WO2012042830A1

WO2012042830A1 - Nonaqueous electrolyte secondary battery

Info

Publication number: WO2012042830A1
Application number: PCT/JP2011/005404
Authority: WO
Inventors: 中井　晴也; 眞中西
Original assignee: パナソニック株式会社
Priority date: 2010-09-30
Filing date: 2011-09-27
Publication date: 2012-04-05
Also published as: JP2013254561A

Abstract

The present invention relates to a nonaqueous electrolyte secondary battery (100) in which an electrode group formed by winding a positive electrode (1) and a negative electrode (2) with a separator (3) interposed therebetween is housed in a battery case (7), the positive electrode including a sheet-shaped positive electrode collector, on the surface of which a positive electrode mixture layer is formed, the negative electrode including a sheet-shaped negative electrode collector, on the surface of which a negative electrode mixture layer is formed. Conventionally, in the secondary battery, a negative electrode lead is welded to a battery case bottom portion. Since current is concentrated at one place, however, there have been the problems of a high internal resistance, the inability of a large current discharge, etc. In the secondary battery of the present invention, the negative electrode is provided with a both surface coating portion in which the negative electrode mixture layer is formed on both surfaces of the negative electrode collector and a one-surface coating portion in which the negative electrode mixture layer is formed on one surface of the negative electrode collector. The above problems are solved, for example, in such a way that the one-surface coating portion is formed in a region positioned at the most outer circumferential portion of the electrode group and an exposed surface (20a) of the negative electrode collector in the one-surface coating portion is made contact with an inner surface of the battery case.

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery with reduced internal resistance and improved large current discharge characteristics.

In recent years, electronic devices have become increasingly portable and cordless, and there is an increasing demand for secondary batteries that are small, light, and have high energy density as power sources for driving such devices. In addition to small consumer applications, large secondary batteries such as power storage devices and power sources for electric vehicles are required to have high output characteristics, long-term durability, and safety. Among secondary batteries, non-aqueous electrolyte secondary batteries having a high voltage and a high energy density have been actively developed.

A non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery has, for example, an electrode group obtained by winding a positive electrode and a negative electrode in which a mixture layer is formed on a sheet-like current collector through a separator. The battery is housed in a battery case together with a non-aqueous electrolyte. In a general cylindrical battery, the outermost peripheral portion of the electrode group is covered with a separator, and the leads connected to the positive electrode and the negative electrode are welded to a sealing plate and a battery case that serve as external terminals. Generally, aluminum is used for the positive electrode lead, and nickel, copper, or a nickel-copper clad plate or the like is used for the negative electrode lead.

Conventionally, in the negative electrode, a method in which the negative electrode lead is welded to the bottom of the battery case has been taken. However, since the current is concentrated in one place, the internal resistance of the battery is increased, and a sufficient large current discharge cannot be performed. there were. In addition, when an external short circuit occurs, abnormal heat may be generated due to current concentration.

For such a problem, Patent Document 1 describes a technique in which leads are attached to a plurality of portions of a sheet-like negative electrode, and are folded to the bottom of an electrode group and welded to a battery case. Thereby, current collection property can be improved and current concentration on the mixture layer around the leads can be reduced.

However, when a plurality of leads are provided, normally, a mixture layer cannot be formed in the lead welded portion, resulting in a capacity loss. Furthermore, since it is necessary to fold and weld a plurality of leads, poor welding is likely to occur.

On the other hand, in Patent Document 2, an electrode group obtained by winding a positive electrode and a negative electrode with a metal foil having a thickness of 0.03 mm or less as a current collector through a separator is accommodated in a battery case, and then the outer diameter of the battery case is measured. Describes a technique in which the exposed surface of the current collector disposed on the outermost periphery of the electrode group is brought into close contact with the inner side surface of the battery case. As a result, even with a weakly elastic electrode using a thin metal foil as a current collector, the exposed surface of the current collector and the inner surface of the battery case are in wide contact with each other. Obtainable.

JP 2000-243376 A Japanese Patent Laid-Open No. 10-172523

However, in the technique described in Patent Document 2, the outer surface of the battery case is reduced, so that the exposed surface of the current collector disposed on the outermost periphery of the electrode group is brought into close contact with the inner peripheral surface of the battery case. When the outer diameter of the group changes, buckling occurs in the electrode plate constituting the electrode group, and the cycle characteristics may be deteriorated.

