JP2018137101A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery arranged so that the increase in internal resistance when repeatedly charged and discharged at a high rate can be suppressed.SOLUTION: A lithium ion secondary battery disclosed herein comprises: an electrode body having a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer and a separator interposed between the positive and negative electrodes; and a nonaqueous electrolyte solution. The electrode body has a first heat-resistant layer between the positive electrode active material layer and the separator, and a second heat-resistant layer between the negative electrode active material layer and the separator, each containing an inorganic filler and a binder. In the lithium ion secondary battery, the positive electrode active material layer is higher, in the permeability of the nonaqueous electrolyte solution, than the negative electrode active material layer. The nonaqueous electrolyte solution holdability of the binder that the first heat-resistant layer contains is higher than the binder in the second heat-resistant layer, or the nonaqueous electrolyte solution permeability of the positive electrode active material layer is lower than that of the negative electrode active material layer, and the nonaqueous electrolyte solution holdability of the binder in the first heat-resistant layer is lower than the binder in the second heat-resistant layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries are lighter and have a higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. Lithium-ion secondary batteries are expected to become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Yes.

  A typical lithium ion secondary battery includes a positive electrode, a negative electrode, an electrode body having a separator interposed between the positive and negative electrodes, and a non-aqueous electrolyte. In addition, a heat-resistant layer may be provided between at least one of the positive electrode and the negative electrode and the separator. For example, Patent Document 1 discloses a separator having a heat-resistant layer containing an inorganic filler as a main component and a binder, and an electrochemical element (electrode body) using the separator.

JP 2014-170752 A

  In lithium ion secondary batteries, a phenomenon occurs in which the internal resistance increases when charging and discharging are repeated at a high rate. This is because when the charge / discharge is repeated at a high rate, the salt concentration in the electrode body decreases due to excessive outflow of the nonaqueous electrolyte outside the electrode body, and the composition of the nonaqueous electrolyte solution in the electrode body is uneven (salt concentration). This is because of the occurrence of bias. In recent years, demand for high-rate charge / discharge characteristics of lithium ion secondary batteries has increased, and it is desired that an increase in internal resistance when charging / discharging is repeated at a high rate is suppressed.

  Therefore, an object of the present invention is to provide a lithium ion secondary battery in which an increase in internal resistance when current is repeatedly charged and discharged at a high rate is suppressed.

In order to suppress such an increase in internal resistance, the present inventors focused on the difference between the permeability of the non-aqueous electrolyte solution of the positive electrode active material layer and the permeability of the non-aqueous electrolyte solution of the negative electrode active material layer, One reason for the increase in internal resistance is the idea that the degree to which the non-aqueous electrolyte is discharged from these active material layers varies depending on the permeability of the non-aqueous electrolyte in these active material layers. As a result, the present invention has been completed.
The lithium ion secondary battery disclosed herein includes a positive electrode, a negative electrode, an electrode body having a separator interposed between the positive and negative electrodes, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The electrode body includes a first heat-resistant layer between the positive electrode active material layer and the separator, and a second heat-resistant layer between the negative electrode active material layer and the separator. Each of the first heat-resistant layer and the second heat-resistant layer contains an inorganic filler and a binder. The lithium ion secondary battery includes the following configuration (A) or (B).
(A) The permeability of the non-aqueous electrolyte of the positive electrode active material layer is higher than the permeability of the non-aqueous electrolyte of the negative electrode active material layer, and the binder contained in the first heat-resistant layer The non-aqueous electrolyte retainability is higher than the non-aqueous electrolyte retainability of the binder contained in the second heat-resistant layer.
(B) The permeability of the non-aqueous electrolyte of the positive electrode active material layer is lower than the permeability of the non-aqueous electrolyte of the negative electrode active material layer, and the binder contained in the first heat-resistant layer The non-aqueous electrolyte retainability is lower than the non-aqueous electrolyte retainability of the binder contained in the second heat-resistant layer.

