JP2018022573A - Secondary battery - Google Patents

Abstract

An object of the present invention is to provide a porous insulating layer that realizes high adhesiveness while maintaining good ion permeability, and to provide a secondary battery including the porous insulating layer as a separator. In the secondary battery disclosed herein, the porous insulating layer that insulates between the positive electrode active material layer and the negative electrode active material layer is a polymer particle made of a polyolefin resin, and at least a carboxyl group is present. In the area ratio of each peak obtained by curve-fitting a C1s spectrum by XPS (X-ray photoelectron spectroscopy), the peak area of O = C—O— A / B ratio (% display) which is a ratio of A) to the peak area (B) of sp3 (C—C and C—H) is 5% or more and 13% or less. [Selection] Figure 3

Description

  The present invention relates to a secondary battery. In detail, it is related with the structure of the separator with which a secondary battery is equipped.

A secondary battery such as a lithium ion secondary battery is preferably used as a portable power source, a high output power source for mounting on a vehicle, and the like because it is lightweight and can obtain a high energy density. For example, an electrode body constituting a lithium ion secondary battery includes a positive electrode including a positive electrode active material such as a lithium transition metal composite oxide, a negative electrode including a negative electrode active material such as a graphite material, and a separator separating the positive and negative electrodes. It has.
By the way, as a separator used for this type of secondary battery, there is a porous polymer film separator (separator sheet) formed from a polyolefin resin such as polyethylene or polypropylene, or a fluororesin such as polytetrafluoroethylene, It has been common to use a sheet placed between a positive electrode and a negative electrode.
For example, Patent Document 1 below discloses a porous sheet-like separator comprising a hydrophilic tetrafluoroethylene stretched membrane and ethylene copolymer particles having side chains supported on the surface of the stretched membrane. ing. In Patent Document 2, a separator-forming aqueous slurry containing a polyolefin resin containing an olefin component and an unsaturated carboxylic acid component as a copolymer component is applied to at least one surface of a porous substrate made of a polyolefin resin or the like. A separator having a porous layer is disclosed.

  By the way, in secondary batteries such as lithium ion secondary batteries used as in-vehicle power supplies, there has been a demand for higher capacity and larger size. As one form of battery that meets the demand, a sheet-like positive electrode and Some of them have a relatively large capacity and large size electrode body (hereinafter referred to as “laminated electrode body”) by laminating a plurality of negative electrodes alternately. In such a laminated electrode body, it is necessary to dispose separator sheets between the laminated positive and negative electrode sheets, but the number of separator sheets used increases as the number of positive and negative electrode sheets to be laminated increases. It can be said that the manufacturing process is complicated due to an increase in the number of parts and the cost is increased.

  In recent years, as an alternative to such a porous sheet-like separator, it has been proposed to directly form a porous insulating layer functioning as a separator on the surface of a positive electrode or a negative electrode. A porous insulating layer (hereinafter also referred to as “electrode-integrated separator”) formed on the surface of such a positive electrode or negative electrode (hereinafter simply referred to as “electrode” when either positive electrode or negative electrode may be used) is employed. By doing so, it is possible to prevent an increase in the number of parts of the electrode body accompanying an increase in capacity and size of the secondary battery (that is, an independent porous sheet-like separator is unnecessary), and an increase in cost can be expected. .

