JP7365566B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a non-aqueous electrolyte secondary battery in which the wettability of a separator and an insulating layer to a non-aqueous electrolyte is appropriately adjusted.

In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries have been used as portable power sources for computers and mobile devices, as well as EVs (electric vehicles) and HVs (hybrid vehicles) because they are lightweight and have high energy density. It is widely used as a power source for driving vehicles such as , PHV (plug-in hybrid vehicle), etc.

A typical non-aqueous electrolyte secondary battery for this type of use includes a positive electrode having a positive electrode current collector and a positive electrode composite material layer disposed on the surface of the positive electrode current collector, a negative electrode current collector and the negative electrode collector. It includes a negative electrode having a negative electrode composite layer disposed on the surface of the electric body, and a separator that insulates the positive electrode and the negative electrode. The positive electrode current collector may have a positive electrode current collector exposed portion where the positive electrode current collector is exposed without being provided with a positive electrode composite material layer. A positive electrode having a positive electrode current collector having such a configuration is disclosed in, for example, Patent Document 1.
Patent Document 1 describes a positive electrode active layer provided on a metal core foil as a positive electrode current collector, and a positive electrode active layer provided on the metal core foil while leaving an uncoated portion of the positive electrode mixture (an exposed portion of the positive electrode current collector). A positive electrode is disclosed that includes a substance mixture layer (positive electrode mixture layer) and an insulating layer provided in a portion where the positive electrode mixture is not coated. Patent Document 1 states that by providing such an insulating layer, internal short circuits between the positive electrode and the negative electrode can be prevented.

Japanese Patent Application Publication No. 2004-259625

By the way, non-aqueous electrolyte secondary batteries for the above-mentioned applications are required to have high-rate output characteristics that output a large current in one charge/discharge. In a non-aqueous electrolyte secondary battery, charging and discharging are performed by charge carriers (for example, lithium ions) in the electrolyte passing through the pores of the separator and moving back and forth between the two electrodes. Therefore, in order to improve high-rate output characteristics in a non-aqueous electrolyte secondary battery, it is necessary to impregnate the positive and negative electrode composite material layers with a sufficient amount of electrolyte. However, when an insulating layer is provided on the positive electrode as described above, the contact area between the positive electrode composite material layer and the electrolyte becomes small, making it impossible to supply sufficient electrolyte to the positive electrode composite material layer, resulting in high rate There was a risk that battery resistance would increase due to charging and discharging. Such an increase in battery resistance is undesirable because it causes a decrease in the high rate output characteristics of the battery.

Further, with the spread of non-aqueous electrolyte secondary batteries, demands for battery safety are increasing further. For example, there is a need for a suitable structure for suppressing a rise in battery temperature in case the battery temperature rises due to overcharging or the like.
Therefore, the present invention was created to solve the above problems, and its purpose is to develop a technology that can both improve high-rate performance and improve safety of non-aqueous electrolyte secondary batteries. It is to provide.

The present inventors focused on the wettability of the separator and the insulating layer with respect to the non-aqueous electrolyte in a non-aqueous electrolyte secondary battery configured to include an insulating layer on the positive electrode. The present inventors have discovered that increasing the wettability of the separator with respect to the non-aqueous electrolyte can improve the high-rate performance of the non-aqueous electrolyte secondary battery, but can also reduce overcharge resistance. As a result of intensive studies by the present inventors, by adjusting the balance between the wettability of the separator to the non-aqueous electrolyte and the wettability of the insulating layer to the non-aqueous electrolyte, high-rate The inventors have discovered that it is possible to achieve both improved performance and improved safety, and have completed the present invention.

According to the technology disclosed herein, a non-aqueous electrolyte secondary battery is provided that includes an electrode body having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and a non-aqueous electrolyte.
The positive electrode includes a positive electrode current collector, a positive electrode composite material layer disposed on the surface of the positive electrode current collector, leaving an exposed portion of the positive electrode current collector where the positive electrode current collector is exposed, and the positive electrode composite material layer. an insulating layer containing an inorganic filler disposed along a boundary between one end of the positive electrode composite material layer and the exposed positive electrode current collector in one predetermined width direction of the electrode. The contact angle of the nonaqueous electrolyte on the surface of the separator is 45° or more and 61° or less, and the contact angle of the nonaqueous electrolyte on the surface of the insulating layer is 3.9° or more and 12° or less. .
According to this configuration, a non-aqueous electrolyte secondary battery is provided that is both improved in high-rate performance and improved in safety.

