JP2016115593A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery, the durability against high rate charge and discharge of which is improved.SOLUTION: A nonaqueous electrolyte secondary battery 100 including a wound electrode body 200 and a nonaqueous electrolyte 90 and a battery case 300 is provided. The wound electrode body 200 includes a positive electrode sheet 220, a negative electrode sheet 240, and separator sheets 260, 280. The separator sheets 260, 280 include a base material layer and a heat-resistant porous layer, where the heat-resistant porous layer contains a filler and a binder. The solubility parameter of the binder located in the winding center of the wound electrode body 200 is closer to that of the nonaqueous electrolyte 90, compared with the solubility parameter of the binder located in the outer periphery of winding.SELECTED DRAWING: Figure 1

Description

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

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are lightweight and have high energy density, so in recent years they have been used as power sources for vehicle driving in addition to so-called portable power sources such as personal computers and portable terminals. It has become to. In a typical configuration of a non-aqueous electrolyte secondary battery, a sheet-shaped separator (separator sheet) is interposed between a sheet-shaped positive electrode (positive electrode sheet) and a sheet-shaped negative electrode (negative electrode sheet). For example, a configuration is known that includes a wound electrode body in which a positive electrode sheet and a negative electrode sheet are overlapped with a separator sheet interposed therebetween and wound. As the separator sheet, a resin porous sheet or the like is used. In addition, a separator sheet having a heat-resistant porous layer on the surface for the purpose of improving heat resistance and suppressing thermal shrinkage is also known. For example, Patent Document 1 describes an electrochemical element separator having a heat-resistant porous layer containing a filler and an organic binder.

JP 2014-170752 A

  By the way, some uses of the non-aqueous electrolyte secondary battery are assumed to be used in a mode in which charging and discharging are repeated in a pattern including charging or discharging at a high rate. A non-aqueous electrolyte secondary battery used as a power source for vehicles is a typical example of a non-aqueous electrolyte secondary battery in which such a usage mode is assumed. However, in the charge / discharge pattern (high rate charge / discharge cycle) in which charging / discharging is repeated in a pattern including charging or discharging at a high rate in this way, the performance of the non-aqueous electrolyte secondary battery is reduced compared to the charging / discharging cycle at a low rate ( Battery resistance rise etc.) tends to be large.

  This invention is made | formed in view of this condition, The main objective is to provide the non-aqueous-electrolyte secondary battery with improved durability with respect to high-rate charging / discharging.

  When a high rate charge / discharge cycle is applied to a non-aqueous electrolyte secondary battery equipped with a wound electrode body, a temperature difference may occur between the wound center portion and the wound outer peripheral portion of the wound electrode body. Specifically, since the winding center portion is likely to generate heat, the temperature of the winding center portion can be increased more than the temperature of the winding outer peripheral portion. On the other hand, the volume of the non-aqueous electrolyte generally increases due to thermal expansion as the temperature rises. When the temperature of the non-aqueous electrolyte penetrating the wound electrode body rises, a part of the non-aqueous electrolyte solution is pushed out from the winding axial end of the wound electrode body due to the increase in volume (discharge) ) As described above, when the temperature of the winding center portion of the wound electrode body rises higher than the temperature of the wound outer peripheral portion, the present inventor Since the thermal expansion is larger than that of the non-aqueous electrolyte penetrating the outer peripheral portion, more is discharged from the end portion in the winding axis direction. It was thought that the amount of retention (liquid retention amount) was uneven (uneven) depending on the location, which promoted partial deterioration of the battery and could contribute to performance degradation due to high-rate charge / discharge cycles. And the above-mentioned subject can be solved by making the winding center part which a temperature rise tends to become large compared with a winding outer periphery part into a structure with high affinity to a nonaqueous electrolyte compared with a winding outer periphery part. As a result, the present invention has been completed.

