JP2015125915A - Positive electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for a 5 V-class lithium ion secondary battery, suppressed in elution of a constitutional metal element from a positive electrode collector.SOLUTION: A positive electrode for a lithium ion secondary battery includes a positive electrode collector and a positive electrode active material layer adhered to a surface of the positive electrode collector. The positive electrode active material layer includes, as a positive electrode active material, lithium manganese composite oxide of a spinel structure having an operating potential of 4.3 V (vs. Li/Li) or more. The positive electrode collector has: an active material layer forming part where the positive electrode active material layer is disposed on a surface of the positive electrode active material layer; and a collector exposed part where the positive electrode active material layer is not disposed. A ratio (Ra/Ra) of the arithmetic average roughness Raof the active material layer forming part to the arithmetic average roughness Raof the collector exposed part is less than 1.29.

Description

The present invention relates to a lithium ion secondary battery. Specifically, the present invention relates to a lithium ion secondary battery including a lithium manganese composite oxide having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or higher.

Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are preferably used for high output power sources mounted on vehicles because they are lighter and have higher energy density than existing batteries.
A positive electrode used in this type of battery typically has a configuration in which a positive electrode active material layer containing a positive electrode active material is fixed on a positive electrode current collector. The positive electrode having such a configuration is typically coated (applied) and dried with a paste-like or slurry-like composition containing the positive electrode active material on the surface of the positive electrode current collector, and rolled (pressed) as necessary. It is produced by this. For example, in paragraph [0014] of Patent Document 1, a positive electrode mixture paste containing lithium spinel manganese oxide as a positive electrode active material, a binder, and a conductive agent is applied on a positive electrode current collector and dried, and then hot It describes that a positive electrode is produced by roll pressing.

JP 2004-006143 A

By the way, in the lithium ion secondary battery, further higher energy density is examined as part of performance improvement. Such high energy density can be realized by using, for example, a positive electrode active material (for example, LiNi _0.5 Mn _1.5 O ₄ ) having a higher operating potential than conventional ones. However, when a positive electrode having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or higher is produced by the method described above, a constituent metal is formed from a positive electrode current collector (typically an aluminum (Al) foil). There was a problem that the element (for example, Al) was eluted and the durability (for example, high temperature cycle characteristics) of the battery was lowered.
This invention is made | formed in view of this situation, The objective is the positive electrode for lithium ion secondary batteries with the said high operating potential (5V class), Comprising: Of the constituent metal element from a positive electrode collector, To provide a positive electrode for a lithium ion secondary battery in which elution is suppressed. Another related object is to provide a highly durable 5 V class lithium ion secondary battery including the positive electrode.

As a result of extensive studies by the present inventors from various angles, it has been found that the elution of the constituent metal elements from the positive electrode current collector is related to the configuration unique to the 5V class battery. That is, the positive electrode current collector is typically made of metal (for example, made of aluminum (Al)), and a passive film (for example, Al ₂ O ₃ or AlF ₃ ) is formed on the surface thereof. Even when exposed to an oxidizing atmosphere of (vs. Li / Li ⁺ ), it exists stably. However, when a compound having a spinel crystal structure (typically having an approximately octahedral shape) is used as the positive electrode active material, the passive film on the surface of the positive electrode current collector in the manufacturing process (for example, a pressing process) Can be severely hurt and destroyed. When exposed to a strong oxidizing atmosphere of 4.3 V (vs. Li / Li ⁺ ) or higher in this state, elution of constituent metal elements from the positive electrode current collector may be accelerated. According to the study of the present inventor, the metal element eluted thereby migrates in the non-aqueous electrolyte and precipitates on the surface of the opposing negative electrode, which may reduce the durability and reliability of the battery.