FIG. 1 is a cross-sectional view schematically showing the internal structure of a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 2 is a schematic diagram showing the configuration of a wound electrode body of a non-aqueous electrolyte secondary battery according to an embodiment. FIG. 1 is a cross-sectional view schematically showing the configuration of a positive electrode of a non-aqueous electrolyte secondary battery according to an embodiment.

Embodiments according to the present invention will be described below. In addition, matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention (for example, the general configuration and manufacturing process of a non-aqueous electrolyte secondary battery that do not characterize the present invention) can be understood as a matter of design by a person skilled in the art based on the prior art in the field. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.
In this specification, the notation "A to B" indicating a numerical range means greater than or equal to A and less than or equal to B, and includes those greater than A and less than B.

Note that in this specification, the term "secondary battery" refers to general electricity storage devices that can be repeatedly charged and discharged, and is a term that includes so-called storage batteries and electricity storage elements such as electric double layer capacitors. A "nonaqueous electrolyte secondary battery" is a secondary battery that achieves charging and discharging using a nonaqueous electrolyte as a charge carrier. The term "active material" refers to a substance that can reversibly absorb and release chemical species that serve as charge carriers in secondary batteries. Hereinafter, the present invention will be explained in detail by taking as an example a case where the non-aqueous electrolyte secondary battery is a lithium ion secondary battery, but it is intended that the present invention be limited to what is described in such embodiments. It's not a thing.

First, the configuration of the non-aqueous electrolyte secondary battery disclosed herein will be explained with reference to FIG.
As illustrated, the non-aqueous electrolyte secondary battery 100 includes a flat wound electrode body 20, a flat square battery case (i.e., outer container) 30, and a non-aqueous electrolyte 80. . Each will be explained below.

The battery case 30 is a container that accommodates the wound electrode body 20. As shown in the figure, the battery case 30 is a flat square container, and includes a square case body 32 with an open top and a plate-shaped lid 34 that closes the opening of the case body 32. ing. The battery case 30 may be made of a metal material (eg, aluminum, aluminum alloy, stainless steel, etc.) that has the required strength.
The battery case 30 includes a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 configured to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher. It is provided. Further, the battery case 30 is provided with a liquid injection hole (not shown), and the non-aqueous electrolyte 80 is injected into the battery case 30 through this liquid injection hole. The positive electrode terminal 42 is electrically connected to the positive current collector plate 42a. The negative electrode terminal 44 is electrically connected to the negative current collector plate 44a.

The non-aqueous electrolyte 80 includes a non-aqueous solvent and a supporting salt. The types of the non-aqueous solvent and supporting salt are not particularly limited, and may be the same as those used as electrolytes in conventional non-aqueous electrolyte secondary batteries.
Suitable examples of nonaqueous solvents include aprotic solvents such as carbonates, esters, and ethers. Among them, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC), and these carbonates are fluorine-containing. It is preferable to contain one or more types of fluorinated chain or fluorinated cyclic carbonates.
A suitable example of the supporting salt is, for example, a lithium salt such as LiPF ₆ or LiBF ₄ .
The concentration of lithium salt in the electrolyte can be, for example, 0.8 to 1.3 mol/L. The non-aqueous electrolyte 80 can also contain additives such as a film forming agent and an overcharge prevention agent.

The wound electrode body 20 is a power generation element housed inside the battery case 30 while being covered with an insulating film (not shown) or the like.
As shown in FIGS. 1 and 2, the wound electrode body 20 includes a positive electrode 50 in the form of a long sheet, a negative electrode 60 in the form of a long sheet, and a separator 70 in the form of a long sheet. The wound electrode body 20 has a configuration in which a positive electrode 50 and a negative electrode 60 are stacked on top of each other with two separators 70 in between and wound in the longitudinal direction.

