JP2012009150A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery in which the thickness can be reduced while ensuring good productivity.SOLUTION: In the nonaqueous secondary battery including a wound electrode body having a flat cross section, a separator has a multilayer structure of a porous layer (A) principally comprising a thermosetting resin having a melting point of 80-170°C, and a porous layer (B) formed via a coating step. When the nonaqueous secondary battery is placed stationarily, the separator is susceptible to warpage in any one direction, and at the inner end of the wound electrode body and in the vicinity thereof, the separator has no porous layer (B) at the part susceptible to warpage.

Description

  The present invention relates to a non-aqueous secondary battery that can be reduced in thickness and has good productivity.

  Non-aqueous secondary batteries such as lithium secondary batteries are widely used as power sources for portable devices such as mobile phones and notebook personal computers because of their high energy density.

  In a non-aqueous secondary battery, as a separator interposed between a positive electrode and a negative electrode, for example, a microporous membrane made of polyolefin is used. A laminated separator in which a functional layer is formed on the surface of the microporous membrane It is also being considered to improve the performance of non-aqueous secondary batteries by using the battery.

  For example, Patent Document 1 discloses a first separator layer composed of a microporous film mainly including a resin for ensuring a shutdown function, and a second separator layer mainly including a filler having a heat resistant temperature of 150 ° C. or higher. It has been proposed that an electrochemical element such as a non-aqueous secondary battery be configured using a laminated separator having In the separator described in Patent Document 1, since the second separator layer acts as a functional layer that suppresses thermal contraction of the entire separator, the use of this makes it difficult for thermal runaway to occur even when abnormal overheating occurs. The non-aqueous secondary battery can be made excellent.

  Patent Document 2 also proposes a separator in which a functional layer composed of heat-resistant resin fibrils and having good heat resistance and ion permeability is formed on the surface of a polyolefin microporous film.

International Publication No. 2007/66768 JP 2010-92882 A

  By the way, in a laminated separator in which a functional layer is formed on the surface of the microporous film, the microporous film is pulled out from, for example, a roll wound with a long microporous film, and the functional layer is formed on the surface of the microporous film. A manufacturing method in which a composition (coating material) containing a constituent material is continuously applied to form a functional layer may be used. At this time, since the stress is applied to the microporous film in the take-off direction, in the manufactured separator, the microporous film portion is shrunk by the residual stress, while the formed functional layer has no stress remaining. Since it does not shrink, warping may occur with the functional layer on the outside. Non-aqueous secondary batteries often use a wound electrode body in which a positive electrode, a negative electrode, and a separator are overlapped and wound in a spiral shape. However, when a separator with a warp as described above is used, The separator that is not in contact with the electrode is warped at the end on the innermost peripheral side of the body, and the thickness of the wound electrode body may increase due to curling and folding on the outer peripheral side. Since the thickness of the body becomes non-uniform, the productivity of the battery decreases.

  In the case of a laminated separator, since the functional layer is provided on the surface of a microporous film or the like serving as a base material, the thickness of the separator as a whole tends to increase. Recent non-aqueous secondary batteries are often required to be smaller and thinner with the downsizing of devices used, and even batteries using stacked separators meet these requirements. Is also required.

  This invention is made | formed in view of the said situation, The objective is to provide a non-aqueous secondary battery which can make thickness small and has favorable productivity.

  The non-aqueous secondary battery according to the present invention that has achieved the above object has a positive electrode, a negative electrode, and two separators interposed between the positive electrode and the negative electrode, which are stacked and wound to have a flat cross section. A non-aqueous secondary battery having a wound electrode body, wherein the separator has a multilayer structure having a porous layer (A) and a porous layer (B), and the porous layer (A) has a melting point. It is a layer mainly composed of a thermoplastic resin at 80 to 170 ° C., and the porous layer (B) is a composition prepared by dispersing or dissolving the constituent material of the porous layer (B) in a solvent. It is a layer formed through a step of applying to one side of the porous layer (A), and the inner end of at least one of the positive electrode and the negative electrode is inside the first bending start portion inside the wound electrode body. When located on the end side, at least one of the two separators is The porous layer (A) side is in contact with one electrode whose inner end position is located closer to the inner end side of the wound electrode body, and at least the inner end position is inner than the wound electrode body. There is no porous layer (B) on the inner end side of the wound electrode body from the position in contact with one electrode located on the end side, and the inner ends of the positive electrode and the negative electrode are the wound electrode. When located on the outer end side of the first bend start portion inside the body, at least one of the two separators is at least the inner end than the first bend start portion inside the wound electrode body On the side, the porous layer (B) is not provided.

  In the nonaqueous secondary battery of the present invention, a porous layer (A) mainly composed of a thermoplastic resin having a melting point of 80 to 170 ° C. and a composition containing a constituent material are applied to the surface of the porous layer (A). A separator having a multilayer structure having a porous layer (B) formed through the process is used, but such a separator is likely to warp in one of the surface directions when left standing. As described above, it is difficult for such a separator to form a wound electrode body having a uniform thickness.

  Therefore, in the present invention, the porous layer (B) is not formed in the inner end of the spirally wound electrode body and in the vicinity thereof at the place where there is a possibility of warping during the formation of the spirally wound electrode body for these two separators. Thus, the separator warpage during the formation of the wound electrode body is suppressed, and the productivity of the non-aqueous secondary battery can be improved.

  In addition, in the inside of the wound electrode body having a flat cross section for the purpose of thinning, the thickness of the wound electrode body increases due to warpage of the separator, as described above, in the present invention, Since generation | occurrence | production of such a curvature can be suppressed, the increase in the thickness of the whole winding electrode body can be suppressed.

  Thus, in the present invention, even when a separator having a porous layer (A) and a porous layer (B) is used, the thickness of the entire flat wound electrode body can be reduced. It is possible to reduce the thickness of the battery.

  According to the present invention, it is possible to provide a non-aqueous secondary battery having a small thickness and good productivity.

It is a schematic diagram showing an example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention. It is a schematic diagram showing the other example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention. It is a schematic diagram showing the other example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention. It is a schematic diagram showing the other example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention.

  In FIG. 1, the schematic diagram showing an example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention is shown. In FIG. 1, for the purpose of facilitating understanding of the structure of the wound electrode body, the current collector and the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer) are shown separately for the positive electrode and the negative electrode. In addition, in the normal battery, for example, each component is compressed in the vertical direction in the drawing so that the gap between the components is as small as possible. The wound electrode body is configured so as to be eliminated (the same applies to FIGS. 2, 3 and 4 described later).

