Method for manufacturing nonaqueous electrolyte secondary battery

Abstract

The present application relates to a manufacturing method of a nonaqueous electrolyte secondary battery, which includes the following steps: an assembly preparation step of preparing an assembly in which an electrode body and a nonaqueous electrolyte are housed in a battery case; an initial charging step of charging the assembly to a prescribed voltage V0; an aging step of storing the assembly at 45°C or higher for 3 hours or longer after the initial charging step; a voltage adjustment step of adjusting the voltage of the assembly to a voltage V1 of 3.585 V or higher after the aging step; a temperature history adjustment step of setting the temperature of the assembly at the start of temperature increase to T1, increasing the temperature of the assembly to a temperature T2 higher than T1, and then decreasing the temperature of the assembly to a temperature T3 lower than T2 after the voltage adjustment step; and a self-discharge inspection step of performing a self-discharge inspection at a temperature T4 lower than T2 after the temperature history adjustment step.

Description

Technical Field

[0001] This disclosure relates to an improvement in the inspection accuracy of micro-short-circuit cells due to reduced temperature dependence of voltage, and more specifically, to a method for manufacturing a non-aqueous electrolyte secondary battery that achieves this improvement. Background Technology

[0002] In portable power supplies for personal computers, portable terminals, etc., and vehicle drive power supplies for BEVs (electric vehicles), HEVs (hybrid electric vehicles), PHEVs (plug-in hybrid electric vehicles), etc., non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are preferred. From the viewpoint of safety during the use of these products, it is desirable that even a minor internal short circuit (micro-short circuit) occurs in a non-aqueous electrolyte secondary battery (cell) and is not used in the product. Therefore, in the manufacturing process of non-aqueous electrolyte secondary batteries, a method for identifying batteries with internal short circuits has been studied. As prior art that discloses such technology, Patent Document 1 can be cited as an example. Patent Document 1 discloses a technology in which, in the manufacturing process of lithium-ion secondary batteries, the presence or absence of an internal short circuit is determined by measuring the self-discharge voltage.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-84332 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Patent Document 1 discloses a technique in which a lithium-ion secondary battery charged at a voltage range of 3.52V to 3.6V is self-discharged during the manufacturing process, and the presence or absence of an internal short circuit is determined based on the voltage difference before and after self-discharge. Although the battery voltage varies with temperature, the variation is small within the aforementioned charging voltage range, enabling high-precision measurement of the battery voltage, i.e., high-precision determination of the presence or absence of an internal short circuit.

[0008] However, the battery voltage of non-aqueous electrolyte secondary batteries such as lithium-ion batteries not only depends on the temperature at the time of measurement, but can also vary due to temperature changes experienced up to the measurement of the battery voltage. Therefore, even if the battery is charged to a charging voltage where the voltage change associated with temperature variations is small, the accuracy of detecting the presence or absence of internal short circuits may be reduced due to temperature changes experienced up to the self-discharge test.

[0009] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide a method for manufacturing a non-aqueous electrolyte secondary battery that can accurately distinguish between cells that have experienced minute internal short circuits and cells that have not experienced minute internal short circuits during the manufacturing process of the non-aqueous electrolyte secondary battery.

[0010] Methods for solving problems

[0011] The method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein includes an electrode body containing a positive electrode and a negative electrode, and a method for manufacturing a non-aqueous electrolyte secondary battery, comprising the following steps:

[0012] An assembly preparation process for preparing an assembly that houses the electrode body and the non-aqueous electrolyte in a battery casing;

[0013] The initial charging process of charging the assembly to a specified voltage V0;

[0014] An aging process in which the assembly is stored at or above 45°C for more than 3 hours after the initial charging process;

[0015] A voltage adjustment process that adjusts the assembly to a voltage V1 of 3.585V or higher after the aging process;

[0016] After the voltage adjustment process, the initial temperature of the assembly is set to T1, the assembly is heated to a temperature T2 higher than T1, and then the assembly is cooled to a temperature T3 lower than T2, undergoing an adjustment process; and

[0017] A self-discharge check process is performed at a temperature T4, which is lower than T2, after the temperature has undergone an adjustment process.

[0018] According to the manufacturing method of the non-aqueous electrolyte secondary battery described above, the temperature dependence of the battery voltage is positive, and its absolute value can be reduced. Furthermore, it allows for high-precision measurement of the battery voltage, i.e., checking for the presence or absence of internal short circuits.

[0019] In a preferred embodiment of the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein, the negative electrode comprises a negative electrode core and a negative electrode active material layer formed on at least one surface of the negative electrode core, the negative electrode active material layer having a density of 1.4 g / mL or more and a coating weight of 185 g / mL. 2That's all. Therefore, through the rise in negative electrode potential accompanying the temperature increase of the secondary battery, charge carriers (lithium ions in the case of lithium-ion secondary batteries) are released from the electric double layer located at the negative electrode interface into the electrolyte. Then, since the charge carriers are difficult to return to the electric double layer located at the negative electrode interface, the temperature dependence of the battery voltage due to changes in the concentration of charge carriers in the electric double layer at the negative electrode interface caused by subsequent temperature variations in the secondary battery can be further mitigated.

[0020] In a preferred embodiment of the disclosed method for manufacturing a non-aqueous electrolyte secondary battery, the aforementioned temperature adjustment process is performed once or repeated two or more times. When repeated two or more times, the temperature difference δT between T2 and T1 in each temperature adjustment process is either the same or different. This promotes the release of charge carriers caused by the increase in negative electrode potential accompanying the temperature rise of the secondary battery, further reducing the temperature dependence of the battery voltage.

