Nonaqueous electrolyte secondary battery and method of manufacturing the same

Abstract

To provide a non-aqueous electrolyte improved in Li precipitation resistance and high-temperature storage characteristics in a non-aqueous electrolyte secondary battery comprising a wound electrode body.SOLUTION: A manufacturing method of a non-aqueous electrolyte secondary battery includes steps of: preparing an assembly storing in a metallic battery case a wound electrode body, in which a laminate including a cathode, an anode and a separator interposed therebetween is wound, and a non-aqueous electrolyte, a ratio of a capacity of the anode with respect to a capacity of the cathode being 1.2 or more, an outermost periphery of the wound electrode body being the anode and an inner surface of the battery case including a coated layer containing a Li compound; applying a voltage between the battery case and the anode so as to decompose the Li compound and supplying Li ions from the Li compound to the anode in the outermost periphery of the wound electrode body; and applying a voltage between the cathode and the anode and applying initial charge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, etc., and as power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] A nonaqueous electrolyte secondary battery typically includes an electrode assembly in which a positive electrode and a negative electrode are insulated by a separator. One common form of the electrode assembly is a wound electrode assembly in which a laminate of a positive electrode, a negative electrode, and a separator is wound. A known technique involves placing a metallic lithium foil or the like inside a battery case of a nonaqueous electrolyte secondary battery including a wound electrode assembly, thereby releasing lithium ions into the nonaqueous electrolyte (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 05-144473 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for even higher capacity non-aqueous electrolyte secondary batteries for use as vehicle driving power sources. One method for achieving higher capacity is to increase the number of windings (i.e., the number of turns) to form a multi-layered wound electrode assembly. As a result of extensive research, the present inventors have found that there is room for improvement in the Li deposition resistance and high-temperature storage characteristics of non-aqueous electrolyte secondary batteries, particularly when the number of turns of the wound electrode assembly is large.

[0006] Therefore, an object of the present invention is to provide a nonaqueous electrolyte secondary battery including a wound electrode body, which has a nonaqueous electrolyte that is excellent in Li deposition resistance and high-temperature storage characteristics. [Means for solving the problem]

[0007] The method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein includes the steps of: preparing an assembly in which a wound electrode body, which is formed by winding a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween, and a non-aqueous electrolyte are housed in a metal battery case, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more, the outermost periphery of the wound electrode body is the negative electrode, and the inner surface of the battery case has a coating layer containing a Li compound; applying a voltage between the battery case and the negative electrode so as to decompose the Li compound, thereby supplying Li ions from the Li compound to the negative electrode at the outermost periphery of the wound electrode body; and applying a voltage between the positive electrode and the negative electrode to perform initial charging.

[0008] According to this configuration, it is possible to provide a nonaqueous electrolyte secondary battery including a wound electrode body, which has excellent resistance to Li deposition and high-temperature storage characteristics.

[0009] The nonaqueous electrolyte secondary battery disclosed herein includes a wound electrode assembly formed by winding a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween, a nonaqueous electrolyte, and a metal battery case that houses these. The ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more. The nonaqueous electrolyte secondary battery has a highly concentrated Li element region on the inner surface of the battery case.

[0010] With this configuration, a nonaqueous electrolyte secondary battery including the wound electrode body has excellent Li deposition resistance and high-temperature storage characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart showing each step of a method for manufacturing a lithium ion secondary battery according to one embodiment of the present invention. [Figure 2] 3 is a cross-sectional view schematically showing the internal structure of an assembly prepared in an assembly preparation step of a manufacturing method according to one embodiment of the present invention. FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line XX in FIG. 2. [Figure 4] FIG. 3 is a schematic exploded view showing the configuration of the wound electrode body of FIG. 2. [Figure 5] 1 is a cross-sectional view schematically showing the internal structure of a lithium-ion secondary battery obtained by a manufacturing method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Matters not mentioned in this specification but necessary for implementing the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. In this specification, a numerical range expressed as "A to B" includes A and B.

