Electrode body, method for manufacturing same, and method for manufacturing secondary battery

Abstract

The invention relates to an electrode body, a method for manufacturing the same, and a method for manufacturing a secondary battery. Provided is an electrode body with which a secondary battery having excellent thermal stability can be obtained. The disclosed electrode assembly (20) is formed by laminating a belt-shaped positive electrode (22) and a belt-shaped negative electrode (24) in an insulated state and winding in the longitudinal direction (LD), the average of the water content in the center portion and the water content in the end portions in the winding axis (WL) direction is 80 ppm or more and 150 ppm or less, and the difference between the water content in the center portion and the water content in the end portions in the winding axis (WL) direction is less than + / -20 ppm.

Description

Technical Field

[0001] This invention relates to an electrode body and its manufacturing method, as well as a method for manufacturing a secondary battery. Background Technology

[0002] To date, secondary batteries including wound electrode bodies and non-aqueous electrolytes are known, wherein the wound electrode body is formed by stacking strip-shaped positive and strip-shaped negative electrodes in an insulating state and winding them in the longitudinal direction. Japanese Patent No. 6067545 is cited as a related prior art document.

[0003] Japanese Patent No. 6067545 discloses the following: By utilizing water that is currently considered to be avoided from entering the battery, the water content at the end of the negative electrode is 200 ppm higher than the water content at the center of the negative electrode, thereby improving the cycle durability of the secondary battery.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6067545 Summary of the Invention

[0007] In recent years, the width of the electrode body along the winding axis has increased in larger secondary batteries. Furthermore, if the electrode body is a wound electrode body, moisture only flows in and / or out from both ends along the winding axis. Therefore, moisture distribution (fluctuations) easily occur along the winding axis. According to the inventors' research, it has been newly determined that if the electrode body has too much moisture, or conversely, if the moisture content of the electrode body is locally too low, the thermal stability of the secondary battery decreases.

[0008] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide an electrode body capable of producing a secondary battery with excellent thermal stability, a method for manufacturing the same, and a method for manufacturing a secondary battery.

[0009] According to the present invention, an electrode body is provided, which is formed by stacking strip-shaped positive and strip-shaped negative electrodes in an insulating state and winding them in a longitudinal direction. The negative electrode has a negative electrode active material layer with a width of 200 mm or more in a winding axis direction orthogonal to the longitudinal direction. The positive electrode has a positive electrode active material layer with a width in the winding axis direction that is the same as or shorter than the negative electrode active material layer. In this electrode body, the average moisture content at the center and the moisture content at the ends in the winding axis direction is 80 ppm or more and 150 ppm or less, and the difference between the moisture content at the center and the moisture content at the ends in the winding axis direction is less than ±20 ppm.

[0010] By using the above-mentioned electrode body to construct a secondary battery, a secondary battery with excellent thermal stability can be obtained. Attached Figure Description

[0011] Figure 1 A perspective view of an electrode body according to one embodiment is shown schematically.

[0012] Figure 2 This is a schematic diagram illustrating the configuration of an electrode body according to one embodiment.

[0013] Figure 3 A perspective view of a non-aqueous electrolyte secondary battery according to one embodiment is shown schematically.

[0014] Figure 4 For along Figure 3 A schematic longitudinal section of line IV-IV.

[0015] Figure 5 A plan view illustrating the sampling location for moisture content determination.

[0016] Explanation of reference numerals in the attached figures

[0017] 10. Shell

[0018] 20 Electrode body (wound electrode body)

[0019] 22 Positive electrode

[0020] 22a Positive Electrode Active Material Layer

[0021] 24 negative electrode

[0022] 24a Negative electrode active material layer

[0023] 100 batteries

[0024] WL winding shaft Detailed Implementation

[0025] 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 necessary for the implementation of the invention (e.g., the general configuration and manufacturing process of electrode bodies and non-aqueous electrolyte secondary batteries that are not features of the invention) can be grasped as design matters 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 scope in this specification includes the meaning of "above A and below B," and also includes the meanings of "greater than A" and "less than B."

[0026] <Electrode 20>

[0027] First, regarding the electrode body 20 disclosed herein (refer to...) Figure 1 , Figure 2 The following explanation is provided. Electrode 20 is used in the non-aqueous electrolyte secondary battery (hereinafter also referred to as the battery) 100 (see reference). Figure 3 , Figure 4 It should be noted that, in this specification, "non-aqueous electrolyte secondary battery" refers to all energy storage devices capable of repeated charging and discharging, in which charge carriers move between the positive and negative electrodes via a non-aqueous electrolyte. The concept of a non-aqueous electrolyte secondary battery includes so-called batteries such as lithium-ion and nickel-metal hydride batteries, as well as capacitors such as lithium-ion capacitors and pseudocapacitive capacitors.

[0028] Figure 1 A perspective view of the electrode body 20 is shown schematically. Figure 2 This is a schematic diagram illustrating the configuration of the electrode body 20. It should be noted that in the following description, the reference numeral LD ​​in the figures indicates the longitudinal direction of the electrode body 20. Figure 2 As shown, the electrode body 20 is a wound electrode body. The electrode body 20 is constructed by stacking strip-shaped positive electrodes 22 and strip-shaped negative electrodes 24 in an insulating state (here, via strip-shaped separators 26) and winding them in the longitudinal direction LD. In the case of a wound electrode body 20, moisture only flows in and / or out from both ends in the winding axis WL direction. Therefore, uneven moisture distribution is easily generated in the winding axis WL direction of the electrode body 20, particularly in the central portion and at the ends. Therefore, the technique disclosed herein is particularly effective.

[0029] Although not particularly limited, the number of turns of the electrode body 20 is preferably 20 or more, more preferably 30 or more, and for example, it may be 150 or less or 100 or less.

[0030] like Figure 1 As shown, the electrode body 20 has a flat shape. The electrode body 20 is preferably flat. The electrode body 20 has a pair of flat portions 20f extending along 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 flat outer surfaces. The curved portions 20r have curved outer surfaces. It should be noted that in this specification, "flat outer surface" is not limited to complete flatness, but includes cases where, for example, it has minute steps, bends, concave portions, convex portions, etc., when observed microscopically.

[0031] The composition of the positive electrode 22 can be the same as before, without any special restrictions. For example... Figure 2As shown, the positive electrode 22 has a positive electrode active material layer 22a. The positive electrode 22 here 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 conductive metals such as aluminum, aluminum alloy, nickel, and stainless steel. The positive electrode current collector 22c here is a metal foil, specifically an aluminum foil.

