Energy storage device and method for manufacturing an energy storage device

Abstract

To provide an energy storage device with excellent thermal stability. [Solution] In the energy storage device disclosed herein, the negative electrode has a negative electrode active material layer with a length of 200 mm or more in the winding axis direction, and the full width at half maximum (Lh / La) calculated based on the ratio of boron elements (B / C) in the central part of the negative electrode active material layer in the winding axis direction is 0.17 or less.

Description

Technical Field

[0001] The present invention relates to a power storage device and a method for manufacturing the power storage device.

Background Art

[0002] Conventionally, a power storage device including a wound electrode body formed by laminating and winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state, and a non-aqueous electrolyte has been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power storage device, typically, a part of the non-aqueous electrolyte is decomposed during the first charge, and a film (Solid Electrolyte Interface film: SEI film) containing the decomposition products is formed on the surface of the negative electrode. This film stabilizes the interface between the negative electrode active material layer and the non-aqueous electrolyte.

[0005] In recent high-capacity power storage devices, the width in the winding axis direction of the wound electrode body has become longer, and it has become difficult for the non-aqueous electrolyte to penetrate into the central portion in the winding axis direction. According to the study by the present inventors, due to this, film formation becomes insufficient in the central portion of the negative electrode active material layer, and there is a risk that the thermal stability is likely to decrease.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a power storage device having excellent thermal stability.

Means for Solving the Problems

[0007] The present invention provides an energy storage device comprising a wound electrode body formed by stacking and winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state, a non-aqueous electrolyte, and a case for housing the wound electrode body and the non-aqueous electrolyte. The above-mentioned negative electrode has a negative electrode active material layer containing carbon material and having a length of 200 mm or more in the winding axis direction, and the negative electrode active material layer is provided with a coating containing boron element, and the ratio of boron element to carbon element (B / C) along the winding axis direction is determined by laser ablation ICP mass spectrometry at the central part of the negative electrode active material layer in the winding axis direction, and the following procedure: (Procedure 1) Create a graph with the measurement position in the winding axis direction on the horizontal axis and the ratio (B / C) on the vertical axis; (Procedure 2) Draw a baseline connecting the two ends of the winding axis direction in the central part, and measure the width at half maximum at the position where the width of the straight line drawn from the peak position with the smallest value of the ratio (B / C) along the vertical axis to the baseline is halved; (Procedure 3) Divide the width at half maximum by the length of the negative electrode active material layer in the winding axis direction; The resulting width at half maximum ratio is 0.17 or less.

[0008] As a result of diligent research, the inventors have found that the above-mentioned full width at half maximum (FWHM) is correlated with thermal stability. With the above configuration, an energy storage device with excellent thermal stability can be realized. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic perspective view showing an energy storage device according to one embodiment. [Figure 2] Figure 2 is a schematic longitudinal cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view along the line III-III in Figure 1. [Figure 4] Figure 4 is a schematic perspective view showing the electrode assembly attached to the sealing plate. [Figure 5] Figure 5 is a schematic perspective view showing a wound electrode body according to one embodiment. [Figure 6] Figure 6 is a schematic diagram showing the configuration of a wound electrode body according to one embodiment. [Figure 7]Figure 7 is a graph showing the pattern of pressure changes during the impregnation process. [Figure 8] Figure 8 is a schematic diagram of the sample used for measurement. [Figure 9] Figure 9 is a graph showing the distribution of the ratio (B / C) related to Example 1. [Figure 10] Figure 10(a) is a graph showing the distribution of the ratio (B / C) for Comparative Example 1, Figure 10(b) is a graph showing the distribution of the ratio (B / C) for Comparative Example 2, Figure 10(c) is a graph showing the distribution of the ratio (B / C) for Example 2, Figure 10(d) is a graph showing the distribution of the ratio (B / C) for Example 3, and Figure 10(e) is a graph showing the distribution of the ratio (B / C) for Comparative Example 3. [Figure 11] Figure 11 is a graph showing the relationship between the first waiting time and the half-width ratio. [Figure 12] Figure 12 is a graph showing the relationship between the full width at half maximum (FWHM) and the heat generated at the negative electrode. [Modes for carrying out the invention]

[0010] Hereinafter, with reference to the drawings, several preferred embodiments of the technology disclosed herein will be described. Matters other than those specifically mentioned herein but necessary for carrying out the present invention (e.g., general configuration and manufacturing processes of energy storage devices not characterizing the present invention) can be understood as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the content disclosed herein and common technical knowledge in the art. In this specification, the notation "A to B" indicating a range encompasses not only the meaning of A or greater and B or less, but also the meanings of "greater than A" and "less than B".

[0011] In this specification, "energy storage device" refers to all energy storage devices that can be repeatedly charged and discharged by the movement of charge carriers between the positive and negative electrodes via a non-aqueous electrolyte. The concept of energy storage devices includes 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 pseudocapacitance capacitors.

[0012] <Battery 100> FIG. 1 is a perspective view of a power storage device (hereinafter, also simply referred to as a battery) 100. FIG. 2 is a schematic longitudinal sectional view taken along line II-II of FIG. 1. FIG. 3 is a schematic cross-sectional view taken along line III-III of FIG. 1. In the following description, the reference signs L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, upper, and lower, respectively, and the reference signs X, Y, and Z in the drawings represent the short-side direction, the long-side direction orthogonal to the short-side direction, and the up-down direction orthogonal to the short-side direction and the long-side direction of the battery 100, respectively. The long-side direction Y is an example of the winding axis direction. However, these are merely directions for convenience of explanation and do not limit the installation form of the battery 100 in any way.

[0013] As shown in FIG. 2, the battery 100 includes a case 10, an electrode body group 20, and a non-aqueous electrolyte (not shown). Here, the battery 100 further includes a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, and a negative electrode current collector 60. Here, the battery 100 is a non-aqueous electrolyte secondary battery, specifically a lithium-ion secondary battery. The battery 100 is preferably a lithium-ion secondary battery.

[0014] The case 10 is a housing that houses the electrode body group 20 and the non-aqueous electrolyte. As shown in FIG. 1, the case 10 here has an outer shape of a flat and bottomed rectangular parallelepiped (rectangular). 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. 2, the case 10 here includes an exterior body 12 having an opening 12h and a sealing plate (lid body) 14 that closes the opening 12h.

[0015] As shown in FIG. 1, the outer package 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 wall 12b is larger than the area of the short side wall 12c. In this specification, the term "substantially rectangular" includes, in addition to a perfect rectangular shape (rectangular shape), for example, a shape in which the corners connecting the long side and the short side of the rectangular shape are R-shaped, a shape having a notch at the corner, and the like.

[0016] As shown in FIG. 1, the sealing plate 14 is substantially rectangular in plan view. As shown in FIG. 2, the sealing plate 14 is attached to the outer package 12 so as to close the opening 12h of the outer package 12. The sealing plate 14 faces the bottom wall 12a of the outer package 12. The case 10 is integrated by joining (for example, welding) the sealing plate 14 to the peripheral edge of the opening 12h of the outer package 12. The case 10 is hermetically sealed.

[0017] As shown in FIG. 2, the sealing plate 14 is provided with a liquid injection hole 15, a gas discharge valve 17, and two terminal lead-out holes 18, 19. The liquid injection hole 15 is for injecting a non-aqueous electrolyte after assembling the sealing plate 14 to the outer package 12. It is preferable that the sealing plate 14 is provided with the liquid injection hole 15. The liquid injection hole 15 is sealed by a sealing member 16. The gas discharge valve 17 is configured to break when the pressure inside the case 10 reaches a predetermined value or more and discharge the gas inside the case 10 to the outside. The terminal lead-out holes 18, 19 are formed at both ends in the long side direction Y of the sealing plate 14 (the left end and the right end in FIG. 2), respectively. The terminal lead-out holes 18, 19 penetrate the sealing plate 14 in the thickness direction (vertical direction Z). The terminal lead-out holes 18, 19 have an inner diameter large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 before being attached to the sealing plate 14 (before caulking) to be inserted therethrough.

[0018] The positive terminal 30 and the negative terminal 40 are fixed to the sealing plate 14 of the case 10. The positive terminal 30 is located on one side of the sealing plate 14 in the long side direction Y (left side in Figures 1 and 2). The negative terminal 40 is located on the other side of the sealing plate 14 in the long side direction Y (right side in Figures 1 and 2). As shown in Figure 2, the positive terminal 30 extends from the inside to the outside of the sealing plate 14 through the terminal lead hole 18. The negative terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal lead hole 19. It is preferable that the positive terminal 30 and the negative terminal 40 are attached to the sealing plate 14. Here, the positive terminal 30 and the negative terminal 40 are crimped to the peripheral portion surrounding the terminal lead holes 18 and 19 of the sealing plate 14 by a crimping process. Crimped portions 30c and 40c are formed at the ends of the outer casing 12 on the positive terminal 30 and the negative terminal 40 (the lower ends in Figure 2).

