Non-aqueous electrolyte secondary battery

Abstract

Disclosed is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode (12), a separator disposed between the positive electrode and the negative electrode (12), and a non-aqueous electrolyte. The negative electrode (12) includes a negative electrode current collector (12a), a negative electrode tab (12b), and a first lithium layer (12c1) containing lithium metal and / or a lithium alloy. In a connection part (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 by means of the first lithium layer (12c1), and the negative electrode current collector (12a) and the negative electrode tab (12b) are not in contact with each other.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Non-aqueous electrolyte secondary batteries have high output and high energy density and are therefore widely used in consumer applications, automotive applications, etc. In recent years, there has been a demand for even higher performance non-aqueous electrolyte secondary batteries. Various proposals have been made 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, further comprising: a negative electrode current collector; a negative electrode active material layer disposed on a partial region of the surface of the negative electrode current collector; a lithium layer containing metallic lithium disposed on a non-disposition region, which is a 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 resistance-welded to the non-disposition region of the negative electrode current collector, wherein the lithium layer is disposed in at least a portion between the negative electrode lead and the negative electrode current collector."

[0004] Patent No. 6219273

[0005] Currently, there is a demand for further improvement in the performance of non-aqueous electrolyte secondary batteries, and to achieve this, efforts are being made to reduce the internal resistance of batteries. In reducing the internal resistance of batteries, it is particularly important to reduce the resistance between the negative electrode current collector and the negative electrode tab. One of the objects of the present disclosure is to provide a non-aqueous electrolyte secondary battery having low resistance between the negative electrode current collector and the negative electrode tab.

[0006] One aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy, and the negative electrode current collector and the negative electrode tab are connected to each other via the first lithium layer at a connection between the negative electrode current collector and the negative electrode tab, and the negative electrode current collector and the negative electrode tab are not in contact with each other.

[0007] According to the present disclosure, a non-aqueous electrolyte secondary battery having low resistance between the negative electrode current collector and the negative electrode tab can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0008] Fig. 1 is a cross-sectional view schematically showing a nonaqueous electrolyte secondary battery of Embodiment 1. Fig. 2 is a cross-sectional view schematically showing an example of a connection portion between a negative electrode current collector and a negative electrode tab in the nonaqueous electrolyte secondary battery shown in Fig. 1. Fig. 3 is a top view schematically showing an example of a connection portion between a negative electrode current collector and a negative electrode tab in the nonaqueous electrolyte secondary battery shown in Fig. 1. Fig. 4 is a cross-sectional view schematically showing another example of a connection portion between a negative electrode current collector and a negative electrode tab in the nonaqueous electrolyte secondary battery shown in Fig. 1.

[0009] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0010] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery according to this embodiment may be referred to as a "secondary battery (B)" below. The secondary battery (B) 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 electrode current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy. At a connection between the negative electrode current collector and the negative electrode tab (hereinafter, sometimes referred to as a "connection (C)"), the negative electrode current collector and the negative electrode tab are connected via the first lithium layer, and the negative electrode current collector and the negative electrode tab are not in contact with each other.

[0011] The lithium layer has lower conductivity than the metal constituting the negative electrode tab. Therefore, the resistance between the negative electrode tab and the negative electrode current collector has been reduced by directly connecting the negative electrode current collector and the negative electrode tab. However, as a result of further investigation, the present inventors have newly discovered that when a lithium layer is formed on the negative electrode current collector, removing the lithium layer at the connection and directly connecting the negative electrode current collector and the negative electrode tab increases the resistance at the connection. After further investigation, the present inventors have newly discovered that the above-described configuration of the secondary battery (B) can significantly reduce the resistance between the negative electrode current collector and the negative electrode tab. The present disclosure is based on this new finding.

[0012] Although the reason for this effect is not clear at present, one possible reason is that the lithium layer is relatively soft. The relatively soft lithium layer functions as a cushion when connecting the negative electrode current collector and the negative electrode tab, allowing for good bonding of the layers at the connection portion, which is thought to result in reduced resistance between the negative electrode current collector and the negative electrode tab.