[0021] In a preferred embodiment of the disclosed method for manufacturing a non-aqueous electrolyte secondary battery, the temperature difference between T2 and T4 is 3°C or more. This facilitates the release of charge carriers generated by the rise in negative electrode potential associated with a decrease in the secondary battery temperature, further reducing the temperature dependence of the battery voltage. Attached Figure Description

[0022] Figure 1 An oblique view schematically representing a non-aqueous electrolyte secondary battery.

[0023] Figure 2 For along Figure 1 A schematic longitudinal section of line II-II.

[0024] Figure 3 An oblique view schematically showing the electrode assembly mounted on the sealing plate.

[0025] Figure 4 An angled view schematically showing the electrode body on which the positive and negative second collectors are installed.

[0026] Figure 5 This is a schematic diagram illustrating the structure of the wound electrode.

[0027] Figure 6 A flowchart illustrating a part of a method for manufacturing a non-aqueous electrolyte secondary battery.

[0028] Figure 7 (A) is a graph showing the temperature dependence of battery voltage at any charging voltage, measured at 25°C. Figure 7 (B) is to Figure 7 (A) is a magnified portion of the chart.

[0029] Figure 8 A diagram illustrating the temperature variation process of an assembly during manufacturing.

[0030] Figure 9 A graph illustrating the temperature dependence of battery voltage in one embodiment. Detailed Implementation

[0031] Several embodiments of the technology disclosed herein will be described below with reference to the accompanying drawings. In the following drawings, components and parts that perform the same function are labeled with the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. It should be noted that matters other than those specifically mentioned in this specification, i.e., matters necessary for implementing the technology disclosed herein (e.g., the general structure and manufacturing method of energy storage devices that are not features of this disclosure), can be grasped as design matters by those skilled in the art based on prior art. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Furthermore, the following description is not intended to limit this disclosure to the following forms.

[0032] In this specification, the notation "A to B" indicating a range means "above A and below B". It also includes the meanings of "above A" and "below B". Furthermore, in this specification, the term "energy storage device" refers to a device capable of charging and discharging. Energy storage devices include batteries such as primary batteries, secondary batteries (e.g., non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries), and capacitors (physical batteries) such as double-layer capacitors. Additionally, the electrolyte can be any of a liquid electrolyte (electrolyte), a gel electrolyte, or a solid electrolyte. The following description uses one embodiment of the energy storage device disclosed herein, namely a lithium-ion secondary battery (hereinafter also simply referred to as "battery 100"), as an example.

[0033] 1. Composition of non-aqueous electrolyte secondary batteries

[0034] In this specification, the term "non-aqueous electrolyte secondary battery" refers to an energy storage device capable of repeated charging and discharging through the movement of charge carriers between the positive and negative electrodes. It is a term encompassing all energy storage devices, including those using non-aqueous electrolytes, and includes so-called storage batteries (chemical batteries) such as lithium-ion and sodium-ion batteries, as well as capacitors (physical batteries) such as electric double-layer capacitors. The main constituent materials of the non-aqueous electrolyte secondary batteries disclosed herein are described below. Furthermore, for constituent materials of other non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, not described herein, conventionally known materials may be used.

[0035] In the case of the non-aqueous electrolyte secondary battery disclosed herein, the electrode body including the positive electrode and the negative electrode and the non-aqueous electrolyte are housed within the battery casing.

[0036] Figure 1 This is a perspective view of a non-aqueous electrolyte secondary battery 100. Figure 2 For along Figure 1 A schematic longitudinal cross-sectional view of line II-II. It should be noted that in the following description, the reference numerals L, R, F, Rr, U, and D in the figures represent left, right, front, back, top, and bottom, respectively, and the reference numerals X, Y, and Z in the figures represent the short side direction, the long side direction orthogonal to the short side direction, and the up-down direction of the non-aqueous electrolyte secondary battery 100, respectively. The long side direction Y is an example of the first direction disclosed herein, and the short side direction is an example of the second direction disclosed herein. However, these are merely directions for ease of explanation and do not impose any limitations on the arrangement of the non-aqueous electrolyte secondary battery 100.

[0037] like Figure 2 As shown, the non-aqueous electrolyte secondary battery 100 includes: a battery casing 10, an electrode assembly 20, a positive terminal 30, a negative terminal 40, a positive current collector 50, and a negative current collector 60. Although the illustration is omitted, the non-aqueous electrolyte secondary battery 100 also includes a non-aqueous electrolyte. The non-aqueous electrolyte secondary battery 100 is a lithium-ion secondary battery.

[0038] The battery casing 10 serves as the outer shell housing the electrode assembly 20. The battery casing 10 has a flat, bottomed cuboid shape (square). The material of the battery casing 10 can be the same as conventionally used materials and is not particularly limited. The battery casing 10 is preferably made of metal, for example, more preferably of aluminum, aluminum alloy, iron, iron alloy, etc. Figure 2 As shown, the battery casing 10 includes an outer body 12 with an opening 12h and a sealing plate (cover) 14 that plugs the opening 12h.

