Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery with excellent cycle characteristics and tab temperature stability. The present invention relates to a lithium secondary battery comprising: a laminate including a plurality of positive electrodes, a plurality of separators, and a plurality of negative electrodes; a plurality of positive electrode tab lead portions extending from the laminate; and a positive electrode tab bonded to the plurality of positive electrode tab lead portions, wherein in the positive electrode tab lead portions, positive electrode current collectors constituting the positive electrodes extend from the laminate, the positive electrode tab lead portions and the positive electrode current collectors include a resin layer and aluminum layers formed on both sides of the resin layer, in the 2θ pattern of X-ray diffraction measurement of the aluminum layers, there is at least a peak A between 38.0° and 39.0° inclusive, the ratio (B / A) of the intensity of a peak B between 44.0° and 45.0° inclusive to the intensity of the peak A is 0.4 or less, and the width at half maximum of the peak A is 0.4° or less.

Description

Lithium secondary battery

[0001] The present invention relates to a lithium secondary battery.

[0002] In recent years, technology for converting natural energy such as solar or wind power into electrical energy has been attracting attention. Accordingly, various secondary batteries have been developed as electricity storage devices that are highly safe and capable of storing a large amount of electrical energy.

[0003] Among them, lithium secondary batteries, which are charged and discharged by the movement of lithium ions between a positive electrode and a negative electrode, are known to exhibit high voltage and high energy density. A typical lithium secondary battery is a lithium-ion secondary battery (LIB), which has active materials capable of retaining lithium elements in the positive electrode and the negative electrode, and is charged and discharged by the exchange of lithium ions between the positive electrode active material and the negative electrode active material.

[0004] For example, Patent Document 1 discloses an electricity storage device comprising: an anode, a cathode, at least one separator disposed between the anode and the cathode, an electrolyte, at least one thin-film current collector in contact with at least one of the anode and the cathode, and at least one tab attached to the at least one thin-film current collector; the tab is attached to the current collector via a connection means, which electrically connects the exposed surface of the tab to the thin-film current collector; one of the anode and the cathode is interposed between at least a portion of the thin-film current collector and the separator; the current collector comprises a conductive material covering a non-conductive material substrate; and at the operating voltage of the electricity storage device, the current collector stops conduction upon short circuit, and the voltage is at least 2.0 volts.

[0005] Furthermore, Patent Document 2 discloses a current collector having a multilayer structure in which an insulating layer is sandwiched between conductive layers, characterized in that the current collector has a folded region in which the end portion is folded back two or more times in the same direction, the conductive layers sandwiching the insulating layer in the folded region are electrically connected to each other, and the inner surfaces of the current collector ends forming the folded region are spaced apart or partially in contact with each other.

[0006] Furthermore, Patent Document 3 discloses a lithium ion secondary battery having a positive electrode and a negative electrode formed by adhering an active material to a current collector via a binder, characterized in that the current collector of at least one of the positive electrode and the negative electrode comprises a low-melting point layer made of a resin that melts when the battery abnormally heats up, and a metal layer interposed between the low-melting point layer and the active material and exchanging electric charges with the active material.

[0007] Japanese Patent Publication No. 2022-527140 Publication No. 2013-016321 Publication No. 11-102711

[0008] Conventionally, aluminum foil or aluminum alloy foil has been used in the positive electrode to ensure electrical conductivity and corrosion resistance. Recently, from the viewpoints of safety and light weight, current collector films in which metal layers are formed on both sides of a resin film have been often used in current collectors, as described in Patent Documents 1 to 3. However, when multiple current collector leads made of such current collector films are welded to a tab, the cycle characteristics of the lithium secondary battery may be reduced due to the weld strength and connection resistance of the weld, and further, the temperature of the tab may increase during charge and discharge.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a lithium secondary battery that has excellent cycle characteristics and temperature stability of the tab when ultrasonic welding is performed on the current collector film.

[0010] A lithium secondary battery according to one embodiment of the present invention includes: a laminate including a plurality of positive electrodes, a plurality of separators, and a plurality of negative electrodes; a plurality of positive electrode tab lead portions extending from the laminate; and positive electrode tabs joined to the plurality of positive electrode tab lead portions, wherein the positive electrode tab lead portion is a positive electrode current collector constituting the positive electrode extending from the laminate, and the positive electrode tab lead portion and the positive electrode current collector include a resin layer and aluminum layers formed on both sides of the resin layer, and a 2θ pattern obtained by X-ray diffraction measurement of the aluminum layer has at least a peak A in an angle of 38.0° or more and 39.0° or less, and a ratio (B / A) of an intensity of a peak B in an angle of 44.0° or more and 45.0° or less to an intensity of the peak A is 0.4° or less.

[0011] According to the present invention, a lithium secondary battery having excellent cycle characteristics and temperature stability of the tab can be provided.

[0012] FIG. 1 is a schematic diagram showing an example of a lithium secondary battery of the present invention. FIG. 2 is a schematic diagram showing an example of a positive electrode of the present invention. FIG. 3 is a schematic diagram showing an example of a cross section of a positive electrode of the present invention. FIG. 4 is a schematic diagram showing an example of joining a positive electrode lead part and a positive electrode tab in a lithium secondary battery of the present invention. FIG. 5 is a schematic diagram showing an example of joining a positive electrode lead part and a positive electrode tab in a lithium secondary battery of the present invention. FIG. 6 is a schematic diagram showing an example of joining a positive electrode lead part and a positive electrode tab in a lithium secondary battery of the present invention. FIG. 7 is a schematic diagram showing an example of a lithium secondary battery of the present invention. FIG. 8 is a 2θ pattern of X-ray diffraction measurement of a positive electrode current collector film of Example 2. FIG. 9 is a 2θ pattern of X-ray diffraction measurement of a positive electrode current collector film of Comparative Example 2.

