Nonaqueous electrolyte secondary battery

Abstract

The disclosed nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode (12), a separator disposed between the positive electrode and the negative electrode (12), and a nonaqueous electrolyte. The negative electrode (12) includes a negative electrode current collector (12a), a negative electrode tab (12b), and a first lithium layer (12c1) containing a lithium metal and / or a lithium alloy. In a connection portion (C) between the negative electrode current collector (12a) and the negative electrode tab (12b), the negative electrode current collector (12a) and the negative electrode tab (12b) are connected via the first lithium layer (12c1), and the negative electrode current collector (12a) and the negative electrode tab (12b) are not in contact.

Description

Technical Field

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

[0002] Non-aqueous electrolyte secondary batteries possess high output and high energy density, thus finding applications in various fields such as consumer electronics and / or automotive. In recent years, there has been a demand for further high performance in non-aqueous electrolyte secondary batteries. Various solutions have been proposed for non-aqueous electrolyte secondary batteries.

[0003] Claim 1 of Patent Document 1 (Japanese Patent No. 6219273) describes "a negative electrode for a lithium secondary battery, which further comprises: a negative electrode current collector; a negative electrode active material layer disposed on a portion of the surface of the negative electrode current collector; a lithium layer comprising metallic lithium disposed on a non-disposal region of the surface of the negative electrode current collector where the negative electrode active material layer is not disposed; and a negative electrode lead resistively bonded to the non-disposal region of the negative electrode current collector, wherein the lithium layer is disposed at least a portion between the negative electrode lead and the negative electrode current collector."

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6219273 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Currently, there is a demand for further high performance in non-aqueous electrolyte secondary batteries; therefore, research has been conducted on reducing the internal resistance of the battery. Among the methods for reducing the internal resistance of the battery, reducing the resistance between the negative electrode current collector and the negative electrode tab is particularly important. One of the objectives of this disclosure is to provide a non-aqueous electrolyte secondary battery with low resistance between the negative electrode current collector and the negative electrode tab.

[0009] Solution for solving the problem

[0010] One aspect of this disclosure relates to a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery includes: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte; the negative electrode includes: a negative current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy; in the connection between the negative current collector and the negative electrode tab, the negative current collector and the negative electrode tab are connected by the first lithium layer, and the negative current collector and the negative electrode tab are not in contact.

[0011] The effects of the invention

[0012] According to this disclosure, a non-aqueous electrolyte secondary battery with low resistance between the negative electrode current collector and the negative electrode tab can be obtained.

[0013] The novel features of the invention are set forth in the claims, but the invention relates to both its structure and content, and will be better understood, together with other objects and features of the invention, by reference to the following detailed description of the accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a schematic cross-sectional view of the non-aqueous electrolyte secondary battery of Embodiment 1.

[0015] Figure 2 It is a schematic representation Figure 1 A cross-sectional view of an example of the connection between the negative current collector and the negative electrode tab in a non-aqueous electrolyte secondary battery.

[0016] Figure 3 It is a schematic representation Figure 1 A top view of an example of the connection between the negative current collector and the negative electrode tab in a non-aqueous electrolyte secondary battery.

[0017] Figure 4 It is a schematic representation Figure 1 A cross-sectional view of another example of the connection between the negative current collector and the negative electrode tab in a non-aqueous electrolyte secondary battery. Detailed Implementation

[0018] The following description illustrates embodiments of this disclosure by way of examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and / or materials are sometimes used as examples, but other numerical values ​​and / or materials can be applied as long as the effects of this disclosure are achieved. In this specification, the description of "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower". In the following description, when lower and upper limits are given for numerical values ​​relating to specific physical properties and / or conditions, any of the lower limits and any of the upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. In the following description, when examples of constituent elements and / or methods are listed, unless specifically stated otherwise, only one of the listed examples can be used, or multiple of the listed examples can be used together.

