JP4707324B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, electronic devices such as mobile communication devices, notebook computers, palmtop computers, integrated video cameras, portable CD (MD) players, cordless telephones, etc. have been reduced in size and weight. As a power source, a battery having a small size and a large capacity is particularly demanded.

  Examples of batteries that are widely used as power sources for these electronic devices include primary batteries such as alkaline manganese batteries, and secondary batteries such as nickel cadmium batteries and lead storage batteries. Among them, the non-aqueous electrolyte secondary battery using a lithium composite oxide for the positive electrode and a carbonaceous material capable of occluding and releasing lithium ions for the negative electrode is small and light, has a high unit cell voltage, and can obtain a high energy density. It is attracting attention.

In Patent Document 1, in a thin non-aqueous electrolyte secondary battery including a container having a thickness of 0.3 mm or less, 15 to 20% by volume of ethylene carbonate, 2 to 35% by volume of propylene carbonate, and 30 to 85% by volume. Although there is a description that when a mixed salt of LiBF ₄ and LiPF ₆ is used in a non-aqueous solvent containing γ-butyrolactone, the charge / discharge cycle life at 45 ° C. is improved, the concentration of each of LiBF ₄ and LiPF ₆ is There is no examination.
JP 2002-15771 A

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery having an improved charge / discharge cycle life.

The nonaqueous electrolyte secondary battery according to the present invention includes an electrode group in which a positive electrode and a negative electrode are wound in a flat shape via a separator, and a positive electrode that is electrically connected to the positive electrode and protrudes from a spiral surface of the electrode group A nonaqueous electrolyte secondary battery comprising a tab, a negative electrode tab electrically connected to the negative electrode and protruding from a spiral surface of the electrode group, and a nonaqueous electrolyte,
The non-aqueous electrolyte comprises 0.001 mol / L to 0.2 mol / L LiBF ₄ , 0.7
mol / L to 1.8 mol / L LiPF ₆ ,
The shortest distance between the positive electrode tab and the negative electrode tab is in the range of 8 mm to 17 mm, and the spiral surface
It is characterized in that the longitudinal width is in the range of 22～65Mm.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having an improved charge / discharge cycle life.

  Hereinafter, the nonaqueous electrolyte secondary battery according to the present invention will be described.

The non-aqueous electrolyte secondary battery includes an electrode group in which a positive electrode and a negative electrode are wound in a flat shape via a separator, a positive electrode tab electrically connected to the positive electrode and protruding from a spiral surface of the electrode group, A non-aqueous electrolyte secondary battery comprising a negative electrode tab electrically connected to the negative electrode and protruding from a spiral surface of the electrode group, and a non-aqueous electrolyte,
The non-aqueous electrolyte includes 0.001 mol / L to 0.2 mol / L LiBF ₄ and 0.7 mol / L to 1.8 mol / L LiPF ₆ .
The shortest distance between the positive electrode tab and the negative electrode tab is in a range of 6 mm to 18 mm.

  The form of the non-aqueous electrolyte secondary battery according to the present invention can be a thin shape exemplified in FIGS. 1 and 2, a square shape exemplified in FIG.

  First, a thin nonaqueous electrolyte secondary battery will be described.

  As shown in FIG. 1, an electrode group 2 is accommodated in a container body 1 having a rectangular cup shape. The electrode group 2 has a structure in which a laminate including a positive electrode 3, a negative electrode 4, and a separator 5 disposed between the positive electrode 3 and the negative electrode 4 is wound into a flat shape. The nonaqueous electrolyte is held in the electrode group 2. A part of the edge of the container body 1 is wide and functions as the lid plate 6. The container body 1 and the cover plate 6 are each composed of a laminate film. The laminate film includes an external protective layer 7, an internal protective layer 8 containing a thermoplastic resin, and a metal layer 9 disposed between the external protective layer 7 and the internal protective layer 8. A lid 6 is fixed to the container body 1 by heat sealing using a thermoplastic resin of the inner protective layer 8, whereby the electrode group 2 is sealed in the container. A positive electrode tab 10 is electrically connected to the positive electrode 3, and a negative electrode tab 11 is electrically connected to the negative electrode 4. The negative electrode tab 11 is drawn out of the container and functions as a positive electrode terminal and a negative electrode terminal.

  In the thin non-aqueous electrolyte secondary battery illustrated in FIGS. 1 and 2, an example using a cup-shaped container has been described, but the shape of the container is not particularly limited, and can be, for example, a bag shape. .

  Next, the prismatic nonaqueous electrolyte secondary battery will be described.

  As shown in FIG. 3, the electrode group 2 is accommodated in a bottomed rectangular cylindrical container 12 made of metal such as aluminum. In the electrode group 2, a positive electrode 3, a separator 5, and a negative electrode 4 are laminated in this order and wound in a flat shape. The spacer 13 having an opening near the center is arranged above the electrode group 2.

  The nonaqueous electrolyte is held in the electrode group 2. A sealing plate 15 having an electrolyte solution inlet 14 and having a circular hole near the center is laser welded to the opening of the container 12. The liquid injection port 14 is sealed with a sealing lid (not shown). The negative electrode terminal 16 is disposed in a circular hole of the sealing plate 15 via a hermetic seal. The negative electrode tab 11 drawn out from the negative electrode 4 is welded to the lower end of the negative electrode terminal 16. On the other hand, a positive electrode tab (not shown) is connected to a container 12 that also serves as a positive electrode terminal.

  An example of the flat electrode group used for this secondary battery is shown in FIGS. 4 to 6, the separator is omitted for easy understanding of the positional relationship between the positive electrode and the negative electrode.

  FIG. 4 is an example of the inner and inner tabs in which both the positive electrode tab 10 and the negative electrode tab 11 are located near the center of the electrode group. The electrode group 2 is produced by winding a flat shape with a separator interposed between the positive electrode 3 and the negative electrode 4, for example. At this time, since the negative electrode 4 is wound before the positive electrode 3, the starting portion of the negative electrode 4 does not face the positive electrode, and it is not necessary to support the negative electrode layer on the starting portion of the negative electrode current collector 30. . The strip-shaped negative electrode tab 11 is welded to the inner surface of the starting portion of the negative electrode current collector 30. The starting part of the positive electrode current collector 31 of the positive electrode 3 is opposed to the starting part of the negative electrode 4 through a separator (not shown), and does not support the charge / discharge reaction, so that the positive electrode layer is not supported. The belt-like positive electrode tab 10 is welded to the inner surface of the starting portion of the positive electrode current collector 31.