[0032] At one end of the winding axis WL direction of the positive current collector 22c ( Figure 2 Multiple positive electrode plates 22t are provided at the left end of the [structure / structure]. Each of the multiple positive electrode plates 22t is convex, facing one side towards the winding axis WL. Figure 2 (The left side) protrudes. The positive electrode 22t is part of the positive current collector 22c and is made of metal foil (aluminum foil). At least a portion of the positive electrode 22t is the exposed portion of the current collector 22c, where the positive active material layer 22a and the positive protective layer 22p are not formed. Figure 1 As shown, multiple positive electrode plates 22t are located at one end of the winding axis WL ( Figure 1 The left end of the electrode is stacked to form a positive electrode assembly 23. The positive electrode assembly 23 is attached (specifically, joined) with a component in the battery 100 for connection with the positive terminal 30 (see reference 30). Figure 3 , Figure 4 The positive terminal of the second collector 52 is electrically connected.

[0033] like Figure 2 As shown, the positive electrode active material layer 22a is arranged in a strip shape along the length 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., lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxides) capable of reversibly attracting and releasing charge carriers. The positive electrode active material layer 22a may contain any components other than the positive electrode active material, such as conductive materials, binders, and various additives. 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.

[0034] While not particularly limited, from the viewpoint of maximizing capacity, the width W1 (average value, excluding the portion formed in the positive electrode sheet 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. 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 later.

[0035] like Figure 2As 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 winding axis WL direction. The positive electrode protective layer 22p is disposed at one end of the positive electrode current collector 22c in the winding axis WL direction. Figure 2 (At the left end). The positive electrode protective layer 22p is configured as a strip 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 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.

[0036] The configuration of the negative electrode 24 can be the same as before, without any particular restrictions. For example... Figure 2 As shown, the negative electrode 24 has a negative electrode active material layer 24a. The negative electrode 24 here 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 conductive metals such as copper, copper alloy, nickel, and stainless steel. The negative electrode current collector 24c here is a metal foil, specifically a copper foil.

[0037] One end of the negative current collector 24c in the direction of the winding axis WL ( Figure 2 Multiple negative electrode plates 24t are provided at the right end. Each of the multiple negative electrode plates 24t is convex, facing one side towards the winding shaft WL. Figure 2 (The right side) protrudes. The negative electrode plate 24t is part of the negative current collector 24c and is made of metal foil (copper foil). At least a portion of the negative electrode plate 24t is the exposed portion of the current collector 24c, where the negative active material layer 24a is not formed. Figure 1 As shown, multiple negative electrode plates 24t are located at one end of the winding shaft WL direction ( Figure 1 The right end of the electrode is stacked to form a negative electrode assembly 25. Attached (specifically, joined) to the negative electrode assembly 25 are components used in the battery 100 for connection with the negative terminal 40 (see reference 40). Figure 3 , Figure 4 The negative terminal of the second collector 62 is electrically connected.

[0038] like Figure 2 As shown, the negative electrode active material layer 24a is arranged in a strip shape along the length 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., carbon material such as graphite) capable of reversibly attracting and releasing charge carriers. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as binders, various additives, etc. As binders, for example, rubbers such as styrene-butadiene rubber (SBR) and cellulose-based materials such as carboxymethyl cellulose (CMC) can be used.

[0039] From the viewpoint of maximizing capacity, the width W2 (average value, excluding the portion formed in the negative electrode sheet 24t) of the negative electrode active material layer 24a in the winding axis WL direction is 200 mm or more, preferably 250 mm or more. The longer the width W2 of the negative electrode active material layer 24a, the more easily uneven moisture content occurs in the winding axis WL direction of the electrode body 20, particularly in the central and end portions. Even in the central portion, the moisture content can easily become locally insufficient. Therefore, 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. While not particularly limited, the width W2 of the negative electrode active material layer 24a can be, for example, 1000 mm or less, or 500 mm or less. This allows the effects of the technology disclosed herein to be achieved at a high level.

[0040] like Figure 2 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 width W3 of the separator 26 in the winding axis WL direction is the same as or longer than the width W2 of the negative electrode active material layer 24a in the winding axis WL direction. The structure of the separator 26 can be the same as conventional and is not particularly limited. As the separator 26, a porous sheet made of resin such as polyethylene (PE) or polypropylene (PP) is preferred. The separator 26 may have functional layers such as a heat resistance layer (HRL) and an adhesive layer on the surface of the substrate portion made of the resin porous sheet. The heat resistance layer is, for example, a layer containing inorganic fillers and adhesives. The adhesive layer is a layer containing adhesives. The heat resistance layer can also serve as an adhesive layer. The structure of the heat resistance layer and the adhesive layer can be the same as conventional.

[0041] If the electrode body 20 contains a large amount of moisture, gas may be generated during charging and discharging, or the battery characteristics may deteriorate. Therefore, it has been conventional to remove as much moisture as possible during the manufacture of the battery 100. However, according to the inventors' research, it has been newly determined that if the electrode body 20 contains too much moisture, or conversely, if the electrode body 20 contains too little moisture locally, the thermal stability of the battery 100 decreases.

[0042] Therefore, in this embodiment, the average of the water content Mc in the central part and the water content Me at the end of the electrode body 20, as determined by the steps described later, is set to 80 to 150 ppm, and the difference between the water content Mc in the central part and the water content Me at the end of the electrode body 20 is less than ±20 ppm. That is, a predetermined amount of water is contained approximately uniformly in the winding axis WL direction, and the unevenness of water content between the central part and the end of the electrode body 20 is reduced. By satisfying the above-mentioned water content range in the electrode body 20, a battery 100 with excellent thermal stability can be obtained. Although not intended to be particularly limiting, the inventors believe the reasons are as follows.

[0043] That is, in battery 100, typically, during initial charging, the non-aqueous electrolyte decomposes, forming a film (Solid Electrolyte Interface film: SEI film) on the surface of the negative electrode 24. As also described in Japanese Patent No. 6067545, the amount of water in the electrode body 20 can affect the amount of SEI film formed. By making the average water content Mc in the central part and Me at the ends of the electrode body 20 150 ppm or less, it is possible to suppress the reduction in the amount of SEI film formed due to the water hindering the impregnation of the non-aqueous electrolyte. In addition, by making the average water content Mc in the central part and Me at the ends of the electrode body 20 80 ppm or more, water readily reacts with the non-aqueous electrolyte (e.g., non-aqueous solvents such as carbonates described later), changing into a stable inorganic film component (e.g., lithium carbonate). Therefore, it is easy to form a high-quality SEI film. Furthermore, by minimizing the difference between the water content Mc in the central part and the water content Me at the end of the electrode body 20 to less than ±20 ppm, an SEI film can be easily and uniformly formed in the winding axis WL direction during initial charging. It is believed that the thermal stability of the battery 100 can be improved through the synergistic effect of the above.