WO94 / 18711 Japanese Patent Laying-Open No. 2015-230796

The porous insulating layer functioning as an electrode-integrated separator as described above does not have a porous substrate such as a separator sheet, and adheres insulating polymer particles such as polyolefin resin to the surface of the electrode. Formed by. A porous insulating layer made of an aggregate of such polymer particles is formed on the electrode surface (typically on the electrode current collector) while ensuring the porosity to achieve good ion permeability (for example, lithium ion permeability). In order to prevent the polymer particles constituting the porous insulating layer from being separated from the electrode active material layer), high adhesion is required. In this regard, the adhesion of the porous insulating layer can be improved by adding a binder (or increasing the binder content), but if there is a large amount of binder, the inside of the battery This is not preferable because it can cause an increase in resistance, and it can also be considered that the porosity decreases and affects the ion permeability.
Therefore, there is still room for improvement with respect to the adhesive performance of the porous insulating layer (electrode-integrated separator) made of conventional polymer particles, and higher adhesiveness is desired.
The present invention was created with the aim of improving the above-described porous insulating layer that can also function as an electrode-integrated separator, and provides a porous insulating layer that achieves high adhesion while maintaining good ion permeability. Another object is to provide a secondary battery provided with the porous insulating layer as a separator (preferably an electrode-integrated separator).

The present inventor has examined the adhesion characteristics of the porous insulating layer constituting the conventional electrode-integrated separator, and maintains good ion permeability (for example, lithium ion permeability) by controlling the abundance of carboxyl groups. However, it has been found that the adhesion performance to the electrode surface (typically an electrode active material layer formed on the electrode current collector) can be improved, and the present invention has been completed.
That is, the secondary battery disclosed here is
A positive electrode having a positive electrode active material layer; a negative electrode having a negative electrode active material layer; and a porous insulating layer that exists between the positive and negative electrodes and insulates between the positive electrode active material layer and the negative electrode active material layer. .
And in the secondary battery disclosed here,
The porous insulating layer is a polymer particle made of a polyolefin resin, and includes a polymer particle having a carboxylated surface in which at least a carboxyl group is present; and
The porous insulating layer has an O = C—O— peak area (A) and sp ³ (C) in an area ratio of each peak obtained by curve fitting a C1s spectrum by XPS (X-ray photoelectron spectroscopy). The A / B ratio (in%), which is the ratio to the peak area (B) of -C and C-H), is from 5% to 13%.

As described above, the secondary battery disclosed herein has a porous insulating layer that functions as a so-called separator that exists between the positive and negative electrodes and insulates between the positive electrode active material layer and the negative electrode active material layer, from a polyolefin resin. The polymer particles mainly include polymer particles having a carboxylated surface in which at least a carboxyl group is present on the surface.
The porous insulating layer has an area ratio of each peak obtained by waveform separation of the C1s spectrum by XPS (X-ray photoelectron spectroscopy) by curve fitting (typically fitting based on nonlinear least squares method). = A / B ratio (shown in%. The same applies hereinafter) which is the ratio of the peak area (A) of C—O— to the peak area (B) of sp ³ (C—C and C—H). It is 5% or more and 13% or less.
As a result of this configuration, a porous insulating layer having high adhesion performance while maintaining good ion permeability can be realized. Therefore, in the secondary battery disclosed herein, a separator (typically an electrode-integrated separator) made of a porous insulating layer having excellent adhesive strength is provided, so that an electrode body made of positive and negative electrodes (especially the above-described laminate). The physical (structural) stability of the mold electrode body is improved, and high reliability and durability can be realized.
Further, by making the porous insulating layer having the above structure function as an electrode-integrated separator in particular, it becomes unnecessary to separately prepare a porous sheet-like separator, increasing the number of parts for constructing the electrode body and increasing the cost. Can be suppressed.

It is a figure for demonstrating typically the structure of the electrode body accommodated in the case of the secondary battery (lithium ion secondary battery) which concerns on one Embodiment. It is the C1s spectrum obtained by the narrow scan analysis of XPS about the porous insulating layer which concerns on one Embodiment. It is a spectrum which shows the result of carrying out waveform separation (curve fitting) of the C1s spectrum of FIG.

