JP6694603B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a non-aqueous electrolyte secondary battery having an electrode body including a sheet-shaped positive electrode and a negative electrode.

  Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are becoming more important as power sources for vehicles or power sources for personal computers, mobile terminals and the like. In particular, a lithium-ion secondary battery that is lightweight and has a high energy density is preferably used as a power supply for mounting on a vehicle.

  The non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “battery”) described above is generally configured by housing a non-aqueous electrolyte and an electrode body in a case. As an example of the electrode body of the non-aqueous electrolyte secondary battery, there is a laminated electrode body in which a plurality of sheet-like positive electrodes and negative electrodes are laminated with a separator interposed therebetween. The sheet-shaped positive electrode is formed by applying a positive electrode mixture layer containing a positive electrode active material on the surface (both sides) of a positive electrode current collector such as an aluminum foil, and the negative electrode is a negative electrode collector such as a copper foil. It is formed by applying a negative electrode mixture layer containing a negative electrode active material to the surface (both sides) of the electric body.

  The non-aqueous electrolyte secondary battery described above may generate heat when an internal short circuit occurs. Patent Document 1 describes a technique for suppressing such heat generation. Specifically, Patent Document 1 discloses a positive electrode in which a protective layer is formed between a positive electrode current collector and a positive electrode mixture layer. The protective layer has a thickness of 1 μm to 5 μm and contains an inorganic compound having a lower oxidizing power than the lithium-containing transition metal oxide (positive electrode active material), and a conductive material. If the current collector and the positive electrode mixture layer are separated from each other by such a protective layer, the redox reaction involving the aluminum current collector can be suppressed, so that the amount of heat generated due to an internal short circuit can be reduced. You can

Further, when the non-aqueous electrolyte secondary battery is mounted on a moving body such as a vehicle and the moving body is run, sharp foreign objects such as nails may fly and stick into the battery. At this time, as shown in FIG. 6, when the sharp foreign matter E is stabbed in the electrode body 180 inside the battery, the constituent materials of the positive electrode 110 (the positive electrode current collector 112, the positive electrode mixture 112) along the traveling direction of the sharp foreign matter E. The material layer 114) is deformed. At this time, when the deformed positive electrode current collector 112 reaches the negative electrode 120, an internal short circuit having an extremely low resistance may occur and a very large Joule heat may be generated.
On the other hand, as shown in FIG. 7, when the protective layer 117 is formed between the positive electrode current collector 112 and the positive electrode mixture layer 114, when the positive electrode current collector 112 is deformed by the progress of the sharp foreign matter E. In addition, since the positive electrode current collector 112 can be prevented from reaching the negative electrode 120, abrupt heat generation due to contact between the positive electrode current collector 112 and the negative electrode 120 can be prevented.

JP, 2016-127,000, A

However, when the protective layer as described above is formed, the battery capacity is reduced, which causes a problem that it is difficult to construct a high performance non-aqueous electrolyte secondary battery. This is because the volume of the positive electrode material mixture layer is reduced by providing the protective layer made of a material that does not contribute to the charge / discharge reaction.
In order to reduce the decrease in battery capacity due to the formation of the protective layer, it is necessary to reduce the thickness of the protective layer 117 as shown in FIG. However, in this case, it becomes difficult to suitably prevent contact between the positive electrode current collector 112 and the negative electrode 120 when the sharp foreign matter E is stabbed, and the possibility of rapid heat generation due to an internal short circuit increases. ..

  The present invention has been made in view of the above points, and its main purpose is to suitably prevent sudden heat generation when a sharp foreign object such as a nail is pierced without significantly reducing the battery capacity. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery capable of achieving the above.

  In order to achieve the above object, a non-aqueous electrolyte secondary battery having the following configuration is provided as one embodiment of the present invention.

The non-aqueous electrolyte secondary battery disclosed here is configured by accommodating a sheet-shaped electrode assembly including a positive electrode and a negative electrode in a case together with the non-aqueous electrolyte.
The positive electrode of such a battery includes a foil-shaped positive electrode current collector made of a conductive metal, a pair of protective layers formed on both surfaces of the positive electrode current collector, and a positive electrode formed on each surface of the pair of protective layers. And a mixture layer. In addition, the negative electrode includes a foil-shaped negative electrode current collector made of a conductive metal and negative electrode mixture layers formed on both surfaces of the negative electrode current collector. The electrode body of such a battery is a laminated electrode body in which a plurality of positive electrodes and negative electrodes are laminated so that the positive electrode mixture layer and the negative electrode mixture layer face each other with the separator interposed therebetween.
Then, in the non-aqueous electrolyte secondary battery disclosed herein, among the pair of protective layers formed on each of the plurality of positive electrodes, the protective layer disposed on the center side in the laminating direction of the laminated electrode body is laminated. It is formed so as to be thicker than the protective layer arranged on the outer side in the direction, the thickness of the protective layer arranged on the center side is 1 μm to 4 μm, and the thickness of the protective layer arranged on the outer side is 0.5 μm. ~ 2 μm.

