Lithium-ion battery

Abstract

This lithium secondary battery comprises: a positive electrode layer formed from a lithium composite oxide sintered body; a negative electrode layer; a separator interposed between the positive electrode layer and the negative electrode layer; an electrolyte solution containing a solvent and an electrolyte with which the positive electrode layer, the negative electrode layer, and the separator are impregnated; and an exterior body that comprises a closed space in which the positive electrode layer, the negative electrode layer, the separator, and the electrolyte solution are accommodated. The ratio of the thickness of the exterior body in the thickness direction of the positive electrode layer at a temperature of 80°C and a pressure of 100 Pa to the thickness of the exterior body at a temperature of 25°C and a pressure of 101,325 Pa is 1.05-2.63.

Description

[Technical Field]

[0001] This disclosure relates to lithium secondary batteries. This application claims priority under Japanese application No. 2023-056460 filed on March 30, 2023, and incorporates all the provisions contained herein. [Background technology]

[0002] Technology relating to pouch-type lithium secondary batteries is disclosed, for example, in Japanese Patent Publication No. 2017-79192 (Patent Document 1). Conventionally, as a positive electrode active material in lithium secondary batteries (also called lithium-ion secondary batteries), powder-dispersed positive electrode active materials are known, which are formed by molding a mixture of lithium composite oxide (i.e., lithium transition metal oxide) powder, a binder, and a conductive agent. On the other hand, Japanese Patent No. 5587052 (Patent Document 2) proposes a technology to increase the capacity of the positive electrode by using a lithium composite oxide sintered plate as the positive electrode active material bonded to the positive electrode current collector. Furthermore, Japanese Patent No. 6943970 (Patent Document 3) proposes a negative electrode containing carbon and styrene-butadiene rubber (SBR) in addition to a lithium composite oxide sintered plate, and lithium borofluoride in a non-aqueous solvent consisting of γ-butyrolactone (GBL), or γ-butyrolactone (GBL) and ethylene carbonate (EC). LiBF A heat-resistant lithium secondary battery that does not expand even at high temperatures of 150°C has been proposed by using an electrolyte containing 4). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-79192 [Patent Document 2] Patent No. 5587052 [Patent Document 3] Patent No. 6943970 [Overview of the project] [Problems that the invention aims to solve]

[0004] Recently, lithium-ion batteries are sometimes used in high-temperature and low-pressure environments. Even in such cases, it is necessary to maintain good characteristics, such as not experiencing a significant decrease in discharge capacity compared to normal temperature and pressure environments.

[0005] Therefore, one of the objectives is to provide a lithium secondary battery that can maintain good characteristics even in high-temperature and low-pressure environments. [Means for solving the problem]

[0006] The lithium secondary battery according to this disclosure is a pouch-type lithium secondary battery. The lithium secondary battery comprises a positive electrode layer made of a lithium composite oxide sintered body, a negative electrode layer, a separator interposed between the positive electrode layer and the negative electrode layer, an electrolyte containing an electrolyte and a solvent impregnated into the positive electrode layer, the negative electrode layer and the separator, and an outer casing having a sealed space in which the positive electrode layer, the negative electrode layer, the separator and the electrolyte are housed. In the thickness direction of the positive electrode layer, the ratio of the thickness of the outer casing at 80°C and 100 Pa to the thickness of the outer casing at 25°C and 101325 Pa is 1.05 or more and 2.63 or less. [Effects of the Invention]

[0007] Such lithium-ion batteries can maintain good performance even in high-temperature and low-pressure environments. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic plan view showing the structure of a lithium secondary battery according to this disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view showing the structure of a lithium secondary battery according to this disclosure. [Figure 3] Figure 3 is a schematic diagram showing a cross-section of a lithium secondary battery according to this disclosure. [Figure 4]FIG. 4 is a schematic diagram showing the assembly process of a lithium secondary battery. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a part of a measuring device used when measuring the thickness of the exterior body. [Embodiment for Carrying Out the Invention]

[0009] [Summary of Embodiment] First, embodiments of the present disclosure will be listed and described. The lithium secondary battery according to the present disclosure is a pouch-type lithium secondary battery. The lithium secondary battery includes a positive electrode layer composed of a lithium composite oxide sintered body, a negative electrode layer, a separator interposed between the positive electrode layer and the negative electrode layer, an electrolytic solution containing an electrolyte and a solvent impregnated in the positive electrode layer, the negative electrode layer, and the separator, and an exterior body having a sealed space and accommodating the positive electrode layer, the negative electrode layer, the separator, and the electrolytic solution therein. In the thickness direction of the positive electrode layer, the ratio of the thickness of the exterior body at a temperature of 80°C and a pressure of 100 Pa to the thickness of the exterior body at a temperature of 25°C and a pressure of 101325 Pa is 1.05 or more and 2.63 or less.

[0010] According to the lithium secondary battery having such a configuration, even in a high-temperature environment and a reduced-pressure environment, the change in thickness is relatively small. Then, it is possible to suppress the expansion of the distance between the positive electrode layer and the negative electrode layer laminated in the thickness direction. Therefore, good characteristics can be maintained even in a high-temperature environment and a reduced-pressure environment.

[0011] In the lithium secondary battery of the above aspect, the positive electrode layer may be a plate-shaped electrode. The negative electrode layer may be a plate-shaped electrode. By doing so, in both the positive electrode layer and the negative electrode layer, it is possible to relatively reduce the dimensional change in the thickness direction due to expansion or the like even in a high-temperature environment and a reduced-pressure environment. Therefore, better characteristics can be maintained even in a high-temperature environment and a reduced-pressure environment.

[0012] In a lithium secondary battery according to any one of the above embodiments, the solvent may be a mixed liquid solvent containing a first substance which is an ester having a carbonate, and a second substance which is an ester different from the first substance and has a carbonate or lactone. The volume ratio of the first substance to the second substance may be in the range of 1:10 to 10:1. An electrolyte using such a solvent has a relatively low vapor pressure and is less likely to generate reaction products due to side reactions. This makes it possible to further suppress the widening of the distance between the positive electrode layer and the negative electrode layer, resulting in a configuration that is less likely to bulge the outer casing. Therefore, better characteristics can be maintained even in high temperature and reduced pressure environments. If the volume ratio is outside this range, it is difficult to obtain the effect of lowering the vapor pressure enough to suppress the bulging of the outer casing in high temperature and reduced pressure environments. Alternatively, the viscosity of the electrolyte may increase, or SEI (Solid Electrolyte) may be present on the electrode surface. Interphase Because a protective film is not easily formed, there is a risk that the battery characteristics may deteriorate.

