JP6622072B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, the development of electric vehicles (EV) and hybrid electric vehicles (HEV) has been promoted against the background of the increasing environmental protection movement. Lithium ion secondary batteries that can be repeatedly charged and discharged have attracted attention as power sources for driving motors of these automobiles. A lithium ion secondary battery is a laminated battery in which a power generation element in which a sheet-like positive electrode and a negative electrode are laminated via a separator is housed in an insulating outer package together with an electrolytic solution. This exterior body is formed by laminating an insulating laminated film in which an insulating layer is laminated on both surfaces of a metal layer (see Patent Document 1).

JP 2009-277397 A

However, for example, in the multilayer lithium ion secondary battery disclosed in Patent Document 1, it is difficult for the electrolyte to flow from the outside to the inside of the power generation element. Therefore, the electrolyte solution at the center of the power generation element is easily depleted, and the life of the lithium ion secondary battery may be reduced.
An object of the present invention is to provide a long-life lithium ion secondary battery in which an electrolytic solution is hardly depleted.

  A lithium ion secondary battery according to one embodiment of the present invention includes a power generation element in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and an electrolytic solution in an outer package. The outer peripheral edge of the separator is located outside the outer peripheral edges of the positive electrode and the negative electrode, and the outer peripheral edges of the adjacent separators are in partial contact with each other. And the electrolyte solution path | route which connects the area | region where the positive electrode of the separator was arrange | positioned and / or the area | region where the negative electrode was arranged, and the outer side of the outer peripheral part of a separator is formed.

  According to the present invention, it is possible to provide a long-life lithium ion secondary battery in which the electrolyte solution is hardly depleted.

1 is a perspective view of a lithium ion secondary battery according to an embodiment of the present invention. It is II-II sectional drawing of the lithium ion secondary battery of FIG. It is a figure which shows the outer-periphery edge part of the separator which contacted partially. It is a figure which expands and shows the contact part and non-contact part of the outer periphery part of a separator. It is a figure explaining the electrolyte solution path formed in the outer periphery part of a separator. It is a graph which shows the correlation with the cycle number of a lithium ion secondary battery, and a capacity | capacitance maintenance factor.

  An embodiment of the present invention will be described in detail. A lithium ion secondary battery 1 according to this embodiment shown in FIGS. 1 and 2 is a stacked battery having a substantially rectangular sheet-like appearance, and a power generation element in which a negative electrode 11 and a positive electrode 12 are stacked via a separator 13. 10 and an electrolyte solution (not shown) are provided in the exterior body 30. Since the negative electrode 11, the positive electrode 12, and the separator 13 are all film-like, the power generation element 10 has a flat plate shape.

  Specifically, as shown in FIG. 2, in the power generation element 10, negative electrode active material layers 11B and 11B containing a negative electrode active material capable of inserting and extracting lithium ions are formed on both main surfaces of the negative electrode current collector 11A. The negative electrode 11 and the positive electrode 12 in which the positive electrode active material layers 12B and 12B containing a positive electrode active material capable of inserting and extracting lithium ions are formed on both main surfaces of the positive electrode current collector 12A A plurality of layers are alternately stacked. In the example of FIG. 2, the negative electrode 11, the positive electrode 12, and the separator 13 have a structure in which a plurality of negative electrodes 11 and two positive electrodes 12 are alternately stacked via four separators 13. The number of is not particularly limited.

  In such a power generation element 10, the adjacent negative electrode active material layer 11 </ b> B, separator 13, and positive electrode active material layer 12 </ b> B constitute one unit cell layer 14. Therefore, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a plurality of single battery layers 14 are stacked and electrically connected in parallel. Note that an insulating layer (not shown) for insulating the adjacent negative electrode current collector 11A and positive electrode current collector 12A may be provided on the outer periphery of the unit cell layer 14.

  A negative electrode terminal 21 and a positive electrode terminal 22 are provided on one side of the peripheral edge of the substantially rectangular outer package 30, and the negative electrode terminal 21 and the positive electrode terminal 22 are led out in the same direction from the inside of the outer package 30 to the outside, respectively. Has been. Of the end portions of the negative electrode terminal 21 and the positive electrode terminal 22, the end portions arranged in the exterior body 30 are respectively connected to the negative electrode current collector 11 </ b> A and the positive electrode current collector 12 </ b> A of the power generation element 10 enclosed in the exterior body 30. It is connected. In the present embodiment, the negative electrode terminal 21 and the positive electrode terminal 22 are provided on the same side of the peripheral portion of the outer package 30, but may be provided on different sides. Further, although the negative electrode terminal 21 and the positive electrode terminal 22 are led out in the same direction, they may be led out in different directions such as opposite directions.

