Electrode body, method of manufacturing the same, and method of manufacturing secondary battery

Abstract

To provide an electrode body capable of obtaining a secondary battery excellent in thermal stability.SOLUTION: The electrode body 20 disclosed herein is formed by laminating a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 in an insulated state and winding them in a longitudinal direction, wherein the average of the water content at the center portion and the water content at the end portion in the winding axis WL direction is 80 ppm or more and 150 ppm or less, and the difference between the water content at the center portion and the water content at the end portion in the winding axis WL direction is less than ± 20 ppm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrode assembly, a method for manufacturing the same, and a method for manufacturing a secondary battery. [Background technology]

[0002] Conventionally, secondary batteries have been known that include a wound electrode assembly formed by stacking a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state and winding them in the longitudinal direction, and a nonaqueous electrolyte solution. Patent Document 1 is an example of a related prior art document.

[0003] Patent Document 1 describes that the cycle durability of a secondary battery can be improved by utilizing moisture, which has traditionally been considered something that should be avoided, and by making the moisture content at the end of the negative electrode 200 ppm or more higher than the moisture content at the center of the negative electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6067545 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent large-sized secondary batteries, the width of the electrode body in the winding axis direction has increased. Furthermore, if the electrode body is a wound electrode body, moisture flows in and / or out only from both ends in the winding axis direction. Therefore, distribution (variation) of the moisture content in the winding axis direction is likely to occur. According to the study by the present inventors, it has been newly discovered that when the moisture content of the electrode body becomes excessive or, conversely, when the moisture content of the electrode body becomes locally insufficient, the thermal stability of the secondary battery decreases.

[0006] The present invention has been made in view of the above circumstances, and aims to provide an electrode body that can provide a secondary battery with excellent thermal stability, a method for manufacturing the same, and a method for manufacturing a secondary battery. [Means for solving the problem]

[0007] The present invention provides an electrode assembly comprising a strip-shaped positive electrode and a strip-shaped negative electrode stacked in an insulated state and wound in the longitudinal direction. The negative electrode has a negative electrode active material layer having a width of 200 mm or more in the direction of the winding axis perpendicular to the longitudinal direction. The positive electrode has a positive electrode active material layer having a width in the direction of the winding axis that is the same as or shorter than that of the negative electrode active material layer. In this electrode assembly, the average moisture content in the center and at the ends in the direction of the winding axis is 80 ppm or more and 150 ppm or less, and the difference between the moisture content in the center and at the ends in the direction of the winding axis is less than ±20 ppm.

[0008] By constructing a secondary battery using the electrode assembly, a secondary battery with excellent thermal stability can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view schematically showing an electrode assembly according to one embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of an electrode assembly according to one embodiment. [Figure 3] FIG. 3 is a perspective view schematically showing a nonaqueous electrolyte secondary battery according to one embodiment. [Figure 4] FIG. 4 is a schematic vertical cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a plan view schematically showing the positions at which samples for measuring moisture content are collected. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, some preferred embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification but necessary for carrying out the present invention (for example, the general configuration and manufacturing process of an electrode assembly or a non-aqueous electrolyte secondary battery that do not characterize the present invention) can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field. In this specification, the expression "A to B" indicating a range includes the meaning of "greater than A" and "smaller than B" as well as the meaning of "greater than A" and "smaller than B."

[0011] <Electrode body 20> First, the electrode assembly 20 (see FIGS. 1 and 2) disclosed herein will be described. The electrode assembly 20 is used in a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as a battery) 100 (see FIGS. 3 and 4) described below. In this specification, the term "nonaqueous electrolyte secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via a nonaqueous electrolyte. The concept of nonaqueous electrolyte secondary batteries encompasses not only so-called secondary batteries such as lithium ion secondary batteries and nickel-metal hydride secondary batteries, but also capacitors that utilize chemical reactions, such as lithium ion capacitors and pseudo-capacitor capacitors.

[0012] FIG. 1 is a perspective view schematically illustrating an electrode assembly 20. FIG. 2 is a schematic diagram illustrating the configuration of the electrode assembly 20. In the following description, the symbol LD in the drawings represents the longitudinal direction of the electrode assembly 20. As shown in FIG. 2, the electrode assembly 20 is a wound electrode assembly. The electrode assembly 20 is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 in an insulated state (here, via a strip-shaped separator 26) and winding them in the longitudinal direction LD. When the electrode assembly 20 is a wound electrode assembly, moisture flows in and / or out only from both ends in the direction of the winding axis WL. Therefore, unevenness in the moisture content is likely to occur in the direction of the winding axis WL of the electrode assembly 20, particularly between the center and ends. Therefore, applying the technology disclosed herein is particularly effective.

[0013] Although not particularly limited, the number of windings (number of turns) of the electrode body 20 is preferably 20 turns or more, more preferably 30 turns or more, and can be, for example, 150 turns or less, or 100 turns or less.

[0014] As shown in FIG. 1, the electrode body 20 here has a flat outer shape. The electrode body 20 preferably has a flat outer shape. The electrode body 20 has a pair of flat portions 20f extending along the direction of the winding axis WL, 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. The curved portions 20r have a curved outer surface. In this specification, the term "flat outer surface" is not limited to a completely flat surface, and includes cases where, for example, when viewed microscopically, there are slight steps, curves, recesses, protrusions, etc.

[0015] The configuration of the positive electrode 22 may be the same as that of a conventional positive electrode, and is not particularly limited. As shown in FIG. 2, the positive electrode 22 has a positive electrode active material layer 22a. In this embodiment, the positive electrode 22 has a positive electrode current collector 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed to at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and can be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. In this embodiment, the positive electrode current collector 22c is a metal foil, specifically, an aluminum foil.

[0016] A plurality of positive electrode tabs 22t are provided at one end of the positive electrode current collector 22c in the winding axis WL direction (the left end in FIG. 2). Each of the plurality of positive electrode tabs 22t is convex and protrudes toward one side in the winding axis WL direction (the left side in FIG. 2). In this example, the positive electrode tab 22t is part of the positive electrode current collector 22c and is made of metal foil (aluminum foil). At least a portion of the positive electrode tab 22t is a current collector exposed portion where the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed and the positive electrode current collector 22c is exposed. As shown in FIG. 1, the plurality of positive electrode tabs 22t are stacked at one end of the winding axis WL direction (the left end in FIG. 1) to form a positive electrode tab group 23. The positive electrode tab group 23 is provided with (more specifically, joined to) a positive electrode second current collecting portion 52 for electrical connection with the positive electrode terminal 30 (see FIGS. 3 and 4) of the battery 100.

[0017] As shown in FIG. 2, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction LD 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 such as lithium nickel cobalt manganese composite oxide) that can reversibly store and release charge carriers. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, and various additives. For example, a carbon material such as acetylene black (AB) can be used as the conductive material. For example, polyvinylidene fluoride (PVdF) can be used as the binder.

[0018] Although not particularly limited, the width W1 (average value, excluding the portion formed on the positive electrode tab 22t) of the positive electrode active material layer 22a in the winding axis WL direction is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more, from the viewpoint of increasing capacity, etc. The width W1 of the positive electrode active material layer 22a is preferably the same as or shorter than the width W2 of the negative electrode active material layer 24a described below.