[0039] External body 12 such Figure 1 As shown, the battery housing 10 includes a bottom wall 12a, a pair of long sidewalls 12b extending from the bottom wall 12a and facing each other, and a pair of short sidewalls 12c extending from the bottom wall 12a and facing each other. The bottom wall 12a is generally rectangular. The bottom wall 12a is opposite to the opening 12h. The area of ​​the short sidewalls 12c is smaller than the area of ​​the long sidewalls 12b. The long sidewalls 12b and short sidewalls 12c are examples of the first and second sidewalls disclosed herein. A sealing plate 14 is installed on the outer casing 12 to plug the opening 12h of the outer casing 12. The sealing plate 14 is opposite to the bottom wall 12a of the outer casing 12. The sealing plate 14 is generally rectangular in plan view. The battery housing 10 is integrated by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the outer casing 12. The battery housing 10 is hermetically sealed (sealed).

[0040] like Figure 2 As shown, the sealing plate 14 is provided with an injection hole 15, a gas discharge valve 17, and two terminal outlet holes 18 and 19. The injection hole 15 is used to inject electrolyte after the sealing plate 14 is installed on the outer casing 12. The injection hole 15 is sealed by a sealing member 16. The gas discharge valve 17 is configured to disconnect when the pressure inside the battery casing 10 reaches a specified value, so as to discharge the gas inside the battery casing 10 to the outside. The terminal outlet holes 18 and 19 are formed at both ends of the sealing plate 14 in the long side direction Y. The terminal outlet holes 18 and 19 pass through the sealing plate 14 in the vertical direction Z. The terminal outlet holes 18 and 19 have an inner diameter that allows the positive terminal 30 and the negative terminal 40 installed before the sealing plate 14 (before riveting) to be inserted.

[0041] The positive terminal 30 and the negative terminal 40 are respectively fixed to the sealing plate 14. The positive terminal 30 is positioned on one side of the long side Y direction of the sealing plate 14. Figure 1 , Figure 2 (Left side). The negative terminal 40 is positioned on the other side of the long side Y direction of the sealing plate 14 ( Figure 1 , Figure 2 (The right side). For example Figure 1 As shown, the positive terminal 30 and the negative terminal 40 are exposed on the outer surface of the sealing plate 14. Figure 2 As shown, the positive terminal 30 and the negative terminal 40 are inserted through the terminal lead-out holes 18 and 19, extending from the inside to the outside of the sealing plate 14. The positive terminal 30 and the negative terminal 40 are riveted to the periphery of the sealing plate 14 surrounding the terminal lead-out holes 18 and 19. At the ends of the positive terminal 30 and the negative terminal 40 on the outer casing 12 side ( Figure 2 The lower end of the part forms a riveting part.

[0042] like Figure 2 As shown, the positive terminal 30 is located inside the outer casing 12 and is electrically connected to the positive terminal 22 of the electrode assembly 20 via the positive current collector 50. The negative terminal 40 is located inside the outer casing 12 and is electrically connected to the negative terminal 24 of the electrode assembly 20 via the negative current collector 60. The positive terminal 30 and the negative terminal 40 are examples of terminals disclosed herein.

[0043] The positive terminal 30 is preferably made of metal, more preferably of aluminum or an aluminum alloy. The negative terminal 40 is preferably made of metal, more preferably of copper or a copper alloy. The negative terminal 40 can be constructed by joining two conductive components together in one piece. For example, the portion connected to the negative current collector 60 can be made of copper or a copper alloy, and the portion exposed on the outer surface of the sealing plate 14 can be made of aluminum or an aluminum alloy.

[0044] like Figure 1 As shown, plate-shaped positive electrode external conductive member 32 and negative electrode external conductive member 42 are mounted on the outer surface of the sealing plate 14. The positive electrode external conductive member 32 is electrically connected to the positive terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative terminal 40. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are components used to install busbars when multiple non-aqueous electrolyte secondary batteries 100 are electrically connected to each other. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are preferably made of metal, more preferably, for example, aluminum or an aluminum alloy. The positive electrode external conductive member 32 and negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external insulating member 92. However, the positive electrode external conductive member 32 and negative electrode external conductive member 42 are not essential and can be omitted in other embodiments.

[0045] Figure 3 An oblique view is shown schematically of the electrode assembly 20 mounted on the sealing plate 14. Figure 4 This is a schematic perspective view of electrode body 20a. In the non-aqueous electrolyte secondary battery 100 of this embodiment, an electrode body group 20 having multiple electrode bodies 20a, 20b, and 20c is housed inside the battery casing 10. However, the number of electrode bodies disposed inside an outer casing 12 is not particularly limited; it can be two or more, or it can be one. Detailed construction will be described later. Electrode bodies 20a, 20b, and 20c have positive electrode group 23 composed of multiple positive electrode plates 22t and negative electrode group 25 composed of multiple negative electrode plates 24t, respectively. A positive current collector 50 forms a conductive path electrically connecting the positive electrode group 23 and the positive terminal 30. Similarly, a negative current collector 60 forms a conductive path electrically connecting the negative electrode group 25 and the negative terminal 40. Specifically, the positive electrode group 23 is located at one end of electrode body 20a, and the negative electrode group 25 is located at the other end.

