Nonaqueous electrolyte secondary battery

Abstract

This nonaqueous electrolyte secondary battery (10) includes: an electrode body (60); and a laminate sheet outer casing (12) which is obtained by folding a laminate sheet including an adhesive resin layer in two along a bottom part (17). The laminate sheet outer casing has: a top part (16) from which a positive electrode tab and a negative electrode tab are derived from an overlapping part of the outer peripheral part of the laminate sheet; and two side parts (18, 20) which connect the top part and the bottom part to each other. The laminate sheet outer casing has a housing part (13) that houses the electrode body inside the overlapping part. Sealing parts (30, 40) are formed on the top part and the two side parts. Each side part has non-sealed parts (31, 41) that are connected to the housing part and the bottom part. Each non-sealed part is separated from the top part.

Description

Non-aqueous electrolyte secondary battery

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

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion batteries have been used as power sources for electronic devices such as smartphones, tablet computers, notebook PCs, etc. In these cases, there is a particular demand for lightweight and thin secondary batteries.

[0003] For this reason, it is conceivable to use a secondary battery having a flat laminate sheet exterior formed by folding a laminate sheet such as an aluminum laminate film in half, as described in Patent Document 1, as a power source for electronic devices.

[0004] Japanese Patent Application Laid-Open No. 2005-285526

[0005] Recently, nonaqueous electrolyte secondary batteries equipped with laminate sheet exterior bodies are required to maintain high battery capacity even during long-term charge-discharge cycles. To achieve this, it is desirable to accommodate a larger amount of electrolyte in the exterior body than before. One possible method for increasing the amount of electrolyte without increasing the battery's external dimensions is to reduce the overall width of the sealing portion at the overlapping portion of the laminate sheet to increase the storage space for the electrolyte. However, this may result in a decrease in the sealing ability of the exterior body.

[0006] An object of the present disclosure is to improve cycle characteristics in a nonaqueous electrolyte secondary battery equipped with a laminate sheet exterior body by increasing the amount of electrolyte that can be accommodated without impairing the sealing properties of the laminate sheet exterior body or increasing the external dimensions.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure comprises: an electrode assembly having a positive electrode connected to a positive electrode tab and a negative electrode connected to a negative electrode tab; and a laminate sheet exterior body formed by folding a laminate sheet including an adhesive resin layer in half along a bottom part, the laminate sheet exterior body having a top part from which the positive electrode tab and the negative electrode tab extend at an overlapping part on the outer periphery of the laminate sheet, and two side parts connecting the top part and the bottom part, and also having a housing part for housing the electrode assembly inside the overlapping part, and sealing parts are formed in the top part and the two side parts, and each of the two side parts has a non-sealing part that connects to the housing part of the electrode assembly and the bottom part, and each non-sealing part is spaced apart from the top part.

[0008] A nonaqueous electrolyte secondary battery including a laminate sheet exterior body according to the present disclosure can increase the amount of electrolyte stored without impairing the sealing properties of the laminate sheet exterior body or increasing the external dimensions, thereby improving cycle characteristics.

[0009] 9 is a perspective view showing a schematic shape of a nonaqueous electrolyte secondary battery according to an embodiment in a state where the side portions are folded. FIG. 10 is a diagram showing a laminate sheet overlapping step, a top portion sealing step, and a first side portion sealing step in a manufacturing process for a nonaqueous electrolyte secondary battery. FIG. 11 is a diagram showing a liquid injection step and a vacuum sealing step. FIG. 12 is a diagram showing a main sealing step, a side cutting step, and a side folding step. FIG. 13 is a cross-sectional view of the secondary battery of FIG. 4 before folding the sides. FIG. 14 is a plan view showing a pressing surface of a mold used to heat and press the two side portions to obtain the secondary battery of FIG. 5. FIG. 15 is a diagram corresponding to FIG. 5 for the secondary battery of Comparative Example 1. FIG. 16 is a plan view showing a pressing surface of a mold used to heat and press the two side portions to obtain the secondary battery of FIG. 7. FIG. 16 is a diagram corresponding to FIG. 5 for the secondary battery of Comparative Example 2. FIG. 17 is a plan view showing a pressing surface of a mold used to heat and press the two side portions to obtain the secondary battery of FIG. 9.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments do not limit the present disclosure, and configurations formed by selectively combining multiple examples are also included in the present disclosure.