[0013] The negative electrode current collector has a first major surface and a second major surface opposite the first major surface. The first lithium layer is disposed on the first major 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 major surface of the negative electrode current collector and faces the first lithium layer across the negative electrode current collector. By forming the second lithium layer, the resistance around the negative electrode tab can be further reduced. Because the second lithium layer is relatively soft, it can function as a cushion when connecting the negative electrode tab and the negative electrode current collector. Therefore, it is believed that the use of the second lithium layer can further reduce the resistance between the negative electrode current collector and the negative electrode tab.

[0014] The first lithium layer can be formed on the first main surface of the negative electrode current collector, although the first lithium layer may also be formed on the surface of the negative electrode tab.

[0015] The thickness of the first lithium layer may 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, and may be 50 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, or 5.0 μm or less. The thickness of the first lithium layer may be 0.1 μm or more and 30 μm or less. By making the thickness of the first lithium layer 0.1 μm or more, the resistance between the negative electrode current collector and the negative electrode tab can be particularly reduced. By making the thickness of the first lithium layer 30 μm or less, an increase in resistance due to the lithium layer can be suppressed. The thickness of the second lithium layer may be within the range exemplified for the thickness of the first lithium layer. The thickness of the first lithium layer and the thickness of the second lithium layer may be the same or different.

[0016] The first lithium layer may be formed only on the surface of the negative electrode current collector in the area where the negative electrode tab is connected, or only on the area where the negative electrode tab is connected and the surrounding area. Alternatively, the first lithium layer may be formed on the entire surface of one side of the negative electrode current collector. The area around the area where the negative electrode tab is connected means an area within 3 mm (e.g., within 1 mm) from the outer edge of the negative electrode tab in a plan view. The second lithium layer may be formed in an area of ​​the negative electrode current collector facing the area where the first lithium layer is formed.

[0017] (Negative electrode current collector) For the negative electrode current collector, metal foils can be used, such as copper foil, copper alloy foil, copper-deposited resin sheets (e.g., polyethylene terephthalate sheets), stainless steel foil, and copper-deposited stainless steel foil. The content of elements other than copper contained in the copper alloy is usually 30% by mass or less (e.g., 10% by mass or less). Examples of elements other than copper include zinc, tin, aluminum, beryllium, nickel, iron, manganese, and the like. Furthermore, forming a conductive film on the current collector is also included.

[0018] A first lithium layer can be formed on part or all of one main surface (first main surface) of the negative electrode current collector. A second lithium layer may be formed on part or all of the other main surface (second main surface) of the negative electrode current collector. The thickness of the negative electrode current collector may be in the range of 6 μm to 20 μm (e.g., in the range of 8 μm to 15 μm).

[0019] The lithium layers (first lithium layer, second lithium layer) contain at least one selected from the group consisting of lithium metal and lithium alloys. The lithium layers may be lithium metal layers or lithium alloy layers. The lithium alloy layers are composed of lithium and elements other than lithium. Examples of other elements (e.g., other metal elements) include magnesium, aluminum, indium, copper, zinc, potassium, calcium, sodium, silver, and gold. The content of the other elements may be 5% by mass or less (e.g., 3% by mass or less).

[0020] The method for forming the lithium layer is not particularly limited, and known methods may be applied. For example, the lithium layer may be formed by pressing a lithium foil onto the negative electrode current collector. Alternatively, the lithium layer may be formed by a vapor deposition method. Alternatively, the lithium layer may be formed using a resin sheet on which a lithium layer has been formed. For example, first, a resin sheet on which a lithium layer has been formed and a negative electrode current collector are laminated and pressed so that the lithium layer and the negative electrode current collector are in contact with each other. Next, the resin sheet is peeled off to obtain a negative electrode current collector on which a lithium layer has been formed. The method using a resin sheet on which a lithium layer has been formed and the vapor deposition method are suitable for forming a thin lithium layer.

