JP7096978B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries have been used for portable power sources such as personal computers and mobile terminals, and for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is suitably used for power supplies and the like.

A non-aqueous electrolyte secondary battery generally has a configuration including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. It is known to use a separator having a multi-layer structure for the purpose of improving the characteristics of a non-aqueous electrolyte secondary battery (see, for example, Patent Documents 1 to 3).

Patent Document 1 discloses a separator having a microporous membrane containing a polymer resin and a microporous membrane provided on the main surface of the microporous membrane and containing inorganic particles. Patent Document 1 defines the average pore diameter, average film thickness, and the like of a microporous membrane containing a polymer resin so that the pores of the separator are retained even when the electrode expands due to charging and discharging. Is being done. Patent Document 2 discloses a separator having a three-layer structure resin porous film in which polypropylene layers are formed on both sides of a polyethylene layer, and a heat-resistant porous layer containing heat-resistant fine particles.

Japanese Unexamined Patent Publication No. 2011-138761 International Publication No. 2012/050152

However, as a result of diligent studies by the present inventors, it has been found that there is room for improvement in both the resistance characteristics of the separator and the short-circuit resistance in the prior art.

In view of such circumstances, it is an object of the present invention to provide a non-aqueous electrolyte secondary battery having both resistance characteristics of a separator and short circuit resistance.

The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The separator includes at least four porous layers in which a first layer, a second layer, a third layer, and a fourth layer are laminated in this order. The first layer is in contact with the positive electrode. The first layer contains ceramic particles. The density of the first layer is 1.0 g / cm ³ or more and 1.5 g / cm ³ or less. The second layer, the third layer, and the fourth layer are resin layers, respectively. The pore diameter of the third layer is 0.11 μm or more and 0.21 μm or less. The ratio of the thickness of the third layer to the thickness of the second layer (thickness of the third layer / thickness of the second layer) is 1.55 or more and 2.5 or less. The total thickness of the first layer, the second layer, the third layer, and the fourth layer is 16 μm or more and 22 μm or less.
According to such a configuration, it is possible to provide a non-aqueous electrolyte secondary battery having both resistance characteristics of a separator and short-circuit resistance.

It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the separator used in one Embodiment of this invention.

Hereinafter, embodiments according to the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, general configurations and manufacturing processes of non-aqueous electrolyte secondary batteries that do not characterize the present invention). Can be grasped as a design matter of a person skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art.

In the present specification, the "secondary battery" generally refers to a power storage device capable of being repeatedly charged and discharged, and is a term including a so-called storage battery and a power storage element such as an electric double layer capacitor.
Hereinafter, the present invention will be described in detail by taking a flat-angle type lithium ion secondary battery as an example, but the present invention is not intended to be limited to those described in such embodiments.

The lithium ion secondary battery 100 shown in FIG. 1 is a closed type in which a flat wound electrode body 20 and a non-aqueous electrolyte 80 are housed in a flat square battery case (that is, an outer container) 30. It is a battery. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. ing. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to the positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material having good thermal conductivity such as aluminum is used.

As shown in FIGS. 1 and 2, the wound electrode body 20 has a positive electrode active material layer 54 formed along the longitudinal direction on one side or both sides (here, both sides) of the long positive electrode current collector 52. The positive electrode sheet 50 and the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 are two long sheets. It has a form of being overlapped with each other via a separator sheet 70 and wound in the longitudinal direction. The positive electrode active material layer non-formed portion 52a (that is, the positive electrode activity) formed so as to protrude outward from both ends of the winding electrode body 20 in the winding axis direction (that is, the sheet width direction orthogonal to the longitudinal direction). A portion where the positive electrode current collector 52 is exposed without forming the material layer 54) and a portion 62a where the negative electrode active material layer is not formed (that is, a portion where the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64). A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are joined to each of the above.

