JP2013030431A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

In a non-aqueous electrolyte secondary battery including a wound electrode group, cycle characteristics are improved.
A laminate including a positive electrode including a positive electrode active material that absorbs and releases lithium ions, a negative electrode including a negative electrode active material that stores and releases lithium ions, and a separator interposed between the positive electrode and the negative electrode is wound. A non-aqueous electrolyte secondary battery comprising a wound electrode group impregnated with a non-aqueous electrolyte, wherein the wound electrode group covers each end at both ends in the winding axis direction. A non-aqueous electrolyte secondary battery comprising a resin coating film.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to an improvement in liquid retention of a non-aqueous electrolyte in a wound electrode group.

  A nonaqueous electrolyte secondary battery (hereinafter also referred to as “alloy secondary battery”) having an alloy-based negative electrode using an alloy-based active material as a negative-electrode active material has a graphite-based negative electrode using graphite as a negative-electrode active material. It is known to have higher capacity and energy density than conventional non-aqueous electrolyte secondary batteries. Therefore, the alloy-based secondary battery is expected not only as a power source for electronic devices but also as a main power source or auxiliary power source for transportation equipment, machine tools, and the like. Known alloy-based active materials include silicon-based active materials such as silicon and silicon oxide, and tin-based active materials such as tin and tin oxide.

  However, the alloy-based active material undergoes significant expansion of its particles during charging and generates internal stress. As a result, the negative electrode active material layer may be detached from the negative electrode current collector, or the negative electrode may be deformed.

  In order to reduce the internal stress generated when the alloy-based active material expands, a negative electrode made of an alloy-based active material and having a plurality of micron-sized columnar bodies formed on the surface of the negative electrode current collector is known ( Patent Document 1). In such a negative electrode, a gap is formed between a pair of adjacent columnar bodies. Such voids alleviate the generation of internal stress when the alloy-based active material expands. That is, even if the alloy-based active material expands significantly during charging, the generation of stress is suppressed by the voids formed between adjacent columnar bodies. As a result, the alloy active material is prevented from dropping from the negative electrode current collector, or the negative electrode is deformed.

  Patent Document 2 discloses an alloy-based secondary battery that includes an inorganic filler and a thermoplastic resin and includes a porous film having high liquid retention as a separator. By using such a separator, an attempt is made to suppress a decrease in cycle characteristics due to expansion of a negative electrode containing an alloy-based active material.

  Patent Document 3 is provided with an electrode group in which a wound electrode group is formed into a flat shape, a positive electrode lead and a negative electrode lead derived from an upper end portion of the electrode group, a belt-like base material layer, and both ends in the width direction thereof. A non-aqueous electrolyte secondary battery including an adhesive layer and an insulating layer that covers a lower end portion of an electrode group is disclosed. More specifically, the coating of the lower end portion with the insulating layer is the outer periphery where the surface of the belt-like base material layer is opposed to the lower end portion of the electrode group, and the adhesive layers at both ends thereof are continued to the lower end portion of the electrode group. This is done by adhering to the surface. With such a configuration, the electrode group and the battery case are insulated without impeding impregnation of the nonaqueous electrolyte from the lower end of the electrode group.

International Publication WO2008 / 026595 JP 2005-228514 A JP 2010-073580 A

  In a non-aqueous electrolyte secondary battery including a wound electrode group, particularly an alloy-based secondary battery, when the number of times of charging / discharging increases, the cycle characteristics may be significantly reduced. As a result of studying the cause, the present inventors have obtained the following knowledge.

  FIG. 7 is a schematic perspective view of a conventional wound electrode group (hereinafter also simply referred to as “electrode group”) 100 including an alloy-based negative electrode. The electrode group 100 is formed by winding a laminate including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and impregnating with a non-aqueous electrolyte. A negative electrode lead 16 is connected to.

  In such an electrode group 100, the alloy-based negative electrode expands greatly during initial charging, so that the impregnated non-aqueous electrolyte is squeezed from the top and bottom of the electrode group 100, and as shown by the arrows, It was found to be extruded. A part of the non-aqueous electrolyte squeezed out of the electrode group 100 is partially absorbed and returned to the inside of the electrode group 100 when the alloy-based negative electrode contracts due to discharge. It was found that it remained outside the group 100.

  In order to maintain the cycle characteristics of the battery high, it is preferable that the non-aqueous electrolyte is sufficiently retained in each surface of the positive electrode and the negative electrode constituting the electrode group. However, particularly when an alloy-based negative electrode is used, as described above, the non-aqueous electrolyte is squeezed out from the electrode group 100, resulting in a variation in the distribution of the non-aqueous electrolyte, or a partial solution. I noticed that some dead areas were created. And as a result, it turned out that the cycling characteristics of a battery fall easily.

  The present invention relates to a non-aqueous electrolyte secondary battery including a wound electrode group including an alloy-based negative electrode, wherein the non-aqueous electrolyte solution is confined inside the wound electrode group, and the non-aqueous electrolyte solution is discharged to the outside. An object of the present invention is to provide a nonaqueous electrolyte secondary battery with improved cycle characteristics by suppressing outflow.

  The non-aqueous electrolyte secondary battery of the present invention is interposed between a positive electrode including a positive electrode active material that absorbs and releases lithium ions, a negative electrode including a negative electrode active material that stores and releases lithium ions, and a positive electrode and a negative electrode. A positive electrode and a negative electrode comprising a positive electrode active material that occludes and releases lithium ions, which is a non-aqueous electrolyte secondary battery including a wound electrode group wound with a laminate including a separator and impregnated with a non-aqueous electrolyte A non-aqueous electrolyte secondary battery comprising a wound electrode group obtained by winding a laminate including a separator interposed between a positive electrode and a negative electrode and impregnating with a non-aqueous electrolyte, The mold electrode group includes a resin coating film covering each end at each of both ends in the winding axis direction. According to the non-aqueous electrolyte secondary battery including such a wound electrode group, even if the electrode group expands greatly during charging, the impregnated non-aqueous electrolyte is squeezed out of the electrode group and externally Can be prevented from flowing out. As a result, since the distribution of the non-aqueous electrolyte in the negative electrode and the positive electrode can be maintained uniformly, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved. In the wound electrode group, since the laminate is wound with a high tension, the non-aqueous electrolyte is unlikely to leak from the end of the winding end.