[0021] (Negative electrode tab) The negative electrode tab is not particularly limited, and a known negative electrode tab may be used. One end of the negative electrode tab is connected to the negative electrode current collector via the first lithium layer at the connection part (C). The other end of the negative electrode tab is electrically connected to the negative electrode terminal (e.g., the battery case).

[0022] The negative electrode tab can be made of metal. A metal foil may be used for the negative electrode tab. Alternatively, a clad material including a metal foil and a nickel layer formed on both sides of the metal foil may be used for the negative electrode tab. Examples of metals constituting the metal foil include copper, copper alloys, iron, and iron alloys. A nickel layer may be present on one of the two main surfaces of the negative electrode tab that contacts the first lithium layer. In a preferred example of the negative electrode tab, a nickel layer is present on both sides.

[0023] The size of the negative electrode tab is determined taking into consideration the discharge capacity, etc. The width of the negative electrode tab may be in the range of 1 mm to 50 mm (e.g., in the range of 1 mm to 5 mm), and the thickness of the negative electrode tab may be in the range of 6 μm to 200 μm (e.g., in the range of 50 μm to 150 μm).

[0024] 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 electrode current collector at each connection portion (C) via the first lithium layer and is not in contact with the negative electrode current collector.

[0025] The ratio Lt / Wc of the length Lt of the negative electrode tab at the connection portion (C) to the width Wc of the negative electrode current collector is not particularly limited and may be in the range of 0.03 to 1.0 (for example, the range of 0.04 to 0.5). When the ratio Lt / Wc=1.0, the negative electrode tab is connected to the negative electrode current collector over the entire width direction of the negative electrode current collector.

[0026] The secondary battery (B) may include an insulating tape (protective tape) attached to the negative electrode so as to cover the negative electrode tab. The use of such an insulating tape can suppress short circuits. The insulating tape is not particularly limited, and any known insulating tape used in batteries may be used. The insulating tape may be a tape made of an insulating resin such as polyimide, polytetrafluoroethylene (PTFE), or polypropylene (PP).

[0027] (Method of connecting negative electrode current collector and negative electrode tab) The negative electrode current collector and negative electrode tab are connected so as to satisfy the following conditions (1) and (2): (1) At the connection portion (C), the negative electrode current collector and negative electrode tab are connected via the first lithium layer; (2) At the connection portion (C), the negative electrode current collector and negative electrode tab are not in contact with each other.

[0028] An example of a connection method is described below. First, a negative electrode current collector having a lithium layer formed on at least one side is prepared. Next, the negative electrode current collector and the negative electrode tab are stacked so that the lithium layer is disposed between them, and the negative electrode current collector, the lithium layer, and the negative electrode tab are connected. If the lithium layer melts and the negative electrode current collector and the negative electrode tab come into direct contact, the above conditions (1) and (2) are not satisfied. Therefore, resistance welding is not used for connection at the connection portion (C). Examples of connection methods that satisfy conditions (1) and (2) include ultrasonic welding and friction stir welding.

[0029] In order to prevent the lithium layer from being melted and removed, the ultrasonic bonding is preferably carried out under conditions that do not melt the lithium layer.

[0030] Examples of components of the secondary battery (B) are described below. Components other than those characteristic of the secondary battery (B) of the present disclosure are not particularly limited, and components used in known non-aqueous electrolyte secondary batteries may be applied.

[0031] The secondary battery (B) may be a lithium secondary battery (lithium metal secondary battery) using lithium metal (or a lithium alloy) as the negative electrode active material, or may be a battery using a material that reversibly absorbs and releases lithium ions as the negative electrode active material.

[0032] (Negative electrode) The negative electrode is selected depending on the type of secondary battery (B). When the secondary battery (B) is a lithium metal secondary battery, lithium metal precipitates in the negative electrode during charging and dissolves in the non-aqueous electrolyte during discharging. In this case, the negative electrode includes the above-mentioned negative electrode current collector. As described above, a lithium layer may be formed on the surface of the negative electrode current collector.