As the positive electrode sheet 50 and the negative electrode sheet 60, the same ones used in the conventional lithium ion secondary battery can be used without particular limitation. A typical aspect is shown below.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil and the like. Examples of the positive electrode active material contained in the positive electrode active material layer 54 include lithium transition metal oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O). ₄ , LiNi _0.5 Mn _1.5 O ₄ , etc.), lithium transition metal phosphate compounds (eg, LiFePO ₄ , etc.) and the like. The positive electrode active material layer 54 may contain components other than the active material, such as a conductive material and a binder. As the conductive material, for example, carbon black such as acetylene black (AB) or other carbon material (eg, graphite or the like) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

Examples of the negative electrode current collector 62 constituting the negative electrode sheet 60 include copper foil and the like. As the negative electrode active material contained in the negative electrode active material layer 64, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer 64 may contain components other than the active material, such as a binder and a thickener. As the binder, for example, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

As shown in the schematic cross-sectional view of FIG. 3, the separator 70 includes four porous layers in which the first layer 72, the second layer 74, the third layer 76, and the fourth layer 78 are laminated in this order. The first layer 72 is arranged on the positive electrode 50 side and is in contact with the positive electrode 50 (specifically, the positive electrode active material layer 54). The fourth layer 78 is arranged on the negative electrode 60 side and is in contact with the negative electrode 60 (specifically, the negative electrode active material layer 64). The separator 70 may have a layer on the negative electrode 60 side in addition to the four layers as long as the effect of the present invention is not significantly impaired.
It is preferable that the separator 70 is in close contact with the positive electrode 50 and the negative electrode 60, for example, because a load is applied from the outside of the battery case 30.

The first layer 72 contains ceramic particles. Therefore, the first layer 72 may have a function as a heat resistant layer (HRL). With this function, it is possible to prevent the resin component of the separator 70 from being melted and the short circuit from spreading due to heat generation due to current concentration at the time of a short circuit.
In the first layer 72, a porous structure is formed by the voids between the ceramic particles.
Examples of the ceramic particles include oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, and zinc oxide, nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride, silicon carbide, calcium carbonate, and boehmite. , Tark, kaolin clay, montmorillonite, mica, zeolite, calcium silicate, magnesium silicate, aluminum silicate, silica sand and the like, and among them, boehmite particles and alumina particles are preferable. These have a high melting point and excellent heat resistance. It also has a relatively high Mohs hardness and is excellent in mechanical strength and durability. Furthermore, since it is relatively inexpensive, the raw material cost can be suppressed.
The content of the ceramic particles in the first layer 72 is not particularly limited, but is preferably 90% by weight or more and 97% by weight or less.

The first layer 72 may further contain a binder or the like, if necessary.
Examples of the binder include a fluorine-based polymer such as polytetrafluoroethylene (PTFE), an acrylic-based binder, a styrene-butadiene rubber (SBR), a polyolefin-based binder and the like.
The content of the binder in the first layer 72 is not particularly limited, but is preferably 3% by weight or more and 10% by weight or less.

The density of the first layer 72 is 1.0 g / cm ³ or more and 1.5 g / cm ³ or less. The significance of this numerical range will be described later.
The thickness of the first layer 72 is preferably 1.5 μm or more and 6 μm or less.

The second layer 74, the third layer 76, and the fourth layer 78 are each a resin layer, specifically, a resin porous layer. Examples of the resin constituting the resin layer include polyolefins such as polyethylene (PE) and polypropylene (PP), polyester, cellulose, polyamide and the like.
Preferably, the second layer 74 is a PP layer, the third layer 76 is a PE layer, and the fourth layer 78 is a PP layer.
These resin layers may be a porous film that has been made porous by stretching or the like. Alternatively, it may be a porous layer formed from resin fine particles.
It is preferable that the second layer 74 and the third layer 76 are joined by heat welding, adhesion with an adhesive, or the like. It is preferable that the third layer 76 and the fourth layer 78 are joined by heat welding, adhesion with an adhesive, or the like.

The pore diameter of the third layer 76 is 0.11 μm or more and 0.21 μm or less. The significance of this numerical range will be described later.
The pore diameter can be determined by, for example, a mercury intrusion method. Specifically, the pore distribution curve of the third layer 76 can be obtained by using a mercury porosimeter, and the pore diameter at the peak position can be set to the pore diameter of the third layer 76.

The ratio of the thickness of the third layer 76 to the thickness of the second layer 74 (thickness of the third layer 76 / thickness of the second layer 74) is 1.5 or more and 2.5 or less. The significance of this numerical range will be described later.
The thickness of the second layer 74 is preferably 3 μm or more and 5 μm or less.
The thickness of the third layer 76 is preferably 4.65 μm or more and 10 μm or less.
The thickness of the fourth layer 78 is preferably 3 μm or more and 5 μm or less.