[0013] In a lithium secondary battery according to any one of the above embodiments, the electrolyte concentration may be 2.0 mol / L or more and 8.0 mol / L or less. By doing so, a relatively high electrolyte concentration results in a relatively low vapor pressure and less generation of reaction products due to side reactions. This makes it possible to further suppress an increase in the distance between the positive electrode layer and the negative electrode layer, resulting in a configuration that is less prone to swelling of the outer casing. Therefore, good characteristics can be maintained even in high-temperature and reduced-pressure environments.

[0014] In a lithium secondary battery according to any one of the above embodiments, an adhesive may be further provided, which is composed of a mixed resin of an acid-modified polyolefin resin and an epoxy resin, for bonding at least one of the positive electrode layer or the negative electrode layer to the outer casing in a sealed space. Exterior By bonding them together, when the lithium secondary battery of this disclosure is used as a power source in a sheet-like device or a flexible device, ExteriorIt can suppress the formation of wrinkles.

[0015] In any one of the above embodiments of a lithium secondary battery, the battery may further include an adhesive composed of a mixed resin of an acid-modified polyolefin resin and an epoxy resin, which bonds at least one of the positive electrode layer or the negative electrode layer to the outer casing in a sealed space. The positive electrode layer may be a plate-shaped electrode. The negative electrode layer may be a plate-shaped electrode or a coated electrode. The solvent may be a mixed solvent containing sulfolane and γ-butyrolactone. The volume ratio of sulfolane to γ-butyrolactone may be 7:3 or more and 4:1 or less. The electrolyte concentration may be 1.5 mol / L or more and 5.0 mol / L or less. A lithium secondary battery with such a configuration can reliably maintain better characteristics even in high-temperature and reduced-pressure environments.

[0016] [Specific examples of embodiments] Next, specific embodiments of the lithium secondary battery of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0017] (Embodiment) This document describes a lithium secondary battery according to this disclosure. Figure 1 is a schematic plan view showing the structure of a lithium secondary battery according to this disclosure (hereinafter sometimes simply referred to as "battery"). Figure 2 is a schematic cross-sectional view showing the structure of a lithium secondary battery according to this disclosure. Figure 3 is a schematic diagram showing a cross-section of a lithium secondary battery according to this disclosure. Note that some components in Figures 1, 2, and 3 are enlarged, emphasized, or omitted for the sake of ease of understanding. Also, the components shown in Figures 1, 2, and 3 do not necessarily reflect the actual dimensional relationships.

[0018] Referring to Figures 1, 2, and 3, the lithium secondary battery 11 according to this disclosure is of pouch type. The battery 11 according to this disclosure is effective when used in high-temperature and low-pressure environments, for example, as a power supply for a temperature sensor used to detect the temperature of a chamber in a semiconductor manufacturing apparatus. A high-temperature environment means, for example, a temperature of 80°C or higher, and a low-pressure environment means, for example, a pressure of 100 Pa (Pascals) or less.

[0019] The battery 11 includes a pair of outer films 13 and 14 constituting the outer casing 12, a positive electrode tab terminal 15, and a negative electrode tab terminal 16. The outer films 13 and 14 have the same rectangular shape in a plan view (i.e., as shown in Figure 1). The four edges of the outer films 13 and 14 are joined to each other, except for the portions facing each other with the positive electrode tab terminal 15 and the negative electrode tab terminal 16 in between. The specific manner of joining is not particularly limited, but for example, they can be joined by adhesive, fusion, etc.

[0020] The battery 11 is small and thin. The dimensions of the battery 11 (external dimensions of the casing 12) are not particularly limited, but for example, the length in the vertical direction may be 10 mm to 46 mm (10 mm or more and 46 mm or less), and the length in the horizontal direction may be 10 mm to 46 mm. The thickness of the battery 11 (thickness of the external dimensions of the casing 12) may be, for example, 0.3 mm to 0.45 mm, preferably 0.4 mm (400 μm (micrometers)) to 0.45 mm. The battery 11 as a whole is a sheet-like or flexible plate-like article.

[0021] In the battery 11, a sealed space 17 is formed between the opposing inner surfaces of the outer films 13 and 14. The battery body is housed in the sealed space 17. The battery 11 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte 24. In the battery 11, the positive electrode 21, negative electrode 22, separator 23, and electrolyte 24 are sometimes collectively referred to as the battery body. The positive electrode 21, negative electrode 22, and separator 23 are stacked in a predetermined overlapping direction. In the example shown in Figure 2, the positive electrode 21, separator 23, and negative electrode 22 are stacked in the vertical direction in Figure 2. That is, the positive electrode 21 and negative electrode 22 face each other via the separator 23. In the following description, the upper and lower sides in Figure 2 will be referred to as the "upper side" and "lower side" of the battery 11, respectively. The vertical direction in Figure 2 will be referred to as the "vertical direction" or "stacking direction."

[0022] The outer casing 12 is a bag formed by joining the periphery of the outer films 13 and 14. The outer films 13 and 14 are each formed from laminate sheets consisting of metal foils 25 and 26 made of a metal such as aluminum (Al), and insulating resin layers 27 and 28. In the outer films 13 and 14, the metal foils 25 and 26 are positioned on the outside of the bag, and the resin layers 27 and 28 are positioned on the inside. The thickness of the outer casing 12 is shown in Figure 3 as thickness T.

[0023] The outer casing 12 covers the entire battery body. The outer casing 12 is a bag-like structure that houses the positive electrode 21, negative electrode 22, separator 23, and electrolyte 24. The electrolyte 24 is continuously present around the positive electrode 21, separator 23, and negative electrode 22. In other words, the electrolyte 24 is interposed between the positive electrode 21 and the negative electrode 22. The electrolyte 24 impregnates the positive electrode 21, separator 23, and negative electrode 22. The positive electrode tab terminal 15 and the negative electrode tab terminal 16 extend to the outside of the outer casing 12. Inside the outer casing 12, the positive electrode tab terminal 15 is connected to the positive electrode current collector 31. This configuration electrically connects the positive electrode tab terminal 15 to the positive electrode 21. The negative electrode tab terminal 16 is connected to the negative electrode current collector 36. This configuration electrically connects the negative electrode tab terminal 16 to the negative electrode 22.

