Secondary battery

Abstract

The present application provides a secondary battery suitable for suppressing diffusion of Li ions in a negative electrode active material layer toward a non-facing end portion of a positive electrode active material layer. The battery disclosed herein has an electrode body. The electrode body is a jelly-roll electrode body in which a strip-shaped positive electrode (21) and a strip-shaped negative electrode (22) are wound along the length direction with a separator (23) interposed therebetween. The positive electrode has a laminated structure of a positive electrode current collector (21C) and a positive electrode active material layer (21A). The negative electrode has a laminated structure of a negative electrode current collector (22C) and a negative electrode active material layer (22A), and includes a facing portion (22f) facing the positive electrode active material layer with the separator interposed therebetween and a non-facing end portion (22e) not facing the positive electrode active material layer. The negative electrode active material layer has a recessed shape portion in which the surface of the negative electrode active material layer is recessed from the separator in a boundary region of the facing portion and the non-facing end portion. The recessed depth of the recessed shape portion in the outermost peripheral region of the electrode body in the negative electrode active material layer is deeper than the recessed depth of the recessed shape portion in the innermost peripheral region of the electrode body.

Description

Technical Field

[0001] This invention relates to secondary batteries. Background Technology

[0002] In recent years, rechargeable batteries, such as lithium-ion batteries, have been used as portable power sources for portable terminals and as power sources for vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). A rechargeable battery includes an electrode body comprising a positive electrode and a negative electrode, and an electrolyte impregnated in the electrode body. Both the positive and negative electrodes have active material layers that bear the battery reaction during charging and discharging. In the case of lithium-ion rechargeable batteries, during charging and discharging, a battery reaction occurs at the positive and negative electrodes of the electrode body, and lithium (Li) ions are inserted and desorbed between the active material layers of the two electrodes. Technology related to such rechargeable batteries is described, for example, in Patent Document 1 below.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-190624 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] One known type of electrode for a secondary battery is the wound electrode. The wound electrode comprises a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator, and is formed by winding the positive and negative electrodes along the length direction with the separator in between. In the wound electrode, in the width direction orthogonal to the length direction, the active material layer of the negative electrode is sometimes wider than that of the positive electrode. In this case, the negative electrode active material layer has a region facing the positive electrode active material layer (facing portion) and a non-facing end region (non-facing end) separated by the separator. This structure helps prevent and suppress the deposition of metallic lithium at the ends of the negative electrode active material layer during charging. However, in the negative electrode active material layer, which is wider than the positive electrode active material layer, Li ions inserted into the facing portion diffuse towards the non-facing end during charging. This diffusion of Li ions causes a decrease in battery voltage and is undesirable.

[0008] The present invention was conceived under such circumstances, and its object is to provide a secondary battery suitable for suppressing the deposition of Li ions in the negative electrode active material layer and suppressing the diffusion of Li ions to the non-opposite ends of the positive electrode active material layer of the negative electrode active material layer.

[0009] Methods for solving problems

[0010] The secondary battery disclosed herein is a secondary battery having a wound electrode body. The wound electrode body comprises a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped separator, and is an electrode body formed by winding the positive and negative electrodes along its length with the separator in between. The positive electrode has a laminated structure including a positive current collector and a positive active material layer. The negative electrode has a laminated structure including a negative current collector and a negative active material layer. The negative active material layer includes an opposing portion facing the positive active material layer with the separator in between, and a non-opposing end with the separator in between. The negative active material layer has a recessed shape portion. The recessed shape portion is the portion of the negative active material layer whose surface recedes from the separator in the boundary region between the opposing portion and the non-opposing end. The recessed depth of the recessed shape portion in the outermost peripheral region of the wound electrode body in the negative active material layer is deeper than the recessed depth of the recessed shape portion in the innermost peripheral region of the wound electrode body.

[0011] In this type of secondary battery, as described above, the negative electrode active material layer of the electrode body includes a non-facing end that is separated from the positive electrode active material layer by a separator. The negative electrode active material layer also includes a non-facing end outside the region (facing portion) that faces the positive electrode active material layer. This is suitable for ensuring the positional relationship between the entire region of the positive electrode active material layer and the negative electrode active material layer (suitable for ensuring tolerances in the positional relationship between the negative and positive electrode active material layers in the event of winding offset during electrode winding, thus contributing to ensuring the productivity of the wound electrode body or the secondary battery). Furthermore, the inclusion of a non-facing end outside the region (facing portion) that faces the positive electrode active material layer is also suitable for homogenizing the insertion of Li ions relative to the negative electrode active material layer during secondary battery charging, thus helping to suppress the deposition of Li ions in the negative electrode active material layer (when the edge of the negative electrode active material layer is located in the region facing the positive electrode active material layer, the insertion density of Li ions tends to increase locally at such edges, making Li ion deposition easier).

[0012] Furthermore, as described above, the negative electrode active material layer has a recessed shape in the boundary region between the facing and non-facing ends, where the surface of the negative electrode active material layer recedes from the separator. This structure is suitable for narrowing the movement path of Li ions from the facing to the non-facing ends in the negative electrode active material layer, thereby suppressing Li ion diffusion. This suppression of Li ion diffusion also helps to suppress the rise of the negative electrode potential in a secondary battery, thereby suppressing the voltage drop caused by self-discharge.