In the present embodiment, the total thickness of the first layer 72, the second layer 74, the third layer 76, and the fourth layer 78 is 16 μm or more and 22 μm or less.
The range of this total thickness in the present embodiment is in a region where the thickness is smaller than the total thickness of the conventional separator. When the thickness of the separator is small, the resistance of the separator can be reduced. However, in the prior art, when the total thickness is small as in the present embodiment, an internal short circuit is likely to occur. This is due to the following phenomenon.
In a non-aqueous electrolyte secondary battery, metal foreign matter existing inside the battery is removed by dissolving it in the electrolyte by an oxidation reaction before shipment, but the foreign matter dissolved in the positive electrode diffuses to the negative electrode. Precipitates as a metal by a reduction reaction. If the total thickness of the separator is small, the deposited metal breaks through the separator and causes an internal short circuit.

In the present embodiment, this internal short circuit is suppressed even though the total thickness is small as described above. The specific contents are as follows.
Since it is necessary to dissolve foreign substances in the positive electrode 50 by an oxidation reaction, it is necessary that a non-aqueous solvent of a non-aqueous electrolyte is sufficiently present in the vicinity of the positive electrode 50. Therefore, in the present embodiment, in the present embodiment, the density of the first layer 72 is limited to a small range of 1.0 g / cm ³ or more and 1.5 g / cm ³ or less. The thickness of the third layer 76 having a pore diameter of 0.11 μm or more and 0.21 μm or less is made larger than the thickness of the second layer 74 (specifically, the thickness of the third layer 76 / the second layer). The thickness of the layer 74 = 1.5 or more and 2.5 or less, that is, the thickness of the third layer 76 is 1.5 to 2.5 times the thickness of the second layer 74). By enlarging the space of the third layer 76 in this way, it is possible to prevent the deposited metal from being trapped and penetrating the separator 70. As a result, an internal short circuit can be suppressed.

The pore volume of the separator 70 is preferably 0.7 mL / g or more, and more preferably 0.75 mL / g or more. On the other hand, the pore volume of the separator 70 is. It is preferably 1.5 mL / g or less, and more preferably 1.2 mL / g or less. The pore volume of the separator 70 can be measured using, for example, a mercury porosimeter.

The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and a supporting salt.
As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones used in the electrolytic solution of a general lithium ion secondary battery shall be used without particular limitation. Can be done. Among them, carbonates are preferable, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and monofluoroethylene carbonate (. MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC) and the like. As such a non-aqueous solvent, one kind may be used alone, or two or more kinds may be used in combination as appropriate.
As the supporting salt, for example, a lithium salt (preferably LiPF ₆ ) such as LiPF ₆ , LiBF ₄ , and LiClO ₄ can be preferably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

The non-aqueous electrolyte 80 is a gas generating agent such as, for example, biphenyl (BP), cyclohexylbenzene (CHB); an oxalate complex compound containing a boron atom and / or a phosphorus atom, as long as the effect of the present invention is not significantly impaired. , A film-forming agent such as vinylene carbonate (VC); a dispersant; various additives such as a thickener.

The lithium ion secondary battery 100 configured as described above can be used for various purposes. Suitable applications include drive power supplies mounted on vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). The lithium ion secondary battery 100 can also be used in the form of an assembled battery, which is typically formed by connecting a plurality of lithium ion secondary batteries in series and / or in parallel.

As an example, a square lithium ion secondary battery 100 provided with a flat wound electrode body 20 has been described. However, the lithium ion secondary battery can also be configured as a lithium ion secondary battery including a laminated electrode body. Further, the lithium ion secondary battery can also be configured as a cylindrical lithium ion secondary battery, a laminated lithium ion secondary battery, or the like. The technique disclosed herein is also applicable to non-aqueous electrolyte secondary batteries other than lithium ion secondary batteries.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Preparation of separator>
A separator sheet having a heat-resistant layer containing inorganic particles was prepared on one side of a three-layer structure (PP / PE / PP) porous film in which polypropylene layers were formed on both sides of the polyethylene layer. In this separator sheet, the heat-resistant layer corresponds to the first layer, the PP layer adjacent thereto corresponds to the second layer, the PE layer corresponds to the third layer, and the PP layer on the negative electrode side corresponds to the fourth layer. Regarding the separator sheet having such a structure, the total thickness, the pore volume, the thickness of each layer, the material of the inorganic particles of the heat-resistant layer (first layer), the density of the heat-resistant layer (first layer), and the fineness of the third layer (PE layer). Those with different hole diameters were prepared. The pore volume of the separator sheet and the pore diameter of the third layer (PE layer) are values measured using a mercury porosimeter.