[0011] "Configuration of Nonaqueous Electrolyte Secondary Battery" Fig. 1 is a perspective view showing the schematic shape of a nonaqueous electrolyte secondary battery 10 according to an embodiment. Hereinafter, the nonaqueous electrolyte secondary battery 10 will be referred to as a secondary battery 10. The secondary battery 10 has a thin rectangular parallelepiped shape overall, and includes an electrode body 60 and a laminate sheet exterior body 12 that accommodates the electrode body 60 and an electrolyte. In this example, the secondary battery 10 is a lithium-ion secondary battery.

[0012] The laminate sheet outer casing 12 is formed by folding a film-like laminate sheet 11 containing an adhesive resin layer in half along the bottom portion 17, and a wound electrode body 60 is housed in a thick rectangular parallelepiped housing portion 13.

[0013] The laminate sheet 11 is a metal layer made of, for example, aluminum or an aluminum alloy, with an inner resin layer, which is an adhesive resin layer, provided on the surface that will be on the inside when the laminate sheet 11 is folded in half and stacked. The inner resin layer is made of, for example, polypropylene. The metal layer and the inner resin layer can be adhered together using, for example, carboxylic acid-modified polypropylene, in which carboxyl groups are added to polypropylene. The electrode body 60 is then wrapped in the folded laminate sheet 11, and the remaining three sides of the laminate sheet 11 are sealed.

[0014] 1 , the laminate sheet exterior body 12 has a top portion 16 on the upper side, a bottom portion 17 on the lower side, a first side portion 18 on the left side, and a second side portion 20 on the right side. The top portion 16 and the first and second side portions 18, 20 are each formed by overlapping the laminate sheet 11, and each has a sealing portion formed therein. The first and second side portions 18, 20 are then folded back in the thickness direction of the laminate sheet 11, so that they overlap the side walls of the storage portion 13.

[0015] At the overlapping portion of the outer periphery of the folded laminate sheet 11, both longitudinal ends of the top portion 16 are overlapped, leading out from the positive electrode tab 22 and the negative electrode tab 24. The positive electrode tab 22 and the negative electrode tab 24 are connected to the positive electrode and the negative electrode of the electrode body 60, respectively. In addition, tab films 26, 28 are welded to the base portions of the positive electrode tab 22 and the negative electrode tab 24.

[0016] The secondary battery 10 equipped with such a laminate sheet exterior body 12 is electrically connected to an external load by the positive electrode tab 22 and the negative electrode tab 24 .

[0017] The bottom portion 17 is a folded portion of the laminate sheet 11 in the laminate sheet exterior body 12. The portion of the bottom portion 17 sandwiched between the two side portions 18, 20 forms a wall portion facing one end face of the electrode body 60 in the winding axis direction, which will be described later.

[0018] The first side portion 18 and the second side portion 20 are arranged along a first direction X corresponding to the winding axis direction of the electrode body 60 so as to connect the top portion 16 and the bottom portion 17 at the overlapping portion of the outer periphery of the folded laminate sheet 11. At the top portion 16 and each side portion 18, 20, the opposing portions of the folded laminate sheet 11 are overlapped with their inner resin layers in contact and welded by heat and pressure. The storage portion 13 is provided inside the overlapping portion of the folded laminate sheet 11 in the laminate sheet exterior body 12, and stores the electrode body 60.

[0019] The laminate sheet 11 may have an outer resin layer on the metal layer that faces outward when folded in half. The outer resin layer may be made of nylon, for example. The metal layer and the outer resin layer may be bonded together using, for example, a dry laminating adhesive.

[0020] "Explanation of Manufacturing Process" The basic steps of the manufacturing process for the secondary battery 10 having the laminate sheet exterior body 12 will be described with reference to FIGS.