[0033] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material and may contain other additives (such as a binder, a conductive material, or a thickener) as necessary. The negative electrode mixture layer is not particularly limited, and a known negative electrode mixture layer may be used.

[0034] The negative electrode active material contained in the negative electrode mixture layer can be a material 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 may contain or be a Si-containing material. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon). Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed within a lithium ion conductive phase (matrix). The negative electrode may contain only one type of negative electrode active material, or may contain two or more types of negative electrode active materials.

[0035] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0036] The conductive material may be, for example, a conductive carbonaceous material. Examples of the conductive carbonaceous material include carbon black, carbon nanotubes, graphite, etc. Examples of carbon black include acetylene black and ketjen black.

[0037] The thickener may be, for example, a cellulose derivative such as cellulose ether. Examples of cellulose derivatives include carboxymethyl cellulose (CMC) and its modified forms, methyl cellulose, etc. Examples of modified CMC include salts of CMC. Examples of salts include alkali metal salts (e.g., sodium salts), ammonium salts, etc.

[0038] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. Examples of materials for the positive electrode current collector include metal materials such as Al, Al alloys, Ti, Ti alloys, and Fe alloys. The Fe alloy may be stainless steel. The positive electrode may include a positive electrode tab.

[0039] The positive electrode mixture layer contains a positive electrode active material and may contain other additives (such as a binder, a conductive material, and a thickener) as needed. The positive electrode mixture layer is not particularly limited, and a known positive electrode mixture layer may be used. The binder, conductive material, and thickener may be the same as those described as materials for the negative electrode mixture layer.

[0040] The positive electrode active material may be a material capable of reversibly absorbing and releasing lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides containing lithium and a transition metal element.

[0041] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. The lithium-containing transition metal oxide may contain only one transition metal element, or may contain two or more transition metal elements. The transition metal element may be at least one selected from the group consisting of Co, Ni, and Mn. The lithium-containing transition metal oxide 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, Bi, etc.

[0042] The method for forming the positive electrode and the negative electrode is not particularly limited, and they may be formed by a known method. In one example of a method for forming the mixture layer (positive electrode mixture layer, negative electrode mixture layer), a coating film is first formed by applying a slurry containing the components of the mixture layer and a dispersion medium onto a current collector. Next, the coating film is dried and pressed. In this way, an electrode plate (positive electrode, negative electrode) containing the mixture layer is obtained.

[0043] (Separator) A porous sheet having ion permeability and insulating properties is used as the separator. Examples of the form of the porous sheet include a microporous film, a woven fabric, and a nonwoven fabric. The separator may be made of a polymer material. Examples of the polymer material include an olefin resin, a polyamide resin, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The separator may contain additives as needed. Examples of the additives include inorganic fillers.

[0044] (Non-aqueous electrolyte) The non-aqueous electrolyte (non-aqueous electrolyte solution) contains a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of the solute include lithium salts. Various additives may be added to the non-aqueous electrolyte. Known additives may be used as the additive.

[0045] The nonaqueous solvent is not particularly limited, and known nonaqueous solvents may be used. Examples of nonaqueous 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). Examples of 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 nonaqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of nonaqueous solvent may be used alone, or two or more types may be used in combination.

[0046] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiPF ２ O ２ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５ SO ２ ) ２and lithium halides (LiCl, LiBr, LiI, etc.). The lithium salts may be used singly or in combination of two or more.

[0047] The concentration of the lithium salt in the electrolyte may be 1 mol / L or more and 2 mol / L or less, or may be 1 mol / L or more and 1.5 mol / L or less.