Hereinafter, a preferred embodiment of a lithium ion secondary battery which is a typical example of the secondary battery disclosed herein will be described. Matters necessary for the manufacture and use of the secondary battery disclosed herein, other than the matters specifically mentioned in the present specification, are understood as design matters by those skilled in the art based on the prior art in this field. obtain.
Note that in this specification, a “secondary battery” refers to a power storage device that can repeatedly extract predetermined electrical energy. For example, a lithium ion secondary battery, a sodium ion secondary battery, or the like, or an electric double layer capacitor (for example, a lithium ion capacitor) in which an alkali metal ion in an electrolyte is responsible for charge transfer is included in the secondary battery here. This is a typical example. The “electrode body” refers to a structure constituting the main body of a battery including a positive electrode, a negative electrode, and a porous insulating layer that functions as a separator. “Positive electrode active material” or “negative electrode active material” (collectively referred to as “electrode active material”) is a chemical species serving as a charge carrier (for example, lithium ion, sodium ion secondary in a lithium ion secondary battery). A compound (positive electrode active material or negative electrode active material) capable of reversibly occluding and releasing (sodium ion in a battery).
In the present specification, the “carboxyl group” is a term including —COOH in which a proton is present in the hydroxy group portion and —COO ⁻ (which may be in the form of a salt) in which the proton is liberated. “Carboxylated surface” refers to the surface of polymer particles into which carboxyl groups have been introduced (become rich in carboxyl groups) by various techniques that are not particularly limited.

As shown in FIG. 1, the lithium ion secondary battery 100 according to this embodiment includes a metal case 50. The case (outer container) 50 includes a flat rectangular parallelepiped case body 52 that is an opening having an open upper surface, and a lid 54 that closes the opening. Due to the shape of the case (outer container), the lithium ion secondary battery 100 according to this embodiment is a sealed nonaqueous electrolyte battery also called a square lithium ion secondary battery. The battery case itself need not be made of metal, and may be a resin case or a laminate film case.
The lid 54 is made of aluminum or aluminum alloy, which is one current collecting terminal and is connected to one end (current collector exposed portion) 16 of the positive electrode 10 of the electrode body (laminated electrode body) 80 according to the present embodiment. There is provided a positive current collector terminal 70 and a negative current collector terminal 72 made of copper or copper alloy which is the other current collector terminal and is connected to one end (current collector exposed portion) 26 of the negative electrode 20 of the electrode body 80. It has been.
In the case 50, a rectangular sheet-like positive electrode (positive electrode sheet) 10 corresponding to the shape of the wide surface of the case 50 and a similar rectangular sheet-like negative electrode (negative electrode sheet) 20 were alternately laminated. The laminated electrode body 80 is accommodated together with a non-aqueous electrolyte (here, a non-aqueous electrolyte). A part of the case 50 is provided with a gas discharge mechanism such as a safety valve for discharging the gas generated inside the case 50 to the outside of the case 50, as in this type of conventional lithium ion secondary battery. The detailed description is omitted because it does not characterize the present invention.

Next, the electrode body 80 according to the present embodiment will be described.
Each negative electrode sheet 20 has a negative electrode current collector 22 made of copper foil or the like, and a negative electrode active material layer (not shown) mainly composed of a negative electrode active material formed on both surfaces thereof. However, the negative electrode active material layer is not formed on one side edge in the width direction of the negative electrode sheet 20 (that is, one end portion in the lateral direction parallel to the battery lid 54), and the negative electrode current collector 22 is not formed. A negative electrode current collector exposed portion 26 is formed in which is exposed with a certain width.
On the other hand, each positive electrode sheet 10 includes a positive electrode current collector 12 made of aluminum foil or the like, and a positive electrode active material layer 14 mainly composed of a positive electrode active material formed on both surfaces thereof. However, the positive electrode active material layer 14 is not provided on one side edge in the width direction of the positive electrode sheet 10 (the end opposite to the negative electrode current collector exposed portion 26). A positive electrode current collector exposed portion 16 exposed at a constant width is formed.

