JP5704405B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery including an electrolytic solution, and more particularly to a secondary battery including a porous insulating layer between an electrode sheet and a separator sheet.

  In recent years, lithium secondary batteries, nickel metal hydride batteries and other secondary batteries (storage batteries) have become increasingly important as power sources for mounting on vehicles or as power sources for personal computers and portable terminals. In particular, a lithium secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source for mounting on a vehicle. One typical configuration of this type of lithium secondary battery includes a positive electrode, a negative electrode, and a porous separator interposed between the positive electrode and the negative electrode. The separator plays a role of forming an ion conduction path between both electrodes by preventing a short circuit due to contact between the positive electrode and the negative electrode and impregnating the electrolyte in the pores of the separator.

  Conventionally, a porous resin sheet made of polyethylene (PE), polypropylene (PP), or the like has been used as a separator. Since the separator is porous, heat shrinkage occurs when the temperature increases. Using this, the shutdown function works. However, if the degree of thermal contraction is large, a local short circuit due to a membrane breakage or the like may occur, and the short circuit may further expand therefrom. In order to prevent direct contact between the positive electrode and the negative electrode even when the separator is thermally contracted, it has been proposed to form a porous insulating layer between the separator and the electrode. The porous insulating layer is formed by applying a coating containing an inorganic filler and a binder to the surface of the separator or electrode and drying it. In addition, instead of forming the porous insulating layer over the entire surface of the separator or electrode, it is also considered to provide the porous insulating layer only partially, for example, at a place where an internal short circuit easily occurs. As this type of prior art, Patent Document 1 describes that a porous heat-resistant layer is partially formed between a separator and an electrode.

JP 2006-120604 A

  However, as in Patent Document 1, when a porous heat-resistant layer is partially formed between the separator and the electrode, the electrolyte solution has a permeability between the portion with the porous heat-resistant layer and the portion without the porous heat-resistant layer. There is a difference. Therefore, in a battery in which a porous insulating layer is partially disposed, the electrolytic solution does not uniformly penetrate the entire electrode body, and the distribution of the electrolytic solution is uneven. If the distribution of the electrolytic solution is uneven, potential unevenness occurs and the capacity retention rate after the cycle decreases, which is not preferable. The present invention has been made in view of such a point, and the main purpose thereof is a secondary battery including a porous insulating layer between a separator and an electrode without causing uneven electrolyte penetration. It is intended to improve the permeability of the electrolytic solution.

  In order to achieve the above object, a non-aqueous electrolyte type secondary battery provided by the present invention includes an electrode body in which a positive electrode sheet and a negative electrode sheet are overlapped with each other via a separator sheet, and an electrolytic solution. It is a secondary battery. A porous insulating layer containing an inorganic filler and a binder is respectively provided in a predetermined direction (typically the sheet) on the opposing surfaces of at least one of the positive electrode sheet and the negative electrode sheet and the separator sheet. In the longitudinal direction). Then, the porous insulating layer formed on both sheets in the facing surface includes a portion in which the porous insulating layer of one sheet is not formed and a pore in contact with the portion in a state where both sheets are overlapped with each other. The end portion of the porous insulating layer (the end portion in the predetermined direction of the porous insulating layer) is disposed so as to be in a positional relationship that can be opposed to the porous insulating layer of the other sheet.

  According to such a configuration, in a state where the electrode sheet and the separator sheet are overlapped with each other, there is a large gap between the portion where the porous insulating layer of one sheet is not formed and the porous insulating layer of the other sheet facing the other. A space is formed. The electrolyte can be circulated from the outside to the inside of the electrode body using the space. As a result, the permeability of the electrolytic solution is improved, and the penetration time of the electrolytic solution (and hence the manufacturing time of the battery) can be reduced. According to such a configuration, since the flow path (space) of the electrolytic solution is formed over the entire surface between both sheets, the electrolytic solution uniformly permeates the entire electrode body. Therefore, it is possible to improve the electrolyte penetration into the electrode body without causing uneven penetration of the electrolyte, and the technical value is high. Furthermore, in the electrode body having such a configuration, the ends of the porous insulating layers of both sheets are arranged so as to overlap (wrap) each other, so when viewed from a direction orthogonal to the opposing surfaces of both sheets In addition, the porous insulating layer is present across the entire surface between the two sheets without any gaps. Therefore, even when the separator sheet is thermally contracted due to overcharge or the like, the occurrence of an internal short circuit can be prevented by preventing direct contact between the positive and negative electrodes by the porous insulating layer. Therefore, according to the present invention, it is possible to provide an optimal secondary battery that is free from internal short circuit and has improved electrolyte permeability.

  In a preferred aspect of the secondary battery disclosed herein, the porous insulating layer on the two opposing sheets is one porous insulating member along a predetermined direction (typically, a longitudinal direction in the sheet). The length of the non-formed portion between the layer and one porous insulating layer adjacent to the layer (that is, the length along the predetermined direction of the portion where the porous insulating layer of both sheets is not formed) is 5 mm to 500 mm It is formed to become. By setting the length of the non-formed portion to 5 mm or more, the space into which the electrolytic solution permeates is expanded, and the permeability of the electrolytic solution is further improved. On the other hand, if the length of the non-formed portion is more than 500 mm, the structure is close to that of the conventional structure in which the porous insulating layer is not intermittently formed, and thus the electrolyte permeability improving effect may be insufficient. . From the viewpoint of improving electrolyte solution permeability, a range of 5 mm to 500 mm is usually appropriate, preferably 10 mm to 300 mm, and particularly preferably 10 mm to 100 mm.