[0019] As shown in Figure 2, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see Figure 6, specifically the positive electrode tab group 23) of the electrode group 20 via the positive electrode current collector 50 inside the case 10. The positive electrode terminal 30 is insulated from the sealing plate 14 by the positive electrode insulating member 70 and the gasket 90. The positive electrode terminal 30 is preferably made of metal, and more preferably of aluminum or an aluminum alloy, for example.

[0020] The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see Figure 6, specifically the negative electrode tab group 25) of the electrode group 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 of copper or a copper alloy. The negative electrode terminal 40 may be constructed by joining and integrating two conductive members. For example, the portion of the negative electrode terminal 40 connected to the negative electrode current collector 60 may be made of copper or a copper alloy, and the portion exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0021] Plate-shaped positive electrode external conductive member 32 and 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 negative electrode external conductive member 42 are members to which busbars are attached when multiple batteries 100 are electrically connected 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 negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external resin member 92. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example. However, the positive electrode external conductive member 32 and negative electrode external conductive member 42 are not essential and can be omitted in other embodiments.

[0022] The electrode group 20 is housed inside the case 10 (more specifically, inside the outer casing 12), as shown in Figure 2. Figure 4 is a schematic perspective view showing the electrode group 20 attached to the sealing plate 14. The electrode group 20 here has three electrodes 20a, 20b, and 20c. When three or more electrodes 20a, 20b, and 20c are arranged inside one case 10, the electrode 20b located in the center of the short-side direction X may be particularly difficult to impregnate with the non-aqueous electrolyte. Therefore, applying the technique disclosed herein is particularly effective. However, the number of wound electrodes arranged inside one case 10 is not particularly limited and may be one or two or more.

[0023] The electrode group 20 may be placed inside the case 10, covered by an insulating electrode holder. In other words, an electrode holder may be interposed between the electrode group 20 and the case 10 (specifically, the outer casing 12). The electrode holder is preferably made of resin.

[0024] Figure 5 is a schematic perspective view of the electrode body 20a. Figure 6 is a schematic diagram showing the configuration of the electrode body 20a. In the following, the electrode body 20a will be explained in detail as an example, but the electrode bodies 20b and 20c can have similar configurations. As shown in Figure 6, the electrode body 20a is a wound electrode body in which a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 are stacked in an insulated state (for example, via a strip-shaped separator 26) and wound around a winding axis WL.

[0025] When the electrode body 20a is a wound electrode body, the non-aqueous electrolyte is supplied only from both ends in the winding axis WL direction. Therefore, the non-aqueous electrolyte does not easily penetrate the central part of the electrode body 20a in the winding axis WL direction, and the amount of coating tends to be insufficient in that central part. Accordingly, it is effective to apply the technology disclosed herein.

[0026] While not particularly limited, the number of turns of the electrode body 20a is preferably 20 turns or more, more preferably 30 turns or more, for example 50 turns or more, and may be, for example, 150 turns or less, or 100 turns or less. As the number of turns increases, it becomes more difficult for the non-aqueous electrolyte to penetrate the central part of the electrode body 20a (the central part in the short side direction X and the central part in the long side direction Y). Therefore, applying the techniques disclosed herein is particularly effective.

[0027] As can be seen from Figures 2 and 6, the electrode body 20a is positioned inside the case 10 with its orientation aligned with the bottom wall 12a (in other words, with the winding axis WL approximately parallel to the long side direction Y). The winding axis WL direction is in this case the same direction as the long side direction Y. The electrode body 20a is positioned inside the case 10 with its winding axis WL parallel to the bottom wall 12a and perpendicular to the short side walls 12c. The electrode body 20a has a pair of end faces (open ends) in the winding axis WL direction that face a pair of short side walls 12c of the outer casing 12. The end faces of the electrode body 20a in the winding axis WL direction serve as inlets for the non-aqueous electrolyte to flow in. In such cases, the application of the technology disclosed herein is particularly effective.

[0028] In this embodiment, the battery 100 has a so-called lateral tab structure, where the positive electrode tab group 23 and the negative electrode tab group 25 are located at both ends of the electrode body 20a in the winding axis WL direction (left and right in Figures 2 and 4). However, in other embodiments, the battery 100 may have a so-called upper tab structure, where the positive electrode tab group 23 and the negative electrode tab group 25 are located at one end of the electrode body 20a in the winding axis WL direction (for example, the upper end in Figures 2 and 4). In this case, the winding axis WL direction may coincide with the vertical direction Z.

[0029] As shown in Figure 5, the electrode body 20a has a flattened shape. It is preferable that the electrode body 20a has a flattened shape. The electrode body 20a has a pair of flat portions 20f that extend along the long side direction Y (winding axis WL direction) and a pair of curved portions (R portions) 20r that connect the pair of flat portions 20f. The flat portions 20f have a flat outer surface (YZ plane in Figure 5). The curved portions 20r have a curved outer surface. In this specification, "flat outer surface" is not limited to perfectly flat surfaces, but includes cases where there are slight steps, curves, recesses, protrusions, etc., when viewed microscopically.

[0030] As can be seen from Figures 2 and 5, in this embodiment, the pair of flat portions 20f face the pair of long side walls 12b of the outer casing 12. The flat portions 20f extend along the long side walls 12b. The pair of curved portions 20r face the bottom wall 12a and the sealing plate 14 of the outer casing 12. The electrode body 20a is preferably arranged inside the case 10 in such a way that the stacking direction (thickness direction) of the positive electrode 22 (see Figure 6) and negative electrode 24 (see Figure 6) in the flat portion 20f coincides with the short side direction X (direction perpendicular to the long side walls 12b), as in this embodiment.

[0031] The positive electrode 22 can be the same as in the conventional design and is not particularly limited. As shown in Figure 6, 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, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode current collector 22c is a metal foil, specifically an aluminum foil.

[0032] Multiple positive electrode tabs 22t are provided at one end (the left end in Figure 6) of the positive electrode current collector 22c in the long side direction Y (winding axis WL direction). Each of the multiple positive electrode tabs 22t is convex and protrudes toward one side (the left side in Figure 6) in the long side direction Y. The multiple positive electrode tabs 22t extend further in the long side direction Y than the separator 26. The multiple positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the positive electrode 22. By providing multiple positive electrode tabs 22t, the resistance of the battery 100 can be reduced. The positive electrode tabs 22t are, in this case, part of the positive electrode current collector 22c and are made of metal foil (aluminum foil).

[0033] As shown in Figure 3, multiple positive electrode tabs 22t are stacked at one end in the long side direction Y (the left end in Figure 3) to form a positive electrode tab group 23. In this embodiment, the multiple positive electrode tabs 22t are stacked and bent so that their outer ends are aligned. This improves the ability to fit into the case 10 and allows for miniaturization of the battery 100. It also improves the volumetric energy density of the battery 100. The positive electrode tab group 23 is attached (more specifically joined) to the positive electrode second current collector 52 of the positive electrode current collector 50, which will be described later. The multiple positive electrode tabs 22t are connected to the positive electrode second current collector 52 in this stacked and bent state. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50.

[0034] As shown in Figure 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (for example, a lithium transition metal composite oxide such as a lithium nickel cobalt manganese-containing composite oxide) that can reversibly absorb and release charge carriers. The positive electrode active material layer 22a may also contain optional components other than the positive electrode active material, such as conductive materials, binders, and various additives. As a conductive material, for example, a carbon material such as acetylene black (AB) can be used. As a binder, for example, polyvinylidene fluoride (PVdF) can be used.

[0035] In high-capacity batteries 100 used for automotive applications, etc., as shown in Figure 6, the length Lc (average value, excluding the portion formed on the positive electrode tab 22t) of the positive electrode active material layer 22a in the long side direction Y (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 length Lc is preferably the same as or shorter than the length La in the long side direction Y of the negative electrode active material layer 24a, which will be described later.

[0036] As shown in Figure 6, 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 long side direction Y. Here, the positive electrode protective layer 22p is provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in Figure 6). 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 also contain optional components other than the inorganic filler, such as conductive materials, binders, various additives, etc. The conductive material and binder may be the same as those exemplified as those that may be included in the positive electrode active material layer 22a.

