Electrode group and secondary battery

Abstract

The objective is to provide an electrode group and a secondary battery that suppress short circuits between the negative electrode mixture layer and the uncoated portion of the positive electrode mixture layer. [Solution] An electrode group comprising a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are wound around each other with a separator in between. The positive electrode has a strip-shaped positive electrode current collector having a long side and a short side, a positive electrode mixture layer on the positive electrode current collector parallel to the long side of the positive electrode current collector, an uncoated portion of the positive electrode mixture layer where no mixture is applied, and an insulating portion covering the interface between the positive electrode mixture layer and the uncoated portion of the positive electrode mixture layer. The negative electrode has a strip-shaped negative electrode current collector having a long side and a short side, and a negative electrode mixture layer on the negative electrode current collector parallel to the long side of the negative electrode current collector. The insulating portion has a first region covering at least a part of the uncoated portion of the positive electrode mixture layer and a second region covering at least a part of the positive electrode mixture layer. The end of the negative electrode mixture layer parallel to the long side is provided at a position opposite to the second region of the insulating portion.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to electrode groups and secondary batteries. [Background technology]

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources for electric vehicles, hybrid vehicles, electric motorcycles, and forklifts. Recently, there has been a surge in development toward the adoption of lithium-ion secondary batteries, which have high energy density, and development is being carried out with consideration for long lifespan and safety.

[0003] For example, in lithium-ion secondary batteries (hereinafter referred to as secondary batteries), the width of the negative electrode mixture layer is formed to be wider than the width of the positive electrode mixture layer, and the area of ​​the negative electrode mixture layer may be larger than the area of ​​the positive electrode mixture layer, in order to accept all the lithium ions supplied from the positive electrode mixture layer. In this type of secondary battery, the negative electrode mixture layer has a portion that faces the uncoated portion of the positive electrode mixture layer (positive electrode current collector) via a separator. At this point where the two face each other, the edge of the negative electrode mixture layer may pierce the separator, causing a short circuit due to electrical contact between the negative electrode mixture layer and the uncoated portion of the positive electrode mixture layer (positive electrode current collector). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-21134 [Patent Document 2] Japanese Patent Publication No. 2011-216403 [Patent Document 3] Japanese Patent Publication No. 2011-23334 [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide an electrode group and a secondary battery that can suppress short circuits between the negative electrode mixture layer and the uncoated portion of the positive electrode mixture layer, and that can realize a secondary battery that ensures sufficient battery capacity. [Means for solving the problem]

[0006] To solve the above problems, the electrode group of the embodiment comprises a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are wound around a separator, and the positive electrode has a strip-shaped positive electrode current collector having a long side and a short side, a positive electrode mixture layer on the positive electrode current collector parallel to the long side of the positive electrode current collector, an uncoated portion of the positive electrode mixture layer where no coating is applied, and an insulating portion covering the interface between the positive electrode mixture layer and the uncoated portion of the positive electrode mixture layer. The negative electrode has a strip-shaped negative electrode current collector having a long side and a short side, and a negative electrode mixture layer on the negative electrode current collector parallel to the long side of the negative electrode current collector. The insulating portion is the uncoated portion of the positive electrode mixture layer It has a first region covering at least a part of the part and a second region covering at least a part of the positive electrode mixture layer. The end of the negative electrode mixture layer, which is parallel to the long side, is provided at a position opposite to the second region of the insulating part. The negative electrode mixture contains a compound whose lithium ion intercalation / release potential is 0.4V (vs. Li / Li+) or higher, relative to metallic lithium. The length B1 of the insulating portion in the width direction parallel to the short side of the positive electrode mixture layer and the length B1' of the second region of the insulating portion in the width direction satisfy the following relationship (1). 0.1 ≤ B1' / B1 ≤ 0.5 (1) [Brief explanation of the drawing]

[0007] [Figure 1] A schematic perspective view showing the electrode group according to the first embodiment. [Figure 2] A partially unfolded perspective view of the electrode group according to the first embodiment, viewed from above. [Figure 3] A schematic cross-sectional view showing the electrode group according to the first embodiment. [Figure 4] A schematic cross-sectional view showing a portion of the positive electrode, including the insulating portion, used in the electrode group according to the first embodiment. [Figure 5] A cross-sectional enlarged view including one insulating portion of the positive electrode used in the electrode group according to the first embodiment. [Figure 6] A schematic perspective view showing the electrode group according to the second embodiment. [Figure 7] Partial developed perspective view of the electrode group according to the second embodiment, viewed from above. [Figure 8] Cross-sectional view schematically showing the electrode group according to the second embodiment. [Figure 9] Cross-sectional view schematically showing a part including the insulating portion of the positive electrode used in the electrode group according to the second embodiment. [Figure 10] Enlarged cross-sectional view including one insulating portion of the positive electrode used in the electrode group according to the second embodiment. [Figure 11] Perspective view schematically showing the secondary battery according to the third embodiment. [Figure 12] Perspective view schematically showing the secondary battery according to the fourth embodiment.

Mode for Carrying Out the Invention

[0008] Hereinafter, the electrode group and the secondary battery of the embodiment will be described with reference to the drawings.

[0009] (First Embodiment) The electrode group 5 of the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view schematically showing the electrode group 5 according to the first embodiment, and FIG. 2 is a partial developed perspective view of the electrode group 5 according to the first embodiment viewed from above.

[0010] For example, as shown in FIGS. 1 and 2, the electrode group 5 is manufactured by winding the positive electrode 13 and the negative electrode 15 with the separator 4 interposed therebetween and pressing the whole into a flat shape. The positive electrode 13 has a strip-shaped positive electrode current collector 13a having a long side 90 (Y direction) and a short side 92 (X direction). On the positive electrode current collector 13a, a positive electrode active material layer 130 coated with a positive electrode active material in parallel with the long side 90 and a non-coated portion 70a of the positive electrode active material layer where no positive electrode active material is coated are formed. The negative electrode 15 has a strip-shaped negative electrode current collector 15a having a long side 90 and a short side 92. On the negative electrode current collector 15a, a negative electrode active material layer 150 coated with a negative electrode active material in parallel with the long side 90 and a non-coated portion 70b of the negative electrode active material layer where no negative electrode active material is coated are formed.

[0011] In the wound electrode group 5, the uncoated portion 70a of the positive electrode mixture layer protrudes in the opposite direction to the protruding direction of the uncoated portion 70b of the negative electrode mixture layer and is provided at both ends of the electrode group 5. However, the protruding directions of the uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer are not limited to these. The uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer may protrude in the same direction, and both may be provided at one end of the electrode group 5.

[0012] In the electrode group 5 of this embodiment, an insulating portion 100 is formed on the positive electrode current collector 13a, covering the interface between the uncoated portion 70a of the positive electrode mixture layer and the positive electrode mixture layer 130. This insulating portion 100 has a first region 100a that covers at least a part of the uncoated portion 70a of the positive electrode mixture layer and a second region 100b that covers at least a part of the positive electrode mixture layer 130.

[0013] The cross-section of the electrode group 5 (cross-section II shown in Figure 1) will be described with reference to Figure 3. Figure 3 is a schematic cross-sectional view of the electrode group 5 according to the first embodiment. As shown in Figure 3, in the case of the wound electrode group 5, the end 150a of the negative electrode mixture layer 150, which is parallel to the long side 90, is positioned opposite the second region 100b of the insulating portion 100. As a result, even if the end 150a of the negative electrode mixture layer 150 penetrates the separator 4, the second region 100b of the insulating portion 100 faces the end 150a of the negative electrode mixture layer 150, thus suppressing electrical contact, i.e., short circuits, between the negative electrode mixture layer 150 and the positive electrode current collector 13a, which is the uncoated portion 70a of the positive electrode mixture layer.

