JP2010009838A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which maintains its high capacity, and at the same time, improves the safety, at the time of internal short-circuit. <P>SOLUTION: In a nonaqueous electrolyte secondary battery containing a group of electrodes having a cathode plate and an anode plate, which are stacked or wound via a porous insulating layer, and a nonaqueous electrolyte, a belt-like current collector having strong anisotropy is used for at least one of the cathode plate and the anode plate. The belt-like current collector having strong anisotropy is, for example, a belt-like current collector 1, having a surface provided with a plurality of grooves 2 extending in a longitudinal direction thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention mainly relates to improvements in current collectors.

  Recently, electronic devices have become increasingly portable and cordless, and a secondary battery that is small and lightweight and has a high energy density is demanded as a driving power source. In addition, not only small consumer applications, but also the development of secondary battery technology for large power supplies that require long-term durability and safety, such as for power storage and electric vehicles, has been accelerated. Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are attracting attention as secondary batteries used for such applications. A lithium ion secondary battery is characterized by being at a high voltage and having a high energy density.

The lithium ion secondary battery includes an electrode group including a positive electrode, a negative electrode, and a separator, and a nonaqueous electrolyte. In lithium ion secondary batteries currently on the market, the positive electrode active material contained in the positive electrode is a lithium cobalt oxide (for example, LiCoO ₂ ) that has a high potential for lithium, is excellent in safety, and is relatively easy to synthesize. It is used. Carbon materials such as graphite are used for the negative electrode active material contained in the negative electrode. For the separator, a porous film made mainly of polyolefin is used. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte (non-aqueous electrolyte) in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an aprotic organic solvent is used.

From the viewpoint of further increasing the capacity of the lithium ion secondary battery, an attempt has been made to use lithium nickel oxide (for example, LiNiCO ₂ ) instead of lithium cobalt oxide as a positive electrode active material, and some of them have been put into practical use. Although lithium nickel oxide certainly has a high capacity, the stability of the crystal is low and has a problem to be solved in terms of safety. The safety of the battery is evaluated by, for example, a nail penetration test. The nail penetration test is a test method for evaluating battery safety by forcing a nail into an electrode group from the surface of the battery to forcibly generate an internal short circuit and examining the degree of heat generation.

  When a nail is pierced into the battery, the positive electrode plate and the negative electrode plate that are insulated via the separator are electrically connected by the nail, and a short-circuit current first flows between the current collectors via the nail, thereby generating Joule heat. When the short-circuit current is a large current or continuously flows, a phenomenon may occur in which the battery temperature becomes abnormally high due to the Joule heat. This phenomenon is called abnormal heat generation. At this time, if the contact area between the current collector of the electrode plate and the nail is small, the contact portion of the current collector with the nail instantly melts due to Joule heat, and the contact between the nail and the current collector is broken. , Joule heat generation becomes very small, and abnormal heat generation of the battery can be suppressed. On the other hand, if the contact area between the current collector and the nail is large, the contact portion between the current collector and the nail becomes insufficiently melted, and the contact between the nail and the current collector cannot be completely blocked. For this reason, an internal short circuit continues and abnormal heat generation of the battery is induced.

  On the other hand, various techniques for processing the surface of the current collector have been proposed. For example, a current collector having a surface with an uneven shape has been proposed (see, for example, Patent Document 1). As a specific example of the concavo-convex shape, a wavy wave having a height of 15 to 40 μm is mentioned. In Patent Document 1, an attempt is made to increase the contact area between the active material and the current collector and improve the output density of the battery by making the current collector surface uneven.

  In addition, a current collector is proposed in which an uneven shape having an average interval between tops of local peaks and a 10-point average roughness of 20 to 70 μm as defined in JIS B0601 is formed on the surface (for example, see Patent Document 2). . In Patent Document 2, it is intended to improve the adhesion between the current collector and the active material layer and to improve the durability of the current collector by providing the surface of the current collector with the uneven shape as described above. Yes.

  However, since the uneven shapes as in Patent Document 1 and Patent Document 2 are formed in an isotropic pattern on the current collector surface, anisotropy does not occur in the strength of the current collector. Moreover, when the degree of unevenness is increased to the extent that strength anisotropy occurs in the uneven shape as in Patent Document 1 and Patent Document 2, an electrode plate manufactured using the current collector is interposed via a separator. In the winding step, the electrode plate is broken.

  In addition, a current collector is proposed in which a plurality of grooves extending linearly from one end to the other end in the longitudinal direction of the current collector are formed on the surface (see, for example, Patent Document 3). The depth of the groove is 3 to 16% of the current collector thickness, and the pitch of the groove in the current collector width direction is 0.1 to 5 mm. In Patent Document 3, by providing the grooves as described above, the diffusibility of the nonaqueous electrolyte in the active material layer is improved, and the charge / discharge cycle characteristics of the lithium ion secondary battery are improved. However, in the current collector of Patent Document 3, since the pitch of the grooves in the width direction of the current collector is rough, depending on the position of the internal short-circuit occurrence point, the short-circuit current flows continuously, and the occurrence of abnormal heat generation is sufficiently suppressed. It may not be possible.