  The non-aqueous electrolyte secondary battery provided by the present invention includes a wound electrode body, a non-aqueous electrolyte, and a battery case that houses the wound electrode body and the non-aqueous electrolyte. The wound electrode body includes a positive electrode sheet, a negative electrode sheet, and a separator sheet interposed between the positive electrode sheet and the negative electrode sheet. The separator sheet includes a base material layer and a heat-resistant porous layer disposed on the base material layer. The heat resistant porous layer contains a filler and a binder. And, the dissolution parameter of the binder located at the winding center part of the wound electrode body is more non-aqueous electrolyte than the dissolution parameter of the binder located at the wound outer peripheral part of the wound electrode body. Close to the solubility parameter. The non-aqueous electrolyte secondary battery having such a configuration can have improved durability against a high rate charge / discharge cycle. For example, an increase in battery resistance due to a high rate charge / discharge cycle can be suppressed.

  Although the scope of the present invention is not limited, for example, the following can be considered as a reason why the above-described configuration solves the problem. That is, the non-aqueous electrolyte secondary battery having the above configuration is positioned at the center of winding of the wound electrode body as compared with the binder included in the heat-resistant porous layer positioned at the outer periphery of the wound electrode body. The binder contained in the heat-resistant porous layer that has a higher affinity for the non-aqueous electrolyte. For this reason, the non-aqueous electrolyte that permeates the winding center is more easily held (difficult to be discharged) than the non-aqueous electrolyte that permeates the winding outer periphery. ing. Therefore, even when the winding center is hotter than the winding outer periphery, the amount of the non-aqueous electrolyte discharged from the winding center to the outside of the winding electrode body and the winding electrode body outside the winding electrode body. It is possible to reduce the difference from the amount of the non-aqueous electrolyte discharged. As a result, non-uniformity in the amount of non-aqueous electrolyte solution held in the winding center and winding outer periphery (and hence unevenness in battery reaction) has been alleviated, thereby improving durability against high-rate charge / discharge cycles. it is conceivable that. Further, a binder having a high affinity for the non-aqueous electrolyte tends to be highly swellable by the non-aqueous electrolyte. By using such a binder in the winding center part, the liquid retention amount in the winding center part can be increased using the swelling. As the amount of liquid retained increases, the specific heat increases and the thermal conductivity also increases, so that the temperature rise in the winding center is suppressed. Thereby, the temperature difference (heat unevenness) between the wound outer peripheral portion and the wound center portion can be reduced. Moreover, the discharge of the nonaqueous electrolyte solution outside the wound electrode body due to the thermal expansion of the nonaqueous electrolyte solution can be suppressed by suppressing the temperature rise in the winding center portion. It is considered that these factors can also contribute to improvement of durability against the high rate charge / discharge cycle.

It is explanatory drawing which shows the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is explanatory drawing which shows the winding electrode body of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is sectional drawing which shows the separator sheet and positive electrode sheet | seat of the nonaqueous electrolyte secondary battery which concern on one Embodiment. It is a characteristic view which shows the relationship between the binder content rate of a center side area | region, and a resistance increase rate.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the following, the present invention will be described in more detail by taking the case where the non-aqueous electrolyte secondary battery is a lithium ion secondary battery as an example, but the application target of the present invention is not intended to be limited.

  A schematic configuration of a lithium ion secondary battery according to an embodiment of the present invention is shown in FIGS. The lithium ion secondary battery 100 has a configuration in which a flat wound electrode body 200 as shown in FIG. 2 is housed in a flat rectangular battery case 300 together with a non-aqueous electrolyte 90. At least a part of the non-aqueous electrolyte 90 is impregnated in the wound electrode body 200.

  The battery case 300 includes a box-shaped case main body 320 having an opening at one end, and a sealing plate (lid body) 340 that is attached to the opening and closes the opening. A positive electrode terminal 420 and a negative electrode terminal 440 for external connection are provided on the upper surface (that is, the lid 340) of the battery case 300. The positive electrode terminal 420 and the negative electrode terminal 440 are electrically connected to the positive electrode sheet 220 and the negative electrode sheet 240 constituting the wound electrode body 200, respectively. As the material of the battery case 300, for example, a metal material such as aluminum or steel can be preferably used.

  The construction (assembly) of the lithium ion secondary battery 100 having such a configuration includes, for example, housing the wound electrode body 200 from the opening of the case body 320 and attaching the lid 340 to the opening, and then the lid An appropriate amount of the non-aqueous electrolyte 90 is injected into the battery case 300 from an injection hole (not shown) provided at 340, and then the injection hole is closed.

