JP2016058169A - Nonaqueous electrolyte secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery provided with a wound-type electrode body having improved safety during overcharge, and a method for producing the same. SOLUTION: A non-aqueous electrolyte solution containing a wound type electrode body, in which a long positive electrode and a negative electrode are opposed to each other via a separator and wound, and a non-aqueous electrolyte solution, are housed in a battery case. It is the next battery. Here, the capacity per unit area of the electrode of the portion forming the innermost circumference of the wound electrode body is defined as CI, and the capacity per unit area of the electrode of the portion forming the outermost circumference of the wound electrode body is represented by CO. And At this time, the non-aqueous electrolyte secondary battery is characterized in that the outermost peripheral capacity reduction rate R defined by the following formula: R=(1-CO/CI)×100 satisfies 0.3≦R≦3. Be attached. [Selection diagram] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery including a wound electrode body with improved safety during overcharging, and a method for manufacturing the same.

  Nonaqueous electrolyte secondary batteries such as lithium ion batteries and nickel metal hydride batteries are preferably used as portable power supplies, high output power supplies for mounting on vehicles, and the like because they are lightweight and provide high energy density. Among these non-aqueous electrolyte secondary batteries, in particular, secondary batteries that have high capacity and repeat high-rate charge / discharge (rapid charge / discharge) (for example, batteries for in-vehicle use) have excellent battery performance. Of course, extremely high safety is required. With regard to the safety of this non-aqueous electrolyte secondary battery, in particular, securing safety against overcharging is regarded as the most important issue. In addition, the Chinese battery standard (QC / T743-2006) stipulates safety and the like when overcharging a lithium ion storage battery for an electric vehicle.

  A non-aqueous electrolyte secondary battery is used in a state where the voltage is controlled so as to be within a predetermined region (for example, 3.0 V or more and 4.2 V or less). Then, the battery may be overcharged beyond a predetermined voltage. Thus, it is known to use a separator having a shutdown function as a safety mechanism for stopping the progress of overcharge. This separator is typically composed of a resin-made microporous sheet, and allows charge carriers to be held and moved between the positive and negative electrodes when a normal battery is used. When the battery becomes high temperature due to overcharging or the like, the separator softens and closes the pores, blocks the movement of charge carriers and stops the charging reaction.

  As another safety mechanism for overcharge, a pressure-sensitive current interrupt device (CID) that interrupts the charging current when the pressure in the battery case exceeds a predetermined value due to overcharge is widely adopted. Yes. For the purpose of operating this CID more quickly, it is referred to as a compound (overcharge additive, gas generating agent, etc.) having a lower oxidation potential (that is, the voltage at which the oxidative decomposition reaction starts) in advance than the nonaqueous solvent of the electrolyte. There is also known a method of containing “overcharge additive”) in an electrolyte. The overcharge additive can be decomposed during overcharge and generate gas to rapidly increase the internal pressure of the battery case, but can become a resistance component of the battery during normal battery use. Therefore, it has been proposed to increase the reaction efficiency of the overcharge additive during overcharge by performing high temperature aging treatment in a predetermined temperature range while suppressing the amount of overcharge additive added (Patent Document 1). Etc.).

JP 2013-0669490 A

However, in a nonaqueous electrolyte secondary battery including a wound electrode body as a power generation element, it is difficult to stop overcharging in a safe state with the shutdown function by the separator because the heat dissipation of the electrode body is poor. There was a case. In addition, the CID has a relatively delicate structure, which greatly increases the manufacturing cost. However, there is a problem that the CID may be damaged or malfunction due to vibration or impact of the vehicle. In addition, the installation of CID in the battery has the disadvantage that the number of parts increases and the battery size (volume) also increases.
This invention is made | formed in view of this situation, The objective is a non-aqueous-electrolyte secondary battery provided with the winding type electrode body by which the safety | security at the time of an overcharge was improved without depending on CID, for example Is to provide. Another object of the present invention is to provide a method capable of suitably producing this nonaqueous electrolyte secondary battery.

In order to solve the above-described problems, the present invention provides a battery case in which a wound electrode body formed by winding a long positive electrode and a negative electrode facing each other with a separator interposed therebetween, and a nonaqueous electrolyte solution are accommodated in a battery case. A non-aqueous electrolyte secondary battery is provided. Here, the capacity per unit area of the electrode constituting the innermost circumference of the wound electrode body (hereinafter sometimes simply referred to as “capacity of the innermost circumference”) may be referred to as C. and _I, the capacity per unit area of the portion of the electrodes constituting the outermost periphery of the wound electrode body (hereinafter, sometimes simply referred to as abbreviated as such "capacity of the outermost peripheral portion.") and C _O In this case, the outermost peripheral capacity reduction rate R defined by the following formula: R = (1-C _O / C _I ) × 100 satisfies 0.3 ≦ R ≦ 3. It is more preferable that the outermost peripheral capacity reduction rate R satisfies 0.95 ≦ R ≦ 1.1. Moreover, said structure can be suitably implement | achieved by the heat processing in the below-mentioned manufacturing process.

  According to the above configuration, the wound electrode body is configured such that the capacity of the outermost peripheral portion is smaller than the capacity of the innermost peripheral portion by a predetermined ratio. In addition, when such a configuration is realized by a heat treatment described later, it is possible to expect the effect that the charging additive is immobilized on the electrode surface on the outer peripheral side. Therefore, when the battery falls into an overcharged state, the overcharge of the outermost peripheral portion relatively proceeds, and the temperature difference between the inner peripheral side and the outer peripheral side of the wound electrode body is made uniform. As a result, the separator can be shut down almost simultaneously on the inner and outer peripheral sides of the wound electrode body during overcharging, preventing abnormal heat generation and stopping overcharging. As a result, for example, a nonaqueous electrolyte secondary battery with improved safety during overcharge without relying on CID is provided.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte contains an overcharge additive that decomposes during overcharge and generates heat or generates gas. It is a feature. For example, the non-aqueous electrolyte secondary battery is not required to contain an overcharge additive because safety at the time of overcharge is improved without relying on CID. However, it is preferable that the non-aqueous electrolyte includes the overcharge additive in this way in that the non-aqueous electrolyte secondary battery can be more easily constructed.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the battery case includes an external connection terminal, and the overturned electrode body and the external connection terminal are It is characterized by not having a CID that cuts off the conductive path between them. Since this non-aqueous electrolyte secondary battery has improved safety at the time of overcharging by adjusting the capacity of the wound electrode body as described above, it does not prevent the provision of the CID, but the CID is provided. There can be no configuration. As a result, compared with a battery having a CID, the possibility of a malfunction or malfunction based on the CID is eliminated at a low cost, and the battery size is reduced (or the volume of the wound electrode body is increased). A water electrolyte secondary battery is provided.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode and the negative electrode are provided with a current collector exposed portion at one end along the longitudinal direction of the long electrode current collector. In addition, an electrode active material layer is provided in a portion other than the current collector exposed portion. Further, the current collector exposed portion of the positive electrode and the current collector exposed portion of the negative electrode are arranged so as to protrude on the opposite side of the width direction perpendicular to the longitudinal direction, and the winding is performed with the width direction as an axis. Has been. The wound electrode body is configured such that current is collected from the positive electrode and the negative electrode in a current collecting unit in which the current collector exposed portions of the positive electrode and the negative electrode are respectively integrated. According to such a current collecting structure, charging and discharging can be performed with high efficiency from the wound electrode body, but there is a drawback in that the heat dissipation of the wound electrode body is hindered. However, the nonaqueous electrolyte secondary battery disclosed herein is configured to suppress temperature unevenness of the wound electrode body during overcharging. Therefore, the technology disclosed herein can be particularly preferably applied to a battery including the above current collecting structure.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the wound electrode body is a flat wound electrode body having a shape bent in a direction perpendicular to the axis. Yes. It is known that a flat wound electrode body is inferior in heat dissipation compared to a cylindrical wound electrode body. Therefore, the technique disclosed here can be applied particularly suitably to a battery including a flat wound electrode body.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the separator has a melting point lower than an abnormal heat generation temperature determined according to a positive electrode active material included in the positive electrode. . It is known that the separator can have a shutdown function that softens based on the temperature of the wound electrode body and blocks the movement of charge carriers between the positive and negative electrodes. In the shutdown function, when the temperature unevenness of the wound electrode body is large, there is a possibility that the shutdown timing may be shifted and lead to abnormal heat generation of the battery. Therefore, it is preferable that the conventional separator has resistance against the abnormal heat generation temperature. However, the nonaqueous electrolyte secondary battery disclosed herein is configured to suppress temperature unevenness of the wound electrode body during overcharging. Therefore, the technique disclosed here can be suitably applied to a battery using a general-purpose separator having a relatively low melting point without being limited to the type of the positive electrode active material.