[0019] (Non-aqueous electrolyte secondary battery)

[0020] Hereinafter, the non-aqueous electrolyte secondary battery of this embodiment will sometimes be referred to as "secondary battery (B)". Secondary battery (B) includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The negative electrode includes a negative current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy. In the connection portion between the negative current collector and the negative electrode tab (hereinafter, sometimes referred to as "connection portion (C)"), the negative current collector and the negative electrode tab are connected by the first lithium layer, and the negative current collector and the negative electrode tab are not in contact.

[0021] The conductivity of the lithium layer is lower than that of the metal constituting the negative electrode tab. Therefore, the resistance between the negative electrode tab and the negative electrode current collector is reduced by directly connecting the negative electrode current collector to the negative electrode tab. However, as a result of research, the inventors of this application have newly discovered that when a lithium layer is formed on the negative electrode current collector, if the lithium layer in the connection portion is removed and the negative electrode current collector is directly connected to the negative electrode tab, the resistance of the connection portion becomes high. As a result of further research, the inventors of this application have newly discovered that, with the above-described configuration of the secondary battery (B), the resistance between the negative electrode current collector and the negative electrode tab can be significantly reduced. This disclosure is based on this new insight.

[0022] The reason for the aforementioned effect is currently unclear, but one possible reason is that the lithium layer is relatively soft. The relatively soft lithium layer functions as a buffer when connecting the negative current collector to the negative electrode tab, thus allowing for good bonding between the layers in the connection area. As a result, it is believed that the resistance between the negative current collector and the negative electrode tab can be reduced.

[0023] The negative electrode current collector has a first main surface and a second main surface opposite to the first main surface. A first lithium layer is disposed on the first main surface. The negative electrode may further include a second lithium layer containing lithium metal and / or a lithium alloy. The second lithium layer is disposed on the second main surface of the negative electrode current collector and is positioned opposite the first lithium layer, sandwiching the negative electrode current collector. By forming the second lithium layer, the resistance around the negative electrode tab can be further reduced. The second lithium layer is relatively soft, and therefore can function as a buffer when connecting the negative electrode tab to the negative electrode current collector. Therefore, it is believed that by using the second lithium layer, the resistance between the negative electrode current collector and the negative electrode tab can be further reduced.

[0024] The first lithium layer can be formed on the first main surface of the negative electrode current collector. However, the first lithium layer can also be formed on the surface of the negative electrode tab.

[0025] The thickness of the first lithium layer can be 0.1 μm or more, 1.0 μm or more, 3.0 μm or more, 5.0 μm or more, or 10 μm or more, or it can be less than 50 μm, 30 μm or less, 20 μm or less, 10 μm or less, or 5.0 μm. The thickness of the first lithium layer can be between 0.1 μm and 30 μm. By setting the thickness of the first lithium layer to 0.1 μm or more, the resistance between the negative electrode current collector and the negative electrode tab can be particularly reduced. By setting the thickness of the first lithium layer to 30 μm or less, the increase in resistance caused by the lithium layer can be suppressed. The thickness of the second lithium layer can be within the range exemplified for the thickness of the first lithium layer. The thicknesses of the first and second lithium layers can be the same or different.

[0026] The first lithium layer may be formed only on the portion of the surface of the negative current collector connected to the negative electrode tab, or it may be formed only on the portion connected to the negative electrode tab and the surrounding area. Alternatively, the first lithium layer may be formed entirely on one side of the negative current collector. The area surrounding the portion connected to the negative electrode tab refers to the area within 3 mm (e.g., within 1 mm) from the outer edge of the negative electrode tab when viewed from above. The second lithium layer may be formed in the area sandwiching the negative current collector and opposite the area where the first lithium layer is formed.

[0027] (Negative current collector)

[0028] The negative current collector can be made of metal foil, such as copper foil and / or copper alloy foil, copper-plated resin sheets (e.g., polyethylene terephthalate sheets), stainless steel foil, or copper-plated stainless steel foil. The content of elements other than copper in the copper alloy is typically less than 30% by mass (e.g., less than 10% by mass). Examples of elements other than copper include zinc, tin, aluminum, beryllium, nickel, iron, and manganese. Furthermore, forming a conductive film on the current collector is also included.