  In a preferred embodiment of the secondary battery disclosed herein, the thickness of at least one of the porous insulating layers on the two opposing sheets is 2 μm to 50 μm. When the thickness of the porous insulating layer is less than 2 μm, in addition to the difficulty of coating, the space for infiltrating the electrolyte may be reduced, and the effect of improving the electrolyte permeability may be insufficient. On the other hand, when the thickness of the porous insulating layer exceeds 50 μm, the amount of the electrode active material in the unit volume of the battery is relatively reduced, and thus the battery capacity may tend to decrease. From the viewpoint of satisfying both the increase in capacity and the effect of improving electrolyte permeability, it is usually in the range of 2 μm to 50 μm, preferably 2 μm to 30 μm, and particularly preferably 2 μm to 10 μm.

  In a preferred embodiment of the secondary battery disclosed herein, the end portions of the porous insulating layers on both sheets overlap each other when viewed from a direction orthogonal to the facing surfaces of the two facing sheets. The width along the predetermined direction is at least 0.1 mm or more. According to this configuration, when the electrode body is a wound electrode body, when the porous insulating layers of both sheets are arranged in the R portion of the wound electrode body, the ends of the porous insulating layer overlap (wrapping). The two sheets can be made to face each other reliably. Therefore, the occurrence of an internal short circuit can be prevented more reliably. The upper limit of the width of the overlapping part is not particularly limited, but if the width of the overlapping part is too large, the space (flow path) for infiltrating the electrolytic solution is opened, so that the electrolytic solution penetrates uniformly into the entire electrode body. There may not be. From the viewpoint of preventing the uneven penetration of the electrolytic solution, approximately 30 mm or less is appropriate, preferably 20 mm or less, and particularly preferably 10 mm or less.

  In a preferred aspect of the secondary battery disclosed herein, the electrode body is a wound in which the long positive electrode sheet and the long negative electrode sheet are wound through the long separator sheet. It is an electrode body. The porous insulating layer is provided both between the positive electrode sheet and the separator sheet and between the negative electrode sheet and the separator sheet. According to such a configuration, compared to the case where the porous insulating layer is formed only between one of the positive electrode sheet and the separator sheet and between the negative electrode sheet and the separator sheet, the space (flow path) for infiltrating the electrolytic solution. More. For this reason, the permeability of the electrolytic solution is remarkably improved, and a secondary battery having better battery performance is obtained.

  As described above, any of the secondary batteries disclosed herein is excellent in electrolyte permeability and has no risk of an internal short circuit. For example, a secondary battery mounted on a vehicle such as an automobile (typically Is suitable as a secondary battery for use as a drive power source. Therefore, according to the present invention, there is provided a vehicle including 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). In particular, a vehicle (for example, a plug-in hybrid vehicle (PHV) or an electric vehicle (EV) that can be charged with a household power source) provided with the secondary battery as a power source is provided.

It is a perspective view which shows typically the external appearance of the secondary battery which concerns on one Embodiment of this invention. It is a figure which shows the II-II cross section of FIG. 1 typically. It is a schematic diagram for demonstrating the wound electrode body used for one Embodiment of this invention. (A) is a top view which shows typically the opposing surface which opposes the separator sheet of a negative electrode sheet, (b) is a top view which shows typically the opposing surface which opposes the negative electrode sheet of a separator sheet. FIG. 3 is a schematic cross-sectional view showing an enlarged main part of a cross section along a winding direction (longitudinal direction) in a state where a negative electrode sheet and a separator sheet are wound on each other and wound. It is a front view which shows typically the wound electrode body used for one Embodiment of this invention. It is a side view which shows typically the vehicle carrying a secondary battery.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, a manufacturing method of a positive electrode active material and a negative electrode active material, a configuration and a manufacturing method of a separator and an electrolyte, a secondary method) General techniques related to battery construction, etc.) can be grasped as design matters of those skilled in the art based on conventional techniques in the field.

  Although not intended to be particularly limited, in the following, a lithium secondary battery in a form in which a wound electrode body (wound electrode body) and a nonaqueous electrolyte solution are housed in a rectangular battery case is taken as an example. The present invention will be described in detail.

  1 to 3 show a schematic configuration of a lithium secondary battery according to an embodiment of the present invention. This lithium secondary battery 100 includes a long positive electrode sheet 10 and a long negative electrode sheet 20 laminated and wound through a long separator sheet 40 (winding electrode). Body) 80 is housed in a battery case 50 having a shape (box shape) capable of housing the wound electrode body 80 together with the nonaqueous electrolytic solution 90 (FIG. 2) impregnated in the electrode body.

  The battery case 50 includes a box-shaped case main body 52 having an open upper end, and a lid 54 that closes the opening. As a material constituting the battery case 50, a metal material such as aluminum, steel, or Ni plating SUS is preferably used. Or the battery case 50 formed by shape | molding resin materials, such as a polyphenylene sulfide resin (PPS) and a polyimide resin, may be sufficient. On the upper surface of the battery case 50 (that is, the lid 54), there are a positive terminal 70 electrically connected to the positive electrode 10 of the wound electrode body 80 and a negative electrode terminal 72 electrically connected to the negative electrode 20 of the wound electrode body 80. Is provided. Inside the battery case 50, the wound electrode body 80 is accommodated together with the non-aqueous electrolyte 90.

<Winded electrode body>
The wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium secondary battery except that the porous insulating layer 30 is provided between the negative electrode sheet 20 and the separator sheet 40. As shown in FIG. 3, the positive electrode sheet 10 and the negative electrode sheet 20 have a structure in which they are laminated and wound via two separator sheets 40.

<Negative electrode sheet>
The negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22. However, the negative electrode active material layer 24 is not attached to one side edge (upper side edge portion in FIG. 3) along the edge in the width direction of the negative electrode sheet 20, and the negative electrode current collector 22 has a constant width. An exposed negative electrode active material layer non-forming portion is formed. For the negative electrode current collector 22, a copper foil or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal oxides (such as lithium titanium oxide), and lithium transition metal nitrides.

  In addition to the negative electrode active material, the negative electrode active material layer 24 can contain one or two or more materials that can be used as a constituent component of the negative electrode active material layer in a general lithium secondary battery, if necessary. Examples of such materials include polymer materials that can function as a binder for the negative electrode active material (for example, styrene butadiene rubber (SBR)), and polymers that can function as a thickener for the paste for forming the negative electrode active material layer. Examples thereof include materials (for example, carboxymethyl cellulose (CMC)).