[0013] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the present embodiment. The present invention can be modified in various ways without departing from the gist of the present invention. In the drawings, the same elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0014] 1. Lithium Secondary Battery The basic configuration of a lithium secondary battery according to one embodiment of the present invention will be described with reference to Figure 1. As shown in Figure 1, the lithium secondary battery according to one embodiment of the present invention includes a plurality of positive electrodes 10, a plurality of separators 20, and a plurality of negative electrodes 30, and the positive electrodes 10 and the negative electrodes 30 are arranged to be spaced apart via the separators 20. Each component will be described in detail below.

[0015] 1.1. Positive Electrode FIG. 2 is a perspective view showing an example of a positive electrode 10 according to the present embodiment. As shown in FIG. 2, the positive electrode 10 according to the present embodiment includes a positive electrode main body 101 and a positive electrode tab lead portion 102. The positive electrode tab lead portion 102 is formed by extending a positive electrode current collector constituting the positive electrode 10 from the positive electrode main body 101. The positive electrode 10 includes a positive electrode current collector and may further include a positive electrode active material. Furthermore, as shown in FIG. 3, when the positive electrode 10 according to the present embodiment is composed of only a positive electrode current collector, the positive electrode 10 is composed of a positive electrode current collector film including a resin layer 202 and aluminum (Al) layers 201 formed on both sides of the resin layer 202.

[0016] 4 , the positive electrode tab 11 is overlapped with and joined by welding to a stack 12 of positive electrode tab lead portions, which are a collection of positive electrode tab lead portions that are the positive electrode side end of the battery stack A. Examples of welding methods include ultrasonic welding, laser welding, resistance welding, and spot welding. Among these, ultrasonic welding is suitable and preferable for the lithium secondary battery of this embodiment, since it is necessary to weld a stack including the resin layer 202.

[0017] The lithium secondary battery of this embodiment includes a plurality of positive electrodes 10, a plurality of positive electrode tab lead portions 102 extending from the laminate, and positive electrode tabs 11 joined to the plurality of positive electrode tab lead portions. The positive electrode tab lead portion 102 is a main body portion of a positive electrode current collector constituting the positive electrode 10 extending from the laminate. The positive electrode main body portion of the positive electrode current collector and the positive electrode tab lead portion 102 include a resin layer 202 and an aluminum layer 201 formed on both sides of the resin layer 202. In a 2θ pattern obtained by X-ray diffraction measurement of the aluminum layer 201, the aluminum layer 201 has at least a peak A in an angle of 38.0° or more and 39.0° or less, and the ratio (B / A) of the intensity of peak B in an angle of 44.0° or more and 45.0° or less to the intensity of peak A is 0.4 or less. The half width of peak A is 0.4° or less.

[0018] In a lithium secondary battery configured as a laminate in which each component is stacked, the positive electrode laminate is joined from the positive electrode lead portion of each positive electrode current collector to a tab terminal, and connected to the outside during charge and discharge. Here, methods such as ultrasonic welding, laser welding, resistance welding, and spot welding are used to join the electrode lead portion to the tab terminal, but when a current collector film having a resin layer 202 and aluminum layers 201 formed on both sides of the resin layer 202 is used, ultrasonic welding is often used because no current flows through the resin layer 202.

[0019] However, the present inventors have confirmed that even when ultrasonic welding is performed under the same conditions, depending on the specifications of the current collector film, the connection resistance increases due to factors such as partial welding, leaving room for improvement in the performance of the lithium secondary battery and the temperature stability of the tab during charge and discharge. After extensive research into this point, they have found that when the 2θ pattern of X-ray diffraction measurement of the aluminum layer 201 has at least a peak A between 38.0° and 39.0°, the ratio of the intensity of peak B between 44.0° and 45.0° to the intensity of peak A (B / A) is 0.4 or less, and the half-width of peak A is 0.4° or less, the performance of the lithium secondary battery and the temperature stability of the tab during charge and discharge are also improved. The reasons for this are presumed to be, but are not limited to, the following.

[0020] Peak A indicates the orientation of the (111) plane in the aluminum layer 201, and Peak B indicates the orientation of the (200) plane. When the intensity of Peak B relative to the intensity of Peak A is 0.4 or less and the half-width of Peak A is 0.4° or less, the orientation and crystallinity of the (111) plane are maximized while suppressing the orientation of the (200) plane. Because the (111) plane is a slip plane of aluminum with a face-centered cubic lattice structure, it is prone to shear deformation and plastic deformation. This is presumably what makes welding by ultrasonic lateral vibration advantageous, reducing the connection resistance between the positive electrode tab 11 and the positive electrode tab lead portion 102. Therefore, the lithium secondary battery of this embodiment is thought to have excellent cycle characteristics and tab temperature stability during charge and discharge due to the synergistic effects of the above factors. However, the factors are not limited to those described above.

[0021] In this specification, the half width is the value of the width of 2θ at exactly half the height of the maximum value of the peak in the 2θ pattern of X-ray diffraction measurement, and is called Full Width at Half Maximum in English, or FWHM.

[0022] The positive electrode current collector of this embodiment includes a resin layer 202 and an aluminum layer 201 formed on both sides of the resin layer 202. Figure 3 is a schematic diagram showing an example of a cross section of a positive electrode 10 including the resin layer 202 and the aluminum layer 201 formed on both sides of the resin layer 202.

[0023] The average thickness of the positive electrode current collector film of this embodiment is preferably 3.5 μm to 13 μm, or 5.0 μm to 10 μm, inclusive. By setting the thickness of the positive electrode current collector film within this range, the ease of ultrasonic welding is improved, and the cycle characteristics of the battery and / or the temperature stability of the tab tend to be improved.

[0024] The resin layer 202 preferably contains at least one selected from the group consisting of polyethylene terephthalate (PET), polypropylene, polyamide, acrylic resin, polycarbonate, polyethylene, polyvinyl chloride, and polystyrene. Furthermore, the resin layer 202 is more preferably made of polyethylene terephthalate or polypropylene. Using the above-described resin layer 202 tends to improve ease of ultrasonic welding and improve the cycle characteristics of the battery and / or the temperature stability of the tab.