[0029] The first lithium layer can be formed in part or all of one main surface (the first main surface) of the negative electrode current collector. The second lithium layer can also be formed in part or all of the other main surface (the second main surface) of the negative electrode current collector. The thickness of the negative electrode current collector can be in the range of 6 μm to 20 μm (e.g., 8 μm to 15 μm).

[0030] The lithium layers (first lithium layer, second lithium layer) contain at least one element selected from the group consisting of lithium metal and lithium alloys. The lithium layers can be either lithium metal layers or lithium alloy layers. The lithium alloy layers consist of lithium and elements other than lithium. Examples of other elements (e.g., other metallic elements) include magnesium, aluminum, indium, copper, zinc, potassium, calcium, sodium, silver, gold, etc. The content of other elements can be less than 5% by mass (e.g., less than 3% by mass).

[0031] There is no particular limitation on the method for forming the lithium layer, and known methods can be used. For example, the lithium layer can be formed by pressing a lithium foil onto a negative electrode current collector. Alternatively, the lithium layer can be formed by vapor deposition. Alternatively, the lithium layer can be formed using a resin sheet on which the lithium layer has been formed. For example, firstly, a resin sheet on which the lithium layer has been formed and a negative electrode current collector are laminated and pressed together with the lithium layer in contact with the negative electrode current collector. Then, by peeling off the resin sheet, a negative electrode current collector on which the lithium layer has been formed is obtained. The method of using a resin sheet on which the lithium layer has been formed and / or vapor deposition is suitable for forming a thin lithium layer.

[0032] (Negative electrode)

[0033] The negative electrode tab is not particularly limited and any known negative electrode tab can be used. One end of the negative electrode tab is connected to the negative current collector in the connection part (C) via the first lithium layer. The other end of the negative electrode tab is electrically connected to the negative terminal (e.g., the battery casing).

[0034] The negative electrode tab can be formed of metal. The negative electrode tab can be made of metal foil. Alternatively, the negative electrode tab can also be made of a cladding material comprising a metal foil and nickel layers formed on both sides of the metal foil. Examples of metals constituting the metal foil include copper, copper alloys, iron, iron alloys, etc. A nickel layer may be present on the main surface of the negative electrode tab that contacts the first lithium layer. In a preferred embodiment, nickel layers are present on both sides of the negative electrode tab.

[0035] The size of the negative electrode tab is determined by factors such as discharge capacity. The width of the negative electrode tab can range from 1mm to 50mm (e.g., 1mm to 5mm). The thickness of the negative electrode tab can range from 6μm to 200μm (e.g., 50μm to 150μm).

[0036] The secondary battery (B) includes at least one negative electrode tab. The secondary battery (B) may include multiple negative electrode tabs. In this case, each of the multiple negative electrode tabs is connected to the negative current collector in its respective connection portion (C) via a first lithium layer, and does not contact the negative current collector.

[0037] The ratio Lt / Wc of the length Lt of the negative electrode tab in the connecting part (C) to the width Wc of the negative electrode current collector is not particularly limited and can be in the range of 0.03 to 1.0 (e.g., 0.04 to 0.5). When the ratio Lt / Wc = 1.0, the negative electrode tab is connected to the negative electrode current collector along the entire width direction of the negative electrode current collector.

[0038] The secondary battery (B) may include an insulating tape (protective tape) attached to the negative electrode in a manner that covers the negative electrode tab. By using such an insulating tape, short circuits can be suppressed. The insulating tape is not particularly limited; any known insulating tape used in batteries can be used. The insulating tape may also be made of insulating resins such as polyimide, polytetrafluoroethylene (PTFE), or polypropylene (PP).

