thereby, the progress of the alloying reaction between the aluminum component of the negative electrode current collector and lithium and the pulverization of the negative electrode current collector can be suppressed. Furthermore, the lithium occlusion potential (open circuit) is preferably in the range of 0.4 V to 3 V with respect to the lithium metal potential. Thereby, a battery voltage can be improved. A more preferable potential range is 0.4 V or more and 2 V or less.

As a metal oxide capable of occluding lithium in the range of 0.4 V or more and 3 V or less, for example, a titanium oxide such as TiO ₂ , for example, Li _{4 + x} Ti ₅ O ₁₂ (x is −1 ≦ x ≦ 3) and lithium titanium oxides such as Li ₂ Ti ₃ O ₇ , tungsten oxides such as WO ₃ , amorphous tin oxides such as SnB _0.4 P _0.6 O _3.1 , tin silicon oxides such as SnSiO _3, etc. Examples thereof include silicon oxide such as SiO. Among these, lithium titanium oxide is preferable.

Examples of the metal sulfide capable of occluding lithium in the range of 0.4 V or more and 3 V or less include lithium sulfide such as TiS ₂ , molybdenum sulfide such as MoS ₂ , such as FeS, FeS ₂ , and Li _x FeS _2. And iron sulfide.

Examples of the metal nitride capable of occluding lithium in the range of 0.4 V or more and 3 V or less include lithium cobalt nitride such as Li _x Co _y N (0 <x <4, 0 <y <0.5). Thing etc. are mentioned.

  A carbon material can be used as a conductive agent for increasing electron conductivity and suppressing contact resistance with the current collector. Examples thereof include acetylene black, carbon black, coke, carbon fiber, and graphite.

  Examples of the binder for binding the active material and the conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene butadiene rubber. Regarding the mixing ratio of the negative electrode active material, the conductive agent, and the binder, the negative electrode active material is 80% by weight to 95% by weight, the conductive agent is 3% by weight to 18% by weight, and the binder is 2% by weight or more. It is preferable to make it into the range of 7 weight% or less.

The density of the negative electrode is desirably 1.5 g / cm ³ or more and 5 g / cm ³ or less. Thereby, a high battery capacity can be obtained. A more preferable range is 2 g / cm ³ or more and 4 g / cm ³ or less.

  The negative electrode is produced, for example, by suspending a negative electrode active material, a conductive agent, and a binder in a suitable solvent, applying the suspension to a current collector, drying, and pressing.

2) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode layer supported on one or both surfaces of the positive electrode current collector and including a positive electrode active material, a conductive agent, and a binder.

  For the positive electrode current collector, for example, an aluminum foil or an aluminum alloy foil can be used. Each of the aluminum foil and the aluminum alloy foil preferably has an average crystal grain size of 50 μm or less. As a result, the strength of the positive electrode current collector is increased, the positive electrode can be densified without breaking the positive electrode current collector, and the capacity density can be improved. More preferably, it is 3 μm or less. Further, it is desirable that the lower limit value of the average crystal grain size is 0.01 μm.

  The thickness of the positive electrode current collector is preferably 20 μm or less in order to increase the capacity. A more preferable range is 15 μm or less. Moreover, it is desirable that the lower limit value of the thickness of the positive electrode current collector be 3 μm.

Examples of the positive electrode active material include oxides, sulfides, and polymers. As the oxide, for example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide such as Li _x Mn ₂ O ₄ or Li _x MnO ₂ , lithium such as Li _x NiO _2, etc. nickel composite oxide, for example, Li _x lithium-cobalt composite oxides such as CoO _2, for example, LiNi _1-y Co _y O ₂ lithium-nickel-cobalt composite oxide such as, for example, lithium manganese cobalt such as LiMn _y Co _1-y O ₂ composite oxides, for example olivine, such as _{Li x Mn 2-y Ni y} O 4 spinel-type lithium-manganese-nickel composite oxide such as, for example, _{Li x FePO 4, Li x Fe} 1-y Mn y PO 4, Li x CoPO 4 Lithium phosphorus oxide having a structure, for example, iron sulfate such as Fe ₂ (SO ₄ ) ₃ , for example, vanadium oxide such as V ₂ O ₅ And so on. In addition, it is preferable that x and y are the range of 0-1.

  Examples of the polymer include conductive polymer materials such as polyaniline and polypyrrole, and disulfide polymer materials. In addition, sulfur (S), carbon fluoride, and the like can be used. Preferred positive electrode active materials include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, spinel type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium phosphorus Examples include acid iron. According to these active materials, a high positive electrode voltage can be obtained.

  Examples of the conductive agent for increasing the electron conductivity and suppressing the contact resistance with the current collector include acetylene black, carbon black, and graphite.