  In the lithium ion secondary battery 1 of this embodiment having such a configuration, the separator 13 is designed to be larger than the negative electrode 11 and the positive electrode 12, so that the outer peripheral edge portion 13 a of the separator 13 is outside the negative electrode 11 and the positive electrode 12. It is located outside the peripheral edge. And the outer peripheral edge part 13a of the adjacent separator 13 contacts partially, and the electrolyte solution path 15 which connects the inner side and the outer side of the outer peripheral edge part 13a of the separator 13 is formed.

More specifically, the outer peripheral edge 13a of the separator 13 is deformed by holding and swelling the electrolyte in the separator 13. Due to the deformation of the outer peripheral edge portion 13a of the separator 13, as shown in FIG. 3, the outer peripheral edge portion 13a has a waveform that undulates along the circumferential direction, for example. That is, when the separator 13 is viewed from the side, as shown in FIG. 3, the end face of the separator 13 has a waveform. 3A is a partial side view of the power generation element 10, FIG. 3B is an enlarged view of a portion surrounded by a broken line in FIG. 3A, and FIG. ) Is a partial perspective view showing an enlarged corner portion of the power generation element 10. 3A, 3B, and 3C, only the separator 13 is shown for convenience of explanation.
As a method of deforming the outer peripheral edge portion 13a of the separator 13 so that the outer peripheral edge portions 13a of the separator 13 are partially in contact with each other, various characteristics such as molecular weight and porosity of the resin material constituting the separator 13 are adjusted. By this, the method of designing suitably the elongation rate of the separator 13 when swollen with electrolyte solution is mention | raise | lifted. Also, a method of designing the dimensions of the separator 13 as appropriate, or a method of designing the dimensions of the exterior body 30 relative to the dimensions of the separator 13 (the dimensions of the exterior body 30 in order to suppress the deformation of the separator 13 by the exterior body 30 and deform it). The outer peripheral edge portion 13a of the separator 13 can be deformed so that the outer peripheral edge portions 13a of the separator 13 are partially in contact with each other. These methods may be used in combination as appropriate.

  When at least one outer peripheral edge portion 13a of two adjacent separators 13 has a waveform that undulates along the circumferential direction, the outer peripheral edge portions 13a of the two adjacent separators 13 have different shapes. Therefore, as shown in FIGS. 3 and 4, the entire outer peripheral edge 13 a of the adjacent separator 13 is unlikely to be in surface contact, and the outer peripheral edges 13 a of the adjacent separator 13 are partially in contact with each other. It will be. 4A is a further enlarged view of FIG. 3B, and FIG. 4B is an AA cross-sectional view of FIG. 4A.

  As a result of the partial contact between the outer peripheral edge portions 13 a of the adjacent separators 13, as can be seen from FIGS. 3 and 4, the outer peripheral edge portions 13 a of the adjacent separators 13 are in contact with the outer peripheral edge portion 13 a of the separator 13. A non-contact part which is not in contact with the contact part is formed. As shown in FIG. 5, the non-contact portion includes a region where the negative electrode 11 inside the outer peripheral edge 13 a of the separator 13 is disposed (inside the power generation element 10) and an outer side of the outer peripheral edge 13 a of the separator 13 (power generation). The electrolyte solution path 15 that communicates with the outside of the element 10 and / or the region where the positive electrode 12 inside the outer peripheral edge portion 13 a of the separator 13 is disposed (inside the power generation element 10), and the outer peripheral edge portion of the separator 13 Since the electrolyte solution path 15 that communicates with the outside of the power generation element 10 (outside of the power generation element 10) is configured, the electrolyte solution inside and outside the power generation element 10 can flow through the electrolyte solution path 15. In addition, the arrow shown in FIG. 5 means the electrolyte solution which distribute | circulates through the electrolyte solution path 15. FIG.

For example, in the lithium ion secondary battery disclosed in Patent Document 1, the outer peripheral edge portions of adjacent separators are fused to each other, so that it is difficult for the electrolytic solution to flow from the outside to the inside of the power generation element. Therefore, the electrolyte solution in the center of the power generation element is likely to be depleted, and the lithium ion secondary battery may have a short life.
On the other hand, in the lithium ion secondary battery 1 of the present embodiment having the above-described configuration, the electrolyte outside the power generation element 10 can flow into the power generation element 10 via the electrolyte path 15, Therefore, it is possible to inflow the liquid so as to be able to follow the charging / discharging. Therefore, the lithium ion secondary battery 1 of the present embodiment has high cycle characteristics and a long life.

Moreover, the strength of the power generating element 10 is improved by forming a waveform in which the outer peripheral edge portion 13a of the separator 13 undulates along the circumferential direction. Even if an external force acts on the outer peripheral edge portion 13a of the separator 13, the waveform is easily maintained.
Furthermore, since there are a plurality of electrolyte paths 15, even if the electrolyte inside the power generation element 10 flows out to the outside through some electrolyte paths 15, along with that, the other electrolyte paths 15 pass through. The electrolyte flows into the power generation element 10. Therefore, in the lithium ion secondary battery 1 of the present embodiment, the electrolyte solution inside the power generation element 10 (particularly the central portion) is not easily depleted.

