Nonaqueous electrolyte secondary battery

Abstract

The invention relates to a non-aqueous electrolyte secondary battery. Provided is a non-aqueous electrolyte secondary battery in which the resistance of the negative electrode is suppressed and the thermal stability is excellent. A negative electrode of a non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode active material layer and a plurality of negative electrode tabs, and when a root portion of the negative electrode active material layer from which the negative electrode tabs extend is measured by a spectrocolorimeter, the a * value in the L * a * b * color system is 1.3 or less, and the b * value in the L * a * b * color system is 1.3 or less. The amount of elemental carbon and the amount of elemental boron are measured by laser ablation ICP mass spectrometry in the width direction of the negative electrode active material layer, and the integrated value of the ratio B / C of the amount of elemental boron to the amount of elemental carbon is 28 or more in a range of + / -20 mm from the center in the width direction.

Description

Technical Field

[0001] This invention relates to non-aqueous electrolyte secondary batteries. Background Technology

[0002] To date, non-aqueous electrolyte secondary batteries are known, comprising an electrode body including a positive electrode and a negative electrode, a positive terminal electrically connected to the positive electrode, a negative terminal electrically connected to the negative electrode, and a non-aqueous electrolyte. In non-aqueous electrolyte secondary batteries, typically during initial charging, a portion of the non-aqueous electrolyte decomposes, forming a film (Solid Electrolyte Interface film: SEI film) containing its decomposition products on the surface of the negative electrode active material layer. This film stabilizes the interface between the negative electrode active material layer and the non-aqueous electrolyte (e.g., Japanese Patent Application Laid-Open No. 2007-165125).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-165125 Summary of the Invention

[0006] According to the inventors' research, in recent high-capacity non-aqueous electrolyte secondary batteries, the width of the electrode body has increased, making it difficult for the non-aqueous electrolyte to penetrate to the central portion in the width direction. Therefore, it has been found that unevenness (fluctuation) in the quantity and quality of the coating occurs in the central portion of the negative electrode active material layer, easily leading to a decrease in thermal stability. Furthermore, in high-capacity non-aqueous electrolyte secondary batteries, the negative electrode has multiple negative electrode plates, which are electrically connected to the negative terminal in a stacked and folded state. In such a configuration, it has been found that unevenness in the quantity and quality of the coating occurs at the root portion of the extended negative electrode plates, easily leading to a local increase in resistance.

[0007] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide a non-aqueous electrolyte secondary battery with suppressed negative electrode resistance and excellent thermal stability.

[0008] According to the present invention, a non-aqueous electrolyte secondary battery is provided, comprising: an electrode body including a positive electrode and a negative electrode, a positive terminal electrically connected to the positive electrode, a negative terminal electrically connected to the negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer comprising carbon material and having a width of 200 mm or more, and a plurality of negative electrode sheets disposed at one end in the width direction. The plurality of negative electrode sheets are electrically connected to the negative terminal in a stacked and folded state. When the root portion of the negative electrode sheets extending from the negative electrode active material layer is measured using a spectrophotometer, the L value is based on Japanese Industrial Standard JIS Z8781-4:2013. ＊ a ＊ b＊ In the color system, a ＊ The value is below 1.3, and the amount of carbon and boron is determined by laser ablation ICP quality analysis along the width direction of the negative electrode active material layer. Within a range of ±20 mm from the center of the width direction, the integral value of the ratio of the amount of boron to the amount of carbon (B / C) is above 28.

[0009] Through in-depth research, the inventors discovered that areas with high resistance manifest as "color spots (uneven color distribution)," which can be determined based on L. ＊ a ＊ b ＊ The above a in the color system ＊ Value identification. It was also found that the battery's heat generation is correlated with the B / C ratio obtained through laser ablation ICP quality analysis. Therefore, in this invention, the above-mentioned a... ＊ The value is adjusted to below a specified value, and the B / C ratio is adjusted to above a specified value. Based on the above configuration, a battery can be provided that exhibits suppressed negative electrode resistance and excellent thermal stability. Attached Figure Description

[0010] Figure 1 A perspective view of a non-aqueous electrolyte secondary battery according to one embodiment is shown schematically.

[0011] Figure 2 For along Figure 1 A schematic longitudinal section of line II-II.

[0012] Figure 3 For along Figure 1 A schematic cross-sectional view of line III-III.

[0013] Figure 4 A perspective view of the electrode assembly mounted on the sealing plate is shown schematically.

[0014] Figure 5 A perspective view of a wound electrode body according to one embodiment is shown schematically.

[0015] Figure 6 This is a schematic diagram illustrating the configuration of a wound electrode body according to one embodiment.

[0016] Figure 7 (a) shows the resistance distribution of Comparative Example 1. Figure 7 (b) shows the resistance distribution of Comparative Example 2. Figure 7 (c) shows the resistance distribution of the embodiment.

[0017] Figure 8 To show the resistance ratio near the negative electrode and a ＊ A coordinate graph showing the relationship between values.

[0018] Figure 9 This is a schematic diagram of the negative electrode (sample for measurement).

[0019] Figure 10 (a) shows the distribution of the ratio (B / C) in Comparative Example 1. Figure 10 (b) shows the distribution of the ratio (B / C) in Comparative Example 2. Figure 10 (c) shows the distribution of the ratio (B / C) for the example.

[0020] Figure 11 A graph showing the relationship between the integral value of the ratio (B / C) in the central part of the negative electrode active material layer and the heat generation of the battery.

[0021] Explanation of reference numerals in the attached figures

[0022] 10 Battery casing

[0023] Electrode bodies 20a, 20b, and 20c (wound electrode bodies)

[0024] 22 Positive electrode

[0025] 24 Negative electrode

[0026] 24a Negative electrode active material layer

[0027] 24c negative current collector

[0028] 24t negative electrode sheet

[0029] 30 Positive extremes

[0030] 40 Negative extremes

[0031] 100 batteries Detailed Implementation

[0032] Hereinafter, with reference to the accompanying drawings, several preferred embodiments of the technology disclosed herein will be described. Furthermore, matters other than those specifically mentioned in this specification and matters necessary for the implementation of the invention (e.g., the general structure and manufacturing process of non-aqueous electrolyte secondary batteries that are not features of the invention) can be understood by those skilled in the art based on prior art. The present invention can be implemented based on the disclosures in this specification and common technical knowledge in the field. It should be noted that the expression "A to B" indicating a scope in this specification includes the meaning of more than A and less than B, and includes the meanings of "greater than A" and "less than B".

[0033] It should be noted that in this specification, "non-aqueous electrolyte secondary battery" refers to all energy storage devices that can be repeatedly charged and discharged by moving charge carriers between the positive and negative electrodes via a non-aqueous electrolyte. The term "non-aqueous electrolyte secondary battery" includes not only so-called secondary batteries such as lithium-ion batteries and nickel-metal hydride batteries, but also capacitors that utilize chemical reactions, such as lithium-ion capacitors and pseudocapacitors.

[0034] <Battery 100>

[0035] Figure 1 This is a three-dimensional view of a non-aqueous electrolyte secondary battery (hereinafter referred to as a battery). Figure 2 For along Figure 1 A schematic longitudinal section of line II-II. Figure 3 For along Figure 1 A schematic cross-sectional view of line III-III. In the following description, the reference numerals L, R, F, Rr, U, and D in the figures represent left, right, front, back, top, and bottom, respectively. The reference numerals X, Y, and Z in the figures represent the short side direction of battery 100, the long side direction orthogonal to the short side direction, and the up-down direction orthogonal to both the short and long side directions, respectively. The long side direction Y is an example of the width direction. However, these are merely directions for ease of explanation and do not limit the arrangement of battery 100.

[0036] like Figure 2 As shown, the battery 100 includes: a battery casing 10, an electrode assembly 20, a positive terminal 30, a negative terminal 40, and a non-aqueous electrolyte (not shown). The battery 100 also includes a positive current collector 50 and a negative current collector 60. The battery 100 is a lithium-ion secondary battery. The battery 100 is preferably a lithium-ion secondary battery.

[0037] The battery casing 10 is a frame that houses the electrode assembly 20 and the non-aqueous electrolyte. For example... Figure 1 As shown, the battery casing 10 has a flat, bottomed cuboid shape (square). The material of the battery casing 10 can be the same as conventionally used materials, and there are no particular limitations. The battery casing 10 is preferably made of metal, and more preferably, for example, aluminum, aluminum alloy, iron, or iron alloy. Figure 2 As shown, the battery casing 10 includes an outer packaging body 12 having an opening 12h and a sealing plate (cover) 14 that blocks the opening 12h.