Therefore, the present inventor has further studied and has come to create the present invention. That is, according to the present invention, there is provided a positive electrode for a lithium ion secondary battery comprising a positive electrode current collector and a positive electrode active material layer fixed to the surface of the positive electrode current collector. The positive electrode active material layer includes a spinel-structure lithium manganese composite oxide having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or higher as the positive electrode active material. The positive electrode current collector includes an active material layer forming portion in which the positive electrode active material layer is disposed on a surface of the positive electrode current collector, and a current collector exposed portion in which the positive electrode active material layer is not disposed. Have Then, the ratio of the arithmetic mean roughness Ra ₁ of the active material layer forming portion with respect to the arithmetic average roughness Ra ₂ of the current collector exposed portion _(Ra 1 / Ra ₂₎ is less than 1.29.

By using a spinel type compound having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or more as a positive electrode active material, a high energy density of the battery can be realized. The ratio of the arithmetic mean roughness _{((Ra 1 / Ra 2)} <1.29) By satisfying, even when used above spinel compound (compound having a substantially octahedral shape) It is possible to prevent damage to the passive film formed on the surface of the positive electrode current collector. For this reason, elution of the constituent metal elements from the positive electrode current collector can be suppressed, and high durability can be realized.

  The arithmetic average roughness Ra can be obtained according to JIS B0601-1994. Specifically, the positive electrode is taken out from the battery and cut into a predetermined size to obtain a sample. At this time, the sample is cut out so as to include both the active material layer forming portion where the positive electrode active material layer is disposed and the current collector exposed portion where the positive electrode active material layer is not disposed. Next, the positive electrode active material layer formed on the positive electrode current collector is removed (for example, wiped off) with a predetermined organic solvent (for example, N-methylpyrrolidone). And arithmetic average roughness Ra is calculated according to JIS B0601-1994 about the said active material layer formation part and collector exposed part, respectively.

According to the study of the present inventor, since a so-called 4V-class battery generally uses a rounded (substantially spherical) LiCoO ₂ or LiNiO ₂ as a positive electrode active material, a positive electrode current collector ( For example, Al foil) surface is hardly damaged. For example, even when LiMn ₂ O ₄ having the same spinel type crystal structure is used as the positive electrode active material, the maximum potential of the positive electrode is suppressed to about 4 V (vs. Li / Li ⁺ ). In addition, the elution of the constituent metal elements from the positive electrode current collector hardly occurs. The invention disclosed here has a remarkable effect as described above when a lithium manganese composite oxide having a spinel structure having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or higher is used as the positive electrode active material. Can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

A positive electrode for a lithium ion secondary battery disclosed herein includes a positive electrode current collector and a positive electrode active material layer fixed (formed) on the positive electrode current collector. The positive electrode current collector includes an active material layer forming portion where the positive electrode active material layer is disposed, and a current collector exposed portion where the positive electrode active material layer is not disposed. The ratio of the arithmetic average roughness Ra ₁ of the active material layer forming portion to the arithmetic average roughness Ra ₂ of the exposed electric portion (Ra ₁ / Ra ₂ : hereinafter, sometimes simply referred to as “roughening degree”). Characterized by being a predetermined value. Therefore, other configurations are not particularly limited.

The positive electrode active material layer includes at least a positive electrode active material, and may include other optional components as necessary. In the invention disclosed herein, a lithium manganese composite oxide having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or more and having a spinel crystal structure can be used as the positive electrode active material. For example, the operating potential (vs. Li / Li ⁺ ) is 4.3 V or higher (typically 4.5 V or higher, such as 4.6 V or higher, preferably 4.7 V or higher). A high voltage positive electrode material of 5 V or less, for example, 5.3 V or less can be used. Thereby, a high energy density can be realized. Examples of the high voltage positive electrode material include LiNi _0.5 Mn _1.5 O ₄ , LiNi _0.5 Mn _1.45 Ti _0.05 O ₄ , and LiNi _0.45 Fe _0.05 Mn _1.5 O _4. , LiNi _0.475 Fe _0.025 Mn _1.475 Ti _0.025 O _{4 and the} like.