  A wound electrode body 10 shown in FIG. 1 is obtained by winding a positive electrode 20, a negative electrode 30, and two separators 40, 50 in a stacked manner and flattening the cross section. In addition, 21 is a positive electrode tab for connecting the positive electrode 20 and the external terminal of the battery, and 31 is a negative electrode tab for connecting the negative electrode 30 and the external terminal of the battery.

  The two separators 40 and 50 are composed of porous layers (A) 41 and 51 mainly composed of a thermoplastic resin having a melting point of 80 to 170 ° C. and a composition containing constituent materials on the surface of the porous layer (A). It is a multilayer structure having porous layers (B) 42 and 52 formed through a coating step, and can be warped in either one of the surface directions when standing [usually a porous layer ( B) Warpage occurs with the forming surface facing outside].

  In the spirally wound electrode body 10 shown in FIG. 1, the inner end (30a) of one electrode (negative electrode 30) is the inner end (inner end portion) than the first bending start portion 11 inside the spirally wound electrode body 10. The same shall apply hereinafter.) One of the two separators 40, 50 (separator 40) is on the porous layer (A) (41) side and the inner end (30a) is on the wound electrode. It is in contact with one electrode (negative electrode 30) located on the inner side of the body 10, and at least the inner end side of the wound electrode body 10 is more porous than the position in contact with the one electrode (negative electrode 30). The quality layer (B) (42) is not formed.

  In the wound electrode body 10 shown in FIG. 1, for example, when the porous layer (B) is formed on the entire surface of one side of the porous layer (A) related to the separator 40, the separator 40 is in contact with the negative electrode 30. , The separator 40 is unlikely to warp, whereas the inner end side of the negative electrode 30 is more likely to warp, for example, with the porous layer (B) forming surface facing outward.

  Of the separator, the part where the porous layer (B) is not formed and only the porous layer (A) exists is warped even after the porous layer (A) contracts after the separator is manufactured. Does not occur. Therefore, by arranging the two separators so that the porous layer (B) does not exist at a location where the separator on the inner end side of the wound electrode body is likely to warp, the warpage of these separators can be suppressed. In addition to facilitating the formation of the wound electrode body, an increase in the thickness of the wound electrode body (the length in the vertical direction in FIG. 1; the same applies to the thickness of the wound electrode body) due to the warpage of the separator is suppressed. can do.

  That is, in the spirally wound electrode body 10 shown in FIG. 1, the porous layer (B) 42 is formed on the inner end side of the spirally electrode body 10 at least from the position in contact with the negative electrode 30 in the separator 40. Without forming the porous electrode (A) 41 alone, the warpage of the separator 40 is suppressed to facilitate the formation of the wound electrode body, and the thickness of the wound electrode body is increased by the warp of the separator 40. Can be suppressed.

  In FIG. 2, the schematic diagram showing the other example of the cross section of the wound electrode body which concerns on the nonaqueous secondary battery of this invention is shown. In the wound electrode body 10 shown in FIG. 2, the inner end 20 a of the positive electrode 20 and the inner end 30 a of the negative electrode 30 are outer ends (outer end portions) than the first bending start portion 11 inside the wound electrode body 10. The same shall apply hereinafter). In this case, for example, the separator 40 is less likely to warp on the outer end side than the first bending start portion 11 inside the spirally wound electrode body 10, but on the inner end side than the first bending start portion 11, for example, is porous. Warping tends to occur with the formation surface of the quality layer (B) on the outside.

  Therefore, in the spirally wound electrode body 10 shown in FIG. 2, the porous layer (B) 42 is formed at least on the inner end side of the separator 40 from the first bending start portion 11 inside the spirally wound electrode body 10. Without forming the porous electrode (A) 41 alone, the warpage of the separator 40 is suppressed to facilitate the formation of the wound electrode body, and the thickness of the wound electrode body is increased by the warp of the separator 40. Can be suppressed.

  Moreover, in FIG. 3, the schematic diagram showing the other example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention is shown. In the spirally wound electrode body 10 shown in FIG. 3, the inner end 30 a of the negative electrode 30 is closer to the inner end side than the first bending start portion 11 inside the spirally wound electrode body 10, similarly to the spirally wound electrode body shown in FIG. 1. positioned. Further, the positive electrode 20 is disposed so as to be interposed between the two separators 40, 50, and the inner end 20 a is positioned on the outer end side with respect to the first bending start portion 11 inside the wound electrode body 10. is doing.

  In the spirally wound electrode body 10 shown in FIG. 3, the separator 40 is in contact with the negative electrode 30 on the porous layer (A) 41 side, as in the spirally wound electrode body 10 shown in FIG. 1, and at least, In addition to not having the porous layer (B) 42 on the inner end side of the wound electrode body 10 from the position in contact with the negative electrode 30, the separator 50 is at least on the inner side of the wound electrode body 10. The porous layer (B) 42 is not provided on the inner end side from the first bending start portion 11. In the case of the spirally wound electrode body 10 shown in FIG. 3, in addition to suppressing the warp of the separator 40, the warp of the separator 50 can be satisfactorily suppressed, so that the formation of the spirally wound electrode body is further facilitated. And an increase in the thickness of the wound electrode body can be further suppressed.

  Furthermore, in FIG. 4, the schematic diagram showing the other example of the cross section of the winding electrode body which concerns on the nonaqueous secondary battery of this invention is shown. 4, the inner end 20a of the positive electrode 20 and the inner end 30a of the negative electrode are the first bend start portion inside the wound electrode body 10, similarly to the wound electrode body shown in FIG. 11 is located on the outer end side.

  The two separators 40, 50 do not have the porous layer (B) 42 at least on the inner end side from the first bending start portion 11 inside the spirally wound electrode body 10. In the case of the spirally wound electrode body 10 shown in FIG. 4, in addition to suppressing the warp of the separator 40, the warp of the separator 50 can be satisfactorily suppressed, so that the formation of the spirally wound electrode body can be further facilitated. And an increase in the thickness of the wound electrode body can be further suppressed.

  Further, in the spirally wound electrode body 10 shown in FIGS. 1 and 2, the tab 21 of the positive electrode 20 which is an electrode located on the outer side is one of the two separators (separator 40) on the outermost periphery of the positive electrode 20. Is provided at a position corresponding to a portion not having the porous layer (B) 42 inside the wound electrode body 10.

  In a wound electrode body having a flat cross section for the purpose of thinning, the thickness of a tab for connecting each electrode to an external terminal of the battery can also be a factor in increasing the thickness of the wound electrode body. Therefore, in the wound electrode body according to the battery of the present invention, the tab of the electrode located on the outer side, and at least one of the two separators on the outermost periphery of the electrode is on the inner side of the wound electrode body. And is preferably provided at a position corresponding to a portion not having the porous layer (B). At the location where the porous layer (B) is not provided inside the spirally wound electrode body, the thickness of the spirally wound electrode body is reduced by the absence of the porous layer (B). By arranging the tab of the electrode, an increase in the thickness of the wound electrode body due to the tab can be further suppressed.