[0024] The positive electrode tab terminal 15 and the negative electrode tab terminal 16 each have a strip-like shape. The positive electrode tab terminal 15 includes a main body made of a conductive material and a protective layer made of resin that covers the surface of the main body. The negative electrode tab terminal 16 also includes a main body made of a conductive material and a protective layer made of resin that covers the surface of the main body, similar to the positive electrode tab terminal 15. As the conductive material constituting the main body, metals such as aluminum (Al) and nickel (Ni) can be used.

[0025] The separator 23 is positioned on the upper surface of the positive electrode 21 in the stacking direction. The negative electrode 22 is positioned on the upper surface of the separator 23. That is, the negative electrode 22 is positioned in contact with the upper side of the separator 23. The positive electrode 21 is positioned in contact with the lower side of the separator 23. The positive electrode 21, negative electrode 22, and separator 23 each have, for example, a rectangular shape in plan view. The positive electrode 21 and negative electrode 22 have approximately the same shape and dimensions as each other in plan view. The separator 23 may have larger dimensions than each of the positive electrode 21 and negative electrode 22 in order to prevent internal short circuits. The positive electrode 21 and negative electrode 22 face each other almost entirely, except for any misalignment that occurs during the manufacturing process or use.

[0026] The dimensions and shape of the positive electrode 21 in plan view (i.e., the dimensions and shape of the main surface of the positive electrode 21) may be, for example, a rectangle with a side length of 9.75 mm to 28.5 mm. Preferably, it may be a rectangle with a side length of 18.15 mm to 25.5 mm. The area of ​​the positive electrode 21 in plan view (i.e., the area of ​​the main surface of the positive electrode 21) may be, for example, 95 mm². 2 ~812mm 2 It may be, preferably 441 mm 2 ~812mm 2 That's fine.

[0027] The dimensions, shape, and area of ​​the negative electrode 22 may be the same as those of the positive electrode 21. Alternatively, the negative electrode 22 may be slightly larger (approximately 4% to 7%) than the positive electrode 21. That is, the dimensions and shape of the negative electrode 22 in plan view (i.e., the dimensions and shape of the main surface of the negative electrode 22) may be, for example, a rectangle with a side length of 10.45 mm to 29.2 mm. Preferably, it may be a rectangle with a side length of 18.8 mm to 26.15 mm. The area of ​​the negative electrode 22 in plan view (i.e., the area of ​​the main surface of the negative electrode 22) may be, for example, 109 mm². 2 ~852mm 2 It may be, preferably 470 mm 2 ~852mm 2 That's fine.

[0028] (Positive electrode structure 1) The positive electrode 21 comprises a positive electrode current collector 31, a positive electrode active material plate 32, and a conductive bonding layer 33. The positive electrode current collector 31 is a conductive sheet-like member. The positive electrode 21 is a so-called plate-shaped electrode. The lower surface of the positive electrode current collector 31 is bonded to the resin layer 27 of the outer casing 12 via the positive electrode bonding layer 34. The positive electrode bonding layer 34 is formed from, for example, a mixed resin of an acid-modified polyolefin resin and an epoxy resin. The positive electrode bonding layer 34 may be formed from other materials. The thickness of the positive electrode bonding layer 34 is, for example, 0.5 μm to 10 μm.

[0029] The positive electrode current collector 31 includes, for example, a metal foil formed of a metal such as aluminum, and a conductive carbon layer laminated on the upper surface of the metal foil. In other words, the main surface of the positive electrode current collector 31 facing the positive electrode active material plate 32 is covered with the conductive carbon layer. The metal foil may be formed of various metals other than aluminum (for example, copper, nickel, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or an alloy containing these). Further, the positive electrode current collector 31 may not include the conductive carbon layer.

[0030] The positive electrode active material plate 32 is a thin plate-like ceramic sintered body containing a lithium composite oxide. Preferably, the positive electrode active material plate 32 is substantially composed only of the lithium composite oxide. A separator 23 is laminated on the upper surface of the positive electrode active material plate 32. Note that gold (Au) or the like may be sputtered on the positive electrode active material plate 32 as a current collecting auxiliary agent.

[0031] The positive electrode active material plate 32 has a structure in which a plurality (i.e., a large number) of primary particles are bonded. The primary particles are composed of a lithium composite oxide having a layered rock salt structure. The lithium composite oxide is a composite oxide of lithium and a transition metal element M (general formula: Li p MO₂ (where 0.05 ≤ p ≤ 1.10)), in which a part is substituted with a substitution metal element which is another metal element. The transition metal element M includes, for example, one or more selected from cobalt (Co), nickel (Ni), and manganese (Mn). The transition metal element M is the main one among the metals other than lithium contained in the lithium composite oxide, and is hereinafter referred to as the "main transition metal element".

[0032] Examples of the composite oxide of lithium and the transition metal element M include, for example, lithium cobalt oxide (Li p CoO₂ (where 1 ≤ p ≤ 1.1)), lithium nickel oxide (LiNiO₂), lithium manganate (Li₂MnO₃), lithium nickel manganate (Li p (Ni 0.5 ,Mn 0.5 )O₂), general formula: Li p(Co x , Ni y , Mn z )O2 (where 0.97 ≤ p ≤ 1.07, x + y + z = 1), a solid solution represented by Li p (Co x , Ni y , Al z )O2 (where 0.97 ≤ p ≤ 1.07, x + y + z = 1, 0 < x ≤ 0.25, 0.6 ≤ y ≤ 0.9, and 0 < z ≤ 0.1), or a solid solution of Li2MnO3 and LiMO2 (where M is a transition metal such as Co, Ni, etc.). Particularly preferably, the lithium composite oxide is lithium cobalt oxide Li p CoO2 (where 1 ≤ p ≤ 1.1), for example, LiCoO2.

[0033] The transition metal element M may be one or more of elements such as magnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), strontium (Sr), yttrium (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), tin (Sn), antimony (Sb), tellurium (Te), barium (Ba), bismuth (Bi), etc. Preferably, it is titanium (Ti) or niobium (Nb).

[0034] The layered rock salt structure is a crystal structure in which lithium layers and transition metal layers other than lithium are alternately stacked with oxygen layers interposed therebetween. That is, the layered rock salt structure is a crystal structure in which a metal ion layer other than lithium and a single lithium layer are alternately stacked via oxide ions. Typically, it is an α-NaFeO2 type structure, that is, a structure in which transition metals and lithium are regularly arranged in the

[0111] axis direction of the cubic rock salt type structure.