[0014] The end portion 150a of the negative electrode mixture layer 150 faces the second region 100b of the insulating portion 100, and the second region 100b of the insulating portion 100 covers the positive electrode mixture layer 130. Here, the second region 100b of the insulating portion 100 and the positive electrode mixture layer 130 are located at the position facing the end portion 150a of the negative electrode mixture layer 150.

[0015] In the positive electrode mixture layer 130 at a position opposite the end 150a of the negative electrode mixture layer 150, metal ions contained in the positive electrode mixture layer 130 may dissolve, potentially causing self-discharge of the positive electrode 13. However, the second region 100b of the insulating portion 100 covers at least a portion of the positive electrode mixture layer 130, thereby suppressing the dissolution of metal ions contained in the positive electrode mixture layer 130. This results in an electrode group 5 that suppresses self-discharge of the positive electrode 13 while ensuring sufficient capacity.

[0016] Furthermore, although the first region 100a of the insulating portion 100 is in contact with the second region 100b of the insulating portion 100, even if a misalignment of the windings of the positive electrode 13 and the negative electrode 15 occurs during the manufacture of the wound electrode group 5, for example, the first region 100a of the insulating portion 100 faces the end 150a of the negative electrode mixture layer 150, thereby suppressing a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode current collector 13a.

[0017] The insulating portion 100 will now be described. The insulating portion 100 contains at least one type of insulating particle. Examples of insulating particles include solid particles of metal oxides, such as aluminum oxide (alumina), zirconium oxide (zirconia), magnesium oxide, and barium sulfate. The most preferred insulating particles are alumina or zirconia, which allow for the inexpensive and simple formation of the insulating portion 100.

[0018] The insulating portion 100 may contain not only insulating particles but also a binder. Examples of binders that can be used include polytetrafluoroethylene, polyvinylidene fluoride, fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, and carboxymethylcellulose. One of these may be used as a binder, or two or more may be used in combination.

[0019] The structure of the insulating portion 100 will be described with reference to Figure 4. Figure 4 is a schematic cross-sectional view showing a portion of the positive electrode 13, including the insulating portion 100, used in the electrode group 5 according to the first embodiment.

[0020] As described above, an insulating portion 100 is formed on the positive electrode current collector 13a, covering the interface between the uncoated portion 70a of the positive electrode mixture layer and the positive electrode mixture layer 130. Here, as shown in Figure 4, in the positive electrode 13 used in the wound electrode group 5, let A1 be the length of the positive electrode mixture layer 130 not covered by the insulating portion 100 in the width direction (X direction) parallel to the short side 92 of the positive electrode mixture layer 130, and let B1 be the length of the insulating portion 100 in the width direction (X direction). Here, it is preferable that the relationship between length A1 and length B1 (B1 / A1) is 0.01 or more and 0.04 or less.

[0021] If the relationship between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 (B1 / A1) is 0.01 or greater, the length B1 of the insulating portion 100 is sufficient for the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100, the second region 100b of the insulating portion 100 faces the end 150a of the negative electrode mixture layer 150, and a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer can be suppressed. Furthermore, if the relationship between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 (B1 / A1) is 0.04 or less, the ratio of the insulating portion 100 to the entire electrode group 5 is appropriate, and an electrode group 5 with sufficient capacity can be obtained.

[0022] A more preferable relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 is 0.015 or more and 0.04 or less. When the relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 is 0.015 or more, short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer can be further suppressed compared to when the relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 is 0.01.

[0023] Furthermore, as shown in Figure 4, in the positive electrode 13 used in the wound electrode group 5, the length of the second region 100b of the insulating portion 100 in the width direction (X direction) of the positive electrode mixture layer 130 is defined as B1'. Here, the relationship between length B1 and length B1' (B1' / B1) is preferably 0.1 or more and 0.5 or less. When the relationship between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 (B1' / B1) is 0.1 or more, the elution of metal ions contained in the positive electrode mixture layer 130 can be suppressed in the positive electrode mixture layer 130 at a position facing the end 150a of the negative electrode mixture layer 150, and an electrode group 5 with sufficient capacity can be obtained.

[0024] Furthermore, by setting the relationship between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 (B1' / B1) to 0.5 or less, it is possible to obtain an electrode group 5 with sufficient capacity without affecting the pressing process of the positive electrode 13, and to set an appropriate pressing pressure. The ductility of the insulating portion 100 may affect the pressing process of the positive electrode 13, and the details will be explained below.

[0025] As mentioned above, the insulating portion 100 contains insulating particles such as alumina and zirconia, and may have worse ductility than the positive electrode mixture layer 130. Therefore, for example, in the process of pressing the positive electrode 13, the second region 100b of the insulating portion 100 may be less prone to crushing than the positive electrode mixture layer 130. If the second region 100b of the insulating portion 100 is less prone to crushing than the positive electrode mixture layer 130 during the pressing process, the overall electrode thickness of the positive electrode 13 will increase, which may reduce the number of turns in the electrode group 5 and potentially decrease the capacitance of the electrode group 5. Also, because the second region 100b of the insulating portion 100 may have worse ductility than the positive electrode mixture layer 130, if the second region 100b of the insulating portion 100 is formed to be wider in the width direction (X direction), a large pressing pressure will be required to press the wide second region 100b of the insulating portion 100. Therefore, in order to ensure sufficient capacity and set an appropriate press pressure without affecting the pressing process of the positive electrode 13, it is necessary to appropriately control the length of the second region 100b of the insulating portion 100. In this embodiment, it is preferable that the relationship (B1' / B1) between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 be 0.5 or less.

[0026] A more preferable relationship (B1' / B1) between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 is 0.1 or more and 0.3 or less. When the relationship (B1' / B1) between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 is 0.3 or less, an electrode group 5 with more sufficient capacitance can be obtained and a more appropriate press pressure can be set, compared to the case where the relationship (B1' / B1) between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion 100 is 0.5.

[0027] The structure of the insulating portion 100 will be further explained with reference to Figure 5. Figure 5 is an enlarged cross-sectional view including one of the insulating portions 100 in the positive electrode 13 used in the electrode group 5 according to the first embodiment.

[0028] As shown in Figure 5, in the positive electrode 13 used in the electrode group 5, a thickness direction (Z direction) perpendicular to the width direction (X direction) of the positive electrode mixture layer 130 is defined. Here, if the thickness of the positive electrode mixture layer 130 not covered by the insulating portion 100 is S, and the thickness of the first region 100a of the insulating portion 100 is T, then the thickness of the positive electrode mixture layer 130 not covered by the insulating portion 100 (S) is greater than the thickness of the first region 100a of the insulating portion 100 (T). Here, thickness S is the thickness at the thickest position among three arbitrary positions selected in the positive electrode mixture layer 130. Thickness T is defined as the thickness of the end portion 102 in the first region 100a of the insulating portion 100.