  As described above, in Patent Documents 1 to 3, irregularities and grooves are formed on the current collector surface. However, the technical idea of giving the current collector anisotropy in strength and thereby improving the safety at the time of internal short-circuiting of the battery is not described. In addition, the current collectors described in Patent Documents 1 to 3 are not sufficient in improving the safety of the battery evaluated by the nail penetration test.

  Further, when winding the electrode group, a constant tension is applied in the longitudinal direction of the electrode group. Therefore, in order to prevent breakage of the electrode group during winding, for example, it is necessary to increase the mechanical strength of the current collector by increasing the thickness of the current collector. However, when the thickness of the current collector is increased, the internal short-circuit continues for a long time during the nail penetration test, and the battery tends to become hot. That is, the improvement in the strength of the current collector and the improvement in the safety of the battery are contradictory characteristics. Therefore, it is very difficult to achieve both prevention of breakage of the electrode group during winding and improvement of battery safety.

JP-A-8-195202 Japanese Patent Laid-Open No. 11-16575 JP 2005-267955 A

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that has a high output and a high energy density, is excellent in safety at the time of an internal short circuit, and is very difficult to break when the electrode is wound. .

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, in the nonaqueous electrolyte secondary battery, a configuration including an electrode plate in which an active material layer is formed on a current collector having strength anisotropy was found. When the present inventors conducted a nail penetration test on a battery having this configuration, the contact area between the nail and the current collector was reduced, and conduction between the nail and the current collector was interrupted by partial melting of the current collector. As a result, it has been found that the progress of the internal short circuit is prevented and the occurrence of abnormal heat generation can be suppressed or prevented. Moreover, according to the said structure, it also discovered that the fracture | rupture of an electrode was suppressed notably at the time of electrode winding. The present inventor has completed the present invention based on these findings.

That is, the present invention is a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and an electrode group obtained by laminating or winding a positive electrode plate and a negative electrode plate via a porous insulating layer,
At least one of the positive electrode plate and the negative electrode plate relates to a nonaqueous electrolyte secondary battery including a strip-shaped current collector having anisotropy in strength.

The band-shaped current collector having anisotropy in strength preferably has a breaking strength and a breaking strength in the longitudinal direction is higher than a breaking strength in the width direction.
More preferably, the breaking strength in the longitudinal direction is greater than 100% and 120% or less with respect to the breaking strength in the width direction.
The strip-shaped current collector having anisotropy in strength preferably has a thin portion extending in the longitudinal direction of the current collector.
The thin portion is preferably a portion that is thinned by forming a groove on the surface of the belt-like current collector.

It is preferable that the plurality of grooves are intermittently formed in at least one selected from the longitudinal direction and the width direction of the strip-shaped current collector.
It is preferable that the pitch of the grooves in the longitudinal direction of the belt-like current collector is 50 μm or less.
It is preferable that the groove pitch in the width direction of the belt-shaped current collector is 3 mm or less.
It is preferable that the length of the groove | channel in the longitudinal direction of a strip | belt-shaped collector is 20 micrometers-10 mm.
It is preferable that the depth of the groove with respect to the surface of the band-shaped current collector is 17% or more of the thickness of the band-shaped current collector.

  According to the present invention, by using an electrode plate including a strip-shaped current collector having anisotropy in strength, the internal short circuit between the current collectors does not continue in the nail penetration test, and abnormal heat generation hardly occurs. A non-aqueous electrolyte secondary battery with extremely high safety at the time is provided. Further, according to the present invention, the electrode breakage during the winding of the electrode is remarkably suppressed, so that both the suppression of the electrode breakage and the improvement of the safety of the battery can be achieved. In addition, the non-aqueous electrolyte secondary battery of the present invention does not show a decrease in battery performance due to the use of a current collector having anisotropy in strength, has a high energy density, and is capable of high output. . Therefore, the non-aqueous electrolyte secondary battery of the present invention is useful as a power source for driving various electric devices and electronic devices.

The nonaqueous electrolyte secondary battery of the present invention is characterized in that at least one of the positive electrode plate and the negative electrode plate includes a strip-shaped current collector having anisotropy in strength.
By using the strip-shaped current collector having anisotropy in strength, the safety at the time of internal short circuit of the battery is improved. In particular, a strip-shaped current collector having anisotropy of strength such that the strength in the longitudinal direction is greater than the strength in the width direction has a high effect of enhancing safety at the time of internal short-circuiting of the battery. Furthermore, when the band-shaped current collector having the strength anisotropy as described above is used, it is possible to prevent the electrode plate that is the positive electrode plate or the negative electrode plate from being broken when the wound electrode group is manufactured.