[0037] As shown in Figure 6, 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, copper alloy, nickel, or stainless steel. Preferably, the negative electrode current collector 24c contains copper or a copper alloy. In this case, the negative electrode current collector 24c is a metal foil, specifically a copper foil.

[0038] Multiple negative electrode tabs 24t are provided at one end (the right end in Figure 6) of the negative electrode current collector 24c in the long side direction Y (winding axis WL direction). Each of the multiple negative electrode tabs 24t is convex and protrudes toward one side (the right side in Figure 6) in the long side direction Y. The multiple negative electrode tabs 24t extend further in the long side direction Y than the separator 26. The multiple negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the negative electrode 24. By providing multiple negative electrode tabs 24t, the resistance of the battery 100 can be reduced. The negative electrode tabs 24t are, in this case, part of the negative electrode current collector 24c and are made of metal foil (copper foil). At least a part of the negative electrode tab 24t is a current collector exposed portion where the negative electrode current collector 24c is exposed without the negative electrode active material layer 24a being formed.

[0039] As shown in Figure 3, multiple negative electrode tabs 24t are stacked at one end in the long side direction Y (the right end in Figure 3) to form a negative electrode tab group 25. In this embodiment, the multiple negative electrode tabs 24t are stacked and bent so that their outer ends are aligned. This improves the ability to fit into the case 10 and allows for miniaturization of the battery 100. It also improves the volumetric energy density of the battery 100. The negative electrode tab group 25 is attached (more specifically joined) to the negative electrode second current collector 62 of the negative electrode current collector 60, which will be described later. The multiple negative electrode tabs 24t are connected to the negative electrode second current collector 62 in this stacked and bent state. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60.

[0040] As shown in Figure 6, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite, or a silicon material containing silicon) that can reversibly absorb and release charge carriers. The negative electrode active material layer 24a essentially contains a carbon material. The carbon material can typically be included as the negative electrode active material. When the total solid content of the negative electrode active material layer 24a is taken as 100% by mass, the negative electrode active material (e.g., graphite or carbon material) may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The negative electrode active material layer 24a may also contain optional components other than the negative electrode active material, such as binders, dispersants, and various additives. As a binder, for example, rubbers such as styrene-butadiene rubber (SBR) can be used. As a dispersant, celluloses such as carboxymethylcellulose (CMC) can be used.

[0041] As shown in Figure 6, the length La (average value, excluding the portion formed on the negative electrode tab 24t) of the negative electrode active material layer 24a in the long side direction Y (winding axis WL direction) is typically the same as or longer than the length Lc of the positive electrode active material layer 22a in the long side direction Y. In this embodiment, the length La of the negative electrode active material layer 24a is 200 mm or more from the viewpoint of increasing capacity, etc. A length La of 250 mm or more is preferable. In the electrode body 20a, the longer the length La, the greater the central M in the long side direction Y. Y The non-aqueous electrolyte does not easily penetrate the central area, including (see Figure 5). As a result, the coating amount tends to be insufficient in the central area along the long side direction Y. Therefore, applying the technology disclosed herein is effective. The length La may be, for example, 1000 mm or less, or 500 mm or less. This allows the technology disclosed herein to be effective at a high level.

[0042] As shown in Figure 5, the height Ha of the negative electrode active material layer 24a located in the flat portion 20f of the electrode body 20a (same as the height of the flat portion 20f) is preferably 110 mm or less, more preferably 50 to 110 mm, even more preferably 70 to 100 mm, and particularly preferably 70 to 90 mm. In the flat portion 20f, the ratio of the length La in the long side direction Y to the height Ha of the negative electrode active material layer 24a (horizontal / vertical ratio) is preferably 1 to 10, more preferably 2 to 7, and even more preferably 3 to 5. This allows the effects of the technology disclosed herein to be realized at a high level.

[0043] The negative electrode active material layer 24a is provided with a coating (SEI film) containing boron (B). This boron is a component derived from a boron-containing compound (B-containing compound), such as a film-forming agent described later, which was added to the non-aqueous electrolyte during the construction of the battery 100. The coating is a decomposition product containing the B-containing compound, which was decomposed during the initial charging described later. Because the boron-containing coating has excellent stability, it can suitably improve the durability and thermal stability of the battery 100.

[0044] As shown in Figure 6, the separator 26 is a component that insulates the positive electrode active material layer 22a of the positive electrode 22 and the negative electrode active material layer 24a of the negative electrode 24. The length Ls of the separator 26 in the long side direction Y (winding axis WL direction) is typically the same as or longer than the length La of the negative electrode active material layer 24a in the long side direction Y. 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 an adhesive layer or a heat resistance layer (HRL) on the surface of the base material portion made of a porous sheet made of resin. The adhesive layer is a layer containing a binder. The heat resistance layer is a layer containing, for example, an inorganic filler such as alumina, silica, boehmite, magnesia, or titania, and a binder such as PVdF. The heat resistance layer can also serve as the adhesive layer. The composition of the heat-resistant layer and adhesive layer may be the same as in the conventional method.

[0045] As shown in Figure 2, the positive electrode current collector 50 constitutes a conductive path that electrically connects the group of positive electrode tabs 23, which consists of a plurality of positive electrode tabs 22t, to the positive electrode terminal 30. The positive electrode current collector 50 may be made of the same metal type as the positive electrode current collector 22c, for example, a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. The positive electrode current collector 50 comprises a first positive electrode current collector 51 connected to the positive electrode terminal 30 and a second positive electrode current collector 52 connected to the group of positive electrode tabs 23. The first positive electrode current collector 51 is attached to the inner surface of the sealing plate 14.

[0046] The positive electrode second current collector 52 extends along the short side wall 12c of the outer casing 12. The positive electrode second current collector 52 is attached to the positive electrode tab group 23 of the electrode body 20a. As shown in Figure 3, a joint J is formed between the positive electrode second current collector 52 and the positive electrode tab group 23. The joint J is a welded joint formed by welding, such as ultrasonic welding, resistance welding, or laser welding, with multiple positive electrode tabs 22t stacked on top of each other. The joint J is arranged with multiple positive electrode tabs 22t positioned towards one side (the front side in Figure 3) in the short-side direction X of the electrode bodies 20a, 20b, and 20c. This allows for the advantageous bending of multiple positive electrode tabs 22t in a stacked state, stably forming a curved positive electrode tab group 23.

[0047] As shown in Figure 2, the negative electrode current collector 60 constitutes a conductive path that electrically connects the negative electrode tab group 25, which consists of a plurality of negative electrode tabs 24t, to the negative electrode terminal 40. The negative electrode current collector 60 may be made of the same metal type as the negative electrode current collector 24c, for example, a conductive metal such as copper, copper alloy, nickel, or stainless steel. The negative electrode current collector 60 includes a negative electrode first current collector 61 connected to the negative electrode terminal 40 and a negative electrode second current collector 62 connected to the negative electrode tab group 25. 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.

[0048] The second negative electrode current collector 62 is attached to the negative electrode tab group 25 of the electrode body 20a. As shown in Figure 3, a joint J is formed between the second negative electrode current collector 62 and the negative electrode tab group 25. Similar to the positive electrode side, the joint J is a welded joint formed by welding, such as ultrasonic welding, resistance welding, or laser welding, with multiple negative electrode tabs 24t stacked on top of each other. The joint J is arranged with multiple negative electrode tabs 24t positioned towards one side (the front side in Figure 3) in the short-side direction X of the electrode bodies 20a, 20b, and 20c. This allows for the multiple negative electrode tabs 24t to be suitably bent in a stacked state, stably forming a curved negative electrode tab group 25.

[0049] Non-aqueous electrolytes typically contain a non-aqueous solvent and an electrolyte salt (supporting salt). One or more non-aqueous solvents conventionally known for use in energy storage devices can be used. Examples of non-aqueous solvents include organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. It is preferable that the non-aqueous solvent contains carbonates. Examples of carbonates include linear carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as propylene carbonate (PC).

[0050] The electrolyte salt is not particularly limited as long as it contains a charge carrier (typically lithium ions), and one or more types of electrolyte salts that have been conventionally known to be usable in energy storage devices can be used. Examples of electrolyte salts include fluorine-containing lithium salts such as LiPF6 and LiBF4, and fluorine-containing sodium salts such as NaPF6. It is preferable that the electrolyte salt contains LiPF6.