As the nonaqueous electrolytic solution 90, the same nonaqueous electrolytic solution that has been conventionally used for lithium ion secondary batteries can be used without particular limitation. Such a non-aqueous electrolyte typically has a composition comprising a supporting salt in a suitable non-aqueous solvent. As the non-aqueous solvent, for example, one or more selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate, and the like are used. be able to. In addition, as the supporting salt, for example, a lithium salt such as LiPF ₆ or LiBF ₄ can be used. The concentration of the supporting salt is not particularly limited, and can be, for example, about 0.9 to 1.2 mol / L.

  As shown in FIG. 2, the wound electrode body 200 includes a long sheet-like positive electrode (positive electrode sheet) 220, a long sheet-like negative electrode (negative electrode sheet) 240, and two long sheet-like separators. (Separator sheets) 260 and 280.

  The positive electrode sheet 220 includes a long sheet-like positive electrode current collector 221 and a positive electrode active material layer 223. As the positive electrode current collector 221, a metal foil having good conductivity such as an aluminum foil is preferably used. In the positive electrode sheet 220, a positive electrode active material layer non-formation part 222 in which the positive electrode current collector 221 is exposed without the formation of the positive electrode active material layer 223 is set along one end in the width direction of the positive electrode current collector 221. ing. The positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the positive electrode active material layer non-forming portion 222.

The positive electrode active material layer 223 includes a positive electrode active material, and may include an optional component such as a conductive material or a binder as necessary. These can be appropriately selected from known materials that can be used for the positive electrode of the lithium ion secondary battery. For example, as the positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (lithium nickel cobalt manganese composite oxide), LiNiO ₂ (lithium nickelate), LiCoO ₂ (lithium cobaltate), LiMn ₂ Lithium transition metal oxides such as O ₄ (lithium manganate) can be used. As the conductive material, a powdery carbon material such as acetylene black (AB) can be used. As the binder, polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and the like can be used.

  The negative electrode sheet 240 includes a long sheet-like negative electrode current collector 241 and a negative electrode active material layer 243. As the negative electrode current collector 241, a metal foil with good conductivity such as a copper foil is preferably used. The negative electrode sheet 240 is provided with a negative electrode active material layer non-formation part 242 where the negative electrode current collector 241 is exposed without forming the negative electrode active material layer 243 along the end of one side in the width direction of the negative electrode current collector 241. ing. The negative electrode active material layer 243 is held on both surfaces of the negative electrode current collector 241 except for the negative electrode active material layer non-forming portion 242.

  The negative electrode active material layer 243 includes a negative electrode active material, and may include an optional component such as a binder as necessary. These can be appropriately selected from known materials that can be used for the negative electrode of a lithium ion secondary battery. For example, carbonaceous particles such as graphite carbon and amorphous carbon can be preferably used as the negative electrode active material. As the binder, polymers such as SBR and CMC can be used.

  The positive electrode active material layer non-formation part 222 and the negative electrode active material layer non-formation part 242 are located at both ends in the winding axis direction of the wound electrode body 200, and the positive electrode terminal 420 and the negative electrode terminal 440 described above, respectively. Electrically connected.

  Separator sheets 260 and 280 are members that separate positive electrode sheet 220 and negative electrode sheet 240. In this example, the separator sheet 260 and the separator sheet 280 have the same configuration. Therefore, the structure of the separator sheet 260 will be described in more detail below as an example.

  As shown in FIG. 3, the separator sheet 260 includes a base material layer 262 and a heat-resistant porous layer 264 disposed on one surface thereof (in the illustrated example, the surface facing the positive electrode active material layer 223). . As the base material layer 262, a resin porous sheet can be used. For example, a porous sheet made of polyolefin resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. The base material layer 262 may have a single layer structure (for example, a single layer structure made of PE resin) or a multilayer structure (for example, a three-layer structure of PP / PE / PP). The heat resistant porous layer 264 is preferably provided over the entire length of the base material layer 262. In a preferred embodiment, the heat resistant porous layer 264 is provided over the entire area of one side of the base material layer 262. As a result, the effect of increasing the heat resistance of the separator sheet 260 and the effect of suppressing heat shrinkage can be better exhibited.