[0035] The conductive bonding layer 33 comprises conductive powder and a binder. The conductive powder is, for example, powder such as acetylene black, flaky natural graphite, carbon nanotubes, carbon nanofibers, carbon nanotube derivatives, or carbon nanofiber derivatives. The binder comprises, for example, a polyimidoamide resin. The polyimidoamide resin contained in the binder may be one type or two or more types. The binder may also contain resins other than polyimidoamide resin. The conductive bonding layer 33 can be formed by applying the above-mentioned conductive powder and binder, as well as a liquid or paste-like adhesive containing a solvent, to the positive electrode current collector 31 or the positive electrode active material plate 32, and then allowing the solvent to evaporate and solidify between the positive electrode current collector 31 and the positive electrode active material plate 32.

[0036] The thickness of the positive electrode current collector 31 is, for example, 9 μm to 50 μm, preferably 9 μm to 20 μm, and more preferably 9 μm to 15 μm. The thickness of the positive electrode active material plate 32 is, for example, 15 μm to 200 μm, preferably 30 μm to 150 μm, and more preferably 50 μm to 100 μm. The thickness of the conductive bonding layer 33 is, for example, 3 μm to 28 μm, and preferably 5 μm to 25 μm.

[0037] (Positive electrode structure 2) In a lithium secondary battery according to this disclosure, the positive electrode 21 is not limited to a plate-shaped electrode. That is, the positive electrode 21 may be a coated electrode. In this case, the positive electrode 21 comprises the positive electrode current collector 31 described above and a positive electrode active material layer coated on the positive electrode current collector 31. The positive electrode active material layer includes the lithium composite oxide, which is the positive electrode active material, and a binder mainly composed of resin. As described above, the lithium composite oxide is a composite oxide of lithium and a main transition metal element (e.g., Co, Ni, Mn), in which a portion is substituted with a substitution metal element (e.g., Nb, Ti). The binder is, for example, styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), or a mixture thereof.

[0038] The following describes an example of a manufacturing method for the positive electrode 21 when the positive electrode 21 is a coated electrode. In the following description, we will describe the case where the main transition metal element and the substituted metal element are Co and Nb, respectively. First, as in the case where the positive electrode 21 comprises a positive electrode active material plate 32, a mixed powder of lithium oxide and the oxide of the main transition metal element (i.e., Co) is prepared. This mixed powder is held at 900°C for 10 hours.

[0039] Next, in the same manner as when the positive electrode 21 is equipped with a positive electrode active material plate 32, Nb2O5 powder (manufactured by Mitsui Mining & Smelting Co., Ltd.) is added to the mixed powder, and the mixture is crushed and pulverized in a pot mill so that the volume-based D50 particle size distribution is 0.8 μm, thereby obtaining the raw material powder. The addition rate of Nb2O5 powder to the raw material powder is 0.03 mass%, and the Nb content in the raw material powder is 0.021 mass%. The volume-based D50 particle size of the raw material powder may be appropriately changed, for example, in the range of 0.2 μm to 10 μm. The Nb content in the raw material powder may also be appropriately changed, for example, in the range of 0.1 mass% to 2.0 mass%.

[0040] Next, 91% by mass of the above raw material powder, 5% by mass of acetylene black, 4% by mass of polyvinylidene fluoride (PVDF), and an N-methylpyrrolidone (NMP) solution are mixed to prepare a slurry. This slurry is then applied to a positive electrode current collector 31 (for example, a 10 μm thick aluminum foil) and dried. After that, the dried coating layer is pressed to produce the coated electrode, which is the positive electrode 21.

[0041] The resulting positive electrode 21 is combined with other components in the same manner as in Example 1 of battery manufacturing to obtain a lithium secondary battery 11.

[0042] (Structure of the negative electrode 1) The negative electrode 22 comprises a negative electrode current collector 36 and a negative electrode active material layer 37. The negative electrode current collector 36 is a conductive sheet-like member. The upper surface of the negative electrode current collector 36 is bonded to the resin layer 28 of the outer film 14 via a negative electrode bonding layer 38. The negative electrode active material layer 37 is coated onto the lower surface of the negative electrode current collector 36. In other words, the negative electrode 22 is a so-called coated electrode. The negative electrode active material layer 37 faces the separator 23 in the vertical direction.

[0043] The negative electrode bonding layer 38 is formed, for example, from a mixed resin of an acid-modified polyolefin resin and an epoxy resin. The negative electrode bonding layer 38 may also be formed from various other materials.

[0044] The negative electrode current collector 36 is a metal foil formed of a metal such as copper. The metal foil may be formed of various metals other than copper (for example, copper, stainless steel, nickel, aluminum, silver, gold, chromium, iron, tin, lead, tungsten, molybdenum, titanium, zinc, or alloys containing these).

[0045] The negative electrode active material layer 37 includes a binder mainly composed of resin and a carbonaceous material which is the negative electrode active material. Examples of carbonaceous materials include natural graphite, artificial graphite, pyrolysis carbon, coke, resin calcined body, mesophase spheres, or mesophase pitch. In the negative electrode 22, a lithium storage material may be used as the negative electrode active material instead of the carbonaceous material. Examples of lithium storage materials include silicon, aluminum, tin, iron, iridium, or alloys, oxides, or fluorides containing these. Examples of binders include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), or mixtures thereof.

[0046] The thickness of the negative electrode current collector 36 is, for example, 5 μm to 25 μm, preferably 8 μm to 20 μm, and more preferably 8 μm to 15 μm. The thickness of the negative electrode active material layer 37 is, for example, 20 μm to 300 μm, preferably 30 μm to 250 μm, and more preferably 30 μm to 150 μm. By increasing the thickness of the negative electrode active material layer 37, the active material capacity per unit area can be increased, thereby increasing the energy density of the battery 11. By making the negative electrode active material layer 37 thinner, the deterioration of battery characteristics (especially the increase in resistance) associated with repeated charging and discharging can be suppressed.

