JP2014137985A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery capable of avoiding deterioration in productivity due to winding looseness in a wound electrode body without causing deterioration in battery performance, in a configuration where a flat-shaped wound electrode body including a separator sheet having a heat-resistant layer formed thereon is used.SOLUTION: The present invention provides a secondary battery including a flat-shaped wound electrode body accommodated in a battery case. In the secondary battery, the wound electrode body includes positive/negative electrode sheets, and a separator sheet arranged between the positive/negative electrode sheets. A heat-resistant layer is formed on a surface of the separator sheet. A resin particle layer is arranged between one of the electrode sheets and the heat-resistant layer so as to be brought into contact with the one of the electrode sheet and the heat-resistant layer.

Description

  The present invention relates to a secondary battery. Specifically, the present invention relates to a secondary battery applicable to a vehicle-mounted power source.

  A secondary battery such as a lithium secondary battery or a nickel hydride battery is preferably used as a power source mounted on a vehicle using electricity as a driving source or a power source mounted on a personal computer, a portable terminal, or other electrical products. Some of such secondary batteries have a heat-resistant layer formed on the surface of the separator for the purpose of preventing an internal short circuit in a high temperature state. Patent document 1 is mentioned as a literature which discloses this kind of prior art. Further, for the purpose of improving the adhesion between the positive and negative electrodes and the separator, it has been proposed to interpose a resin film between the electrode and the separator. Patent document 2 is mentioned as a literature which discloses this kind of prior art. In Patent Document 2, an oriented polystyrene film that exhibits adhesiveness when contacted with a non-aqueous electrolyte is used as a resin film interposed between an electrode and a separator.

  On the other hand, in a secondary battery using a flat-shaped wound electrode body, the wound state may be loosened after being formed into an electrode body having a predetermined shape. This phenomenon is hereinafter referred to as sag loosening (spring back). Patent Document 3 describes that a polymer having adhesive properties such as polyvinylidene fluoride is disposed between positive and negative electrodes and a separator for the purpose of preventing the above-described loosening.

JP 2009-283273 A JP 2011-129497 A JP 2000-315481 A

  As described above, in a secondary battery in which an electrode body having a heat-resistant layer is configured and used as a flat wound electrode body, the heat-resistant layer tends to be loosened due to the characteristics of the heat-resistant layer (rigidity, low adhesion, etc.). There is a concern that the degree of rolling and loosening will be greater than in a configuration that does not have. If the degree of winding looseness is large, for example, inconveniences such as difficulty in housing the wound electrode body in the battery case and difficulty in connecting the current collecting terminals may occur. When such an inconvenience occurs, additional steps such as re-molding and a shape-holding step after molding are required, which may reduce productivity.

  When the present inventors examined the above-described loosening, it is clear that the loosening in the secondary battery using the wound electrode body having the heat-resistant layer is significant when the heat-resistant layer is formed on the separator sheet surface. Became. However, when a heat-resistant layer is formed on the electrode surface, the binder may penetrate into the electrode and cause deterioration of battery characteristics, and impart good characteristics (for example, strength and elongation) to the separator sheet. From the viewpoint, there is a demand for forming a heat-resistant layer on the separator sheet surface. As a result of further investigations, the present inventors have completed the present invention by finding a means that can effectively suppress the occurrence of loosening even when a heat-resistant layer is formed on the separator sheet surface. That is, the present invention was created to solve the above problems, and its purpose is to improve battery performance in a configuration using a flat wound electrode body having a separator sheet on which a heat-resistant layer is formed. It is an object of the present invention to provide a secondary battery that can avoid a decrease in productivity due to loosening of a wound electrode body without lowering.

  In order to achieve the above object, the present invention provides a secondary battery in which a flat wound electrode body is accommodated in a battery case. In the secondary battery, the wound electrode body includes a positive and negative electrode sheet and a separator sheet disposed between the positive and negative electrode sheets. Further, a heat resistant layer is formed on the surface of the separator sheet. Further, a resin particle layer is disposed between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer.

  As described above, the loosening phenomenon occurs remarkably when the heat-resistant layer is formed on the separator sheet surface instead of the positive and negative electrode sheet surfaces. The following can be considered as the cause. For example, between the electrode sheet and the separator sheet, or between the heat-resistant layer formed on the electrode sheet and the separator sheet, the separator sheet bites into the electrode sheet or the heat-resistant layer when the wound electrode body is formed, and thereby the anchor effect is exhibited. Therefore, it is considered that a good adhesion state is easily obtained. On the other hand, it is considered that a sufficient anchor effect cannot be obtained and a good adhesion state cannot be obtained between the heat-resistant layer and the electrode sheet formed on the separator sheet. Therefore, in the present invention, a resin particle layer is disposed between one (at least one) of the electrode sheets and the heat-resistant layer. As a result, after forming the wound electrode body, the electrode sheet and the heat-resistant layer are well bonded (indirect bonding) via the resin particle layer, so that the loosening caused by the separation of the electrode sheet and the heat-resistant layer is suppressed. Is done. As a result, in a secondary battery using a flat wound electrode body that includes a separator sheet on which a heat-resistant layer is formed, a decrease in productivity due to the loosening can be avoided. In addition, the resin particle layer described above may be one that does not impair battery performance, such as being excellent in charge carrier passage, unlike a resin film obtained by solution polymerization, for example. That is, according to the present invention, in a configuration using a flat wound electrode body including a separator sheet with a heat-resistant layer, a secondary battery having good battery performance and excellent productivity is provided. .

  In a preferred aspect of the secondary battery disclosed herein, the separator sheet has a heat-resistant layer-forming surface on which the heat-resistant layer is formed, and a heat-resistant layer non-formed surface on which the heat-resistant layer is not formed. Further, the resin particle layer as the first resin particle layer is disposed between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. Further, a second resin particle layer is disposed between the other of the electrode sheets and the heat-resistant layer non-formation surface of the separator sheet so as to be in contact with the other of the electrode sheets and the heat-resistant layer non-formation surface. .

  As described above, it is easy to obtain a good adhesion state due to the anchor effect between the electrode sheet and the separator sheet, but in the process of study, in the separator sheet in which the heat-resistant layer is formed, after forming the wound electrode body, It was confirmed that it was difficult to obtain a good adhesion state between the surface of the separator sheet where the heat-resistant layer was not formed and the electrode sheet. This is considered to be due to the fact that when the heat-resistant layer is formed on the separator sheet, the physical properties of the separator sheet are changed (for example, the compressibility is lowered), and the anchor effect on the non-heat-resistant layer forming surface of the separator sheet is also reduced. . Therefore, in the above-described preferred embodiment, the second resin particle layer is also disposed between the surface of the separator sheet where the heat-resistant layer is not formed and the electrode sheet. Thereby, an electrode sheet and a separator sheet adhere | attach favorably (indirect adhesion | attachment) via a 2nd resin particle layer. As a result, after forming the wound electrode body, a good adhesion state is obtained not only between the electrode sheet and the heat-resistant layer but also between the electrode sheet and the separator sheet, and the winding and loosening of the wound electrode body is suitably suppressed.

  In a preferred embodiment of the secondary battery disclosed herein, the resin particle layer is a dispersion type resin particle layer formed from a dispersion containing resin particles. Such a dispersion-type resin particle layer is typically a layer in which resin particles are stacked while having predetermined pores (spaces), and therefore has excellent charge carrier permeability and a battery. The performance may not be hindered. Therefore, the above dispersion-type resin particle layer can suitably exhibit the function of preventing the loosening without lowering the battery performance.

  The resin constituting the resin particle layer is preferably at least one selected from the group consisting of polytetrafluoroethylene, styrene butadiene rubber and polyolefin. These resins are suitable resins as a binder that favorably bonds the electrode sheet and the heat-resistant layer.

  In the suitable one aspect | mode of the secondary battery disclosed here, the said heat resistant layer contains an inorganic filler in the ratio of 50 mass% or more. A heat-resistant layer containing an inorganic filler in the above ratio tends to cause loosening due to its properties (rigidity, low adhesion, etc.). By arranging the resin particle layer according to the present invention between the heat-resistant layer and the electrode sheet for the secondary battery having such a heat-resistant layer, the loosening of the wound electrode body is effectively suppressed.

  In a preferred aspect of the secondary battery disclosed herein, the wound electrode body has a flat portion having a thickness of 10 mm or more. As described above, in a wound electrode body having a large amount of winding (or can be grasped as the number of times of winding), there is a tendency that winding looseness is likely to occur. By applying the configuration of the present invention to such a secondary battery, the loosening of the wound electrode body is effectively suppressed.

  In addition, according to the present invention, a method for manufacturing a secondary battery is provided. This manufacturing method includes: preparing positive and negative electrode sheets; preparing a separator sheet on which a heat-resistant layer is formed; winding the separator sheet on which the heat-resistant layer is formed between the positive and negative electrode sheets To produce a wound electrode body; to form the wound electrode body into a flat shape by pressing; and to house the wound electrode body shaped into the flat shape in a battery case. Including. In addition, the production of the wound electrode body further includes disposing a resin particle layer between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. . According to the manufacturing method including the above steps, after forming the wound electrode body, the electrode sheet and the heat-resistant layer are favorably bonded via the resin particle layer, and the electrode sheet and the heat-resistant layer are separated from each other. Looseness is suppressed. Moreover, the said resin particle layer may be what does not inhibit battery performance. In short, by disposing the resin particle layer in a predetermined region, in a secondary battery using a flat wound electrode body including a separator sheet on which a heat-resistant layer is formed, the above-mentioned winding is performed without reducing battery performance. A decrease in productivity due to looseness can be avoided.