[0013] In this specification, the term "secondary battery" refers to an electricity storage device that can be repeatedly charged and discharged, and is a term that encompasses so-called storage batteries and electricity storage elements such as electric double layer capacitors. In addition, in this specification, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

[0014] As shown in the flowchart of FIG. 1 , the method for manufacturing a nonaqueous electrolyte secondary battery according to this embodiment includes the steps of: preparing an assembly S101 in which a wound electrode body, which is formed by winding a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween, and a nonaqueous electrolyte housed in a metal battery case; wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more, the outermost periphery of the wound electrode body is the negative electrode, and the inner surface of the battery case has a coating layer containing a Li compound; applying a voltage between the battery case and the negative electrode so as to decompose the Li compound, thereby supplying Li ions from the Li compound to the outermost negative electrode of the wound electrode body (hereinafter also referred to as a “voltage application step”) S102; and applying a voltage between the positive electrode and the negative electrode to perform initial charging (hereinafter also referred to as an “initial charging step”) S103.

[0015] Hereinafter, each step of the method for manufacturing a nonaqueous electrolyte secondary battery according to this embodiment will be described in detail using a flat prismatic lithium ion secondary battery having a flat wound electrode body and a flat battery case as an example, but it is not intended that the present invention be limited to the embodiment described.

[0016] 2 to 4 show the assembly 100 prepared in the assembly preparation step S101. Fig. 2 is a cross-sectional view schematically showing the internal structure of the assembly 100. Fig. 3 is a cross-sectional view of the assembly 100 taken along line XX in Fig. 2. Fig. 4 is a schematic exploded view showing the configuration of the wound electrode body 20.

[0017] 2 and 3, the assembly 100 includes a flat wound electrode assembly 20, a non-aqueous electrolyte 80, and a battery case (i.e., an outer container) 30 that houses the wound electrode assembly 20 and the non-aqueous electrolyte 80. Note that Figures 2 and 3 do not accurately represent the amount of non-aqueous electrolyte 80.

[0018] 2 and 4, the wound electrode body 20 has a configuration in which a laminate, in which a positive electrode sheet 50 and a negative electrode sheet 60 are stacked with two long first separators 70 interposed therebetween, is wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long negative electrode current collector 62. The positive electrode active material layer-free portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer-free portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the wound electrode body 20. The positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a are joined to the positive electrode current collector 42a and the negative electrode current collector 44a, respectively.

[0019] In this embodiment, the outermost periphery of the wound electrode body 20 is the negative electrode 60. Therefore, as shown in Fig. 4, in the wound electrode body 20, the positive electrode 50 is located on the inner periphery side (in other words, on the winding axis side).

[0020] The greater the number of windings of the wound electrode assembly 20, the greater the effect of improving Li precipitation resistance and high-temperature storage characteristics. Therefore, the number of windings of the wound electrode assembly 20 is preferably 4 turns (in other words, 4 times) or more, more preferably 10 turns or more, even more preferably 20 turns or more, still more preferably 25 turns or more, and particularly preferably 30 turns or more. The number of windings of the wound electrode assembly 20 may be 100 turns or less, 70 turns or less, or 50 turns or less.

[0021] The ratio of the capacity of the negative electrode 60 to the capacity of the positive electrode 50 (negative electrode 60 / positive electrode 50) is 1.2 or more. A capacity ratio of 1.2 or more can improve the Li deposition resistance of the resulting lithium ion secondary battery 200. From the viewpoint of higher Li deposition resistance, the capacity ratio is preferably 1.3 or more. On the other hand, the capacity ratio may be less than 2.0, 1.8 or less, or 1.5 or less. Note that the capacities of the positive electrode 50 and the negative electrode 60 are both theoretical capacities and can be calculated according to known methods.

[0022] A known positive electrode current collector used in lithium ion secondary batteries may be used as the positive electrode current collector 52 constituting the positive electrode sheet 50, and examples thereof include aluminum foil, etc. The thickness of the positive electrode current collector 52 is not particularly limited and is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0023] The positive electrode active material layer 54 contains a positive electrode active material. The positive electrode active material may be a known positive electrode active material used in lithium-ion secondary batteries. Specific examples of the positive electrode active material include lithium composite oxides and lithium transition metal phosphate compounds. The crystal structure of the positive electrode active material is not particularly limited, and may be a layered structure, a spinel structure, an olivine structure, or the like.

[0024] Examples of the lithium composite oxide include lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide.