[0021] First, a flat, wound electrode assembly 60 is fabricated. The electrode assembly 60 is formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator interposed therebetween. At this time, tab films 26, 28 are welded to the positive electrode tab 22 and the negative electrode tab 24, respectively. Next, the positive electrode tab 22 is welded to an exposed portion of a metal positive electrode core that forms the positive electrode, and the negative electrode tab 24 is welded to an exposed portion of a metal negative electrode core that forms the negative electrode.

[0022] A positive electrode active material layer is formed on the surface of the positive electrode core, and a negative electrode active material layer is formed on the surface of the negative electrode core. The positive electrode core is made of, for example, aluminum foil, and the negative electrode core is made of, for example, copper foil. The positive electrode active material layer contains a positive electrode active material such as a lithium transition metal composite oxide, and the negative electrode active material layer contains a negative electrode active material such as graphite. The winding direction end of the electrode body 60 is fixed to the outermost peripheral surface of the electrode body 60 with tape.

[0023] 2( a) and 2(b), the laminate sheet 11 is folded in half so that the electrode body 60 is wrapped in the inner resin layer of the laminate sheet 11. At this time, the positive electrode tab 22 and the negative electrode tab 24 are led out from the side opposite the side of the folded-back portion 11a of the laminate sheet 11. A top portion 16 is formed on the end of the laminate sheet 11 from which the positive electrode tab 22 and the negative electrode tab 24 lead out.

[0024] In this example, the length of the laminate sheet 11 in the second direction (the vertical direction in FIG. 2 ) is made sufficiently larger than the length of the electrode body 60 in the second direction, and an excess portion 11b of the laminate sheet 11 is provided in the portion adjacent to the electrode body 60. This excess portion 11b is used to remove gas by reducing pressure from the portion of the laminate sheet exterior body 12 that will become the storage section 13, as will be described later.

[0025] Then, one end in the first direction (the right end in Figure 2), which becomes the top portion 16 of the folded laminate sheet 11, is heated and pressed using a mold to weld the inner resin layers together, thereby sealing the top portion 16 as shown in Figure 2(b).

[0026] Next, one end (the lower end in FIG. 2(c)) in the second direction (the vertical direction in FIG. 2(c)) of the laminate sheet 11 encasing the electrode body 60 is heated and pressed by a mold to weld the inner resin layers together, thereby sealing the first side portion 18. This forms a first intermediate body 61 in which the electrode body 60 is encased in a bag-shaped laminate sheet 11 with one end open.

[0027] Next, as shown in FIG. 3( a), with the first intermediate 61 placed in the dry box 70, an electrolyte solution is poured from the upper opening of the laminate sheet 11. The electrolyte solution includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and mixed solvents thereof. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0028] After the electrolyte solution is poured into the first intermediate 61, the open end of the laminate sheet 11 is temporarily sealed to form the second intermediate 62. Next, the electrolyte solution is allowed to permeate into the electrode body 60, and then the second intermediate 62 is charged to a predetermined amount.

[0029] After charging of the second intermediate 62 is completed, as shown in FIG. 3B, the second intermediate 62 is housed in a decompression box 74, and the middle part of the excess part 11b is sealed while the pressure inside the housing part 13 of the second intermediate 62 is reduced, forming a reduced pressure sealed part 11c. This removes gas from the part that will become the housing part 13 by the reduced pressure. Thereafter, the reduced pressure sealed part 11c is cut, and a third intermediate 63 is formed from which the excess part 11b is cut off.

[0030] Next, as shown in Fig. 4(a), the second side portion 20 of the third intermediate body 63, which is adjacent to the temporarily sealed storage portion 13, is heated and pressed by a mold to weld the inner resin layers together, thereby finally sealing the second side portion 20. Then, as shown in Fig. 4(b), the portion outside the second side portion 20 is cut off, and unnecessary portions of the laminate sheet 11 are removed.