[0051] The non-aqueous electrolyte may also contain additional additives. As additives, one or more types of those conventionally known to be addable to non-aqueous electrolytes can be used. Examples include boron-based additives containing boron, such as lithium bisoxalate borate (LiBOB) and lithium difluoro(oxalato) borate (LiODFB); and phosphorus-based additives containing phosphorus, such as lithium difluorophosphate (LiPO2F2) and lithium difluorooxalate phosphate (LiDFOP). These additives may decompose (at a low potential) before the non-aqueous solvent and / or electrolyte salt during the initial charge, and deposit as a film on the surface of the negative electrode active material layer 24a, thus acting as so-called film-forming agents.

[0052] The non-aqueous electrolyte preferably contains a compound containing boron (B), such as a lithium salt containing boron (B-containing lithium salt). Examples of B-containing compounds (e.g., B-containing lithium salts) include oxalate complex compounds containing boron, such as LiBF4 as a supporting salt as exemplified above, and LiBOB, LiODFB, etc. as boron-based additives as exemplified above.

[0053] Furthermore, additives added to the non-aqueous electrolyte during manufacturing (for example, the boron-based additives mentioned above) are electrically decomposed during the initial charge, etc., and consumed to form a film on the negative electrode active material layer 24a, etc. Therefore, in the state of battery 100, the non-aqueous electrolyte may or may not contain (remain in) the additives mentioned above.

[0054] Incidentally, according to the inventors' studies, in the electrode body 20a, the length (width) of the negative electrode active material layer 24a in the long side direction Y (winding axis WL direction) is 200 mm or more, which is longer than conventional materials, in order to increase capacity, etc. As a result, the non-aqueous electrolyte does not easily penetrate to the center of the long side direction Y. According to the inventors' studies, this may lead to insufficient film formation in the center of the negative electrode active material layer 24a in the long side direction Y, which may easily reduce thermal stability.

[0055] Therefore, in the technology disclosed herein, the amount of carbon and boron elements is measured along the winding axis WL direction by laser ablation ICP mass spectrometry (LA-ICP-MS) at the central part of the negative electrode active material layer 24a, and the ratio of boron to carbon (B / C) is determined. For example, as shown in Figure 9 (test example) described later, the following procedure is followed: (Procedure 1) Create a graph with the measurement position in the winding axis WL direction on the horizontal axis and the above ratio (B / C) on the vertical axis; (Procedure 2) A base is drawn connecting the two ends (E1, E2) of the winding axis WL direction at the central part of the negative electrode active material layer 24a. A line BL is drawn, and the width W of the straight line drawn from the peak position P1 with the smallest ratio (B / C) along the vertical axis to the baseline BL is used as a reference. At the position where the width W of the above straight line is halved (1 / 2W), the full width at half maximum Lh (mm) along the horizontal axis is measured; (Step 3) The full width at half maximum Lh (mm) is divided by the length La (mm) of the winding axis WL direction of the negative electrode active material layer 24a; the resulting full width at half maximum ratio (Lh / La) is set to 0.17 or less.

[0056] As will be described in detail in the examples below, our inventors' studies have shown that the above-mentioned full width at half maximum (or full width at half maximum Lh) correlates with the amount of heat generated. Specifically, the smaller the value of the above-mentioned full width at half maximum, the less heat is generated. Therefore, by setting the value of the full width at half maximum to a predetermined value or less, we can provide a battery 100 with excellent thermal stability. Furthermore, the time required for impregnation with the non-aqueous electrolyte can also be shortened.

[0057] In this specification, "the central part of the negative electrode active material layer in the winding axis direction" refers to the central part M of the negative electrode active material layer 24a in the winding axis direction WL. Y (See Figure 5) Includes the central M Y With the reference point (center), this refers to a range of approximately 49% (with an error of about ±1%) of the total length La (mm) of the negative electrode active material layer 24a in the winding axis direction WL. For example, if the length La (mm) is 286 mm, the center M in the winding axis direction WL (long side direction Y) is... Y This refers to a range of approximately ±70mm (totaling approximately 140mm) from the specified value.

[0058] From the viewpoint of demonstrating the effects of the technologies disclosed herein at a high level, the full width at half maximum (Lh / La) is preferably 0.16 or less, more preferably 0.15 or less, and even more preferably 0.13 or less. From the viewpoint of suppressing resistance and improving work efficiency and productivity, the full width at half maximum (Lh / La) is preferably 0.05 or more, and more preferably 0.1 or more.

[0059] Furthermore, the above-mentioned full width at half maximum (or full width at half maximum Lh) can be suitably adjusted not only by the amount of non-aqueous electrolyte injected during the construction of the battery 100 and the concentration of additives (compounds containing boron element) in the non-aqueous electrolyte, but also by conditions in the impregnation process (step 2) in the manufacturing method described later, particularly the waiting time before pressurization begins and the pressurization conditions.

[0060] <Method for manufacturing battery 100> The battery 100 described above can be manufactured, for example, by a manufacturing method that includes the following steps in this order: a battery assembly construction step (step 1), an impregnation step (step 2), and an initial charging step (step 3). However, other steps may be included at any stage. For example, a conventionally known aging step (step 4) may be included after the initial charging step (step 3).

[0061] In the construction process (step 1), the electrode group 20 (electrodes 20a, 20b, 20c) is placed inside the case 10, and a non-aqueous electrolyte is poured in to construct the battery assembly. In this specification, "battery assembly" refers to an intermediate product assembled to the state before the initial charging process (step 3) in the manufacturing process of the battery 100.

[0062] In one preferred embodiment, the process typically includes a placement step (step 1-1), a welding step (step 1-2), a drying step (step 1-3), and a liquid injection step (step 1-4), in this order. However, the drying step (step 1-3) is optional and can be omitted in other embodiments. In other embodiments, the order of the welding step (step 1-2) and the drying step (step 1-3) may be reversed. Furthermore, other steps may be included at any stage.

[0063] In the placement process (step 1-1), the electrode group 20 is placed inside the outer casing 12. In this embodiment, for example, first, as shown in Figure 4, a combined body is made in which the sealing plate 14 and the electrode group 20 are integrated. Next, the electrode group 20 is housed inside the outer casing 12 by fitting the sealing plate 14 into the opening 12h of the outer casing 12. As a result, the electrodes 20a, 20b, and 20c are housed inside the outer casing 12 with their winding axis WL oriented along the bottom wall 12a. Next, in the welding joining process (step 1-2), the sealing plate 14 is welded to the periphery of the opening 12h of the outer casing 12 to integrate the outer casing 12 and the sealing plate 14.

[0064] Next, in the drying process (steps 1-3), with the liquid injection hole 15 open, the outer casing 12 containing the electrode group 20 is dried to remove moisture from inside the outer casing 12. In particular, moisture inside the electrode group 20 is removed. Moisture removal can be carried out in the same manner as in the past, for example, by using a heating and drying apparatus or a vacuum drying apparatus, and by performing operations such as heating and depressurization individually or in appropriate combinations. The heating temperature is preferably set to a temperature that allows for proper evaporation of moisture under reduced pressure and does not cause thermal degradation of the separator 26 of the electrode group 20. The heating temperature is preferably set within the range of 50 to 200°C.

[0065] Next, in the injection step (steps 1-4), a non-aqueous electrolyte is first prepared. The non-aqueous electrolyte contains a B-element compound as described above (for example, a B-element lithium salt). In one example, the non-aqueous electrolyte preferably contains a boron-based additive in addition to the non-aqueous solvent and electrolyte salt. Although not particularly limited, the concentration of the boron-based additive in the non-aqueous electrolyte is preferably 0.01 mol / L or more, and more preferably 0.05 mol / L or more, as it facilitates the formation of a suitable amount and / or quality of film on the negative electrode active material layer 24a. On the other hand, from the viewpoint of suppressing an increase in battery resistance, the concentration of the boron-based additive in the non-aqueous electrolyte is preferably 1 mol / L or less, more preferably 0.5 mol / L or less, and even more preferably 0.1 mol / L or less.

[0066] Then, a predetermined amount of non-aqueous electrolyte is injected into the case 10 through the injection hole 15 of the sealing plate 14. The injection may be carried out at atmospheric pressure, or it may be carried out under reduced pressure below atmospheric pressure inside the case 10, for example, to improve the impregnation of the non-aqueous electrolyte into the electrode group 20 (electrodes 20a, 20b, 20c). Furthermore, the predetermined amount of non-aqueous electrolyte may be injected all at once, or it may be injected in multiple stages in N steps (where N is an integer of 2 or more).