[0047] (Negative electrode structure 2) In a lithium secondary battery according to this disclosure, the negative electrode is not limited to a coated electrode. The configuration corresponding to the negative electrode active material layer 37 is lithium titanate Li4Ti5O 12 The negative electrode may be constructed using a sintered plate of LTO (hereinafter sometimes referred to as LTO). The LTO sintered plate has a structure in which multiple (i.e., many) primary particles are bonded together. These primary particles are composed of LTO. LTO is typically known to have a spinel-type structure, but other structures can also be adopted during charging and discharging. For example, LTO may have Li4Ti5O 12 (Spinel structure) and Li7Ti5O 12 The reaction proceeds in the coexistence of two phases (rock salt structure). Therefore, LTO is not limited to a spinel structure.

[0048] The primary particle size, which is the average particle size of the multiple primary particles constituting the LTO sintered plate, may be 1.2 μm or less. Preferably, it is 0.02 to 1.2 μm, and more preferably 0.05 to 0.7 μm. The thickness of the LTO sintered plate may be 10 to 290 μm. Preferably, it is 10 to 200 μm, more preferably 40 to 200 μm, even more preferably 40 to 175 μm, and particularly preferably 50 to 160 μm. The thicker the LTO sintered plate, the easier it is to realize a battery with high capacity and high energy density.

[0049] The LTO sintered plate contains pores. The presence of pores, particularly open pores, in the LTO sintered plate facilitates the penetration of electrolyte into the plate when it is incorporated into a battery as a negative electrode. As a result, lithium-ion conductivity can be improved. The porosity of the LTO sintered plate is, for example, 21-45%, more preferably 22-40%, and even more preferably 25-35%. Within this range, it is easy to achieve both lithium-ion conductivity and electronic conductivity. Furthermore, the open pore ratio, which is the ratio of open pores to total pores in the LTO sintered plate, may be 60% or more. More preferably 65% ​​or more, even more preferably 70% or more, and particularly preferably 80% or more. The open pore ratio may also be 100%. A higher number of open pores makes it easier to sufficiently penetrate the electrolyte into the sintered plate, thus improving lithium-ion conductivity.

[0050] (Separator) The separator 23 is a sheet-like or thin plate-like insulating member. The separator 23 is, for example, a single-layer separator formed of resin. As the resin, for example, polyimide, polyester (e.g., polyethylene terephthalate (PET)), cellulose, etc. can be used. The thickness of the separator 23 is, for example, 15 μm or more, preferably 18 μm or more, and more preferably 20 μm or more. Alternatively, the thickness of the separator 23 is, for example, 31 μm or less, preferably 28 μm or less, and more preferably 26 μm or less. By making the separator thicker, even if lithium dendrites (lithium dendritic crystals) precipitate, short circuits between the positive and negative electrodes due to lithium dendrites can be prevented. Also, by making the separator thinner, the permeability of the electrolyte and lithium ions can be facilitated, and the internal resistance of the battery 11 can be reduced.

[0051] The structure of the separator 23 can be changed to a known structure other than those described above. For example, it may be a configuration in which two or three or more layers of ceramic and resin are laminated. Alternatively, it may be a microporous film formed solely of ceramic. The ceramic is, for example, at least one selected from MgO, Al2O3, ZrO, SiC, Si3N4, AlN, and cogenelite, and preferably at least one selected from MgO, Al2O3, and ZrO2.

[0052] (electrolyte) The electrolyte 24 is a liquid obtained by adding an electrolyte and an additive to a solvent. For example, lithium hexafluoride phosphate (LiPF6) is used as the electrolyte. The electrolyte may be changed, for example, lithium borofluoride (LiBF4). The concentration of the electrolyte 24 may be, for example, 1.0 to 8.0 mol / L. Preferably, it is 1.5 mol / L or higher, more preferably 2.0 mol / L or higher, even more preferably 4.0 mol / L or higher, and even more preferably 5.0 mol / L or higher. A preferred numerical range for the concentration of the electrolyte 24 is, for example, 1.5 mol / L to 8.0 mol / L, more preferably 2.0 mol / L to 8.0 mol / L, and even more preferably 4.0 mol / L to 5.0 mol / L.

[0053] The solvent of the electrolyte 24 is a non-aqueous solvent such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), or methyl butyrate (MB) propyl acetate (PA). The solvent may also include, for example, EC and EMC.

[0054] (Thickness of lithium secondary batteries under high-temperature and reduced-pressure environments) In a lithium secondary battery according to this disclosure, the ratio of the thickness of the outer casing 12 in a high-temperature, reduced-pressure environment to the thickness of the outer casing 12 in a normal temperature, normal pressure environment is 1.05 or more and 2.63 or less. Specifically, the ratio of the thickness of the outer casing 12 at a temperature of 80°C and a pressure of 100 Pa to the thickness of the outer casing 12 at a temperature of 25°C and a pressure of 101325 Pa is 1.05 or more and 2.63 or less. More preferably, the ratio of the thickness of the outer casing 12 at a temperature of 80°C and a pressure of 100 Pa to the thickness of the outer casing 12 at a temperature of 25°C and a pressure of 101325 Pa is 1.05 or more and 1.50 or less. [Examples]

[0055] The lithium secondary batteries of this disclosure will be described in more detail by examples and comparative examples.

[0056] (Example 1) Lithium secondary batteries were fabricated according to the methods described in (1) to (3) below. The obtained lithium secondary batteries were evaluated according to the method described in (4).

[0057] In the following examples and comparative examples, the viscosity of the slurry was measured using a Brookfield LVT viscometer during the preparation of the green sheets. Furthermore, the doctor blade method was used when forming the slurry onto the PET film.

[0058] (1) Preparation of the positive electrode (1a) Preparation of LiCoO2 (LCO) green sheet Co3O4 powder (manufactured by Seido Chemical Industry Co., Ltd.) and Li2CO3 powder (manufactured by Honjo Chemical Co., Ltd.), weighed to have a Li / Co molar ratio of 1.01, were mixed and held at 780°C for 5 hours. The resulting powder was then processed using a pot mill to obtain volume standard D 50The powder was ground to a size of 0.4 μm. 100 parts by weight of the obtained LCO powder was mixed with 100 parts by weight of a dispersion medium (toluene:isopropanol = 1:1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), 4 parts by weight of a plasticizer (DOP: Di(2-ethylhexyl)phthalate, manufactured by Kurogane Kasei Co., Ltd.), and 2 parts by weight of a dispersant (product name Rheodol SP-O30, manufactured by Kao Corporation). The resulting mixture was stirred under reduced pressure to remove bubbles and adjust the viscosity to 4000 cP to prepare a LiCoO2 slurry. A LiCoO2 green sheet was formed by molding the prepared slurry into a sheet on a PET film. The thickness of the LiCoO2 green sheet after drying was 98 μm.