[0013] Furthermore, as described above, the depth of the recessed portion of the negative electrode active material layer in the outermost peripheral region of the wound electrode body is greater than its depth in the innermost peripheral region. With this structure, when the recessed portion has a groove shape, by retaining the electrolyte in the recessed portion of the negative electrode active material layer in the outermost peripheral region, the release of electrolyte to the electrode body can be suppressed, thereby suppressing rapid degradation of the electrode body.

[0014] As described above, the secondary battery of the present invention is suitable for suppressing the precipitation of Li ions in the negative electrode active material layer and suppressing the diffusion of Li ions to the non-opposite ends of the positive electrode active material layer of the negative electrode active material layer. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view schematically illustrating the internal structure of a secondary battery according to an embodiment of the present invention.

[0016] Figure 2 It means Figure 1 The diagram shows the structure of the electrode body of the secondary battery.

[0017] Figure 3 yes Figure 2 A partial, omitted cross-sectional schematic diagram of a stacked unit in the electrode body shown.

[0018] Figure 4 (A)~(C) are schematic representations Figure 3 An enlarged cross-sectional view of the recessed shape of the negative electrode active material layer and its vicinity.

[0019] Figure 5 This indicates the stamping process for winding the electrode body.

[0020] Figure 6 It is a schematic example of a deformed recessed shape and an enlarged cross-sectional view of its vicinity.

[0021] Figure 7 The measurement data represent the cross-sectional shape of the concave part in Example 1. Detailed Implementation

[0022] Hereinafter, as one embodiment of the secondary battery of the present invention, a lithium-ion secondary battery will be described with reference to the accompanying drawings. In this specification, "secondary battery" refers to a general energy storage device capable of repeated charging and discharging. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Matters other than those specifically mentioned in this specification and matters necessary for the implementation of the present invention (e.g., the general structure and manufacturing process of a secondary battery not characterized by the present invention) can be understood as design matters by those skilled in the art based on prior art.

[0023] Figure 1 This is a schematic cross-sectional view showing the internal structure of a battery 100 according to one embodiment of the present invention. The battery 100 includes a casing 10, an electrode body 20, a positive terminal 30, a negative terminal 40, and a non-aqueous electrolyte (not shown). In this embodiment, the battery 100 is a lithium-ion secondary battery.

[0024] The housing 10 is the frame of the battery 100, housing the electrode body 20 and the non-aqueous electrolyte. In this embodiment, the housing 10 has a flat, rectangular (e.g., square) shape and extends along a first direction D1. In this embodiment, the housing 10 has a height in a second direction D2 orthogonal to the first direction D1, and a thickness in a direction orthogonal to both the first and second directions D2. Examples of materials used to construct the housing 10 include aluminum, aluminum alloys, iron, and iron alloys. From the viewpoint of balancing lightweight design and required rigidity, aluminum or an aluminum alloy is preferred as the material for the housing 10.

[0025] The housing 10 has a safety valve 11. In this embodiment, the safety valve 11 is located in the housing 10. Figure 1 The upper surface of the housing 10 is located between the positive terminal 30 and the negative terminal 40. The safety valve 11 is a thin-walled portion configured to break when the gas pressure inside the housing 10 rises above a predetermined value. Through this breakage of the safety valve 11, the gas inside the housing 10 is discharged outside the housing 10, preventing or suppressing further pressure increases within the housing 10. Additionally, the housing 10 has an injection port (not shown) for injecting a non-aqueous electrolyte into the housing 10. The injection port is sealed by a sealing component after the non-aqueous electrolyte is injected.

[0026] Figure 2 This is a schematic diagram showing the structure of electrode body 20. Electrode body 20 includes a stacked structure of a positive electrode 21, a negative electrode 22, and a separator 23 between them. Electrode body 20 is a flat, wound electrode body, formed by winding a stacked body of elongated sheets (having a width in a direction orthogonal to its length direction) sequentially arranged with a strip-shaped positive electrode 21, a strip-shaped separator 23, a strip-shaped negative electrode 22, and another strip-shaped separator 23. After winding, the wound electrode body is flattened by stamping. Such an electrode body 20 (wound electrode body) has its winding axis Ax at... Figure 1 The electrode body 20 is housed within the housing 10, extending along the first direction D1. Alternatively, the electrode body 20 may be a stacked electrode body consisting of a square positive electrode and a square negative electrode stacked in an insulated manner.

[0027] The positive electrode 21 has a stacked structure including a positive current collector 21C and a positive active material layer 21A. In this embodiment, as... Figure 3As shown, the positive electrode 21 has a positive electrode active material layer 21A on both sides of the positive electrode current collector 21C ( Figure 3 This is a partially omitted cross-sectional schematic diagram of a stacked unit in electrode body 20.

[0028] Examples of positive current collectors 21C include conductive metal foil and resin sheets with conductive metal layers on both sides. Examples of conductive metals used for positive current collectors 21C include aluminum, aluminum alloys, nickel, titanium, and stainless steel, with aluminum being preferred.

[0029] From the viewpoint of reducing the thickness of the positive current collector 21C, the thickness of the positive current collector 21C is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. Reducing the thickness of the positive current collector 21C is advantageous for ensuring high energy density in the electrode body 20 or the battery 100. From the viewpoint of ensuring the strength of the positive current collector 21C, the thickness of the positive current collector 21C is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more.

