JP2014013778A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with excellent battery characteristics such as output characteristics by improving moldability of a flat electrode body.SOLUTION: A nonaqueous electrolyte secondary battery includes: a positive electrode plate containing a lithium transition metal composite oxide as a positive electrode active material; a negative electrode plate containing a carbon material capable of absorbing/desorbing lithium ions as a negative electrode active material; and a flat electrode body wound with the electrodes laminated via a separator. A protective layer constituted by inorganic oxide and an insulation binding material is provided on the front surface of the negative electrode plate. The separator has arithmetic mean surface roughness which is different between the front and rear surfaces. The surface of the separator with larger arithmetic mean surface roughness is placed in contact with the protective layer. The separator is a porous material made of polyolefin.

Description

  The present invention relates to a flat electrode body in which a positive electrode plate including a positive electrode active material capable of occluding and releasing lithium ions and a negative electrode plate including a negative electrode active material capable of occluding and releasing lithium ions are stacked and wound via a separator. The present invention relates to a non-aqueous electrolyte secondary battery having

As a battery used in portable electronic / communication equipment such as a small video camera, a cellular phone, and a laptop computer, a negative electrode active material is a carbon material or alloy that can occlude / release lithium ions, lithium cobalt oxide (LiCoO ₂ ), A non-aqueous electrolyte secondary battery using a lithium transition metal composite oxide such as lithium manganate (LiMn ₂ O ₄ ) or lithium nickel oxide (LiNiO ₂ ) as a positive electrode active material is small, lightweight, high in voltage, and high in capacity. It has been put to practical use as a chargeable / dischargeable battery.

  In recent years, the development of electric vehicles (EV), hybrid vehicles (HEV), and the like using nonaqueous electrolyte secondary batteries has been actively conducted. The nonaqueous electrolyte secondary battery used for an electric vehicle (EV), a hybrid vehicle (HEV) or the like is preferably a rectangular battery in which a power generation element is housed in a rectangular battery outer can in order to improve space efficiency and heat dissipation.

  As an example, the structure of a prismatic nonaqueous electrolyte secondary battery will be described with reference to FIG. FIG. 1A is a front view (perspective view) of the prismatic nonaqueous electrolyte secondary battery 30, and FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A.

  The prismatic nonaqueous electrolyte secondary battery 30 includes a flat electrode plate 1 in which a positive electrode plate (not shown) and a negative electrode plate (not shown) are stacked and wound via a separator (not shown), together with a nonaqueous electrolyte. The outer can 2 is housed inside the outer can 2, and the outer can 2 is sealed with a sealing plate 3. The flat electrode body 1 includes a positive electrode core exposed portion 4 that does not form a positive electrode active material mixture layer at one end in the winding axis direction, and does not form a negative electrode active material mixture layer at the other end. A negative electrode core exposed portion 5 is provided. The positive electrode core exposed portion 4 is connected to the positive electrode terminal 7 via the positive electrode current collector 6, and the negative electrode core exposed portion 5 is connected to the negative electrode terminal 9 via the negative electrode current collector 8.

  A positive current collector receiving member (not shown) is connected to a portion facing the positive electrode current collector 6 through the positive electrode core exposed portion 4, and the negative electrode current collector through the negative electrode core exposed portion 5. A negative current collector receiving member 13 is connected to a portion facing 8. The positive electrode terminal 7 and the negative electrode terminal 9 are fixed to the sealing plate 3 via insulating materials 11 and 12, respectively. The positive electrode terminal 7 and the negative electrode terminal 9 have plate portions 7a and 9a arranged in parallel with the sealing plate 3, and bolt portions 7b and 9b connected to the plate portions 7a and 9a, respectively. , 9b are connected to other adjacent rectangular nonaqueous electrolyte secondary batteries.