  The reason why such an excellent effect can be obtained is assumed as follows. Normally, if the current collector has a substantially uniform strength, the current collector contacts the nail over a wide area during the nail penetration test, and the low-resistance short circuit continues. As a result, the amount of Joule heat generated may increase. However, if the strength of the current collector is anisotropic, the nail-pierced portion of the current collector tends to tear in the direction of low strength, and the contact area between the nail and the current collector becomes very small. If this contact area is small, the current collector in contact with the nail is melted by Joule heat, the conduction between the nail and the current collector is interrupted in a short time, and the low-resistance short circuit is immediately interrupted at that time. It is thought that. The strength anisotropy of the current collector is important to have a weak direction in the current collector, regardless of whether the direction of weak strength is the longitudinal direction or the short direction of the current collector. It is.

  Further, when the electrode is wound, tension is applied in the longitudinal direction of the strip-shaped current collector. In the prior art, in order to prevent the electrode from being broken when the electrode is wound, for example, the thickness of the current collector is increased. However, if the thickness of the current collector is large, the contact area between the nail and the current collector increases during the nail penetration test, the internal short circuit continues, and the safety of the battery decreases. On the other hand, in the present invention, for example, even if the longitudinal strength of the belt-like current collector is set so that it can withstand the tension during winding of the electrode and the current collector is significantly prevented from breaking, Safety is improved. That is, even if the thickness of the belt-shaped current collector is increased, if the groove extending in the longitudinal direction is formed, the strength in the lateral direction can be made lower than the strength in the longitudinal direction while maintaining the strength in the longitudinal direction. . Thereby, in this invention, it succeeded in making the electrode breakage prevention at the time of electrode winding and the safety | security improvement of a battery compatible.

The non-aqueous electrolyte secondary battery of the present invention includes a laminated or wound electrode group composed of a positive electrode, a negative electrode, and a porous insulating layer, and a non-aqueous electrolyte.
The positive electrode includes a positive electrode current collector and a positive electrode active material layer.

  The positive electrode current collector is a band-shaped current collector having strength anisotropy. The strength anisotropy in the band-shaped current collector is preferably an anisotropy in which the strength in the longitudinal direction of the band-shaped current collector is larger than the strength in the width direction (short direction) of the band-shaped current collector. The strength is preferably a breaking strength. Thereby, safety at the time of an internal short circuit of the battery is ensured, and the positive electrode plate is prevented from being broken when the wound electrode group is formed. Further, the breaking strength in the longitudinal direction is more preferably more than 100% and 120% or less, particularly preferably 102% to 120%, with respect to the breaking strength in the width direction. By selecting the breaking strength in the longitudinal direction from the above range, it is possible to realize safety at the time of internal short circuit of the battery and prevention of breaking of the electrode at the time of manufacturing the wound electrode at a higher level.

  The band-shaped current collector having strength anisotropy is, for example, a band-shaped current collector in which a thin portion is formed. Here, the thin portion is a portion whose thickness is smaller than the thickness of the belt-like current collector. By forming the thin portion so as to extend in the longitudinal direction, anisotropy in which the strength in the longitudinal direction is greater than the strength in the width direction is exhibited. Further, when the nail is pierced into the thin wall portion, since the thickness is small, the contact area between the nail and the current collector is further reduced, and the effect of improving the safety when the battery is short-circuited is further improved. Therefore, a very safe battery can be obtained by forming a plurality of thin-walled portions and appropriately selecting the arrangement of the strip-shaped current collector.

Further, the thin portion may be a portion where the thickness is reduced by forming a groove on the surface of the belt-like current collector, for example. The groove is preferably formed in the longitudinal direction of the belt-like current collector, similarly to the thin portion.
FIG. 1 is a top view schematically showing a configuration of a strip-like current collector 1 which is one embodiment of the present invention. The strip-shaped current collector 1 is a metal foil having strength anisotropy and having a plurality of grooves 2 extending in the longitudinal direction on the surface 1a. The grooves 2 are formed on a straight line in the longitudinal direction at intervals. A plurality of grooves arranged on a straight line are called a row of grooves unless otherwise specified. There are a plurality of rows of grooves, which are arranged in the short direction of the strip-shaped current collector 1.

  The pitch in the longitudinal direction of the grooves 2 in the row of grooves is not particularly limited, but is preferably 50 μm or less, and more preferably 10 μm to 50 μm. When the pitch in the longitudinal direction of the grooves 2 exceeds 50 μm, the strength anisotropy becomes insufficient, and the short-circuit current blocking effect due to melting of the current collector may be reduced. In some cases, abnormal heat generation may occur. Even if the pitch in the longitudinal direction of the grooves 2 is less than 10 μm, the effect of improving the safety of the battery can be obtained, but a very precise groove 2 forming process is required, which may increase the manufacturing cost of the current collector. is there.

