JP6384477B2 - Lithium ion secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a lithium ion secondary battery having a structure in which a positive electrode or a negative electrode is accommodated in a bag-shaped separator and a method for manufacturing the same.

  With the rapid market expansion of notebook computers, mobile phones, hybrid cars, etc., power storage devices such as capacitors and lithium ion secondary batteries are being actively researched. In particular, lithium ion secondary batteries have a higher energy density than nickel / cadmium batteries and nickel / hydrogen batteries.

  Since a lithium ion secondary battery has a high energy density that can be stored, it can be charged and discharged with a larger current than a conventional battery. If charging or discharging is performed with a large current, heat generation in the battery increases, so heat dissipation of the battery becomes a problem. If the heat generated inside cannot be released to the outside, the battery becomes hot, and there is a concern that the performance may be deteriorated or the life may be shortened.

  In the structure of the electrode body of the lithium ion secondary battery, a strip-shaped positive electrode and a negative electrode are overlapped through a strip-shaped separator and wound to form a roll; a strip-shaped positive electrode; There is a laminated electrode body in which a negative electrode is laminated via a strip-like separator. When a laminated electrode body is used, a battery having a flat surface area and a large surface area is obtained as compared with a wound electrode body having the same charge / discharge capacity. Due to the flat shape, the laminated electrode body is advantageous in securing the heat dissipation performance required for the lithium ion battery.

  Currently, it has been proposed to use a metal such as tin or silicon or an alloy or oxide thereof as a negative electrode active material as a lithium ion secondary battery having a higher energy density than before. However, the higher the energy density of the battery, the greater the energy that can be released.

  In power storage devices such as lithium ion secondary batteries, the separator plays a role of preventing a short circuit between the positive electrode and the negative electrode and effectively moving lithium ions. So far, polyolefin-based microporous separators such as polypropylene and polyethylene have been mainly used. One of the reasons is that when the battery generates heat more than expected due to excessive discharge, etc., the fine holes, which are lithium ion passages in the separator, are thermally contracted and shut down, and the battery operation is performed. It is for showing the effect | action which stops. However, in a battery having a high energy density, the separator melts before the temperature rises rapidly and the shutdown effect is obtained, and there is a possibility that a short circuit between the electrodes occurs over a wide area.

  Patent Document 1 (Japanese Patent No. 4042413) discloses that a high-heat-resistant material, for example, a separator made of a polyester resin, is used in a lithium ion battery instead of a polyolefin-based microporous separator. Patent Document 2 (Japanese Patent No. 3661104) shows that a cellulose nonwoven fabric having no melting point is used for a lithium ion secondary battery. These materials cannot be expected to have the shutdown effect of the polyolefin-based microporous membrane, but may not be short-circuited between the electrodes over a large area even at a high temperature, and may have better safety than the polyolefin-based separator.

  It is considered that the deformation of the electrode body is also related to the safety of the lithium ion battery exposed to high temperature. Lithium-ion battery exteriors include cylindrical and square cans and those made of laminated films of metal and resin films. In any of the exterior bodies, by providing a safety valve mechanism that operates when the electrolyte solution that has reached a high temperature evaporates and the internal pressure of the battery increases, the evaporated electrolyte solution can be released to the outside. In a battery having a fixed exterior body such as a can, since the deformation of the electrode body is suppressed by the exterior body, the deformation of the electrode body is small even when the internal pressure of the battery increases. On the other hand, when the internal pressure of a battery having an exterior body made of a laminate film increases, the exterior body expands to a pressure at which the safety valve operates, so that the electrode body is deformed. If the electrode body is deformed, the electrode and the separator may be displaced and the positive electrode and the negative electrode may be short-circuited. Therefore, not only the heat-resistant separator but also prevention of displacement between the electrode and the separator is required to improve safety at high temperatures.

  In order to prevent displacement between the electrode and the separator when the electrode body is deformed, it is effective to form the separator in a bag shape and accommodate at least one of the positive electrode and the negative electrode therein. Since at least one of the positive electrode and the negative electrode is housed in the bag-like separator, contact between the positive electrode and the negative electrode can be prevented even if the electrode body is deformed.

When a positive electrode is housed in a bag-shaped separator to produce a laminated body, there is an advantage that the misalignment in producing the electrode laminated body can be easily reduced as described below.

  In an electrode laminate in which positive and negative electrodes cut into strips are alternately laminated via separators, it is important to properly align the lamination positions of the positive, separator, and negative electrodes. If the electrodes and the separator are all the same size, for example, the two stacked sides can be aligned by aligning two adjacent sides. However, if these are the same dimensions, lithium ions that could not be accommodated in the negative electrode at the electrode end face may precipitate, or the positive electrode and the negative electrode may be short-circuited due to cutting dimension errors of the electrode or separator or misalignment of the stacking position . In order to avoid this, the positive electrode is often designed to be smaller than the negative electrode or the separator. Therefore, for example, even if the sides and vertices of the electrodes and separators are aligned at the same position, the stacking positions cannot be matched.

  Deviations in the stacking position of the electrodes and separators cause variations in battery capacity, precipitation of metallic lithium at the ends of the electrodes after long-term use, and short-circuit accidents between the positive and negative electrodes. As a method of improving the alignment accuracy at the time of lamination using a bag-shaped separator, the periphery of a microporous plastic film such as polyethylene having a low melting point is welded to Patent Document 3 (Patent No. 3380935) with heat. It is shown that it is processed into a bag shape, and the positive electrode is accommodated therein and laminated with the negative electrode. In this method, since the positive electrode is fixed in the separator bag, if the separator and the negative electrode have the same dimensions, the stacked positions of the negative electrode, the separator, and the positive electrode can be aligned by aligning two adjacent sides.

  However, since the separator in Patent Document 3 has low heat resistance, it contracts and melts at a high temperature and loses its function as a separator. Therefore, a separator made of a high heat resistant material is required, but since it is highly heat resistant, it is difficult to process into a bag shape by heat welding.

  As a technique for forming a high heat resistant film separator into a bag shape, in Patent Document 4 (Japanese Patent Laid-Open No. 2006-059717), a separator film containing fibers of aramid and polyimide is thermally welded at 400 ° C. to 600 ° C., A technique for processing into a bag-like separator is shown. In order to produce a bag separator containing electrodes and bonded on the four sides of the bag, at least one side must be welded with the electrode sandwiched between separator films, but the welding temperature is as high as 400 ° C to 600 ° C. For this reason, there is a possibility that the electrode is altered. Moreover, the method of heat-welding at a high temperature cannot be applied to cellulose that carbonizes without melting when high heat is applied.

  As a method other than thermal welding for processing a highly heat-resistant separator into a bag shape, Patent Document 5 (Japanese Patent Laid-Open No. 2012-33399) describes the use of an adhesive. However, since the adhesive requires application and drying, the process is complicated, and the separator is designed to absorb the liquid well. There is a problem that the inner dimensional accuracy of the separator is lowered.

  As a method of processing a separator into a bag shape other than thermal welding or adhesive, the peripheral portion of the separator sheet superimposed on Patent Document 6 (Japanese Patent Laid-Open No. 2007-201248) is drawn and bent to form a bag. In this method, the width of the notch is required for the separator, and the overall area becomes large, and the process for processing is complicated. is there.

  In addition, as separators for lead-acid batteries, the separator sheet is folded in U-shape in Patent Document 7 (Utility Model Publication No. Hei 3-22857) and Patent Document 8 (Utility Model Registration Publication No. 2523460). The separator which processed the bag shape by forming an unevenness | corrugation in the both ends open part is shown. Concavities and convexities in the open portions at the left and right ends are formed through a pressurizing jig composed of a meshing gear.