[0067] In some embodiments, it is preferable to inject a predetermined amount of non-aqueous electrolyte in N steps (N≧2). This makes it easier to impregnate the electrode group 20, particularly the central part in the long side direction Y (winding axis WL direction), with the non-aqueous electrolyte. Although not particularly limited, from the viewpoint of improving work efficiency and productivity, the number of injections N is preferably 5 or less (N≦5), more preferably 3 or less (N=2 or 3), and even more preferably 2 (N=2).

[0068] When injecting a predetermined amount of non-aqueous electrolyte in N steps (N≧2), it is preferable to provide a certain standing period between the first injection and the second injection. By providing a standing period, the non-aqueous electrolyte can be suitably impregnated into the inside of the electrode bodies 20a, 20b, and 20c, causing the liquid level of the non-aqueous electrolyte to drop, and allowing more non-aqueous electrolyte to be injected in the injection after the standing period (second injection). In some embodiments, it is preferable not to include operations such as pressurization or depressurization between the first injection and the second injection.

[0069] The amount of non-aqueous electrolyte injected (the "determined amount" mentioned above) is preferably such that there is excess electrolyte between case 10 and electrode bodies 20a, 20b, and 20c. In some embodiments, the ratio of the volume Vl of the injected non-aqueous electrolyte to the internal volume Va of case 10 (Vl / Va) is preferably approximately 0.2 to 0.4, and more preferably 0.25 to 0.3. For example, if the length La in the long side direction Y of the negative electrode active material layer 24a is 200 mm or more (preferably 250 mm or more), the amount of non-aqueous electrolyte injected (determined amount) can be approximately 200 to 600 g, for example, 300 to 500 g or 400 to 450 g.

[0070] In one preferred embodiment, 50±10% (40-60%) of a predetermined amount is injected in the first injection, and the second injection is performed at least 3 hours after the first injection. This ensures that even if the length La of the long side Y of the negative electrode active material layer 24a is 200 mm or more (preferably 250 mm or more), the non-aqueous electrolyte can be firmly impregnated into the electrode group 20, particularly the central part in the long side Y direction (winding axis WL direction). The amount injected in the first injection is more preferably 50% or more (e.g., 50-60%) of the predetermined amount. Furthermore, from the viewpoint of productivity and work efficiency, the timing of the second injection is preferably within 5 hours of the first injection, and more preferably, for example, 3-4 hours after the first injection.

[0071] In some embodiments, it is preferable to perform the impregnation process (particularly pressurizing or depressurizing) after a predetermined amount of non-aqueous electrolyte has been injected. In other words, it is preferable not to inject non-aqueous electrolyte after the impregnation process. This allows a sufficient amount of non-aqueous electrolyte to be present in the case 10 from the beginning of the impregnation process.

[0072] In the impregnation step (step 2), after the construction step (specifically the liquid injection step), the non-aqueous electrolyte is impregnated into the electrode bodies 20a, 20b, and 20c, particularly the central part in the long side direction Y (winding axis WL direction), by pressurizing at least the inside of case 10 so that the central part of the negative electrode active material layer 24a has the above-mentioned full width at half maximum ratio. In a preferred embodiment, this step includes a pressurization step (step 2-A) and a depressurization step (step 2-B). However, the depressurization step (step 2-B) is optional and can be omitted in other embodiments. Furthermore, the order of the pressurization step (step 2-A) and the depressurization step (step 2-B) is not particularly limited; the depressurization step (step 2-B) may be performed before the pressurization step (step 2-A), or after the pressurization step (step 2-A). In addition, other steps may be included at any stage. This step may be carried out in a room temperature environment (approximately 25°C ± 10°C).

[0073] In some embodiments, it is preferable to perform the pressurization step (step 2-A) after a first waiting period has elapsed following the injection of at least a portion of the non-aqueous electrolyte in the construction step (more specifically, the injection step). In other words, it is preferable to leave (hold) the battery assembly at atmospheric pressure (normal pressure) for a first waiting period between the completion of injection of at least a portion of the non-aqueous electrolyte and the start of the pressurization step (step 2-A). More specifically, for example, if a predetermined amount of non-aqueous electrolyte is injected in N steps (N≧2), it is preferable to perform the pressurization step (step 2-A) after the first injection is completed and the first waiting period has elapsed. On the other hand, if the entire predetermined amount of non-aqueous electrolyte is injected in one step, it is preferable to perform the pressurization step (step 2-A) after the first waiting period has elapsed following the completion of the injection of the entire amount in one step.

[0074] The first waiting time is preferably 8 hours or more, more preferably 10 hours or more, even more preferably 12 hours or more, and particularly preferably 20 hours or more. Furthermore, the first waiting time is preferably 40 hours or less, more preferably 35 hours or less, even more preferably 30 hours or less, and particularly preferably 25 hours or less. According to the inventors' studies, the waiting time is correlated with the above-mentioned full width at half maximum (FWHM) ratio of the negative electrode active material layer 24a. Therefore, by setting the waiting time within the above range, it becomes easier to adjust the FWHM ratio to a desired range (for example, 0.17 or less). In addition, the impregnation of the non-aqueous electrolyte into the interior of the electrode bodies 20a, 20b, and 20c, particularly into the central part in the long side direction Y, is promoted, and the time required for impregnation can be shortened.

[0075] Furthermore, when a predetermined amount of non-aqueous electrolyte is injected in N steps (N≧2), it is preferable to perform the pressurization step (step 2-A) after all N injections have been completed and the entire predetermined amount of non-aqueous electrolyte has been injected, and after the second waiting period has elapsed. In other words, it is preferable to leave (hold) the battery assembly at atmospheric pressure (normal pressure) for the second waiting period between the completion of the injection of the entire amount of non-aqueous electrolyte and the start of the pressurization step (step 2-A).

[0076] The second waiting period is preferably 4 hours or more, more preferably 6 hours or more, even more preferably 8 hours or more, and particularly preferably 16 hours or more. Furthermore, the second waiting period is preferably 36 hours or less, more preferably 31 hours or less, even more preferably 26 hours or less, and particularly preferably 21 hours or less.

[0077] In the pressurization step (step 2-A), the inside of the battery assembly is pressurized so that the pressure inside the case 10 is higher than atmospheric pressure (normal pressure). In one example, the battery assembly is first placed in a pressure-adjustable chamber with the liquid injection hole 15 open (in other words, with no pressure difference between the inside and outside of the case 10). Then, the inside of the chamber is pressurized until a predetermined pressurized state is reached. Preferably, this pressurized state is maintained for a predetermined time. The pressurization conditions, such as the target pressure (degree of pressurization) and the holding time in the pressurized state (pressurization holding time), are preferably adjusted as appropriate by the length La of the long side Y of the negative electrode active material layer 24a, the waiting time until the start of the pressurization step described above, etc.

[0078] For example, if the length La in the long side direction Y of the negative electrode active material layer 24a is 200 mm or more (preferably 250 mm or more), it is preferable to pressurize until the pressure (pressure level) inside the case 10 reaches 0.4 MPa or more. The pressure level is preferably 0.5 MPa or more, more preferably 0.6 MPa or more, and even more preferably 0.8 MPa or more. This effectively promotes the impregnation of the non-aqueous electrolyte into the interior of the electrode bodies 20a, 20b, and 20c, particularly into the central part in the long side direction Y, making it easier to adjust the above-mentioned full width at half maximum of the negative electrode active material layer 24a to a desired range (for example, 0.17 or less). On the other hand, once the pressure becomes high enough, the impregnation promotion effect plateaus and it also takes time to increase the pressure, so from the viewpoint of improving work efficiency and productivity, the pressure level is preferably 2 MPa or less, more preferably 1.5 MPa or less, and even more preferably 1 MPa or less.

[0079] Furthermore, in some embodiments, it is preferable to maintain the pressure inside the case 10 at the above-mentioned pressure level (e.g., 0.4 MPa or higher) for a predetermined time. The holding time at the above-mentioned pressure level (pressure holding time) is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more. This effectively promotes the impregnation of the non-aqueous electrolyte into the interior of the electrode bodies 20a, 20b, and 20c, particularly the central part in the long-side direction Y, making it easier to adjust the above-mentioned full width at half maximum of the negative electrode active material layer 24a to a desired range (e.g., 0.17 or less). From the viewpoint of improving work efficiency and productivity, the pressure holding time is preferably 5 hours or less, more preferably 2 hours or less, and even more preferably 1 hour or less (e.g., 30 minutes to 1 hour).

[0080] In this context, "pressure holding time" typically refers to the continuous holding time. Specifically, in this process, it is preferable to hold the pressurized state continuously for 20 minutes or more, and more preferable to hold it continuously for 30 minutes or more. However, it is also permissible to reduce the pressure to less than 0.4 MPa for a very short time (e.g., a few seconds to less than 1 minute) during the process.