The heat resistant porous layer 264 includes a filler and a binder. As the filler, either an inorganic filler or an organic filler can be used, and an inorganic filler and an organic filler may be used in combination. Inorganic fillers can be preferably used from the viewpoints of heat resistance and electrochemical stability. Preferable examples of the inorganic filler include alumina (Al ₂ O ₃ ), alumina hydrate (for example, boehmite (Al ₂ O ₃ .H ₂ O)), magnesium hydroxide (Mg (OH) ₂ ), magnesium carbonate (MgCO ₃ ) And the like. As the organic filler, resin particles having a melting point higher than that of the constituent material of the base material layer (for example, high heat resistant resin particles such as aramid, polyimide, polyphenylene sulfide, etc.) can be used. The binder used for the heat resistant porous layer 264 is not particularly limited, and for example, an appropriate one can be selected from SBR, CMC, PVDF, PTFE, PE, acrylic resin, ethylene-vinyl acetate copolymer, and the like.

  Of the heat-resistant porous layer 264, the portion Bin of the winding electrode body 200 (center side region) 264A, the binder Bin of the winding outer peripheral portion (outer side region) 264B of the binder Bout In this case, materials having different solubility parameters (hereinafter also referred to as “SP values”) are used. Here, in the longitudinal direction of the separator sheet 260 (left-right direction in FIG. 3), the center side region 264A of the heat resistant porous layer 240 is wound around the center side end (in the wound electrode body 200, the separator is closer to the outer periphery side region 264B). The sheet 260 is disposed at the end corresponding to the winding start side). In other words, the outer peripheral side region 264B of the heat-resistant porous layer 240 is arranged at the wound outer peripheral side end (the end corresponding to the winding end side of the separator sheet 260 in the wound electrode body 200) than the central side region 264A. Yes.

The difference between the Bin SP value (SPin) and the SP value (SPe) of the non-aqueous electrolyte 90 is such that the Bin SP value (SPe) of the Bout and the SP value (SPe) of the non-aqueous electrolyte 90 are different. Is selected to be smaller than the difference. That is, SPin, SPout and SPe have a relationship satisfying the following formula (1).
| SPe-SPin | <| SPe-SPout | (1)

  Here, the SP value refers to the intermolecular force as the SP value (solubility parameter) when it is assumed that the force acting between the solvent and the solute is only the intermolecular force. As the SP value (SPe) of the non-aqueous electrolyte, the SP value of the non-aqueous solvent contained in the non-aqueous electrolyte can be used. When a plurality of types of non-aqueous solvents are included, the SP value of each non-aqueous solvent is used. A value obtained by multiplying by the volume ratio can be used. As the SP value of each non-aqueous solvent, values described in known materials can be used. In the technique disclosed herein, 14.7 is used as the SP value of EC, 8.8 is used as the SP value of DEC, 9.4 is used as the SP value of EMC, and 9.9 is used as the SP value of DMC.

  As the SP value (SPin) of the binder Bin, the SP value of the resin constituting the binder Bin can be used. When the binder Bin includes a plurality of types of resins, the SP value of each resin is multiplied by the weight ratio and added up. Values can be used. As the SP value of each resin, a value described in publicly known materials can be used, and when the SP value information is disclosed by the manufacturer of the resin, the SP value can be adopted. When there is no SP value information, a theoretical value calculated based on the Fedors method can be adopted. The same applies to the SP value of the binder Bout.