<Evaluation of separator resistance>
Using the separators prepared above, three types of CR2032 coin batteries with different numbers of separators were produced. Specifically, one, two, or three separators punched out with a diameter of 18 mm were arranged between two aluminum foils and impregnated with a non-aqueous electrolyte to prepare a battery. The non-aqueous electrolyte contains ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 4: 3, as a supporting salt. The solution of LiPF ₆ at a concentration of 1.1 mol / L was used.
The impedance of this battery was measured, the number of separators and the DC component value of the impedance were plotted, and the slope of the linear approximation line was obtained as the separator resistance.
Table 1 shows the configuration of the separator used and the evaluation result of the separator resistance for each test example.

<Short circuit resistance evaluation>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are used as LNCM :. A slurry for forming a positive electrode active material layer was prepared by mixing with N-methylpyrrolidone (NMP) at a mass ratio of AB: PVdF = 90: 8: 2. This slurry was applied to both sides of a long aluminum foil in a strip shape, dried, and then pressed to prepare a positive electrode sheet.
Natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are mixed in a mass ratio of C: SBR: CMC = 98: 1: 1. To prepare a slurry for forming a negative electrode active material layer by mixing with ion-exchanged water. This slurry was applied to both sides of a long copper foil in a strip shape, dried, and then pressed to prepare a negative electrode sheet.
A flat-shaped wound electrode body is produced by laminating the positive electrode sheet, the negative electrode sheet, and the two prepared separator sheets prepared above, winding them, and then pressing them from the side surface direction to pull them away. did. At the time of laminating, the heat-resistant layer of the separator sheet was made to face (contact) the positive electrode.
An iron plate having a predetermined thickness was punched into a columnar shape and inserted into the wound electrode.
Next, the positive electrode terminal and the negative electrode terminal were connected to the wound electrode body and housed in a square battery case having an electrolytic solution injection port.
Subsequently, a non-aqueous electrolyte was injected from the electrolyte injection port of the battery case, and the injection port was hermetically sealed. The non-aqueous electrolyte is a mixed solvent containing ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 4: 3, and a supporting salt. LiPF ₆ was dissolved at a concentration of 1.1 mol / L.
The evaluation lithium ion secondary battery thus produced was charged to 4 V at a current value of 4 C and then aged at 63 ° C. for 20 hours. After that, it was left for 3 days. Based on the voltage at 20 ° C., the amount of voltage drop when left for 3 days was measured. It was determined that there was a short circuit with respect to the battery having a voltage drop of 0.2 V or more.
The thickness of the iron plate inserted into the winding electrode was changed to check for the presence or absence of a short circuit, and the smallest thickness (μm) of the iron plate with the short circuit was used as an index of short circuit resistance.
Table 1 shows the configurations of the separators used and the evaluation results of short-circuit resistance for each test example.

From the results in Table 1, it can be seen that the separator resistance increases as the total thickness of the separator increases. In Test Example 1 in which the total thickness of the separator was 24 μm, the separator resistance was too high, and in Test Examples 2 to 11 in which the total thickness of the separator was 16 μm to 22 μm, good resistance values were obtained.
Further, among the test examples in which the total thickness of the separator was 16 μm to 22 μm, the short-circuit resistance was low in the test examples 2 and 3 in which the ratio (thickness ratio) of the thickness of the third layer to the thickness of the second layer was small. On the other hand, in Test Examples 4 to 11 having a thickness ratio of 1.55 to 2.5, good short-circuit resistance was obtained.
Therefore, in order to achieve both separator resistance and short-circuit resistance, the total thickness of the separator should be 16 μm to 22 μm, and the thickness of the third layer should be increased. Specifically, the ratio of the thickness of the third layer to the thickness of the second layer. It can be seen that it is effective to set the value to 1.55 to 2.5.