[0038] like Figure 1As shown, the outer packaging body 12 includes: a generally rectangular base wall 12a, a pair of long side walls 12b extending from the long side of the base wall 12a and facing each other, and a pair of short side walls 12c extending from the short side of the base wall 12a and facing each other. The base wall 12a is opposite to the opening 12h. The area of ​​the long side walls 12b is larger than the area of ​​the short side walls 12c. It should be noted that in this specification, "generally rectangular" includes not only a perfect rectangle (rectangular shape), but also, for example, shapes where the corners connecting the long and short sides of a rectangle are R-shaped, or shapes with cutouts at the corners, etc.

[0039] like Figure 1 As shown, the sealing plate 14 is roughly rectangular when viewed from above. Figure 2 As shown, the sealing plate 14 is installed on the outer packaging body 12 in a manner that blocks the opening 12h of the outer packaging body 12. The sealing plate 14 is opposite to the bottom wall 12a of the outer packaging body 12. The battery housing 10 is integrated by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the outer packaging body 12. The battery housing 10 is hermetically sealed (airtight).

[0040] like Figure 2 As shown, the sealing plate 14 is provided with an injection hole 15, an vent valve 17, and two terminal outlet holes 18 and 19. The injection hole 15 is used to inject non-aqueous electrolyte after the sealing plate 14 is installed on the outer packaging body 12. Preferably, the sealing plate 14 is provided with an injection hole 15. The injection hole 15 is sealed by a sealing member 16. The vent valve 17 is configured to break when the pressure inside the battery housing 10 reaches a specified value, thereby venting the gas inside the battery housing 10 to the outside. The terminal outlet holes 18 and 19 are respectively formed at both ends in the Y direction of the long side of the sealing plate 14. Figure 2 (Left and right ends). Terminal lead-out holes 18 and 19 penetrate the sealing plate 14 in the thickness direction (vertical direction Z). Terminal lead-out holes 18 and 19 have inner diameters that allow the positive terminal 30 and negative terminal 40 installed in front of the sealing plate 14 (before riveting) to be inserted.

[0041] The positive terminal 30 and the negative terminal 40 are respectively fixed to the sealing plate 14 of the battery casing 10. The positive terminal 30 is disposed on one side of the long side Y direction of the sealing plate 14. Figure 1 , Figure 2 (Left side). The negative terminal 40 is positioned on the other side of the long side Y direction of the sealing plate 14 ( Figure 1 , Figure 2 (The right side). For example Figure 2As shown, the positive terminal 30 extends from the inside of the sealing plate 14 to the outside by inserting into the terminal lead-out hole 18, and the negative terminal 40 extends from the inside of the sealing plate 14 to the outside by inserting into the terminal lead-out hole 19. Preferably, the positive terminal 30 and the negative terminal 40 are mounted on the sealing plate 14. The positive terminal 30 and the negative terminal 40 are riveted to the periphery of the sealing plate 14 surrounding the terminal lead-out holes 18 and 19. At the side ends of the outer casing 12 of the positive terminal 30 and the negative terminal 40 ( Figure 2 The lower end of the part has riveting portions 30c and 40c.

[0042] like Figure 2 As shown, the positive terminal 30 is located inside the battery casing 10 via the positive current collector 50 and the positive electrode 22 of the electrode assembly 20 (see reference). Figure 6 Specifically, the positive electrode assembly 23) is electrically connected. The positive terminal 30 is insulated from the sealing plate 14 by a positive electrode insulating member 70 and a washer 90. The positive terminal 30 is preferably made of metal, more preferably, for example, aluminum or an aluminum alloy.

[0043] The negative terminal 40 is located inside the battery casing 10 via the negative current collector 60 and the negative terminal 24 of the electrode assembly 20 (see reference). Figure 6 Specifically, the negative electrode assembly 25) is electrically connected. The negative terminal 40 is insulated from the sealing plate 14 by a negative electrode insulating member 80 and a washer 90. The negative terminal 40 is preferably made of metal, more preferably, for example, copper or a copper alloy. The negative terminal 40 may be constructed by joining two conductive members into a single unit. Alternatively, the portion of the negative terminal 40 connected to the negative current collector 60 may be made of copper or a copper alloy, while the portion exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0044] Plate-shaped positive electrode external conductive member 32 and negative electrode external conductive member 42 are mounted on the outer surface of the sealing plate 14. The positive electrode external conductive member 32 and negative electrode external conductive member 42 serve as busbars when multiple batteries 100 are electrically connected to each other. The positive electrode external conductive member 32 is electrically connected to the positive terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative terminal 40. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external resin member 92. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are preferably made of metal, more preferably, for example, aluminum or an aluminum alloy. However, the positive electrode external conductive member 32 and negative electrode external conductive member 42 are not essential and can be omitted in other embodiments.

[0045] like Figure 2 As shown, the electrode assembly 20 is housed inside the battery casing 10 (specifically, inside the outer packaging 12). Figure 4This is a perspective view schematically showing the electrode assembly 20 mounted on the sealing plate 14. The electrode assembly 20 here has three wound electrodes 20a, 20b, and 20c. However, the number of wound electrodes disposed inside the battery housing 10 is not particularly limited; it can be two or more, or it can be one. The electrode assembly 20 can be disposed inside the battery housing 10 in a state covered by an insulating electrode support. In other words, an electrode support can exist between the electrode assembly 20 and the battery housing 10 (specifically, the outer packaging 12). The electrode support is preferably made of resin.

[0046] Figure 5 A perspective view of the wound electrode body 20a is shown schematically. Figure 6 This is a schematic diagram illustrating the configuration of the wound electrode body 20a. It should be noted that the following detailed explanation uses the wound electrode body 20a as an example; the wound electrode bodies 20b and 20c can also have the same configuration. Figure 6 As shown, electrode body 20a includes a positive electrode 22 and a negative electrode 24. The positive electrode 22 and the negative electrode 24 are insulated by a separator 26. Electrode body 20a is a wound electrode body here. Electrode body 20a is constructed by stacking strip-shaped positive electrode 22 and strip-shaped negative electrode 24 in an insulated state (e.g., via strip-shaped separator 26) and winding them around a winding shaft WL. However, in another embodiment, electrode body 20a may be a stacked electrode body formed by stacking multiple square positive electrodes and multiple square negative electrodes in an insulated state.

[0047] The electrode body 20a is preferably a wound electrode body. When the electrode body 20a is a wound electrode body, the non-aqueous electrolyte is supplied only from both ends in the direction of the winding shaft WL. Therefore, the non-aqueous electrolyte is particularly difficult to penetrate to the central portion of the electrode body 20a in the direction of the winding shaft WL, where unevenness in the quantity or quality of the film is easily generated. Therefore, the technique disclosed herein is particularly effective.

[0048] Although not particularly limited, the number of turns (wounds) of the winding electrode body 20a is preferably 20 turns or more, more preferably 30 turns or more, and even more preferably 50 turns or more. For example, it can be 150 turns or less, or 100 turns or less.

[0049] Depend on Figure 2 , Figure 6 As can be seen, the wound electrode body 20a is arranged inside the battery housing 10 with the winding axis WL approximately parallel to the long side direction Y. The direction of the winding axis WL is consistent with the long side direction Y (width direction). The wound electrode body 20a is arranged inside the battery housing 10 with the winding axis WL parallel to the bottom wall 12a and orthogonal to the short side wall 12c.

[0050] In this battery 100, the positive electrode assembly 23 and the negative electrode assembly 25 are located at both ends of the winding axis WL of the electrode body 20a. Figure 2 , Figure 4 The so-called transverse electrode structure (left and right). However, in other embodiments, the battery 100 may also have the positive electrode group 23 and the negative electrode group 25 located at one end of the winding axis WL direction of the electrode body 20a (e.g., the left and right sides). Figure 2 , Figure 4 The so-called upper electrode structure (at the upper end). In this case, the winding axis WL direction can be the same as the vertical direction Z.

[0051] like Figure 5 As shown, the wound electrode body 20a has a flat shape. The shape of the wound electrode body 20a is preferably flat. The wound electrode body 20a has: a pair of flat portions 20f extending along the long side direction Y (winding axis WL direction), and a pair of curved portions (R portions) 20r connecting the pair of flat portions 20f. The flat portions 20f have a flat outer surface ( Figure 5 (YZ plane). The curved portion 20r has a curved outer surface. It should be noted that in this specification, "flat outer surface" is not limited to being completely flat, but includes situations where, for example, minute steps, bends, concave portions, convex portions, etc., exist when observed microscopically.