[0019] As shown in FIG. 2, the positive electrode protective layer 22p is provided between the positive electrode current collector 22c and the positive electrode active material layer 22a in the direction of the winding axis WL. Here, the positive electrode protective layer 22p is provided at one end (the left end in FIG. 2) of the positive electrode current collector 22c in the direction of the winding axis WL. The positive electrode protective layer 22p is provided 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 the inorganic filler, such as a conductive material, a binder, various additive components, and the like. The conductive material and binder may be the same as those exemplified as those that may be contained in the positive electrode active material layer 22a.

[0020] The configuration of the negative electrode 24 may be the same as that of a conventional negative electrode, and is not particularly limited. As shown in FIG. 2, the negative electrode 24 has a negative electrode active material layer 24a. Here, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. Here, the negative electrode current collector 24c is a metal foil, specifically, a copper foil.

[0021] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector 24c in the winding axis WL direction (the right end in FIG. 2). Each of the plurality of negative electrode tabs 24t is convex and protrudes toward one side in the winding axis WL direction (the right side in FIG. 2). Here, the negative electrode tab 24t is part of the negative electrode current collector 24c and is made of metal foil (copper foil). At least a portion of the negative electrode tab 24t is a current collector exposure portion where the negative electrode active material layer 24a is not formed and the negative electrode current collector 24c is exposed. As shown in FIG. 1, the plurality of negative electrode tabs 24t are stacked at one end in the winding axis WL direction (the right end in FIG. 1) to form a negative electrode tab group 25. A negative electrode second current collecting portion 62 is attached (more specifically, joined) to the negative electrode tab group 25 for electrical connection to the negative electrode terminal 40 (see FIGS. 3 and 4) of the battery 100.

[0022] As shown in Fig. 2, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction LD of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly store and release charge carriers. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder and various additive components. Examples of binders that can be used include rubbers such as styrene butadiene rubber (SBR) and celluloses such as carboxymethyl cellulose (CMC).

[0023] The width W2 of the negative electrode active material layer 24a in the winding axis WL direction (average value, excluding the portion formed on the negative electrode tab 24t) is 200 mm or more, preferably 250 mm or more, from the viewpoint of increasing capacity, etc. The longer the width W2 of the negative electrode active material layer 24a, the more likely it is that the moisture content will be uneven in the winding axis WL direction of the electrode body 20, particularly between the center and the edges. This in turn makes it more likely that the moisture content will be locally insufficient in the center. Therefore, applying the technology disclosed herein is particularly effective. The width W2 of the negative electrode active material layer 24a is preferably the same as or longer than the width W1 of the positive electrode active material layer 22a. Although not particularly limited, the width W2 of the negative electrode active material layer 24a may be, for example, 1000 mm or less, or 500 mm or less. This allows the effects of the technology disclosed herein to be exerted at a high level.

[0024] As shown in FIG. 2 , the separator 26 is a member 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 width W3 of the separator 26 in the winding axis WL direction is equal to or longer than the width W2 of the negative electrode active material layer 24a in the winding axis WL direction. The configuration of the separator 26 may be the same as that of a conventional separator and is not particularly limited. The separator 26 is preferably a resin porous sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may have a functional layer, such as a heat-resistant layer (HRL) or an adhesive layer, on the surface of a substrate portion made of a resin porous sheet. The heat-resistant layer is, for example, a layer containing an inorganic filler and a binder. The adhesive layer is a layer containing a binder. The heat-resistant layer may also serve as an adhesive layer. The configurations of the heat-resistant layer and adhesive layer may be the same as those of a conventional separator.

[0025] Incidentally, if the electrode assembly 20 contains a large amount of moisture, gas may be generated during charging and discharging, and the battery characteristics may deteriorate. For this reason, it has been customary to remove as much moisture as possible when manufacturing the battery 100. However, according to the study by the present inventors, it has been newly discovered that the thermal stability of the battery 100 decreases when the electrode assembly 20 contains too much moisture or, conversely, when the electrode assembly 20 contains too little moisture in certain areas.

[0026] Therefore, in this embodiment, the average of the central moisture content Mc and the end moisture content Me of the electrode assembly 20, which are determined by the procedure described below, is set to 80 to 150 ppm, and the difference between the central moisture content Mc and the end moisture content Me of the electrode assembly 20 is set to less than ±20 ppm. In other words, a predetermined amount of moisture is contained substantially uniformly in the direction of the winding axis WL, thereby reducing unevenness in the moisture content between the central and end portions of the electrode assembly 20. When the electrode assembly 20 satisfies the above moisture content range, a battery 100 with excellent thermal stability can be obtained. Although no particular limitation is intended, the inventors believe the reason for this is as follows.

[0027] That is, in the battery 100, the nonaqueous electrolyte typically decomposes during initial charging, forming a coating (Solid Electrolyte Interface film: SEI film) on the surface of the negative electrode 24. As described in Patent Document 1, the amount of moisture in the electrode assembly 20 can affect the amount of SEI film formed. By setting the average of the moisture content Mc at the center and the moisture content Me at the edge of the electrode assembly 20 to 150 ppm or less, it is possible to prevent moisture from impregnating the nonaqueous electrolyte and reducing the amount of SEI film formed. Furthermore, by setting the average of the moisture content Mc at the center and the moisture content Me at the edge of the electrode assembly 20 to 80 ppm or more, moisture reacts with the nonaqueous electrolyte (e.g., a nonaqueous solvent such as carbonates, as described below) and is more likely to convert into a stable inorganic coating component (e.g., lithium carbonate). This facilitates the formation of a high-quality SEI film. Furthermore, by reducing the difference between the moisture content Mc at the center and the moisture content Me at the end of the electrode assembly 20 to less than ±20 ppm, it becomes easier to form a uniform SEI film in the direction of the winding axis WL during initial charging. The combined effects of these factors are thought to improve the thermal stability of the battery 100.

[0028] In addition, by setting the average of the central water content Mc and the edge water content Me of the electrode assembly 20 to 150 ppm or less, it is possible to prevent water from reacting with the nonaqueous electrolyte (for example, an electrolyte salt such as LiPF6 described below) to generate corrosive HF, which can lead to the elution of metal from the positive electrode current collector 22c, thereby reducing battery resistance.

[0029] In the electrode assembly 20, the average of the central water content Mc and the edge water content Me is preferably 140 ppm or less, more preferably 130 ppm or less, and particularly preferably 120 ppm or less, 110 ppm or less, or even 100 ppm or less. This makes it easier for a larger amount of SEI film to be formed on, for example, the negative electrode 24, and can further improve the thermal stability of the battery 100.

[0030] In some embodiments, it is preferable that the central moisture content Mc is higher than the end moisture content Me (Me < Mc). Thereby, for example, a high-quality SEI film containing a stable inorganic film component is likely to be formed at the central portion in the winding axis WL direction, and the thermal stability of the battery 100 can be further improved. The difference between the two (Mc - Me) is preferably 5 ppm or more, and more preferably 10 ppm or more. However, in the electrode body 20, the magnitude relationship between the central moisture content Mc and the end moisture content Me is not limited, and in some other embodiments, the central moisture content Mc may be less than the end moisture content Me.