Further, when the electrode group is accommodated in the battery case, if the exposed surface of the current collector disposed on the outermost periphery of the electrode group touches the battery case, the strength of the thin current collector is weak. Misalignment and deformation of the electrode group may occur. In particular, this problem becomes apparent when the outer diameter of the electrode group is made close to the inner diameter of the battery case in order to reduce the loss of battery capacity.

The present invention has been made in view of such a point, and a main object thereof is to provide a non-aqueous electrolyte secondary battery with reduced internal resistance and low battery capacity loss.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery in which an electrode group in which a positive electrode and a negative electrode are wound through a separator is accommodated in a battery case, and the positive electrode has a sheet shape The positive electrode current collector layer is formed on the surface of the negative electrode current collector, the negative electrode has the negative electrode material mixture layer formed on the surface of the sheet-like negative electrode current collector, and the negative electrode has negative electrodes on both sides of the negative electrode current collector. It has a double-sided coating part in which a mixture layer is formed, and a single-sided coating part in which a negative electrode mixture layer is formed on one side of a negative electrode current collector, and the single-sided coating part is on the outermost peripheral part of the electrode group The exposed surface of the negative electrode current collector that is formed at a position where the single-sided coating portion is provided is in contact with the inner surface of the battery case.

In a preferred embodiment, the negative electrode further has an uncoated portion where both surfaces of the negative electrode current collector are exposed at a portion located in an inner peripheral portion of the electrode group, and the negative electrode current collector in the uncoated portion The negative electrode lead is connected to the battery case, and the negative electrode lead is connected to the battery case.

In another preferred embodiment, the outer diameter of the electrode group when the electrode group is accommodated in the battery case is in the range of 95 to 99% with respect to the inner diameter of the battery case.

According to the present invention, the exposed surface of the negative electrode current collector in the single-side coated portion provided on the outermost peripheral portion of the electrode group is brought into contact with the inner side surface of the battery case, thereby reducing internal resistance and battery capacity. It is possible to provide a non-aqueous electrolyte secondary battery with a small loss. Thereby, it is possible to realize a non-aqueous electrolyte secondary battery having excellent large current discharge characteristics and excellent safety at the time of external short circuit.

It is sectional drawing which showed the structure of the nonaqueous electrolyte secondary battery in one Embodiment of this invention. It is the figure which showed the structure of the negative electrode in one Embodiment of this invention, (a) is a top view, (b) is sectional drawing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment. Moreover, it can change suitably in the range which does not deviate from the range which has the effect of this invention. Furthermore, combinations with other embodiments are possible.

FIG. 1 is a cross-sectional view showing a configuration of a nonaqueous electrolyte secondary battery 100 according to an embodiment of the present invention.

As shown in FIG. 1, an electrode group 4 in which a positive electrode 1 and a negative electrode 2 are wound through a separator 2 is housed in a bottomed cylindrical battery case 7 together with a non-aqueous electrolyte. Here, the positive electrode 1 has a positive electrode mixture layer (not shown) formed on the surface of a sheet-like positive electrode current collector (not shown), and the negative electrode 2 has a surface of a sheet-like negative electrode current collector (not shown). A negative electrode mixture layer (not shown) is formed on the substrate.

Ring-

shaped insulating plates

9 and 10 are respectively arranged above and below the electrode group 4, and the positive electrode 1 is connected to the filter 12 through the positive electrode lead 5. The filter 12 is connected to an inner cap 13, the protrusion of the inner cap 13 is connected to a metal valve plate 14, and the valve plate 14 is connected to a terminal plate 8 that also serves as a positive electrode terminal. The terminal plate 8, the valve plate 14, the inner cap 13, and the filter 12 are integrated to seal the opening of the battery case 7 via the gasket 11.

2A and 2B are diagrams showing the configuration of the negative electrode 2, in which FIG. 2A is a plan view and FIG. 2B is a cross-sectional view.

As shown in FIGS. 2A and 2B, the negative electrode 2 includes a double-sided coating portion 2 a in which a negative electrode mixture layer 21 is formed on both surfaces of the negative electrode current collector 20, and one surface of the negative electrode current collector 20. And a single-side coated portion 2b on which a negative electrode mixture layer 21 is formed. Here, the single-side coated portion 2 b is formed at a portion located at the outermost peripheral portion of the electrode group 4. In addition, in this embodiment, in the site | part located in the inner peripheral part of the electrode group 4, it further has the uncoated part 2c which both surfaces of the negative electrode collector 20 exposed, but it is not necessarily the uncoated part 2c. May not be provided. In this case, the negative electrode lead 6 is connected to the negative electrode current collector 20 in the uncoated portion 2c.