[0052] from Figure 2 , Figure 5 As can be seen, in this embodiment, a pair of flat portions 20f face a pair of long sidewalls 12b of the outer packaging body 12. The flat portions 20f extend along the long sidewalls 12b. A pair of curved portions 20r face the bottom wall 12a and the sealing plate 14 of the outer packaging body 12. As in this embodiment, the electrode body 20a preferably has the positive electrode 22 of the flat portion 20f (see reference). Figure 6 ) and negative electrode 24 (refer to) Figure 6 The stacking direction (thickness direction) of the battery casing 10 is aligned with the short side direction X (the direction perpendicular to the long sidewall 12b).

[0053] The positive electrode 22 can be the same as before, without any special restrictions. For example... Figure 6 As shown, the positive electrode 22 has a positive current collector 22c, and a positive active material layer 22a and a positive protective layer 22p fixed on at least one surface of the positive current collector 22c. However, the positive protective layer 22p is not necessary and can be omitted in other embodiments. The positive current collector 22c is strip-shaped here. The positive current collector 22c is made of conductive metals such as aluminum, aluminum alloy, nickel, and stainless steel. The positive current collector 22c is a metal foil here, specifically an aluminum foil.

[0054] At one end of the positive current collector 22c in the long side direction Y (width direction, winding axis WL direction) Figure 6 Multiple positive electrode plates 22t are provided at the left end of the electrode. Each of the multiple positive electrode plates 22t is convex, facing towards the long side Y ( Figure 6 (On the left side) protrudes. Multiple positive electrode plates 22t extend relative to the separator 26 in the long side direction Y. Multiple positive electrode plates 22t are arranged at intervals (intermittently) along the length direction of the positive electrode 22. By arranging multiple positive electrode plates 22t, the resistance of the battery 100 can be reduced. The positive electrode plates 22t here are part of the positive current collector 22c and are made of metal foil (aluminum foil).

[0055] like Figure 3 As shown, multiple positive electrode plates 22t are located at one end of the long side Y ( Figure 3 The positive electrode sheets 22t are stacked at their left ends to form a positive electrode assembly 23. Multiple positive electrode sheets 22t are stacked and bent with their outer ends aligned. This improves the capacity within the battery casing 10, enabling miniaturization of the battery 100. Furthermore, it increases the volumetric energy density of the battery 100. A second positive current collector 52, described later, is attached (specifically, joined) to the positive electrode assembly 23. The multiple positive electrode sheets 22t are connected to the second positive current collector 52 in a stacked and bent state. The positive electrode assembly 23 is electrically connected to the positive terminal 30 via the positive current collector 50.

[0056] like Figure 6 As shown, the positive electrode active material layer 22a is arranged in a strip shape along the length direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (e.g., a lithium transition metal composite oxide containing lithium nickel cobalt manganese composite oxide, etc.) capable of reversibly attracting and releasing charge carriers. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as conductive materials, binders, various additives, etc. As a conductive material, carbon materials such as acetylene black (AB) can be used, for example. As a binder, polyvinylidene fluoride (PVdF) can be used, for example.

[0057] Although there are no specific restrictions, but such as Figure 6 As shown, in the high-capacity battery 100 used as a vehicle battery, the length Lc (average value, excluding the portion formed on the positive electrode sheet 22t) of the long side direction Y (winding axis WL direction) of the positive electrode active material layer 22a is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more. The length Lc is preferably the same as or shorter than the length La of the long side direction Y of the negative electrode active material layer 24a described later.

[0058] like Figure 6As shown, the positive electrode protective layer 22p is disposed between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. The positive electrode protective layer 22p is disposed at one end of the positive electrode current collector 22c in the long side direction Y. Figure 6 (At the left end). The positive electrode protective layer 22p is arranged in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than inorganic fillers, such as conductive materials, binders, various additives, etc. The conductive materials and binders may be the same as those exemplified as substances that may be contained in the positive electrode active material layer 22a.

[0059] like Figure 6 As shown, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed on at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is in the form of a strip. The negative electrode current collector 24c is made of conductive metals such as copper, copper alloys, nickel, or stainless steel. The negative electrode current collector 24c preferably contains copper or a copper alloy. The negative electrode current collector 24c is in the form of a metal foil, specifically a copper foil.

[0060] At one end of the negative electrode current collector 24c in the long side direction Y (width direction, winding axis WL direction) Figure 6 Multiple negative electrode plates 24t are provided at the right end. Each of the multiple negative electrode plates 24t is convex, and they are respectively oriented towards one side of the long side Y ( Figure 6 The right side of the negative electrode 24 protrudes. Multiple negative electrode plates 24t extend relative to the separator 26 in the long side direction Y. The multiple negative electrode plates 24t are spaced apart (intermittently) along the long side direction of the negative electrode 24. By providing multiple negative electrode plates 24t, the resistance of the battery 100 can be reduced. The negative electrode plates 24t are part of the negative current collector 24c and are made of metal foil (copper foil). Preferably, at least a portion of the negative electrode plates 24t is an exposed portion of the current collector 24c where the negative active material layer 24a is not formed.

[0061] like Figure 3 As shown, multiple negative electrode plates 24t are located at one end in the long side direction Y ( Figure 3 The negative electrode sheets 24t are stacked at their right ends to form a negative electrode assembly 25. Multiple negative electrode sheets 24t are stacked and bent with their outer ends aligned. This improves the capacity within the battery casing 10, allowing for miniaturization of the battery 100. Furthermore, it increases the volumetric energy density of the battery 100. The negative electrode assembly 25 is equipped with a second negative current collector 62, described later, attached to the negative current collector 60. The multiple negative electrode sheets 24t are connected to the second negative current collector 62 in their stacked and bent state. The negative electrode assembly 25 is electrically connected to the negative terminal 40 via the negative current collector 60.

[0062] like Figure 6 As shown, the negative electrode active material layer 24a is arranged in a strip shape along the length direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., carbon materials such as graphite, silicon materials) capable of reversibly adsorbing and releasing charge carriers. When the total solid content of the negative electrode active material layer 24a is set to 100% by mass, the negative electrode active material (e.g., graphite) can account for approximately 80% by mass or more, typically 90% by mass or more, for example 95% by mass or more. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as binders, dispersants, various additives, etc. As a binder, rubbers such as styrene-butadiene rubber (SBR) can be used. As a dispersant, cellulose-based materials such as carboxymethyl cellulose (CMC) can be used.

[0063] like Figure 6 As shown, the length La (average value, excluding the portion formed on the negative electrode sheet 24t) of the long side direction Y (winding axis WL direction) of the negative electrode active material layer 24a is typically the same as or longer than the length Lc of the long side direction Y of the positive electrode active material layer 22a. While not particularly limited, from the viewpoint of high capacity, the length La of the negative electrode active material layer 24a is preferably 200 mm or more, more preferably 250 mm or more. In the electrode body 20a, the longer the length La, the more difficult it is for the non-aqueous electrolyte to penetrate to the central M including the long side direction Y. Y (Refer to Figure 5 The central portion of the film. As a result, unevenness in the quantity or quality of the film is easily generated at the central portion in the long side direction Y. Therefore, the technique disclosed herein is particularly effective. The length La can be, for example, 1000 mm or less, or 500 mm or less. Thus, the effects of the technique disclosed herein can be achieved at a high level.

[0064] like Figure 5 As shown, the height Ha of the negative electrode active material layer 24a located in the flat portion 20f of the electrode body 20a (which is the same as the height of the flat portion 20f) is preferably 110 mm or less, more preferably 50 to 110 mm, even more preferably 70 to 100 mm, and particularly preferably 70 to 90 mm. In the flat portion 20f, the ratio (horizontal / vertical ratio) of the length La in the long side direction Y to the height Ha of the negative electrode active material layer 24a is preferably 1 to 10, more preferably 2 to 7, and even more preferably 3 to 5. Therefore, the effects of the technology disclosed herein can be achieved at a high level.

[0065] The negative electrode active material layer 24a typically includes a boron (B)-containing film (SEI film). This boron is derived from a boron-containing compound (a compound containing B) added to the non-aqueous electrolyte during the construction of the battery 100, such as a film-forming agent described later. The aforementioned film may, for example, be a decomposition product of a compound containing B that decomposes during initial charging. Due to the excellent stability of the boron-containing film, the durability and thermal stability of the battery 100 can be appropriately improved.

[0066] According to the inventors' research, at the root portion of the negative electrode 24t extending from the negative electrode active material layer 24a (hereinafter also simply referred to as "near the negative electrode 24t"), the resistance tends to increase locally due to the bending and folding of multiple negative electrode 24ts. While not intended to be interpreted in a particularly limiting way, for example, if the negative electrode 24t is bent and folded (in other words, if an external force is applied to the negative electrode 24t), the inter-electrode distance between the positive electrode 22 and the negative electrode 24 tends to increase locally near the negative electrode 24t. As a result, non-aqueous electrolyte tends to accumulate at this location. It is believed that if initial charging is performed under these conditions, the decomposition of the non-aqueous solvent is promoted, thus increasing the amount of organic film from the non-aqueous solvent and causing the resistance to increase.