[0046] like Figure 2 As shown, the positive electrode current collector 50 includes: a plate-shaped conductive member extending along the inner side of the sealing plate 14, namely the first positive electrode current collector 51, and a plate-shaped conductive member extending along the vertical direction Z, namely the second positive electrode current collector 52. The lower end of the positive terminal 30 extends into the battery casing 10 through the terminal lead-out hole 18 of the sealing plate 14 and is connected to the first positive electrode current collector 51 (see reference). Figure 2 On the other hand, such as Figure 2As shown, the positive electrode second current collector 52 has one end connected to the positive electrode first current collector 51 and the other end connected to the positive electrode sheet group 23 of the electrode body assembly 20, forming a connection portion J. The positive electrode sheet group 23 of the electrode body assembly 20 is bent such that the positive electrode second current collector 52 faces the side of the positive electrode sheet group 23 having electrode bodies 20a, 20b, and 20c. This reduces the width of the positive electrode sheet group 23 in the long side direction Y. As a result, the coating width of the positive electrode active material layer 22a and the negative electrode active material layer 24a of the electrode body assembly 20 (described later) in the long side direction Y can be increased, thus enabling a high-capacity non-aqueous electrolyte secondary battery 100. Furthermore, the positive electrode first current collector 51 and the positive electrode second current collector 52 are preferably made of metal, such as aluminum, aluminum alloy, nickel, or stainless steel.

[0047] like Figure 2 As shown, the negative electrode current collector 60 includes: a plate-shaped conductive member extending along the inner side of the sealing plate 14, namely the negative electrode first current collector 61, and a plate-shaped conductive member extending along the vertical direction Z, namely the negative electrode second current collector 62. The lower end of the negative terminal 40 extends into the battery casing 10 through the terminal lead-out hole 18 of the sealing plate 14 and is connected to the negative electrode first current collector 61 (see reference). Figure 2 On the other hand, such as Figure 2 As shown, regarding the second negative electrode current collector 62, one end is connected to the first negative electrode current collector 61, and the other end is connected to the negative electrode sheet group 25 of the electrode body assembly 20, forming a connection portion J. The negative electrode sheet group 25 of the electrode body assembly 20 is bent so that the second negative electrode current collector 62 faces the side of the negative electrode sheet group 25 having electrode bodies 20a, 20b, and 20c. Therefore, similar to the configuration described above where the positive electrode sheet group 23 is bent, a high capacity non-aqueous electrolyte secondary battery 100 can be achieved. Furthermore, the first negative electrode current collector 61 and the second negative electrode current collector 62 are preferably made of metal, such as copper, copper alloy, nickel, or stainless steel.

[0048] In the non-aqueous electrolyte secondary battery 100 of this embodiment, various insulating components are installed between the components to prevent conduction between any components.

[0049] An insulating member to prevent conductivity is installed between the battery casing 10 and the electrode assembly 20. Specifically, an external insulating member 92 (see reference 1) is provided between the positive electrode external conductive member 32 (or the negative electrode external conductive member 42) and the outer surface of the sealing plate 14. Figure 2 Therefore, it is possible to prevent the positive electrode external conductive component 32, the negative electrode external conductive component 42 from conducting with the sealing plate 14.

[0050] Washers 90 are installed in each of the terminal outlet holes 18 and 19 of the sealing plate 14. This prevents the positive terminal 30 (or negative terminal 40) inserted into the terminal outlet holes 18 and 19 from conducting with the sealing plate 14.

[0051] An internal insulating member 94 is disposed between the positive electrode first current collector 51 (or the negative electrode first current collector 61) and the inner surface of the sealing plate 14. This internal insulating member 94 includes a plate-shaped base 94a that mediates between the positive electrode first current collector 51 (or the negative electrode first current collector 61) and the inner surface of the sealing plate 14. This prevents the positive electrode first current collector 51, the negative electrode first current collector 61, and the sealing plate 14 from conducting. Furthermore, the internal insulating member 94 includes a protrusion 94b that protrudes from the inner surface of the sealing plate 14 toward the electrode assembly 20. This restricts the movement of the electrode assembly 20 in the vertical direction Z, preventing direct contact between the electrode assembly 20 and the sealing plate 14.

[0052] There are no particular restrictions on the materials used for the aforementioned insulating components, as long as they possess the specified insulation properties. For example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)) and fluorine resins (e.g., perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0053] Figure 5 This is a schematic diagram illustrating the structure of electrode 20a. The following explanation uses electrode 20a as an example; electrode bodies 20b and 20c can be configured with the same structure. Figure 5 As shown, the electrode body 20a has a positive electrode 22 and a negative electrode 24. The electrode body 20a is a flat, wound electrode body formed by stacking strip-shaped positive electrodes 22 and strip-shaped negative electrodes 24 via strip-shaped separators 26 and winding them around a winding shaft WL. The positive electrode 22 and negative electrode 24 are examples of the first and second electrodes disclosed herein.

[0054] Electrode body 20a is disposed inside the outer casing 12 in a direction parallel to the long side direction Y of the winding shaft WL. In other words, electrode body 20a is disposed inside the outer casing 12 in a direction parallel to the bottom wall 12a and orthogonal to the short side wall 12c of the winding shaft WL. The end face of electrode body 20a (in other words, the laminated surface where the positive electrode 22, negative electrode 24, and separator 26 are stacked) Figure 5 The end face of the long side in the Y direction is opposite to the short sidewall 12c. However, the electrode body 20a may be a stacked electrode body formed by overlapping multiple square (typically rectangular) positive electrodes 22 and multiple square (typically rectangular) negative electrodes in an insulated state.

[0055] Positive electrode 22 Figure 5As shown, it has a positive electrode core 22c and a positive electrode active material layer 22a formed on at least one surface (here, both surfaces) of the positive electrode core 22c.