[0031] In this way, a secondary battery 10 before side folding is obtained, in which a rectangular parallelepiped housing portion 13 called a cup in which the electrode body 60 is enclosed is provided in the laminate sheet exterior body 12. In the secondary battery 10 shown in Figure 4(b), the housing portion 13 protrudes only on one side (the front side of Figure 4) with respect to an imaginary plane including the top portion 16 and each side portion 18, 20. Alternatively, rectangular parallelepiped housing portions each having a thickness approximately half that of the housing portion 13 may be formed on both sides of the imaginary plane including the top portion 16 and each side portion 18, 20, and the electrode body 60 may be housed in the rectangular parallelepiped space formed by combining the two housing portions.

[0032] Then, as shown in Fig. 4(c), in the secondary battery 10 before the sides are folded, each side portion 18, 20 of the laminate sheet exterior body 12 is folded so as to overlap the side surface of the housing portion 13, thereby obtaining the secondary battery 10 of Fig. 1. In Fig. 1, the side portions 18, 20 of the secondary battery 10 are folded so as to overlap the housing portion 13, but the secondary battery may be completed in an extended state as shown in Fig. 4(b) without folding the side portions 18, 20.

[0033] In the secondary battery 10 fabricated as described above, sealed portions are formed in the top portion 16 and the two side portions 18, 20. Conventionally, the sealed portions are formed by welding the entire overlapping portion of a laminate sheet folded in half in the top portion and each side portion. However, in this case, the secondary battery has a limited electrolyte capacity unless the external dimensions are enlarged. Therefore, there is room for improvement in the electrolyte capacity from the perspective of improving cycle characteristics. Therefore, in this embodiment, the above-mentioned problem is solved by appropriately forming sealed and non-sealed portions in the top portion 16 and each side portion 18, 20. Below, the characteristic features of this embodiment are specifically described using Figures 5 and 6.

[0034] Fig. 5 is a cross-sectional view of the secondary battery 10 before the sides are folded in Fig. 4. Fig. 6 is a plan view showing the pressing surfaces of molds 90 and 91 used to heat and press the two side portions 18 and 20 to obtain the secondary battery 10 in Fig. 5.

[0035] As shown in FIG. 5 , in the secondary battery 10 before the side folding, each of the two side portions 18, 20 has a non-sealed portion 31, 41 that connects to the housing portion 13 and the bottom portion 17, including the bottom portion 17 side. Each of the non-sealed portions 31, 41 has a generally triangular shape that widens toward the bottom portion 17. For example, when forming the sealed portions 30, 40 in the side portions 18, 20, each of the non-sealed portions 31, 41 is formed by preventing welding of a portion of the overlapping portion of the laminate sheet folded in half. More specifically, when heat-pressing the overlapping portion of the laminate sheet 11 from both sides using a mold in each side portion 18, 20, molds 90, 91 are used, each having a pressing surface with a pentagonal planar shape, as shown in FIG. 6 . In other words, the pressing surface of the mold 90, 91 has a planar shape that is a rectangle excluding the triangular region facing the non-sealed portion 31, 41.

[0036] As a result, each of the non-sealed portions 31, 41 is spaced apart from the top portion 16. Furthermore, in each of the two side portions 18, 20, the inner edges 51, 52 of the sealing portions 30, 40 on the storage portion 13 side have first edges 53, 54 extending linearly from the top portion 16 parallel to the first direction X, and second edges 55, 56 extending from the middle of the side portions 18, 20 in the first direction X toward the bottom portion 17 so as to widen outward from the side portions 18, 20. In other words, the widths of the non-sealed portions 31, 41 of each of the two side portions 18, 20 change so as to widen toward the bottom portion 17. In FIG. 5 , the second edges 55, 56 are linear and inclined with respect to the first direction X, but they may also be gently curved.

[0037] In this way, each of the non-sealed portions 31, 41 is connected to the accommodation portion 13, and therefore each of the non-sealed portions 31, 41 functions as a space for accommodating the electrolyte. Furthermore, each of the non-sealed portions 31, 41 is connected to the bottom portion 17, and one end face 60a of the electrode body 60 in the direction of the winding axis along the first direction X faces the bottom portion 17. This makes it easier for the electrolyte to be supplied to the end face 60a of the electrode body 60.