  Examples of the binder for binding the active material and the conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  Regarding the mixing ratio of the positive electrode active material, the conductive agent and the binder, the positive electrode active material is 80% by weight to 95% by weight, the conductive agent is 3% by weight to 18% by weight, and the binder is 2% by weight to 7%. It is preferable to make it into the range below weight%.

  The positive electrode is produced, for example, by suspending a positive electrode active material, a conductive agent, and a binder in an appropriate solvent, applying the suspension to a positive electrode current collector, drying, and pressing.

3) Non-aqueous electrolyte As the non-aqueous electrolyte, a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel non-aqueous electrolyte obtained by combining a liquid electrolyte and a polymer material, or a lithium salt electrolyte A solid non-aqueous electrolyte in which molecular materials are combined is mentioned. Moreover, you may use the normal temperature molten salt (ionic melt) containing lithium ion as a non-aqueous electrolyte.

  The liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in an organic solvent at a concentration of 0.5 to 2 mol / L.

Examples of the electrolyte include LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Li (CF ₃ SO ₂ ). ₃ C, LiB [(OCO) ₂ ] _{2 and the} like. The type of electrolyte used can be one type or two or more types.

  Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC), dimethoxyethane ( Examples thereof include chain ethers such as DME) and dietoethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolane (DOX), γ-butyrolactone (GBL), acetonitrile (AN) and sulfolane (SL). These organic solvents can be used alone or in the form of a mixture of two or more.

  Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like.

  The room temperature molten salt (ionic melt) is preferably composed of lithium ions, organic cations and organic anions. The room temperature molten salt is desirably in a liquid state at 100 ° C. or less, preferably at room temperature or less.

4) Separator As the separator, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or the like can be used.

5) Container It is desirable that the thickness of the laminate film constituting the laminate film container is 0.5 mm or less. Moreover, it is desirable that the lower limit value of the thickness of the laminate film be 0.01 mm.

  Examples of the laminate film include a multilayer film including a metal layer and a resin layer that covers the metal layer. In order to reduce the weight, the metal layer is preferably an aluminum foil or an aluminum alloy foil. The resin layer is for reinforcing the metal layer, and can be formed of a polymer such as polypropylene (PP), polyethylene (PE), nylon, polyethylene terephthalate (PET). A laminate film container can be obtained, for example, by laminating a laminate film by thermal fusion.

  As the container, a metal container may be used instead of the laminate film container illustrated in FIG. 1 described above. The thickness of the metal container is desirably 0.5 mm or less. The lower limit of the metal container is desirably 0.05 mm.

  The metal container is preferably made of aluminum or an aluminum alloy. The average crystal grain size of each of aluminum and aluminum alloy is preferably 50 μm or less. By setting the average crystal grain size to 50 μm or less, the strength of a metal container made of aluminum or an aluminum alloy is increased, and sufficient mechanical strength can be ensured even if the thickness of the container is reduced. In addition, More preferably, it is 10 micrometers or less. Further, it is desirable that the lower limit value of the average crystal grain size is 0.01 μm. These features are suitable for batteries that require high temperature conditions, high energy density, etc., for example, in-vehicle secondary batteries. For the same reason as the negative electrode current collector, the purity of aluminum is preferably 99.99% or more. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferable. On the other hand, it is preferable that the content of transition metals such as iron, copper, nickel, and chromium in aluminum and aluminum alloy is 100 ppm or less. The metal container can be sealed with a laser.

  The shape of the container depends on the form of the nonaqueous electrolyte secondary battery. Examples of the form of the nonaqueous electrolyte secondary battery include a flat battery, a square battery, a sheet battery, a large battery mounted on an electric vehicle, and the like.

[Example]
Embodiments of the present invention will be described below with reference to the drawings described above. It should be noted that the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

Example 1
<Production of negative electrode>
As the negative electrode active material, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) powder having an average particle diameter of 1 μm and a Li storage potential of 1.55 V (vs. Li / Li ⁺ ) was prepared. A negative electrode active material, a carbon powder having an average particle diameter of 0.4 μm as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were blended so as to have a weight ratio of 90: 7: 3, and these were n- A slurry was prepared by dispersing in methylpyrrolidone (NMP) solvent.

On the other hand, an aluminum foil (purity 99.99%) having a thickness of 15 μm and an average crystal grain size of 50 μm was prepared as a negative electrode current collector. A slurry was applied to the obtained negative electrode current collector, dried, and then pressed to prepare a negative electrode. After cutting the obtained negative electrode so that a solid portion (region where the negative electrode active material-containing layer is not formed) is located at one end portion in the long side direction, an aluminum negative electrode lead portion having a cross-sectional area of 0.4 mm ² is formed. Welded to obtain a negative electrode in which the effective length L of the current collector, the width W in the short side direction, the thickness t of the active material-containing layer, and the thickness T of the current collector satisfy the conditions shown in Table 1 below.