[0030] The positive electrode active material layer 21A contains a positive electrode active material capable of reversibly adsorbing and releasing charge carriers. The positive electrode active material is preferably a lithium transition metal composite oxide. Specific examples of this oxide include lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide, and lithium nickel cobalt manganese composite oxide. The positive electrode active material layer 21A may also contain additives other than the positive electrode active material. Examples of additives include conductive materials, binders, and trilithium phosphate. Examples of conductive materials include acetylene black, Ketjen black, graphite, and carbon nanotubes. Examples of binders include fluorinated resins such as polyvinylidene fluoride (PVDF) and rubbers such as styrene-butadiene rubber (SBR).

[0031] From the viewpoint of ensuring the battery capacity of the battery 100, the thickness of the positive electrode active material layer 21A is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. From the viewpoint of ensuring good rate characteristics in the battery 100, the thickness of the positive electrode active material layer 21A is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0032] In such a positive electrode 21, in this embodiment, the positive current collector 21C is located at one end in the width direction W of the electrode body 20 or the positive electrode 21 (in... Figure 2The left end (middle) has multiple tabs 21t. The width direction W is orthogonal to the length direction of the strip-shaped laminate described above. In the positive current collector 21C, the tabs 21t are contained in the area exposed where the positive active material layer 21A is not laminated. In the electrode body 20, which is a wound electrode body, multiple tabs 21t overlap in the lamination direction of the laminated structure of the electrode body 20 to form a positive electrode tab portion 21T ( Figure 1 (As shown) (In the positive current collector 21C, tabs 21t are provided in such a configuration). The positive tabs 21T function as current collectors in the positive electrode 21. The tabs 21t are connected to the positive current collector plate 50 (the positive current collector plate 50 is provided with each positive tab 21T) in such an overlapping and integrated state. As a constituent material of the positive current collector plate 50, aluminum and aluminum alloys are examples. As a connection method between the positive current collector plate 50 and the positive tabs 21T in the positive electrode 21, ultrasonic bonding and laser welding are examples.

[0033] The negative electrode 22 has a stacked structure including a negative electrode current collector 22C and a negative electrode active material layer 22A. In this embodiment, as... Figure 3 As shown, the negative electrode 22 has a negative electrode active material layer 22A on both sides of the negative electrode current collector 22C.

[0034] Examples of negative current collectors 22C include conductive metal foil and resin sheets with conductive metal layers on both sides. Examples of conductive metals used for negative current collectors 22C include copper, copper alloys, nickel, and stainless steel, with copper foil being preferred.

[0035] From the viewpoint of reducing the thickness of the negative electrode current collector 22C, the thickness of the negative electrode current collector 22C is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. Reducing the thickness of the negative electrode current collector 22C is advantageous for ensuring high energy density in the electrode body 20 or the battery 100. From the viewpoint of ensuring the strength of the negative electrode current collector 22C, the thickness of the negative electrode current collector 22C is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more.

[0036] The negative electrode active material layer 22A contains a negative electrode active material capable of reversibly adsorbing and releasing charge carriers. Examples of negative electrode active materials include graphite or carbon materials such as hard carbon and soft carbon. Graphite can be natural graphite or artificial graphite. The negative electrode active material layer 22A may also contain additives other than the negative electrode active material. Examples of additives include adhesives and tackifiers. Examples of adhesives include rubbers such as styrene-butadiene rubber (SBR) and fluorinated resins such as polyvinylidene fluoride (PVDF). Examples of tackifiers include cellulose-based materials such as carboxymethyl cellulose (CMC).

[0037] From the perspective of achieving high energy density and high capacity in battery 100, the density of the negative electrode active material layer 22A is preferably 1.0 g / cm³. 3 The above, more preferably 1.2 g / cm³ 3 The above is further optimized to 1.4 g / cm³. 3 That's all. From the viewpoint of ensuring good rate characteristics in battery 100, the density of the negative electrode active material layer 22A is preferably 2.0 g / cm³. 3 The preferred value is 1.8 g / cm³. 3 The following is a further preferred value of 1.6 g / cm³. 3 the following.

[0038] From the viewpoint of ensuring the battery capacity of battery 100, the average thickness of the negative electrode active material layer 22A is preferably 50 μm or more, more preferably 70 μm or more, and even more preferably 80 μm or more. From the viewpoint of ensuring good rate characteristics in battery 100, the average thickness of the negative electrode active material layer 22A is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0039] The negative electrode active material layer 22A includes opposing portions 22f and non-opposing ends 22e. The negative electrode active material layer 22A has non-opposing ends 22e at both ends in the width direction W. The opposing portions 22f are regions in the negative electrode active material layer 22A that face the positive electrode active material layer 21A across the separator 23. The non-opposing ends 22e are regions in the negative electrode active material layer 22A that do not face the positive electrode active material layer 21A across the separator 23. This structure, where the negative electrode active material layer 22A also includes non-opposing ends 22e outside the opposing portions 22f facing the positive electrode active material layer 21A, helps suppress defects caused by winding misalignment when winding the positive electrode 21, negative electrode 22, and the separator 23 between them. In addition, the above structure is suitable for homogenizing the insertion of Li ions relative to the negative electrode active material layer 22A during battery 100 charging, and thus also helps to suppress the precipitation of Li ions in the negative electrode active material layer 22A.