[0038] On the other hand, unlike the above embodiment, it is also possible to form non-sealed portions 31a, 41a on the top portion 16 side of each side portion 18b, 20b so as to connect to the top portion 16, as in Comparative Example 2 shown in Figure 9 described below. However, in such Comparative Example 2, when sealing the top portion 16, resin from the inner resin layer flows into the non-sealed portions 31a, 41a, causing problems such as blocking the supply path of electrolyte from the non-sealed portions 31a, 41a to the end surface 60b of the electrode body 60 and preventing an increase in the amount of electrolyte in the secondary battery. The embodiment shown in Figure 5 can prevent such problems.

[0039] In the embodiment shown in Fig. 5, the minimum width D1 of each sealing portion 30, 40 in each of the two side portions 18, 20 is preferably 1 mm or greater. In this example, the minimum width D1 is the width of the sealing portion 30, 40 at the end on the bottom portion 17 side. This preferred configuration can further increase the reliability of the sealing of the electrolyte in each side portion 18, 20. In the configuration shown in Fig. 5, the shapes of the two side portions 18, 20 are symmetrical with respect to the center line of the battery 10 along the first direction X.

[0040] Furthermore, in each of the two side portions 18, 20, the ratio of the area of ​​the non-sealed portion 31, 41 to the total area of ​​the sealed portion 30, 40 and the non-sealed portion 31, 41 when viewed in the thickness direction is preferably 10% or more and 30% or less. This preferred configuration can further increase the reliability of the sealing performance of each side portion 18, 20. In particular, in a configuration in which the minimum width D1 is 1 mm or more, it is more preferable to set the ratio of the area of ​​the non-sealed portion to the total area to 10% or more and 30% or less, in terms of increasing the reliability of the sealing performance of each side portion 18, 20. That is, for the side portion 18, when the area of ​​the sealed portion 30 is S1 and the area of ​​the non-sealed portion 31 is S2, it is preferable that S1 and S2 satisfy the relationship 10≦S2×100 / (S1+S2)≦30.

[0041] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples.

[0042] <Examples> [Preparation of non-aqueous electrolyte] A non-aqueous electrolyte solution was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 (at 25°C). ６ ) was dissolved in a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte solution.

[0043] [Secondary Battery Fabrication] A wound electrode assembly 60 was fabricated by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween. The electrode assembly 60 was housed in a laminate sheet exterior 12 so that both end faces 60a, 60b of the electrode assembly 60 in the winding axis direction faced the bottom portion 17 and the top portion 16, respectively. The shape of the laminate sheet exterior 12 was the same as that of the secondary battery 10 before side folding shown in FIG. 5 . Furthermore, the positive electrode tab 22 connected to the positive electrode of the electrode assembly 60 and the negative electrode tab 24 connected to the negative electrode were extended from the top portion 16 of the laminate sheet exterior 12. Furthermore, a nonaqueous electrolyte was injected into the laminate sheet 11 housing the electrode assembly 60 and sealed using a method similar to that shown in FIGS. 2 to 4 . This resulted in the fabrication of the secondary battery 10 of Example 1. In the fabricated secondary battery 10, the minimum width D1 of the sealing portions 30, 40 of each side portion 18, 20 was 1 mm. In each of the side portions 18, 20, the height D2 of the non-sealed portions 31, 41 along the first direction X is 40 mm. The maximum width of the sealed portions 30, 40, which coincides with the maximum width of each of the side portions 18, 20, is 4 mm.

[0044] In the fabricated secondary battery 10, the height along the first direction X, excluding the lead-out portions of the positive electrode tab 22 and the negative electrode tab 24, is 69 mm, the width along the second direction Y is 56 mm, and the thickness in the direction perpendicular to both the first direction X and the second direction Y is 4.9 mm.