[0059] (1b) Fabrication of LiCoO2 sintered plate A LiCoO2 green sheet, peeled from a PET film, was cut into 50mm squares using a cutter and placed in the center of a magnesia setter (90mm square, 1mm high) to serve as the lower setter. A porous magnesia setter was then placed on top of the LiCoO2 sheet to serve as the upper setter. With the LiCoO2 sheet sandwiched between the setters, it was placed inside a 120mm square alumina sheath (manufactured by Nikkatoh Co., Ltd.). At this time, the alumina sheath was not sealed, but a 0.5mm gap was left when the lid was closed. The resulting laminate was heated to 600°C at a heating rate of 200°C / h, degreased for 3 hours, then heated to 920°C at 200°C / h and held for 4 hours for firing. After firing, the fired body was allowed to cool to room temperature and then removed from the alumina sheath. By these procedures, a 90μm thick LiCoO2 sintered plate was obtained as the positive electrode. The obtained positive electrode was cut to 9.75mm × using a laser processing machine. 18.15mm rectangular shape It was cut to obtain a chip-shaped positive electrode.

[0060] (2) Fabrication of the negative electrode (2a)Li4Ti5O 12 (LTO) Green Sheet Production First, LTO powder (by volume D 50100 parts by weight of 0.06 μm particle size (manufactured by Sigma-Aldrich Japan LLC), 100 parts by weight of dispersion medium (toluene:isopropanol = 1:1), 20 parts by weight of binder (polyvinyl butyral: product code BM-2, manufactured by Sekisui Chemical Co., Ltd.), 4 parts by weight of plasticizer (DOP: Di(2-ethylhexyl)phthalate, manufactured by Kurogane Kasei Co., Ltd.), and 2 parts by weight of dispersant (product name Rheodol SP-O30, manufactured by Kao Corporation) were mixed. The resulting negative electrode raw material mixture was stirred under reduced pressure to remove bubbles and adjust the viscosity to 4000 cP to prepare an LTO slurry. An LTO green sheet was formed by molding the prepared slurry into a sheet on a PET film. The thickness of the LTO green sheet after drying was adjusted to 110 μm after firing.

[0061] (2b) Firing of LTO green sheets The obtained green sheet was cut into 25mm squares with a utility knife and placed on an embossed zirconia setter. The green sheet on the setter was placed in an alumina sheath and held at 500°C for 5 hours, then the temperature was increased at a rate of 200°C / h and fired at 800°C for 5 hours. An Au film (100nm thick) was formed as a current collecting layer on the surface of the obtained LTO sintered plate that had been in contact with the setter by sputtering, and then it was laser-cut into a rectangular shape of 9.12mm × 17.52mm.

[0062] (3) Assembly of lithium secondary batteries A lithium secondary battery 11, which is a lithium secondary battery in the form schematically shown in Figure 1, was manufactured using the following procedure. An overview of the manufacturing process is schematically shown in Figure 4. Figure 4 is a schematic diagram showing the assembly process of a lithium secondary battery.

[0063] Two aluminum laminate films (manufactured by Showa Denko Packaging, 61 μm thick, 3-layer structure of polypropylene film / aluminum foil / nylon film) were prepared as outer films 13 and 14. As shown in Figure 4(1), one positive electrode active material plate 32 was laminated onto one outer film 13 via a positive electrode current collector 31 (aluminum foil with a thickness of 9 μm) to form a positive electrode assembly 41. In this case, the positive electrode current collector 31 is not fixed to the outer film 13 with adhesive. The positive electrode tab terminal 15 is fixed to the positive electrode current collector 31 by welding, extending from the positive electrode current collector 31. On the other hand, a negative electrode active material layer 37 was laminated onto the other outer film 14 via a negative electrode current collector 36 (aluminum foil with a thickness of 9 μm) to form a negative electrode assembly 42. In this case, the negative electrode current collector 36 is not fixed to the outer film 14 with adhesive. Furthermore, the negative electrode tab terminal 16 is fixed to the negative electrode current collector 36 by welding, so as to extend from the negative electrode current collector 36.

[0064] As separator 23, a cellulose membrane (manufactured by Nippon Kodo Paper Industry, thickness 20 μm, density 0.47 g / cm³) is used. 3 A positive electrode assembly 41, a separator 23, and a negative electrode assembly 42 were prepared. As shown in Figure 4(2), the positive electrode assembly 41, the separator 23, and the negative electrode assembly 42 were stacked in order so that the positive electrode active material plate 32 and the negative electrode active material layer 37 faced the separator 23. A laminate 43 was obtained in which both sides were covered with outer films 13 and 14, and the outer peripheral portions of the outer films 13 and 14 protruded from the outer edge of the battery elements. The thickness of the battery elements (positive electrode current collector 31, positive electrode active material plate 32, separator 23, negative electrode active material layer 37, and negative electrode current collector 36) constructed inside the laminate 43 was 0.33 mm. Its size and shape were a rectangle of 1.3 cm × 2.2 cm.

[0065] As shown in Figure 4(3), the three sides of the resulting laminate 43 were sealed. This sealing was performed by using a heat bar (applied to the outer periphery of the laminate 43) adjusted to a sealing width of 2.0 mm, and heating and pressing it at 200°C and 1.5 MPa for 15 seconds, thereby heat-fusing the outer films 13 and 14 (aluminum laminate films) together at the outer periphery.

[0066] As shown in Figure 4(4), after sealing the three sides, the laminate 43 was placed in a vacuum dryer 44 to remove moisture and dry the adhesive.

[0067] Next, as shown in Figure 4(5), a gap was formed between the outer films 13 and 14 at the remaining unsealed side of the laminate 43, which had three outer edges sealed, inside the glove box 45. An injection device 46 was then inserted into this gap to inject the electrolyte 24.

[0068] As shown in Figure 4(6), one unsealed side was temporarily sealed using a simple sealer under reduced pressure of 5 kPa absolute pressure. As the electrolyte, a solution was used in which LiBF4 was dissolved at a concentration of 1.5 mol / L in an organic solvent mixture of ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volume ratio of 1:3.

[0069] As shown in Figure 4(7), the temporarily sealed laminate 43 was subjected to initial charging and aging at 120°C for 1 hour.

[0070] As shown in Figure 4(8), after the aging process was complete, the outer edge of the last sealed side (the end portion that does not contain the battery element) was cut off to release the gas.