[0044] Furthermore, by averaging the water content Mc in the central part and the water content Me at the ends of the electrode body 20 to 150 ppm or less, it is possible to suppress the reaction between water and non-aqueous electrolytes (such as electrolyte salts like LiPF6 described later) that would produce corrosive HF, thereby preventing the metal from dissolving from the positive electrode current collector 22c. Therefore, the battery resistance can be reduced.

[0045] In the electrode body 20, the average water content Mc in the central part and the water content Me at the end are preferably 140 ppm or less, more preferably 130 ppm or less, and particularly preferably 120 ppm or less, 110 ppm or less, and even more preferably 100 ppm or less. As a result, for example, more SEI film can be easily formed on the negative electrode 24, which can further and sufficiently improve the thermal stability of the battery 100.

[0046] In several embodiments, it is preferable that the central water content Mc is greater than the terminal water content Me (Me < Mc). This facilitates the formation of a high-quality SEI film containing stable inorganic coating components in the central portion along the winding axis WL, for example, thereby improving the thermal stability of the battery 100. The difference between the two (Mc-Me) is preferably 5 ppm or more, more preferably 10 ppm or more. However, in the electrode body 20, the relationship between the central water content Mc and the terminal water content Me is not limited; in other embodiments, the central water content Mc may be less than the terminal water content Me.

[0047] While not particularly limited, the moisture content Mc in the central portion of the electrode body 20 is preferably 160 ppm or less, more preferably 150 ppm or less, even more preferably 140 ppm or less, and particularly preferably 130 ppm or less, 120 ppm or less, 110 ppm or less, and further preferably 100 ppm or less. By keeping the moisture content Mc in the central portion below a predetermined value, for example, more SEI film is easily formed in the central portion in the winding axis WL direction, which can improve the thermal stability of the battery 100. Furthermore, the moisture content Me at the ends of the electrode body 20 is preferably 140 ppm or less, more preferably 130 ppm or less, even more preferably 120 ppm or less, and particularly preferably 110 ppm or less, 100 ppm or less, and further preferably 90 ppm or less. By keeping the moisture content Me at the ends below a predetermined value, more SEI film is easily formed at the ends in the winding axis WL direction, which can improve the thermal stability of the battery 100.

[0048] Furthermore, the water content of electrode 20 can be determined as follows. That is, firstly, the water content of electrode 20 is... Figure 2 The electrode body 20 is unwound, and then one turn is cut out for each turn of the positive electrode 22 and the negative electrode 24 located in the intermediate peripheral part in the longitudinal direction LD. Next, for the positive electrode active material layer 22a of the positive electrode 22, test pieces of a specified size (e.g., 20mm × 20mm) are cut out at the center and both ends in the winding axis WL direction. Similarly, for the negative electrode active material layer 24a of the negative electrode 24, test pieces of a specified size (e.g., 20mm × 20mm) are cut out at the center and both ends in the winding axis WL direction. It should be noted that the "center part" in the winding axis WL direction refers to the central part M including the winding axis WL direction. Y (Refer to Figure 1The portion (half the width of the entire width from the very end (edge) of the active material layer along the winding axis WL direction) is defined as the portion approximately 5 mm inward from the very end (edge) of the active material layer along the winding axis WL direction. Preferably, multiple test pieces (two or more) are used at each measurement point, more preferably three or more. Next, for each cut test piece, the Karl Fischer method (typically a water vaporization method-electroelectric titration method) is used to quantify the amount of water vaporized at heating temperatures ranging from room temperature to 150°C.

[0049] Then, the arithmetic mean of the water content in the central part of the positive electrode active material layer 22a and the water content in the central part of the negative electrode active material layer 24a is calculated as the "central part water content Mc" of the electrode body 20. In addition, the arithmetic mean of the water content at the end of the positive electrode active material layer 22a and the water content at the end of the negative electrode active material layer 24a is calculated as the "end water content Me" of the electrode body 20.

[0050] Furthermore, the moisture content of the electrode body 20 (the moisture content Mc in the central part and / or the moisture content Me at the ends) can be appropriately adjusted, for example, by using the conditions of the manufacturing process (process 2), the moisture absorption process (process 3), and the subsequent drying process (process 5) in the manufacturing method described later. In particular, the humidity of the moisture absorption process (process 3), the heating temperature of the drying process (process 5), or the vacuum level can be appropriately adjusted.

[0051] <Battery 100>

[0052] Next, the battery 100, which includes the electrode body 20 disclosed herein, will be described. Figure 3 This is a 3D view of battery 100. Figure 4 For along Figure 3 A schematic longitudinal section view of line IV-IV. 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, and the reference numerals X, Y, and Z in the figures represent the thickness direction, the width direction orthogonal to the thickness direction, and the up-down direction orthogonal to both the thickness and width directions, respectively. However, these are merely directions for ease of explanation and do not limit the arrangement of the battery 100.

[0053] like Figure 4 As shown, the battery 100, in addition to the electrode body 20, also includes: a casing 10, a positive terminal 30, a negative terminal 40, a positive current collector 50, a negative current collector 60, and a non-aqueous electrolyte (not shown). The battery 100 is a lithium-ion secondary battery. The battery 100 is preferably a lithium-ion secondary battery.

[0054] The housing 10 is a frame that accommodates the electrode body 20 and the non-aqueous electrolyte. For example... Figure 3 As shown, the housing 10 has a flat, bottomed cuboid shape (square). The material of the housing 10 can be the same as conventionally used materials, and there are no particular limitations. The housing 10 is preferably made of metal, and more preferably of aluminum, aluminum alloy, iron, iron alloy, etc. Figure 4 As shown, the housing 10 here includes: an outer packaging body 12 having an opening 12h, and a sealing plate (cap) 14 that blocks the opening 12h. The housing 10 preferably includes the outer packaging body 12 and the sealing plate 14.

[0055] like Figure 3 As shown, the outer packaging body 12 includes: a generally rectangular bottom wall 12a, a pair of long side walls 12b extending from the long side of the bottom wall 12a and opposite to each other, and a pair of short side walls 12c extending from the short side of the bottom wall 12a and opposite to each other. The bottom 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.

[0056] like Figure 3 As shown, the sealing plate 14 is roughly rectangular when viewed from above. Figure 4 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 housing 10 is integrally formed by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the outer packaging body 12. The housing 10 is airtightly sealed (sealed).