  However, since the electrode plate is placed in a bag-shaped separator that is open on only one side, there is a need for a margin in the inner dimensions of the bag for work, and the positioning accuracy of the electrode is lowered. In addition, the separator is folded in advance and then passed between the meshing gears, but a thin separator used in a lithium ion battery, for example, a separator having a thickness of 50 μm or less, rotates the gear when passing between the meshing gears. There is a risk of breaking with power. Since the teeth of the meshing gear are limited in height and width due to rotation, it is difficult to form appropriate irregularities on a thin separator. Further, in the method of passing between the meshing gears, the fixed portions of the two separators are continuous, so that unnecessary air is expelled due to penetration of the electrolyte solution into the electrode laminate in the manufacturing process, and the battery is charged. This hinders the movement of the gas generated in the electrode stack during discharge to the outside of the electrode stack.

Patent Document 1: Japanese Patent No. 4042413 Patent Document 2: Japanese Patent No. 3661104 Patent Document 3: Japanese Patent No. 3380935 Patent Document 4: Japanese Patent Laid-Open No. 2006-059717 Patent Document 5: Japanese Patent Laid-Open No. 2012-33399 Patent Document 6: Japanese Patent Application Laid-Open No. 2007-201248 Patent Document 7: Utility Model Publication No. 3-22857 Patent Document 8: Utility Model Registration Publication No. 2523460

  An object of the present invention is to provide a lithium ion secondary battery excellent in safety and a method for manufacturing the same, using a heat-resistant separator while preventing the electrode and the separator from being displaced when a high temperature is generated. In addition to the above object, another object of the present invention is to enable good and easy alignment of the positive electrode and the negative electrode, and to suppress problems caused by misalignment between the positive electrode and the negative electrode.

According to one aspect of the present invention, in a lithium ion secondary battery in which a positive electrode and a negative electrode that are electrodes are stacked via a separator,
The separator has a pair of rectangular separator sheets made of a material that does not melt even when heated to 180 ° C.
The stacked separator sheets are fixed to each other by meshing of a meshing structure including a concave portion and a convex portion formed in at least a part of at least two sides adjacent to each other in the outer peripheral portion of the separator sheet,
One of the positive electrode and the negative electrode is disposed between the two separator sheets, and a lithium ion secondary battery is provided.

According to another aspect of the present invention, in a method of manufacturing a lithium ion secondary battery in which a positive electrode and a negative electrode, which are electrodes, are stacked via a separator,
Preparing at least one set of two rectangular separator sheets made of a material that does not melt even when heated to 180 ° C .;
Either one of the positive electrode and the negative electrode is disposed between the two separator sheets that are overlapped with each other, and the two stacked separator sheets are adjacent to each other in the outer peripheral portion of the separator sheet. Forming an electrode assembly with a separator fixed by meshing of a meshing structure comprising a concave portion and a convex portion formed on at least a part of at least two sides that meet each other;
Superposing the electrode assembly with separator and another electrode different from the electrode disposed between the two separator sheets;
Encapsulating the separator-attached electrode assembly with the separator and the other electrode together with an electrolyte in an exterior body;
The manufacturing method of the lithium ion secondary battery characterized by including is provided.

  According to the present invention, even in the case of a separator made of a heat-resistant material that is difficult to heat-weld, a displacement between the electrode and the separator at the time of high temperature generation is prevented, and as a result, a lithium ion secondary battery excellent in safety and A manufacturing method thereof can be provided. Furthermore, by arranging the positive electrode between two separator sheets fixed to each other, the positive electrode and the negative electrode can be aligned well and easily, so that there is little variation in characteristics, and reliability and safety are improved. Can be improved.

1 is an exploded perspective view of a lithium ion secondary battery according to an embodiment of the present invention. It is a disassembled perspective view of the electrode laminated body shown in FIG. It is a disassembled perspective view of the positive electrode pinched | interposed into the separator sheet shown in FIG. It is a cross-sectional schematic diagram of a negative electrode (A) and a positive electrode (B). It is a cross-sectional schematic diagram when forming a meshing structure in the separator sheet which piled up. It is the schematic diagram which looked at the rectangular meshing structure from the top. It is the schematic diagram which looked at the meshing structure which provided the bending in the center from the top. It is a schematic diagram which shows the preparation flow of the structure where the positive electrode was accommodated in the separator sheet piled up. It is a schematic diagram which shows the other production flow of the structure which accommodated the positive electrode in the separator sheet piled up. It is a schematic diagram which shows the method of lamination | stacking of the positive electrode accommodated between the negative electrode and the separator sheet. It is a top view of the glass cloth impregnated with resin which can be used as a separator sheet in this invention. It is typical sectional drawing of the meshing structure explaining the depth of the recessed part in this invention, and the height of a convex part.

  The lithium ion secondary battery by one Embodiment of this invention has the positive electrode and negative electrode which are electrodes, and the separator arrange | positioned between these positive electrodes and negative electrodes. The separator is made of a material that does not melt even when heated up to 180 ° C., and has a pair of separator sheets that are superposed on each other. Either one of the positive electrode and the negative electrode is composed of these two separators. It is arranged between. The superposed separator sheets are fixed to each other by meshing of a meshing structure formed on at least a part of the outer periphery of the separator sheet.

  Hereinafter, each of the above-described constituent members and constituent materials will be described.

<Separator>
The separator has a pair of rectangular separator sheets that are stacked on each other. At least a part of the outer peripheral portion of each separator sheet is formed with recesses and projections alternately as a meshing structure for meshing two separator sheets. These concave portions and convex portions can be formed in at least a part of each of at least two adjacent sides of the separator sheet. The two separator sheets are brought into close contact with each other by the engagement of the concave and convex portions, and the two separator sheets are fixed to each other by the frictional force acting by the engagement of the concave and convex portions. A positive electrode is disposed between the two separator sheets, and the active material coating surface of the positive electrode is within the plane of the separator sheet. Moreover, the active material coating surface of the positive electrode is contained in the active material coating surface of the negative electrode facing with the separator sheet interposed therebetween. The negative electrode may be disposed between the two separator sheets, but in the following description, the case where the positive electrode is disposed between the two separator sheets will be described as an example.

  The concave portion and the convex portion that fix the two stacked separator sheets to each other are formed along the side of the separator sheet, but are not formed over the entire length of the side, and the concave portion and the convex portion are not formed. It is preferable to create a location. When the separator sheets are engaged with each other over the entire length of the sides of the stacked separator sheets, in the step of injecting the electrolyte solution during the battery manufacturing process, the electrolyte solution enters the electrode laminate body, or from the electrode laminate body. There is a risk of hindering the escape of air. In addition, gas may be generated inside the battery along with charging / discharging, and the movement of this gas into the gap outside the electrode stack may also be hindered by the engagement of the concave and convex portions.

  In order to confirm the preferable shape of the meshing structure formed in the separator, the following two experiments were conducted.

  First, as Experiment 1, the relationship between the height of the meshing structure and the fixing strength of the separator was examined. Table 1 shows the relationship between the meshing height and the fixing strength of the separator.

  In Table 1, the “engagement height” is defined by the height of the convex portion and the depth H of the concave portion formed on the separator sheet 22 that do not include the thickness of the separator sheet 22 shown in FIG. Since the two separator sheets 22 are in close contact with each other by the engagement of the concave portions and the convex portions formed in each, the height of the convex portions is equal to the depth of the concave portions.

  The fixing strength of the separator was evaluated by the following method. A separator sheet prepared by cutting a cellulose nonwoven fabric having a thickness of 25 μm into a width of 70 mm and a length of 100 mm was prepared. Two sheets of the prepared separator sheets were stacked with a weight interposed therebetween. The central part of each of the four sides of the stacked separator sheets was pressed with two pressure plates having concave and convex parts that are meshed with each other on the surface. As a result, an evaluation sample was obtained in which the two separator sheets were fixed to each other by meshing the unevenness formed on the two separator sheets. As the pressure plate for forming the concave-convex meshing structure on the separator sheet, six types having different convex part heights (concave part depths) were used. The shape of the unevenness formed on the separator sheet was such that there was no flat part between the concave part and the convex part. The width of the concavo-convex part was from the edge of the separator sheet to 1.5 mm on the inside, and 8 concavo-convex periods were formed.