[0056] The positive electrode core 22c is in the form of a strip and is made of conductive metals such as aluminum, aluminum alloy, nickel, and stainless steel. In this case, the positive electrode core 22c is a metal foil, specifically an aluminum foil.

[0057] Positive electrode active material layer 22a, such as Figure 5 As shown, the positive electrode active material comprises a strip-shaped arrangement along the longitudinal direction of the strip-shaped positive electrode core 22c, capable of reversibly absorbing and releasing charge carriers. From the viewpoint of mitigating the temperature dependence of battery voltage (described later), the density of the positive electrode active material layer is preferably 3.0 g / ml or more, more preferably about 3.5 g / ml or more. Furthermore, from the same viewpoint, the coating amount of the positive electrode active material layer 24a is preferably 380 g / ml. 2 The above, preferably 410g / m 2 The above is a preferred option, with 440g / m³. 2 Left or right or above.

[0058] As the positive electrode active material, it is preferable to contain at least one of Ni, Co, and Mn. For example, lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxides can be used. When the total solid content of the positive electrode active material layer 22a is set to 100% by mass, the positive electrode active material can account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more.

[0059] The positive electrode active material layer 22a may contain any components other than the positive electrode active material, such as conductive materials, binders, and various additives. For example, carbon materials such as carbon black (e.g., acetylene black (AB)) and carbon nanotubes can be used as conductive materials. For example, PVdF can be used as a binder.

[0060] Negative electrode 24 Figure 5 As shown, it has a negative electrode core 24c and a negative electrode active material layer 24a formed on at least one surface (here, both surfaces) of the negative electrode core 24c.

[0061] The negative electrode core 24c is in the form of a strip, and is made of conductive metals such as copper, copper alloy, nickel, or stainless steel. In this case, the negative electrode core 24c is a metal foil, specifically a copper foil.

[0062] like Figure 5As shown, the negative electrode active material layer 24a comprises a negative electrode active material arranged in a strip shape along the longitudinal direction of the strip-shaped negative electrode core 24c, capable of reversibly absorbing and releasing charge carriers. From the viewpoint of reducing the temperature dependence of battery voltage (described later), the density of the negative electrode active material layer is preferably 1.4 g / ml or more, more preferably about 1.5 g / ml or more. Furthermore, from the same viewpoint, the coating amount of the negative electrode active material layer 24a is preferably 185 g / ml. 2 The above is preferred, with 220g / m 2 The above is a preferred option, with 250g / m³. 2 Left or right or above.

[0063] The negative electrode active material is a negative electrode active material that can reversibly absorb, store, and release charge carriers (such as carbon materials like graphite, Si, SiO2). x The silicon dioxide and Li shown are (0.05 < x < 1.95). x Si y O z (x, y, z independently satisfy 0 ≤ x, y, z ≤ 1) Lithium silicon oxide, Li 21 When the solid composition of the negative electrode active material layer 24a is set to 100% by mass (as shown in Si5, lithium-silicon alloy containing lithium), the negative electrode active material can account for approximately 80% or more by mass, typically 90% or more by mass, and for example, 95% or more by mass.

[0064] The negative electrode active material layer 24a may contain any components other than the negative electrode active material, such as binders, dispersants, and various additives. For example, rubbers such as styrene-butadiene rubber (SBR) can be used as binders. For example, cellulose-based materials such as carboxymethyl cellulose (CMC) can be used as dispersants.

[0065] 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. Preferably, the separator 26 is a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). Furthermore, a heat resistance layer (HRL) containing inorganic fillers may be provided on the surface of the resin sheet. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titanium dioxide. Additionally, an adhesive layer is preferably provided on one or both surfaces of the separator 26. The adhesive layer improves adhesion to the contacting positive electrode active material layer 22a or negative electrode active material layer 24a. The adhesive layer contains, for example, polyvinylidene fluoride (PVdF) as an adhesive component. Alternatively, the adhesive layer may contain inorganic particles such as alumina or boehmite. The adhesive layer may be provided on the surface of the resin sheet or on the surface of the HRL.

[0066] The non-aqueous electrolyte can be the same as before, without any particular limitations. For example, the non-aqueous electrolyte may contain a non-aqueous solvent and a supporting salt. The non-aqueous solvent may include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt may be a fluorinated lithium salt such as LiPF6. However, the non-aqueous electrolyte may be in solid form (solid electrolyte) and can be integrated with the electrode assembly 20.

[0067] 2. Manufacturing method of non-aqueous electrolyte secondary battery

[0068] Figure 6 This is a flowchart illustrating a part of the manufacturing method of a non-aqueous electrolyte secondary battery. The following describes each step.

[0069] Assembly Process

[0070] In the assembly preparation process, an assembly is prepared in which the aforementioned electrode body and the aforementioned non-aqueous electrolyte are housed within the aforementioned battery casing. In this specification, "assembly" refers to a non-aqueous electrolyte secondary battery prior to the initial charging process described later.

[0071] <Initial Charging Process>

[0072] In the initial charging process, the assembly is charged to a specified voltage V0. Specifically, the electrodes of the external charging device are connected to the electrode terminals of the assembly, and the assembly is charged to the specified voltage V0 at room temperature (e.g., around 20°C to 30°C).