[0029] As mentioned above, the insulating portion 100 contains insulating particles such as alumina and zirconia, and may have poorer ductility than the positive electrode mixture layer 130. Therefore, for example, in the process of pressing the positive electrode 13, by making the thickness (S) of the positive electrode mixture layer 130 not covered by the insulating portion 100 thicker than the thickness (T) of the first region 100a of the insulating portion 100, sufficient pressing pressure can be applied to the positive electrode mixture layer 130 not covered by the insulating portion 100. This pressing process makes it possible to increase the number of turns of the electrode group 5 by reducing the overall electrode thickness of the positive electrode 13, and to obtain an electrode group 5 with sufficient capacity.

[0030] Furthermore, in this embodiment, in the case of the wound electrode group 5, the end portion 150a of the negative electrode mixture layer 150 parallel to the long side 90 is provided in a position facing the second region 100b of the insulating portion 100. However, due to the misalignment of the windings of the positive electrode 13 and the negative electrode 15, the first region 100a of the insulating portion 100 may face the end portion 150a of the negative electrode mixture layer 150. The first region 100a of the insulating portion 100 does not affect the capacitance of the electrode group 5 and is formed to suppress short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer. Therefore, the thickness (T) of the first region 100a of the insulating portion 100 may be thinner than the thickness (S) of the positive electrode mixture layer 130. Even if the thickness (T) of the first region 100a of the insulating portion 100 is formed to be thinner than the thickness (S) of the positive electrode mixture layer 130, if the first region 100a of the insulating portion 100 faces the end portion 150a of the negative electrode mixture layer 150, a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer can be suppressed, and the manufacturing cost of the insulating portion 100 can be reduced because it is thinner than the thickness (S) of the positive electrode mixture layer 130.

[0031] Furthermore, as shown in Figure 5, at the interface between the positive electrode mixture layer 130 not covered by the insulating portion 100 and the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100, the total thickness of the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100 and the second region 100b is denoted as U. Also, at the interface between the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100 and the first region 100a of the insulating portion 100, the total thickness of the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100 and the second region 100b is denoted as U'.

[0032] Here, the combined thickness (U) of the positive electrode mixture layer 130 covering the second region 100b of the insulating portion 100 and the second region 100b is greater than the combined thickness (U') of the positive electrode mixture layer 130 covering the second region 100b of the insulating portion 100 and the second region 100b. Furthermore, the combined thickness (U) of the positive electrode mixture layer 130 covering the second region 100b of the insulating portion 100 and the second region 100b is formed to become thinner toward the combined thickness (U') toward the first region 100a of the insulating portion 100 (towards the width direction X), resulting in a cross-sectional inclined structure.

[0033] As described above, the thickness (S) of the positive electrode mixture layer 130 not covered by the insulating portion 100 is formed to be thicker than the thickness (T) of the first region 100a of the insulating portion 100. This allows sufficient pressing pressure to be applied to the positive electrode mixture layer 130 not covered by the insulating portion 100, and also reduces the manufacturing cost of the insulating portion 100. Although the thickness (S) of the positive electrode mixture layer 130 is formed to be thicker than the thickness (T) of the first region 100a of the insulating portion 100, the second region 100b of the insulating portion 100 covers the positive electrode mixture layer 130. To facilitate the thin insulating portion 100 overlaying the positive electrode mixture layer 130 which is thicker than the insulating portion 100, the combined thickness (U) of the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100 and the second region 100b is designed with a cross-sectional gradient structure toward the combined thickness (U') of the positive electrode mixture layer 130 covered by the second region 100b of the insulating portion 100 and the second region 100b.

[0034] Furthermore, in the positive electrode 13 of this embodiment, a portion of the insulating portion 100 may be formed between the positive electrode mixture layer 130 and the positive electrode current collector 13a.

[0035] The material of electrode group 5 in this embodiment will be described. The negative electrode mixture layer 150 has a lithium ion intercalation / deintercalation potential of 0.4V (vs.Li / Li) relative to metallic lithium. +It is preferable, but not limited to, compounds having a value of ) or higher. Such a negative electrode mixture layer 150 can suppress the deposition of lithium metal due to charging and discharging, and since the deposited lithium metal does not penetrate the separator 4, it can suppress short circuits between the positive electrode 13 and the negative electrode 15.

[0036] A specific preferred compound in the negative electrode mixture layer 150 is Li 4+x Ti5O 12 Lithium titanate, which has a spinel-type crystal structure represented by (-1≦x≦3), Li 2+x Lithium titanate, which has a ramsteride-type crystal structure represented as Ti3O7 (-1≦x≦3), Li x These include niobium titanium composite oxides having a monoclinic crystal structure represented by Nb2TiO7 (0≦x≦5), and metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. The negative electrode mixture layer 150 preferably contains at least one of these compounds.

[0037] The most preferred compound for the negative electrode mixture layer 150 is lithium titanate having a spinel-type crystal structure or lithium titanate having a ramsteride-type crystal structure. In the electrode group 5 of this embodiment, the second region 100b of the insulating portion 100 faces the end 150a of the negative electrode mixture layer 150, which can suppress short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer. However, there is a possibility that the end 150a of the negative electrode mixture layer 150 may penetrate not only the separator 4 but also the second region 100b of the insulating portion 100. If the end 150a of the negative electrode mixture layer 150 penetrates the second region 100b of the insulating portion 100, the end 150a of the negative electrode mixture layer 150 may come into contact with the positive electrode mixture layer 130, potentially causing a short circuit. However, even in this case, if the negative electrode mixture layer 150 contains lithium titanate, the lithium titanate at the short-circuit point will insulate, suppressing the short-circuit current. As a result, even if the end 150a of the negative electrode mixture layer 150 comes into contact with the positive electrode mixture layer 130 and causes a short circuit, the large current caused by the short circuit can be suppressed, ensuring the safety of the electrode group 5.

[0038] The positive electrode mixture layer 130 is, for example, a lithium manganese composite oxide of spinel structure such as Li x Mn2O4 (0 < x ≤ 1), Li x MnO2 (0 < x ≤ 1), a lithium nickel aluminum composite oxide of Li x Ni 1-y Al y O2 (0 < x ≤ 1, 0 < y < 1), a lithium cobalt composite oxide of Li x CoO2 (0 < x ≤ 1), a lithium nickel cobalt manganese composite oxide of Li x Ni 1-y-z Co y Mn z O2 (0 < x ≤ 1, 0 < y < 1, 0 ≤ z < 1), a lithium manganese cobalt composite oxide of Li x Mn y Co 1-y O2 (0 < x ≤ 1, 0 < y < 1), a spinel-type lithium manganese nickel composite oxide of Li x Mn 1-y Ni y O4 (0 < x ≤ 1, 0 < y < 2, 0 < 1 - y < 1), etc., are included.

[0039] In the electrode group 5 of the first embodiment described above, the end portion 150a of the negative electrode mixture layer 150 is provided at a position facing the second region 100b of the insulating portion 100. Thereby, even when the end portion 150a of the negative electrode mixture layer 150 breaks through the separator 4, since the second region 100b of the insulating portion 100 faces the end portion

[0039] 150a of the negative electrode mixture layer 150, a short circuit between the negative electrode mixture layer 150 and the non-coated portion 70a of the positive electrode mixture layer can be suppressed.

[0040] Also, in the electrode group 5 of the first embodiment, in the positive electrode mixture layer 130 at a position facing the end portion 150a of the negative electrode mixture layer 150, the second region 100b of the insulating portion 100 covers at least a part of the positive electrode mixture layer 130. Thereby, while suppressing the self-discharge of the positive electrode 13 due to the elution of metal ions contained in the positive electrode mixture layer 130, an electrode group 5 having a sufficient capacity can be obtained.