  Two types of evaluation samples were prepared, one with a 100 g weight and one with a 20 g weight. Regarding the obtained sample, when the upper separator sheet was lifted out of the two separator sheets, the separator sheet that was not released from the fixing state was indicated as “◯”, and the removed sheet as “X”.

  When a battery made using a separator in which separator sheets are fixed to each other by a meshing structure is heated, the internal electrolyte is vaporized, the internal pressure rises, and the electrode laminate is deformed. Occurs. This experiment was carried out in order to evaluate whether the separator sheets are fixed with a fixing force sufficient to withstand the force of peeling the separator sheets. The weight of the weight of 100 g is a value determined by experimentally obtaining a fixing force sufficient to withstand the peeling force of the separator sheet. In the case where a weight of 100 g is sandwiched between the sheets evaluated as “◯” in the above evaluation, it is considered that the separator sheets are not fixed even if the electrode laminate is deformed. Also, the 20 g weight is used as an index for knowing whether or not the separator sheet has a certain degree of fixing force or is hardly fixed even when the separator sheets are unfixed by the 100 g weight. It was.

  From the results shown in Table 1, it is preferable that the meshing height of the meshing structure formed on the separator is 100 μm or more and 400 μm or less. If the meshing height is smaller than 100 μm, the frictional force acting between the two separator sheets becomes small, and the separator sheet may not be sufficiently fixed. On the other hand, if the mesh height exceeds 400 μm, the separator sheet may be torn when the mesh structure is formed, and the force for fixing the two separators to each other may be reduced.

  Next, as Experiment 2, a change in the fixing strength of the separator depending on the angle of the side wall of the meshing structure was examined. Table 2 shows the relationship between the side wall angle of the meshing structure and the fixing strength of the separator.

  In Table 2, the “side wall angle” is defined by the angle θ of the side wall of the concave portion or convex portion with respect to the direction perpendicular to the bottom surface of the concave portion or the top surface of the convex portion shown in FIG.

  The separator fixing strength was evaluated in the same manner as in Experiment 1 except that the pressure plate used to form the meshing structure with the separator was changed. As the pressure plate, four types having different side wall angles were used.

  From the results of Table 2, the side wall angle is preferably within 37 degrees. If the angle of the side wall is larger than 37 degrees, the two separator sheets may be unfixed when a force in the direction perpendicular to the surface of the separator sheet is applied.

  In Experiment 1, the side wall angle of the evaluation sample was between 32 degrees and 37 degrees. Moreover, in Experiment 2, the meshing height of the evaluation sample was between 200 μm and 300 μm.

  In the above description, it has been shown that a concave portion and a convex portion are formed in each separator sheet as a meshing structure. However, it is not necessary that both the concave portion and the convex portion are formed on one separator sheet, and at least one convex portion is formed on one separator sheet, and at least one concave portion meshing with the other is formed on the other separator sheet. The mesh structure formed in the separator sheet may be sufficient.

  The thickness of the separator sheet is preferably 50 μm or less. If the separator is thicker than 50 μm, the amount of necessary electrolyte increases, and the decrease in energy density per unit weight and volume of the battery cannot be ignored. In addition, if the separator is thick, the movement distance of lithium ions between the positive electrode and the negative electrode separated by the separator becomes long, so that the input / output characteristics of the battery may be deteriorated.

  The material constituting the separator sheet is preferably a material that does not melt even when heated to 180 ° C., such as polyethylene terephthalate, polyimide, polyamideimide, aramid, and cellulose. More specifically, the separator sheet is preferably formed of an organic material having a melting point exceeding 180 ° C., or not thermally melted, and starting thermal decomposition at a temperature exceeding 180 ° C. In particular, using a non-woven fabric using thin fibers of these materials as the separator sheet has a large number of holes through which lithium ions in the electrolytic solution pass and prevents the short circuit between the positive electrode and the negative electrode. preferable.

  A separator sheet can also be formed of fibers of inorganic materials. As the fiber of the inorganic material, glass fiber is widely used industrially and can be easily obtained. However, even if two glass cloths made of glass fiber are stacked and fixed by meshing the concave and convex portions, depending on the depth of the concave portion (height of the convex portion), the glass fiber may break, There is a case where the engagement is easily disengaged. In such a case, it is preferable to use the glass cloth in combination with the resin because the glass fiber is prevented from being broken and the frictional force between the glass cloths is increased.

  An example of a separator sheet made of glass cloth combined with resin is shown in FIG. The separator sheet 32 shown in FIG. 11 includes a glass cloth 32a that is a glass fiber fabric and a resin 32b attached to the glass cloth 32a. Such a separator sheet 32 can be obtained, for example, by impregnating a molten resin 32b from above a glass cloth 32a placed on a mesh and solidifying the resin 32b. Since the resin 32b that could not be held by the glass cloth 32a is discharged under the mesh, as shown in FIG. 11, the resin 32b does not penetrate into the mesh of the glass cloth 32a, and the glass fiber is left in a state of leaving the mesh. to bound. Therefore, even if the glass cloth is combined with the resin, the ion conductivity required for the separator can be ensured.

  In both cases of the organic material and the inorganic material, when the surface of the separator sheet is smooth, the friction between the concave portion and the convex portion is small, and the meshing structure may be easily disengaged. In that case, the frictional force between the separator sheets can be increased by sandwiching a resin sheet having a thickness equal to or smaller than that of an electrode in a portion that forms a meshing structure of two separator sheets.

  Further, by forming a meshing structure for fixing the separator sheets to at least two sides adjacent to each other, the two adjacent sides of the electrode (positive electrode or negative electrode) disposed between the separator sheets are formed into this meshing structure. By abutting, it is possible to easily align the separator and the electrode. The electrode usually has an extended portion that is extended for current extraction, but the shape excluding this extended portion is rectangular like the separator sheet, so it is easy to abut the electrode on the meshing structure. is there.

  The meshing structure is preferably formed on four sides of the separator sheet. As a result, the positions of the rectangular electrodes arranged between the separator sheets are regulated by the meshing structure on all four sides, so that the active material coating portion of the electrodes sandwiched between the separator sheets may protrude from the separator. Disappear. To form the meshing structure on the four sides of the separator sheet, first form the meshing structure on the two sides of the stacked separator sheet, fix the two separator sheets, and insert the electrode between the separator sheets with the position aligned To do. At this time, the shape of the electrode and the arrangement of the meshing structure are set so that the extension portion for extracting the current from the electrode protrudes out of the separator sheet. Next, a meshing structure is formed on the remaining two sides of the stacked separator sheets, and the separator sheets are fixed also on the remaining two sides. At this time, a meshing structure is not formed in a portion sandwiching the extended portion protruding to the outside of the separator sheet.

  Alternatively, an electrode is placed on one separator sheet, and another separator sheet is placed thereon, and then a meshing structure is formed on the four sides around the electrode to fix the separator sheets together. Alternatively, a plurality of electrodes are placed on a sufficiently large separator sheet with a space between each other, and another separator sheet is placed thereon to form a meshing structure on the four sides around each electrode. May be. Thereafter, the separator sheet is cut into a predetermined size at a predetermined location, whereby the electrode accommodated in the bag-shaped separator can be efficiently produced.

<Configuration of electrode laminate and lithium ion secondary battery>
The structure of the electrode body of the lithium ion secondary battery is roughly classified into a wound type and a laminated type, but the present invention is preferably applied to the laminated type. As a form of a secondary battery to which the present invention can be applied, there is a laminated laminate type in which an electrode laminate is housed in an exterior body made of a laminate film of a resin film and a metal film. Hereinafter, a laminated laminate type secondary battery will be described.