  In general, when the SP values of two kinds of materials are close (in other words, the difference between the SP values is small), the affinity of these materials tends to increase. Therefore, SPin, SPout and SPe satisfy the above formula (1) means that the binder Bin included in the central region 264A is more than the binder Bout included in the outer peripheral region 264B of the heat resistant porous layer 264. This means that the affinity for the non-aqueous electrolyte 90 is higher. Thus, by disposing the binder Bin having higher affinity for the non-aqueous electrolyte 90 in the winding center, the non-aqueous electrolyte 90 penetrating into the winding center is in the winding electrode body 200. It becomes easy to be held (maintained). Therefore, even when the winding center portion becomes hotter than the winding outer peripheral portion, the winding electrode body 200 is discharged from the winding center portion to the outside of the winding electrode body 200 at the winding axis direction end portion 200A. The difference between the amount of the non-aqueous electrolyte 90 and the amount of the non-aqueous electrolyte 90 discharged from the wound outer peripheral portion to the outside of the wound electrode body 200 can be reduced. Thereby, the non-aqueous electrolyte non-uniformity of the nonaqueous electrolyte solution at the winding center portion and the winding outer peripheral portion (and consequently the non-uniformity of the battery reaction) can be alleviated and the durability against the high rate charge / discharge cycle can be improved.

  The binder Bin and the binder Bout can be selected so that the difference between | SPe−SPout | and | SPe−SPin | is greater than 0, and the above difference is 1.0 or more (more preferably 1.5). As described above, it is preferable to select so as to be 2 or more. The upper limit of the difference between | SPe−SPout | and | SPe−SPin | is not particularly limited, but is usually 7 or less, typically 6 or less, for example 5 or less. Although not particularly limited, the value of | SPe−SPin | is typically 3.5 or less, preferably 3.0 or less, and preferably 2.5 or less (for example, 2. 19 or less) is more preferable.

  Note that the SP value of the non-aqueous electrolyte can be adjusted by the type of non-aqueous solvent used in the non-aqueous electrolyte and the ratio of the amounts used when a plurality of types of non-aqueous solvents are used. The SP values of Bin and Bout can be adjusted by the type of raw material monomer for each binder, the use amount ratio of a plurality of types of raw material monomers, the structure of the polymer, and the like. A person skilled in the art can appropriately select or synthesize a material having a desired SP value from commercially available products.

  Although it does not specifically limit, the ratio for which the length of center side area | region 264A of the heat resistant porous layer 264 occupies the full length of the separator sheet 260 can be 10 to 90%, for example. From the viewpoint of better exhibiting the effect of different SP values of the binder in the center side region 264A and the outer peripheral side region 264B, it is usually appropriate to set the ratio to 30 to 70%. %, Preferably 45 to 55%.

  The formation method of the heat resistant porous layer 264 is not particularly limited. For example, a method in which a slurry containing a filler, a binder, and a solvent is applied to the surface (here, one surface) of the base material layer 262 and then dried can be preferably employed. As the solvent used in the slurry, water or a mixed solvent mainly composed of water can be preferably used.

  The binder content in the heat resistant porous layer 264 is not particularly limited. From the viewpoints of appropriately binding the filler, adhering the heat-resistant porous layer 264 to the base material layer 262 with an appropriate peel strength, and suppressing an increase in internal resistance, each of the central region 264A and the outer peripheral region 264B The binder content can be, for example, 0.5 to 5% by weight, usually 1 to 3% by weight, and preferably 1 to 2.6% by weight. Moreover, the content rate of Bin in center side area | region 264A can be 1 weight% or more, for example. From the viewpoint of enhancing the discharge suppression effect of the non-aqueous electrolyte, the Bin content is preferably 1.5% by weight or more, and more preferably 2% by weight or more.

  Further, the Bin content in the central region 264A is preferably equal to or greater than the Bout content in the outer peripheral region 264B. As a result, the amount of the non-aqueous electrolyte discharged from the wound central portion to the outside of the wound electrode body 200 and the amount of the non-aqueous electrolyte discharged from the wound outer peripheral portion to the outside of the wound electrode body 200. Difference can be more effectively reduced. The Bin content in the central region 264A is higher than the Bout content in the outer peripheral region 264B (for example, the Bin content is about 0.5 to 1.5% by weight higher than the Bout content). In this way, a more remarkable effect can be realized.

  The non-aqueous electrolyte secondary battery disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are electrically connected) can be excellent in durability against high-rate charge / discharge. Therefore, taking advantage of such properties, it can be suitably used as a power source for a drive source such as a motor for driving a vehicle, for example. The type of vehicle is not particularly limited, and examples thereof include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, electric scooters, electric assist bicycles, electric wheelchairs, electric railways, and the like.