In the present embodiment, the positive electrode active material and the negative electrode active material are not particularly limited as long as they are used in this type of conventional battery. Lithium-containing compound (lithium transition metal composite oxide) that is a material capable of occluding and releasing lithium ions as a positive electrode active material of a lithium ion secondary battery and containing lithium element and one or more transition metal elements Can be suitably used. The average particle diameter of the positive electrode active material particles (secondary particles) is preferably about 1 μm or more and 25 μm or less. The particle diameter (and average particle diameter: D50) of the positive electrode active material particles can be determined by a method known in the art, for example, measurement based on a laser diffraction / light scattering method or a call counter method.
On the other hand, as a suitable example of the negative electrode active material of the lithium ion secondary battery, a carbon material such as graphite can be cited. In particular, the use of a graphite material is preferable.
The form of the graphite material used as the negative electrode active material is not particularly limited, and may be a so-called scaly shape (flake shape) or a spherical shape. Moreover, the average particle diameter of the graphite particles is not particularly limited, but those having a particle size of about 5 μm to 50 μm can be preferably used. The particle diameter (and average particle diameter: D50) of the negative electrode active material particles can also be measured by the same method (laser diffraction / light scattering method, call counter method, etc.) as the positive electrode active material particles.

  Each of the positive electrode active material layer and the negative electrode active material layer is a composition prepared by mixing a positive electrode active material (or a negative electrode active material) with various additives (for example, a paste (slurry) prepared by adding a solvent) A supply material or a granulated product obtained by granulating an active material together with an additive) is attached to the positive electrode current collector 12 (or the negative electrode current collector 22) to a predetermined thickness, and is dried if necessary. It can be formed by performing a press treatment or the like. Examples of the additive include a conductive material and a binder in the positive electrode active material layer, and a binder in the negative electrode active material layer. These additive types are conventionally used in this type of lithium ion secondary battery. There is no particular limitation as long as it is.

  In addition, in order to improve the heat resistance of the electrode body 80, a porous heat resistant layer (HRL) may be formed on the active material layer in either or both of the positive electrode and the negative electrode. The heat-resistant layer typically comprises mainly inorganic fillers (particles) such as alumina, boehmite, silica, and titania having an average particle size of 3 μm or less, and typically further includes a binder. As the binder, the same binder as that used for forming the active material layer can be preferably used. The heat-resistant layer may be formed by a conventionally known method, and no special method is required.

The laminated electrode body 80 according to the present embodiment includes an electrode-integrated separator in place of a sheet-like separator made of a general polymer film. Details will be described below.
As shown in the broken portion in FIG. 1, in this embodiment, the porous insulating layer 40 constituting the electrode integrated separator is formed on the negative electrode active material layer. Specifically, the porous insulating layer 40 is composed of polymer particles made of a polyolefin resin (hereinafter simply referred to as “polymer particles”). The porous insulating layer 40 may contain various additive components as long as the function as a separator in the secondary battery is not lost. For example, a suitable amount of a linker for linking polymer particles (for example, a fiber material such as cellulose nanofiber) or a thickener such as carboxymethyl cellulose (CMC) can be added.

The porous insulating layer 40 is for forming a porous insulating layer by dispersing polymer particles as main components and various additive components added as desired in an appropriate solvent (for example, an aqueous solvent such as distilled water). A suspension is prepared, and the suspension is formed by applying the suspension on the negative electrode active material layer by various coating methods such as a die nozzle method, a blade method, and a gravure roll method, and further evaporating the solvent by drying. Can do.
Note that the porous insulating layer 40 provided in the secondary battery disclosed herein is not necessarily required to be formed on the negative electrode active material layer, and may be formed on the positive electrode active material layer. Or even if it forms on both active material layers, it should just function as a separator. Alternatively, the separator may be provided separately from the positive and negative electrodes by forming the porous insulating layer 40 on the surface of another sheet-like porous substrate without using the electrode integrated separator.

The polymer particles constituting the porous insulating layer 40 may be polymer particles made of polyolefin resin, and are not particularly limited, but those made of polyethylene resin or polypropylene resin have good insulating properties and chemical stability. It is a preferable material from the viewpoint.
The particle size of the polymer particles used is not particularly limited as long as it functions as a separator, but the average particle size based on the Cole counter method (referred to as the median diameter (D50)) is 1 μm or more and 10 μm or less. It is preferably 2 μm or more and particularly preferably 5 μm or less.