  According to such a configuration, it is possible to suppress discharge of the non-aqueous electrolyte from the active material layer side having a higher non-aqueous electrolyte permeability by the heat-resistant layer including a binder having a high non-aqueous electrolyte retention. As a result, excessive discharge of the nonaqueous electrolytic solution outside the electrode body can be suppressed. On the other hand, the discharge of the non-aqueous electrolyte from the active material layer side having a lower permeability of the non-aqueous electrolyte can be relatively facilitated by the heat-resistant layer containing a binder having a low non-aqueous electrolyte retention. . As a result, the non-aqueous electrolyte solution is discharged on the active material layer side where the non-aqueous electrolyte solution is higher, and the non-aqueous electrolyte solution is discharged on the active material layer side where the non-aqueous electrolyte solution is lower. Therefore, it is possible to reduce the composition unevenness of the non-aqueous electrolyte in the electrode body. Therefore, according to such a configuration, it is possible to provide a lithium ion secondary battery in which an increase in internal resistance when charging / discharging is repeated at a high rate is suppressed.

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 sectional drawing along the lamination direction which shows typically a part of laminated structure of the winding electrode body of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the cycle number of charging / discharging and a resistance increase rate about the lithium ion secondary battery which changed the kind of binder of the side with low nonaqueous electrolyte retention.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a lithium ion secondary battery that does not characterize the present invention) are as follows. Therefore, it can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a power storage element such as a so-called storage battery and an electric double layer capacitor.
Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as a charge carrier and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes.

Hereinafter, the present invention will be described in detail by taking a flat rectangular lithium ion secondary battery as an example, but the present invention is not intended to be limited to those described in the embodiment.
The lithium ion secondary battery 100 shown in FIG. 1 has a flat wound electrode body 20 and a non-aqueous electrolyte (not shown) accommodated in a flat rectangular battery case (that is, an exterior container) 30. This is a sealed lithium ion secondary battery 100 to be constructed. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set so as to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Yes. In addition, the battery case 30 is provided with an inlet (not shown) for injecting a non-aqueous electrolyte. The positive terminal 42 is electrically connected to the positive current collector 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 light metal material having good thermal conductivity such as aluminum is used.

The non-aqueous electrolyte can be the same as that of a conventional lithium ion secondary battery. Typically, a non-aqueous electrolyte containing a supporting salt in an organic solvent (non-aqueous solvent) can be used. As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones and the like used in electrolytes of general lithium ion secondary batteries are used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), Examples thereof include monofluoromethyl difluoromethyl carbonate (F-DMC) and trifluorodimethyl carbonate (TFDMC). Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , LiClO ₄ (preferably LiPF ₆ ) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

  In addition, the non-aqueous electrolyte is a gas generating agent such as biphenyl (BP) or cyclohexylbenzene (CHB); an oxalato complex compound containing a boron atom and / or a phosphorus atom, as long as the effects of the present invention are not significantly impaired. And film forming agents such as vinylene carbonate (VC); dispersants; various additives such as thickeners.

  As shown in FIGS. 1 and 2, the wound electrode body 20 is formed on one side or both sides (here, both sides as shown in FIG. 3) of the elongated positive electrode current collector 52 along the longitudinal direction. The negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides as shown in FIG. 3) of the positive electrode sheet 50 on which the material layer 54 is formed and the long negative electrode current collector 62. The formed negative electrode sheet 60 is overlapped via two long separator sheets 70 and wound in the longitudinal direction. The positive electrode active material layer non-forming portion 52a (that is, the positive electrode) formed so as to protrude outward from both ends in the winding axis direction of the wound electrode body 20 (referred to as the sheet width direction orthogonal to the longitudinal direction). The portion where the active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer non-formed portion 62a (that is, the portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed). ) Are joined with a positive current collector 42a and a negative current collector 44a, respectively.