The positive electrode 50 includes a foil-shaped positive electrode current collector 52 (for example, aluminum foil) and a positive electrode composite material layer 54 formed on the surface (preferably both surfaces) of the positive electrode current collector 52. Further, the positive electrode current collector 52 has a portion where the positive electrode current collector 52 is exposed without the positive electrode composite material layer 54 formed thereon (ie, a positive electrode current collector exposed portion 52a). In other words, the positive electrode composite material layer 54 is formed on the surface of the positive electrode current collector 52, leaving the positive electrode current collector exposed portion 52a where the positive electrode current collector 52 is exposed. As illustrated, the positive electrode current collector exposed portion 52a extends from one end of the wound electrode body 20 in the winding axis direction Y (that is, in the sheet width direction perpendicular to the longitudinal direction). It is formed to protrude outward.
The positive electrode 50 includes an insulating layer 56 disposed on the positive electrode current collector 52. The insulating layer 56 is arranged along the edge of the positive electrode composite material layer 54, and is located between the positive electrode composite material layer 54 and the positive electrode current collector exposed portion 52a in the surface direction of the positive electrode 50. . The insulating layer 56 is arranged at the boundary between the positive electrode composite material layer 54 and the positive electrode current collector exposed portion 52a in the Y direction. The insulating layer 56 may be placed on both sides of the positive electrode current collector 52, or may be placed on one side.
A positive electrode current collector plate 42a is bonded to the positive electrode current collector exposed portion 52a.

The end structure of the positive electrode composite material layer 54 will be described with reference to FIGS. 2 and 3 as appropriate.
As shown in the figure, the positive electrode composite material layer 54 is provided closer to the main body portion A1 and the positive electrode current collector exposed portion 52a than the main body portion A1, and is provided at the end (end portion) of the positive electrode composite material layer 54 in the Y1 direction. E2).
The main body portion A1 is formed on the surface of the positive electrode current collector 52. The main body portion A1 has a substantially constant thickness. The average thickness of the main body portion A1 is not particularly limited, but can be approximately 10 μm to 200 μm, typically 20 μm to 150 μm, for example 40 μm to 100 μm. The main body portion A1 includes the center of the positive electrode composite material layer 54 in the width direction Y.

End portion A2 extends from main body portion A1. The end portion A2 is a region sandwiched between the end portion (end portion E1) in the Y1 direction of the main body portion A1 and the end portion E2. In cross-sectional view, the end portion A2 has an inclined surface S whose thickness decreases continuously as it approaches the end portion of the positive electrode current collector 52 in the Y1 direction (i.e., the side of the positive electrode current collector exposed portion 52a). . At least a portion of the inclined surface S is covered with an insulating layer 56.
The length of the end portion A2 in the Y direction is typically shorter than the length of the main body portion A1 in the Y direction.

The positive electrode composite material layer 54 contains a granular positive electrode active material. Examples of positive electrode active materials include lithium nickel cobalt manganese composite oxides (e.g., LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , etc.), lithium nickel, which are capable of reversibly intercalating and deintercalating lithium ions. Lithium transition metals such as composite oxides (e.g., LiNiO ₂ , etc.), lithium cobalt composite oxides (e.g., LiCoO ₂ , etc.), lithium nickel manganese composite oxides (e.g., LiNi _0.5 Mn _1.5 O ₄ , etc.) Examples include composite oxides. These can be used alone or in combination of two or more. When the entire solid content of the positive electrode composite material layer 54 is 100% by mass, the positive electrode active material may occupy approximately 50% by mass or more, for example, 80% by mass or more.
The positive electrode mixture layer 54 may contain components other than the active material, such as a conductive material, a binder, lithium phosphate, and the like. As the conductive material, carbon black such as acetylene black (AB) and other carbon materials (eg, graphite, etc.) can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) can be used.

As illustrated, the insulating layer 56 is located between the main body portion A1 of the positive electrode composite material layer 54 and the positive electrode current collector exposed portion 52a in the Y direction. The insulating layer 56 is located closer to the Y1 direction than the main body portion A1. The length of the insulating layer 56 in the Y direction is not particularly limited, but is typically approximately the same as or longer than the length of the end A2 of the positive electrode composite layer 54 in the Y direction.