The porous insulating layer disclosed herein has the following characteristics:
(1) polymer particles comprising a polyolefin resin, including polymer particles having a carboxylated surface in which at least a carboxyl group is present; and
(2) In the area ratio of each peak obtained by curve fitting the C1s spectrum by XPS (X-ray photoelectron spectroscopy), O = C—O— peak area (A) and sp ³ (C—C and C A / B ratio (in%) which is a ratio of -H) to the peak area (B) is 5% or more and 13% or less;
It is characterized by having.
A porous insulating layer including polymer particles having such carboxyl group-rich surface characteristics and having an abundance of carboxyl groups in a predetermined range can improve the adhesion performance with the electrode active material layer. For this reason, the said porous insulating layer becomes difficult to peel from an electrode active material layer (this embodiment negative electrode active material layer), and the structural stability of a laminated electrode body can be improved more.

Such polymer particles having carboxyl group-rich surface properties (carboxylated surface) can be produced by carboxylating the surface of polymer particles made of a polyolefin resin as a base material by various conventionally known methods. .
For example, physical means such as plasma treatment and ozone treatment, and various chemical means for introducing a carboxyl group onto the surface of polymer particles by reacting a monomer having a carboxyl group can be employed. Note that the technique itself for introducing a desired amount of carboxyl groups on the surface of the polymer particles is within the scope of the prior art and does not characterize the present invention, and therefore will not be described in detail.

The feature of the above (2) disclosed here can be determined by surface analysis using a commercially available XPS apparatus. In other words, the amount of carboxyl groups in the porous insulating layer (and thus the surface of the polymer particles) can be adjusted to a predetermined level while using surface analysis using an XPS apparatus as an index.
Although not particularly limited, for example, a commercially available XPS device (μ-XPS device) is used, and a sample of a porous insulating layer (for example, a negative electrode slice in which a porous insulating layer is formed on a negative electrode active material layer). On the other hand, surface analysis is performed under the conditions of X-ray: monochromatic AlKa line, detection region: 50 μm to 200 μm (for example, 100 μm), detection depth: 4 nm to 5 nm (extraction angle 45 °).
Specifically, for a C1s spectrum obtained with a narrow scan (typically 0.1 eV step narrow scan including a binding energy range of 280 eV to 295 eV), the CC (C—H) peak of SP ³ Is corrected to a position of approximately 284.8 eV, and then waveform separation and curve fitting (typically nonlinear minimum two) is performed under the condition that the O = C-O-peak is around 288 to 289 eV (for example, 288.9 eV). (Fitting based on multiplicative method), and in the area ratio of each peak obtained, the peak area (A) of O = C—O— and the peak area (B) of sp ³ (C—C and C—H) A / B ratio (in%) can be obtained.
In the technique disclosed herein, the porous insulating layer includes the porous insulating layer so that the A / B ratio is 5% or more and 13% or less (more preferably 11% or more and 13% or less). The porous insulating layer may be formed by adjusting the degree of carboxylation of the polymer particles, or by mixing a plurality of types of polymer particles having different degrees of carboxylation.

Then, the current collector exposed portions 16 and 26 protrude from the lateral sides of the negative electrode sheet 20 including the positive electrode sheet 10 and the porous insulating layer (electrode-integrated separator) manufactured as described above. The positive electrode sheet 10 and the negative electrode sheet 20 are overlapped with a slight shift in the width direction. At this time, the positive and negative electrode sheets 10 and 20 laminated by the adhesion function of the porous insulating layer (electrode-integrated separator) formed on each negative electrode sheet 20 are bonded to each other to prevent misalignment, and the laminated electrode The structural stability of the body 80 can be improved.
In the laminated electrode body 80 constructed in this manner, the current collector exposed portions 16 and 26 of the positive electrode sheet 10 and the negative electrode sheet 20 protrude from both ends in the lateral direction, respectively. Part of the positive electrode current collector terminal 70 and the negative electrode current collector terminal 72 is joined to the positive electrode side protruding portion and the negative electrode side protruding portion by a joining means such as welding.