[0025] In this specification, the term "lithium nickel cobalt manganese composite oxide" refers to oxides containing Li, Ni, Co, Mn, and O as constituent elements, as well as oxides containing one or more additional elements. Examples of such additional elements include transition metal elements and typical metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additional element may also be a metalloid element such as B, C, Si, or P, or a nonmetal element such as S, F, Cl, Br, or I. This also applies to the lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide.

[0026] Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate.

[0027] These positive electrode active materials may be used alone or in combination of two or more. The positive electrode active material is preferably a lithium nickel cobalt manganese composite oxide.

[0028] The average particle diameter (median diameter: D50) of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm to 25 μm, preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm. The average particle diameter (D50) of the positive electrode active material can be determined, for example, by a laser diffraction scattering method.

[0029] The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is, for example, 80 mass % or more, preferably 85 mass % or more, and more preferably 90 mass % or more.

[0030] The positive electrode active material layer 54 may contain components other than the positive electrode active material (i.e., optional components). Examples of the optional components include a conductive material, a binder, etc. Suitable conductive materials include carbon materials such as carbon black (e.g., acetylene black), carbon nanotubes (CNTs), and graphite. Suitable binders include polyvinylidene fluoride (PVDF), etc. When CNTs are used as the conductive material, the positive electrode active material layer 54 may further contain a dispersant for the CNTs.

[0031] The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 13% by mass. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass to 15% by mass, and more preferably 1.5% by mass to 10% by mass.

[0032] The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0033] The positive electrode sheet 50 may contain an insulating layer (not shown) at the boundary between the positive electrode active material layer non-forming portion 52a and the positive electrode active material layer 54. The insulating layer contains, for example, ceramic particles.

[0034] A known negative electrode current collector used in lithium ion secondary batteries, such as copper foil, may be used as the negative electrode current collector 62 that constitutes the negative electrode sheet 60. The thickness of the negative electrode current collector 62 is not particularly limited and is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0035] The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0036] The average particle diameter (median diameter: D50) of the negative electrode active material is not particularly limited, but is, for example, 0.1 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 5 μm to 20 μm. The average particle diameter (D50) of the negative electrode active material can be determined, for example, by a laser diffraction scattering method.

[0037] The negative electrode active material layer 64 may contain components other than the active material, such as a binder or a thickener. Examples of binders that may be used include styrene butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of thickeners that may be used include carboxymethyl cellulose (CMC).

[0038] The content of the negative electrode active material in the negative electrode active material layer 64 is preferably 90% by mass or more, and more preferably 95% by mass or more and 99% by mass or less. The content of the binder in the negative electrode active material layer 64 is preferably 0.1% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less. The content of the thickener in the negative electrode active material layer 64 is preferably 0.3% by mass or more and 3% by mass or less, and more preferably 0.5% by mass or more and 2% by mass or less.

[0039] The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0040] The first separator 70 may be a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the first separator 70. The thickness of the first separator 70 is not particularly limited, but is, for example, 5 μm to 50 μm, and preferably 10 μm to 30 μm.

[0041] The nonaqueous electrolyte 80 typically contains a nonaqueous solvent and a supporting salt (electrolyte salt). As the nonaqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in electrolyte solutions for lithium-ion secondary batteries can be used without any particular limitation. Of these, carbonates and esters are preferred, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl acetate, and methyl propionate. One of these nonaqueous solvents can be used alone, or two or more can be used in appropriate combination.

[0042] As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI) (preferably LiPF6) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0043] The nonaqueous electrolyte 80 may contain various additives other than the above-mentioned components, such as film-forming agents such as vinylene carbonate (VC) and oxalate complexes; gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); and thickeners, as long as the effects of the present invention are not significantly impaired.

[0044] The battery case 30 includes a case body 32 and a lid 34. The case body 32 has a flattened rectangular parallelepiped shape, with one of its faces (the top face in the figure) forming an opening. The lid 34 has a generally rectangular shape that fits the shape of the opening. The lid 34 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, as well as a thin-walled safety valve 36 that is designed to release internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. The lid also has an injection hole (not shown) for injecting a nonaqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a.

[0045] In the voltage application step S102 described below, a current is passed between the battery case 30 and the negative electrode 60, so the battery case 30 has electrical conductivity. Therefore, the material of the battery case 30 is a metal (e.g., aluminum, stainless steel, nickel-plated steel, etc.). The battery case 30 is preferably made of aluminum because it has good electrical conductivity, thermal conductivity, strength, and is lightweight.