In cross-sectional view, the insulating layer 56 is formed so that at least a portion thereof overlaps the surface of the inclined surface S of the positive electrode composite material layer 54.
According to the technology disclosed herein, by adjusting the height of the positive electrode composite material layer 54 and the height of the insulating layer 56 to a suitable range, it is possible to more efficiently impregnate the positive electrode composite material layer 54 with the nonaqueous electrolyte. can.
As shown in FIG. 3, the height H1 of the positive electrode composite material layer 54 is the length in the stacking direction X from the surface of the positive electrode current collector 52 to the surface of the main body portion A1. The height H1 may be approximately the same as the average thickness of the main body portion A1. The height H2 of the insulating layer 56 is the maximum length in the X direction from the surface of the positive electrode current collector 52 to the surface of the insulating layer 56, as illustrated.
The ratio (H2/H1) between the height H1 of the positive electrode composite material layer 54 and the height H2 of the insulating layer 56 is set to 1 or less (for example, 1 ), preferably 0.96 or less. The ratio (H2/H1) can be, for example, 0.95 or less, 0.9 or less, 0.85 or less, 0.8 or less, or 0.75 or less. By setting the ratio (H2/H1) in such a range, a part of the positive electrode composite layer 54 (typically end portion A2) can be exposed to the non-aqueous electrolyte, and capillary action The positive electrode mixture layer 54 can be impregnated with the non-aqueous electrolyte. On the other hand, from the viewpoint of efficiently flowing the electrolyte into the positive electrode composite layer 54 by capillarity, the ratio (H2/H1) can be set to 0.6 or more (for example, 0.62 or more), and 0.65 It is preferably at least 0.7, and more preferably at least 0.71 (for example, 0.71 or more). By setting the ratio (H2/H1) within this range, the effects of the present invention can be more suitably achieved.

Although the height H2 of the insulating layer 56 is not particularly limited, it can be set to 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more from the viewpoint of sufficiently suppressing short circuits between the positive electrode 50 and the negative electrode 60. Further, from the viewpoint of workability, the thickness of the insulating layer 56 is preferably 65 μm or less, more preferably 35 μm or less.

The insulating layer 56 contains an inorganic filler. Examples of the inorganic filler include oxides such as alumina, magnesia, silica, and titania, clay minerals such as boehmite, mullite, mica, talc, zeolite, apatite, and kaolin, and quartz glass. These can be used alone or in combination of two or more. When the entire solid content of the insulating layer 56 is 100% by mass, the inorganic filler may account for approximately 50% by mass or more, for example, 80% by mass or more.
The insulating layer 56 may contain arbitrary components other than the inorganic filler, such as a binder and various additive components. As the binder, for example, polyolefin binders such as polyvinylidene fluoride (PVdF) and polyethylene (PE), polytetrafluoroethylene (PTFE), acrylic resin, and styrene-butadiene rubber (SBR) can be used. The binder may be of the same type as the binder of the positive electrode composite material layer 54, or may be of a different type.

The contact angle of the nonaqueous electrolyte on the surface of the insulating layer 56 is 3.9° or more and 12° or less. As a means for realizing such a contact angle, for example, the surface of the insulating layer 56 may be subjected to a liquid-repellent treatment against the non-aqueous electrolyte. Specifically, by coating the surface of the insulating layer 56 with a liquid repellent (oil repellent) (described later) that has the property of repelling the non-aqueous electrolyte, the size of the contact angle (i.e., the degree of wettability) can be adjusted. Can be adjusted. Alternatively, the contact angle can be adjusted by appropriately adjusting the amount of binder in the insulating layer 56.
By setting the wettability of the insulating layer 56 to the non-aqueous electrolyte (ie, the contact angle described above) within this range, the efficiency of impregnating the positive electrode composite layer 54 with the non-aqueous electrolyte can be improved. Further, such a configuration can improve both high-rate performance and safety in the non-aqueous electrolyte secondary battery 100.