  In the negative electrode 4, since only the outer surface faces the positive electrode layer from the beginning of winding to the first round, the negative electrode layer 32 is formed only on the outer surface of the negative electrode current collector 30. Since then, both surfaces are opposed to the positive electrode layer 33, so that the negative electrode layer 32 is formed on both surfaces of the negative electrode current collector 30.

  On the other hand, since both sides of the positive electrode 3 face the negative electrode layer 32 after the beginning of rolling, the positive electrode layer 33 is formed on both surfaces of the positive electrode current collector 31. However, since the outermost periphery of the electrode group 2 is the positive electrode 3 and only the inner surface of the portion constituting the outermost periphery of the electrode group 2 faces the negative electrode layer 32, the positive electrode layer 33 is formed only on the inner surface of the positive electrode current collector 31. Is formed.

  One of the two protective tapes 34 for preventing a short circuit due to the positive electrode tab covers the positive electrode tab 10 welded to the positive electrode current collector 31, and the other is attached to the back side of the welded portion. The outermost peripheral end of the electrode group 2 is fixed to the outermost peripheral surface with a wrapping tape 35. Note that the protective tape 34 and the squeeze tape 35 may be omitted.

  In addition, in FIG. 4 mentioned above, although the example which attached the tab to the starting part of the electrode was demonstrated, the attachment position of the tab in the case of setting it as the structure of an inner / inner tab is not restricted to this. The positive electrode tab 10 can be disposed at an arbitrary position on the inner periphery of the outermost periphery of the positive electrode 3 instead of the starting portion. On the other hand, the negative electrode tab 11 can be arrange | positioned in the arbitrary locations in the inner periphery rather than the periphery located in the outermost part in the negative electrode 4, instead of the starting part.

  5 and 6 are examples of inner and outer tabs in which the positive electrode tab 10 is disposed on the outermost periphery of the electrode group and the negative electrode tab 11 is positioned near the center of the electrode group.

  In FIG. 5, the starting portion of the negative electrode 4 precedes the positive electrode and does not participate in the charge / discharge reaction, so there is no need to form a negative electrode layer. Since the starting portion of the positive electrode 3 facing this also does not participate in the charge / discharge reaction, the positive electrode layer is not formed. In the negative electrode 4, the negative electrode layer 32 is formed only on the outer surface of the negative electrode current collector 30 because only one outer surface of the negative electrode 4 faces the positive electrode layer 33, and thereafter both surfaces are positive electrodes. A negative electrode layer 32 is formed on both surfaces of the negative electrode current collector 30 so as to face the layer 33.

  On the other hand, in the positive electrode 3, the positive electrode layer 33 is formed on both surfaces of the positive electrode current collector 31 because both surfaces of the positive electrode 3 are opposed to the negative electrode layer 32 after the beginning of rolling. However, since only the inner surface faces the negative electrode layer 32 at the outermost periphery, the positive electrode layer 33 is formed only on the inner surface of the positive electrode current collector 31. The strip-shaped positive electrode tab 10 is welded to the inner surface of the end portion of the positive electrode current collector 31. On the other hand, the strip-shaped negative electrode tab 11 is welded to the inner surface of the starting portion of the negative electrode current collector 30. FIG. 5 shows an example of a left-handed / even layer, but FIG. 6 shows an example of a left-handed / odd layer in which the number of times of wrinkles is half that of FIG.

  In FIG. 6, the end portion of the positive electrode current collector 31 and the end portion of the negative electrode current collector 30 are positioned at the rear by a half circumference from FIG. 5. A belt-like positive electrode tab 10 is welded to the inner surface of the end portion of the positive electrode current collector 31. On the other hand, the strip-shaped negative electrode tab 11 is welded to the inner surface of the starting portion of the negative electrode current collector 30.

  5 and 6, the example in which the tab of one electrode is disposed at the end of the electrode and the tab of the other electrode is disposed at the beginning of the electrode has been described. The tab arrangement for configuring is not limited to this. For example, it may be arranged on the outermost circumference of the electrode instead of being arranged at the end of the electrode, or it may be located on the outermost side of the electrode instead of being arranged at the beginning of the electrode. It can arrange | position to the circumference inside the circumference | surroundings to perform.

  In FIGS. 4 to 6 described above, the example in which the outermost periphery of the electrode group is the positive electrode has been described, but the outermost periphery of the electrode group can be the negative electrode. In this case, the negative electrode tab 11 can be disposed at the end of the negative electrode 4 and the positive electrode tab 10 can be disposed at the start of the positive electrode 3. Moreover, it is good also as a separator instead of making the outermost periphery of an electrode group into a positive electrode or a negative electrode.

  In FIGS. 4 to 6 described above, the example in which the positive electrode tab 10 and the negative electrode tab 11 are welded to the positive electrode current collector 31 and the negative electrode current collector 30 has been described. A part of which is partially extended can be used as a positive electrode tab, or a part of the negative electrode current collector 30 can be extended as a negative electrode tab.

  In FIG. 4 to FIG. 6 described above, the inner / inner tab structure and the inner / outer tab structure have been described, but the present invention is not limited to this. For example, the outermost periphery of the electrode group is a positive electrode, a tab is disposed at the end of the positive electrode, and the negative electrode facing this positive electrode and the separator is extended so that the end of the electrode protrudes from the end of the positive electrode. Further, an outer / outer tab structure in which a negative electrode tab is disposed at the end portion of the negative electrode at the end of winding may be employed. In the outer / outer tab structure, the outermost periphery of the electrode group is the negative electrode, the negative electrode tab is disposed at the end of the negative electrode, and the positive electrode tab is disposed at the end of the positive electrode facing the outermost negative electrode. It is also possible to do.

  The positive electrode tab 10 can be formed from aluminum, stainless steel, or nickel, for example. On the other hand, the negative electrode tab 11 can be formed from nickel, copper, or stainless steel, for example.