[0057] like Figure 4 As shown, the sealing plate 14 is provided with an injection hole 15, an exhaust 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 exhaust valve 17 is configured to break when the pressure inside the housing 10 reaches a predetermined value, thereby venting the gas inside the housing 10 to the outside. The terminal outlet holes 18 and 19 are respectively formed at both ends in the width direction Y of the sealing plate 14. Figure 4 (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.

[0058] The positive terminal 30 and the negative terminal 40 are respectively fixed to the sealing plate 14 of the housing 10. The positive terminal 30 is disposed on one side of the sealing plate 14 in the width direction Y. Figure 3 , Figure 4(Left side). The negative terminal 40 is configured on the other side of the sealing plate 14 in the width direction Y. Figure 3 , Figure 4 (The right side). For example Figure 4 As 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 ends of the positive terminal 30 and the negative terminal 40 on the outer packaging 12 side ( Figure 4 The lower end of the part has riveting portions 30c and 40c.

[0059] like Figure 4 As shown, the positive terminal 30 is located inside the housing 10 via the positive current collector 50 and the positive terminal 22 of the electrode body 20 (see reference). Figure 2 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.

[0060] On the other hand, the negative terminal 40 is located inside the housing 10 via the negative current collector 60 and the negative terminal 24 of the electrode body 20 (see reference). Figure 2 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 together and integrating them. For example, the portion of the negative terminal 40 connected to the negative electrode current collector 60 may be made of copper or a copper alloy, and the portion of the negative terminal 40 exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0061] A plate-shaped positive electrode external conductive member 32 and a negative electrode external conductive member 42 are mounted on the outer surface of the sealing plate 14. When multiple batteries 100 are electrically connected to each other, the positive electrode external conductive member 32 and the negative electrode external conductive member 42 are members with attached busbars. 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 the 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 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 the negative electrode external conductive member 42 are not essential and can be omitted in other embodiments.

[0062] like Figure 4As shown, the electrode body 20 is housed inside the housing 10 (specifically, inside the outer packaging 12). The number of electrode bodies 20 disposed inside a single housing 10 is not particularly limited; it can be one or more. The electrode body 20 can be disposed inside the housing 10 covered by an insulating electrode body support. The electrode body support is preferably made of resin.

[0063] Depend on Figure 4 As can be seen, the electrode body 20 is arranged inside the housing 10 with the winding axis WL approximately parallel to the width direction Y. The direction of the winding axis WL is consistent with the width direction Y. The electrode body 20 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.

[0064] Electrode 20 here consists of positive electrode assembly 23 and negative electrode assembly 25 located at both ends in the direction of winding shaft WL. Figure 1 , Figure 4 The so-called transverse electrode structure (left and right). However, in other embodiments, the electrode body 20 may also be located at one end of the winding axis WL direction, where the positive electrode group 23 and the negative electrode group 25 are located (e.g., on the left and right). Figure 1 , 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.

[0065] Depend on Figure 1 , Figure 4 It can be seen that a pair of flat portions 20f of the electrode body 20 are opposite to 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 of the electrode body 20 are opposite to the bottom wall 12a and the sealing plate 14 of the outer packaging body 12. As in this embodiment, the electrode body 20 preferably has a positive electrode 22 in the flat portion 20f (see reference). Figure 2 ) and negative electrode 24 (refer to) Figure 2 The stacking direction (thickness direction) of the ) is aligned with the thickness direction X (the direction perpendicular to the long sidewall 12b) inside the housing 10.

[0066] like Figure 4 As 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, and 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 and a second positive current collector 52. The first positive current collector 51 is mounted on the inner surface of the sealing plate 14. 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 of the electrode body 20.

[0067] like Figure 4 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, and 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 and a second negative current collector 62. The configuration and arrangement of the first negative current collector 61 and the second negative current collector 62 are the same as those of the first positive current collector 51 and the second positive current collector 52 of the positive current collector 50. The second negative current collector 62 is attached to the negative electrode assembly 25 of the electrode body 20.

[0068] Non-aqueous electrolytes typically comprise a non-aqueous solvent and an electrolyte salt (supporting salt). One or more previously known non-aqueous solvents suitable for this application 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 dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); and cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC).

[0069] As an electrolyte salt, there are no particular limitations as long as it contains a charge carrier (typically lithium ions), and one or more electrolyte salts previously known to be used in secondary batteries can be used. Examples of electrolyte salts include fluorine-containing lithium salts such as LiPF6 and LiBF4. LiPF6 is preferably included as the electrolyte salt.

[0070] The non-aqueous electrolyte may further contain added components (additives). As additives, one or more previously known additives that can be added to non-aqueous electrolytes can be used. Examples include boron-based additives containing boron, such as lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalate)borate (LiODFB). The additive may be a so-called film-forming agent that decomposes earlier (at lower potential) than 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.

[0071] Furthermore, regarding additives in the non-aqueous electrolyte (such as the boron-based additives mentioned above), they are typically consumed through electrolysis during initial charging, 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.

[0072] <Manufacturing Method of Electrode 20 and Battery 100>

[0073] The battery 100 described above can be manufactured, for example, by a manufacturing method comprising the following steps in sequence: preparation step (step 1), fabrication step (step 2), moisture absorption step (step 3), containment step (step 4), drying step (step 5), electrolyte injection step (step 6), initial charging step (step 7), degassing step (step 8), sealing step (step 9), and aging step (step 10). The containment step (step 4) and electrolyte injection step (step 6) are examples of construction steps.

[0074] However, the moisture absorption process (process 3), the degassing process (process 8), and the aging process (process 10) are optional and can be omitted in other embodiments. Furthermore, the order of the containment process (process 4) and the drying process (process 5) can be interchanged. Additionally, other processes can be further included in any stage. The preparation process (process 1), the manufacturing process (process 2), and the drying process (process 4) can be considered as the manufacturing method of the electrode body 20.

[0075] The preparation process (process 1) includes: a positive electrode preparation process (process 1A) of preparing a strip-shaped positive electrode 22 having a positive electrode active material layer 22a, and a negative electrode preparation process (process 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 can be purchased commercially or made by oneself.

[0076] The positive electrode preparation process (process 1A) may include, for example, the following steps in sequence: a positive electrode composite slurry preparation process (process 1A-1), a positive electrode composite slurry application process (process 1A-2), and a positive electrode composite slurry drying process (process 1A-3). The positive electrode preparation process (process 1A) may further include a pressing process for pressing a layer of positive electrode active material.