As shown in FIG. 1, in the electrode group 4 accommodated in the battery case 7, the exposed surface 20 a of the negative electrode current collector 20 in the single-side coated portion 2 b formed in the portion located at the outermost peripheral portion is a negative electrode terminal. Is in contact with the inner surface of the battery case 7. As a result, the negative electrode 2 is electrically connected to the battery case 7 serving as a negative electrode terminal. However, the exposed surface 20a of the negative electrode current collector 20 in the single-side coated portion 2b covers a wide area with the inner side surface of the battery case 7. Since they are in contact, the internal resistance of the battery 100 can be reduced. As a result, a battery excellent in large current discharge characteristics can be realized, and current concentration at the time of an external short circuit can be prevented, so that a highly safe battery can be realized.

Further, since the negative electrode mixture layer 21 is formed on the surface opposite to the exposed surface 20a of the negative electrode current collector 20 in the single-side coated portion 2b, the negative electrode current collector having a small thickness (for example, 5 to 30 μm) is formed. Even when the body 20 is used, the strength of the single-side coated portion 2b can be maintained. Thereby, when the electrode group 4 is accommodated in the battery case 7, even if the exposed surface 20 a of the negative electrode current collector 20 in the one-side coated portion 2 b provided on the outermost periphery of the electrode group 4 touches the battery case 7. The displacement of the

electrode plates

1 and 2 and the deformation of the electrode group 4 can be prevented. As a result, since the outer diameter of the electrode group 4 can be made close to the inner diameter of the battery case 7, it is possible to realize a high-capacity battery with a small battery capacity loss.

Further, the negative electrode mixture layer 21 formed on the surface opposite to the exposed surface 20a of the negative electrode current collector 20 in the single-side coated portion 2b is opposed to the positive electrode mixture layer of the positive electrode 1 on the inner peripheral surface thereof. Therefore, it is possible to further increase the capacity of the battery.

Here, the outer diameter of the electrode group 4 when the electrode group 4 is accommodated in the battery case 7 is preferably in the range of 95 to 99% with respect to the inner diameter of the battery case 7. At this time, a good contact state between the battery case 7 and the electrode group 4 is obtained, and the internal resistance of the battery is reduced. The outer diameter of the electrode group 4 refers to the diameter in a cross section (substantially circular surface) perpendicular to the axial direction of the electrode group 4. As the value of the diameter of the electrode group 4, for example, the maximum value among the obtained measured values is used by measuring a plurality of positions with calipers or the like.

In addition, after the electrode group 4 is accommodated in the battery case 7 to produce the battery 100, the battery 100 is charged and discharged, whereby the positive electrode 1 and the negative electrode 2 expand, and the outer diameter of the electrode group 4 increases. Therefore, the contact area between the electrode group 4 and the battery case 7 is increased compared to when the electrode group 4 is accommodated in the battery case 7, and a better connection can be obtained. However, when the ratio of the outer diameter of the electrode group 4 to the inner diameter of the battery case 7 (hereinafter referred to as the ratio A) is less than 95%, it is difficult to obtain a uniform contact state, and the internal resistance cannot be sufficiently reduced. In some cases. If the ratio A exceeds 99%, it becomes difficult to accommodate the electrode group 4 in the battery case 7, and even if the electrode group 4 can be accommodated in the battery case 7, Deviation and deformation of the electrode group 4 may occur. In order to further reduce the internal resistance, the ratio A is more preferably in the range of 98 to 99%.

In addition, as shown in the present embodiment, an uncoated portion 2 c where both surfaces of the negative electrode current collector 20 are exposed may be further provided in a portion located in the inner peripheral portion of the electrode group 4. By connecting the negative electrode lead 6 connected to the negative electrode current collector 20 in the uncoated part 2c to the bottom of the battery case 7, the current collection efficiency can be further increased, thereby further reducing the internal resistance of the battery. can do. In addition, when an external short circuit occurs, local heat generation can be suppressed by dispersing the short circuit current, and an internal short circuit due to separator melting can be prevented.