When a sharp foreign substance such as a nail pierces the non-aqueous electrolyte secondary battery, the sharp foreign substance advances from the outer side to the center side in the stacking direction of the stacked electrode body. The non-aqueous electrolyte secondary battery disclosed here is made based on such knowledge.
That is, in the non-aqueous electrolyte secondary battery disclosed herein, the protective layer formed on the center side in the stacking direction, which is the direction in which the positive electrode current collector is deformed when a sharp foreign substance is stabbed, is 1 μm to 4 μm. It has a sufficient thickness. Therefore, it is possible to preferably prevent the deformed positive electrode current collector from reaching the negative electrode.

Further, the protective layer formed on the outer side of the pair of protective layers in the stacking direction is deformed so as to press the positive electrode current collector when a sharp foreign matter is stabbed. Therefore, if the outer protective layer is formed too thick, the amount of deformation of the positive electrode current collector increases and the possibility of reaching the negative electrode increases.
The non-aqueous electrolyte secondary battery disclosed herein also takes this point into consideration, and the outer protective layer is made thinner than the central protective layer. As a result, it is possible to prevent the positive electrode current collector from being pressed and largely deformed by the deformed outer protective layer.

Further, in the non-aqueous electrolyte secondary battery disclosed herein, the outer protective layer that does not contribute to the suppression of deformation of the positive electrode current collector is formed with a very thin thickness of 0.5 μm to 2 μm. For this reason, the total thickness of the pair of protective layers can be made significantly smaller than in the conventional case, and the decrease in battery capacity due to the provision of the protective layers can be reduced.
As described above, according to the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode current collector is deformed and reaches the negative electrode when a sharp foreign matter is stabbed without significantly reducing the battery capacity. Since this can be suitably prevented, rapid heat generation due to contact between the positive electrode current collector and the negative electrode can be suitably suppressed.

It is a perspective view which shows typically the lithium ion secondary battery which concerns on one Embodiment of this invention. It is explanatory drawing which shows typically each member which comprises the electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a perspective view which shows typically the structure of the electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is sectional drawing when the electric power generation area | region of the electrode body shown in FIG. 3 is cut | disconnected along the lamination direction. FIG. 3 is a cross-sectional view that schematically shows a state in which a sharp foreign object has stuck into an electrode body of a lithium-ion secondary battery according to an embodiment of the present invention. It is sectional drawing which shows typically an example of the state which the sharp foreign material stuck in the conventional lithium ion secondary battery. It is sectional drawing which shows typically the other example of the state which the sharp foreign material stuck in the conventional lithium ion secondary battery. It is sectional drawing which shows typically the other example of the state which the sharp foreign material stuck in the conventional lithium ion secondary battery.

Hereinafter, a lithium ion secondary battery will be described as an example of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. The non-aqueous electrolyte secondary battery disclosed here is not limited to the lithium ion secondary battery, and may be another secondary battery (for example, a nickel hydrogen battery).
Further, in the following drawings, the same reference numerals are given to the members / sites that have the same effect. Note that the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. In addition, matters other than matters particularly referred to in the present specification and matters necessary for carrying out the present invention (for example, the material and the manufacturing method of the nonaqueous electrolytic solution) are based on those of ordinary skill in the art. Can be understood as a design item.

1. Structure of Lithium Ion Secondary Battery The lithium ion secondary battery according to this embodiment will be described below.
FIG. 1 is a perspective view schematically showing the lithium-ion secondary battery according to this embodiment. FIG. 2 is an explanatory view schematically showing each member constituting the electrode body of the lithium ion secondary battery according to this embodiment, and FIG. 3 is an electrode body of the lithium ion secondary battery according to this embodiment. It is a perspective view which shows a structure typically. Further, FIG. 4 is a cross-sectional view of the power generation region of the electrode body shown in FIG. 3 taken along the stacking direction.
In the drawings of the present specification, the symbol X indicates the "width direction" of the battery, the symbol Y indicates the "thickness direction", and the symbol Z indicates the "height direction".