Examples of the positive electrode current collector 52 constituting the positive electrode sheet 50 include aluminum foil. Examples of the positive electrode active material included 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 can include 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) and other (eg, graphite) carbon materials can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) can be used.

The positive electrode active material is typically particulate. The average particle size of the particulate positive electrode active material is not particularly limited, but is usually 20 μm or less (typically 1 μm to 20 μm, for example, 5 μm to 15 μm). In this specification, the “average particle diameter” means a particle diameter (median diameter) corresponding to a cumulative 50% from the fine particle side in a particle size distribution measured by a general laser diffraction / light scattering method. Say. Further, the BET specific surface area of the positive electrode active material is not particularly limited, but is usually 0.1 m ² / g or more (typically 0.7 m ² / g or more, for example 0.8 m ² / g or more), On the other hand, it is usually 5 m ² / g or less (typically 1.3 m ² / g or less, for example 1.2 m ² / g or less).

The average thickness per one surface of the positive electrode active material layer 54 is not particularly limited, but is, for example, 20 μm or more (typically 40 μm or more, preferably 50 μm or more), and 100 μm or less (typically 80 μm or less). is there. The density of the positive electrode active material layer 54 is not particularly limited, but is, for example, 1 g / cm ³ or more (typically 1.5 g / cm ³ or more), on the other hand, for example, 4 g / cm ³ or less (typical Is 3.5 g / cm ³ or less).

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

The negative electrode active material is typically particulate. The average particle size of the particulate negative electrode active material is not particularly limited, but is usually 50 μm or less (typically 20 μm or less, for example, 1 μm to 20 μm, preferably 5 μm to 15 μm). The BET specific surface area of the negative electrode active material is not particularly limited, but is usually 1 m ² / g or more (typically 2.5 m ² / g or more, for example, 2.8 m ² / g or more), Usually, it is 10 m ² / g or less (typically 3.5 m ² / g or less, for example, 3.4 m ² / g or less).

The thickness per side of the negative electrode active material layer 64 is not particularly limited, but is usually 40 μm or more (typically 50 μm or more), and is usually 100 μm or less (typically 80 μm or less). Further, the density of the negative electrode active material layer 64 is not particularly limited, but is usually 0.5 g / cm ³ or more (typically 1 g / cm ³ or more), and usually 2 g / cm ³ or less (typical) Is 1.5 g / cm ³ or less.

  As the separator 70, for example, a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, or polyamide can be used. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). The thickness of the porous sheet is not particularly limited, but is usually 10 μm or more, typically 15 μm or more, for example, 17 μm or more. On the other hand, the thickness of the porous sheet is usually 40 μm or less, typically 30 μm or less, for example, 25 μm or less.

  FIG. 3 is a schematic cross-sectional view showing a part of a structure in which the positive electrode 50 and the negative electrode 60 are stacked with the separator 70 interposed therebetween in the wound electrode body 20. In the present embodiment, as shown in FIG. 3, the wound electrode body 20 includes a first heat-resistant layer 81 and a negative electrode active material layer of the negative electrode 60 between the positive electrode active material layer 54 of the positive electrode 50 and the separator 70. A second heat-resistant layer 82 is provided between the separator 64 and the separator 70.

The first heat-resistant layer 81 may be a layer provided on the positive electrode active material layer 54 or a layer provided on the main surface of the separator 70 on the positive electrode 50 side.
The second heat-resistant layer 82 may be a layer provided on the negative electrode active material layer 64, or may be a layer provided on the main surface of the separator 70 on the negative electrode 60 side.
Therefore, the first heat-resistant layer 81 and the second heat-resistant layer 82 can be formed according to a known method.