  The shortest distance D between the positive electrode tab 10 and the negative electrode tab 11 is preferably in the range of 6 mm to 18 mm. This is due to the reason explained below. The positive electrode tab 10 and the negative electrode tab 11 are, for example, heat sealed in a state of being sandwiched between films in the case of a laminate film container, and welded to the inner surface of the container in the case of a metal container. Since it is fixed to the container and is made of metal and has rigidity, expansion and contraction due to charging / discharging of the positive electrode and the negative electrode can be regulated. When the shortest distance D is less than 6 mm, the stress generated by the expansion / contraction is not uniform because it is close to the state where the expansion / contraction of the electrode is regulated by one tab rather than by two tabs. As a result, the electrolyte is unevenly distributed, charging / discharging reaction spots increase, and the charge / discharge cycle life is shortened. On the other hand, if the shortest distance D exceeds 18 mm, the expansion / contraction associated with the charge / discharge reaction of the positive and negative electrodes located between the positive electrode tab and the negative electrode tab cannot be regulated by the tab and becomes large. Therefore, charge / discharge reaction spots increase, and the charge / discharge cycle life is reduced. A more preferable range of the shortest distance D is 8 mm to 17 mm, and a most preferable range is 10 mm to 16 mm.

  In order to more evenly diffuse the stress generated by the expansion / contraction of the electrode group, it is preferable that the longitudinal width L (shown in FIG. 4) of the spiral surface of the electrode group 2 be in the range of 22 to 65 mm. This is because, even if the longitudinal width L of the spiral surface is long or short, the stress is biased and easily diffuses. A more desirable range is 22 to 55 mm, and a further preferred range is 22 to 45 mm.

  The width of the positive electrode tab 10 (the width on the short side) and the width of the negative electrode tab 11 (the width on the short side) are preferably in the range of 2 mm to 5 mm, respectively. Moreover, when providing the positive electrode tab 10 separately from the positive electrode collector 31 and integrating these by welding etc., the thickness of the positive electrode tab 10 can be made into the range of 40 micrometers-150 micrometers. When a part of the positive electrode current collector 31 is used as the positive electrode tab 10, the thickness of the positive electrode tab 10 is naturally equal to the thickness of the positive electrode current collector 31. The thickness of the positive electrode current collector 31 can be, for example, in the range of 5 μm to 20 μm.

  On the other hand, when the negative electrode tab 11 is provided separately from the negative electrode current collector 30 and integrated by welding or the like, the thickness of the negative electrode tab 11 can be in the range of 40 μm to 150 μm. When a part of the negative electrode current collector 30 is used as the negative electrode tab 11, the thickness of the negative electrode tab 11 is naturally equal to the thickness of the negative electrode current collector 30. The thickness of the negative electrode current collector 30 can be, for example, in the range of 5 μm to 20 μm.

  Hereinafter, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte, and the container will be described.

1) Positive electrode The positive electrode includes a current collector and a positive electrode layer that is supported on one or both surfaces of the current collector and includes an active material.

  The positive electrode layer preferably further includes a binder and a conductive agent.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and lithium. Examples thereof include vanadium oxide and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, when a lithium-containing cobalt oxide (for example, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ) is used. This is preferable because a high voltage can be obtained. As the positive electrode active material, one kind of oxide may be used alone, or two or more kinds of oxides may be mixed and used.

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethersulfone, ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). be able to.

  The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 85 to 98% by weight of the positive electrode active material, 1 to 10% by weight of the conductive agent, and 1 to 5% by weight of the binder.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel.

  The positive electrode is produced, for example, by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, drying it, and pressing it.

2) Negative electrode The negative electrode includes a current collector and a negative electrode layer supported on one side or both sides of the current collector.

  The negative electrode layer preferably contains a carbonaceous material that absorbs and releases lithium ions and a binder.

Examples of the carbonaceous material include graphite materials, carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic vapor phase carbonaceous material, and resin fired body; thermosetting resin, isotropic pitch, mesophase pitch, and the like. Graphite material or carbonaceous material obtained by heat-treating carbon-based carbon, mesophase pitch-based carbon fiber, mesophase microspheres, etc. at 500 to 3000 ° C .; a carbon layer having a surface of the graphite material particles having lower crystallinity than the particles Can be mentioned. Among them, it is preferable to use a graphite material having a graphite crystal having a (002) plane spacing _d002 of 0.34 nm or less. A nonaqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can greatly improve battery capacity and large current discharge characteristics. More preferably, the surface interval _d002 is 0.337 nm or less.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene - propylene - diene copolymer (EPDM), styrene - butadiene rubber (SBR), and carboxymethyl cellulose (CMC) Can be used.

  The blending ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 10% by weight of the binder.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel.

  The negative electrode is, for example, kneaded with a carbonaceous material that occludes / releases lithium ions and a binder in the presence of a solvent, and the resulting suspension is applied to a current collector and dried, followed by a desired pressure. It is produced by pressing once or multistage pressing 2-5 times.

3) Separator As this separator, a microporous film, a woven fabric, a non-woven fabric, a laminate of the same material or different materials among these can be used. Examples of the material for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-butene copolymer. As a material for forming the separator, one type or two or more types selected from the types described above can be used.

  The thickness of the separator is preferably 30 μm or less, and more preferably 25 μm or less. Moreover, it is preferable that the lower limit of thickness is 5 micrometers, and a more preferable lower limit is 8 micrometers.

  The separator preferably has a heat shrinkage rate of 20% or less at 120 ° C. for 1 hour. The heat shrinkage rate is more preferably 15% or less.

  The separator preferably has a porosity in the range of 30 to 60%. A more preferable range of the porosity is 35 to 50%.

The separator is preferably air permeability of 600 sec / 100 cm ³ or less. The air permeability means time (seconds) required for 100 cm ³ of air to pass through the separator. The upper limit of the air permeability is more preferably to 500 seconds / 100 cm ^3. The lower limit value of the air permeability is preferably 50 seconds / 100 cm ^3, and a more preferable lower limit value is 80 seconds / 100 cm ³ .

  The width of the separator is desirably wider than the width of the positive electrode and the negative electrode. By adopting such a configuration, it is possible to prevent the positive electrode and the negative electrode from coming into direct contact without a separator.

4) Non-aqueous electrolyte As the non-aqueous electrolyte, one having a substantially liquid or gel form can be used.

  The nonaqueous electrolyte is prepared, for example, by the method described in (I) to (IV) below.

  (I) A nonaqueous electrolyte is obtained by dissolving an electrolyte (for example, lithium salt) in a nonaqueous solvent (liquid nonaqueous electrolyte).