In another aspect, the present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery. This manufacturing method is characterized by including the following steps (a1) to (a3).
(A1) Preparing a wound electrode body in which a long positive electrode and a negative electrode are wound so as to face each other via a separator. Here, the wound electrode body, a capacity per unit area of the portion of the electrode constituting the innermost circumference of the wound electrode body and C _I, constituting the outermost periphery of the wound electrode body When the capacity per unit area of the electrode of the part is C 2 _O , the outermost peripheral capacity reduction rate R defined by the following formula: R = (1−C 2 _O / C _I ) × 100 is 0.3 ≦ R ≦ 3 is satisfied.
(A2) A battery assembly in which the wound electrode body and the nonaqueous electrolytic solution are housed in a battery case is prepared.
(A3) A conditioning process is performed on the battery assembly.
As a result, it is possible to manufacture the nonaqueous electrolytic secondary battery including the wound electrode body configured such that the capacity of the outermost peripheral portion is smaller than the capacity of the innermost peripheral portion by a predetermined ratio. .

In still another aspect, the present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery. Such a manufacturing method is characterized by including the following steps (b1) to (b3).
(B1) A wound electrode body in which a long positive electrode and a negative electrode are wound while being opposed to each other via a separator, and a non-aqueous electrolyte containing an overcharge additive that generates gas during overcharge. Prepare a battery assembly housed in a battery case.
(B2) A conditioning process is performed on the battery assembly.
(B3) The battery assembly after the conditioning treatment is subjected to a local high-temperature aging treatment that is maintained for at least 5 minutes and at most 2 hours in a temperature range of at least 40 ° C. to 95 ° C.
Even with such a configuration, the above-described non-aqueous electrolytic secondary battery including the wound electrode body configured such that the capacity of the outermost peripheral portion is smaller than the capacity of the innermost peripheral portion by a predetermined ratio is manufactured. can do.

It is sectional drawing which shows typically the structure of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a schematic diagram explaining the structure of a wound electrode body.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, battery structures that do not characterize the present invention) can be obtained by those skilled in the art based on the prior art in this field. It can be grasped as a design item. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, dimensional relationships (length, width, thickness, etc.) in the drawings shown below do not necessarily reflect actual dimensional relationships.
In the present specification, the “non-aqueous electrolyte secondary battery” refers to a general battery that can be repeatedly charged and discharged using a non-aqueous electrolyte as an electrolyte. For example, a secondary battery that uses lithium ions (Li ions) or sodium ions (Na ions) as electrolyte ions (charge carriers) and realizes charge and discharge by movement of charges associated with Li ions and Na ions between the positive and negative electrodes. Is included. A secondary battery generally referred to as a lithium ion battery (or a lithium ion secondary battery), a lithium polymer battery, or the like is a typical example included in the lithium secondary battery in this specification. Further, in this specification, the “active material” refers to a material that can reversibly occlude and release chemical species (lithium ions) serving as a single charge.

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view showing a configuration of a non-aqueous electrolyte secondary battery 100 as one embodiment. This non-aqueous electrolyte secondary battery 100 is essentially composed of a wound electrode body 20 in which a long positive electrode 30 and a negative electrode 40 are disposed to face each other with a separator 50 interposed therebetween, and a non-aqueous electrolyte solution. (Not shown) is housed in the battery case 10. Hereinafter, the present invention will be described using a lithium secondary battery 100 as a preferred embodiment as an example. FIG. 2 is a diagram illustrating the configuration of the wound electrode body 20.

[Positive electrode]
The positive electrode 30 typically includes a long positive electrode current collector 32 and a positive electrode active material layer 34 held on the positive electrode current collector 32. The positive electrode current collector 32 may be provided with a portion where the positive electrode active material layer 34 is formed and a positive electrode current collector exposed portion 33 where the current collector 32 is exposed without forming the positive electrode active material layer 34. . The positive electrode current collector exposed portion 33 is typically provided in a strip shape at one end portion (one end portion in the width direction) along the longitudinal direction of the long positive electrode current collector 32. The positive electrode active material layer 34 is provided on the surface of the positive electrode current collector 32 excluding the positive electrode current collector exposed portion 33. The positive electrode active material layer 34 may be provided on both surfaces of the positive electrode current collector 32 or may be provided only on one of the surfaces. As the positive electrode current collector 32, a conductive member made of a metal having good conductivity (for example, aluminum, nickel and an alloy thereof) is suitable. The positive electrode active material layer 34 includes at least a positive electrode active material.

As the positive electrode active material, a material capable of inserting and extracting charge carriers can be used. In the case of a lithium ion secondary battery, a lithium-containing compound containing a lithium element and one or more transition metal elements (for example, a lithium transition metal composite oxide) is preferably used as the positive electrode active material. For example, a lithium transition metal oxide having a layered rock salt type or spinel type crystal structure is a preferred example. Such a lithium transition metal oxide is, for example, a lithium nickel composite oxide (eg, LiNiO ₂ ), a lithium cobalt composite oxide (eg, LiCoO ₂ ), a lithium manganese composite oxide (eg, LiMn ₂ O ₄ ), or lithium nickel cobalt. It may be a ternary lithium-containing composite oxide such as a manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). In addition, a polyanionic compound (for example, LiFePO ₄₎ whose general formula is represented by LiMPO _4, LiMVO _4, or Li ₂ MSiO ₄ (wherein M is at least one element of Co, Ni, Mn, and Fe), etc. ₄ , LiMnPO ₄ , LiFeVO ₄ , LiMnVO ₄ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ CoSiO ₄ ) may be used as the positive electrode active material.

  In addition to the positive electrode active material, the positive electrode active material layer 34 requires one or more materials that can be used as a component of the positive electrode active material layer in a general non-aqueous electrolyte secondary battery. Can be contained accordingly. Examples of such a material include a conductive material and a binder. As the conductive material, for example, carbon materials such as various carbon blacks (for example, acetylene black and ketjen black), activated carbon, graphite, and carbon fiber can be suitably used. As the binder, for example, a halogenated vinyl resin such as polyvinylidene fluoride (PVdF), or a polyalkylene oxide such as polyethylene oxide (PEO) can be preferably used. In addition, various additives (for example, an inorganic compound that generates gas during overcharge, a dispersant, a thickener, and the like) can be included as long as the effects of the present invention are not significantly impaired.

  The proportion of the positive electrode active material in the entire positive electrode active material layer 34 is suitably about 60% by mass or more (typically 60% by mass to 98% by mass) from the viewpoint of realizing a high energy density. Usually, it is preferable that it is about 70 mass%-98 mass%. Moreover, when using a binder, the ratio of the binder to the whole positive electrode active material layer shall be about 0.5 mass%-10 mass% from a viewpoint of ensuring mechanical strength (shape retainability) suitably, for example. Usually, it is preferably about 1% by mass to 5% by mass. When using a conductive material, from the viewpoint of achieving both high output characteristics and energy density, the proportion of the conductive material in the entire positive electrode active material layer can be, for example, approximately 1% by mass to 15% by mass, Usually, it is preferable to set it as about 2 mass%-10 mass%.