[0081] It is preferable to apply pressure when the liquid level of the excess electrolyte injected in the liquid injection process (steps 1-4) is above the lower end of the electrode bodies 20a, 20b, and 20c, and more preferably above the lower end of the flat portion 20f. This makes it easier for the non-aqueous electrolyte to flow into the interior of the electrode bodies 20a, 20b, and 20c, and promotes the impregnation of the non-aqueous electrolyte. It is also preferable to apply pressure when the liquid level of the excess electrolyte is below the upper end of the electrode bodies 20a, 20b, and 20c, and more preferably below the upper end of the positive electrode tab group 23 and the upper end of the negative electrode tab group 25. This makes it easier for the air replaced by the non-aqueous electrolyte to be degassed, and promotes the impregnation of the non-aqueous electrolyte to a higher level.

[0082] In some embodiments, it is preferable that the pressurization operation to raise the pressure to a predetermined level is performed only once during the pressurization process. In other words, it is preferable not to repeat the pressurization operation multiple times. This shortens the time required for pressurization and improves productivity and work efficiency. However, in other embodiments, the pressurization operation may be repeated two or more times, for example, with a period of depressurization in between.

[0083] While not particularly limited, in some embodiments, it is preferable that the total time required for the pressurization process (step 2-A) is shorter than the waiting time before the start of the pressurization process (first waiting time, and / or second waiting time). For example, it is preferable that it be 5 hours or less, more preferably 2 hours or less, and even more preferably 1 hour or less (e.g., 30 minutes to 1 hour).

[0084] In the depressurization step (step 2-B), before or after the pressurization step, the pressure inside case 10 is reduced until the pressure inside case 10 is lower than atmospheric pressure (normal pressure). By reducing the pressure inside case 10, residual air remaining inside, for example, the electrode bodies 20a, 20b, and 20c can be effectively degassed, and the impregnation of the non-aqueous electrolyte can be better promoted. When the length La in the long side direction Y of the negative electrode active material layer 24a is 200 mm or more (preferably 250 mm or more), the depressurization pressure (degree of depressurization) is preferably -55 kPa or less, more preferably -70 to -100 kPa, and even more preferably -80 to -90 kPa.

[0085] In some embodiments, it is preferable that the pressure inside case 10 maintains the above-mentioned degree of reduced pressure for a predetermined time. The holding time at the above-mentioned degree of reduced pressure (reduced pressure holding time) is preferably shorter than the pressurized holding time. The reduced pressure holding time is preferably 1 minute or more, for example, 1 to 10 minutes. Also, in some embodiments, it is preferable that the depressurization operation to reduce the pressure to a predetermined degree of reduced pressure is performed only once in the depressurization process. In other words, it is preferable not to repeat the depressurization operation multiple times.

[0086] Furthermore, a waiting period may be provided as needed between the completion of the pressurization or depressurization process and the start of the initial charging process. In other words, between the completion of the pressurization process (e.g., pressurization holding time) or depressurization process (e.g., depressurization holding time) and the start of the initial charging process (step 3), the battery assembly may be left (held) for a third waiting period at atmospheric pressure (normal pressure). Although not particularly limited, the total time required for the impregnation process (step 2), including the waiting time, is preferably about 10 to 50 hours, and more preferably 30 to 48 hours, based on the time when at least a portion of the non-aqueous electrolyte is injected in the liquid injection process (steps 1-4), from the viewpoint of improving work efficiency and productivity.

[0087] In the initial charging step (step 3), the battery assembly is charged at least once after the impregnation step. During the initial charging, the B-element-containing compound (e.g., boron-based additive) in the non-aqueous electrolyte is electrolyzed. This causes a boron-containing film (SEI film) to form on the surface of the negative electrode active material layer 24a. More specifically, a film (SEI film) containing the decomposition products of the B-element-containing compound is formed on the surface of the negative electrode active material layer 24a.

[0088] The battery assembly can be charged in the same manner as in the conventional method. Typically, an external power supply is connected between the positive electrode terminal 30 and the negative electrode terminal 40 of the battery assembly, and charging is performed until a predetermined voltage is reached between the terminals. If the non-aqueous electrolyte contains a boron-based additive, it is preferable to charge the battery assembly at least up to the decomposition potential of the boron-based additive. The battery assembly is preferably charged until its State of Charge (SOC) reaches 5% or more, and more preferably until it reaches 10% or more. The State of Charge (SOC) of the battery assembly in this process is preferably 50% or less, preferably 40% or less, and more preferably 30% or less. The charging rate can be, for example, around 0.1 to 2C. Charging may be performed only once, or it may be repeated two or more times, for example, with a discharge in between. This process may be performed in a normal temperature environment (e.g., around 25°C ± 10°C, 25°C ± 5°C), or in a high-temperature environment, for example, around 45°C. Charging in a high-temperature environment can promote film formation.

[0089] In some embodiments, after the initial charging process, it is preferable to exhaust gases from inside the case 10, such as air or gases generated by the decomposition of the non-aqueous electrolyte during the initial charging process, to the outside of the case 10. Gas exhaust can be performed, for example, by reducing the pressure inside the case 10. After exhausting the gas from inside the case 10, the liquid injection hole 15 is sealed with the sealing member 16. This seals the case 10 airtight.

[0090] In the aging process (step 4), the battery assembly after the initial charge is kept in a predetermined temperature environment for a predetermined aging period. The temperature environment is preferably 15 to 40°C, and may be room temperature (approximately 25°C ± 10°C). The aging period may vary depending on factors such as the length La of the long side Y of the negative electrode active material layer 24a and the conditions of the impregnation process (step 2), but is generally preferred to be 5 days or more, and more preferably 6 days or more (e.g., 6 to 10 days). In this process, the voltage adjusted in the initial charging process may be maintained. In this way, the battery 100 can be suitably manufactured.

[0091] <Uses of Battery 100> The battery 100 can be used for various applications, but for example, because it has high capacity and excellent thermal stability, it can be suitably used as a power source (driving power supply) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). The battery 100 can also be suitably used as a battery pack in which multiple batteries 100 are arranged in a predetermined arrangement direction and a load is applied from the arrangement direction by a restraining mechanism.

[0092] The following describes some embodiments of the present invention, but it is not intended to limit the present invention to these embodiments.

[0093] <Preparation of evaluation batteries> In the construction process (Step 1), battery assemblies with the same configuration (Examples 1-3, Comparative Examples 1-3) were constructed. Specifically, lithium nickel cobalt manganese composite oxide (LiNi) was used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 and NCM were prepared. A strip-shaped positive electrode sheet was fabricated by placing a positive electrode active material layer containing this positive electrode active material, a carbon material (AB) as a conductive material, and PVdF as a binder in a mass ratio of NCM:AB:PVdF = 97.5:1.5:1.0 on top of an aluminum foil as the positive electrode current collector. A strip-shaped negative electrode sheet was also fabricated by placing a negative electrode active material layer containing graphite (C) as the negative electrode active material, and SBR and CMC as binders in a mass ratio of C:(SBR+CMC) = 98.5:1.5 on top of a copper foil as the negative electrode current collector.

[0094] Next, the positive electrode sheet and negative electrode sheet prepared above were placed opposite each other via a separator sheet and wound into a flattened shape to produce a wound electrode body (number of turns: 30). The separator sheet used was a PE base material with a heat-resistant layer (which also serves as an adhesive layer) containing alumina and PVdF on its surface. The length La of the negative electrode active material layer in the long side direction (winding axis direction) was 286 mm, and the height Ha was 90 mm.

[0095] Next, as a non-aqueous electrolyte, a mixture of EC, EMC, and DMC was prepared by dissolving LiPF6 in this mixture, and then adding LiBOB as an additive to a concentration of 0.05 mol / L. The wound electrode body prepared above and a predetermined amount of the non-aqueous electrolyte were then placed in a rectangular parallelepiped case to construct a battery assembly.

[0096] The non-aqueous electrolyte was injected in two separate doses. Specifically, in the first injection, 238g, representing approximately 58% of the total volume (411g), was injected. After being left at atmospheric pressure for 4 hours, 173g, representing approximately 42% of the total volume (411g), was injected in the second injection.

[0097] In the impregnation process (step 2), the wound electrode body was impregnated with a non-aqueous electrolyte so as to have different half-width ratios. Here, for Examples 1-3 and Comparative Examples 2 and 3, the waiting time from the completion of the first injection in the construction process to the pressurization process (first waiting time) was changed, as shown in Table 1. Table 1 also shows the waiting time from the completion of the second injection to the pressurization process (second waiting time, first waiting time - 4 hours).