  (II) An organic polymer compound and a lithium salt are dissolved in a solvent to prepare a polymer solution. Next, this polymer solution is applied or impregnated into an electrode (at least one of a positive electrode and a negative electrode), a separator, or both an electrode and a separator, and the solvent is evaporated to cast. Next, an electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. This is accommodated in a container, a non-aqueous electrolyte is injected, and this is held by a cast polymer film, thereby obtaining a secondary battery including a gel-like non-aqueous electrolyte.

  (III) In the method (II) described above, a crosslinked polymer may be used instead of the organic polymer compound. For example, (a) a prepolymer solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and a solvent, and this is used as an electrode (at least one of a positive electrode and a negative electrode), a separator, or an electrode and a separator. After applying or impregnating both, the compound having a crosslinkable functional group is crosslinked. Next, an electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. The crosslinking step may be performed before or after the solvent is volatilized, and may be crosslinked while the solvent is volatilized in the case of crosslinking by heating. Alternatively, (b) after applying or impregnating the prepolymer solution to the electrode (at least one of the positive electrode and the negative electrode), the separator, or both of the electrode and the separator, the positive electrode and the negative electrode are interposed between them. An electrode group is obtained. Thereafter, a crosslinking step can be performed.

  The method for crosslinking is not particularly limited, but heat polymerization or photopolymerization with ultraviolet rays is preferable from the viewpoint of simplicity of the apparatus and cost. When crosslinking is performed by heating or ultraviolet irradiation, it is necessary to add a polymerization initiator suitable for the polymerization method to the prepolymer solution. Moreover, a polymerization initiator is not restricted to one type, You may mix and use 2 or more types.

  (IV) An organic polymer compound and a lithium salt are directly dissolved in a nonaqueous solvent to obtain a gel electrolyte. This gel electrolyte is applied or impregnated into an electrode (at least one of a positive electrode and a negative electrode), a separator, or both of the electrode and the separator, and subsequently, a separator is interposed between the positive electrode and the negative electrode to obtain an electrode group. Thus, a secondary battery provided with a gel-like nonaqueous electrolyte is obtained.

  (V) In the method (IV) described above, a crosslinked polymer can be used instead of the organic polymer compound. For example, a pregel solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and a nonaqueous solvent, and this is applied to an electrode (at least one of a positive electrode and a negative electrode), a separator, or both an electrode and a separator. After application or impregnation, the compound having a crosslinkable functional group is crosslinked. This crosslinking step may be performed before or after the electrode group is manufactured.

  The method for crosslinking is not particularly limited, and examples thereof include those described in the above (III).

  (VI) An electrode group in which a separator is interposed between a positive electrode and a negative electrode is accommodated in a container. Next, after impregnating the electrode group with the above-described gel-like nonaqueous electrolyte (IV), the container is sealed to obtain a secondary battery including the gel-like nonaqueous electrolyte. Alternatively, after the electrode group is impregnated with the pregel solution of (V), the pregel solution is crosslinked before or after sealing the container to obtain a secondary battery having a gel-like nonaqueous electrolyte.

  Examples of the organic polymer compound in (II) and (IV) described above include polymers having a backbone of alkylene oxide such as polyethylene oxide and polypropylene oxide or derivatives thereof; vinylidene fluoride, propylene hexafluoride, tetrafluoroethylene , Perfluoroalkyl vinyl ether, or a copolymer thereof; a polyacrylate polymer having polyacrylonitrile or polyacrylonitrile as a main component and a copolymer of methyl acrylate, vinyl pyrrolidone, vinyl acetate, etc .; polyether polymer Polycarbonate polymer; polyacrylonitrile polymer; polyethylene terephthalate, polybutylene terephthalate or their derivatives as the backbone, ethyl methacrylate, styrene, vinyl acetate, etc. A polyester-based polymer that is a copolymer with the above; a fluororesin; a polyolefin-based resin; a polyether-based resin; and a copolymer composed of two or more of these; Further, a prepolymer solution (III) and a pregel solution (V) can be prepared from monomers and oligomers which are precursors of these polymers.

  Next, the nonaqueous solvent and the electrolyte contained in the liquid nonaqueous electrolyte and the gel nonaqueous electrolyte will be described.

The electrolyte contains 0.001 mol / L to 0.2 mol / L LiBF ₄ and 0.7 mol / L to 1.8 mol / L LiPF ₆ .

The concentration of LiBF ₄ to define the ranges are the reasons described below. When the concentration of LiBF ₄ exceeds 0.2 mol / L, a rapid capacity drop occurs in the latter stage of the charge / discharge cycle, and the charge / discharge cycle life is shortened. By setting the concentration of LiBF ₄ to 0.2 mol / L or less, it is possible to suppress a decrease in capacity in the latter stage of the charge / discharge cycle and to improve the charge / discharge cycle life. The concentration of LiBF ₄ is desirably 0.15 mol / L or less, and a more preferable range is 0.13 mol / L or less. However, when the concentration of LiBF ₄ was less than 0.001 mol / L, the effect of improving the charge / discharge cycle life was not observed. In order to obtain a sufficient effect, the lower limit of the concentration of LiBF ₄ is preferably 0.005 mol / L or more, and more preferably 0.01 mol / L or more.

The concentration of LiPF ₆ to define the ranges are the reasons described below. When the LiPF ₆ concentration is less than 0.7 mol / L, not only the charge / discharge cycle life is not improved, but also the low-temperature discharge characteristics are deteriorated. In order to sufficiently obtain the effect of improving the charge / discharge cycle life, it is more preferable to set the concentration of LiPF ₆ to 0.8 mol / L or more, but if the concentration of LiPF ₆ exceeds 1.8 mol / L, Since there is a possibility that safety may be lowered, the upper limit of the concentration of LiPF ₆ is desirably 1.8 mol / L. A more preferred range is 1.6 mol / L or less, a further preferred range is 1.3 mol / L or less, and a most preferred range is 1.2 mol / L or less.

The total concentration of LiBF ₄ and LiPF ₆ is preferably 0.7-2 mol / L. A more preferable range is 0.8 to 1.6 mol / L.

  Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, sultone compounds (sultone compounds having at least one double bond in the ring, 1,3-propane sultone (PS), etc.), vinylene carbonate (VC), Vinylethylene carbonate (VEC), phenylethylene carbonate (phEC), γ-butyrolactone (GBL), γ-valerolactone (VL), methyl propionate (MP), ethyl propionate (EP), 2-methylfuran (2Me- F), furan (F), thiophene (TIOP), catechol carbonate (CATC), ethylene sulfite (ES), 12-crown-4 (Crown), tetraethylene glycol dimethyl ether (Ether), cyclohexylbenzene (CHB), 2 , 4-Diff Examples include Luoloanisole (DFA). The type of the other solvent can be one type or two or more types.