[0031] Although not particularly limited, the central moisture content Mc of the electrode body 20 is preferably 160 ppm or less, more preferably 150 ppm or less, still more preferably 140 ppm or less, for example, particularly preferably 130 ppm or less, 120 ppm or less, 110 ppm or less, and even 100 ppm or less. By setting the central moisture content Mc to a predetermined value or less, for example, more SEI films are likely to be formed at the central portion in the winding axis WL direction, and the thermal stability of the battery 100 can be further improved. Also, the end moisture content Me of the electrode body 20 is preferably 140 ppm or less, more preferably 130 ppm or less, still more preferably 120 ppm or less, for example, particularly preferably 110 ppm or less, 100 ppm or less, and even 90 ppm or less. By setting the end moisture content Me to a predetermined value or less, more SEI films are likely to be formed at the end portion in the winding axis WL direction, and the thermal stability of the battery 100 can be further improved.

[0032] Incidentally, the moisture content of the electrode body 20 can be determined as follows. That is, first, when the electrode body 20 as shown in FIG. 2 is unwound, the positive electrode 22 and the negative electrode 24 located at the intermediate circumferential portion in the longitudinal direction LD are cut out one turn at a time. Next, for the positive electrode active material layer 22a of the positive electrode 22, test pieces of a predetermined size (for example, 20 mm × 20 mm) are cut out at the central portion and both end portions in the winding axis WL direction, respectively. Similarly, for the negative electrode active material layer 24a of the negative electrode 24, test pieces of a predetermined size (for example, 20 mm × 20 mm) are cut out at the central portion and both end portions in the winding axis WL direction, respectively. The "central portion" in the winding axis WL direction refers to the center M in the winding axis WL direction.Y The term "edge" refers to the portion including the active material layer (see Figure 1) (half the total width from the extreme end (edge) in the direction of the winding axis WL), and the "edge" in the direction of the winding axis WL refers to the portion approximately 5 mm inward from the extreme end (edge) in the direction of the winding axis WL of the active material layer. It is preferable to use multiple test pieces (two or more) at each measurement point, and more preferably three or more. Next, the amount of water vaporized from each cut-out test piece at heating temperatures from room temperature to 150°C is quantified using the Karl Fischer method (typically, moisture vaporization method-coulometric titration method).

[0033] The moisture content value at the center of the positive electrode active material layer 22a and the moisture content value at the center of the negative electrode active material layer 24a are then arithmetically averaged to calculate the "center moisture content Mc" of the electrode body 20. The moisture content value at the end of the positive electrode active material layer 22a and the moisture content value at the end of the negative electrode active material layer 24a are also arithmetically averaged to calculate the "end moisture content Me" of the electrode body 20.

[0034] The moisture content of the electrode body 20 (the moisture content Mc in the center and / or the moisture content Me at the edge) can be suitably adjusted, for example, by the conditions of the fabrication step (step 2), the conditions of the moisture absorption step (step 3), the conditions of the subsequent drying step (step 5), etc. in the manufacturing method described below. In particular, it can be suitably adjusted by the humidity in the moisture absorption step (step 3) and the heating temperature and degree of vacuum in the drying step (step 5).

[0035] <Battery 100> Next, a battery 100 including the electrode assembly 20 disclosed herein will be described. FIG. 3 is a perspective view of the battery 100. FIG. 4 is a schematic longitudinal cross-sectional view taken along line IV-IV in FIG. 3. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the thickness direction of the battery 100, the width direction perpendicular to the thickness direction, and the up-down direction perpendicular to the thickness direction and width direction, respectively. However, these directions are merely used for convenience of description and do not limit the installation form of the battery 100 in any way.

[0036] 4, the battery 100 here includes, in addition to the electrode assembly 20, a case 10, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, a negative electrode current collector 60, and a non-aqueous electrolyte (not shown). The battery 100 here is a lithium ion secondary battery. The battery 100 is preferably a lithium ion secondary battery.

[0037] The case 10 is a housing that houses the electrode assembly 20 and the non-aqueous electrolyte. As shown in FIG. 3, the case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the case 10 may be the same as that conventionally used, and is not particularly limited. The case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 4, the case 10 here includes an exterior body 12 having an opening 12h, and a sealing plate (lid) 14 that closes the opening 12h. The case 10 preferably includes the exterior body 12 and the sealing plate 14.

[0038] 3, the exterior body 12 includes a substantially rectangular bottom wall 12a, a pair of long side walls 12b extending from the long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short sides of the bottom wall 12a and facing each other. The bottom wall 12a faces the opening 12h. The area of ​​the long side walls 12b is larger than the area of ​​the short side walls 12c.

[0039] As shown in Fig. 3, the sealing plate 14 has a substantially rectangular shape in a plan view. As shown in Fig. 4, the sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The case 10 is integrated by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The case 10 is hermetically sealed (sealed).

[0040] As shown in FIG. 4, the sealing plate 14 is provided with a liquid inlet 15, a gas release valve 17, and two terminal holes 18 and 19. The liquid inlet 15 is for injecting nonaqueous electrolyte after the sealing plate 14 is assembled to the exterior body 12. The sealing plate 14 preferably has the liquid inlet 15. The liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is configured to break when the pressure inside the case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the case 10 to the outside. The terminal holes 18 and 19 are formed at both ends of the sealing plate 14 in the width direction Y (the left and right ends in FIG. 4). The terminal holes 18 and 19 penetrate the sealing plate 14 in the thickness direction (the up-down direction Z). The terminal pull-out holes 18, 19 have inner diameters large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before being attached to the sealing plate 14 (before being crimped).

[0041] The positive electrode terminal 30 and the negative electrode terminal 40 are each fixed to the sealing plate 14 of the case 10. The positive electrode terminal 30 is disposed on one side of the sealing plate 14 in the width direction Y (the left side in FIGS. 3 and 4). The negative electrode terminal 40 is disposed on the other side of the sealing plate 14 in the width direction Y (the right side in FIGS. 3 and 4). As shown in FIG. 4, the positive electrode terminal 30 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 18. The negative electrode terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 19. The positive electrode terminal 30 and the negative electrode terminal 40 are preferably attached to the sealing plate 14. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portions of the sealing plate 14 surrounding the terminal lead-out holes 18 and 19 by crimping. The positive electrode terminal 30 and the negative electrode terminal 40 have crimped portions 30c, 40c formed at their ends on the exterior body 12 side (lower ends in FIG. 4).

[0042] As shown in Fig. 4, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see Fig. 2, specifically, the positive electrode tab group 23) of the electrode body 20 inside the case 10 via the positive electrode current collecting portion 50. The positive electrode terminal 30 is insulated from the sealing plate 14 by a positive electrode insulating member 70 and a gasket 90. The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example.