[0046] The inventors have found that when a wound electrode assembly is multilayered, uniform diffusion of Li ions is likely to be insufficient, resulting in uneven salt concentration in the outermost negative electrode of the wound electrode assembly, which leads to a deterioration in high-temperature storage characteristics (particularly, capacity degradation during long-term storage at high temperatures). Therefore, in this embodiment, in order to supply Li ions to the outermost negative electrode 60 of the wound electrode assembly 20, the inner surface of the battery case 30 (particularly the inner surface of the case body 32) has a coating layer 90 containing a Li compound. The Li compound is a compound that can decompose to release Li ions upon application of a voltage in the voltage application step S102 described below. Suitable examples include at least one selected from the group consisting of lithium carbonate, lithium chloride, lithium nitrate, lithium dihydrogen carbonate, and lithium phosphate, with lithium carbonate being particularly preferred. The use of such a Li compound allows for the release of more Li ions at lower cost than the use of a lithium ion donor (typically, a compound that can be used as a positive electrode active material) that releases Li ions without decomposition upon application of a voltage.

[0047] The coating layer 90 may contain only a Li compound, or may contain other components. For example, when the coating layer 90 contains a conductive material (e.g., carbon black) in addition to a Li compound, the Li compound contained in the coating layer 90 can be efficiently electrolyzed. The content of the conductive material in the coating layer 90 is, for example, 1% by mass to 20% by mass, and preferably 5% by mass to 15% by mass.

[0048] The coating layer 90 may be formed on any inner surface of the battery case 30 as long as it can release Li ions into the non-aqueous electrolyte 80. The position of the coating layer 90 on the inner surface of the battery case 30 is not particularly limited. Typically, at least a portion (preferably the entirety) of the coating layer 90 is in contact with the non-aqueous electrolyte 80. In the illustrated example, the coating layer 90 is formed on the inner surface of the case main body 32, on the surface facing the flat surface of the wound electrode body 20. In this case, it is particularly easy to supply Li ions to the negative electrode 60 at the outermost periphery of the wound electrode body 20. Note that the wound electrode body 20 has a flat portion and rounded portions at both ends thereof, and the flat surface of the wound electrode body 20 refers to the main surface of this flat portion (i.e., the surface with the largest area). Note that the flat surface of the wound electrode body 20 does not have to be completely flat.

[0049] Here, the wound electrode body 20 has a pair of (i.e., two) flat surfaces. Two of the inner surfaces of the battery case 30 face these two flat surfaces, respectively. In the illustrated example, a coating layer 90 is formed on one of the inner surfaces of the battery case 30 and faces one of the flat surfaces of the wound electrode body 20. The coating layer 90 is preferably provided on the two inner surfaces of the battery case 30 that face the flat surfaces of the wound electrode body 20. In this case, the Li deposition resistance and high-temperature storage characteristics of the obtained lithium-ion secondary battery 200 are further improved.

[0050] The coating layer 90 is not in contact with the wound electrode assembly 20 but is separated from it. The coating layer 90 is insulated from the wound electrode assembly 20 via a second separator 72. The second separator 72 may be the same as or similar to the first separator 70. The second separator 72 may be wound around the wound electrode assembly 20 and surround the outer periphery of the wound electrode assembly 20. Alternatively, the second separator 72 may have a bag shape and house the wound electrode assembly 20 inside. Note that the method for insulating the coating layer 90 from the wound electrode assembly 20 is not limited to this.

[0051] The assembly 100 can be prepared, for example, as follows. First, a battery case 30 including a case body 32 and a lid 34, and a coating liquid containing a Li compound are prepared. The coating liquid may be a solution or a dispersion. The coating liquid is applied to the inner surface of the case body 32 of the battery case 30 and dried to form a coating layer 90. Meanwhile, a positive terminal 42, a negative terminal 44, a positive current collector plate 42a, and a negative current collector plate 44a are attached to the lid 34 of the battery case 30.