[0071] Next, as shown in Figure 4(9), the opening created by the removal of the temporary seal was sealed inside the glove box 45 under a reduced pressure atmosphere of 5 kPa absolute pressure. This sealing was also performed by heating and pressing the outer periphery of the laminate 43 at 200°C and 1.5 MPa for 15 seconds, thereby heat-sealing the outer films 13 and 14 together at the outer periphery. Lithium-ion battery The battery 11 was constructed in the form shown above. The battery 11 was removed from the glove box 45, and the excess portions around the outer perimeter of the outer films 13 and 14 were trimmed to shape the battery 11. In this way, a lithium secondary battery 11 was obtained in which the four outer edges of the battery element were sealed with a pair of outer films 13 and 14, and the electrolyte 24 was injected. The obtained battery 11 was a rectangle with dimensions of 27 mm × 17 mm and a thickness of 0.40 mm (400 μm).

[0072] (4) (Evaluation) (Measurement of the thickness of the outer casing) Here, we will briefly explain the method for measuring the thickness of the outer casing 12. Figure 5 is a schematic cross-sectional view showing a part of the measuring device 51 used when measuring the thickness of the outer casing 12. Referring to Figure 5, first prepare a Pelger-type vacuum oven (Shibata Scientific Co., Ltd., BV-001 model). Then, fix a dial gauge (Mitutoyo Corporation) 52 on the Pelger-type vacuum oven using double-sided tape and polyimide tape. Then, at room temperature and atmospheric pressure, place polyimide sheets 54, 55, 56, and 57 on a plate 53, and place the battery 11 (outer casing 12) on top of them. At this time, position the tip 58 of the dial gauge 52 in the center of the battery 11. Here, the number of polyimide sheets 54, 55, 56, and 57 is adjusted so that the tip 58 contacts the battery 11, and the value of the dial gauge 52 is 0 when in contact. Once the adjustment of the dial gauge 52 is complete, remove the battery 11 from the plate 53.

[0073] Next, set the temperature of the Pelger-type vacuum oven and wait until the set temperature (80°C) stabilizes. During this time, polyimide sheets 54, 55, 56, and 57 are also heated.

[0074] Next, place the battery 11 on top of the polyimide sheets 54, 55, 56, and 57 that are on the plate 53 and wait for 2 minutes. The number of polyimide sheets 54, 55, 56, and 57 should be adjusted to the specified number. At this time, ensure that the tip 58 of the dial gauge 52 is positioned in the center of the battery 11.

[0075] Next, place the Peljar over the container and begin vacuuming (reducing pressure). Read the value on the dial gauge 52 when the vacuum gauge reaches 100 Pa. The thickness of the outer casing 12 is the sum of (the value on the dial gauge 52) and (the thickness of the outer casing 12 at room temperature and normal pressure). (Thickness of outer casing 12 = (Value on the dial gauge 52) + (Thickness of outer casing 12 at room temperature and normal pressure)).

[0076] If the needle of the dial gauge 52 swings to its limit and measurement is not possible, remove one polyimide sheet 54, 55, 56, or 57 at a time from under the battery 11 and repeat the measurement until measurement is possible. Each time a polyimide sheet 54, 55, 56, or 57 is removed, the thickness of the outer casing 12 is calculated as (value of dial gauge 52) + (thickness of polyimide sheets 54, 55, 56, or 57 × number of sheets removed) + (thickness of outer casing 12 at room temperature and normal pressure).

[0077] Furthermore, if measurement is not possible even with 0 polyimide sheets 54, 55, 56, 57 (all polyimide sheets 54, 55, 56, 57 removed), the value shall be greater than or equal to the value calculated by (maximum value of dial gauge 52) + (thickness of polyimide sheets 54, 55, 56, 57 × number of sheets removed) + (thickness of outer casing 12 at room temperature and normal pressure).

[0078] (Method for evaluating charge and discharge) The charge and discharge evaluation was performed as follows: The lithium secondary battery was charged to the charging voltage value with a constant current of 0.2C, and then charged again with a constant voltage until the current reached 0.02C. The battery was then discharged to the discharge voltage value with a constant current of 0.5C, and the discharge capacity W0 at room temperature and pressure was measured. For measurements in high-temperature and reduced-pressure environments, the temperature of a Peljar-type vacuum oven was set and stabilized. The battery 11 was then placed on a plate, covered with the Peljar, and the pressure was reduced to 100 Pa. The charge and discharge evaluation was then performed in the same manner as at room temperature and pressure, and the discharge capacity W1 under reduced pressure was measured. The discharge capacity retention rate (%) was calculated by dividing the discharge capacity W1 by the discharge capacity W0 and expressing it as a percentage.

[0079] (Example 2) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent, a mixture of ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volume ratio of 7:3, was used as the electrolyte 24. The evaluation was carried out in the same manner as in Example 1.

[0080] (Example 3) A lithium secondary battery was obtained in the same manner as in Example 1, except that the positive electrode current collector 31 was fixed to the outer film 13 with adhesive and the negative electrode current collector 36 was fixed to the outer film 14 with adhesive. The adhesive used was composed of a mixed resin of acid-modified polyolefin resin and epoxy resin. Specifically, Hardlen® (manufactured by Toyobo Co., Ltd.) was used as the adhesive. Evaluation was carried out in the same manner as in Example 1.

[0081] (Example 4) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent mixture of ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volume ratio of 7:3 was used as the electrolyte 24, and LiBF4 was dissolved in it to a concentration of 4.0 mol / L. The evaluation was carried out in the same manner as in Example 1.

[0082] (Example 5) The evaluation was carried out in the same manner as in Example 4, using the same lithium secondary battery and except that the evaluation temperature was set to 120°C.

[0083] (Example 6) A lithium secondary battery was obtained in the same manner as in Example 1, except that the electrolyte 24 used was an organic solvent mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 3:1, to which LiPF6 was dissolved at a concentration of 1.0 mol / L. The evaluation was carried out in the same manner as in Example 1.

[0084] (Example 7) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent mixture of sulfolane (SL) and γ-butyrolactone (GBL) in a volume ratio of 7:3 was used as the electrolyte 24, and a plate-shaped electrode was used as the negative electrode 22. The evaluation was carried out in the same manner as in Example 1.