[0077] In the positive electrode composite slurry preparation process (process 1A-1), a positive electrode composite slurry containing at least a positive electrode active material is prepared. Specifically, the solid component materials of the aforementioned positive electrode active material layer 22a (e.g., positive electrode active material, conductive material, binder, various additives, etc.) are mixed with a specified solvent. As the solvent, a non-aqueous solvent such as N-methyl-2-pyrrolidone (NMP) is preferred. The solid content of the positive electrode composite slurry is preferably 70% by mass or more, and more preferably, for example, 70 to 85% by mass. It should be noted that in this specification, the term "slurry" refers to a mixture in which some or all of the solid components are dispersed in a solvent, and is a term that includes pastes, inks, etc.

[0078] In the positive electrode composite slurry application process (process 1A-2), the above-prepared positive electrode composite slurry is applied to the strip-shaped positive electrode current collector 22c. The application of the positive electrode composite slurry can be performed using conventionally known coating apparatus, such as a gravure coater, a notched wheel coater, a slot coater, or a die-casting coater. The coating conditions can also be the same as before. The coating width of the positive electrode composite slurry is the same as or greater than the coating width of the negative electrode composite slurry.

[0079] In the positive electrode slurry drying process (process 1A-3), the positive electrode current collector 22c, which has been coated with the positive electrode slurry, is dried using conventionally known methods (e.g., air drying, heat drying, vacuum drying, etc.) to remove the solvent from the positive electrode slurry on the positive electrode current collector 22c. From the viewpoint of manufacturing efficiency, heat drying is preferred. The heating temperature varies depending on the type of solvent used in the positive electrode slurry preparation process, and is preferably set to 75–125°C, more preferably increasing the temperature in stages within the above temperature range. As described above, by fixing a positive electrode active material layer 22a containing the positive electrode active material to at least one surface of the positive electrode current collector 22c, a strip-shaped positive electrode 22 can be obtained.

[0080] The negative electrode preparation process (process 1B) may include, for example, the following steps in sequence: negative electrode composite slurry preparation process (process 1B-1), negative electrode composite slurry application process (process 1B-2), and negative electrode composite slurry drying process (process 1B-3). The negative electrode preparation process (process 1B) may further include a pressing process for pressing a negative electrode active material layer.

[0081] 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 component materials of the aforementioned negative electrode active material layer 24a (e.g., negative electrode active material, binder, various additives, etc.) are mixed with a specified solvent. As the solvent, an aqueous solvent such as ion-exchanged water is preferred. The solid content of the negative electrode composite slurry is preferably 50% by mass or more, for example, more preferably 50 to 65% by mass.

[0082] In the negative electrode slurry application process (process 1B-2), the aforementioned prepared negative electrode slurry is applied to the strip-shaped negative electrode current collector 24c. The application of the negative electrode slurry can be performed using a conventionally known coating apparatus, depending on the application of the positive electrode slurry. The coating width of the negative electrode slurry is set to 200 mm or more.

[0083] In the negative electrode slurry drying process (process 1B-3), a conventionally known drying method is performed on the negative electrode current collector 24c to remove the solvent from the negative electrode slurry on the negative electrode current collector 24c. From the viewpoint of manufacturing efficiency, heating drying is preferable. The heating temperature varies depending on the type of solvent used in the negative electrode slurry preparation process, and is preferably set to 60 to 130°C, more preferably increasing the temperature in stages within the above temperature range. As described above, by fixing a negative electrode active material layer 24a containing negative electrode active material to at least one surface of the negative electrode current collector 24c, a strip-shaped negative electrode 24 can be obtained.

[0084] In the manufacturing process (process 2), the strip-shaped positive electrode 22 and strip-shaped negative electrode 24 prepared in the preparation process are stacked and wound in an insulated state (e.g., via a separately prepared strip-shaped separator 26) to create a wound body. The wound body can be manufactured by, for example, using a conventionally known winding device, winding the strip-shaped positive electrode 22, strip-shaped negative electrode 24, and strip-shaped separator 26 into a roll with the winding shaft WL as the center. It should be noted that the wound body obtained in this process (the wound body before the moisture absorption process) can be in a state where the central part and the ends in the direction of the winding shaft WL contain moisture in a substantially uniform manner.

[0085] In the desiccation process (process 3), the wound body is placed in a moisture-containing environment in a roll shape, and moisture is absorbed from the end of the winding axis (WL direction) of the wound body. Therefore, even if the moisture content of multiple electrode bodies 20 varies from batch to batch, such as up to the manufacturing process, the variation in moisture content per batch can be reduced. In a preferred embodiment, the wound body is stored for a predetermined time, for example, at atmospheric pressure in a place where temperature and humidity can be controlled. The temperature conditions for storing the wound body may vary depending on the drying conditions in the preparation process, the amount of moisture remaining in the wound body during the manufacturing process, etc., and are therefore not particularly limited. In several embodiments, the temperature for storing the wound body is preferably room temperature (20–30°C), more preferably 23–25°C. The humidity for storing the wound body is preferably 10–50% RH, more preferably 10–30% RH. In one example, it is preferable to place the wound body in an environment at room temperature and atmospheric pressure with a humidity of 10–50% RH. The preferred storage time is 24 hours or more (e.g., 24 to 240 hours), and more preferably 24 to 72 hours.

[0086] In this process, 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 WL direction becomes greater than the moisture content at the center of the wound body in the WL direction. Since the wound body is in a coil shape, moisture easily flows out from both ends in the WL direction during the drying process (process 5) described later, making drying easy. Therefore, by making the moisture content at the ends greater than the moisture content at the center, an electrode body 20 with a uniform moisture content in the WL direction can be easily obtained after the drying process described later.

[0087] In the housing process (process 4), the wound body obtained above is housed in the housing 10. Specifically, firstly, the positive electrode second current collector 52 is bonded to the positive electrode assembly 23 of the wound body, and the negative electrode second current collector 62 is bonded to the negative electrode assembly 25. Secondly, typically in a moisture-controlled environment (e.g., inside a glove box), the wound body is housed inside the outer packaging 12 through the opening 12h. Next, a sealing plate assembly is prepared that integrates the sealing plate 14, the positive terminal 30, the negative terminal 40, the positive electrode first current collector 51 of the positive current collector 50, the negative electrode first current collector 61 of the negative current collector 60, the positive electrode insulating member 70, the negative electrode insulating member 80, and the two gaskets 90. Next, the positive electrode second current collector 52 is bonded to the positive electrode first current collector 51 of the sealing plate assembly (e.g., by welding). Thus, the positive electrode 22 of the electrode body 20 is electrically connected to the positive terminal 30. Similarly, the negative electrode second current collector 62 is joined (e.g., welded) to the negative electrode first current collector 61 of the sealing plate assembly. Thus, the negative electrode 24 of the electrode body 20 is electrically connected to the negative terminal 40. This integrates the sealing plate assembly with the electrode body 20.