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

<Preparation of separator sheet>
As described below, separator sheets of Samples 1 to 7 including a base material layer and a heat-resistant porous layer disposed on one side of the base material layer were produced. As a base material layer of each separator sheet, a single layer PE porous sheet having a thickness of 20 μm was used. Alumina particles were used as the inorganic filler for the heat resistant porous layer. As the binder, SBR having an SP value of 7 (hereinafter referred to as “SBR (7)”) and SBR having an SP value of 9 (hereinafter referred to as “SBR (9)”) were used. The thickness of the heat-resistant porous layer in each sample was adjusted to be approximately the same.

  Sample 1: Slurry A1 containing alumina particles, SBR (7), and water in 50% of the entire length of the PE porous sheet disposed on the winding center side (the binder content is the solid content) 1.5% by weight) was applied by a gravure coater. Continuously (that is, without drying the applied slurry A1), the slurry A1 is applied to the remaining part of the total length of the porous porous sheet made of PE, that is, 50% of the part disposed on the outer periphery of the winding. Was applied. And the heat resistant porous layer was formed by drying the whole.

  Sample 2: Instead of slurry A1, slurry B1 containing SBR (9) instead of SBR (7) (the binder content is 1.5 wt% based on solid content) was used. The other points were the same as Sample 1, and a separator sheet of Sample 2 was produced.

  Sample 3: Slurry A1 was applied by a gravure coater to the 50% portion on the winding center side, and slurry B1 was applied to the 50% portion on the winding outer periphery side by a die coater. Other points were the same as in Sample 1, and a separator sheet of Sample 3 was produced.

  Sample 4: Slurry B2 in which the binder content in slurry B1 was changed to 1.0% by weight was applied by a gravure coater to 50% of the winding center side. Other points were the same as in Sample 1, and a separator sheet of Sample 4 was produced.

  Sample 5: Slurry B1 was applied to 50% of the winding center side by a gravure coater. Other points were the same as in Sample 1, and a separator sheet of Sample 5 was produced.

Sample 6: A slurry B3 in which the binder content in the slurry B1 was changed to 2.0% by weight was applied to a 50% portion on the winding center side by a gravure coater. The other points were the same as in Sample 1, and a separator sheet of Sample 6 was produced.
Sample 7: A slurry B4 in which the binder content in the slurry B1 was changed to 2.6% by weight was applied to a 50% portion on the winding center side by a gravure coater. Other points were the same as in Sample 1, and a separator sheet of Sample 7 was produced.

<Production of lithium ion secondary battery>
Lithium ion secondary batteries were produced using the separator sheets of Samples 1-7.
As a positive electrode sheet, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as a positive electrode active material, PVDF as a binder, and acetylene black as a conductive material in a weight ratio of 96: 2: 2. A composition for forming a positive electrode active material layer mixed with N-methyl-2-pyrrolidone is applied in a band shape on an aluminum foil (thickness 15 μm) as a positive electrode current collector, dried, and then rolled by a roll press. We used what we did.
As the negative electrode sheet, a composition for forming a negative electrode active material layer in which natural graphite powder as a negative electrode active material, SBR as a binder, and CMC as a thickener are mixed with water at a weight ratio of 98: 1: 1. Was applied onto a copper foil (thickness 10 μm) as a negative electrode current collector in a band shape, dried, and rolled by a roll press.
As the non-aqueous electrolyte, EC (SP value 14.7), DMC (SP value 9.9) and EMC (SP value 9.4) were mixed at a volume ratio of 30:40:30, and LiPF ₆ was mixed. What was dissolved at a concentration of 1.1 mol / L was used. The non-aqueous solvent used in this non-aqueous electrolyte has an SP value of 9 to 10 on a volume basis. The average SP value of the non-aqueous solvent is 11.19.