The first heat-resistant layer 81 and the second heat-resistant layer 82 each contain an inorganic filler and a binder.
As the inorganic filler, an insulating inorganic filler used for a heat-resistant layer provided in an electrode body of a secondary battery of a conventional lithium ion secondary battery may be used. Examples of inorganic fillers include inorganic oxides such as alumina (Al ₂ O ₃ ), magnesia (MgO), silica (SiO ₂ ), titania (TiO ₂ ), nitrides such as aluminum nitride and silicon nitride, calcium hydroxide Metal hydroxides such as magnesium hydroxide and aluminum hydroxide, mica, talc, boehmite, zeolite, apatite, kaolin and other clay minerals, and glass fibers. Of these, alumina, boehmite, and magnesia are preferably used. These inorganic fillers have a high melting point and excellent heat resistance. It also has a relatively high Mohs hardness and excellent mechanical strength and durability. Furthermore, since it is relatively inexpensive, raw material costs can be suppressed.
The ratio of the inorganic filler in the 1st heat resistant layer 81 and the 2nd heat resistant layer 82 is 50 mass% or more, for example, Preferably, it is 70 mass%-95 mass%.
Examples of the binder include styrene butadiene rubber (SBR); polyolefin such as polyethylene (PE); cellulose resin such as carboxycellulose (CMC); polyvinyl alcohol (PVA); polyalkylene oxide such as polyethylene oxide (PEO); acrylic acid Polymers of acrylic and methacrylic monomers such as methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methyl methacrylate, 2-ethylhexyl acrylate, butyl acrylate (especially homopolymers); Fluorine resins such as vinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) can also be used.

In the present embodiment, the lithium ion secondary battery 100 includes any of the following configurations (A) and (B).
Configuration (A): The permeability of the non-aqueous electrolyte of the positive electrode active material layer 54 is higher than the permeability of the non-aqueous electrolyte of the negative electrode active material layer 64 and the non-binding property of the binder contained in the first heat-resistant layer 81. The water electrolyte retainability is higher than the nonaqueous electrolyte retainability of the binder contained in the second heat-resistant layer 82.
Configuration (B): The permeability of the non-aqueous electrolyte of the positive electrode active material layer 54 is lower than the permeability of the non-aqueous electrolyte of the negative electrode active material layer 64 and the non-binding property of the binder contained in the first heat-resistant layer 81. The water electrolyte retainability is lower than the nonaqueous electrolyte retainability of the binder contained in the second heat-resistant layer 82.

  The method for evaluating the permeability of the non-aqueous electrolyte solution of the positive electrode active material layer 54 and the negative electrode active material layer 64 is not particularly limited. For example, the non-aqueous electrolyte solution is applied to each active material layer having a predetermined volume at a constant pressure. It can be evaluated by allowing it to flow in and measuring the flow velocity at that time. Alternatively, for example, the evaluation can be performed by flowing a non-aqueous electrolyte into each active material layer having a predetermined volume at a constant speed and measuring the pressure at that time.

  There are no particular restrictions on the method for evaluating the retention of the binder contained in the first heat-resistant layer 81 and the non-aqueous electrolyte of the binder contained in the second heat-resistant layer 82. For example, the binder is non-aqueous electrolyzed. It is immersed in a liquid and can be evaluated from a change in weight before and after immersion. Alternatively, for example, an indicator such as a dissolution parameter (SP value) may be used. When using the SP value, it can be said that the closer the SP value of the non-aqueous electrolyte solution is to the SP value of the binder, the higher the non-aqueous electrolyte retention of the binder. There are various measurement methods for SP value (for example, a method for estimating from a physical property value or a method for estimating from a molecular structure), but the measurement method is not particularly limited, and a known data collection such as a handbook is used. The values disclosed in the above may be used for evaluation.

  When charging / discharging is performed at a high rate, the electrode body expands and contracts as charge carriers are stored and released during charging / discharging, and the nonaqueous electrolyte is moved out of the electrode body due to the expansion and contraction of the electrode body. Can be spilled. When this outflow occurs excessively, the salt concentration in the electrode body decreases. Alternatively, the composition of the electrolytic solution in the electrode body is uneven (salt concentration). As a result, the internal resistance of the lithium ion secondary battery increases.