[0048] (Shape, etc.) The positive electrode, the negative electrode, and the separator constitute an electrode body. The electrode body may be a wound electrode body. A wound electrode body can be formed by winding a positive electrode, a negative electrode, and a separator so that the separator is disposed between the positive electrode and the negative electrode. The electrode body may have a form other than a wound form. For example, the electrode body may be an electrode body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween (a stacked electrode body). The form of the secondary battery (B) may be cylindrical or prismatic. The secondary battery (B) includes an exterior body corresponding to these forms. The exterior body houses the electrode body and the non-aqueous electrolyte. The exterior body is not particularly limited, and a known exterior body may be used.

[0049] An example of the secondary battery (B) will be specifically described below with reference to the drawings. However, the secondary battery (B) is not limited to the configuration shown in the drawings. Components other than those essential to the secondary battery (B) may be omitted. The examples described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment.

[0050] (Embodiment 1) FIG. 1 is a cross-sectional view schematically illustrating a nonaqueous electrolyte secondary battery 10 according to Embodiment 1. The nonaqueous electrolyte secondary battery 10 is a cylindrical battery. The nonaqueous electrolyte secondary battery 10 includes a cylindrical battery case and a wound electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in the battery case. The battery case includes a cylindrical case body 15 with a bottom and a sealing body 16 that seals the opening of the case body 15. The case body 15 is made of metal. A gasket 27 is disposed between the case body 15 and the sealing body 16 to ensure the hermeticity of the battery case. The case body 15, the sealing body 16, and the gasket 27 form an exterior body. Insulating plates 17 and 18 are disposed at both ends of the electrode assembly 14 in the direction of the winding axis.

[0051] The case body 15 has a step 21. The step 21 supports the sealing body 16 and the gasket 27. The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The above-mentioned components constituting the sealing body 16 are electrically connected to each other except for the insulating member 24. The cap 26 functions as a positive electrode terminal. The case body 15 functions as a negative electrode terminal.

[0052] The electrode assembly 14 is a wound electrode assembly made up 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.

[0053] One end of the positive electrode tab 11b is connected to the positive electrode current collector of the positive electrode 11. The other end of the positive electrode tab 11b is connected to the sealing body 16 (filter 22). That is, the positive electrode current collector of the positive electrode 11 is electrically connected to the cap 26 via the positive electrode tab 11b. One end of the negative electrode tab 12b is connected to the negative electrode current collector of the negative electrode 12. The other end of the negative electrode tab 12b is connected to the case body 15. That is, the negative electrode current collector of the negative electrode 12 is electrically connected to the case body 15 via the negative electrode tab 12b.

[0054] FIG. 2 schematically shows a cross section of a connection C (connection (C)) between the negative electrode current collector 12a and the negative electrode tab 12b. FIG. 3 also shows a top view of the connection C. FIG. 3 also shows the width direction WD of the negative electrode current collector 12a and the length Lt (length in the width direction WD) of the negative electrode tab 12b at the connection C. The width direction WD of the negative electrode current collector 12a is a direction parallel to the winding axis of the wound electrode body 14. The ratio of the length Lt to the width Wc of the negative electrode current collector 12a (length of the negative electrode current collector 12a in the width direction WD) may be within the range described above.

[0055] The example negative electrode 12 shown in FIG. 2 includes a negative electrode current collector 12a, a negative electrode tab 12b, and a first lithium layer 12c1. As shown in FIG. 2, at connection portion C, the first lithium layer 12c1 is present between the negative electrode tab 12b and the negative electrode current collector 12a without being removed. At 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, at connection portion C, the negative electrode current collector 12a and the negative electrode tab 12b are not in contact with each other.

[0056] One example of a method for connecting the negative electrode current collector 12a and the negative electrode tab 12b is ultrasonic bonding. For example, a first lithium layer 12c1 is formed on one side of the negative electrode current collector 12a, and ultrasonic bonding is performed using an apparatus including an anvil (base) and an ultrasonic horn so that the negative electrode current collector 12a and the negative electrode tab 12b are connected via the first lithium layer 12c1. Specifically, the surface of the negative electrode current collector 12a opposite to the surface on which the first lithium layer 12c1 is formed is placed on an anvil (base), and the negative electrode tab 12b is stacked on top of the first lithium layer 12c1. Next, ultrasonic waves are applied from the negative electrode tab 12b side using the ultrasonic horn to bond the negative electrode tab 12b and the first lithium layer 12c1.