  FIG. 1 is an exploded perspective view of a lithium ion secondary battery 1 according to an embodiment of the present invention. The electrode laminate 10 is surrounded by the exterior materials 11 and 12 from both sides in the thickness direction. Further, the exterior body made of the exterior materials 11 and 12 also contains an electrolyte solution. A negative electrode tab 13 and a positive electrode tab 14 are connected to the electrode laminate 10, and each part protrudes from the exterior body.

  As shown in FIG. 2, the electrode laminate 10 is configured by alternately laminating a plurality of negative electrodes 21 and a plurality of electrode assemblies 25 with separators. As shown in FIG. 3, the electrode assembly with a separator 25 includes two separator sheets 22 that are overlapped with each other, and a positive electrode 27 that is disposed therebetween. The two separator sheets 22 are fixed to each other by a meshing structure 26 formed on the outer peripheral portion thereof. The separator sheet 22 prevents the negative electrode 21 and the positive electrode 27 from coming into direct contact. In the positive electrode 27 and the negative electrode 21, the active material coated surface of the negative electrode 21 has a larger area than the active material coated surface of the positive electrode 27, and the active material coated surface of the positive electrode 27 is laminated with the negative electrode 21 in the corresponding negative electrode. It is within the active material coating surface. The negative electrode 21 and the positive electrode 27 have extensions 23a and 24a, respectively. The extension part 24a of the positive electrode 27 protrudes from the separator sheet 22, and the positive electrode 21 and the negative electrode 27 are laminated so that the extension parts 23a and 24a extend outside the electrode laminate 10 without interfering with each other. The extensions 23a of all the negative electrodes 21 are collected together and connected to the negative electrode tab 13 shown in FIG. 1 by welding. Similarly, the positive portions 27 of all the positive electrodes 27 are gathered together and connected to the positive electrode tab 14 shown in FIG. 1 by welding.

<Negative electrode>
The lithium ion secondary battery of this embodiment includes a negative electrode having a negative electrode active material. The negative electrode active material is bound on the negative electrode current collector by a negative electrode binder. FIG. 4A is a schematic cross-sectional view of a negative electrode. The negative electrode 21 includes a negative electrode current collector 23 formed of a metal foil, and a negative electrode active material 41 coated on both surfaces of the negative electrode current collector 23. The negative electrode current collector 23 is formed having an extension 23a connected to the negative electrode tab 13 in FIG. 1, and the negative electrode active material 41 is not applied to the extension 23a.

  The negative electrode active material in the present embodiment is not particularly limited. For example, the carbon material (a) that can occlude and release lithium ions, the metal (b) that can be alloyed with lithium, and the lithium ions are occluded and released. The metal oxide (c) etc. which can be mentioned.

  Examples of the carbon material (a) include carbon, amorphous carbon, diamond-like carbon, carbon nanotubes, and composites thereof. Here, carbon with high crystallinity has high electrical conductivity, and is excellent in adhesiveness and voltage flatness with a negative electrode current collector made of a metal such as copper. On the other hand, since amorphous carbon having low crystallinity has a relatively small volume expansion, it has a high effect of relaxing the volume expansion of the entire negative electrode, and deterioration due to non-uniformity such as crystal grain boundaries and defects hardly occurs.

  Examples of the metal (b) include Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, or alloys of two or more thereof. It is done. Moreover, you may use these metals or alloys in mixture of 2 or more types. These metals or alloys may contain one or more non-metallic elements.

  Examples of the metal oxide (c) include silicon oxide, aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and composites thereof. In this embodiment, it is preferable that tin oxide or silicon oxide is included as a negative electrode active material, and it is more preferable that silicon oxide is included. This is because silicon oxide is relatively stable and hardly causes a reaction with other compounds. Moreover, 0.1-5 mass% of 1 type, or 2 or more types of elements chosen from nitrogen, boron, and sulfur can also be added to a metal oxide (c). By carrying out like this, the electrical conductivity of a metal oxide (c) can be improved.

  All or part of the metal oxide (c) preferably has an amorphous structure. The metal oxide (c) having an amorphous structure can suppress volume expansion of the carbon material (a) and the metal (b) which are other negative electrode active materials. Although this mechanism is not clear, it is presumed that the formation of a film on the interface between the carbon material (a) and the electrolytic solution has some influence due to the amorphous structure of the metal oxide (c). The amorphous structure is considered to have relatively few elements due to non-uniformity such as crystal grain boundaries and defects. In addition, it can be confirmed by X-ray diffraction measurement (general XRD measurement) that all or part of the metal oxide (c) has an amorphous structure. Specifically, when the metal oxide (c) does not have an amorphous structure, a peak specific to the metal oxide (c) is observed, but all or part of the metal oxide (c) is amorphous. In the case of having a structure, the intrinsic peak of the metal oxide (c) is broad and observed.

  The metal (b) is preferably silicon, and the metal oxide (c) is preferably silicon oxide. That is, the negative electrode active material is preferably composed of a composite of silicon, silicon oxide, and carbon material. It is also possible to use a material in which the negative electrode active material is chemically and thermally doped with lithium in advance. For example, chemical dope can be obtained by a method in which lithium is forcibly doped into an active material using a solvent containing a lithium metal or a lithium compound and a reducing agent. In thermal doping, the negative electrode active material can be doped with lithium by bringing the negative electrode active material into contact with lithium metal and warming the whole.

  The binder for the negative electrode is not particularly limited. For example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer. Rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide, polyacrylic acid, or the like can be used. Of these, polyimide or polyamideimide is preferred because of its high binding properties. The amount of the binder for the negative electrode to be used is preferably 5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. .

  As the negative electrode current collector, aluminum, nickel, stainless steel, chromium, copper, silver, and alloys thereof are preferable from the viewpoint of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.

<Positive electrode>
The lithium ion secondary battery of this embodiment includes a positive electrode having a positive electrode active material. The positive electrode is formed by binding the positive electrode active material so as to cover the positive electrode current collector with the positive electrode binder. FIG. 4B is a schematic cross-sectional view of the positive electrode. The positive electrode 27 includes a positive electrode current collector 24 formed of a metal foil, and a positive electrode active material 42 coated on both surfaces of the positive electrode current collector 24. The positive electrode current collector 24 is formed to have an extension part 24a connected to the positive electrode tab 14 of FIG. 1, and the positive electrode active material 42 is not applied to the extension part 24a.

The positive electrode active material has a layered structure such as LiMnO ₂ , LixMn ₂ O ₄ (0 <x <2), Li ₂ MnO ₃ , Li _x Mn _1.5 Ni _0.5 O ₄ (0 <x <2). Lithium manganate or lithium manganate having a spinel structure, LiCoO ₂ , LiNiO ₂ or a part of these transition metals replaced with other metals, LiNi _1/3 Co _1/3 Mn _1/3 O _2, etc. Lithium transition metal oxides whose specific transition metals are less than half, those in which these lithium transition metal oxides have an excess of Li over the stoichiometric composition, those having an olivine structure such as LiFePO ₄ , etc. It is done. Further, these metal oxides were partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. Materials can also be used. In _{particular, Li α Ni β Co γ Al} δ O 2 (1 ≦ α ≦ 2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0.2) or _{Li α Ni β Co γ Mn δ} O 2 (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6, γ ≦ 0.2). A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

  A radical material or the like can also be used as the positive electrode active material.

  As the positive electrode binder, the same binder as the negative electrode binder can be used. The amount of the binder for the positive electrode to be used is preferably 2 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoints of “sufficient binding force” and “high energy” in a trade-off relationship. .

  As the positive electrode current collector 24, the same one as the negative electrode current collector can be used.

  A conductive auxiliary material may be added to the coating layer of the positive electrode active material for the purpose of reducing impedance. Examples of the conductive auxiliary material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.