<Positive electrode sheet>
Similarly to the negative electrode sheet 20, the positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a long sheet-like foil-like positive electrode current collector 12. However, the positive electrode active material layer is not attached to one side edge (the lower side edge portion in FIG. 3) along the edge in the width direction of the positive electrode sheet 10, and the positive electrode current collector 12 has a constant width. An exposed positive electrode active material layer non-forming portion is formed. For the positive electrode current collector 12, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, one type or two or more types of materials conventionally used in lithium secondary batteries can be used without any particular limitation. As a preferable application object of the technology disclosed herein, lithium and one kind of lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), lithium manganese oxide (for example, LiMn ₂ O ₄ ) or the like A positive electrode active material mainly containing an oxide (lithium transition metal oxide) containing two or more transition metal elements as constituent metal elements can be given.

  In addition to the positive electrode active material, the positive electrode active material layer 14 can contain one or two or more materials that can be used as a constituent component of the positive electrode active material layer in a general lithium secondary battery, if necessary. An example of such a material is a conductive material. As the conductive material, carbon materials such as carbon powder (for example, acetylene black (AB)) and carbon fiber are preferably used. Alternatively, conductive metal powder such as nickel powder may be used. In addition, examples of the material that can be used as a component of the positive electrode active material layer include various polymer materials (for example, polyvinylidene fluoride (PVDF)) that can function as a binder for the positive electrode active material.

<Separator sheet>
As the separator 40 used between the positive and negative electrodes, for example, a polyolefin-based resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. The structure of the separator 40 may be a single layer structure or a multilayer structure. Here, the separator 40 is made of PE resin. As the PE resin, a homopolymer of ethylene is preferably used. The PE resin is a resin containing 50% by mass or more of a repeating unit derived from ethylene, and is a copolymer obtained by polymerizing an α-olefin copolymerizable with ethylene, or at least copolymerizable with ethylene. It may be a copolymer obtained by polymerizing one kind of monomer. Examples of the α-olefin include propylene. Examples of other monomers include conjugated dienes (for example, butadiene) and acrylic acid.

  Moreover, it is preferable that the separator sheet 40 is comprised from PE whose shutdown temperature is about 120 to 140 degreeC (typically 125 to 135 degreeC). The shutdown temperature is sufficiently lower than the heat resistant temperature of the battery (for example, about 200 ° C. or higher). Examples of such PE include polyolefins generally referred to as high-density polyethylene or linear (linear) low-density polyethylene. Alternatively, various types of branched polyethylene having medium density and low density may be used. Moreover, additives, such as various plasticizers and antioxidants, can also be contained as needed.

  As the separator 40, a uniaxially or biaxially stretched porous resin sheet can be suitably used. Among these, a porous resin sheet uniaxially stretched in the longitudinal direction (MD direction: Machine Direction) is particularly preferable because it has an appropriate strength and has little heat shrinkage in the width direction. For example, when a separator having such a uniaxially stretched resin sheet in the longitudinal direction is used, thermal contraction in the longitudinal direction can be suppressed in an aspect wound with the long sheet-like positive electrode and negative electrode. Therefore, the porous resin sheet uniaxially stretched in the longitudinal direction is particularly suitable as a material for the separator constituting such a wound electrode body.

  The thickness of the separator 40 is preferably about 10 μm to 30 μm, and more preferably about 16 μm to 20 μm. If the thickness of the separator 40 is too large, the ion conductivity of the separator 40 may be reduced. On the other hand, if the thickness of the separator 40 is too small, film breakage may occur. Note that the thickness of the separator 40 can be obtained by image analysis of an image taken by the SEM. The porosity of the separator sheet 40 is preferably about 20% to 60%, and more preferably about 30% to 50%, for example. When the porosity of the separator sheet 40 is too large, the strength may be insufficient, and film breakage may occur easily. On the other hand, when the porosity of the separator sheet 40 is too small, the amount of the electrolyte solution that can be held in the separator sheet 40 decreases, and the ionic conductivity may decrease.

  In addition, although the separator sheet 40 is comprised by the single layer structure of PE layer here, the resin sheet of a multilayer structure may be sufficient. For example, you may comprise by 3 layer structure of PP layer, PE layer laminated | stacked on PP layer, and PP layer laminated | stacked on PE layer. In this case, the porous insulating layer 30 can be laminated on the PP layer that appears on the surface of the separator sheet 40. The number of layers of the resin sheet having a multilayer structure is not limited to 3, and may be 2 or 4 or more.

<Porous insulating layer>
In the present embodiment, as shown in FIG. 3, the porous insulating layers 30 (30 </ b> A and 30 </ b> B) are respectively provided along the longitudinal direction (winding direction) on the opposing surfaces of the negative electrode sheet 20 and the separator sheet 40. It is formed intermittently. The porous insulating layer 30 includes an inorganic filler and a binder, and exhibits a function of preventing the positive electrode sheet 10 and the negative electrode sheet 20 from coming into direct contact when the separator sheet 40 is thermally contracted. In the porous insulating layer 30, the inorganic filler is fixed to the surfaces of the negative electrode sheet 20 and the separator sheet 40 by the binder, and the particles of the inorganic filler are bound to each other. In addition, a large number of voids are formed between the inorganic filler grains at sites not bound by the binder. By impregnating the voids with a non-aqueous electrolyte, the movement of Li ions between the positive electrode sheet 10 and the negative electrode sheet 20 is ensured, and sufficient battery output is exhibited.

  Furthermore, the porous insulating layer according to the present embodiment will be described in detail with reference to FIGS. FIG. 4A is a plan view schematically showing a facing surface of the negative electrode sheet 20 facing the separator sheet 40, and FIG. 4B schematically shows a facing surface of the separator sheet 40 facing the negative electrode sheet 20. FIG. FIG. 5 is a schematic cross-sectional view showing an enlarged main part of a cross section along the winding direction (longitudinal direction) in a state in which the negative electrode sheet 20 and the separator sheet 40 are wound on each other. .