[0039] (Method for connecting the negative current collector and the negative electrode tab)

[0040] The negative current collector and the negative electrode tab are connected in a manner that satisfies the following conditions (1) and (2).

[0041] (1) In the connecting part (C), the negative current collector and the negative electrode tab are connected by the first lithium layer.

[0042] (2) In the connection part (C), the negative current collector is not in contact with the negative electrode tab.

[0043] The following describes an example of a connection method. First, a negative electrode current collector with a lithium layer formed on at least one side is prepared. Next, the negative electrode current collector and a negative electrode tab are stacked with the lithium layer disposed between them, and the negative electrode current collector, the lithium layer, and the negative electrode tab are connected. At this time, if the lithium layer melts and the negative electrode current collector and the negative electrode tab are in direct contact, the above conditions (1) and (2) are not satisfied. Therefore, resistance welding is not used in the connection of the connection part (C). Examples of methods for connection in a manner that satisfies conditions (1) and (2) include ultrasonic bonding, friction stirring bonding, etc.

[0044] To avoid the lithium layer melting and being removed, ultrasonic bonding is preferably performed under conditions where the lithium layer does not melt.

[0045] The following describes examples of the constituent elements of a secondary battery (B). There are no particular limitations on the constituent elements other than those characteristic of the secondary battery (B) of this disclosure; constituent elements used in known non-aqueous electrolyte secondary batteries may be applied.

[0046] The secondary battery (B) can be a lithium secondary battery (lithium metal secondary battery) that uses lithium metal (or lithium alloy) as the negative electrode active material. Alternatively, the secondary battery (B) can also be a battery that uses a material that reversibly absorbs and releases lithium ions as the negative electrode active material.

[0047] (negative electrode)

[0048] The negative electrode is selected based on the type of secondary battery (B). In the case of a lithium metal secondary battery, lithium metal is deposited in the negative electrode during charging and dissolves in the non-aqueous electrolyte during discharging. In this case, the negative electrode comprises the aforementioned negative electrode current collector. As described above, a lithium layer can be formed on the surface of the negative electrode current collector.

[0049] The negative electrode may comprise a negative current collector and a negative electrode binder layer formed on the negative current collector. The negative electrode binder layer contains a negative electrode active material and may also contain other additives (binders, conductive materials, thickeners, etc.) as needed. There are no particular limitations on the negative electrode binder layer, and known negative electrode binder layers can be used.

[0050] The negative electrode active material contained in the negative electrode composite layer can be a substance capable of reversibly absorbing and releasing lithium ions. Examples of such negative electrode active materials include carbonaceous materials and Si-containing materials. The negative electrode active material can contain Si-containing materials or be Si-containing materials alone. Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds (silicon oxides, etc.), and composite materials in which a silicon phase is dispersed within the lithium ion conducting phase (matrix). The negative electrode can contain only one type of negative electrode active material or two or more types of negative electrode active materials.

[0051] Examples of adhesives include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0052] Conductive materials can be made from conductive carbonaceous materials, such as carbon black, carbon nanotubes, and graphite. Examples of carbon black include acetylene black and Ketjen black.

[0053] Thickeners can be, for example, cellulose derivatives such as cellulose ethers. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. Examples of CMC modified forms include salts of CMC. As salts, alkali metal salts (e.g., sodium salts), ammonium salts, etc., can be listed.

[0054] (positive electrode)

[0055] The positive electrode may include, for example, a positive current collector and a positive flux layer formed on the positive current collector. Examples of materials for the positive current collector include metallic materials such as Al, Al alloys, Ti, Ti alloys, and Fe alloys. Fe alloys may also be stainless steel. The positive electrode may also include a positive electrode tab.

[0056] The positive electrode layer contains positive electrode active material and may also contain other additives (binders, conductive materials, thickeners, etc.) as needed. There are no particular limitations on the positive electrode layer; known positive electrode layers can be used. The binder, conductive material, and thickener can each be the binder, conductive material, and thickener specified in the material description for the negative electrode layer.