  The pitch in the width direction of the row of grooves is not particularly limited, but is preferably 10 μm to 3 mm. If the pitch in the width direction is less than 10 μm, the rigidity of the entire belt-shaped current collector 1 is lowered, and cracks and the like are likely to occur in the belt-shaped current collector 1 as the charge / discharge cycle is repeated. Peeling easily occurs. As a result, battery performance may be reduced. On the other hand, if the pitch in the width direction exceeds 3 mm, the anisotropy of the strength of the strip-shaped current collector 1 is insufficient, and the electrical conduction between the material that caused the short circuit at the time of the internal short circuit and the current collector is insufficient. There is a risk of becoming.

  The length of the groove 2 in the longitudinal direction of the belt-like current collector is not particularly limited, but is preferably 20 μm or more, and more preferably 20 μm to 10 mm. If the length of the groove 2 is less than 20 μm, the difference between the strength in the longitudinal direction and the strength in the width direction of the strip-shaped current collector 1 is reduced, and the contact area between the nail and the current collector 1 is reduced when the nail is stabbed. The effect may be reduced. As a result, there is a possibility of abnormal heat generation during an internal short circuit. If it exceeds 10 mm, the strength in the longitudinal direction of the strip-shaped current collector 1 decreases to such an extent that it cannot withstand the stress during winding of the electrode, and the strip-shaped current collector 1 may be broken during winding of the electrode.

The depth of the groove 2 is not particularly limited, but is preferably 17% or more, more preferably 17% to 80% of the thickness of the strip-shaped current collector 1. When the depth of the groove 2 is less than 17%, the difference between the strength in the longitudinal direction and the strength in the width direction of the strip-shaped current collector 1 becomes small, and the contact area between the nail and the current collector 1 becomes small when the nail is stabbed. There is a risk that the effect of reducing. As a result, there is a possibility of abnormal heat generation during an internal short circuit. Further, when the depth of the groove 2 exceeds 80%, the rigidity of the entire belt-like current collector 1 is lowered, and it is possible to observe a decrease in current collecting property, generation of cracks, partial peeling of the active material layer, and the like. There is sex. Furthermore, there is a possibility that the electrode plate breaks when the electrode is wound.
The groove 2 may be formed on one surface of the strip-shaped current collector 1 or may be formed on both surfaces of the strip-shaped current collector 1.

  The positive electrode current collector is a metal foil made of stainless steel, aluminum, an aluminum alloy, titanium, or the like, in which a thin portion as described above, preferably the groove 2 is formed. Although the thickness of metal foil is not specifically limited, Preferably it is 1-500 micrometers, More preferably, it is 5-20 micrometers. By selecting the thickness of the metal foil from the above range, it is possible to reduce the battery weight while maintaining the rigidity of the electrode plate. The groove 2 can be formed by, for example, laser processing, etching processing, or the like.

The positive electrode active material layer is formed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material, and further contains a binder, a conductive material, and the like as necessary.
As the positive electrode active material, those commonly used in the field of non-aqueous electrolyte secondary batteries can be used, but lithium-containing composite metal oxides, olivine-type lithium salts, and the like are preferable in view of capacity, safety, and the like.

Examples of the lithium-containing composite metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _{1 -y} O ₂ , Li _x Co _y M _{1 -y} O _z , and Li _{x. Ni 1-y M y O z} , Li x Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M in the formula Na, Mg, Sc, Y, Mn, It represents at least one element selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B. x represents the molar ratio of lithium atoms and is 0 to 1.2. y represents the molar ratio of transition metal atoms, and is 0 to 0.9, and z represents the molar ratio of oxygen atoms, and is 2 to 2.3. The value x indicating the molar ratio of lithium atoms increases and decreases with charge and discharge, and more preferably 0.8 to 1.5. The value of y is more preferably more than 0 and 0.9 or less. Examples of the olivine type lithium salt include LiFePO ₄ . A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

  The binder is not particularly limited, and those commonly used in the field of nonaqueous electrolyte secondary batteries can be used. For example, for example, polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, rubber particles and the like can be used. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. A binder can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  Examples of the conductive material include carbon materials such as carbon blacks such as Tennobu graphite, artificial graphite graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. A conductive material can be used individually by 1 type or in combination of 2 or more types.