  The properties of the positive electrode active material are typically in the form of particles or powder. The average particle diameter of the particulate positive electrode active material may be 20 μm or less (typically 1 to 20 μm, for example, 5 to 15 μm). The shape typically has an octahedral (double quadrangular pyramid) structure, that is, a molecular structure in which two triangular pyramids are bonded together on the bottom surface. For this reason, in the conventional method for producing a positive electrode, the surface of the positive electrode current collector is damaged by the apex portion of the triangular pyramid, and the passive film formed on the positive electrode current collector may be damaged (broken). there were. However, according to the manufacturing method disclosed herein, damage to the passive film can be suitably prevented, and elution of constituent metal elements from the positive electrode current collector can be highly suppressed.

  The positive electrode active material layer may contain other optional components as necessary. Examples of such optional components include a binder and a conductive material. As the binder, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or the like can be suitably used. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be suitably used.

  As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc., preferably aluminum) can be suitably used. As the shape of the current collector, a plate-like body, a foil-like body or the like can be used, and the foil-like body can be suitably used from the viewpoint of energy density and the like. The thickness of the foil-like current collector is not particularly limited, but a thickness of about 5 to 50 μm (more preferably 10 to 30 μm) can be suitably used in consideration of the energy density and mechanical strength.

The positive electrode current collector has an active material layer forming portion in which the positive electrode active material layer is disposed, and a current collector exposed portion in which the positive electrode active material layer is not disposed. The ratio of the arithmetic average roughness Ra ₁ of the active material layer forming portion to the arithmetic average roughness Ra ₂ of the current collector exposed portion (Ra ₁ / Ra ₂ : roughness) is less than 1.29 (typical Specifically, it is 1.28 or less, for example, 1.25 or less, or 1.23 or less. In other words, the roughening of the surface of the positive electrode current collector accompanying the formation of the positive electrode active material layer is highly suppressed. Thereby, high durability is realizable.
In a preferred embodiment, the roughening degree is less than 1.23 (for example, 1.21 or less). Thereby, elution of the constituent metal elements from the positive electrode current collector can be dramatically suppressed (for example, to 1/3 or less).

Such a positive electrode can be suitably manufactured, for example, generally by the following procedure.
First, the above-mentioned positive electrode active material and other optional components (binder, conductive material, etc.) are dispersed in a suitable solvent to prepare a slurry composition. Next, this composition is applied to the positive electrode current collector and dried. Thereby, a positive electrode provided with a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector can be produced.
In addition, the produced positive electrode active material layer can be subjected to a compression (press) treatment as necessary within a range where the degree of roughening is less than 1.29. In other words, after coating and drying the composition, pressing may be performed in a range where the degree of roughening is less than 1.29, or pressing may not be performed.

  The positive electrode disclosed here can be used to construct a lithium ion secondary battery. In other words, a lithium ion secondary battery including the positive electrode is disclosed. The lithium ion secondary battery disclosed herein can be compatible with energy density and durability at a high level. Such a lithium ion secondary battery typically has a configuration in which an electrode body including the positive electrode and a nonaqueous electrolyte are accommodated in a battery case. As the battery case, for example, a lightweight metal such as aluminum can be suitably used.

The electrode body can be constructed by laminating the positive electrode and the negative electrode, typically via a separator.
As the negative electrode, it is possible to suitably use a negative electrode active material that is fixed on a negative electrode current collector together with a binder, a thickener and the like to form a negative electrode active material layer. As the negative electrode active material, carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like can be used, and among them, graphite can be preferably used. As the binder, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE) or the like can be suitably used. As the thickener, a cellulose-based material of carboxymethyl cellulose (CMC) can be suitably used. As the negative electrode current collector, a conductive material made of a highly conductive metal (for example, copper) can be suitably used.
As the separator, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. Especially, what has a porous heat resistant layer in the one or both surfaces of the said porous resin sheet is preferable.