  Furthermore, for example, lithium ion secondary batteries for automobiles are often exposed to vibration, but the lithium ion secondary battery is more corrugated than when the outer peripheral edge of the separator is flat. When the battery is exposed to vibration, a flow tends to occur in the electrolyte outside the power generation element. Therefore, when the lithium ion secondary battery 1 of the present embodiment is exposed to vibration, the electrolyte outside the power generation element 10 tends to flow into the power generation element 10 through the electrolyte path 15.

  The electrolyte path 15 may be formed over the entire circumference of the outer peripheral edge portion 13a of the separator 13, or may be formed in a part of the circumferential direction of the outer peripheral edge portion 13a of the separator 13. For example, it may be formed only on one side, two sides, or three sides of the outer peripheral edge portion 13a of the separator 13. However, since a large amount of electrolyte flows into the power generation element 10 and is easily generated, it is preferable that the portion where the electrolyte path 15 is formed is larger.

  Such a lithium ion secondary battery 1 of this embodiment can be used for various applications. For example, it can be used for various vehicles such as an electric vehicle, a hybrid vehicle (a vehicle that uses both an internal combustion engine and an electric motor as a prime mover), a motorcycle, an electrically assisted bicycle, and a railway vehicle. It can also be used for aircraft, ships, agricultural machinery, construction machinery, transportation machinery, power tools, medical equipment, welfare equipment, robots, power storage devices, and the like. Furthermore, it can also be used for portable devices such as notebook personal computers, digital cameras, mobile phone terminals, and portable game machine terminals.

  In particular, lithium ion secondary batteries mounted on electric vehicles and hybrid vehicles and lithium ion secondary batteries for power storage use require a long life (high number of cycles) because they are used for a long time and are frequently charged and discharged. . In addition, because of the large capacity, the areas of the negative electrode and the positive electrode are large, so that it is difficult for the electrolytic solution to flow into the center of the power generation element, and the electrolytic solution is easily depleted. Therefore, a lithium ion secondary battery mounted on an electric vehicle or a hybrid vehicle or a lithium ion secondary battery for power storage tends to have a short life.

  However, in the lithium ion secondary battery 1 of the present embodiment, even when the areas of the negative electrode 11 and the positive electrode 12 are large, the electrolytic solution easily flows into the power generation element 10 through the electrolytic solution path 15. It is particularly suitable as a lithium ion secondary battery mounted on an electric vehicle or a hybrid vehicle or a lithium ion secondary battery for power storage. When mounted on an electric vehicle or a hybrid vehicle, the capacity of the power generation element 10 of the lithium ion secondary battery 1 is preferably 5 Ah or more and 70 Ah or less.

Below, each component which comprises the lithium ion secondary battery 1 of this embodiment is demonstrated in detail.
1. About the negative electrode terminal 21 and the positive electrode terminal 22 The negative electrode terminal 21 and the positive electrode terminal 22 are comprised, for example with electroconductive metal foil. Specific examples of the metal foil include a metal foil made of a single metal such as aluminum, copper, titanium and nickel, and a metal foil made of an alloy such as an aluminum alloy and stainless steel. The material of the negative electrode terminal 21 and the material of the positive electrode terminal 22 may be the same or different. Further, as in the present embodiment, the negative electrode terminal 21 and the positive electrode terminal 22 that are separately prepared may be connected to the negative electrode current collector 11A and the positive electrode current collector 12A, respectively, or the negative electrode current collector 11A and the positive electrode current collector The negative terminal 21 and the positive terminal 22 may be formed by extending the body 12A.

2. About Negative Electrode 11 The negative electrode 11 has a structure in which negative electrode active material layers 11B and 11B are formed on both main surfaces of the negative electrode current collector 11A. The negative electrode active material layer 11B contains, for example, a negative electrode active material, a conductive additive, and a binder (binder). The conductive additive is contained in a state dispersed in the negative electrode active material layer 11B. Moreover, by making the content rate of the binder in the negative electrode 11 into a predetermined preferable range, the negative electrode active materials are bound to each other in a state where the binder covers at least a part of the particles of the negative electrode active material. .

2-1 About the negative electrode current collector 11A As a material of the negative electrode current collector 11A, for example, a metal such as copper, nickel, titanium, or an alloy (for example, stainless steel) containing one or more of these metals is used. it can.
2-2 Negative electrode active material As the negative electrode active material, for example, a crystalline carbon material such as graphite can be used. Specific examples of graphite include natural graphite, artificial graphite such as non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon, and MCF (mesocarbon fiber). These crystalline carbon materials may be used individually by 1 type, and may use 2 or more types together.

