JP2013211193A - Porous sheet and secondary battery using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film enhancing diffusion and convection of an electrolyte and to provide a secondary battery whose cycle characteristics are improved by using the same.SOLUTION: A poreless area is formed on a porous sheet so as to suppress an electrolyte from staying on an electrode. Diffusion and convection of the electrolyte is enhanced due to existence of the poreless area on the surface of the porous sheet. Local degradation of the electrolyte is suppressed and cycle characteristics of a secondary battery can be improved.

Description

  The present invention relates to a porous sheet and a secondary battery using the same.

  The development of portable devices in recent years has been remarkable, and high energy batteries are the main driving force. In particular, lithium ion secondary batteries are expected as the mainstay of next-generation batteries. In the development of such a lithium ion secondary battery, improvement of components such as a positive electrode, a negative electrode, and an electrolytic solution is being promoted in order to achieve higher performance. In particular, various improvements have been made in order to suppress deterioration of characteristics due to decomposition of the electrolyte on the negative electrode surface.

  For example, Patent Document 1 discloses that EC in initial charging is obtained by adding 1,3-propane sultone as an additive in an electrolytic solution using a cyclic carbonate such as ethylene carbonate (EC) as an electrolytic solution solvent. A technique is disclosed in which 1,3-propane sultone is reduced on the surface of the negative electrode carbon material before reductive decomposition, and the surface of the carbon material is coated with a passive film. Here, the passive film is a film formed so as to cover the surface of the negative electrode, which is an electrode, due to the decomposition of the additive added in the electrolytic solution, and has a good lithium ion permeability. And a film having an action of suppressing the decomposition reaction of the electrolytic solution in the negative electrode. Thereby, it is going to suppress degradation of electrolyte solution and deterioration of the negative electrode accompanying this.

  Further, for example, in Patent Document 2 and Patent Document 3, by adding vinylene carbonate (VC) as an additive to propylene carbonate (PC), which is suitable for improving low temperature characteristics as an electrolyte solvent, during initial charging. A technique is disclosed in which VC is reductively decomposed on the surface of a negative electrode carbon material before the reductive decomposition of PC, and the surface of the carbon material is coated with a passive film. Thereby, it is going to suppress degradation of electrolyte solution and the accompanying deterioration of a negative electrode.

  In the technologies disclosed in these Patent Documents 1 to 3, an additive is added to the electrolytic solution to form a passive film on the surface of the carbon material that is an electrode. If the additive is not supplied to the electrode surface, If present, a passive film is not formed. In particular, a large battery takes a long time to diffuse the electrolyte because the cell size is large, and the influence of local deterioration of the electrolyte tends to be remarkable. Such local deterioration of the electrolytic solution causes deterioration of cycle characteristics even in a lithium ion secondary battery. As described above, since the concentration distribution of the additive in the electrolytic solution is not taken into consideration in the entire cell structure, it is still insufficient as a countermeasure against the characteristic deterioration caused by the electrolytic solution.

JP 2000-3724 A JP-A-8-45545 JP 2001-167797 A

  In view of the above problems, an object of the present invention is to provide a porous sheet that can promote diffusion and convection of an electrolytic solution on a porous sheet facing an electrode, and a secondary battery with improved cycle characteristics.

As a result of intensive studies to solve the above problems, the present inventors have reached the following invention.
In the porous sheet having a large number of pores according to the present invention, the porous sheet has a non-porous portion larger than the pores on the surface thereof. By configuring the porous sheet in such a manner, the diffusion and convection of the electrolytic solution are promoted, and the porous sheet effectively acts on the deterioration of the electrolytic solution. In addition, when applied to a secondary battery, the cycle characteristics can be improved.

  Although this principle is not necessarily clear, for example, when a deteriorated component is locally generated on the electrode surface, the deteriorated component may diffuse into the porous sheet and stay as it is. To avoid this situation, even if a deterioration component is generated on the electrode surface, the flow of the electrolyte solution diffused from the electrode to the porous sheet spreads in the film surface direction due to the presence of the above-mentioned non-porous portion. Therefore, it is considered that the porous sheet according to the present invention promotes the diffusion of the electrolytic solution without the deterioration component stagnation.

  A secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and has the porous sheet described above between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are predetermined at one end thereof. A non-porous portion extends in a direction crossing the predetermined direction on the surface of the porous sheet that is electrically connected to an electrode terminal drawn in a direction and faces at least one of the positive electrode and the negative electrode. Preferably it is formed.

  Since a resistance component also exists in the electrode or the current collector itself inside the electrode, the electrode reaction becomes stronger as it is closer to the electrode terminal. Therefore, the deterioration of the electrolytic solution becomes more severe as the distance from the terminal is shorter. According to such a configuration, by disposing the non-porous portion in a direction transverse to the drawing direction of the electrode terminal, the diffusibility can be greatly improved and local electrode deterioration can be prevented. As a result, the cycle characteristics of the secondary battery can be further improved.

  The secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and has the above-described porous sheet between the positive electrode and the negative electrode, and the positive electrode and the negative electrode have a predetermined direction at one end thereof. A large number of non-porous portions are unevenly distributed on the surface of the porous sheet that is electrically connected to the electrode terminal drawn out and faces in the vicinity of the electrode terminal of at least one of the positive electrode and the negative electrode. preferable.