The thickness of the positive electrode active material layer 34 is not particularly limited, but may be, for example, 20 μm or more, typically 30 μm or more, and 200 μm or less, typically 100 μm or less. The mass (weight per unit area) of the positive electrode active material layer 34 provided per unit area of the positive electrode current collector 32 is 3 mg / cm ² or more (for example, 5 mg) per side of the positive electrode current collector 32 from the viewpoint of realizing a high energy density. / Cm ² or more, typically 7 mg / cm ² or more). From the viewpoint of realizing excellent output characteristics, the positive electrode current collector 32 may be 100 mg / cm ² or less per side (for example, 70 mg / cm ² or less, typically 50 mg / cm ² or less). The average thickness per one side of the positive electrode active material layer 34 is, for example, 20 μm or more (typically 40 μm or more), and may be 100 μm or less (typically 80 μm or less). Further, the density of the positive electrode active material layer 34 is, for example, 1.0 g / cm ³ or more (typically 2.0 g / cm ³ or more) and 4.5 g / cm ³ or less (for example, 4.0 g / cm ³ ). ³ or less).

[Negative electrode]
The negative electrode 40 typically includes a long negative electrode current collector 42 and a negative electrode active material layer 44 formed on the negative electrode current collector 42. The negative electrode current collector 42 is provided with a portion where the negative electrode active material layer 44 is formed and a negative electrode current collector exposed portion 43 where the current collector 42 is exposed without the negative electrode active material layer 44 being provided. . The negative electrode current collector exposed portion 43 is typically provided in a strip shape at one end portion (one end portion in the width direction) along the longitudinal direction of the negative electrode current collector 42. The negative electrode active material layer 44 is provided on the surface of the negative electrode current collector 42 excluding the negative electrode current collector exposed portion 43. As the negative electrode current collector 42, a conductive member made of a metal having good conductivity (for example, copper, nickel and an alloy thereof) is suitable. The negative electrode active material layer 44 includes at least a negative electrode active material.

As the negative electrode active material, one kind or two or more kinds of various materials known to be usable as the negative electrode active material of the nonaqueous electrolyte secondary battery can be adopted. Preferable examples include carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon nanotubes, or a combination of these. Among these, from the viewpoint of energy density, graphite-based materials such as natural graphite (graphite) and artificial graphite can be preferably used. As such a graphite-based material, a material in which amorphous carbon is disposed on at least a part of the surface can be preferably used. More preferably, almost all of the surface of the granular carbon is covered with an amorphous carbon film. Note that amorphous carbon has a large number of edge surfaces exposed on its surface, and has a high charge carrier acceptability (that is, the charge carrier is occluded / released quickly). Graphite has a large theoretical capacity and is excellent in energy density. Therefore, by using amorphous carbon-coated graphite as the negative electrode active material, it is possible to realize a non-aqueous electrolyte secondary battery having a large capacity, a high energy density, and excellent input / output characteristics. In addition to the carbon-based material, lithium transition metal composite oxides such as lithium titanium composite oxides such as Li ₄ Ti ₅ O ₁₂ and lithium transition metal composite nitrides can be used.

  In addition to the negative electrode active material, the negative electrode active material layer 44 requires one or more materials that can be used as a constituent of the negative electrode active material layer 44 in a general nonaqueous electrolyte secondary battery. Depending on the content. Examples of such materials include binders and various additives. As a binder, the thing similar to the binder used for the negative electrode of a general lithium ion secondary battery can be employ | adopted suitably. For example, the same binder as in the positive electrode 30 can be used, and other polymer materials such as rubbers such as styrene butadiene rubber (SBR), polyethylene oxide (PEO), and vinyl acetate copolymer can be preferably used. In addition, various additives such as a thickener, a dispersant, and a conductive material can be appropriately used for the negative electrode active material layer 44. For example, examples of the thickener include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and cellulose acetate phthalate (CAP).

  The proportion of the negative electrode active material in the entire negative electrode active material layer is suitably about 50% by mass or more, and usually 90% to 99% by mass (for example, 95% to 99% by mass). preferable. Thereby, a high energy density is realizable. When using a binder, the ratio of the binder to the whole negative electrode active material layer can be made into about 1 mass%-10 mass%, for example, and it is usually preferable to set it about 1 mass%-5 mass%. Thereby, the mechanical strength (shape retention) of a negative electrode active material layer can be ensured suitably, and favorable durability can be implement | achieved. When using a thickener, the ratio of the thickener to the whole negative electrode active material layer can be made into about 1 mass%-10 mass%, for example, Usually, it shall be about 1 mass%-5 mass%. Is preferred.

The mass (weight per unit area) of the negative electrode active material layer 44 provided per unit area of the negative electrode current collector 42 is 5 mg / cm ² per side of the negative electrode current collector 42 from the viewpoint of realizing high energy density and output density. It is good if it is above (typically 7 mg / cm ² or more) and about 20 mg / cm ² or less (typically 15 mg / cm ² or less). Further, the thickness per one side of the negative electrode active material layer 44 is, for example, 40 μm or more (typically 50 μm or more) and 100 μm or less (typically 80 μm or less). The density of the negative electrode active material layer 44 is, for example, 0.5 g / cm ³ or more (typically 1.0 g / cm ³ or more) and 2.0 g / cm ³ or less (typically 1.g / cm ³ or more). 5 g / cm ³ or less).

[Separator]
The nonaqueous electrolyte secondary battery 100 disclosed herein can include a separator 50 as a constituent component that insulates the positive electrode 30 and the negative electrode 40. The separator 50 is made of an insulating material, and is typically disposed between the positive electrode 30 and the negative electrode 40. The separator 50 is configured to hold the charge carrier and allow the charge carrier to pass therethrough. Such a separator 50 can be suitably constituted by a microporous sheet made of an insulating resin. Although not particularly limited, the separator 50 is configured to have a shutdown function that softens or melts when the wound electrode body 20 reaches a predetermined temperature and blocks the passage of charge carriers. May be. For example, a microporous sheet made of a polyolefin resin typified by polyethylene (PE) or polypropylene (PP) has a shutdown temperature of 80 ° C. to 140 ° C. (typically 110 ° C. to 140 ° C. while being relatively inexpensive. For example, the separator 50 is preferable because it can be suitably set within a range of 120 ° C to 135 ° C.

In addition, the separator 50 has an inorganic aggregate (for example, alumina (Al ₂ O ₃ ), boehmite (Al ₂ O ₃ .H ₂ O), magnesia (MgO), silica on one side or both sides. It is possible to provide a heat resistant layer (HRL, not shown) made of (SiO ₂ ), titania (TiO ₂ ) or other powdered inorganic oxide) and a binder. Thereby, for example, even if the temperature of the wound electrode body 20 is higher than the melting point of the separator 50 and the separator 50 breaks, it is possible to prevent the positive electrode 30 and the negative electrode 40 from being short-circuited. it can.

  The average thickness of the separator 50 is not particularly limited, but is usually 10 μm or more, typically 15 μm or more, for example, 17 μm or more. The upper limit may be 40 μm or less, typically 30 μm or less, for example, 25 μm or less. When the average thickness of the substrate is within the above range, the charge carrier permeability can be kept good, and a minute short circuit (leakage current) is less likely to occur. For this reason, input / output density and safety can be achieved at a high level.