[0098] Then, for each example, after the waiting time had elapsed, the battery assembly was placed in a pressure-adjustable chamber with the injection port open, and the depressurization and pressurization processes were performed in the order shown in Figure 7. Specifically, the depressurization process involved reducing the pressure inside the case to -90 kPa in 1 minute and holding it at -90 kPa for 1 minute, then returning it to atmospheric pressure (normal pressure) in 1 minute, and then gradually (stepwise) pressurizing the inside of the case to 0.8 MPa over 10 minutes at a rate of 0.1 MPa / 1 min 15 sec, and holding it at 0.8 MPa for 39.5 minutes. Finally, the inside of the case was restored to atmospheric pressure in 1 minute. The depressurization and pressurization processes were performed once each. In Comparative Example 1, the impregnation process (depressurization and pressurization processes) was omitted, and the battery assembly was left (held) at atmospheric pressure (normal pressure).

[0099] Next, X-ray CT was used to confirm the impregnation status of the non-aqueous electrolyte in the wound electrode body. Although detailed results are not shown here, the X-ray transmission image shows a difference in color between areas impregnated with the non-aqueous electrolyte and areas that are not, allowing us to understand the impregnation status of the non-aqueous electrolyte. For Examples 1-3 and Comparative Examples 2 and 3, the battery assemblies after the depressurization process were observed at predetermined time intervals. In Comparative Example 1, since no impregnation process was performed, the battery assembly was observed at predetermined time intervals from the completion of the second electrolyte injection. The time it took for the non-aqueous electrolyte to impregnate the central part of the wound electrode body was then confirmed. The results are shown in Table 1. Note that in Table 1, the time taken is shown starting from the completion of the first electrolyte injection.

[0100] As shown in Table 1, Comparative Example 1, which did not undergo an impregnation process, required the longest time for impregnation. In contrast, Examples 1-3 and Comparative Examples 2 and 3, which included an impregnation process, required relatively shorter impregnation times. In particular, Examples 1-3, where the first waiting time was set to 10-29 hours (in other words, the second waiting time was set to 6-25 hours), required even shorter impregnation times.

[0101] In the initial charging process (step 3), for each example, the battery assembly was charged to a state of charge (SOC) of 12% at a charging rate of 0.2C in a temperature environment of 25°C. Next, the pressure inside the case was reduced to -90kPa, and the electrolyte injection holes were sealed with a sealing material while the inside of case 10 was under reduced pressure. Next, in the aging process (step 4), the battery assembly after the initial charging was kept in a temperature environment of 25°C for 6 days. In this manner, evaluation batteries (Examples 1-3, Comparative Examples 1-3) were manufactured.

[0102] [Table 1]

[0103] <Preparation of the Measurement Sample> After aging, the evaluation battery was discharged until the voltage reached 3.0V. Then, it was disassembled in a dry air atmosphere (for example, with a dew point of about -50°C), and the wound electrode body was removed from the case. The winding of the wound electrode body was then unwound, and the negative electrode was separated. The negative electrode was then cut to an appropriate size along the long side, cleaned with DMC, and prepared as the measurement sample. The cutting position was the flat section located at the 17th turn (mid-circumference) from the starting end of the winding. Figure 8 is a schematic diagram of the measurement sample.

[0104] <Calculation of Full Width at Half Max> First, using LA-ICP-MS, a laser was irradiated along the winding axis direction (long side direction) at the center of the negative electrode active material layer of the sample to be measured, and ICP mass spectrometry was continuously performed while the sample at the laser irradiation site was atomized. Then, the ratio of the amount of boron (B) element to the amount of carbon (C) element (B / C) was determined at each point. The measurement range was defined as including the center of the flat part of the negative electrode active material layer (center in the short side direction and center in the long side direction), and within 49% of the total length La (286 mm) of the negative electrode active material layer in the winding axis direction, as shown in Figure 8. Y The range was defined as ±70mm from the 143mm position (the range of 73-213mm in Figure 8, totaling 140mm).

[0105] Next, a graph was created showing the distribution of the ratio (B / C), specifically, the measurement position in the winding axis direction (mm) on the horizontal axis and the above ratio (B / C, unitless) on the vertical axis (Procedure 1). Figure 9 is a graph showing the distribution of the ratio (B / C) related to Example 1. Also, Figure 10(a) shows the distribution of the ratio (B / C) related to Comparative Example 1, Figure 10(b) shows the distribution of the ratio (B / C) related to Comparative Example 2, Figure 10(c) shows the distribution of the ratio (B / C) related to Example 2, Figure 10(d) shows the distribution of the ratio (B / C) related to Example 3, and Figure 10(e) shows the distribution of the ratio (B / C) related to Comparative Example 3.

[0106] As shown in Figures 9 and 10(a) to 10(e), each graph has a convex shape, and the ratio (B / C) is smaller towards the center in the direction of the winding axis, meaning that the amount of boron is lower.

[0107] Next, the full width at half maximum (FWHM) Lh (mm) was determined (Procedure 2). As an example, in Example 1, as shown in Figure 9, first, a baseline BL was drawn connecting the two ends (E1, E2 in Figure 9) in the winding axis direction of the measurement range (the central part of the negative electrode active material layer 24a). Next, a straight line was drawn from the peak position P1, where the ratio (B / C) value was smallest, along the vertical axis to the baseline BL. Next, the intersection point P2 of this line and the baseline BL was found, and the difference between the intersection point P2 and the peak position P1 (|P2-P1|) was defined as the width W. Next, the FWHM Lh (mm) along the horizontal axis was measured at the position where the width W was halved (1 / 2W). The results are shown in Table 1.

[0108] Then, the obtained full width at half maximum (FWHM) Lh (mm) was divided by the length La (286 mm) of the negative electrode active material layer 24a in the winding axis WL direction to obtain the FWHM ratio (Lh / La) (Step 3). Here, the procedure for Example 1 is shown in detail as an example, but the FWHM ratio (Lh / La) was obtained in the same manner for other examples (Examples 2, 3, Comparative Examples 1, 2). The results are shown in Table 1.

[0109] Figure 11 is a graph showing the relationship between the first waiting time (hours) and the half-width ratio (Lh / La). As shown in Figure 11 and Table 1, a correlation was observed between the half-width ratio and the waiting time. Specifically, up to a first waiting time of about 10 hours, there was a tendency for the half-width ratio to decrease as the first waiting time increased. On the other hand, when the first waiting time exceeded approximately 30 hours, there was a tendency for the half-width ratio to increase as the first waiting time increased. From the above, it was found that the half-width ratio can be kept small by setting the first waiting time to between 10 and 30 hours.

[0110] <Evaluation of Heat Generation of the Negative Electrode> First, for each example, a sample for differential scanning calorimetry (DSC) measurement was prepared. Specifically, a battery that had been activated in an Ar atmosphere (aging process) in accordance with the <Preparation of Evaluation Batteries> described above was disassembled, and the positive electrode with a positive electrode active material layer (□20mm×20mm) and the negative electrode with a negative electrode active material layer (□22mm×22mm) were cut out from the center of the electrode plate (17 turns) shown in Figure 8. Next, the cut-out positive and negative electrodes were placed facing each other with a separator in a dry air atmosphere (dew point: -50℃) and contained with 0.4 mL of non-aqueous electrolyte to construct a laminate cell. Next, the laminate cell was charged with a constant current of 8 mA to 4.25 V, and then charged with a constant voltage for 5 hours.

[0111] Next, the charged laminate cell was disassembled in a glove box (Ar atmosphere). Then, the electrolyte was collected, and the positive and negative electrodes were removed. The positive electrode composite material was peeled off from the central region of the positive electrode active material layer, and the negative electrode composite material was peeled off from the central region of the negative electrode active material layer. Next, 1 mg of the positive electrode composite material peeled off from the positive electrode, 2 mg of the negative electrode composite material peeled off from the negative electrode, and 4 mg of the collected electrolyte were placed in a sample container. This sample container was pressed and sealed at 20 MPa, and then set in a DSC along with a standard substance (Al2O3, 2 mg). Then, under an inert atmosphere, the temperature was raised from 25°C to 350°C at a rate of 2°C / min, and the amount of heat generated (J) between 75 and 200°C was determined by integration. The results are shown in Table 1. Table 1 also shows the relative values ​​with the amount of heat generated in Comparative Example 1, which did not undergo the impregnation process, set as the standard (1.00).