Moreover, the negative electrode lead 6 provided in the inner peripheral part of the electrode group 4 is separated from the outermost current collecting part (exposed surface 20a of the negative electrode current collector 20 in the one-side coated part 2b) from the viewpoint of dispersing current collection. It is preferably provided at a position, and more preferably provided at an end portion on the innermost peripheral side of the electrode group 4. The negative electrode lead 6 is preferably copper, nickel, a nickel-copper clad plate, or a copper-iron clad plate from the viewpoint of conductivity.

Hereinafter, each component of the nonaqueous electrolyte secondary battery 100 in the present embodiment will be described in more detail.

(Positive electrode)
The positive electrode 1 includes a sheet-like positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector. As the positive electrode current collector, for example, a metal foil formed of aluminum, aluminum alloy, stainless steel, titanium, titanium alloy, or the like can be used. The thickness of the positive electrode current collector is, for example, 1 to 100 μm, preferably 10 to 50 μm.

The positive electrode mixture layer may contain a conductive agent, a binder, a thickener and the like in addition to the positive electrode active material. As the positive electrode active material, for example, a composite metal oxide of lithium and a transition metal such as cobalt, manganese, or nickel can be used. The positive electrode active materials may be used singly or in combination of two or more.

The binder is not particularly limited as long as it can be dissolved or dispersed in the dispersion medium by kneading. Examples of the binder include fluororesins, rubbers, acrylic polymers or vinyl polymers (monomers or copolymers of monomers such as acrylic monomers such as methyl acrylate and acrylonitrile, vinyl monomers such as vinyl acetate, etc.). it can. Examples of the fluororesin include polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, and polytetrafluoroethylene. Examples of rubbers include acrylic rubber, modified acrylonitrile rubber, and styrene butadiene rubber (SBR). You may use a binder individually or in combination of 2 or more types.

Examples of the conductive agent include acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and other carbon blacks; various graphites such as natural graphite and artificial graphite; conductive fibers such as carbon fibers and metal fibers Can be used.

(Negative electrode)
The negative electrode 2 includes a sheet-like negative electrode current collector 20 and a negative electrode mixture layer 21 disposed on the surface of the negative electrode current collector 20. As the negative electrode current collector 20, for example, a metal foil formed of copper, copper alloy, nickel, nickel alloy, or the like can be used.

The negative electrode mixture layer 21 may contain a conductive agent, a binder, a thickener and the like in addition to the negative electrode active material. Examples of the negative electrode active material include carbon materials such as natural graphite, spherical or fibrous artificial graphite, non-graphitizable carbon (hard carbon), and graphitizable carbon (soft carbon).

As the binder and the conductive agent, those exemplified for the positive electrode can be used.

(Separator)
The thickness of the separator 3 can be selected, for example, from the range of 5 to 35 μm, and may preferably be 10 to 30 μm, or 12 to 20 μm. If the thickness of the separator is too small, a minute short circuit tends to occur inside the battery. If the thickness is too large, the thickness of the positive electrode and the negative electrode needs to be reduced, and the battery capacity may be insufficient.

The material of the separator 3 can be a polyolefin material or a combination of a polyolefin material and a heat resistant material. Examples of the polyolefin porous film include polyethylene, polypropylene, and a porous film of an ethylene-propylene copolymer. These resins can be used alone or in combination of two or more. If necessary, other thermoplastic polymers may be used in combination with the polyolefin. As the heat resistant porous film, a single film of a heat resistant resin and an inorganic filler, or a mixture of a heat resistant resin and an inorganic filler can be used.

(Non-aqueous electrolyte)
The nonaqueous electrolyte is prepared by dissolving a lithium salt in a nonaqueous solvent. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate and diethyl carbonate; and lactones such as γ-butyrolactone. A non-aqueous solvent can be used individually or in combination of 2 or more types.

Examples of the lithium salt include lithium salts having a strong electron-withdrawing property, such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ). ₂ and LiC (SO ₂ CF ₃ ) ₃ . A lithium salt can be used individually or in combination of 2 or more types. The concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 1.5M, preferably 0.7 to 1.2M.