[0025] The resin layer 202 is preferably in the form of a film (sheet), and its average thickness is preferably 3.0 μm to 10 μm, and more preferably 4.0 μm to 7.0 μm. By setting the thickness of the resin layer 202 within the above range, the ease of ultrasonic welding is improved, and the cycle characteristics of the battery and / or the temperature stability of the tab tend to be improved.

[0026] The positive electrode current collector of this embodiment has aluminum (Al) layers 201 formed as conductive layers on both sides of a resin layer 202. The aluminum layers 201 of this embodiment have an Al element content of 99% by mass or more, 99.9% by mass or more, 99.99% by mass or more, or 99.9999% by mass or more.

[0027] In the 2θ pattern of X-ray diffraction measurement of the aluminum layer 201, the aluminum layer 201 has a peak A at least between 38.0° and 39.0°, but may also have a peak A between 38.1° and 38.9° or between 38.2° and 38.8°. The aluminum layer 201 having a peak A means that a (111) plane is formed. Furthermore, in the aluminum layer 201, the half-width of the peak A is 0.4° or less, preferably 0.3° or less, more preferably 0.2° or less, and even more preferably 0.15° or less. A half-width within this range indicates high crystallinity of the (111) crystal plane. Using a positive electrode current collector including an aluminum layer 201 exhibiting such orientation and crystallinity improves the cycle characteristics of the battery and the temperature stability of the tab. The half-width of the peak A may be 0.01° or more, 0.05° or more, or 0.1° or more.

[0028] In addition, in the 2θ pattern of the aluminum layer 201, the ratio (B / A) of the intensity of Peak B at 44.0° to 45.0° to the intensity of Peak A is 0.4 or less, preferably 0.35 or less, more preferably 0.3 or less, even more preferably 0.2 or less, even more preferably 0.15 or less, and particularly preferably 0.1 or less. An intensity ratio (B / A) of 0.4 or less means that the orientation of the (111) plane is significantly more prevalent than the (200) plane. By using a positive electrode current collector including the aluminum layer 201 exhibiting such an orientation, the cycle characteristics of the battery and the temperature stability of the tab are improved. The position of Peak B may be 44.1° to 44.9° or 44.2° to 44.8°.

[0029] In the aluminum layer 201, the half-width of Peak B is preferably 0.3° or less, 0.2° or less, or 0.1° or less. When the half-width of Peak B is within the above range, the cycle characteristics of the battery and the temperature stability of the tab tend to be further improved. Furthermore, the half-width of Peak B may be 0.01° or more, or 0.05° or more.

[0030] In the aluminum layer 201, the ratio (C / A) of the intensity of Peak C at an angle of 64.6° to 65.6° to the intensity of Peak A is preferably 0.2 or less, more preferably 0.1 or less, even more preferably 0.05 or less, and even more preferably 0.03 or less. An intensity ratio (C / A) of 0.2 or less means that the orientation of the (111) plane is significantly more prevalent than that of the (220) plane. Use of a positive electrode current collector including an aluminum layer 201 exhibiting such an orientation improves the cycle characteristics of the battery and the temperature stability of the tab. The position of Peak C may be 64.7° to 65.5° or 64.8° to 65.4°.

[0031] The X-ray diffraction measurement may be performed by a conventionally known method using a commercially available X-ray diffraction measurement device. For example, measurement may be performed using a "RINT-Ultima" (X-ray diffraction device) manufactured by Rigaku Corporation, using CuKα rays as an X-ray source.

[0032] The average thickness of each aluminum layer 201 is preferably 0.2 μm to 10 μm, 0.3 μm to 5.0 μm, 0.5 μm to 3.0 μm, or 0.8 μm to 2.0 μm. By setting the thickness of each aluminum layer 201 within the above range, the cycle characteristics of the battery and / or the temperature stability of the tab tend to be improved.

[0033] In this embodiment, the average thickness of each layer is calculated by cutting the layer in the thickness direction, observing the exposed cross section with an SEM, and taking the arithmetic mean of measurements taken three or more times, preferably five or ten or more times.

[0034] In the positive electrode current collector film of this embodiment, the ratio of the total thickness of the aluminum layer 201 to the thickness of the resin layer 202 is preferably 0.1 to 1.0, 0.2 to 0.6, or 0.3 to 0.5. By setting the thickness ratio of the aluminum layer 201 to the resin layer 202 within the above range, the cycle characteristics of the battery and / or the temperature stability of the tab tend to be improved.

[0035] The method for producing the positive electrode current collector film of this embodiment is not particularly limited as long as it is a method that can produce a current collector film having the above-mentioned characteristics, and for example, it may be produced by a conventionally known method. Examples of known methods include a method in which a base film (resin sheet) that will become the resin layer 202 is used, and vapor deposition or sputtering is performed on both sides of the base film to form the aluminum layer 201, but vapor deposition is preferred. In this case, for example, when performing vapor deposition, the degree of vacuum should not be too high, thereby further increasing the orientation of the (111) plane, and for example, 1×10 －２ It is preferable to set the pressure to 1×10 Pa or more. －２ Pa or more 5×10 －１ It is more preferable to set the pressure to 5×10 Pa or less.－２ 5x10 or more －１ It is more preferable to set the pressure at 0.1 Pa or less. Furthermore, if processing such as rolling is performed after the aluminum layer 201 is formed, the orientation of the (111) plane tends to decrease. Therefore, it is preferable not to perform processing such as rolling after the aluminum layer 201 is formed. Similarly, after a battery is fabricated using the positive electrode current collector film of this embodiment, the orientation of the aluminum layer tends to change. Furthermore, for example, increasing the temperature of the substrate during vapor deposition tends to improve the crystallinity of the resulting aluminum layer 201. The temperature is, for example, 50°C or higher, and taking into account the heat resistance temperature of the base film used, it is preferably 50°C or higher and 200°C or lower, and more preferably 50°C or higher and 150°C or lower. When forming the aluminum layer 201, one layer of the aluminum layer 201 having the desired thickness may be formed in one go, or multiple vapor depositions or sputterings may be performed to form one layer of the aluminum layer 201 having the desired thickness. Note that a manufactured product may be used as the positive electrode current collector film of this embodiment.