  3 and 4, the tab 21 of the positive electrode 20, which is an electrode located on the outer side, is wound by both of the two separators 40 and 50 on the outermost periphery of the positive electrode 20. It is provided at a position corresponding to the location not having the porous layer (B) inside the electrode body 10, and in this case, since the increase in the thickness of the wound electrode body due to the tab can be further suppressed, More preferred.

  In the battery of the present invention, the porous layer (A) in the separator according to the present invention is a layer having an original function of transmitting a separator while preventing a short circuit between the positive electrode and the negative electrode. The porous layer (A) has a melting point of 80 ° C. or higher and 170 ° C. or lower, that is, a melting temperature measured by using a differential scanning calorimeter (DSC) according to JIS K 7121. (Preferably 100 ° C. or more) The main component is a thermoplastic resin having a temperature of 170 ° C. or less. By using the separator having such a porous layer (A), the heat of the battery of the present invention becomes high. A so-called shutdown function can be secured in which the plastic resin melts and closes the pores of the separator.

  The thermoplastic resin constituting the porous layer (A) has a melting point of 80 ° C. or higher and 170 ° C. or lower, has an electrical insulating property, is electrochemically stable, and has a battery that will be described in detail later. There is no particular limitation as long as it is a stable thermoplastic resin for the medium used in the aqueous electrolyte and the composition for forming the porous layer (B), but polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer Polyolefins such as coalescence are preferred.

  For the porous layer (A), for example, a microporous film composed of the above-mentioned exemplified thermoplastic resin used as a separator in a known non-aqueous secondary battery or the like, that is, a solvent extraction method, a dry or wet stretching An ion-permeable microporous membrane produced by a method or the like can be used.

  As a suitable specific example of the microporous film constituting the porous layer (A), for example, a single-layer microporous film mainly composed of PE, or a laminated microporous film in which 2 to 5 layers of PE and PP are laminated. Examples include membranes.

  Further, the porous layer (A) may contain a filler or the like in order to improve the strength and the like within a range not impairing the shutdown function. Examples of the filler that can be used in the porous layer (A) include various fine particles exemplified later as heat-resistant fine particles that can be used in the porous layer (B).

  The porous layer (A) is mainly composed of a thermoplastic resin having a melting point of 80 ° C. or higher and 170 ° C. or lower. The term “mainly used” as used herein refers to a thermoplastic resin having a melting point of 80 ° C. or higher and 170 ° C. or lower. In the total volume of the constituent components of the porous layer (A), it means that 50% by volume or more is contained. Further, the content of the thermoplastic resin having a melting point of 80 ° C. or higher and 170 ° C. or lower in the porous layer (A) is preferably as follows, for example, in order to make it easier to obtain the shutdown effect. The volume of the plastic resin having a melting point of 80 ° C. or more and 170 ° C. or less in all constituent components of the separator is preferably 10% by volume or more, and more preferably 20% by volume or more. Further, the volume of the thermoplastic resin having a melting point of 80 ° C. or higher and 170 ° C. or lower is preferably 70% by volume or more, more preferably 80% by volume or more in all the constituent components of the porous layer (A). (The thermoplastic resin having a melting point of 80 ° C. or higher and 170 ° C. or lower may be 100% by volume). Furthermore, the porosity of the porous layer (B) obtained by the method described later is 20 to 60%, and the volume of the thermoplastic resin having a melting point of 80 ° C. or more and 170 ° C. or less is that of the porous layer (B). It is preferably 50% or more of the pore volume.

  Thickness of porous layer (A) [when the separator has a plurality of porous layers (A), the total thickness thereof. The same applies to the thickness of the porous layer (A). ] Is preferably 10 μm or more and more preferably 12 μm or more from the viewpoint of ensuring a better shutdown function. However, if the porous layer (A) is too thick, the load characteristics and energy density of the battery may be reduced, and therefore, the thickness is preferably 30 μm or less, and more preferably 25 μm or less.

  The porous layer (B) according to the separator is a functional layer for imparting a specific function to the separator, and is a composition (coating material) prepared by dispersing or dissolving the constituent material of the porous layer (B) in a solvent. ) Is applied to the surface of the porous layer (A) (details of the separator manufacturing method will be described later).

  As for the porous layer (B), as long as it is formed through the above steps, its function and configuration are not particularly limited, but is more heat resistant than the porous layer (A). A high layer is preferable, and, for example, the heat resistance of the entire separator can be increased as compared with a separator using only a microporous film constituting the porous layer (A).

  The “heat resistance” of the porous layer (A) and the porous layer (B) is determined by the temperature at which deformation such as softening is observed. That is, in the case of a separator having a porous layer (B) having higher heat resistance than the porous layer (A), the heat resistance temperature of the porous layer (B) (a temperature at which deformation such as softening does not occur. The same applies to the “heat-resistant temperature” relating to the filler having a temperature of 150 ° C. or higher. ”Must be higher than the heat-resistant temperature of the porous layer (A). It is preferable that the temperature is higher than or equal to ° C, and more preferably higher than or equal to 180 ° C.

  As the porous layer (B), for example, a layer mainly containing a filler having a heat resistant temperature of 150 ° C. or higher is preferable. Such a porous layer (B) can ensure a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the battery is increased by a filler having a heat resistant temperature of 150 ° C. or higher. it can. That is, when the battery becomes high temperature, even if the porous layer (A) shrinks, the porous layer (B) which does not easily shrink can directly generate positive and negative electrodes that can be generated when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact. Moreover, since the porous layer (B) containing a filler having a heat resistant temperature of 150 ° C. or more acts as a skeleton of the separator, it can suppress the thermal contraction of the porous layer (A), that is, the thermal contraction of the entire separator. it can.

  The filler having a heat-resistant temperature of 150 ° C. or higher used for the porous layer (B) is stable to the non-aqueous electrolyte of the battery, and is electrochemically stable to be hardly oxidized or reduced in the battery operating voltage range. Any organic particles or inorganic particles may be used as long as they are fine, but fine particles are preferable from the viewpoint of dispersion and the like, and inorganic fine particles are more preferably used from the viewpoint of stability (particularly oxidation resistance).