<Electrolyte>
As the electrolytic solution used in the present embodiment, a nonaqueous electrolytic solution containing a lithium salt (supporting salt) and a nonaqueous solvent that dissolves the supporting salt can be used.

  As the non-aqueous solvent, an aprotic organic solvent such as a carbonic acid ester (chain or cyclic carbonate), a carboxylic acid ester (chain or cyclic carboxylic acid ester), or a phosphoric acid ester can be used.

  Examples of carbonate solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. (EMC), chain carbonates such as dipropyl carbonate (DPC); and propylene carbonate derivatives.

  Examples of the carboxylic acid ester solvent include aliphatic carboxylic acid esters such as methyl formate, methyl acetate, and ethyl propionate; and lactones such as γ-butyrolactone.

  Among these, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), dipropyl carbonate Carbonic acid esters (cyclic or chain carbonates) such as (DPC) are preferred.

  Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trioctyl phosphate, and triphenyl phosphate.

  Other solvents that can be contained in the non-aqueous electrolyte include, for example, ethylene sulfite (ES), propane sultone (PS), butane sultone (BS), dioxathilane-2,2-dioxide (DD), and sulfolene. 3-methylsulfolene, sulfolane (SL), succinic anhydride (SUCAH), propionic anhydride, acetic anhydride, maleic anhydride, diallyl carbonate (DAC), dimethyl 2,5-dioxahexanoate, 2,5 -Dioxahexaneniate dimethyl, furan, 2,5-dimethylfuran, diphenyl disulfide (DPS), dimethoxyethane (DME), dimethoxymethane (DMM), diethoxyethane (DEE), ethoxymethoxyethane, chloroethylene carbonate , Dimethyl ether, methyl ether Ether, methyl propyl ether, ethyl propyl ether, dipropyl ether, methyl butyl ether, diethyl ether, phenyl methyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), tetrahydropyran (THP), 1,4-dioxane (DIOX), 1,3-dioxolane (DOL), methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, methyl difluoroacetate, methyl propionate, ethyl propionate, propyl propionate, methyl formate , Ethyl formate, ethyl butyrate, isopropyl butyrate, methyl isobutyrate, methyl cyanoacetate, vinyl acetate, diphenyl Disulfide, dimethyl sulfide, diethyl sulfide, adiponitrile, valeronitrile, glutaronitrile, malononitrile, succinonitrile, pimonitrile, suberonitrile, isobutyronitrile, biphenyl, thiophene, methyl ethyl ketone, fluorobenzene, hexafluorobenzene, carbonate electrolyte, glyme , Ether, acetonitrile, propiononitrile, γ-butyrolactone, γ-valerolactone, dimethyl sulfoxide (DMSO) ionic liquid, phosphazene, methyl formate, methyl acetate, ethyl propionate and other aliphatic carboxylic acid esters, or these compounds In which a part of the hydrogen atoms are substituted with fluorine atoms.

As the supporting salt in the present embodiment, LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN ( CF ₃ SO _{2) 2} normal lithium salt which can be used in lithium ion batteries or the like can be used. The supporting salt can be used alone or in combination of two or more.

  A non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types.

<Exterior body>
The exterior body can be appropriately selected as long as it is stable to the electrolytic solution and has a sufficient water vapor barrier property. For example, in the case of a laminated laminate type secondary battery, it is preferable to use a laminate film of aluminum and resin as the outer package. An exterior body may be comprised with a single member and may be comprised combining several members.

<Manufacturing method>
Below, the manufacturing method of the electrode assembly 25 with a separator which has the structure where the positive electrode 27 was pinched | interposed between the two separator sheets 22, and the manufacturing method of an electrode laminated body are demonstrated.

  FIG. 5 is a schematic cross-sectional view illustrating an example of a method for forming a meshing structure composed of a concave portion and a convex portion on two stacked separator sheets 22. Between the pair of pressure plates 51, 52 having the concave portions 51b, 52b and the convex portions 51a, 52a formed on the surface, the side portions of the two separator sheets 22 overlapped are sandwiched, and the convex portions 51a of the pressure plate 51 Pressurization is performed so that the concave portion 52b of the pressure plate 52, the concave portion 51b of the pressure plate 51, and the convex portion 52a of the pressure plate 52 are engaged with each other. Thereby, the meshing structure which consists of the recessed part 61 and the convex part 62 as shown in FIG. In this way, by forming the meshing structure with the separator sheet 22 by sandwiching the separator sheet 22 between the pressure plates 51 and 52, the separator sheet 22 is broken even if the separator sheet 22 is thin, for example, having a thickness of less than 50 μm. A meshing structure can be formed satisfactorily without any problems.

  The number of the concave portions 51b and 52b and the convex portions 51a and 52a formed in the pressure plates 51 and 52 may be arbitrary. For example, even if the pressurizing plates 51 and 52 each have one concave portion 51b and 52b and the convex portions 51a and 52a, the separator sheet 22 is repeatedly pressed and moved as appropriate. A meshing structure having a desired number of concave portions and convex portions can be formed on the 22.

  Further, when the planar shapes of the concave portions and the convex portions formed on the surfaces of the pressure plate 51 and the plate 52 are formed to have a bent portion, the concave portions 71 and the convex portions 72 formed in the separator sheet 22 as shown in FIG. The outer peripheral length of the can be increased. Thereby, the fixing force between the separator sheets 22 can be increased. In the example shown in FIG. 7, the bending is only at one central portion, but the uneven portion may be zigzag at two or more locations.

FIG. 8 is a view for explaining a method for producing an electrode assembly with a separator having a structure in which a positive electrode 27 is sandwiched between two separators 22. Hereinafter, it demonstrates according to a figure.
(Step A1) First, two separator sheets 22 are stacked.
(Step A2) Next, a meshing structure 26 is formed on two adjacent sides of the stacked separator sheets 22, and the two separator sheets 22 are fixed to each other.
(Step A3) Next, the positive electrode 27 is inserted between the two separator sheets 22. At this time, the positional relationship between the positive electrode 27 and the separator sheet 22 is determined by abutting the two sides of the positive electrode 27 with the two sides fixed by the meshing structure 26 of the separator sheet 22.
(Step A4) Next, in order to prevent the positive electrode 27 from shifting, a meshing structure is formed on the remaining two sides of the stacked separator sheets 22.

  Of the series of steps described above, in step A2, the engagement structure 26 is formed on the three sides excluding the upper side from which the extension for the positive electrode 27 current extraction projects, and the electrode 27 is inserted from the opening on the other side. May be. However, in this case, depending on the size of the opening on the remaining one side, the operation of the step A3 for inserting the positive electrode 27 between the separator sheets 22 may be difficult as compared with the case where the two adjacent sides are fixed.

A method different from FIG. 8 will be described with reference to FIG.
(Step B1) First, the positive electrode 27 is placed on one separator sheet 81. At this time, the number of the positive electrodes 27 may be one. However, as shown in FIG. 9, the size of the separator sheet 81 is set to a size that allows the plurality of positive electrodes 27 to be arranged at intervals. This is preferable because it is advantageous for shortening the production time.
(Step B2) Next, another separator sheet 82 is overlaid on the separator sheet 81 on which one or more positive electrodes 27 are placed.
(Step B3) Next, the meshing structure 26 is formed in portions of the two separator sheets 81 and 82 that are overlapped, corresponding to the four sides around the positive electrode 27.
(Step B4) Finally, the separator sheets 81 and 82 are cut at predetermined positions to obtain the electrode assembly 25 with a separator including one positive electrode 27 and the meshing structure 26 around it. As shown in FIG. 9, when simultaneously processing a plurality of positive electrodes 27, the separator sheets 81 and 82 are cut at positions between the respective positive electrodes 27, whereby each positive electrode 27 and its surrounding meshing structure are cut. A plurality of electrode assemblies 25 with separators 27 are obtained.