[0073] As an example of the charging process at this time, constant current charging at approximately 0.1C to 10C can be performed until the voltage between the terminals (the voltage between the positive and negative terminals) reaches a specified value, followed by constant voltage charging until the battery voltage reaches approximately 3.4V to 3.6V (CC-CV charging). However, there are no particular restrictions on the charging conditions in this process, and they can be appropriately changed according to the specifications of the non-aqueous electrolyte secondary battery being manufactured.

[0074] Furthermore, there is no particular limit to the number of times the charging process is performed in this step. For example, in this step, a charge-discharge cycle combining charging and discharging processes can be repeated multiple times.

[0075] During the initial charging of a non-aqueous electrolyte secondary battery, the electrode active material can decompose the electrolyte components, additives, and other organic matter in contact above a specified potential. These decomposition products deposit as an SEI film on the surface of the electrode active material. In other words, the SEI film is formed by the mixture of decomposition products from electrolyte components, additives, etc. Although the SEI film is not electronically conductive, it allows ion passage because it is not a completely continuous membrane. Therefore, the SEI film can stabilize and deactivate the surface of the electrode active material, inhibiting excessive decomposition of electrolyte components, etc.

[0076] From the viewpoint of forming a high-quality SEI film in the initial charging process, the voltage V0 specified above is preferably 3.48V or higher, and may be 3.54V or higher, or may be 3.58V or higher.

[0077] <Aging Process>

[0078] In the aging process, the assembly after the initial charging process described above is held in a high-temperature environment. By implementing the aging process, excess components of the SEI film formed on the surface of the negative electrode using the initial charging process described above are decomposed, thereby modifying the SEI film.

[0079] Furthermore, the conditions of the aging process can be appropriately adjusted according to the required SEI film modification method, and there are no particular limitations. For example, the aging temperature in the aging process can be set to 30°C or higher, preferably 40°C or higher, such as 50°C or higher, and further, 60°C or higher. There is no particular upper limit to the aging temperature; for example, it can be set to around 80°C or lower. Temperature management in the aging process can be achieved, for example, using a constant temperature bath. The duration of the aging process (aging time) can be appropriately changed according to the aging temperature, and there are no particular limitations. For example, when the aging temperature is around 45–70°C, the aging time is preferably around 3–20 hours. Additionally, when the aging temperature is around 70–75°C, the aging time is preferably around 1–15 hours.

[0080] Furthermore, during the aging process, it is preferable to apply a load along the short side (X) of the assembly while aging. The amount of load applied to the assembly during the aging process is not particularly limited, but is preferably 0.5 to 0.7 MPa.

[0081] <Voltage Adjustment Process>

[0082] In the voltage adjustment process, the assembly after the aging process is adjusted to a specified voltage V1. The temperature of the non-aqueous electrolyte secondary battery during the voltage adjustment process only needs to be lower than the temperature during the aging process, for example, room temperature (around 20-30°C). Furthermore, from the end of the aging process until the start of the voltage adjustment process, the non-aqueous electrolyte secondary battery can be intentionally cooled to room temperature, or allowed to cool naturally. The specified voltage V1 is determined based on the temperature dependence of the battery voltage. Therefore, in the manufacture of the non-aqueous electrolyte secondary battery disclosed herein, as a preparation, it is necessary to measure the temperature dependence of the battery voltage at any charging voltage for a secondary battery that is actually intended for use. In this specification, the temperature dependence of the battery voltage refers to the change in battery voltage associated with each unit change in temperature of the battery.

[0083] As a method for deriving the temperature dependence of the battery voltage, the charging voltage of the non-aqueous electrolyte secondary battery is adjusted to an arbitrary value (e.g., 3.5V), and the battery voltage (v1, v2) is measured at two arbitrary temperature points (e.g., t1 = 25°C, t2 = 30°C). Then, the voltage is derived according to the following formula (1).

[0084] Temperature dependence of battery voltage = (v2-v1) / (t2-t1) Equation (1)

[0085] Then, when the temperature dependence of the battery voltage is >0, the temperature dependence of the battery voltage of the non-aqueous electrolyte secondary battery is set to positive.

[0086] Figure 7 (A) is a graph showing the temperature dependence of battery voltage at any charging voltage, measured at 25°C. Figure 7 (B) is to Figure 7 (A) is a partially enlarged diagram. Furthermore, self-discharge checks do not necessarily need to be performed at 25°C; there are no temperature restrictions. For example... Figure 7 As shown, in the non-aqueous electrolyte secondary battery disclosed herein, when the charging voltage is less than 3.585V, the temperature dependence of the battery voltage becomes negative. On the other hand, when the charging voltage is 3.585V or higher, the temperature dependence of the battery voltage becomes positive.

[0087] When the temperature dependence of battery voltage is positive, the battery voltage increases with increasing battery temperature. At this time, although the negative electrode potential increases with increasing battery temperature, the charge carriers (in this case, lithium ions) forming the double layer at the negative electrode interface are released from near the interface into the electrolyte. Based on their concentration change, the negative electrode potential decreases. Then, when the battery is cooled back to its original temperature, since the aforementioned charge carriers have not completely returned to the double layer at the negative electrode interface, the negative electrode potential remains at a corresponding decrease, resulting in an increase in battery voltage as a whole. Furthermore, in non-aqueous electrolyte secondary batteries that have undergone the aforementioned temperature change process, the concentration of charge carriers in the double layer at the negative electrode interface is relatively low (the released charge carriers have not completely returned), so even with further temperature changes, the change in charge carrier concentration in the double layer is small, making it difficult for the battery voltage to fluctuate. Moreover, the above explanation of the mechanism of action of this technology is speculative and does not limit the scope of this technology.