[Winded electrode body]
As shown in FIG. 2, the long positive electrode 30 and the negative electrode 40 are typically wound in the longitudinal direction with a total of two long separators 50 interposed therebetween. In other words, the winding is performed with the width direction orthogonal to the longitudinal direction as the winding axis. Thereby, the wound electrode body 20 is constructed. At the time of lamination, the positive electrode current collector exposed portion 33 of the positive electrode 30 and the negative electrode current collector exposed portion 43 of the negative electrode 40 protrude from the two sides in the width direction of the separator 50 to different sides. And the negative electrode 40 may be overlapped with a slight shift in the width direction. As a result, in the winding axis direction of the wound electrode body 20, the positive electrode current collector exposed portion 33 and the negative electrode current collector exposed portion 43 respectively have a wound core portion (that is, the positive and negative active material layers 34 and 44 are It protrudes outward from the facing part. Thus, by integrating these current collector exposed portions 33 and 43 to form a current collector, charging and discharging of the positive electrode and the negative electrode can be realized with high efficiency in this current collector. The wound electrode body 20 may be cylindrical, for example, by crushing the cylindrical wound electrode body 20 from the side (in a direction perpendicular to the winding axis). It may be a flat shape.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte, typically, a supporting salt (for example, a lithium salt, a sodium salt, a magnesium salt, etc., or a lithium salt in a lithium ion secondary battery) is dissolved or dispersed in a non-aqueous solvent. Can be adopted.
As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones that are used as electrolytes in general non-aqueous electrolyte secondary batteries are used without particular limitation. be able to. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Such a non-aqueous solvent can be used alone or in combination of two or more.
As the supporting salt, various types used for general non-aqueous electrolyte secondary batteries can be appropriately selected and employed. For example, the use of lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ is exemplified. Such supporting salts may be used singly or in combination of two or more. Such a supporting salt is preferably prepared so that the concentration in the non-aqueous electrolyte is within the range of 0.7 mol / L to 1.3 mol / L.

  In addition, the nonaqueous electrolyte may contain various additives and the like as long as the characteristics of the nonaqueous electrolyte secondary battery of the present invention are not impaired. As such an additive, as a film forming agent, an overcharge additive, etc., one or more of the battery input / output characteristics improvement, cycle characteristic improvement, initial charge / discharge efficiency improvement, safety improvement, etc. Can be used for purposes. Specific examples of such film forming agents include film forming agents such as lithium bis (oxalato) borate (LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC); biphenyl (BP ), An overcharge additive composed of a compound capable of generating gas at the time of overcharge typified by an aromatic compound such as cyclohexylbenzene (CHB); a surfactant; a dispersant; a thickener; and the like. The concentration of these additives relative to the entire nonaqueous electrolyte varies depending on the type of additive, but is usually about 0.1 mol / L or less (typically 0.005 mol / L to 0.05 mol / L) for the film forming agent. L) and an overcharge additive, typically about 6% by mass or less (typically 0.5% to 4% by mass).

[Capacity of wound electrode body]
Further, when the wound electrode body has a capacitance C _I per unit area of the electrode constituting the innermost circumference and a capacitance C _O per unit area of the electrode constituting the outermost circumference, The outermost peripheral capacity reduction rate R defined by the following formula: R = (1−C 2 _O / C _I ) × 100 is expressed by the following formula:
0.3 ≦ R ≦ 3
It is adjusted to meet.

That is, the capacitance C _O of the outermost peripheral portion, with respect to the capacitance C _I of the innermost portion, the outermost volume reduction rate R is reduced in the range satisfying the above relationship. The effect of reducing the capacity _CO of the outermost peripheral part will be described below.
In general, when charging / discharging is performed in the nonaqueous electrolyte secondary battery 100, power loss is generated in proportion to the inevitable internal resistance, and this power loss generates heat. Since this heat generation is stored toward the inner peripheral side of the wound electrode body having a low heat dissipation property, the innermost peripheral portion is likely to have a higher temperature than the outermost peripheral portion. Therefore, for example, when the heat generation of the wound electrode body becomes significant due to overcharging or the like, the temperature difference between the innermost peripheral portion and the outermost peripheral portion of the wound electrode body also increases. At this time, for example, for the nonaqueous electrolyte secondary battery 100 including the separator 50 having the shutdown function, the ion conduction between the electrodes (shutdown) based on the softening point (shutdown temperature) of the polymer constituting the separator 50 is reduced. Deviations in timing can occur. Therefore, even if the separator located on the inner peripheral side shuts down early in the overcharge, the overcharge proceeds without shutting down on the outer peripheral side, and further temperature rise (for example, abnormal heat generation) may be caused. Then, due to such overcharging, the separator 50 on the inner peripheral side is further overheated, and heat shrinkage or melting and breakage (breakage) may cause a short circuit.

  In contrast, the nonaqueous electrolyte secondary battery 100 disclosed herein is configured such that the capacity of the outermost peripheral portion is smaller than the innermost peripheral portion by the amount satisfying the outermost peripheral capacity reduction rate R. Therefore, in the overcharged state, overcharging is likely to proceed at the outermost peripheral portion, and the temperature at the outermost peripheral portion is likely to rise. Thereby, the temperature unevenness at the time of overcharging in the wound electrode body 20 is eliminated, and the shutdown by the separator is performed almost simultaneously on the outer peripheral side and the inner peripheral side of the wound electrode body 20. As a result, further abnormal heat generation is prevented in advance, the occurrence of internal short circuit is suppressed, and the electrochemical reaction in the battery can be stopped safely. Thereby, the nonaqueous electrolyte secondary battery 100 excellent in safety against overcharging is realized.

  Here, when the outermost peripheral capacity reduction rate R exceeds 0, an effect of reducing temperature unevenness generated in the wound electrode body at the time of overcharging is expressed, and is 0.3 or more. This is preferable because a temperature unevenness reducing effect can be obtained with certainty. The outermost peripheral capacity reduction rate R is preferably 0.7 or more, more preferably 0.9 or more, and further preferably 0.95 or more, for example 0.96 or more. If the outermost peripheral capacity reduction rate R is too large, the energy density of the battery decreases, which is not preferable. Therefore, from the viewpoints of charge / discharge balance and weight per unit area when using a normal battery, the outermost peripheral capacity reduction rate R is preferably 3 or less, more preferably 2 or less, particularly 1.5 or less, for example, 1 More preferably, it is 1 or less.

  In the present specification, the “electrode of the portion constituting the innermost circumference” (the innermost circumference portion) in the wound electrode body means the most of the electrode portion that contributes to charge and discharge of the wound electrode body. This is a part constituting one turn of the wound electrode body on the inner peripheral side. In addition, “the electrode of the part constituting the outermost periphery” (outermost part) means that one part of the wound electrode body on the outermost periphery side of the wound electrode body among the electrode parts contributing to charge / discharge. It is a component part. A region where the positive and negative active material layers face each other can be considered as the electrode portion contributing to charging / discharging. Therefore, for example, a negative electrode active material layer portion that does not face a positive electrode active material that can be generally formed to make up for irreversible capacity, a separator winding portion that can exist in the innermost circumference as a shaft of a wound electrode body, etc. For the purpose of insulation from the battery case, etc., the separator terminal portion that is wound around the outermost periphery of the wound electrode body corresponds to the innermost or outermost portion of the electrode here. do not do.

Further, the capacities C _I and C _O per unit area of the innermost peripheral portion or the outermost peripheral portion are the innermost peripheral portion or the outermost peripheral portion (that is, the innermost peripheral portion or the outermost peripheral portion). (Electrode) is a value obtained by dividing the electrode capacity by the area. For example, the capacity measured for an evaluation battery (small battery) configured using an electrode punched out from the part with a predetermined area and an appropriate nonaqueous electrolyte is adopted as the electrode capacity of the innermost peripheral part or the outermost peripheral part. be able to. In this case, the punched-out part of the electrode can be, for example, one innermost circumference and one outermost circumference, and is determined as a predetermined area portion in the center of the planar portion of the electrode active material layer of these parts. You can also In the latter case, the punching shape is preferably circular.