Specific examples of the constituent material of the inorganic particles include inorganic oxides such as iron oxide, Al ₂ O ₃ (alumina), SiO ₂ (silica), TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride, etc. Inorganic nitrides of the above; poorly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; covalent bonds such as silicon and diamond; clays such as montmorillonite; Here, the inorganic oxide may be boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or other mineral resource-derived substances or artificial products thereof. In addition, the surface of a conductive material exemplified by metal, SnO ₂ , conductive oxide such as tin-indium oxide (ITO), carbonaceous material such as carbon black, graphite, etc., is a material having electrical insulation ( For example, the particle | grains which gave the electrical insulation property by coat | covering with the said inorganic oxide etc. may be sufficient. As the inorganic particles, from the viewpoint of further improving the oxidation resistance of the porous layer (B), the above-mentioned inorganic oxide particles (fine particles) are preferable, and among these, alumina, silica, boehmite, and the like are more preferable.

  Organic particles (organic powder) include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include various crosslinked polymer particles and heat-resistant polymer particles such as polysulfone, polyacrylonitrile (PAN), aramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).

  As the filler having a heat-resistant temperature of 150 ° C. or higher, only one kind of those exemplified above may be used, or two or more kinds may be used in combination.

  As a form of the filler having a heat resistant temperature of 150 ° C. or more, for example, the filler may have a shape close to a sphere, or may have a plate shape, but the porous layer (B) includes the above-mentioned It is preferable that at least a part of the filler is plate-like particles. All of the fillers may be plate-like particles. When the porous layer (B) contains the plate-like particles, it is possible to suppress the force that the porous film (A) contracts due to the collision between the plate-like particles. Further, the use of plate-like particles increases the path between the positive electrode and the negative electrode in the separator, that is, the so-called curvature. Therefore, even when dendrite is generated, it becomes difficult for the dendrite to reach the positive electrode from the negative electrode, and the reliability against a dendrite short can be improved.

Examples of the plate-like filler include various commercially available products, such as “Sun Lovely (trade name)” (SiO ₂ ) manufactured by Asahi Glass S-Tech, and “NST-B1 (trade name)” manufactured by Ishihara Sangyo Co., Ltd. (TiO ₂ ), Sakai Chemical Industry's plate-like barium sulfate “H series (trade name)”, “HL series (trade name)”, Hayashi Kasei Co., Ltd. “micron white (trade name)” (talc), “Bengel (trade name)” (bentonite) manufactured by Hayashi Kasei Co., Ltd. “BMM (trade name)” or “BMT (trade name)” (boehmite) manufactured by Kawai Lime Co., Ltd. Name) ”[Alumina (Al ₂ O ₃ )],“ Seraph (trade name) ”(alumina) manufactured by Kinsei Matech Co., Ltd.,“ Yodogawa Mica Z-20 (trade name) ”(sericite), etc. Is possible. In addition, SiO ₂ , Al ₂ O ₃ , ZrO ₂ , and CeO ₂ can be produced by the method disclosed in Japanese Patent Laid-Open No. 2003-206475.

  As a form in the case where the filler is a plate-like particle, the aspect ratio (ratio between the maximum length in the plate-like particle and the thickness of the plate-like particle) is preferably 5 or more, more preferably 10 or more, Is 100 or less, more preferably 50 or less. The aspect ratio of the plate-like particles referred to in the present specification is a value determined by image analysis of an image taken with a scanning electron microscope (SEM).

  Further, since the plate-like filler has a problem of being easily cracked by impact when it is thin, the average thickness is preferably 0.02 μm or more, and more preferably 0.05 μm or more. However, if the thickness of the plate-like filler is too large, the separator becomes thick and the discharge capacity is reduced, or the porous layer (B) is easily cracked during the production of the battery, so the average thickness is 0. 0.7 μm or less is preferable, and 0.5 μm or less is more preferable.

  The average thickness of the plate-like filler is obtained as an average value (number average value) of 100 fillers by observing the cross section of the separator with an SEM.

Moreover, it is preferable that at least a part of the filler contained in the porous layer (B) is a fine particle having a secondary particle structure in which primary particles are aggregated. All of the filler may be fine particles having the secondary particle structure. When the porous layer (B) contains the filler having the secondary particle structure, it is possible to obtain the same heat shrinkage suppression effect and the dendrite short suppression effect as in the case of using the plate-like particles described above. Examples of the filler having the secondary particle structure include “Boehmite C06 (trade name)”, “Boehmite C20 (trade name)” (boehmite) manufactured by Daimei Chemical Co., Ltd., “ED-1 (trade name) manufactured by Yonesho Lime Industry Co., Ltd. ) ”(CaCO ₃ ), J. et al. M.M. Examples include “Zeolex 94HP (trade name)” (clay) manufactured by Huber.

  The average particle diameter of the filler relating to the porous layer (B) is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 5 μm or less. In addition, the average particle diameter as used in this specification is the number measured by dispersing these fine particles in a medium in which the filler is not dissolved using, for example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). Average particle size.

  In the porous layer (B), the amount of the filler having a heat resistant temperature of 150 ° C. or higher is the total amount of the constituent components of the porous layer (B) when the filler is mainly used. The same applies to the content of the constituent components. ], 50% by volume or more, preferably 70% by volume or more, more preferably 80% by volume or more, and still more preferably 90% by volume or more. By making the filler in the porous layer (B) high as described above, it is possible to better suppress the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode when the battery becomes high temperature. Moreover, the thermal contraction of the whole separator can be suppressed favorably.

  Moreover, the porous layer (B) binds fillers having a heat resistant temperature of 150 ° C. or higher, or binds the porous layer (A) and the porous layer (B) as necessary. Therefore, it is preferable to contain an organic binder. From such a viewpoint, the suitable upper limit of the filler amount having a heat resistant temperature of 150 ° C. or higher in the porous layer (B) is, for example, a constituent component of the porous layer (B). Is 99.5% by volume. If the amount of the filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (B) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (B). The pores of the porous layer (B) are easily filled with an organic binder, and the function as a separator may be reduced. When the porous layer is made porous with a pore-opening agent, the fillers There is a possibility that the effect of suppressing the heat shrinkage may be reduced due to the excessively large interval.

  When plate-like particles are used as the filler having a heat-resistant temperature of 150 ° C. or higher, the plate-like particles in the porous layer (B) preferably have a flat plate surface substantially parallel to the separator surface, More specifically, the plate-like particles in the vicinity of the surface of the separator preferably have an average angle between the flat plate surface and the separator surface of 30 ° or less [most preferably, the average angle is 0 °, ie, the separator The plate-like flat surface in the vicinity of the surface is parallel to the separator surface]. Here, “near the surface” refers to a range of about 10% from the surface of the separator to the entire thickness. By increasing the orientation of the plate-like particles so that the form of the plate-like particles is in the state as described above, it becomes possible to more strongly exert the heat shrinkage suppressing action of the porous layer (B). In addition, internal short-circuiting that may be caused by lithium dendrite deposited on the electrode surface or protrusions of the active material on the electrode surface can be more effectively prevented. In addition, the presence form of the plate-like particles in the porous layer (B) can be grasped by observing the cross section of the separator with an SEM.