[0043] The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see FIG. 2 , specifically, the negative electrode tab group 25) of the electrode body 20 via the negative electrode current collector 60 inside the case 10. The negative electrode terminal 40 is insulated from the sealing plate 14 by a negative electrode insulating member 80 and a gasket 90. The negative electrode terminal 40 is preferably made of metal, and more preferably made of copper or a copper alloy, for example. The negative electrode terminal 40 may be formed by joining two conductive members together. For example, the portion of the negative electrode terminal 40 that is connected to the negative electrode current collector 60 may be made of copper or a copper alloy, and the portion that is exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0044] A plate-shaped positive electrode external conductive member 32 and a plate-shaped negative electrode external conductive member 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are members to which bus bars are attached when electrically connecting multiple batteries 100 to each other. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the plate-shaped 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 the plate-shaped negative electrode external conductive member 42 are preferably made of metal, more preferably aluminum or an aluminum alloy. However, the positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are not essential and may be omitted in other embodiments.

[0045] As shown in FIG. 4, the electrode assembly 20 is housed inside the case 10 (more specifically, inside the exterior housing 12). There is no particular limitation on the number of electrode assemblies 20 placed inside one case 10, and it may be one or two or more (plural). The electrode assembly 20 may be placed inside the case 10 while covered with an insulating electrode assembly holder. The electrode assembly holder is preferably made of resin.

[0046] 4, the electrode assembly 20 is disposed inside the case 10 with the winding axis WL oriented approximately parallel to the width direction Y. Here, the direction of the winding axis WL coincides with the width direction Y. The electrode assembly 20 is disposed inside the case 10 with the winding axis WL oriented parallel to the bottom wall 12a and perpendicular to the short side wall 12c.

[0047] Here, the electrode assembly 20 has a so-called horizontal tab structure in which the positive electrode tab group 23 and the negative electrode tab group 25 are located at both ends in the winding axis WL direction (left and right in FIGS. 1 and 4). However, in other embodiments, the electrode assembly 20 may have a so-called top tab structure in which the positive electrode tab group 23 and the negative electrode tab group 25 are located at one end in the winding axis WL direction (for example, the upper end in FIGS. 1 and 4). In this case, the winding axis WL direction may coincide with the up-down direction Z.

[0048] 1 and 4, a pair of flat portions 20f of the electrode body 20 face a pair of long side walls 12b of the exterior body 12. The flat portions 20f extend along the long side walls 12b. A pair of curved portions 20r of the electrode body 20 face the bottom wall 12a and the sealing plate 14 of the exterior body 12. As in this embodiment, the electrode body 20 is preferably disposed inside the case 10 such that the stacking direction (thickness direction) of the positive electrode 22 (see FIG. 2) and the negative electrode 24 (see FIG. 2) in the flat portions 20f coincides with the thickness direction X (direction perpendicular to the long side walls 12b).

[0049] As shown in FIG. 4, the positive electrode current collector 50 forms a conductive path that electrically connects the positive electrode tab group 23, which is composed of multiple positive electrode tabs 22t, to the positive electrode terminal 30. The positive electrode current collector 50 may be made of the same metal as the positive electrode current collector 22c, such as a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The positive electrode current collector 50 includes a positive electrode first current collector 51 and a positive electrode second current collector 52. The positive electrode first current collector 51 is attached to the inner surface of the sealing plate 14. The positive electrode second current collector 52 extends along the short side wall 12c of the exterior body 12. The positive electrode second current collector 52 is attached to the positive electrode tab group 23 of the electrode body 20.

[0050] As shown in FIG. 4 , the negative electrode current collector 60 forms a conductive path that electrically connects the negative electrode tab group 25, which is made up of multiple negative electrode tabs 24t, to the negative electrode terminal 40. The negative electrode current collector 60 may be made of the same metal as the negative electrode current collector 24c, such as a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode current collector 60 includes a negative electrode first current collector 61 and a negative electrode second current collector 62. The configuration and arrangement of the negative electrode first current collector 61 and the negative electrode second current collector 62 may be the same as those of the positive electrode first current collector 51 and the positive electrode second current collector 52 of the positive electrode current collector 50. The negative electrode second current collector 62 is attached to the negative electrode tab group 25 of the electrode assembly 20.

[0051] The non-aqueous electrolyte typically contains a non-aqueous solvent and an electrolyte salt (supporting salt). As the non-aqueous solvent, one or more of those known to be usable for this type of application can be used. Examples of the non-aqueous solvent include organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. The non-aqueous solvent preferably contains a carbonate. Examples of carbonates include linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC).

[0052] The electrolyte salt is not particularly limited as long as it contains a charge carrier (typically, lithium ions), and one or more of those known to be usable for this type of application can be used. Examples of the electrolyte salt include fluorine-containing lithium salts such as LiPF6 and LiBF4. The electrolyte salt preferably contains LiPF6.

[0053] The non-aqueous electrolyte may further contain additional components (additives). One or more additives known to be additives to non-aqueous electrolytes may be used. Examples include boron-based additives containing boron, such as lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiODFB). The additive may be a so-called film-forming agent that decomposes (at a low potential) prior to the non-aqueous solvent and / or electrolyte salt during initial charging and deposits as a film on the surface of the negative electrode active material layer 24a.

[0054] The additives in the non-aqueous electrolyte (for example, the boron-based additives described above) are typically electrically decomposed by initial charging or the like and consumed to form a coating 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 (remain) the additives described above.

[0055] <Method of manufacturing the electrode assembly 20 and the battery 100> The above-described battery 100 can be manufactured by a manufacturing method including, for example, the following steps in this order: a preparation step (step 1), a fabrication step (step 2), a moisture absorption step (step 3), a housing step (step 4), a drying step (step 5), a liquid injection step (step 6), an initial charging step (step 7), a degassing step (step 8), a sealing step (step 9), and an aging step (step 10). The housing step (step 4) and the liquid injection step (step 6) are examples of the construction steps.

[0056] However, the moisture absorption step (step 3), degassing step (step 8), and aging step (step 10) are optional and may be omitted in other embodiments. The order of the accommodation step (step 4) and drying step (step 5) may be reversed. Further, other steps may be included at any stage. The preparation step (step 1), fabrication step (step 2), and drying step (step 4) may also be understood as a manufacturing method for the electrode body 20.

[0057] The preparation step (step 1) includes a positive electrode preparation step (step 1A) of preparing a strip-shaped positive electrode 22 having a positive electrode active material layer 22a, and a negative electrode preparation step (step 1B) of preparing a strip-shaped negative electrode 24 having a negative electrode active material layer 24a. The strip-shaped positive electrode 22 and the strip-shaped negative electrode 24 may be commercially available or may be prepared by the user.

[0058] The positive electrode preparation step (step 1A) includes, for example, a positive electrode composite slurry preparation step (step 1A-1), a positive electrode composite slurry application step (step 1A-2), and a positive electrode composite slurry drying step (step 1A-3), in this order. The positive electrode preparation step (step 1A) may further include a pressing step of pressing the positive electrode active material layer.