[0036] The positive electrode active material is a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, in the positive electrode 10. The positive electrode active material of the present embodiment is not particularly limited, but is, for example, contained in a positive electrode active material composition containing a binder, a conductive additive, a sacrificial positive electrode agent, and other additives, and the positive electrode active material composition is applied to at least one or both surfaces of a positive electrode current collector and press-molded to form a positive electrode active material layer on at least one or both surfaces of the positive electrode current collector.

[0037] The method for disposing the positive electrode active material layer on the positive electrode current collector is not limited to press molding, and examples thereof include a method in which a thermosetting compound is added to a positive electrode active material composition and the composition is heated to harden it, a method in which a photocurable compound is added to a positive electrode active material composition and the composition is hardened by irradiating it with light, and a method in which the positive electrode active material composition is a two-component hardening composition and the two components are mixed to harden it.

[0038] The positive electrode active material layer of this embodiment is a compound represented by the general formula: Li ｚ Ni ｘ Co ｙ M １－ｘ－ｙ O ２＋α(wherein 0.5≦x≦1.0, 0≦y≦0.35, 0.9≦z≦1.3, −0.2≦α≦0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B).

[0039] Preferably, the positive electrode active material layer is a compound represented by the general formula: Li ｚ Ni ｘ Co ｙ M １－ｘ－ｙ O ２＋α (wherein 0.7≦x≦1.0, 0≦y≦0.35, 0.9≦z≦1.3, −0.2≦α≦0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B). By including the above-mentioned compound with a high nickel ratio as the positive electrode active material, the energy density of the lithium secondary battery tends to be further improved. Furthermore, as the nickel ratio increases, a redox shuttle reaction is more likely to occur, but by including an additive, which will be described in detail below, in the electrolyte, the reaction is suppressed, and the electrolyte tends to have excellent performance stability at high temperatures.

[0040] The positive electrode active material may include other positive electrode active materials in addition to the above-mentioned compounds. Specifically, the other positive electrode active material of this embodiment may be a host material of lithium element (typically, lithium ion). Such other positive electrode active materials include, but are not limited to, metal oxides and metal phosphates. The metal oxides include, but are not limited to, cobalt oxide-based compounds, manganese oxide-based compounds, and nickel oxide-based compounds. The metal phosphates include, but are not limited to, iron phosphate-based compounds and cobalt phosphate-based compounds. Typical other positive electrode active materials include LiCoO ２ , LiNi ｘ Mn ｙ O(x+y=1), LiNiO ２ , LiMn ２ O ４ , LiFePO , LiCoPO , LiFeOF , LiNiOF , and TiS２ The other positive electrode active materials may be used alone or in combination of two or more.

[0041] The positive electrode active material composition may contain a binder. By including a binder, the positive electrode active material layer is more easily bound to the positive electrode current collector, and flexibility is improved after the positive electrode active material layer is disposed on the positive electrode current collector. The binder of this embodiment is not particularly limited, but examples thereof include polyvinylidene fluoride; modified polyvinylidene fluoride obtained by introducing functional groups such as hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, phenyl groups, and methyl groups into polyvinylidene fluoride; polytetrafluoroethylene; modified polytetrafluoroethylene obtained by introducing functional groups such as hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, phenyl groups, and methyl groups into polytetrafluoroethylene; block copolymers, random copolymers, or graft copolymers having tetrafluoroethylene as a structural unit; styrene butadiene rubber; carboxymethyl cellulose; acrylic resins; and polyimide resins. The binder may be used alone or in combination of two or more.

[0042] The positive electrode active material composition of this embodiment may contain a sacrificial positive electrode agent. The sacrificial positive electrode agent of this embodiment is a lithium-containing compound that undergoes an oxidation reaction and does not substantially undergo a reduction reaction in the charge / discharge potential range of the positive electrode active material. The sacrificial positive electrode agent is not particularly limited, but examples thereof include Li ２ O ２ Lithium oxides such as Li ３ Lithium nitrides such as N; Li ２ S-P ２ S ５ , Li ２ S-LiCl, Li ２ S-LiBr and Li ２ Lithium sulfide-based solid solutions such as S-LiI; Li １＋ｘ (Ti １－ｙ Fe ｙ ) １－ｘ O ２ (0<x≦0.25, 0.4<y≦0.9), Li ２－ｘ Ti １－ｚ Fe ｚO ３－ｙ (0≦x<2, 0≦y≦1, 0.05≦z≦0.95), Li ５ FeO ４ The sacrificial positive electrode agent may be used alone or in combination of two or more.

[0043] 1.2 Positive Electrode Tab When joining the positive electrode tab 11 and the laminate 12 of the positive electrode tab lead portion by ultrasonic welding, the ultrasonic welding may be performed while applying pressure. When ultrasonic welding is performed while applying pressure, heat is generated at the positive electrode tab joint 13, as shown in FIG. 5, for example, and the positive electrode tab joint 13 tends to become thinner.

[0044] The positive electrode tab 11 may be made of, for example, at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. The positive electrode tab 11 is preferably made of at least one material selected from the group consisting of aluminum, nickel, and alloys thereof, and more preferably made of aluminum or an aluminum alloy.

[0045] As shown in Fig. 6, the positive electrode tab 11 is preferably joined by welding to a stack 12 of positive electrode tab lead portions obtained by assembling positive electrode tab lead portions 102, which are the positive electrode side ends of the battery stack B, with auxiliary metal foil 14 sandwiched between them. By sandwiching the auxiliary metal foil 14, the thickness of the aluminum layer 201, which is thinned by ultrasonic welding, can be compensated for, and conductivity tends to be easily maintained. The auxiliary metal foil 14 is not particularly limited, but examples include aluminum foil and aluminum alloy foil.

[0046] The thickness of the positive electrode tab 11 is preferably 0.1 mm to 0.8 mm, 0.15 mm to 0.5 mm, or 0.2 mm to 0.4 mm. By setting the thickness of the positive electrode tab 11 within the above range, the cycle characteristics of the lithium secondary battery and the temperature stability of the tab tend to be further improved.