  In the non-aqueous electrolyte secondary battery, the degree of swelling of the resin coating film with respect to the non-aqueous electrolyte is preferably 3% or less. When the degree of swelling of the resin coating film with respect to the non-aqueous electrolyte is within such a range, the resin coating film itself does not absorb the non-aqueous electrolyte too much. The distribution can be kept more homogeneous.

  Further, the tensile modulus of elasticity at 25 ° C. of the resin coating film is 0.1 to 20 GPa so as to follow the change in the diameter of the electrode group due to the expansion of the negative electrode that occurs when the electrode group is charged. It is preferable from the viewpoint of maintaining strength over a long period of time.

  Specific examples of the resin for forming such a resin coating film include at least one resin material selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, and polyamide.

  In addition, the negative electrode includes an alloy-based active material that occludes and releases lithium ions, and in particular, is supported on the surface of the negative electrode current collector having a plurality of convex portions formed on the surface and spaced apart from each other. When the negative electrode active material layer including a plurality of columnar bodies made of an alloy-based active material is provided, the effect of providing the resin coating film becomes remarkable.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery excellent in cycling characteristics can be provided.

It is a longitudinal cross-sectional schematic diagram of the nonaqueous electrolyte secondary battery 1 of embodiment which concerns on this invention. 1 is a schematic perspective view showing an appearance of a wound electrode group 2 that is an element of a nonaqueous electrolyte secondary battery 1. FIG. 3 is a schematic diagram for explaining a method of manufacturing the nonaqueous electrolyte secondary battery 1. FIG. 3 is a schematic diagram for explaining a method of manufacturing the nonaqueous electrolyte secondary battery 1. FIG. It is explanatory drawing which shows the structure of an electron beam type vacuum evaporation system. It is a longitudinal cross-sectional schematic diagram which shows the structure of the alloy type negative electrode in an Example. It is explanatory drawing for demonstrating the winding type electrode group provided with the conventional alloy type negative electrode.

  FIG. 1 is a schematic vertical sectional view of a nonaqueous electrolyte secondary battery 1 according to an embodiment of the present invention. A non-aqueous electrolyte secondary battery 1 (hereinafter also referred to as “battery 1”) is formed by winding a laminate of a strip-shaped negative electrode 10, a strip-shaped positive electrode 11 and a strip-shaped separator 12 and impregnating a non-aqueous electrolyte solution (not shown). The wound electrode group 2, the resin coating films 3 a and 3 b covering the both ends 4 a and 4 b of the electrode group 2 in the winding axis direction, and the bottomed cylindrical battery case 13 that houses the electrode group 2. A sealing plate 14 that seals the opening of the battery case 13, a gasket 15 that insulates the battery case 13 and the sealing plate 14, and a negative electrode lead 16 that connects the negative electrode 10 and the battery case 13 that also functions as a negative electrode terminal. And a positive electrode lead 17 that conducts the positive electrode 11 and the sealing plate 14 that also functions as a positive electrode terminal, and is a cylindrical lithium ion secondary battery. The negative electrode 10 includes, for example, a negative electrode current collector (not shown) and a negative electrode active material layer including an alloy-based active material supported on both surfaces of the negative electrode current collector. The positive electrode 11 includes a positive electrode current collector (not shown) and a positive electrode active material layer formed on both surfaces of the positive electrode current collector.

  The battery 1 of the present embodiment includes resin coating films 3a and 3b that cover both ends 4a and 4b at both ends 4a and 4b in the winding axis direction of the electrode group 2 so as to seal them. Thereby, the outflow of the non-aqueous electrolyte from the electrode group 2 is suppressed, and variations in the distribution of the non-aqueous electrolyte in the electrode group 2 and liquid dying are less likely to occur. As a result, the battery 1 having excellent cycle characteristics can be obtained.

  FIG. 2 is a schematic perspective view showing the appearance of the wound electrode group 2 on which the resin coating films 3a and 3b are formed. As shown in FIG. 2, both ends 4a and 4b in the winding axis direction of the wound electrode group 2 are covered with resin coating films 3a and 3b so as to seal them. Further, the positive electrode lead 17 penetrates the resin coating film 3a in the thickness direction, and the negative electrode lead 16 penetrates the resin coating film 3b in the thickness direction.

  An example of a manufacturing method of the battery 1 having such an electrode group 2 will be described with reference to FIG. In the manufacturing method of the battery 1 of the present embodiment, first, one end of the positive electrode lead 17 is connected to a predetermined position of the positive electrode 11 and one end of the negative electrode lead 16 is a predetermined position of the negative electrode 10 as shown in FIG. A wound type electrode group 2 connected to is prepared. In addition, the connection of the positive electrode lead 17 to the positive electrode 11 and the connection of the negative electrode lead 16 to the negative electrode 10 are connected to a current collector (not shown) of each electrode by resistance welding, ultrasonic welding, plasma welding, or the like. Is done. As the negative electrode lead, for example, a copper lead, a copper alloy lead, a nickel lead, or the like can be used. For example, an aluminum lead can be used as the positive electrode lead.