An additive may be appropriately added to the nonaqueous electrolyte. For example, in order to form a good film on the positive and negative electrodes, vinylene carbonate (VC), cyclohexylbenzene (CHB), and modified products thereof may be used. As an additive that acts when the lithium ion secondary battery is overcharged, for example, terphenyl, cyclohexylbenzene, diphenyl ether, or the like may be used. The additives may be used alone or in combination of two or more. The ratio of these additives is not particularly limited, but is, for example, about 0.05 to 10% by weight with respect to the non-aqueous electrolyte.

Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

Example 1
A cylindrical lithium ion secondary battery was produced by the following procedure.

(1) Production of positive electrode A positive electrode plate was produced by the following method. As a positive electrode active material, 3 kg of lithium cobaltate, 1 kg of N-methyl-2-pyrrolidone (NMP) solution containing 12% by mass of PVDF as a binder, 90 g of acetylene black as a conductive agent, and an appropriate amount of NMP The mixture was stirred to obtain a positive electrode mixture paste. This positive electrode mixture paste was applied to a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode mixture layer on the positive electrode current collector, whereby a positive electrode 1 was obtained. At this time, the thickness of the positive electrode 1 including the positive electrode current collector and the positive electrode mixture layer was set to 100 μm.

The density of the positive electrode active material in the positive electrode mixture layer was 3.2 g / cm ³ . The positive electrode was cut into a strip shape so as to be accommodated in the battery case (length in the width direction 56 mm and length in the longitudinal direction 800 mm). A part of the positive electrode was provided with an exposed surface of the positive electrode current collector.

(2) Production of negative electrode A negative electrode plate was produced by the following method. As a negative electrode active material, 3 kg of artificial graphite, 75 g of an aqueous dispersion containing 40% by weight of a styrene-butadiene copolymer (rubber particles) as a binder, 30 g of carboxymethyl cellulose as a thickener, an appropriate amount of water, Were stirred to obtain a negative electrode mixture paste. The negative electrode mixture paste was applied to a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode mixture layer on the negative electrode current collector to obtain a negative electrode. At this time, the thickness of the negative electrode comprising the negative electrode current collector and the negative electrode mixture layer was 120 μm.

The density of the negative electrode active material in the negative electrode mixture layer was 1.5 g / cm ³ .

The negative electrode was cut into a strip shape so that it could be inserted into the battery case (length in the width direction of 58 mm and length in the longitudinal direction Z of 900 mm). The negative electrode was provided with a single-side coated portion (length in the longitudinal direction 50 mm) at the end. In addition, an uncoated portion (length of 15 mm in the longitudinal direction) was provided in a portion disposed on the innermost peripheral portion of the electrode group in order to weld the negative electrode lead.

(3) non-aqueous electrolyte volume ratio and prepared EC and MEC of 1: non-aqueous solvent in a mixing ratio of 3 was prepared by dissolving LiPF ₆ at a concentration of 1.5 mol / L nonaqueous electrolyte.

(4) Battery assembly A copper negative electrode lead (thickness: 0.10 mm and width: 3 mm) was spot welded to one side of the uncoated portion provided in the innermost peripheral portion of the negative electrode group obtained above.

The positive electrode lead (thickness 0.15 mm and width 3.5 mm) made of aluminum was spot welded to the uncoated portion of the positive electrode obtained above.

Thereafter, the positive electrode and the negative electrode were wound through a separator between them to constitute an electrode group. As the separator, a microporous polyethylene film having a thickness of 20 μm was used. At this time, the electrode group was configured such that the negative electrode single-side coated portion was disposed on the outermost peripheral part of the electrode group, and the exposed surface of the negative electrode current collector was located on the outer peripheral side (surface facing the battery case). Further, the negative electrode lead provided in the innermost uncoated part was folded and inserted into a bottomed cylindrical stainless steel battery case.

The ratio A of the diameter of the electrode group when the battery case was accommodated to the inner diameter of the battery case was 98%.

A ring-shaped insulating plate was arranged on each of the upper and lower parts of the electrode group. The end of the negative electrode lead was welded to the inner bottom surface of the battery case, and the end of the positive electrode lead was welded to the filter. 5.8 g of the nonaqueous electrolyte obtained above was injected into the battery case. The open end of the battery case was caulked and sealed through a gasket. In this way, a 18650 size cylindrical lithium ion secondary battery (diameter 18 mm, height 65 mm) was produced.

(Example 2)
By adjusting the amount of mixture paste applied to the positive and negative electrode current collectors, the thickness of the positive electrode was set to 105 μm, the thickness of the negative electrode was set to 125 μm, and the ratio A was set to 99%. A battery was produced.