As the non-aqueous electrolyte, a non-aqueous solvent containing a supporting salt (non-aqueous electrolyte) can be preferably used. As the nonaqueous solvent, various organic solvents known to be usable for secondary batteries can be used. Among them, those having high oxidation resistance (that is, high oxidation decomposition potential) are preferable, and fluorinated products (fluorine-containing nonaqueous solvent) such as carbonates, ethers, esters, nitriles, sulfones, and lactones are suitably used. Can be used. In particular, the use of fluorinated carbonate is preferred. Specifically, a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC); a fluorinated chain carbonate such as methyl (2,2,2-trifluoroethyl) carbonate (MTFEC); can be preferably used. Thereby, even if it is a case where the said high voltage positive electrode material (positive electrode active material with a high operating potential) is used for a positive electrode, the battery excellent in the lifetime characteristic is realizable. As the supporting salt, lithium salts, sodium salts, magnesium salts, and the like can be used, and among them, lithium salts such as LiPF ₆ and LiBF ₄ can be preferably used.

  The lithium ion secondary battery (so-called 5V class battery) provided with the positive electrode disclosed herein can be used for various applications. However, the operating potential of the positive electrode active material is increased and the constituent metal elements from the positive electrode current collector are increased. Due to the effect of suppressing the elution, it is possible to realize a battery characteristic higher than the conventional one. For example, both high energy density and high durability can be achieved. Therefore, taking advantage of such properties, it can be suitably used as a drive power source mounted on vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV).

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

[Production of positive electrode]
Here, the type of positive electrode active material to be used and the production conditions (press conditions) were varied to produce a total of seven types of positive electrodes.
In Example 1, first, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder Were weighed so that the mass ratio of these materials would be LNCM: AB: PVdF = 87: 10: 3 and charged into a kneader, and kneaded while adjusting the viscosity using N-methylpyrrolidone (NMP) as a dispersion solvent. Thus, a slurry for forming a positive electrode active material layer was prepared. This slurry is applied to the surface of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and is roll-pressed after drying, whereby a positive electrode active material layer (electrode density: 2.3 g / cm) is formed on the positive electrode current collector. ³ ) A positive electrode (Example 1) was prepared.
In Example 2, a positive electrode (Example 2) having a positive electrode active material layer (electrode density: 1.1 g / cm ³ ) on a positive electrode current collector was prepared in the same manner as in Example 1 except that roll pressing was not performed. .
In Example 3, a positive electrode active material layer (electrode density: 1.3) was formed on the positive electrode current collector in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ (LNM) was used as the positive electrode active material. A positive electrode (Example 3) comprising ˜2.3 g / cm ³ ) was produced.
Example 4 Example 6, to adjust the load pressure of the roll press, as in Example 3 except that having different electrode density in the range of 2.0~1.3g / cm ^3, on the positive electrode current collector A positive electrode (Example 4 to Example 6) having a positive electrode active material layer (electrode density: 2.0 to 1.3 g / cm ³ ) was prepared.
In Example 7, a positive electrode active material layer (electrode density: 1.1 g) was formed on the positive electrode current collector in the same manner as in Example 2 except that LiNi _0.5 Mn _1.5 O ₄ (LNM) was used as the positive electrode active material. / Cm ³ ) to produce a positive electrode (Example 7).

[Measurement of Arithmetic Average Roughness Ra of Positive Current Collector]
Surface roughness Ra was measured using the laser microscope in the active material layer formation part (coating part) of the positive electrode collector (aluminum foil) and the collector exposed part (uncoated part). Specifically, a part of the produced positive electrode was cut out so that a coated part and an uncoated part were included, and the positive electrode active material layer was removed (wiped off) with NMP so as not to damage the surface. And in each of a coating part and an uncoated part, it measured by measurement length of 300 micrometers, and calculated the surface roughness according to JISB0601-1994. This was performed at three arbitrary locations, and the arithmetic average roughness Ra was determined for each. Further, by dividing the coating section the arithmetic mean roughness Ra ₂ of the uncoated portion the arithmetic mean roughness Ra ₁ of (active material layer forming portion) (collector-exposed portion), calculates the roughening degree did. The results are shown in the corresponding column of Table 1. In addition, when the surface roughness of the unused aluminum foil was separately measured as a reference value, the arithmetic average roughness Ra was 0.11.