  The prismatic nonaqueous electrolyte secondary battery 30 is manufactured by the following procedure. First, an insulating material (not shown) is disposed on the inner surface of a through hole (not shown) provided in the sealing plate 3, the battery outer surface around the through hole, and the battery inner surface. Then, the positive electrode current collector 6 is placed on the insulating material located on the battery inner surface of the sealing plate 3 so that the through hole of the sealing plate 3 and the through hole (not shown) provided in the positive electrode current collector 6 overlap. Position. Thereafter, the insertion portion (not shown) of the positive electrode terminal 7 is inserted from the outside of the battery into the through hole of the sealing plate 2 and the through hole of the positive electrode current collector 6. In this state, the diameter of the lower portion (battery inner side) of the insertion portion is widened, and the positive electrode terminal 7 is caulked and fixed to the sealing plate 3 together with the positive electrode current collector 6.

Similarly, the negative electrode terminal 9 is fixed to the sealing plate 3 together with the negative electrode current collector 8 on the negative electrode side. The members are integrated by these operations, and the positive electrode current collector 6 and the positive electrode terminal 7 and the negative electrode current collector 6 and the negative electrode terminal 9 are connected to each other so as to be energized. Further, the positive and negative terminals 7 and 9 protrude from the sealing plate 3 while being insulated from the sealing plate 3.

  Thereafter, the flat electrode body 1 integrated with the sealing plate 3 is inserted into the outer can 2, and the sealing plate 3 is laser welded to the opening of the outer can 2. Then, a nonaqueous electrolytic solution is injected from an electrolytic solution injection hole (not shown), and the electrolytic solution injection hole is sealed.

  While various developments are being made on non-aqueous electrolyte secondary batteries, the safety of non-aqueous electrolyte secondary batteries used in electric vehicles (EV), hybrid vehicles (HEV) and the like as described above is further increased. There is a need for improvement.

  In order to improve the safety of non-aqueous electrolyte secondary batteries, various countermeasures have been studied with battery materials or mechanisms, etc. As an example, for the purpose of preventing internal short circuit on the surface of either the positive electrode plate or the negative electrode plate A technique for providing an insulating protective layer made of an inorganic oxide such as alumina and an insulating binder has been proposed (Patent Document 1).

JP 2009-91461 A JP-A-9-245762

  However, when a flat electrode body is produced using a negative electrode plate on which a protective layer made of an inorganic oxide such as alumina and an insulating binder is formed based on the prior art, the formability of the electrode body is reduced. The problem that occurred. Thus, when the moldability of an electrode body falls, when inserting an electrode body into an armored can, the bad effect of becoming the thickness which cannot be inserted in an armored can etc. will arise, and there exists a concern about the fall of a yield. In addition, there is a concern about deterioration of battery characteristics such as output characteristics of the obtained nonaqueous electrolyte secondary battery.

  As a result of various studies, the inventors have found that when a flat electrode body is produced using a negative electrode plate on which a protective layer is formed, the adhesion between the separator and the protective layer formed on the surface of the negative electrode plate is reduced. Thus, it has been found that the moldability of the electrode body is lowered.

Here, in Patent Document 2, when a separator having an arithmetic average surface roughness Ra of 0.3 to 0.6 μm is used, the adhesion between the electrode plate and the separator is improved after the electrode body is hot-pressed. It is disclosed.
However, Patent Document 2 does not disclose that an insulating protective layer made of an inorganic oxide and an insulating binder is provided on the negative electrode plate surface.

  The present invention solves the above problems, and in a flat electrode body using a negative electrode plate on which a protective layer made of an inorganic oxide such as alumina and an insulating binder is formed, the moldability of the electrode body is improved. The goal is to improve.

The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode plate containing a lithium transition metal composite oxide as a positive electrode active material and a negative electrode plate containing a carbon material capable of occluding and releasing lithium ions as a negative electrode active material. In the nonaqueous electrolyte secondary battery having a flat electrode body laminated and wound through, a protective layer made of an inorganic oxide and an insulating binder is provided on the surface of the negative electrode plate, and the separator It has different arithmetic average surface roughness on the front and back surfaces, and the separator has a large arithmetic average surface roughness surface so as to be in contact with the protective layer, and the separator is a porous polyolefin. To do.

  As a result of the study, the inventors have arranged that the surface having a different arithmetic average surface roughness on the front and back surfaces of the separator and having a large arithmetic surface roughness on the separator is in contact with the protective layer formed on the negative electrode plate. Furthermore, it has been found that by using a polyolefin porous material as a separator, the adhesion between the separator and the protective layer can be improved and the moldability of the electrode body can be improved.