<Short circuit rate evaluation>
A positive electrode sheet and a negative electrode sheet were produced by the same method as the above-mentioned short-circuit resistance evaluation.
The prepared positive electrode sheet, the negative electrode sheet, and the two separator sheets prepared above were laminated, wound, and then pressed from the side surface direction to be swollen to prepare a flat-shaped wound electrode body. At the time of laminating, the heat-resistant layer of the separator sheet was made to face (contact) the positive electrode.
Next, the positive electrode terminal and the negative electrode terminal were connected to the wound electrode body and housed in a square battery case having an electrolytic solution injection port.
Subsequently, a non-aqueous electrolyte was injected from the electrolyte injection port of the battery case, and the injection port was hermetically sealed. The non-aqueous electrolyte is a mixed solvent containing ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC: EMC: DMC = 3: 4: 3, and a supporting salt. LiPF ₆ was dissolved at a concentration of 1.1 mol / L.
1000 evaluation lithium ion secondary batteries thus produced were produced.
Each evaluation lithium ion secondary battery was charged to 4 V at a current value of 4 C and then aged at 63 ° C. for 20 hours. After that, it was left for 3 days. Based on the voltage at 20 ° C., the amount of voltage drop when left for 3 days was measured. It was determined that there was a short circuit with respect to the battery having a voltage drop of 0.2 V or more.
The ratio of the 1000 evaluation lithium ion secondary batteries having a short circuit was determined as the short circuit rate (%).
Table 2 shows the configuration of the separator used and the evaluation result of the short-circuit rate for each test example.

From the results in Table 2, it can be seen that the short circuit rate tends to decrease when the pore volume of the separator is large.
Here, as a method of increasing the pore volume of the separator, there is a method of increasing the thickness of each layer such as the third layer, but as described above, the total thickness of the separator is limited from the viewpoint of resistance. Not a good idea.
In order to suppress an internal short circuit, it is first necessary to dissolve foreign substances by an oxidation reaction. Therefore, considering that a large amount of non-aqueous solvent of non-aqueous electrolyte is retained in the vicinity of the positive electrode, the density of the first layer should be increased. It is considered effective to make it smaller. Further, it is considered effective to control the pore diameter of the third layer, which is thicker than the second layer.
From these facts, from the results in Table 2, the density of the first layer is in a small range of 1.0 g / cm ³ or more and 1.5 g / cm ³ or less, and the pore diameter of the third layer is 0.11 μm or more and 0.21 μm. It can be said that the following range is effective.

Integrating the above results, in the separator provided with the first layer containing the inorganic particles and the second to fourth layers which are resin layers, the density of the first layer is 1.0 g / cm ³ or more and 1.5 g. / Cm ³ or less, the pore diameter of the third layer is 0.11 μm or more and 0.21 μm or less, and the ratio of the thickness of the third layer to the thickness of the second layer (third layer / second layer) is 1.55 or more. It can be seen that if the thickness is 2.5 or less and the total thickness of the four layers is 16 μm or more and 22 μm or less, both the resistance characteristics of the separator and the short-circuit resistance can be achieved.
That is, it can be seen that the non-aqueous electrolyte secondary battery of the present embodiment described above can achieve both the resistance characteristics of the separator and the short-circuit resistance.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

20 Winding electrode body 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode sheet (positive electrode)
52 Positive electrode current collector 52a Positive electrode active material layer non-formed portion 54 Positive electrode active material layer 60 Negative electrode sheet (negative electrode)
62 Negative electrode current collector 62a Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator sheet (separator)
72 1st layer 74 2nd layer 76 3rd layer 78 4th layer 80 Non-aqueous electrolyte 100 Lithium ion secondary battery

Claims (1)

With the positive electrode
With the negative electrode
A separator interposed between the positive electrode and the negative electrode,
A non-aqueous electrolyte secondary battery equipped with
The separator has a four- layer structure including four porous layers in which the first layer, the second layer, the third layer, and the fourth layer are laminated in this order.
The first layer is in contact with the positive electrode and is in contact with the positive electrode.
The first layer contains ceramic particles and contains ceramic particles.
The density of the first layer is 1.0 g / cm ³ or more and 1.5 g / cm ³ or less.
The second layer, the third layer, and the fourth layer are resin layers, respectively.
The pore diameter of the third layer is 0.11 μm or more and 0.21 μm or less.
The ratio of the thickness of the third layer to the thickness of the second layer (thickness of the third layer / thickness of the second layer) is 1.55 or more and 2.5 or less.
The total thickness of the first layer, the second layer, the third layer, and the fourth layer is 16 μm or more and 22 μm or less .
The pore volume of the separator is 0.7 mL / g or more and 1.5 mL / g or less.
Non-aqueous electrolyte secondary battery.

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