(1) Case As shown in FIG. 1, the lithium-ion secondary battery 100 according to the present embodiment includes a flat rectangular case 50. The case 50 includes a flat rectangular case body 52 having an open upper surface, and a plate-like lid 54 that closes the opening of the upper surface of the case body 52. It is preferable that the case main body 52 and the lid 54 are mainly composed of a metal material that is lightweight and has good heat conductivity, and examples of such a metal material include aluminum.
In addition, in the lithium-ion secondary battery 100, electrode terminals 60 and 62 are provided on the lid 54 on the upper surface of the case 50. The electrode terminals 60 and 62 are formed so as to project outside the case 50, and are connected to an external device such as another battery or a vehicle motor.
The shape and material of the case do not limit the present invention. For example, a lithium ion secondary battery can be constructed even when a resin laminated film is used as a case and an electrode body and a non-aqueous electrolyte solution described later are enclosed in the laminated film.

(2) Electrode Body In the lithium ion secondary battery 100 according to the present embodiment, the electrode body is housed inside the case 50 shown in FIG. As shown in FIGS. 2 and 3, the electrode body 80 of the lithium-ion secondary battery 100 according to the present embodiment is a laminated electrode body in which a plurality of sheet-shaped positive electrodes 10 and negative electrodes 20 are provided with a separator 40 interposed therebetween. Is. As shown in FIGS. 3 and 4, the laminated electrode body 80 is formed by laminating the positive electrode 10, the separator 40, and the negative electrode 20 along the thickness direction Y of the battery. Therefore, the “stacking direction of the stacked electrode body” in the present embodiment is the same direction as the thickness direction Y of the battery. The symbol CL in FIG. 4 indicates the center line of the stacked electrode body 80 in the stacking direction Y.

(A) Positive Electrode As shown in FIG. 2, the positive electrode 10 is formed by applying the positive electrode mixture layer 14 to the surface (both sides) of the positive electrode current collector 12. Then, at one end of the positive electrode 10 in the width direction X, a positive electrode exposed portion 16 in which the positive electrode mixture layer 14 is not provided and the positive electrode current collector 12 is exposed is formed.
Further, as shown in FIG. 4, in the positive electrode 10 of this embodiment, protective layers 17 a and 17 b are formed between the positive electrode current collector 12 and the positive electrode mixture layer 14. In other words, in the present embodiment, the protective layers 17a and 17b are formed on each surface of the positive electrode current collector 12, and the positive electrode mixture layer 14 is formed on each surface of the pair of protective layers 17a and 17b. ing.

Next, each material forming the positive electrode 10 will be described.
The positive electrode current collector 12 is a foil-shaped member made of a conductive metal. Examples of the conductive metal forming the positive electrode current collector 12 include aluminum and aluminum alloys. The thickness of the positive electrode current collector 12 is preferably about 5 μm to 20 μm.

The positive electrode mixture layer 14 is formed by drying a positive electrode paste containing a positive electrode active material. A lithium composite oxide capable of inserting and extracting lithium ions is used as the positive electrode active material. As such a lithium composite oxide, a lithium transition metal composite oxide containing lithium and a transition metal element can be preferably used. For example, lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _{1 / 3} O ₂ ), lithium nickel composite oxide (LiNiO ₂ ), lithium cobalt composite oxide (LiCoO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ) and the like can be used.
Further, the positive electrode mixture layer 14 may contain additives such as a conductive agent and a binder. As the conductive agent, acetylene black or the like can be used, and as the binder, polyvinylidene fluoride (PVdF) or carboxymethyl cellulose (CMC) can be used.
The material of the positive electrode mixture layer 14 may be the same as that used in a general lithium ion secondary battery without any particular limitation, and is not limited to the above-mentioned materials.
Further, in the lithium-ion secondary battery 100 according to the present embodiment, it is preferable that the density of the positive electrode mixture layer 14 is 3.5 g / cm ³ or more from the viewpoint of high capacity.