  In a preferred embodiment of the production method disclosed herein, in the production of the wound electrode body: the separator sheet is formed on only one surface of both surfaces of the separator sheet, whereby the separator sheet And a first resin particle layer between the electrode sheet and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. A resin particle layer as the second electrode sheet and a second heat-resistant layer non-formation surface of the separator sheet between the other of the electrode sheets and the non-heat-resistant layer non-formation surface. Disposing a resin particle layer. Thereby, not only the electrode sheet-heat resistant layer but also the adhesion state between the electrode sheet-separator sheet becomes favorable, and the loosening of the wound electrode body is suitably suppressed.

In one preferred embodiment of the manufacturing method disclosed herein, the wound electrode body, wherein the wound electrode body pars plana immediately after the press thickness T _A and the press completion from 5 minutes after wound electrode plana the thickness _{T B} of the part is measured, the _{formula: (T B -T a) /} T a × 100; a sought spring back ratio is 5% or less. Since the wound electrode body having the above-described springback rate is one in which the loosening is preferably suppressed, the reduction in productivity due to the loosening can be more preferably avoided.

  As for the secondary battery disclosed here, the loosening after winding electrode body preparation is suppressed. Considering that the above-mentioned loosening is likely to occur with a larger battery, a driving power source of a vehicle to which a larger battery can be applied (for example, a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), an electric vehicle (EV)) It can be suitably used as a vehicle drive power source. According to the present invention, there is provided a vehicle equipped with any of the secondary batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected).

It is a perspective view which shows typically the structure of the lithium secondary battery which concerns on 1st Embodiment. It is sectional drawing in the II-II line of FIG. It is a perspective view which shows typically the state which winds and produces the electrode body which concerns on 1st Embodiment. It is a figure which shows typically the cross section orthogonal to the winding axis | shaft of the winding electrode body of FIG. It is a schematic cross section which expands and shows a part between positive and negative electrodes in the flat part of the winding electrode body of FIG. It is a figure corresponding to FIG. 5, Comprising: It is a schematic cross section which expands and shows a part between positive and negative electrodes in the flat part of the winding electrode body which concerns on 2nd Embodiment. It is a side view showing typically a vehicle (automobile) provided with a lithium secondary battery concerning one embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator, a battery ( The general technology related to the construction of the battery, such as the shape of the case), etc. can be grasped as a design matter of those skilled in the art based on the conventional technology 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. Further, in the following drawings, members / parts having the same action are described with the same reference numerals, and overlapping descriptions may be omitted or simplified.

  As a preferred embodiment of the secondary battery disclosed herein, a lithium secondary battery will be described as an example, but the application target of the present invention is not intended to be limited to the battery. For example, the present invention can also be applied to a non-aqueous electrolyte secondary battery that uses a metal ion (for example, sodium ion) other than lithium ion (Li ion) as a charge carrier. In addition, the application object of this invention should just be a battery using the wound electrode body which has a flat shape, and is not limited to a nonaqueous electrolyte secondary battery. In the present specification, “secondary battery” generally refers to a battery that can be repeatedly charged and discharged. In addition to a storage battery (ie, a chemical battery) such as a lithium secondary battery, a capacitor (ie, a physical battery) such as an electric double layer capacitor. ). Further, in this specification, the “lithium secondary battery” refers to a secondary battery that uses Li ions as electrolyte ions and is charged / discharged by the movement of charges accompanying Li ions between the positive and negative electrodes. A battery generally called a lithium ion secondary battery is a typical example included in the lithium secondary battery in this specification.

  As shown in FIGS. 1 and 2, the lithium secondary battery 100 according to the first embodiment includes a box-shaped battery case 10 and a wound electrode body 20 accommodated in the battery case 10. The battery case 10 has an opening 12 on the upper surface. The opening 12 is sealed by the lid 14 after the wound electrode body 20 is accommodated in the battery case 10 from the opening 12. A non-aqueous electrolyte solution 25 is also accommodated in the battery case 10. The lid body 14 is provided with an external positive terminal 38 and an external negative terminal 48 for external connection, and a part of the terminals 38 and 48 protrudes to the surface side of the lid body 14. A part of the external positive terminal 38 is connected to the internal positive terminal 37 inside the battery case 10, and a part of the external negative terminal 48 is connected to the internal negative terminal 47 inside the battery case 10. The battery case is preferably a member made of metal (aluminum, stainless steel, nickel-plated steel, etc.) having a predetermined rigidity or more. Preferable examples include light metal (for example, aluminum) battery cases having a thickness of 0.3 mm or more (for example, 0.3 to 3 mm, typically 0.5 to 2 mm).

  As shown in FIG. 3, the wound electrode body 20 includes a long sheet-like positive electrode (positive electrode sheet) 30 and a long sheet-like negative electrode (negative electrode sheet) 40. The positive electrode sheet 30 includes a long positive electrode current collector 32 and a positive electrode active material layer 34 formed on at least one surface (typically both surfaces) thereof. The negative electrode sheet 40 includes a long negative electrode current collector 42 and a negative electrode active material layer 44 formed on at least one surface (typically both surfaces) thereof. The wound electrode body 20 also includes two long sheet-like separators (separator sheets) 50A and 50B. The positive electrode sheet 30 and the negative electrode sheet 40 are laminated via two separator sheets 50A and 50B. Specifically, the positive electrode sheet 30, the separator sheet 50A, the negative electrode sheet 40, and the separator sheet 50B are laminated in this order. The laminated body is formed into a wound body by being wound in the longitudinal direction, and further formed into a flat shape by pressing the wound body from the side surface direction and causing it to be ablated. The obtained flat wound electrode body 20 has a substantially rounded rectangular shape in a cross section orthogonal to the winding axis, for example, as shown in FIG. And a semicircular R portion 22 located on both sides of the flat portion 21. In addition, the shape of the wound body before pressing is not particularly limited, and may be a circular shape, an elliptical shape, a rectangular shape, or the like in the cross section.

  The positive electrode active material layer 34 formed on the surface of the positive electrode current collector 32 and the surface of the negative electrode current collector 42 are formed at the center in the width direction of the wound electrode body 20 (direction orthogonal to the winding direction). The negative electrode active material layer 44 thus formed is overlapped and densely stacked. Further, at one end in the width direction of the positive electrode sheet 30, a portion where the positive electrode current collector 32 is exposed without forming the positive electrode active material layer 34 (positive electrode active material layer non-forming portion 36) is provided. . This positive electrode active material layer non-forming portion 36 is in a state of protruding from the separator sheets 50 </ b> A and 50 </ b> B and the negative electrode sheet 40. That is, at one end in the width direction of the wound electrode body 20, a positive electrode current collector laminated portion 35 in which the positive electrode active material layer non-forming portion 36 of the positive electrode current collector 32 overlaps is formed. Further, similarly to the case of the positive electrode sheet 30 at one end, the negative electrode current collector stack in which the negative electrode active material layer non-forming portion 46 of the negative electrode current collector 42 is overlapped with the other end in the width direction of the wound electrode body 20. A portion 45 is formed. The separator sheets 50 </ b> A and 50 </ b> B have a width that is larger than the width of the laminated portion of the positive electrode active material layer 34 and the negative electrode active material layer 44 and smaller than the width of the wound electrode body 20. By arranging this so as to be sandwiched between the stacked portions of the positive electrode active material layer 34 and the negative electrode active material layer 44, the positive electrode active material layer 34 and the negative electrode active material layer 44 are prevented from contacting each other and causing an internal short circuit. .

  Separator sheet 50A is composed of a porous resin layer. As shown in FIG. 5, a heat-resistant layer 51 is formed on the surface 50Aa of the separator sheet 50A on the positive electrode sheet 30 (positive electrode active material layer 34) side. The heat-resistant layer 51 is formed over the entire surface of the separator sheet 50A, that is, over the entire length direction (winding direction) and width direction of the separator sheet 50A. Hereinafter, the positive electrode sheet 30 side surface 50Aa of the separator sheet 50A is also referred to as a heat-resistant layer forming surface 50Aa.

  A resin particle layer (first resin particle layer) 52A is formed on the surface of the heat-resistant layer 51 (surface facing the positive electrode sheet 30 (positive electrode active material layer 34)) 51a. The first resin particle layer 52 </ b> A is disposed between the positive electrode sheet 30 (positive electrode active material layer 34) and the heat-resistant layer 51, and both the positive electrode sheet 30 and the heat-resistant layer 51 in the flat portion 21 of the wound electrode body 20. Touching. The first resin particle layer 52A is composed of resin particles having adhesiveness. Thereby, after forming the wound electrode body 20, the positive electrode sheet 30 and the heat-resistant layer 51 are favorably bonded via the first resin particle layer 52A, and the wound electrode body 20 is prevented from being loosened. The first resin particle layer 52 </ b> A is formed on the entire surface of the heat-resistant layer 51.