[0047] 1.3. Separator The separator 20 of this embodiment is not particularly limited as long as it has the function of physically and / or electrically isolating the positive electrode 10 and the negative electrode 30 and the function of ensuring ionic conductivity of lithium ions. Examples of such a separator include an insulating porous material, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte. Typically, the separator 20 includes at least one material selected from the group consisting of an insulating porous material, a polymer electrolyte, and a gel electrolyte. Furthermore, as the separator 20, one type of material may be used alone, or two or more types of materials may be used in combination.

[0048] The separator 20 is preferably made of an insulating porous material, a polymer electrolyte, or a gel electrolyte, either singly or in combination. When an insulating porous material is used alone as the separator 20, the lithium secondary battery must further include an electrolytic solution. Examples of the polymer electrolyte include, but are not limited to, solid polymer electrolytes primarily containing a polymer and an electrolyte, and semi-solid polymer electrolytes primarily containing a polymer, an electrolyte, and a plasticizer. Examples of the gel electrolyte include, but are not limited to, those primarily containing a polymer and a liquid electrolyte (i.e., a solvent and an electrolyte).

[0049] Polymers that may be contained in polymer electrolytes and gel electrolytes include, but are not limited to, polymers containing functional groups containing oxygen atoms such as ethers and esters, halogen groups, and polar groups such as cyano groups. Specific examples include resins having ethylene oxide units in the main chain and / or side chains such as polyethylene oxide (PEO), resins having propylene oxide units in the main chain and / or side chains such as polypropylene oxide (PPO), acrylic resins, vinyl resins, ester resins, nylon resins, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polysiloxane, polyphosphazene, polymethyl methacrylate, polyamide, polyimide, aramid, and polytetrafluoroethylene. The above-mentioned resins may be used alone or in combination of two or more.

[0050] Examples of electrolytes contained in the polymer electrolyte and gel electrolyte include salts of Li, Na, K, Ca, and Mg. Typically, in this embodiment, the polymer electrolyte and gel electrolyte contain a lithium salt. The lithium salt is not particularly limited, but may be, for example, one that can be contained in the electrolyte solution described below. Such salts or lithium salts may be used alone or in combination of two or more.

[0051] The compounding ratio of the polymer to the lithium salt in the polymer electrolyte and the gel electrolyte may be determined by the ratio of the polar group of the polymer to the lithium atom of the lithium salt. For example, when the polymer contains oxygen atoms, the compounding ratio may be determined by the ratio ([Li] / [O]) of the number of oxygen atoms of the polymer to the number of lithium atoms of the lithium salt. In the polymer electrolyte and the gel electrolyte, the compounding ratio of the polymer to the lithium salt can be adjusted so that the ratio ([Li] / [O]) is, for example, 0.02 to 0.20, 0.03 to 0.15, or 0.04 to 0.12.

[0052] The solvent contained in the gel electrolyte is not particularly limited, and for example, the solvents that can be contained in the electrolyte solution described below can be used alone or in combination of two or more. Examples of preferred solvents are the same as those in the electrolyte solution described below. The plasticizer contained in the semi-solid polymer electrolyte is not particularly limited, and examples include the same components as the solvents that can be contained in the gel electrolyte and various oligomers.

[0053] When the separator 20 includes an insulating porous member, the pores of the member are filled with an ion-conductive substance, which allows the member to exhibit ion conductivity. Thus, in this embodiment, the pores are filled with, for example, the electrolyte solution of this embodiment or a gel electrolyte containing the electrolyte solution of this embodiment.

[0054] The material constituting the insulating porous member is not particularly limited, and examples thereof include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). That is, the separator 20 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure thereof.

[0055] 1.4. Negative Electrode The negative electrode 30 of this embodiment includes a negative electrode current collector and, if necessary, a negative electrode active material layer. The lithium secondary battery of this embodiment may be an anode-free battery that does not substantially include a negative electrode active material, or may include a negative electrode active material. In an anode-free lithium secondary battery, the negative electrode 30 does not include a negative electrode active material and is therefore composed of a negative electrode current collector. After initial charging, lithium metal is deposited on the negative electrode 30, and the deposited lithium metal is further electrolytically eluted to charge and discharge the battery. Therefore, anode-free batteries have the advantage of, in principle, having a high energy density because the volume and mass of the negative electrode active material are reduced, thereby reducing the overall volume and mass of the battery.

[0056] The negative electrode current collector may have a positive electrode current collector film including a resin layer containing polyethylene terephthalate (PET), polypropylene, or the like, and metal layers provided on both sides of the resin layer, or may have only the metal layers without the resin layer. When the negative electrode current collector film is provided, the metal layers are formed by bonding the metal layers to both surfaces of the resin layer by vapor deposition, sputtering, electrolytic plating, or with an adhesive.

[0057] The resin layer of the negative electrode current collector is an insulator and prevents electrical conduction between the metal layers provided on both sides of the resin layer. The resin constituting the resin layer is not particularly limited, but may be, for example, a sheet-like (film-like) or fibrous resin. The resin may include at least one selected from the group consisting of polyethylene terephthalate (PET), polypropylene, polyamide, acrylic resin, polycarbonate, polyethylene, polyvinyl chloride, and polystyrene. The above resins may be used alone or in combination of two or more.

[0058] In addition to the resins described above, the resin layer of the negative electrode current collector may contain other additives as appropriate depending on the desired physical properties. The additives are not particularly limited, but examples thereof include colorants, flame retardants, and surfactants.

[0059] When the negative electrode current collector has a negative electrode current collector film, the thickness of the metal layer is not particularly limited, but is, for example, 0.1 μm to 4.0 μm, 0.2 μm to 3.0 μm, 0.3 μm to 2.5 μm, or 0.4 μm to 2.0 μm. When the negative electrode current collector has a metal layer without a resin layer, the thickness of the metal layer is not particularly limited, but is, for example, 4.0 μm to 20.0 μm, 6.0 μm to 17.5 μm, or 8.0 μm to 15.0 μm.