[0112] Figure 12 is a graph showing the relationship between the full width at half maximum (FWHM) ratio (Lh / La) and the heat generated by the negative electrode (relative value). As shown in Figure 12 and Table 1, a correlation was observed between the FWHM ratio and the heat generated. That is, the smaller the FWHM ratio, the more the heat generated was suppressed. For example, it was found that if the FWHM ratio was 0.17 or less, the heat generated could be suppressed to about 80% of that in Comparative Example 1, thereby improving the thermal stability of the battery. These results demonstrate the significance of the technology disclosed herein.

[0113] Although several embodiments of the present invention have been described above, these 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 herein and common technical knowledge in the art. The technologies described in the claims include various modifications and changes to the embodiments illustrated above. For example, it is possible to replace parts of the above embodiments with other modifications, and it is also possible to add other modifications to the above embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0114] As described above, specific embodiments of the technology disclosed herein include those described in the following sections. Item 1: A wound electrode body comprising a strip-shaped positive electrode and a strip-shaped negative electrode laminated and wound together in an insulated state, a non-aqueous electrolyte, and a case for housing the wound electrode body and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material layer containing carbon material and having a length of 200 mm or more in the winding axis direction, the negative electrode active material layer has a coating containing boron element, and in the central part of the negative electrode active material layer in the winding axis direction, the ratio of boron element to carbon element (B / C) along the winding axis direction is determined by laser ablation ICP mass spectrometry. A power storage device in which the calculated half-width ratio is 0.17 or less, obtained by following the steps below: (Step 1) Create a graph with the measurement position in the winding axis direction on the horizontal axis and the ratio (B / C) on the vertical axis; (Step 2) Draw a baseline connecting the two ends in the winding axis direction in the central part, and measure the half-width at the position where the width of the straight line drawn from the peak position with the smallest value of the ratio (B / C) along the vertical axis to the baseline is halved; (Step 3) Divide the half-width by the length of the negative electrode active material layer in the winding axis direction; Item 2: The energy storage device according to Item 1, wherein the non-aqueous electrolyte contains a compound containing the element boron. Item 3: A wound electrode body comprising a strip-shaped positive electrode and a strip-shaped negative electrode stacked and wound in an insulated state, a non-aqueous electrolyte, and a case for housing the wound electrode body and the non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material layer containing carbon material and having a length of 200 mm or more in the winding axis direction, the negative electrode active material layer has a coating containing boron element, and the ratio of boron element to carbon element (B / C) along the winding axis direction is determined by laser ablation ICP mass spectrometry at the central part of the negative electrode active material layer in the winding axis direction, using the following procedure: (Procedure 1) Create a graph with the measurement position in the winding axis direction on the horizontal axis and the ratio (B / C) on the vertical axis; (Procedure 2) Draw a baseline connecting both ends in the winding axis direction of the central part A method for manufacturing an energy storage device, wherein the width at half maximum is calculated by: (step 3) dividing the width at half maximum by the length in the winding axis direction of the negative electrode active material layer; and the resulting width at half maximum ratio is 0.17 or less, comprising: a battery assembly construction step of housing a wound electrode body in a case and pouring a non-aqueous electrolyte containing a compound containing boron element into it; an impregnation step of impregnating the wound electrode body with the non-aqueous electrolyte so as to achieve the width at half maximum ratio by pressurizing the case at least once after the construction step; and an initial charging step of charging the battery assembly at least once after the impregnation step. A method for manufacturing an energy storage device, including the method described above. Item 4: The manufacturing method according to Item 3, wherein in the impregnation step, pressurization is performed 10 to 30 hours after at least a portion of the non-aqueous electrolyte has been injected in the construction step. Item 5: The manufacturing method according to Item 4, wherein in the impregnation step, the pressurization is carried out until the pressure inside the case reaches 0.4 MPa or more, and the state of the pressure inside the case being 0.4 MPa or more is maintained for 20 minutes or more. Item 6: The manufacturing method according to item 4 or 5, wherein, in the impregnation step, the pressure inside the case is reduced before or after the pressurization step until the pressure inside the case becomes lower than atmospheric pressure. Item 7: The manufacturing method according to any one of items 3 to 6, wherein in the above construction step, a predetermined amount of the non-aqueous electrolyte is injected in N installments (N≧2), 50±10% of the predetermined amount is injected in the first injection, and the second injection is performed 3 hours or more after the first injection. Item 8: The manufacturing method according to any one of items 3 to 7, wherein in the impregnation step, the entire amount of the predetermined amount of the non-aqueous electrolyte is injected by the N injections described above, and then pressurization is performed after 6 to 26 hours have elapsed. [Explanation of Symbols]

[0115] 10 cases 20a, 20b, 20c electrode body (wound electrode body) 22 Positive electrode 24 Negative electrode 24a Negative electrode active material layer 100 batteries WL winding shaft Y direction (winding axis direction)

Claims

1. The device comprises a wound electrode body formed by stacking and winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state, a non-aqueous electrolyte, and a case for housing the wound electrode body and the non-aqueous electrolyte. The negative electrode has a negative electrode active material layer containing a carbon material and having a length of 200 mm or more in the winding axis direction. The negative electrode active material layer comprises a coating containing boron element, In the central portion of the negative electrode active material layer in the winding axis direction, the ratio of boron to carbon (B / C) along the winding axis direction is determined by laser ablation ICP mass spectrometry, and the following procedure is followed: (Procedure 1) Create a graph with the measurement position in the winding direction on the horizontal axis and the ratio (B / C) on the vertical axis; (Procedure 2) Draw a baseline connecting the two ends of the central part in the direction of the winding axis, and measure the width at half maximum at the position where the width of the line drawn from the peak position with the smallest ratio (B / C) value along the vertical axis to the baseline is halved; (Step 3) Divide the full width at half maximum by the length of the negative electrode active material layer in the winding axis direction; A battery storage device in which the calculated full width at half maximum (FWHM) is 0.17 or less.

2. The non-aqueous electrolyte contains a compound containing the element boron. The energy storage device according to claim 1.

3. The device comprises a wound electrode body formed by stacking and winding a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state, a non-aqueous electrolyte, and a case for housing the wound electrode body and the non-aqueous electrolyte. The negative electrode has a negative electrode active material layer containing a carbon material and having a length of 200 mm or more in the winding axis direction. The negative electrode active material layer comprises a coating containing boron element, In the central portion of the negative electrode active material layer in the winding axis direction, the ratio of boron to carbon (B / C) along the winding axis direction is determined by laser ablation ICP mass spectrometry, and the following procedure is followed: (Procedure 1) Create a graph with the measurement position in the winding direction on the horizontal axis and the ratio (B / C) on the vertical axis; (Procedure 2) Draw a baseline connecting the two ends of the central part in the direction of the winding axis, and measure the width at half maximum at the position where the width of the line drawn from the peak position with the smallest ratio (B / C) value along the vertical axis to the baseline is halved; (Step 3) Divide the full width at half maximum by the length of the negative electrode active material layer in the winding axis direction; A method for manufacturing an energy storage device, wherein the half-width ratio calculated by is 0.17 or less, The battery assembly construction process involves housing a wound electrode body inside a case and pouring in a non-aqueous electrolyte containing a compound with boron element, After the construction step, an impregnation step is performed in which the wound electrode body is impregnated with the non-aqueous electrolyte by pressurizing at least the inside of the case so that the half-width ratio is met. After the impregnation step, an initial charging step is performed in which the battery assembly is charged at least once. A manufacturing method that includes this.

4. In the impregnation step, pressurization is performed 10 to 30 hours after at least a portion of the non-aqueous electrolyte has been injected in the construction step. The manufacturing method according to claim 3.

5. In the impregnation step, pressurization is carried out until the pressure inside the case reaches 0.4 MPa or higher, and the state of the pressure inside the case being 0.4 MPa or higher is maintained for 20 minutes or more. The manufacturing method according to claim 4.

6. In the impregnation step, before or after the pressurization, the pressure inside the case is reduced until the pressure inside the case becomes lower than atmospheric pressure. The manufacturing method according to claim 4 or 5.

7. In the construction step described above, a predetermined amount of the non-aqueous electrolyte is injected in N installments (N≧2), In the first injection, 50 ± 10% of the predetermined amount is injected, and a second injection is performed at least 3 hours after the first injection. The manufacturing method according to any one of claims 3 to 5.

8. In the impregnation step, after the entire predetermined amount of the non-aqueous electrolyte has been injected in the N injections, pressurization is performed after 6 to 26 hours have elapsed. The manufacturing method according to claim 7.

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