  The separator may have different arithmetic average surface roughness Ra depending on the manufacturing method. This is because when the strip-shaped separator moves on the roll in the manufacturing process of the separator, the arithmetic average surface roughness Ra of the surface in contact with the roll in the separator becomes smaller than that of the other surface due to friction with the roll. Here, when the separator moves on the roll, a plurality of separators may be moved in an overlapping manner to improve production efficiency. At that time, when the separator after passing through the roll is peeled off, the arithmetic average surface roughness of the peeled surface is removed. Ra is larger than the surface in contact with the roll.

  From this point of view, when considering the cost, it is necessary to use not only separators having the same arithmetic average surface roughness Ra on the front and back sides but also separators having different arithmetic average surface roughness Ra on the front and back sides.

  On the other hand, when the arithmetic average surface roughness Ra of the separator is large on both sides, the active material mixture layer is deeply bitten into the separator, and even if a protective layer is provided on the negative electrode plate, there is a high possibility that an internal short circuit will occur. It is considered to be.

  The inventors have found that the adhesion of the positive electrode plate to the separator is higher than that of the negative electrode plate on which the protective layer is formed. For this reason, it turned out that arithmetic mean surface roughness Ra of the surface which touches the positive electrode plate of a separator can be set small.

  From the above, when using a separator having a different arithmetic average surface roughness Ra on the front and back and a negative electrode plate formed with a protective layer, the surface having a large arithmetic average surface roughness Ra is in contact with the protective layer formed on the negative electrode plate. Arrange as follows. With such a configuration, it is possible to improve the adhesion between the protective layer formed on the separator and the negative electrode plate and to reduce the probability of occurrence of a short circuit between the positive and negative electrodes. Furthermore, since the polyolefin is microporous as a separator, it is possible to further improve the adhesion with the protective layer formed on the negative electrode plate.

  Here, in the present invention, the arithmetic average surface roughness Ra of the surface in contact with the protective layer formed on the negative electrode plate of the separator (the surface having the larger arithmetic average surface roughness Ra) is set to 0.40 μm to 3.50 μm. It is preferable. In addition, since the adhesion strength between the positive electrode plate and the separator is not insufficient, the arithmetic average surface roughness Ra of the surface of the separator that contacts the positive electrode plate (the surface with the smaller arithmetic average surface roughness Ra) is the active material for the separator. In order to avoid deeper biting of the mixture layer, the thickness is preferably 0.05 μm to 0.25 μm.

  In the present invention, by setting the arithmetic average surface roughness Ra of the surface in contact with the protective layer of the separator to 0.40 μm or more, the adhesion between the separator and the protective layer can be further improved, and the moldability of the electrode body can be improved. Moreover, it is preferable that arithmetic mean surface roughness Ra of the surface which touches the protective layer of a separator is 3.50 micrometer or less.

As the insulating binder contained in the protective layer, a binder generally used in nonaqueous electrolyte secondary batteries can be used. Specifically, a copolymer containing an acrylonitrile structure, a polyimide resin, a styrene-butadiene-rubber (SBR), an ethylene-tetrafluoroethylene copolymer (ETFE), a polyvinylidene fluoride (PVdF), a tetrafluoroethylene resin ( At least one selected from PTFE) and carboxymethylcellulose (CMC) is preferable.

  It is preferable that the binder in the negative electrode plate of the present invention is different from the insulating binder in the protective layer. When the same binder is used for the insulating binder between the negative electrode plate binder and the protective layer, it becomes difficult to clearly separate and arrange the layers at the interface between the negative electrode plate and the protective layer, There is a possibility that the function as the protective layer cannot be fully exhibited. In consideration of these, the binder for the negative electrode plate is preferably soluble in the aqueous slurry, and the insulating binder for the protective layer is preferably soluble in the non-aqueous slurry.