[0060] The average thickness of the negative electrode 30 is not particularly limited, but is, for example, 20 μm to 100 μm, 30 μm to 80 μm, or 40 μm to 70 μm, although the average thickness of the negative electrode 30 can be adjusted appropriately depending on the desired battery capacity, etc.

[0061] The negative electrode active material is a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, in the negative electrode 10. The negative electrode active material of the present embodiment is not particularly limited, but is, for example, contained in a negative electrode active material composition containing a binder, a conductive additive, a sacrificial negative electrode agent, and other additives, and the negative electrode active material composition is applied to at least one or both surfaces of a negative electrode current collector and press-molded to form a negative electrode active material layer on at least one or both surfaces of the negative electrode current collector.

[0062] The negative electrode active material is not particularly limited, but examples thereof include lithium metal and alloys containing lithium metal, carbon-based materials, metal oxides, and metals that can be alloyed with lithium and alloys containing such metals. The carbon-based materials are not particularly limited, but examples thereof include graphene, graphite, hard carbon, and carbon nanotubes. The metal oxides are not particularly limited, but examples thereof include titanium oxide-based compounds and cobalt oxide-based compounds. The metals that can be alloyed with lithium are not particularly limited, but examples thereof include silicon, germanium, tin, lead, aluminum, and gallium.

[0063] 1.5 Negative Electrode Tab The negative electrode tab may be made of at least one material selected from the group consisting of copper, titanium, stainless steel, nickel, and alloys thereof. The negative electrode tab is preferably made of at least one material selected from the group consisting of copper, nickel, and alloys thereof, and more preferably made of copper plated with nickel.

[0064] The thickness of the negative electrode tab 11 is preferably 0.1 mm to 0.5 mm, and more preferably 0.2 mm to 0.4 mm. By setting the thickness of the negative electrode tab 11 within the above range, the cycle characteristics of the lithium secondary battery and the temperature stability of the tab tend to be further improved.

[0065] 1.6. Electrolyte A lithium secondary battery may contain an electrolyte. An electrolyte is a liquid containing a solvent and an electrolyte and has ion conductivity. The electrolyte may also be referred to as a liquid electrolyte and acts as a conductive path for lithium ions. Therefore, when a lithium secondary battery contains an electrolyte, the internal resistance can be reduced, and the energy density, capacity, and cycle characteristics can be improved.

[0066] The electrolytic solution is, for example, a solution that fills the housing (pouch) of the lithium secondary battery. The electrolytic solution may be impregnated into the separator 20, or may be held in a polymer to form a polymer electrolyte or a gel electrolyte.

[0067] The electrolyte contained in the electrolytic solution may be a lithium salt, such as LiI, LiCl, LiBr, LiF, or LiBF.４ , LiPF ６ , LiAsF ６ , LiSO ３ CF ３ , LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ CF ３ CF ３ ) ２ , LiB(O ２ C ２ H ４ ) ２ , LiB(C ２ O ４ ) ２ , LiB(O ２ C ２ H ４ ) F ２ , LiB(OCOCF ３ ) ４ , LiNO ３ , and Li ２ SO ４ It may be one or a combination of two or more selected from the group consisting of:

[0068] As the solvent contained in the electrolytic solution, for example, a non-aqueous solvent containing fluorine atoms (hereinafter referred to as a "fluorinated solvent") and a non-aqueous solvent containing no fluorine atoms (hereinafter referred to as a "non-fluorinated solvent") may be added.

[0069] Examples of fluorinated solvents include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0070] Examples of non-fluorine-containing solvents include triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane, dimethoxypropane, dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

[0071] The above fluorinated solvents and / or non-fluorinated solvents may be used alone or in any combination of two or more in any ratio. The contents of the fluorinated solvent and non-fluorinated solvent are not particularly limited, and the ratio of the fluorinated solvent to the total solvent may be 0 to 100% by volume, or the ratio of the non-fluorinated solvent to the total solvent may be 0 to 100% by volume.

[0072] 2. Manufacturing Method of Lithium Secondary Battery There are no particular limitations on the manufacturing method of a lithium secondary battery, as long as it is a method that can manufacture a lithium secondary battery having the above-mentioned battery configuration. For example, the following method can be mentioned.

[0073] The positive electrode 10, separator 20, and negative electrode 30 described above are prepared. The components and reagents used for the components may be produced by conventionally known methods, or commercially available products may be used. The positive electrode 10, separator 20, and negative electrode 30 prepared in this manner are stacked in this order with the positive electrode 10 and the separator 20 facing each other to obtain a laminate. The resulting laminate is sealed in a sealed container together with an electrolyte solution to obtain a lithium secondary battery. The sealed container is not particularly limited, but examples thereof include laminate films.

[0074] 1, a plurality of positive electrodes 10 and negative electrodes 30 may be alternately stacked with a separator 20 sandwiched between them, which tends to further improve battery performance such as energy density. As a stacking method, for example, as shown in FIG. 7, the positive electrodes 10 and negative electrodes 30 may be wrapped so that they do not contact each other and face opposite sides of the separator 20, and the separator 20 may be stacked without cutting. Such stacking is preferable from the viewpoints of preventing short circuits and improving productivity.

[0075] When producing a lithium ion battery, the battery may be produced in the same manner as the above-described battery production method, except that a lithium host material is used for the negative electrode 30. The method for producing the negative electrode 30 having such a host material (negative electrode active material) is not particularly limited, but is, for example, as follows. If necessary, the above-described negative electrode active material is mixed with a binder, a conductive additive, and other additives, which will be described in detail below, to obtain a negative electrode active material composition. The negative electrode active material or the obtained negative electrode active material composition is applied to both sides or one side of the negative electrode current collector, and press-molded to form a negative electrode active material layer on both sides or one side of the negative electrode current collector, thereby obtaining a molded body. The obtained molded body is punched to a predetermined size to obtain the negative electrode 30.