As shown in FIGS. 1 and 2, the negative electrode 60 includes a foil-shaped negative electrode current collector 62 (for example, copper foil) and a negative electrode composite material formed on the surface (preferably both surfaces) of the negative electrode current collector 62. layer 64. Further, the negative electrode current collector 62 has a portion where the negative electrode current collector 62 is exposed without the negative electrode composite material layer 64 formed thereon (namely, a negative electrode current collector exposed portion 62a). As illustrated, the negative electrode current collector exposed portion 62a is formed to protrude outward from one end in the Y direction.

The negative electrode composite material layer 64 contains a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, and soft carbon, which are capable of reversibly intercalating and deintercalating lithium ions. These can be used alone or in combination of two or more. When the entire solid content of the negative electrode composite material layer 64 is 100% by mass, the negative electrode active material may occupy approximately 50% by mass or more, for example, 80% by mass or more.
The negative electrode composite 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) can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

Separator 70 is interposed between positive electrode 50 and negative electrode 60 to prevent these electrodes from coming into direct contact. Although not shown, a plurality of fine holes are formed in the separator 70, and charge carriers (in the case of a lithium ion secondary battery, lithium ions) are configured to move. For the separator 70, a resin sheet or the like having the required heat resistance is used. For example, porous resin sheets made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide are suitable. The separator 70 may have a single-layer structure, or may have a laminated structure of two or more layers, for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer.

The contact angle of the nonaqueous electrolyte 80 on the surface of the separator 70 is set to 61° or less. Further, the contact angle is suitably 45° or more, preferably 50° or more, and more preferably 56° or more. As a means for achieving such a contact angle, for example, the surface of the separator 70 may be subjected to a liquid-repellent treatment such as a coating treatment. Specifically, by applying a liquid repellent (oil repellent) having a property of repelling the non-aqueous electrolyte to the surface of the separator 70 facing the positive electrode composite layer 54, the contact angle can be increased. (that is, the degree of wettability) can be adjusted. Examples of the liquid repellent include fluororesin.
If the wettability of the separator 70 with respect to the non-aqueous electrolyte 80 is too high, the separator 70 will absorb the non-aqueous electrolyte 80, which may reduce the impregnation of the non-aqueous electrolyte 80 into the positive electrode composite layer 54. On the other hand, if the wettability of the separator 70 with respect to the non-aqueous electrolyte 80 is too low, a liquid pool may occur, and impregnation of the non-aqueous electrolyte 80 into the positive electrode composite layer 54 may be reduced. By adjusting the wettability of the separator 70 with respect to the non-aqueous electrolyte 80 to an appropriate range, the high-rate performance of the non-aqueous electrolyte secondary battery 100 can be improved.

The nonaqueous electrolyte secondary battery 100 configured as described above includes a separator whose wettability with respect to the nonaqueous electrolyte is appropriately adjusted. In addition, the non-aqueous electrolyte secondary battery includes a positive electrode having an insulating layer whose wettability with respect to the non-aqueous electrolyte is appropriately adjusted. As a result, the non-aqueous electrolyte secondary battery 100 has significantly improved high-rate performance and safety.
The non-aqueous electrolyte secondary battery 100 can be used for various purposes. Suitable applications include driving power sources installed in vehicles such as electric vehicles (EVs), plug-in hybrid vehicles (PHVs), and hybrid vehicles (HVs). The lithium ion secondary battery 100 can also typically be used in the form of a battery pack in which a plurality of batteries are connected in series and/or in parallel.
As an example, a square non-aqueous electrolyte secondary battery 100 including a flat wound electrode body 20 has been described. However, the nonaqueous electrolyte secondary battery can also be configured as a nonaqueous electrolyte secondary battery including a stacked electrode body. Further, the nonaqueous electrolyte secondary battery can also be configured as a cylindrical type, a laminate type, or the like. Furthermore, the technology disclosed herein is also applicable to nonaqueous electrolyte secondary batteries other than lithium ion secondary batteries.
Note that an example of a method for constructing the non-aqueous electrolyte secondary battery 100 is shown in the following example.