[0088] With regard to the specified voltage V1, the temperature dependence of the battery voltage of the non-aqueous electrolyte secondary battery disclosed herein is set to a positive value, and from the viewpoint of preferably achieving the effect of reducing its absolute value, it is preferably 3.585V or more, more preferably 3.600V or more, and particularly preferably 3.800V or more.

[0089] <Temperature adjustment process>

[0090] In the temperature adjustment process, the initial temperature of the assembly after the voltage adjustment process is set as T1. The assembly is heated until it reaches a temperature T2 that is higher than T1. Then, the assembly is cooled down until it reaches a temperature T3 that is lower than T2.

[0091] The temperature T1 mentioned above refers to the temperature of the non-aqueous electrolyte secondary battery during the initial temperature adjustment process, and is not particularly limited; for example, it can be room temperature (e.g., around 20-30°C). From the viewpoint of preferably reducing the temperature dependence of the battery voltage of the non-aqueous electrolyte secondary battery according to this disclosure, the temperature difference between T1 and T2 is preferably 3°C or more, more preferably 5°C or more, and particularly preferably 7°C or more. Furthermore, there is no particular limitation on the upper limit of the temperature difference; for example, it can be below 20°C or below 15°C. There is no particular limitation on the method for heating the assembly from T1 to T2; for example, a constant temperature bath can be used.

[0092] The aforementioned T3 refers to the temperature at which the temperature adjustment process ends. It can be the same as or different from T1, as long as the above criteria are met. It should be noted that there are no particular limitations on the method for cooling the assembly from T2 to T3; for example, a constant temperature bath can be used. Furthermore, from the viewpoint of reducing the temperature dependence of the battery voltage in the non-aqueous electrolyte secondary battery disclosed herein, the holding time after reaching T2 or T3 is preferably 24 hours or more, more preferably 36 hours or more, and particularly preferably 48 hours or more.

[0093] In a preferred embodiment of the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein, the temperature adjustment process is performed once or repeated two or more times. When repeated two or more times, the temperature difference δT between T2 and T1 in each temperature adjustment process may be the same or different. Furthermore, the temperature adjustment process may not require cooling after heating and can be completed after the non-aqueous electrolyte secondary battery has been heated.

[0094] <Self-discharge inspection procedure>

[0095] After the temperature adjustment process described above, a self-discharge test is performed at a temperature T4, which is lower than T2. ​​T4 is the temperature at which the self-discharge test begins; it can be the same as or different from T3, as long as the above criteria are met. From the viewpoint of preferably reducing the temperature dependence of the battery voltage of the non-aqueous electrolyte secondary battery involved in this disclosure, the temperature difference between T2 and T4 is preferably 3°C or more, more preferably 5°C or more, and particularly preferably 7°C or more.

[0096] In the self-discharge inspection, the assembled body after the temperature adjustment process is maintained at room temperature (for example, around 20 to 30 °C), and the amount of decrease in the battery voltage due to self-discharge is measured. Then, based on the amount of decrease in the battery voltage, an inspection is performed to determine whether an internal short circuit has occurred in the assembled body (whether it is a qualified product). Compared with a battery without an internal short circuit, a battery with an internal short circuit has a larger amount of discharge generated by self-discharge and tends to have a larger difference in battery voltage before and after self-discharge. Furthermore, there is no particular limitation on the method of temperature adjustment during the self-discharge inspection. For example, a thermostatic bath can be used.

[0097] Figure 8 A diagram schematically showing the temperature change process of the assembled body during the manufacturing process. Moreover, the manufacturing method of the non-aqueous electrolyte secondary battery related to the present disclosure includes the above processes. Furthermore, for the subsequent manufacturing processes, they can be carried out according to the conventionally well-known manufacturing methods.

[0098] 1. Test Example

[0099] The following describes test examples related to the technology disclosed herein, and it is not intended to limit the technology disclosed herein to these test examples.

[0100] (1) Assembled Body Preparation Process

[0101] [1] Examples 1 to 3

[0102] Lithium nickel cobalt manganese composite oxide (NCM) as the positive electrode active material, polyvinylidene fluoride (PVdF) as the binder, and carbon nanotubes (CNT) as the conductive material were weighed so that the mass ratio became NCM:PVdF:CNT = 97.5:1.5:1, and they were mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode paste with a density of 3.55 g / mL. The positive electrode paste was coated on both sides of a long strip-shaped positive electrode core (aluminum foil, 12 μm thick), and dried. It was cut into a specified size and rolled by a roll press to obtain a positive electrode sheet having a positive electrode active material layer with a coating amount of 450 g / m 2 on both sides of the positive electrode core.

[0103] Next, natural graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the tackifier were weighed so that the mass ratio became C:SBR:CMC = 98.5:1:0.5, and they were mixed in water to prepare a negative electrode paste with a density of 1.50 g / mL. The negative electrode paste was coated on both sides of a long strip-shaped negative electrode core (copper foil, 9 μm thick), and dried. It was cut into a specified size and rolled by a roll press to obtain a negative electrode sheet having a negative electrode active material layer with a coating amount of 250 g / m 2 on both sides of the negative electrode core.

[0104] Next, a three-layer structure of PE / PP / PE, with a thickness of 14μm, is prepared and stacked in the order of positive electrode, separator, and negative electrode. After the electrode terminals are installed on the fabricated electrode body, it is housed in the battery casing together with the non-aqueous electrolyte.