[0040] The extension length L of the non-opposing end 22e of the electrode body 20 in the width direction W, extending from the edge 21e of the positive electrode active material layer 21A, is preferably 0.5 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. This structure is preferred for suppressing the deposition of Li ions in the negative electrode active material layer 22A. From the viewpoint of ensuring the volumetric energy density of the electrode body 20, the extension length L is preferably 3.0 mm or less, more preferably 2.6 mm or less, and even more preferably 2.3 mm or less.

[0041] The negative electrode active material layer 22A has a recessed shape portion 22r. The recessed shape portion 22r is a portion in the boundary region between the opposing portion 22f and the non-opposing end 22e, where the positive electrode active material layer 21A side surface of the negative electrode active material layer 22A retracts from the separator 23. In this embodiment, the negative electrode active material layer 22A, which serves as a wound electrode body 20, has a recessed shape portion 22r throughout its entire length direction. This entire region includes the outermost and innermost peripheral regions of the electrode body 20, which serves as a wound electrode body. The recessed shape portion 22r of the negative electrode active material layer 22A is suitable for narrowing the movement path of Li ions from the opposing portion 22f to the non-opposing end 22e of the negative electrode active material layer 22A, thereby suppressing the diffusion of Li ions. This suppression of Li ion diffusion also helps to suppress the rise of the negative electrode potential in the battery 100, thereby suppressing the voltage drop caused by self-discharge.

[0042] In this embodiment, the recessed portion 22r is a groove-shaped portion 22g that opens towards the separator 23. Non-aqueous electrolyte can be stored in the groove 22g. The negative electrode active material layer 22A has such a groove 22g, which is suitable for suppressing the release of non-aqueous electrolyte that has permeated into the electrode body 20 out of the electrode body 20. Suppressing the release of non-aqueous electrolyte from the electrode body 20 helps to suppress the increase in internal resistance (rapid degradation) caused by high-speed charging and discharging in the battery 100.

[0043] From the viewpoint of suppressing the diffusion of Li ions, the depth of the groove portion 22g (recessed shape portion 22r) is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. From the viewpoint of suppressing the shedding of active material from the negative electrode active material layer 22A, the depth of the groove portion 22g is preferably 70 μm or less, more preferably 60 μm or less, and even more preferably 55 μm or less. The depth of the groove portion 22g refers to the length (dimension) of the groove portion 22g in the thickness direction of the negative electrode active material layer 22A.

[0044] From the viewpoint of suppressing the diffusion of Li ions, the width of the groove portion 22g (recessed shape portion 22r) is preferably 0.3 mm or more, more preferably 0.7 mm or more, and even more preferably 1.0 mm or more. From the viewpoint of suppressing the shedding of the active material, the width of the groove portion 22g is preferably 3.5 mm or less, more preferably 3.2 mm or less, and even more preferably 3.0 mm or less. The width of the groove portion 22g refers to the length (dimension) of the open end of the groove portion 22g in a direction orthogonal to the extending direction of the groove portion 22g.

[0045] The ratio (d / T) of the depth d (recess depth) of the groove 22g to the thickness T of the negative electrode active material layer 22A is preferably 0.02 or more, more preferably 0.10 or more, and even more preferably 0.20 or more. This structure is preferred in suppressing the diffusion of Li ions from the opposing portion 22f to the non-opposing end 22e of the negative electrode active material layer 22A. The ratio (d / T) is preferably 0.70 or less, more preferably 0.65 or less, and even more preferably 0.60 or less. This structure is preferred from the viewpoint of suppressing the shedding of the aforementioned active material.

[0046] Figure 4 (A) to (C) are enlarged cross-sectional views schematically showing the recessed shape 22r (groove 22g) of the negative electrode active material layer 22A and its vicinity. Specifically, Figure 4 (A) represents the outermost peripheral region R of the electrode body 20, which serves as the wound electrode body. OM The recessed shape 22r and its vicinity, Figure 4 (B) represents the middle region R of electrode body 20. MID The recessed shape 22r and its vicinity, Figure 4 (C) represents the innermost circumferential region R of electrode body 20. IM The recessed shape 22r and its vicinity within the electrode body 20. The central region R of the electrode body 20. MID It is the outermost peripheral region R in electrode body 20 OM with the innermost region R IM In this embodiment, the region between [regions] is defined as the area from the outermost periphery R. OM and the innermost peripheral region R IM Regions separated by the same number of stacked layers (outermost region R) OM with the innermost region R IM (The case where the number of layers between them is odd) or a region with 2 layers (the outermost region R) OM with the innermost region R IM (The case where the number of layers is even).

[0047] The outermost peripheral region R of electrode body 20 OM The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (A) shows the innermost circumferential region R of the electrode body 20. IM The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (C) shows the depth. This structure has the following advantages: by keeping the electrolyte in the outermost peripheral region R... OM In the recessed shape portion 22r of the negative electrode active material layer 22A, the release of electrolyte to the electrode body 20 can be suppressed, thereby suppressing the rapid deterioration of the electrode body 20.