Hereinafter, specific test examples related to the technology disclosed herein will be described, but these test examples are not intended to limit the present invention.
<<Example 1: Study of contact angle size>>
<1. Construction of sample battery>
As sample batteries, nonaqueous electrolyte secondary batteries according to Examples 1 to 13 were constructed.
-Example 1-
A lithium nickel cobalt manganese-containing composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ :NCM) as a positive electrode active material, acetylene black (AB) as a conductive aid, and polyfluoride as a binder. A positive electrode paste was prepared by blending vinylidene (PVdF) at a mass ratio of NCM:AB:PVdF = 90:8:2 and kneading it with N-methyl-2-pyrrolidone (NMP) as a solvent.
Boehmite as an inorganic filler and PVdF as a binder were mixed in NMP to prepare an insulating layer paste.
A long aluminum foil with a thickness of 12 μm was prepared as a positive electrode current collector. The positive electrode paste and the insulating layer paste were simultaneously coated on both sides of the aluminum foil using a die coater, dried, and pressed. This coating was performed along the longitudinal direction of the aluminum foil, and the aluminum foil was provided with an uncoated area along one end in the width direction where the positive electrode composite layer was not formed. In this way, a positive electrode including a positive electrode current collector, a positive electrode composite layer, and an insulating layer was prepared. After constructing the sample battery, a liquid repellent having a property of repelling the non-aqueous electrolyte was applied to the surface of the insulating layer so that the contact angle of the non-aqueous electrolyte on the surface of the insulating layer was 3.9°.

Graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener at a mass ratio of C:SBR:CMC=98:1:1. A negative electrode paste was prepared by blending and kneading with ion-exchanged water. A long copper foil with a thickness of 10 μm was prepared as a negative electrode current collector. The negative electrode paste was applied to both sides of the copper foil using a die coater, dried, and pressed. This coating was performed along the longitudinal direction of the copper foil, and the copper foil was provided with an uncoated portion along one end in the width direction where the negative electrode composite material layer was not formed. In this way, a negative electrode including a negative electrode current collector and a negative electrode composite material layer was prepared.

As a separator, a porous polyolefin sheet having a three-layer structure of PP/PE/PP in which polypropylene layers (PP layers) were laminated on both sides of a polyethylene layer (PE layer) was prepared. After constructing the sample battery, a liquid repellent having a property of repelling the non-aqueous electrolyte was applied to the surface of the separator so that the contact angle of the non-aqueous electrolyte on the surface of the separator was 56°.
Next, the positive electrode and the negative electrode were alternately stacked and wound with a separator interposed therebetween, and then crushed to produce a wound electrode body. After electrically connecting the wound electrode body and external terminals (positive electrode terminal, negative electrode terminal), it was housed in a battery case together with a non-aqueous electrolyte. A sample battery according to Example 1 was constructed by sealing the battery case. As the non-aqueous electrolyte, a supporting salt (LiPF ₆ ) dissolved in an organic mixed solvent (EC:EMC:DMC=3:3:4) at a concentration of about 1 mol/L was used.

-Examples 2 to 12-
After constructing the sample battery, a liquid repellent was applied to the surface of the insulating layer so that the contact angle of the nonaqueous electrolyte on the surface of the insulating layer was as shown in Table 1. After constructing the sample battery, a liquid repellent was applied to the surface of the separator so that the contact angle of the nonaqueous electrolyte on the surface of the separator was as shown in Table 1. Sample cells according to Examples 2-12 were otherwise constructed using the materials and procedures used in constructing the sample cells according to Example 1.

-Example 13-
An insulating layer paste was prepared by mixing boehmite as an inorganic filler and PVdF as a binder in NMP. An insulating layer is formed on the surface of the separator by applying such an insulating layer paste on one side of the separator facing the positive electrode and facing the positive electrode composite layer using a gravure roll and drying it. Formed. As the separator, a separator (conventional product) was used in which the contact angle of the nonaqueous electrolyte on the surface of the separator was 11° after construction of the sample battery. Furthermore, in Example 13, the insulating layer was not disposed along one end of the positive electrode composite material layer in one predetermined width direction. A sample cell according to Example 13 was otherwise constructed using the materials and procedures used in constructing the sample cell according to Example 1.