  Examples of the composition of the non-aqueous solvent include those containing a cyclic carbonate and a chain carbonate, and those containing a cyclic carbonate and GBL. Examples of the cyclic carbonate include ethylene carbonate (EC) and propylene carbonate (PC). The chain carbonate preferably contains methyl ethyl carbonate (MEC), and only MEC may be used as the chain carbonate, or other chain carbonate may be used in combination with MEC. The other chain carbonate is preferably at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC).

  In a non-aqueous solvent containing EC and a chain carbonate, the EC content in the non-aqueous solvent is 25% by volume to 50% by volume, and the chain carbonate content is 40% by volume to 80% by volume. Is desirable. Thereby, a long charge / discharge cycle life can be obtained. A more preferable range of the EC content is 25% to 45% by volume. On the other hand, the more preferable range of the chain carbonate content is 50% by volume to 80% by volume, and the more preferable range is 55% by volume to 75% by volume.

  Moreover, when adding GBL to a nonaqueous solvent, it is preferable that content of GBL in a nonaqueous solvent shall be 10 volume% or less. This is because when the GBL content exceeds 10% by volume, the cycle life may not be improved by using the mixed salt. A more preferable range is 0.1 to 10% by volume, and a further preferable range is 0.5 to 8% by volume.

  In order to further improve the cycle life, it is desirable to add at least one selected from the group consisting of VC, VEC and a sultone compound having at least one double bond in the ring in a non-aqueous solvent. The ratio of these additive components is preferably 10% by volume or less. This is because if the ratio of the additive component exceeds 10% volume, a long charge / discharge cycle life may not be obtained. The cause of the decrease in the cycle life is that the sultone compound causes the electrode and the separator to be in close contact with each other so as to prevent the diffusion of stress caused by expansion / contraction due to charge / discharge, or the resistance increases due to film formation by VC or VEC. For example, the charge / discharge reaction occurs non-uniformly, and the stress generated by the expansion and contraction is biased. The ratio of the additive component is more preferably 4% volume or less. In addition, in order to obtain a sufficient cycle life improvement effect, it is desirable to ensure a ratio of the additive component of at least 0.01% by volume. Furthermore, if the ratio of the additive component is 0.1% by volume or more, a sufficient cycle life can be exhibited even at a higher temperature such as 60 ° C.

  When both VC and VEC are used as additive components, the total volume of VEC and VC in the non-aqueous solvent is desirably 6% by volume or less, and a more preferable range is 4% by volume or less. At this time, the ratio of VEC to the total volume of the non-aqueous solvent is desirably 0.05 to 2% by volume, and more preferably 0.1 to 2% by volume. Furthermore, the ratio of VC with respect to the total volume of the nonaqueous solvent is desirably 0.05% by volume or more, and a more preferable range is 0.1% by volume or more.

The sultone compound having at least one double bond in the ring is a sultone compound A represented by the general formula shown in the following chemical formula 1, or a sultone compound in which at least one H of the sultone compound A is substituted with a hydrocarbon group B can be used. In the present application, sultone compound A or sultone compound B may be used alone, or both sultone compound A and sultone compound B may be used.

In Chemical Formula 1, C _m H _n is a linear hydrocarbon group, and m and n are integers of 2 or more that satisfy 2m> n.

  Since a sultone compound having at least one double bond in the ring opens a double bond by reaction with the negative electrode to cause a polymerization reaction, a lithium ion-permeable protective film can be formed on the negative electrode surface. Among the sultone compounds, a compound in which sultone compound A has m = 3 and n = 4, that is, 1,3-propene sultone (PRS), or a compound in which m = 4 and n = 6, that is, 1 , 4-butylene sultone (BTS). As the sultone compound, 1,3-propene sultone (PRS) or 1,4-butylene sultone (BTS) may be used alone, or these PRS and BTS may be used in combination.

  The liquid non-aqueous electrolyte preferably contains a surfactant such as trioctyl phosphate (TOP) in order to improve the wettability with the separator. The addition amount of the surfactant is preferably 3% or less, and more preferably in the range of 0.1 to 1%.

  The amount of the liquid non-aqueous electrolyte is preferably 0.15 to 0.55 g per 100 mAh of battery unit capacity. A more preferable range of the liquid nonaqueous electrolytic mass is 0.2 to 0.5 g / 100 mAh.

5) Container (storage container)
The shape of the container can be, for example, a bottomed rectangular tube shape, a bag shape, or a cup shape as described above.

  This container can be formed from, for example, a sheet including a resin layer, a metal plate, a metal film, or the like.

  The resin layer contained in the sheet can be formed from, for example, polyolefin (for example, polyethylene, polypropylene), polyamide or the like. The sheet may be composed of only one type or two or more types of resin layers, but may include a metal layer. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel.

  The metal plate and the metal film can be formed of, for example, iron, stainless steel, or aluminum.

  When forming a container with a sheet including a resin layer, the thickness of the sheet is desirably 0.3 mm or less, a more preferable range is 0.25 mm or less, a further preferable range is 0.15 mm or less, and the most preferable range. Is 0.12 mm or less. Further, from the viewpoint of securing the strength of the container, the lower limit value of the sheet thickness is preferably 0.05 mm.

  When forming a container from aluminum, it is preferable that the plate | board thickness of the wide surface among container side surfaces shall be 0.4 mm or less, a more preferable range is 0.3 mm or less, and a more preferable range is 0.25 mm or less. . Moreover, in order to ensure the strength of the container, it is desirable to set the lower limit value of the plate thickness of the wide surface to 0.1 mm, and a more desirable lower limit value is 0.15 mm.

As a result of intensive studies, the present inventors have determined that in a secondary battery including a flat electrode group, the shortest distance between the positive electrode tab and the negative electrode tab is 6 to 18 mm, and the LiBF ₄ concentration in the nonaqueous electrolyte is 0.001 mol / By setting the LiPF ₆ concentration to 0.7 mol / L to 1.8 mol / L in addition to L to 0.2 mol / L, capacity reduction in the latter stage of the charge / discharge cycle is suppressed, and the charge / discharge cycle life is improved. Was found. The mechanism by which the effect of the present invention is obtained is not clear, but the bias when the stress generated by the expansion / contraction associated with charging / discharging of the flat electrode group is diffused by the shortest tab distance being within the above-described range. It is presumed to be related that the strain was relaxed and the distortion of the electrode group was reduced.