[0048] In this embodiment, the outermost peripheral region R of the electrode body 20 OM The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (A) shows a difference between the middle region R and the middle region R. MID The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (B) shows the depth. Meanwhile, the innermost circumferential region R of electrode body 20... IM The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (C) shows a difference between the middle region R and the middle region R. MID The recess depth d of the recessed shape portion 22r (groove portion 22g) inside Figure 4 (C) shows shallow.

[0049] In such a negative electrode 22, in this embodiment, the negative electrode current collector 22C is located at the other end (in the width direction W) of the electrode body 20 or the negative electrode 22. Figure 2 The right end (middle) has multiple tabs 22t. In the negative electrode current collector 22C, the tabs 22t are contained in the area exposed where the negative electrode active material layer 22A is not stacked. In the electrode body 20, which is a wound electrode body, multiple tabs 22t overlap in the stacking direction of the above-described stacking structure of the electrode body 20 to form a negative electrode tab portion 22T ( Figure 1 (As shown) (In the negative current collector 22c, tabs 22t are provided in such a configuration). The negative tabs 22T function as current collectors in the negative electrode 22. The tabs 22t are connected to the negative current collector plate 60 (the negative current collector plate 60 is provided with each negative tab 22T) in such an overlapping and integrated state. As a constituent material of the negative current collector plate 60, copper and copper alloys are examples. As a method of connecting the negative current collector plate 60 to the negative tabs 22T in the negative electrode 22, ultrasonic bonding and laser welding are examples.

[0050] The separator 23 is a component used to insulate the positive electrode active material layer 21A from the negative electrode active material layer 22A and to maintain ion conductivity of the non-aqueous electrolyte between the two layers. The separator 23 is preferably a porous resin sheet made of a polyolefin resin. Examples of polyolefin resins include polyethylene (PE) and polypropylene (PP). A heat resistance layer (HRL) containing inorganic fillers may also be provided on the surface of the separator 23. Examples of materials constituting the inorganic fillers include alumina, boehmite, aluminum hydroxide, and titanium dioxide.

[0051] In the manufacturing process of the electrode body 20 described above, a stamping process is performed after the winding process. Specifically, after winding the elongated sheet-shaped laminate containing the elongated sheet-shaped positive electrode 21, the elongated sheet-shaped separator 23, the elongated sheet-shaped negative electrode 22, and another elongated sheet-shaped separator 23, as shown... Figure 5 As shown, the wound body 20P is flattened by stamping (stamping process). In the stamping process, for example, the wound body 20P is clamped between a pair of stamping plates P1 and P2 of a stamping machine, and a load (stamping pressure) is applied to the wound body 20P between the stamping plates P1 and P2. By adjusting this stamping pressure, the wound body 20P can be flattened, and the aforementioned recessed shape portion 22r is formed, thereby obtaining the electrode body 20. Furthermore, by adjusting the stamping pressure and the aforementioned extension length L, the dimensions (depth, width) of the recessed shape portion 22r can be adjusted. The stamping pressure in the stamping process is preferably 0.80 kN / cm. 2 The above, more preferably 0.90 kN / cm 2 The above is further preferred to be 1.00 kN / cm. 2 The preferred value is 1.80 kN / cm. 2 The preferred value is 1.60 kN / cm. 2 The following is a further preferred value: 1.40 kN / cm 2 the following.

[0052] In battery 100, such as Figure 1 As shown, the positive terminal 30 is mounted on the housing 10. For example, the housing 10 has a terminal opening that extends through its constituent parts (plates) in the thickness direction, and the positive terminal 30 is mounted in this opening with an insulating washer sandwiched between it and the housing 10. Riveting is one possible method for mounting the positive terminal 30. Furthermore, the positive terminal 30 is exposed both outside and inside the housing 10. Inside the housing 10, the positive terminal 30 is connected to the positive current collector 50. The positive terminal 30 is electrically connected to the positive electrode 21 of the electrode body 20 via the positive current collector 50. Such a positive terminal 30 is preferably made of metal, more preferably of aluminum or an aluminum alloy.

[0053] The negative terminal 40 is also mounted on the housing 10 (the mounting method is the same as described above for the positive terminal 30). The negative terminal 40 is exposed both on the outside and inside the housing 10. Inside the housing 10, the negative terminal 40 is connected to the negative current collector 60. The negative terminal 40 is electrically connected to the negative terminal 22 of the electrode body 20 via the negative current collector 60. Such a negative terminal 40 is preferably made of metal, more preferably of copper or a copper alloy.

[0054] The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte (supporting electrolyte). Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The non-aqueous solvent can be used alone or in combination with two or more. The electrolyte is a lithium salt, preferably a fluorinated lithium salt. Examples of fluorinated lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium bis(fluorosulfonyl)imide (LiN(SO2F)2). The electrolyte can be used alone or in combination with two or more. This non-aqueous electrolyte permeates into the electrode body 20 within the housing 10. Any remaining non-aqueous electrolyte that does not permeate into the electrode body 20 can also be stored inside the housing 10.