  By adopting such a configuration, the diffusibility is greatly improved, and local electrode deterioration can be further prevented. As a result, the cycle characteristics of the secondary battery can be further improved.

  A secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and has the porous sheet described above between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are predetermined at one end thereof. The surface of the porous sheet that is electrically connected to an electrode terminal drawn in a direction and faces at least one of the positive electrode and the negative electrode is on the same line extending in the same direction as the predetermined direction. It is preferable that the parts are arranged intermittently.

  Dispersion and convection of the electrolytic solution are promoted rather than being continuously present on the same line as described above, and therefore it is preferable to dispose the non-porous portions intermittently.

  A secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, and has the porous film described above between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are at one end thereof. It is electrically connected to the electrode terminal drawn in a predetermined direction, and a non-porous portion is formed on each of the one main surface and the other main surface of the porous sheet, and the one surface of the porous sheet is formed on the one surface. It is preferable that the non-hole part formed and the non-hole part formed on the other surface are arranged so as not to overlap each other in a projected image when viewed from a direction perpendicular to the main surface.

  By adopting such a configuration, the diffusibility is greatly improved and local electrode deterioration can be prevented. As a result, the cycle characteristics of the secondary battery can be improved.

  According to the present invention, it is possible to provide a secondary battery that can promote diffusion and convection of an electrolytic solution and thereby improve cycle characteristics by forming a non-porous portion on the surface of the porous sheet.

It is a cross-sectional schematic diagram of the porous sheet of this embodiment. It is an example of this embodiment when it projects from the separator upper surface of the laminated body produced by laminating | stacking the positive electrode, the separator, and the negative electrode. It is a schematic diagram which shows the winding structure of the secondary battery of this embodiment.

  Hereinafter, preferred embodiments of the porous film of the present invention will be described in detail. FIG. 1 is a schematic explanatory view showing a porous structure used in the present embodiment. The porous sheet 14 according to this embodiment is disposed between the positive electrode 12 and the negative electrode 13. The porous sheet 14 itself is composed of a porous part 15, but a non-porous part 16 is formed on the surface of the porous sheet 14.

  By making the porous sheet in such a configuration, diffusion and convection of the electrolytic solution are promoted, and the porous sheet effectively acts on the deterioration of the electrolytic solution. In addition, when applied to a secondary battery, the cycle characteristics can be improved.

  In FIG. 1, the non-porous portions are formed on both sides of the porous sheet, but the effect can be obtained with only one side. That is, this non-porous part may exist only on the negative electrode side or may exist only on the positive electrode side. Since the oxidation catalyst ability of the positive electrode active material is particularly high in a high temperature environment, the oxidative decomposition of the solvent in the electrolytic solution tends to occur on the positive electrode surface. Therefore, the composition of the electrolytic solution changes. Due to the presence of the non-porous part, the electrolytic solution whose composition is changed in the porous sheet thickness direction, that is, the negative electrode direction, is effectively diffused.

  The material for the porous sheet used in the present embodiment is not particularly limited, but a thermoplastic tree can be preferably used. Examples of this thermoplastic tree include homopolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, copolymers, and mixtures thereof. However, among these, ultra high molecular weight polyethylene resin is preferably used in the present embodiment.

The ultra high molecular weight polyolefin resin composition may contain other polyolefin resins together with the ultra high molecular weight polyolefin resin. The polyolefin resin other than the ultrahigh molecular weight polyolefin resin has a weight average molecular weight of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , and preferably 1 × 10 ^{4 to} 3 × 10 ⁵ . Examples of such a polyolefin resin include homopolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, copolymers, and mixtures thereof. However, among these, high-density polyethylene resin is preferably used in the present embodiment.

  In this embodiment, when an ultrahigh molecular weight polyolefin resin composition is used, the composition needs to contain at least 15% by weight of the ultrahigh molecular weight polyolefin resin.

  In the production of the porous sheet according to the present embodiment, first, the above-mentioned ultrahigh molecular weight polyolefin resin (composition) is 5 to 30% by weight, preferably 8 to 20% by weight, and the solvent 95 having a freezing point of −10 ° C. or lower. -70 wt%, preferably 92-80 wt% was mixed in a uniform slurry, and this was heated and stirred to dissolve the ultrahigh molecular weight polyolefin resin (composition) in the solvent. The solution-like mixture is kneaded at a temperature in the range of 115 to 185 ° C. to prepare a kneaded product.

  The solvent is not particularly limited as long as it dissolves the ultrahigh molecular weight polyolefin resin (composition) well and has a freezing point of −10 ° C. or lower. Those having a freezing point in the range of -10 ° C to -45 ° C are preferably used. Preferable specific examples of such a solvent include, for example, aliphatic or cyclic hydrocarbons such as decane, decalin, and liquid paraffin, and mineral oil fractions corresponding to these freezing points. However, among these, a non-volatile solvent such as liquid paraffin is preferable, and in particular, a non-volatile solvent having a freezing point of −15 ° C. or lower and a kinematic viscosity at 40 ° C. of 65 cSt or lower is preferably used.

  When the ultra high molecular weight polyolefin resin (composition) exceeds 30% by weight in the solution mixture of the ultra high molecular weight polyolefin resin (composition) and the solvent, the solubility of the ultra high molecular weight polyolefin resin in the solvent is particularly significant. Insufficient, the ultra-high molecular weight polyolefin resin is not stretched and is not unwound near the kneading state, and it is difficult to obtain sufficient entanglement of the polymer chains. Furthermore, as will be described later, when the kneaded product is cooled, it is molded into a sheet, the resin is crystallized, and then stretched to obtain a stretched film. On the other hand, when the ultra-high molecular weight polyolefin resin (composition) is less than 5% by weight, the resulting porous sheet is inferior in strength.