[0045] [Charge-Discharge Cycle Test] The secondary battery 10 was charged at a constant current of 1.0 C (3150 mA) in a 25°C environment until the battery voltage reached 4.4 V, and then charged at a constant voltage of 4.4 V until the current reached 0.05 C (158 mA). After a 10-minute pause, the battery was discharged at a constant current of 1.0 C (3150 mA) until the battery voltage reached 3.0 V. The discharge capacity at this time was defined as the initial capacity. The initial capacity of the example was 3150 mAh. This charge-discharge cycle was repeated 500 times, with a 20-minute pause between each cycle, and the ratio of the discharge capacity after 500 cycles to the initial capacity was calculated as the capacity retention rate. The capacity retention rate was calculated for 10 secondary batteries, and the average of the capacity retention rates was also calculated.

[0046] [Evaluation of the amount of liquid in the battery] The maximum amount of nonaqueous electrolyte that could be contained in the secondary battery 10 was injected, and the weight of the obtained secondary battery 10 was measured before and after the injection of the nonaqueous electrolyte to evaluate the amount of liquid in the battery, which is the mass of the nonaqueous electrolyte in the secondary battery 10. The amount of liquid in the battery was evaluated for 30 secondary batteries, and the average amount of liquid in the batteries was also calculated.

[0047] [Leakage Test] The secondary batteries 10 in a predetermined charged state were stored for 10 days in a high-temperature and high-humidity environment at a temperature of 80°C and a humidity of 90%, and the presence or absence of electrolyte leakage was confirmed. The leakage test was performed on 10 secondary batteries.

[0048] Comparative Example 1 Fig. 7 is a diagram corresponding to Fig. 5 of a secondary battery 81 of Comparative Example 1. Fig. 8 is a plan view showing the pressing surfaces of molds 90a and 91a used to heat and press the two side portions 18a and 20a to obtain the secondary battery 81 of Fig. 7 . As shown in Fig. 7 , in Comparative Example 1, in the secondary battery 81 before the sides are folded, the laminate sheet exterior body 12a has the entire portions of the overlapping portion of the laminate sheet folded in half that become the two rectangular side portions 18a and 20a welded together, and a rectangular sealing portion is formed over the entire side portions 18a and 20a. Therefore, when heat-pressing the overlapping portion of the laminate sheet from both sides of each side portion 18a and 20a using a mold, molds 90a and 91a having pressing surfaces with a rectangular planar shape are used, as shown in Fig. 8 . In addition, in each of the two side portions 18a, 20a, the inner edges 51a, 52a on the housing portion 13 side extend linearly in parallel to the first direction X so as to connect the top portion 16 and the bottom portion 17. In Comparative Example 1, a secondary battery 81 was fabricated and evaluated in the same manner as in Example except for the above.

[0049] Comparative Example 2 Fig. 9 is a diagram corresponding to Fig. 5 of a secondary battery of Comparative Example 2. Fig. 10 is a plan view showing the pressing surfaces of molds 90b and 91b used to heat and press two side portions 18b and 20b to obtain the secondary battery 82 of Fig. 9 . As shown in Fig. 9 , in Comparative Example 2, in the secondary battery 82 before the sides are folded, the laminate sheet exterior body 12b has non-sealed portions 31a and 41a connected to the storage portion 13 and the top portion 16 on each side portion 18b and 20b, respectively, on the top portion 16 side. Each of the non-sealed portions 31a and 41a has a generally triangular shape widening toward the top portion 16. Each of the non-sealed portions 31a and 41a is formed by preventing welding of a portion of the overlapping portion of the folded laminate sheet when forming the sealing portions 30a and 40a on the side portions 18b and 20b. More specifically, when heat-pressing the overlapping portion of the laminate sheet from both sides using a mold in each side portion 18b, 20b, molds 90b, 91b are used, whose width decreases toward the top portion 16 and whose pressing surface has a pentagonal planar shape, as shown in Fig. 10. In other words, the pressing surface of molds 90b, 91b has a rectangular planar shape excluding a triangular region facing the non-sealed portion 31a, 41a.