[0057] As positive electrode active materials, substances capable of reversibly absorbing and releasing lithium ions can be used. Examples of positive electrode active materials include lithium-containing transition metal oxides containing lithium and transition metal elements.

[0058] Examples of transition metal elements contained in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain only one transition metal element or two or more. The transition metal element can be at least one element selected from the group consisting of Co, Ni, and Mn. Lithium-containing transition metal oxides may contain one or more typical metal elements as needed. Examples of typical metal elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi.

[0059] There are no particular limitations on the methods for forming the positive and negative electrodes; they can be formed using known methods. In one example of the method for forming the flux layers (positive electrode flux layer, negative electrode flux layer), firstly, a coating film is formed by coating a slurry containing the constituent components of the flux layer and a dispersion medium onto a current collector. Next, the coating film is dried and pressed. This yields electrode plates (positive electrode, negative electrode) containing the flux layers.

[0060] (Separator)

[0061] The separator uses a porous sheet with ion permeability and insulation. Examples of porous sheet forms include microporous films, woven fabrics, and nonwoven fabrics. The separator can be made of polymer materials. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may contain additives as needed. Examples of additives include inorganic fillers.

[0062] (Non-aqueous electrolyte)

[0063] Non-aqueous electrolytes (non-aqueous solutions) consist of a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of solutes include lithium salts. Various additives can be added to non-aqueous electrolytes. Well-known additives can be used.

[0064] There are no particular limitations on the non-aqueous solvent; any known non-aqueous solvent can be used. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One non-aqueous solvent can be used alone, or two or more can be used in combination.

[0065] Examples of lithium salts include: lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB). 10 Cl 10 Lithium salts include those containing fluorine acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorinated imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). A single lithium salt can be used, or two or more can be used in combination.

[0066] The concentration of lithium salt in the electrolyte can be above 1 mol / L and below 2 mol / L, or above 1 mol / L and below 1.5 mol / L.

[0067] (shape, etc.)

[0068] A positive electrode, a negative electrode, and a separator constitute an electrode body. The electrode body can also be a wound electrode body. A wound electrode body is formed by winding the positive electrode, negative electrode, and separator with the separator positioned between the positive and negative electrodes. The electrode body can also have shapes other than wound. For example, the electrode body can be a stacked electrode body consisting of a positive electrode and a negative electrode sandwiching a separator (a stacked electrode body). The secondary battery (B) can be cylindrical or square. The secondary battery (B) includes an outer casing corresponding to these shapes. The outer casing houses the electrode body and the non-aqueous electrolyte. The outer casing is not particularly limited and known outer casings can be used.

[0069] Hereinafter, an example of a secondary battery (B) will be specifically described with reference to the accompanying drawings. However, the secondary battery (B) is not limited to the configuration shown in the drawings. Other components besides those necessary for the secondary battery (B) may be omitted. The examples described below can be modified based on the above description. Furthermore, the matters to be explained below can be applied to the embodiments described above.

[0070] (Implementation Method 1)

[0071] Figure 1 This is a schematic cross-sectional view of the non-aqueous electrolyte secondary battery 10 according to Embodiment 1. The non-aqueous electrolyte secondary battery 10 is a cylindrical battery. The non-aqueous electrolyte secondary battery 10 includes a cylindrical battery casing, a wound electrode body 14 housed within the battery casing, and a non-aqueous electrolyte (not shown). The battery casing includes a bottomed cylindrical casing body 15 and a sealing body 16 that seals the opening of the casing body 15. The casing body 15 is made of metal. The airtightness of the battery casing is ensured by a gasket 27 disposed between the casing body 15 and the sealing body 16. The casing body 15, the sealing body 16, and the gasket 27 constitute the outer casing. Insulating plates 17 and 18 are disposed at both ends of the electrode body 14 in the winding axis direction.