  In this embodiment, when kneading a solution obtained by dissolving the above ultrahigh molecular weight polyolefin resin (composition) in a solvent, when kneading at a temperature exceeding 185 ° C., the viscosity of the solution is too low, A sufficient shearing force cannot be applied to the kneaded product, and on the other hand, when the kneading temperature is lower than 115 ° C., the mixture cannot be effectively kneaded, and thus in the kneading of the mixture, It is difficult to obtain sufficient entanglement of the polymer chains of the ultrahigh molecular weight polyolefin resin as described above.

  In order to obtain sufficient entanglement of the polymer chains of such ultra-high molecular weight polyolefin resin, kneading while applying a high shear force to the solution-like mixture of the ultra-high molecular weight polyolefin resin (composition) and the solvent. Is preferred. If sufficient shearing force cannot be applied during kneading, sufficient entanglement of the polymer chains of the ultrahigh molecular weight polyolefin resin may not be obtained. Therefore, according to this embodiment, for kneading a solution-like mixture of an ultrahigh molecular weight polyolefin resin (composition) and a solvent, a kneader or a twin screw extruder that can give a strong shearing force to the mixture is usually used. Is preferably used.

  Next, according to the present embodiment, the temperature below the freezing point of the solvent using a solution-like kneaded product of the ultrahigh molecular weight polyolefin resin (composition) thus obtained and the solvent, preferably −10 ° C. To a temperature in the range of −45 ° C., preferably in the range of −15 ° C. to −40 ° C., and molded into a gel-like sheet to crystallize the ultrahigh molecular weight polyolefin resin (and high density polyethylene resin). Make it. The range of 0.1 to 5.0 mm is usually appropriate for the thickness of the gel sheet.

  Thus, the cooling to a temperature below the freezing point of the solvent using a solution-like kneaded product of the ultrahigh molecular weight polyolefin resin (composition) and the solvent is not particularly limited. Two metal plates may be cooled with dry ice, the kneaded material is sandwiched between these metal plates, and the kneaded material may be pressed to be formed into a sheet.

  According to this embodiment, when the kneaded material is cooled and molded into a sheet, the kneaded material is rapidly cooled in order to finely crystallize the resin not only to the surface layer of the obtained sheet but also to the center of the sheet. Therefore, the cooling rate is preferably 50 ° C./min or more on average. In the solution state, that is, when the cooling rate at the time of molding from the kneaded product to the sheet is slow, the fibrils that are stretched and entangled return to the shape of the hair by forming kneading, forming a thick fiber. Therefore, it is difficult to form a porous membrane structure composed of uniform fibrils, and a porous membrane structure having large through holes is partially formed.

  That is, in general, when a crystalline high molecular weight resin is crystallized, a lamellar crystal is formed, and the thickness of the lamellar crystal greatly depends on the crystallization temperature, and as the difference between the melting point and the crystallization temperature increases, the lamellar crystal The thickness of becomes smaller. According to this embodiment, the kneaded product of the ultrahigh molecular weight polyolefin resin (composition) and the solvent is changed from a high temperature of 115 to 185 ° C. to a temperature below the freezing point of the solvent used, that is, a temperature of −10 ° C. or less. Since it is formed into a gel-like sheet while cooling, preferably while rapidly cooling, the thickness of the lamellar crystals is very small. Therefore, when the stretched film is obtained by stretching the gel-like sheet, the lamellar crystals are microcrystalline. As a result, the porous sheet having a microfibril structure can be obtained which is composed of fibrils having a small fiber diameter and uniform, and has a very large curvature, which is a ratio of a penetration path to a film thickness. It seems to be.

  Even if the kneaded product is rapidly cooled from the solution state and formed into a gel-like sheet and the resin is crystallized according to the present embodiment, the crystal structure of the resin in such a gel-like sheet is higher than the freezing point of the solvent used. When this gel-like sheet is stored at the same temperature as in the case where the cooling rate is slow, the fibrils that are stretched and entangled by kneading return to a hair-like shape, form thick fibers, and are fine. It is difficult to form a uniform porous structure, and large through holes are partially formed. Accordingly, if the kneaded product of the ultrahigh molecular weight polyolefin resin composition and the solvent is rapidly cooled, it is formed into a gel-like sheet, and thus the gel-like sheet having a crystal structure is immediately stretched or stored. It is desirable to store the obtained gel-like sheet at a temperature below the freezing point of the solvent.

  As described above, when the cooling rate at the time of forming the kneaded material into a sheet is slow or when the obtained sheet is stored at a temperature equal to or higher than the freezing point of the solvent, the above-described phenomenon occurs and is obtained. The porous sheet lacks the fineness and uniformity of the structure of the microporous portion, and relatively large pores are formed, so that the strength, particularly the piercing strength, is inferior.