[0067] Therefore, in the disclosed technology, when measuring the root portion (near the negative electrode 24t) of the negative electrode active material layer 24a extending from the negative electrode plate 24t using a spectrophotometer, the L value based on Japanese Industrial Standard JIS Z8781-4:2013 is used. ＊ a ＊ b ＊ In the color system, a ＊ Set the value to below 1.3. In L ＊ a ＊ b ＊ In a color system, coordinate axes can be divided into white / black (lightness) and yellow / cyan / red / green (chroma). Specifically, in the embodiments described later, according to the inventors' research, the high-resistivity portion of the negative electrode active material layer 24a is manifested as a "color spot," thus enabling the determination of L... ＊ a ＊ b ＊ Color system a ＊ Identification is based on the value (red tone). This is achieved by using a... ＊ By adjusting the value to below the specified value, high resistance is suppressed near the negative electrode plate 24t, thereby improving battery characteristics.

[0068] Furthermore, while the intensity (darkness) of a "spot" can be visually identified, individual differences exist in the human eye, and the determination of the presence or absence of a spot can vary from person to person. In contrast, using objective values ​​obtained from a spectrophotometer, as disclosed herein, reduces the likelihood of accuracy deviations. Additionally, it can identify color differences that the human eye cannot discern. Therefore, it is easier to stably suppress resistance.

[0069] Furthermore, in this specification, "the root portion extending from the negative electrode sheet" refers to a range of approximately 40 mm along the long side direction Y (width direction) starting from the negative electrode sheet 24t. Regarding the above measurement, considering deviations, it can be performed at multiple locations within the root portion. In this case, multiple locations are more preferable. ＊ All values ​​were below the specified values. Furthermore, when the electrode body 20a is a wound electrode body, the above measurements were performed at one or more locations at the root portion of each turn, more preferably at one of the multiple turns. ＊ All values ​​are below the specified values.

[0070] a at the root of the negative electrode 24t ＊ From the viewpoint of maximizing the effectiveness of the technology disclosed herein, a value of 1.2 or less is preferred, 1.1 or less is more preferred, 1.0 or less is even more preferred, and 0.9 or less is particularly preferred. The a value of the negative electrode active material layer 24a... ＊ The value is typically 0.1 or higher, for example, it can be 0.6 or higher, or 0.7 or higher.

[0071] Furthermore, according to the inventors' research, non-aqueous electrolytes have difficulty penetrating the central portion of the negative electrode active material layer 24a along the long side direction Y (width direction). Therefore, unevenness in the quantity or quality of the coating easily occurs in the central portion of the negative electrode active material layer 24a along the long side direction Y. Consequently, thermal stability can sometimes be reduced.

[0072] Therefore, in the disclosed technology, the carbon and boron content is determined by laser ablation ICP mass spectrometry (LA-ICP-MS) along the long side direction Y (width direction) of the negative electrode active material layer 24a, and the carbon and boron content is determined at the center M of the long side direction Y (width direction). Y (Refer to Figure 5Within a range of ±20 mm, the integral value of the ratio of boron to carbon (B / C) is set to 28 or higher. Regarding the integral value of the above ratio (B / C), a larger value indicates a greater amount of boron (B) in the central part of the long side direction Y of the negative electrode active material layer 24a. Specifically, in the embodiments described later, according to the inventors' research, the integral value of the above B / C ratio is correlated with the heat generation of the battery 100. In detail, the larger the integral value of the above B / C ratio, the more the heat generation of the battery 100 is suppressed. Therefore, by adjusting the above B / C ratio to a predetermined value or higher, a battery 100 with suppressed heat generation and excellent thermal stability can be provided.

[0073] From the viewpoint of achieving a high level of effectiveness of the technology disclosed herein, the integral value of the aforementioned ratio (B / C) is preferably 30 or more, more preferably 35 or more, even more preferably 40 or more, and particularly preferably 50 or more. From the viewpoint of suppressing resistance, the integral value of the aforementioned ratio (B / C) is preferably 100 or less, more preferably 80 or less.

[0074] To clarify, the above a ＊ The integral value of the value and / or the above ratio (B / C) can be adjusted not only by the amount of non-aqueous electrolyte injected during the construction of the battery 100 and the concentration of additives (compounds containing boron) in the non-aqueous electrolyte, but also by the conditions of, for example, the electrolyte impregnation process (process 2) in the manufacturing method described later, especially the conditions of the pressure-reduced impregnation process (process 2-1), and the conditions of the initial charging process (process 3), such as the extrusion pressure (constraint load).

[0075] like Figure 6 As shown, the separator 26 is a component that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The length Ls of the separator 26 in the long side direction Y (winding axis WL direction) is typically the same as or longer than the length La of the long side direction Y of the negative electrode active material layer 24a. The separator 26 is preferably, for example, a porous sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may have a functional layer such as an adhesive layer or a heat resistance layer (HRL) on the surface of the substrate portion made of the resin porous sheet. The adhesive layer is a layer containing an adhesive. The heat resistance layer is, for example, a layer containing inorganic fillers such as alumina, silica, boehmite, magnesium oxide, and titanium dioxide, and an adhesive such as PVdF. The heat resistance layer can also serve as an adhesive layer. The composition of the heat resistance layer and the adhesive layer can be the same as conventional.

[0076] like Figure 2As shown, the positive current collector 50 forms a conductive path that electrically connects the positive electrode assembly 23, composed of multiple positive electrode plates 22t, to the positive terminal 30. The positive current collector 50 can be made of the same type of metal as the positive current collector 22c, such as conductive metals like aluminum, aluminum alloy, nickel, and stainless steel. The positive current collector 50 includes a first positive current collector 51 connected to the positive terminal 30 and a second positive current collector 52 connected to the positive electrode assembly 23. The first positive current collector 51 is mounted on the inner surface of the sealing plate 14.

[0077] The second positive current collector 52 extends along the short sidewall 12c of the outer packaging body 12. The second positive current collector 52 is attached to the positive electrode assembly 23 wound around the electrode body 20a. (As shown...) Figure 3 As shown, a junction J with the positive electrode assembly 23 is formed in the second current collector 52 of the positive electrode. The junction J is, for example, a welded junction formed by ultrasonic welding, resistance welding, laser welding, or other welding methods when multiple positive electrode pieces 22t are overlapped. The junction J is positioned such that the multiple positive electrode pieces 22t are close to the side of the short side in the X direction of the wound electrode bodies 20a, 20b, and 20c. Figure 3 The positive electrode 22t is arranged on the front side. Thus, multiple positive electrode sheets 22t can be appropriately bent in a stacked state to stably form a curved positive electrode sheet group 23.

[0078] like Figure 2 As shown, the negative current collector 60 forms a conductive path that electrically connects the negative electrode assembly 25, composed of multiple negative electrode pieces 24t, to the negative terminal 40. The negative current collector 60 can be made of the same type of metal as the negative current collector 24c, such as copper, copper alloy, nickel, stainless steel, or other conductive metals. The negative current collector 60 includes a first negative current collector 61 connected to the negative terminal 40 and a second negative current collector 62 connected to the negative electrode assembly 25. The configuration and arrangement of the first negative current collector 61 and the second negative current collector 62 can be the same as those of the first positive current collector 51 and the second positive current collector 52 of the positive current collector 50.

[0079] The negative electrode second current collector 62 is attached to the negative electrode plate group 25 of the electrode body 20a. For example... Figure 3 As shown, a junction J with the negative electrode assembly 25 is formed in the second current collector 62 of the negative electrode. The junction J, like the one on the positive electrode side, is a welded junction formed, for example, by ultrasonic welding, resistance welding, laser welding, or welding when multiple negative electrode pieces 24t are overlapped. The junction J is positioned such that the multiple negative electrode pieces 24t are close to the side of the short side in the X direction of the wound electrode bodies 20a, 20b, and 20c. Figure 3 The negative electrode 24t is arranged on the front side. Thus, multiple negative electrode sheets 24t can be appropriately bent in a stacked state to stably form a curved negative electrode sheet group 25.

[0080] Non-aqueous electrolytes typically comprise a non-aqueous solvent and a supporting salt (electrolyte salt). One or more non-aqueous solvents previously known for use in non-aqueous electrolyte secondary batteries can be used as the non-aqueous solvent. Examples of non-aqueous solvents include organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. Carbonates are preferably included as the non-aqueous solvent. Examples of carbonates include, for instance, chain carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as propylene carbonate (PC).