In the nonaqueous electrolyte secondary battery of the present invention, a lithium transition metal composite oxide capable of occluding and releasing lithium ions can be used as the positive electrode active material. Examples of the lithium transition metal composite oxide capable of inserting and extracting lithium ions include lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and lithium nickel manganese composite oxide ( LiNi _1-x Mn _x O ₂ (0 <x <1)), lithium nickel cobalt composite oxide LiNi _1-x Co _x O ₂ (0 <x <1), lithium nickel cobalt manganese composite oxide (LiNi _x Mn and lithium transition metal oxides such as _y Co _z O ₂ (0 <x <1, 0 <y <1, 0 <z <1, x + y + z = 1). Al in the composite oxide, Ti, Zr, Nb, B, Mg or those such as the addition of Mo can be used. for _{example, Li 1 + a Ni x Co} y Mn z _{b O 2 (M = Al,} Ti, Zr, Nb, B, Mg, at least one element selected from Mo, 0 ≦ a ≦ 0.2,0.2 ≦ x ≦ 0.5,0.2 ≦ and lithium transition metal composite oxides represented by y ≦ 0.5, 0.2 ≦ z ≦ 0.4, 0 ≦ b ≦ 0.02, and a + b + x + y + z = 1).

In the non-aqueous electrolyte secondary battery of the present invention, it is preferable to 0.9~1.4g / cm ³ a packing density of the negative electrode plate, and more preferably to 1.0~1.2g / cm ^3. If the packing density of the negative electrode plate is less than 0.9 g / cm ³ , the energy density of the battery is lowered, which is not preferable. Moreover, when the packing density of a negative electrode plate exceeds 1.4 g / cm < ³ >, the expansion / contraction of the electrode by charging / discharging becomes large and is unpreferable. Here, the packing density of the negative electrode plate means the packing density of the negative electrode active material mixture layer containing the negative electrode active material, and does not include the protective layer formed on the negative electrode plate surface and the negative electrode core.

In the non-aqueous electrolyte secondary battery of the present invention, the packing density of the positive electrode plate is preferably in a 2.5~2.9g / cm ^3, and more preferably to 2.5~2.8g / cm ³ . Here, the packing density of the positive electrode plate means the packing density of the positive electrode active material mixture layer including the positive electrode active material, and does not include the positive electrode core.

If the packing density of the positive electrode plate is less than 2.5 g / cm ^3, it is not preferable because sufficient output characteristics cannot be obtained. When the packing density of the positive electrode plate exceeds 2.8 g / cm ³ , the elongation of the core increases, so that the electrode plate bends, the adhesion between the positive electrode plate and the separator decreases, or the pressure resistance due to winding misalignment during winding. Defects may occur.

  In the nonaqueous electrolyte secondary battery of the present invention, a porous separator made of polyolefin such as polypropylene (PP) or polyethylene (PE) is used as a separator, and a three-layer structure (PP / PE) of polypropylene (PP) and polyethylene (PE). It is preferable to use a separator having / PP or PE / PP / PE).

In the present invention, as the inorganic oxide contained in the protective layer, at least one selected from the group consisting of alumina, titania, and zirconia can be used. Moreover, it is preferable to use an inorganic oxide having an average particle size of 0.1 to 1.0 μm.

  In the nonaqueous electrolyte secondary battery of the present invention, a carbon material capable of occluding and releasing lithium ions can be used as the negative electrode active material. Examples of the carbon material capable of inserting and extracting lithium ions include graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke, and carbon black. In particular, it is preferable to use graphite.

  In the nonaqueous electrolyte secondary battery of the present invention, as a nonaqueous solvent (organic solvent) constituting the nonaqueous electrolyte, carbonates, lactones, ethers generally used in nonaqueous electrolyte secondary batteries, Esters can be used, and two or more of these solvents can be mixed and used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate can be used. In particular, it is preferable to use a mixed solvent of a cyclic carbonate and a chain carbonate. Moreover, unsaturated cyclic carbonates such as vinylene carbonate (VC) can also be added to the nonaqueous electrolyte.

As the solute of the non-aqueous electrolyte in the present invention, a lithium salt generally used as a solute in a non-aqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , LiB (C ₂ O _{4) 2, LiB (C 2} O 4) F 2, LiP (C 2 O 4) 3, LiP (C 2 O 4) 2 F 2, LiP (C 2 O 4) F 4 , etc., and mixtures thereof examples Is done. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

It is a figure which shows a square nonaqueous electrolyte secondary battery. 1A is a front view (perspective view) of a prismatic nonaqueous electrolyte secondary battery, and FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A. It is a figure explaining the method of the adhesive strength measurement of an electrode-separator.