  Next, when the melting point of the ultrahigh molecular weight polyolefin resin is M ° C., the gel-like sheet has a temperature in the range of (M + 5) ° C. to (M−30) ° C., preferably M ° C. to (M−25) ° C. Biaxial stretching at a temperature in the range of This biaxial stretching may be either sequential or simultaneous biaxial stretching, but preferably simultaneous biaxial stretching. In this embodiment, the stretch ratio of the gel sheet is 3 to 32 times in one direction, and the area stretch ratio is suitably in the range of 9 to 1024 times, preferably 3 to 20 times in one direction. The area stretch ratio is in the range of 9 to 400 times.

  Next, the biaxially stretched film thus obtained is washed with an appropriate solvent to remove the solvent remaining in the film to form a porous sheet, preferably after this, to prevent thermal shrinkage of this film In order to do so, heat and heat set (heat setting). Examples of the solvent used for the desolvation treatment include volatile solvents such as hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, and ethers such as diethyl ether and dioxane. Is preferably used. These solvents are appropriately selected depending on the solvent used for preparing the solution of the ultrahigh molecular weight polyolefin resin (composition). In order to remove the solvent remaining in the sheet, for example, the sheet may be immersed in the solvent.

  In this way, a porous sheet having an average pore size of 0.05 μm to 0.3 μm and a porosity of 20 to 70% can be obtained.

  Next, a non-porous part is formed on the obtained porous sheet. The non-porous portion can be formed by pressing a heated portion such as a heated rubber roll on the porous sheet against the surface of the porous sheet. Although there are pores on the surface of the porous sheet, only the part in contact with the rubber roll is melted and closed to form a non-porous part. When the melting temperature of the porous sheet is Tm, the heating temperature is (Tm−15) ° C. as a guide temperature. In the case of a polyethylene porous sheet, the heating temperature of the rubber roll is 100 to 140 ° C, preferably 105 to 125 ° C. If the heating temperature of the rubber roll is too high, the closed pore region also advances inside the membrane, reducing the porosity of the entire membrane, and consequently ionic conductivity.

  The non-porous part is formed only on the surface, and the thickness is preferably 0.1 to 1.0 μm. Similarly to the above, when the thickness of the non-porous portion is increased, the ionic conductivity is lowered, and the charge / discharge characteristics of the battery are lowered.

  The porous sheet itself may be composed of a single layer or a plurality of laminated porous films.

  Empirically, this non-porous part is required to be 5 times or more, more preferably 10 times or more the shortest part of the fibril formed in the porous part. The presence of a non-porous portion larger than the fibril promotes diffusion of the electrolyte discharged from the negative electrode side. Here, the shortest part of the fibril refers to the fiber diameter of the fibril formed in a fiber shape and can be confirmed by a scanning electron microscope.

  The width of the non-porous part in the shortest part direction is preferably 0.3 to 10.0 μm, more preferably 1.0 to 7.0 μm. A non-porous portion having a size of 10.0 μm or more greatly reduces the ionic conductivity rather than the diffusibility of the electrolytic solution.

  The non-porous portions may be arranged at random, or may have a regular pattern, for example, a linear shape or a grid shape.

  In the case where the non-hole portions are arranged as a pattern, for example, a line shape or a grid shape, it is desirable that the non-hole portions are arranged in a direction crossing the drawing direction of the electrode terminals.

  In addition, a non-porous part means the area | region where the void | hole which has on the surface of the porous sheet which has many void | holes in the main surface of a separator does not exist. In the cross section, there is a resin constituting the separator between the holes, but when the distance between the holes is smaller than the average hole diameter of the holes, It is judged that there is no porous part. Moreover, since the non-porous part is made of a resin constituting the porous sheet, the resin adhering to the porous sheet is not intended. Therefore, the non-porous part is formed inside the main surface of the porous sheet.

  FIG. 2 is an example showing the positional relationship between the non-porous portion on the porous sheet and the electrode terminal. With respect to the direction in which the positive electrode terminal 17 and the negative electrode terminal 18 are drawn, a non-porous portion 161 formed in the porous sheet 141 is arranged in a direction crossing them. Such a configuration is preferable.

  Moreover, the non-hole part arrange | positioned on the same line extended in the same direction as the direction where the positive electrode terminal 17 and the negative electrode terminal 18 are pulled out is also preferable as a structure arrange | positioned intermittently.

  Considering the resistance component of the current collector and active material, the closer the terminal is, the stronger the reaction at the electrode. Therefore, the deterioration of the electrolytic solution becomes more severe as the distance from the terminal is shorter. With such a transverse arrangement, the electrolytic solution can be more effectively moved away from the terminal and diffused, and the local concentration distribution of the degradation component in the electrolytic solution can be effectively reduced.

  From the above viewpoint, it is also preferable that the position where the non-hole portion is formed is unevenly distributed in the electrode terminal drawing direction. Even in such a structure, when the non-porous portions are formed on both the positive electrode surface side and the negative electrode surface side of the porous sheet 141, the non-porous portions are preferably arranged in a positional relationship that does not overlap each other. Convection tends to stagnate in the portion where the non-porous portions overlap each other, and the concentration distribution of the additive is conversely expanded.

  The porous sheet having a large number of pores according to the present embodiment thus obtained has a thickness in the range of 1 to 60 μm, preferably 5 to 45 μm.

  The porous sheet having a large number of pores has a porosity of 35 to 75%, preferably 50 to 70%, and an air permeability of 100 to 800 seconds / 100 cc, preferably 100 to 500 seconds / 100 cc. The porosity may be measured by a mercury intrusion method.