2-3 Conductive aid As the conductive aid, for example, an amorphous carbon material such as carbon black or a crystalline carbon material such as graphite can be used. Specific examples of carbon black include ketjen black, acetylene black, channel black, lamp black, oil furnace black, and thermal black. Specific examples of graphite are the same as those shown in Section 2-2. These carbon materials may be used individually by 1 type, and may use 2 or more types together.

2-4 Binder The binder is not particularly limited as long as it can bind the particles of the negative electrode active material and the particles of the conductive auxiliary agent. For example, a fluororesin may be used. it can. Specific examples of the fluororesin include polyvinylidene fluoride and vinylidene fluoride polymers obtained by copolymerizing vinylidene fluoride and other fluorine monomers. Note that the binder may be made of only a fluororesin or may be made of a mixture of the fluororesin and other components as long as the electrolyte solution can permeate.

3. About Positive Electrode 12 The positive electrode 12 has a structure in which positive electrode active material layers 12B and 12B are formed on both main surfaces of the positive electrode current collector 12A. The positive electrode active material layer 12B contains, for example, a positive electrode active material, and a conductive additive and a binder that are added as necessary. As the conductive auxiliary agent and binder, those that can be generally used for conventional lithium ion secondary batteries (for example, those shown in the items 2-3 and 2-4) are appropriately selected and used. it can.

3-1 About the positive electrode current collector 12A As a material of the positive electrode current collector 12A, for example, a metal such as aluminum, nickel, titanium, or an alloy (for example, stainless steel) containing one or more of these metals is used. it can.

3-2 Positive Electrode Active Material Examples of the positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), nickel cobalt lithium manganate (NCM), and the like. The lithium-containing oxide can be used. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

4). About Separator 13 Separator 13 is a microporous membrane having a large number of fine holes, and holds the electrolytic solution sealed in outer package 30 by accommodating the electrolytic solution in the holes. In the present embodiment, the outer peripheral edge portion 13a is deformed by holding and swelling the electrolytic solution in at least one of the two adjacent separators 13. The elongation percentage of the separator 13 when swollen with the electrolytic solution may be 0.3% or more. By doing so, the deformation of the outer peripheral edge portion 13a of the separator 13 is increased, so that the electrolyte solution path 15 is easily formed.

In order to form the electrolyte solution path 15 more reliably, it is preferable that at least one of the two adjacent separators 13 has an elongation rate of 0.5% or more when swollen with the electrolyte solution . On the other hand, the elongation percentage of the separator 13 when swollen with the electrolytic solution may be 2% or less, and preferably 1% or less.

Further, if a separator having an elongation rate of 0.3% or more when swollen with an electrolytic solution is adjacent to a separator having less than 0.3%, the electrolytic solution path 15 is easily formed. Therefore, it is preferable to alternately arrange separators having an elongation percentage of 0.3% or more and separators less than 0.3% when swollen with the electrolytic solution .

  The material of the separator 13 is not particularly limited as long as it has electrical insulating properties, is electrochemically stable, and is stable with respect to the electrolyte solution. For example, polyolefin such as polyethylene and polypropylene, and polyfluoride Examples thereof include microporous membranes made of fluororesins such as vinylidene and polytetrafluoroethylene, polyesters such as polyethylene terephthalate, and polyamides such as aliphatic polyamide and aromatic polyamide (aramid).

  Moreover, as a material of the separator 13, the resin composition containing said resin and a filler can also be used. The type of filler is not particularly limited as long as it is electrochemically stable and stable with respect to the electrolytic solution, and examples thereof include inorganic particles and organic particles. Specific examples of the inorganic particles include metal oxides such as iron oxide, alumina, silica, titanium dioxide, and zirconia, and ceramic fine particles such as aluminum nitride and silicon nitride. Specific examples of the organic particles include fine particles of resin such as crosslinked polymethyl methacrylate and crosslinked polystyrene.

Further, the separator 13 may be a resin base material coated with a heat-resistant layer. By having the heat resistant layer, the heat resistance and mechanical properties of the separator 13 are improved. The heat-resistant layer is composed of ceramic particles, and the type of ceramic is not particularly limited, and examples thereof include alumina, silica, titanium dioxide, zirconia, aluminum nitride, silicon nitride, and silicon carbide.
In addition, since the base material and the resin layer have different elongation rates due to contact with the electrolytic solution and swell, the separator 13 in which the heat-resistant layer is coated on the surface of the resin base material is likely to be deformed. The electrolytic solution path 15 is easily formed.

  If the separator which coat | covered the heat-resistant layer on the surface of the resin-made base material and the separator made entirely of resin are made to adjoin, the electrolyte solution path 15 will be easy to be formed. Therefore, it is preferable to alternately arrange separators in which the surface of the resin base material is coated with a heat-resistant layer and separators made entirely of resin.