As the non-aqueous electrolyte (typically liquid or polymer (gel) non-aqueous electrolyte) accommodated in the case 50, the same one as used in the conventional lithium ion secondary battery is used without particular limitation. be able to. A typical liquid non-aqueous electrolyte (non-aqueous electrolyte) includes a composition in which a supporting salt is contained in a suitable non-aqueous solvent. For example, a carbonate-based solvent such as ethylene carbonate can be used. As the supporting salt, a lithium salt such as LiPF ₆ can be used. As an example, a non-solvent containing LiPF ₆ at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (eg, volume ratio 3: 4: 3). A water electrolyte may be mentioned.

  Then, the electrode body 80 is accommodated in the main body 52 from the opening provided in the upper surface portion of the case main body 52, in which the lid body 54, the electrode body 80, and the positive and negative current collecting terminals 70 and 72 are integrated. Thus, the non-aqueous electrolyte is supplied (injected) into the case body 52 from an injection hole (not shown) provided in the lid 54. Thereafter, the injection hole is sealed, and the opening is sealed by welding with the lid 54 or the like, thereby completing the construction of the battery assembly of the lithium ion secondary battery 100 according to the present embodiment. In addition, the sealing process of case 50 and the arrangement | positioning (injection) process of electrolyte solution may be the same as the method currently performed by manufacture of the conventional lithium ion secondary battery, and do not characterize this invention.

Next, an initial charging process is performed on the battery assembly constituting the lithium ion secondary battery 100 constructed as described above. Typically, an external power source is connected between the positive electrode (positive electrode current collector terminal 70) and the negative electrode (negative electrode current collector terminal 72) of the battery assembly, and at room temperature (typically about 25 ° C. ± 5 ° C.). The battery is charged until the voltage between the terminals reaches a predetermined value.
In the initial charging process, for example, a voltmeter is connected between the positive electrode current collector terminal 70 and the negative electrode current collector terminal 72 in the lithium ion secondary battery 100, and the measured voltage value is monitored by this voltmeter, and is set in advance. The process may be terminated when the predetermined voltage value is reached. In addition, after the completion of the initial charging process, as a conditioning process, a discharging process may be performed at a current value approximately equal to the charging rate during the constant current charging, and then charging is performed at a rate approximately equal to the current value. The discharge cycle may be repeated several times. Alternatively, the charge / discharge cycle may be repeated several times at a rate different from the charge / discharge rate of the charge / discharge cycle.
By performing such a conditioning process, the lithium ion secondary battery 100 in a suitably usable state is provided.

  Hereinafter, some test examples relating to the porous insulating layer disclosed herein will be described, but the scope of the present invention is not intended to be limited to those shown in the test examples.

<Example of production of a negative electrode for a lithium ion secondary battery provided with a porous insulating layer (electrode-integrated separator): Example 1>
Graphite having an average particle diameter of about 8 μm is used as the negative electrode active material, and carboxymethyl cellulose (CMC) as a thickener and styrene butadiene rubber (SBR) as a binder have a mass ratio of 98: 1: 1 was mixed with ion-exchanged water to prepare a paste-like negative electrode active material layer forming material. This material was uniformly applied on both sides of a copper foil (negative electrode current collector: thickness 10 μm), dried, and then subjected to compression treatment by a roll press to prepare a negative electrode sheet.
An emulsion (Mitsui Chemicals Co., Ltd. product) containing polyethylene particles having a carboxylated surface on the negative electrode active material layer of the prepared negative electrode sheet (average particle diameter based on the coal counter method (hereinafter the same): 3 μm) : Chemipearl (registered trademark) W type) was appropriately diluted with an aqueous solvent, and a suspension for forming a porous insulating layer was prepared while adding an appropriate amount of a thickener to adjust the viscosity to an appropriate level. Next, the prepared suspension was applied on the negative electrode active material layer of the negative electrode sheet prepared by reverse microgravure coating.
Then, the negative electrode sheet which concerns on Example 1 with which the 12-micrometer-thick porous insulating layer was formed on the negative electrode active material layer was produced by drying.