[0041] (Second Embodiment) The electrode group 5' of the second embodiment will be described with reference to Figures 6 and 7. Figure 6 is a schematic perspective view of the electrode group 5' according to the second embodiment, and Figure 7 is a partially exploded perspective view of the electrode group 5' according to the second embodiment, viewed from above.

[0042] As shown in Figure 6, the electrode group 5' is manufactured by stacking a positive electrode 13' and a negative electrode 15' via a separator 4'. As shown in Figure 7, the positive electrode 13' has a rectangular positive electrode current collector 13a' having a long side 90' ​​and a short side 92'. On the positive electrode current collector 13a', there is a positive electrode mixture layer 130' where the positive electrode mixture is applied parallel to the short side 92', and an uncoated portion 70a' of the positive electrode mixture layer where the positive electrode mixture is not applied. The negative electrode 15' has a strip-shaped negative electrode current collector 15a' having a long side 90' ​​and a short side 92'. On the negative electrode current collector 15a', there is a negative electrode mixture layer 150' where the negative electrode mixture is applied parallel to the short side 92', and an uncoated portion 70b' of the negative electrode mixture layer where the negative electrode mixture is not applied.

[0043] In the electrode group 5' of this embodiment, an insulating portion 100' is formed on the positive electrode current collector 13a' that covers the interface between the uncoated portion 70a' of the positive electrode mixture layer and the positive electrode mixture layer 130'. This insulating portion 100' has a first region 100a' that covers at least a part of the uncoated portion 70a' of the positive electrode mixture layer and a second region 100b' that covers at least a part of the positive electrode mixture layer 130'.

[0044] The cross-section of the electrode group 5' (the II-II cross-section shown in Figure 6) will be explained with reference to Figure 8. Figure 8 is a schematic cross-sectional view of the electrode group 5' according to the second embodiment. As shown in Figure 8, in the case of the laminated electrode group 5', the end portion 150a' of the negative electrode mixture layer 150' parallel to the short side 92' is positioned opposite the second region 100b' of the insulating portion 100'. As a result, even if the end portion 150a' of the negative electrode mixture layer 150' penetrates the separator 4', the second region 100b' of the insulating portion 100' faces the end portion 150a' of the negative electrode mixture layer 150', thus suppressing a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer.

[0045] The end portion 150a' of the negative electrode mixture layer 150' faces the second region 100b' of the insulating portion 100', and the second region 100b' of the insulating portion 100' covers the positive electrode mixture layer 130'. Here, the second region 100b' of the insulating portion 100' and the positive electrode mixture layer 130' are located at the position facing the end portion 150a' of the negative electrode mixture layer 150'.

[0046] In the positive electrode mixture layer 130' at a position opposite the end 150a' of the negative electrode mixture layer 150', metal ions contained in the positive electrode mixture layer 130' may dissolve, potentially causing self-discharge of the positive electrode 13'. However, the second region 100b' of the insulating portion 100' covers at least a part of the positive electrode mixture layer 130', suppressing the dissolution of metal ions contained in the positive electrode mixture layer 130'. As a result, an electrode group 5' with sufficient capacity is obtained while suppressing self-discharge of the positive electrode 13'.

[0047] Furthermore, although the first region 100a' of the insulating portion 100' is in contact with the second region 100b' of the insulating portion 100', even if misalignment of the stacking of the positive electrode 13' and the negative electrode 15' occurs during the manufacturing of the laminated electrode group 5', the first region 100a' of the insulating portion 100' faces the end 150a' of the negative electrode mixture layer 150', thereby suppressing a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer.

[0048] The material of the insulating portion 100' is the same as that of the insulating portion 100 in the first embodiment.

[0049] The structure of the insulating portion 100' will be described with reference to Figure 9. Figure 9 is a schematic cross-sectional view showing a portion of the positive electrode 13', including the insulating portion 100', used in the electrode group 5' according to the second embodiment.

[0050] As described above, an insulating portion 100' is formed on the positive electrode current collector 13a' that covers the interface between the uncoated portion 70a' of the positive electrode mixture layer and the positive electrode mixture layer 130'. Here, as shown in Figure 9, in the positive electrode 13' used in the electrode group 5' of the laminated structure, let A2 be the length of the positive electrode mixture layer 130' that is not covered by the insulating portion 100' in the width direction (X direction) parallel to the long side 90' ​​of the positive electrode mixture layer 130', and let B2 be the length of the insulating portion 100' in the width direction (X direction). Here, it is preferable that the relationship between length A2 and length B2 (B2 / A2) is 0.01 or more and 0.04 or less.

[0051] If the relationship between the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100' and the length B2 of the insulating portion 100' (B2 / A2) is 0.01 or greater, the length B2 of the insulating portion 100' is sufficient for the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100', the second region 100b' of the insulating portion 100' faces the end 150a' of the negative electrode mixture layer 150', and a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer can be suppressed. Furthermore, if the relationship between the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100' and the length B2 of the insulating portion 100' (B2 / A2) is 0.04 or less, the ratio of the insulating portion 100' to the entire electrode group 5' is appropriate, and an electrode group 5' with sufficient capacity can be obtained.

[0052] A more preferable relationship (B2 / A2) between the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100' and the length B2 of the insulating portion 100' is 0.015 or more and 0.04 or less. When the relationship (B2 / A2) between the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100' and the length B2 of the insulating portion 100' is 0.015 or more, short circuits between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer can be further suppressed compared to when the relationship (B2 / A2) between the length A2 of the positive electrode mixture layer 130' not covered by the insulating portion 100' and the length B2 of the insulating portion 100' is 0.01.

[0053] Furthermore, as shown in Figure 9, in the positive electrode 13' used in the electrode group 5' of the laminated structure, the length of the second region 100b' of the insulating portion 100' in the width direction (X direction) of the positive electrode mixture layer 130' is defined as B2'. Here, the relationship between length B2 and length B2' (B2' / B2) is preferably 0.1 or more and 0.5 or less, similar to the relationship between length B1 and length B1' (B1' / B1).

[0054] If the relationship between the length B2 of the insulating portion 100' and the length B2' of the second region 100b' of the insulating portion 100' (B2' / B2) is 0.1 or greater, the elution of metal ions contained in the positive electrode mixture layer 130' can be suppressed in the positive electrode mixture layer 130' at a position opposite the end 150a' of the negative electrode mixture layer 150', and an electrode group 5' with sufficient capacity can be obtained.

[0055] Furthermore, by setting the relationship (B2' / B2) between the length B2 of the insulating portion 100' and the length B2' of the second region 100b' of the insulating portion 100' to 0.5 or less, it is possible to obtain an electrode group 5' with sufficient capacity without affecting the pressing process of the positive electrode 13', and to set an appropriate pressing pressure. The ductility of the insulating portion 100' may affect the pressing process of the positive electrode 13, and the details will be explained below.