(Example 3)
By adjusting the amount of mixture paste applied to the positive and negative electrode current collectors, the thickness of the positive electrode was set to 95 μm, the thickness of the negative electrode was set to 115 μm, and the ratio A was set to 95%. A battery was produced.

Example 4
The amount of the mixture paste applied to the current collector of the positive electrode and the negative electrode was adjusted so that the thickness of the positive electrode was 106 μm, the thickness of the negative electrode was 126 μm, and the ratio A was 99.5%. A battery was produced by the method.

(Example 5)
The amount of the mixture paste applied to the current collector of the positive electrode and the negative electrode was adjusted so that the thickness of the positive electrode was 94 μm, the thickness of the negative electrode was 114 μm, and the ratio A was 94.5%. A battery was produced by the method.

(Example 6)
There is no uncoated part on the innermost periphery (no negative electrode lead is welded), and the current collection of the negative electrode is only the contact between the current collector exposed part of the one-side coated part of the outermost part of the electrode group and the battery case A battery was produced in the same manner as in Example 1 except that.

(Comparative Example 1)
A battery was fabricated in the same manner as in Example 1, except that the uncoated portion was provided on the outermost negative electrode and the negative electrode lead was welded, and the negative electrode lead provided on the innermost periphery was welded to the bottom of the case.

The following evaluation was performed for each battery obtained as described above.

(Evaluation 1) Evaluation of electrode displacement 50 electrode groups of Examples 1 to 6 and Comparative Example 1 were prepared. After each electrode group was inserted into the battery case, the state of the electrode group (positive and negative electrodes) inserted into the battery case was confirmed by X-ray, and the positive and negative electrodes were shifted when the battery case was inserted among the 50 electrode groups. The number was examined.

(Evaluation 2) Battery capacity evaluation At an environmental temperature of 25 ° C., the battery was charged with a constant current of 1 ItmA until the closed circuit voltage of the battery reached 4.2V. After the closed circuit voltage of the battery reached 4.2V, the battery was charged at a constant voltage of 4.2V until the current value reached 50 mA. After the charging, the IR of the battery was first measured, and then the battery was discharged at a constant current of 0.2 ItmA until the closed circuit voltage of the battery reached 2.5 V, and the discharge capacity was determined.

(Evaluation 3) Large Current Discharge Test At an environmental temperature of 25 ° C., the battery was charged with a constant current of 1 ItmA until the closed circuit voltage of the battery reached 4.2V. After the closed circuit voltage of the battery reached 4.2V, the battery was charged at a constant voltage of 4.2V until the current value reached 50 mA. After the above charging, the IR of the battery was first measured, and then the battery was discharged at a constant current of 10 A until the closed circuit voltage of the battery reached 2.5 V to obtain the discharge capacity.

(Evaluation 4) External short circuit test At an environmental temperature of 25 ° C., the battery was charged with a constant current of 1 ItmA until the closed circuit voltage of the battery reached 4.25V. After the closed circuit voltage of the battery reached 4.25 V, the battery was charged at a constant voltage of 4.25 V until the current value reached 50 mA. The battery after charging was externally short-circuited in a 60 ° C. environment. And the surface temperature of the location which opposes a negative electrode lead in a battery case was measured, and the highest reached temperature at this time was calculated | required. A thermocouple was used to measure the surface temperature of the battery. In this external short circuit test, the case where the maximum temperature of the battery was 120 ° C. or higher at which the separator melted was determined as NG. The number of tests for each battery was three.

Table 1 shows the results of evaluations 1 to 4.

In the electrode deviation evaluation of Evaluation 1, in Comparative Example 1 in which the uncoated portion is located on the outermost peripheral portion of the electrode group, it is difficult to smoothly insert the electrode group, and a lot of deviation between positive and negative occurs when the battery case is inserted. did. Further, in Example 4 in which the ratio A is 99.5%, the diameter of the electrode group is increased, and the insertion pressure of the electrode group is increased. Therefore, when the electrode group is inserted into the battery case, the insertion pressure of the electrode group is increased. In addition, an electrode group in which the positive and negative electrodes were shifted was observed. If the positive and negative electrodes are shifted, the positive electrode and the negative electrode may come into contact with each other to cause a short circuit. Therefore, when the outermost peripheral portion of the electrode group is a single-side coated portion, the ratio A is preferably 99% or less.