  Then, as shown in FIG. 3B, a resin paste is applied so as to cover the end portion 4b on the side where the negative electrode lead 16 of the electrode group 2 is disposed, and is dried, whereby the resin coating film 3b. Form. At this time, in the next step, after the electrode group 2 is inserted into the battery case 13, the resin coating film 3 b is formed around the negative electrode lead 16 in order to connect the negative electrode lead 16 to the battery case 13 by welding or the like. It is preferable to form a gap v that is not formed.

  The resin material used for forming the resin coating film is not particularly limited as long as it is a resin component exhibiting adhesiveness to the electrode group, and specifically, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyimide And polyamide, or a mixture thereof. These resin materials are inert to the electrochemical reaction that occurs in the battery and are chemically relatively stable in the battery.

  Further, the resin coating film has a degree of swelling with respect to the non-aqueous electrolyte of 5% or less, more preferably 3% or less, and the amount of the non-aqueous electrolyte due to the resin coating film absorbing the non-aqueous electrolyte. It is preferable from the viewpoint that fluctuations of If the swelling degree of the resin coating film with respect to the non-aqueous electrolyte is too high, a large amount of non-aqueous electrolyte may be absorbed into the resin coating film, which may cause variation or shortage of the amount of the non-aqueous electrolyte. . Moreover, there is a possibility that the nonaqueous electrolytic solution permeates the resin coating film.

The degree of swelling of the resin material forming the resin coating film with respect to the non-aqueous electrolyte is measured as follows. First, a resin material is dissolved in an organic solvent to prepare a resin solution, and this resin solution is applied to a substrate and dried to form a sheet having a thickness of 100 μm. This sheet is cut into 10 mm × 10 mm and used as a sample. This sample is put in a sealed container together with a non-aqueous electrolyte and immersed in the non-aqueous electrolyte at 25 ° C. for 24 hours. And the degree of swelling is calculated | required according to a following formula as an increase rate of the mass (B) of the sample after immersion in a non-aqueous electrolyte with respect to the mass (A) of the sample before immersion in a non-aqueous electrolyte.
Swelling degree (%) = {(BA) / A} × 100

  Moreover, the tensile elastic modulus at 25 ° C. of the resin material forming the resin coating film is 0.1 to 20 GPa, more preferably 0.5 to 15 GPa, and particularly preferably 1 to 10 GPa. In addition, even when the electrode group expands during charging and the diameter of the electrode group increases, the resin coating film follows the change in diameter, and the close contact with both ends of the electrode group is sufficiently maintained. If the tensile modulus of the resin material forming the resin coating film is too high, the resin coating film is difficult to stretch, and it is difficult to follow the expansion of the electrode group during charging, which may cause tearing or peeling. . Moreover, when the tensile modulus is too low, the strength tends to decrease due to expansion of the electrode group during charging. The tensile elastic modulus is measured by a measuring method according to JIS K7162.

  The thickness of the resin coating film is not particularly limited, but specifically, for example, about 0.1 to 0.5 mm is preferable from the viewpoint of maintaining durability and adhesion for a long period of time.

  The resin paste used for forming the resin coating film can be prepared by dissolving or dispersing the resin material in an organic solvent. As the organic solvent used for preparing the resin paste, a non-aqueous solvent contained in the non-aqueous electrolyte can be used without any particular limitation. Specific examples of the non-aqueous solvent include dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone, dimethylamine, acetone, cyclohexanone, and the like.

  Although the viscosity (25 degreeC) of a resin paste is not specifically limited, It is preferable to adjust to the range of about 1000-50000 cps. Thereby, it is suppressed that the resin paste penetrates between the negative electrode and the separator or between the positive electrode and the separator. Moreover, the workability | operativity at the time of apply | coating a resin paste does not fall. The viscosity of the resin paste can be adjusted, for example, by changing the amount of the resin material dissolved in the non-aqueous solvent, the molecular weight of the resin material, and the like.

  The method for applying the resin paste is not particularly limited, and examples thereof include dipping, roll coating, and brush coating. The drying temperature of the resin paste is appropriately selected according to the type of resin material and non-aqueous solvent contained in the resin paste, but is preferably about 60 to 100 ° C. The drying time of the resin paste is also appropriately selected according to the type of resin material and non-aqueous solvent contained in the resin paste, but is preferably about 1 to 6 hours. When the drying temperature is too high or the drying time is too long, the separator is softened or melted, or when the nonaqueous electrolyte is impregnated, the nonaqueous electrolyte is evaporated. Is not preferable.

  Then, the electrode group 2 having the resin coating film 3b formed on the negative electrode lead 16 side is connected to the battery case 13 from the end 4b side on which the resin coating film 3b is formed, as shown in FIG. Insert group 2. Then, the other end of the negative electrode lead 16 is joined to the bottom of the battery case 13 by welding or the like, and similarly, the other end of the positive electrode lead 17 is joined to the sealing plate 14 prepared in advance by welding or the like. At this time, if necessary, an insulating plate may be disposed on the bottom or top of the battery case, or an aperture groove for fixing the electrode group 2 in the battery case 13 may be formed.

  Next, after welding of the negative electrode lead 16, the resin from the space S formed along the winding axis of the electrode group 2 into the gap v formed around the negative electrode lead 16, as shown in FIG. The gap v is filled with the resin paste by applying and drying the paste. Thus, the resin coating film 3b in which the end 4b is completely sealed is formed. In addition, as a method of filling the gap v, a method of inserting a dispenser from the space S and potting the resin paste into the gap v can be cited.