<2. Measurement of high rate resistance increase rate>
Initial charging was performed on the sample batteries according to each of the above examples.
Specifically, at 25° C., constant current charging was performed at a rate of 1/3C until the voltage reached 4.2V, and then constant voltage charging was performed until the current reached 1/50C. Next, constant current discharge was performed at a rate of 1/3C until the voltage reached 3.0V. Note that "1C" means a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode active material in one hour.
Next, the sample battery was subjected to a cycle test in which high-rate charging and discharging were repeated.
First, a sample battery was placed in a constant temperature bath set at 25° C., and the SOC (state of charge) was adjusted to 60%. Next, a predetermined number of charging/discharging cycles were performed in which one cycle was a combination of pulse charging and pulse discharging described below. Then, with the initial (first cycle) IV resistance as 100%, the IV resistance of the sample battery after the predetermined number of cycles was calculated as a "high rate resistance increase rate." The results are shown in the appropriate column of Table 1.
Pulse charging: Current = 10C, charging time = 80 seconds Pulse discharging: Current = 2C, discharge time = 400 seconds

<3. Evaluation of overcharge resistance>
An overcharge test was conducted on the sample batteries according to each of the above examples.
Specifically, the sample battery was first charged with a constant current at a rate of 1/3C to 4.2V in a temperature environment of 25°C, rested for 5 minutes, and then charged at a rate of 1/3C to 3.0V. Conditioning treatment was performed by discharging a constant current at a rate of . A thermocouple was attached to the center of the outside of the battery case of each sample battery. Next, the sample battery was overcharged to 25V at a constant current of 10C in a temperature environment of -10°C. Then, the positive electrode and the negative electrode were brought into conduction to shut down the sample battery. The overcharge resistance of each sample battery was evaluated by measuring the temperature rise rate (ΔT) due to heat generation of the battery 30 seconds after the sample battery was shut down.
The results are shown in the appropriate column of Table 1. Note that sample batteries whose ΔT was less than 10° C. were evaluated as having overcharge resistance. Sample batteries with ΔT of 10° C. or higher were evaluated as having no overcharge resistance. In Table 1, "〇" indicates overcharge resistance, and "x" indicates no overcharge resistance.

As shown in Table 1, from the comparison of Examples 1 to 13, it was confirmed that as the contact angle of the nonaqueous electrolyte on the surface of the separator was increased, the high rate resistance increase rate tended to decrease. When the wettability of the separator with respect to the non-aqueous electrolyte is reduced, excessive absorption of the non-aqueous electrolyte in the separator is suppressed and impregnation of the non-aqueous electrolyte in the positive electrode composite layer is promoted, thereby increasing high-rate resistance. The rate of increase can be reduced. It was also confirmed that as the contact angle of the nonaqueous electrolyte on the surface of the insulating layer was increased, the high rate resistance increase rate tended to decrease. This is because lowering the wettability of the insulating layer to the non-aqueous electrolyte can suppress excessive absorption of the non-aqueous electrolyte in the insulating layer and promote impregnation of the non-aqueous electrolyte in the positive electrode composite layer. it is conceivable that.

Comparing Examples 1 to 7 and Examples 8 to 12, it was confirmed that the sample batteries in which the contact angle of the nonaqueous electrolyte on the surface of the insulating layer was within a predetermined range had good overcharge resistance. In particular, in Examples 1 to 7, both suppression of the high-rate resistance increase rate and good overcharge resistance were achieved. On the other hand, as seen in Examples 9 to 12, it was confirmed that if the wettability of the insulating layer with respect to the non-aqueous electrolyte was reduced too much, the overcharge resistance could be reduced. If such wettability is made too low, liquid pools are likely to occur. In this case, during overcharging, the sample battery starts to generate heat from a relatively low temperature, which may cause a delay in shutting down the battery. As a result, the temperature rise after shutdown accelerates, and it is thought that the overcharge resistance of the battery decreases.