Also, from the result of Evaluation 2, it can be seen that the batteries of Examples 1 to 6 have an increased battery capacity compared to Comparative Example 1. This is because the amount of the active material in the battery is increased by providing the single-side coated portion on the outermost periphery of the negative electrode.

In addition, since the battery of Example 5 has a small ratio A, contact between the outermost negative electrode current collector and the battery case cannot be sufficiently obtained, and the internal resistance (IR) of the battery is smaller than that of Examples 1 to 4. It became bigger. However, in all the batteries of Examples 1 to 5, the large current discharge capacity at 10 A was larger than that of the battery of Comparative Example 1. In particular, in a battery having a large ratio A and a thick electrode plate, a high capacity was obtained.

Furthermore, from the results of the external short-circuit test of Evaluation 4, in the batteries of Examples 1 to 5, the maximum temperature reached 120 ° C. or lower, whereas in the battery of Comparative Example 1, a battery of 120 ° C. or higher was generated. . This is because each of the batteries of Examples 1 to 5 has two current collectors: a contact part between the outermost negative electrode current collector and the battery case, and a weld part between the innermost negative electrode lead and the battery case. This is probably because the short-circuit current at the time of the short-circuit is dispersed, and as a result, the local temperature rise is eliminated and the temperature rise of the entire battery is suppressed. On the other hand, in Comparative Example 1, since the short-circuit current concentrates on the negative electrode lead weld, it seems that the temperature at which the separator melts due to local heat generation of the battery. In Example 6, since the short-circuit current was concentrated on the outermost peripheral portion, it seems that the temperature reached the temperature at which the separator melts due to local heat generation of the battery.

From the above evaluations, in the batteries of Examples 1 to 6, there is no displacement of the electrode plate when the electrode group is accommodated in the battery case, the internal resistance is reduced, and the battery capacity loss is small. It was found that an excellent battery can be obtained.

The present invention is suitably used for a non-aqueous electrolyte secondary battery that requires large current discharge characteristics.

1 Positive electrode
2 Negative electrode
2a Double-side coating part
2b One side coating part
2c Uncoated part
3 Separator
4 Electrode group
5 Positive lead
6 Negative lead
7 Battery case
8 Terminal board
9, 10 Insulation plate
11 Gasket
12 Filter
13 Inner cap
14 Valve plate
20 Negative electrode current collector
20a Exposed surface
21 Negative electrode mixture layer
100 Non-aqueous electrolyte secondary battery

Claims

An electrode group in which a positive electrode and a negative electrode are wound through a separator is a nonaqueous electrolyte secondary battery housed in a battery case,
The positive electrode has a positive electrode mixture layer formed on the surface of a sheet-like positive electrode current collector,
The negative electrode has a negative electrode mixture layer formed on the surface of a sheet-like negative electrode current collector,
The negative electrode includes a double-sided coating part in which the negative electrode mixture layer is formed on both sides of the negative electrode current collector, and a single-sided coating part in which the negative electrode mixture layer is formed on one side of the negative electrode current collector. Have
The one-side coated part is formed in a portion located at the outermost peripheral part of the electrode group, and the exposed surface of the negative electrode current collector in the one-side coated part is in contact with the inner side surface of the battery case. A non-aqueous electrolyte secondary battery.
The negative electrode further has an uncoated part where both surfaces of the negative electrode current collector are exposed at a portion located in an inner peripheral part of the electrode group,
The nonaqueous electrolyte secondary battery according to claim 1, wherein a negative electrode lead is connected to the negative electrode current collector in the uncoated portion, and the negative electrode lead is connected to the battery case.
The nonaqueous electrolyte according to claim 1 or 2, wherein an outer diameter of the electrode group when the electrode group is accommodated in the battery case is in a range of 95 to 99% with respect to an inner diameter of the battery case. Secondary battery.
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the thickness of the negative electrode current collector is in the range of 5 to 30 µm.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the uncoated part is formed at an innermost peripheral end of the electrode group.
The non-aqueous electrolyte secondary battery according to claim 2, wherein the negative electrode lead is connected to a bottom portion of the battery case.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the battery case has a cylindrical shape also serving as a negative electrode terminal.
3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the negative electrode lead is one selected from the group consisting of a Cu plate, a Ni plate, a Cu and Ni clad plate, and a Cu and Fe clad plate.