[0056] Similar to the insulating portion 100 in the first embodiment, the insulating portion 100' contains insulating particles such as alumina and zirconia, and may have worse ductility than the positive electrode mixture layer 130'. Therefore, for example, in the process of pressing the positive electrode 13', the second region 100b' of the insulating portion 100' may be less easily crushed than the positive electrode mixture layer 130'. If the second region 100b' of the insulating portion 100' is less easily crushed than the positive electrode mixture layer 130' in the pressing process, the overall electrode thickness of the positive electrode 13' will increase, which may reduce the number of turns of the electrode group 5' and potentially decrease the capacitance of the electrode group 5'. Also, because the second region 100b' of the insulating portion 100' may have worse ductility than the positive electrode mixture layer 130', if the second region 100b' of the insulating portion 100' is formed to be wider in the width direction (X direction), a large pressing pressure will be required to press the wide second region 100b' of the insulating portion 100'. Therefore, in order to ensure sufficient capacity and set an appropriate press pressure without affecting the pressing process of the positive electrode 13', it is necessary to appropriately control the length of the second region 100b' of the insulating portion 100'. In this embodiment, it is preferable that the relationship (B2' / B2) between the length B2 of the insulating portion 100' and the length B2' of the second region 100b' of the insulating portion 100' be 0.5 or less.

[0057] A more preferable relationship (B2' / B2) between the length B2 of the insulating portion 100' and the length B2' of the second region 100b of the insulating portion 100' is 0.1 or more and 0.3 or less. When the relationship (B2' / B2) between the length B2 of the insulating portion 100' and the length B2' of the second region 100b of the insulating portion 100' is 0.3 or less, an electrode group 5' with more sufficient capacitance can be obtained, and a more appropriate press pressure can be set, compared to the case where the relationship (B2' / B2) between the length B2 of the insulating portion 100' and the length B2' of the second region 100b' of the insulating portion 100' is 0.5.

[0058] The structure of the insulating portion 100' will be further explained with reference to Figure 10. Figure 10 is an enlarged cross-sectional view including one of the insulating portions 100' in the positive electrode 13' used in the electrode group 5' according to the second embodiment.

[0059] As shown in Figure 10, in the positive electrode 13' used in electrode group 5', a thickness direction (Z direction) perpendicular to the width direction (X direction) of the positive electrode mixture layer 130' is defined. Here, if the thickness of the positive electrode mixture layer 130' not covered by the insulating portion 100' is S, and the thickness of the first region 100a' of the insulating portion 100' is T, then the thickness of the positive electrode mixture layer 130' not covered by the insulating portion 100' (S) is greater than the thickness of the first region 100a' of the insulating portion 100' (T). Here, thickness S is the thickness at the thickest position among three arbitrary positions selected in the positive electrode mixture layer 130'. Thickness T is defined as the thickness of the end portion 102' in the first region 100a' of the insulating portion 100'.

[0060] As mentioned above, the insulating portion 100' contains insulating particles such as alumina and zirconia, and may have poorer ductility than the positive electrode mixture layer 130'. Therefore, for example, in the process of pressing the positive electrode 13', by making the thickness (S) of the positive electrode mixture layer 130' not covered by the insulating portion 100' thicker than the thickness (T) of the first region 100a' of the insulating portion 100', sufficient pressing pressure can be applied to the positive electrode mixture layer 130' not covered by the insulating portion 100'. This pressing process makes it possible to increase the number of turns of the electrode group 5' by reducing the overall electrode thickness of the positive electrode 13', and to obtain an electrode group 5' with sufficient capacity.

[0061] Furthermore, in this embodiment, in the case of the laminated electrode group 5', the end portion 150a' of the negative electrode mixture layer 150' parallel to the short side 92' is provided in a position facing the second region 100b' of the insulating portion 100'. However, due to the misalignment of the stacking of the positive electrode 13' and the negative electrode 15', the first region 100a' of the insulating portion 100' may face the end portion 150a' of the negative electrode mixture layer 150'. The first region 100a' of the insulating portion 100' does not affect the capacitance of the electrode group 5' and is formed to suppress short circuits between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer. Therefore, the thickness (T) of the first region 100a' of the insulating portion 100' may be thinner than the thickness (S) of the positive electrode mixture layer 130'. Even if the thickness (T) of the first region 100a' of the insulating portion 100' is formed to be thinner than the thickness (S) of the positive electrode mixture layer 130', if the first region 100a' of the insulating portion 100' faces the end portion 150a' of the negative electrode mixture layer 150', a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer can be suppressed, and the manufacturing cost of the insulating portion 100' can be reduced because it is thinner than the thickness (S) of the positive electrode mixture layer 130'.

[0062] Furthermore, as shown in Figure 10, at the interface between the positive electrode mixture layer 130' not covered by the insulating portion 100' and the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100', the total thickness of the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100' and the second region 100b' is defined as U. Also, at the interface between the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100' and the first region 100a' of the insulating portion 100', the total thickness of the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100' and the second region 100b' is defined as U'.

[0063] Here, the combined thickness (U) of the positive electrode mixture layer 130' covered in the second region 100b' of the insulating portion 100' and the second region 100b' is greater than the combined thickness (U') of the positive electrode mixture layer 130' covered in the second region 100b' of the insulating portion 100' and the second region 100b'. Furthermore, the combined thickness (U) of the positive electrode mixture layer 130' covered in the second region 100b' of the insulating portion 100' and the second region 100b' is formed to become thinner toward the combined thickness (U') toward the first region 100a' of the insulating portion 100' (towards the width direction X), resulting in a cross-sectional inclined structure.

[0064] As described above, the thickness (S) of the positive electrode mixture layer 130' not covered by the insulating portion 100' is formed to be thicker than the thickness (T) of the first region 100a' of the insulating portion 100', thereby allowing sufficient pressing pressure to be applied to the positive electrode mixture layer 130' not covered by the insulating portion 100', and reducing the manufacturing cost of the insulating portion 100'. Although the thickness (S) of the positive electrode mixture layer 130' is formed to be thicker than the thickness (T) of the first region 100a' of the insulating portion 100', the second region 100b' of the insulating portion 100' covers the positive electrode mixture layer 130'. To facilitate the thin insulating portion 100' overlaying the positive electrode mixture layer 130' which is thicker than the insulating portion 100', the combined thickness (U) of the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100' and the second region 100b' is designed with a cross-sectional gradient structure toward the combined thickness (U') of the positive electrode mixture layer 130' covered by the second region 100b' of the insulating portion 100' and the second region 100b'.

[0065] Furthermore, in the positive electrode 13' of this embodiment, a portion of the insulating portion 100' may be formed between the positive electrode mixture layer 130' and the positive electrode current collector 13a'.

[0066] The material of electrode group 5' in this embodiment is the same as that of electrode group 5 in the first embodiment.

[0067] In the electrode group 5' of the second embodiment described above, the end portion 150a' of the negative electrode mixture layer 150' is positioned opposite the second region 100b' of the insulating portion 100'. As a result, even if the end portion 150a' of the negative electrode mixture layer 150' penetrates the separator 4', the second region 100b' of the insulating portion 100' faces the end portion 150a' of the negative electrode mixture layer 150', thus suppressing a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer.

[0068] Furthermore, in the electrode group 5' of the second embodiment, in the positive electrode mixture layer 130' at a position opposite the end 150a' of the negative electrode mixture layer 150', the second region 100b' of the insulating portion 100' covers at least a part of the positive electrode mixture layer 130'. This makes it possible to obtain an electrode group 5' that ensures sufficient capacity while suppressing the self-discharge of the positive electrode 13' due to the elution of metal ions contained in the positive electrode mixture layer 130'.

[0069] (Third embodiment) The secondary battery 1 of the third embodiment will be described with reference to Figure 11. Figure 11 is a schematic perspective view showing the secondary battery 1 according to the third embodiment.