[0055] In the battery 100 with the structure described above, as mentioned above, the negative electrode active material layer 22A of the negative electrode 22 of the electrode body 20 includes a non-facing end 22e that is not facing the positive electrode active material layer 21A across the separator 23. The negative electrode active material layer 22A also includes a non-facing end 22e outside the region (facing portion 22f) facing the positive electrode active material layer 21A. This is suitable for ensuring the positional relationship between the entire region of the positive electrode active material layer 21A and the negative electrode active material layer 22A (suitable for ensuring the tolerance of the positional relationship between the negative electrode active material layer 22A and the positive electrode active material layer 21A in the event of a winding offset in the electrode body 20, thus helping to ensure the productivity of the electrode body 20 or the battery 100). In addition, the negative electrode active material layer 22A also includes a non-facing end 22e outside the region (facing portion 22f) facing the positive electrode active material layer 21A. This is suitable for homogenizing the insertion of Li ions relative to the negative electrode active material layer 22A during battery charging. Therefore, it helps to suppress the precipitation of Li ions in the negative electrode active material layer 22A (when the edge of the negative electrode active material layer is located in the region facing the positive electrode active material layer, the insertion density of Li ions tends to increase locally at such edge, and Li ions are more likely to be precipitated).

[0056] Furthermore, as described above, the negative electrode active material layer 22A has a recessed shape 22r in the boundary region between the facing portion 22f and the non-facing end 22e, where the surface of the negative electrode active material layer 22A recedes from the separator 23. This structure is suitable for narrowing the movement path of Li ions from the facing portion 22f to the non-facing end 22e in the negative electrode active material layer 22A, thereby suppressing Li ion diffusion. This suppression of Li ion diffusion also helps to suppress the rise of the negative electrode potential in the battery 100, thereby suppressing the voltage drop caused by self-discharge.

[0057] Furthermore, as described above, the recessed shape portion 22r of the negative electrode active material layer 22A is located in the outermost peripheral region R of the electrode body 20 (wound electrode body). OM The depth ratio within the innermost circumference region R IM The depth is deep. Based on this structure, through the outermost peripheral region R... OM The electrolyte is retained in the recessed portion 22r of the negative electrode active material layer 22A, which can suppress the release of electrolyte to the electrode body 20, thereby suppressing the rapid deterioration of the electrode body 20.

[0058] As described above, the battery 100 is adapted to suppress the deposition of Li ions in the negative electrode active material layer 22A and suppress the diffusion of Li ions from the phase-facing portion 22f to the non-phase-facing end 22e in the negative electrode active material layer 22A, thereby suppressing the voltage drop caused by self-discharge.

[0059] Such a battery 100 can be used for various purposes. For example, the battery 100 can be appropriately used as a power source (drive power source) for electric motors in vehicles such as passenger cars and trucks. There is no particular limitation on the type of vehicle, but examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0060] The recessed shape 22r of the negative electrode active material layer 22A may also have a shape other than the groove shape described above. Figure 6 This is an example of another shape representing the recessed shape portion 22r. Figure 6 The recessed portion 22r shown has an inclined shape. Specifically, the recessed portion 22r has an inclined shape in the boundary region between the opposing portions 22f and the non-opposing ends 22e of the negative electrode active material layer 22A, such that the surface of the negative electrode active material layer 22A recedes from the diaphragm 23. Figure 6 As shown, the depth d of the inclined recessed portion 22r is the retreat length from the reference plane, with the surface of the facing portion 22f as the reference plane, at a position in the negative electrode active material layer 22A facing the edge of the positive electrode active material layer 21A. The width dw of the inclined recessed portion 22r is the dimension of the inclined surface in the width direction W of the negative electrode 22. The recessed portion 22r may also have such an inclined shape.

[0061] [Experimental Example]

[0062] The following describes test examples related to the present invention, but it is not intended to limit the present invention to the contents shown in these test examples.

[0063] [Example 1]

[0064] <The Making of Positive Electrode>

[0065] First, a positive current collector and a positive electrode slurry for forming the positive electrode active material layer are prepared. The positive current collector is a strip of aluminum foil (13 μm thick). The positive electrode slurry is obtained by mixing a mixture containing positive electrode active material (CAM), carbon black (CB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of CAM:CB:PVDF = 97.5:1.5:1.0, and further containing a specified amount of N-methyl-2-pyrrolidone (NMP) as a solvent. Lithium nickel cobalt manganese composite oxide (CAM) is used as the positive electrode active material. Next, the positive electrode slurry is applied to a specified area (strip) on one side of the positive current collector (strip) to form a coating film, which is then dried. Then, the positive electrode slurry is applied to a specified area (strip) on the other side of the positive current collector to form a coating film, which is then dried. Thus, a positive electrode active material layer (strip) is formed on both sides of the positive current collector. Next, the positive current collector with the positive active material layer is rolled using rolling rolls to make each positive active material layer 60 μm thick. Then, the positive current collector with the positive active material layer is cut into a specified shape. As described above, the positive electrode sheet (positive active material layer / positive current collector / positive active material layer) in Example 1 is fabricated.

[0066] The positive electrode has a first edge (extended linearly along its length) at one end in the width direction. The first edge is formed by cutting the positive current collector and the positive active material layers on both sides of the electrode linearly along the length of the electrode. Additionally, on the other side of the positive electrode in the width direction, it has multiple tabs spaced at predetermined intervals in the length direction. Figure 2 The electrode has a tab 21t in the middle, and between the tabs there is a second edge (extending in a straight line along the length direction). In the width direction, the edge of the positive electrode active material layer (extending in a straight line along the length direction) is located at a position that is recessed from the second edge.