  As shown to Fig.4 (a), the porous insulating layer 30A is intermittently formed in the opposing surface facing the separator sheet 40 of the negative electrode sheet 20 along a longitudinal direction. In this embodiment, the porous insulating layer 30A is provided on the surface of the negative electrode active material layer 24, and between the one porous insulating layer 30A along the longitudinal direction and the one porous insulating layer 30A adjacent thereto. The surface of the negative electrode active material layer 24 is exposed in the non-formed portion 32A. Similarly, as shown in FIG. 4B, the porous insulating layer 30 </ b> B is intermittently formed along the longitudinal direction on the facing surface of the separator sheet 40 facing the negative electrode sheet 20. In this embodiment, the porous insulating layer 30B is provided on the main surface of the separator sheet 40, and the non-between the one porous insulating layer 30B along the longitudinal direction and the one porous insulating layer 30B adjacent thereto. The surface of the separator sheet 40 is exposed at the formation portion 32B.

  And, as shown in FIG. 5, the porous insulating layers 30A and 30B formed on the respective sheets 20 and 40 in the facing surface have the negative electrode in a state where the sheets 20 and 40 are overlapped with each other and wound. A portion (non-formed portion) 32A where the porous insulating layer 30A of the sheet 20 is not formed and an end 34A in the longitudinal direction of the porous insulating layer 30A in contact with the portion 32A are the porous insulating layer 30B on the separator sheet 40. Are arranged so that they can be opposed to each other. Similarly, the portion (non-formed portion) 32B where the porous insulating layer 30B is not formed in the separator sheet 40 and the end portion 34B in the longitudinal direction of the porous insulating layer 30B in contact with the portion 32B are porous on the negative electrode sheet 20. The insulating layers 30A are arranged so as to be in a positional relationship that can face each other. Thereby, the portion 32A (32B) where the porous insulating layer 30A (30B) of one sheet 20 (40) is not formed and the porous insulating layer 30B (30A) of the other sheet 40 (20) opposite thereto A large space S is formed between the two.

  Here, in the general configuration in which the porous insulating layer is formed over the entire surface of either the separator sheet 40 or the negative electrode sheet 20, the flow of the electrolytic solution is inhibited by the porous insulating layer during injection. Therefore, a battery having a porous insulating layer is less likely to penetrate the electrolytic solution into the wound electrode body 80 than a battery having no porous insulating layer, and it takes time to penetrate the electrolytic solution. There was a problem. On the other hand, according to the configuration of the present embodiment, the porous insulating layer 30A (30B) of one sheet 20 (40) is formed in a state where the negative electrode sheet 20 and the separator sheet 40 are overlapped with each other and wound. A large space (space) S is formed between the portion 32A (32B) that is not present and the porous insulating layer 30B (30A) of the other sheet 40 (20) facing it. Using the space S, the electrolytic solution can be circulated from the outside to the inside of the wound electrode body 80.

  That is, when the wound electrode body 80 is impregnated with the electrolytic solution, the electrolytic solution enters from both ends in the width direction intersecting with the wound direction of the wound electrode body 80 (longitudinal direction of the sheet). This intrusion direction substantially coincides with the direction orthogonal to the paper surface of FIG. That is, the infiltrated electrolyte enters from both ends in the width direction intersecting the winding direction (longitudinal direction) of the wound electrode body 80, and a part of the porous insulating layers 30 </ b> A and 30 </ b> B of both sheets 20 and 40. It penetrates into the central portion of the wound electrode body 80 via a space S provided in a portion where they are not facing each other. As a result, the permeability of the electrolytic solution is improved, and the penetration time of the electrolytic solution (and hence the manufacturing time of the battery) can be reduced. According to such a configuration, the electrolyte solution flow path (space) S is formed over the entire surface between the sheets 20 and 40, so that the electrolyte solution uniformly permeates the entire wound electrode body. Therefore, the electrolyte solution permeability to the wound electrode body 80 can be improved without causing uneven electrolyte solution penetration, and the technical value is high.

  Further, in the wound electrode body 80 disclosed herein, the end 34A of the porous insulating layer 30A of the negative electrode sheet 20 and the end 34B of the porous insulating layer 30B of the separator sheet 40 overlap (wrap) each other. ), The porous insulating layers 30A and 30B exist over the entire surface between the two sheets without any gaps when viewed from the direction orthogonal to the opposing surfaces of the two sheets. Therefore, even when the separator sheet 40 is thermally contracted due to overcharge or the like, the occurrence of an internal short circuit can be prevented by preventing direct contact between the positive and negative electrodes by the porous insulating layers 30A and 30B. Therefore, according to the configuration of the present embodiment, it is possible to provide an optimal secondary battery 100 that has no fear of an internal short circuit and has improved electrolyte permeability.

  As shown in FIGS. 4A and 4B, the porous insulating layer 30 on the two opposing sheets 20 and 40 includes one porous insulating layer 30 along the longitudinal direction and one porous layer adjacent thereto. The length L of the non-formed portions 32A and 32B between the porous insulating layers 30 (that is, the length along the longitudinal direction of the porous insulating layer non-formed portions 32A and 32B) is 5 mm to 500 mm (more preferably 10 mm to 500 mm). It is desirable to be formed so as to be. By setting the length L of the porous insulating layer non-forming portions 32A and 32B to 5 mm or more, the space S into which the electrolytic solution is permeated is expanded, and the permeability of the electrolytic solution is further improved. On the other hand, if the lengths of the non-formed portions 32A and 32B are more than 500 mm, the structure is close to that of the conventional structure in which the porous insulating layer is not intermittently formed, so that the electrolyte solution permeability improving effect is insufficient. May be. From the viewpoint of improving electrolyte solution permeability, a range of 5 mm to 500 mm is usually appropriate, preferably 10 mm to 300 mm, and particularly preferably 10 mm to 100 mm.