  The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture paste to the surface of the positive electrode current collector, drying, and rolling as necessary. The positive electrode mixture paste can be prepared, for example, by adding a positive electrode active material to a dispersion medium together with a binder, a conductive material, and the like, if necessary. As the dispersion medium, for example, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, dimethylformamide and the like can be used.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer.
The negative electrode current collector is a strip-shaped current collector having anisotropy in strength similar to the positive electrode current collector. The band-shaped current collector having strength anisotropy is, for example, a band-shaped current collector in which a thin portion is formed. This has the same configuration as that described in the section of the positive electrode current collector. Moreover, the strip | belt-shaped electrical power collector in which the thin part was formed also includes the strip | belt-shaped electrical power collector with which the groove | channel was formed in the electrical power collector surface. The band-shaped current collector having grooves formed on the surface has the same structure as that described in the section of the positive electrode current collector.

  The negative electrode current collector is formed by forming a thin portion, preferably a groove, on a metal foil made of, for example, stainless steel, nickel, copper, copper alloy or the like. The thickness of the metal foil is preferably 1 to 500 μm, more preferably 5 to 20 μm. By selecting the thickness of the metal foil from the above range, the battery can be reduced in weight while maintaining the rigidity of the negative electrode plate.

  In the present invention, the effect of the present invention can be obtained by configuring either one or both of the positive electrode current collector and the negative electrode current collector with a band-shaped current collector having strength anisotropy. When a band-shaped current collector having strength anisotropy is used for one of the positive electrode current collector and the negative electrode current collector, the other current collector is a generally used nonporous or porous metal foil, metal fiber Nonwoven fabric, woven fabric, etc. can be used. The metal which becomes these materials is stainless steel, aluminum, aluminum alloy, titanium or the like for the positive electrode current collector, and stainless steel, nickel, copper, copper alloy or the like for the negative electrode current collector.

The negative electrode active material layer contains a negative electrode active material, and contains a binder and a conductive material as necessary.
Examples of the negative electrode active material include a carbon material, an alloy-based negative electrode active material, and an alloy material. Examples of the carbon material include various natural graphite, coke, graphitized carbon, carbon fiber, spherical carbon, various artificial graphite, amorphous carbon, and the like.
The alloy-based negative electrode active material is an active material that occludes and releases lithium when alloyed with lithium. Examples of the alloy-based negative electrode active material include an alloy-based negative electrode active material containing silicon and an alloy-based negative electrode active material containing tin.

Examples of the alloy-based negative electrode active material containing silicon include silicon, silicon oxide, silicon nitride, silicon-containing alloy, and silicon compound. Examples of the silicon oxide include silicon oxide represented by the composition formula: SiO _a (0.05 <a <1.95). Examples of the silicon nitride include silicon nitride represented by the composition formula: SiN _b (0 <b <4/3). Examples of the silicon-containing alloy include an alloy containing silicon and one or more elements selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. It is done. As the silicon compound, for example, a part of silicon contained in silicon, silicon oxide, silicon nitride or silicon-containing alloy is B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Examples thereof include compounds substituted with one or more elements selected from the group consisting of Nb, Ta, V, W, Zn, C, N and Sn.

Examples of the alloy-based negative electrode active material containing tin include tin, tin oxide, a tin-containing alloy, and a tin compound. Examples of the tin oxide include SnO ₂ and silicon oxide represented by a composition formula: SnO _d (0 <d <2). Examples of the tin-containing alloy include a Ni—Sn alloy, a Mg—Sn alloy, a Fe—Sn alloy, a Cu—Sn alloy, and a Ti—Sn alloy. Examples of the tin compound include SnSiO ₃ , Ni ₂ Sn ₄ , and Mg ₂ Sn.
A negative electrode active material can be used individually by 1 type, or can be used in combination of 2 or more type.

  As the binder and the conductive material, the same binder and conductive material that may be contained in the positive electrode active material layer can be used. As the binder, fluororesin, styrene butadiene rubber and the like are preferable.

The negative electrode active material layer can be formed, for example, by applying a negative electrode mixture paste to the surface of the negative electrode current collector, drying, and rolling as necessary. The negative electrode mixture paste can be prepared, for example, by adding a negative electrode active material to a dispersion medium together with a binder, a conductive material, a thickener, and the like as necessary. Examples of the thickener include carboxymethyl cellulose. As the dispersion medium, for example, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, dimethylformamide, water and the like can be used.
When an alloy-based negative electrode active material is used as the negative electrode active material, the negative electrode active material layer may be formed by vapor deposition, sputtering, chemical vapor deposition, or the like.

  The porous insulating layer is disposed between the positive electrode and the negative electrode, and insulates the positive electrode and the negative electrode. Examples of the porous insulating layer include a synthetic resin porous sheet. Examples of the synthetic resin constituting the porous sheet include polyolefins such as polyethylene and polypropylene, polyamides, and polyamideimides. The synthetic resin porous sheet includes non-woven fabrics and woven fabrics of resin fibers. Among these, a porous sheet in which the diameter of pores formed inside is about 0.05 to 0.15 μm is preferable. Such a porous sheet has high levels of ion permeability, mechanical strength, and insulation. Moreover, the thickness of a porous sheet should just be 5-20 micrometers, for example.

Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, a solid electrolyte (for example, a polymer solid electrolyte), and the like.
The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary. Solutes usually dissolve in non-aqueous solvents. For example, the insulating layer is impregnated with the liquid nonaqueous electrolyte.

The solute can be one commonly used in this field, 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 lithium carboxylates, LiCl, LiBr, LiI, chloroborane lithium, borates, imide salts and the like. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') and bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate Etc. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate ((CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) NLi) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. A solute may be used individually by 1 type, or may be used in combination of 2 or more type as needed. The amount of the solute dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2 mol / L.

  As the non-aqueous solvent, those commonly used in this field can be used, and examples thereof include cyclic carbonate esters, chain carbonate esters, and cyclic carboxylic acid esters. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, or may be used in combination of 2 or more type as needed.

  Examples of the additive include a material that improves charge / discharge efficiency and a material that inactivates the battery. A material that improves charge / discharge efficiency, for example, decomposes on the negative electrode to form a film having high lithium ion conductivity, and improves charge / discharge efficiency. Specific examples of such materials include, for example, vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4-propyl vinylene. Examples include carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), divinyl ethylene carbonate, and the like. These may be used alone or in combination of two or more. Among these, at least one selected from vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate is preferable. In the above compound, part of the hydrogen atoms may be substituted with fluorine atoms.

  The material that inactivates the battery inactivates the battery by, for example, decomposing when the battery is overcharged to form a film on the electrode surface. Examples of such a material include benzene derivatives. Examples of the benzene derivative include a benzene compound containing a phenyl group and a cyclic compound group adjacent to the phenyl group. As the cyclic compound group, for example, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, a phenoxy group and the like are preferable. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether, and the like. A benzene derivative can be used individually by 1 type, or can be used in combination of 2 or more type. However, the content of the benzene derivative in the liquid nonaqueous electrolyte is preferably 10 parts by volume or less with respect to 100 parts by volume of the nonaqueous solvent.

  The gel-like non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a polymer material that holds the liquid non-aqueous electrolyte. The polymer material used here is capable of gelling a liquid material. As the polymer material, those commonly used in this field can be used, and examples thereof include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, and polyacrylate.

  The solid electrolyte includes a solute (supporting salt) and a polymer material. Solutes similar to those exemplified above can be used. Examples of the polymer material include polyethylene oxide (PEO), polypropylene oxide (PPO), a copolymer of ethylene oxide and propylene oxide, and the like.

  FIG. 2 is a longitudinal sectional view schematically showing a configuration of a cylindrical nonaqueous electrolyte secondary battery 10 which is one embodiment of the present invention. The cylindrical nonaqueous electrolyte secondary battery 10 includes a positive electrode 11, a negative electrode 12, a separator 13, a positive electrode lead 14, a negative electrode lead 15, an upper insulating plate 16, a lower insulating plate 17, a battery case 18, a sealing plate 19, a positive electrode terminal 20, and This is a wound battery including a non-aqueous electrolyte (not shown). The current collectors of the positive electrode 11 and the negative electrode 12 are band-shaped current collectors having a plurality of grooves extending in the longitudinal direction formed on the surface.

  The positive electrode 11, the negative electrode 12, and the separator 13 are superposed in the order of the positive electrode 11, the separator 13, and the negative electrode 12, and are wound in a spiral shape. Thereby, a wound electrode group is formed. The positive electrode lead 14 has one end connected to the positive electrode 11 and the other end connected to the sealing plate 19. The material of the positive electrode lead 14 is, for example, aluminum. The negative electrode lead 15 has one end connected to the negative electrode 12 and the other end connected to the bottom inner wall of the battery case 18 serving as a negative electrode terminal. The material of the negative electrode lead 15 is, for example, nickel. The battery case 18 is a bottomed cylindrical container member, and one end in the longitudinal direction is an opening and the other end is a bottom, and functions as a negative electrode terminal. The upper insulating plate 16 and the lower insulating plate 17 are resin members, are arranged so as to sandwich the wound electrode group from above and below, and insulate the wound electrode group from other members. The material of the battery case 18 is, for example, iron. For example, nickel plating is applied to the inner surface of the battery case 18. The sealing plate 19 includes a positive electrode terminal 20.

  The cylindrical nonaqueous electrolyte secondary battery 1 can be manufactured, for example, as follows. First, the upper insulating plate 16 and the lower insulating plate 17 are attached to the upper end portion and the lower end portion of the wound electrode group, respectively, and housed in the battery case 18 in that state. The positive lead 14 is used for connection. The negative electrode 12 and the bottom of the battery case 18 that also serves as a negative electrode terminal are connected by a negative electrode lead 15. Next, a nonaqueous electrolyte is poured into the battery case 18, and the opening of the battery case 18 is sealed using the sealing plate 19. Thereby, the nonaqueous electrolyte secondary battery 10 is obtained. The sealing plate 19 may be fitted into the opening of the battery case 18 with a gasket attached to the peripheral edge thereof.