<Example 2>
An equal amount of commercially available non-carboxylated polyethylene particles (average particle size: 3 μm) were blended so that the mass ratio was 1: 1 with respect to the polyethylene particles having a carboxylated surface contained in the emulsion. A negative electrode sheet according to Example 2 was produced by the same process as in Example 1 except that the suspension for forming the porous insulating layer was prepared.

<Example 3>
Two times the amount of non-carboxylated commercially available polyethylene particles (average particle size: 3 μm) was blended so that the mass ratio was 1: 2 with respect to the polyethylene particles having a carboxylated surface contained in the emulsion. A negative electrode sheet according to Example 3 was produced by the same process as in Examples 1 and 2 except that the suspension for forming a porous insulating layer was prepared.

<Example 4>
Three times the amount of non-carboxylated commercially available polyethylene particles (average particle diameter: 3 μm) was blended so that the mass ratio was 1: 3 with respect to the polyethylene particles having a carboxylated surface contained in the emulsion. A negative electrode sheet according to Example 4 was produced by the same process as in Examples 1 to 3 except that the suspension for forming a porous insulating layer was prepared.

<Comparative Example 1>
A heat-resistant layer (thickness 4 μm) composed of an inorganic filler (alumina and boehmite) and a binder was formed on one surface of a commercially available separator sheet (three-layer sheet made of PP / PE / PP having a thickness of 20 μm). The separator sheet was Comparative Example 1.

<Surface analysis by XPS>
Next, the surface analysis by XPS was performed on the negative electrode (porous insulating layer) of Examples 1 to 4 and the separator sheet of Comparative Example 1.
Specifically, the negative electrode or separator sheet to be analyzed was cut into a square having a side of about 5 mm and placed in a sample holder of an XPS apparatus. As the XPS device, “QuanteraSXM” (trademark) manufactured by Physical Electronics Co., Ltd. is used, and the surface is X-ray: monochromatic AlKa line, detection region: 100 μm, detection depth: 4 nm to 5 nm (extraction angle 45 °). Analysis was carried out.
The C1s spectrum obtained by narrow scan is shown in FIG. Furthermore, after performing the charge correction so that the C—C (C—H) peak of SP ³ is positioned at 284.8 eV, the condition that the O═C—O— peak is around 288 to 289 eV (for example, 288.9 eV). Waveform separation (curve fitting) was performed. The results are shown in FIG. The separation peaks of C2, C3, C4, and C5 shown in FIG. 3 indicate C—C (& C—H), C—O, C═O, and O═C—O—, respectively.
From the result of such fitting, the A / B ratio (%), which is the ratio between the peak area (A) of O = C—O— and the peak area (B) of sp ³ (C—C and C—H). Display). The results are shown in the corresponding column of Table 1.
As shown in Table 1, Examples 1-4 showed a higher A / B ratio as the content of polymer particles having a carboxylated surface was higher (Example 1>2>3> 4). . About the separator sheet of the comparative example 1, as a result of not having introduce | transduced the carboxyl group intentionally, A / B ratio showed the value considerably lower than each Example.

<Measurement of air permeability>
The suspension for forming a porous insulating layer used in each of the above Examples 1 to 4 was impregnated into a wire mesh of a predetermined size having an air permeability of 2 seconds / 100 cc, and the porous materials having the same thickness on the wire mesh. Insulating layers were formed (Examples 1 to 4). In addition, the separator sheet used in Comparative Example 1 was also attached to the wire mesh and subjected to air permeability measurement.
The air permeability was measured using a Gurley type densometer (air permeability tester) manufactured by Toyo Seiki Seisakusho. Specifically, the metal mesh with the porous insulating layer (separator) of Examples 1 to 4 and Comparative Example 1 prepared above was set in a densometer, and the time required for 100 ml of air to pass through was counted as the air permeability. . The results are shown in the corresponding column of Table 1.
About Examples 1-4 which do not have the base material which consists of polyolefin resins, all showed favorable air permeability.