Subsequently, the secondary battery using the above-described porous sheet will be described by taking the secondary battery as an example.
(Electrode wound body)

  FIG. 3 is a schematic cross-sectional view showing the configuration of the electrode winding body of the secondary battery. In some cases, the configuration of a lithium ion secondary battery will be described as an example. The structure of the secondary battery shown in FIG. 3 is produced by stacking the positive electrode 12, the porous sheet 14 indicated by the dotted line, and the negative electrode 13, and winding them around the positive electrode terminal 18. And the porous sheet 14 located in the outermost periphery is being fixed by the fixing tape 19 in the edge part. Reference numeral 17 in the figure denotes a negative terminal.

  By arranging the porous sheet so that the positive and negative electrodes do not come into contact with each other and rotating the winding core, the electrodes and the porous sheet are swirled in a spiral shape, A wound electrode body can be produced. Each electrode only needs to be bent at least one of the electrodes at least once.

  The non-porous portion present in the porous sheet when constituting the electrode winding body is present on one main surface or the other main surface of the porous sheet, and one main surface when viewed from the main surface. It is preferable that the upper non-hole portion and the non-hole portion on the other main surface are arranged so as not to overlap each other.

  A general method can be used for supplying the positive and negative electrodes and the porous sheet to the core. For example, it is continuously supplied in the form of a reel, and the electrode is cut to a predetermined length during or simultaneously with the winding operation. Alternatively, the electrode or the porous sheet can be cut in advance to a predetermined length, supplied, and wound. It is preferable that the electrode to be supplied and the porous sheet are supplied while applying a load in the winding direction because the adhesion of the electrode can be obtained at the time of winding.

  When winding, place at least one of the electrodes so that it is positioned at the center of the winding machine's core, or place one end of the electrode in the longitudinal direction facing the winding machine's core. can do. Further, both ends of the positive and negative electrodes in the longitudinal direction may face the same direction, but the positive and negative electrodes may be arranged so that one ends in the longitudinal direction face each other.

  The porous sheet can be arranged in the same manner as the electrode.

  When winding, the positive and negative electrodes are wound on the core with the electrode and / or the porous sheet interposed between the cores. At that time, the end point in the longitudinal direction of the electrode and the end point of the core can be aligned. It can also be used as a lead of one electrode without pulling out the core after winding. When the core also serves as the lead, the core and the electrode may be electrically connected, but the lead and the electrode are preferably welded by a general method.

  When the core is pulled out without being wound inside the spiral wound electrode body after winding, contact resistance is generated between the core and the electrode when it is pulled out. Thus, the peeled mixture may cause a short circuit. Therefore, it is possible to prevent misalignment by starting to roll after the porous sheet is arranged so as to contact the core so that the electrode does not directly contact the core.

  In addition, the contact between the porous sheet and the core may cause a decrease in strength and poor insulation due to cracking, cutting, and abrasion of the porous sheet, and the porous sheet in contact with the core is preferably wound twice or more. The shape of the core used when winding the positive electrode and the negative electrode in a spiral shape may be a perfect circle, but it may be an ellipse, a rectangle, a rhombus, other polygons, or a process such as chamfering the corner (corner). Such a shape may be used. The material of the core is not particularly limited, but is preferably made of stainless steel. The core is not necessarily composed of a single part, but may be a structure divided into a plurality of parts.

  The positive and negative electrodes are wound in a spiral shape, and when the winding is completed, the entire circumference or a part of the outermost circumference of the electrode or porous sheet located on the outermost circumference of the wound electrode body is fixed. When a material whose outermost periphery is particularly heat-melted is used for the porous sheet, the porous sheet can be directly fixed by thermal welding. In order to fix the outermost periphery, an adhesive tape or a rectangular cylindrical fixing tape can also be used. When a heat resistant material is used for the porous sheet, a heat shrinkable tube can be used on the outermost periphery. Moreover, the outermost periphery is an electrode, and if the electrical connection is maintained and fixed to the exterior case, there is no need to provide positive and negative terminals respectively. In this case, it is desirable to use an electronically conductive material in order to make electrical connection advantageous.

  These fixings prevent battery performance deterioration by minimizing the vertical displacement of the electrode winding and loosening of the winding in the winding direction, and prevent fallen objects from shorting between the two electrodes. Therefore, it is possible to facilitate transport to the next process using the wound electrode body, and to easily insert the wound electrode body into the outer case.

  After inserting the wound electrode body into the outer case, the electrolytic solution is injected. The injection of the electrolyte solution may be performed all at once, but is preferably performed in two or more steps. In addition, when the electrolyte is injected in two or more times, the composition of each electrolyte may be changed, but it is preferable to use the same electrolyte.

  As a welding method for the outer case, the battery sealing lid, the electrode, the lead, and the electrode terminal, electrical resistance welding using direct current or alternating current, laser welding, ultrasonic welding, or the like can be used. Further, the outer case and the battery sealing lid can be sealed by mechanical caulking or screwing or sealing using a resin sealing material via packing. In particular, it is preferable to use a two-layer / three-layer laminate film of maleic acid-modified polyethylene resin / high-density polyethylene resin / maleic acid-modified polyethylene resin as the resin sealing material. It is also possible to seal the outer case and / or battery sealing lid by providing a flange or the like.

  The material of the outer case is not particularly limited, and examples thereof include a cylindrical (such as a rectangular tube or a cylindrical) steel can or an aluminum can that are employed in a conventionally known secondary battery. In addition, a laminate film obtained by vapor-depositing a metal on a resin film can be used for the exterior body.