In addition, the protective layers 17a and 17b contain a filler and a conductive agent. As the filler, a chemically stable metal oxide can be preferably used. Further, specific examples of the filler include aluminum oxide (alumina), boehmite, titanium oxide (titania), and the like. Further, in order to electrically connect the positive electrode current collector 12 and the positive electrode mixture layer 14, the protective layers 17a and 17b need to contain a conductive agent. As the conductive agent for the protective layers 17a and 17b, the same material (for example, acetylene black) as the conductive agent for the positive electrode mixture layer 14 can be used.
Further, the protective layers 17a and 17b may contain a binder and the like. Polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), or the like can be used as the binder.

Then, in the lithium-ion secondary battery 100 according to the present embodiment, the pair of protective layers 17a and 17b formed on both surfaces of the positive electrode current collector 12 is arranged on the center side in the stacking direction Y (center line CL side). The protective layer 17b (hereinafter, also referred to as "center side protective layer 17b") is thicker than the protective layer 17a (hereinafter, also referred to as "outer protective layer 17a") arranged outside in the stacking direction Y. Is formed.
Further, in the present embodiment, the thickness t2 (see FIG. 5) of the protective layer 17b on the center side is 1 μm to 4 μm while satisfying the condition that the protective layer 17b on the center side is thicker than the protective layer 17a on the outer side. Thus, the respective protective layers 17a and 17b are formed so that the thickness t1 of the outer protective layer 17a is 0.5 μm to 2 μm. Further, the total thickness t1 of the outer protective layer 17a and the thickness t2 of the central protective layer 17b is set to 1.5 μm to 5 μm.
As will be described later in detail, in the lithium-ion secondary battery 100 according to the present embodiment, since such a pair of protective layers 17a and 17b is formed, sharp edges such as nails do not significantly reduce the battery capacity. It is possible to preferably prevent sudden heat generation when a foreign object is stuck.

(B) Negative Electrode As shown in FIG. 2, the negative electrode 20 is formed by applying the negative electrode mixture layer 24 to the surface (both sides) of the negative electrode current collector 22. Then, at one end of the negative electrode 20 in the width direction X, a negative electrode exposed portion 26 where the negative electrode current collector 22 is exposed without forming the negative electrode mixture layer 24 is formed.

Next, each material forming the negative electrode 20 will be described.
The negative electrode current collector 22 is a foil-shaped member made of a conductive metal. As the conductive metal forming the negative electrode current collector 22, for example, copper or the like can be used. The thickness of the negative electrode current collector 22 is preferably about 5 μm to 20 μm.

The negative electrode mixture layer 24 is formed by drying the negative electrode paste containing the negative electrode active material. A carbon material capable of inserting and extracting lithium ions is used for the negative electrode active material. As such a carbon material, graphite, non-graphitizable carbon (hard carbon), easily graphitizable carbon (soft carbon), carbon nanotube, or the like can be used.
In addition to the above-mentioned negative electrode active material, the negative electrode mixture layer 24 may contain a thickener such as carboxymethyl cellulose, a binder such as styrene butadiene rubber, and the like.
Similar to the positive electrode mixture layer 14 described above, the negative electrode mixture layer 24 may be made of any material used in a general lithium ion secondary battery without any particular limitation, and is not limited to the above-mentioned materials.

(C) Separator The separator 40 is arranged so as to be interposed between the positive electrode 10 and the negative electrode 20. Specific examples of the separator 40 include a sheet material having a single layer structure made of a porous polyolefin resin and a sheet material having a laminated structure in which a plurality of types of resin sheets are laminated.

(D) Laminated structure of electrode body As described above, the laminated electrode body 80 in the present embodiment is formed by stacking a plurality of positive electrodes 10 and negative electrodes 20 with the separator 40 interposed therebetween. At this time, as shown in FIG. 3, a power generation region 80a, in which the positive electrode mixture layer 14 and the negative electrode mixture layer 24 are laminated so as to face each other, is formed in the central portion in the width direction X of the laminated electrode body 80. It Further, a positive electrode connecting region 80b in which the positive electrode exposed portion 16 is laminated is formed at one end portion of the electrode body 80 in the width direction X, and a negative electrode connecting region 80c in which the negative electrode exposed portion 26 is laminated is formed at the end portion. To be done. Each of the positive electrode connecting region 80b and the negative electrode connecting region 80c is electrically connected to the electrode terminals 60 and 62 shown in FIG.