[0067] <The Making of the Negative Electrode>

[0068] First, a negative electrode current collector and a negative electrode slurry for forming the negative electrode active material layer are prepared. The negative electrode current collector is a strip of copper foil (8 μm thick). The negative electrode slurry is obtained by mixing graphite (as the negative electrode active material (AAM), styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a tackifier in ion-exchanged water at a mass ratio of AAM:SBR:CMC = 98.3:0.7:1.0. Next, the negative electrode slurry is applied to a designated area (strip-shaped) on one side of the negative electrode current collector (strip-shaped) to form a coating film, and then the coating film is dried. Then, the negative electrode slurry is applied to a designated area (strip-shaped) on the other side of the negative electrode current collector to form a coating film, and then the coating film is dried. Thus, a negative electrode active material layer (strip-shaped) is formed on both sides of the negative electrode current collector. Next, the negative electrode current collector with the negative electrode active material layer is rolled using rolling rolls, so that the thickness T of each negative electrode active material layer is 88 μm. Therefore, the density of the negative electrode active material layer is 1.51 g / cm³. 3 Next, the negative electrode current collector with the negative electrode active material layer is cut into a specified shape. As described above, the negative electrode sheet (negative electrode active material layer / negative electrode current collector / negative electrode active material layer) in Example 1 is fabricated.

[0069] The negative electrode has multiple tabs spaced at predetermined intervals on one side in the width direction and in the length direction. Figure 2 The negative electrode sheet has a tab 22t in the middle, and has an edge (first edge) extending in a straight line along the length direction between the tabs. In addition, the negative electrode sheet has an edge (second edge) extending in a straight line along the entire length direction at the other end in the width direction. The first edge and the second edge are formed by cutting the negative current collector and the negative active material layer on both sides of it in a straight line along the length direction of the sheet.

[0070] <Fabrication of Electrodes>

[0071] First, in addition to the aforementioned positive and negative electrode sheets, a long strip-shaped separator (2 rolls) is prepared. The separator is a separator comprising a porous substrate layer made of polyethylene (PE) resin. Next, the long strip-shaped laminate, in which the positive electrode sheet, separator, negative electrode sheet, and another separator are sequentially arranged, is wound to obtain a wound body. The number of turns of the wound body is 33. In the width direction of the long strip-shaped laminate, the first edge end on the negative electrode tab side of the negative electrode sheet extends outward compared to the first edge end of the positive electrode sheet (the side without the positive electrode tab), and the negative electrode active material layer has a non-facing end that is separated from the positive electrode active material layer by the separator (in... Figure 3The non-facing end 22e is shown in the middle. The extension length L of the non-facing end of the negative electrode active material layer on the first edge side (negative electrode tab side) is set to 1.4 mm. In the width direction of the strip-shaped laminate, the aforementioned second edge of the negative electrode sheet extends outward compared to the edge of the positive electrode active material layer on the positive electrode tab side of the positive electrode sheet, and the negative electrode active material layer has a non-facing end that is separated from the positive electrode active material layer by a separator (in the middle). Figure 3 The non-facing end 22e is shown in the middle. The extension length L of the non-facing end of the negative electrode active material layer on the second edge side is set to 1.4 mm. Next, in the stamping process, the wound body is stamped for 3 seconds to flatten it (see...). Figure 5 In this stamping process, the stamping load is set to 250 kN (stamping pressure is 1.08 kN / cm). 2 Therefore, in the phase-facing portion ( ) of the negative electrode active material layer Figure 3 The opposing portions 22f and the non-opposing ends (in the middle) Figure 3 A groove is formed in the boundary region of the non-opposing end 22e (in the middle). Figure 3 (22g of the groove in the middle). As described above, a flat wound electrode body of Example 1 is manufactured.

[0072] Shape Measurement

[0073] First, the wound electrode body is disassembled to remove the negative electrode sheet, which is then unfolded along its length. For this negative electrode sheet, visual inspection confirms that a groove is formed in the boundary region between the opposing and non-opposing ends in the negative electrode active material layer, from the beginning of the winding (the innermost circumference of the wound electrode body) to the end of the winding (the outermost circumference of the wound electrode body). Figure 3 The case of the groove portion (22g) was examined. Next, the dimensions of the groove portion were measured using a three-dimensional shape measuring instrument (trade name "VR-5000", manufactured by Keyence). Specifically, the depth d and width were measured for the groove portions on the first edge side (negative electrode tab side) and second edge side in the outermost peripheral region of the wound electrode body, the groove portions on the first edge side (negative electrode tab side) and second edge side in the middle region, and the groove portions on the first edge side (negative electrode tab side) and second edge side in the innermost peripheral region. The results are shown in Table 1. Table 1 also shows the ratio (d / T) of the depth d (μm) to the thickness T (μm) of the negative electrode active material layer. Additionally, as an example of the shape measurement results from the three-dimensional shape measuring instrument, Figure 7 The image data shown represents the non-opposing ends of the negative electrode active material layer on the first edge side of the outermost peripheral region of the wound electrode body in Example 1, and its vicinity. Figure 7 The depth and width of the recessed shape (groove) on the first edge side of the negative electrode active material layer were determined from the image data.