[0070] As shown in Figure 11, the secondary battery 1 has an outer case 3, and the electrode group 5 with a wound structure according to the first embodiment is housed inside the outer case 3. Inside the outer case 3, the electrode group 5 is impregnated with an electrolyte (not shown), and the electrolyte is injected, for example, through an injection port (not shown) provided on the lid member 7, and the injection port is sealed with a sealing plate 19 after the electrolyte has been injected. The electrolyte used is a non-aqueous electrolyte prepared by dissolving an electrolyte (e.g., a lithium salt) in a non-aqueous solvent. The non-aqueous solvent may be used alone or in a mixture of two or more types.

[0071] A gas discharge valve 21 may be provided on the surface of the lid member 7 together with the sealing plate 19. Furthermore, for example, a pair of external terminals 23 are attached to the surface of the lid member 7, and the external terminals 23 are formed from a conductive material such as metal. One of the external terminals 23 is a positive external terminal 23a, and the other is a negative external terminal 23b, and the external terminals 23 are electrically connected to the uncoated portion 70a of the positive electrode mixture layer and the uncoated portion 70b of the negative electrode mixture layer of the electrode group 5, respectively. A terminal insulator 35 may be provided between the external terminals 23 and the lid member 7 to maintain insulation between them.

[0072] The secondary battery 1 of the third embodiment described above is equipped with the electrode group 5 of the first embodiment. As a result, even if the end 150a of the negative electrode mixture layer 150 penetrates the separator 4 in the electrode group 5, the second region 100b of the insulating portion 100 faces the end 150a of the negative electrode mixture layer 150, thereby providing a secondary battery 1 that can suppress a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer.

[0073] Furthermore, in the electrode group 5, in the positive electrode mixture layer 130 at a position opposite the end 150a of the negative electrode mixture layer 150, the second region 100b of the insulating portion 100 covers at least a part of the positive electrode mixture layer 130. Therefore, it is possible to provide a secondary battery 1 that ensures sufficient capacity while suppressing self-discharge of the positive electrode 13 due to the elution of metal ions contained in the positive electrode mixture layer 130.

[0074] (Fourth embodiment) The secondary battery 1' of the fourth embodiment will be described with reference to Figure 12. Figure 12 is a schematic perspective view showing the secondary battery 1' according to the fourth embodiment.

[0075] As shown in Figure 12, the secondary battery 1' has an outer case 3', and the electrode group 5' of the stacked structure of the second embodiment is housed inside the outer case 3'. Inside the outer case 3', the electrode group 5' is impregnated with an electrolyte (not shown).

[0076] The secondary battery 1' of the fourth embodiment described above is equipped with the electrode group 5' of the second embodiment. As a result, even if the end 150a' of the negative electrode mixture layer 150' penetrates the separator 4' in the electrode group 5', the second region 100b' of the insulating portion 100' faces the end 150a' of the negative electrode mixture layer 150', thus providing a secondary battery 1' that can suppress a short circuit between the negative electrode mixture layer 150' and the uncoated portion 70a' of the positive electrode mixture layer.

[0077] Furthermore, in the electrode group 5', in the positive electrode mixture layer 130' at a position opposite the end 150a' of the negative electrode mixture layer 150', the second region 100b' of the insulating portion 100' covers at least a part of the positive electrode mixture layer 130'. Therefore, it is possible to provide a secondary battery 1' that ensures sufficient capacity while suppressing the self-discharge of the positive electrode 13' due to the elution of metal ions contained in the positive electrode mixture layer 130'.

[0078] According to the electrode group 5 of at least one embodiment described above, the end portion 150a of the negative electrode mixture layer 150 is positioned opposite the second region 100b of the insulating portion 100. As a result, even if the end portion 150a of the negative electrode mixture layer 150 penetrates the separator 4, the second region 100b of the insulating portion 100 is opposite the end portion 150a of the negative electrode mixture layer 150, thus suppressing a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer.

[0079] Furthermore, in the electrode group 5 of at least one embodiment, in the positive electrode mixture layer 130 at a position facing the end 150a of the negative electrode mixture layer 150, the second region 100b of the insulating portion 100 covers at least a part of the positive electrode mixture layer 130. This makes it possible to obtain an electrode group 5 that ensures sufficient capacity while suppressing self-discharge of the positive electrode 13 due to the elution of metal ions contained in the positive electrode mixture layer 130.

[0080] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0081] Examples are described below, but the present invention is not limited to the examples listed below, unless it exceeds the spirit of the present invention.

[0082] (Example 1) The secondary battery 1 of Example 1 was fabricated by following the procedure below.

[0083] <Method for manufacturing positive electrode 13> As a compound (positive electrode active material) in the positive electrode mixture layer, LiNi 0.8 Co 0.1 Mn 0.1 A lithium nickel cobalt manganese composite oxide represented by O2 was prepared. The positive electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive agent were mixed in a ratio of 100 parts by mass (93% by mass): 2 parts by mass (2% by mass): 5 parts by mass (5% by mass). The positive electrode active material, binder, conductive agent, and N-methylpyrrolidone (NMP) were placed in a planetary mixer. All the materials were stirred in the planetary mixer to obtain a slurry of the positive electrode mixture.

[0084] In addition, alumina was prepared as insulating particles. Alumina and polyvinylidene fluoride as a binder were mixed in a ratio of 100 parts by mass (85% by mass): 15 parts by mass (15% by mass). The alumina, binder, and NMP were placed in a planetary mixer. All the materials were stirred in the planetary mixer to obtain an alumina slurry.

[0085] A slurry of positive electrode mixture was applied to both sides of a positive electrode current collector 13a made of aluminum foil. An alumina slurry was then applied to both sides of the positive electrode current collector 13a, covering the interface between the positive electrode mixture layer 130 and the uncoated portion 70a of the positive electrode mixture layer, and the coating was dried. Here, the relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) was set to 0.02. The relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) was set to 0.3. The dried coating was subjected to a roll press treatment. In this way, a coating was formed on both sides of the positive electrode current collector 13a, with an electrode density (excluding the positive electrode current collector 13a) of 3.3 g / cm³. 3 A positive electrode 13 comprising a positive electrode mixture layer 130 and alumina was fabricated.

[0086] <Method for manufacturing negative electrode 15> As a compound (negative electrode active material) in the negative electrode mixture layer, Li4Ti5O 12 Lithium titanate having a spinel-type crystal structure represented by [formula] was prepared. The negative electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive agent were prepared in a mixing ratio of 100 parts by mass (94% by mass): 2 parts by mass (2% by mass): 4 parts by mass (4% by mass). The negative electrode active material, binder, conductive agent, and N-methylpyrrolidone (NMP) were placed in a planetary mixer. All the materials were stirred in the planetary mixer to obtain a slurry of the negative electrode mixture.

[0087] A slurry of the negative electrode mixture was applied to both sides of a negative electrode current collector 15a made of aluminum foil, and the coating was dried. Furthermore, the dried coating was subjected to a roll press treatment. In this way, an electrode density (excluding the negative electrode current collector 15a) of 2.1 g / cm³ was formed on both sides of the negative electrode current collector 15a. 3 A negative electrode 15 was fabricated, comprising a negative electrode mixture layer 150.

[0088] <Fabrication of electrode group 5> The positive electrode 13 and negative electrode 15, prepared as described above, were wound together with a separator 4 in between to create a wound electrode group 5. At this time, the second region 100b of the insulating portion 100 was positioned opposite the end 150a of the negative electrode mixture layer 150.