  Hereinafter, the present invention will be described in detail using reference experiments, examples, and comparative examples. However, the examples shown below show examples for embodying the technical idea of the present invention, and are not intended to specify the present invention to these examples. The present invention can be equally applied to various modifications without departing from the technical idea shown in the above-mentioned range.

  First, a method for manufacturing a positive electrode plate and a negative electrode plate common to the reference experiments, examples, and comparative examples will be described.

[Production of positive electrode plate]
Li ₂ CO ₃ and (Ni _0.35 Co _0.35 Mn _0.3 ) ₃ O ₄ have a molar ratio of Li and (Ni _0.35 Co _0.35 Mn _0.3 ) of 1: 1. It mixed so that it might become. Next, this mixture was fired at 900 ° C. for 20 hours in an air atmosphere to obtain a lithium transition metal composite oxide represented by LiNi _0.35 Co _0.35 Mn _0.3 O ₂ , and a positive electrode active material and did. The positive electrode active material obtained as described above, exfoliated graphite and carbon black as a conductive agent, polyvinylidene fluoride (PVdF) N-methyl-2-pyrrolidone (NMP) solution as a binder, lithium transition metal The composite oxide: exfoliated graphite: carbon black: polyvinylidene fluoride (PVdF) was kneaded so as to have a mass ratio of 88: 7: 2: 3 to prepare a positive electrode slurry. The prepared positive electrode slurry was applied as a positive electrode core to one surface of an aluminum alloy foil (thickness: 15 μm), and then dried to remove NMP used as a solvent during slurry preparation to form a positive electrode active material mixture layer. In the same manner, a positive electrode active material mixture layer was also formed on the other surface of the aluminum alloy foil. Then, it rolled until it became a predetermined | prescribed packing density (2.61 g / cm < ³ >) using the rolling roll, and it cut | disconnected to the predetermined dimension, and produced the positive electrode plate A. FIG.

A positive electrode plate B was prepared in the same manner as the positive electrode plate A, except that the packing density of the positive electrode plate was 2.39 g / cm ³ .

Furthermore, a positive electrode plate C was produced in the same manner as the positive electrode plate A, except that the packing density of the positive electrode plate was 2.88 g / cm ³ .

[Production of negative electrode plate]
Artificial graphite as a negative electrode active material, carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder were kneaded with water to prepare a negative electrode slurry. Here, it mixed so that mass ratio of negative electrode active material: carboxymethylcellulose (CMC): styrene-butadiene-rubber (SBR) might be set to 98: 1: 1. Next, after applying the prepared negative electrode slurry to one surface of a copper foil (thickness: 10 μm) as a negative electrode core, it was dried to remove water used as a solvent at the time of slurry preparation, and a negative electrode active material mixture layer was formed. Formed. A negative electrode active material mixture layer was formed on the other surface of the copper foil by the same method. Then, it rolled until it became a predetermined filling density (1.11 g / cm < ³ >) using the rolling roller.

  Next, alumina powder, a binder (a copolymer containing an acrylonitrile structure), and NMP as a solvent are mixed at a weight ratio of 30: 0.9: 69.1, and mixed and dispersed in a bead mill. And a protective layer slurry was prepared. After the protective layer slurry thus prepared was applied on the negative electrode active material mixture layer on one surface, NMP used as a solvent was removed by drying, and the negative electrode plate surface was made of an insulating material composed of alumina and a binder. A protective layer was formed. In the same manner, a protective layer was formed on the negative electrode active material mixture layer on the other side. Then, it cut | disconnected to the predetermined dimension and produced the negative electrode plate A. FIG. The thickness of the layer made of alumina and a binder was 3 μm.

  Further, a negative electrode plate B was produced in the same manner as the negative electrode plate A, except that no protective layer was provided.

A negative electrode plate C was prepared in the same manner as the negative electrode plate A, except that the packing density of the negative electrode plate was 0.90 g / cm ³ and no protective layer was provided.