  The surface 50Ab of the separator sheet 50A opposite to the heat resistant layer forming surface 50Aa faces the negative electrode sheet 40 (negative electrode active material layer 44), and no heat resistant layer is formed on the surface 50Ab. Hereinafter, the surface 50Ab is also referred to as a heat resistant layer non-formed surface 50Ab. In the present embodiment, the resin particle layer (second resin particle layer) 52B is also formed on the heat-resistant layer non-forming surface 50Ab of the separator sheet 50A. The second resin particle layer 52 </ b> B is disposed between the heat resistant layer non-forming surface 50 </ b> Ab of the separator sheet 50 </ b> A and the negative electrode sheet 40 (negative electrode active material layer 44), and in the flat portion 21 of the wound electrode body 20. 50A and the negative electrode sheet 40 are both in contact. Further, the second resin particle layer 52B is composed of resin particles having adhesiveness in the same manner as the first resin particle layer 52A. Thereby, the negative electrode sheet 40 and the separator sheet 50A are in a state of being favorably bonded via the second resin particle layer 52B, and the loosening of the wound electrode body 20 is prevented. The second resin particle layer 52B is formed on the entire heat resistant layer non-forming surface 50Ab of the separator sheet 50A. The configuration of separator sheet 50B and its peripheral configuration (typically the arrangement of the heat-resistant layer, the resin particle layer, etc.) are basically the same as the configuration of separator sheet 50A and its peripheral configuration, and therefore the description will not be repeated. .

  FIG. 6 is an enlarged schematic cross-sectional view showing a part between the positive and negative electrodes in the flat portion of the wound electrode body according to the second embodiment. Since the configuration of the second embodiment is basically the same as the configuration of the first embodiment, differences will be mainly described. In the second embodiment, the resin particle layer 52 is formed on the surface 51a of the heat-resistant layer 51. However, the resin particle layer is not disposed between the separator sheet 50A and the negative electrode sheet 40. And different. Since the loosening of the wound electrode body 20 is mainly caused by the separation of the electrode sheet (positive electrode sheet 30) and the heat-resistant layer 51, the loosening can be suppressed also by the configuration of the second embodiment.

  In the above embodiment, the resin particle layer (first resin particle layer) is formed on the surface of the heat-resistant layer. However, the present invention is not limited to this, and the resin particle layer is heat-resistant to one of the positive and negative electrode sheets. What is necessary is just to be arrange | positioned between layers. For example, a resin particle layer may be formed on one surface of a positive and negative electrode sheet (typically an active material layer). Similarly, in the said 1st Embodiment, although the 2nd resin particle layer was formed in the surface of a separator sheet, it is not limited to this, A 2nd resin particle layer is the other of a positive / negative electrode sheet, and a separator. What is necessary is just to arrange | position between sheets. For example, a resin particle layer may be formed on the other surface of the positive and negative electrode sheets (typically the active material layer). Moreover, the structure (for example, composition and thickness) of a 1st resin particle layer and a 2nd resin particle layer may be the same, and may differ.

  In the above embodiment, the heat resistant layer is only one layer. However, the present invention is not limited to this, and two or more heat resistant layers may be disposed between the positive and negative electrode sheets. A typical example is a structure in which heat-resistant layers are formed on both sides of a separator sheet. Alternatively, for example, a configuration in which a heat-resistant layer is formed on one surface (one surface) of the separator sheet and one surface of the positive and negative electrode sheets may be employed. As such a configuration, for example, a structure in which a heat-resistant layer is formed on the surface of the electrode sheet facing the other surface (heat-resistant layer non-formed surface) of the separator sheet can be mentioned. When a plurality of heat-resistant layers are provided, the structures (for example, composition and thickness) of the plurality of heat-resistant layers may be the same or different.

  Next, each component which comprises the above-mentioned lithium secondary battery is demonstrated. As the positive electrode current collector constituting the positive electrode (positive electrode sheet) of the lithium secondary battery, a conductive member made of a metal having good conductivity is preferably used. As such a conductive member, for example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector may be a sheet shape, a foil shape, a mesh shape, or the like. The thickness of the positive electrode current collector is not particularly limited, and can be, for example, 5 to 30 μm. In addition to the positive electrode active material, the positive electrode active material layer can contain additives such as a conductive material and a binder as necessary.

As the positive electrode active material, lithium transition metal composite oxide containing lithium (Li) and at least one transition metal element (preferably at least one of nickel (Ni), cobalt (Co) and manganese (Mn)) Is mentioned. Examples of the composite oxide include so-called binary lithium transition metal composite oxides containing one kind of the transition metal element, so-called binary lithium transition metal composite oxides containing two kinds of the transition metal elements, and transition metal elements. Examples include so-called ternary lithium transition metal composite oxides containing Ni, Co and Mn as constituent elements, and solid solution lithium-excess transition metal composite oxides. These can be used alone or in combination of two or more. As the positive electrode active material, the general formula is LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and A polyanionic compound represented by the following formula is also preferably used: an element selected from the group consisting of V. Among these, a ternary lithium transition metal composite oxide containing Ni, Co, and Mn as transition metal elements as constituent elements is preferable. Typical examples of the ternary lithium transition metal composite oxide include a general formula:
Li (Li _a Ni _x Co _y Mn _z ) O ₂
(A, x, y, and z in the above general formula are real numbers satisfying a + x + y + z = 1); and a ternary lithium transition metal composite oxide represented by:

  Further, the positive electrode active material is selected from the group consisting of Al, Cr, V, Mg, Ca, Ti, Zr, Nb, Mo, Cu, Zn, Ga, In, Sn, La, W, and Ce, or Two or more kinds of metal elements may be further added. The addition amount (blending amount) of these metal elements is not particularly limited, but is 0.01 to 5% by mass (for example, 0.05 to 2% by mass, typically 0.1 to 0.8% by mass). Is appropriate.

  As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. Also, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be used singly or as a mixture of two or more. .

  As the binder, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVdF), and the like conventionally used in compositions for forming a positive electrode active material layer. One kind or two or more kinds of agents may be used alone or in combination. In addition, the binder illustrated above may be used as a thickener and other additives.

  The ratio of the positive electrode active material to the positive electrode active material layer is preferably more than about 50% by mass, for example, 70 to 97% by mass (typically 75 to 95% by mass). Further, the ratio of the additive to the positive electrode active material layer is not particularly limited, but the ratio of the conductive material is about 1 to 20 parts by mass (for example, 2 to 10 parts by mass, typically 100 parts by mass of the positive electrode active material). 3-7 parts by mass). The ratio of the binder is preferably about 0.8 to 10 parts by mass (for example, 1 to 7 parts by mass, typically 2 to 5 parts by mass) with respect to 100 parts by mass of the positive electrode active material.

The basis weight per unit area of the positive electrode active material layer on the positive electrode current collector (the coating amount in terms of solid content of the composition for forming the positive electrode active material layer) is not particularly limited, but a sufficient conductive path From the viewpoint of securing (conductive path), it is 3 mg / cm ² or more (for example, 6 mg / cm ² or more, typically 12 mg / cm ² or more) per side of the positive electrode current collector, and 45 mg / cm ² or less (for example, 28 mg / cm ² or less, typically 22 mg / cm ² or less). The density of the positive electrode active material layer is not particularly limited, but is 1.0 g / cm ³ or more (for example, 1.5 g / cm) in consideration of battery performance and adhesiveness with a facing material (for example, a separator sheet or a resin particle layer). cm ³ or more, and typically 2.0 g / cm ³ or more), 3.8 g / cm ³ or less (e.g., 3.5 g / cm ³ or less, typically be 3.0 g / cm ³ or less) preferable. It is preferable to produce the positive electrode sheet so that the density of the positive electrode active material layer falls within the above range.

  The porosity (porosity) of the positive electrode active material layer is not particularly limited, and is suitably 20% or more (for example, 25% or more, typically 35% or more) from the same viewpoint as the density. 60% or less (for example, 50% or less, typically 40% or less). What is necessary is just to employ | adopt what was computed from the apparent volume, mass, and true density of the positive electrode active material layer for the said porosity. The density and porosity of the positive electrode active material layer can be adjusted by the composition of the constituent components, the coating method, the drying method, the compression method, and the like. The positive electrode sheet is preferably prepared so that the porosity of the positive electrode active material layer falls within the above range.

  As the negative electrode current collector constituting the negative electrode (negative electrode sheet), a conductive member made of a metal having good conductivity is preferably used as in the conventional lithium secondary battery. As such a conductive member, for example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector may be a sheet shape, a foil shape, a mesh shape, or the like. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, about 5 to 30 μm.

  The negative electrode active material layer includes a negative electrode active material capable of occluding and releasing Li ions serving as charge carriers. There is no restriction | limiting in particular in a composition and a shape of a negative electrode active material, The 1 type (s) or 2 or more types of the material conventionally used for a lithium secondary battery can be used. Examples of such a negative electrode active material include carbon materials that are generally used in lithium secondary batteries. Representative examples of the carbon material include graphite carbon (graphite) and amorphous carbon. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Of these, the use of a carbon material mainly composed of natural graphite is preferred. The natural graphite may be a spheroidized graphite. Alternatively, a carbonaceous powder having a graphite surface coated with amorphous carbon may be used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination. Metal lithium may be used as the negative electrode active material. The proportion of the negative electrode active material in the negative electrode active material layer is preferably more than about 50% by mass and about 90 to 99% by mass (for example, 95 to 99% by mass, typically 97 to 99% by mass).