  As described above, the non-aqueous electrolyte secondary battery 100 disclosed herein is configured such that temperature unevenness hardly occurs in the wound electrode body 20 in an overcharged state, and abnormal heat generation is not easily induced. Therefore, since the temperature of the wound electrode body 20 is suppressed from exceeding the melting point of the separator 50, the nonaqueous electrolyte secondary battery 100 disclosed herein includes the separator 50 that does not include the HRL. It may be a preferable form to provide. Furthermore, it may be a preferable embodiment that the separator 50 is made of a material having a melting point at a temperature lower than the abnormal heat generation temperature determined according to the positive electrode active material. For example, in the non-aqueous electrolyte secondary battery 100 disclosed herein, a lithium nickel manganese cobalt composite oxide (so-called ternary lithium transition metal oxide, abnormal heating temperature: 200 ° C.) is used as the positive electrode active material. In this case, a single-layer separator made of a PE or PP microporous sheet that is not provided with HRL, or a laminated separator made of a porous sheet on which PP or PE is laminated can be suitably used in combination.

  The abnormal heat generation temperature determined according to the positive electrode active material means that when the battery is constructed using the positive electrode active material for the positive electrode and a carbon material (typically graphite) for the negative electrode, the battery voltage is 4. It is the thermal decomposition temperature of the positive electrode active material in the state of 1V. The abnormal heat generation temperature is, for example, that when the positive electrode charged in a predetermined charging state is taken out and differential scanning calorimetry (DSC) is taken, the heat generation peak temperature seen by thermal decomposition is regarded as the abnormal heat generation temperature. Can do. In addition, about the well-known positive electrode active material material, the approximate abnormal heat generation temperature is known. For example, as an example, the abnormal heating temperature when a lithium cobaltate material is used as the positive electrode active material is about 200 ° C., the abnormal heating temperature when a lithium nickelate material is used is about 180 ° C., and lithium manganate. The abnormal heat generation temperature in the case of using a system material can be about 220 ° C., and the heat generation temperature in the case of using an iron phosphate material can be over 400 ° C.

  In addition, as described above, the current collecting structure in which the positive and negative current collector exposed portions 33 and 43 are respectively integrated in the wound electrode body 20 to be a current collecting portion can perform high-efficiency charging / discharging. Since the heat dissipation path from the body is obstructed, the structure can also promote the heat generation of the wound electrode body. However, the wound electrode body 20 disclosed herein can suppress temperature unevenness during overcharging as compared to the conventional wound electrode body. Moreover, even if the battery is in an overcharged state, the wound electrode body 20 is prevented from abnormally generating heat. Therefore, it may be a preferable aspect that the non-aqueous electrolyte secondary battery 20 adopts a current collecting structure in which the current collector exposed portions 33 and 43 as described above are integrated to form a current collecting portion.

[Battery case]
Then, the produced electrode body is accommodated in a predetermined battery case 10. As the battery case 10, a battery case 10 having a material or shape conventionally used for a nonaqueous electrolyte secondary battery can be used according to the purpose. Examples of the material of the battery case 10 include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among them, a relatively light metal (for example, aluminum or aluminum alloy) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. Further, the shape of the case (outer shape of the container) is not particularly limited. For example, the shape (cylindrical shape, coin shape, button shape), hexahedron shape (cuboid shape, cube shape), bag shape, and the like are processed and deformed. It can be a shape or the like.

  Note that, in the nonaqueous electrolyte secondary battery 100 disclosed herein, temperature unevenness during overcharging in the wound electrode body 20 is suppressed as described above. Therefore, at the time of overcharging, for example, charging can be stopped safely and promptly by using the shutdown function of the separator. Therefore, it is not necessary to provide the battery case with a safety mechanism such as CID that can detect an increase in internal pressure and interrupt the current when the battery is overcharged.

  The battery case 10 typically includes a case main body (exterior case) 12 that houses the wound electrode body 20 and the non-aqueous electrolyte, and a sealing body 14 that closes the opening of the case main body 12. . In the example of FIG. 1, a battery case 10 made of aluminum alloy and having a thin rectangular shape (cuboid shape), which has a bottomed box-shaped case body 12 having an opening on one surface of the rectangular parallelepiped, and a plate shape that closes the opening. It is comprised from the combination with the sealing body 14 of this. The sealing body 14 is provided with a positive electrode terminal 60 that is electrically connected to the positive electrode 30 of the wound electrode body 20 and a negative electrode terminal 70 that is electrically connected to the negative electrode 40. The sealing body 14 is typically formed with an inlet (not shown) for injecting a non-aqueous electrolyte into the case body 12 in which the wound electrode body 20 is accommodated. Further, similarly to the case of the conventional lithium ion secondary battery, the sealing body 14 is provided with a safety valve 82 for discharging the gas generated inside the battery case 10 to the outside of the battery case 10 when the battery is abnormal. It may be.

  In assembling the secondary battery, typically, the wound electrode body 20 can be housed in the case body 12 with the wound electrode body 20 fixed to the sealing body 14. For example, the positive electrode current collector exposed portion 33 of the wound electrode body 20 can be electrically connected to the positive electrode terminal 60 (for example, made of aluminum) via the positive electrode current collector member 62. Similarly, the negative electrode current collector exposed portion 43 can be electrically connected to the negative electrode terminal 70 (for example, made of nickel) via the negative electrode current collecting member 72. The positive and negative current collecting members 62 and 72, the positive and negative electrode terminals 60 and 70, and the positive and negative electrode current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like. Then, the secondary battery 100 can be assembled by sealing the opening of the case body 12 with the sealing body 14. The sealing body 14 and the case body 12 can be joined by welding or the like. Thereby, the non-aqueous electrolyte secondary battery 100 disclosed herein is provided.

In addition, although the manufacturing method in particular of the nonaqueous electrolyte secondary battery 100 disclosed here is not restrict | limited, For example, it can manufacture suitably according to the two methods shown below.
[Production Method 1]
That is, the first manufacturing method includes the following steps (a1) to (a3).
(A1) Preparing a wound electrode body in which a long positive electrode and a negative electrode are wound so as to face each other via a separator. Here, the wound electrode body, a capacity per unit area of the portion of the electrode constituting the innermost circumference of the wound electrode body and C _I, constituting the outermost periphery of the wound electrode body When the capacity per unit area of the electrode of the part is C 2 _O , the outermost peripheral capacity reduction rate R defined by the following formula: R = (1−C 2 _O / C _I ) × 100 is 0.3 ≦ R ≦ 3 is satisfied.
(A2) A battery assembly in which the wound electrode body and the nonaqueous electrolytic solution are housed in a battery case is prepared.
(A3) Conditioning processing (also referred to as initial charging processing) is performed on the battery assembly.

In the manufacturing method 1, in the step (a1), when the long electrodes (positive electrode and negative electrode) are formed, the outermost peripheral portion capacity C _O is larger than the innermost peripheral portion capacity C _I by a predetermined outermost peripheral capacity. Adjustment is made so that the reduction rate R becomes smaller. The capacity of the electrode is not particularly limited as long as the relationship of the outermost peripheral capacity reduction rate R is satisfied between the outermost peripheral part and the innermost peripheral part, and the capacity of the intermediate part between them is not particularly limited. The capacity of the intermediate part may be adjusted so that the capacity gradually decreases from the innermost part toward the outermost part, or may be adjusted to the same capacity as the innermost part. Since it is desirable that the non-aqueous electrolyte secondary battery 100 has a higher capacity, it is preferable that the non-aqueous electrolyte secondary battery 100 is gradually gradually formed in the vicinity of the outermost peripheral portion (for example, about 30% of the number of windings from the outer peripheral side). although capacity until the capacity C _O of the outermost peripheral portion is reduced, for the other parts it is to a capacitance C _I of the innermost portion. Step (a1), steps (a2) and (a3) other than adjusting the electrode capacity can be carried out according to a conventional method.