[0076] The lithium secondary battery of this embodiment can be made into an anode-free lithium battery, a lithium ion battery, a lithium metal battery, a lithium sulfur battery, a lithium oxygen battery, or a lithium air battery by adding additional components or changing the materials used in each component, and among these, the anode-free lithium battery, lithium ion battery, and lithium metal battery configurations are particularly suitable.

[0077] The shape of the battery of the lithium secondary battery of this embodiment is not particularly limited, and may be, for example, a sheet type, a laminated sheet type, a thin shape, a cylindrical shape with a bottom, a prismatic shape with a bottom, etc. From the viewpoint of more effectively and reliably achieving the effects of this embodiment, the sheet type, laminated sheet type, or thin shape is preferred.

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0079] 1. Fabrication of Lithium Secondary Batteries Lithium ion secondary batteries of Examples and Comparative Examples were fabricated as follows.

[0080] 1.1. Preparation of Positive Electrode 1.1.1. Preparation of Positive Electrode Current Collector (Example 1) A 6 μm polyethylene terephthalate (PET) film obtained by injection molding was placed in a vapor deposition apparatus, and a 1 μm thin aluminum film was formed on both sides of the PET film to obtain a current collector film. Using the method described below, a 60 μm positive electrode active material layer was formed on both sides of the current collector film, and the film was cut out to obtain a positive electrode main body portion (4 cm × 4 cm) with a size corresponding to a 0.5 cm × 3 cm positive electrode tab lead, thereby obtaining a positive electrode with a thickness of 128 μm.

[0081] Example 2: A 6 μm PET film obtained by injection molding was placed in a vapor deposition apparatus as a positive electrode current collector, and a 1 μm thin aluminum film was formed on both sides of the PET film to obtain a current collector film. A positive electrode active material layer was formed by the method described below, and the film was cut out to obtain a negative electrode of the same size and shape as in Example 1, thereby obtaining a positive electrode. The 2θ pattern of the X-ray diffraction measurement performed on this positive electrode current collector film is shown in FIG.

[0082] Comparative Example 1: A 1 μm thick PET film obtained by injection molding was placed in a vapor deposition apparatus as a positive electrode current collector, and a 6 μm thick aluminum thin film was formed on both sides of the PET film to obtain a current collector film. A positive electrode active material layer was formed by the method described below, and the resultant was cut out to obtain a negative electrode of the same size and shape as in Example 1, thereby obtaining a positive electrode.

[0083] Comparative Example 2: A 1 μm thick PET film obtained by injection molding was placed in a vapor deposition apparatus as a positive electrode current collector, and a 6 μm thick aluminum film was formed on both sides of the PET film to obtain a current collector film. A positive electrode active material layer was formed by the method described below, and the film was cut out to obtain a negative electrode of the same size and shape as in Example 1, thereby obtaining a positive electrode. The 2θ pattern of the X-ray diffraction measurement performed on this positive electrode current collector film is shown in FIG.

[0084] X-ray diffraction measurement was performed on the positive electrode current collector film obtained above using "RINT-Ultima" manufactured by Rigaku Corporation, and the accompanying software was used to detect each peak and calculate the full width at half maximum (FWHM). The measurement conditions were as follows. <Conditions for X-ray diffraction measurement> Goniometer: Ultima IV (Protectus ADS) Attachment: Standard sample stage Scanning Mode: 2Theta / Theta Scanning Type: Continuous Scanning X-ray: 40 kV / 40 mA Divergence slit: 1 / 2° Divergence vertical limiting slit: 10 mm Scattering slit: 8 mm Receiving slit: Open

[0085] 1.1.2. Formation of Positive Electrode Active Material Layer LiNi was dissolved in N-methyl-pyrrolidone (NMP) as a solvent. ０．８ Co ０．１５ Al ０．０５ O ２ A positive electrode active material composition was prepared by mixing 96 parts by mass of the above-mentioned cellulose acetate copolymer, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder. This positive electrode active material composition was applied to parts of both surfaces of a positive electrode current collector so as to have a basis weight of 15 mg / cm. ２ The positive electrode active material layer was formed on both sides of the positive electrode current collector film by coating with a coating solution of 10 ...

[0086] 1.2. Preparation of Negative Electrode A current collector film was used as the negative electrode current collector, which was a 6.0 μm-thick resin layer of PET film with a 1.0 μm-thick metal layer of copper vapor-deposited on both sides. A negative electrode active material composition was prepared by mixing 97.0 parts by mass of graphite as the negative electrode active material, 0.5 parts by mass of carbon black as a conductive additive, and 1.5 parts by mass of carboxymethyl cellulose (CMC) and 1.0 part by mass of styrene-butadiene rubber (SBR) as binders with water as the solvent. This negative electrode active material composition was applied to a portion of both sides of the negative electrode current collector film obtained above, with a basis weight of 15 mg / cm. ２The negative electrode active material layer was formed on both sides of the negative electrode current collector by applying the coating and pressing the coating so that the negative electrode active material layer was formed on both sides of the negative electrode current collector. The negative electrode 30 was obtained by cutting out a piece of a predetermined size (4 cm × 4 cm) from this molded body so that the portion where the negative electrode active material layer was formed would become the negative electrode current collector portion and the portion where the negative electrode active material layer was not formed would become the negative electrode lead portion.

[0087] 1.3. Preparation of separator Polyvinylidene fluoride (PVDF) and Al ２ O ３ A polyethylene microporous film sheet (thickness: 15 μm, 4 cm×4 cm) whose surface was coated with the mixture was prepared as separator 20 .

[0088] 1.4. Preparation of Electrolyte Solution Lithium hexafluorophosphate (LiPF) was dissolved in a solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7. ６ ) was dissolved at a concentration of 1 M. The total amount of the solvent (LiPF ６ The content ratios of lithium difluorophosphate (LiPO) to the total mass of EC and DMC (excluding ２ F ２ ) and vinylene carbonate (VC) were added to the solvent. Thus, an electrolyte solution was prepared.