The packing density of the above-described positive electrode plate and negative electrode plate was determined by the following method.
[Measurement of packing density]
Cut out electrode plate 10 cm ^2, measuring the mass A of the electrode plate 10cm ² (g), the thickness of the electrode plate C (cm). Moreover, the mass B (g) of the core body 10 cm ² and the core body thickness D (cm) are measured. Then, the packing density is obtained from the following equation.
Packing density = (A−B) / [(C−D) × 10 cm ² ]
Here, when the protective layer is formed in the negative electrode plate surface, it is set as the packing density of the negative electrode active material mixture layer except a protective layer.

<Reference experiment>
As a reference experiment, the arithmetic average surface roughness Ra of the positive electrodes A to C and the negative electrodes A to C and the arithmetic average surface roughness Ra of each surface of the separator were examined by the following method.

[Measurement of arithmetic average surface roughness Ra of positive and negative electrode plates and separator]
About the positive electrode plate, the negative electrode plate, and the separator, the surface was observed with a laser microscope (VK-9710 manufactured by Keyence Corporation), and in accordance with JIS B0601: 1994 using analysis software (VK-Analyzer manufactured by Keyence Software Corporation). The arithmetic average surface roughness Ra was determined under the above conditions.

  Next, the adhesion strength between the positive plates A to C and the negative plates A to C and separators having different arithmetic average surface roughness Ra was examined by the following method.

[Measurement of adhesion between electrode plate and separator]
First, as shown in FIG. 2, a plate-like jig 20 having a length of 120 mm and a width of 30 mm is fixed to a pedestal (not shown), and a double-sided adhesive tape 21 having a length of 90 mm and a width of 20 mm is attached to the upper surface thereof. At this time, the center line in the width direction of the plate-shaped jig 20 and the center line in the width direction of the double-sided adhesive tape 21 are aligned. Further, one end in the length direction of the plate-like jig 20 and one end in the length direction of the double-sided adhesive tape 21 are aligned ((a) in FIG. 2).

  Next, a separator 22 having a length of 150 mm and a width of 28 mm is pasted on the double-sided adhesive tape 21. At this time, the center line in the width direction of the separator 22 and the center line in the width direction of the double-sided pressure-sensitive adhesive tape 21 are aligned. Further, one end portion in the length direction of the separator 22 is aligned with one end portion in the length direction of the plate-like jig 20 in the double-sided pressure-sensitive adhesive tape 21 ((b in FIG. 2). )).

  Then, a test electrode 23 (positive electrode plate or negative electrode plate) having a length of 160 mm and a width of 25 mm is disposed on the separator 22. At this time, the center line in the width direction of the test electrode 23 and the center line in the width direction of the separator 22 are aligned. In addition, one end portion in the length direction of the test electrode 23 is aligned with one end portion in the length direction of the double-sided pressure-sensitive adhesive tape 21 in the separator 22 ((c) in FIG. 2). .

  Thereafter, the entire surface of the test electrode 23 (positive electrode plate or negative electrode plate) positioned on the plate-like jig 20 is pressed from above with a load of 40 kN. Then, from the end of the test electrode plate 23 (positive electrode plate or negative electrode plate) not located on the plate-like jig 20 with a tensile testing machine (SHIMAZU AG-IS, manufactured by Shimadzu Corporation) A peel test was performed by grasping a 1 cm region and pulling the plate-shaped jig 20 in the vertical direction at a speed of 1 mm / sec. At this time, from the position corresponding to the end in the length direction of the plate-like double-sided adhesive tape 21 in the test electrode plate 23 (the end on the side not aligned with the end of the plate-like jig 20), the test is performed. The convex point average stress in the region X ((a) and (c) of FIG. 2) of up to 50 mm in the length direction of the electrode plate 23 is defined as the adhesion strength (according to JIS C6481).

  About said positive electrode plate AC and negative electrode plate AC, packing density, arithmetic mean surface roughness Ra, and adhesive strength with a separator (Ra = 0.16 micrometer, 0.42 micrometer, 0.46 micrometer, 0.62 micrometer) are set. The results are shown in Table 1 and Table 2. In addition, "-" in a table | surface shows unmeasured.