[0057] The ultrasonic bonding is performed under the condition that the first lithium layer 12c1 is removed, thereby preventing direct contact between the negative electrode current collector 12a and the negative electrode tab 12b. Specifically, the ultrasonic bonding is performed under the condition that the first lithium layer 12c1 is not excessively heated.

[0058] (Embodiment 2) Figure 4 is a cross-sectional view schematically illustrating a negative electrode included in a nonaqueous electrolyte secondary battery according to Embodiment 2. The example negative electrode 12 illustrated in Figure 4 includes a negative electrode current collector 12a, a negative electrode tab 12b, a first lithium layer 12c1, and a second lithium layer 12c2. As illustrated in Figure 4, at the connection C, lithium layers 12c (the first lithium layer 12c1 and the second lithium layer 12c2) are disposed on both sides of the negative electrode current collector 12a. The first lithium layer 12c1 is present between the negative electrode tab 12b and the negative electrode current collector 12a without being removed. At the connection 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, at the connection portion C, the negative electrode current collector 12a and the negative electrode tab 12b are not in contact with each other.

[0059] As in the first embodiment, an example of a method for connecting the negative electrode current collector 12a and the negative electrode tab 12b is ultrasonic bonding. For example, lithium layers 12c (first lithium layer 12c1 and second lithium layer 12c2) are formed on both sides of the negative electrode current collector 12a, and ultrasonic bonding is performed using an apparatus including an anvil (base) and an ultrasonic horn so that the negative electrode current collector 12a and the negative electrode tab 12b are connected via the first lithium layer 12c1. Specifically, the negative electrode current collector 12a having lithium layers 12c formed on both sides is placed so that the second lithium layer 12c2 is on the anvil (base), and the negative electrode tab 12b is stacked on top of the first lithium layer 12c1. Next, ultrasonic waves are applied from the negative electrode tab 12b side using the ultrasonic horn to bond the negative electrode tab 12b and the first lithium layer 12c1. At this time, it is preferable to perform a process to prevent the second lithium layer 12c2 from adhering to the anvil. For example, a process to form a coating on the anvil may be performed. The coating may be made of diamond-like carbon (DLC), SiC, ceramics (e.g., Al ２ O ３ Alternatively, a tape may be placed on the anvil. For example, a tape made of polyethylene (PE) or polypropylene (PP) may be used.

[0060] (Additional Notes) The above description discloses the following techniques: (Technology 1) A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy, and at a connection portion between the negative electrode current collector and the negative electrode tab, the negative electrode current collector and the negative electrode tab are connected via the first lithium layer, and the negative electrode current collector and the negative electrode tab are not in contact with each other. (Technology 2) The nonaqueous electrolyte secondary battery according to Technology 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 further includes a second lithium layer containing lithium metal and / or a lithium alloy, the second lithium layer is disposed on the second main surface and faces the first lithium layer with the negative electrode current collector sandwiched therebetween. (Technology 3) The nonaqueous electrolyte secondary battery according to Technology 1 or 2, wherein the thickness of the first lithium layer is 0.1 μm or more and 30 μm or less.

[0061] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples. In these examples, the negative electrode current collector and the negative electrode tab were connected under different connection conditions. Then, the cross section of the connection between the negative electrode current collector and the negative electrode tab was observed and the resistance was measured.

[0062] Example 1 In Example 1, first, a copper foil (thickness: 12 μm) having a first lithium layer (thickness: 10 μm) formed on one side was prepared. The first lithium layer was formed by pressing the lithium foil onto the copper foil and laminating them. Furthermore, a negative electrode tab (thickness: 100 μm, width: 3 mm) was prepared. The negative electrode tab was made of a clad material in which nickel layers were formed on both sides of the copper foil.