[0059] In the positive electrode mixture slurry preparation step (step 1A-1), a positive electrode mixture slurry containing at least a positive electrode active material is prepared. Specifically, the solid materials of the positive electrode active material layer 22a (e.g., the positive electrode active material, conductive material, binder, various additive components, etc.) as described above are mixed with a predetermined solvent. The solvent is preferably a non-aqueous solvent such as N-methyl-2-pyrrolidone (NMP). The solid content of the positive electrode mixture slurry is preferably 70 mass % or more, more preferably, for example, 70 to 85 mass %. In this specification, the term "slurry" refers to a mixture in which some or all of the solids are dispersed in a solvent, and is a term that encompasses paste, ink, etc.

[0060] In the positive electrode composite slurry application step (step 1A-2), the positive electrode composite slurry prepared above is applied to the strip-shaped positive electrode current collector 22c. The positive electrode composite slurry can be applied using a conventionally known coating device, such as a gravure coater, comma coater, slit coater, or die coater. The coating conditions may also be the same as conventional ones. The coating width of the positive electrode composite slurry is set to be equal to or greater than the coating width of the negative electrode composite slurry.

[0061] In the cathode composite slurry drying step (step 1A-3), the cathode current collector 22c to which the cathode composite slurry has been applied (coated) is subjected to a conventional drying method, such as air drying, heat drying, or vacuum drying, to remove the solvent from the cathode composite slurry on the cathode current collector 22c. Heat drying is preferably employed from the viewpoint of production efficiency. The heating temperature, which depends on the type of solvent used in the cathode composite slurry preparation step, is preferably set to 75 to 125°C, and it is more preferable to increase the temperature stepwise within the above temperature range. In this manner, a cathode active material layer 22a containing a cathode active material is fixed to at least one surface of the cathode current collector 22c, thereby obtaining a strip-shaped cathode 22.

[0062] The negative electrode preparation step (step 1B) includes, for example, a negative electrode composite slurry preparation step (step 1B-1), a negative electrode composite slurry application step (step 1B-2), and a negative electrode composite slurry drying step (step 1B-3), in this order. The negative electrode preparation step (step 1B) may further include a pressing step of pressing the negative electrode active material layer.

[0063] In the negative electrode composite slurry preparation step (step 1B-1), a negative electrode composite slurry containing at least a negative electrode active material is prepared. Specifically, the solid materials of the negative electrode active material layer 24a (e.g., the negative electrode active material, binder, various additive components, etc.) as described above are mixed with a predetermined solvent. The solvent is preferably an aqueous solvent such as ion-exchanged water. The solid content of the negative electrode composite slurry is preferably 50 mass % or more, and more preferably, for example, 50 to 65 mass %.

[0064] In the negative electrode composite slurry application step (step 1B-2), the negative electrode composite slurry prepared above is applied to the strip-shaped negative electrode current collector 24c. The application of the negative electrode composite slurry can be performed using a conventionally known application device, similar to the application of the positive electrode composite slurry. The application width of the negative electrode composite slurry is 200 mm or more.

[0065] In the negative electrode composite slurry drying step (step 1B-3), the negative electrode current collector 24c to which the negative electrode composite slurry has been applied (coated) is subjected to a conventionally known drying method to remove the solvent from the negative electrode composite slurry on the negative electrode current collector 24c. From the viewpoint of production efficiency, heat drying can be preferably employed. The heating temperature, although depending on the type of solvent used in the negative electrode composite slurry preparation step, is preferably set to 60 to 130°C, and it is more preferable to increase the temperature stepwise within the above temperature range. In this manner, a negative electrode active material layer 24a containing a negative electrode active material is fixed to at least one surface of the negative electrode current collector 24c, thereby obtaining a strip-shaped negative electrode 24.

[0066] In the preparation step (step 2), the strip-shaped positive electrode 22 and strip-shaped negative electrode 24 prepared in the preparation step are stacked and wound in an insulated state (for example, via a separately prepared strip-shaped separator 26) to prepare a wound body. The wound body can be prepared, for example, by using a conventionally known winding device to wind the strip-shaped positive electrode 22, strip-shaped negative electrode 24, and strip-shaped separator 26 into a roll around the winding axis WL. The wound body obtained in this step (the wound body before the moisture absorption step) can be in a state in which moisture is contained approximately uniformly in the center and end portions in the direction of the winding axis WL.

[0067] In the moisture absorption step (step 3), the wound body is placed in a moist environment while still in a rolled state, and moisture is absorbed from the end of the wound body in the winding axis WL direction. This reduces the variation in moisture content between lots, even if the moisture content of multiple electrode assemblies 20 varies between lots before the fabrication step. In a preferred embodiment, the wound body is stored for a predetermined time, for example, at atmospheric pressure in a location where temperature and humidity can be controlled. The temperature conditions for storing the wound body are not particularly limited, as they may vary depending on, for example, the drying conditions in the preparation step and the amount of moisture remaining in the wound body during the fabrication step. In some embodiments, the temperature for storing the wound body is preferably room temperature (20 to 30°C), more preferably 23 to 25°C. The humidity for storing the wound body is preferably 10 to 50% RH, more preferably 10 to 30% RH. In one example, the wound body is preferably stored in an environment at room temperature, atmospheric pressure, and with a humidity of 10 to 50% RH. The storage time is preferably 24 hours or more (for example, 24 to 240 hours), and more preferably 24 to 72 hours.

[0068] In this step, it is preferable to place the wound body in a moisture-containing environment until the moisture content at the ends of the wound body in the winding axis WL direction becomes greater than the moisture content at the center of the wound body in the winding axis WL direction. Because the wound body is in a roll shape, moisture tends to flow out from both ends in the winding axis WL direction in the drying step (step 5) described below, making it easier to dry. Therefore, by making the moisture content at the ends greater than the moisture content at the center, it becomes easier to obtain an electrode body 20 that contains moisture uniformly in the winding axis WL direction after the drying step described below.

[0069] In the accommodation step (step 4), the wound body obtained above is accommodated in the case 10. Specifically, first, the positive electrode second current collecting portion 52 is joined to the positive electrode tab group 23 of the wound body, and the negative electrode second current collecting portion 62 is joined to the negative electrode tab group 25. Next, the wound body is accommodated inside the exterior body 12 through the opening 12h, typically in a moisture-controlled environment (e.g., inside a glove box). Next, a sealing plate assembly is prepared in which the sealing plate 14, the positive electrode terminal 30, the negative electrode terminal 40, the positive electrode first current collecting portion 51 of the positive electrode current collecting portion 50, the negative electrode first current collecting portion 61 of the negative electrode current collecting portion 60, the positive electrode insulating member 70, the negative electrode insulating member 80, and two gaskets 90 are integrated. Next, the positive electrode second current collecting portion 52 is joined (e.g., welded) to the positive electrode first current collecting portion 51 of the sealing plate assembly. This electrically connects the positive electrode 22 of the electrode body 20 to the positive electrode terminal 30. Similarly, the negative electrode second current collecting portion 62 is joined (for example, welded) to the negative electrode first current collecting portion 61 of the sealing plate assembly. This electrically connects the negative electrode 24 of the electrode body 20 to the negative electrode terminal 40. This integrates the sealing plate assembly and the electrode body 20.