As shown in Table 1, regarding the positive plates A to C in which the protective layer is not formed, the adhesion strength with the separator varies depending on the arithmetic average surface roughness Ra of the separator, but all have an adhesion strength of 50 mN / or more. Have. This shows that the adhesion between the positive electrode plate and the separator does not become insufficient even when the arithmetic average surface roughness Ra of the surface in contact with the positive electrode plate of the separator is smaller than 0.40 μm.
Moreover, it turns out that the arithmetic mean surface roughness Ra of a positive electrode plate changes with the change of the packing density of a positive electrode plate, and adhesive strength with a separator changes with this. Therefore, the packing density of the positive electrode plate, preferably in the 2.88 g / cm ³ or less, and more preferably set to 2.80 g / cm ³ or less.

  Regarding the negative electrode side, as shown in Table 2, the negative electrode plate B and the negative electrode plate C in which the protective layer was not formed showed the same degree of adhesion strength regardless of the arithmetic average surface roughness Ra of the separator. On the other hand, in the negative electrode plate A on which the protective layer was formed, when the arithmetic average surface roughness Ra of the separator was 0.16 μm, the adhesion strength was a low value of 44.6 mN / cm. On the other hand, when the arithmetic average surface roughness Ra of the separator was 0.42 μm, 0.46 μm, 0.62 μm, and 2.14 μm, the adhesion strength was a value of 50 mN / cm or more. From these facts, by making the arithmetic average surface roughness Ra of the surface in contact with the protective layer formed on the negative electrode plate of the separator 0.40 μm or more, the adhesion between the protective layer formed on the negative electrode surface and the separator is increased. It turns out that it is possible to do.

  As described above, based on the results of the reference experiment, a flat electrode body was actually produced, and the influence of the arithmetic average surface roughness Ra of the separator on the moldability of the flat electrode body was examined.

[Example 1]
[Production of flat electrode body]
First, the above positive electrode plate A and negative electrode plate A were prepared. Here, the positive electrode plate A has a strip shape having a width of 104.8 mm, a length of 3870 mm, and a thickness of 69 μm, and an electrode active material mixture layer is formed on both sides of the core body at one end along the longitudinal direction. The one having no exposed core (width 15.2 mm) was used.
Further, the negative electrode plate B has a strip shape having a width of 106.8 mm, a length of 4020 mm, and a thickness of 71 μm, and an electrode active material mixture layer is not formed on both sides of the core body at one end along the longitudinal direction. What has a core exposure part (width 10.0mm) was used.

  Next, a positive electrode plate A, a negative electrode plate B, and a separator made of a polyethylene microporous film (width 100 mm, length 4310 mm, thickness 30 μm) are placed so that different core exposed portions are opposite to each other in the winding direction. The three members were aligned and overlapped so that a separator was interposed between the active material mixture layers having different polarities, and wound by a winder. And the winding end part of the wound electrode body was fixed with the insulating anti-winding tape. At this time, the arithmetic average surface roughness Ra of the surface in contact with the positive electrode plate A in the separator was 0.16 μm, and the arithmetic average surface roughness Ra of the surface in contact with the negative electrode plate A was 0.62 μm.

  Then, the electrode body wound in a spiral shape was pressed at 110 kN at room temperature (25 ° C.) to produce a flat electrode body of Example 1.

[Comparative Example 1]
Example except that the separator is arranged so that the surface having the arithmetic average surface roughness Ra of 0.62 μm is in contact with the positive electrode plate A and the surface having the arithmetic average surface roughness Ra of 0.16 μm is in contact with the negative electrode plate A A flat electrode body of Comparative Example 1 was produced in the same manner as in 1.

[Example 2]
Example except that the separator is arranged so that the surface having the arithmetic average surface roughness Ra of 0.42 μm is in contact with the positive electrode plate A and the surface having the arithmetic average surface roughness Ra of 0.46 μm is in contact with the negative electrode plate A A flat electrode body of Comparative Example 2 was produced in the same manner as in 1.

[Reference Example 1]
Arithmetic average surface roughness of the separator: The surface of Ra is 0.46 μm and the positive electrode plate A are in contact, and the arithmetic average surface roughness: the separator is disposed so that the negative electrode plate A is in contact with the surface of Ra of 0.42 μm. A flat electrode body of Comparative Example 3 was produced in the same manner as in Example 1.