  Since the heat-resistant layer easily absorbs the electrolytic solution, for example, when the ceramic particles in the heat-resistant layer come into contact with the electrolytic solution, the electrolytic solution may be decomposed to generate gas. However, since the gas generated inside the power generation element 10 is easily discharged to the outside of the power generation element 10 through the electrolyte path 15, the performance of the lithium ion secondary battery 1 due to the accumulation of gas inside the power generation element 10. Decline is unlikely to occur.

5. Electrolytic Solution As the electrolytic solution, for example, a solution in which a lithium salt that is an electrolyte is dissolved in a non-aqueous solvent (organic solvent) can be used. The electrolytic solution is not limited to liquid and may be gel. The electrolytic solution may further contain a conventional additive.
The type of lithium salt is not particularly limited as long as it can be dissociated in a non-aqueous solvent to generate lithium ions, but specific examples include lithium hexafluorophosphate (LiPF ₆ ), hexafluoride. Lithium arsenate (LiAsF ₆ ), lithium aluminum tetrachloride (LiAlCl ₄ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroantimonate (LiSbF ₆ ), LiPOF ₂ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _{(C 4 F 9 SO 2)} , LiN (CF 3 CF 2 CO) 2 and the like. Among these lithium salts, it is particularly preferable to use lithium hexafluorophosphate and lithium tetrafluoroborate. These lithium salts may be used individually by 1 type, and may use 2 or more types together.

The non-aqueous solvent is selected from the group consisting of, for example, cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, and fluorinated derivatives thereof. There may be mentioned at least one organic solvent.
Specific examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and fluorinated derivatives thereof. Specific examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and fluorinated derivatives thereof.

  Specific examples of the aliphatic carboxylic acid esters include methyl formate, methyl acetate, ethyl acetate, ethyl propionate, and fluorinated derivatives thereof. Specific examples of γ-lactones include γ-butyrolactone and fluorinated derivatives thereof. Specific examples of the cyclic ethers include dioxane, tetrahydrofuran, 2-methyltetrahydrofuran and the like. Specific examples of the chain ethers include 1,2-ethoxyethane, ethoxymethoxyethane, diethyl ether, and fluorinated derivatives thereof.

  Specific examples of other non-aqueous solvents include dimethyl sulfoxide, 1,3-dioxolane, formaldehyde, acetamide, dimethylformamide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, sulfolane, methyl Examples include sulfolane, 1,3-dimethyl-2-yl ether, 1,3-propane sultone, anisole, N-methyl-2-pyrrolidone, and fluorinated carboxylic acid ester. These nonaqueous solvents may be used alone or in combination of two or more.

6). About the exterior body 30 The exterior body 30 may be a laminate exterior body formed of a flexible laminate film made of a laminate of a heat-fusion layer, a metal layer, and a protective layer, or may be a metal, a resin, or the like. It may be an exterior body formed by a rectangular or cylindrical container.
The laminate outer package is preferable from the viewpoints of weight reduction and improvement in battery energy density. In addition, a laminate type lithium ion secondary battery using a laminate outer package as the outer package 30 is also excellent in heat dissipation.

  Further, in the laminated lithium ion secondary battery, an external force acts on the power generation element 10 due to the atmospheric pressure. Therefore, if the outer peripheral edge portion 13a of the separator 13 is flat, the outer peripheral edge portions 13a of the two adjacent separators 13 There is a possibility that the entire surface is in surface contact and the electrolyte path 15 is not formed. However, in the lithium ion secondary battery 1 of the present embodiment, the outer peripheral edge portion 13a of the separator 13 has a waveform. Therefore, even if an external force is applied to the power generation element 10 due to atmospheric pressure, the outer peripheral edge portion 13a of the two adjacent separators 13 is partially in contact with each other to form a wave shape. Retained and secured. Therefore, the present invention is more suitable for a laminate type lithium ion secondary battery.

  The metal layer is made of, for example, a metal foil (for example, aluminum foil, SUS foil), and the heat-sealing layer covering the inner surface is made of a resin (for example, polyethylene or polypropylene) that can be heat-sealed, and the outer surface of the metal layer The protective layer for covering is made of a resin having excellent durability (for example, polyethylene terephthalate, nylon). A laminate film having a larger number of layers can also be used.

  The exterior body 30 of the lithium ion secondary battery 1 shown in FIGS. 1 and 2 includes two laminate films, one laminate film disposed on the lower surface side of the power generation element 10 and another laminate film disposed on the upper surface side. A sheet structure is formed, and the power generation element 10 is wrapped from above and below in the stacking direction. And the four sides of the peripheral part of these two laminated films are piled up and heat-bonded to each other, thereby forming a bag shape having a joint part where the end parts are joined together.