<Preparation of positive electrode>
Lithium cobalt oxide (LiCoO ₂ ) as the positive electrode active material, graphite powder as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were blended in a weight ratio of 87: 8: 5. A slurry was prepared by dispersing in n-methylpyrrolidone (NMP) solvent. The slurry was applied to an aluminum foil (purity 99.99%) having a thickness of 15 μm and an average crystal particle diameter of 10 μm, dried, and then pressed to produce a positive electrode. After cutting the obtained positive electrode so that a plain portion (region where the positive electrode active material-containing layer is not formed) is located at one end portion in the long side direction, an aluminum positive electrode lead portion having a cross-sectional area of 0.4 mm ² is formed. Welded to obtain a positive electrode in which the effective length L of the current collector, the width W in the short side direction, the thickness t of the active material-containing layer, and the thickness T of the current collector satisfy the conditions shown in Table 1 below.

  An aluminum-containing laminate film having a thickness of 0.1 mm was prepared as a container forming material. The aluminum layer of this aluminum-containing laminate film had a film thickness of about 0.03 mm and an average crystal particle diameter of about 100 μm. Polyethylene was used as the resin for reinforcing the aluminum layer. A concave portion was formed in the laminate film to obtain a container.

Next, a separator made of a polyethylene porous film having a thickness of 25 μm was interposed between the positive electrode and the negative electrode and wound into a flat spiral shape to obtain an electrode group. An electrode group was inserted into the recess of the container. Lithium salt LiBF ₄ was dissolved in an organic solvent in which EC and GBL were mixed at a volume ratio (EC: GBL) of 1: 2 to prepare a liquid nonaqueous electrolyte. The obtained non-aqueous electrolyte was poured into a container, and then sealed by heat sealing, having the structure shown in FIG. 1 described above, thickness 3.1 mm, width 24 mm (width in the short side direction of the battery) A flat non-aqueous electrolyte secondary battery having a length of 32 {width in the long side direction of the battery (excluding positive and negative electrode lead portions)} mm was prepared.

(Example 2)
Lead portions are provided at both ends of the long side, and the effective length L of the current collector, the width W in the short side direction, the thickness t of the active material-containing layer, and the thickness T of the current collector are as shown in Table 1 below. A positive electrode and a negative electrode were produced in the same manner as described in Example 1 except that the setting was set to. A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1, except that the obtained positive electrode and negative electrode were used. For each of the two positive electrode lead portions and negative electrode lead portions drawn from the same end face of the electrode group, the positive electrode lead portions welded together are connected to the positive electrode tab, and the negative electrode lead portions are welded together. Was connected to the negative electrode tab, and the positive electrode tab and the negative electrode tab were pulled out of the container.

(Examples 3-5, 7-8)
A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the current collector, the active material-containing layer, and the negative electrode active material satisfied the conditions shown in Table 1 below.

(Example 6)
The positive electrode and the negative electrode produced in Example 2 were cut at a position where the length of the long side was halved, and two positive electrodes and two negative electrodes were obtained. Electrode groups were prepared from each, and two sets of electrode groups were obtained. Weld the positive lead part of one electrode group to the positive lead part of the other electrode group, the negative lead part of one electrode group to the negative lead part of the other electrode group, The positive and negative electrodes of the electrode group were electrically connected. Positive electrode tabs were welded to the welded positive electrode lead parts, and negative electrode tabs were welded to the negative electrode lead parts. A flat nonaqueous electrolyte secondary battery was fabricated in the same manner as described in Example 1 except that the electrode group having the configuration described above was used.

(Comparative Example 1)
A positive electrode and a negative electrode produced in the same manner as described in Example 1 were strip-shaped and punched out so that a lead portion was formed at one end of the short side. The width in the long side direction of the positive electrode and the negative electrode is W, and the distance between the lead portion and the long side located on the opposite side of the lead portion is L, and is shown in Table 1 below.

  Sixteen leaves for the positive electrode and 15 leaves for the negative electrode were prepared, and the positive electrode and the negative electrode were alternately stacked with a separator interposed therebetween to obtain a stacked electrode group. Subsequently, the lead portion of the positive electrode was integrated by laser welding, and the lead portion of the negative electrode was integrated by laser welding. The obtained electrode group was fixed with an insulating tape.

  The electrode group thus obtained was impregnated with a non-aqueous electrolyte having the same composition as described in Example 1, and then sealed in a container to produce a flat non-aqueous electrolyte secondary battery. did.