[0050] The non-sealed portions 31a, 41a are spaced apart from the bottom portion 17. In each of the two side portions 18b, 20b, the inner edges 51b, 52b of the sealed portions 30a, 40a on the storage portion 13 side have first edges 53a, 54a extending linearly from the bottom portion 17 in parallel to the first direction X, and second edges 55a, 56a extending in a direction inclined with respect to the first direction X so as to spread outward from the middle of the side portions 18b, 20b in the first direction X toward the top portion 16. This allows the non-sealed portions 31a, 41a to be connected to the top portion 16.

[0051] In the fabricated secondary battery 82, the minimum width D5 of the sealed portions 30 a, 40 a of each side portion 18 b, 20 b was 1 mm. The height D6 of the unsealed portions 31 a, 41 a of each side portion 18 b, 20 b along the first direction X was 40 mm. In Comparative Example 2, a secondary battery 82 was fabricated and evaluated in the same manner as in Example except for the above.

[0052] Table 1 shows the evaluation results of the secondary batteries 10, 81, and 82 according to the example and comparative examples 1 and 2, including the amount of electrolyte in the battery, the capacity retention rate after 500 cycles, and the leakage test.

[0053]

[0054] In the column of the amount of electrolyte in the battery in Table 1, the range of the measured values ​​is shown in parentheses together with the average value of the measured values ​​for N=30 test samples.

[0055] In the column of capacity retention rate after 500 cycles in Table 1, the number of test samples N=10 is shown, and the range of the evaluation results is also shown in parentheses along with the average value of the evaluation results.

[0056] The column for leakage test in Table 1 shows the ratio of the number of test samples that did not leak to the total number of test samples, for a number of test samples N=10.

[0057] As can be seen from the results shown in Table 1, the amount of electrolyte in the battery was increased in both the Example and Comparative Example 2 compared to Comparative Example 1. This is because, in Comparative Example 1, the entire overlapping portion of each side portion 18a, 20a is sealed, and the gaps in the overlapping portions cannot be used as spaces for accommodating electrolyte. On the other hand, in the Example and Comparative Example 2, the laminate sheet is not welded to the overlapping portions of each side portion 18, 20, 18b, 20b that form the non-sealed portions 31, 41, 31a, 41a. Therefore, the gaps in the overlapping portions of the non-sealed portions 31, 41, 31a, 41a that are not welded can be used as spaces for accommodating electrolyte. As a result, the Example and Comparative Example 2 can increase the amount of electrolyte in the battery compared to Comparative Example 1.

[0058] Furthermore, as can be seen from the results shown in Table 1, the increase in the amount of electrolyte in the battery of the Example was greater than that of Comparative Example 2. In Comparative Example 2, non-sealed portions 31a, 41a are formed in the portion including the top portion 16 side so as to connect to the top portion 16. Therefore, in Comparative Example 2, compared to the Example, it is thought that resin protrudes from the inner resin layer of the laminate sheet into the non-sealed portions 31a, 41a during heat pressing of the sealed portion of the top portion 16, limiting the storage space for the electrolyte in the non-sealed portions 31a, 41a. On the other hand, in the Example, the non-sealed portions 31, 41 are not affected by the protrusion of resin from the top portion 16. This is thought to be why the increase in the amount of electrolyte in the battery of the Example relative to Comparative Example 1 was greater than that of Comparative Example 2.

[0059] Furthermore, with regard to the capacity retention rate after 500 cycles, the capacity retention rate of the Example is higher than that of Comparative Examples 1 and 2 as the amount of electrolyte in the battery increases.

[0060] Furthermore, regarding the reliability of the sealing portion, the results of the leakage test in Table 1 show that no leakage from the secondary batteries was confirmed in any of the Example, Comparative Example 1, and Comparative Example 2, and that the battery was normal. Although not shown in Table 1, it was confirmed that the thickness of the secondary battery in Comparative Example 2 was slightly greater than that of the Example. This is thought to be because, unlike the bottom portion 17 side, in Comparative Example 2, the non-sealed portions 31a and 41a are formed to connect to the top portion 16 near the leading edge of the laminate sheet, making it easier to absorb moisture from outside the secondary battery and resulting in an increased thickness. On the other hand, in the Example, the non-sealed portions 31 and 41 are formed to connect to the bottom portion 17, which is the folded portion of the laminate sheet, so moisture absorption from outside did not occur and no increase in the thickness of the secondary battery was confirmed. Therefore, it is thought that the reliability of the sealing portion in the Example is higher than that in Comparative Example 2.