  Further, when plate-like particles are used as a filler having a heat-resistant temperature of 150 ° C. or higher, in the porous layer (B), they are laminated on those plate-like surfaces (if they are laminated in the thickness direction on a wide surface forming a flat plate). The horizontal positions of the upper and lower fillers may be deviated from each other), and the number of stacked fillers is preferably 5 or more, and more preferably 10 or more. The presence of the plate-like filler in the porous layer (B) related to the separator can increase the strength of the separator (for example, penetration strength measured by a measurement method described later). However, if the number of laminated layers of the plate-like filler in the porous layer (B) is too large, the thickness of the porous layer (B) and thus the thickness of the separator may be increased, and the energy density of the battery may be decreased. is there. Therefore, the number of laminated plate-like fillers in the porous layer (B) is preferably 50 or less, and more preferably 20 or less. In addition, the number of laminated plate-like fillers in the porous layer (B) can be measured by the method employed in the examples described later.

  The porous layer (B) preferably contains an organic binder in order to ensure the shape stability of the separator and to integrate the porous layer (B) and the porous layer (A). Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. In particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  In addition, when using the said organic binder for a porous layer (B), if it uses in the form of the emulsion dissolved or disperse | distributed to the solvent of the composition for porous layer (B) formation mentioned later. Good.

  Moreover, as the porous layer (B), it is sufficient that the heat resistance is higher than that of the porous layer (A). In addition to the porous layer mainly composed of the filler having a heat-resistant temperature of 150 ° C. or more, various functions are possible. The layer which has is mentioned. Examples of such a porous layer (B) include a layer in which fibrous materials are mixed together with the filler. Here, the fibrous material has a heat-resistant temperature of 150 ° C. or higher, has an electrical insulating property, is electrochemically stable, and is used for manufacturing a non-aqueous electrolyte solution and a separator as described in detail below. The material is not particularly limited as long as the solvent used at the time is stable. The “fibrous material” in the present specification means an aspect ratio [length in the longitudinal direction / width in the direction perpendicular to the longitudinal direction (diameter)] of 4 or more. The ratio is preferably 10 or more.

  Specific examples of the constituent material of the fibrous material include, for example, cellulose and modified products thereof [carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), etc.], polyolefin [polypropylene (PP), propylene copolymer, etc.], Polyester [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.], polyacrylonitrile (PAN), polyaramid, polyamideimide, polyimide, and other resins; glass, alumina, zirconia, silica, and other inorganic materials An oxide; etc. can be mentioned, and two or more of these constituent materials may be used in combination to form a fibrous material. The fibrous material may contain various known additives (for example, an antioxidant in the case of a resin) as necessary.

  The thickness of the separator according to the present invention is preferably 6 μm or more, and more preferably 10 μm or more, from the viewpoint of more reliably separating the positive electrode and the negative electrode. On the other hand, if the separator is too thick, the energy density of the battery may be lowered. Therefore, the thickness is preferably 50 μm or less, and more preferably 30 μm or less.

  Further, when the thickness of the porous layer (A) constituting the separator is a (μm) and the thickness of the porous layer (B) is b (μm), the ratio a / b between a and b is 10 or less. Preferably, it is 5 or less, more preferably 1 or more, and more preferably 2 or more. In the separator according to the present invention, for example, when the porous layer (B) is a layer mainly containing a filler having a heat-resistant temperature of 150 ° C. or higher, the thickness ratio of the porous layer (A) is increased and the porous layer ( Even if B) is made thin, it is possible to highly suppress the occurrence of a short circuit due to thermal contraction of the separator while ensuring a good shutdown function. In the separator, when there are a plurality of porous layers (A), the thickness a is the total thickness, and when there are a plurality of porous layers (B), the thickness b is the total thickness. .

  In terms of specific values, the thickness of the porous layer (A) [when the separator has a plurality of porous layers (A), the total thickness] is preferably 5 μm or more, It is preferable that it is 30 micrometers or less. The thickness of the porous layer (B) [when the separator has a plurality of porous layers (B), the total thickness] is preferably 1 μm or more, more preferably 2 μm or more, and 4 μm. More preferably, it is 20 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less. If the porous layer (A) is too thin, the shutdown function may be weakened. If the porous layer is too thick, the energy density of the battery may be lowered. There exists a possibility that the effect | action which suppresses the thermal contraction of the whole separator may become small. Moreover, if the porous layer (B) is too thin, the effect that can be ensured by the formation of the porous layer (B) may be reduced. If it is too thick, the thickness of the entire separator is increased.

The porosity of the separator as a whole is preferably 30% or more in a dried state in order to secure the amount of electrolyte solution retained and to improve ion permeability. On the other hand, from the viewpoint of securing separator strength and further suppressing internal short-circuiting, the porosity of the separator is preferably 70% or less in a dry state. The porosity of the separator: P (%) can be calculated by obtaining the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (1).
P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (1)
Here, in the above formula, a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: thickness of separator (cm).

In the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (A), and t is the thickness (cm) of the porous layer (A). The porosity: P (%) of the porous layer (A) can also be obtained using the equation (1). It is preferable that the porosity of the porous layer (A) calculated | required by this method is 30 to 70%.

Furthermore, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (B), and t is the thickness (cm) of the porous layer (B), The porosity: P (%) of the porous layer (B) can also be obtained using the equation (1). It is preferable that the porosity of the porous layer (B) calculated | required by this method is 20 to 60%.

The separator according to the present invention is measured by a method according to JIS P 8117, and has a Gurley value of 10 to 300 sec indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ^2. It is desirable that If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. By employ | adopting the said structure, it can be set as the separator which has such air permeability.

  Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated. For example, the separator having the piercing strength can be obtained by forming the porous layer (B) mainly including a filler having a heat resistant temperature of 150 ° C. or higher.

  The shutdown characteristic of the battery of the present invention having the separator having the above-described configuration can be obtained, for example, by the temperature change of the internal resistance of the battery. Specifically, the measurement can be performed by installing the battery in a thermostatic chamber, increasing the temperature from room temperature at a rate of 1 ° C. per minute, and determining the temperature at which the internal resistance of the battery increases. In this case, the internal resistance of the battery at 150 ° C. is preferably 5 times or more of room temperature, more preferably 10 times or more, and such a characteristic is ensured by using the separator having the above-described configuration. be able to.