[0074] [Example 2]

[0075] The stamping pressure for the wound electrode body in the above stamping process is set to 350 kN (stamping pressure is 1.51 kN / cm). 2 In the negative electrode active material layer within the outermost peripheral region of the wound electrode body, in the phase-facing portion ( Figure 6 The opposing portions 22f and the non-opposing ends (in the middle) Figure 6 The boundary region of the non-opposing end 22e in the middle is formed with an inclined concave shape. Figure 6 In addition to the recessed shape portion 22r, the wound electrode body of Example 2 was manufactured in the same manner as the wound electrode body of Example 1. Then, in the same manner as described above with respect to Example 1, the wound electrode body was disassembled and the negative electrode sheet was removed. The dimensions of the recessed shape portion of the negative electrode sheet were measured using the aforementioned three-dimensional shape measuring instrument. The results are shown in Table 1.

[0076] [Example 3]

[0077] The stamping pressure on the wound electrode body in the above stamping process is set to 125 kN (stamping pressure is 0.54 kN / cm). 2 (No recessed shape portion was formed). Except as otherwise provided, the wound electrode body of Example 3 was manufactured in the same manner as the wound electrode body of Example 1. Then, the wound electrode body was disassembled and the negative electrode sheet was removed. The shape of the negative electrode sheet at the same measurement location as that described in Example 1 was measured using the aforementioned three-dimensional shape measuring instrument. The results are shown in Table 1.

[0078] [Table 1]

[0079]

[0080] The batteries disclosed herein can also be secondary batteries other than lithium-ion batteries. These secondary batteries include, in addition to those commonly referred to as lithium-ion batteries or lithium secondary batteries, batteries such as nickel-metal hydride batteries.

[0081] As described above, the structures described in the following items are examples of specific methods of the technology disclosed herein.

[0082] Item 1:

[0083] A secondary battery comprising wound electrode bodies, wherein...

[0084] The wound electrode body comprises a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped diaphragm. It is an electrode body formed by winding the positive electrode and the negative electrode along the length direction with the diaphragm in between.

[0085] The positive electrode has a layered structure comprising a positive current collector and a positive active material layer.

[0086] The negative electrode has a layered structure comprising a negative electrode current collector and a negative electrode active material layer.

[0087] The negative electrode active material layer includes:

[0088] The opposing portions, which face each other across the separator, are opposite to the positive electrode active material layer; and

[0089] The non-facing end is separated from the positive electrode active material layer by the membrane.

[0090] The negative electrode active material layer has a recessed shape in the boundary region between the opposing portion and the non-opposing end, where the surface of the negative electrode active material layer retracts from the diaphragm.

[0091] The depth of the recessed shape portion in the outermost peripheral region of the wound electrode body in the negative electrode active material layer is greater than the depth of the recessed shape portion in the innermost peripheral region of the wound electrode body.

[0092] Item 2:

[0093] According to item 1, the secondary battery wherein the recessed shape portion is a groove portion.

[0094] Item 3:

[0095] According to item 2, the secondary battery has a depth of 1~70μm.

[0096] Item 4:

[0097] According to item 2 or 3, the width of the groove is 0.3~3.5mm.

[0098] Item 5:

[0099] The secondary battery according to any one of items 2 to 4, wherein the depth of the groove in the negative electrode active material layer is in a ratio of 0.02 to 0.70 to the thickness in the outermost peripheral region of the wound electrode body.

[0100] Item 6:

[0101] The secondary battery according to any one of claims 1 to 5, wherein the density of the negative electrode active material layer is 1.0 to 2.0 g / cm³. 3 .

[0102] Item 7:

[0103] The secondary battery according to any one of claims 1 to 6, wherein the negative electrode active material layer has an average thickness of 50 to 200 μm.

[0104] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of protection of the claims. The technology described within the scope of the claims includes technologies obtained by various modifications and alterations to the specific examples described above.

Claims

1. A secondary battery comprising wound electrode bodies, wherein, The wound electrode body comprises a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped diaphragm. It is an electrode body formed by winding the positive electrode and the negative electrode along the length direction with the diaphragm in between. The positive electrode has a layered structure comprising a positive current collector and a positive active material layer. The negative electrode has a layered structure comprising a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer includes: The opposing portions, which face each other across the separator, are opposite to the positive electrode active material layer; and The non-facing end is separated from the positive electrode active material layer by the membrane. The negative electrode active material layer has a recessed shape in the boundary region between the opposing portion and the non-opposing end, where the surface of the negative electrode active material layer retracts from the diaphragm. The depth of the recessed shape portion in the outermost peripheral region of the wound electrode body in the negative electrode active material layer is deeper than the depth of the recessed shape portion in the innermost peripheral region of the wound electrode body.

2. The secondary battery as described in claim 1, wherein, The recessed shape is a groove.

3. The secondary battery as described in claim 2, wherein, The depth of the groove is 1~70μm.

4. The secondary battery as described in claim 2, wherein, The width of the groove is 0.3~3.5mm.

5. The secondary battery as described in claim 2, wherein, The ratio of the depth of the groove to the thickness of the negative electrode active material layer is 0.02 to 0.

70.

6. The secondary battery as described in claim 1, wherein, The density of the negative electrode active material layer is 1.0~2.0 g / cm³. 3 .

7. The secondary battery according to any one of claims 1 to 6, wherein, The negative electrode active material layer has a thickness of 50~200μm.

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