That is, in the step (a1), for example, the above-described positive and negative electrode constituent materials are mixed, dispersed in an appropriate dispersion medium in a powder state or prepared in a paste form, and supplied to a positive and negative current collector. . The positive and negative electrodes can be prepared by forming (typically rolling) the positive and negative electrode constituent materials so as to achieve a desired basis weight, density, and the like. By using the positive and negative electrodes (and separator) prepared as described above and winding them as described above, the wound electrode body 20 can be configured.
For step (a2), a battery assembly can be prepared, for example, according to the secondary battery assembly method described above.
For step (a3), an external power source is connected between the positive electrode and negative electrode terminals of the assembly, and a voltage including a driving voltage region (for example, 2.7 to 4.1 V) of the battery at a predetermined charging rate. It can be implemented by charging within the range. This charging may be performed once or may be performed a plurality of times (typically 2 to 3 times). Thereby, the assembly is adjusted to a state where it can actually be used as a battery (that is, the non-aqueous electrolyte secondary battery 100).

[Production Method 2]
The second manufacturing method includes the following steps (b1) to (b3).
(B1) A wound electrode body in which a long positive electrode and a negative electrode are wound while being opposed to each other via a separator, and a non-aqueous electrolyte containing an overcharge additive that generates gas during overcharge. Prepare a battery assembly housed in a battery case.
(B2) A conditioning process is performed on the battery assembly.
(B3) The battery assembly after the conditioning treatment is subjected to a local high-temperature aging treatment that is maintained for 5 minutes to 2 hours in a temperature range of at least 60 ° C to 85 ° C.

Even with such a configuration, the above-described non-aqueous electrolytic secondary battery including the wound electrode body configured such that the capacity of the outermost peripheral portion is smaller than the capacity of the innermost peripheral portion by a predetermined ratio is manufactured. can do.
In this manufacturing method 2, instead of preparing the wound electrode body 20 with the capacity of the outermost periphery reduced in advance as in the manufacturing method 1 described above, the step (b3 ) Is subjected to the local high-temperature aging treatment to reduce the outermost peripheral capacity. Specifically, in the step (b1), an overcharge additive is previously added to the non-aqueous electrolyte. The battery assembly is subjected to at least the local high-temperature aging treatment after the conditioning treatment step (b2), so that the capacity _CO of the outermost peripheral portion of the wound electrode body 20 becomes the innermost peripheral portion. and so as to adjust a predetermined outermost capacity reduction rate R only smaller as well than the capacitance C _I.

  The battery assembly containing the overcharge additive in the non-aqueous electrolyte is exposed to a temperature of 45 ° C. or higher and 95 ° C. or lower, for example, while being charged by the initial charging process, thereby reducing the electrode capacity. In such a high temperature environment, it is considered that the overcharge additive is efficiently immobilized on the surface of the positive electrode (for example, the surface of the positive electrode active material and the conductive material) and contributes to reduction of the electrode capacity. And, by setting the time of exposure to this high temperature environment to 5 minutes or more and 2 hours or less (local high temperature aging treatment), the electrode capacity is locally reduced from the outermost peripheral side to the inner peripheral side of the wound electrode body. be able to. The relationship between the temperature and time of these local high-temperature aging treatments is, for example, the configuration of the target nonaqueous electrolyte secondary battery (for example, the material and thickness of the battery case, the outermost peripheral portion of the battery case and the wound electrode body) And the like can be appropriately adjusted according to the thermal conductivity between them.

The temperature of the local high-temperature aging treatment is preferably about 60 ° C. or higher, for example, 65 ° C. or higher, more preferably 70 ° C. or higher (70 ° C. or higher), from the viewpoint that local electrode capacity can be reduced in a short time. More than 75 ° C. However, processing at too high temperatures can cause damage to electrode capacity and other battery properties. Therefore, the upper limit of the temperature of the local high-temperature aging treatment is preferably 95 ° C., and can be, for example, 85 ° C. or less.
If the time of the local high-temperature aging treatment is too long, the aging action can reach the center of the wound electrode body, that is, the innermost peripheral portion. Therefore, the treatment exceeding 2 hours is not preferable because the effect of locally reducing the electrode capacity may not be obtained. From this viewpoint, the time for the local high-temperature aging treatment is preferably 1.5 hours or less, more preferably 1 hour or less, and further preferably 40 minutes or less. However, if the processing time for local high temperature aging is too short, the capacity of the outermost peripheral portion may not be sufficiently reduced. Therefore, the time for the local high-temperature aging treatment can be 5 minutes or more.
By performing the local high temperature aging treatment under such conditions, a nonaqueous electrolyte secondary battery in which the outermost peripheral capacity reduction rate R satisfies 0.3 ≦ R ≦ 3 can be easily and suitably manufactured. .

  In addition, in the manufacturing method 2, the overcharge additive added in a process (b1) can use 1 type (s) or 2 or more types of well-known overcharge additive without a restriction | limiting in particular. As such an overcharge additive, the oxidation potential is not less than the operating voltage of a lithium secondary battery (for example, 4.2 V or more in the case of a lithium secondary battery that is currently widely used). Any compound that generates gas can be used without particular limitation. For example, as an overcharge inhibitor, cyclohexylbenzene (CHB), 4-alkylcyclohexylbenzene, or biphenyl (BP) represented by the following chemical formula (I) can be given as a suitable example.

Here, in chemical formula (I), R is a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms represented by R include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, and n-pentyl. Group and n-hexyl group. Among them, an alkyl group having 1 to 4 carbon atoms is preferable. For example, trans-4-butylcyclohexylbenzene having an n-butyl group is preferable.
The overcharge additive is preferably added to the non-aqueous electrolyte at a ratio of 0.1% by mass to 4% by mass (for example, 0.2% by mass to 3% by mass). In addition, in the battery after manufacture, this overcharge additive is typically contained in the non-aqueous electrolyte, but may be contained in a fixed state on the surface of the positive electrode. Further, a part of the product may be decomposed on the surface of the positive electrode and may exist in the form of a decomposition product (when the overcharge additive is CHB, a part of the decomposition product may be BP).

  Moreover, the condition of the conditioning process of a process (b2) is not restrict | limited in particular, It can implement according to a conventional method. For example, at a charging rate of about 0.1 to 10 C, the voltage between the positive and negative terminals (typically the highest attained voltage) is approximately 60% or more (typically 80% or more, typically 90% or more, for example 90%). It is exemplified that the battery is charged to a voltage range that is in a range of ˜105%. For example, in the case of a battery that is fully charged at 4.2 V, it is exemplified that the adjustment is made in the range of about 3.8 to 4.2 V. The charging process may be performed once, for example, it may be repeated twice or more with the discharging process interposed therebetween.

  In addition, in the manufacturing method 1, in addition to the conditioning process of the step (a1), various processes for improving battery characteristics and the like can be performed in combination. Also in the manufacturing method 2, in addition to the conditioning process in step (b2) and the local high-temperature aging process in step (b3), various processes for improving battery characteristics and the like may be performed in combination. An example of such a process is a known aging process that is distinguished from the local high-temperature aging process. Such an aging process may be a process in which a battery assembly in a charged state is allowed to stand for a certain period of time at a certain high temperature or room temperature. This aging process is distinguished from the local high-temperature aging process in that it is intended to perform a predetermined aging process substantially uniformly on the entire wound electrode body. As such an aging treatment, for example, a temperature range of 20 ° C. to 60 ° C. (more preferably, 40 ° C. to 60 ° C.) is maintained for about 1 hour to 240 hours (more preferably 1 hour to 48 hours). The process is illustrated. By such an aging process, for example, the metal foreign matter mixed in the electrode body can be rendered harmless, or the battery quality can be managed by inspecting for the presence of a micro short circuit. This aging process may be performed at any timing after the conditioning process. For example, it may be performed before or after the local high temperature aging treatment in the step (b3) in the production method 2.