[0070] Next, sealing plate 14 is welded to the periphery of opening 12h of exterior body 12 to integrate exterior body 12 and sealing plate 14. This completes case 10, resulting in a housing. Note that in this specification, the term "housing" refers to an assembly that includes the wound body and case 10 that houses the wound body, and does not contain nonaqueous electrolyte (before injection).

[0071] In some embodiments, the moisture content of the wound body before the drying step (the arithmetic mean of the moisture content in the center and the moisture content at the edges) is preferably 180 to 220 ppm, for example, by adjusting the moisture content in the moisture absorption step (step 3).

[0072] In the drying step (step 5), the wound body is dried. In this embodiment, the container is dried with the liquid injection hole 15 open to remove moisture from inside the case 10. In particular, a portion of the moisture inside the wound body is removed. The moisture can be removed by a conventionally known drying method, such as heat drying or vacuum drying, either alone or in combination as appropriate. The heating temperature is preferably set to a temperature that allows the moisture to evaporate appropriately and does not cause thermal degradation of the separator 26, etc. The heating temperature may vary depending on the material of the separator 26, etc., but is preferably set within the range of 50 to 150°C, for example.

[0073] In this embodiment, the wound body is dried so that the average of the central moisture content Mc and the end moisture content Me is 80 to 150 ppm, and the difference between the central moisture content Mc and the end moisture content Me is less than ±20 ppm. In other words, the drying is completed with a predetermined amount of moisture remaining in the wound body. This makes it possible to obtain an electrode assembly 20 with high thermal stability. The drying conditions are adjusted appropriately so that the moisture content falls within the above-mentioned range, and are not particularly limited, as they may vary depending on, for example, the moisture content of the wound body after the moisture absorption step (step 3).

[0074] In some embodiments, this process preferably includes, in this order, a preheating step of performing heat drying under atmospheric pressure and a vacuum drying step of performing vacuum drying. Although not particularly limited, the heating temperature in the preheating step is preferably set to 60°C or higher (e.g., 60 to 120°C), more preferably set to 70°C or higher (e.g., 70 to 110°C), and even more preferably set to 100 to 110°C or higher. The preheating time is preferably 1 to 10 hours, more preferably 3 to 6 hours.

[0075] Although not particularly limited, the vacuum drying temperature in the vacuum drying step is preferably the same as or higher than the heating temperature in the preheating step. The vacuum drying temperature is preferably set to 60°C or higher (e.g., 60 to 120°C), more preferably 70°C or higher (e.g., 70 to 110°C), and even more preferably 100 to 110°C or higher. The degree of vacuum in the vacuum drying step is preferably set to an absolute pressure of 100 Pa or less (so-called medium vacuum). The vacuum drying time is preferably 1 to 10 hours, more preferably 3 to 6 hours. In this way, an electrode assembly 20 can be obtained in which a predetermined amount of moisture is intentionally left.

[0076] In the liquid injection step (step 6), a nonaqueous electrolyte is injected into the case 10 (the dried container) containing the electrode assembly 20. Specifically, a nonaqueous electrolyte is first prepared. The nonaqueous electrolyte contains the above-mentioned electrolyte salt (e.g., LiPF6) and a nonaqueous solvent (e.g., carbonates), and may further contain additional components (additives). The prepared nonaqueous electrolyte is then injected into the case 10 through the liquid injection hole 15 in the sealing plate 14. The liquid injection is preferably performed under reduced pressure inside the case 10 to improve the impregnation of the nonaqueous electrolyte into the electrode assembly 20. This results in a battery assembly. In this specification, the term "battery assembly" refers to an intermediate product assembled to a state prior to the initial charging step (step 7) in the manufacturing process of the battery 100.

[0077] After the injection, it is preferable to apply pressure or vacuum as appropriate to improve the impregnation of the nonaqueous electrolyte into the electrode body 20, particularly into the central portion in the direction of the winding axis WL. In one example, it is preferable to house the battery assembly in a pressure-adjustable chamber, and with the injection hole 15 open (in other words, with no pressure difference between the inside and outside of the case 10), perform at least one of the following operations: reducing the pressure inside the chamber at least once and maintaining the vacuum state for a predetermined time; and pressurizing the chamber at least once and maintaining the pressurized state for a predetermined time.

[0078] In the initial charging step (step 7), the battery assembly is charged until at least a portion of the non-aqueous electrolyte is decomposed. The battery assembly can be charged in a conventional manner. Typically, an external power source is connected between the positive and negative electrode terminals of the battery assembly, and charging is performed until a predetermined final voltage is reached between the positive and negative electrode terminals. The final voltage is set so that at least a portion of the non-aqueous electrolyte (e.g., non-aqueous solvent or additives) is electrically decomposed. For example, when the negative electrode active material is a carbon material, the final voltage is set to approximately 2.5 V or higher, preferably 3 V or higher, for example, 3.5 V or higher, or 4 V or higher. The charge rate can be, for example, about 0.1 C to 2 C. Charging can be performed once, or can be repeated two or more times, for example, with a discharge in between. The initial charging forms a coating (SEI film) containing decomposition products of the non-aqueous electrolyte on the surface of the negative electrode active material layer 24a.

[0079] In the degassing step (step 8), after the initial charging step, gas inside the case 10, such as air and gas generated by decomposition of the nonaqueous electrolyte solution during the initial charging step, is exhausted to the outside of the case 10. The gas can be exhausted, for example, by creating a vacuum inside the case 10.

[0080] In the sealing step (step 9), the liquid inlet hole 15 is sealed with a sealing member 16. The liquid inlet hole 15 is preferably sealed with the pressure inside the case 10 reduced. This makes the case 10 airtightly sealed (hermetically sealed).

[0081] In the aging step (step 10), the battery assembly with the sealed liquid inlet 15 is maintained in a predetermined temperature environment for a predetermined aging period. The aging temperature is preferably 25 to 70°C, and may be, for example, room temperature (approximately 25°C ± 10°C). The aging period may vary depending on, for example, the aging temperature, but is preferably 24 hours or longer. In this step, the battery assembly is preferably restrained in the thickness direction X (thickness direction of the electrode body 20) and maintained in a state where a predetermined restraining load is applied. In this case, the restraining load is preferably 1 to 6 kN. In this manner, the battery 100 can be suitably manufactured.

[0082] <Uses of Battery 100> Battery 100 can be used for a variety of purposes, but because of its high capacity and excellent thermal stability, it can be suitably used as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). Battery 100 can also be suitably used as a battery pack formed by arranging a plurality of batteries 100 in a predetermined arrangement direction and applying a load from the arrangement direction using a restraining mechanism.

[0083] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to these examples.

[0084] In this test example, a number of battery assemblies (Examples 1 to 3, Comparative Examples 1 and 2) having the same configuration were constructed, and the thermal stability was examined when the drying conditions of the electrode assembly (amount of water in the electrode assembly) were varied.