[0081] As a supporting salt, there are no particular limitations as long as it contains a charge carrier (typically lithium ions), and one or more supporting salts previously known to be used in non-aqueous electrolyte secondary batteries can be used. Examples of supporting salts include fluorine-containing lithium salts such as LiPF6 and LiBF4. LiPF6 is preferably included as the supporting salt.

[0082] The non-aqueous electrolyte may further contain additives. As additives, one or more additives previously known to be added to non-aqueous electrolytes may be used. Examples include boron-based additives containing boron, such as lithium dioxaborate (LiBOB) and lithium difluoro(oxalate)borate (LiODFB); and phosphorus-based additives containing phosphorus, such as lithium difluorophosphate (LiPO2F2) and lithium difluorooxalate phosphate (LiDFOP). These additives may be so-called film-forming agents that decompose earlier (at lower potentials) than the non-aqueous solvent and / or supporting salt during initial charging and deposit as a film on the surface of the negative electrode active material layer 24a.

[0083] Non-aqueous electrolytes preferably contain compounds containing boron (B), such as lithium salts containing boron. Examples of compounds containing boron (e.g., lithium salts containing boron) include LiBF4 as a supporting salt, and oxalic acid complexes containing boron, such as LiBOB and LiODFB as boron-based additives.

[0084] Furthermore, additives (such as the boron-based additives mentioned above) added to the non-aqueous electrolyte during manufacturing are electrolyzed during initial charging and thus consumed, forming a film on the negative electrode active material layer 24a, etc. Therefore, in the state of the battery 100, the non-aqueous electrolyte may or may not contain the aforementioned additives.

[0085] <Manufacturing Method of Battery 100>

[0086] Battery 100 can be manufactured, for example, using a manufacturing method that sequentially includes the following steps: a battery assembly construction step (step 1), an electrolyte impregnation step (step 2), an initial charging step (step 3), a degassing step (step 4), a filling hole sealing step (step 5), and an aging step (step 6). However, the degassing step (step 4) is optional and can be omitted in other embodiments. Furthermore, other steps may be further included at any stage. For example, an activation step may be further included after the aging step (step 6).

[0087] In the construction process (process 1), typically, within a glove box, the electrode assembly 20 (electrode bodies 20a, 20b, 20c) and non-aqueous electrolyte are contained in the battery housing 10 to construct the battery assembly. It should be noted that, in this specification, "battery assembly" refers to an intermediate state assembled during the manufacturing process of the battery 100 up to the initial charging process (process 3). There are no particular restrictions on the order in which the electrode assembly 20 and non-aqueous electrolyte are contained in the battery housing 10. Preferably, the non-aqueous electrolyte is injected into the battery housing 10 after the electrode assembly 20 has been contained within it.

[0088] In a preferred embodiment, the process typically includes, in sequence: a preparation step (step 1-1), a welding and joining step (step 1-2), a drying step (step 1-3), and a liquid injection step (step 1-4). However, the drying step (step 1-3) is optional and may be omitted in other embodiments. Furthermore, in other embodiments, the order of the welding and joining steps (step 1-2) and the drying steps (step 1-3) may be reversed. Additionally, other steps may be further included at any stage.

[0089] In the configuration process (process 1-1), the electrode assembly 20 is configured inside the outer packaging body 12. Specifically, the electrode assembly 20 is accommodated inside the outer packaging body 12 through the opening 12h. Next, in the welding and joining process (process 1-2), a sealing plate 14 is welded around the opening 12h of the outer packaging body 12, making the outer packaging body 12 and the sealing plate 14 an integral unit. Next, in the drying process (process 1-3), with the injection hole 15 open, the outer packaging body 12 containing the electrode assembly 20 is dried to remove moisture from the inside of the outer packaging body 12. In particular, moisture is removed from the electrode assembly 20. Moisture removal can be performed using a heating drying device, a vacuum drying device, etc., and heating or depressurization operations can be performed individually or appropriately in combination, as in the past. The heating temperature is preferably set to a temperature that allows moisture to evaporate appropriately under depressurization and prevents thermal degradation of the separators of the electrode assembly 20. The heating temperature can be set in the range of, for example, 50 to 200°C.

[0090] Next, in the electrolyte injection process (processes 1-4), firstly, a non-aqueous electrolyte is prepared. The non-aqueous electrolyte preferably contains the aforementioned compound containing element B (e.g., a lithium salt containing element B). In one example, the non-aqueous electrolyte preferably contains a boron-based additive in addition to the non-aqueous solvent and the electrolyte salt. While not particularly limited, from the perspective of easily forming a preferred amount or quality film on the surface of the negative electrode active material layer 24a, the concentration of the boron-based additive in the non-aqueous electrolyte is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more. On the other hand, from the viewpoint of suppressing the increase in battery resistance, the concentration of the boron-based additive in the non-aqueous electrolyte is preferably 1 mol / L or less, more preferably 0.5 mol / L or less, and even more preferably 0.1 mol / L or less. Then, the prepared non-aqueous electrolyte is injected into the interior of the battery casing 10 through the injection hole 15 of the sealing plate 14. Regarding electrolyte injection, in order to improve the impregnation of the non-aqueous electrolyte into the electrode assembly 20 (electrode bodies 20a, 20b, 20c), it is preferable to perform the injection under reduced pressure inside the battery casing 10.

[0091] In the electrolyte impregnation step 2 (step 2), after the battery assembly construction step (specifically, the electrolyte injection step), the impregnation of the non-aqueous electrolyte into the electrode assembly 20, particularly towards the central portion in the long side direction Y, is improved. This step can be performed at room temperature (approximately 25°C ± 10°C). In a preferred embodiment, this step sequentially includes a depressurization impregnation step (step 2-1) and a second impregnation step (step 2-2). Furthermore, other steps may be further included at any stage. The required time for this step (the combined time of the depressurization impregnation step and the second impregnation step) is preferably 10 to 200 hours. As a result, a preferred amount or quality of film can be easily formed on the surface of the negative electrode active material layer 24a, enabling the high-level application of the techniques disclosed herein.

[0092] In the pressure-reduction impregnation process (process 2-1), the internal structure of the battery assembly is pressurized and depressurized. In one example, firstly, with the injection port 15 open (in other words, there is no pressure difference between the inside and outside of the battery casing 10), the battery assembly is housed in a pressure-adjustable chamber. Then, a pressurization operation is performed, which involves pressurizing the chamber and maintaining the pressurized state for a specified time, and a depressurization operation is performed, which involves depressurizing the chamber and maintaining the depressurized state for a specified time. There is no particular limitation on the order of the pressurization and depressurization operations; in one example, it is preferable to perform the depressurization operation after the pressurization operation.

[0093] The pressurization and depressurization conditions, such as pressure and holding time, are preferably adjusted appropriately according to the length Lc of the long side Y of the negative electrode active material layer 24a. In one example, when the length Lc of the long side Y of the negative electrode active material layer 24a is 200 mm or more, the pressurization pressure (pressure level) in this process is preferably 0.60 mPa or more, more preferably 0.80 mPa or more. The holding time under pressurization is preferably 30 minutes or more (e.g., 30 minutes to 120 minutes), more preferably 40 minutes or more.

[0094] According to the inventors' research, a positive correlation was found between the holding time under pressure in this process and the integral value of the ratio (B / C) at the center of the negative electrode active material layer 24a. That is, as the holding time under pressure increases, the integral value of the ratio (B / C) at the center of the negative electrode active material layer 24a tends to increase. In other words, there is a tendency for an increase in boron (B) content at the center in the long side direction Y. Therefore, by making the holding time under pressure a predetermined value or higher, it is easy to adjust the integral value of the ratio (B / C) to the aforementioned range (e.g., 28 or higher).

[0095] Furthermore, the pressure (degree of pressure reduction) in this process is preferably -0.070 to -0.098 mPa (-70 to -100 kPa), more preferably -0.080 to -0.090 mPa (-80 to -90 kPa). The holding time under reduced pressure is preferably shorter than the holding time under increased pressure. The holding time under reduced pressure is preferably 1 minute to 10 minutes, more preferably, for example, 5 minutes or more.

[0096] In this process, the pressurization operation and the depressurization operation are preferably performed once each. According to the inventors' research, if the number of repetitions of the pressurization and depressurization operations increases, the inter-electrode distance between the positive electrode 22 and the negative electrode 24 near the negative electrode 24t increases, resulting in a tendency for the resistance to rise. By performing the pressurization and depressurization operations once each, the increase in the inter-electrode distance between the positive electrode 22 and the negative electrode 24 can be suppressed, thus suppressing the increase in resistance. Therefore, it is easier to reduce the resistance near the negative electrode 24t. ＊ Adjust the value to the range mentioned above (e.g., below 1.3).