(Comparative Example 2)
A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the current collector, the active material-containing layer, and the negative electrode active material satisfied the conditions shown in Table 1 below.

  With respect to the obtained secondary battery, the 20C charge capacity retention ratio and the capacity density were measured under the conditions described below, and the results are shown in Table 2 below. The time required to produce the electrode group is also shown in Table 2 below.

<20C charge capacity maintenance rate>
In a 20 ° C environment, the charge capacity when a constant voltage of 2.8V is charged for 3 hours at a current value of 1C is measured to obtain a 1C charge capacity. Furthermore, in a 20 ° C environment, the current value of 20C Measure the charge capacity when charging at a constant voltage of 2.8 V in 10 minutes and set it to 20 C charge capacity. The ratio of the 20C charge capacity when the 1C charge capacity is 100 was defined as the 20C charge capacity maintenance rate.

<Capacity density>
Under a 20 ° C. environment, a constant voltage of 2.8 V was charged at a current value of 1 C for 3 hours, and then the discharge capacity when discharged to 0 V at a current value of 1 C was measured to obtain a 1 C discharge capacity. . The 1C discharge capacity was divided by the volume V obtained from the thickness, width, and length of the battery to calculate the capacity density.

  As is clear from Tables 1 and 2, according to the secondary batteries of Examples 1 to 8 using a wound electrode group with (L / W) of 30 or less, an electrode excellent in the 20C charge capacity retention rate and capacity density Groups can be manufactured in a short time.

  From the comparison of Examples 1, 5, and 7, it can be seen that when the thickness ratio (t / T) is 3 or less, a higher 20C charge capacity retention rate can be obtained. Further, it is understood from comparison between Examples 1, 5, and 8 that the current collector thickness of 20 μm or less is effective in improving the capacity density.

  On the other hand, in the secondary battery of Comparative Example 1 using the laminated electrode group, it took time to weld the lead portions of the positive electrode and the negative electrode, and the electrode group manufacturing tact was as long as 30 seconds. Moreover, in the secondary battery of Comparative Example 2 using the wound electrode group with (L / W) exceeding 30, the 20C charge capacity maintenance rate and the capacity density are higher than those of the secondary batteries of Examples 1 to 8. It was low.

Example 9
A nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the average particle diameter of the negative electrode active material was changed to 5 μm. The obtained secondary battery had a 20C charge capacity retention rate of 15%, a capacity density of 42 (mAH / cm ² ), and an electrode group manufacturing tact of 9 seconds.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view which shows the nonaqueous electrolyte secondary battery which concerns on embodiment of this invention. The cross-sectional view of the nonaqueous electrolyte secondary battery of FIG. The expanded sectional view of the A section of FIG. The top view which shows an example of the negative electrode used for the nonaqueous electrolyte secondary battery of FIG. Sectional drawing of the negative electrode of FIG. The top view which shows the other example of the negative electrode used for the nonaqueous electrolyte secondary battery of FIG. The perspective view which shows the other example of the electrode group used for the nonaqueous electrolyte secondary battery of FIG.

Explanation of symbols

1, 1 ₁ , 1 ₂ ... electrode group, 2 ... positive electrode, 2a ... positive electrode current collector, 2b ... positive electrode active material-containing layer, 3 ... negative electrode, 3a ... negative electrode current collector, 3b ... negative electrode active material-containing layer, 4 ... Separator, 5, 5 ₁ , 5 ₂ ... Positive electrode lead part, 6, 6 ₁ , 6 ₂ ... Negative electrode lead part, 7 ... Container, 8 ... Sealing part.

Claims (5)

A non-aqueous electrolyte secondary battery comprising an electrode group in which a positive electrode and a negative electrode are wound in a flat spiral shape via a separator,
Each of the positive electrode and the negative electrode is carried by the current collector, a current collector made of aluminum or an aluminum alloy, at least one lead portion connected to a long side end of the current collector, and A non-aqueous electrolyte secondary battery comprising an active material-containing layer and satisfying the following formula (1):
(L / W) ≦ 30 (1)
Here, L is the effective current collector length per one lead portion, and W is the width in the short side direction of the current collector.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the lead portion of the positive electrode and the lead portion of the negative electrode are drawn from the same end face of the electrode group.   The positive electrode and the negative electrode have a current collector thickness of 20 μm or less, and a ratio (t / T) between the thickness t of the active material-containing layer and the thickness T of the current collector is 3 The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein:   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material includes lithium titanium oxide particles having an average particle diameter of 1 μm or less.   The number of the said electrode groups is two or more, The nonaqueous electrolyte secondary battery of any one of Claims 1-4 characterized by the above-mentioned.

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