[Example]
Hereinafter, detailed description of the embodiments of the present invention with reference to the drawings mentioned above.

Example 1
<Preparation of positive electrode>
First, 90% by weight of lithium cobalt oxide (Li _x CoO ₂ ; X is 0 <X ≦ 1) powder, 5% by weight of acetylene black, and 5% by weight of polyvinylidene fluoride (PVdF) dimethylformamide (DMF) solution was added and mixed to prepare a slurry. A structure in which the positive electrode layer is supported on both surfaces of the current collector by applying the slurry to both surfaces of a current collector made of aluminum foil having a thickness of 15 μm, excluding the positive electrode tab welds, and then drying and pressing. A positive electrode was prepared. It should be noted that the thickness of the positive electrode layer was a single-sided per 60μm.

<Production of negative electrode>
As a carbonaceous material, 95% by weight of powder of mesophase pitch-based carbon fiber (having a (002) plane interval (d ₀₀₂ ) of 0.336 nm determined by powder X-ray diffraction) heat-treated at 3000 ° C. and polyvinylidene fluoride ( (PVdF) 5% by weight dimethylformamide (DMF) solution was mixed to prepare a slurry. The slurry was applied to both sides of a current collector made of copper foil having a thickness of 12 μm, excluding the negative electrode tab welds, dried, and pressed to form a negative electrode having a structure in which the negative electrode layer was supported on the current collector. Produced. It should be noted that the thickness of the negative electrode layer was a single-sided per 55μm.

The surface spacing d ₀₀₂ of (002) plane of the carbonaceous material were respectively determined by the powder X-ray diffraction spectrum half width midpoint method. At this time, scattering correction such as Lorentz scattering was not performed.

<Separator>
Thickness was prepared separator made of a microporous polyethylene membrane of 25 [mu] m.

<Preparation of liquid nonaqueous electrolyte (nonaqueous electrolyte)>
A nonaqueous solvent was prepared by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) so that the volume ratio (EC: MEC) was a value shown in Table 1 below. A liquid nonaqueous electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) in the obtained nonaqueous solvent so that the concentrations thereof are as shown in Table 1 below. Was prepared.

<Production of electrode group>
A positive electrode tab made of a strip-shaped aluminum foil (thickness 100 μm, width 4 mm on the short side) is ultrasonically welded to the uncoated portion of the positive electrode current collector, and a strip shape is formed on the uncoated portion of the negative electrode current collector. After ultrasonic welding a negative electrode tab made of nickel foil (thickness: 100 μm, short side width: 4 mm), the positive electrode and the negative electrode are wound in a spiral shape through the separator therebetween, and then flattened. molded, to prepare an electrode group having an inner in the tab structure shown in FIG. 4 described above. In the obtained electrode group, the shortest distance D between the positive electrode tab and the negative electrode tab was 14 mm. The longitudinal width L of the spiral surface of the electrode group 2 was 32 mm.

  An aluminum sheet having a thickness of 250 μm was formed into a rectangular can having a thickness of 4 mm, a width of 34 mm, and a height of 43 mm, and the electrode group was housed in the obtained container.

  Subsequently, the electrode group in the container was vacuum dried at 80 ° C. for 12 hours to remove moisture adsorbed on the electrode group and the aluminum can.

  By injecting the liquid non-aqueous electrolyte into the electrode group in the container so that the amount per battery capacity of 1 Ah is 3 g and sealing, the rectangular non-aqueous electrolyte secondary battery having the structure shown in FIG. Assembled.

(Example 2 12,14～19,21～ 25 and Reference Examples 13, 20)
Except for setting the composition of the non-aqueous solvent, the concentration of the electrolyte, and the shortest distance D between the positive electrode tab and the negative electrode tab as shown in Tables 1 and 2 below, the same as described in Example 1 above. A rectangular nonaqueous electrolyte secondary battery was assembled.

(Example 26)
A laminate film having a thickness of 100 μm in which both surfaces of an aluminum foil were covered with polyethylene was formed into a rectangular cup shape by a press machine, and the same electrode group as described in Example 1 was accommodated in the obtained container.

  Next, the electrode group in the container was vacuum dried at 80 ° C. for 12 hours to remove moisture contained in the electrode group and the laminate film.

  A liquid non-aqueous electrolyte similar to that described in Example 1 was injected into the electrode group in the container so that the amount per battery capacity 1 Ah was 4.8 g, sealed by heat sealing, and then the above-described FIG. 2, a thin nonaqueous electrolyte secondary battery having a thickness of 3.6 mm, a width of 35 mm, and a height of 62 mm was assembled.

(Example 27)
A thin nonaqueous electrolyte secondary battery was assembled in the same manner as described in Example 26 except that the composition of the nonaqueous solvent was set as shown in Table 2 below.

(Examples 28 to 38)
Except for setting the composition of the nonaqueous solvent, the electrolyte concentration, and the shortest distance D between the positive electrode tab and the negative electrode tab as shown in Tables 2 to 3 below, the same as described in Example 1 above. A prismatic nonaqueous electrolyte secondary battery was assembled.

(Example 39)
As shown in FIG. 5, the positive electrode tab is disposed at the end of the positive electrode and the negative electrode tab is disposed at the start of the negative electrode, as described in the first embodiment. A prismatic nonaqueous electrolyte secondary battery was assembled.

(Example 40)
As described above with reference to FIG. 6, except that the positive electrode tab is disposed at the end of the positive electrode, the negative electrode tab is disposed at the start of the negative electrode, and the number of times of winding is increased by a half of that in Example 38, A square nonaqueous electrolyte secondary battery was assembled in the same manner as described in Example 1 above.

(Comparative Examples 1-9)
Except that the composition of the nonaqueous solvent, the type and concentration of the electrolyte, and the shortest distance D between the positive electrode tab and the negative electrode tab are set as shown in Table 4 below, the same as described in Example 1 above. A rectangular nonaqueous electrolyte secondary battery was assembled.

(Comparative Example 10)
A thin nonaqueous electrolyte secondary battery was assembled in the same manner as described in Example 26 described above except that LiBF ₄ was not added.