  A method for manufacturing the electrode stack will be described with reference to FIGS. As shown in FIG. 10, two positioning blocks 101 arranged orthogonally are used for manufacturing the electrode stack, in order to determine the positions of two adjacent sides of the stack. An electrode stack is produced by alternately stacking the negative electrode 21 and the electrode assembly 25 with a separator containing the positive electrode on the positioning block 101 while abutting two adjacent sides. When the negative electrode 21 and the electrode assembly 25 with separator are stacked, the extension of the negative electrode 21 and the extension of the positive electrode housed in the assembly 25 with separator are not overlapped. After a predetermined number of layers are stacked, the negative electrode tab is connected to the negative electrode extension by welding, and the positive electrode tab is connected to the positive electrode extension by welding.

Next, specifically described by experiments embodiment of the present invention.

<Experimental Example 1>
<Production of battery>
(Preparation of positive electrode)
As a positive electrode active material, a lithium manganese composite oxide (LiMn ₂ O ₄ ) material is mixed in an amount of 85% by mass, acetylene black as a conductive auxiliary agent is 7% by mass, and a binder is 8% by mass of polyvinylidene fluoride. After being dispersed in methylpyrrolidone (NMP) to form a slurry, it was applied to an aluminum foil (thickness 15 μm) as a positive electrode current collector and dried. After applying the active material to both sides of the current collector, the electrode was pressed to produce a thickness of 80 μm after the treatment. Further, this was punched into a shape with an extended portion protruding. The active material application portion had a width of 66 mm and a length of 96 mm. The extension portion had a length of 15 mm and a width of 20 mm along the long side direction of the active material application portion. No active material is applied to the extension.

(Preparation of negative electrode)
As a negative electrode active material, 90% by mass of a graphite material and 10% by mass of polyvinylidene fluoride as a binder were mixed and dispersed in N-methylpyrrolidone (NMP) to form a slurry, and then a negative electrode current collector having a thickness of 10 μm. It was applied to copper foil and dried. After the active material was applied to both sides of the current collector, the electrode was pressed to produce a thickness of 65 μm after the treatment. Further, this was punched into a shape with an extended portion protruding. The active material application portion had a width of 70 mm and a length of 100 mm. The extension part was formed with a length of 15 mm and a width of 20 mm along the long side direction of the active material application part. No active material is applied to the extension.

(Preparation of electrode assembly with separator)
As a separator sheet, a cellulose nonwoven fabric having a thickness of 25 μm was cut into a strip shape having a width of 70 mm and a length of 100 mm. Two sheets of the obtained strip-shaped separator sheets were overlapped, and the two adjacent sides were pressed between two pressure plates having a concave portion and a convex portion having a rectangular planar shape on the surface. As a result, the two separator sheets were formed with a meshing structure in which the concave portions and the convex portions by the pressure plate were meshed with each other, and the two separator sheets were fixed by this meshing structure. The meshing structure has no flat portion between the concave portion and the convex portion, the length of the bottom surface of the concave portion and the top surface of the convex portion in the direction along the side of the separator sheet is 0.4 mm, and the period of the concave and convex portions is 1. The length was 4 mm, and the length was 8 periods at both ends of the side of the overlapping separator sheet. The width of the meshing structure defined by the length of the meshing structure from the edge of the separator sheet in the direction perpendicular to the side of the separator sheet was 1.5 mm. The meshing height of the concave and convex portions is 0.4 mm, and the angle of the side wall portion of the meshing structure calculated from the above dimensions is 37 degrees.

  Next, the positive electrode was sandwiched between the two separator sheets while the two sides of the positive electrode were brought into contact with the meshing structure formed on the two sides of the separator sheet and aligned. Next, the same meshing structure was formed on the two sides where the separator sheet was not fixed, and the separator sheet was fixed on the four outer peripheral sides of the positive electrode. Thereby, the electrode assembly with a separator which accommodated the positive electrode was produced. In addition, the meshing structure was not formed in the part of the separator sheet from which the extension part of the positive electrode protruded.

(Production of electrode laminate)
Lamination of the electrodes, that is, lamination of the negative electrode and the electrode assembly with a separator was performed using the same positioning block as in FIG. The stacking was performed in the order of the negative electrode, the electrode assembly with separator, and the negative electrode so that the four positive electrodes and the five negative electrodes were alternately overlapped. The outermost surface is a negative electrode, but does not operate as a battery because there is no positive electrode surface facing it.

(Production of battery)
The positive electrode tab and the negative electrode tab were joined to the extension part of the positive electrode and the negative electrode extension part of the electrode laminate by ultrasonic welding, respectively. Next, the electrode laminated body to which the positive electrode tab and the negative electrode tab were joined was sealed in the exterior body with the positive electrode tab and the negative electrode tab protruding, thereby producing a battery. The sealing of the electrode laminate was performed according to the following procedure.

First, two laminate films of aluminum and resin were prepared as exterior materials. These two laminate films were overlapped with the electrode laminate interposed therebetween. At this time, the electrode laminate is. It arrange | positions so that a positive electrode tab and a negative electrode tab may protrude from a laminate film. The laminated laminate films were heat-welded on the three sides of the outer periphery of the electrode laminate. After the laminate film was thermally welded, an electrolyte solution was injected into the laminate film from the remaining one side not thermally welded as a liquid injection port. After injecting the electrolytic solution, the injection port was sealed by heat welding in a vacuum atmosphere, thereby completing the battery. As the electrolytic solution, a solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 2 was used as a solvent, and 1 mol of LiPF ₆ was dissolved per liter of the solvent.

<Battery evaluation>
Ten batteries (cells) were produced according to the above procedure, and the presence or absence of an internal short circuit of the battery was examined with ten batteries before the first charge. Next, for five of the batteries, the presence or absence of internal deposition after 100 cycles of charging / discharging with a lower limit voltage of 2.5 V and an upper limit voltage of 4.2 V was examined, and the remaining five batteries were kept at a constant temperature up to 180 ° C. The presence or absence of an internal short circuit when heated in the bath was examined. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal precipitation after 100 cycles of the charge / discharge test was 0, and when heated to 180 ° C., the battery outer body swelled due to the evaporation of the electrolyte during the temperature rise. A part of the side of the welded outer package was opened, but there were no internal short circuits. When the battery heated to 180 ° C. was disassembled after cooling, the separator covered the positive electrode, and there was no place where the positive electrode and the negative electrode contacted.

<Experimental Example 2>
<Production of battery>
After the two sides of the positive electrode were sandwiched between the separator sheets while abutting the adjacent long and short sides fixed to the separator sheet and aligning the positions, no meshing structure was formed on the remaining two sides of the separator sheet. Except this, the battery was fabricated in the same manner as Experiment Example 1. When the electrodes were stacked, the two sides fixed to the separator sheet were abutted against the positioning block shown in FIG. 10 for positioning.

<Battery evaluation>
Evaluation was performed produced ten batteries in the same manner as Experiment Example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0.

<Experimental Example 3>
<Production of battery>
A 30 μm thick nonwoven fabric formed from polyimide microfibers was used as a separator sheet. Two separator sheets were overlapped with one polypropylene sheet sandwiched between locations where the separator sheet meshing structure was formed. The thickness of the polypropylene sheet was 25 μm. The sandwiched polypropylene sheet was arranged so as not to be applied to the positive electrode. Others, a battery was prepared in the same manner as in Experiment Example 1. This experimental example corresponds to an example of the present invention.

<Battery evaluation>
Evaluation was performed produced ten batteries in the same manner as Experiment Example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0.

  The reason why an internal short circuit did not occur even when heated to a temperature exceeding the melting point of polypropylene is considered to be that the melted polypropylene stayed between the polyimide nonwoven fabrics even at a temperature higher than the melting temperature of polypropylene. It is presumed that the polypropylene stayed between the polyimide nonwoven fabrics strengthened the fixing force between the polyimide nonwoven fabrics due to the meshing structure formed on the polyimide nonwoven fabric, and prevented the polyimide sheet from shifting.