[0105] As a non-aqueous electrolyte, the product containing LiPF6 as a supporting salt was dissolved at a concentration of 1.15 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:3:4.

[0106] [2] Comparative Example 1

[0107] The assemblies were fabricated in the same manner as in Examples 1-3.

[0108] (2) Evaluation of experimental preparation

[0109] [1] Example 1

[0110] • Initial charging process

[0111] The assembly prepared in the assembly preparation process was charged to the specified upper limit voltage at a constant current of 0.1C in an environment of 25°C, and then discharged to 3.58V under constant current for initial charging.

[0112] • Aging process

[0113] The assembly, after initial charging, was kept at 57°C for 6 hours.

[0114] • Voltage adjustment process

[0115] After the aging process, the assembly is cooled to 25°C and then charged and discharged to a charging voltage of 3.603V.

[0116] • Temperature undergoes adjustment process

[0117] After the voltage adjustment process, the assembly at 25°C (T1) is kept at 30°C for 24 hours, and then heated to 30°C (T2). Then, it is cooled to 25°C (T3 and T4).

[0118] [2] Example 2

[0119] Except for the two temperature increases described above after the voltage adjustment process, the evaluation test preparation was performed in the same manner as in Example 1. Furthermore, the non-aqueous electrolyte secondary battery was intentionally cooled in a constant temperature bath at 25°C between the first and second temperature increases.

[0120] [3] Example 3

[0121] Except for the three heating cycles described above after the voltage adjustment process, the evaluation test preparation was performed in the same manner as in Example 1. Furthermore, the non-aqueous electrolyte secondary battery was intentionally cooled in a constant temperature bath at 25°C between the first and second heating cycles and between the second and third heating cycles.

[0122] [4] Comparative Example 1

[0123] Except for the absence of a temperature adjustment process, the evaluation test preparation was carried out in the same manner as in Examples 1-3.

[0124] 2. Evaluation Test

[0125] [1] Examples 1-3

[0126] The voltage E1 of the above assembly was measured at 30°C (T2) during the final temperature rise after the temperature adjustment process. Then, after maintaining the assembly at 25°C for 24 hours (T4), the voltage E2 was measured. The temperature dependence of the battery voltage was determined by dividing the difference between E2 and E1 by the temperature change.

[0127] [2] Comparative Example 1

[0128] The voltage E1 of the assembly at 25°C (equivalent to T4) after the voltage adjustment process (without a temperature adjustment process) was measured. Then, after maintaining the assembly at 30°C for 24 hours, the voltage E2 was measured. The temperature dependence of the battery voltage was determined by dividing the difference between E2 and E1 by the temperature change. That is, in Examples 1-3 and Comparative Example 1, the temperatures at which E1 and E2 were measured were reversed.

[0129] The experimental results are summarized in Table 1. Figure 9 .

[0130] Table 1

[0131]

[0132] In Examples 1-3, the temperature dependence of the battery voltage showed positive values, and its absolute value was relatively small. Furthermore, the more times the temperature was raised, the more significant the effect of reducing temperature dependence was observed. On the other hand, in Comparative Example 1, although the charging voltage of 3.585V or higher, where the temperature dependence of the battery voltage became positive, was adjusted during the voltage adjustment process, no temperature adjustment was performed, therefore its absolute value was relatively large.

[0133] The above-described specific embodiments are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations to the embodiments described above.

[0134] Explanation of reference numerals in the attached figures

[0135] 10 Battery casing

[0136] 12 outer body

[0137] 14 Sealing board

[0138] 20 electrode assembly

[0139] Electrode bodies 20a, 20b, and 20c

[0140] 22 Positive electrode

[0141] 22a Positive electrode active material layer

[0142] 22c positive electrode core

[0143] 22t positive electrode sheet

[0144] 24 Negative electrode

[0145] 24a Negative electrode active material layer

[0146] 24C negative electrode core

[0147] 24t negative electrode sheet

[0148] 26 partitions

[0149] 30 Positive extremes

[0150] 40 Negative extremes

[0151] 50 Positive current collector

[0152] 60 Negative current collector

[0153] 100 Non-aqueous electrolyte secondary battery

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising an electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte, comprising the following steps: An assembly preparation process for preparing an assembly that houses the electrode body and the non-aqueous electrolyte in a battery casing; The initial charging process of charging the assembly to a specified voltage V0; An aging process in which the assembly is stored at or above 45°C for more than 3 hours after the initial charging process; A voltage adjustment process that adjusts the assembly to a voltage V1 of 3.585V or higher after the aging process; After the voltage adjustment process, the initial temperature of the assembly is set to T1. The assembly is then heated to a temperature T2, which is higher than T1. Finally, the assembly is cooled to a temperature T3, which is lower than T2, undergoing an adjustment process. A self-discharge check process is performed at a temperature T4, which is lower than T2, after the temperature has undergone an adjustment process.

2. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein, The negative electrode comprises a negative electrode core and a negative electrode active material layer formed on at least one surface of the negative electrode core, the negative electrode active material layer having a density of 1.4 g / mL or more and a coating amount of 185 g / mL. 2 above.

3. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The temperature adjustment process is performed once or repeated more than twice, wherein when it is repeated more than twice, the temperature difference δT between T2 and T1 in each temperature adjustment process is the same or different.

4. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 3, wherein, The temperature difference between T2 and T4 is greater than 3°C.

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