  Next, a nonaqueous electrolytic solution is injected and impregnated from the end 4a side which is the upper part of the electrode group 2 accommodated in the battery case 13. At this time, since the resin coating film 3 b is formed on the end 4 b side which is the lower part of the electrode group 2, the non-aqueous electrolyte does not leak from the lower part of the electrode group 2 or hardly leaks. Then, after the electrode group 2 is sufficiently impregnated with the non-aqueous electrolyte, a resin paste is applied to the end portion 4a on the side where the positive electrode lead 17 of the electrode group 2 is disposed, and dried to obtain a resin coating. A covering film 3a is formed. In this way, the electrode group 2 provided with the resin coating films 3a and 3b for sealing both ends 4a and 4b in the winding axis direction as shown in FIG. 2 is formed.

  After the resin coating films 3a and 3b are formed on the electrode group 2, the battery 1 is manufactured in the same process as the manufacturing method of a normal nonaqueous electrolyte secondary battery. Specifically, for example, a sealing plate 14 and a gasket 15 that insulates the battery case 13 and the sealing plate 14 are disposed in the opening of the battery case 13, and the battery case 13 is caulked to be sealed. Is obtained.

Next, other components constituting the nonaqueous electrolyte secondary battery 1 will be described in detail.
The negative electrode 10 includes a negative electrode current collector and a negative electrode active material layer supported by the negative electrode current collector. As a negative electrode current collector, in addition to conductive substrates such as non-porous foils, sheets, and films, which are conventionally used as negative electrode current collectors for non-aqueous electrolyte secondary batteries, mesh bodies, net bodies, punching A sheet, a lath body, a porous body, etc. are mentioned. As the material of the conductive substrate, stainless steel, titanium, nickel, copper, copper alloy, or the like is used without particular limitation. Of these, copper and copper alloys are preferred.

  The negative electrode active material layer includes various carbon materials such as graphite materials, negative electrode active materials such as silicon-based active materials and tin-based active materials, which are conventionally used as negative electrode active materials for non-aqueous electrolyte secondary batteries. Contains substances. A negative electrode active material may be used individually by 1 type, or may be used in combination of 2 or more type. In addition, the negative electrode active material layer may contain a binder, a conductive agent, an additive, and the like as necessary as long as the effects of the present invention are not impaired. In the present invention, when an alloy-based active material is used as the negative electrode active material, a particularly remarkable effect is achieved.

  The alloy-based active material occludes lithium by alloying with lithium at the time of charging under a negative electrode potential, and releases lithium at the time of discharging. As the alloy-based active material, a silicon-based active material is particularly preferable.

The type of the silicon-based active material is not particularly limited, and specific examples include silicon, silicon compounds, silicon partial substitutes, silicon compound partial substitutes, and silicon compound solid solutions. Specific examples of the silicon compound include silicon oxide represented by the formula: SiO _a (0.05 <a <1.95), silicon carbide represented by the formula: SiC _b (0 <b <1), formula : Silicon nitride represented by SiN _c (0 <c <4/3), silicon alloy which is an alloy of silicon and a different element A, and the like. In the silicon alloy, the different element A includes at least one element selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti.

  The partially substituted silicon is a compound in which a part of silicon contained in silicon and a silicon compound is substituted with a different element B. Specific examples of the different element B include, for example, B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. Can be mentioned. Among these silicon-based active materials, silicon compounds are preferable, and silicon oxide is more preferable.

Specific examples of the tin-based active material include tin, a tin compound, tin oxide represented by the formula SnO _d (0 <d <2), tin dioxide (SnO ₂ ), tin nitride, Ni—Sn alloy, Mg -Tin alloys such as -Sn alloy, Fe-Sn alloy, Cu-Sn alloy, Ti-Sn alloy, and tin compounds such as SnSiO ₃ , Ni ₂ Sn ₄ , Mg ₂ Sn, and the like. Among these tin-based active materials, tin oxide, tin alloy, tin compound and the like are preferable.

  As a negative electrode active material layer containing an alloy-based active material, a layer composed of an aggregate of columnar bodies formed by a vapor phase method on a negative electrode current collector having a large number of protrusions on the surface as described later, or a vapor phase method The thin film of the alloy-based active material formed on the surface of the negative electrode current collector or the mixture obtained by mixing the particles of the alloy-based active material with the binder or conductive agent is applied to the surface of the negative electrode current collector and Examples thereof include a layer formed by rolling. In these, the layer which consists of the aggregate | assembly of the columnar body and the thin film of an alloy type active material formed by the vapor phase method are preferable from the point which can maintain a high capacity | capacitance.

  Specific examples of the vapor phase method include vacuum vapor deposition, sputtering, ion plating, laser ablation, chemical vapor deposition, plasma chemical vapor deposition, and thermal spraying. Among these, vacuum deposition is particularly preferable.

  The layer composed of the columnar body formed on the negative electrode current collector having a large number of convex portions is, for example, a negative electrode current collector having a plurality of regularly arranged convex portions having a height of about 3 to 20 μm. This is a layer in which a columnar body made of an alloy-based active material is formed on the surface for each convex portion. The width of the convex portion is preferably 5 to 20 μm. Examples of the arrangement of the convex portions include a staggered lattice arrangement, a lattice arrangement, and a close-packed arrangement.

  The alloy-based active material thin film formed on the negative electrode current collector surface by the vapor phase method is made of an alloy-based active material formed on the negative electrode current collector surface, for example, an amorphous film having a thickness of 3 to 50 μm. Or a thin film having a low crystallinity.

  The negative electrode active material layer may occlude an amount of lithium corresponding to the irreversible capacity. The insertion of lithium into the negative electrode active material layer is performed, for example, by supplying lithium vapor to the surface of the negative electrode active material layer by vacuum deposition.