  However, the exterior body 30 is not limited to such a two-sheet structure, and may have a single-sheet structure as described below. That is, in the outer package 30, the power generation element 10 is arranged on the inner side in a state where one relatively large laminate film is folded (folded in two) (the power generation element 10 is sandwiched between the two folded laminate films). In addition, the three sides of the peripheral portion may be overlapped and thermally bonded to each other to form a bag shape having a joint portion where the end portions are joined to each other.

  The joint portion of the outer package 30 is preferably located at the center in the stacking direction of the power generation element 10 (may be substantially the center in the stacking direction). When the joint portion of the outer package 30 is positioned closer to the stacking direction end than the center of the power generation element 10 in the stacking direction, the outer peripheral edge portion 13a of the separator 13 is pressed by the inner surface of the outer package 30, and the electrolyte path 15 However, if the joint portion of the exterior body 30 is located at the center in the stacking direction of the power generation element 10, the outer peripheral edge portion 13 a of the separator 13 is not easily pressed by the inner surface of the exterior body 30.

  The outer package 30 is preferably larger than the power generation element 10. For example, a gap is preferably formed between the inner surface of the exterior body 30 and the outermost end portion of the outer peripheral edge portion 13a of the separator 13. With such a configuration, the outer peripheral edge 13 a of the separator 13 is hardly pressed by the inner surface of the exterior body 30.

7). About the manufacturing method of the lithium ion secondary battery 1 An example of the manufacturing method of the lithium ion secondary battery 1 of this embodiment is demonstrated.
A slurry is obtained by dispersing graphite as a negative electrode active material, carbon black as a conductive additive, and fluororesin as a binder in a solvent such as N-methyl-2-pyrrolidone in a predetermined blending amount. The slurry is applied to a negative electrode current collector 11A such as a copper foil and dried to form a negative electrode active material layer 11B, thereby producing the negative electrode 11. The obtained negative electrode 11 may be compressed to a suitable density by a method such as a roll press.

  Further, a lithium manganese composite oxide as a positive electrode active material, a conductive additive, and a binder are dispersed in a solvent such as N-methyl-2-pyrrolidone in a predetermined blending amount to obtain a slurry. This slurry is applied to a positive electrode current collector 12A such as an aluminum foil on a hot plate using a doctor blade or the like, and dried to form a positive electrode active material layer 12B, whereby the positive electrode 12 is manufactured. The obtained positive electrode 12 may be compressed to a suitable density by a method such as a roll press.

  Next, after the negative electrode 11, the separator 13, and the positive electrode 12 are stacked to form the power generation element 10, the negative electrode terminal 21 is attached to the negative electrode 11 and the positive electrode terminal 22 is attached to the positive electrode 12. Then, the power generation element 10 is sandwiched between a pair of laminate films, and the peripheral edges excluding one side of the pair of laminate films are heat-sealed while the tips of the negative electrode terminal 21 and the positive electrode terminal 22 protrude from the laminate film, respectively. Thus, a bag-shaped exterior body 30 having an opening is provided.

Next, an electrolytic solution containing a lithium salt such as lithium hexafluorophosphate and an organic solvent such as ethylene carbonate is injected into the inside through the opening of the outer package 30 to bring the electrolytic solution into contact with the power generation element 10. Then, the power generation element 10 is impregnated with the electrolytic solution by vacuum treatment or the like. By contact with the electrolytic solution, the outer peripheral edge portion 13a of the separator 13 is deformed to form a waveform, and the electrolytic solution path 15 is formed. When the electrolytic solution has been poured, the opening of the exterior body 30 is heat-sealed to make the exterior body 30 hermetically sealed. Thereby, the laminate-type lithium ion secondary battery 1 is completed.
At this time, in the first charge after the assembly of the lithium ion secondary battery 1, gas is generated inside the power generation element 10 due to contact between the active material and the electrolytic solution, and the generated gas is supplied to the electrolytic solution path 15. It is easy to be discharged to the outside of the power generation element 10 via the. Therefore, since it is possible to suppress the accumulation of gas inside the power generation element 10 and the occurrence of non-uniform charge / discharge reaction, the performance of the lithium ion secondary battery 1 is hardly deteriorated.