  If the outer case and the battery sealing lid are made of metal and the joints thereof are fixed by, for example, laser welding while maintaining electrical connection, there is no need to provide positive and negative terminals on the battery sealing lid, respectively. When the battery outer case also serves as an electrode current collector, the outer case can also serve as a lead.

(Positive electrode)
Next, the positive electrode will be described. The positive electrode is produced by forming a positive electrode active material layer on both sides of the positive electrode current collector.

  The positive electrode current collector may be a conductive plate material, and for example, a metal thin plate of aluminum, copper, or nickel foil can be used.

  The positive electrode active material layer includes an active material, a binder, and an amount of a conductive aid as required.

As the positive electrode active material, for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), layered lithium manganate (LiMnO ₂ ), or LiMn _x Ni _y Co, which is a composite oxide containing a plurality of transition metals. Layered compounds such as _z O ₂ (x, y and z satisfy the formula x + y + z = 1, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ x <1), and one or more kinds of these compounds Substituted transition metal element, lithium manganate (Li _{1 + x} Mn _2−x O ₄ (where x is a number from 0 to 0.33)), Li _{1 + x} Mn _2−xy M _y O ₄ (however, , M includes at least one metal selected from the group consisting of Ni, Co, Cr, Cu, Fe, Al, and Mg, x represents a number from 0 to 0.33, and y is from 0 to 1.0. Number and x and y satisfy the formula of 2-xy> 0), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , LiMn _2−x M _x O ₂ (where M is Co, Ni, Fe, Cr, Including at least one metal selected from the group consisting of Zn and Ta, x represents a number of 0.01 to 0.1, Li ₂ Mn ₃ MO ₈ (where M is Fe, Co, Ni, At least one metal selected from the group consisting of Cu and Zn), copper-lithium oxide (Li ₂ CuO ₂ ), iron-lithium oxide (LiFe ₃ O ₄ ), LiFePO ₄ , LiV ₃ O ₈ , Examples include vanadium oxides such as V ₂ O ₅ and Cu ₂ V ₂ O ₇ , disulfide compounds, and Fe ₂ (MoO ₄ ) ₃ .

(Conductive aid)
Examples of the conductive assistant include metals such as nickel, aluminum, copper, and silver, and conductive carbon materials. Examples of the conductive carbon material include carbon blacks such as acetylene black and ketjen black, and carbon fibers such as graphite and carbon nanofibers. As the conductive assistant, carbon black is particularly preferable. In addition, it is not necessary to contain a conductive support agent.

(Binder)
As the binder, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene (CTFE) copolymer (PVDF-CTFE), vinylidene fluoride-hexa Fluorine polymers such as fluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber (PVDF-TFE-HFP), vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether fluororubber, and the like are preferable. As the vinylidene fluoride-based polymer, those in which vinylidene fluoride is 50% by weight or more, particularly 70% by weight or more are preferable, and in particular, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene (HFP), A copolymer of vinylidene fluoride and ethylene trifluoride (PVDF-CTFE) is preferred.

  Next, the negative electrode will be described. The negative electrode is produced by forming a negative electrode active material layer on both sides of the positive electrode current collector.

  The negative electrode current collector may be a conductive plate material, and for example, a metal thin plate of aluminum, copper, or nickel foil can be used.

  As the negative electrode active material, for example, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. One kind or a mixture of two or more kinds of carbon-based materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, 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. Then, 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 is finished into a molded body using the current collector as a core material. A negative electrode mixture layer can be formed on the current collector surface.

(Electrolytes)
Although not shown in the drawings, the electrolyte is contained in the electrode winding body. The electrolyte is not particularly limited, and, for example, in the present embodiment, an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. For example, as the non-aqueous solvent, methyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3 -The organic solvent which consists only of 1 type, such as dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, or these 2 or more types of mixed solvents is mentioned.

Examples of the lithium _{salt, 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] and the like.

  The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  Furthermore, the non-aqueous electrolyte solution contains sulfur-containing organic compounds such as propane sultone of an ester having a double bond such as vinylene carbonate for the purpose of improving the charge / discharge cycle characteristics and load characteristics of the battery; It is preferable to add an additive such as an aromatic compound.

  In the present embodiment, the electrolyte may be a gel electrolyte obtained by adding a gelling agent in addition to liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

  As mentioned above, although the manufacturing method of the porous sheet of this embodiment and an example of the secondary battery using a porous sheet were demonstrated, this embodiment is not limited to the said embodiment. The porous sheet and the like of the present embodiment can be set as appropriate according to the usage and the like.

  For example, the porous sheet of this embodiment can also be used for electrochemical elements other than secondary batteries. As the electrochemical element, a secondary battery other than a secondary battery such as a metal lithium secondary battery (using the active material of the present embodiment as a cathode and metal lithium as an anode), or an electrochemical such as a lithium capacitor A capacitor etc. are mentioned. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

Example 1
15% by weight of ultrahigh molecular weight polyethylene resin (melting point 134 ° C.) with a weight average molecular weight of 2 million, liquid paraffin (kinematic viscosity 59 cSt at a freezing point of −15 ° C. and 40 ° C.) 83.5% by weight, and polyacrylonitrile 1.5% by weight % In a slurry form, charged in a small kneader, heated at a temperature of 160 ° C. for about 50 minutes, dissolved and kneaded to obtain a kneaded product of ultrahigh molecular weight polyethylene resin and solvent. It was. Thereafter, the kneaded product was molded into a sheet having a thickness of 0.5 mm while rapidly cooling to −15 ° C. to crystallize the ultrahigh molecular weight polyethylene resin.