  The positive electrode 11 includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. As the positive electrode current collector, a conductive substrate conventionally used as a positive electrode current collector of a non-aqueous electrolyte secondary battery is used without any particular limitation. Specific examples of the conductive substrate include metal substrates such as stainless steel, titanium, aluminum, and aluminum alloys, and conductive substrates such as a conductive resin. Examples of the conductive substrate include a non-porous conductive substrate, a mesh body, a net body, a punching sheet, a lath body, and a porous body. Examples of the non-porous conductive substrate include a foil and a film. Although the thickness of a conductive substrate is not specifically limited, For example, the thing about 1-500 micrometers, Furthermore, about 5-50 micrometers can be used preferably.

  The positive electrode active material layer includes a positive electrode active material, and includes a conductive agent, a binder, and the like as necessary. As a positive electrode active material, the material conventionally used as a positive electrode active material of a nonaqueous electrolyte secondary battery is used without particular limitation. Specific examples include lithium-containing composite oxides and olivine type lithium phosphate. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.

  The lithium-containing composite oxide is a metal oxide containing lithium and a transition metal element or a metal oxide in which a part of the transition metal element in the metal oxide is substituted with a different element. Examples of the transition metal element include at least one transition metal element selected from the group consisting of Sc, Y, Mn, Fe, Co, Ni, Cu, and Cr. Among these transition metal elements, Mn, Co, and Ni are preferable. Examples of the different element include at least one different element selected from the group consisting of Na, Mg, Zn, Al, Pb, Sb, and B. Among these different elements, Mg, Al, etc. are preferable.

Specific examples of the lithium-containing composite _{oxide, Li X CoO 2, Li X} NiO 2, Li X MnO 2, Li X Co m Ni 1-m O 2, Li X Co m A 1-m O n, Li X _{Ni 1-m A m O n} , Li X Mn 2 O 4, Li X Mn 2-m A n O 4 ( in each of the formulas above, A is Sc, Y, Mn, Fe, Co, Ni, Cu, Cr, It represents at least one element selected from the group consisting of Na, Mg, Zn, Al, Pb, Sb and B. 0 <X ≦ 1.2, m = 0 to 0.9, n = 2.0 to 2. 3). Among these lithium-containing composite oxide, the _{Li X Co m A 1-m} O n more preferred. In the above formulas, the value indicating the molar ratio of lithium is a value immediately after the production of the positive electrode active material, and increases or decreases due to charge / discharge.

Specific examples of the olivine type lithium phosphate include LiYPO ₄ , Li ₂ YPO ₄ F (wherein Y represents at least one element selected from the group consisting of Co, Ni, Mn and Fe). is there.

  As the conductive agent, graphites such as natural graphite and artificial graphite, which are conventionally used as conductive agents for non-aqueous electrolyte secondary batteries; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal Carbon blacks such as black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum; conductive whiskers such as zinc oxide whiskers; conductive metal oxides such as titanium oxide; phenylene derivatives An organic conductive material such as is used without particular limitation.

  As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene, polypropylene, polyamide, polyimide, polyamideimide, which are conventionally used as binders for non-aqueous electrolyte secondary batteries, Polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyether Resin materials such as polyether sulfone; rubber materials such as styrene butadiene rubber and modified acrylic rubber; water-soluble polymer compounds such as carboxymethyl cellulose; A copolymer containing two or more types of monomer compounds can be used as a binder. Examples of the monomer compound include tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, hexadiene and the like. A binder may be used individually by 1 type, or may be used in combination of 2 or more type.

  The positive electrode active material layer is formed, for example, by applying a positive electrode mixture slurry on the surface of the positive electrode current collector, and drying and rolling the obtained coating film. The positive electrode mixture slurry can be prepared by dissolving or dispersing a positive electrode active material and, if necessary, a conductive agent, a binder and the like in a dispersion medium. As the dispersion medium, dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone, dimethylamine, acetone, cyclohexanone, and the like can be used.

  As the separator disposed between the negative electrode and the positive electrode, for example, a porous sheet having ion permeability can be used. Specific examples of the porous sheet include a microporous film, a woven fabric, and a non-woven fabric. The material of the separator is preferably a polyolefin such as polyethylene or polypropylene from the viewpoints of durability, shutdown function, battery safety, and the like. Although the thickness of a separator is not specifically limited, It is preferable that it is about 10-300 micrometers, Furthermore, about 10-40 micrometers. The porosity of the separator is preferably 30 to 70%. The porosity is a percentage of the total pore volume with respect to the separator volume.

The nonaqueous electrolytic solution impregnated in the electrode group contains a lithium salt and a nonaqueous solvent, and may further contain an additive. Specific examples of the lithium salt include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid Examples thereof include lithium, LiCl, LiBr, LiI, LiBCl ₄ , borates, and imide salts. A lithium salt may be used individually by 1 type, or may be used in combination of 2 or more type. The amount of lithium salt dissolved in the non-aqueous solvent is preferably 0.5 to 2 mol / L.

  As the non-aqueous solvent, those conventionally used as non-aqueous solvents for non-aqueous electrolyte secondary batteries can be used without any particular limitation. Specifically, for example, cyclic carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate; chain carbonates such as diethyl carbonate, ethylmethyl carbonate and dimethyl carbonate; cyclic carboxylic acids such as γ-butyrolactone and γ-valerolactone Ester; etc. are mentioned. A non-aqueous solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

  Additives such as vinylene carbonate, vinylene carbonate substituted with 1 or 2 alkyl groups of 1 to 2 carbon atoms, vinyl ethylene carbonate, divinyl ethylene carbonate, halogenated ethylene carbonate, etc., decompose on the negative electrode to form lithium ions Carbonate compounds that form highly conductive films and improve charge and discharge efficiency; such as cyclohexylbenzene, biphenyl, diphenyl ether, etc., decompose during battery overcharge to form a film on the electrode surface and inactivate the battery Benzene compound; and the like.

  The battery case 13 and the sealing plate 14 can be produced by molding a metal material such as iron or stainless steel into a predetermined shape. The gasket 15 can be manufactured by molding an electrically insulating material, preferably a resin material or a rubber material into a predetermined shape.