  The non-aqueous electrolyte secondary battery 100 disclosed herein can be used for various applications, but has the same battery performance (for example, high energy density, high input / output characteristics, cycle characteristics, etc.) as the conventional product, and safety. And can be combined. In addition, these excellent battery performance and reliability (including safety during overcharge) can be compatible at a high level. Therefore, taking advantage of these characteristics, applications requiring high capacity (for example, theoretical capacity of 10 to 100 Ah), high energy density, high input / output density and cycle characteristics, and high reliability are required. In particular, it can be preferably used. Examples of such applications include drive power supplies mounted on vehicles such as plug-in hybrid vehicles (PHV), hybrid vehicles (HV), and electric vehicles (EV). Such a non-aqueous electrolyte secondary battery can also be used in the form of a battery pack typically formed by connecting a plurality of non-aqueous electrolyte secondary batteries in series and / or in parallel.

Hereinafter, as a specific example, the non-aqueous electrolyte secondary battery disclosed herein was manufactured and its characteristics were evaluated. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.
[Construction of evaluation lithium-ion battery]
[Positive electrode]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM, average particle size 6 μm, specific surface area 0.7 m ² / g) as a positive electrode active material, acetylene black (AB) as a conductive material, binder Polyvinylidene fluoride (PVdF) as a material is weighed so that the mass ratio of these materials is NCM: AB: PVdF = 91: 6: 3, and the solid content concentration (NV) is about 50% by mass. -A slurry for forming a positive electrode active material layer was prepared by adding and kneading methylpyrrolidone (NMP). The basis weight per one side of this slurry is 13.5 mg / cm ^{2 on} both sides of a long aluminum foil having a thickness of 15 μm as a positive electrode current collector in a region having a width of 94 mm from one end in the longitudinal direction. The positive electrode sheet was produced by applying in a strip shape and drying (drying temperature 80 ° C., 5 minutes). And this was rolling-pressed and it adjusted so that the density of a positive electrode active material layer might be set to about 2.6 g / cm < ³ >. In addition, the thickness of the positive electrode active material layer after the rolling press was about 50 μm per side (115 μm for the whole positive electrode).

[Negative electrode]
Graphite (C, average particle size 25 μm, specific surface area 2.5 m ² / g) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, The weight ratio of C: SBR: CMC = 98: 1: 1 was weighed, and ion-exchanged water was added and kneaded to prepare a negative electrode active material layer forming slurry. The basis weight per one side of this slurry is 7.3 mg / cm ^{2 on} both sides of a long copper foil having a thickness of 10 μm as a negative electrode current collector in a region having a width of 100 mm from one end in the longitudinal direction. The negative electrode sheet was produced by applying in a strip shape and drying (drying temperature 100 ° C., 5 minutes). And this was rolling-pressed and it adjusted so that the density of a negative electrode active material layer might be set to about 1.1 g / cm < ³ >. In addition, the thickness of the negative electrode active material layer after the rolling press was about 60 μm per side (130 μm for the whole negative electrode).

[Separator]
As the separator, a long microporous sheet having a three-layer structure (PP / PE / PP) having a width of 105 mm and an average thickness of 25 μm and having both sides of polyethylene (PE) sandwiched between polypropylene (PP) Was used.

The positive electrode and the negative electrode prepared above were overlapped via a separator and wound into an elliptical cross section. In this case, the negative electrode active material layer covers the positive electrode active material layer in the width direction, and the exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector protrude on different sides in the width direction. And arranged. Further, the separator was disposed so that the positive and negative active material layers were insulated with the HRL facing the positive electrode side. The wound body was formed into a wound electrode body by pressing a flat plate at room temperature (25 ° C.) at a pressure of 4 kN / cm ² for 2 minutes and forming into a flat shape.

  Next, a positive electrode terminal and a negative electrode terminal are attached to the sealing body of the battery case, and the positive electrode current collector exposed portion and the negative electrode current collector exposed portion projecting from the wound electrode body through these current collector terminals. And welded respectively. Then, the wound electrode body connected to the sealing body in this way is accommodated in the inside of the aluminum battery case body (width 150 mm × height 90 mm × thickness 26 mm) from inside the opening. The part and the sealing body were welded. A battery case without a CID was used.

As a non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC: DMC: EMC = 3: 4: 3 is used as a supporting salt. LiPF ₆ was dissolved at a concentration of 1.0 mol / L, and CHB as an overcharge additive was dissolved at a ratio of 0.2% by mass. And the non-aqueous electrolyte was inject | poured from the injection hole provided in the cover body of the said battery case, and the lithium ion battery for evaluation (theoretical capacity | capacitance 30Ah) was constructed | assembled.

[Outer circumference capacity adjustment processing]
The lithium ion battery produced as described above was charged at a charge rate of 0.1 C at 25 ° C. until the voltage between the positive and negative terminals reached 4.1 V, and after resting for 10 minutes, the battery was discharged at 0.1 C. A conditioning treatment was performed in which the operation of constant discharge to 3.0 V at a rate was repeated three times. In addition, 1C means the electric current value which can charge the battery capacity (Ah) estimated from the theoretical capacity | capacitance of the positive electrode in 1 hour.
And the heat processing (outer periphery capacity | capacitance adjustment process) in any of the following Examples 1-8 were performed with respect to the lithium ion battery after a conditioning process.

(Example 1)
Hold at 60 ° C. for 20 hours.
(Example 2)
Hold at 70 ° C. for 20 hours.
(Example 3)
Hold at 80 ° C. for 20 hours.
(Example 4)
Hold at 80 ° C. for 40 hours.

(Example 5)
After holding at 70 ° C. for 19 hours, it was held at 80 ° C. for 10 minutes.
(Example 6)
After holding at 70 ° C. for 19 hours, it was held at 80 ° C. for 20 minutes.
(Example 7)
After holding at 70 ° C. for 15 hours, it was held at 80 ° C. for 1 hour.
(Example 8)
After holding at 60 ° C. for 15 hours, it was held at 80 ° C. for 1 hour.

[Inner and outer capacity measurement]
The lithium ion battery after the above peripheral capacity adjustment treatment was discharged until the open circuit voltage became 3.0 V, then disassembled, and the wound electrode body was taken out. Next, the unrolled wound electrode body is developed in a stacked state of a long positive electrode / separator / negative electrode / separator, while the outermost peripheral portion (one turn) of the wound electrode body and the innermost periphery A portion (one turn) was cut out, and each central portion was punched into a circle having a diameter of 15 mm to form an electrode test piece, which was subjected to capacity measurement.

The capacity measurement was performed according to the following procedure. That is, first, the area of the portion where the active material layer of the electrode test piece was formed was measured. Then, connect the external electrode terminal to the positive electrode current collector exposed portion and the negative electrode current collector exposed portion of the electrode test piece, and insert into a bag made of a laminate film together with the same non-aqueous electrolyte solution as above to seal. Thus, a laminate cell for capacity measurement was constructed. The laminate cell was charged at 25 ° C. with a constant current (CC) of 1 mA until the voltage between the positive and negative terminals reached 4.1 V, and then the voltage of 4.1 V until the total charging time reached 10 hours. Charge at a constant voltage (CV), then discharge to 3.0 V with a constant current (CC) of 1 mA, and then discharge at a constant voltage (CV) of 3.0 V until the total discharge time reaches 10 hours. Discharge was performed. The discharge capacity at this time was taken as the capacity of the electrode test piece.
This capacity measurement was performed for 10 batteries in each example. Then, from the result of capacitance measurement, and the capacitance C _On per unit area of the outermost portion of the electrode, per unit area of the innermost portion and the capacitance C _{an In} calculating each of Table 1 and the average value C _O, and it is shown in the column of _{C I.} In addition, the reduction rate of the capacitance C _I per unit area of the outermost peripheral portion with respect to the capacitance C _O per unit area of the innermost peripheral portion of the electrode is expressed by the following formula: (1−C _O / C _I ) × 100; Based on the calculation, the results are shown in Table 1.