  The nonaqueous electrolyte battery of the present invention can take any shape such as a cylindrical shape, a square shape, a flat plate shape, a coin shape, and a laminate shape. The electrode group may be a wound type or a laminated type.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
Example 1
(1) Production of positive electrode current collector A strip-shaped aluminum foil (58 mm × 750 mm) having a thickness of 15 μm, a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), and a length in the longitudinal direction (hereinafter simply referred to as “long” A groove-shaped positive electrode current collector having a breaking strength in the longitudinal direction larger than that in the width direction was formed by laser processing to form grooves having a thickness of 25 μm and a pitch of 50 μm. This positive electrode current collector had a breaking strength in the longitudinal direction of 102% of the breaking strength in the width direction.

(2) Production of positive electrode plate 100 parts by weight of the positive electrode active material, 2 parts by weight of acetylene black (conductive material) and 3 parts by weight of polyvinylidene fluoride (PVDF, binder) are added to N-methyl-2-pyrrolidone (NMP). The dissolved solution was mixed to prepare a positive electrode mixture paste. Lithium cobaltate was used as the positive electrode active material. A positive electrode mixture paste was intermittently applied to both surfaces of the positive electrode current collector obtained above for positive electrode lead welding, dried, and then rolled to form a positive electrode. Thereafter, the positive electrode was cut into a predetermined size to obtain a belt-like positive electrode plate. The total thickness of the positive electrode active material layers on both sides and the current collector was 150 μm.

(3) Production of Negative Electrode Plate Scale-like artificial graphite was pulverized and classified to adjust the average particle size to 20 μm to obtain a negative electrode active material. A negative electrode mixture paste was prepared by mixing 100 parts by weight of the negative electrode active material, 1 part by weight of styrene butadiene rubber (binder) and 100 parts by weight of a 1% by weight aqueous solution of carboxymethyl cellulose. The negative electrode mixture paste was applied to both sides of a 10 μm thick copper foil (negative electrode current collector), dried, and then rolled to form a negative electrode. Thereafter, the negative electrode was cut into a predetermined size to obtain a strip-shaped negative electrode plate. The total thickness of the negative electrode active material layers on both sides and the current collector was 155 μm.

(4) Production of Laminate Battery One end of an aluminum positive electrode lead was attached to the positive electrode current collector, and one end of a nickel negative electrode lead was attached to the negative electrode current collector. The positive electrode plate and the negative electrode plate were wound through a polyethylene porous film (porous insulating layer) having a thickness of 20 μm to produce an electrode group. This electrode group was inserted into an outer case made of an aluminum laminate sheet together with a nonaqueous electrolyte. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1 was used.

  After impregnating the nonaqueous electrolyte into the positive electrode, the negative electrode, and the polyethylene porous membrane, respectively, the other ends of the positive electrode lead and the negative electrode lead were led out of the outer case. In this state, while reducing the pressure inside the outer case, the end portion of the outer case was welded and sealed to produce a nonaqueous electrolyte secondary battery (capacity 30 mAh) of the present invention.

(Example 2)
Example 1 except that a positive electrode current collector in which a groove having a depth of 4.1 μm (about 27% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 50 μm is formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. The nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as described above.

(Example 3)
Example 1 except that a positive electrode current collector in which grooves having a depth of 5.6 μm (about 37% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 50 μm are formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. The nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as described above.

Example 4
Example 1 except that a positive electrode current collector in which grooves having a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), a length of 45 μm, and a pitch of 50 μm are formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. The nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as described above.

(Example 5)
The nonaqueous electrolyte of the present invention is the same as in Example 1 except that a positive electrode current collector in which grooves having a depth of 2.6 μm, a length of 65 μm, and a pitch of 50 μm are formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. A secondary battery was prepared.

(Example 6)
Example 1 except that a positive electrode current collector in which a groove having a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 40 μm is formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. The nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as described above.

(Example 7)
Example 1 except that a positive electrode current collector in which a groove having a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 30 μm is formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. The nonaqueous electrolyte secondary battery of the present invention was produced in the same manner as described above.
In all of the positive electrode current collectors obtained in Examples 2 to 7, the breaking strength in the longitudinal direction was greater than 100% and 120% or less with respect to the breaking strength in the width direction.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a positive electrode current collector that did not form grooves on the surface of a 15 μm thick strip-shaped aluminum foil was used.

(Comparative Example 2)
Example 1 is used except that a positive electrode current collector in which grooves having a depth of 1.5 μm (about% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 50 μm are formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. Similarly, a nonaqueous electrolyte secondary battery was prepared.