[0097] Secondly, in the second impregnation process (process 2-2), the battery assembly is placed (held) under atmospheric pressure. This further promotes the impregnation of the non-aqueous electrolyte into the interior of the electrode bodies 20a, 20b, and 20c, especially in the central part along the long side direction Y.

[0098] In the initial charging step (step 3), the battery assembly is charged at least once after the electrolyte impregnation step. During the initial charging, additives in the non-aqueous electrolyte (e.g., boron-based additives) are typically electrolyzed preferentially over other components in the non-aqueous electrolyte (non-aqueous solvents, electrolyte salts), thereby forming a film (SEI film) on the surface of the negative electrode active material layer 24a. For example, if the non-aqueous electrolyte contains a compound containing element B (typically a lithium salt containing element B), a film (SEI film) containing the decomposition products of the compound containing element B is formed on the surface of the negative electrode active material layer 24a.

[0099] Initial charging is preferably performed while the battery casing 10 is compressed in a defined area. Specifically, it is preferably performed while the positive electrode active material layer 22a and the negative electrode active material layer 24a of the flat portion 20f are opposite each other. It is particularly preferable to perform the charging near the positive electrode 22t and the negative electrode 24t (where the distance between the positive and negative electrodes is open and non-aqueous electrolyte easily accumulates). This prevents the localized increase in the distance between the electrodes near the positive electrode 22t and the negative electrode 24t, and makes it easier to adjust the a* value at the root portion of the negative electrode 24t to the range described above (e.g., 1.3 or less).

[0100] In a preferred embodiment, firstly, a battery cell press equipped with a pair of constraint plates is prepared. Additionally, an extrusion member is prepared for extruding a defined area of ​​the battery casing 10. The size of the extrusion member is preferably smaller than the long sidewall 12b of the battery casing 10, and preferably smaller than the electrode body 20a within the battery casing 10. The extrusion member is preferably capable of extruding the positive electrode assembly 23 and the negative electrode assembly 25 without significantly compressing them in the long side direction Y, and capable of extruding from the root portion of the positive electrode assembly 23 to the root portion of the negative electrode assembly 25. In the long side direction Y, the length of the extrusion member is preferably the same as or longer than the length of the portion of the positive active material layer 22a and the negative active material layer 24a opposite each other (here, the length Lc of the positive active material layer 22a). This allows for high-level suppression of locally increased inter-electrode distance. The length of the extrusion member is preferably longer than the length La of the negative active material layer 24a. The extrusion member is preferably the length capable of extruding approximately the entire length La of the negative active material layer 24a. The length of the extrusion member is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more.

[0101] Furthermore, in this embodiment, the height of the extrusion member in the vertical direction Z is smaller than the overall height of the electrode body 20a, and further smaller than the height Ha (height of the flat portion 20f) of the negative electrode active material layer 24a. This ensures the flow path of the non-aqueous electrolyte, allowing initial charging to occur while the non-aqueous electrolyte is fully immersed in the electrode assembly 20 (electrode bodies 20a, 20b, 20c). The height of the extrusion member is preferably 100 mm or less, more preferably 50 to 100 mm, even more preferably 60 to 90 mm, and particularly preferably 70 to 80 mm.

[0102] In this process, the battery assembly's pair of long sidewalls 12b are then clamped from the short side direction X by two extrusion members. Specifically, the battery assembly is positioned opposite the extrusion members such that the center of the long sidewall 12b of the battery casing 10 aligns with the center of the extrusion members. In this state, the battery assembly is charged while a predetermined extrusion force (constraint load) is applied to it between a pair of constraint plates disposed on the press. From the viewpoint of maximizing the effectiveness of the technology disclosed herein, the constraint load is preferably set to 10 kN or more, and more preferably 15 kN or more (e.g., 17 kN).

[0103] The battery assembly is charged while the battery casing 10 is being compressed. Charging the battery assembly can be performed in the same manner as before. Typically, an external power source is connected between the positive and negative terminals of the battery assembly, and charging continues until a predetermined voltage is reached between the positive and negative terminals. In the case of non-aqueous electrolytes containing additives, charging is preferably performed until at least the decomposition potential of the additives is reached. Regarding the voltage reached, for example, when the negative electrode active material is a carbon material such as graphite, it can be set to approximately 3V or higher, typically 3.5V or higher, for example, 4V or higher. The charging rate can be set, for example, to approximately 0.1C to 2C. Charging can be performed once, or, for example, it can be performed twice or more while simultaneously discharging. Furthermore, this process can be performed at room temperature (e.g., approximately 25°C ± 10°C, 25°C ± 5°C), or, for example, at a high temperature of approximately 45°C. Charging at a high temperature promotes film formation.

[0104] In the degassing process (process 4), after the initial charging process, the gas inside the battery casing 10 (e.g., air, gas generated during the initial charging process due to the decomposition of non-aqueous electrolyte, etc.) is vented to the outside of the battery casing 10. This venting can be achieved, for example, by depressurizing the pressure inside the casing 10. Then, in the liquid injection hole sealing process (process 5), the liquid injection hole 15 is sealed with the sealing member 16 while maintaining normal pressure or depressurization inside the battery casing 10. This airtightly seals (seales) the battery casing 10.

[0105] In the aging process (step 6), the initially charged battery assembly is constrained and maintained for a specified aging period under a specified temperature environment and with a specified constraint load applied from the short side direction X (the thickness direction of the electrode assembly 20). The temperature environment is preferably set to 15 to 40°C, for example, it can be set to room temperature (about 25°C ± 10°C). The constraint load can be set to 1 to 6 kN. In a preferred embodiment, firstly, a battery cell press including a pair of constraint plates is prepared. Secondly, the initially charged battery assembly is arranged between the pair of constraint plates with the pair of long sidewalls 12b of the battery casing 10 facing each other. In this state, the constraint load is applied to the initially charged battery assembly using the press, and the specified aging period is maintained. The aging period varies, for example, depending on the length La of the long side direction Y of the negative electrode active material layer 24a, the conditions of the electrolyte impregnation process (step 2), etc., and is preferably about 5 days or more, more preferably 6 days or more. In this process, the voltage adjusted in the initial charging process can be maintained. In this way, the battery 100 can be manufactured appropriately.

[0106] <Inspection method for negative electrode 24>

[0107] For example, for the battery assembly after initial charging and the battery 100 that has undergone the aging process (process 6) described above, quality management of resistance deviation and thermal stability is carried out by sampling inspection (sampling inspection). In the sampling inspection, the negative electrode 24 can be used as the inspection object. Therefore, in the inspection method disclosed here, for the battery assembly (or battery 100) that has undergone at least the construction process (process 1), electrolyte impregnation process (process 2), and initial charging process (process 3) of the manufacturing method described above, the following processes are performed in sequence: a disassembly process (process 7) to disassemble the battery assembly or battery 100, and a measurement process (process 8). In this embodiment, after the measurement process (process 8), an evaluation process (process 9) is also included to evaluate the resistance and thermal stability of the battery assembly or battery 100. In addition, other processes may be included at any stage.

[0108] In the disassembly process (process 7), the battery assembly is disassembled. To prevent deterioration of the negative electrode 24 or the separator 26, the disassembly of the battery assembly is preferably carried out in a dry air atmosphere (e.g., a dew point of approximately -50°C), such as inside a glove box. For the battery assembly, for example, the sealing plate 14 can be separated from the outer packaging 12 by first cutting the battery casing 10 with a tool such as an end mill or a laser, and then the electrode assembly 20 can be removed from inside the outer packaging 12. Then, the electrode 20a is separated from the removed electrode assembly 20, and the winding is unwound, allowing separation into the positive electrode 22, the negative electrode 24, and the separator 26.

[0109] The measurement process (process 8) includes the measurement of a ＊The process includes a first measurement step (step 8a) and a second measurement step (step 8b) to measure the B / C ratio and calculate the integral value. In the first measurement step (step 8a), after the disassembly step, a spectrophotometer is used to measure the value of a near the negative electrode plate 24t of the negative electrode active material layer 24a (the root portion of the negative electrode plate 24t extending out). ＊ Value. Measurements can be performed multiple times, taking into account bias. In this case, the arithmetic mean of the multiple measurements can be used as a. ＊ Value. As mentioned above, the above a ＊ The value of a has a positive correlation with the resistance value. Therefore, by measuring the above a ＊ The value allows for easy identification of areas with high resistance. In the second measurement step (step 8b), after the disassembly step, the B / C ratio is measured at the center of the long side direction Y of the negative electrode active material layer 24a using LA-ICP-MS, and the integral value is calculated. As mentioned above, the integral value of the B / C ratio has a negative correlation with the heat generation of the battery 100. Therefore, by measuring the B / C ratio and calculating the integral value, the thermal stability (heat generation behavior) of the battery 100 can be easily predicted or confirmed.