[Overcharge test]
A constant current (CC) of 0.67 C (20 A) until the voltage between the positive and negative terminals reaches an overcharged state of 10 V exceeding the upper limit charging voltage (4.2 V) with respect to the lithium ion battery after the above peripheral capacity adjustment processing ) And allowed to stand for 10 minutes, and then the voltage between the positive and negative terminals was measured. The average value of the measurement results for 10 batteries in each example is shown in the “Voltage after 10 minutes” column of Table 1.

As shown in Table 1, even in the evaluation lithium ion battery (battery assembly) having the same configuration, the electrode capacities of the innermost peripheral portion and the outermost peripheral portion depend on the content of the heat treatment after the conditioning treatment. Found that could be different.
That is, as shown in Examples 1 to 4, when the wound electrode body is subjected to a heat treatment at a temperature corresponding to high temperature aging (here, 60 ° C. to 80 ° C.), for example, 15 hours or more is sufficiently long. When time is spent, the high temperature aging treatment acts uniformly on the outermost and innermost peripheral portions of the wound electrode body, and the outermost and innermost portions of the wound electrode body after the heat treatment are applied. It was found that there was no difference in capacity. It was also found that the higher the temperature of this high temperature aging and the longer the aging treatment time, the lower the capacity of the wound electrode body in both the outermost peripheral part and the innermost peripheral part.

  In Examples 5 to 8, two-stage heat treatment was performed by adding high-temperature and short-time second high-temperature aging by the first high-temperature aging within a range in which the total heat treatment amount was less than in Examples 1 to 4. . The second high temperature aging corresponds to the local high temperature aging treatment disclosed herein. As a result, in the second and higher temperature aging for a short time, the heat treatment effect does not reach the innermost part of the wound electrode body, and the capacity of the innermost part of the wound electrode body is maintained. As it was, it was confirmed that the capacity of the outermost peripheral portion was reduced. In other words, according to the second high temperature aging, it was found that the high temperature aging treatment can be locally applied to the outermost peripheral portion of the wound electrode body. As a result, it has been found that the capacity of the outermost peripheral portion of the wound electrode body can be locally reduced.

  In addition, the voltage after 10 minutes of overcharge in Examples 1 to 4 is less than 3.5 V (eg, 3.45 V or less), and the voltage after 10 minutes of Examples 5 to 8 is 3.5 V or more (eg, 3.55 V). And a significant difference was observed in the amount of voltage drop after overcharging depending on the content of the heat treatment. Specifically, it was confirmed that the voltage of the battery having a reduced electrode capacity at the outermost peripheral portion of the wound electrode body was maintained higher after overcharging.

  In addition, the voltage drop after overcharging is considered to be a voltage drop based on inevitable natural discharge and a discharge due to an internal short circuit. Further, it is known that a general wound electrode body accumulates heat toward the inner peripheral side, and a short circuit is likely to occur in the inner peripheral portion during overcharge. From this, it is considered that the voltage drop after overcharging in the batteries of Examples 1 to 4 is due to the occurrence of an internal short circuit. And the decrease in the voltage drop after overcharging in the batteries of Examples 5 to 8 is considered to be due to the suppression of the occurrence of internal short circuits. That is, in the batteries of Examples 5 to 8, the capacity of the outermost peripheral portion was reduced as compared with the innermost peripheral portion of the wound electrode body. That is, it is considered that the capacity is reduced toward the outer peripheral side. Therefore, when the overcharge test results in an overcharge state, the overcharge state is advanced from the inner periphery side by an amount corresponding to the actual capacity reduction amount. Thus, heat generation due to overcharge on the outer peripheral side is also advanced, and it is considered that temperature unevenness with the inner peripheral side where the temperature is increased by heat storage is suppressed.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. For example, from the above, by reducing the capacity of the outermost peripheral part of the wound electrode body by a predetermined ratio from the innermost peripheral part, the safety when overcharging the nonaqueous electrolyte secondary battery Was confirmed to be improved. It was confirmed that the capacity adjustment of the outermost peripheral portion of the wound electrode body can be suitably realized by high-temperature aging for a short time after the initial charging, as exemplified in the above embodiment. However, those skilled in the art can easily understand that the capacity adjustment is not limited to the above examples and can be performed by reducing the active material layer in the innermost peripheral portion. As described above, the techniques described in the claims of the present application include various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Battery case 12 Case main body 14 Sealing body 20 Electrode body 30 Positive electrode (positive electrode sheet)
32 Positive electrode current collector 33 Positive electrode current collector exposed portion 34 Positive electrode active material layer 40 Negative electrode (negative electrode sheet)
42 Negative electrode current collector 43 Negative electrode current collector exposed portion 44 Negative electrode active material layer 50 Separator 60 Positive electrode terminal 70 Negative electrode terminal 82 Safety valve 100 Battery

Claims (9)

A wound electrode body formed by winding a long positive electrode and a negative electrode facing each other with a separator and a nonaqueous electrolyte solution is a nonaqueous electrolyte secondary battery housed in a battery case. And
The capacity per unit area of the electrode constituting the innermost circumference of the wound electrode body is C _I ,
When the capacitance per unit area of the portion of the electrodes constituting the outermost periphery of the wound electrode body was C _O, the following equation: R = (1-C O / C I) outermost defined by × 100 Capacity reduction rate R is
0.3 ≦ R ≦ 3
Satisfying the non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the outermost peripheral capacity reduction rate R satisfies 0.95 ≦ R ≦ 1.1.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte includes an overcharge additive that decomposes during overcharge to generate gas. The battery case includes an external connection terminal,
The non-aqueous electrolyte 2 according to any one of claims 1 to 3, which does not include a current interrupt device that interrupts a conductive path between the wound electrode body and the external connection terminal during overcharging. Next battery. The positive electrode and the negative electrode are
A current collector exposed portion is provided at one end along the longitudinal direction of the long electrode current collector, and an electrode active material layer is provided in a portion other than the current collector exposed portion,
The current collector exposed portion of the positive electrode and the current collector exposed portion of the negative electrode are arranged so as to protrude to the opposite side of the width direction orthogonal to the longitudinal direction, and are wound around the width direction as an axis. And
The wound electrode body is:
The non-aqueous solution according to any one of claims 1 to 4, wherein current collectors each collecting the current collector exposed portions of the positive electrode and the negative electrode are configured to collect current from the positive electrode and the negative electrode. Electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the wound electrode body is a flat wound electrode body having a shape bent in a direction perpendicular to the axis.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a melting point of the separator is lower than an abnormal heat generation temperature determined according to a positive electrode active material included in the positive electrode. Preparing a wound electrode body in which a long positive electrode and a negative electrode are wound oppositely with a separator interposed therebetween, wherein the wound electrode body comprises:
The capacity per unit area of the electrode constituting the innermost circumference of the wound electrode body is C _I ,
When the capacity per unit area of the electrode constituting the outermost periphery of the wound electrode body is _CO ,
The outermost peripheral capacity reduction rate R defined by the following formula: R = (1−C _O / C _I ) × 100
0.3 ≦ R ≦ 3
Configure to meet the
Preparing a battery assembly in which the wound electrode body and the non-aqueous electrolyte are housed in a battery case;
Subjecting the battery assembly to a conditioning process;
A method for producing a non-aqueous electrolyte secondary battery. A battery case comprising: a wound electrode body in which a long positive electrode and a negative electrode are wound with a separator disposed therebetween; and a non-aqueous electrolyte containing an overcharge additive that generates gas during overcharge. Preparing a contained battery assembly;
Subjecting the battery assembly to a conditioning process;
Subjecting the battery assembly after the conditioning treatment to a local high temperature aging treatment for holding at least in the temperature range of 40 ° C. to 95 ° C. for 5 minutes to 2 hours,
A method for producing a non-aqueous electrolyte secondary battery.

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