  As shown in FIG. 5, the thickness H of at least one of the porous insulating layers 30 on the two opposing sheets 20 and 40 is 2 μm to 50 μm. When the thickness H of the porous insulating layer 30 is less than 2 μm, in addition to the difficulty of coating, the space S for allowing the electrolyte to permeate is reduced and the effect of improving the electrolyte permeability is insufficient. May be. On the other hand, when the thickness H of the porous insulating layer 30 exceeds 50 μm, the amount of the negative electrode active material in the unit volume of the battery is relatively reduced, so that the battery capacity may tend to decrease. From the viewpoint of satisfying both the increase in capacity and the effect of improving electrolyte permeability, it is usually in the range of 2 μm to 50 μm, preferably 2 μm to 30 μm, and particularly preferably 2 μm to 10 μm.

  Furthermore, as shown in FIGS. 4A and 4B, when viewed from the direction orthogonal to the facing surfaces of the two opposing sheets 20 and 40, the end of the porous insulating layer 30A on the negative electrode sheet 20 The width W along the longitudinal direction of the portion where 34A and the end portion 34B of the porous insulating layer 30B on the separator sheet 40 overlap (wrap) each other is at least 0.1 mm or more (for example, 0.1 mm to 30 mm, preferably 0.5 mm or more, for example, 0.5 mm to 30 mm) is preferable. Thus, when the porous insulating layers 30A and 30B of both sheets 20 and 40 are arranged in the R portion of the wound electrode body 80, the end portions 34A and 34B of the porous insulating layers overlap (wrap) each other. The two sheets 20 and 40 can be reliably opposed to each other. Therefore, the occurrence of an internal short circuit can be prevented more reliably. The upper limit value of the width W of the overlapping portion is not particularly limited. However, if the width W of the overlapping portion is too large, the space (flow path) S through which the electrolytic solution permeates is opened, so that the electrolytic solution is applied to the entire wound electrode body. It may not penetrate evenly. From the viewpoint of preventing the uneven penetration of the electrolytic solution, approximately 30 mm or less is appropriate, preferably 20 mm or less, and particularly preferably 10 mm or less.

  In the example described above, the case where the porous insulating layers 30A and 30B are disposed between the negative electrode sheet 20 and the separator sheet 40 has been described, but the present invention is not limited to this. For example, the porous insulating layer 30 can be disposed between the positive electrode sheet 10 and the separator sheet 40. The porous insulating layer 30 may be disposed both between the positive electrode sheet 10 and the separator sheet 40 and between the negative electrode sheet 20 and the separator sheet 40. According to such a configuration, compared to the case where the porous insulating layer is disposed only between one of the positive electrode sheet 10 and the separator sheet 40 and between the negative electrode sheet 20 and the separator sheet 40, the space into which the electrolyte solution permeates. (Flow path) S is further increased (typically doubled). For this reason, the permeability of the electrolytic solution is remarkably improved, and a secondary battery having better battery performance is obtained.

  The porosity of the porous insulating layers 30A and 30B is not particularly limited, but is preferably about 40% to 70%, and more preferably about 50% to 60%, for example. If the porosity of the porous insulating layers 30A and 30B is too large, the mechanical strength is insufficient, and the porous insulating layers 30A and 30B may be easily damaged. On the other hand, if the porosity of the porous insulating layers 30A and 30B is too small, the amount of electrolyte solution that can be held in the porous insulating layers 30A and 30B decreases, and the ionic conductivity may decrease.

<Inorganic filler>
The material that can constitute the inorganic filler used in the porous insulating layers 30 </ b> A and 30 </ b> B is preferably a material that has high electrical insulation and a higher melting point than the separator sheet 40. Examples thereof include inorganic compounds such as alumina, boehmite, magnesia, titania, silica, zirconia, zinc oxide, iron oxide, ceria, and yttria. Particularly preferred inorganic compounds include alumina, boehmite, magnesia and titania. These inorganic materials may be used individually by 1 type, and may be used in combination of 2 or more types. The shape (outer shape) of the inorganic filler is not particularly limited. From the viewpoints of mechanical strength, manufacturability, etc., generally spherical inorganic filler particles can be preferably used. The size (average particle size) of the inorganic filler particles is preferably larger than the average pore size of the separator sheet. For example, it is preferable to use inorganic filler particles having an average particle size of about 0.1 μm or more, more preferably about 0.3 μm or more, and particularly preferably 0.5 μm or more.

<Binder>
In the secondary battery according to the present embodiment, the inorganic filler is contained in the porous insulating layers 30A and 30B together with the binder. As the binder, when the porous insulating layer forming coating described later 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. Can be used. Examples of the polymer that is dispersed or dissolved in the aqueous solvent include acrylic resins. As the acrylic resin, a homopolymer obtained by polymerizing monomers such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methyl methacrylate, ethylhexyl acrylate and butyl acrylate. Is preferably used. The acrylic resin may be a copolymer obtained by polymerizing two or more of the above monomers. Further, a mixture of two or more of the above homopolymers and copolymers may be used. In addition to the acrylic resins described above, polyolefin resins such as styrene butadiene rubber (SBR) and polyethylene (PE), polytetrafluoroethylene (PTFE), and the like can be used. These polymers can be used alone or in combination of two or more. Among these, it is preferable to use an acrylic resin. The form of the binder is not particularly limited, and a particulate (powdered) form may be used as it is, or a solution prepared in the form of a solution or an emulsion may be used. Two or more kinds of binders may be used in different forms.

  The porous insulating layers 30A and 30B can contain materials other than the above-described inorganic filler and binder as necessary. Examples of such materials include various polymer materials that can function as a thickener for a porous insulating layer-forming paint described later. In particular, when an aqueous solvent is used, it is preferable to contain a polymer that functions as the thickener. As the polymer that functions as the thickener, carboxymethyl cellulose (CMC) and methyl cellulose (MC) are preferably used.