Therefore, in order to suppress such an increase in internal resistance, in the present embodiment, the lithium ion secondary battery 100 includes the above configuration (A) or (B).
Here, a case where the lithium ion secondary battery 100 includes the above configuration (A) will be described. In the case of the configuration (A), a first heat resistance containing a binder having a high nonaqueous electrolyte retention (hereinafter also referred to as “liquid retention”) on the positive electrode active material layer 54 side having a high nonaqueous electrolyte permeability. The layer 81 is present, and the second heat-resistant layer 82 containing a binder having low liquid retention is present on the negative electrode active material layer 64 side having low permeability of the nonaqueous electrolytic solution. In general, when the permeability of the non-aqueous electrolyte in the active material layer is high, the non-aqueous electrolyte tends to be excessively discharged. However, the presence of the first heat-resistant layer 81 containing a highly liquid-retaining binder on the positive electrode active material layer 54 side allows the non-aqueous electrolyte discharged from the positive electrode active material layer 54 to be retained to some extent, Thereby, discharge | emission of a non-aqueous electrolyte can be suppressed in the positive electrode active material layer 54 side. As a result, it is possible to suppress excessive discharge of the nonaqueous electrolytic solution to the outside of the electrode body 20. On the other hand, since the second heat-resistant layer 82 containing a binder with low liquid retention is present on the negative electrode active material layer 64 side where the nonaqueous electrolyte is low in permeability, nonaqueous electrolysis is present on the negative electrode active material layer 64 side. The discharge of the liquid is relatively accelerated. Therefore, although the positive electrode active material layer 54 and the negative electrode active material layer 64 have different nonaqueous electrolyte permeability, the nonaqueous water from the negative electrode active material layer 64 side covered with the second heat-resistant layer 82 is used. The dischargeability of the electrolytic solution can be made close to the dischargeability of the nonaqueous electrolytic solution from the positive electrode active material layer 54 side covered with the first heat-resistant layer 81, and can be made comparable. The closer the dischargeability of the nonaqueous electrolyte from the negative electrode active material layer 64 side and the dischargeability of the nonaqueous electrolyte solution from the positive electrode active material layer 54 side, the more uneven the composition of the electrolyte in the electrode body. Can be suppressed.
The same principle applies when the lithium ion secondary battery 100 includes the above-described configuration (B). That is, the second heat-resistant layer 82 containing a binder having a high liquid retaining property exists on the negative electrode active material layer 64 side having a high nonaqueous electrolyte permeability, and the positive electrode active material layer 54 having a low nonaqueous electrolyte permeability. A first heat-resistant layer 81 including a binder having low liquid retention is present on the side. The presence of the second heat-resistant layer 82 containing a binder having a high liquid retaining property on the negative electrode active material layer 64 side can suppress discharge of the non-aqueous electrolyte from the negative electrode active material layer 64 side. It is possible to suppress excessive discharge of the nonaqueous electrolytic solution on the negative electrode active material layer 64 side where the electrolytic solution has high permeability. In addition, the presence of the first heat-resistant layer 81 containing a binder with low liquid retention on the positive electrode active material layer 54 side where the non-aqueous electrolyte has low permeability allows the non-aqueous electrolyte solution on the positive electrode active material layer 54 side. Emissions are relatively promoted. Thus, the non-aqueous electrolyte can be discharged from the negative electrode active material layer 64 side covered with the second heat-resistant layer 82, and the non-aqueous electrolyte from the positive electrode active material layer 54 side covered with the first heat-resistant layer 81. The discharge property of the electrolytic solution can be made closer (and the same level can be obtained), and the occurrence of uneven composition of the electrolytic solution in the electrode body can be suppressed.
Thus, the lithium ion secondary battery 100 according to this embodiment includes any one of the above-described configurations (A) and (B), thereby increasing the internal resistance when charging and discharging are repeated at a high rate. Can be suppressed.