  Further, as shown in FIG. 4, the laminated electrode body 80 in the present embodiment is formed so as to be line-symmetrical with respect to the center line CL in the laminating direction Y. Specifically, in the upper half of the laminated electrode body 80 in FIG. 4 (above the center line CL), the relatively thick protective layer 17b is formed on the lower surface side of the positive electrode current collector 12, and the The protective layer 17b "is formed, and the thin protective layer 17a is formed on the upper surface side of the positive electrode current collector 12 to be the" outer protective layer 17b ". On the other hand, in the lower half (below the center line CL), the relatively thick protective layer 17b is formed on the upper surface side of the positive electrode current collector 12 to serve as the "center side protective layer 17b", and the thin protective layer 17a is the positive electrode. It is formed on the lower surface side of the current collector 12 to serve as the “outer protective layer 17b”.

(3) Non-Aqueous Electrolyte Solution In the present embodiment, the non-aqueous electrolyte solution is housed in the case 50 together with the above-mentioned laminated electrode body 80. As such a non-aqueous electrolyte, the same non-aqueous electrolyte as conventionally used in lithium-ion secondary batteries can be used without particular limitation.
Typically, non-aqueous electrolytes are prepared by including a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, for example, a group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane and the like. One kind or two or more kinds of solvents selected from can be used. Examples of the supporting salt include lithium such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) _3. Salt can be used.
As a specific example of such a non-aqueous electrolyte, about 1 mol / L of LiPF ₆ is added to a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (for example, volume ratio 3: 4: 3). An electrolytic solution contained at a concentration of

3. When a sharp foreign matter is stabbed The lithium-ion secondary battery 100 according to the present embodiment having the above structure is suitable for rapid heat generation when a sharp foreign matter such as a nail is stabbed without significantly reducing the battery capacity. Can be prevented. Hereinafter, a case where a sharp foreign object such as a nail is stuck into the lithium ion secondary battery 100 according to the present embodiment will be described.

  FIG. 5 is a cross-sectional view schematically showing a state in which a sharp foreign object has stuck into the electrode body of the lithium-ion secondary battery according to this embodiment. As shown in FIG. 5, when a sharp foreign substance E is stuck into the laminated electrode body 80 of the lithium-ion secondary battery, the foreign substance E penetrates each of the positive electrode 10, the separator 40, and the negative electrode 20 constituting the laminated electrode body 80. While advancing from the outer side in the stacking direction Y toward the center side (downward in FIG. 5).

At this time, in the present embodiment, since the protective layer 17b having a sufficient thickness of 1 μm to 4 μm is formed on the center side in the stacking direction Y, when the positive electrode current collector 12 is deformed as the foreign matter E progresses. In addition, it is possible to preferably prevent the positive electrode current collector 12 from reaching the negative electrode 20.
Further, in this embodiment, the outer protective layer 17a is formed to be relatively thin. Thereby, when the outer protective layer 17a is deformed by the progress of the foreign matter E, it is possible to preferably suppress the outer protective layer 17a from pressing and deforming the positive electrode current collector 12.
Therefore, according to the present embodiment, it is possible to preferably prevent the positive electrode current collector 12 from being deformed and reaching the negative electrode 20, so that abrupt heat generation due to contact between the positive electrode current collector 12 and the negative electrode 20 is preferable. Can be prevented. The contact between the positive electrode current collector 12 and the negative electrode 20 is preferably prevented until the foreign matter E exceeds the center line CL of the laminated electrode body 80 to ensure safety, and the energy of the battery can be sufficiently reduced in the meantime. Therefore, even if the foreign matter E penetrates the battery, it is possible to preferably prevent abrupt heat generation.

  Further, in the lithium-ion secondary battery 100 according to the present embodiment, the outer protective layer 17a is formed with a thickness of 0.5 μm to 2 μm, which is thinner than the conventional thickness. As described above, since the outer protective layer 17a does not contribute to the suppression of deformation of the positive electrode current collector 12, even if it is formed thin as described above, abrupt heat generation due to contact between the positive electrode current collector 12 and the negative electrode 20 is caused. Can be preferably prevented. Then, since the total thickness of the protective layers 17a and 17b becomes thinner than the conventional one, it is possible to secure a sufficient volume of the positive electrode mixture layer 14 and obtain a suitable battery capacity.