[0052] The wound electrode body 20 is produced according to a known method. For example, a positive electrode sheet 50, a negative electrode sheet 60, and two first separator sheets 70 are prepared. Using a known winding machine, the positive electrode sheet 50 and the negative electrode sheet 60 are stacked and wound with the first separator sheet 70 interposed between them. The obtained wound body is pressed from its side to form a flat shape, thereby producing the wound electrode body 20.

[0053] A positive electrode current collector 42a and a negative electrode current collector 44a are attached to the fabricated wound electrode body 20 by resistance welding, ultrasonic welding, or the like. This connects the wound electrode body 20 to the lid 34 of the battery case 30. A second separator 72 is prepared, and the second separator 72 is abutted against the wound electrode body 20. The wound electrode body 20 is inserted into the case body 32 through the opening of the case body 32. At this time, the second separator 72 is positioned between the wound electrode body 20 and the coating layer 90 on the inner surface of the case body 32. The case body 32 and the lid 34 are then sealed by laser welding or the like.

[0054] The non-aqueous electrolyte 80 is prepared according to a known method. The non-aqueous electrolyte 80 is poured into the battery case 30 through the pouring hole in the lid 34 of the battery case 30, and the pouring hole is then sealed. In this manner, the assembly 100 can be obtained.

[0055] Next, the voltage application step S102 will be described. The voltage application step S102 can be performed using a known voltage application device (not shown). Specifically, for example, terminals of a voltage application device (e.g., a charger) are attached to the battery case 30 and the negative electrode terminal 44, respectively, and a voltage is applied between the battery case 30 and the negative electrode 60. At this time, the voltage is applied with the battery case 30 as the anode and the negative electrode 60 as the cathode.

[0056] The magnitude of the voltage is appropriately set depending on the type of Li compound, specifically, the decomposition starting potential of the Li compound, and preferably a voltage equal to or higher than the decomposition starting potential of the Li compound is selected. The voltage applied in the voltage application step S102 is 4.10 V to 4.50 V (vs Li + / Li), and more preferably 4.20V to 4.35V (vsLi + / Li).

[0057] This voltage application decomposes the Li compound, and Li ions are released from the Li compound into the nonaqueous electrolyte 80. These Li ions move to the negative electrode 60 at the outermost periphery of the wound electrode body 20, and are supplied to the negative electrode 60. In this manner, the voltage application step S102 can be performed.

[0058] Here, by using a compound that decomposes when a voltage is applied as the Li compound, the Li ions can be supplied efficiently. Also, by supplying Li ions to the negative electrode 60 at the outermost periphery of the wound electrode body 20, it is possible to eliminate uneven salt concentration in the negative electrode 60, thereby improving the high-temperature storage characteristics of the resulting lithium-ion secondary battery 200.

[0059] Next, the initial charging step S103 will be described. The initial charging step S103 can be performed according to a known method using a known voltage application device (not shown). The voltage application device may be the same as that used in the voltage application step S102.

[0060] Specifically, for example, terminals of a voltage application device are attached to the positive electrode terminal 42 and the negative electrode terminal 44, respectively, and a voltage is applied between the positive electrode 50 and the negative electrode 60. At this time, the voltage is applied with the positive electrode 50 as the anode and the negative electrode 60 as the cathode. The voltage application may be set appropriately depending on the configuration of the assembly (particularly, the type of positive electrode active material, the type of negative electrode active material, the composition of the non-aqueous electrolyte 80, etc.), and known conditions may be used.

[0061] This allows the lithium ion secondary battery 200 to be obtained. After the initial charging step S103, a step of performing an aging treatment on the lithium ion secondary battery 200 may be further performed. The aging treatment can further eliminate uneven salt concentration in the negative electrode 60 at the outermost periphery of the wound electrode body 20, thereby further improving high-temperature storage characteristics. The aging treatment is preferably performed at 60°C or higher in a charged state where the potential of the negative electrode 60 is 0.5V or higher. The aging temperature is more preferably 60°C to 80°C. The aging time is, for example, 1 hour or more, and preferably 5 to 48 hours.

[0062] The lithium ion secondary battery 200 obtained as described above has excellent high-temperature storage characteristics. Specifically, capacity degradation when placed at high temperatures for a long period of time is suppressed. Therefore, the lithium ion secondary battery 200 has excellent durability. Furthermore, the lithium ion secondary battery 200 also has excellent resistance to Li precipitation.