[0063] Next, the copper foil on which the first lithium layer was formed was ultrasonically bonded to the negative electrode tab by the ultrasonic bonding method described above, thereby connecting the negative electrode current collector and the negative electrode tab via the first lithium layer.

[0064] In Examples 2 to 5, the negative electrode current collector and the negative electrode tab were connected in the same manner and under the same conditions as in Example 1, except that the presence or absence and thickness of the lithium layer were changed as shown in Table 1. The first lithium layer in Example 2 was formed by vapor-depositing lithium metal on copper foil.

[0065] Comparative Example 1 In Comparative Example 1, the negative electrode current collector and the negative electrode tab were connected in the same manner and under the same conditions as in Example 1, except that no lithium layer was formed on the negative electrode current collector.

[0066] Comparative Example 2 In Comparative Example 2, the negative electrode current collector and the negative electrode tab were connected in the same manner and under the same conditions as in Example 1, except that resistance welding was used instead of ultrasonic welding.

[0067] The cross section of the connection between the negative electrode current collector and the negative electrode tab thus prepared was observed using a scanning electron microscope (SEM) to evaluate whether the negative electrode current collector and the negative electrode tab were in direct contact with each other. The resistance of the connection was also measured.

[0068] Table 1 shows some of the manufacturing conditions for the connection part and the evaluation results. "Lithium layer" in Table 1 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 surface of the negative electrode current collector, and a second lithium layer (thickness: 10 μm) was formed on the other surface. "Contact state" in Table 1 refers to the contact state between the negative electrode current collector and the negative electrode tab, and "contact" indicates that they are in direct contact.

[0069]

[0070] Examples 1 to 5 are connection parts used in the secondary battery (B) according to the present disclosure. Comparative Examples 1 and 2 are connection parts of comparative examples. As shown in Table 1, in the connection parts of Examples 1 to 5, the negative electrode current collector and the negative electrode tab were not in contact with each other, but were connected via the first lithium layer. In the connection part of Comparative Example 2, a portion of the lithium layer was removed, and the negative electrode current collector and the negative electrode tab were in contact with each other.

[0071] The resistance at the connection parts of Examples 1 to 5 was significantly lower than the resistance at the connection parts of Comparative Examples 1 and 2. The resistance at the connection part of Example 4, which used the second lithium layer, was lower than the resistance at the connection part of Example 1, which used only the first lithium layer. As described above, the configuration of the secondary battery (B) can reduce the internal resistance of the battery.

[0072] When there was no lithium layer in Comparative Example 1, there were gaps in some areas between the negative electrode current collector (copper foil) and the nickel layer of the negative electrode tab. On the other hand, no such gaps were observed in the connection part of Example 4, and the lithium layer of the negative electrode current collector and the nickel layer of the negative electrode tab were in good contact with each other.

[0073] The present disclosure can be used in non-aqueous electrolyte secondary batteries. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to cover all modifications and alterations that do not depart from the true spirit and scope of the present invention.

[0074] 10: Non-aqueous electrolyte secondary battery 11: Positive electrode 12: Negative electrode 12a: Negative electrode current collector 12b: Negative electrode tab 12c: Lithium layer 12c1: First lithium layer 12c2: Second lithium layer 13: Separator C: Connection portion

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, wherein the negative electrode comprises a negative electrode current collector, a negative electrode tab, and a first lithium layer containing lithium metal and / or a lithium alloy, and at a connection between the negative electrode current collector and the negative electrode tab, the negative electrode current collector and the negative electrode tab are connected via the first lithium layer, and the negative electrode current collector and the negative electrode tab are not in contact with each other.

2. The nonaqueous 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, and the negative electrode further includes a second lithium layer containing lithium metal and / or a lithium alloy, and the second lithium layer is disposed on the second main surface and faces the first lithium layer with the negative electrode current collector in between.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the thickness of the first lithium layer is 0.1 μm or more and 30 μm or less.

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