[0072] The housing body 15 has a stepped portion 21. The sealing body 16 and the gasket 27 are supported by the stepped portion 21. The sealing body 16 includes a perforated metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. All components constituting the sealing body 16, except for the insulating member 24, are electrically connected to each other. The cover 26 functions as the positive terminal. The housing body 15 functions as the negative terminal.

[0073] The electrode body 14 is a wound electrode body composed of a positive electrode 11, a negative electrode 12, and a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped.

[0074] One end of the positive electrode tab 11b is connected to the positive current collector of the positive electrode 11. The other end of the positive electrode tab 11b is connected to the sealing body 16 (perforated metal plate 22). That is, the positive current collector of the positive electrode 11 is electrically connected to the cover 26 via the positive electrode tab 11b. One end of the negative electrode tab 12b is connected to the negative current collector of the negative electrode 12. The other end of the negative electrode tab 12b is connected to the housing body 15. That is, the negative current collector of the negative electrode 12 is electrically connected to the housing body 15 via the negative electrode tab 12b.

[0075] A cross-section of the connection portion C (connection portion (C)) between the negative current collector 12a and the negative electrode tab 12b is schematically shown. Figure 2 .in addition, Figure 3 A schematic top view of the connecting part C. Figure 3The diagram shows the width direction WD of the negative current collector 12a and the length Lt (length in the width direction WD) of the negative electrode tab 12b at the connection portion C. The width direction WD of the negative current collector 12a is parallel to the winding axis of the wound electrode body 14. The ratio of the length Lt of the negative current collector 12a to the width Wc (length of the negative current collector 12a in the width direction WD) can be within the range described above.

[0076] Figure 2 The negative electrode 12 shown in one example includes a negative current collector 12a, a negative electrode tab 12b, and a first lithium layer 12c1. For example... Figure 2 As shown, in the connection portion C, the first lithium layer 12c1 is not removed and exists between the negative electrode tab 12b and the negative electrode current collector 12a. In the connection portion C, the first lithium layer 12c1 is in contact with both the negative electrode tab 12b and the negative electrode current collector 12a. That is, the negative electrode tab 12b is connected to the negative electrode current collector 12a via the first lithium layer 12c1. Furthermore, in the connection portion C, the negative electrode current collector 12a and the negative electrode tab 12b are not in contact.

[0077] As an example of the method for connecting the negative current collector 12a and the negative electrode tab 12b, ultrasonic bonding can be used. For example, ultrasonic bonding is performed using a device including an anvil (base) and an ultrasonic welding head, in a manner where a first lithium layer 12c1 is formed on one side of the negative current collector 12a, and the negative current collector 12a and the negative electrode tab 12b are connected by means of the first lithium layer 12c1. Specifically, the side of the negative current collector 12a opposite to the side where the first lithium layer 12c1 is formed is disposed on the anvil (base), and the negative electrode tab 12b is stacked on the first lithium layer 12c1. Then, ultrasonic waves are applied from the negative electrode tab 12b side using the ultrasonic welding head to bond the negative electrode tab 12b to the first lithium layer 12c1.

[0078] Ultrasonic bonding is performed under the condition that the negative electrode current collector 12a and the negative electrode tab 12b are not in direct contact due to the removal of the first lithium layer 12c1. Specifically, ultrasonic bonding is performed under the condition that the first lithium layer 12c1 is not overheated.

[0079] (Implementation Method 2)

[0080] Figure 4 This is a schematic cross-sectional view showing the negative electrode of the non-aqueous electrolyte secondary battery of Embodiment 2. Figure 4 The negative electrode 12 shown in one example includes a negative current collector 12a, a negative electrode tab 12b, a first lithium layer 12c1, and a second lithium layer 12c2. For example... Figure 4As shown, in the connection portion C, lithium layers 12c (first lithium layer 12c1 and second lithium layer 12c2) are disposed on both sides of the negative electrode current collector 12a. The first lithium layer 12c1 is not removed and exists between the negative electrode tab 12b and the negative electrode current collector 12a. In the connection portion C, the first lithium layer 12c1 is in contact with both the negative electrode tab 12b and the negative electrode current collector 12a. That is, the negative electrode tab 12b is connected to the negative electrode current collector 12a by means of the first lithium layer 12c1. Furthermore, in the connection portion C, the negative electrode current collector 12a and the negative electrode tab 12b are not in contact.