[0063] In the completed lithium-ion secondary battery 200, the Li compounds in the coating layer 90 have been decomposed. Therefore, the portion where the coating layer 90 was present contains remaining Li compounds and decomposed products of the Li compounds, and thus may remain as a region with a high Li content. Therefore, FIG. 5 shows a schematic cross-sectional view of the lithium-ion secondary battery 200 corresponding to FIG. 3. As shown in FIG. 5, the lithium-ion secondary battery 200 may have a high Li element accumulation region 92 on the inner surface of the battery case 30. In this specification, the "high Li element accumulation region" refers to a region on the inner surface of the battery case 30 where deposits are present, and where the deposits contain Li elements. The deposits may particularly contain Li compounds or decomposed products of the Li compounds. In the deposits, the ratio of Li atoms to all atoms may be 5 atomic % or more, or 10 atomic % or more. This Li atom ratio can be measured by a known method (e.g., ICP atomic emission spectroscopy, etc.).

[0064] From another perspective, the lithium-ion secondary battery 200 disclosed herein includes a wound electrode assembly 20 formed by winding a laminate including a positive electrode 50, a negative electrode 60, and a first separator 70 interposed therebetween, a nonaqueous electrolyte 80, and a metal battery case 30 that houses these. The ratio of the capacity of the negative electrode 60 to the capacity of the positive electrode 50 is 1.2 or greater. The lithium-ion secondary battery 200 has a highly concentrated Li element region 92 on the inner surface of the battery case 30.

[0065] The lithium ion secondary battery 200 can be used for a variety of purposes. Specific applications include portable power sources for personal computers, portable electronic devices, portable terminals, etc.; power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); and storage batteries for small-sized power storage devices, with the battery for driving vehicles being preferred. The lithium ion secondary battery 200 can also be used in the form of a battery pack, typically consisting of a plurality of batteries connected in series and / or parallel.

[0066] The above describes, as an example, a rectangular lithium ion secondary battery 200 including a flat wound electrode body 20. However, the lithium ion secondary battery can also be configured as a cylindrical lithium ion secondary battery or the like.

[0067] The secondary battery according to this embodiment can be constructed as a non-aqueous electrolyte secondary battery other than a lithium ion secondary battery according to a known method.

[0068] Examples of the present invention will be described in detail below, but it is not intended that the present invention be limited to those shown in these examples.

[0069] Example 1 An aluminum battery case was prepared. This battery case included a case body and a lid and had a rectangular parallelepiped shape. An inlet hole was provided in the lid. A paste containing lithium carbonate and acetylene black (AB) in a mass ratio of 90:10 was prepared. The paste was applied to one of the largest inner surfaces of the battery case body and allowed to dry. This formed a coating layer containing lithium carbonate and AB.

[0070] LiNi as a positive electrode active material powder 0.5 Co 0.2 Mn 0.3 O2 (NCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a mass ratio of NCM:AB:PVdF = 90:5:5. This prepared a slurry for forming a positive electrode active material layer. This slurry was applied to both sides of an aluminum foil and then dried to form a positive electrode active material layer. The total basis weight of both sides at this time was 10 mg / cm. 2 Next, the positive electrode active material layer was 3 A positive electrode sheet was obtained by rolling and pressing the sheet so that the thickness became

[0071] A negative electrode active material layer was prepared by mixing natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener with ion-exchanged water in a mass ratio of C:SBR:CMC = 97:2:1. This slurry was applied to both sides of copper foil and then dried to form a negative electrode active material layer. The total basis weight of both sides was 9 mg / cm. 2 Next, the negative electrode active material layer was coated with a 1.2 g / cm 3 A negative electrode sheet was obtained by rolling and pressing the sheet so that the thickness of the negative electrode sheet became 1 / 3.

[0072] Additionally, polyolefin porous membranes were prepared as two first separators and one second separator. The prepared positive electrode sheet and negative electrode sheet were stacked with the first separator interposed therebetween. The resulting laminate was wound 30 turns to prepare a wound electrode assembly. At this time, the outermost periphery of the wound electrode assembly was the negative electrode. Furthermore, a second separator sheet was wound around the outermost periphery of the wound electrode assembly, and the outermost negative electrode was covered with the second separator sheet.