  The non-aqueous electrolyte secondary battery 1 described in the present embodiment is a cylindrical battery including the electrode group 2, but is not limited thereto and can take various forms. Specific examples thereof include a rectangular battery including the electrode group 2 and a rectangular battery including a flat electrode group obtained by forming the electrode group 2 into a flat shape.

  The present invention will be described more specifically with reference to the following examples. The scope of the present invention is not construed as being limited by the examples.

[Example 1]
(A) Production of positive electrode 93 g of powder of positive electrode active material (LiNi _0.85 Co _0.15 Al _0.05 O ₂ ), 3 g of acetylene black (conductive agent), 4 g of polyvinylidene fluoride (binder) and 50 ml of N-methyl-2-pyrrolidone Mixing was performed to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the obtained coating film was dried and rolled to have a total thickness of 130 μm, a width of 29.5 mm, and a length of 166 mm. A positive electrode was produced. A part (56 mm × 5 mm) of the positive electrode active material layer on both surfaces of the positive electrode was excised, and a current collector exposed portion was provided. One end of an aluminum lead was connected to the exposed portion of the current collector by ultrasonic welding.

(B) Production of negative electrode A plurality of concave portions were formed by laser processing on the surface of a forged steel roller (Daido Machinery Co., Ltd., diameter 50 mm, roll width 100 mm). The plurality of recesses were in a close-packed arrangement in which the distance between the axes of a pair of adjacent recesses was 20 μm. The opening shape of the concave portion was almost rhombus with a long diagonal of 19.5 μm and a short diagonal of 9.8 μm. The depth of the concave portion was 8 μm, and the bottom portion thereof was substantially flat at the center, and the portion where the peripheral edge of the bottom portion and the side surface of the concave portion were connected was rounded. In this way, a convex roller was produced. The two convex rollers were brought into pressure contact at a linear pressure of 1 t / cm so that their axes were parallel to form a pressure nip portion.

  On the other hand, an alloy copper foil (trade name: HCL-02Z, thickness 20 μm, manufactured by Hitachi Cable Ltd.) containing zirconium in a proportion of 0.03% by mass with respect to the total amount is 30 at 600 ° C. in an argon gas atmosphere. Heated for minutes and annealed. This alloy copper foil was passed through the pressure nip portion, and the alloy copper foil was pressure-molded to produce a negative electrode current collector 49 as shown in FIG. The negative electrode current collector 49 had a plurality of convex portions 52 on both surfaces in the thickness direction. The average height of the protrusions 52 was about 8 μm. The shape of the convex part 52 is substantially rhombus. The plurality of convex portions 52 were arranged in the closest packing on the surface of the negative electrode current collector 49. In FIG. 6, only one surface of the negative electrode current collector 49 is shown.

  FIG. 5 is an explanatory diagram schematically showing the configuration of an electron beam vacuum deposition apparatus 40 (hereinafter also referred to as “deposition apparatus 40”). Using the vapor deposition apparatus 40 as shown in FIG. 5, one columnar body 54 was formed on the surface of each convex portion 52 of the negative electrode current collector 49 to produce the negative electrode 50.

  The vapor deposition apparatus 40 includes a feed roller 42 around which a negative electrode current collector 49 is wound, transport rollers 43 a, 43 b, 43 c, 43 d, 43 e, 43 f, vapor deposition sources 46 a, 46 b, and a silicon-based surface on each convex portion 52. A take-up roller 45 for winding the negative electrode current collector 49 on which the active material layer is formed, a pair of shielding plates 47 and 48 for regulating the supply region of the silicon-based active material vapor, and oxygen for supplying oxygen (not shown) A nozzle, an electron beam irradiation device (not shown), a chamber 41 for accommodating these, and a vacuum pump 39 for reducing the pressure in the chamber 41 are provided. The shielding plate 47 includes shielding pieces 47a, 47b, and 47c. The shielding plate 48 includes shielding pieces 48a, 48b, and 48c. In the vapor deposition apparatus 40, in the conveyance direction of the negative electrode current collector 49, a first vapor deposition region is provided between the shielding pieces 47a and 47b, a second vapor deposition region is provided between the shielding pieces 47b and 47c, and the shielding pieces 48c and 48b. A third vapor deposition region is provided therebetween, and a fourth vapor deposition region is provided between the shielding pieces 48b and 48a.

Scrap silicon (silicon single crystal, purity 99.9999%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as a silicon-based active material material, and this was accommodated in vapor deposition sources 46a and 46b. After the chamber 41 was evacuated to 5 × 10 ⁻³ Pa by the vacuum pump 39, 50 sccm of oxygen was supplied into the chamber 41 from unillustrated oxygen nozzles installed in the first to fourth vapor deposition regions. Next, the vapor deposition sources 46a and 46b were irradiated with an electron beam (acceleration voltage: 10 kV, emission: 500 mA) to generate silicon vapor.

  On the other hand, the negative electrode current collector 49 is fed from the feed roller 42 at a feed rate of 2 cm / min, and a mixture of silicon vapor and oxygen is vapor-deposited on the surface of each convex portion 52 of the negative electrode current collector 49 running in the first deposition region. As a result, a mass 54a shown in FIG. 6 was formed. Next, a mass 54b was formed on the surface of the convex portion 52 and the surface of the mass 54a of the negative electrode current collector 49 running in the second vapor deposition region. Further, in the third and fourth vapor deposition regions, the masses 54a and 54b are stacked on the surface of each convex portion 52 on the surface opposite to the surface where the masses 54a and 54b are formed in the first and second vapor deposition regions. .