[0081] As an example of the connection method between the negative current collector 12a and the negative electrode tab 12b, ultrasonic bonding can be used, similar to Embodiment 1. For example, ultrasonic bonding is performed using a device including an anvil (base) and an ultrasonic welding head, in which lithium layers 12c (first lithium layer 12c1 and second lithium layer 12c2) are formed on both sides of the negative current collector 12a, and the negative current collector 12a and the negative electrode tab 12b are connected by the first lithium layer 12c1. Specifically, in the negative current collector 12a with lithium layers 12c formed on both sides, the second lithium layer 12c2 is arranged on the anvil (base), and the negative electrode tab 12b is stacked on the first lithium layer 12c1. Then, ultrasonic waves are applied from the negative electrode tab 12b side using the ultrasonic welding head to bond the negative electrode tab 12b to the first lithium layer 12c1. At this time, it is preferable to perform a treatment to prevent the second lithium layer 12c2 from adhering to the anvil. For example, a coating can be formed on the anvil. This coating can be made of diamond-like carbon (DLC), SiC, ceramics (e.g., Al2O3), etc. Alternatively, a strip can be placed on the anvil. This strip can be made of polyethylene (PE) and / or polypropylene (PP).

[0082] (Postscript)

[0083] The following technology is disclosed through the above description.

[0084] (Technology 1)

[0085] A non-aqueous electrolyte secondary battery includes: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0086] The aforementioned negative electrode comprises: a negative current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or lithium alloy.

[0087] In the connection between the negative current collector and the negative electrode tab, the negative current collector and the negative electrode tab are connected by the first lithium layer, and the negative current collector and the negative electrode tab are not in contact.

[0088] (Technology 2)

[0089] According to the non-aqueous electrolyte secondary battery of technology 1, the negative electrode current collector has a first main surface and a second main surface opposite to the first main surface.

[0090] The first lithium layer is disposed on the first main surface.

[0091] The aforementioned negative electrode also includes a second lithium layer containing lithium metal and / or lithium alloy.

[0092] The second lithium layer is disposed on the second main surface and sandwiches the negative current collector opposite to the first lithium layer.

[0093] (Technology 3)

[0094] According to the non-aqueous electrolyte secondary battery of technology 1 or 2, the thickness of the first lithium layer is 0.1 μm or more and 30 μm or less.

[0095] Example

[0096] The present disclosure will now be described in detail based on embodiments, but the present disclosure is not limited to the following embodiments. In this embodiment, the connection conditions are changed, and the negative current collector is connected to the negative electrode tab. Then, the cross-section of the connection between the negative current collector and the negative electrode tab is observed and the resistance is measured.

[0097] (Example 1)

[0098] In Example 1, firstly, a copper foil (thickness: 12 μm) with a first lithium layer (thickness: 10 μm) formed on one side is prepared. The first lithium layer is formed by pressing the lithium foil onto the copper foil. Additionally, a negative electrode tab (thickness: 100 μm, width: 3 mm) is prepared. The negative electrode tab uses a coating material with nickel layers formed on both sides of the copper foil.

[0099] Next, the copper foil with the first lithium layer formed thereon is ultrasonically bonded to the negative electrode tab using the ultrasonic bonding method described above. In this way, the negative current collector and the negative electrode tab are connected by the first lithium layer.

[0100] (Examples 2-5)

[0101] In Examples 2-5, the presence and thickness of the lithium layer were changed as shown in Table 1. Otherwise, the negative current collector and the negative electrode tab were connected using the same method and conditions as in Example 1. It should be noted that the first lithium layer in Example 2 was formed by vapor-depositing lithium metal onto a copper foil.