  Moreover, it is preferable that the separator which concerns on the battery of this invention sets the heat shrink rate in 150 degreeC in the location in which the porous layer (B) was formed to 5% or less. In the case of a separator having such characteristics, even when the inside of the battery reaches about 150 ° C., there is almost no shrinkage at the location where the separator is interposed between the positive electrode and the negative electrode. Can be prevented more reliably, and the safety of the battery at high temperatures can be further increased. For example, by forming a porous layer (B) mainly including a filler having a heat resistant temperature of 150 ° C. or higher, a separator having the above heat shrinkage rate can be obtained.

  The “150 ° C. heat shrinkage rate” refers to the size of the separator before putting the separator in a thermostat, raising the temperature to 150 ° C. and leaving it for 3 hours, and then putting it in the thermostat. The reduction ratio of the dimension calculated | required by this is expressed in percentage.

  Heretofore, the porous layer (B) as a layer for improving the heat resistance of the separator has been described. However, the porous layer (B) having the above structure has a surface area that is larger than that of the porous layer (A). Since such a separator can also be configured to have good sliding properties, when such a separator is used, for example, a laminated body of positive and negative electrodes and two separators is wound around a winding core to form a wound electrode body. When producing, by arranging the porous layer (B) in contact with the winding core, the winding core can be easily extracted. Therefore, in this case, the winding electrode body can be prevented from being disturbed when the winding core is pulled out, and the productivity of the winding electrode body and hence the productivity of the battery can be improved. Moreover, when the slipperiness of the surface of a porous layer (B) is favorable as mentioned above, in the preparation process of a separator or a winding electrode body, the roll which conveys a separator, and a porous layer (B) The effect of increasing the productivity of the wound electrode body and thus the productivity of the battery can be expected by reducing the friction between them and suppressing the occurrence of wrinkles of the separator.

  Thus, the porous layer (B) can also act as a functional layer for improving slipperiness. Therefore, when the improvement of the heat resistance of the separator is not required for the porous layer (B) and only the function as a functional layer for improving the slipperiness is required, among the porous layers (B), the comparison is made. It is good also as a structure with low static heat resistance.

  In addition, the porous layer (B) is not only a heat-resistant layer and a functional layer for improving slipperiness, but also, for example, an electrolyte solution holding layer for increasing the amount of non-aqueous electrolyte solution, It is good also as a functional layer. For example, when a functional layer for suppressing static electricity is used, a known surfactant can be further added to the porous layer (B) as the heat-resistant layer.

  The separator according to the battery of the present invention comprises a porous layer (B) forming composition (paste, slurry) containing a component and a solvent for constituting the porous layer (B), and the porous layer (A). It is manufactured through a process of applying to a surface such as a microporous film and drying. In the case of producing a separator by such a method, the porous layer (B) forming composition is usually applied to the surface of the microporous film while applying stress to the microporous film, and dried to obtain the porous layer (B). Since the porous layer (A) shrinks after the production of the separator, the porous layer (B) does not shrink. Therefore, when the separator is allowed to stand, it is [mainly porous layer ( Warping occurs with the formation surface of B) as the outside.

  For example, in the case of a separator having a porous layer (B) mainly containing a filler having a heat-resistant temperature of 150 ° C. or higher, the porous layer (B) forming composition may be organic if necessary in addition to the filler. A binder or the like is used, and these are dispersed in a solvent (including a solvent and a dispersion medium; the same applies hereinafter). Note that the organic binder can be dissolved in a solvent. In this case, the solvent used in the composition for forming the porous layer (B) may be any solvent that can uniformly disperse the filler and the like, and can dissolve or disperse the organic binder uniformly. Common organic solvents such as aromatic hydrocarbons, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The composition for forming a porous layer (B) for forming a porous layer (B) mainly comprising a filler having a heat resistant temperature of 150 ° C. or higher is a solid containing a filler having a heat resistant temperature of 150 ° C. or higher and an organic binder. The content is preferably 10 to 80% by mass, for example.

  Moreover, in the porous layer (B), as described above, in order to increase the orientation of the plate-like filler, the porous layer (B) forming composition containing the plate-like filler is made porous. After applying and impregnating the microporous film constituting the layer (A), a method of applying shear or a magnetic field to the composition may be used. For example, as described above, the composition for forming the porous layer (B) containing the plate-like filler is applied to the microporous film, and then the composition is shared by passing through a certain gap. Can do.

  Further, in order to more effectively exhibit the action of the other components constituting the filler and the porous layer (B), these components are unevenly distributed so that the components are parallel or substantially parallel to the surface of the separator. It is good also as a form gathered in layers.

  The porous layer (A) and the porous layer (B) do not have to be one each, and a plurality of layers may be present in the separator. However, increasing the number of layers may increase the thickness of the separator and increase the internal resistance of the battery or decrease the energy density. Therefore, it is not preferable to increase the number of layers, and the porous layer in the separator is not preferable. The total number of layers (A) and the porous layer (B) is preferably 5 or less.

  For example, depending on the mode of the porous layer (B), a long separator having a desired size may be used, such as a separator having a porous layer (B) mainly containing a filler having a heat resistant temperature of 150 ° C. or higher. The separator according to the present invention is at least partially porous, although it may be difficult to cut at the time of molding into a small piece, or a small piece (such as the filler) may be easily lost from the porous layer (B) at the time of cutting. Since a portion where the layer (B) is not formed is provided, cutting at such a portion can also be expected to have an effect of preventing difficulty in cutting and missing of small pieces.

As the positive electrode according to the battery of the present invention, a positive electrode used in a conventionally known non-aqueous secondary battery, for example, a positive electrode containing an active material capable of occluding and releasing Li ions can be used. For example, as an active material, lithium-containing transition metal oxide represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); lithium manganese such as LiMn ₂ O ₄ Oxide; LiMn _x M _(1-x) O _{2 in} which part of Mn of LiMn ₂ O ₄ is substituted with another element; olivine type LiMPO ₄ (M: Co, Ni, Mn, Fe); LiMn _0.5 Ni _0.5 O ₂ ; Li _{(1 + a)} Mn _x Ni _y Co _(1-xy) O ₂ (−0.1 <a <0.1, 0 <x <0.5, 0 <y <0. 5); can be applied, and a known conductive additive (carbon material such as carbon black) or a binder such as polyvinylidene fluoride (PVDF) is appropriately added to these positive electrode active materials. The positive electrode mixture is formed from a current collector as a core material (ie, Such as those finished electrode mixture layer) may be used.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The tab on the positive electrode side usually leaves an exposed portion of the current collector without forming a positive electrode mixture layer on a part of the current collector when the positive electrode is manufactured, and an aluminum foil or the like is connected to it later. Provided by. In addition, it is preferable that the thickness of the tab of a positive electrode is 30-100 micrometers.