[0073] Terminals were attached to this electrode assembly, which was then attached to the lid of the battery case. The electrode assembly was then housed in the battery case body, and the battery case and the lid were hermetically sealed. The negative electrode on the outermost periphery of the wound electrode assembly faced the coating layer. The capacity ratio of the negative electrode to the positive electrode (negative electrode / positive electrode) in the wound electrode assembly was 1.2.

[0074] A mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 25:40:35 was prepared. LiPF6 was dissolved in this mixed solvent at a concentration of 1.1 mol / L to prepare a nonaqueous electrolyte. The prepared nonaqueous electrolyte was poured into the battery case through the inlet, and the inlet was then sealed to obtain an assembly.

[0075] A commercially available charger was prepared. Using this charger, the battery case was used as the anode and the negative terminal as the cathode, and a voltage of 4.3 V (vsLi) was applied between the battery case and the negative terminal of the assembly.+ A voltage of ( / Li) was applied. As a result, lithium carbonate in the coating layer on the inner surface of the battery case was decomposed, and Li ions were inserted into the outermost negative electrode of the wound electrode body.

[0076] Next, using this charger, with the positive electrode terminal as the anode and the negative electrode terminal as the cathode, the assembly was subjected to constant current charging up to 4.15 V at a current value of 0.1 C, and then discharged at a constant current down to 3 V. This charge and discharge were performed 2 times as the initial charge. The capacity at the time of the second discharge was measured and taken as the initial capacity.

[0077] After discharging the obtained lithium ion secondary battery down to 2 V, it was subjected to an aging treatment for 12 hours in a constant temperature layer at 60 °C. In this way, the lithium ion secondary battery for evaluation of Example 1 was obtained.

[0078] [Example 2] A lithium ion secondary battery for evaluation was obtained in the same manner as in Example 1, except that the capacity ratio of the negative electrode to the positive electrode (negative electrode / positive electrode) was changed to 1.3.

[0079] [Comparative Example 1] A lithium ion secondary battery for evaluation was obtained in the same manner as in Example 1, except that the capacity ratio of the negative electrode to the positive electrode (negative electrode / positive electrode) was changed to 1.1.

[0080] [Comparative Example 2] A lithium ion secondary battery for evaluation was obtained in the same manner as in Example 1, except that no voltage was applied between the battery case and the negative electrode.

[0081] [Comparative Example 3] A lithium ion secondary battery for evaluation was obtained in the same manner as in Example 1, except that a coating layer containing lithium carbonate and AB was not formed on the inner surface of the battery case and no voltage was applied between the battery case and the negative electrode.

[0082] Each lithium-ion secondary battery for evaluation prepared as described above was adjusted to an SOC of 50% in a 25°C environment. Then, the battery was placed in a -10°C environment and subjected to 200 charge-discharge cycles, each consisting of a 10-second charge at 20C and a 100-second discharge at 2C. The battery was then placed in a 25°C environment and the discharge capacity was measured in the same manner as for the initial capacity. The capacity retention rate (%) was calculated using the formula: (discharge capacity after charge-discharge cycles / initial capacity) × 100. The results are shown in Table 1. Because these charge-discharge cycles are conditions that favor metallic lithium precipitation, a higher capacity retention rate indicates less capacity loss due to metallic lithium precipitation and a higher resistance of the lithium-ion secondary battery to Li precipitation.

[0083] <High-temperature storage characteristic evaluation> Each of the lithium-ion secondary batteries for evaluation prepared above was adjusted to an SOC of 80% in a temperature environment of 25°C. Each of these lithium-ion secondary batteries for evaluation was placed in a thermostatic chamber at 60°C and stored for 60 days. Thereafter, the discharge capacity after storage was measured using the same method as for the initial capacity. The capacity retention rate (%) was calculated using the formula: (discharge capacity after high-temperature storage / initial capacity) x 100. The results are shown in Table 1. Note that a higher capacity retention rate indicates a higher durability of the lithium-ion secondary battery.

[0084] [Table 1]

[0085] As shown in Table 1, by setting the capacity ratio of the negative electrode to the positive electrode to 1.2 or more, providing a coating layer containing lithium carbonate on the inner surface of the battery case, and applying a voltage between the battery case and the negative electrode at which the lithium carbonate decomposes to supply lithium ions to the negative electrode at the outermost periphery of the wound electrode assembly, it is clear that both Li deposition resistance and high-temperature storage characteristics are excellent. Therefore, it is clear that the manufacturing method for a nonaqueous electrolyte secondary battery disclosed herein can provide a nonaqueous electrolyte secondary battery including a wound electrode assembly, which has a nonaqueous electrolyte that is excellent in Li deposition resistance and high-temperature storage characteristics.