For the obtained secondary batteries of Examples 1 to 12, 14 to 19, 21 to 40, Reference Examples 13 and 20, and Comparative Examples 1 to 10, the capacity retention rate at 500 cycles was measured by the method described below. The results are shown in Tables 1 to 4 below.

  Each secondary battery was subjected to constant current / constant voltage charging to 0.2 V at 0.2 C at room temperature for 10 hours as an initial charge / discharge process, and then discharged to 3.0 V at 0.2 C at room temperature.

  Next, a charge / discharge cycle in which a constant current and constant voltage charge at a charge rate of 1.0 C and a charge end voltage of 4.2 V is performed for 3 hours and then discharged to 1.0 V at 1.0 C is repeated at 20 ° C. The discharge capacity at the cycle was measured, the discharge capacity at the first cycle was taken as 100%, the capacity retention rate at 500 cycles was calculated, and the results are shown in Tables 1 to 4 below.

  Here, 1C is a current value necessary for discharging the nominal capacity (Ah) in one hour.

  In Table 1 to Table 4, EC is ethylene carbonate, MEC methyl ethyl carbonate, DEC diethyl carbonate, DMC dimethyl carbonate, GBL is γ- butyrolactone, PC propylene carbonate, VC is vinylene carbonate, VEC vinyl ethylene Carbonate and PRS represent 1,3-propene sultone.

As is clear from Tables 1 to 4, the secondary batteries of Examples 1 to 12, 14 to 19 , 21 to 40 have a capacity maintenance rate at 500 cycles as compared with the secondary batteries of Comparative Examples 1 to 10. it was high.

In Comparative Examples 1 and 10, LiBF ₄ is not added. In Comparative Example 4, the LiBF ₄ concentration exceeds 0.2 mol / L. In Comparative Examples 2 and 3, the shortest tab distance is 6 mm to 18 mm. Since the LiPF ₆ concentration was out of the range of 0.7 to 1.8 mol / L in Comparative Examples 5 and 6, the capacity retention rate at 500 cycles was low. Further, from the comparison between Examples 26 to 27 and Comparative Example 10, it is possible to obtain the same effect as in the case of a rectangular battery even in a thin secondary battery that uses a laminate film container instead of a rectangular metal container. Recognize.

By comparing the results of Examples 1 to 12, with respect to the LiBF ₄ concentration, the capacity retention rate is higher when the concentration is 0.005 to 0.15 mol / L, and is further improved when the upper limit is 0.13 mol / L. I understood it.

Further, by comparing the results of Examples 14 to 19 and Reference Examples 13 and 20 , with regard to the shortest tab distance, a higher capacity retention rate is obtained when the distance is 8 to 17 mm, and is further increased when the distance is 10 to 16 mm. I understood it.

On the other hand, from Examples 21 to 25, regarding the LiPF ₆ concentration, when the lower limit value is set to 0.8 mol / L, the capacity retention rate is further increased, and on the other hand, the upper limit value is preferably set to 1.6 mol / L. Further, it was found that 1.3 mol / L is more preferable.

  Furthermore, not only the inner and inner tabs as in the first embodiment but also the inner and outer tabs as in the 39th and 40th embodiments, the capacity maintenance rate could be improved.

  In addition, when the cylindrical nonaqueous electrolyte secondary battery was prepared as the comparative examples 11 and 12, and the charge / discharge cycle test was performed, the following results were obtained.

(Comparative Example 11)
A positive electrode, a negative electrode, and a separator similar to those described in Example 1 were prepared, and a cylindrical electrode group was produced by winding in a spiral with a separator interposed between the positive electrode and the negative electrode.

  After housing the electrode group in a metal cylindrical container that also serves as the negative electrode terminal, a liquid nonaqueous electrolyte similar to that described in Example 1 was injected. Next, the positive electrode tab drawn out from the upper surface of the electrode group was welded to the inner surface of the lid that also serves as the positive electrode terminal. In addition, about the conduction | electrical_connection of a negative electrode, it ensured by making the outermost periphery of an electrode group into a negative electrode, and making it contact with the container inner surface. Subsequently, a cylindrical nonaqueous electrolyte secondary battery of 18650 size (diameter: 18 mm, height: 65 mm) was assembled by performing a sealing treatment.

(Comparative Example 12)
A cylindrical nonaqueous electrolyte secondary battery having the same configuration as that described in Comparative Example 11 was assembled except that the composition of the liquid nonaqueous electrolyte was changed to the same as that in Comparative Example 4 described above.

  The obtained cylindrical secondary batteries of Comparative Examples 11 and 12 were subjected to constant current / constant voltage charging for 10 hours up to 4.2 V at 0.2 C at room temperature as the initial charge / discharge process, and then 0.2 C at room temperature. Was discharged to 3.0V.

Next, a charge / discharge cycle in which a constant current and constant voltage charge at a charge rate of 1.0 C and a charge end voltage of 4.2 V is performed for 3 hours and then discharged to 1.0 V at 1.0 C is repeated at 20 ° C. When the discharge capacity at the cycle was measured and the capacity maintenance rate at 500 cycles was calculated with the discharge capacity at the first cycle as 100%, the secondary battery of Comparative Example 11 having a LiBF ₄ concentration of 0.05 mol / L was 40. In contrast, the secondary battery of Comparative Example 12 having a LiBF ₄ concentration of 0.25 mol / L was 80%. From this, it became clear that in the secondary battery using the cylindrical electrode group, when the LiBF ₄ concentration is 0.2 mol / L or less, the charge / discharge cycle life is decreased. Although the mechanism for obtaining such a result is not clear, it is presumed as follows.

In other words, in a secondary battery using a cylindrical electrode group, the stress generated by the expansion / contraction of the electrode accompanying charge / discharge is easily diffused due to the shape of the electrode group. It is assumed that the cause is not the distortion of the electrode group but the uneven distribution of the lithium salt caused by the large movement of the liquid nonaqueous electrolyte accompanying expansion / contraction. LiPF ₆ is likely to be unevenly distributed when the movement of the liquid non-aqueous electrolyte during expansion / contraction is severe, and by adding more than 0.2 mol / L of LiBF ₄ , which has a lower diffusion rate than LiPF ₆ , a lithium salt It can be considered that the uneven distribution of water is mitigated and the charge / discharge cycle life is improved.