  Next, the feeding direction of the negative electrode current collector 49 is reversed by reversing the rotation direction of the feed roller 42 and the take-up roller 45, and the mass 54 c is formed on the surfaces of the masses 54 a and 54 b on both sides of the negative electrode current collector 49. , 54d were laminated. Thereafter, one reciprocal deposition was performed in the same manner. Thus, as shown in FIG. 6, the columnar body 54, which is a laminated body of the masses 54a, 54b, 54c, 54d, 54e, 54f, 54g, and 54h, was formed on the surface of the convex portion 52 of the negative electrode current collector 49. . In this way, a negative electrode 50 was obtained.

The columnar body 54 was supported by the surface of the convex portion 52 and grew to extend outward from the negative electrode current collector 49. The three-dimensional shape of the columnar body 54 was substantially cylindrical. The columnar body 54 had an average height of 20 μm and an average width of 40 μm. Further, when the amount of oxygen contained in the columnar body 54 was quantified by a combustion method, the composition of the columnar body 54 was SiO _0.25 .

  The negative electrode active material layer 53 composed of the plurality of columnar bodies 54 of the negative electrode 50 thus obtained was supplemented with irreversible capacity lithium using a resistance heating vacuum deposition apparatus. The vapor deposition apparatus includes: a feed roller around which a strip-like negative electrode 50 is wound in advance; a can in which a cooling device is disposed; a take-up roller that winds up the negative electrode 50 supplemented with lithium; and a transport roller that transports the negative electrode 50 A tantalum evaporation source that contains metallic lithium, a shielding plate that restricts the supply of lithium vapor to the surface of the negative electrode 50, and a pressure-resistant chamber that accommodates these.

First, the inside of the chamber of the vapor deposition apparatus was replaced with an argon atmosphere, and the degree of vacuum in the chamber was set to 1 × 10 ⁻¹ Pa with a vacuum pump. Next, a current of 50 A is supplied to the evaporation source to generate lithium vapor, and the negative electrode 50 is fed from the feed roller at a speed of 2 cm / min. When the negative electrode 50 passes through the can surface, the negative electrode activation of the negative electrode 50 is increased. Lithium for the irreversible capacity was deposited on the surface of the material layer. Lithium was deposited on both negative electrode active material layers 53 of the negative electrode 50. In this way, a negative electrode 50 (total thickness 85 μm, width 30.9 mm, length 244 mm) supplemented with lithium was produced. In addition, the collector exposed part which does not carry | support a negative electrode active material layer was previously provided in both surfaces of the negative electrode 50. FIG. One end of a copper lead was connected to the exposed portion of the current collector by ultrasonic welding.

(C) Separator A polyethylene microporous membrane (trade name: Hypore, thickness 20 μm, manufactured by Asahi Kasei E-Materials Co., Ltd.) was used as the separator. The separator had a width of 33.3 mm and a length of 328 mm. This separator was used as a first separator and a second separator.

(D) Preparation of non-aqueous electrolyte LiPF ₆ was dissolved at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1 to prepare a non-aqueous electrolyte.

(E) Preparation of resin paste Polyimide (swelling degree 2% by mass with respect to non-aqueous electrolyte, tensile modulus 2 GPa) 10 g of N-methyl-2-pyrrolidone was dissolved in 10 ml, and a resin paste having a viscosity of 15000 cps at 25 ° C. Prepared.

(F) Assembly of battery and production of resin coating film A negative electrode, a second separator, and a positive electrode are stacked in this order on the first separator to form a laminate, and these are wound with the first separator on the outside. Thus, a wound electrode group was produced. And the resin paste was brush-coated to the edge part which the copper lead which is a negative electrode terminal protrudes, and the obtained coating film was dried at 85 degreeC for 2 hours. Thereby, the resin coating film was formed in the edge part by the side of the negative electrode terminal of an electrode group. A slight gap was formed between the copper lead and the resin coating film. The film thickness of the obtained resin coating film was in the range of 0.1 to 0.2 mm.

  Thus, the electrode group in which the resin coating film was formed on the end portion on the negative electrode terminal side was housed in a bottomed cylindrical iron battery case with the side from which the copper lead protruded facing downward. Then, the other end of the copper lead was connected to the bottom inner surface of the battery case. Then, the resin paste was applied and dried so as to fill the gap between the copper lead and the resin coating film from the gap at the center of the battery group.

  Next, the other end of the aluminum lead as the positive electrode terminal was welded to a stainless steel sealing plate having a safety valve. Then, a gasket made of polypropylene was attached to the periphery of the sealing plate, and in this state, the sealing plate was attached to the opening of the battery case.

  The electrode group was dried at 85 ° C. for 2 hours while being housed in the battery case. Then, after drying, a non-aqueous electrolyte was poured into the electrode group and sufficiently impregnated by reducing the pressure. And the resin paste was brushed to the edge part by the side of the positive electrode terminal which the aluminum lead has protruded, and the obtained coating film was dried at 85 degreeC for 2 hours. The battery case was hermetically sealed by caulking the open end of the battery case toward the sealing plate. In this way, a cylindrical lithium ion secondary battery having an outer diameter of 14 mm and a height of 40 mm was produced.

(G) Evaluation The obtained lithium ion secondary battery was evaluated according to the following evaluation method.
[Capacity maintenance rate]
The lithium ion secondary battery was housed in a constant temperature bath at 25 ° C., and charging / discharging (constant current charging and subsequent constant voltage charging) and discharging (constant current discharging) were repeated 3 cycles under the following charging / discharging conditions. In addition, charge / discharge was performed by standing a cylindrical lithium ion secondary battery.
Constant current charge: 0.3 C, end-of-charge voltage of 4.2 V.
Constant voltage charging: 4.2 V, charging end current 0.05 C, rest time 20 minutes.
Constant current discharge: 0.2 C, discharge end voltage 2.5 V, rest time 20 minutes.
Then, the lithium ion secondary battery was determined to have a constant current discharge current value of 1 C, and a discharge capacity (1 C capacity) was obtained to obtain an initial battery capacity. Next, 300 cycles of charge and discharge were repeated, and the discharge capacity after 300 cycles was determined. Then, the capacity retention rate (%) of the discharge capacity after 300 cycles with respect to the initial battery capacity was determined. The results are shown in Table 1.