  As described above, according to the lithium-ion secondary battery 100 according to the present embodiment, rapid heat generation due to contact between the positive electrode current collector 10 and the negative electrode 20 can be appropriately suppressed without significantly reducing the battery capacity. You can

  Further, in the present embodiment, since the protective layers 17a and 17b are formed on both surfaces of the positive electrode current collector 12, the aluminum positive electrode current collector 12 can be protected when the sharp foreign matter E is stabbed in the laminated electrode body 80. It is possible to suppress the exposure and contact with the negative electrode mixture layer 24. Therefore, it is possible to prevent the occurrence of a short circuit by melting the positive electrode current collector 12 before a low resistance short circuit occurs between the positive electrode current collector 12 and the negative electrode mixture layer 24.

[Test example]
Hereinafter, test examples relating to the present invention will be described, but the following test examples are not intended to limit the present invention.

1. Samples 1-12
In this test example, 12 types of lithium ion secondary batteries (Samples 1 to 12) having different structures for the protective layer of the positive electrode were prepared.

Specifically, first, a metal oxide filler, a conductive material (acetylene black: AB), and a binder (polyvinylidene fluoride: PVdF) are mixed at a ratio of 93.5: 5: 1.5, A paste for a protective layer was prepared by dispersing in a dispersion medium (N-methylpyrrolidone: NMP). Then, the protective layer paste was applied to both surfaces of the positive electrode current collector (aluminum foil) and then dried to form a pair of protective layers.
Here, in this test example, the type of metal oxide constituting the filler, the thickness and the basis weight of each of the pair of protective layers were made different for each sample. The specific contents are shown in Table 1 below. In addition, in sample 7, the protective layer was not formed.

Next, a positive electrode active material (lithium-nickel-cobalt-aluminum composite oxide (NCA)), a conductive material (acetylene black: AB), and a binder (polyvinylidene fluoride: PVdF) in a ratio of 98: 1: 1. Was mixed and dispersed in a dispersion medium (NMP) to prepare a positive electrode paste.
Then, a positive electrode paste was applied to both surfaces of the positive electrode current collector on which the protective layer was formed, and the positive electrode paste was dried to produce a sheet-shaped positive electrode. In this test example, the produced positive electrode was rolled to adjust the density of the positive electrode mixture layer to 3.5 g / cm ³ .

Next, in this test example, a negative electrode active material (graphite), a binder (styrene butadiene rubber: SBR), and a thickener (carboxymethyl cellulose: CMC) were mixed at a ratio of 98: 1: 1 to prepare a dispersion medium. It was dispersed in (water) to prepare a negative electrode paste.
Then, after applying the negative electrode paste to both surfaces of the negative electrode current collector (copper foil), it was dried and rolled to prepare a sheet-shaped negative electrode.

  Next, a laminated electrode body having a thickness of 3 mm was produced by alternately laminating eight positive electrodes and nine negative electrodes via a separator. Then, the produced laminated electrode body was connected to the electrode terminals and then housed inside the case. The separator used in this test example is a separator (thickness 16 μm) having a three-layer structure (PP / PE / PP) in which a polyethylene (PE) layer is sandwiched between two polypropylene (PP) layers. ..

Next, a supporting solvent (LiPF ₆ ) of about 1 mol / L was added to a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 4: 3. The lithium ion secondary batteries (rated capacity: 750 mAh) of Samples 1 to 12 were produced by filling the case with a non-aqueous electrolytic solution contained at a concentration and impregnating the laminated electrode body with the non-aqueous electrolytic solution.

2. Evaluation test (1) Measurement of battery capacity In this test example, the capacities of the batteries of Samples 1 to 12 described above were measured. Specifically, the battery of each sample was kept under the temperature condition of room temperature (25 ° C.), and charged to 4.1 V at a current density of 1 C by a constant current-constant voltage (CCCV) method, and then 5 minutes. Paused. Then, at the same current density, a constant current discharge was performed up to 3.0 V, and a rest was performed for 5 minutes. After that, the initial capacity (battery capacity) is measured by performing CCCV charging (up to 4.1V, rate 1C, 0.1C cut) and CCCV discharge (up to 3.0V, rate 1C, 0.1C cut). did. The measurement results are shown in Table 1.

(2) Nail penetration test Next, a nail penetration test was performed on the batteries of each sample. Specifically, the battery of each sample was adjusted to a SOC 100% charged state in a room temperature environment of 25 ° C. Then, two thermocouples were attached to the outer surface of the case of each battery, and a nail made of tungsten was pierced along the battery thickness direction (electrode body stacking direction) Y. The nail had a diameter of 1 mm, a length of 20 mm, and a tip angle of 20 °, and was pierced at a right angle at a speed of 0.1 mm / sec so as to pierce the power generation region of the laminated electrode body.
Then, the change in the battery temperature for 5 seconds after the nail was pierced was continuously detected by the thermocouple and the maximum temperature reached was measured. The measurement results are shown in Table 1.