<Experimental Example 4>
<Production of battery>
A glass cloth having a thickness of 25 μm in which E glass fibers were woven was used as a separator. The weaved glass cloth is easily misaligned. Therefore, the texture of the glass cloth was fixed by superimposing the polypropylene film on the glass cloth and heating it to 200 ° C. to melt and infiltrate and solidify it between the glass fibers. The amount of polypropylene was 20% by weight with respect to the entire separator sheet. Others, a battery was prepared in the same manner as in Experiment Example 1.

<Battery evaluation>
Evaluation was performed produced ten batteries in the same manner as Experiment Example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0. The reason why the internal short circuit did not occur even when heated to a temperature exceeding the melting point of polypropylene was that the molten polypropylene stayed between the glass fibers even above the melting temperature of the polypropylene, preventing the glass cloth from being deformed. I guess because.

<Experimental Example 5>
<Production of battery>
The shape of the meshing structure formed on the separator sheet is such that there is no flat portion between the concave portion and the convex portion, and the length of the bottom surface of the concave portion and the top surface of the convex portion in the direction along the side of the separator sheet is 0.4 mm. The period of the unevenness was 1.0 mm, and 8 periods were formed at both ends of the sides of the separator sheets that were superimposed. The meshing height of the concave and convex portions is 0.1 mm, and the angle of the side wall portion of the meshing structure calculated from the above dimensions is 34 degrees. Others, a battery was prepared in the same manner as in Experiment Example 1.

<Battery evaluation>
Evaluation was performed produced ten batteries in the same manner as Experiment Example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0.

<Experimental Example 6>
<Production of battery>
As a separator sheet, a cellulose nonwoven fabric having a thickness of 25 μm was cut into a rectangular shape having a width of 140 mm and a length of 100 mm. Two positive electrodes were placed side by side on one separator sheet. At this time, the 100 mm side of the separator sheet and the 96 mm side of the positive electrode are parallel, the distance between the sides of the adjacent positive electrode is 4 mm, the other positive electrode side (excluding the extension) and the side of the separator sheet The distance was set to 2 mm. Next, another separator sheet was stacked thereon. Next, a distance of 0.5 mm from the four sides of each of the two positive electrodes was taken, and an interlocking structure composed of concave portions and convex portions was formed on the overlapping separator sheets. Except that the width of the engagement structure between the adjacent positive electrode (the length of the engagement structure in the direction perpendicular to the direction along the side of the positive electrode) was 3mm formed a similar engagement structure as Experiment Example 1 . Next, the separator sheet was cut at the center of a 4 mm gap between adjacent positive electrodes. Thus, the same separator with the electrode assembly and the obtained by experiment example 1 were obtained two simultaneously. Thus with a separator with an electrode assembly fabricated by, a battery was fabricated in the same manner as in Experiment Example 1.

<Battery evaluation>
Evaluation was performed prepared similarly ten batteries with experimental example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0.

<Experimental Example 7>
<Production of battery>
In Experiment Example 3, no intervening polypropylene sheet between the separator sheet made of polyimide non-woven fabric, further, similarly planar shape of the engagement structure, a rectangular, except that it has a bent shape in the central portion and the experimental Example 3 Thus, a battery was produced. The bending angle in the planar shape of the meshing structure was 120 degrees.

<Battery evaluation>
Evaluation was performed prepared similarly ten batteries with experimental example 1. As a result, the number of internal short circuits of the battery before charging was 0, the number of internal deposits after 100 cycles of charge / discharge test was 0, and the number of internal short circuits when heated to 180 ° C. was 0.

<Comparative Example 1>
<Production of battery>
Using polypropylene microporous sheet having a thickness of 25μm as a separator sheet, to produce a battery fixing of the separator sheet between the exception that was performed by thermal welding in the same manner as in Experiment Example 1.

<Battery evaluation>
Evaluation was performed prepared similarly ten batteries with experimental example 1. As a result, the internal short circuit of the battery before charging was 0, and the internal deposition after the 100-cycle charge / discharge test was 0, but when heated to 180 ° C., the internal short circuit occurred in all 5 batteries tested. Occurred. The battery outer body was swollen with the vaporized electrolyte, and a part of the thermally welded side was opened. When the battery heated to 180 ° C. was decomposed after cooling, the separator contracted, and the positive electrode surface and the negative electrode surface were in contact with each other.

<Comparative example 2>
<Production of battery>
It did not form a mesh structure to the separator sheet, that is, except that no fixing the separator sheets together was prepared in the same manner as the battery as Experiment Example 1. Alignment during lamination, with the same positioning block as Experiment Example 1, although the negative electrode and the separator sheet aligned position abutting to the positioning block, the positive electrode is abutting to the positioning block for small dimensions The position was adjusted visually.

<Battery evaluation>
Evaluation was performed prepared similarly ten batteries with experimental example 1. As a result, although the number of internal short circuits of the battery before charging was zero, precipitation was observed at the end of the negative electrode in one out of five after the 100-cycle charge / discharge test. This is probably because the positive electrode was displaced in the electrode laminate during assembly and did not protrude from the separator, but protruded from the negative electrode facing surface. When heated to 180 ° C., internal short circuit occurred in 2 out of 5 tested. The outer package of the battery swelled due to the evaporated electrolyte, and a part of the thermally welded side was opened. When the battery which caused the internal short circuit was disassembled after cooling, the separator was not contracted, but there was a portion where the positive electrode and the negative electrode contacted. This is probably because the electrode stack was deformed when the electrolyte was vaporized and the battery expanded, and the separator moved.

<Reference Example 1>
<Production of battery>
Similar to Experiment Example 1, using the thickness 25μm of the cellulose nonwoven fabric as the separator sheet. The meshing structure has no flat portion between the concave portion and the convex portion, the length of the bottom surface of the concave portion and the top surface of the convex portion in the direction along the side of the separator sheet is 0.4 mm, and the period of the concave and convex portions is 1.3 mm. It was formed with a length of about 8 cycles (about 10 mm) at both ends of the sides of the stacked separator sheets. The meshing height of the concave and convex portions is 0.2 mm, and the angle of the side wall portion of the meshing structure calculated from these dimensions is 45 degrees. Next, the positive electrode was sandwiched between the separator sheets while abutting the two sides of the positive electrode against the fixing position of the separator sheet, and fixing the separator sheets to each other when a strong force was applied when the positive electrode was applied. There was something that came off.

<Reference Example 2>
Similar to Experiment Example 1, using the thickness 25μm of the cellulose nonwoven fabric as the separator sheet. The meshing structure has no flat portion between the concave portion and the convex portion, the length of the bottom surface of the concave portion and the top surface of the convex portion in the direction along the side of the separator sheet is 0.4 mm, and the period of the concave and convex portions is 1.0 mm. It was formed with a length of 8 cycles at both ends of the sides of the separator sheets that were overlapped. The meshing height of the concave and convex portions is 0.08 mm, and the angle of the side wall portion of the meshing structure calculated from these dimensions is about 37 degrees. Next, the positive electrode was sandwiched between the separator sheets while abutting the two sides of the positive electrode against the fixing position of the separator sheet, and fixing the separator sheets to each other when a strong force was applied when the positive electrode was applied. There was something that came off.

<Reference Example 3>
Similar to Experiment Example 1, using the thickness 25μm of the cellulose nonwoven fabric as the separator sheet. The meshing structure has no flat portion between the concave portion and the convex portion, the length of the bottom surface of the concave portion and the top surface of the convex portion in the direction along the side of the separator sheet is 0.4 mm, and the period of the concave and convex portions is 1.4 mm. It was formed with a length of 8 cycles at both ends of the sides of the separator sheets that were overlapped. The meshing height of the concave and convex portions is 0.5 mm, and the angle of the side wall portion of the meshing structure calculated from these dimensions is about 29 degrees. Next, the positive electrode was sandwiched between the separator sheets while abutting the two sides of the positive electrode against the fixing position of the separator sheet, and fixing the separator sheets to each other when a strong force was applied when the positive electrode was applied. There was something that came off.