(Comparative Example 3)
Example 1 except that a positive electrode current collector in which grooves having a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), a length of 20 μm, and a pitch of 50 μm are formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. In the same manner, a nonaqueous electrolyte secondary battery was produced.

(Comparative Example 4)
Example 1 except that a positive electrode current collector in which a groove having a depth of 2.6 μm (about 17% of the thickness of the aluminum foil), a length of 25 μm, and a pitch of 60 μm is formed on the surface of a strip-shaped aluminum foil having a thickness of 15 μm is used. In the same manner, a nonaqueous electrolyte secondary battery was produced.

(Test Example 1)
[Safety evaluation]
An internal short circuit test was performed using the batteries of Examples 1 to 7 and Comparative Examples 1 to 4. The test was carried out by passing a 3 mmφ nail through the battery at a constant speed and then applying 4.2 V with an external power source to generate a short circuit. After the occurrence of the short circuit, it was measured whether the short circuit continued for 1 second or more.

[Evaluation of positive electrode breakage during winding]
The positive electrode and the negative electrode obtained in the same manner as in Example 1 (2) Production of positive electrode plate and (3) Production of negative electrode plate were cut into a width of 3 cm and a length of 50 cm, respectively, to produce a positive electrode plate and a negative electrode plate. did. The positive electrode plate and the negative electrode plate were wound with a 3 mmφ winding core through a polyethylene porous film to prepare an electrode group. After the electrode group was disassembled, it was visually observed whether or not the positive electrode plate was broken at the innermost periphery. The results are shown in Table 1.

From Table 1, it can be seen that the batteries of Examples 1 to 7 have a lower short-circuit temperature around the batteries of Comparative Examples 1, 3, and 4. This is thought to be due to the fact that the contact area between the nail and the current collector is reduced during penetration because the breaking strength in the width direction is reduced due to the groove processing of the current collector. In addition, it can be seen that the battery of Example 1 is less susceptible to electrode breakage during winding than the battery of Comparative Example 2. This is presumably because the strength in the longitudinal direction was reduced because the current collector of Comparative Example 2 was grooved in the width direction.
In the above embodiment, a laminate type battery is used, but the same effect can be obtained by using a battery having a different shape such as a cylinder or a square.

  The non-aqueous electrolyte secondary battery of the present invention has a high energy density and is capable of high output as well as excellent safety during internal short circuit. Therefore, the nonaqueous electrolyte secondary battery of the present invention is a driving source for portable electric and electronic devices such as notebook personal computers, mobile phones, digital still cameras, and small machine tools, and also for power storage that requires high output. It is useful as a power source for electric vehicles.

It is a top view which simplifies and shows the structure of the strip | belt-shaped collector which is one of the embodiment of this invention. It is a longitudinal section showing typically the composition of the cylindrical type nonaqueous electrolyte secondary battery which is one of the embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Band-shaped collector 2 Groove 10 Cylindrical non-aqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead 15 Negative electrode lead 16 Upper insulating plate 17 Lower insulating plate 18 Battery case 19 Sealing plate 20 Positive electrode terminal

Claims (10)

A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte and an electrode group obtained by laminating or winding a positive electrode plate and a negative electrode plate via a porous insulating layer,
A nonaqueous electrolyte secondary battery in which at least one of a positive electrode plate and a negative electrode plate includes a strip-shaped current collector having anisotropy in strength.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the band-shaped current collector having anisotropy in strength has a breaking strength and a breaking strength in the longitudinal direction is higher than a breaking strength in the width direction.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the breaking strength in the longitudinal direction is greater than 100% and 120% or less with respect to the breaking strength in the width direction.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the belt-like current collector having anisotropy in strength has a thin portion extending in a longitudinal direction of the current collector.   The non-aqueous electrolyte secondary battery according to claim 4, wherein the thin portion is a portion thinned by forming a groove on the surface of the belt-like current collector.   The nonaqueous electrolyte secondary battery according to claim 5, wherein the plurality of grooves are intermittently formed in at least one selected from the longitudinal direction and the width direction of the belt-like current collector.   The nonaqueous electrolyte secondary battery according to claim 6, wherein the pitch of the grooves in the longitudinal direction of the strip-shaped current collector is 50 μm or less.   The nonaqueous electrolyte secondary battery according to claim 6 or 7, wherein the pitch of the grooves in the width direction of the belt-like current collector is 3 mm or less.   The nonaqueous electrolyte secondary battery according to any one of claims 6 to 8, wherein the length of the groove in the longitudinal direction of the belt-like current collector is 20 µm to 10 mm.   The nonaqueous electrolyte secondary battery according to any one of claims 6 to 9, wherein the depth of the groove with respect to the surface of the band-shaped current collector is 17% or more of the thickness of the band-shaped current collector.

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