[0110] In the evaluation process (process 9), the resistance and thermal stability of the battery assembly or battery 100 are evaluated. In a preferred embodiment, based on the above a... ＊ The integral value of the value and the B / C ratio mentioned above is used to determine whether the product is good (or qualified). For example, the above a ＊ If the value is below a specified value (e.g., below 1.3) and the integral value of the B / C ratio is above a specified value (e.g., above 28), it is judged as a good product. In this case, the battery assembly or battery 100 judged as good can be a product with low resistance, excellent thermal stability, and small quality fluctuations. As a result, a highly reliable battery 100 can be appropriately provided to the market.

[0111] <Uses of Battery 100>

[0112] The battery 100 can be used for various applications. For example, due to its high capacity, low resistance, and excellent thermal stability, it is suitable as a power source (drive power supply) for motors in vehicles such as cars and trucks. There is no particular limitation on the type of vehicle; examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). The battery 100 can also be suitably used as a battery pack formed by arranging multiple batteries 100 in a predetermined arrangement direction and applying a load from the arrangement direction using a constraint mechanism.

[0113] The following describes several embodiments related to the present invention, but it is not intended to limit the present invention to these embodiments.

[0114] <Evaluation of Battery Manufacturing>

[0115] In the construction process (process 1), identical battery assemblies are constructed (Examples, Comparative Examples 1 and 2). Specifically, firstly, lithium nickel cobalt manganese composite oxide (LiNi) is prepared as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2, NCM). Then, a strip-shaped positive electrode sheet is fabricated on an aluminum foil serving as the positive current collector, comprising a layer of positive active material containing the positive active material, carbon material (AB) as a conductive material, and PVdF as a binder in a mass ratio of NCM:AB:PVdF = 97.5:1.5:1.0. Additionally, a strip-shaped negative electrode sheet is fabricated on a copper foil serving as the negative current collector, comprising a layer of negative active material containing graphite (C) as the negative active material, and SBR and CMC as binders in a mass ratio of C:(SBR+CMC) = 98.5:1.5.

[0116] Next, the positive and negative electrode sheets prepared above are wound together into a flat shape with the separator sheet facing each other, thereby producing a wound electrode body. It should be noted that the separator sheet is a heat-resistant layer (which also serves as an adhesive layer) comprising alumina and PVdF on the surface of the PE substrate. Furthermore, the length La in the long side direction (winding axis direction) of the negative electrode active material layer is set to 290 mm, and the height Ha is set to 90 mm.

[0117] Next, as a non-aqueous electrolyte, LiPF6 was dissolved in a mixed solvent containing EC, EMC, and DMC, and then LiBOB was added as an additive to obtain a non-aqueous electrolyte with a concentration of 0.05 mol / L. Then, the above-prepared wound electrode and non-aqueous electrolyte were housed in a cuboid-shaped battery casing to construct a battery assembly.

[0118] In the electrolyte impregnation process (process 2), firstly, for each example, the battery assembly is housed in a pressure-adjustable chamber with the injection port open. Then, in the embodiments, as shown in Table 1, the battery casing is pressurized to 0.8 MPa, maintained at this state for 50 minutes, and then depressurized to -90 kPa, maintained at this state for 5 minutes. Then, the battery casing is repressurized (restored pressure) back to 0 mPa (pressure and depressurization impregnation process (process 2-1)). In Comparative Example 1, the depressurization operation was performed only under the conditions shown in Table 1, and in Comparative Example 2, the pressurization operation was performed only under the conditions shown in Table 1. In Comparative Example 2, the battery casing was pressurized to 0.8 mPa, maintained at this state for 6 minutes, and then the battery casing was repressurized back to 0 mPa. This operation was repeated 20 times. Then, for each example, the battery assembly is placed (second impregnation process (process 2-2)). Table 1 shows the ratio (relative value) of the total time required for the electrolyte impregnation process (process 2).

[0119] In the initial charging process (process 3), firstly, an extrusion member is prepared. Next, using the center of the long sidewall of the constructed battery assembly as a reference, the extrusion member is positioned, and the battery assembly and the extrusion member are constrained by the constraint load shown in Table 1. This constrains the portion of the flat portion of the wound electrode body where the positive and negative active material layers face each other using the extrusion member. Along the long side direction, the flat portion of the wound electrode body, from the root of the positive electrode group to the root of the negative electrode group, is extruded by the extrusion member. Next, the battery assembly with the constraint load applied is charged to 12% SOC at a charging rate of 0.2C. Next, in the degassing process (process 4), the pressure inside the battery casing is reduced to -0.09 mPa. Next, in the liquid injection hole sealing process (process 5), the liquid injection hole is sealed with a sealing member while the pressure inside the battery casing 10 is reduced. Next, in the aging process (process 6), the battery assembly is maintained for 5 days at a temperature of 25°C with a constraint load of 4 kN applied to it after the initial charging. Then, an activation process is performed, and the arrowhead portion is extracted. As described above, an evaluation battery (Examples, Comparative Examples 1 and 2) is manufactured.

[0120] Table 1

[0121] Table 1

[0122]

[0123] <Disassembly of the battery for evaluation>

[0124] In the disassembly process (process 7), the evaluation battery after the activation process is discharged until the voltage reaches 3.0V, and then disassembled in a dry air atmosphere (e.g., with a dew point of approximately -50°C) to remove the wound electrode from the battery casing. Then, the winding of the wound electrode is unwound to separate the negative electrode.

[0125] <Identification of the discoloration on the negative electrode and resistance measurement>

[0126] First, the negative electrode was cut to an appropriate size along its width and cleaned with DMC to prepare a test piece for resistance measurement. The cut was made at the flat portion of the 15th turn (middle circumference) from the beginning of the winding. Next, the discoloration of the negative electrode active material layer (especially near the negative electrode sheet) was visually observed. The results are shown in Table 1. As shown in Table 1, in Comparative Example 1, where only a depressurization operation was performed in the electrolyte impregnation process, and in the examples where a pressurization operation and a depressurization operation were performed once each in the electrolyte impregnation process, no discoloration of the negative electrode active material layer was found. On the other hand, in Comparative Example 2, where a pressurization operation was repeatedly performed in the electrolyte impregnation process, both dark and light discoloration areas were visually identified. This is believed to be because, due to repeated pressurization in the electrolyte impregnation process, the inter-electrode space between the positive and negative electrodes opened, and non-aqueous electrolyte accumulated locally. As a result, a large amount of organic film from the non-aqueous solvent was generated during the initial charging.

[0127] Next, a resistance testing device is prepared, which includes a mounting section for housing a test sample and a non-aqueous electrolyte, a probe in contact with a measurement point, and an AC impedance measuring section. For the configuration of the resistance testing device, reference can be made, for example, to Japanese Patent Application Publication No. 2014-25850. The probe, for example, includes: a cylindrical main body containing the non-aqueous electrolyte and a counter electrode (metallic Li); and a measuring section connected to the lower end of the main body and in contact with a portion of the negative electrode active material layer of the test sample (the measurement point). The probe is configured to be movable, for example, along the long side (width direction) of the test sample. The diameter of the measuring section is, for example, approximately φ1mm to 10mm. The AC impedance measuring section is configured to measure the impedance by inputting an AC current or AC voltage between the working electrode in contact with the negative electrode and the measurement point (counter electrode) where the measuring section of the probe contacts the working electrode.

[0128] Next, the mounting section of the resistance testing device was filled with a non-aqueous electrolyte (only non-aqueous solvent and supporting salt, without additives), and the test specimen was placed in the mounting section. Then, with the working electrode in contact with the negative electrode, the probe was moved along the long side (width direction) at measurement intervals of approximately 10 mm from the root portion extending from the negative electrode of the negative electrode active material layer, and the surface resistance of the negative electrode active material layer was measured locally using AC impedance spectroscopy. Specifically, for each measurement point, the difference (ΔΩ) in resistance from DC to the end of the impedance arc was obtained. Then, a resistance distribution showing the relationship between the measurement position and the resistance difference (ΔΩ) was created. The resistance distribution of Comparative Example 1 is shown below. Figure 7 (a) The resistance distribution of Comparative Example 2 is shown in... Figure 7 (b) The resistance distribution of the embodiment is shown in Figure 7 (c)

[0129] Additionally, for Comparative Example 1 and the Example, the area near the negative electrode sheet of the negative electrode active material layer ( Figure 7 (a) Figure 7 The resistance values ​​of (c) of (1) are shown in Table 1. For Comparative Example 2, the resistance values ​​of the part of the discolored spot near the negative electrode sheet of the negative electrode active material layer are shown in Table 1. Figure 7 The resistance values ​​of portions (1) to (3) of (b) are shown in Table 1. As shown in Table 1, it can be seen that the resistance value is higher in the portion where the discoloration is visually confirmed. Furthermore, Table 1 also shows the resistance ratio when the resistance near the negative electrode sheet (the end of the negative electrode active material layer) of the negative electrode active material layer in Comparative Example 1 is set as a reference (1.0). It can be seen that in the embodiment, the resistance ratio is less than 2 times, while in Comparative Example 2, the resistance ratio exceeds 2 times.