[0089] 1.5. Battery Assembly The positive electrode 10, separator 20, and negative electrode 30 obtained as described above were stacked multiple times in this order, with the negative electrode 30 facing the separator 20, as shown in FIG. 1 , to obtain a laminate. The lead portions of the stacked positive and negative electrodes were then ultrasonically welded to a 100 μm Al terminal for the positive electrode and a 100 μm Ni terminal for the negative electrode, and inserted into a laminate exterior. The resulting electrolyte was then injected into the exterior and sealed, yielding lithium-ion secondary batteries for each of the Examples and Comparative Examples.

[0090] 2. Evaluation of Lithium Secondary Battery 2.1. Rate Retention Rate The lithium secondary battery obtained above was initially CC charged to 4.2 V at a charge rate of 0.1 C in an environment of 25°C, and then initially CC discharged to 3.0 V at a discharge rate of 0.1 C. The battery was then CC charged again to 4.2 V at 0.1 C, and after charging was completed, CC discharge was performed at 3 C. The ratio of the discharge capacity at a discharge rate of 3.0 C to the initial discharge capacity (discharge rate at 0.1 C) obtained in this manner was calculated as the rate retention rate (%).

[0091] 2.2 Tab Temperature During Current Flow Each lithium secondary battery for which the rate retention rate had been measured was again CC charged to 4.2 V at a charge rate of 0.1 C, and then CC discharged to 2.5 V at a rate of 10 C. Two minutes after discharge was completed, the temperature (°C) at the center of the positive electrode tab was measured. A lower tab temperature means less heat generation, and therefore better tab temperature stability.

[0092]

[0093] As shown in Table 1, Examples 1 and 2 were confirmed to be superior in rate characteristics and temperature stability of the tab during current application compared to Comparative Examples 1 and 2, which did not include a laminate including a plurality of positive electrodes, a plurality of separators, and a plurality of negative electrodes, a plurality of positive electrode tab lead portions extending from the laminate, and a positive electrode tab joined to the plurality of positive electrode tab lead portions, wherein the positive electrode tab lead portion was a positive electrode current collector constituting a positive electrode extending from the laminate, and the positive electrode tab lead portion and the positive electrode current collector included a resin layer and aluminum layers formed on both sides of the resin layer, and in a 2θ pattern obtained by X-ray diffraction measurement of the aluminum layer, the aluminum layer had at least Peak A in the range of 38.0° to 39.0°, and the ratio (B / A) of the intensity of Peak B in the range of 44.0° to 45.0° to the intensity of Peak A was 0.4° or less.

[0094] <Additional Notes> Embodiments of the present disclosure include the following aspects: [1] A lithium secondary battery comprising: a laminate including a plurality of positive electrodes, a plurality of separators, and a plurality of negative electrodes; a plurality of positive electrode tab lead portions extending from the laminate; and positive electrode tabs joined to a plurality of the positive electrode tab lead portions, wherein the positive electrode tab lead portion is a positive electrode current collector constituting the positive electrode extending from the laminate, the positive electrode tab lead portion and the positive electrode current collector include a resin layer and aluminum layers formed on both sides of the resin layer, wherein a 2θ pattern obtained by X-ray diffraction measurement of the aluminum layer has at least a peak A in an angle of 38.0° or more and 39.0° or less, a ratio (B / A) of the intensity of a peak B in an angle of 44.0° or more and 45.0° or less to the intensity of the peak A is 0.4° or less, and the half width of the peak A is 0.4° or less. [2] The lithium secondary battery according to [1], wherein the resin layer has an average thickness of 3.0 μm or more and 10.0 μm or less, and the aluminum layer has an average thickness of 0.5 μm or more and 3.0 μm or less. [3] The lithium secondary battery according to [1] or [2], wherein the resin layer contains at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polyamide, acrylic resin, polycarbonate, polyethylene, polyvinyl chloride, and polystyrene. [4] The lithium secondary battery according to any one of [1] to [3], wherein the resin layer is made of polyethylene terephthalate or polypropylene. [5] The lithium secondary battery according to any one of [1] to [4], wherein the positive electrode tab lead portion is joined to the positive electrode tab by ultrasonic welding.

[0095] The lithium secondary battery according to the present invention has excellent cycle characteristics and temperature stability of the tab, and therefore has industrial applicability as an electricity storage device for a variety of uses.

[0096] A, B... battery laminate, 10... positive electrode, 11... positive electrode tab, 12... laminate of positive electrode tab lead portion, 13... positive electrode tab joint portion, 14... auxiliary metal foil, 20... separator, 30... negative electrode, 101... positive electrode main body portion, 102... positive electrode tab lead portion, 201... aluminum layer, 202... resin layer.

Claims

1. A lithium secondary battery comprising: a laminate including a plurality of positive electrodes, a plurality of separators, and a plurality of negative electrodes; a plurality of positive electrode tab leads extending from the laminate; and a positive electrode tab joined to the plurality of positive electrode tab leads, wherein the positive electrode tab lead is an extension of a positive electrode current collector constituting the positive electrode from the laminate, and the positive electrode tab lead and the positive electrode current collector include a resin layer and aluminum layers formed on both surfaces of the resin layer, and in the 2θ pattern of the X-ray diffraction measurement of the aluminum layer, it has a peak A at least at 38.0° or more and 39.0° or less, the ratio (B / A) of the intensity of a peak B at 44.0° or more and 45.0° or less to the intensity of the peak A is 0.4 or less, and the full width at half maximum of the peak A is 0.4° or less.

2. The lithium secondary battery according to claim 1, wherein the average thickness of the resin layer is 3.0 μm or more and 10.0 μm or less, and the average thickness of the aluminum layer is 0.5 μm or more and 3.0 μm or less.

3. The lithium secondary battery according to claim 1, wherein the resin layer contains at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polyamide, acrylic resin, polycarbonate, polyethylene, polyvinyl chloride, and polystyrene.

4. The lithium secondary battery according to claim 1, wherein the resin layer is made of polyethylene terephthalate or polypropylene.

5. The lithium secondary battery according to claim 1, wherein the positive electrode tab lead is joined to the positive electrode tab by ultrasonic welding.

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