[0088] Next, a sealing plate 14 is welded around the opening 12h of the outer packaging body 12, integrating the outer packaging body 12 with the sealing plate 14. Thus, the shell 10 is constructed, resulting in a containment body. It should be noted that in this specification, the term "containment body" refers to a composite material containing the winding body and the shell 10 containing the winding body, excluding non-aqueous electrolyte (before liquid injection).

[0089] In several embodiments, the moisture content of the wound body before the drying process (arithmetic mean of the moisture content in the central part and the moisture content at the ends) is preferably 180 to 220 ppm, for example, by humidification in the moisture absorption process (process 3).

[0090] In the drying process (process 5), the wound body is dried. In this embodiment, the housing is dried with the injection hole 15 open, removing moisture from the interior of the housing 10. Specifically, a portion of the moisture inside the wound body is removed. Moisture removal can be performed by conventionally known drying methods, such as heating drying or vacuum drying, individually or in appropriate combinations. The heating temperature is preferably set to a temperature that allows moisture to evaporate appropriately without thermal degradation of the separator 26, etc. The heating temperature can vary depending on the material of the separator 26, etc., and is preferably set in, for example, the range of 50 to 150°C.

[0091] In this embodiment, the wound body is dried such that the average moisture content Mc in the central part and the moisture content Me at the end are 80 to 150 ppm, and the difference between the moisture content Mc in the central part and the moisture content Me at the end is less than ±20 ppm. In other words, drying is completed with a specified amount of moisture remaining in the wound body. As a result, an electrode body 20 with high thermal stability can be obtained. As for the drying conditions, they can be appropriately adjusted to reach the above-mentioned range of moisture content, for example, depending on the moisture content of the wound body after the moisture absorption process (process 3), and therefore there is no particular limitation.

[0092] In several embodiments, this process preferably includes, sequentially, a preheating step involving heating and drying at atmospheric pressure, and a vacuum drying step involving vacuum drying. While not particularly limited, the heating temperature of the preheating step is preferably set to 60°C or higher (e.g., 60–120°C), more preferably 70°C or higher (e.g., 70–110°C), and even more preferably 100–110°C or higher. The preheating time is preferably 1–10 hours, more preferably 3–6 hours.

[0093] While not particularly limited, the vacuum drying temperature in the vacuum drying process is preferably the same as or higher than the heating temperature in the preheating process. The vacuum drying temperature is preferably set to 60°C or higher (e.g., 60–120°C), more preferably 70°C or higher (e.g., 70–110°C), and even more preferably 100–110°C or higher. The vacuum degree in the vacuum drying process is preferably set to an absolute pressure of 100 Pa or less (so-called medium vacuum). The vacuum drying time is preferably 1–10 hours, more preferably 3–6 hours. This allows for the obtaining of an electrode body 20 in which a specified amount of moisture is intentionally retained.

[0094] In the electrolyte injection process (step 6), a non-aqueous electrolyte is injected into the housing 10 (the dried containment body) containing the electrode body 20. Specifically, firstly, a non-aqueous electrolyte is prepared. The non-aqueous electrolyte contains the aforementioned electrolyte salt (e.g., LiPF6) and a non-aqueous solvent (e.g., carbonates), and may further contain added components (additives). Then, the prepared non-aqueous electrolyte is injected into the interior of the housing 10 through the injection hole 15 of the sealing plate 14. Regarding the electrolyte injection, in order to improve the impregnation of the non-aqueous electrolyte into the electrode body 20, it is preferable to perform the injection under reduced pressure inside the housing 10. Thus, a battery assembly is obtained. It should be noted that the term "battery assembly" in this specification refers to an intermediate product assembled in the manufacturing process of the battery 100 up to the state before the initial charging process (step 7) is performed.

[0095] After electrolyte injection, in order to improve the impregnation of the non-aqueous electrolyte into the electrode body 20, especially towards the central portion in the direction of the winding shaft WL, it is preferable to appropriately apply pressure or vacuum. In one example, it is preferable to perform at least one of the following operations: with the battery assembly housed in a pressure-regulating chamber, and with the injection port 15 open (in other words, without a pressure difference between the inside and outside of the housing 10), depressurize the chamber at least once and maintain it in a vacuum state for a predetermined time; and pressurize the chamber at least once and maintain it in a pressurized state for a predetermined time.

[0096] In the initial charging step (step 7), the battery assembly is charged until at least a portion of the non-aqueous electrolyte decomposes. Charging of 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 is performed until a predetermined arrival voltage is reached between the positive and negative terminals. The arrival voltage is set to electrolyze at least a portion of the non-aqueous electrolyte (e.g., non-aqueous solvent, additives). As an example, when the negative electrode active material is a carbon material, the arrival voltage can be set to approximately 2.5V or higher, preferably 3V or higher, for example, 3.5V or higher, or 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, with alternating discharge, repeated two or more times. Through the initial charging, a film containing the decomposition products of the non-aqueous electrolyte (SEI film) is formed on the surface of the negative electrode active material layer 24a.

[0097] In the degassing process (process 8), 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 casing 10. The venting of the gas can be performed, for example, by creating a vacuum inside the casing 10.

[0098] In the sealing process (process 9), the injection port 15 is sealed with the sealing member 16. The sealing of the injection port 15 is preferably performed while the pressure inside the housing 10 is reduced. This results in the housing 10 being airtightly sealed (sealed).

[0099] In the aging process (step 10), the battery assembly with the injection hole 15 sealed is maintained at a specified temperature for a specified aging period. The aging temperature is preferably 25 to 70°C, for example, room temperature (approximately 25°C ± 10°C). The aging period varies depending on the aging temperature, but is preferably 24 hours or more. In this step, it is preferable to maintain the battery assembly under a specified constraint load while constrained in the thickness direction X (thickness direction of the electrode body 20). In this case, the constraint load can be 1 to 6 kN. As described above, the battery 100 can be suitably manufactured.

[0100] <Uses of Battery 100>

[0101] The battery 100 can be used for various purposes. For example, due to its high capacity and excellent thermal stability, it is suitable as a power source (drive power supply) for motors in vehicles such as cars and trucks. There are no particular limitations 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 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.

[0102] The following describes several embodiments related to the present invention, but it is not intended to limit the present invention to these embodiments.