The Ra ₂ value of the uncoated part in Examples 1 to 7 was almost equal to the Ra value (= 0.11) of the unused aluminum foil. From this, it was found that the uncoated part (current collector exposed part) was hardly damaged in the process of producing the positive electrode.
Moreover, in Example 1 and Example 2, the value of Ra ₁ of the coated part and the value of Ra ₂ of the uncoated part showed substantially the same value. A possible reason for this is the shape of the positive electrode active material. That is, since LNCM has a relatively rounded (substantially spherical) shape, it was difficult to damage the surface of the positive electrode current collector in the process of producing the positive electrode (the surface of the positive electrode current collector was roughened). It was difficult).
On the other hand, in Examples 3 to 7 in which LNM was used as the positive electrode active material, it was found that the surface roughness (Ra ₁ / Ra ₂ ) increased as the density of the positive electrode active material layer increased. The reason for this is that since the LNM has an octahedral shape derived from the spinel structure, the corners of the particles are sharp, and thus the positive electrode current collector during the positive electrode manufacturing process (typically press treatment). It is conceivable that the surface of the surface was damaged (roughened). From this, it was found that by adjusting the pressing conditions (releasing the pressing conditions) or not performing the pressing, it is possible to suppress the degree of roughening to a small level (control the surface of the positive electrode current collector not to be rough). .

[Construction of lithium ion secondary battery]
Next, a lithium ion secondary battery was constructed using the produced positive electrode, and durability was evaluated. Specifically, first, a natural graphite material (C, average particle diameter: 20 μm, lattice constant (C ₀ ): 0.67 nm, crystallite size (Lc): 27 nm), and styrene-butadiene copolymer as a binder. The coalescence (SBR) and carboxymethyl cellulose (CMC) as a thickener are weighed so that the mass ratio of these materials is C: SBR: CMC = 98: 1: 1 and charged into a kneader to perform ion exchange. A slurry for forming a negative electrode active material layer was prepared by kneading while adjusting the viscosity using water as a dispersion solvent. By applying this slurry to the surface of a copper foil (negative electrode current collector) having a thickness of 10 μm so that the mass ratio of the positive electrode active material and the negative electrode active material is 2: 1, roll pressing after drying, A negative electrode having a negative electrode active material layer on a negative electrode current collector was produced.

Next, after adjusting the electrode size so that the produced positive electrode and the negative electrode had a design capacity of 60 mAh, an electrode body was prepared by facing them through a separator. Further, as a non-aqueous electrolyte, fluoroethylene carbonate (FEC) as a fluorinated cyclic carbonate and methyl (2,2,2-trifluoroethyl) carbonate (MTFEC) as a fluorinated chain carbonate, FEC: A solution prepared by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / L in a mixed solvent containing MTFEC at a volume ratio of 50:50 was prepared.
And the said electrode body and the non-aqueous electrolyte were enclosed with the cell made from a laminate, and seven types of evaluation batteries (Example 1-Example 7) were constructed | assembled.

[Check initial capacity]
The batteries (Example 1 to Example 7) constructed above were placed in a thermostatic bath at 25 ° C., charged with a constant current of 1/5 C (CC charge) until the voltage between the positive and negative electrodes became 4.9 V, and then positive The operation of discharging (CC discharge) with a constant current of 1/5 C until the voltage between the negative electrodes became 3.5 V was set as one cycle, and this was repeated three cycles.
Next, CC charging is performed at 1/5 C until the voltage between the positive and negative electrodes becomes 4.9 V, and then charging at a constant voltage (CV charging) until the current value becomes 1/50 C, then the voltage between the positive and negative electrodes CC was discharged at 1/5 C until the voltage reached 3.5 V, and the CC discharge capacity at this time was defined as the initial capacity.

[High-temperature cycle test (60 ° C)]
Next, after confirming the initial capacity, the battery was placed in a thermostat having an environmental temperature of 60 ° C., and after the temperature became constant, a high temperature cycle test was performed. Specifically, CC charging with a constant current of 2 C until the voltage between the positive and negative electrodes becomes 4.9 V, and then CC discharge with a constant current of 2 C until the voltage between the positive and negative electrodes becomes 3.5 V is 1 This was repeated 500 cycles as a cycle. Thereafter, the CC discharge capacity was measured in the same procedure as the measurement of the initial capacity to obtain the battery capacity after the cycle test. Then, the capacity retention rate (%) was calculated by dividing the battery capacity after the cycle test by the initial capacity and multiplying by 100. The results are shown in the corresponding column of Table 2.