  However, in the manufacturing method of the lithium ion secondary battery 1 of the present embodiment, the electrolyte solution is brought into contact with the power generation element 10 by injecting the electrolyte solution into the exterior body 30 containing the power generation element 10. The lithium ion secondary battery 1 is not limited to the method, but also by a method in which the power generation element 10 brought into contact with the electrolytic solution is accommodated in the exterior body 30 after the electrolyte solution is brought into contact with the power generation element 10 outside the exterior body 30. Can be manufactured. For example, the power generation element 10 is manufactured by applying a gel electrolyte solution to the separator 13 outside the exterior body 30 and laminating the negative electrode 11 and the positive electrode 12 through the separator 13 coated with the gel electrolyte solution. Also good.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. In addition, various changes or improvements can be added to the present embodiment, and forms to which such changes or improvements are added can also be included in the present invention. For example, in the lithium ion secondary battery 1 of this embodiment, the outer peripheral edge portion 13a of the separator 13 is deformed by contact with the electrolytic solution and swells to form the electrolyte path 15, but the outer peripheral edge portion 13a is corrugated. You may use the separator 13 formed in this. That is, you may use the separator 13 whose outer peripheral edge part 13a is a waveform before contact with electrolyte solution.

  In addition, the lithium ion secondary battery 1 of the present embodiment is a stacked battery having a substantially rectangular sheet-like appearance, but may be a wound battery having a cylindrical appearance. However, since the laminated battery has more outer peripheral edge portions 13a of the separator 13 than the wound battery, the number of electrolyte paths 15 formed is likely to increase. Therefore, since the electrolytic solution easily flows into the power generation element 10 through the electrolytic solution path 15, the electrolytic solution inside the power generation element 10 is more difficult to be depleted.

〔Example〕
The following examples illustrate the present invention more specifically. The lithium ion secondary battery (Example) having the same configuration as the lithium ion secondary battery shown in FIGS. 1 to 5 and the outer peripheral edge of an adjacent separator are flat and almost the entire outer peripheral edge is in surface contact. A lithium ion secondary battery (comparative example) in which the electrolyte path was not sufficiently formed was produced. And the cycle test which repeats charging / discharging and measures a capacity | capacitance was done, and the lifetime of the lithium ion secondary battery was evaluated. Below, each raw material and manufacturing method of both lithium ion secondary batteries are demonstrated.

<Production of negative electrode>
Spherical natural graphite powder (average particle size: 20 μm) coated with amorphous carbon as a negative electrode active material, polyvinylidene fluoride as a binder, carbon black as a conductive additive, and a solid content mass ratio of 96 By adding and stirring to N-methyl-2-pyrrolidone (NMP) as a solvent at a ratio of .5: 3: 0.5, these materials were uniformly dispersed in NMP to prepare a slurry. The obtained slurry was applied onto a 10 μm thick copper foil serving as a negative electrode current collector. Next, the slurry was heated at 125 ° C. for 10 minutes to evaporate NMP, thereby forming a negative electrode active material layer. Furthermore, the negative electrode which applied the negative electrode active material layer on the single side | surface of the negative electrode collector was produced by pressing a negative electrode active material layer.

<Preparation of positive electrode>
Li _1.1 Mn _1.9 O ₄ powder (BET specific surface area 0.25 m ² / g) having a spinel structure as a positive electrode active material and lithium / nickel / cobalt / lithium manganate (Ni / Li molar ratio 0.7, BMP specific surface area of 0.5 m ² / g), polyvinylidene fluoride as a binder, and carbon black as a conductive additive, NMP as a solvent in a mass ratio of 69: 23: 4: 4 Added in.

  Furthermore, by adding 0.03 part by mass of succinic anhydride (molecular weight 126) as an organic moisture scavenger to this mixture with respect to 100 parts by mass of the solid content obtained by removing NMP from the above mixture, the mixture was stirred. These materials were uniformly dispersed to prepare a slurry. The obtained slurry was applied onto an aluminum foil having a thickness of 20 μm serving as a positive electrode current collector. Next, the slurry was heated at 125 ° C. for 10 minutes to evaporate NMP, thereby forming a positive electrode active material layer. Furthermore, the positive electrode which applied the positive electrode active material layer on the single side | surface of the positive electrode collector was produced by pressing a positive electrode active material layer.

<Production of lithium ion secondary battery>
The positive electrode produced as described above was cut into a rectangle having a width of 20 cm and a length of 21 cm, and the negative electrode was cut into a rectangle having a width of 21 cm and a length of 22 cm. A portion of 5 cm × 1 cm on one side of the peripheral portion is an active material uncoated portion for connecting a terminal, and the active material layer is the remaining 20 cm × 20 cm in the positive electrode and the remaining 21 cm in the negative electrode. It is formed in a portion of × 21 cm. Of the positive electrode terminal made of aluminum having a width of 5 cm, a length of 3 cm, and a thickness of 0.2 mm, a portion having a length of 1 cm, which is an end, was ultrasonically welded to the positive electrode active material uncoated portion. Similarly, a 1-cm-long portion of the negative electrode terminal made of nickel having the same size as that of the positive electrode terminal was ultrasonically welded to the active material uncoated portion of the negative electrode.