[0061] Thus, according to the configuration of the present disclosure, by forming the non-sealed portions 31, 41 at appropriate positions in each of the side portions 18, 20, it is possible to partially create a space capable of accommodating the electrolyte in each of the side portions 18, 20. This makes it possible to increase the amount of electrolyte that can be accommodated and improve cycle characteristics without impairing the sealing properties of the laminate sheet exterior body 12 or increasing the outer dimensions.

[0062] The present disclosure is further described by the following embodiments. Configuration 1: A nonaqueous electrolyte secondary battery comprising: an electrode assembly having a positive electrode connected to a positive tab and a negative electrode connected to a negative tab; and a laminate sheet exterior body formed by folding a laminate sheet including an adhesive resin layer in half along a bottom portion, wherein the laminate sheet exterior body has a top portion from which the positive electrode tab and the negative electrode tab extend at an overlapping portion of the outer periphery of the laminate sheet, and two side portions connecting the top portion and the bottom portion, and also has a housing portion inside the overlapping portion that houses the electrode assembly, wherein sealed portions are formed in the top portion and the two side portions, and each of the two side portions has an unsealed portion connecting to the housing portion and the bottom portion, and each of the unsealed portions is spaced apart from the top portion. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the width of the unsealed portion of each of the two side portions varies so as to widen toward the bottom portion. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the electrode body is a wound type in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and both end faces of the electrode body in the winding axis direction face the bottom portion and the top portion.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the minimum width of the sealed portion in each of the two side portions is 1 mm or more.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the ratio of the area of ​​the unsealed portion to the total area of ​​the sealed portion and the unsealed portion when viewed in the thickness direction in each of the two side portions is 10% or more and 30% or less.

[0063] 10 Non-aqueous electrolyte secondary battery (secondary battery), 11 Laminate sheet, 12 Laminate sheet exterior body, 13 Storage section, 16 Top section, 17 Bottom section, 18, 18a, 18b First side section, 20, 20a, 20b Second side section, 22 Positive electrode tab, 24 Negative electrode tab, 26, 28 Tab film, 30, 30a Sealed section, 31, 31a Non-sealed section, 40, 40a Sealed section, 41, 41a Non-sealed section, 51, 52, 51a, 52a, 51b, 52b Inner edge, 53, 54, 53a, 54a First edge section, 55, 56, 55a, 56a Second edge section, 60 Electrode body, 61 First intermediate body, 62 Second intermediate body, 63 Third intermediate body, 81, 82 Secondary battery, 90, 91, 90a, 91a, 90b, 91b mold.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly having a positive electrode connected to a positive electrode tab, and a negative electrode connected to a negative electrode tab; and a laminate sheet exterior body formed by folding a laminate sheet including an adhesive resin layer in half along a bottom part, wherein the laminate sheet exterior body has a top part from which the positive electrode tab and the negative electrode tab lead out at an overlapping part at the outer periphery of the laminate sheet, and two side parts connecting the top part and the bottom part, and also has a housing part for housing the electrode assembly inside the overlapping part, wherein sealed parts are formed in the top part and the two side parts, and each of the two side parts has a non-sealed part connected to the housing part and the bottom part, and each of the non-sealed parts is spaced apart from the top part.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the width of said unsealed portion of each of said two side portions varies so as to widen toward said bottom portion.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode body is a wound type in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and both end faces of the electrode body in the winding axis direction face the bottom portion and the top portion.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the minimum width of the sealing portion in each of the two side portions is 1 mm or more.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein in each of the two side portions, the ratio of the area of ​​the non-sealed portion to the total area of ​​the sealed portion and the non-sealed portion when viewed in the thickness direction is 10% or more and 30% or less.

Images