  As the negative electrode according to the battery of the present invention, a negative electrode used in a conventionally known non-aqueous secondary battery, for example, a negative electrode containing an active material capable of occluding and releasing Li ions can be used. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb and In and alloys thereof, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture obtained by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials, and a molded body (negative electrode mixture layer) using a current collector as a core material And those having a negative electrode agent layer such as those obtained by using the above-mentioned various alloys and lithium metal foils alone or those obtained by forming the alloy or lithium metal layer on a current collector.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

  As with the lead portion on the negative electrode side, the negative electrode layer (including a layer having a negative electrode active material and a negative electrode mixture layer) is usually formed on a part of the current collector during the preparation of the negative electrode. Instead, the exposed portion of the current collector is left, and a copper foil or the like is connected thereto later. In addition, it is preferable that the thickness of the tab of a negative electrode is 30-100 micrometers.

  The electrode is used in the form of a wound electrode body in which the positive electrode and the negative electrode are laminated via the two separators, and further wound, and the cross section is shaped flat. To do.

  In the wound electrode body, in particular, when a separator having a porous layer (B) mainly containing a filler having a heat resistant temperature of 150 ° C. or higher is used, the separator porous layer (B) faces the positive electrode. It is preferable. By disposing the separator in this way, it is possible to suppress the oxidative deterioration of the separator particularly during overcharge.

  In the wound electrode body, the separator porous layer (A) is preferably opposed to the negative electrode. In this case, although the detailed reason is unknown, in the case where the separator is arranged so that the porous layer (A) faces at least the negative electrode, when the shutdown occurs rather than the case where it is arranged on the positive electrode side, The ratio of the thermoplastic resin melted from the porous layer (A) that is absorbed by the electrode mixture layer is reduced, and the melted thermoplastic resin is used more effectively to close the pores of the separator. The effect of shutdown is better.

  Furthermore, for example, when a non-aqueous secondary battery has a mechanism for lowering the internal pressure of the battery by discharging the gas inside the battery to the outside when the internal pressure of the battery increases due to temperature rise, In addition, the internal non-aqueous electrolyte may volatilize and the electrode may be directly exposed to air. When the battery is in a charged state, when the negative electrode and air (oxygen or moisture) come into contact, Li ions occluded in the negative electrode, lithium deposited on the negative electrode surface, and air react to generate heat. And sometimes it catches fire. Moreover, the temperature of the battery rises due to this heat generation, causing a thermal runaway reaction of the positive electrode active material, and as a result, the battery may ignite.

  However, in the case of a battery using a wound electrode body configured such that the porous layer (A) mainly composed of a thermoplastic resin having a melting point of 80 to 170 ° C. faces the negative electrode, the porous layer ( Since the thermoplastic resin as the main component of A) melts and covers the negative electrode surface, the reaction between the negative electrode and air accompanying the operation of the mechanism for discharging the gas inside the battery to the outside can be suppressed. Therefore, there is no fear of heat generation due to the operation of the mechanism for discharging the gas inside the battery to the outside, and the battery can be kept safer. Moreover, reaction of a porous layer (A) and a positive electrode can be prevented because a porous layer (B) faces a positive electrode.

As the nonaqueous electrolytic solution according to the battery of the present invention, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group]; it can.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as ethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, t are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. -Additives such as butylbenzene, acid anhydride, sulfurated ester, vinyl ethylene carbonate (VEC) may be added as appropriate.

  The concentration of the lithium salt in the organic electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  Also, instead of the organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.

  Further, a polymer material that contains the non-aqueous electrolyte and gels may be added, and the non-aqueous electrolyte may be gelled and used for a battery. Polymeric materials for making the organic electrolyte into a gel include PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide Examples of the host polymer capable of forming a gel electrolyte such as a copolymer, a crosslinked polymer having an ethylene oxide chain in the main chain or a side chain, and a crosslinked poly (meth) acrylic ester.

  Examples of the form of the battery of the present invention include a tubular shape (such as a rectangular tube shape) using a steel can, an aluminum can, or the like as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The non-aqueous secondary battery of the present invention is applied to various uses in which conventionally known non-aqueous secondary batteries are used, including power supply applications for portable devices such as mobile phones and notebook personal computers. Can do.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of separator>
An organic binder SBR emulsion (solid content ratio 40% by mass): 150 g and water: 6000 g were placed in a container and stirred at room temperature until evenly dispersed. Boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10): 2000 g, which is a filler having a heat resistance temperature of 150 ° C. or higher, was added to this dispersion in 4 portions, and the mixture was uniformly stirred at 2800 rpm for 5 hours with a disper. A slurry [a slurry for forming a porous layer (B), a solid content ratio of 25.3 mass%] was prepared. While taking a PE microporous membrane [porous layer (A): thickness 12 μm, porosity 40%, pore diameter 0.033 μm, PE melting point 135 ° C.], the slurry was applied to the surface by a microgravure coater. The separator was produced by applying and drying to form a porous layer (B) having a thickness of 2.6 μm. In addition, the part which does not form a porous layer (B) was provided in a part of PE microporous film.

The porous layer (B) in the obtained separator had a mass per unit area of 3.4 g / m ² . Further, the volume content of the plate boehmite in the porous layer (B) of this separator was 88% by volume, and the porosity of the porous layer (B) was 55%. Further, since the porous layer (B) of this separator was not deformed at 250 ° C., it can be said that the heat resistant temperature is 250 ° C. or higher. Moreover, this separator was left still and it confirmed that curvature generate | occur | produced by making the formation surface side of a porous layer (B) outside.

<Preparation of positive electrode>
85 parts by mass of LiCoO _{2 as a} positive electrode active material, 10 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of PVDF as a binder are uniformly mixed with N-methyl-2-pyrrolidone (NMP) as a solvent. It mixed so that positive electrode mixture containing paste might be prepared. This paste is intermittently applied on both sides of a 15 μm thick aluminum foil serving as a current collector so that the coating length is 320 mm on the front surface and 250 mm on the back surface, dried, and then calendered to a total thickness of 150 μm. Thus, the thickness of the positive electrode material mixture layer was adjusted and cut so as to have a width of 43 mm to produce a positive electrode having a length of 340 mm and a width of 43 mm. Further, the exposed portion of the aluminum foil of the positive electrode was tabbed.

<Production of negative electrode>
Also, a negative electrode mixture-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied on both sides of a 10 μm-thick current collector made of copper foil so that the coating length is 200 mm on the front surface and 260 mm on the back surface, dried, and then calendered to obtain a total thickness. The thickness of the negative electrode mixture layer was adjusted to 142 μm and cut to a width of 45 mm to produce a negative electrode having a length of 330 mm and a width of 45 mm. Further, a tab was attached to the exposed portion of the copper foil of the negative electrode.