  The sheet was simultaneously biaxially stretched 4 × 4 times in length and width at a temperature of about 115 ° C. and then immersed in methylene chloride to remove the solvent. The porous sheet thus obtained was further heat set at 120 ° C. for 10 seconds to obtain a porous sheet having a thickness of 20.4 μm and a porosity of 40%.

Next, a heating roll having a linear pattern was pressed against the porous sheet, and a non-porous portion was linearly formed on one side of the porous sheet. The non-hole forming width in the direction parallel to the electrode terminals was 3 μm, and the forming interval was 10 μm. The temperature of the heating roll was 110 ° C., the roll pressure was 300 g / cm ² , and the heating speed was 3 m / min.

  The characteristics of the porous sheet were evaluated as follows.

(Thickness)
The cross section of the porous sheet was measured with a 10,000 times scanning electron microscope (SEM).

(Air permeability)
It measured by the method based on JISP8117.

An electrode winding body as shown in FIG. 3 is produced using the obtained porous sheet. The porous sheet is cut into a width of 45 mm and a length of 1080 mm. The material of the current collector of the positive electrode is a thin flat plate having a smooth surface made of aluminum. The positive electrode current collector has a length of 425 mm, a width of 39 mm, and a thickness of 10 μm. A conductive paste layer is provided on the positive electrode current collector. The conductive paste layer is preliminarily coated with a paste in which graphite having a fine particle size is dispersed with a water-soluble binder, heated and dried with hot air, and then subjected to a rolling pressure bonding treatment. The surface coated with the conductive paste has a length of 412 mm, a width of 39 mm, and a thickness of 5 μm. There is an application surface of the positive electrode mixture on the conductive paste layer. The positive electrode mixture is a mixture of LiCoO ₂ and a PVDF polymer binder and graphite as a conductive aid. The mixing weight ratio is 85: 10: 5 wt%, respectively. As the positive electrode mixture, a paste using n-methyl-2-pyrrolidone as a dispersion medium is applied onto a conductive paste, dried and rolled. The molded positive electrode has a length of 425 mm, a width of 39 mm, and a thickness of 130 μm. 3 is a negative electrode. The negative electrode current collector is made of copper and is a thin flat plate having a smooth surface. The negative electrode current collector has a length of 492 mm, a width of 41 mm, and a thickness of 20 μm. A conductive paste layer is provided on the negative electrode current collector. The conductive paste layer is preliminarily coated with a paste in which fine particle size graphite is dispersed with an epoxy binder, and then heated and dried with hot air. The surface coated with the conductive paste has a length of 487 mm, a width of 41 mm, and a thickness of 5 μm. There is an application surface of the negative electrode mixture on the conductive paste layer. The negative electrode mixture is a mixture of silicon oxide, graphite, and a binder made of polyacrylic acid polymer. The mixing weight ratio is 45:40:15 wt%, respectively. As the negative electrode mixture, a paste using pure water as a dispersion medium is applied onto a conductive paste, dried and rolled. The molded negative electrode has a length of 492 mm, a width of 41 mm, and a thickness of 70 μm.

  The negative electrode lead is made of nickel and has a length of 49 mm, a width of 2.5 mm, and a thickness of 0.1 mm. The negative electrode lead was ultrasonically welded directly to the surface of the negative electrode current collector on which the conductive paste was not applied before being used for winding. Reinforcing and insulating tape was applied to cover the ultrasonic welded surface of the lead. The tape is based on polyimide, and the adhesive is acrylic. The width of the tape is 6 to 10 mm, the length is 20 to 41 mm, and the total thickness including the adhesive layer is 55 μm. Reference numeral 18 denotes a positive electrode lead. The positive electrode lead is made of aluminum and has a length of 49 mm, a width of 2.5 mm, and a thickness of 0.1 mm. The positive electrode lead was ultrasonically welded directly to the surface of the positive electrode current collector not coated with the conductive paste before being used for winding. Tape was applied for reinforcement and insulation so as to cover the ultrasonic welded surface of the lead. Further, for insulation, this tape was used to cover a portion other than the welding surface of the negative electrode lead. Reference numeral 19 denotes a tape for fixing the final part of the wound electrode body. The tape is a polypropylene substrate and has a rubber-based adhesive.

  The porous sheet was disposed so as to be located in the center of the core, and the positive and negative electrodes were supplied from opposite directions and fixed by being sandwiched between the cores while heating. In Example 1, the formation direction of the non-hole portion was arranged in a direction crossing the electrode terminal drawing direction, and a wound body was produced. Table 1 shows the positional relationship between the non-porous portion and the electrode terminal when the laminated wound body is manufactured.

  A spiral wound electrode body was obtained by rotating the core so as to keep applying a load to the positive and negative electrodes and the porous sheet. The final part of the wound electrode body was fixed with tape. The obtained wound electrode body was designated as A, compressed to fit the inner diameter of the metal battery outer case, and inserted into a rectangular battery outer case. The lead attached to the positive and negative electrodes and the electrode attached to the battery sealing lid are welded, and after the battery sealing lid is laser welded, the electrolytic solution is injected from the electrolytic solution injection port provided on the battery sealing lid, and the electrolytic solution injection port is Sealed.