[0085] <Secondary battery manufacturing> First, in the preparation step (step 1), a strip-shaped positive electrode and a strip-shaped negative electrode were prepared. The positive electrode was first prepared using LiNi 0.6 Co 0.2 Mn 0.2 O2, a carbon material as a conductive material, and PVdF as a binder were mixed in a mass ratio of positive electrode active material:conductive material:PVdF=97.5:1.5:1, and NMP was added as a solvent to prepare a positive electrode composite slurry (solid content 79 mass%). Next, the prepared positive electrode composite slurry was applied to a positive electrode current collector (aluminum foil) and dried to form a positive electrode active material layer. In this manner, a strip-shaped positive electrode was obtained.

[0086] The negative electrode was prepared by mixing graphite as the negative electrode active material with SBR and CMC as binders in a mass ratio of 98:1:1 (negative electrode active material:SBR:CMC), and adding ion-exchanged water as a solvent to prepare a negative electrode composite slurry (solid content: 56 mass%). The prepared negative electrode composite slurry was then applied to a negative electrode current collector (copper foil) with a width of 285 mm and dried to form a negative electrode active material layer. Thus, a negative electrode was obtained.

[0087] Next, in the fabrication step (step 2), a heat-resistant separator was prepared, in which a functional layer (a layer that served as both a heat-resistant layer and an adhesive layer) containing alumina and PVdF was provided on one side of a porous sheet made of PE. Next, the fabricated positive electrode and negative electrode were stacked with the separator interposed therebetween, and wound into a flat shape to fabricate a roll-shaped wound body (33 turns in total, with each turn counting as one turn).

[0088] Next, in the moisture absorption step (step 3), the produced wound body was stored in a storage cabinet in roll form at room temperature (25°C), atmospheric pressure, and humidity of 10% RH for 24 hours, allowing the wound body to absorb moisture from the ends in the winding axis direction. This adjusted the moisture content of the wound body (arithmetic average of the moisture content in the center and the moisture content at the ends) to approximately 180 to 190 ppm. Next, in the storage step (step 4), the wound body with the adjusted moisture content was stored in a case to obtain a storage body.

[0089] Next, in the drying step (step 5), the housings of Examples 1 to 3 and Comparative Example 1 were dried under the conditions shown in Table 1 with the inlet hole open to dry the wound body in the case. For example, in Example 1, preheating (heating temperature: 105°C, preheating time: 4 hours) was followed by vacuum drying (vacuum drying temperature: 105°C, vacuum degree: 100 Pa, vacuum drying time: 220 minutes). This step was not performed on the housing of Comparative Example 2.

[0090] Next, in the liquid injection step (step 6), a non-aqueous electrolyte was injected into the container to obtain a battery assembly. The non-aqueous electrolyte used in each example was a mixed solvent (nonaqueous solvent) containing EC, DMC, and EMC in a mass ratio of 29.1:31.5:22.4, and LiPF6 as an electrolyte salt in a proportion of 13.3 mass%.

[0091] Next, in the initial charging step (step 7), constant current charging was performed at a charge rate of 1C up to 3V. Next, in the degassing step (step 8), the pressure inside the case was reduced to -0.09 MPa. Next, in the aging step (step 9), the battery assembly after the initial charge was left at room temperature (25°C) with a restraint load of 4 kN applied for 5 days or more. In this manner, a lithium-ion secondary battery was produced.

[0092] <Measurement of the moisture content of the electrode body> First, the lithium-ion secondary battery was disassembled in a dry oven under a dry air atmosphere, and the electrode assembly was removed from the case. Next, the electrode assembly was unwound, and the positive and negative electrodes located at the 17th turn (the middle portion in the longitudinal direction) were cut out in one-turn lengths. Next, as shown in Figure 5, three 20 mm x 20 mm test pieces were cut from the center (Pc in Figure 5) and both end portions (Pe1 and Pe2 in Figure 5) of the positive electrode in the winding axis WL direction. Similarly, three 20 mm x 20 mm test pieces were cut from the center and both end portions of the negative electrode in the winding axis direction. The end portions were located approximately 5 mm inward from the outermost end of the winding axis of the active material layer. Next, a set of three test pieces was placed in a Karl Fischer moisture analyzer (Nitto Seiko Analytech, Model: CA-310). Then, using Aquamicron (registered trademark) manufactured by Mitsubishi Chemical Corporation as the Karl Fischer reagent, moisture was vaporized from the test piece at a vaporization temperature of 150°C for a vaporization time of 2 minutes, and the amount of moisture that reacted with the Karl Fischer reagent was quantified by coulometric titration.

[0093] Next, the quantitative values ​​at both ends (Pe1 and Pe2 in Figure 5) of each positive and negative electrode were arithmetically averaged to determine the moisture content at the "ends." The moisture content at the ends of the positive electrode and the negative electrode was then arithmetically averaged to calculate the "moisture content at the ends of the electrode body, Me." The moisture content at the center of the positive electrode and the center of the negative electrode was also arithmetically averaged to calculate the "moisture content at the center of the electrode body, Mc." The results are shown in Table 1.

[0094] <Heat generation evaluation> First, the discharged battery was disassembled in a glove box under an Ar gas atmosphere. Next, the electrolyte was collected, and the positive and negative electrodes, each measuring 50 mm x 115 mm, were removed. Next, the positive and negative electrodes were placed opposite each other with a separator interposed between them and sealed in an aluminum pouch together with the collected electrolyte to prepare a laminated cell. Next, the prepared laminated cell was fully charged and then disassembled, and the negative electrode composite was scraped off from the negative electrode. Next, the scraped negative electrode composite was placed in a sample container (SUS pan) together with the electrolyte. This sample container was press-sealed at 20 MPa and then placed in a differential scanning calorimeter (DSC; Shimadzu Corporation, Model: DSC-60A) together with a reference material (Al2O3, 2 mg). After waiting for 85 minutes at 30°C in an inert atmosphere, the temperature was increased from 30°C to 350°C at a rate of 2°C / min, and a DSC chart was obtained. The calorific value (J) was calculated from the integrated value (peak area value) between 100 and 180° C. on the obtained DSC chart. The results are shown in Table 1.

[0095] [Table 1]

[0096] As shown in Table 1, in Comparative Example 2, in which the drying step was not performed, the moisture content (average) of the electrode assembly was relatively high. In Comparative Example 1, in which the drying step was repeated twice, the moisture content (average) of the electrode assembly was relatively low. Furthermore, in Comparative Examples 1 and 2, the heat generation amount was relatively large. In contrast to these Comparative Examples, in Examples 1 to 3, in which the average of the central moisture content Mc and the edge moisture content Me was 80 to 150 ppm and the difference between the central moisture content Mc and the edge moisture content Me was less than ±20 ppm, the heat generation amount was suppressed and the thermal stability was high. These results demonstrate the significance of the technology disclosed herein.