[0089] <Preparation of non-aqueous electrolyte> A mixed solvent of propylene carbonate and diethyl carbonate (volume ratio 33:53) was prepared. Lithium hexafluoride phosphate (LiPF6) was dissolved in this solvent at a concentration of 14% by mass. In this way, a non-aqueous electrolyte was prepared.

[0090] <Assembly> The electrode group 5 and non-aqueous electrolyte prepared as described above were placed inside the outer case 3, and the container was sealed to assemble 1000 secondary batteries 1.

[0091] <Measurement of 0.2C discharge capacity> The 0.2C discharge capacity of secondary battery 1 was verified using the following procedure. First, the secondary battery was charged with a constant current (CC charging) at 1C until the battery voltage reached 2.7V, and then charged with a constant voltage (CV charging) until the current value was 0.05C at 2.7V. The secondary battery in this state was then discharged with a constant current of 0.2C until the battery voltage reached 1.5V, and the discharge capacity at this discharge was defined as the 0.2C discharge capacity.

[0092] <Measurement of Short Circuit Ratio> After measuring the 0.2C discharge capacity, the short-circuit rate of 1000 secondary batteries 1 was checked. Using a tester, secondary batteries 1 with a resistance of a few milliohms were considered to be short-circuited.

[0093] (Example 2) The relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) is set to 0.01, and all other conditions are the same as in Example 1.

[0094] (Example 3) The relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) is set to 0.04, and all other conditions are the same as in Example 1.

[0095] (Example 4) The relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) is set to 0.005, and all other conditions are the same as in Example 1.

[0096] (Example 5) The relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) is set to 0.05, and all other conditions are the same as in Example 1.

[0097] (Example 6) The relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is set to 0.1, and all other conditions are the same as in Example 1.

[0098] (Example 7) The relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is set to 0.5, and all other conditions are the same as in Example 1.

[0099] (Example 8) The relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is set to 0.7, and all other conditions are the same as in Example 1.

[0100] (Comparative Example 1) The relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is set to 0, and the second region 100b of the alumina is not formed; otherwise, the procedure is the same as in Example 1.

[0101] (Comparative Example 2) Alumina is not formed, and the positive electrode mixture layer 130 is positioned opposite the end 150a of the negative electrode mixture layer 150; otherwise, the configuration is the same as in Example 1.

[0102] (Comparative Example 3) The negative electrode active material is graphite, and the rest is the same as in Example 1.

[0103] Table 1 shows the short-circuit rate and 0.2C discharge capacity for each example and comparative example.

[0104] [Table 1]

[0105] As shown in Table 1, Examples 1 to 8 exhibited low short-circuit rates of 0.0 to 1.0% and sufficient 0.2C discharge capacity. This verified that the alumina has a first region 100a and a second region 100b, and that the second region 100b of the alumina faces the end 150a of the negative electrode mixture layer 150, thereby suppressing short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer, and also providing sufficient 0.2C discharge capacity.

[0106] Among Examples 1 to 8, particularly in Examples 1 to 3 and Examples 6 to 8, when the relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina is between 0.01 and 0.04, the short-circuit rate is very low, between 0.0 and 0.1%. Although Example 4 had a low short-circuit rate of 1.0%, it was higher than the case where (B1 / A1) was between 0.01 and 0.04. From this, it was verified that when the length B1 of the alumina is very small compared to the length A1 of the positive electrode mixture layer 130 not covered by alumina, the second region 100b of the insulating portion 100 does not face the end 150a of the negative electrode mixture layer 150, making it difficult to suppress short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer.

[0107] Furthermore, in Example 5, the 0.2C discharge capacity was smaller compared to the case where (B1 / A1) was between 0.01 and 0.04. From this, it was verified that when the relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina increases to 0.05 or more, the proportion of alumina to the entire electrode group 5 increases, and the 0.2C discharge capacity decreases.

[0108] From the above, it was verified that, from the viewpoint of preventing short circuits and ensuring discharge capacity, the preferred range for the relationship (B1 / A1) between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina is 0.01 or more and 0.04 or less.

[0109] Furthermore, regarding the relationship between the length A1 of the positive electrode mixture layer 130 not covered with alumina and the length B1 of the alumina (B1 / A1), the short-circuit rate in Example 2 was slightly higher than in Example 1. Therefore, it was verified that the more favorable relationship between the length A1 of the positive electrode mixture layer 130 not covered with alumina and the length B1 of the alumina (B1 / A1) is between 0.015 and 0.04.

[0110] Furthermore, among Examples 1 to 8, particularly Examples 1 to 3, 6 and 7, when the relationship between the length A1 of the positive electrode mixture layer 130 not covered by alumina and the length B1 of the alumina (B1 / A1) was 0.01 or more and 0.04 or less, and the relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) was 0.1 or more and 0.5 or less, a low short-circuit rate and a sufficient 0.2C discharge capacity were obtained. In Example 8, although the short-circuit rate was low at 0.1%, the 0.2C discharge capacity was smaller compared to the case where (B1' / B1) was 0.1 or more and 0.5 or less. From this, it was verified that when the relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is 0.7 or more, the second region 100b of the alumina cannot be sufficiently pressed during the pressing process of the positive electrode 13, the overall electrode thickness of the positive electrode 13 increases, the number of turns of the electrode group 5 decreases, and the 0.2C discharge capacity decreases.

[0111] Furthermore, regarding the relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1), the 0.2C discharge capacity of Example 7 was slightly smaller compared to Examples 1 to 3 and Example 6. Therefore, it was verified that the more favorable relationship between the length B1 of the alumina and the length B1' of the second region 100b of the alumina (B1' / B1) is between 0.1 and 0.3.

[0112] Comparative Example 1 has a discharge capacity of 0.2C smaller than that of Examples 1 to 3. This indicates that by not forming the second region 100b of the insulating portion 100, metal ions contained in the positive electrode mixture layer 130 dissolve at the position of the positive electrode mixture layer 130 opposite the end 150a of the negative electrode mixture layer 150, and self-discharge of the positive electrode 13 progresses.

[0113] Comparative Example 2 shows a higher short-circuit rate compared to the Example. This confirms that when the positive electrode mixture layer 130 faces the end 150a of the negative electrode mixture layer 150 without forming an insulating portion 100, it is not possible to suppress short circuits between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer.

[0114] Comparative Example 3 has a significantly higher short-circuit rate compared to the Example, and charging and discharging are impossible due to the short circuit. This is because the lithium ion intercalation and release potential of graphite is 0.1V (vs. Li / Li) relative to metallic lithium. + This is because lithium metal is deposited on the graphite due to charging and discharging. It has been verified that this lithium metal penetrates the separator 4, causing a short circuit between the positive electrode 13 and the negative electrode 15.

[0115] The above results are used in the electrode group 5 of this embodiment. Specifically, an insulating portion 100 is formed on the positive electrode current collector 13a to cover the interface between the uncoated portion 70a of the positive electrode mixture layer and the positive electrode mixture layer 130. The relationship between the length A1 of the positive electrode mixture layer 130 not covered by the insulating portion 100 and the length B1 of the insulating portion 100 (B1 / A1) is set to be between 0.01 and 0.04. In addition, the relationship between the length B1 of the insulating portion 100 and the length B1' of the second region 100b of the insulating portion (B1' / B1) is set to be between 0.1 and 0.5.