[0086] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0087] That is, the nonaqueous electrolyte secondary battery disclosed herein has the following items [1] to [9]. [1] A step of preparing an assembly in which a wound electrode body in which a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween is wound, and a nonaqueous electrolyte are housed in a metal battery case, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more, the outermost periphery of the wound electrode body is the negative electrode, and the inner surface of the battery case has a coating layer containing a Li compound; applying a voltage between the battery case and the negative electrode so as to decompose the Li compound, thereby supplying Li ions from the Li compound to the negative electrode at the outermost periphery of the wound electrode body; and applying a voltage between the positive electrode and the negative electrode to perform an initial charge; The method for producing a non-aqueous electrolyte secondary battery includes the steps of: [2] The manufacturing method according to item [1], wherein the number of turns of the wound electrode body is 20 or more. [3] The manufacturing method according to item [1] or [2], wherein the coating layer is formed on the inner surface of the battery case, facing the flat surface of the wound electrode body. [4] The method according to any one of items [1] to [3], wherein the coating layer further contains a conductive material. [5] The method according to any one of items [1] to [4], wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.3 or more. [6] The method according to any one of items [1] to [5], wherein the Li compound is at least one selected from the group consisting of lithium carbonate, lithium chloride, lithium nitrate, lithium dihydrogen carbonate, and lithium phosphate. [7] The method according to item [6], wherein the Li compound is lithium carbonate. [8] The method according to any one of items [1] to [7], further comprising a step of performing an aging treatment at a temperature of 60°C or higher in a charged state where the potential of the negative electrode is 0.5V or higher after the initial charge. [9] A wound electrode body in which a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween is wound. a non-aqueous electrolyte, and A metal battery case that houses these Equipped with the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more; The inner surface of the battery case has a high Li element accumulation region. Nonaqueous electrolyte secondary battery. [Explanation of symbols]

[0088] 20 Wound electrode body 30 Battery case 36 Safety valve 42 Positive terminal 42a Positive current collector plate 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheet (positive electrode) 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheet (negative electrode) 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 First separator sheet (separator) 72 Second separator sheet (separator) 80 Non-aqueous electrolyte 90 coating layer 92 Lithium-rich region 100 assemblies 200 Lithium-ion secondary battery

Claims

1. a step of preparing an assembly in which a wound electrode body in which a laminate including a positive electrode, a negative electrode, and a separator interposed therebetween is wound, and a non-aqueous electrolyte are housed in a metal battery case, wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.2 or more, the outermost periphery of the wound electrode body is the negative electrode, and the inner surface of the battery case has a coating layer containing a Li compound; a step of applying a voltage between the battery case and the negative electrode so as to decompose the Li compound, thereby supplying Li ions from the Li compound to the negative electrode at the outermost periphery of the wound electrode body; and A step of applying a voltage between the positive electrode and the negative electrode to perform an initial charge; The method for producing a non-aqueous electrolyte secondary battery includes the steps of:

2. The manufacturing method according to claim 1 , wherein the number of turns of the wound electrode body is 20 or more.

3. The manufacturing method according to claim 1 , wherein the coating layer is formed on an inner surface of the battery case, the surface facing the flat surface of the wound electrode body.

4. The manufacturing method according to claim 1 , wherein the coating layer further contains a conductive material.

5. The method according to claim 1 , wherein the ratio of the capacity of the negative electrode to the capacity of the positive electrode is 1.3 or more.

6. 2. The method according to claim 1, wherein the Li compound is at least one selected from the group consisting of lithium carbonate, lithium chloride, lithium nitrate, lithium dihydrogen carbonate, and lithium phosphate.

7. The method according to claim 6, wherein the Li compound is lithium carbonate.

8. The manufacturing method described in claim 1, further comprising a step of performing an aging treatment at a temperature of 60°C or higher in a charged state where the potential of the negative electrode is 0.5 V or higher after the initial charging.

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