[0102] (Comparative Example 1)

[0103] In Comparative Example 1, no lithium layer was formed on the negative current collector. Otherwise, the negative current collector was connected to the negative electrode tab in the same way and under the same conditions as in Example 1.

[0104] (Comparative Example 2)

[0105] Comparative Example 2 uses resistance welding instead of ultrasonic bonding. Otherwise, the negative current collector is connected to the negative electrode tab in the same way and under the same conditions as in Example 1.

[0106] For the connection between the negative current collector and the negative electrode tab fabricated as described above, the cross-section was observed using a scanning electron microscope (SEM) to evaluate whether the negative current collector and the negative electrode tab were in direct contact. Additionally, the resistance of the connection was measured.

[0107] Table 1 shows some of the fabrication conditions and evaluation results for the connection. In Table 1, “Lithium Layer” refers to the lithium layer formed on the negative electrode current collector. In Example 4, a first lithium layer (thickness: 10 μm) was formed on one side of the negative electrode current collector, and a second lithium layer (thickness: 10 μm) was formed on the other side. In Table 1, “Contact State” indicates the contact state between the negative electrode current collector and the negative electrode tab; “Contact” means they are in direct contact.

[0108] [Table 1]

[0109]

[0110] Examples 1-5 are connection portions used in the secondary battery (B) of this disclosure. Comparative Examples 1 and 2 are connection portions of comparative examples. As shown in Table 1, in the connection portions of Examples 1-5, the negative electrode current collector is not in contact with the negative electrode tab, but is connected by means of the first lithium layer. In the connection portion of Comparative Example 2, a portion of the lithium layer is removed, and the negative electrode current collector is in contact with the negative electrode tab.

[0111] The resistance of the connection portions in Examples 1-5 is significantly lower than that in Comparative Examples 1 and 2. The resistance of the connection portion in Example 4, which uses a second lithium layer, is lower than that in Example 1, which uses only a first lithium layer. As described above, the internal resistance of the battery can be reduced according to the configuration of the secondary battery (B).

[0112] In Comparative Example 1, where there is no lithium layer, there is a gap between the negative current collector (copper foil) and the nickel layer of the negative electrode tab. On the other hand, no such gap was found in the connection portion of Example 4, where the lithium layer of the negative current collector and the nickel layer of the negative electrode tab are well bonded.

[0113] Industrial availability

[0114] This disclosure can be used for non-aqueous electrolyte secondary batteries.

[0115] The present invention has been described with reference to preferred embodiments, but such disclosure should not be interpreted as limiting. Various modifications and alterations will be apparent to those skilled in the art from the foregoing disclosure. Therefore, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0116] Explanation of reference numerals in the attached figures

[0117] 10: Non-aqueous electrolyte secondary battery

[0118] 11: Positive electrode

[0119] 12: Negative electrode

[0120] 12a: Negative current collector

[0121] 12b: Negative electrode tab

[0122] 12c: Lithium layer

[0123] 12c1: First lithium layer

[0124] 12c2: Second lithium layer

[0125] 13: Separator

[0126] C: Connecting part

Claims

1. A non-aqueous electrolyte secondary battery, comprising: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode comprises: a negative current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or lithium alloy. In the connection between the negative current collector and the negative electrode tab, the negative current collector and the negative electrode tab are connected by the first lithium layer, and the negative current collector and the negative electrode tab are not in contact.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The negative electrode current collector has a first main surface and a second main surface opposite to the first main surface. The first lithium layer is disposed on the first main surface. The negative electrode also includes a second lithium layer containing lithium metal and / or lithium alloy. The second lithium layer is disposed on the second main surface and sandwiches the negative electrode current collector opposite to the first lithium layer.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The thickness of the first lithium layer is greater than 0.1 μm and less than 30 μm.

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