[0085] (Example 8) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent mixture of ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volume ratio of 7:3 was used as the electrolyte 24, and LiBF4 was dissolved in it to a concentration of 4.0 mol / L, and a plate-shaped electrode was used as the negative electrode 22. The evaluation was carried out in the same manner as in Example 1.

[0086] (Example 9) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent mixture of ethylene carbonate (EC) and γ-butyrolactone (GBL) in a volume ratio of 7:3 was used as the electrolyte 24, and LiBF4 was dissolved in it to a concentration of 4.0 mol / L, and a coated electrode was used as the positive electrode 21. The evaluation was carried out in the same manner as in Example 1.

[0087] (Example 10) A lithium secondary battery was obtained in the same manner as in Example 1, except that an organic solvent mixture of sulfolane (SL) and γ-butyrolactone (GBL) in a volume ratio of 4:1 was used as the electrolyte 24, and LiBF4 was dissolved in it to a concentration of 5.0 mol / L. The evaluation was carried out in the same manner as in Example 1.

[0088] (Comparative Example 1) As the electrolyte 24, an organic solvent was used, which was a mixture of diethyl carbonate (DEC), propylene carbonate (PC), and ethylene carbonate (EC) in a volume ratio of 5:1:1. LiPF A lithium secondary battery was obtained in the same manner as in Example 1, except that a solution of 6 was dissolved to a concentration of 1.0 mol / L, and a coated electrode was used as the positive electrode 21. The evaluation was carried out in the same manner as in Example 1.

[0089] (Comparative Example 2) As the electrolyte 24, an organic solvent was used, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:3. LiBFA lithium secondary battery was obtained in the same manner as in Example 1, except that a solution of 4 was dissolved to a concentration of 1.0 mol / L, and a coated electrode was used as the positive electrode 21. The evaluation was carried out in the same manner as in Example 1.

[0090] Table 1 summarizes the evaluation results of lithium secondary batteries for Examples 1-10 and Comparative Examples 1-2.

[0091] [Table 1]

[0092] As shown in Table 1, lithium secondary batteries in which the ratio of the thickness of the outer casing 12 at 80°C and 100 Pa to the thickness of the outer casing 12 at 25°C and 101325 Pa is 1.05 or more and 2.63 or less maintain a discharge capacity retention rate of 70% or more and 98% or less even under high temperature and reduced pressure environments, specifically under an environment of 80°C and 100 Pa. That is, Examples 1- 10 The lithium secondary battery can maintain good characteristics even in high-temperature and low-pressure environments. Regarding Examples 3, 7, and 8, Exterior It can suppress the formation of wrinkles.

[0093] On the other hand, the lithium secondary batteries of Comparative Examples 1 and 2, in which the thickness ratio was greater than 2.63, had a discharge capacity retention rate of 5% or less. Such lithium secondary batteries cannot maintain good performance in high-temperature and low-pressure environments.

[0094] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0095] 11 Lithium secondary battery (battery), 12 Outer casing, 13,14 Outer film, 15 Positive electrode tab terminal, 16 Negative electrode tab terminal, 17 Sealed space, 21 Positive electrode, 22 Negative electrode, 23 Separator, 24 Electrolyte, 25,26 Metal foil, 27,28 Resin layer, 31 Positive electrode current collector, 32 Positive electrode active material plate, 33 Conductive bonding layer, 34 Positive electrode bonding layer, 36 Negative electrode current collector, 37 Negative electrode active material layer, 38 Negative electrode bonding layer, 41 Positive electrode assembly, 42 Negative electrode assembly, 43 Laminate, 44 Vacuum dryer, 45 Glove box, 46 Injection device, 51 Measuring device, 52 Dial gauge, 53 Plate, 54,55,56,57 Polyimide sheet, 58 Tip.

Claims

1. It is a pouch-type lithium secondary battery, A positive electrode layer composed of a lithium composite oxide sintered body, The negative electrode layer, A separator interposed between the positive electrode layer and the negative electrode layer, An electrolyte solution comprising an electrolyte and a solvent impregnated into the positive electrode layer, the negative electrode layer, and the separator, An outer casing comprising a sealed space, the positive electrode layer, the negative electrode layer, the separator, and the electrolyte contained within the sealed space, It comprises a positive tab terminal and a negative tab terminal that extend to the outside of the outer casing, The aforementioned outer casing is a bag formed by joining the periphery of an outer film, and is made of a laminate film in which a metal foil and an insulating resin layer are laminated. The positive electrode layer is bonded to the resin layer on the positive electrode layer side via a positive electrode bonding layer. The negative electrode layer is bonded to the resin layer on the negative electrode layer side via a negative electrode bonding layer. The positive electrode junction layer extends to the positive electrode tab terminal, The negative electrode bonding layer extends to the negative electrode tab terminal. In the thickness direction of the positive electrode layer, A lithium secondary battery in which the ratio of the thickness of the outer casing at 80°C and 100 Pa to the thickness of the outer casing at 25°C and 101325 Pa is 1.05 or more and 2.63 or less.

2. The positive electrode layer is a plate-shaped electrode, The lithium secondary battery according to claim 1, wherein the negative electrode layer is a plate-shaped electrode.

3. The aforementioned solvent is A mixed liquid solvent comprising a first substance which is an ester having a carbonate, and a second substance which is an ester different from the first substance and has a carbonate or lactone, The lithium secondary battery according to claim 1 or claim 2, wherein the volume ratio of the first substance to the second substance is in the range of 1:10 or more and 10:1 or less.

4. The lithium secondary battery according to claim 1 or claim 2, wherein the electrolyte content is 2.0 mol / L or more and 8.0 mol / L or less.

5. A lithium secondary battery according to claim 1 or 2, further comprising an adhesive for bonding at least one of the positive electrode layer or the negative electrode layer to the outer casing in the sealed space, wherein the adhesive is composed of a mixed resin of an acid-modified polyolefin resin and an epoxy resin.

6. It is composed of a mixed resin of an acid-modified polyolefin resin and an epoxy resin, and further comprises an adhesive for bonding at least one of the positive electrode layer or the negative electrode layer to the outer casing in the sealed space, The positive electrode layer is a plate-shaped electrode, The negative electrode layer is a plate-shaped electrode or a coated electrode. The solvent is a mixed solvent containing sulfolane and γ-butyrolactone. The volume ratio of the sulfolane to the γ-butyrolactone is 7:3 or more and 4:1 or less. The lithium secondary battery according to claim 1, wherein the electrolyte content is 1.5 mol / L or more and 5.0 mol / L or less.

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