  The resulting lithium ion secondary battery was allowed to stand for a certain period of time, and the charge / discharge test was performed when the electrolyte was impregnated. The test conditions were a current of 400 mA, an upper limit voltage of 4.2 V, and a constant current and a constant voltage of 2.5 V. Thereafter, a discharge test at 0.5 C was performed. As a result, a discharge capacity of 720 mAh was obtained. This was defined as the initial discharge capacity.

(Cycle characteristics and high-temperature storage test)
As the cycle characteristics, the discharge capacity after a 500 cycle charge / discharge test at a discharge rate of 0.5 C was also measured, and the relative value (unit:%) was calculated with the initial discharge capacity measured in advance as 100. The later discharge capacity was described as a ratio to the initial discharge capacity. Further, as a high temperature storage test, an output voltage (unit V) after being held for 1000 hours in a temperature environment of 60 ° C. was measured. The results are also shown in Table 1 as the storage voltage.

(Example 2)
A battery having the same configuration as in Example 1 was used except for the non-porous portion formation pattern, and a battery was obtained in the same manner. The width of the non-hole portion in the direction parallel to the electrode terminal is 3 μm, the length of the non-hole portion located in the direction transverse to the electrode terminal is 5 μm, the interval between the non-hole portions in the direction parallel to the electrode terminal is 10 μm, The hole forming interval was 5 μm. The non-hole portions in the transverse direction and the electrode terminal were arranged at positions shifted by 5 μm from the terminal side in the transverse direction of the electrode terminal, so that the non-hole portions were not continuous in the electrode terminal parallel direction. In this way, the porous sheet in which the non-porous portion is arranged is overlapped with the positive electrode, the negative electrode, and the porous sheet so that the non-porous portion short direction is the same direction as the electrode terminal pulling direction. Obtained. The completed battery was subjected to the same evaluation test as in Example 1. As a result, a discharge capacity of 720 mAh was obtained.

(Example 3)
A battery having the same configuration as in Example 1 was used except for the non-porous portion formation pattern, and a battery was obtained in the same manner.
The width of the non-hole portion in the direction parallel to the electrode terminal is 3 μm, the length of the non-hole portion located in the direction transverse to the electrode terminal is 5 μm, the interval between the non-hole portions in the direction parallel to the electrode terminal is 10 μm, The hole forming interval was 5 μm. The non-hole portions in the direction parallel to the electrode terminals were arranged so that the non-hole portion ends were aligned in the respective directions. The non-porous portions were 30 μm in length and 50 μm in width, and were formed at 100 μm intervals in the longitudinal direction. The interval in the short direction was 100 μm. The completed battery was subjected to the same evaluation test as in Example 1. As a result, a discharge capacity of 720 mAh was obtained.

Example 4
The formation pattern of the non-porous part was the same as that of Example 1, the non-porous part was formed on both surfaces thereof, members having the same configuration were used, and a battery was obtained in the same manner. The non-porous part is formed on the upper and lower surfaces of the sheet in the same direction as the electrode terminal drawing direction, the line width of the non-porous part is 3 μm, the line interval is 10 μm, The non-porous portions above and below the film surface were not overlapped.

(Comparative Example 1)
A battery was obtained in the same manner using a member having exactly the same structure as in Example 1 except that a porous sheet not forming a non-porous portion was used.

  As shown in Table 1, it can be seen that the example is a lithium ion secondary battery excellent in cycle characteristics, which seems to be due to the promotion of the diffusion and convection of the electrolyte compared to the comparative example.

12 Positive electrode 13 Negative electrode 14 Porous sheet 15 Porous part 16 Non-porous part

Claims (4)

  In the porous sheet having a large number of pores, the porous sheet has a non-porous portion larger than the pores on the surface thereof. Including a positive electrode, a negative electrode, and an electrolyte, and having the porous sheet according to claim 1 between the positive electrode and the negative electrode;
The positive electrode and the negative electrode are electrically connected to an electrode terminal drawn in a predetermined direction at one end thereof,
A lithium ion secondary characterized in that a non-porous portion extends in a direction crossing the predetermined direction on the surface of the porous sheet facing at least one of the positive electrode and the negative electrode. battery. A positive electrode, a negative electrode, and an electrolyte, the porous film according to claim 1 between the positive electrode and the negative electrode;
The positive electrode and the negative electrode are electrically connected to an electrode terminal drawn in a predetermined direction at one end thereof,
A lithium ion secondary battery in which a large number of non-porous portions are unevenly distributed on the surface of the porous sheet facing each other in the vicinity of the electrode terminal of at least one of the positive electrode and the negative electrode. A positive electrode, a negative electrode, and an electrolyte, the porous film according to claim 1 between the positive electrode and the negative electrode;
The positive electrode and the negative electrode are electrically connected to an electrode terminal drawn in a predetermined direction at one end thereof,
Non-porous portions are respectively formed on one main surface and the other main surface of the porous sheet,
The non-porous portion formed on the one main surface of the porous sheet and the non-porous portion formed on the other main surface overlap each other in a projection image when viewed from a direction perpendicular to the main surface. A lithium ion secondary battery, wherein the lithium ion secondary battery is arranged so as not to become.

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