[Judgment of formability of electrode body]
The formability of the flat electrode body was judged from the thickness (electrode body thickness) of the central portion of the flat electrode body produced in Examples 1, 2, Reference Example 1 and Comparative Example 1.

  Table 3 shows the survey results of the formability of the flat electrode bodies of Examples 1 and 2, Reference Example 1 and Comparative Example 1. The electrode body thicknesses of Examples 1 and 2, Reference Example 1 and Comparative Example 1 in Table 3 are values in which the thickness of the electrode body of Example 1 is 100%.

In the flat electrode body of Comparative Example 1 in which the negative electrode plate A on which the protective layer is formed and the surface of the separator having an arithmetic average surface roughness Ra of 0.16 μm are in contact with each other, the shape of the electrode body is low. In Examples 1 and 2 and Reference Example 1 where the arithmetic average surface roughness Ra of the negative electrode plate A on which the layer was formed and the separator were in contact with 0.42 μm, 0.46 μm, and 0.62 μm, respectively, It can be seen that the formability of the flat electrode body is excellent due to the high adhesion strength between the formed protective layer and the separator.

  From these facts, it is understood that the moldability of the electrode body can be improved by setting the arithmetic average surface roughness Ra of the surface of the separator in contact with the protective layer formed on the negative electrode plate to 0.40 or more.

[Effect of the invention]
As described above, according to the present invention, the protection formed on the negative electrode plate by setting the arithmetic average surface roughness Ra of the surface in contact with the protective layer formed on the negative electrode plate of the separator to 0.40 to 3.50 μm. The adhesion strength between the layer and the separator can be increased, and the moldability of the flat electrode body can be improved.

1: Flat electrode body 2: Exterior can 3: Sealing plate 4: Positive electrode core exposed part 5: Negative electrode core exposed part 6: Positive electrode current collecting member 7: Positive electrode terminal 8: Negative electrode current collecting member 9: Negative electrode terminal 7a, 9a: Plate-like part 7b, 9b: Bolt part 11, 12: Insulating material 13: Negative electrode collector receiving member 20: Plate-shaped jig 21: Double-sided adhesive tape 22: Separator 23: Test electrode (positive electrode plate or negative electrode plate) 30) Square non-aqueous electrolyte secondary battery

Claims (7)

A positive electrode plate containing a lithium transition metal composite oxide as a positive electrode active material;
A negative electrode plate containing a carbon material capable of occluding and releasing lithium ions as a negative electrode active material;
In a nonaqueous electrolyte secondary battery having a flat electrode body laminated and wound through a separator,
A protective layer made of an inorganic oxide and an insulating binder is provided on the surface of the negative electrode plate,
The separator has different arithmetic average surface roughness on the front and back surfaces,
The large arithmetic average surface roughness of the separator is disposed so as to be in contact with the protective layer,
The separator is a polyolefin porous,
Non-aqueous electrolyte secondary battery characterized. The insulating binder is at least selected from a copolymer containing an acrylonitrile structure, a polyimide resin, a styrene-butadiene-rubber, an ethylene-tetrafluoroethylene copolymer, a polyvinylidene fluoride, a tetrafluoroethylene resin, and carboxymethylcellulose. That it is one kind,
The non-aqueous electrolyte secondary battery according to claim 1. The negative electrode plate further contains a binder,
The binder of the negative electrode plate and the insulating binder of the protective layer are different from each other.
The nonaqueous electrolyte secondary battery according to claim 1 or 2, characterized in that The positive electrode active material is Li _{1 + a} Ni _x Co _y Mn _z M _b O ₂ (M = at least one element selected from Al, Ti, Zr, Nb, B, Mg, Mo, 0 ≦ a ≦ 0.2 0.2 ≦ x ≦ 0.5, 0.2 ≦ y ≦ 0.5, 0.2 ≦ z ≦ 0.4, 0 ≦ b ≦ 0.02, a + b + x + y + z = 1)
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3. The negative electrode plate has a packing density of 0.9 to 1.4 g / cm ³ .
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4. The packing density of the positive electrode plate is 2.5 to 2.9 g / cm ³ .
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5. The separator is at least one selected from polypropylene, polyethylene, and a three-layer structure of polypropylene and polyethylene.
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6.

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