Further, FIG. 4 shows the actual examination results of the inventor.
FIG. 4 shows that the permeability of the non-aqueous electrolyte of the negative electrode active material layer is higher than the permeability of the non-aqueous electrolyte of the positive electrode active material layer, and ethylene carbonate (EC), dimethyl carbonate (DMC) are used as solvents of the non-aqueous electrolyte. ) And diethyl carbonate (DEC) mixed solvent (SP value 20), and lithium using PVDF (SP value 18.5) as a binder contained in the second heat-resistant layer between the separator and the negative electrode active material layer It is an examination result about the case where the kind of binder contained in the 1st heat-resistant layer between a separator and a negative electrode active material layer is changed in an ion secondary battery.
The binders included in the first heat resistance are shown in the following table.

  FIG. 4 is a graph showing the relationship between the number of charge / discharge cycles and the rate of increase in resistance when the charge / discharge cycle of charging at 30C for 10 seconds, resting for 5 seconds, and discharging at 4C for 75 seconds is performed at least 3000 cycles. . The battery (1) is a reference battery and does not have the first heat-resistant layer. From comparison of the batteries (2) to (9), as the SP value of the binder contained in the first heat-resistant layer on the side of the positive electrode active material layer having low permeability of the nonaqueous electrolyte solution is smaller, charging / discharging is performed at a higher rate. It can be seen that the increase in resistance can be suppressed when repeated. That is, the lower the non-aqueous electrolyte retention of the binder contained in the first heat-resistant layer on the side of the positive electrode active material layer with low non-aqueous electrolyte permeability, the more the resistance increase can be suppressed. Recognize. And about SP value used as the parameter | index of the retention property of the non-aqueous electrolyte of a binder, SP value (PVDF: 18.5) of the binder contained in a 2nd heat resistant layer WHEREIN: The binder contained in a 1st heat resistant layer It can be seen that a smaller SP value is effective in suppressing an increase in resistance.

  Further, referring to the above examination results, among the binders included in the first heat-resistant layer and the second heat-resistant layer, the SP value of the binder having higher non-aqueous electrolyte retention is that of the non-aqueous electrolyte. The difference between the SP value and the SP value of the non-aqueous electrolyte is preferably 2.5 or more. preferable.

  The lithium ion secondary battery 100 configured as described above can be used for various applications. Suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). The lithium ion secondary battery 100 can also be used in the form of a battery pack typically formed by connecting a plurality of lithium ion secondary batteries 100 in series and / or in parallel.

  As an example, the rectangular lithium ion secondary battery 100 including the 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 stacked electrode body. The lithium ion secondary battery can also be configured as a cylindrical lithium ion secondary battery.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 wound 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 Current Collector 52a Positive Electrode Active Material Layer Non-Forming 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 81 First heat resistant layer 82 Second heat resistant layer 100 Lithium ion secondary battery

Claims (1)

An electrode body having a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes;
A non-aqueous electrolyte,
A lithium ion secondary battery comprising:
The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector,
The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector,
The electrode body has a first heat-resistant layer between the positive electrode active material layer and the separator, and a second heat-resistant layer between the negative electrode active material layer and the separator,
Each of the first heat-resistant layer and the second heat-resistant layer contains an inorganic filler and a binder,
A lithium ion secondary battery comprising the following configuration (A) or (B).
(A) The permeability of the non-aqueous electrolyte of the positive electrode active material layer is higher than the permeability of the non-aqueous electrolyte of the negative electrode active material layer, and the binder contained in the first heat-resistant layer The non-aqueous electrolyte retainability is higher than the non-aqueous electrolyte retainability of the binder contained in the second heat-resistant layer.
(B) The permeability of the non-aqueous electrolyte of the positive electrode active material layer is lower than the permeability of the non-aqueous electrolyte of the negative electrode active material layer, and the binder contained in the first heat-resistant layer The non-aqueous electrolyte retainability is lower than the non-aqueous electrolyte retainability of the binder contained in the second heat-resistant layer.

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