<Measurement of peel strength>
The negative electrode sheet which concerns on the said Examples 1-4 was bonded together with the positive electrode sheet with a heat-resistant layer, and peeling strength was investigated. Specifically, it is as follows.
A ternary lithium-containing composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having an average particle size of about 15 μm is used as the positive electrode active material, and acetylene black as a conductive material and polyfluoride as a binder. Vinylidene chloride (PVdF) was mixed with N-methylpyrrolidone (NMP) so that the mass ratio of these materials was 94: 3: 3 to prepare a paste-form positive electrode active material layer forming material. This material was uniformly applied to both surfaces of an aluminum foil (positive electrode current collector: thickness 15 μm), dried, and then subjected to compression treatment by a roll press to prepare a positive electrode sheet. Next, a heat-resistant layer (thickness 4 μm) composed of an inorganic filler (alumina and boehmite) and a binder was formed on one surface of the positive electrode active material layer.

Then, any one of the negative electrode sheets according to Examples 1 to 4 and the produced positive electrode sheet were cut into a width of 20 mm and a length of about 300 mm, respectively, and an appropriate load was applied with a roll press while the negative electrode side was applied. Test pieces (Examples 1 to 4) were prepared by bonding the porous insulating layer and the heat-resistant layer on the positive electrode side so as to face each other.
A 90 ° peel test was performed in which the negative electrode side of the test piece thus obtained was fixed to a fixing jig with a double-sided tape, and the positive electrode side was pulled vertically by an autograph. At that time, the maximum peel strength was determined with the horizontal axis as the tensile distance and the vertical axis as the tensile strength (peel strength). The results are shown in the corresponding column of Table 1.
Examples 1 to 4 all exhibited high peel strength. In particular, Example 1 and Example 2 having an A / B ratio of 11% or more showed high peel strength with a peel strength exceeding 10 mN / cm. This indicates that the greater the amount of carboxyl groups in the porous insulating layer functioning as a separator (in other words, the polymer particles contained in the porous insulating layer), the higher the peel strength.

As mentioned above, although this invention was demonstrated in detail, said preferred embodiment and an Example are only illustrations to the last, Comprising: The above-mentioned specific example is variously modified and changed in the invention disclosed here. .
For example, in the above embodiment and test example, the porous insulating layer is formed on the negative electrode sheet side. However, the present invention is not limited to this form, and the same effect as described above forms the porous insulating layer on the positive electrode sheet side. You can also play it.
The form of the secondary battery embodying the present invention is not limited to the lithium ion secondary battery, and can be applied to various types of secondary batteries such as a sodium ion secondary battery, an electric double layer capacitor, and the like.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 16 Positive electrode collector exposed part 20 Negative electrode sheet 22 Negative electrode collector 26 Negative electrode collector exposed part 40 Porous insulating layer (electrode integrated separator)
50 Battery Case 52 Case Body 54 Lid 70 Current Collection Terminal (Positive Current Collection Terminal)
72 Current collector terminal (Negative electrode current collector terminal)
80 Multilayer electrode body 100 Lithium ion secondary battery

Claims (1)

A positive electrode having a positive electrode active material layer;
A negative electrode having a negative electrode active material layer;
A porous insulating layer that exists between the positive and negative electrodes and insulates between the positive electrode active material layer and the negative electrode active material layer;
A secondary battery comprising:
The porous insulating layer is
Polymer particles comprising a polyolefin resin, comprising polymer particles having a carboxylated surface in which at least a carboxyl group is present, and
In the area ratio of each peak obtained by curve fitting the C1s spectrum by XPS (X-ray photoelectron spectroscopy), O = C—O— peak area (A) and sp ³ (C—C and C—H) A / B ratio (in%) which is a ratio to the peak area (B) of 5% or more and 13% or less,
A secondary battery characterized by that.

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