On both sides of a separator made of polyethylene and polypropylene having a square shape of 22 cm on a side, a negative electrode and a positive electrode were arranged so that the active material layers faced each other across the separator to obtain a power generation element. However, the separator used for the lithium ion secondary battery of the example has an elongation of 0.54% when swollen with the electrolyte , and the separator used for the lithium ion secondary battery of the comparative example is the electrolyte. The elongation when swollen is 0.26%.

  Next, two rectangular aluminum laminate films having a width of 24 cm and a length of 25 cm were prepared, and the portions having a width of 5 mm on the three sides excluding one long side thereof were adhered by thermal fusion to form an opening. A bag-shaped laminate outer package having the above was produced. Then, the power generation element was inserted into the laminate outer package so that a gap of 1 cm was formed between one short side of the laminate outer package and the end of the power generation element.

  The electrolytic solution to be injected into the laminate outer package was prepared as follows. A non-aqueous solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 30: 70 (volume ratio) has a concentration of 1.0 mol of lithium hexafluorophosphate as an electrolyte. / L was dissolved. And in this solution, the chain | strand-shaped disulfonic acid ester was dissolved so that a density | concentration might be 0.5 mass% as an additive, and electrolyte solution was prepared.

  This electrolytic solution was injected into the laminate outer package and vacuum treatment was performed to impregnate the negative electrode, the positive electrode, and the separator of the power generation element with the electrolytic solution. In the lithium ion secondary battery of the example, the outer peripheral edge of the separator was deformed due to the impregnation of the electrolytic solution to form a waveform, and a large number of electrolytic solution paths were formed. On the other hand, in the lithium ion secondary battery of the comparative example, even when the electrolyte was impregnated, the outer peripheral edge of the separator was hardly deformed, and the electrolyte path was hardly formed. Then, heat fusion was performed under reduced pressure, and the opening of the laminate outer package was sealed with a width of 5 mm to obtain lithium ion secondary batteries of Examples and Comparative Examples. The capacity of these lithium ion secondary batteries is about 30 Ah.

The lithium ion secondary batteries of Examples and Comparative Examples thus obtained were subjected to a cycle test in which the capacity was measured by repeatedly charging and discharging, and the life of the lithium ion secondary batteries was evaluated. The conditions of the cycle test are as follows.
Constant current and constant voltage charging with current that charges from 0% capacity to 100% capacity in 1 hour and constant current discharge with current that discharges from 100% capacity to 0% capacity in 1 hour under the environment of 25 ° C 1000 cycles were repeated. The voltage of the lithium ion secondary battery when the capacity is 100% is 4.15V. The capacity retention rate due to this charge / discharge was calculated by the following formula: (battery capacity after each cycle) / (initial battery capacity). The results are shown in the graph of FIG.

  As can be seen from the graph of FIG. 6, the lithium ion secondary batteries of the examples had a higher capacity retention rate and a longer life than the lithium ion secondary batteries of the comparative examples. For example, the capacity retention ratio at the time of 700 cycles was 88% for the lithium ion secondary battery of the example and 86% for the lithium ion secondary battery of the comparative example. From this result, it is understood that the lithium ion secondary battery has a long life when the electrolyte path is sufficiently formed in the outer peripheral edge portion of the separator.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Electric power generation element 11 Negative electrode 12 Positive electrode 13 Separator 13a Outer peripheral edge 15 Electrolyte path 30 Exterior body

Claims (6)

A lithium ion secondary battery comprising a power generation element in which a positive electrode and a negative electrode are laminated via a separator, and an electrolyte,
The outer peripheral edge portion of the separator is located outside the outer peripheral edge portions of the positive electrode and the negative electrode, and at least one outer peripheral edge portion of two adjacent separators has a waveform that undulates along the circumferential direction. The outer peripheral edge portions of the adjacent separators are partially in contact with each other, and the region where the positive electrode is disposed and / or the region where the negative electrode is disposed on the separator and the outer peripheral edge portion of the separator. A communicating electrolyte path is formed ,
At least one of the two adjacent separators is a lithium ion secondary battery having an elongation rate of 0.3% or more and 1% or less when swollen with the electrolytic solution . 2. The lithium ion secondary battery according to claim 1, wherein at least one of the separators is obtained by coating a surface of a resin base material with a heat resistant layer. The lithium ion secondary battery according to claim 1, wherein the power generation element has a flat plate shape. The lithium ion secondary battery according to any one of claims 1 to 3 , wherein the power generation element has a capacity of 5 Ah or more and 70 Ah or less. The exterior body wraps the power generation element from above and below in the stacking direction, has a bag shape having a joint portion where ends are joined together, and the joint portion is located at the center in the stacking direction of the power generation element. The lithium ion secondary battery as described in any one of Claims 1-4 . The lithium ion secondary battery according to any one of claims 1 to 5 , wherein the exterior body is formed of a laminate film.

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