[0130] <Determination using a spectrophotometer>

[0131] In the first measurement step (step 8a), a Konica Minolta diffuse illumination spectrophotometer (model: CM-26dG) was used. The SCI (Specular Component Include) method, which uses a positively reflected light trap to capture positively reflected light, was employed to measure a portion of the aforementioned resistance value of the negative electrode active material layer (i.e., Figure 7 (a) Figure 7 (c) part (1), and Figure 7 (b) The surface of parts (1) to (3) was measured based on the L value according to Japanese Industrial Standard JIS Z8781-4:2013. ＊ a ＊ b ＊ Color system a ＊ Values. The results are shown in Table 1.

[0132] exist Figure 8 The figure shows the resistivity ratio near the negative electrode plate of the negative electrode active material layer and a. ＊ The relationship between values. For example... Figure 8 As shown, it can be seen that as long as a ＊ If the value is below 1.3, there will be no discoloration near the negative electrode, and the resistance will be suppressed.

[0133] <Identification of the discoloration on the negative electrode and resistance measurement>

[0134] In the second measurement process (process 8b), firstly, preparations were made. Figure 9 The negative electrode (sample for measurement) is shown. Then, using a laser ablation ICP mass analyzer, the sample is irradiated with laser light along its long side (width direction) from near the negative electrode plate of the negative electrode active material layer. While the sample at the laser-irradiated area is micronized, continuous ICP mass analysis is performed. Furthermore, the measurement range in the width direction is set to... Figure 9 The "measurement range (0~180mm)" is also specified. Figure 9 The arrow indicates the direction of the laser's travel.

[0135] Then, the ratio of boron (B) to carbon (C) (B / C) was calculated, and a coordinate graph was created with the measurement location (mm) on the horizontal axis and the ratio (B / C) on the vertical axis. The distribution of the ratio (B / C) of Comparative Example 1 is shown in the graph. Figure 10 (a) The distribution of the ratio (B / C) of Comparative Example 2 is shown in... Figure 10 (b) The distribution of the ratio (B / C) of the embodiments is shown in Figure 10 (c) Additionally, in Table 1, [the following will be included]. Figure 9 The integral values ​​(integral values) of the "integral range (0-100mm)" are shown together. As shown in Table 1, it can be seen that in Comparative Example 2, where the pressurization operation was repeatedly performed in the electrolyte impregnation process, the integral value of the above ratio (B / C) is relatively large compared to Comparative Example 1, where only the depressurization operation was performed in the electrolyte impregnation process, and the amount of element B increases in the central part of the negative electrode active material layer. In addition, in the example where the pressurization operation and the depressurization operation were performed once each in the electrolyte impregnation process, it can be seen that the integral value of the above ratio (B / C) is even larger, and the amount of element B increases significantly in the central part of the negative electrode active material layer.

[0136] <Battery Heat Generation Evaluation>

[0137] First, samples for DSC measurement were prepared. Specifically, a tandem battery cell was constructed by placing a positive electrode with a positive active material layer (□20mm×20mm) and a negative electrode with a negative active material layer (□22mm×22mm) opposite each other in a dry air atmosphere (dew point: -50°C) with 0.4 mL of non-aqueous electrolyte between them. Next, the tandem battery cell was charged with a constant current of 8 mA until it reached 4.25V, followed by a constant voltage charge for 5 hours. Then, the charged tandem battery cell was disassembled in a glove box (Ar atmosphere). Next, the electrolyte was collected, and the positive and negative electrodes were removed. The positive electrode material was peeled off from the center region of the positive active material layer, and the negative electrode material was peeled off from the center region of the negative active material layer. Then, 1 mg of the peeled positive electrode material, 2 mg of the peeled negative electrode material, and 4 mg of the collected electrolyte were collected in a sample container. The sample container was sealed under pressure of 20 MPa and placed together with a standard substance (Al₂O₃, 2 mg) in a differential scanning calorimeter (DSC). The temperature was then increased from 25 °C to 350 °C at a rate of 2 °C / min under an inert atmosphere, and the calorific value (J) between 75 and 200 °C was calculated by integration. The results are shown in Table 1.

[0138] exist Figure 11 The figure shows the relationship between the integral value of the ratio (B / C) of the central part of the negative electrode active material layer and the heat generation of the battery. For example... Figure 11 As shown, a correlation was found between the integral value of the ratio (B / C) and the heat generation of the battery. That is, the larger the integral value of the ratio (B / C), in other words, the more B element there is, the more the heat generation of the battery is suppressed. Therefore, it can be seen that if the integral value of the ratio (B / C) is 28 or higher, the heat generation will be suppressed to a low level (e.g., below 20 J, preferably below 18 J), which can improve the thermal stability of the battery.

[0139] Several embodiments of the present invention have been described above, but these embodiments are merely examples. The present invention can also be implemented in various other ways. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. The technology described in the claims includes various modifications and alterations to the above-described illustrative embodiments. For example, a portion of the above embodiments may be replaced with other modifications, or other modifications may be added to the above embodiments. In addition, if a technical feature is not described as an essential feature, it may be appropriately deleted.

[0140] As described above, specific solutions to the technology disclosed herein can be listed in the following items.

[0141] Item 1: A non-aqueous electrolyte secondary battery, comprising: an electrode body including a positive electrode and a negative electrode, a positive terminal electrically connected to the positive electrode, a negative terminal electrically connected to the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material layer comprising carbon material and having a width of 200 mm or more, and a plurality of negative electrode sheets disposed at one end of the negative electrode active material layer in the width direction, the plurality of negative electrode sheets being electrically connected to the negative terminal in a stacked and folded state, and when the root portion of the negative electrode sheets extending from the negative electrode active material layer is measured using a spectrophotometer, based on the L of Japanese Industrial Standard JIS Z8781-4:2013. ＊ a ＊ b ＊ In the color system, a ＊ The value is below 1.3, and the amount of carbon and boron is determined by laser ablation ICP quality analysis along the width direction of the negative electrode active material layer. Within a range of ±20 mm from the center of the width direction, the integral value of the ratio of the amount of boron to the amount of carbon (B / C) is above 28.

[0142] Item 2: The non-aqueous electrolyte secondary battery according to Item 1, wherein the electrode body is a wound electrode body formed by stacking and winding the strip-shaped positive electrode and the strip-shaped negative electrode in an insulating state.

[0143] Item 3: The non-aqueous electrolyte secondary battery according to Item 1 or Item 2, wherein the width direction is the same as the winding axis direction of the wound electrode body.

[0144] Item 4: A non-aqueous electrolyte secondary battery according to any one of Items 1 to 3, wherein the non-aqueous electrolyte comprises a compound containing boron.

Claims

1. A nonaqueous electrolyte secondary battery comprising: An electrode body including a positive electrode and a negative electrode, a positive electrode terminal electrically connected to the positive electrode, a negative electrode terminal electrically connected to the negative electrode, and a nonaqueous electrolyte solution, The negative electrode has a negative electrode active material layer including a carbon material and having a width of 200 mm or more, and a plurality of negative electrode tabs provided at one end portion in the width direction, The plurality of negative electrode tabs are electrically connected to the negative electrode terminal in a state of being laminated and folded, The root portion of the negative electrode tab, from which the negative electrode active material layer protrudes, is measured using a spectrophotometer, and the L value based on Japanese Industrial Standards JIS Z 8781-4:2013 is 1.3 or less, and the a value in the color specification system is 0.5 or less. ＊ a ＊ b ＊ The a value in the color specification system is 1.3 or less. ＊ value in the color specification system is 0.5 or less. The amount of carbon element and the amount of boron element are measured by laser ablation ICP mass analysis along the width direction of the negative electrode active material layer, and the integral value of the ratio B / C of the amount of boron element to the amount of carbon element in a range of ±20 mm from the center in the width direction is 28 or more.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The electrode body is a wound electrode body in which the strip-shaped positive electrode and the strip-shaped negative electrode are laminated and wound in an insulating state.

3. The nonaqueous electrolyte secondary battery according to claim 2, wherein The width direction is a direction coinciding with the winding axis direction of the wound electrode body.

4. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein The nonaqueous electrolyte solution contains a compound containing a boron element.

Images