<Content ratio>
Although not particularly limited, the proportion of the inorganic filler in the entire porous insulating layer is suitably about 50% by mass or more (for example, 50% by mass to 99% by mass), preferably 80% by mass or more (for example, 80% by mass). % To 99% by mass), particularly preferably about 90% to 99% by mass. The binder ratio in the porous insulating layers 30A and 30B is suitably about 40% by mass or less, preferably 10% by mass or less, and particularly preferably 5% by mass or less (eg, about 0.5% by mass to 3% by mass). Further, when a porous insulating layer forming component other than the inorganic filler and binder, for example, a thickener is contained, the content of the thickener is preferably about 3% by mass or less, and about 2% by mass or less ( For example, it is preferably about 0.5% by mass to 1% by mass). If the ratio of the binder is too small, the anchoring properties of the porous insulating layers 30A and 30B and the strength (shape retention) of the porous insulating layers 30A and 30B themselves may be reduced, resulting in defects such as cracks and peeling. is there. When the proportion of the binder is too large, gaps between the particles of the porous insulating layers 30A and 30B are insufficient, and the ion permeability of the porous insulating layer 30 is lowered (as a result, using the porous insulating layers 30A and 30B). The resistance of the constructed secondary battery may increase).

<Method for forming porous insulating layer>
Next, a method for forming the porous insulating layers 30A and 30B according to the present embodiment will be described. As a coating material for forming a porous insulating layer for forming the porous insulating layers 30A and 30B, a paste in which an inorganic filler, a binder and a solvent are mixed and dispersed (including slurry or ink, the same applies hereinafter). Used. The porous insulating layers 30A and 30B can be intermittently formed by applying the paste-like paint intermittently along the longitudinal direction on the surfaces of the negative electrode sheet 20 and the separator sheet 40 and further drying. . In the present embodiment, the negative electrode sheet 20 may be intermittently coated with a porous insulating layer forming coating on both surfaces of the negative electrode sheet 20. On the other hand, the separator sheet 40 may be intermittently coated with a porous insulating layer forming coating on one side of the separator sheet 40.

  Examples of the solvent used for the coating material for forming the porous insulating layer include water or a mixed solvent mainly composed of water. As a solvent other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. Alternatively, it may be an organic solvent such as N-methylpyrrolidone (NMP), pyrrolidone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, dimethylformamide, dimethylacetamide, or a combination of two or more thereof. Although the content rate of the solvent in the coating material for forming a porous insulating layer is not particularly limited, it is preferably 40 to 90% by mass, particularly about 50% by mass, based on the entire coating material.

  The operation of mixing the inorganic filler and binder with a solvent is performed by using a suitable kneader such as a ball mill, homodisper, dispermill (registered trademark), Claremix (registered trademark), fillmix (registered trademark), or an ultrasonic disperser. Can be used. Porous insulating layers 30A and 30B are applied to the surfaces of the negative electrode sheet 20 and the separator sheet 40 by intermittently coating the porous coating material for forming the porous insulating layer on the surfaces of the negative electrode sheet 20 and the separator sheet 40 along the longitudinal direction and drying. It can be formed intermittently.

  The operation of intermittently applying the coating material for forming the porous insulating layer onto the negative electrode sheet 20 and the separator sheet 40 can be used without any particular limitation on conventional general coating means. For example, using a suitable coating apparatus (gravure coater, slit coater, die coater, comma coater, etc.), a predetermined amount of the coating material for forming a porous insulating layer is longitudinally applied to the surfaces of the negative electrode sheet 20 and the separator sheet 40. It can be applied by coating intermittently along the direction. Thereafter, the coating material is dried by a suitable drying means (typically, a temperature lower than the melting point of the separator sheet 40, for example, 110 ° C. or less, for example, 30 to 80 ° C.), whereby Remove the solvent. The porous insulating layers 30A and 30B can be formed by removing the solvent from the porous insulating layer-forming coating material.

  Next, a method for producing the wound electrode body 80 using the negative electrode sheet 20 and the separator sheet 40 on which the porous insulating layers 30A and 30B are formed will be described. In producing the wound electrode body 80, as shown in FIG. 3, the positive electrode sheet 10, the negative electrode sheet 20, and the two separator sheets 40 are overlapped, and tension is applied to each of the sheets 10, 20, and 40. The wound electrode body 80 can be produced by winding in the longitudinal direction of the sheet. At that time, the positive electrode sheet 10 and the negative electrode sheet 20 are formed such that the positive electrode active material layer non-formation part of the positive electrode sheet 10 and the negative electrode active material layer non-formation part of the negative electrode sheet 20 protrude from both sides in the width direction of the separator sheet 40. Are overlapped slightly in the width direction. Further, in a state where the negative electrode sheet 20 and the separator sheet 40 are wound on each other and wound, a portion (non-formed portion) 32A in which the porous insulating layer 30A is not formed and a porous portion in contact with the portion 32A. The end portions 34A of the porous insulating layer 30A are arranged so as to be in a positional relationship that can face the porous insulating layer 30B of the separator sheet 40. Similarly, a portion (non-formed portion) 32B where the porous insulating layer 30B of the separator sheet 40 is not formed and an end portion 34B of the porous insulating layer 30B in contact with the portion 32B are formed on the porous insulating layer on the negative electrode sheet 20. It arrange | positions so that it may become the positional relationship which can mutually oppose 30A.

  In this way, the positive electrode sheet 10, the negative electrode sheet 20, and the two separator sheets 40 are overlapped and wound in the longitudinal direction of the sheets while applying tension to each of the sheets 10, 20, 40, thereby winding the electrode body. 80 can be made.