  In addition to the negative electrode active material, the negative electrode active material layer requires one or more binders, thickeners, and other additives that can be incorporated into the negative electrode active material layer of a typical lithium secondary battery. It can be contained accordingly. Examples of the binder include various polymer materials. For example, what can be contained in the positive electrode active material layer can be preferably used with respect to the aqueous composition or the solvent-based composition. Such a binder may be used as a thickener or other additives in addition to being used as a binder. The ratio of these additives in the negative electrode active material layer is not particularly limited, but is preferably about 0.8 to 10% by mass (for example, about 1 to 5% by mass, typically 1 to 3% by mass).

The basis weight per unit area of the negative electrode active material layer on the negative electrode current collector (the coating amount in terms of solid content of the composition for forming the negative electrode active material layer) is not particularly limited, but a sufficient conductive path From the viewpoint of securing a (conduction path), it is 2 mg / cm ² or more (for example, 3 mg / cm ² or more, typically 4 mg / cm ² or more) per side of the negative electrode current collector, and 40 mg / cm ² or less (for example, 22 mg / cm ² or less, typically 10 mg / cm ² or less). The density of the negative electrode active material layer is not particularly limited, but is 1.0 g / cm ³ or more (for example, 1.2 g / cm 2) in consideration of battery performance and adhesiveness with a facing material (for example, a separator sheet or a resin particle layer). cm ³ or more, typically 1.3 g / cm ³ or more), 3.0 g / cm ³ or less (for example, 2.0 g / cm ³ or less, typically 1.5 g / cm ³ or less). preferable. It is preferable to prepare the negative electrode sheet so that the density of the negative electrode active material layer falls within the above range.

  The porosity (porosity) of the negative electrode active material layer is not particularly limited, and is suitably 20% or more (for example, 25% or more, typically 35% or more) from the same viewpoint as the density. 55% or less (eg, 50% or less, typically 40% or less). In addition, what is necessary is just to calculate the porosity of a negative electrode active material layer with the method similar to the porosity of a positive electrode active material layer. In addition, the density and porosity of the negative electrode active material layer can be adjusted by the composition of the constituent components, the coating method, the drying method, the compression method, and the like. The negative electrode sheet is preferably prepared so that the porosity of the negative electrode active material layer is in the above range.

  The separator (separator sheet) disposed so as to separate the positive electrode sheet and the negative electrode sheet may be a member that insulates the positive electrode active material layer and the negative electrode active material layer and allows the electrolyte to move. As said separator sheet, the thing similar to the separator sheet in the conventional lithium secondary battery can be used. Examples of such a member include a porous body, a nonwoven fabric, and a cloth. Especially, the porous sheet (porous resin sheet) which consists of resin can be used preferably.

  Preferable examples of the porous resin sheet include a sheet mainly composed of a thermoplastic resin such as polyolefin (polyethylene (PE), polypropylene (PP), etc.), polyester, and polyamide. As a preferred example, a sheet having a single-layer structure or a multilayer structure (polyolefin-based sheet) mainly composed of one or more kinds of polyolefin-based resins can be given. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which a PP layer is laminated on both sides of the PE layer can be suitably used. The PE may be any polyethylene generally referred to as high-density polyethylene (HDPE), low-density polyethylene (LDPE), or linear (linear) low-density polyethylene (LLDPE), or a mixture thereof. May be. Moreover, the said separator sheet can also contain additives, such as various plasticizers and antioxidant, as needed.

The porosity (porosity) of the separator sheet is preferably about 20 to 70%, and more preferably about 30 to 60%, for example. When the porosity of the separator sheet is too large, the strength may be insufficient or the heat shrinkage may be remarkable. On the other hand, if the porosity is too small, the amount of the electrolyte solution that can be held in the separator sheet decreases, the charge carrier (typically ions) passability decreases, and the charge / discharge characteristics tend to decrease. possible. The porosity of the separator sheet can be calculated by the following method. The apparent volume occupied by the separator sheet of the unit area (surface area) is V1 [cm ³ ], and the mass of the separator sheet of the unit area is W [g]. The ratio between the mass W and the true density ρ [g / cm ³ ] of the resin material constituting the separator sheet, that is, W / ρ is V0. Note that V0 is a volume occupied by a dense body of resin material having a mass W. The porosity of the separator sheet can be calculated from [(V1-V0) / V1] × 100. The porosity of the separator sheet can be adjusted by the material of the resin, the stretching strength, and the like.

  Although the thickness of a separator sheet is not specifically limited, About 5-40 micrometers (for example, 10-30 micrometers, typically 15-25 micrometers) is preferable. When the thickness of the separator sheet is within the above range, the charge carrier passage property of the separator sheet becomes better, and film breakage is less likely to occur.

  A heat resistant layer is formed on the surface of the separator sheet. This heat-resistant layer may contain a filler such as an inorganic filler or an organic filler. A typical example is a heat-resistant layer containing a filler as a main component. In the present specification, the “main component” refers to a component having the largest blending ratio (mass basis) among the blending components, and typically may be a component having a blending ratio of 50% by mass or more. The filler that can be included in the heat-resistant layer may be an organic filler, an inorganic filler, or a combination of an organic filler and an inorganic filler. However, in consideration of heat resistance, dispersibility, and stability, an inorganic filler may be used. preferable. In general, a heat-resistant layer mainly composed of an inorganic filler tends to cause loosening due to the heat-resistant layer due to its properties (rigidity, low adhesion, etc.). Therefore, the suppression of loosening by the resin particle layer in the technology disclosed herein can be suitably exerted for a configuration having a heat-resistant layer mainly composed of an inorganic filler.

  Although it does not specifically limit as an inorganic filler, For example, a metal oxide, a metal hydroxide, etc. are mentioned. Specifically, inorganic oxides such as alumina, boehmite, silica, titania, zirconia, calcia, magnesium hydroxide, and iron oxide, inorganic hydroxides such as aluminum nitride, carbonates such as magnesium carbonate, sulfuric acid Sulfates such as barium, chlorides such as magnesium chloride, fluorides such as barium fluoride, covalent bonds such as silicon, talc, clay, mica, bentonite, montmorillonite, zeolite, apatite, kaolin, mullite, sericite, etc. Mineral materials or artificial products thereof. These can be used alone or in combination of two or more. Of these, alumina, boehmite, silica, titania, zirconia, calcia, and magnesium hydroxide are preferred because of their high electrochemical stability and excellent heat resistance and mechanical strength. Boehmite, alumina, titania, and hydroxide Magnesium is particularly preferred.

  Examples of the organic filler include high heat-resistant resin particles such as aramid, polyimide, polyamideimide, polyethersulfone, polyetherimide, polycarbonate, polyacetal, polyetheretherketone, polyphenylene ether, and polyphenylene sulfide.

  Moreover, when using together an inorganic filler and an organic filler, the compounding ratio (inorganic filler: organic filler) is not particularly limited, but is 10:90 to 90:10 (for example, 20:80 to 70:30, on a mass basis). Typically, it is preferably 30:70 to 60:40).

The form of the filler is not particularly limited, and may be, for example, a particle shape, a fiber shape, a plate shape (flake shape) or the like. The average particle size of the filler is not particularly limited, but it is suitably 0.1 to 15 μm (for example, 0.1 to 5 μm, typically 0.2 to 1.5 μm) in consideration of dispersibility and the like. . As the average particle diameter of the filler, a median diameter (average particle diameter D ₅₀ : 50% volume average particle diameter) that can be derived from the particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method can be employed. .

  The ratio of the filler (for example, inorganic filler) in the entire heat-resistant layer is not particularly limited, but is preferably about 50% by mass or more (for example, 70 to 99.5% by mass, typically 90 to 99% by mass). When the ratio of the filler is within the above range, a desired heat resistance effect can be exhibited, and the anchoring property of the heat resistant layer and the strength (shape retention) of the heat resistant layer itself are improved. Moreover, when forming a heat-resistant layer on a separator sheet, it is easy to adjust the intensity | strength and elongation rate of a separator sheet to a suitable range.

  The heat-resistant layer preferably also contains an additive such as a binder. When the heat-resistant layer forming composition is an aqueous solvent (a solution using water or a mixed solvent containing water as a main component as a binder dispersion medium), the binder is dispersed or dissolved in the aqueous solvent. Polymers can be used. Examples of the polymer that is dispersed or dissolved in the aqueous solvent include, for example, acrylic resins (including homopolymers, copolymers, and modified products), SBR, acrylic acid-modified SBR resins (SBR latex), rubber such as gum arabic Class: Polyolefin resin such as PE; Cellulose polymer such as CMC; PVA; Vinyl acetate polymer; Polyalkylene oxide such as polyethylene oxide (PEO); These polymers can be used alone or in combination of two or more. Of these, acrylic resins, SBR, polyolefin resins, and CMC are preferable.

  When the heat-resistant layer forming composition is a solvent-based solvent (a solution in which the binder dispersion medium is mainly an organic solvent), the binder should be a polymer that is dispersed or dissolved in the solvent-based solvent. Can do. Examples of the polymer dispersed or dissolved in the solvent-based solvent include vinyl halide resins such as PVdF. As PVdF, a homopolymer of vinylidene fluoride is preferably used. Furthermore, PVdF may be a copolymer of a vinyl monomer copolymerizable with vinylidene fluoride. Examples of vinyl monomers copolymerizable with vinylidene fluoride include hexafluoropropylene, tetrafluoroethylene, and ethylene trichloride fluoride. Alternatively, polyacrylonitrile, polymethyl methacrylate, or the like is also preferably used as the polymer that is dispersed or dissolved in the solvent solvent. These may be used alone or in combination of two or more. The materials exemplified above may be used as a thickener or other additives in addition to being used as a binder.