(VEC detection method)
For the secondary battery of Example 30, after the initial charge / discharge step, the circuit was opened for 5 hours or more to sufficiently settle the potential, and then the Ar concentration was 99.9% or more and the dew point was −50 ° C. or less. It decomposed | disassembled in the glove box and took out the electrode group. The electrode group was put in a centrifuge tube, dimethyl sulfoxide (DMSO) -d ₆ was added and sealed, removed from the glove box, and centrifuged. Thereafter, a mixed solution of the electrolytic solution and the DMSO-d ₆ was collected from the centrifuge tube in the glove box. The mixed solvent was placed about 0.5ml to NMR sample tube of 5 mm.phi, was subjected to NMR measurement. The apparatus used for the NMR measurement is JNM-LA400WB manufactured by JEOL Ltd., the observation nucleus is ¹ H, the observation frequency is 400 MHz, and the residual proton signal slightly contained in dimethyl sulfoxide (DMSO) -d ₆ is used as an internal reference. (2.5 ppm). The measurement temperature was 25 ° C. ^{In the 1} HNMR spectrum, a peak corresponding to EC is observed at around 4.5 ppm, and a peak corresponding to VEC is observed at around 5.2, 5.4, 6 ppm, and is present in the secondary battery of Example 30 after the initial charge / discharge process. It was confirmed that VEC was contained in the non-aqueous solvent. Further, when the ratio of the VEC NMR integrated intensity to the EC NMR integrated intensity was determined, it was found that the ratio of VEC to the entire non-aqueous solvent was reduced from before the secondary battery assembly. The ¹ HNMR spectrum of the non-aqueous electrolyte used in Example 30 with reference shown in Fig.

(PRS and VC detection method)
Further, with respect to the secondary battery of Example 35, after the initial charge / discharge step, the circuit was opened for 5 hours or more to sufficiently settle the potential, and then the Ar concentration was 99.9% or more and the dew point was −50 ° C. It decomposed | disassembled in the following glove boxes and took out the electrode group. The electrode group was put in a centrifuge tube, dimethyl sulfoxide (DMSO) -d ₆ was added and sealed, removed from the glove box, and centrifuged. Thereafter, a mixed solution of the electrolytic solution and the DMSO-d ₆ was collected from the centrifuge tube in the glove box. The mixed solvent was placed about 0.5ml to NMR sample tube of 5 mm.phi, was subjected to NMR measurement. The apparatus used for the NMR measurement is JNM-LA400WB manufactured by JEOL Ltd., the observation nucleus is ¹ H, the observation frequency is 400 MHz, and the residual proton signal slightly contained in dimethyl sulfoxide (DMSO) -d ₆ is used as an internal reference. (2.5 ppm). The measurement temperature was 25 ° C. ^{In the 1} HNMR spectrum, a peak corresponding to EC was observed near 4.5 ppm, and a peak corresponding to VC was observed near 7.7 ppm. On the other hand, peaks corresponding to PRS were observed in the vicinity of 5.1 ppm (P ₁ ), 7.05 ppm (P ₂ ), and 7.2 ppm (P ₃ ) as shown in the spectrum of FIG. From these results, it was confirmed that VC and PRS were contained in the nonaqueous solvent present in the secondary battery of Example 35 after the initial charge / discharge step.

Further, when ¹³ CNMR measurement was performed with an observation frequency of 100 MHz and dimethyl sulfoxide (DMSO) -d ₆ (39.5 ppm) as an internal reference substance, a peak corresponding to EC was around 66 ppm, and a peak corresponding to VC was 133 ppm. In the vicinity, peaks corresponding to PRS were observed at around 74 ppm, around 124 ppm and around 140 ppm. From this result as well, VC and PRS were found in the nonaqueous solvent present in the secondary battery of Example 35 after the initial charge / discharge process. It was confirmed that it was included.

Further, in the ¹ H NMR spectrum, the ratio of the NMR integrated intensity of the VC to the NMR integrated intensity of the EC and the ratio of the NMR integrated intensity of the PRS to the NMR integrated intensity of the EC were determined. It was confirmed that the ratios of both were lower than before the secondary battery assembly.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view which shows the thin nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery concerning this invention. The fragmentary sectional view which cut | disconnected the thin nonaqueous electrolyte secondary battery of FIG. 1 along the II-II line. The partial notch perspective view which shows the square nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery which concerns on this invention. FIG. 4 is a cross-sectional view illustrating an example of an electrode group used in the nonaqueous electrolyte secondary battery in FIG. 1 or FIG. 3. FIG. 4 is a cross-sectional view showing another example of an electrode group used in the nonaqueous electrolyte secondary battery in FIG. 1 or FIG. 3. FIG. 4 is a cross-sectional view showing still another example of an electrode group used in the nonaqueous electrolyte secondary battery in FIG. 1 or FIG. 3. Characteristic diagram showing The ¹ HNMR spectrum of the VEC contained in the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery of Example 30. The characteristic view which shows the < ¹ > HNMR spectrum about PRS contained in the nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of Example 35.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Container main body, 2 ... Electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Separator, 6 ... Cover plate, 7 ... External protective layer, 8 ... Internal protective layer, 9 ... Metal layer, 10 ... Positive electrode tab, 11 ... negative electrode tab, D ... shortest distance between positive electrode tab and negative electrode tab, L ... width in the longitudinal direction of the spiral surface of the electrode group.

Claims (3)

An electrode group in which a positive electrode and a negative electrode are wound in a flat shape via a separator, and electrically connected to the positive electrode, a positive electrode tab protruding from a spiral surface of the electrode group, and electrically connected to the negative electrode, A nonaqueous electrolyte secondary battery comprising a negative electrode tab protruding from a spiral surface of the electrode group and a nonaqueous electrolyte,
The non-aqueous electrolyte comprises 0.001 mol / L to 0.2 mol / L LiBF ₄ , 0.7
mol / L to 1.8 mol / L LiPF ₆ ,
The shortest distance between the positive electrode tab and the negative electrode tab is in the range of 8 mm to 17 mm, and the spiral surface
A nonaqueous electrolyte secondary battery having a longitudinal width in a range of 22 to 65 mm . The positive electrode tab is electrically connected to the positive electrode on the inner periphery of the outermost periphery, and the negative electrode tab is electrically connected to the negative electrode on the inner periphery of the outermost periphery. The nonaqueous electrolyte secondary battery according to claim 1. The positive electrode tab is electrically connected to the positive electrode on the outermost periphery, and the negative electrode tab is electrically connected to the negative electrode on the inner periphery of the outermost periphery. Non-aqueous electrolyte secondary battery.

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