<<Example 2: Examination of the ratio of the height of the insulating layer and the height of the positive electrode composite layer>>
<1. Construction of sample battery>
-Examples 14 to 18-
A porous polyolefin sheet with a three-layer structure of PP/PE/PP was prepared as a separator. After constructing the sample battery, a liquid repellent having a property of repelling the nonaqueous electrolyte was applied to the surface of the separator so that the contact angle of the nonaqueous electrolyte on the surface of the separator was 61°.
The above materials were used as separators. The positive electrode paste and the insulating layer paste were applied to an aluminum foil serving as a positive electrode current collector so that the ratio of the height of the insulating layer to the height of the positive electrode composite layer was the value shown in Table 2. Furthermore, after constructing the sample battery, a liquid repellent having a property of repelling the non-aqueous electrolyte was applied to the surface of the insulating layer so that the contact angle of the non-aqueous electrolyte on the surface of the insulating layer was 12°. Sample cells according to Examples 14-18 were otherwise constructed using the materials and procedures used in constructing the sample cells according to Example 1.

<2. Measurement of high rate resistance increase rate>
The high rate resistance increase rate (%) of the sample batteries of Examples 14 to 18 was measured in the same manner as in Example 1 above. Then, the ratio of the high-rate resistance increase rate (%) of the sample batteries according to Examples 14 to 17 to the high-rate resistance increase rate (%) of the sample battery according to Example 18 was calculated as the "high-rate resistance increase ratio". The results are shown in the appropriate column of Table 2.

The above example shows that the increase in high rate resistance increase rate (%) is suppressed when the contact angle of the non-aqueous electrolyte on the separator surface and the contact angle of the non-aqueous electrolyte on the insulating layer surface are within a predetermined range. 1.
As shown in Table 2, when comparing Examples 14 to 18, it was confirmed that when the height of the insulating layer was lower than the positive electrode composite layer, the high rate resistance increase rate tended to decrease. Furthermore, as seen in Examples 15 to 17, it was confirmed that when the height ratio was within the range of 0.71 to 0.90, the effect of reducing the high rate increase rate of resistance could be more preferably achieved.
Although detailed data is not shown, it has been confirmed that all of the sample batteries of Examples 14 to 18 have good overcharge resistance.

From the above, in a non-aqueous electrolyte secondary battery including an electrode body having a structure in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween, and a non-aqueous electrolyte, a positive electrode current collector is used as a positive electrode, and the positive electrode collector is A positive electrode composite material layer disposed on the surface of the positive electrode current collector, leaving an exposed portion of the positive electrode current collector where the electric body is exposed, and the positive electrode composite material layer in one predetermined width direction of the positive electrode composite material layer. and an insulating layer containing an inorganic filler disposed along the boundary between one end of the separator and the exposed portion of the positive electrode current collector, and the contact angle of the non-aqueous electrolyte on the surface of the separator is 45° or more and 61° or less. It was also shown that when the contact angle of the non-aqueous electrolyte on the surface of the insulating layer is set to 3.9° or more and 12° or less, excellent high-rate performance and excellent safety can be achieved.

Although the present invention has been described in detail above, the above-mentioned embodiments and examples are merely illustrative, and the invention disclosed herein includes various modifications and changes of the above-mentioned specific examples.

20 Wound electrode body 30 Battery case 32 Case body 34 Lid body 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 52 Positive electrode current collector 52a Positive electrode current collector exposed portion 54 Positive electrode composite material Layer 56 Insulating layer 60 Negative electrode 62 Negative current collector 62a Negative current collector exposed portion 64 Negative electrode composite layer 70 Separator 80 Non-aqueous electrolyte 100 Non-aqueous electrolyte secondary battery X Direction Y Direction H1 Height of positive electrode composite layer H2 Insulating layer height A1 Main body A2 End S Slanted surface

Claims (1)

A non-aqueous electrolyte secondary battery comprising an electrode body having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and a non-aqueous electrolyte,
The positive electrode is
a positive electrode current collector;
a positive electrode composite material layer disposed on the surface of the positive electrode current collector, leaving an exposed portion of the positive electrode current collector where the positive electrode current collector is exposed;
an insulating layer containing an inorganic filler disposed along a boundary between one end of the positive electrode composite layer and the exposed positive electrode current collector in one predetermined width direction of the positive electrode composite layer;
Equipped with
The contact angle of the nonaqueous electrolyte on the surface of the separator is 56 ° or more and 61° or less, and the contact angle of the nonaqueous electrolyte on the surface of the insulating layer is 3.9° or more and 12° or less. , non-aqueous electrolyte secondary battery.

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