  As shown in FIG. 6, a wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10 and the negative electrode active material layer 24 of the negative electrode sheet 20) is formed in the central portion of the wound electrode body 80 in the winding axis direction. A portion in which the separator 40 is densely stacked) is formed. In addition, the electrode active material layer non-formed portions of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends in the winding axis direction of the wound electrode body 80. A positive electrode current collector plate 74 and a negative electrode current collector plate 76 are provided on the positive electrode side protruding portion (that is, the non-formed portion of the positive electrode active material layer 14) 84 and the negative electrode side protruding portion (that is, the non-formed portion of the negative electrode active material layer 24) 86. Are respectively attached and electrically connected to the positive terminal 70 and the negative terminal 72 described above.

<Non-aqueous electrolyte>
Then, the wound electrode body 80 is accommodated in the main body 52 from the upper end opening of the case main body 52, and an appropriate nonaqueous electrolytic solution 90 is disposed (injected) in the case main body 52. Such a non-aqueous electrolyte typically has a composition in which a supporting salt is contained in a suitable non-aqueous solvent. As said non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 can be preferably used a lithium salt of SO ₃ and the like.

  Thereafter, the opening is sealed by welding or the like with the lid 54, and the assembly of the lithium secondary battery 100 according to the present embodiment is completed. The sealing process of the case 50 and the process of placing (injecting) the electrolyte may be the same as those used in the production of a conventional lithium secondary battery, and do not characterize the present invention. In this way, the construction of the lithium secondary battery 100 according to this embodiment is completed.

  The lithium secondary battery 100 constructed as described above exhibits excellent battery performance because it is excellent in electrolyte permeability and has no risk of an internal short circuit. For example, it is possible to provide a secondary battery that satisfies at least one (preferably all) of excellent cycle characteristics (high capacity retention after cycling) and low battery heat generation.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to the following test examples.

<Example 1>
(1) Production of positive electrode sheet LiCoO ₂ powder as a positive electrode active material, AB (conductive material), and PVDF (binder) are mixed with N-methylpyrrolidone (mass ratio of 85: 10: 5). NMP) to prepare a positive electrode active material layer forming paste. The positive electrode active material layer forming paste is applied to both sides of a long aluminum foil (positive electrode current collector) 12 having a thickness of 15 μm in a strip shape and dried, whereby a positive electrode active material layer is formed on both sides of the positive electrode current collector 12. The positive electrode sheet 10 provided with 14 was produced. The coating amount of the positive electrode active material layer forming paste was adjusted so as to be about 30 mg / cm ² (solid content basis) for both surfaces.

(2) Preparation of negative electrode sheet Natural graphite powder as a negative electrode active material, SBR, and CMC are mixed with water so that the mass ratio of these materials becomes 98: 1: 1, and a negative electrode active material layer is formed. A paste was prepared. This negative electrode active material layer forming paste is applied to both sides of a long copper foil (negative electrode current collector) 22 having a thickness of 10 μm and dried, whereby the negative electrode active material layer 24 is formed on both surfaces of the negative electrode current collector 22. The provided negative electrode sheet 20 was produced. The coating amount of the negative electrode active material layer paste was adjusted so as to be about 20 mg / cm ² (solid content basis) for both surfaces.

(3) Formation of porous insulating layer Alumina powder as an inorganic filler, an acrylic polymer as a binder, and CMC as a thickener, the mass ratio of these materials being 96: 2: 2 in solid content ratio Then, it was mixed with water so that a coating material for forming a porous insulating layer was prepared. The porous insulating layer-forming coating material is intermittently applied to both surfaces (negative electrode active material layer 24) of the obtained negative electrode sheet 20 with a gravure roll and dried, so that both surfaces of the negative electrode sheet 20 are porous. The negative electrode sheet 20 in which the insulating layer 30A was intermittently formed was obtained. In addition, a coating material for forming a porous insulating layer was prepared in the same procedure, and this was intermittently applied to one side of a separator sheet (a porous polyethylene material having a thickness of 20 μm) with a gravure roll. By drying, the separator sheet 40 in which the porous insulating layer 30B was intermittently formed on one side of the separator sheet 40 was obtained. As shown in FIG. 4, in this example, the non-formation portions 32A and 32B between one porous insulating layer 30A and 30B along the longitudinal direction and one porous insulating layer 30A and 30B adjacent to the porous insulating layer 30A and 30B are arranged. The length L was 40 mm. The length of one porous insulating layer (porous insulating layer forming portion) 30A, 30B along the longitudinal direction was set to 50 mm. Furthermore, the thickness of the porous insulating layers 30A and 30B was 5 μm.

(4) Construction of Lithium Secondary Battery A lithium secondary battery for evaluation tests was produced using the negative electrode sheet 20 and the separator sheet 40 on which the porous insulating layers 30A and 30B were intermittently formed. A lithium secondary battery for evaluation test was produced as follows.

As shown in FIG. 3, the positive electrode sheet 10, the negative electrode sheet 20, and the two separator sheets 40 were overlapped and wound in the longitudinal direction of the sheet to obtain a wound body. At that time, on the opposing surfaces of the negative electrode sheet 20 and the separator sheet 40, both sheets 20, so that the porous insulating layers 30A, 30B formed on both sheets 20, 40 are in a predetermined positional relationship (see FIG. 5). 40 were placed facing each other. A flat wound electrode body 80 was produced by crushing the obtained wound body from the side surface direction. The wound electrode body is housed in a box-type battery case (75 mm long, 120 mm wide, 15 mm thick, with a case thickness of 1 mm used) together with a non-aqueous electrolyte, and the opening of the battery case is hermetically sealed. Sealed. As the non-aqueous electrolyte, a mixed solvent containing EC, EMC, and DEC at a volume ratio of 3: 5: 2 and containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter was used. In this way, a lithium secondary battery was assembled. Thereafter, initial charge / discharge treatment (conditioning) was performed by a conventional method to obtain a test lithium secondary battery. The theoretical capacity of this lithium secondary battery is 4 Ah.

<Example 2>
The lithium secondary for testing was the same as in Example 1 except that the porous insulating layers 30A and 30B were arranged not between the negative electrode sheet 20 and the separator sheet 40 but between the positive electrode sheet 10 and the separator sheet 40. A battery was obtained.