  When the heat-resistant layer contains additives such as a binder and a thickener, the proportion of the additive in the heat-resistant layer is about 10% by mass or less (for example, 0.5 to 8% by mass, typically 1 to 5%). Mass%) is preferred. When the ratio of the filler, if necessary, the binder and other additives is within the above range, the anchoring property of the heat-resistant layer and the strength (shape retention) of the heat-resistant layer itself are improved. Moreover, it becomes easy to adjust the porosity of the heat-resistant layer within a favorable range, and the charge carrier passage tends to be further improved. Furthermore, it is easy to adjust the strength and elongation of the separator sheet on which the heat-resistant layer is formed within a suitable range.

  The porosity (porosity) of the heat-resistant layer is not particularly limited, but 40% or more (for example, 45% or more, typically, in consideration of battery performance, adhesiveness with a facing material (for example, resin particle layer), etc. Is preferably 50% or more), and is preferably about 70% or less (for example, 65% or less, typically 60% or less). The porosity can be determined by appropriately applying the method for calculating the porosity of the separator sheet. The porosity of the heat-resistant layer can be adjusted by the composition of the constituent components, the application method, the drying method, the compression method and the like.

  The thickness of the heat-resistant layer is not particularly limited, but is preferably about 0.5 μm or more (for example, 1 μm or more, typically 2 μm or more). The thickness is preferably about 12 μm or less (for example, 8 μm or less, typically 5 μm or less). When the thickness of the heat-resistant layer is within the above range, a sufficient short-circuit prevention effect can be obtained. Moreover, if the thickness of the heat-resistant layer becomes too large, it is disadvantageous in terms of energy density, and may increase the battery resistance. Furthermore, by adjusting the thickness of the heat-resistant layer, the strength and elongation of the separator sheet on which the heat-resistant layer is formed can be easily adjusted within a suitable range. The thickness of the heat-resistant layer can be obtained by analyzing an image taken with a SEM (Scanning Electron Microscope).

  In the technology disclosed herein, a resin particle layer is disposed between at least one (typically either) of the positive and negative electrode sheets and the heat-resistant layer. The resin particle layer is in contact with either one of the positive and negative electrode sheets (typically the positive and negative active material layers) and the heat-resistant layer. Thereby, at the time of forming the wound electrode body, the electrode sheet and the heat-resistant layer are well bonded (indirectly bonded) through the resin particle layer, and the loosening due to the separation of the electrode sheet and the heat-resistant layer is prevented. It is suppressed. The resin particle layer typically has a structure (porous structure) in which resin particles are stacked while having predetermined pores (spaces). Such a resin particle layer has excellent charge carrier permeability, and can hardly increase battery resistance. Therefore, even if the resin particle layer is present between the positive and negative electrodes, a decrease in battery performance is prevented or suppressed.

  The resin constituting the resin particle layer is not particularly limited. For example, acrylic resins (including modified acrylic resins), SBR, acrylic acid-modified SBR resins (SBR latex), rubbers such as gum arabic; polyolefin resins such as PE and PP; polytetrafluoroethylene (PTFE) , Fluorine resins such as copolymers (PTFE copolymers) of tetrafluoroethylene and other copolymerization components (for example, ethylene, propylene, perfluoroalkyl vinyl ether, etc.); vinyl acetate polymers; poly, such as PEO Alkylene oxide; etc. can be used. These resins can be used alone or in combination of two or more. Of these, PTFE, SBR, and polyolefin resin are preferable. In addition, a resin that is made into a fiber by pressing at the time of forming the wound electrode body is particularly preferable because the bonding action is improved by making it into a fiber. A typical example of such a resin is PTFE. Furthermore, from the viewpoint of improving the adhesion between the electrode sheet and the heat-resistant layer, the resin is preferably a material different from the binder used for the heat-resistant layer.

  Moreover, it is preferable that the resin does not melt or burn at a temperature near the melting point of the separator sheet. For example, the melting point of the resin is preferably higher than the melting point of the separator sheet, and more preferably about 10 ° C. or higher (for example, 30 ° C. or higher, typically 50 to 100 ° C.) higher than the melting point of the separator sheet.

  Although the average particle diameter of the resin particles is not particularly limited, it is suitably about 0.01 to 1 μm from the viewpoint of not exerting the battery performance and exhibiting a good adhesive action. The average particle diameter of the resin particles is preferably about 0.05 to 0.8 μm (for example, 0.1 to 0.6 μm, typically 0.15 to 0.4 μm). The average particle diameter of the resin particles can be obtained based on the light scattering method.

  The resin particle layer is preferably a dispersion type resin particle layer formed from a dispersion containing resin particles. The dispersion type resin particle layer can be formed by applying a dispersion liquid in which resin particles are dispersed to, for example, an electrode sheet or a heat-resistant layer and drying. The dispersion type resin particle layer is more preferable as the resin particle layer because it can be a layer in which the battery performance is more difficult to deteriorate. Preferable examples of the dispersion type resin particle layer include an aqueous dispersion type resin particle layer formed from a resin particle-containing emulsion obtained by emulsion polymerization. Alternatively, water-dispersed resin particles in which a resin polymerized by a solution polymerization method or the like is dispersed in water together with an appropriate emulsifier may be used. In addition to the resin particles, the dispersion may contain conventionally known additives such as emulsifiers in an arbitrary ratio (for example, 10 mass% or less, typically 0.01 to 8 mass%).

  The dispersion containing the resin particle layer has a solid content of approximately 20 to 80% by mass (for example, 30 to 75% by mass, typically, measured in accordance with JIS K6893 from the viewpoint of workability, film formation, and the like. 40 to 65% by mass). The viscosity is preferably about 1 to 150 mPa · s (for example, 10 to 80 mPa · s, typically 15 to 60 mPa · s) for the same reason as in the case of the solid content. The viscosity may be measured with a B-type viscometer.

  The thickness of the resin particle layer is not particularly limited, but is preferably about 0.1 to 10 μm. By setting the thickness to 0.1 μm or more, a good adhesive action can be exhibited. Here, in addition to the adhesive action (binder effect) of the resin particles themselves, the term “adhesive action” includes the adhesive action by the so-called anchor effect in which the resin particle layer bites into the opposing electrode sheet by pressing during molding. Used in When the thickness exceeds 10 μm, it is disadvantageous in terms of energy density, and the resin particle layer may cause an increase in battery resistance. The thickness of the resin particle layer is 0.5 μm or more (for example, 0.8 μm or more, typically 1 μm or more), and more preferably 8 μm or less (for example, 6 μm or less, typically 5 μm or less). From the standpoint of preventing loosening, the thickness of the resin particle layer is particularly preferably 1.2 μm or more (for example, 1.5 μm or more, typically 2 μm or more). The thickness of the resin particle layer can be obtained by analyzing an image photographed by SEM.

  As a method for forming the resin particle layer disclosed herein, for example, the following method is employed. A dispersion containing the resin particles (hereinafter also referred to as a resin particle dispersion) is prepared. This resin particle dispersion may be a commercially available dispersion or may be prepared by mixing and dispersing compounding components such as resin particles. Mixing and dispersing operations can be performed using an appropriate kneader such as a disper mill, a clear mix, a fill mix, a ball mill, a homodisper, or an ultrasonic disperser. Furthermore, the solid content concentration and viscosity may be adjusted by adding or removing a solvent as necessary. As the solvent used in the dispersion, water or a mixed solvent mainly containing water is preferable. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol such as ethanol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

  Next, an appropriate amount of the resin particle dispersion is applied to the surface of a member to be applied (positive or negative electrode sheet or heat-resistant layer, in the case of the second resin particle layer, positive or negative electrode sheet or separator sheet), and further dried. By doing so, a resin particle layer can be formed. The operation of applying the resin particle dispersion can be performed without any particular limitation on conventional general application means. For example, using a suitable coating device (gravure coater, slit coater, die coater, comma coater, dip coat, etc.), a predetermined amount of the above resin particle dispersion is uniformly formed on the surface of the coating target member. Apply. Thereafter, the solvent in the resin particle dispersion is removed by drying the coated product by an appropriate drying means. The drying may be performed at a temperature lower than the melting point of the material constituting the separator sheet (for example, 110 ° C. or lower, typically 30 to 80 ° C.). Or you may hold | maintain under low temperature pressure reduction, and may make it dry. In this way, a resin particle layer can be formed.

  Moreover, in the technique disclosed here, it is preferable that the 2nd resin particle layer is arrange | positioned between either one of the positive and negative electrode sheets, and the heat resistant layer non-formation surface of a separator sheet. By interposing the second resin particle layer between the electrode sheet and the separator sheet, the electrode sheet and the separator sheet are bonded via the second resin particle layer after forming the wound electrode body, so that the electrode sheet A good adhesion state is obtained not only between the heat-resistant layers but also between the electrode sheet and the separator sheet, and the loosening of the wound electrode body is suitably suppressed. In addition, since the structure (composition, thickness, etc.) of the 2nd resin particle layer, the formation method, etc. are the same as that of the above-mentioned resin particle layer (1st resin particle layer), description is not repeated. The configuration of the second resin particle layer may be the same as or different from that of the first resin particle layer.