<Formation of wound electrode body>
Using the two separators, the positive electrode, and the negative electrode, the winding electrode body having the structure shown in FIG. 4 is formed by overlapping and winding it so as to have the arrangement shown in FIG. Formed.

<Battery assembly>
The wound electrode body is put in an aluminum outer can having a thickness of 6 mm, a height of 50 mm, and a width of 34 mm, and a nonaqueous electrolyte (a solvent in which ethylene carbonate and ethylmethyl carbonate are mixed at a volume ratio of 1: 2 is mixed with LiPF. ₆ ) was injected at a concentration of 1.2 mol / l, and then sealed to prepare a non-aqueous secondary battery.

Example 2
A wound electrode body was formed in the same manner as in Example 1 except that the wound electrode body was wound so as to have the structure shown in FIG. 3, and Example 1 except that this wound electrode body was used. A non-aqueous secondary battery was produced in the same manner.

Example 3
A wound electrode body was formed in the same manner as in Example 1 except that the wound electrode body was wound so as to have the structure shown in FIG. A non-aqueous secondary battery was produced in the same manner.

Example 4
A wound electrode body was formed in the same manner as in Example 1 except that the wound electrode body was wound so as to have the structure shown in FIG. A non-aqueous secondary battery was produced in the same manner.

Comparative Example 1
A non-aqueous secondary battery was produced in the same manner as in Example 1 except that the separator having the porous layer (B) formed on the entire surface was used as the PE microporous film used in the production of the separator in Example 1. did.

  In manufacturing 100 non-aqueous secondary batteries of Examples 1 to 4 and Comparative Example 1, the ease (insertability) of inserting the wound electrode body into the outer can was evaluated. The evaluation is “◎” when all the wound electrode bodies were not easily caught when inserted into the outer can, and the number of the wound electrode bodies that were caught when inserted into the outer can. Was 1 or 2, and the case where the number of the wound electrode bodies that were caught when inserted into the outer can was 3 or more was designated as “Δ”. These results are shown in Table 1.

  The maximum thickness (maximum length in the thickness direction) of each of the nonaqueous secondary batteries of Examples 1 to 4 and Comparative Example 1 was measured, and the standard deviation value was obtained. These results are also shown in Table 1.

  Further, the nonaqueous secondary batteries of Examples 1 to 4 and Comparative Example 1 were discharged at a constant current at room temperature (25 ° C.) at a constant current of 240 mA (0.2 C) until the battery voltage reached 3.0 V. Then, after charging at a constant current of 240 mA (0.2 C) to 4.2 V, constant voltage charging at 4.2 V is performed until the total charging time is 8 hours, followed by a constant current of 240 mA (0.2 C). Then, constant current discharge was performed until the battery voltage became 3.0 V, and the discharge capacity was measured. These results are also shown in Table 1. In Table 1, the room temperature discharge capacity of each battery is shown as a relative value when the value of the battery of Comparative Example 1 is 100.

  As is clear from Table 1, in the batteries of Examples 1 to 4, there is no wound electrode body that is caught when inserted into the outer can, and the insertability is good. Thus, in the case of a battery having a wound electrode body with good insertability, as described above, it is difficult for damage to occur when inserted into an outer can, and it can be said that the productivity of the battery is good. Further, in the batteries of Examples 1 to 4, the standard deviation value of the maximum thickness is small and does not include variation (that is, a battery in which the outer can is deformed by a wound electrode body having a very large thickness). Also from such a point, it can be said that the batteries of Examples 1 to 4 have good productivity. In particular, in both of the two separators, in the batteries of Examples 1 and 2 configured so that the warpage can be satisfactorily suppressed, the insertability of the wound electrode body into the outer can is better, and the standard of the maximum thickness Since the deviation value is also smaller, the productivity is better.

  Furthermore, in the batteries of Examples 1 to 4, no decrease in discharge capacity was observed, and it was confirmed that charging and discharging could be performed satisfactorily.

10 wound electrode body 20 positive electrode 30 negative electrode 40, 50 separator 41, 51 porous layer (A)
42, 52 Porous layer (B)

Claims (6)

A non-aqueous secondary battery having a positive electrode, a negative electrode, and a wound electrode body in which two separators interposed between the positive electrode and the negative electrode are overlapped and wound, and the cross section is flattened,
The separator is a multilayer structure having a porous layer (A) and a porous layer (B),
The porous layer (A) is a layer mainly composed of a thermoplastic resin having a melting point of 80 to 170 ° C.,
The porous layer (B) is a layer formed through a step of applying a composition prepared by dispersing or dissolving the constituent material of the porous layer (B) in a solvent to one side of the porous layer (A). And
When the inner end of at least one of the positive electrode and the negative electrode is located on the inner end side of the first bending start portion inside the wound electrode body, at least one of the two separators is The porous layer (A) side is in contact with one of the electrodes whose inner end position is located closer to the inner end side of the wound electrode body, and at least the inner end position is the inner side of the wound electrode body. There is no porous layer (B) on the inner end side of the wound electrode body from the position in contact with one electrode located on the end side,
When the inner ends of the positive electrode and the negative electrode are located on the outer end side with respect to the first bending start portion inside the wound electrode body, at least one of the two separators is at least the wound electrode body The non-aqueous secondary battery is characterized in that it does not have a porous layer (B) on the inner end side of the first bend start portion inside.   Of the positive electrode and the negative electrode, a tab for connecting an electrode located on the outer side of the wound electrode body and the external terminal of the battery is the 2 in the outermost periphery of the electrode located on the outer side of the wound electrode body. The non-aqueous secondary battery according to claim 1, wherein at least one of the separators is provided at a position corresponding to a location not having the porous layer (B) inside the wound electrode body.   At least the inner end of the negative electrode is located closer to the inner end than the first bending start portion inside the wound electrode body, and the separator that contacts the negative electrode on the porous layer (A) side is at least in contact with the negative electrode. 3. The nonaqueous secondary battery according to claim 1, wherein a porous layer (B) is not provided on an inner end side of the wound electrode body with respect to a position.   The inner ends of the positive electrode and the negative electrode are located on the outer end side with respect to the first bend start portion inside the wound electrode body, and the two separators are at least the first bend inside the wound electrode body. The nonaqueous secondary battery according to claim 1 or 2, wherein the porous layer (B) is not provided on the inner end side of the start portion.   The nonaqueous secondary battery according to any one of claims 1 to 4, wherein the porous layer (B) in the separator mainly contains a filler having a heat resistant temperature of 150 ° C or higher.   The nonaqueous secondary battery according to claim 5, wherein the separator porous layer (B) faces the positive electrode.

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