  A lithium ion secondary battery having a schematic configuration shown in FIGS. 1 to 3 was constructed using the positive electrode sheet, the negative electrode sheet, the two separator sheets, and the nonaqueous electrolytic solution. More specifically, the positive electrode sheet, the negative electrode sheet, and the separator sheet were overlapped and wound, and pressed from the side to produce a flat wound electrode body. At this time, each of the two separator sheets was disposed such that the surface on which the heat resistant porous layer was formed faced the positive electrode active material layer. The wound electrode body was accommodated in an aluminum box-shaped battery case, and after pouring a non-aqueous electrolyte from the injection hole of the battery case, the injection hole was sealed. Thus, the lithium ion secondary batteries of Examples 1 to 7 corresponding to the separator sheets of Samples 1 to 7 were produced.

<Charge / discharge cycle test>
The charging / discharging cycle test which repeats charging / discharging at a high rate was done with respect to the lithium ion secondary battery of Examples 1-7. Specifically, in a room temperature (about 25 ° C.) environment, a high rate of discharging at a constant current of 30 C for 10 seconds, resting for 10 minutes, charging at a constant current of 5 C for 60 seconds, and resting for 10 minutes The charge / discharge cycle was repeated 30000 times. At that time, the SOC (State of Charge) was adjusted to 60% every 500 cycles. And, from the IV resistance (the initial resistance of the battery) before the charge / discharge cycle test and the IV resistance after the charge / discharge cycle test, [IV resistance after charge / discharge cycle test / IV resistance before charge / discharge cycle test]. Was used to calculate the resistance increase rate (times).

  Here, “1C” means the amount of current that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour. In addition, the IV resistance before and after the charge / discharge cycle was measured by adjusting the battery to SOC 60%, charging at 10 ° C for 1 second at 1C, 3C and 5C in an environment of 25 ° C. Is plotted on the vertical axis, and the voltage drop value ΔV, which is a value obtained by subtracting the voltage value at the time of 10 seconds from the initial voltage value, is plotted on the vertical axis, and the slope is obtained. The results are shown in Table 1.

  As shown in Table 1, the SP value of the binder in the central region is larger than that of the lithium ion secondary batteries in Examples 1 and 2 in which there is no difference in the SP value of the binder in the central region and the peripheral region. The lithium ion secondary batteries of Examples 4 to 7, which are closer to the SP value of the non-aqueous electrolyte (11.19) than the SP value of the binder in the side region, have a small resistance increase rate due to the high-rate charge / discharge cycle, and have excellent durability. Showed sex. In contrast to this, in the lithium ion secondary battery of Example 3, the SP value of the binder in the outer peripheral region is closer to the SP value of the non-aqueous electrolyte than the SP value of the binder in the central region, contrary to Examples 4-7. The resistance increase rate was larger than those of Examples 1 and 2.

  The graph which plotted the resistance increase rate of the lithium ion secondary battery of Examples 4-7 with respect to the binder content rate of a center side area | region is shown in FIG. In a configuration in which the SP value of the binder in the central region is closer to the SP value of the non-aqueous electrolyte than the SP value of the binder in the outer peripheral region, if the binder content in the central region is high, the effect of reducing the resistance increase rate is There was a tendency to become larger. Moreover, when the binder content rate of the center side region became equal to or higher than the binder content rate of the outer peripheral side region (Examples 5 to 7), the resistance increase rate reducing effect on the binder content rate was further increased.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

90 Nonaqueous electrolyte 100 Lithium ion secondary battery (Nonaqueous electrolyte secondary battery)
200 Winding electrode body 200A Winding axial direction end 220 Positive electrode sheet 240 Negative electrode sheet 260, 280 Separator sheet 262 Base material layer 264 Heat-resistant porous layer 264A Center side region 264B Outer periphery side region

Claims (1)

A wound electrode body having a positive electrode sheet, a negative electrode sheet, and a separator sheet interposed between the positive electrode sheet and the negative electrode sheet;
A non-aqueous electrolyte,
A battery case containing the wound electrode body and the non-aqueous electrolyte,
The separator sheet includes a base material layer, and a heat-resistant porous layer disposed on the base material layer,
The heat resistant porous layer includes a filler and a binder,
The dissolution parameter of the binder located at the winding center part of the wound electrode body is more soluble than the dissolution parameter of the binder located at the wound outer peripheral part of the wound electrode body. Non-aqueous electrolyte secondary battery close to parameters.

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