  Referring to FIG. 5, the total thickness (T1 + T2) of the first resin particle layer thickness T1 and the second resin particle layer thickness T2 is 2 μm or more (eg, 3 μm or more, typically 5 μm or more). ) Is preferable. Thereby, the adhesive action of the resin particle layer is suitably exhibited. The total thickness (T1 + T2) is preferably 10 μm or less (for example, 8 μm or less, typically 6 μm or less). If the total thickness is too large, it is disadvantageous in terms of energy density, and the resin particle layer may cause an increase in battery resistance.

  The flat-shaped wound electrode body in the technique disclosed herein is one in which one of the positive and negative electrode sheets and the heat-resistant layer are well bonded via the resin particle layer (first resin particle layer), Since the other of the positive and negative electrode sheets and the separator sheet can be well bonded via the second resin particle layer, the loosening of the wound electrode body is sufficiently suppressed. Specifically, the wound electrode body has a springback rate of 15% or less (for example, 0 to 10%, typically 0 to 5%) as measured by the method described in Examples described later. Is preferred. The springback rate is particularly preferably substantially 0%.

  The size of the wound electrode body is not particularly limited. However, in general, the larger the size of the wound electrode body, the larger the amount of winding (or it can be grasped as the number of times of winding) proportionally. Therefore, it is preferable to apply the configuration of the present invention to a wound electrode body having a flat portion thickness of 10 mm or more (for example, 12 mm or more, typically 15 mm or more). For the same reason, the larger the battery size (typically the battery capacity), the greater the risk of whispering and loosening. From the viewpoint of effectively avoiding this, it is preferable to apply the configuration of the present invention to a secondary battery having a rated capacity (design capacity) of 5 Ah or more (for example, 10 Ah or more, typically 15 Ah or more). In the present specification, the “thickness of the flat portion of the wound electrode body” refers to the maximum thickness of the flat portion of the flat wound electrode body. Specifically, the thickness indicated by the symbol T in the cross section of the wound electrode body schematically shown in FIG.

  As the nonaqueous solvent and the supporting salt constituting the nonaqueous electrolyte disclosed herein, those conventionally used for lithium secondary batteries can be used without particular limitation. The non-aqueous electrolyte is typically an electrolytic solution having a composition in which a supporting salt is contained in an appropriate non-aqueous solvent (typically, an electrolyte that exhibits a liquid state at room temperature of about 25 ° C., that is, an electrolytic solution). .

  As the non-aqueous solvent, various carbonates, ethers, esters, nitriles, sulfones, lactones, and the like can be used as in the electrolyte solution of a general lithium secondary battery. The carbonates mean to include cyclic carbonates and chain carbonates. The ethers mean to include cyclic ethers and chain ethers. Specific examples of the compound that can be used as the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC). And fluorinated products thereof (preferably, fluorinated carbonates such as monofluoroethylene carbonate (MFEC) and difluoroethylene carbonate (DFEC)) and the like. These can be used individually by 1 type or in mixture of 2 or more types. Of these, a mixed solvent of EC, DMC and EMC is preferable.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , One or more lithium compounds (lithium salts) such as LiI can be used. The concentration of the supporting salt is not particularly limited, but it may be about 0.1 to 5 mol / L (for example, 0.5 to 3 mol / L, typically 0.8 to 1.5 mol / L). it can.

Further, the nonaqueous electrolytic solution may contain an optional additive as required, as long as the object of the present invention is not significantly impaired. The additive may be used for the purpose of, for example, improving the output performance of the battery, improving the storage stability (suppressing the decrease in capacity during storage, etc.), improving the cycle characteristics, improving the initial charge / discharge efficiency. Examples of preferable additives include fluorophosphate (preferably difluorophosphate, for example, lithium difluorophosphate represented by LiPO ₂ F ₂ ), lithium bisoxalate borate (LiBOB), and the like. Further, for example, additives such as cyclohexylbenzene and biphenyl that can be used as a countermeasure against overcharge may be used.

  Next, as a preferred example of the method for manufacturing a secondary battery disclosed herein, a method for manufacturing a lithium secondary battery will be described, but the application target of the present invention is not intended to be limited to the method. . The manufacturing method disclosed herein includes preparing positive and negative electrode sheets, preparing a separator sheet on which a heat-resistant layer is formed, and placing the separator sheet on which a heat-resistant layer is formed between the positive and negative electrode sheets. Making a wound electrode body by winding (winding step), forming the wound electrode body into a flat shape by pressing (molding step), and winding electrode formed into a flat shape Housing the body in a battery case. In addition, the production process of the flat wound electrode body in this manufacturing method may include at least the winding process and the molding process described above. In addition to this, the manufacturing method may include, for example, steps of producing a positive electrode sheet, a negative electrode sheet, a separator sheet, a battery case, and the like. This is not specifically described here. Further, since the construction of the secondary battery in general is the same as described above, it will not be particularly described here.

  In the technique disclosed herein, the production of the wound electrode body may further include disposing a resin particle layer in contact with the electrode sheet and the heat-resistant layer between the electrode sheet and the heat-resistant layer. preferable. The resin particle layer exhibits a good adhesive action when the wound electrode body is molded. Therefore, the electrode sheet and the heat-resistant layer are favorably bonded via the resin particle layer. Thereby, the loosening resulting from the separation of the electrode sheet and the heat-resistant layer can be suppressed. For example, the above-described arrangement can be obtained by forming a resin particle layer on the surface of the heat-resistant layer or on the surface of the electrode sheet (either one of the positive and negative electrode sheets) facing the heat-resistant layer. Among these, it is particularly preferable to form a resin particle layer on the surface of the heat-resistant layer. Since the composition and the like are as described above, description thereof will not be repeated here.

  In the production method disclosed herein, in the production of the wound electrode body, it is preferable to form the heat-resistant layer only on one surface of both surfaces of the separator sheet. Thereby, the separator sheet is configured to have a heat-resistant layer forming surface and a heat-resistant layer non-forming surface. In this configuration, as described above, the resin particle layer (first resin particle layer) is disposed between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. . And in said structure, a 2nd resin particle layer is arrange | positioned so that the other side of an electrode sheet and the heat-resistant layer non-formation surface of a separator sheet may contact between the other of an electrode sheet and the heat-resistant layer non-formation surface of a separator sheet It is preferable to do. Thereby, not only the electrode sheet-heat resistant layer but also the adhesion state between the electrode sheet-separator sheet becomes favorable, and the loosening of the wound electrode body is suitably suppressed. Since the configuration and arrangement method of the second resin particle layer are as described above, description thereof will not be repeated here.

  In the technique disclosed herein, a separator electrode on which a heat-resistant layer is formed is placed between positive and negative electrode sheets and wound to produce a wound electrode body, and then the produced wound electrode body is pressed. To form a flat shape. The pressing conditions may vary depending on the battery size and the like, but are not particularly limited. For example, about 100 to 100000 kgf (for example, 500 to 50000 kgf, typically 1000 to 10000 kgf) from the side surface at normal temperature with respect to one wound electrode body. The press may be performed under a condition of about 5 to 600 seconds (for example, 10 to 300 seconds).

  The flat-shaped wound electrode body formed in this way is held in a state where the positive and negative electrode sheets and the heat-resistant layer are bonded via the resin particle layer in the flat portion. Preferably, in the flat portion (typically a flat portion that has been flattened by pressing), one of the positive and negative electrode sheets that can be opposed to the heat-resistant layer and the heat-resistant layer are interposed via the resin particle layer. It can be in close contact. Preferably, the other of the positive and negative electrode sheets and the surface of the separator sheet where the heat-resistant layer is not formed can be in close contact with each other via the second resin particle layer. Such a wound electrode body can typically have the above-described springback rate.

  Moreover, the manufacturing method disclosed here may not have a remolding process or a shape holding process after the wound electrode body is formed into a flat shape. In the wound electrode body provided with the resin particle layer disclosed herein between the positive and negative electrode sheets and the heat-resistant layer, the loosening of the winding is suppressed because the resin particle layer has good adhesiveness. Therefore, there is no need for a re-molding step or a shape holding step that can be performed when the loosening occurs. Here, the re-molding step may be a step similar to the above-described molding step (for example, a step of pressing under the same conditions). The shape holding step is a step of holding the shape after pressing so that no loosening occurs, and the conditions and the like are not particularly limited. For example, after the pressing by applying a predetermined pressing pressure as necessary at about 40 ° C. or higher (for example, 50 to 90 ° C., typically 60 to 80 ° C.) for 1 hour or longer (for example, 2 to 8 hours). It may be a step of maintaining the shape.

  Thereafter, the wound electrode body formed into a flat shape is accommodated in the battery case. Since the resin particle layer disclosed here exhibits good adhesion between the positive and negative electrode sheets and the heat-resistant layer, the loosening is prevented or suppressed. For this reason, the winding electrode body cannot be accommodated in the battery case due to the large degree of loosening of the winding. In addition, if the degree of loosening is large, the gap at the winding center of the wound electrode body becomes small, so there is a possibility that the current collector terminal welding work will be hindered because the current collector terminal welding jig does not enter. By applying the resin particle layer, such inconvenience is unlikely to occur. Therefore, a decrease in productivity due to the loosening can be avoided. A non-aqueous electrolyte is accommodated (typically injected) in the battery case at an appropriate timing before and after (typically after the electrode body is accommodated in the battery case), and the inside of the battery case is sealed. Thus, a lithium secondary battery is constructed.