[0103] In this experimental example, multiple battery assemblies with the same structure were constructed (Examples 1-3, Comparative Examples 1 and 2), and the thermal stability was studied when the drying conditions (moisture content in the electrode body) of the electrode body were different.

[0104] <Manufacturing of Secondary Batteries>

[0105] First, in the preparation process (process 1), strip-shaped positive and negative electrodes are prepared. Regarding the positive electrode, LiNi is first used as the active material. 0.6 Co 0.2 Mn 0.2O2, carbon material as a conductive material, and PVdF as a binder are mixed in a mass ratio of positive electrode active material: conductive material: PVdF = 97.5:1.5:1. NMP is added as a solvent to prepare a positive electrode composite slurry (79% by mass solids). Next, the prepared positive electrode composite slurry is coated onto a positive electrode current collector (aluminum foil) and dried to form a positive electrode active material layer. As described above, a strip-shaped positive electrode is obtained.

[0106] Regarding the negative electrode, graphite (as the negative electrode active material), SBR (as a binder), and CMC (as a binder) were mixed to form a negative electrode active material with a mass ratio of SBR:CMC = 98:1:1. Ion-exchanged water was added as a solvent to prepare a negative electrode composite slurry (56% by mass solids). Next, the prepared negative electrode composite slurry was coated onto a negative electrode current collector (copper foil) with a width of 285 mm and dried to form a negative electrode active material layer. The negative electrode was thus obtained as described above.

[0107] Secondly, in the manufacturing process (process 2), a heat-resistant separator is prepared, which has a functional layer (which also serves as a heat-resistant layer and an adhesive layer) containing alumina and PVdF on one side of a porous PE sheet. Next, the positive and negative electrodes prepared above are stacked through the separator and wound into a flat shape, thereby creating a rolled body (each fold is considered one turn, for a total of 33 turns).

[0108] Next, in the moisture absorption process (process 3), the manufactured wound body is stored in a storage room at room temperature (25°C) and atmospheric pressure with a humidity of 10% RH for 24 hours in a rolled state, allowing it to absorb moisture from the ends of the wound body along the winding axis. This adjusts the moisture content of the wound body (the arithmetic mean of the moisture content in the central part and the moisture content at the ends) to approximately 180–190 ppm. Next, in the containment process (process 4), the wound body with adjusted moisture content is contained in a housing, resulting in a containment body.

[0109] Secondly, in the drying process (process 5), the containers of Examples 1-3 and Comparative Example 1 were dried under the conditions shown in Table 1 with the injection hole open, so that the winding inside the shell was dried. For example, in Example 1, after preheating (heating temperature: 105°C, preheating time: 4 hours), vacuum drying was performed (vacuum drying temperature: 105°C, vacuum degree: 100 Pa, vacuum drying time: 220 minutes). However, this process was not performed on the container of Comparative Example 2.

[0110] Next, in the electrolyte injection process (process 6), a non-aqueous electrolyte is injected into the housing to obtain a battery assembly. As the non-aqueous electrolyte, in each example, a product containing LiPF6 as an electrolyte salt at a ratio of 13.3% by mass in a mixed solvent (non-aqueous solvent) containing EC, DMC, and EMC in a mass ratio of 29.1:31.5:22.4 is used.

[0111] Next, in the initial charging process (process 7), constant current charging was performed at a charging rate of 1C until 3V. Next, in the degassing process (process 8), the pressure inside the casing was reduced to -0.09MPa. Next, in the aging process (process 10), the battery assembly was placed at room temperature (25°C) under a constraint load of 4kN for more than 5 days. As described above, a lithium-ion secondary battery was manufactured.

[0112] <Determination of Moisture Content in Electrodes>

[0113] First, in a dry chamber with a dry air atmosphere, the lithium-ion secondary battery is disassembled, and the electrode body is removed from the casing. Next, the electrode body is unwound, and one turn each of the positive and negative electrodes located at the 17th turn (the middle circumference in the longitudinal direction) is cut off. Then, as... Figure 5 As shown, in the central part of the winding axis WL direction of the positive electrode ( Figure 5 Pc) and both ends ( Figure 5 Three 20mm × 20mm test pieces were cut from Pe1 and Pe2, respectively. Similarly, three 20mm × 20mm test pieces were cut from the center and both ends of the negative electrode along the winding axis. Note that the end is approximately 5mm inside the outermost part of the active material layer along the winding axis. Next, the three test pieces were placed as a group in a Karl Fischer moisture analyzer (Nitto Seiko Analytech, model CA-310). Then, using Mitsubishi Chemical's AQUAMICRON (registered trademark) as the Karl Fischer reagent, moisture was vaporized from the test pieces at a vaporization temperature of 150°C and a vaporization time of 2 minutes. The moisture reacting with the Karl Fischer reagent was quantified by electrostatic titration.

[0114] Secondly, for each positive and negative electrode, the two ends ( Figure 5 The quantitative values ​​of Pe1 and Pe2 were arithmetically averaged and designated as the "end" moisture content. Then, the moisture content at the end of the positive electrode and the moisture content at the end of the negative electrode were arithmetically averaged to calculate the "end moisture content Me of the electrode body". In addition, the moisture content at the center of the positive electrode and the moisture content at the center of the negative electrode were arithmetically averaged to calculate the "central moisture content Mc of the electrode body". The results are shown in Table 1.

[0115] <Calorie Evaluation>

[0116] First, the discharged battery was disassembled in a glove box under an Ar atmosphere. Next, the electrolyte was collected, and the positive and negative electrodes were each removed in 50mm × 115mm dimensions. Then, the positive and negative electrodes were positioned opposite each other via a separator and sealed together with the collected electrolyte in an aluminum bag to fabricate a laminated battery cell. Next, the fabricated laminated battery cell was fully charged, disassembled, and the negative electrode assembly was cut from the negative electrode. Next, the cut negative electrode assembly and electrolyte were placed together in a sample container (SUS dish). The sample container was then sealed under pressure at 20MPa and placed together with a standard substance (Al₂O₃, 2mg) in a differential scanning calorimeter (DSC: Differential Scanning Calorimetry, Shimadzu Corporation, model: DSC-60A). Then, after standing at 30°C for 85 minutes under an inactive atmosphere, the temperature was increased from 30°C to 350°C at a rate of 2°C / min to obtain the DSC curve. The calorific value (J) was calculated from the integral value (peak area value) between 100 and 180 °C of the obtained DSC plot. The results are shown in Table 1.