Above, the results of Experiment Examples 1-7, superimposed separator sheet by a material having high heat resistance which does not melt even when heated to 180 ° C., and fixed to each other by structural engagement both by concave and convex portions, the positive electrode therebetween It was confirmed that, in the lithium ion battery having the laminated electrode body, the effect of eliminating the stacking deviation inside the laminated electrode body and suppressing the internal short circuit when exposed to high temperature can be obtained. In addition, since the effect of this invention expresses with the property of the material used for a separator, and the structure of the laminated separator sheet, it does not depend on the kind of electrolyte solution, unless the specification of a positive electrode and a negative electrode, or a separator sheet is changed.

Further, using the experimental example 3, a nonwoven fabric made from polyimide fibers as a separator sheet, but sandwich the polypropylene sheet between two separator sheets, the polypropylene sheet is not an essential component. However, polyamide fibers and aramid fibers, which are one of the materials that do not melt even when heated up to 180 ° C, have a small variation in fiber diameter, so that the fixing force between separator sheets due to the meshing structure is lower than other fiber materials. There is a small tendency. Even in such a case, for example, or increasing the number of recesses and protrusions, or increasing the height engagement, or to reduce the angle of the sidewall of the concave and convex portions, engagement as Experiment Example 7 By devising the planar shape of the structure or combining two or more of these, the fixing force between the separator sheets can be increased.

  The present invention can be used in all industrial fields that require a power source, as well as industrial fields related to the transport, storage and supply of electrical energy. Specifically, power supplies for mobile devices such as mobile phones and laptop computers, electric vehicles such as electric cars, hybrid cars, electric bikes, electric assist bicycles, power supplies for mobile and transport media such as trains, satellites, and submarines, UPS It can be used for backup power sources such as, power storage facilities that store power generated by solar power generation, wind power generation, etc.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Electrode laminated body 11 Exterior material 12 Exterior material 13 Negative electrode tab 14 Positive electrode tab 21 Negative electrode 22, 81, 82 Separate sheet 23 Negative electrode current collector 24 Positive electrode current collector 25 Separator electrode assembly 26 Engagement structure 27 Positive electrode 41 Negative electrode active material 42 Positive electrode active material 51, 52 Pressure plate 61, 71 Concave portion 62, 72 Convex portion 101 Positioning block

Claims (17)

In a lithium ion secondary battery in which a positive electrode and a negative electrode, which are electrodes, are stacked via a separator,
The separator has a pair of rectangular separator sheets made of a material that does not melt even when heated to 180 ° C.
The stacked separator sheets are fixed to each other by meshing of a meshing structure including a concave portion and a convex portion formed in at least a part of at least two sides adjacent to each other in the outer peripheral portion of the separator sheet,
A polypropylene sheet sandwiched between the two separator sheets at least at a portion where the meshing structure is formed;
One of the positive electrode and the negative electrode is disposed between the two separator sheets, and is a lithium ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein the electrode disposed between the separator sheets is a positive electrode having a size smaller than that of the negative electrode.   The electrode disposed between the separator sheets has a current collector formed with an extension extending from one side thereof and protruding to the outside of the separator, and the meshing structure is a portion where the extension is formed. The lithium ion secondary battery according to claim 1 or 2, wherein the lithium ion secondary battery is formed on four sides of the separator sheet. The thickness of the separator sheet, lithium-ion secondary battery according to any one of claims 1 3, characterized in that not more than 50μm per sheet.   5. The lithium ion according to claim 1, wherein a value of the depth of the concave portion and the height of the convex portion not including the thickness of the separator sheet is 100 μm or more and 400 μm or less. Secondary battery.   6. The lithium ion according to claim 1, wherein an angle of a side wall of the concave portion and the convex portion with respect to a direction perpendicular to a bottom surface of the concave portion or an upper surface of the convex portion is 37 degrees or less. Secondary battery.   The lithium ion secondary battery according to claim 1, wherein the meshing structure has a bent planar shape. Wherein the polypropylene sheet, the two sheets of lithium ion secondary battery according to any one of claims 1-7, characterized in that it comprises a thickness less than or equal to that of the electrodes disposed between the separator sheet . The lithium ion secondary battery according to any one of claims 1 to 8 , further comprising an exterior body that houses the positive electrode, the negative electrode, and the separator together with an electrolytic solution. In a lithium ion secondary battery in which a positive electrode and a negative electrode, which are electrodes, are stacked via a separator,
The separator has a pair of rectangular separator sheets made of polyimide fibers and superposed on each other, and is formed on at least a part of at least two adjacent sides of the outer periphery of the separator sheet. It is constituted by fixing the two separator sheets to each other by meshing of a meshing structure consisting of a concave part and a convex part,
A polypropylene sheet sandwiched between the two separator sheets at least at a portion where the meshing structure is formed;
One of the positive electrode and the negative electrode is disposed between the two separator sheets, and is a lithium ion secondary battery. The separator sheet is a lithium ion secondary battery according to claim 1 0, characterized in that the non-woven fabric. The engagement structure is a lithium ion secondary battery according to claim 1 0 or 1 1, characterized in that it has a bent planar shape. In the method for producing a lithium ion secondary battery in which a positive electrode and a negative electrode, which are electrodes, are laminated via a separator,
Preparing at least one set of two rectangular separator sheets made of a material that does not melt even when heated to 180 ° C .;
Either one of the positive electrode and the negative electrode is disposed between the two separator sheets that are overlapped with each other, and the two stacked separator sheets are adjacent to each other in the outer peripheral portion of the separator sheet. Forming an electrode assembly with a separator fixed by meshing of a meshing structure comprising a concave portion and a convex portion formed on at least a part of at least two sides that meet each other;
Superposing the electrode assembly with separator and another electrode different from the electrode disposed between the two separator sheets;
Encapsulating the separator-attached electrode assembly with the separator and the other electrode together with an electrolyte in an exterior body;
Only including,
Process is the production of a lithium ion secondary battery, characterized including Mukoto that sandwich the polypropylene sheet at least during the engagement two of said separator sheet at a portion where the structure is formed for forming the separator with the electrode assembly Method. Forming the separator-attached electrode assembly comprises:
In a state where the two separator sheets are overlapped, the two separator sheets are joined to each other by forming the meshing structure on at least a part of two adjacent sides of the outer periphery of the overlapped separator sheets. Fixing, and
Inserting one of the positive electrode and the negative electrode between the two separator sheets fixed to each other;
Method for producing a lithium ion secondary battery according to claim 1 3 comprising a. The step of forming the separator-attached electrode assembly includes:
The method further includes the step of further forming the meshing structure on at least one other side of the two separator sheets having either one of the positive electrode and the negative electrode inserted therebetween, where the meshing structure is not formed. method for producing a lithium ion secondary battery according to 1 4. The step of forming the separator-attached electrode assembly includes:
Placing at least one of the positive electrode and the negative electrode on one separator sheet;
Superimposing another separator sheet on the separator sheet on which the electrodes are placed; and
Fixing the two separator sheets to each other by forming the meshing structure on the two separator sheets superimposed on at least a part of the periphery of the electrodes;
Method for producing a lithium ion secondary battery according to claim 1 3 comprising a. The step of placing the electrodes includes placing a plurality of the positive electrodes on one separator sheet at intervals, and after the step of fixing the two separator sheets to each other, 17. The lithium ion according to claim 16 , further comprising a step of cutting the separator sheet so as to include one of the electrodes disposed therebetween and the meshing structure formed in at least a part of the periphery of the electrode. A method for manufacturing a secondary battery.

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