  As a result of comparing Samples 1 to 4 with Samples 10 and 11, it was confirmed that when the thickness of the protective layer on the center side was increased, the maximum temperature reached in the nail penetration test was lowered. From this, it is possible to prevent the deformed positive electrode current collector from reaching the negative electrode when a sharp foreign object such as a nail is pierced by providing the protective layer arranged on the center side in the stacking direction with a sufficient thickness. However, it was found that abrupt heat generation due to contact between the positive electrode current collector and the negative electrode can be prevented.

  On the other hand, comparing Sample 1, Sample 8 and Sample 9 in which the thickness of the protective layer on the center side is the same, the maximum attainable temperature of Sample 1 having a thin outer protective layer is lower than that of Samples 8 and 9. The fever was suppressed. From this, it has been found that the thinner outer protective layer can suppress the heat generation when a sharp foreign matter is stuck. This is because the outer protective layer may deform and press the positive electrode current collector when a sharp foreign matter is stabbed.However, if the outer protective layer is thinned, the deformed outer protective layer may cause the positive electrode current collector to deform. It is understood that it is possible to suppress the deformation of the body.

  As a result of comparing all of Samples 1 to 12, it was confirmed that the battery capacity was improved when the total thickness of the protective layer on the center side and the protective layer on the outer side was reduced. In particular, as in Sample 10, the battery capacity falls below 700 mAh / g when the thickness on both sides is 6 μm or more. Therefore, it was found that the thickness on both sides needs to be less than 6 μm in order to construct a battery having a suitable capacity. It was

  From the above results, it was found that it is preferable to thicken the protective layer on the center side and thin the protective layer on the outer side in order to suitably suppress heat generation when a sharp foreign object such as a nail is stabbed. When the outer protective layer is thinned, the total thickness of the protective layers is thinned and the positive electrode mixture layer having a sufficient thickness can be formed. It has been found that it is possible to preferably prevent sudden heat generation when a sharp foreign object is stuck.

  As a result of comparing Samples 2, 5, and 6, it was confirmed that the metal oxide forming the filler contained in the protective layer may be any of alumina, boehmite, and titanium oxide.

10, 110 Positive electrode 12, 112 Positive electrode current collector 14, 114 Positive electrode mixture layer 16 Positive electrode exposed portion 17a (Outer side) Protective layer 17b (Center side) Protective layer 20, 120 Negative electrode 22 Negative electrode current collector 24 Negative electrode mixture Layer 26 Negative electrode exposed portion 40 Separator 50 Case 52 Case body 54 Lid body 60, 62 Electrode terminal 80, 180 Electrode body (laminated electrode body)
80a Power generation region 80b Positive electrode connection region 80c Negative electrode connection region 100 Lithium ion secondary battery 117 Protective layer CL Center line E Sharp foreign matter t1 Outer protective layer thickness t2 Central side protective layer thickness X Width direction Y Thickness direction (lamination Electrode body stacking direction)
Z height direction

Claims (1)

A non-aqueous electrolyte secondary battery in which an electrode body having a sheet-shaped positive electrode and a negative electrode is housed in a case together with a non-aqueous electrolyte solution,
The positive electrode is a foil-shaped positive electrode current collector made of a conductive metal, a pair of protective layers formed on both surfaces of the positive electrode current collector, and a positive electrode mixture formed on each surface of the pair of protective layers. With a material layer,
The negative electrode includes a foil-shaped negative electrode current collector made of a conductive metal, and a negative electrode mixture layer formed on both surfaces of the negative electrode current collector,
The electrode body is a laminated electrode body in which a plurality of the positive electrode and the negative electrode are laminated so that the positive electrode mixture layer and the negative electrode mixture layer face each other via a separator,
Of the pair of protective layers formed on each of the plurality of positive electrodes, the protective layer arranged on the center side of the laminated electrode body in the laminating direction is thicker than the protective layer arranged on the outer side of the laminating direction. Is formed so that
A non-aqueous electrolyte secondary battery in which the thickness of the protective layer disposed on the center side is 1 μm to 4 μm, and the thickness of the protective layer disposed on the outer side is 0.5 μm to 2 μm.

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