  As described above, the lithium secondary battery according to the technology disclosed herein is excellent in productivity because the loosening after the wound electrode body is manufactured is suppressed. Therefore, it can be preferably used as a battery for various applications. Further, considering that the above-mentioned loosening is likely to occur in a larger battery, the effect of suppressing the above-mentioned loosening can be more suitably exhibited in a larger battery. Therefore, for example, as shown in FIG. 7, the lithium secondary battery 100 is mounted on a vehicle 1 such as an automobile and can be suitably used as a power source for a drive source such as a motor that drives the vehicle 1. Therefore, the present invention provides a vehicle (typically an automobile, particularly a hybrid automobile (HV), a plug-in hybrid automobile (including a battery pack typically formed by connecting a plurality of series-connected batteries) 100 as a power source. PHV), an electric vehicle (EV), a vehicle equipped with an electric motor such as a fuel cell vehicle) 1 can be provided.

  Next, several examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in these examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Reference Example 1>
[Preparation of positive electrode sheet]
Lithium nickel manganese cobaltate (Li [Ni _1/3 Mn _1/3 Co _1/3 ] O ₂ ) powder as a positive electrode active material, acetylene black as a conductive material, PVdF as a binder, A paste-like composition for forming a positive electrode active material layer was prepared by mixing with N-methyl-2-pyrrolidone so that the mass ratio was 93: 4: 3. This composition was uniformly applied to both sides of a long sheet-like aluminum foil (thickness 15 μm) so that the coating amount per side was 15 mg / cm ² (solid content basis), and after drying, By compressing, a sheet-like positive electrode (positive electrode sheet) was produced. The density of the positive electrode active material layer was 2.8 g / cm ³ .

[Preparation of negative electrode sheet]
As the negative electrode active material, spherical graphite particles (carbon-coated spherical graphite particles) in which natural graphite powder was coated with amorphous carbon were prepared. The graphite particles, SBR as a binder, and CMC as a thickener are mixed with ion-exchanged water so that the mass ratio of these materials becomes 98: 1: 1, and a paste-like negative electrode active material A layer forming composition was prepared. The composition is uniformly applied to both sides of a long sheet-like copper foil (thickness 10 μm), dried, and then compressed, whereby the basis weight per side (solid content basis) is 7.5 mg / cm. ² sheet-like negative electrode (negative electrode sheet) was produced. The density of the negative electrode active material layer was 1.4 g / cm ³ .

[Preparation of separator sheet with heat-resistant layer]
As the separator sheet, a long sheet-like single layer film (thickness: 16 μm) made of PE was used. A heat resistant layer was formed on one side of the separator sheet. Specifically, a paste-like composition was prepared by mixing boehmite as a filler and an acrylic binder as a binder at a mass ratio of 95: 5 with ion-exchanged water. Mixing was performed using an ultrasonic disperser “CLEAMIX” manufactured by M Technique Co., Ltd. for 5 minutes at 15000 rpm and for 15 minutes at 20000 rpm. The obtained composition for forming a heat-resistant layer was applied by a gravure coating method so as to cover the entire surface of the separator sheet, and dried at a temperature of 70 ° C. to form a heat-resistant layer. In this way, a separator sheet with a heat-resistant layer in which a heat-resistant layer having a thickness of 3 μm was formed on one side was produced.

[Production of flat wound electrode body]
The produced positive electrode sheet and negative electrode sheet are laminated so that two separator sheets with a heat-resistant layer are arranged one by one between the positive electrode sheet and the negative electrode sheet, and the laminate is wound to wind the wound body (Winding step). The separator sheet was disposed so that the heat-resistant layer faced the positive electrode sheet. The flat wound electrode body (thickness of the flat part: 12 mm) according to Reference Example 1 was produced by pressing the obtained wound body from the side direction and causing it to be bent (molding step). The press was performed at 1000 kgf at room temperature for 300 seconds.

[Preparation of prismatic lithium secondary battery]
In order to suppress the loosening of the flat wound electrode body, the flat surface was restrained at 70 ° C. for 4 hours (shape holding step). For the flat wound electrode body thus obtained, the electrode terminals were joined to the ends of the positive and negative electrode current collectors, respectively, and accommodated in an aluminum square battery case together with the non-aqueous electrolyte, and then the battery The case was sealed. As the non-aqueous electrolyte, a mixed solvent containing EC, EMC, and DMC at a volume ratio of 3: 3: 4 and containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / L was used. . In this manner, a prismatic lithium secondary battery (design capacity: 5 Ah) according to Reference Example 1 was produced.

<Reference Example 2>
[Production of positive electrode sheet with heat-resistant layer]
A heat-resistant layer was formed on one side of the positive electrode sheet produced in Reference Example 1. Specifically, the heat-resistant layer forming composition prepared in Reference Example 1 was applied by a gravure coating method so as to cover the entire surface of the positive electrode sheet, and dried at a temperature of 70 ° C. to form a heat-resistant layer. In this way, a positive electrode sheet with a heat-resistant layer in which a heat-resistant layer having a thickness of 3 μm was formed on one side was produced.

[Production of flat wound electrode body]
The positive electrode sheet with the heat-resistant layer produced above and the negative electrode sheet produced by the same method as in Reference Example 1 were separated into two separator sheets (long sheet-like single-layer film made of PE (thickness: 16 μm)). Were laminated so that one sheet was placed between the positive electrode sheet and the negative electrode sheet, and the laminate was wound to produce a wound body. A flat wound electrode body according to Reference Example 2 was produced in the same manner as Reference Example 1 except that this wound body was used.

[Measurement of springback rate]
During manufacturing the wound electrode body, and a thickness T _B of the wound electrode body flat portion after 5 minutes from the winding thickness T _A and press the end of the electrode body pars plana immediately after the press (press opening) It was measured. The measured thickness is specifically the thickness T of the flat portion 21 of the wound electrode body 20 schematically shown in FIG. Formula: spring back ratio _{(%) = (T B -T} A) / T A × 100; was determined from the spring-back rate. The results are shown in Table 1. In Reference Example 1, measurement was performed on a sample before the shape holding step.

  As shown in Table 1, in Reference Example 1 in which a heat-resistant layer was formed on the separator sheet surface, the springback rate was a high value of 29.2%, whereas in Reference Example, a heat-resistant layer was formed on the positive electrode sheet surface. In 2, the springback rate was 0%. From this result, in the secondary battery of this configuration, even if a heat-resistant layer is formed on the surface of the positive electrode sheet, no loosening occurs, and the loosening occurs remarkably when the heat-resistant layer is formed on the separator sheet surface. Recognize.

<Example 1>
About the separator sheet with a heat-resistant layer produced in Reference Example 1, a PTFE aqueous dispersion (solid content: 60% by mass, viscosity: 25 mPa · s, average particle diameter of resin particles on both surfaces of the separator sheet where the heat-resistant layer is not formed and the surface of the heat-resistant layer. 0.20 to 0.25 μm) was applied by a gravure coating method and dried at a temperature of 70 ° C., thereby forming a 1 μm-thick resin particle layer made of PTFE resin particles on each surface. A flat wound electrode body was produced in the same manner as in Reference Example 1 except that the separator sheet with a heat-resistant layer on which the resin particle layer was formed was used, and the springback rate was measured. The results are shown in Table 2. The resin particle layer formed on the surface of the heat-resistant layer is referred to as a first resin particle layer, and the resin particle layer formed on the surface of the separator sheet where the heat-resistant layer is not formed is referred to as a second resin particle layer. For convenience, in the table, the thickness of the first resin particle layer is expressed as the first thickness, and the thickness of the second resin particle layer is expressed as the second thickness.

<Examples 2 to 6>
A flat wound electrode body according to Examples 2 to 5 was produced in the same manner as in Example 1 except that the resin particle layer was formed to have a thickness (2 to 5 μm) shown in Table 2, and the springback rate was It was measured. The results are shown in Table 2. In Table 2, the outline and results of Reference Example 1 are shown as Example 6 for comparison. In addition, a rectangular lithium secondary battery according to Example 3 was fabricated in the same manner as in Reference Example 1 except that the flattened wound electrode body according to Example 3 was not subjected to the shape holding step.

<Examples 7 to 12>
A long sheet-like three-layer structure film (thickness: 20 μm) made of PP / PE / PP was used as the separator sheet. A heat resistant layer was formed on one side of the separator sheet in the same manner as in Example 1, and a resin particle layer was further formed thereon. Other than that, a flat wound electrode body according to Example 7 was produced in the same manner as in Example 1. Moreover, the flat-shaped wound electrode body which concerns on Examples 8-11 was produced like Example 7 except having formed the resin particle layer so that it might become thickness (2-5 micrometers) shown in Table 2. FIG. Further, a flat wound electrode body according to Example 12 was produced in the same manner as Example 7 except that the resin particle layer was not formed. For the wound electrode body according to each example, the springback rate was measured at the time of production. The results are shown in Table 2.

<Examples 13 to 15>
A flat wound electrode body according to Examples 13 to 15 was produced in the same manner as in Example 3 except that the filler was changed from boehmite to alumina (Example 13), titania (Example 14) or magnesium hydroxide (Example 15). The springback rate was measured. The results are shown in Table 2.

<Examples 16 to 18>
Example 16 is the same as Example 3 except that the resin particle layer forming material is changed from the PTFE aqueous dispersion to the SBR aqueous dispersion (Example 16), the PE aqueous dispersion (Example 17), and the PP aqueous dispersion (Example 18). A flat-shaped wound electrode body according to -18 was produced, and the springback rate was measured. The results are shown in Table 2.