[Non-aqueous electrolyte leakage]
The lithium ion secondary battery after 300 cycles when measuring the capacity retention rate was disassembled, and the presence or absence of leakage of the non-aqueous electrolyte from the electrode group was examined visually. The results are shown in Table 1.

[Example 2]
Cylindrical lithium ion secondary battery in the same manner as in Example 1 except that polyamideimide (swelling degree with respect to non-aqueous electrolyte 1%, tensile elastic modulus 12 GPa) was used instead of polyimide as the resin material of the resin paste. Were made and evaluated. The results are shown in Table 1.

[Example 3]
Cylindrical lithium in the same manner as in Example 1 except that polytetrafluoroethylene (swelling degree 5% with respect to nonaqueous electrolytic solution, tensile elastic modulus 0.7 GPa) was used instead of polyimide as the resin material of the resin paste. An ion secondary battery was fabricated and evaluated. The results are shown in Table 1.

[Example 4]
Cylindrical lithium ion in the same manner as in Example 1 except that polyvinylidene fluoride (swelling degree with respect to non-aqueous electrolyte 12%, tensile elastic modulus 0.2 GPa) was used instead of polyimide as the resin material of the resin paste. A secondary battery was fabricated and evaluated. The results are shown in Table 1.

[Example 5]
Example 1 except that instead of polyimide, a mixture of polyvinylidene fluoride and polyamideimide (weight ratio 1: 3, degree of swelling 3% with respect to non-aqueous electrolyte, tensile modulus 4 GPa) was used as the resin material for the resin paste. In the same manner as above, a cylindrical lithium ion secondary battery was produced and evaluated. The results are shown in Table 1.

[Comparative Example 1]
A cylindrical lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the resin coating film was not formed on both ends of the electrode group. The results are shown in Table 1.

[Comparative Example 2]
A cylindrical lithium ion secondary battery was fabricated and evaluated in the same manner as in Example 1 except that the resin coating film was formed only on the end portion from which the copper lead of the electrode group protruded. The results are shown in Table 1.

  From Table 1, the lithium ion secondary batteries of Examples 1 to 4 in which the resin coating layer was formed at both ends in the winding axis direction of the wound electrode group had a high capacity retention rate and excellent cycle characteristics. . On the other hand, the lithium ion secondary battery of Comparative Example 1 in which the resin coating layer is not formed, and the lithium ion secondary battery of Comparative Example 2 in which the resin coating layer is formed only on the negative electrode side from which the copper lead connected to the bottom of the battery case protrudes. The secondary battery had a low capacity maintenance rate. Further, in the lithium ion secondary batteries of Examples 1 and 5 having a particularly high capacity retention rate, there was no leakage of the non-aqueous electrolyte. This is presumably because no leakage occurred because the swelling degree and tensile modulus of the resin forming the resin coating film with respect to the non-aqueous electrolyte were appropriate. On the other hand, in the lithium ion secondary batteries of Examples 2 to 4 having a somewhat low capacity retention rate, some leakage of the non-aqueous electrolyte was observed.

  The non-aqueous electrolyte secondary battery of the present invention can be used for the same applications as conventional non-aqueous electrolyte secondary batteries, and in particular, main power sources for electronic equipment, electrical equipment, machine tools, transportation equipment, power storage equipment, etc. Or it is useful as an auxiliary power source. Electronic devices include personal computers, mobile phones, mobile devices, portable information terminals, portable game devices, and the like. Electrical equipment includes vacuum cleaners and video cameras. Machine tools include electric tools and robots. Transportation equipment includes electric vehicles, hybrid electric vehicles, plug-in HEVs, fuel cell vehicles, and the like. Examples of power storage devices include uninterruptible power supplies.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Winding type electrode group 3a, 3b Resin coating film 4a, 4b End part of winding type electrode group 5 Winding shaft 10, 50 Negative electrode 11 Positive electrode 12 Separator 13 Battery case 14 Sealing plate DESCRIPTION OF SYMBOLS 15 Gasket 16 Negative electrode lead 17 Positive electrode lead 40 Electron beam type vacuum evaporation system 54 Columnar body

Claims (7)

Winding a laminate including a positive electrode including a positive electrode active material that absorbs and releases lithium ions, a negative electrode including a negative electrode active material that stores and releases lithium ions, and a separator interposed between the positive electrode and the negative electrode, A non-aqueous electrolyte secondary battery comprising a wound electrode group impregnated with a water electrolyte,
The wound electrode group includes a resin coating film covering each end portion at each of both end portions in the winding axis direction.   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin coating film covers each end so that the non-aqueous electrolyte impregnated in the electrode group does not flow out from each end. .   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a degree of swelling of the resin coating film with respect to the nonaqueous electrolyte is 3% or less.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the resin coating film has a tensile elastic modulus at 25 ° C of 0.1 to 20 GPa.   The non-aqueous electrolysis according to any one of claims 1 to 4, wherein the resin coating film contains at least one resin material selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, and polyamide. Liquid secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode includes an alloy-based active material that occludes and releases lithium ions.   A negative electrode active material comprising a negative electrode current collector having a plurality of convex portions formed on the surface so that the negative electrodes are spaced apart from each other, and a plurality of columnar bodies made of the alloy-based active material supported by the convex portions. A nonaqueous electrolyte secondary battery according to claim 6, comprising a layer.

Images