[0117] Table 1

[0118]

[0119] As shown in Table 1, in Comparative Example 2, which did not undergo a drying process, the average moisture content of the electrode body was relatively high. In Comparative Example 1, where the drying process was repeated twice, the average moisture content of the electrode body was relatively low. Furthermore, the heat generation in Comparative Examples 1 and 2 was relatively high. Compared to these comparative examples, in Examples 1 to 3, where the average moisture content Mc in the central part and Me at the end was 80–150 ppm and the difference between the moisture content Mc in the central part and Me at the end was less than ±20 ppm, heat generation was suppressed, and thermal stability was high. These results demonstrate the significance of the technology disclosed herein.

[0120] 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, features of the technology that are not described as essential features may be appropriately deleted.

[0121] As described above, specific embodiments of the technology disclosed herein can be listed in the following items.

[0122] Item 1: An electrode body is formed by stacking strip-shaped positive and negative electrodes in an insulating state and winding them in the longitudinal direction. The negative electrode has a negative electrode active material layer with a width of 200 mm or more in the winding axis direction orthogonal to the longitudinal direction. The positive electrode has 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. The average moisture content of the central portion and the moisture content of the ends, as determined by the following steps, 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 ends is less than ±20 ppm.

[0123] Step 1: Cut out one turn from each of the positive and negative electrodes located in the middle circumference of the longitudinal direction;

[0124] Step 2: For the positive electrode active material layer of the positive electrode, test pieces are cut out at the center and both ends in the winding axis direction, respectively; for the negative electrode active material layer of the negative electrode, test pieces are cut out at the center and both ends in the winding axis direction, respectively.

[0125] Step 3: For each test piece cut out in Step 2, the water content is quantified using the Karl Fischer method at heating temperatures ranging from room temperature to 150°C.

[0126] Step 4: Calculate the average of the water content in the central part of the positive electrode active material layer and the water content in the central part of the negative electrode active material layer as the "central part water content" of the electrode body, and calculate the average of the water content at both ends of the positive electrode active material layer and the water content at both ends of the negative electrode active material layer as the "end water content" of the electrode body.

[0127] Item 2: The electrode body according to Item 1, wherein the water content in the central portion is greater than the water content in the end portion.

[0128] Item 3: A method for manufacturing an electrode body, which is a method for manufacturing an electrode body according to Item 1 or Item 2, comprising: 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 stacking and winding the strip-shaped positive electrode and the strip-shaped negative electrode in an insulating state to form a wound body; and a drying step of drying the wound body, wherein, in the drying step, the wound body is dried such that the average moisture content of the central portion and the moisture content of the ends 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 ends is less than ±20 ppm.

[0129] Item 4: The manufacturing method according to Item 3, wherein, between the manufacturing step and the drying step, a moisture absorption step is further included: placing the wound body in a moisture-containing environment and absorbing moisture from the end of the wound body in the direction of the winding axis.

[0130] Item 5: According to the manufacturing method of Item 4, in the moisture absorption process, the wound body is placed in a moisture-containing environment until the moisture content at the end of the wound body in the winding axis direction becomes greater than the moisture content at the center of the wound body in the winding axis direction.

[0131] Item 6: The manufacturing method according to Item 4 or 5, wherein, in the moisture absorption process, the wound body is placed at room temperature and atmospheric pressure in an environment with a humidity of 10% RH or higher and 50% RH or lower.

[0132] Item 7: The manufacturing method according to any one of items 3 to 6, wherein the drying step includes: a preheating step of heating and drying at atmospheric pressure, at a temperature of 70°C or higher and 110°C or lower; and a vacuum drying step of vacuum drying at a temperature of 70°C or higher and 110°C or lower after the preheating step.

[0133] Item 8: A method for manufacturing a secondary battery, comprising: a construction step of constructing a battery assembly comprising an electrode body obtained by any one of the manufacturing methods of items 3 to 7, a non-aqueous electrolyte, and a casing housing 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 decomposes.

Claims

1. An electrode body, which is an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked in an insulating state and wound in a longitudinal direction, the negative electrode having a negative electrode active material layer having a width of 200 mm or more in a winding axis direction orthogonal to the longitudinal direction, the positive electrode having 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 average of the central portion moisture content and the end portion moisture content is 80 ppm or more and 150 ppm or less, and the difference between the central portion moisture content and the end portion moisture content is less than ± 20 ppm, which is obtained by the following steps: Step 1: cutting out an amount of one turn of the positive electrode and the negative electrode each from a middle peripheral portion in the longitudinal direction; Step 2: cutting out test pieces from the central portion and both end portions in the winding axis direction for the positive electrode active material layer of the positive electrode, and cutting out test pieces from the central portion and both end portions in the winding axis direction for the negative electrode active material layer of the negative electrode; Step 3: quantifying the moisture content of each of the test pieces cut out in Step 2 by the Karl Fischer method at a heating temperature of room temperature to 150°C; Step 4: calculating the average of the central portion moisture content of the positive electrode active material layer and the central portion moisture content of the negative electrode active material layer as the "central portion moisture content" of the electrode body, and calculating the average of the end portion moisture content of the positive electrode active material layer and the end portion moisture content of the negative electrode active material layer as the "end portion moisture content" of the electrode body.

2. The electrode body of claim 1, wherein, The central portion moisture content is more than the end portion moisture content.

3. A method of manufacturing an electrode body, which is the method of manufacturing the electrode body according to claim 1, comprising: a preparation step of preparing a strip-shaped negative electrode having a negative electrode active material layer having a width of 200 mm or more in a winding axis direction, and a strip-shaped positive electrode having 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; a production step of stacking the strip-shaped positive electrode and the strip-shaped negative electrode in an insulating state and winding them, thereby producing a wound body; and a drying step of drying the wound body, wherein in the drying step, the wound body is dried in such a manner that the average of the central portion moisture content and the end portion moisture content is 80 ppm or more and 150 ppm or less, and the difference between the central portion moisture content and the end portion moisture content is less than ± 20 ppm.

4. The manufacturing method according to claim 3, wherein, The method further includes, between the production step and the drying step, a moisture absorption step of placing the wound body in an environment in which moisture is present, and absorbing moisture from the end portions in the winding axis direction of the wound body.

5. The manufacturing method according to claim 4, wherein, In the moisture absorption step, the wound body is placed in an environment in which moisture is present until the moisture content of the end portions in the winding axis direction of the wound body becomes more than the moisture content of the central portion in the winding axis direction of the wound body.

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

7. The production method according to claim 4, 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.

8. A manufacturing method of a secondary battery, 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 nonaqueous electrolyte, and a case that houses the electrode body and the nonaqueous electrolyte; and an initial charging step of charging the battery assembly until at least a part of the nonaqueous electrolyte is decomposed. ​

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