<Example 19>
About the separator sheet with a heat-resistant layer produced in Reference Example 1, a resin particle layer made of PTFE resin particles having a thickness of 3 μm was formed only on the surface of the heat-resistant layer. The resin particle layer is not formed on the heat-resistant layer non-formation surface of this separator sheet with a heat-resistant layer. A flat wound electrode body was produced in the same manner as in Example 1 except that this separator sheet with a heat-resistant layer was used, and the springback rate was measured. The results are shown in Table 2.

<Example 20>
For the separator sheet with a heat-resistant layer produced in Reference Example 1, a gravure solution containing an acrylic resin (non-dispersion type resin) obtained by solution polymerization on both the heat-resistant layer non-formation surface and the heat-resistant layer surface of the separator sheet By applying by a coating method and drying at a temperature of 70 ° C., a resin layer (thickness 3 μm) made of an acrylic resin was formed on each surface. A flat wound electrode body was prepared in the same manner as in Example 1 except that the separator sheet with a heat-resistant layer on which the resin layer was formed was used, and the springback rate was measured. The results are shown in Table 3. Further, a square lithium secondary battery according to Example 20 was produced in the same manner as Example 3 except that this wound electrode body was used. In addition, as a result of performing cross-sectional observation by SEM about the said resin layer after drying, the resin which comprises the said resin layer has a form which forms a film | membrane and covers the to-be-adhered body surface, and is not a particulate form. confirmed.

<Example 21>
For the separator sheet with a heat-resistant layer produced in Reference Example 1, a solution containing a polyacrylamide resin (non-dispersion type resin) obtained by solution polymerization on both the non-heat-resistant layer surface and the heat-resistant layer surface of the separator sheet is gravure. By applying by a coating method and drying at a temperature of 70 ° C., a resin layer (thickness 3 μm) made of polyacrylamide resin was formed on each surface. A flat wound electrode body was prepared in the same manner as in Example 1 except that the separator sheet with a heat-resistant layer on which the resin layer was formed was used, and the springback rate was measured. The results are shown in Table 3. Further, a rectangular lithium secondary battery according to Example 21 was produced in the same manner as Example 3 except that this wound electrode body was used. In addition, as a result of performing cross-sectional observation by SEM about the said resin layer after drying, the resin which comprises the said resin layer has a form which forms a film | membrane and covers the to-be-adhered body surface, and is not a particulate form. confirmed.

  As shown in Table 2, in Examples 1 to 5, 7 to 11, and 13 to 19 in which the resin particle layer is disposed between the heat resistant layer of the separator sheet with a heat resistant layer and the electrode sheet (positive electrode sheet), the springback rate Was as low as 5% or less. This is presumably because the electrode sheet and the heat-resistant layer were favorably bonded through the resin particle layer when the resin particle layer was in contact with the electrode sheet and the heat-resistant layer. More specifically, in addition to the adhesive action of the resin particles themselves, it is considered that the resin particle layer bites into the electrode sheet by pressing at the time of molding the electrode body, and the adhesive action due to the so-called anchor effect is suitably exhibited. On the other hand, in Examples 6 and 12 in which the resin particle layer was not provided, the springback rate was a high value of 25% or more. From these results, it can be seen that the loosening can be suppressed by disposing the resin particle layer between the electrode sheet and the heat-resistant layer.

  Further, in Examples 16 to 18 in which SBR, PE, and PP are used as the resin constituting the resin particle layer, the springback rate tends to be higher than that in Example 3 in which the PTFE resin particle layer having the same thickness is disposed. It was. From these results, it can be seen that PTFE is particularly preferable as the resin constituting the resin particle layer. The reason is considered that PTFE was made into a fiber by a press at the time of forming the wound electrode body and exhibited a better adhesive action. Further, in Example 19 in which the resin particle layer was disposed only between the electrode sheet and the heat-resistant layer, the PTFE resin particle layer having the same thickness was disposed also between the electrode sheet and the surface of the separator sheet where the heat-resistant layer was not formed. Compared to Example 3, there was a tendency for the springback rate to be high. From this result, in the configuration in which the heat-resistant layer is formed on the separator sheet, the resin particle layer is disposed not only between the electrode sheet and the heat-resistant layer but also between the electrode sheet and the surface where the heat-resistant layer is not formed on the separator sheet. It is clear that this is desirable. Furthermore, it can be seen from the results of Examples 7 to 11 and 13 to 15 that even if the configuration of the separator and the configuration of the heat-resistant layer are changed, the springback suppressing effect by the resin particle layer can be exhibited.

  Although not clearly shown, the battery according to Example 3 in which the resin particle layer is disposed between the heat-resistant layer of the separator sheet with a heat-resistant layer and the electrode sheet exhibited good battery performance (typically low resistance). . In other words, no particular deterioration in battery performance due to the arrangement of the resin particle layer was observed. On the other hand, in the batteries according to Examples 20 and 21 in which the layer made of the non-dispersion resin is disposed between the electrode sheet and the heat-resistant layer, the battery performance tends to be significantly reduced (typically, low-temperature IV resistance). Tended to rise significantly). Therefore, the resin layer disposed between the electrode sheet and the heat-resistant layer is desirably a resin particle layer (preferably a dispersion type resin particle layer) from the viewpoint of battery performance. Thus, according to the present invention, the spring back of the flat wound electrode body can be suppressed without deteriorating the battery performance. Therefore, according to the present invention, it is possible to avoid a decrease in productivity due to loosening without reducing battery performance.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein may include various modifications and alterations of the specific examples described above.

1 Automobile (vehicle)
DESCRIPTION OF SYMBOLS 10 Battery case 12 Opening part 14 Cover body 20 Winding electrode body 21 Flat part 25 Non-aqueous electrolyte 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 35 Positive electrode collector laminated part 36 Positive electrode active material layer non-formation part 37 Internal positive electrode terminal 38 External positive electrode terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 45 Negative electrode current collector laminated portion 46 Negative electrode active material layer non-formation portion 47 Internal negative electrode terminal 48 External negative electrode terminal 50A, 50B Separator sheet 50Aa Heat-resistant layer forming surface 50Ab Heat-resistant layer non-forming surface 51 Heat-resistant layer 52 Resin particle layer 52A First resin particle layer 52B Second resin particle layer 100 Lithium secondary battery

Claims (10)

A secondary battery in which a flat wound electrode body is housed in a battery case,
The wound electrode body includes a positive and negative electrode sheet, and a separator sheet disposed between the positive and negative electrode sheets,
A heat-resistant layer is formed on the surface of the separator sheet,
A secondary battery in which a resin particle layer is disposed between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. The separator sheet has a heat-resistant layer forming surface on which the heat-resistant layer is formed, and a heat-resistant layer non-formed surface on which the heat-resistant layer is not formed,
Between one of the electrode sheets and the heat-resistant layer, the resin particle layer as the first resin particle layer is disposed so as to be in contact with one of the electrode sheets and the heat-resistant layer,
A second resin particle layer is disposed between the other of the electrode sheets and the non-heat-resistant layer-forming surface of the separator sheet so as to be in contact with the other of the electrode sheets and the non-heat-resistant layer-forming surface. Item 11. The secondary battery according to Item 1.   The secondary battery according to claim 1, wherein the resin particle layer is a dispersion type resin particle layer formed from a dispersion containing resin particles.   The secondary battery according to any one of claims 1 to 3, wherein the resin constituting the resin particle layer is at least one selected from the group consisting of polytetrafluoroethylene, styrene butadiene rubber, and polyolefin.   The secondary battery according to claim 1, wherein the heat-resistant layer contains an inorganic filler at a ratio of 50% by mass or more.   The secondary battery according to claim 1, wherein the wound electrode body has a flat portion having a thickness of 10 mm or more. A method for manufacturing a secondary battery, comprising:
Preparing positive and negative electrode sheets,
Preparing a separator sheet on which a heat-resistant layer is formed;
Producing a wound electrode body by placing and winding the separator sheet on which the heat-resistant layer is formed between the positive and negative electrode sheets;
Pressing the produced wound electrode body into a flat shape, and accommodating the wound electrode body shaped into the flat shape in a battery case,
Including
The production of the wound electrode body further includes disposing a resin particle layer between one of the electrode sheets and the heat-resistant layer so as to be in contact with one of the electrode sheets and the heat-resistant layer. A method for manufacturing a secondary battery. In producing the wound electrode body,
By forming the heat-resistant layer only on one surface of both surfaces of the separator sheet, the separator sheet is configured to have a heat-resistant layer forming surface and a heat-resistant layer non-forming surface,
Between one of the electrode sheets and the heat-resistant layer, disposing a resin particle layer as a first resin particle layer so as to be in contact with one of the electrode sheets and the heat-resistant layer; and the other of the electrode sheets Disposing the second resin particle layer in contact with the other surface of the electrode sheet and the heat-resistant layer non-formed surface between the heat-resistant layer non-formed surface of the separator sheet;
The manufacturing method of Claim 7 which further includes these. The wound electrode body measures the thickness T _B of the thickness T _A and wound electrode body flat portion after 5 minutes from the press end of wound electrode body flat portion of the press immediately following formula: _{T B -T a) / T a} × 100; a sought spring back ratio is 5% or less, the production method according to claim 7 or 8. A vehicle comprising the secondary battery according to claim 1.

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