[0116] In the electrode group 5 of this embodiment, the end portion 150a of the negative electrode mixture layer 150 is positioned opposite the second region 100b of the insulating portion 100, which covers at least a part of the positive electrode mixture layer 130. As a result, even if the end portion 150a of the negative electrode mixture layer 150 penetrates the separator 4, the second region 100b of the insulating portion 100 faces the end portion 150a of the negative electrode mixture layer 150, thus suppressing a short circuit between the negative electrode mixture layer 150 and the uncoated portion 70a of the positive electrode mixture layer.

[0117] Furthermore, the negative electrode mixture layer 150 has a lithium ion absorption / desorption potential of 0.4V (vs.Li / Li) relative to metallic lithium. + It is preferable to include a compound that is ) or greater, as the lithium metal deposited by charging and discharging does not penetrate the separator 4, thereby suppressing the occurrence of a short circuit between the positive electrode 13 and the negative electrode 15.

[0118] Furthermore, in the electrode group 5 of this embodiment, in the positive electrode mixture layer 130 at a position opposite the end 150a of the negative electrode mixture layer 150, the second region 100b of the insulating portion 100 covers at least a part of the positive electrode mixture layer 130. This makes it possible to obtain an electrode group 5 that ensures sufficient capacity while suppressing self-discharge of the positive electrode 13 due to the elution of metal ions contained in the positive electrode mixture layer 130. [Explanation of symbols]

[0119] 1...Secondary battery, 1'...Secondary battery, 3...Outer case, 3'...Outer case, 4...Separator, 4'...Separator, 5...Electrode group, 5'...Electrode group, 7...Lid member, 13...Positive electrode, 13'...Positive electrode, 13a...Positive electrode current collector, 13a'...Positive electrode current collector, 15...Negative electrode, 15'...Negative electrode, 15a...Negative electrode current collector, 15a'...Negative electrode current collector, 19...Sealing plate, 21...Gas discharge valve, 23...External terminal, 23a...Positive electrode external terminal, 23b...Negative electrode external terminal, 35...Terminal insulator, 70a...Positive electrode mixture layer Uncoated portion, 70a'...Uncoated portion of positive electrode mixture layer, 70b...Uncoated portion of negative electrode mixture layer, 70b'...Uncoated portion of negative electrode mixture layer, 90...Long side, 90'...Long side, 92...Short side, 92'...Short side, 100...Insulating portion, 100'...Insulating portion, 100a...First region, 100a'...First region, 100b...Second region, 100b'...Second region, 102...End portion, 130...Positive electrode mixture layer, 130'...Positive electrode mixture layer, 150...Negative electrode mixture layer, 150'...Negative electrode mixture layer, 150a...End portion, 150a'...End portion.

Claims

1. Equipped with a positive electrode and a negative electrode, An electrode group in which the positive electrode and the negative electrode are wound around each other via a separator, The positive electrode comprises a strip-shaped positive electrode current collector having a long side and a short side, a positive electrode mixture layer on the positive electrode current collector parallel to the long side of the positive electrode current collector, an uncoated portion of the positive electrode mixture layer, and an insulating portion covering the interface between the positive electrode mixture layer and the uncoated portion of the positive electrode mixture layer. Equipped with, The negative electrode comprises a strip-shaped negative electrode current collector having a long side and a short side, and a negative electrode mixture layer on the negative electrode current collector in which a negative electrode mixture is applied parallel to the long side of the negative electrode current collector. The insulating portion has a first region that covers at least a part of the uncoated portion of the positive electrode mixture layer, and a second region that covers at least a part of the positive electrode mixture layer. The end portion of the negative electrode mixture layer, which is parallel to the long side, is provided at a position facing the second region of the insulating portion. The aforementioned negative electrode mixture contains a compound whose lithium ion intercalation / release potential is 0.4 V (vs. Li / Li+) or higher, relative to metallic lithium. An electrode group wherein the length B1 of the insulating portion in the width direction parallel to the short side of the positive electrode mixture layer and the length B1' of the second region of the insulating portion in the width direction satisfy the following relationship (1). 0.1 ≤ B1' / B1 ≤ 0.5 (1)

2. Equipped with a positive electrode and a negative electrode, An electrode group in which the positive electrode and the negative electrode are stacked with a separator in between, The positive electrode comprises a rectangular positive electrode current collector having a long side and a short side, a positive electrode mixture layer on the positive electrode current collector in which a positive electrode mixture is applied parallel to the short side of the positive electrode current collector, an uncoated portion of the positive electrode mixture layer, and an insulating portion covering the interface between the positive electrode mixture layer and the uncoated portion of the positive electrode mixture layer. Equipped with, The negative electrode comprises a rectangular negative electrode current collector having a long side and a short side, and a negative electrode mixture layer on the negative electrode current collector in which a negative electrode mixture is applied parallel to the short side of the negative electrode current collector. The insulating portion has a first region that covers at least a part of the uncoated portion of the positive electrode mixture layer, and a second region that covers at least a part of the positive electrode mixture layer. The end of the negative electrode mixture layer, parallel to the short side, is provided at a position facing the second region of the insulating portion. The aforementioned negative electrode mixture contains a compound whose lithium ion intercalation / release potential is 0.4 V (vs. Li / Li+) or higher, relative to metallic lithium. An electrode group wherein the length B2 of the insulating portion in the width direction parallel to the long side of the positive electrode mixture layer and the length B2' of the second region of the insulating portion in the width direction satisfy the following relationship (2). 0.1 ≤ B2' / B2 ≤ 0.5 (2)

3. The electrode group according to claim 1, wherein the length A1 of the positive electrode mixture layer not covered by the insulating portion in the width direction parallel to the short side of the positive electrode mixture layer and the length B1 of the insulating portion in the width direction satisfy the following relationship (3). 0.01 ≤ B1 / A1 ≤ 0.04 (3)

4. The electrode group according to claim 2, wherein the length A2 of the positive electrode mixture layer not covered by the insulating portion in the width direction parallel to the long side of the positive electrode mixture layer and the length B2 of the insulating portion in the width direction satisfy the following relationship (4). 0.01 ≤ B² / A² ≤ 0.04 (4)

5. The electrode group according to claim 1 or 2, wherein the thickness of the positive electrode mixture layer not covered by the insulating portion is greater than the thickness of the first region of the insulating portion.

6. The electrode group according to claim 1 or 2, wherein the total thickness of the positive electrode mixture layer covering the second region of the insulating portion and the second region decreases toward the first region of the insulating portion.

7. The electrode group according to claim 1 or 2, wherein the insulating portion includes insulating particles.

8. The electrode group according to claim 7, wherein the insulating portion includes at least one selected from the group consisting of alumina and zirconia.

9. The negative electrode mixture layer contains Li ４＋ｘ Ti ５ O １２ lithium titanate having a spinel-type crystal structure represented by Li ２＋ｘ Ti ３ O ７ lithium titanate having a ramsdellite-type crystal structure represented by Li ｘ Nb ２ TiO ７ niobium titanium composite oxide having a monoclinic crystal structure represented by (0 ≦ x ≦ 5), and at least one of metal composite oxides containing at least one element selected from the group consisting of Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. The electrode group according to claim 1 or claim 2.

10. A group of electrodes as described in either claim 1 or 2, A secondary battery comprising an electrolyte.

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