As shown in Table 2, Example 1 and Example 2 using LNCM as the positive electrode active material had substantially the same capacity retention rate after the high temperature cycle test. From this, it was found that the invention disclosed herein is not effective when such a material is used as the positive electrode active material.
On the other hand, in Examples 3 to 7 in which LNM was used as the positive electrode active material, the capacity retention rate was higher when the initial roughness was smaller. Specifically, Examples 6 and 7 having an initial roughening degree of less than 1.29 (typically 1.28 or less, for example, 1.25 or less, dare to say 1.23 or less) The capacity retention rate (excellent durability) was significantly higher than those of Examples 3 to 5 in which the degree of roughening was 1.29 or more.
From the above results, when LiNi _0.5 Mn _1.5 O ₄ having a spinel type crystal structure is used as the positive electrode active material, it is between the initial roughness and durability (capacity maintenance ratio). In order to achieve high energy density and durability, the pressing process is performed so that the initial surface roughness is less than 1.29 (preferably less than 1.23), or the pressing process is not performed. It was found that a lithium ion secondary battery having both of the above can be realized.

[Measurement of arithmetic average roughness Ra of positive electrode current collector after cycle]
The battery after the end of the cycle test was disassembled, the positive electrode was taken out, and the arithmetic average roughness Ra and the roughening degree in each part were calculated in the same manner as described above. The results are shown in the corresponding column of Table 2.

As shown in Table 2, the arithmetic average roughness after the cycle test was almost the same as the initial value (before the cycle test), but for example, a slight surface roughness Ra ₁ in the coated portion of Example 3 was observed. There was also an increase. This is because (1) Al ions were eluted from the surface of the aluminum foil by setting the operating potential to 4.3 V (vs. Li ^/ Li ⁺ ), and ( ² ) with the insertion and release of lithium ions. It is considered that the positive electrode active material expanded and contracted, and the surface of the aluminum foil was further roughened.

[Analysis of eluted Al element]
The battery after the end of the cycle test was disassembled, the negative electrode was taken out, washed lightly with a non-aqueous solvent, and then a sample for ICP (Inductively Coupled Plasma) analysis was obtained. The analytical sample was heated and dissolved in an acid solvent (here, sulfuric acid), and ICP analysis was performed on the solution to quantify the aluminum element content (μg). The results are shown in Table 2. In addition, the detection lower limit value of the ICP analysis performed this time is 0.005 mg.

As shown in Table 2, when LiNi _0.5 Mn _1.5 O ₄ having a spinel crystal structure is used as the positive electrode active material, the initial roughening degree is less than 1.29 (preferably 1 It was found that elution of aluminum element from the positive electrode current collector can be dramatically suppressed (for example, to 1/3 or less). As a result, the internal resistance can be greatly reduced, and high durability (for example, high-temperature cycle characteristics) can be realized. This result shows the technical significance of the present invention.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations, What included various deformation | transformation and change of the above-mentioned specific example is included in the invention disclosed here.

Claims (1)

A positive electrode for a lithium ion secondary battery comprising a positive electrode current collector and a positive electrode active material layer fixed to the surface of the positive electrode current collector,
The positive electrode active material layer includes a lithium manganese composite oxide having a spinel structure having an operating potential of 4.3 V (vs. Li / Li ⁺ ) or more as a positive electrode active material,
The positive electrode current collector has an active material layer forming portion in which the positive electrode active material layer is disposed on a surface of the positive electrode current collector, and a current collector exposed portion in which the positive electrode active material layer is not disposed. And
For the lithium ion secondary battery, the ratio (Ra ₁ / Ra ₂ ) of the arithmetic average roughness Ra ₁ of the active material layer forming portion to the arithmetic average roughness Ra ₂ of the current collector exposed portion is less than 1.29. Positive electrode.