<Example 3>
Test lithium was added in the same manner as in Example 1 except that the porous insulating layers 30A and 30B were placed between the negative electrode sheet 20 and the separator sheet 40 and also between the positive electrode sheet 10 and the separator sheet 40. A secondary battery was obtained.

<Comparative example>
The lithium secondary battery for testing was the same as in Example 1 except that the porous insulating layer 30B was not formed on the separator sheet 40, and the porous insulating layer was continuously formed over the entire surface of the negative electrode sheet 20. Got. The thickness of the porous insulating layer was 5 μm.

(5) Measurement of initial capacity Next, for the test lithium secondary battery constructed as described above, the initial capacity was determined by the following steps 1 to 4 at a temperature of 25 ° C. and a voltage range of 3.0 V to 4.1 V. It was measured.
Procedure 1: Charge to 4.1V with a constant current of 1C and pause for 5 minutes.
Procedure 2: Discharge to 3.0 V at a constant current of 1 C and rest for 5 minutes.
Procedure 3: Charge to 4.1 V with a constant current of 1 C, and then charge at a constant voltage until the current value reaches 0.1 C.
Procedure 4: After Procedure 3, discharge to 3.0 V with a constant current of 1 C, and then discharge with a constant voltage until the current value reaches 0.1 C.
Then, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 4 was set as the initial capacity.

(6) Charging / discharging cycle test After the initial capacity was measured, the test lithium secondary battery was charged to 4.1 V with a constant current of 2C in a thermostat at 50 ° C, and then with a constant current of 2C. The charge / discharge cycle of discharging to 3.0 V was continuously performed 1000 times. Then, the discharge capacity of the charge / discharge cycle test is measured in the same procedure as the measurement of the initial capacity, and the capacity retention rate after 1000 cycles (“charge / discharge” is determined from the ratio between the initial capacity and the discharge capacity after the charge / discharge cycle test. The discharge capacity after the cycle test / initial capacity) ”× 100) was calculated. The results are shown in Table 1.

  As is clear from Table 1, the lithium secondary battery according to the comparative example in which the porous insulating layer was formed on the entire surface of the negative electrode sheet had poor electrolyte permeability and potential unevenness. Therefore, charging and discharging were repeated 1000 cycles. After that, the capacity maintenance rate decreased. On the other hand, the lithium according to Examples 1 to 3 in which a porous insulating layer is intermittently formed on both the negative electrode sheet and the separator sheet, and arranged so as to be in a predetermined positional relationship (see FIG. 5). The secondary battery has a large space for allowing the electrolytic solution to penetrate into the porous insulating layer. Therefore, the permeability of the electrolytic solution is improved, and the capacity retention rate after the charge / discharge cycle is higher than that of the comparative example. In particular, in the battery of Example 3 in which the porous insulating layer is disposed between the positive electrode sheet and the separator sheet and between the negative electrode sheet and the separator sheet, an extremely high capacity retention rate of 80% or more can be achieved. It was. From the viewpoint of increasing the capacity retention rate, it is preferable to dispose a porous insulating layer between the positive electrode sheet and the separator sheet and between the negative electrode sheet and the separator sheet.

  As described above, any of the secondary batteries disclosed herein has no fear of an internal short circuit and is excellent in electrolyte permeability, so that it is particularly suitable for a motor (electric motor) power source mounted on a vehicle such as an automobile. Can be suitably used. Therefore, as schematically shown in FIG. 7, the present invention provides a vehicle 1 (typically an automobile, particularly a hybrid automobile) provided with such a secondary battery 100 (typically, a battery pack formed by connecting a plurality of batteries in series) as a power source. , Automobiles equipped with electric motors such as electric vehicles and fuel cell vehicles).

As mentioned above, although this invention was demonstrated by suitable embodiment and an Example, such description is not a limitation matter, Of course, various modifications are possible.
For example, in the above-described embodiment, the lithium secondary battery has been described as a typical example of the secondary battery, but the present invention is not limited to the secondary battery of this form. For example, a non-aqueous electrolyte secondary battery, a nickel metal hydride battery, or a nickel cadmium battery that uses a metal ion other than lithium ion (for example, sodium ion) as a charge carrier may be used.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 30 Porous insulating layers 32A and 32B Non-formed portions 34A and 34B End portion 40 Separator sheet 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 80 Winding electrode body 82 Winding core portion 90 Electrolytic solution 100 Secondary battery

Claims (2)

A secondary battery comprising a wound electrode body wound with a long electrode sheet and a separator sheet superimposed on each other, and an electrolyte solution,
A porous insulating layer containing an inorganic filler and a binder is formed intermittently along the longitudinal direction on both opposing surfaces of the electrode sheet and the separator sheet, and is formed on both sheets on the opposing surfaces. In the state in which the porous insulating layer is rolled up with both sheets stacked on each other, the portion of one sheet where the porous insulating layer is not formed and the end of the porous insulating layer in contact with the portion are: It is arranged to be in a positional relationship that can be opposed to the porous insulating layer of the other sheet ,
The porous insulating layer on the two opposing sheets has a length of a non-formed portion between one porous insulating layer along the longitudinal direction and one porous insulating layer adjacent thereto in a length direction of 5 mm to 500 mm. Formed to be
The thickness of at least one of the porous insulating layers on the two opposing sheets is 2 μm to 50 μm,
When viewed from the direction perpendicular to the facing surfaces of the two opposing sheets, the width along the longitudinal direction of the portion where the ends of the porous insulating layers on the two sheets overlap is 0.1 mm to 30 mm. There is a secondary battery. The wound electrode body is a wound electrode body in which a positive electrode sheet and a negative electrode sheet are wound through the separator sheet,
The secondary battery according to claim 1, wherein the porous insulating layer is provided both between the positive electrode sheet and the separator sheet and between the negative electrode sheet and the separator sheet.

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