[0097] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modifications, or to add other modifications to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0098] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked in an insulated state and wound in a longitudinal direction, wherein the negative electrode has a negative electrode active material layer having a width of 200 mm or more in a winding axis direction perpendicular to the longitudinal direction, and the positive electrode has a positive electrode active material layer having a width in the winding axis direction that is the same as or shorter than that of the negative electrode active material layer, wherein the following steps are performed: (Step 1) Cut out one turn of the positive electrode and the negative electrode located in the intermediate circumferential portion in the longitudinal direction; (Step 2) Cut out test pieces from the center and both end portions of the positive electrode active material layer of the positive electrode in the winding axis direction, and cut out test pieces from the center and both end portions of the negative electrode active material layer of the negative electrode in the winding axis direction; (Step 3) For each test piece cut out in Step 2 above, quantify the moisture content by the Karl Fischer method at heating temperatures ranging from room temperature to 150°C; (Step 4) calculating the average of the moisture content in the center portion of the positive electrode active material layer and the moisture content in the center portion of the negative electrode active material layer as the "moisture content in the center portion" of the electrode body, and calculating the average of the moisture content in the both end portions of the positive electrode active material layer and the moisture content in the both end portions of the negative electrode active material layer as the "moisture content in the end portions" of the electrode body; The average of the moisture content of the central portion and the moisture content of the edge portion, calculated by the above formula, is 80 ppm or more and 150 ppm or less, and the difference between the moisture content of the central portion and the moisture content of the edge portion is less than ±20 ppm. Item 2: The electrode assembly according to item 1, wherein the moisture content in the central portion is greater than the moisture content in the end portion. Item 3: A method for producing an electrode assembly according to item 1, comprising: a preparation step of preparing a strip-shaped negative electrode having a negative electrode active material layer with a width in the winding axis direction of 200 mm or more; and a strip-shaped positive electrode having a positive electrode active material layer with a width in the winding axis direction that is the same as or shorter than that of the negative electrode active material layer; a fabrication step of stacking and winding the strip-shaped positive electrode and the strip-shaped negative electrode in an insulated state to produce a wound assembly; and a drying step of drying the wound assembly, In the drying step, the wound body is dried so that the average of the moisture content in the central portion and the moisture content at the end portions is 80 ppm or more and 150 ppm or less, and the difference between the moisture content in the central portion and the moisture content at the end portions is less than ±20 ppm. Item 4: The manufacturing method according to Item 3, further comprising a moisture absorption step between the fabrication step and the drying step, in which the wound body is placed in a moisture-containing environment to absorb moisture from the end of the wound body in the winding axis direction. Item 5: The manufacturing method according to Item 4, wherein in the moisture absorption step, the wound body is placed in a moisture-containing environment until the moisture content at the end portion of the wound body in the winding axis direction becomes greater than the moisture content at the center portion of the wound body in the winding axis direction. Item 6: The manufacturing method according to Item 4 or 5, wherein in the moisture absorption step, the wound body is placed in an environment at room temperature and atmospheric pressure, with a humidity of 10% RH or more and 50% RH or less. Item 7: The manufacturing method according to any one of Items 3 to 6, wherein the drying step includes a preheating step of performing heat drying at 70°C or higher and 110°C or lower under atmospheric pressure, and a vacuum drying step of performing vacuum drying at 70°C or higher and 110°C or lower after the preheating step. Item 8: A method for manufacturing a secondary battery, further comprising: a construction step of constructing a battery assembly including an electrode body obtained by the manufacturing method according to any one of claims 3 to 7, a non-aqueous electrolyte, and a case that accommodates the electrode body and the non-aqueous electrolyte; and an initial charging step of charging the battery assembly until at least a portion of the non-aqueous electrolyte is decomposed. [Explanation of symbols]

[0099] 10 cases 20 Electrode body (wound electrode body) 22 Positive electrode 22a Cathode active material layer 24 Negative electrode 24a Negative active material layer 100 batteries WL winding shaft

Claims

1. An electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked in an insulated state and wound in the longitudinal direction, the negative electrode has a negative electrode active material layer having a width of 200 mm or more in a direction of a winding axis perpendicular to the longitudinal direction, the positive electrode has a positive electrode active material layer having a width in the winding axis direction that is equal to or smaller than that of the negative electrode active material layer, Now, follow these steps: (Step 1) cutting out one turn of the positive electrode and the negative electrode located in the intermediate circumferential portion in the longitudinal direction; (Step 2) Cutting out test pieces from the center and both end portions of the positive electrode active material layer of the positive electrode in the winding axis direction, and cutting out test pieces from the center and both end portions of the negative electrode active material layer of the negative electrode in the winding axis direction; (Step 3) For each test piece cut out in Step 2, the moisture content is quantified by the Karl Fischer method at heating temperatures from room temperature to 150°C; (Step 4) calculating the average of the moisture content of the central portion of the positive electrode active material layer and the moisture content of the central portion of the negative electrode active material layer as the "moisture content of the central portion" of the electrode body, and calculating the average of the moisture content of the moisture content of the both end portions of the positive electrode active material layer and the moisture content of the both end portions of the negative electrode active material layer as the "moisture content of the both end portions" of the electrode body; The average of the moisture content of the central portion and the moisture content of the edge portion, calculated by the above formula, is 80 ppm or more and 150 ppm or less, and the difference between the moisture content of the central portion and the moisture content of the edge portion is less than ±20 ppm. Electrode body.

2. The moisture content of the central portion is greater than the moisture content of the end portion. The electrode assembly according to claim 1 .

3. The method for manufacturing the electrode assembly according to claim 1, a preparation step of preparing a strip-shaped negative electrode having a negative electrode active material layer with a width of 200 mm or more in the winding axis direction, and a strip-shaped positive electrode having a positive electrode active material layer with a width in the winding axis direction that is the same as or shorter than that of the negative electrode active material layer; a manufacturing step of manufacturing a wound body by stacking and winding the strip-shaped positive electrode and the strip-shaped negative electrode in an insulated state; a drying step of drying the wound body; Including, In the drying step, the wound body is dried so that the average of the moisture content at the center portion and the moisture content at the end portion is 80 ppm or more and 150 ppm or less, and the difference between the moisture content at the center portion and the moisture content at the end portion is less than ±20 ppm. A method for manufacturing an electrode body.

4. The method further includes a moisture absorption step between the fabrication step and the drying step, in which the wound body is placed in a moisture-containing environment to absorb moisture from the end of the wound body in the winding axis direction. The method of claim 3.

5. In the moisture absorption step, the wound body is placed in a moisture-containing environment until the amount of moisture at the end portion of the wound body in the winding axis direction becomes greater than the amount of moisture at the center portion of the wound body in the winding axis direction. The method of claim 4.

6. In the moisture absorption step, the wound body is placed in an environment at room temperature and atmospheric pressure with a humidity of 10% RH or more and 50% RH or less. The method of claim 5.

7. The drying step includes: a preheating step of heating and drying the mixture at a temperature of 70°C or higher and 110°C or lower under atmospheric pressure; a vacuum drying step of performing vacuum drying at 70°C or higher and 110°C or lower after the preheating step; Including, The method of claim 4.

8. a construction step of constructing a battery assembly including an electrode assembly obtained by the manufacturing method according to any one of claims 3 to 7, a non-aqueous electrolyte, and a case that accommodates the electrode assembly and the non-aqueous electrolyte; an initial charging step of charging the battery assembly until at least a portion of the nonaqueous electrolyte is decomposed; further comprising: A method for manufacturing a secondary battery.

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